Mol. Nutr. Food Res. 2013, 00, 1–25 DOI 10.1002/mnfr.201300522 1
REVIEW
Chemoprevention of nonalcoholic fatty liver
disease
by dietary natural compounds
Min-Hsiung Pan1,2, Ching-Shu Lai1, Mei-Ling Tsai3 and Chi-Tang Ho4∗
1 Institute
of Food Science and Technology, National Taiwan University, Taipei, Taiwan
2 Department
of Medical Research, China Medical University Hospital, China Medical University,
Taichung, Taiwan
3 Department
of Seafood Science, National Kaohsiung Marine University, Kaohsiung, Taiwan
4 Department
of Food Science, Rutgers University, New Brunswick, NJ, USA
Nonalcoholic fatty liver disease (NAFLD) refers to a wide spectrum of liver disease that is
not from excess alcohol consumption, but is often associated with obesity, type 2 diabetes,
and metabolic syndrome. NAFLD pathogenesis is complicated and involves oxidative stress,
lipotoxicity, mitochondrial damage, insulin resistance, inflammation, and excessive dietary fat
intake,which increase hepatic lipid influx and de novo lipogenesis and impair insulin signaling,
thus promoting hepatic triglyceride accumulation and ultimately NAFLD. Overproduction
of proinflammatory adipokines from adipose tissue also affects hepatic metabolic function.
Current NAFLD therapies are limited; thus,much attention has been focused on identification
of potential dietary substances from fruits, vegetables, and edible plants to provide a new
strategy for NAFLD treatment. Dietary natural compounds, such as carotenoids, omega-3PUFAs, flavonoids, isothiocyanates, terpenoids, curcumin, and resveratrol, act through a variety
of mechanisms to prevent and improve NAFLD. Here, we summarize and briefly discuss the
currently known targets and signaling pathways as well as the role of dietary natural compounds
that interfere with NAFLD pathogenesis.
Keywords:
Chemoprevention / Nonalcoholic fatty liver disease / Dietary natural compounds
Received: July 19, 2013
Revised: September 25, 2013
Accepted: October 9, 2013
Correspondence: Dr. Min-Hsiung Pan, Institute of Food Science
and Technology,National TaiwanUniversity,No.1, Section 4, Roosevelt
Road, Taipei 10617, Taiwan
E-mail: mhpan@ntu.edu.tw
Fax: +886-2-33661771
Abbreviations: _-SMA, _-smooth muscle actin; ACC, acetylcoenzyme
A carboxylase; ACO, acyl-coenzyme A oxidase; ALT,
alanine aminotransferase; AMPK, AMP-activated protein kinase;
AST, aspartate aminotransferase; CAT, catalase; CPT-1, carnitine
palmitoyl transferase 1; CYP, cytochrome P450; DHA, docosahexaenoic
acid; DR5, death receptor 5; EGCG, epigallocatechin3-gallate; EPA, eicosapentaenoic acid; FA, fatty acid; FAS, FA
synthase; FFA, free FA; FOXO, forkhead box protein O; G6Pase,
glucose 6-phosphatase; GPx, GSH peroxidase; GSH, glutathione;
GST, GSH S-transferase; HFD, high-fat diet; HMG-CoA, 3hydroxy-3-methylglutaryl-coenzyme A; HSC, hepatic stellate cell;
HSL, hormone-sensitive lipase; IRS-1, insulin receptor substrate
1; JNK, c-Jun N-terminal kinase; LDL, low-density lipoprotein;
MCP-1, monocyte chemotactic protein 1; NAFLD, nonalcoholic
fatty liver disease; NASH, nonalcoholic steatohepatitis; NF-_B,
nuclear factor-_B; Nrf2, NF-E2-related factor 2; PEPCK, phosphoenolpyruvate
carboxykinase; PI3K, phosphatidylinositol-3 kinase;
PPAR, peroxisome proliferator-activated receptor; Pten, phosphatase
and tensin homolog; ROS, reactive oxygen species; SCD1, stearoyl-CoA desaturase 1; SFAs, saturated FAs; SIRT, sirtuin;
1 Introduction
Nonalcoholic fatty liver disease (NAFLD) has emerged as a
common liver disorder that is characterized by abnormal hepatic
triglyceride (TG) accumulation in the absence of excessive
alcohol consumption. This disease represents a histological
spectrum ranging from simple hepatic steatosis (defined as
hepatic TG >5% by liver weight) that can progress to inflammatory
nonalcoholic steatohepatitis (NASH), fibrosis, cirrhosis,
and ultimately end-stage liver failure or hepatocellular
carcinoma [1]. Simple hepatic steatosis is a benign process
without inflammation, whereas lobular inflammation and
hepatocellular injury followed by fibrosis are common in
NASH and are believed to drive progression to cirrhosis [2].
Liver biopsies are currently the gold standard for NASH clinical
diagnosis and staging because there are no specific symptoms
to distinguish this disease. Other clinical diagnostic
SOCS, suppressor of cytokine signaling; SOD, superoxide dismutase;
SREBP-1, sterol regulatory element binding protein 1;
TF-1, theaflavin; TG, triglyceride; TGF-_1, transforming growth
factor _1; TNF-_, tumor necrosis factor _; UCP, uncoupling
protein; VLDL, very-low-density lipoprotein
∗Additional
corresponding author: Dr. Chi-Tang Ho,
E-mail: ho@aesop.rutgers.edu
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indices include increased serum aspartate aminotransferase
(AST) and alanine aminotransferase (ALT), elevated BMI, and
metabolic syndrome [1, 3].
NAFLD prevalence has increased worldwide in the past
20 years, reflecting its emergence as a major public health
problem. Epidemiological studies demonstrated that NAFLD
prevalence is different and varies wildly depending on population
and diagnostic methods or definition [4]. Population
studies estimate that approximately 25–30% of the general
population in the United States [5,6] and 13–60% of the population
from Japan, Italy,China, andKorea haveNAFLD[7–10].
The increasing NAFLD prevalence is not only in adults, but
also in children (3–10%) and is rising up to 40–70% among
obese children [11]. Although NASH is the most serious form
of NAFLD, it is difficult to diagnose without a liver biopsy,
which results in less population-based prevalence studies.
Previous epidemiological research demonstrated that approximately
30% of simple steatosis cases progress to NASH
in NAFLD patients, and approximately 20% of NASH patients
develop cirrhosis. Once developed, 30–40% of cirrhosis
patients succumb to liver-related death over a 10-year period
[12].NASHpatients had increased cardiovascular disease
and liver-related disease-induced mortality compared to simple
steatosis patients. Most of these patients were diagnosed
with diabetes or impaired glucose tolerance and had increased
weight gain [13]. Previously, researchers suggested a number
of risk factors implicated in NAFLD, including age, race, genetics,
and chronic infection, and NAFLD was also strongly
associated with metabolic conditions, such as obesity, type 2
diabetes, hypertension, and dyslipidemia, which are regarded
as hepatic manifestations of metabolic syndrome [3, 4].
2 NAFLD pathogenesis
The liver is a necessary and important organ for whole body
metabolism and energy homeostasis. Hepatic TG accumulation
is a hallmark of NAFLD that results from several
sources, including increased free fatty acid (FFA) delivery
from adipose tissue (as lipolysis), dietary fatty acids (FAs), elevated
hepatic de novo lipogenesis, reduced very-low-density
lipoprotein (VLDL) export, and decreased FA _-oxidation. Except
for hepatic steatosis, other histological and biological
changes associated with NAFLD include lobular and portal
inflammation, hepatocyte ballooning and apoptosis, increased
AST levels, collagen deposition, and hepatic fibrosis
[6]. This process also involves hepatocyte lipotoxicity, increased
oxidative stress from mitochondrial _-oxidation, inflammatory
cytokine release, and immune cell and hepatic
stellate cell (HSC) activation. A classic two-hit model has been
proposed to explain NAFLD pathogenesis by Day and James
in 1998 [14]. The first hit refers to hepatic TG accumulation
(steatosis) that increases liver sensitivity to a variety of second
hits, such as inflammatory cytokines and oxidative stress
that cause hepatic injury, necroinflammation, and fibrosis.
However, this hypothesis has been challenged because some
steatosis patients develop NASH without implicating secondhit
but other external injury.
A number of in vitro and in vivo epidemiological studies
strongly suggest that obesity and hepatic insulin resistance
are critical pathogenic factors in NAFLD. Dysfunctions in
these signaling and regulation mechanisms impair hepatocellular
functions and predispose patients to NAFLD pathogenesis.
Although the precisemechanisms for NAFLD development
and progression remain incompletely understood,
NAFLD is currently recognized as a consequence of a multihit
hypothesis, involving obesity, insulin resistance, oxidative
stress, and proinflammatory processes [15].
2.1 Obesity and adipokines
Obesity is defined as excessive fat accumulation in adipose
tissue and it is associated with numerous metabolic diseases
such as cardiovascular disease, type 2 diabetes, and
NAFLD [10,16]. Several population studies demonstrated that
the prevalence of simple steatosis,NASH, andNAFLD was increased
in overweight and obese individuals [10,17–20]. High
NASH and NAFLD prevalence also occurred in severely and
morbidly obese individuals, indicating that its incidence is
highly associated with the degree of obesity [21–23]. Moreover,
NAFLD was also found in obese insulin-resistant children
and those with elevated serum ALT levels [24, 25].
As caloric intake increases, adipocytes store energy in the
form of TGs that result in enhanced adipogenesis, increased
adipose tissue mass, and consequently obesity [26]. Insulin
inhibits adipose tissue lipolysis by lowering cyclic adenosine
monophosphate levels and activating phosphodiesterase 3b,
thereby attenuating protein kinase A activity and decreasing
protein kinase A dependent hormone-sensitive lipase (HSL)
activation, or through dephosphorylation of HSL at regulatory
and basal phosphorylation sites by protein phosphatase
[27, 28]. FFAs released from adipose tissue by enhanced TG
hydrolysis via insulin resistance-mediated HSL increases resulted
in elevated plasma FFAs. Subsequently, these FFAs are
transported to the liver via the hepatic artery and portal vein
and thus increase hepatic FFA influx. Increased FFAs delivered
to the liver from visceral adipose tissue induce hepatic
insulin resistance via reduced hepatic insulin clearance and
increased circulating insulin levels, which decreases insulinstimulated
glucose uptake through IRS-1-associated (where
IRS-1 is insulin receptor substrate 1) phosphatidylinositol3 kinase (PI3K) signaling impairment and reduced insulinmediated
hepatic glucose output suppression and endogenous
glucose production [29–31]. FFAs also stimulate hepatic
gluconeogenesis and TG synthesis and directly cause hepatic
lipotoxicity, which promote NAFLD pathogenesis.
One study demonstrated the contribution of the FFA
source in NAFLD patients using multiple stable isotope techniques.
Of the hepatic TG, 59% was from serum nonesterified
FAs, 26% was derived from hepatic de novo lipogenesis, and
only 15% was from dietary sources [32]. This study suggested
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that although increased FFAs from other pathways also account
for hepatic lipid accumulation, elevated FAs from peripherally
expanded adipose tissue and de novo lipogenesis
are the major sources of hepatic and lipoprotein fat accumulation
in NAFLD. Fat distribution may also be more important
than total adipose tissuemass in obesity [33]. Visceral adipose
tissue is strongly associated with metabolic complications including
hepatic steatosis [34, 35] and contributes to hepatic
inflammation and fibrosis inNAFLD patients [36]. Compared
with subcutaneous adipose tissue, visceral adipose tissue increases
insulin resistance, metabolic activity, lipogenesis, and
lipolysis [37, 38].
Deregulated adipokine secretion from adipose tissue is another
mechanism by which obesity is involved in NAFLD via
impaired insulin signaling and proinflammatory properties.
Most adipokines are increased in obese adipose tissue, and
some of these have been linked to insulin resistance, such
as tumor necrosis factor-_ (TNF-_), leptin, and IL-6 [39].
Visceral adipose tissue-generated adipokines directly transported
to the liver and cause harmful effects on hepatocytes.
Obesity is significantly associated with chronic low-grade inflammation
and insulin resistance, which is first evidenced by
TNF-_ release from adipocytes [40]; in addition, using TNF-_
neutralizing antibodies improves insulin resistance. TNF-_
knockout mice or its receptor have ameliorated insulin resistance
in both diet-induced obese and leptin-deficient (ob/ob)
mice that develop severe type 2 diabetes and hypercholesterolemia
[41]. Clinical studies demonstrated that both serum
and hepatic TNF-_ is increased in NASH patients compared
with simple steatosis patients, and the increased TNF-_ levels
are correlatedwith the severity of histological changes [42–44].
Inhibition of endogenous TNF-_ production improved steatosis,
steatohepatitis, and insulin resistance in NASH patients
as well as both HFD-fed (where HFD is high-fat diet) and
leptin-deficient (ob/ob) mice [45–47]. These studies reveal the
role of TNF-_ in insulin signaling impairment in NAFLD.
At the molecular level, increased TNF-_ is observed by FFA
treatment of mouse hepatocytes, which downregulates insulin
receptor phosphorylation and thus blocks insulin signaling
[48, 49]. FFA exposure also caused hepatocyte lipotoxicity
by promoting TNF-_ production and, thus, I_B kinase
_/nuclear factor-_B (NF-_B) activation, resulting in abundant
proinflammatory cytokine expression [48]. TNF-_ also stimulated
hepatic FA synthesis and increased serum TGlevels [50].
IL-6 is another proinflammatory cytokine that is produced
from visceral adipose tissue and with systemic effects on the
immune response. Increased IL-6 is found in obese patients,
is decreased by weight loss [51, 52], and is a predictor of insulin
resistance [53]. Secreted IL-6 levels from abdominal
adipose tissue are higher than that from subcutaneous adipose
tissue [54]. In severely obese patients, IL-6 and TNF-_
mRNA expression in both subcutaneous and visceral adipose
tissue ismore than 100-fold greater than liver tissue [51]. Visceral
adipose tissue-derived IL-6 enters the liver; therefore,
the liver might be a major IL-6 target organ. Several studies
suggested that IL-6 caused hepatic insulin resistance by
inhibiting receptor autophosphorylation, IRS-1 phosphorylation,
and downstream PI3K/Akt signaling via suppressor
of cytokine signaling (SOCS) 3 activation [51, 55]. An HFD
animal study also demonstrated that adipose tissue-derived
IL-6 increased hepatic SOCS3 expression followed by reduced
insulin-stimulated AKT activation and consequent hepatic insulin
resistance [56].
Leptin is mainly produced by adipocytes and is an important
adipokine in the regulation of energy expenditure,
food intake, energy balance, and the immune system [57, 58].
Increased serum leptin levels are found in NAFLD patients
[59, 60] and are correlated with hepatic steatosis severity, but
not with inflammation or fibrosis [61, 62]. Comparatively,
a 6-month follow-up study revealed no association between
serum leptin levels and NAFLD severity [63]. Leptin-deficient
(ob/ob) mice develop obesity, fatty liver, and insulin resistance
[64]. Although there is no correction of leptin and hepatic
fibrosis in human studies, much evidence suggests that
leptin is a fibrogenic factor that is implicated in hepatic fibrosis.
Leptin is essential for HSC activation and transforming
growth factor _1 (TGF-_1) production that promotes collagen
synthesis and is involved in hepatic fibrosis [65,66]. However,
an in vitro study demonstrated that the fibrogenic effect of
leptin andHSC activation is because of interactions with hepatic
Kupffer cells but not direct effects on HSC [67].
Adiponectin is an anti-inflammatory adipokine that is
also produced by adipocytes and is suggested to inhibit
NAFLD [43, 68]. Decreased adiponectin is observed in NASH
patients compared with simple steatosis and is associated
with more extensive hepatic necroinflammation [43]. Increased
levels of TNF-_ and IL-6, two major proinflammatory
adipokines, inhibit adiponectin expression [69]. Adiponectin
inhibits NAFLD and exerts a hepatoprotective effect through
multiple mechanisms, including suppression of steatosis,
fibrosis, inflammation, lipotoxicity, and an increase in insulin
sensitivity and as has been described in recent reviews
[70, 71]. Recombinant adiponectin significantly attenuated
hepatomegaly, steatosis, and hepatic inflammation in
leptin-deficient (ob/ob) mice and cultured hepatocytes via enhancement
of hepatic FA oxidation and reduced FA synthesis
as well as TNF-_ production [72, 73].
2.2 Insulin resistance
Insulin signaling is essential for carbohydrate and lipid
metabolism in various organs and tissues and is crucial
for homeostatic regulation of blood glucose levels by the
liver [74]. In physiological states, pancreatic _ cells secrete
insulin in response to increased blood glucose levels after
feeding. Insulin stimulates hepatic glucose uptake and conversion
of glucose into glycogen, TG synthesis, and export
to adipose tissue as VLDL. This biological function of insulin
is triggered by insulin binding to the insulin receptor
and activation of the intracellular signaling cascade. Once
bound, the insulin receptor _-subunit with tyrosine kinase
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activity phosphorylates IRS family members, further activating
various signaling pathways that are involved in the
metabolic effects of insulin [75], which involves downstream
targeted insulin/IRS and PI3K/Akt pathway activation. PI3Kmediated
Akt activation is important for glucose transport,
glycogen and protein synthesis as well as hepatic gluconeogenesis
suppression. Akt-dependent forkhead box protein O
(FOXO) transcription factor phosphorylation results in their
exclusion from the nucleus to the cytoplasm, thus blocking
the DNA binding ability of FOXOs and subsequent downstream
gluconeogenic gene transcription including genes,
such as phosphoenolpyruvate carboxykinase (PEPCK) and
glucose 6-phosphatase (G6Pase) [75, 76]. Akt also promotes
translocation of glucose transporter 4 to cell membranes together
with the Cbl/Tc10 pathway that facilitates glucose uptake
[77] and subsequently reduces hepatic gluconeogenesis
and blood glucose levels. In addition to regulating hepatic
glucose metabolism, insulin signaling stimulates hepatic de
novo lipogenesis through sterol regulatory element binding
protein 1 (SREBP-1) transcription factor activation that upregulates
acetyl-coenzyme A carboxylase (ACC) and FA synthase
(FAS) [78].
Insulin resistance is a physiological condition that is described
as decreased target cell sensitivity to the normal insulin
concentrations and, hence, insulin-mediated uptake
and glucose utilization in insulin-sensitive organs and tissue
including the liver, adipose, and muscle tissue. Insulin resistance
has been linked to metabolic syndrome and is a major
cause of type 2 diabetes because of pancreatic _ cell dysfunction
[79]. Extensive research also has highlighted the implication
of insulin resistance in NAFLD. Increased NAFLD
prevalence is found in patients with impaired glucose tolerance
or diagnosed diabetes [10, 25, 80]. A study of type 2
diabetic patients demonstrated thatNAFLD is extremely common
in type 2 diabetes patients with 69.5% prevalence [81].
A population-based matched retrospective cohort study also
demonstrated that a higher risk of advanced liver disease is
found in newly diagnosed diabetic individuals compared with
those who do not have type 2 diabetes [82]. Moreover, insulin
resistance is associated with the degree of NAFLD, advanced
fibrosis, and mortality [83, 84].
The mechanism underlying hepatic insulin resistance is
poorly understood, but may involve FFA overflow, proinflammatory
adipokines, hyperinsulinemia, hyperglycemia, and
adipose tissue insulin resistance. Insulin signaling inactivates
adipose tissue HSL to suppress lipolysis, whereas adipose
tissue insulin resistance results in increased hepatic FFA
influx and further lipid accumulation [27, 28]. It has been
demonstrated that in HSL knockout mice, hepatic insulin
sensitivity is increased by reducing TG concentrations [85].
Increased FFAs also contribute to hepatic insulin resistance
as described above (Section 2.1). FFAs and proinflammatory
adipokines, such as IL-6 and TNF-_, from adipose tissue
impaired hepatic insulin signaling via c-Jun N-terminal kinase
(JNK), I_B kinase/NF-_B, and SOCS protein activation,
resulting in IRS inactivation or degradation [86, 87]. High
glucose-induced hyperinsulinemia in blood caused hepatic
SREBP-1 activation and promoted hepatic de novo lipogenesis
[88]. This hyperinsulinemia also inhibited FFA oxidation
by upregulating malonyl-CoA levels, resulting in carnitine
palmitoyl transferase 1 (CPT-1) inhibition, thus decreasing
FA shuttling intomitochondria and reduced hepatic lipid utilization
[89, 90]. The pathogenic role of insulin resistance in
NAFLD is complicated by the involvement of multiple factors
and molecules between organs that amplify deregulated
signaling cascades and thus alter hepatic gene expression as
well as glucose and lipid metabolism.
2.3 Lipotoxicity and lipoapoptosis
Accumulation of FFAs and their metabolites causes cell damage
and death known as lipotoxicity and lipoapoptosis. Indeed,
apoptosis is a prominent feature of NASH that correlates
with histological hepatic inflammation and fibrosis [91].
As mentioned before, hepatic TG accumulation per se does
not directly cause hepatotoxicity, whereas FFAs and a wide
range of lipid metabolites potently cause lipotoxicity and
lipoapoptosis. FFAs cause lipotoxic effects through various
mechanisms, including lysosomal destabilization, mitochondrial
pathways, death receptor signaling, and ER stress. FFA
exposure in mouse hepatocytes causes Bax translocation to
lysosomes and lysosomal destabilization with lysosomal cysteine
protease (cathepsin B) release that contributes to loss of
lysosomal integrity. Downregulating Bax and inhibiting lysosomal
permeabilization reduced FFA-induced toxicity [92].
FFA treatment decreased Bcl-xL, which is an anti-apoptotic
BCl-2 family protein, while overexpression blocked lysosomal
permeabilization and apoptosis [92]. FFAs also caused NF_B-dependent TNF-_ expression that may further promote
insulin resistance and hepatic lipogenesis [48, 93]. A recent
study found that saturated FAs (SFAs) induced cytotoxicity
and apoptosis both in human and mouse hepatocytes, but
MUFAs only resulted in lipid accumulation [94]. SFAs such
as palmitate and stearic acid trigger hepatic lipoapoptosis
via Bim activation, which is a BH3 domain-only protein that
further binds to Bax and triggers mitochondrial apoptosis
pathways [95]. Pharmacological and genetic JNK inhibition
or Bim knockdown by siRNA both attenuated SFA-induced
cell death [95]. A further study demonstrated that FFAs mediated
protein phosphatase 2A-dependent FOXO3a dephosphorylation
that in turn stimulated FoxO3a-dependent Bim
expression and hepatocyte apoptosis [96]. Elevated Fas receptor
(CD95) expression occurred in liver specimens from
NASH patients and correlated with disease severity [97]. In
carbohydrate-fed mice, hepatocyte Fas expression was increased
and accompanied by hepatic steatosis [98, 99]. Fas agonist
administration increased hepatocyte apoptosis and liver
injury in diet-induced obese mice [98]. Upregulated Fas expression
was noted in FFA-treated HepG2 cells and increased
the sensitivity to Fas agonist-induced apoptosis [98]. FFA
treatment of hepatocytes caused JNK-dependent TNF-related
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apoptosis-inducing ligand receptor death receptor 5 (DR5)
upregulation and sensitization to TNF-related apoptosisinducing
ligand mediated apoptosis [100]. Increased DR4 and
DR5 expression was also demonstrated in livers from human
NASH patients [100,101]. A recent study suggested that FFAinducedDR5
expression was transcribed by C/EBP homology
protein (CHOP), an ER stress-mediated transcription factor.
This study also suggested that FFAs induced lipoapoptosis
by promoting DR5 clustering and lipid raft redistribution
within the plasma membrane [102]. These studies indicated
that DR upregulation during steatosis increased hepatocyte
susceptibility to apoptosis through other mechanisms. Cellular
lipid accumulation also induces ER stress. Hepatocyte
FFA exposure disrupts ER homeostasis, induces ER stress,
and promotes apoptosis [103]. Mice fed a high saturated fat
diet had hepatic steatosis and increased ER stress via spliced
X-box binding protein 1, upregulated glucose-regulated protein
78 levels and increased hepatic apoptosis [104]. Eukaryotic
initiation factor-2_ phosphorylation and increased levels
of both glucose-regulated protein 78 and X-box binding protein
1 were observed in NAFLD and diet-induced NASH patients
[105,106]. Upregulation of these signalingmolecules is
linked to lipid accumulation, insulin resistance, and hepatic
inflammation via JNK, NF-_B, and reactive oxygen species
(ROS) production [107].
2.4 Oxidative stress
Oxidative stress is a redox imbalance that results from excessive
ROS or free radicals and decreased antioxidant defense.
Elevated free radicals, increased DNA damage, and
lipid peroxidation as well as reduced antioxidants have been
observed in NAFLD patients [108, 109]. In addition to the
direct hepatotoxic effect, FFA overload induces ROS production
via mitochondrial dependent _-oxidation or microsomal
enzymes. Increased hepatic microsomal FA oxidizing
enzyme cytochrome P450 (CYP) 2E1 was found in mice
with diet-induced hepatic steatosis and NASH patients and is
considered to be a source of ROS [110, 111]. Mitochondrial
_-oxidation is regulated by CPT-1, while FFAs induce peroxisome
proliferator-activated receptor (PPAR) _ to up-regulate
CPT-1 expression [112]. ROS overproduction causes an attack
on DNA, protein, and cellular membranes, which induces
lipid peroxidation and results in mitochondrial dysfunction
that contributes to hepatocellular damage. Mitochondrial
abnormalities include ultrastructural lesions, mitochondrial
DNA depletion, impaired ATP synthesis, and decreased respiratory
chain complex activity are associated with NAFLD
and might result in further ROS production [113, 114]. TNF_ is also involved in mitochondrial dysfunction through induction
of mitochondrial swelling and interference among
mitochondrial respiratory chain complexes [115, 116]. PUFA
peroxidation induced apolipoprotein B100 degradation, a critical
protein component of VLDL; thus, decreased VLDL secretion
may be relevant to hepatic lipid accumulation [117].
Moreover, Cu/Zn superoxide dismutase (SOD), glutathione
(GSH) peroxidase (GPx), and catalase (CAT) activities are increased
in NAFLD patients compared with simple steatosis,
reflecting the state of oxidative stress [118].
2.5 Hepatic inflammation
NASH is an extreme form of NAFLD and has gotten more
attention recently because it can progress to fibrosis and cirrhosis.
NASH is characterized by steatosis with mixed lobular
inflammation and hepatocyte ballooning with or without fibrosis
[2,119]. Other features are also included such as portal
inflammation or panacinar steatosis, which are associated
with advanced liver fibrosis [119, 120]. Hepatic inflammation
is a complicated condition that is caused by various factors,
including FFAs, cytokines, adipokines, and oxidative stress
that results in hepatocellular injury, further inflammatory
cell recruitment, which releases various oxidants and proinflammatory
molecules, andHSC activation, which is involved
in hepatic fibrosis [2]. Themajor source of hepatic TNF-_ and
IL-6 is derived from injured hepatocytes, immune cells, and
activated Kupffer cells. Increased TNF-_ activates JNK signaling
and results in hepatocyte apoptosis [121]. Studies have
revealed that NF-_B and JNK activation are essential for inflammatory
cell recruitment in NASH [122, 123]. A recent
study demonstrated that hepatocytes release danger signals
leading to activation of mononuclear cells and production of
IL-1_ and TNF-_ after FFA exposure [124]. The role of IL-6 in
liver pathology is very complicated because it is considered to
have hepatoprotective effect and promote liver regeneration.
Although the way IL-6 participates in NAFLD is still unclear,
studies have suggested a positive correlation between hepatic
IL-6 and degree of disease. Increased IL-6 expression in hepatocytes
is found in patients with NASH and correlated to degree
of inflammation, stage of fibrosis, and systemic insulin
resistance [125]. Blockade of IL-6 signaling by neutralizing
antibody against the IL-6 receptor (MR16–1) enhanced hepatic
steatosis but improved hepatic injury in mice fed with an
methionine choline-deficient diet [126].
Overproduction of cytokines, such as TGF-_ by Kupffer
cells, infiltrating inflammatory cells, and fibroblasts triggers
HSC activation and differentiation into myofibroblast-like
cells, promotes collagen synthesis and blocks extracellular
matrix degradation by enhancing tissue inhibitors of matrix
metalloprotease expression [127]. Furthermore, adipose
tissue-generated leptin increased the collagen I and III production
inHSCs via a JAK- and PI3K-mediated pathway [128].
In rats with diet-induced steatohepatitis, hepatocytes are the
source of lipid peroxidation at early stages followed by hepatocellular
injury, further inflammatory cell recruitment, and
HSC activation [129]. Activation of Kupffer cells and other
inflammatory cells also generates ROS through NADPH oxidase
[130, 131]. Although oxidative stress may not initiate
hepatic inflammation, ROS overproduction could cause hepatocyte
damage or death and, in turn, cytokine release that
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provides positive feedback on inflammatory signaling and
promotes NASH pathogenesis.
3 Molecular mechanism of dietary natural
compounds used to treat NAFLD
Development and progression of NAFLD andNASHis amultifactorial
process. Despite understanding the process and
mechanism, there is no established treatment or therapy for
NAFLD. Epidemiological studies suggested a combination
of lifestyle interventions, such as decreased caloric intake,
altered dietary composition, weight loss and physical exercise,
is safe and effective for improving obesity-mediated
insulin resistance and NAFLD [132]. Current pharmaceutical
drugs, such as insulin-sensitizers, thiazolidinediones,
statins, antioxidants, and Omega-3 PUFAs, which targeting
the mechanisms involved in metabolic syndrome have
been evaluated in animal and clinical studies [132,133]. However,
some of these therapeutic agents tested in patients with
limited findings and inconsistent outcomes, and because of
short durations and randomized trails, some of these have
safety concerns [134, 135]. Evidence has supported the concept
that NAFLD is associated with diet-associated obesity
and insulin resistance. This evidence also offers novel targets
for NAFLD intervention and treatment by dietary and
nutritional components. Currently, researchers have become
increasingly interested in searching for natural products from
dietary and herbal plants that can both prevent and control
NAFLD via a chemopreventive strategy. Many dietary natural
compounds isolated from fruits, vegetables, and edible
plants reportedly possess health-promoting properties,
such as anti-inflammation, antioxidation, antiobesity, and increased
insulin sensitivity. Furthermore, in vivo and in vitro
studies demonstrated thatmany herbal plants have been used
for management of fatty liver conditions and improvement
of NAFLD by their hypoglycemic, antihyperlipidemic, and
hepatoprotective effect, and without major side effect [133].
Convincing scientific evidence in animal and human studies
displays the potential of these dietary natural compounds
for NAFLD treatment.Understanding the regulatory role and
mechanism of these dietary natural compounds may help to
prevent and treat NAFLD. The chemopreventive effects and
molecular targets of selected dietary natural compounds in
NAFLD are highlighted below (Table 1).
3.1 Carotenoids
Carotenoids are fat-soluble pigments and potent antioxidants
that are rich in many plants, fruits, and flowers. Lycopene
is a member of the carotenoid family, with a highly unsaturated
40-carbon molecule that contains 11 conjugated and
two unconjugated double bonds. The main sources of lycopene
are tomato, watermelon, papaya, and orange grapefruit.
Rats administered 2 and 4 mg/kg lycopene for 6 wk
displayed reduced serum ALT and AST activities and TG and
cholesterol levels. Hepatic steatosis and inflammation were
also reduced, followed by decreased lipid peroxidation and
increased GSH as well as lowered serum TNF-_ [136]. In a
NASH-promoted hepatocarcinogenesis animal study, dietary
lycopene reduced HFD- and diethylnitrosamine-induced hepatic
precancerous lesions. This inhibitory effect is associated
with decreased hepatic lipid peroxidation, NF-_B levels, and
upregulation of both nuclear NF-E2-related factor 2 (Nrf2) and
its target gene heme oxygenase 1. Increased lycopene levels
are found in HFD-fed but not control diet-fed rat livers, indicating
that lycopene is incorporated into micelles along with
dietary fat and that it has efficacy in target organs [137]. Dietary
lycopene feeding in gerbils also restored HFD-induced
decreased liver antioxidant enzyme defenses, including CAT,
GSH reductase, and GSH S-transferase (GST) activities [138].
These studies suggested that lycopene has potent antioxidative
activity by alleviating oxidative stress and upregulating
antioxidants to prevent HFD-induced NAFLD. In addition to
the antioxidative property, a recent study demonstrated that
lycopene decreased HFD-induced hepatic steatosis and FFAinduced
lipid accumulation in hepatocytes viamicroRNA-21dependent FA-binding protein 7 inhibition [139]. _-Carotene
is one of the most abundant carotenoids and antioxidants in
vegetables and fruits. _-Carotene consumption is distributed
in a variety of tissues including liver and adipose tissues [140].
3T3-L1 adipocytes treated with _-carotene have reduced TNF_-mediated ROS production and restored adiponectin and
glucose transporter 4 production thatmay improve insulin resistance
[141]. _-carotene supplementation decreased retinol
deficiency-induced hepatic lipid peroxidation and enhanced
CAT and GST activities, thus reducing hepatic oxidative
stress [142]. Similar to lycopene, _-carotene acts as an antioxidant
in liver or modulates adipokine production from
adipose tissue to display indirect effects against NAFLD.
Lutein is also a common carotenoid that is found in most
fruits and vegetables that reduces hepatic free cholesterol,
lipid peroxidation, and TNF-_ because of decreased NF-_B
p65 DNA binding activity in high cholesterol diet-fed Hartley
guinea pigs [143]. Fucoxanthin is a carotenoid from edible
brown algae that is characterized by its unique structure
including an allenic bond and 5, 6-monoepoxide that differs
from common carotenoids and has exhibited antiobesity
and antidiabetic effects [144, 145]. Mice fed a fucoxanthinsupplemented
HFD had reduced proinflammatory cytokine
levels, including leptin, TNF-_, monocyte chemotactic protein
1 (MCP-1), and IL-6, and increased adiponectin in plasma
and adipose tissue [146, 147]. Fucoxanthin also decreased
hepatic TG and cholesterol levels by suppressing activities
of malic enzyme, FAS, glucose-6-phosphate dehydrogenase,
3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase,
and acyl coenzyme A: cholesterol acyltransferase, thus
decreasing hepatic lipogenesis and increasing _-oxidation
[146]. Fucoxanthin reduces hyperglycemia and hyperinsulinemia
both in HFD-fed C57BL/6N mice and diabetic/obese
KK-A(y) mice [146, 147]. Fucoxanthin also decreased hepatic
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Mol. Nutr. Food Res. 2013, 00, 1–25 7
Table 1. Chemopreventive activities and mechanisms of dietary natural compounds on NAFLD
Class Compound Structure Dietary source Molecular mechanisms and targets References
Upregulation Downregulation
Carotenoids Lycopene Tomatoes,
watermelon,
papaya and orange
_ Antioxidants (GSH, CAT,
GR, and GST; SD rats,
gerbils)
_ Nrf2-dependent HO-1 (SD
rats)
_ Hepatic inflammation
(SD rats)
_ Lipid peroxidation (SD rats)
_ FABP7 (C57BL6/J mice)
[136–139]
_-Carotene Red palm oil,
pumpkin, and leafy
green vegetables
_ Adiponectin (3T3-L1 cells)
_ Glut4 (3T3-L1 cells)
_ Antioxidants (CAT and GST;
RD rats)
_ Lipid peroxidation (RD rats)
_ ROS production (3T3-L1 cells)
[140–142]
Lutein Spinach and kale - _ Lipid peroxidation (Guinea
pigs)
_ NF-_B-mediated TNF-_
(Guinea pigs)
[143]
Fucoxanthin Brown algae _ Plasma adiponectin
(C57BL6/N mice)
_ Proinflammatory adipokines
(C57BL6/N mice, KK-A(y) mice)
_ Hepatic lipogenesis (FAS,
G6PD, and HMG-CoA
reductase) (C57BL6/N mice)
_ SCD-1 (KK-A(y) mice)
[146–148]
Omega-3
PUFAs
EPA Fish oils and golden
algae oil
_ Plasma adiponectin
(Balb/cA mice)
_ CPT-1 (Medaka)
_ AMPK_ and PPAR_
(Pten-deficient mice)
_ Hepatocytes necrosis (Balb/cA
mice)
_ Inflammatory cells infiltration
(Balb/cA mice)
_ Oxidative stress (Balb/cA mice)
_ SREBP-1 transcription factor
(Medaka)
_ Lipogenic and fibrogenic genes
(HepG2 cells, Medaka, Wistar
rats)
[156–159,
161–163]
DHA _ SOD activity (Balb/c mice)
_ Plasma adiponectin
(C57BL6/N mice)
_ Genes involved in lipolysis
and _-oxidation (Kunming
mice)
_ Insulin sensitivity
(C57BL6/N mice)
_ Inflammation and fibrosis
(Ldlr(−/−), ob/ob mice)
_ Hepatic lipogenesis (FAS and
SREBP-1; ob/ob, Kunming
mice)
_ Kupffer cells activation (Ldlr
(−/−) mice)
_ IL-1_ and TNF-_ (Ldlr (−/−)
mice)
[169–176]
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8 M.-H. Pan et al. Mol. Nutr. Food Res. 2013, 00, 1–25
Table 1. Continued
Class Compound Structure Dietary source Molecular mechanisms and targets References
Upregulation Downregulation
Flavones Apigenin Parsley and celery _ AMPK signaling in
adipocytes (3T3-L1 cells)
_ HSL and lipolysis in
adipocytes (3T3-L1 cells)
[178]
Luteolin Parsley and celery _ CPT-1 (HepG2 cells)
_ AMPK-dependent ACC
phosphorylation (HepG2
cells)
_ SREBP-1 and FAS (HepG2
cells)
[179]
Nobiletin Citrus peels _ Adiponectin secretion
(ST-13 preadipocytes,
3T3-L1 cells)
_ Insulin sensitivity (ob/ob,
C57BL/6J mice)
_ Proinflammatory
adipokines (ob/ob,
C57BL/6J mice)
[180–183]
Baicalein Baical Skullcap _ FA oxidation (C57BL/6J
mice)
_ AMPK_ and PPAR_
(C57BL/6J mice)
_ Hepatic inflammation
(C57BL/6J mice)
_ SREBP-1-dependent
lipogenic genes
(C57BL/6J mice)
[184]
Flavonols Quercetin Onion and broccoli
and GPx) (C57BL/6, db/db
mice)
_ Nrf2-targeted genes
(Wistar rats)
_ _-oxidation (C57BL/6J
mice)
_ Glucose uptake (HepG2
cells)
_ Proinflammatory
cytokines (C57BL/6 mice,
HepG2 cells)
_ Antioxidants (SOD, CAT,
_ Lipogenic and fibrogenic
genes (C57BL/6J, C57BL/6
mice)
_ NF-_B and JNK signaling
(Wistar rats, C57BL/6
mice)
_ Lipoperoxidation and
DNA damage (C57BL/6
mice)
[185–192]
Kaempferol Broccoli and tea - _ ROS production (Chang
liver cells)
[193]
Flavanols
(catechins)
Epigallocatechin3-gallate
(EGCG)
Tea _ PI3K/Akt signaling
_ FA oxidation (UCP-2,
SCD-1; New Zealand
black mice)
_ Dietary lipid oxidation
(New Zealand black mice)
_ Oxidative stress (SD rats)
_ Hepatic inflammation,
necrosis and fibrosis
(TGF/SMAD signaling; SD
rats)
_ Plasma adipokines
(C57BL/6 mice)
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Mol. Nutr. Food Res. 2013, 00, 1–25 9
Table 1. Continued
Class Compound Structure Dietary source Molecular mechanisms and targets References
Upregulation Downregulation
_ Inflammatory molecules
(iNOS, COX-2, and TNF-_;
SD rats)
_ FOXO1 and NF-_B (SD
rats)
_ Dietary lipids incorporate
to liver (C57BL/6 mice)
[194–199]
Theaflavin (TF-1) Black tea _ AMPK signaling (HepG2
cells)
_ FA oxidation (HepG2
cells)
_ ACC activity (HepG2 cells)
_ Oxidative stress and
hepatocytes apoptosis
(I/R injury mice)
_ Inflammatory cytokines
(I/R injury mice)
[200, 201]
Flavanones Naringenin Citrus
_ FA oxidation (CYP450
IVA1, PPAR_, and
PGC-1_-targeted aCPT-1,
ACO; ICR, Ldlr (−/−) mice)
_ Insulin sensitivity (Ldlr
(−/−) mice)
_ VLDL-TG and VLDL-apoB
secretion (Ldlr (−/−)
mice)
_ Lipogenic genes (Ldlr
(−/−) mice)
[202–204]
Hesperetin Citrus - _ PAP activity and TG
synthesis (SD rats)
[205]
Anthocyanidins
Cyanidin-3-O-_glucoside
Cherries and
strawberries
_ GSH synthesis (HepG2
cells, db/db mice)
_ AMPK signaling (HepG2
cells)
_ FA oxidation (CPT-1)
(HepG2 cells)
_ TG synthesis (mtGPAT1;
HepG2 cells, KK-A(y)
mice)
_ Neutrophil infiltration
(db/db mice)
_ Plasma adipokines (db/db
mice)
_ ROS production (HepG2
cells, db/db mice)
_ JNK signaling (db/db
mice)
_ ACC activity (HepG2 cells)
[207–210]
Isoflavones Daidzein Soybean _ Antioxidants (SOD-2 and
GST; Wistar rats)
_ De novo lipogenesis
(C57BL/6J mice)
_ SCD-1(Wistar rats,
C57BL/6J mice)
[211, 212]
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10 M.-H. Pan et al. Mol. Nutr. Food Res. 2013, 00, 1–25
Table 1. Continued
Class Compound Structure Dietary source Molecular mechanisms and targets References
Upregulation Downregulation
_ Blood insulin and
adipokines (C57BL/6J
mice)
Genistein _ FA oxidation (PGC-1,
PPAR_ and CPT-1; HepG2
cells, C57BL/6J mice)
_ Anti-oxidants (GPx, GR,
and GSH; Wistar rats)
_ IRS-1/PI3K/Akt signaling
and Glut1 (HepG2 cells)
_ Glucokinase activity
(db/db mice)
_ Hepatic inflammation
and apoptosis (C57BL/6J
mice)
_ SREBP-1 and lipogenic
genes (SD rats)
_ Proinflammatory
cytokines (C57BL/6J
mice, SD rats)
_ JNK and NF-_B signaling
(SD rats, HepG2 cells)
_ PEPCK and G6Pase
(db/db mice)
[213–225]
Other phenolic
compounds
Resveratrol Grapes, red wine _ FA oxidation (CPT-1 and
ACO; Zucker, SD rats)
_ Nrf2-targeted genes and
antioxidants (SD rats)
_ UCP-2 (Wistar rats)
_ IRS-1/PI3K/Akt signaling
and insulin sensitivity
(C57BL/6J, KK-A(y) mice)
_ SIRT1 activity and AMPK
signaling (HepG2 cells,
SD rats)
_ FOXO deacetylation
(HepG2 cells)
_ Lipogenic genes
(SREBP-1, FAS, ACC,
G6PD, and HMG-CoA
reductase; HepG2 cells,
C57BL/6J mice, hamsters)
_ Lipid peroxidation and
oxidative stress (Wistar
rats)
_ Proinflammatory
cytokines (Wistar rats)
_ ER stress (HepG2 cells)
[226–229,
231–240]
Curcumin Turmeric _ Mitochondria biogenesis
and function (ob/ob mice,
New Zealand rabbits,
primary hepatocytes)
_ Adiponectin of
adipocytes (ob/ob mice)
_ Insulin sensitivity (Akt
signaling; HSCs)
_ GCL activity (HSCs)
_ AMPK signaling (HSCs)
_ SREBP-1 and HMG-CoA
reductase (ob/ob mice,
SD rats)
_ ROS production (New
Zealand rabbits, primary
hepatocytes, AML-12
hepatocytes)
_ Inflammatory cells
infiltration (NMRI mice)
_ HSC activation and
fibrogenic genes
expression (HSCs)
[242–255]
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Mol. Nutr. Food Res. 2013, 00, 1–25 11
Table 1. Continued
Class Compound Structure Dietary source Molecular mechanisms and targets References
Upregulation Downregulation
_ Proinflammatory
cytokines (ob/ob, NMRI
mice, SD rats)
_ JNK, NF-_B, and SOCS3
(primary hepatocytes,
ob/ob, NMRI mice)
_ LDLR and LOX-1 (HSCs)
[242–255]
FABP7, FA-binding protein 7; G6PD, glucose-6-phosphate dehydrogenase; GCL, glutamate-cysteine ligase GR, GSH
reductase; ICR, institute for cancer research; iNOS, inducible nitric
oxide synthase; RD, retinol deficiency.
stearoyl-CoA desaturase 1 (SCD-1) expression,which is an enzyme
that catalyzes MUFA biosynthesis from SFAs through
leptin signaling regulation that suppresses 18:0 desaturation
into 18:1n-9 in the liver [148].
3.2 Omega-3 PUFAs
Growing evidence clearly demonstrates that an increased intake
of marine omega-3 PUFAs, such as eicosapentaenoic
acid (20:5 n-3, EPA) and docosahexaenoic acid (22:6 N-3,
DHA), is beneficial to diverse physiological functions and
human health, including the improvement of metabolic syndrome.
Omega-3 PUFA supplementation has been shown to
ameliorate hepatic steatosis in human studies and in different
animal models [149–152]. Basically, the beneficial function
of omega-3 PUFAs to NAFLD most likely is contributed by
their incorporation into plasma phospholipids that modulate
membrane fluidity and intracellular signaling or that alter the
lipid composition of the liver [153].
In patients who have been diagnosed with a NASH, daily
dietary intake of 2700 mg of EPA for 12 months resulted
in decreasing the serum ALT, FFA, and thioredoxin levels,
which contribute to hepatic oxidative stress. Among the 23 patients,
seven of them showed improvement in hepatic steatosis
and fibrosis. Decreased hepatocyte ballooning and lobular
inflammation were found in six patients. The most safety
concern of EPA is bleeding tendency, whereas there is no
adverse event that has occurred during EPA treatment in all
patients of this study [154]. A cross-sectional observational
study showed the positive effect of dietary EPA in Japanese
men with NAFLD but not in women that with unidentified
reason [155]. In HFD-fed mice, dietary intake of EPA
is effective in reducing fatty droplets by decreasing the hepatic
cholesterol, TG, and nonesterified FAs [156, 157]. When
mice were fed high sucrose/HFD supplemented with EPA,
reduced D-galactosamine-induced hepatic injury occurred, as
evidenced by a decreased hepatocyte necrosis and inflammatory
cell infiltration. This result was also accompanied
by lowered hepatic TG levels via the reduction of FAS and
SCD-1 gene expression, decreased ROS production, and increased
plasma adiponectin [158]. These effects could contribute
to suppressing the progression of hepatitis. Moreover,
EPA intake is found to abrogate HFD-induced SREBP-1,
FAS, and ACC1 mRNAs, while increasing the CPT-1 expression;
thus, it could decrease FA synthesis and promote mitochondrial
_-oxidation [159]. A diet that is deficient in methyl
groups, such as methionine and choline, is another animal
model of NAFLD that is caused by impairedmitochondrial _oxidation [160]. Several studies have demonstrated that EPA
decreased hepatic steatosis and the progression of fibrosis by
suppressing TG synthesis and the expression of fibrogenic
genes, such as TGF-_1, _-smoothmuscle actin (_-SMA), and
collagen [161, 162]. In Pten-deficient (liver-specific deletion
of phosphatase and tensin homolog) mice, an NAFLD animal
model characterized by increased hepatic lipogenesis,
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12 M.-H. Pan et al. Mol. Nutr. Food Res. 2013, 00, 1–25
EPA improved steatohepatitis by reducing steatosis, lobular
inflammation, and hepatocytes ballooning. Additionally,
supplementation with dietary EPA for 76 wk reduced the
amount of hepatocellular carcinoma. The suppressed effect
of EPA is due to a decrease in hepatic ROS production and
upregulation of AMP-activated protein kinase (AMPK) _ and
PPAR_ expression, which may repress the expression of lipogenic
genes. Analyzing the lipid composition of the liver
showed that EPA causes a dramatic change in the content of
arachidonic acid and that EPAserves as the anti-inflammatory
mechanism that acts as an inactive lipid mediator compared
to arachidonic acid [163]. A recent study revealed that EPA
and the oxidized form suppressed the liver X receptor agonistinduced
TG synthesis in HepG2 cells by the downregulation
of SREBP-1, a transcription factor that is involved in the expression
of lipogenic genes, including FAS, ACC, and SCD1 [164].
Two controlled trial studies showed that children with
NAFLD supplemented with 250 and 500 mg DHA per day for
6–24 months had improved liver steatosis and insulin sensitivity
accompanied by lowered TG and ALT levels [165, 166].
Moreover, no adverse effect was found in 60 children with
biopsy-proven NAFLD when supplemented with DHA supplementation
at dosage of 250 and 500 mg for 6 months [161].
In animal models of diet-induced NAFLD, which included
a high carbohydrate diet, HFD, and choline-deficient diet,
the dietary intake of DHA reduced hepatic steatosis, inflammation,
and fibrosis and decreased hepatic and serum
total cholesterol levels and lipid peroxidation [167–169]. Increased
SOD activity and decreased activity of SREBP-1 account
for the inhibitory effect of DHA [167, 168]. Furthermore,
alteration of the lipid and FA compositions and increases
in omega-3 PUFAs in the liver provide a possible
mechanism for the protective effect of DHA against NAFLD
and NASH [169]. DHA was also found to ameliorate hepatic
steatosis and inflammation by the downregulation of the expression
of genes that are involved in TG synthesis (FAS,
SREBP-1c, and PPAR_). The suppression of Kupffer cells
and macrophage activation, inflammatory cytokine production
(IL-1_ and TNF-_), and nuclear NF-_B accumulation
occurred in dietary DHA-treated Ldlr−/− (deficient in the
low-density lipoprotein [LDL] receptor) and leptin-deficient
(ob/ob) mice [170, 171]. Mice treated with trans-10, cis-12conjugated linoleic acid developed NAFLD and insulin resistance,
while supplementation with DHA reduced fatty
liver, TG, and insulin levels and improved insulin resistance
[172]. Compared to EPA, DHA is effective at restoring
serum adiponectin levels, which contributes to improving
hepatic insulin function [173]. An in vitro study showed
that DHA decreased palmitate-induced lipid accumulation
and inflammatory cytokine production through suppressing
the activation of nucleotide-binding oligomerization domain
(NOD) like receptor protein 3 inflammasomes, thus, in turn,
blocking caspase-1-mediated IL-1_ and IL-18 release [174].
There are a number of studies that have demonstrated that
both EPA and DHA regulate a variety of genes that are implicated
in lipogenesis, lipolysis, and _-oxidation in liver and
adipose tissue, which suggests that they function on hepatic
lipid metabolism and NAFLD [175, 176]. Although dietary
intake of omega-3 PUFAs is exerting a beneficial effect on
NAFLD, studies exhibited that increased hepatic lipid peroxidation
also occurred. With regard to this finding, the addition
of antioxidants is suggested for omega-3 PUFAs in the intervention
of diseases [177].
3.3 Polyphenols
Previous studies showed thatmany polyphenolic compounds
in nature exert health-promoting effects when consumed in
food.
3.3.1 Flavonoids
Flavonoids are plant secondary metabolites that appear ubiquitously
in fruits, vegetables, nuts, and seeds and can be classified
into seven subgroups as follows: flavones, flavanones,
flavonols, flavanonols, isoflavones, flavanols (catechins), and
anthocyanidins, based on differences in the structure of the
aglycone C ring. The diversity of the functional groups (by
hydroxylation, methoxylation, or glycosylation) provides the
structural variation and different biological properties of the
flavonoids. More than 1000 natural flavonoids have been identified,
and some of them exhibit a broad spectrum of biological
properties and widespread beneficial effects for human
health.
3.3.1.1 Flavones
Apigenin (4_,5,7-trihydroxyflavone) belongs to the flavone
class and is most prevalent in parsley and celery. It has been
reported that apigenin inhibited lipolysis of 3T3-L1 adipocytes
by decreasing HSL gene expression and upregulating AMPK
signaling, which can attenuate adipogenesis and FFA release
from adipocytes [178]. Luteolin is another flavone and ismost
often present in thyme and other plants, including Brussels
sprouts, cabbage, onion, broccoli, and cauliflower. Luteolin is
also found to reduce palmitate-stimulated lipid accumulation
in HepG2 cells by decreasing SREBP-1 and FAS as well as
increasing CPT-1 gene expression. In addition, luteolin treatment
induced AMPK signaling and, in turn, phosphorylated
ACC (thus inhibiting the ACC activity) and reduced the production
of malonyl-CoA, an allosteric inhibitor of CPT-1 that
contributes to increased _-oxidation [179]. Nobiletin is a polymethoxyflavone
that is rich in citrus peel and is reported to
suppress proinflammatory adipokine production, such as the
production ofMCP-1 and TNF-_, and to increase adiponectin
secretion in adipocytes, both in vitro and in vivo [180–183].
In HFD-fed mice and leptin-deficient (ob/ob) mice, dietary
intake of nobiletin improved plasma glucose tolerance and
insulin sensitivity [181, 182], which suggests that insulin
is acting on the improvement of adipose tissue-mediated
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Mol. Nutr. Food Res. 2013, 00, 1–25 13
insulin resistance, which plays a central role in the pathogenesis
ofNAFLD. Baicalein naturally occurs in the roots of Scutellaria
baicalensis and has been found to reduce HFD-induced
hepatic inflammation and lipid ectopic deposition by inhibiting
SREBP-1-dependent lipogenic gene expression. Baicalein
also enhances hepatic phosphorylated AMPK, PPAR_, and its
targeted gene expression and, thus, represses FA and cholesterol
synthesis and promotes FA oxidation [184].
3.3.1.2 Flavonols
Quercetin is a natural flavonol that is typically present in
onions, broccoli, and leafy green vegetables. Many in vivo
studies have supported the preventive and therapeutic efficacy
of quercetin against NAFLD. In HFD-fed animals, the
dietary feeding of quercetin reduced hepatic lipid accumulation,
the infiltration of inflammatory cells, and portal fibrosis,
and it improved insulin resistance [185–187]. The mechanisms
include the reduction of lipogenic gene expression,
induction of _-oxidation, upregulation of Nrf2-targeted antioxidative
enzyme expression, and a decrease in NF-_B and
serum IL-18 levels. Dietary quercetin also reduced hepatocellular
fibrosis in HFD-fed gerbils through the regulation
of Sirtuin (SIRT) 1, an NAD+-dependent protein deacetylase
that is known to impair the activity of PPAR_,which results in
a decrease in FA oxidation [188]. Feedingmice a methionineand
choline-deficient diet supplemented with quercetin decreased
liver steatosis and inflammatory cell accumulation
through attenuating NF-_B and JNK as well as reducing the
fibrogenic gene expression, such as the expression of _-SMA,
TGF-_1, Col1_1, and Col3_1 [189]. The reduction of hepatic
lipoperoxidation, DNA damage, and increased SOD, CAT,
and GPx activities also contributes to the preventive action
of quercetin against NAFLD [189,190]. In addition, quercetin
has been shown to ameliorate hyperglycemia and to increase
glucose uptake in diabetic db/db mice and oleic acid-treated
HepG2 cells via increasing intracellular antioxidants and decreasing
TNF-_ and IL-8 expression [191, 192]. Kaempferol is
another typical flavonol that is present in broccoli, tea, and
various vegetables. Both kaempferol and quercetin prevented
the production of peroxides, superoxide anion, and nitric oxide
induced by proinflammatory cytokines in Chang Liver
cells, which could reduce hepatic oxidative stress [193].
3.3.1.3 Flavanols (catechins)
Catechins and theaflavins (TFs) are bioactive compounds in
green tea and black tea that have been shown to possess wide
health benefits. Epigallocatechin-3-gallate (EGCG) is the most
abundant polyphenolic compound in green tea, and the dietary
feeding of EGCG reduced HFD-induced hepatic steatosis,
inflammation, and fibrosis, which can be attributed to
decreased lipid peroxidation and _-SMA expression and increased
GSH levels in liver [194,195]. EGCG prevented HFDinduced
oxidative stress, and toxicity could be associated with
reduced hepatic CYP2E1 that is overexpressed inNASH[194].
Long-term feeding of EGCG is effective in the reduction of
HFD-induced hyperglycemia and plasma insulin levels and
the improvement of insulin resistance, which could be the
result of decreasing serum MCP-1, C-reactive protein, and
IL-6 [195, 196]. Rats that received intraperitoneal injections
of EGCG also reduced their HFD-induced hepatic fatty score,
necrosis, inflammatory foci, and fibrosis, followed by decreasing
TGF-_1, _-SMA, TNF-_, inducible nitric oxide synthase,
and cyclooxygenase 2 gene expression through the modulation
of the TGF/SMAD, PI3K/Akt/FOXO1, and NF-_B signaling
pathways [197]. Male New Zealand black mice that
received orally administered EGCG decreased gene expressions
of malic enzyme, SCD-1, and glucokinase in the liver,
whereas uncoupling protein 2 (UCP-2) was increased, which
could possibly be the cause of increased FA oxidation [198].
Another study used 13C-labeled palmitate and a diet that
was supplemented with corn oil as a natural source of 13Cenriched
lipids; this study showed that EGCG increased the
oxidation of dietary lipids and decreased the incorporation of
dietary lipids in the liver, thus reducing HFD-induced lipid
accumulation in the liver [199]. TFs are major polyphenols in
black tea that include theaflavin (TF-1), theaflavin-3-gallate,
and theaflavin-3,3_-digallate. In human HepG2 cells, TF-1,
theaflavin-3-gallate, and theaflavin-3,3_-digallate are more effective
than (-)-epicatechin (EC), (-)-epicatechin gallate (ECG),
(-)-epigallocatechin (EGC), and EGCG on reduction of mixture
of long-chain FA-induced lipid accumulation. These
theaflavins are potent at inducing the activation of AMPK
and the inactivation of ACC, both in HepG2 cells and in the
livers of HFD-fed mice [200]. By measuring the rates of incorporation
of [14C]acetate into the hepatic FAs, theaflavins
were found to reduce FA synthesis while increasing FA oxidation
[200]. Dietary TF-1 reduced hepatic steatosis, oxidative
stress, hepatocyte apoptosis, andmacrophage infiltration
in methionine- and choline-deficient diet-fed and ischemiareperfusion
(I/R) injuredmice. Reduced ROS production and
decreased TNF-_, IL-6, and inducible nitric oxide synthase expression
could be the major mechanisms of TF-1 [201].
3.3.1.4 Flavanones
Citrus peels are a rich source of naringenin and hesperetin,
both belong to the flavanones subgroup. An animal study
showed that a normal diet supplemented with naringenin
can increase gene and activity of various enzymes that are involved
in hepatic FA oxidation, including carnitine octanoyltransferase,
acyl-coenzyme A oxidase (ACO), bifunctional enzyme,
and 3-ketoacyl-coenzyme A thiolase, as well as their
gene expression, while they are not found in hesperetintreated
mice.Naringenin also significantly increased the gene
expression of microsomal CYP IV A1, which is involved in
the _-oxidation of FAs [202]. Similar effects also occurred
in HFD-fed Ldlr−/− mice. Dietary feeding of naringenin
ameliorated hepatic steatosis, which is evidenced by a reduction
in hepatic TG and VLDL–TG and VLDL–apolipoprotein
B secretion. This effect resulted from naringenin increasing
PPAR_ and PPAR_ peroxisome proliferator-activated
receptor _ coactivator-1_, which is mediated by CPT-1 and
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14 M.-H. Pan et al. Mol. Nutr. Food Res. 2013, 00, 1–25
acyl-CoA oxidase gene expression (which are enzymes that
are involved in mitochondrial and peroxisomal FA oxidation)
[203]. In high cholesterol-fed mice, in addition to increased
FA oxidation, naringenin also reduced hyperlipidemia and
hepatic steatosis by the reduction of cholesterol and FA synthesis
via downregulation of the expression of various genes
in liver [204]. Moreover, improved glucose utilization and
insulin sensitivity were found in naringenin-supplemented
mice [203,204]. Another citrus flavanone, hesperetin, is found
to decrease orotic acid induced hepatic TG accumulation and
cholesterol levels, which contributes to reducing hepatic microsomal
phosphatidate phosphohydrolaseactivity, which is
the rate-limiting enzyme for TG synthesis [205].
3.3.1.5 Anthocyanidins
Anthocyanidins are plant pigments that have red and blue
colors and that commonly occur in fruits and vegetables,
such as blueberries and grapes. Several in vitro and in vivo
studies revealed the function of cyanidin-3-O-_-glucoside
on insulin-resistance-associated NAFLD. Diabetic/obese
KK-A(y) mice are an animal model of type 2 diabetes that exhibit
a phenotype with severe obesity, hyperlipidemia, and insulin
resistance [206]. Feeding cyanidin-3-O-_-glucoside ameliorated
hepatic steatosis by the reduction of TG synthesis
via the downregulation of mitochondrial acyl-CoA:glycerolsn3-phosphate acyltransferase 1, an enzyme that is involved
in converting glycerol-3-phosphate and acyl-CoA into
phosphatidic acid, which is a precursor of TG and glycerophospholipids
[207]. In both HFD-fed and diabetic db/db
mice, the oral administration of cyanidin-3-O-_-glucoside
reduced hepatic steatosis and neutrophil infiltration [208].
Cyanidin-3-O-_-glucoside also attenuated obesity-associated
insulin resistance by lowering the fasting glucose levels. Additionally,
cyanidin-3-O-_-glucoside decreased proinflammatory
adipokine expression in adipose tissue and in plasma
through the suppression of JNK signaling [208]. Another
study showed the effect of cyanidin-3-O-_-glucoside on the
reduction of hepatic steatosis, neutrophil infiltration, and
hepatocyte apoptosis through preventing oxidative injury that
is evidenced by the inhibition of ROS production and the increase
of GSH synthesis, both in high glucose-treated HepG2
cells and in diabetic db/db mice [209]. In addition to the antioxidative
property, cyanidin-3-O-_-glucoside increases cellular
AMPK activity and suppresses ACC activity, thus causing decreased
malonyl-CoA levels and further stimulation of CPT-1,
which leads to enhanced FA _-oxidation and finally inhibits
lipid accumulation in HepG2 cells [210].
3.3.1.6 Isoflavones
Isoflavones, such as genistein and daidzein, are abundant
in soybeans; these isoflavones are a subclass of flavonoids.
Isoflavones have been considered to be phytoestrogens and
are recognized for improving health and aiding in the prevention
of various diseases. In HFD-fed mice, daidzein reduced
hepatic steatosis and de novo lipogenesis by downregulating
gene expressions of ACC_, FAS, adenosine triphosphate citrate
lyase, and 1-acylglycerol-3-phosphate O-acyltransferase2 [211]. Daidzein also restored HFD-induced lowered SOD-2
and GST _3 gene levels. Another study also suggested that
a reduction in PPAR_ and SCD-1 could be an additional
mechanism of daidzein-reduced hepatic steatosis [212]. Moreover,
both studies showed that daidzein supplementation improved
insulin resistance through decreasing blood insulin
and adipokine (TNF-_, leptin) levels.
Genistein represents a potent chemopreventive agent that
acts against NAFLD through the interaction of many different
mechanisms that are related to lipid metabolism, energy
metabolism, insulin sensitivity, and mitochondrial function.
A study compared the activity of genistein and daidzein in the
modulation of lipid metabolic gene expression in liver using
microarray analysis. The result demonstrated that genistein
was more effective than daidzein in lowering TG levels by targetingmany
genes that are involved in lipid and carbohydrate
metabolism [213], although another in vitro study suggested
that both genistein and daidzein upregulated CPT-1A enzyme
activity [214]. Two in vitro studies also showed the ability of
genistein to modulate gene expression that is involved in
FA oxidation and to suppress lipogenesis via targeting the
transcription factors PPAR_ and SREBP-1 [215, 216]. Dietary
intake of genistein decreased hepatic steatosis, inflammatory
cells infiltration, and hepatocyte ballooning in HFD-fed
rats and mice. These effects could contribute to genistein
alternating between adipocytemetabolism and reduced TNF_ production [217, 218]. Moreover, genistein decreased liver
fat accumulation, possibly through increasing FA oxidation,
as evidenced by increased PGC-1 and PPAR_-target genes,
peroxisomal acyl-CoA oxidase, and mitochondrial medium
chain acyl-CoA dehydrogenase, as well as UCP-2 [219]. A
study that used neonatal rats fed a diet with genistein showed
decreased hepatic steatosis and inflammation by reducing
FAS and SREBP-1 expression, but there was no effect on
PEPCK and G6Pase.Hepatocyte apoptosis and hepatic TNF-_
expression were also reduced [220]. Genistein treatment decreased
HFD-induced hepatic inflammationwith lowered levels
of TNF-_ and IL-6 in male sprague dawley (SD) rats. The
results of molecular studies showed genistein suppression
of JNK and NF-_B inflammatory signaling, which suggests
that anti-inflammation is one of the mechanisms that accounts
for genistein impacting the prevention ofNASH [221].
High glucose-treated rats supplemented with genistein had
improved insulin resistance and liver injury through the increased
activities of enzymatic (GPx, GSH reductase, and
GSH) and nonenzymatic (vitamin C and E) antioxidants as
well as by decreased 3-nitrotyrosine, a biomarker of inflammation
that is formed by the reaction between ONOO− and
the free tyrosine or tyrosine residues found in proteins [222].
Genistein also improved hepatic insulin signaling by the
upregulation of IRS-1/PI3K-Akt signaling in high fructoseand
HFD-fed mice [223]. Genistein supplementation elevated
hepatic glucokinase activity, while suppressing the
elevation of hepatic gluconeogenic G6Pase and PEPCK
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Mol. Nutr. Food Res. 2013, 00, 1–25 15
activities in diabetic db/db mice, which modulates hepatic
glucosemetabolism and contributes to improved insulin sensitivity
[224]. In palmitate-treated HepG2 cells, genistein is
found to improve glucose uptake by the upregulation of IRS1/PI3K signaling and Glut1 as well as by the inhibition of
JNK signaling [225]. These studies suggested that genistein
could act as an insulin sensitizer that contributes to improving
insulin resistance mediated by NAFLD.
3.3.2 Resveratrol
Resveratrol (3,5,4_-trihydroxystilbene), a compound found
largely in the skins of red grapes, is widely accepted as a
chemopreventive agent and exerts positive health effects by
its multiple biological activities, such as antioxidative, antiinflammatory,
anticancer, antiobesity, antidiabetic, and antiaging
properties. The beneficial effect of resveratrol on
metabolic syndrome has also been addressed. A number of
in vivo animal models of NAFLD have exhibited the potential
inhibitory effect of resveratrol. In several models of HFDinduced
NAFLD, dietary intake of resveratrol efficiently suppressed
hepatic steatosis; reduced lipid, cholesterol, and TG
accumulation; inhibited inflammatory cell infiltration; and
inhibited insulin resistance. The molecular mechanisms include
decreased lipogenesis, as shown by reduced gene expression
levels of SREBP-1, FAS, ACC, glucose-6-phosphate
dehydrogenase, and HMG-CoA reductase, and increased FA
oxidation by the upregulation of CPT-1 and ACO [226–230].
However, two studies showed that a dose–response effect was
not found in resveratrol treatment [229, 231]. Male C57BL/6J
mice fed 0.005% or 0.02% resveratrol reduced HFD-induced
hepatic steatosis, whereas the lower dose of resveratrol
(0.005%) appeared to be more beneficial than the higher dose
(0.02%). Another study showed that male fa/fa Zucker rats,
an animal model of obesity and liver steatosis, orally administered
resveratrol at 15 and 45 mg/kg body weight reduced
liver weight, TG content, and oxidative stress. This inhibitory
effect of resveratrol contributes to increase enzyme activity
of CPT-1 and ACO. Nevertheless, a dose–response pattern
was not found of resveratrol treatment in this study. By using
microarray analysis, dietary resveratrol is found to modulate
the expression of various genes that are involved in hepatic
lipid metabolism, including cholesterol, FA, and lipid synthesis
and metabolism as well as transport [232]. Resveratrol
has been shown to possess potent antioxidative activity that
prevents hepatic steatosis by decreasing oxidative stress and
upregulating antioxidative enzymes. Resveratrol upregulated
hepatic UCP-2, an anion transporter that is located in the
inner mitochondrial membrane that functions to reduce the
electrochemical gradient over the membrane, and it increased
the mitochondria content; thus, it could protect against HFDinduced
mitochondrial dysfunction in hepatocytes [233]. The
oral consumption of resveratrol is shown to suppress lipid
peroxidation by the upregulation of Nrf2 and by antioxidants,
including catalase, SOD, GSH, and vitamin C, which reduced
fructose-induced hepatic oxidative stress [234]. Lowered hepatic
TNF-_ has also occurred in resveratrol-treated rats, which
suggests that there is an anti-inflammatory function of resveratrol
in HFD-induced NAFLD [235]. Resveratrol attenuated
insulin resistance and reduced blood glucose, serum insulin,
and the hepatic glycogen content in HFD-fed mice and diabetic/
obese KK-A(y) mice, which is attributed to the upregulation
of IRS/PI3K/Akt signaling in the liver and improved
insulin sensitivity [236, 237]. Moreover, resveratrol is known
to induce SIRT1, amember of the mammalian SIRTs, which
are highly conserved protein deacetylases, and AMPK signaling
that might contribute to the modulation of many transcription
factors and molecules that are involved in lipogenesis
and insulin signaling. In palmitate-treated HepG2 cells,
treatment by resveratrol-induced SIRT1 and FOXO further
downregulated SREBP-1 expression and reduced lipid accumulation
[238]. When HepG2 cells were exposed to high glucose,
resveratrol abrogated the impairment of the phosphorylation
of AMPK and its downstream target, ACC, as well as
counteracted increased expression of FAS and lipid accumulation.
In addition, the activation of AMPK signaling is correlated
with resveratrol-stimulated SIRT1 activity [239]. A new
study showed that resveratrol ameliorated palmitate-induced
deregulation of insulin signaling and ER stress through the
activation of SIRT1-dependent FOXO deacetylation [240].
3.3.3 Curcumin
Curcumin (diferuloylmethane) is the major pigment from
dried rhizomes of the turmeric plant (Curcuma longa Linn)
and has been used as a spice and traditionalmedicine in Asia
for centuries. The chemopreventive property of curcumin
against various diseases and cancers has been confirmed in
a number of studies. Many previous in vivo studies have
also demonstrated the protective and therapeutic potential
of curcumin on NASH and NAFLD using different animal
models [241]. The mechanisms included anti-inflammatory
and antioxidative properties, inhibition ofHSC activation, reduced
lipogenesis, and improved insulin sensitivity. Dietary
curcumin decreased hepatic TG levels by the downregulation
of SREBP-1 and HMG-CoA reductase gene expression
and by increased mitochondrial biogenesis in HFD-fed obese
mice [242, 243]. Curcumin also suppressed macrophage infiltration
in liver tissue with lowered NF-_B, SOCS3, MCP1, and TNF-_ in HFD-fed mice and leptin-deficient (ob/ob)
mice [242–244]. In HFD-fed New Zealand rabbits, a diet supplemented
with curcumin reduced hepatic steatosis, inflammation,
and fibrosis, which is attributed to lower mitochondrial
ROS and improved mitochondrial function [245]. Improved
insulin and glucose tolerance occurs from curcumin
treatment in HFD-fed C57BL/6J mice, leptin-deficient (ob/ob)
mice, and cultivated human adipose tissues, and could contribute
to the lowered adipose tissue-derived proinflammatory
adipokines and increased adiponectin [244, 246]. TNF-_
is known to trigger the recruitment of inflammatory cells
and is a pathogenic factor in NAFLD. In mice administered
TNF-_ intraperitoneally, curcumin repressed the infiltration
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16 M.-H. Pan et al. Mol. Nutr. Food Res. 2013, 00, 1–25
Figure 1. Pathogenesis and development of NAFLD/NASH. Increased FFAs overflow from adipose tissue or diet activates
JNK and NF-_B
signaling where induces transcriptional expression of proinflammatory cytokines (such as TNF-_) and further cause IR.
Adipokines derived
from adipose tissue also cause hepatic insulin receptor (IR) via JNK and SOCS3 mediates IRS-1 serine phosphorylation,
results in decreasing
glucose uptake and promoting gluconeogenesis. FFAs trigger de novo lipogenesis through SREBP-1 transcription factor
mediated lipogenic
genes resulting TG accumulation. Upregulated PPAR_ by FFAs induce CPT-1 expression that facilitates FFAs import
tomitochondria. PPAR_
also increases enzymes involved in peroxisomal and mitochondrial oxidation. Increased ROS from FAs oxidation and
CYP2E1 results in
lipid peroxidation and oxidative stress contributes to mitochondria dysfunction and hepatocytes injury. FFAs activated JNK,
TNF-_, and
oxidative stress are contributed to hepatocytes lipotoxicity and apoptosis, further induce recruitment of inflammatory cells that
enhance
release of cytokines and activation of HSCs. Transactivated HSCs produce fibrogenic molecules that facilitate NASH
development.
of Kupffer cells and neutrophils in the liver and further reducedmyeloperoxidase
activity, lipid peroxidation, and nitrite
content [247]. In vitro studies exhibited that curcumin treatment
restored mitochondrial dysfunction and suppressed
ROS production and PEPCK and G6Pase production as well
as activating Akt signaling, which occurs via blocking the
JNK signaling. These effects might further improve insulin
sensitivity in FFA and iron overload mediated insulin resistance
hepatocytes [248, 249]. Many studies suggested that the
suppression of HSC activation by curcumin could be an important
mechanism in preventing NASH progression. The
activation of HSC occurs in response to hepatic injury and is
involved in the development of hepatic fibrosis. When hepatic
injury occurs, quiescent HSCs undergo enhanced cell proliferation,
the loss of lipid droplets, expression of _-SMA, and
excessive production of extracellular matrix. Treatment with
curcumin inhibited insulin-stimulated HSC activation by increased
intracellular lipid droplets and the expression of fibrogenic
genes. Molecular studies demonstrated that curcumin
interrupts insulin signaling and suppresses gene expression
of the insulin receptor in HSCs. Moreover, curcumin eliminated
insulin-induced ROS production and increased the
activity of glutamate-cysteine ligase in activated HSCs, which
indicates that ROS is implicated in insulin-mediatedHSC activation
[250]. In high glucose- and leptin-treated HSCs, curcumin
suppressed HSC activation by abrogated membrane
translocation of Glut proteins. These two studies showed
that curcumin interfered with hyperleptinemia-triggered p38
mitogen-activated protein kinase and IRS/PI3K/Akt signaling,
which lead to inhibiting HSC activation [251, 252]. Additionally,
curcumin stimulated glucokinase activity, increasing
the conversion of glucose to glucose-6-phosphate in
HSCs [252]. Further study revealed that curcumin abrogated
leptin-induced HSC activation contributes to the upregulation
of AMPK and the induction of gene expression of
PPAR_, SREBP-1, and CCAAT/enhancer binding protein _,
which leads to the accumulation of lipids [253]. Hypercholesterolemia
is characterized by elevated levels of plasma LDL
and is associated with NAFLD. Cellular uptake of oxidized
LDL is mediated by binding to cell-surface LDL receptors
of different cell types in the liver, which subsequently leads
to cholesterol uptake and increased ROS. Curcumin treatment
is found to suppress LDL and oxidized LDL induced
activation of HSCs, especially through downregulated LDL
receptor and lectin-like oxidized LDL receptor 1 expression,
which results in decreased fibrogenic gene expression and
intracellular cholesterol [254, 255]. Although curcumin is
known to have various biological properties, poor absorption
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Mol. Nutr. Food Res. 2013, 00, 1–25 17
and systemic bioavailability have been considered as a major
limitation for its application in clinic [256].
4 Conclusion
NAFLD pathogenesis is a complicated process that is involved
not only in molecular changes within the liver, but
also in metabolic signaling between organs. Understanding
the pathogenic factors, signaling networks, and molecular
mechanisms that are implicated in NAFLD could provide
biomarkers for treatment and intervention. Considerable accomplishments
in NAFLD research over the past few decades
have verified that increased oxidative stress, lipotoxicity, insulin
resistance, ER stress, hepatic inflammation, and obesity
play causal roles in the development and progression
of this disease and also offer opportunities for using nutritional
components as prevention or intervention. Furthermore,
dietary natural compounds provide a novel strategy
for obesity-associated NAFLD treatment. These dietary natural
compounds have great potential to not only influence
development and NAFLD progression, but also to target obesity
and insulin resistance-mediated pathogenesis. This general
beneficial effect of dietary natural compounds demonstrates
a complex interaction of many different mechanisms,
including a reduction in lipogenesis, an increase in FA oxidation,
an improvement in insulin signaling, an inhibition
of adipokine production, an elimination of oxidative stress,
and the suppression of hepatic inflammation by targeting
multiple signaling pathways, transcription factors, and enzymes.
The coordination of metabolic function between liver
and adipose tissue by dietary natural compounds also represents
a potential mechanism to prevent hepatic steatosis,
inflammation, and fibrosis (Fig. 1). Although the current
knowledge suggests that dietary natural compounds could be
helpful for NAFLD prevention and treatment, most of these
dietary natural compounds are lack of understanding about
relevance to human, such as the dosage, bioavailability, and
possible adverse effects. Well-designed experiments, appropriately
powered and large-scale trials are needed to examine
the applicability and roles of these dietary natural compounds
as chemopreventive agents of NAFLD.
This study was supported by the National Science Council
NSC 101–2628-B-022–001-MY4, 102-2628-B-002-053-MY3.
The authors have declared no conflict of interest.
5 References
[1] Angulo, P., Nonalcoholic fatty liver disease. N. Engl. J.Med.
2002, 346, 1221–1231.
[2] Shifflet, A., Wu, G. Y., Non-alcoholic steatohepatitis: an
overview. J. Formos. Med. Assoc. 2009, 108, 4–12.
[3] Neuschwander-Tetri, B. A., Clark, J. M., Bass, N. M., Van
Natta, M. L. et al., Clinical, laboratory and histological associations
in adults with nonalcoholic fatty liver disease.
Hepatology 2010, 52, 913–924.
[4] Vernon, G., Baranova, A., Younossi, Z. M., Systematic review:
the epidemiology and natural history of non-alcoholic
fatty liver disease and non-alcoholic steatohepatitis in
adults. Aliment. Pharmacol. Ther. 2011, 34, 274–285.
[5] Bhala, N., Jouness, R. I., Bugianesi, E., Epidemiology and
natural history of patients with NAFLD. Curr. Pharm. Des.
2013, 19, 5169–5176.
[6] Levene, A. P., Goldin, R. D., The epidemiology, pathogenesis
and histopathology of fatty liver disease. Histopathology
2012, 61, 141–152.
[7] Fan, J. G., Zhu, J., Li, X. J., Chen, L. et al., Prevalence of
and risk factors for fatty liver in a general population of
Shanghai, China. J. Hepatol. 2005, 43, 508–514.
[8] Jimba, S., Nakagami, T., Takahashi, M.,Wakamatsu, T. et al.,
Prevalence of non-alcoholic fatty liver disease and its association
with impaired glucose metabolism in Japanese
adults. Diabet. Med. 2005, 22, 1141–1145.
[9] Bedogni, G., Miglioli, L.,Masutti, F., Tiribelli, C. et al., Prevalence
of and risk factors for nonalcoholic fatty liver disease:
the Dionysos nutrition and liver study. Hepatology 2005, 42,
44–52.
[10] Kwon, Y. M., Oh, S. W., Hwang, S. S., Lee, C. et al., Association
of nonalcoholic fatty liver disease with components
of metabolic syndrome according to body mass index
in Korean adults. Am. J. Gastroenterol. 2012, 107,
1852–1858.
[11] Bellentani, S., Scaglioni, F., Marino, M., Bedogni, G., Epidemiology
of non-alcoholic fatty liver disease. Dig. Dis.
2010, 28, 155–161.
[12] McCullough, A. J., The clinical features, diagnosis and natural
history of nonalcoholic fatty liver disease. Clin. Liver
Dis. 2004, 8, 521–533.
[13] Ekstedt, M., Franzen, L. E., Mathiesen, U. L., Thorelius, L.
et al., Long-term follow-up of patients with NAFLD and elevated
liver enzymes. Hepatology 2006, 44, 865–873.
[14] Day, C. P., James, O. F., Steatohepatitis: a tale of two “hits”?
Gastroenterology 1998, 114, 842–845.
[15] Tilg, H., Moschen, A. R., Evolution of inflammation in nonalcoholic
fatty liver disease: the multiple parallel hits hypothesis.
Hepatology 2010, 52, 1836–1846.
[16] Reaven, G., Abbasi, F., McLaughlin, T., Obesity, insulin resistance,
and cardiovascular disease. Recent Prog. Horm.
Res. 2004, 59, 207–223.
[17] Ong, J. P., Elariny, H., Collantes, R., Younoszai, A. et al.,
Predictors of nonalcoholic steatohepatitis and advanced fibrosis
in morbidly obese patients. Obes. Surg. 2005, 15,
310–315.
[18] Colicchio, P., Tarantino, G., del, G. F., Sorrentino, P. et al.,
Non-alcoholic fatty liver disease in young adult severely
obese non-diabetic patients in South Italy. Ann. Nutr.
Metab. 2005, 49, 289–295.
[19] Liew, P. L., Lee, W. J., Wang, W., Lee, Y. C. et al., Fatty liver
disease: predictors of nonalcoholic steatohepatitis and gallbladder
disease in morbid obesity. Obes. Surg. 2008, 18,
847–853.
[20] Huang, H. L., Lin, W. Y., Lee, L. T., Wang, H. H.
et al., Metabolic syndrome is related to nonalcoholic
C_
2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.mnf-journal.com
18 M.-H. Pan et al. Mol. Nutr. Food Res. 2013, 00, 1–25
steatohepatitis in severely obese subjects. Obes. Surg.
2007, 17, 1457–1463.
[21] Dolce, C. J., Russo, M., Keller, J. E., Buckingham, J.
et al., Does liver appearance predict histopathologic findings:
prospective analysis of routine liver biopsies during
bariatric surgery. Surg. Obes. Relat. Dis. 2009, 5, 323–328.
[22] Harnois, F.,Msika, S., Sabate, J.M., Mechler, C. et al., Prevalence
and predictive factors of non-alcoholic steatohepatitis
(NASH) in morbidly obese patients undergoing bariatric
surgery. Obes. Surg. 2006, 16, 183–188.
[23] Gholam, P. M., Flancbaum, L., Machan, J. T., Charney, D.
A. et al., Nonalcoholic fatty liver disease in severely obese
subjects. Am. J. Gastroenterol. 2007, 102, 399–408.
[24] Yoo, J., Lee, S., Kim, K., Yoo, S. et al., Relationship between
insulin resistance and serum alanine aminotransferase as
a surrogate of NAFLD (nonalcoholic fatty liver disease) in
obese Korean children. Diabetes Res. Clin. Pract. 2008, 81,
321–326.
[25] Patton, H. M., Yates, K., Unalp-Arida, A., Behling, C. A. et al.,
Association between metabolic syndrome and liver histology
among children with nonalcoholic Fatty liver disease.
Am. J. Gastroenterol. 2010, 105, 2093–2102.
[26] Galic, S., Oakhill, J. S., Steinberg, G. R., Adipose tissue
as an endocrine organ. Mol. Cell Endocrinol. 2010, 316,
129–139.
[27] Choi, S. M., Tucker, D. F., Gross, D. N., Easton, R. M. et al.,
Insulin regulates adipocyte lipolysis via anAkt-independent
signaling pathway. Mol. Cell Biol. 2010, 30, 5009–5020.
[28] Stralfors, P., Honnor, R. C., Insulin-induced dephosphorylation
of hormone-sensitive lipase. Correlation with lipolysis
and cAMP-dependent protein kinase activity. Eur. J.
Biochem. 1989, 182, 379–385.
[29] Lam, T. K., Yoshii, H., Haber, C. A., Bogdanovic, E. et al., Free
fatty acid-induced hepatic insulin resistance: a potential
role for protein kinase C-delta. Am. J. Physiol. Endocrinol.
Metab. 2002, 283, E682–E691.
[30] Boden, G., Cheung, P., Stein, T. P., Kresge, K. et al., FFA cause
hepatic insulin resistance by inhibiting insulin suppression
of glycogenolysis. Am. J. Physiol. Endocrinol.Metab. 2002,
283, E12–E19.
[31] Boden, G., Chen, X., Ruiz, J.,White, J. V. et al., Mechanisms
of fatty acid-induced inhibition of glucose uptake. J. Clin.
Invest. 1994, 93, 2438–2446.
[32] Donnelly, K. L., Smith, C. I., Schwarzenberg, S. J., Jessurun,
J. et al., Sources of fatty acids stored in liver and secreted
via lipoproteins in patients with nonalcoholic fatty liver disease.
J. Clin. Invest. 2005, 115, 1343–1351.
[33] Kissebah, A. H., Krakower, G. R., Regional adiposity and
morbidity. Physiol. Rev. 1994, 74, 761–811.
[34] van der, K. K., Leenen, R., Seidell, J. C., Deurenberg, P. et al.,
Abdominal diameters as indicators of visceral fat: comparison
between magnetic resonance imaging and anthropometry.
Br. J. Nutr. 1993, 70, 47–58.
[35] Nielsen, S., Guo, Z., Johnson, C. M., Hensrud, D. D. et al.,
Splanchnic lipolysis in human obesity. J. Clin. Invest. 2004,
113, 1582–1588.
[36] van der, P. D., Milner, K. L., Hui, J., Hodge, A. et al., Visceral
fat: a key mediator of steatohepatitis in metabolic liver disease.
Hepatology 2008, 48, 449–457.
[37] Ibrahim, M. M., Subcutaneous and visceral adipose tissue:
structural and functional differences. Obes. Rev. 2010, 11,
11–18.
[38] Preis, S. R., Massaro, J.M., Robins, S. J., Hoffmann,U. et al.,
Abdominal subcutaneous and visceral adipose tissue and
insulin resistance in the Framingham heart study. Obesity
(Silver Spring) 2010, 18, 2191–2198.
[39] Guilherme, A., Virbasius, J. V., Puri, V., Czech, M. P.,
Adipocyte dysfunctions linking obesity to insulin resistance
and type 2 diabetes. Nat. Rev. Mol. Cell Biol. 2008, 9,
367–377.
[40] Hotamisligil, G. S., Shargill, N. S., Spiegelman, B. M.,
Adipose expression of tumor necrosis factor-alpha: direct
role in obesity-linked insulin resistance. Science 1993, 259,
87–91.
[41] Uysal, K. T., Wiesbrock, S. M., Marino, M. W., Hotamisligil,
G. S., Protection from obesity-induced insulin resistance
inmice lacking TNF-alpha function. Nature 1997, 389,
610–614.
[42] Haukeland, J. W., Damas, J. K., Konopski, Z., Loberg, E. M.
et al., Systemic inflammation in nonalcoholic fatty liver disease
is characterized by elevated levels of CCL2. J. Hepatol.
2006, 44, 1167–1174.
[43] Hui, J. M., Hodge, A., Farrell, G. C., Kench, J. G.
et al., Beyond insulin resistance in NASH: TNF-alpha or
adiponectin? Hepatology 2004, 40, 46–54.
[44] Crespo, J., Cayon, A., Fernandez-Gil, P., Hernandez-Guerra,
M. et al., Gene expression of tumor necrosis factor alpha
and TNF-receptors, p55 and p75, in nonalcoholic steatohepatitis
patients. Hepatology 2001, 34, 1158–1163.
[45] Li, Z., Yang, S., Lin, H., Huang, J. et al., Probiotics and
antibodies to TNF inhibit inflammatory activity and improve
nonalcoholic fatty liver disease. Hepatology 2003, 37,
343–350.
[46] Van Wagner, L. B., Koppe, S. W., Brunt, E. M., Gottstein,
J. et al., Pentoxifylline for the treatment of non-alcoholic
steatohepatitis: a randomized controlled trial. Ann. Hepatol.
2011, 10, 277–286.
[47] Yalniz,M., Bahcecioglu, I. H., Kuzu, N., Celebi, S. et al., Amelioration
of steatohepatitis with pentoxifylline in a novel
nonalcoholic steatohepatitis model induced by high-fat
diet. Dig. Dis. Sci. 2007, 52, 2380–2386.
[48] Feldstein, A. E., Werneburg, N. W., Canbay, A., Guicciardi,
M. E. et al., Free fatty acids promote hepatic lipotoxicity by
stimulating TNF-alpha expression via a lysosomal pathway.
Hepatology 2004, 40, 185–194.
[49] Chakraborty, C., Biochemical andmolecular basis of insulin
resistance. Curr. Protein Pept. Sci. 2006, 7, 113–121.
[50] Feingold, K. R., Soued, M., Serio, M. K., Adi, S. et al., The
effect of diet on tumor necrosis factor stimulation of hepatic
lipogenesis. Metabolism 1990, 39, 623–632.
[51] Moschen, A. R., Molnar, C., Geiger, S., Graziadei, I. et al.,
Anti-inflammatory effects of excessive weight loss: potent
suppression of adipose interleukin 6 and tumour necrosis
factor alpha expression. Gut 2010, 59, 1259–1264.
C_
2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.mnf-journal.com
Mol. Nutr. Food Res. 2013, 00, 1–25 19
[52] Fernandez-Real, J.M., Vayreda, M., Richart, C., Gutierrez, C.
et al., Circulating interleukin 6 levels, blood pressure, and
insulin sensitivity in apparently healthy men and women.
J. Clin. Endocrinol. Metab. 2001, 86, 1154–1159.
[53] Wang, X., Bao,W., Liu, J., Ouyang, Y. Y. et al., Inflammatory
markers and risk of type 2 diabetes: a systematic review
and meta-analysis. Diabetes Care 2013, 36, 166–175.
[54] Fontana, L., Eagon, J. C., Trujillo, M. E., Scherer, P. E. et al.,
Visceral fat adipokine secretion is associated with systemic
inflammation in obese humans. Diabetes 2007, 56, 1010–
1013.
[55] Senn, J. J., Klover, P. J., Nowak, I. A., Zimmers, T. A. et al.,
Suppressor of cytokine signaling-3 (SOCS-3), a potential
mediator of interleukin-6-dependent insulin resistance in
hepatocytes. J. Biol. Chem. 2003, 278, 13740–13746.
[56] Sabio, G., Das, M., Mora, A., Zhang, Z. et al., A stress signaling
pathway in adipose tissue regulates hepatic insulin
resistance. Science 2008, 322, 1539–1543.
[57] Friedman, J. M., Halaas, J. L., Leptin and the regulation of
body weight in mammals. Nature 1998, 395, 763–770.
[58] Lam, Q. L., Lu, L., Role of leptin in immunity. Cell. Mol.
Immunol. 2007, 4, 1–13.
[59] Huang, X. D., Fan, Y., Zhang, H., Wang, P. et al., Serum
leptin and soluble leptin receptor in non-alcoholic fatty liver
disease. World J. Gastroenterol. 2008, 14, 2888–2893.
[60] Lemoine, M., Ratziu, V., Kim, M., Maachi, M. et al., Serum
adipokine levels predictive of liver injury in non-alcoholic
fatty liver disease. Liver Int. 2009, 29, 1431–1438.
[61] Chitturi, S., Farrell, G., Frost, L., Kriketos, A. et al., Serum
leptin in NASH correlates with hepatic steatosis but not
fibrosis: a manifestation of lipotoxicity? Hepatology 2002,
36, 403–409.
[62] Huang, X. D., Fan, Y., Zhang, H., Wang, P. et al., Serum
leptin and soluble leptin receptor in non-alcoholic fatty liver
disease. World J. Gastroenterol. 2008, 14, 2888–2893.
[63] Canbakan, B., Tahan, V., Balci, H., Hatemi, I. et al., Leptin
in nonalcoholic fatty liver disease. Ann. Hepatol. 2008, 7,
249–254.
[64] Anania, F. A., Leptin, liver, and obese mice—fibrosis in the
fat lane. Hepatology 2002, 36, 246–248.
[65] Ikejima, K., Takei, Y., Honda, H., Hirose, M. et al., Leptin
receptor-mediated signaling regulates hepatic fibrogenesis
and remodeling of extracellularmatrix in the rat. Gastroenterology
2002, 122, 1399–1410.
[66] Leclercq, I. A., Farrell, G. C., Schriemer, R., Robertson, G.
R., Leptin is essential for the hepatic fibrogenic response to
chronic liver injury. J. Hepatol. 2002, 37, 206–213.
[67] Wang, J., Leclercq, I., Brymora, J. M., Xu, N. et al., Kupffer
cells mediate leptin-induced liver fibrosis. Gastroenterology
2009, 137, 713–723.
[68] Targher, G., Bertolini, L., Scala, L., Poli, F. et al., Decreased
plasma adiponectin concentrations are closely associated
with nonalcoholic hepatic steatosis in obese individuals.
Clin. Endocrinol. (Oxf.) 2004, 61, 700–703.
[69] Louthan, M. V., Barve, S., McClain, C. J., Joshi-Barve, S.,
Decreased serum adiponectin: an early event in pediatric
nonalcoholic fatty liver disease. J. Pediatr. 2005, 147, 835–
838.
[70] Buechler, C., Wanninger, J., Neumeier, M., Adiponectin, a
key adipokine in obesity related liver diseases. World J.
Gastroenterol. 2011, 17, 2801–2811.
[71] Tilg, H., The role of cytokines in non-alcoholic fatty liver
disease. Dig. Dis. 2010, 28, 179–185.
[72] Xu, A.,Wang, Y., Keshaw, H., Xu, L. Y. et al., The fat-derived
hormone adiponectin alleviates alcoholic and nonalcoholic
fatty liver diseases in mice. J. Clin. Invest. 2003, 112, 91–100.
[73] Awazawa, M., Ueki, K., Inabe, K., Yamauchi, T. et al.,
Adiponectin suppresses hepatic SREBP1c expression in an
AdipoR1/LKB1/AMPK dependent pathway. Biochem. Biophys.
Res. Commun. 2009, 382, 51–56.
[74] Saltiel, A. R., Kahn, C. R., Insulin signalling and the regulation
of glucose and lipid metabolism. Nature 2001, 414,
799–806.
[75] Taniguchi, C.M., Emanuelli, B., Kahn, C. R., Critical nodes in
signalling pathways: insights into insulin action. Nat. Rev.
Mol. Cell Biol. 2006, 7, 85–96.
[76] Puigserver, P., Rhee, J., Donovan, J., Walkey, C. J.
et al., Insulin-regulated hepatic gluconeogenesis through
FOXO1-PGC-1alpha interaction. Nature 2003, 423, 550–555.
[77] Chiang, S. H., Baumann, C. A., Kanzaki, M., Thurmond, D.
C. et al., Insulin-stimulated GLUT4 translocation requires
the CAP-dependent activation of TC10. Nature 2001, 410,
944–948.
[78] Postic, C., Girard, J., Contribution of de novo fatty acid synthesis
to hepatic steatosis and insulin resistance: lessons
from genetically engineered mice. J. Clin. Invest. 2008, 118,
829–838.
[79] Kahn, S. E., The relative contributions of insulin resistance
and beta-cell dysfunction to the pathophysiology of Type 2
diabetes. Diabetologia 2003, 46, 3–19.
[80] Browning, J. D., Szczepaniak, L. S., Dobbins, R., Nuremberg,
P. et al., Prevalence of hepatic steatosis in an urban
population in the United States: impact of ethnicity. Hepatology
2004, 40, 1387–1395.
[81] Targher, G., Bertolini, L., Padovani, R., Rodella, S. et al.,
Prevalence of nonalcoholic fatty liver disease and its association
with cardiovascular disease among type 2 diabetic
patients. Diabetes Care 2007, 30, 1212–1218.
[82] Porepa, L., Ray, J. G., Sanchez-Romeu, P., Booth, G. L.,
Newly diagnosed diabetes mellitus as a risk factor for serious
liver disease. Can. Med. Assoc. J. 2010, 182, E526–E531.
[83] Prashanth, M., Ganesh, H. K., Vima, M. V., John, M. et al.,
Prevalence of nonalcoholic fatty liver disease in patients
with type 2 diabetes mellitus. J. Assoc. Physicians India
2009, 57, 205–210.
[84] Adams, L. A., Harmsen, S., St Sauver, J. L., Charatcharoenwitthaya,
P. et al., Nonalcoholic fatty liver disease increases
risk of death among patients with diabetes: a communitybased
cohort study. Am. J. Gastroenterol. 2010, 105, 1567–
1573.
[85] Voshol, P. J., Haemmerle, G., Ouwens, D. M., Zimmermann,
R. et al., Increased hepatic insulin sensitivity together with
C_
2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.mnf-journal.com
20 M.-H. Pan et al. Mol. Nutr. Food Res. 2013, 00, 1–25
decreased hepatic triglyceride stores in hormone-sensitive
lipase-deficient mice. Endocrinology 2003, 144, 3456–3462.
[86] Smith, B. W., Adams, L. A., Nonalcoholic fatty liver disease
and diabetes mellitus: pathogenesis and treatment. Nat.
Rev. Endocrinol. 2011, 7, 456–465.
[87] Tarantino, G., Caputi, A., JNKs, insulin resistance and inflammation:
a possible link between NAFLD and coronary
artery disease.World J. Gastroenterol. 2011, 17, 3785–3794.
[88] Schwarz, J. M., Linfoot, P., Dare, D., Aghajanian, K., Hepatic
de novo lipogenesis in normoinsulinemic and hyperinsulinemic
subjects consuming high-fat, low-carbohydrate
and low-fat, high-carbohydrate isoenergetic diets. Am. J.
Clin. Nutr. 2003, 77, 43–50.
[89] bu-Elheiga, L., Matzuk, M. M., bo-Hashema, K. A., Wakil, S.
J., Continuous fatty acid oxidation and reduced fat storage
in mice lacking acetyl-CoA carboxylase 2. Science 2001,
291, 2613–2616.
[90] An, J., Muoio, D. M., Shiota, M., Fujimoto, Y. et al., Hepatic
expression of malonyl-CoA decarboxylase reverses muscle,
liver and whole-animal insulin resistance. Nat. Med.
2004, 10, 268–274.
[91] Feldstein, A. E., Canbay, A., Angulo, P., Taniai, M. et al.,
Hepatocyte apoptosis and fas expression are prominent
features of human nonalcoholic steatohepatitis. Gastroenterology
2003, 125, 437–443.
[92] Feldstein, A. E., Werneburg, N. W., Li, Z., Bronk, S. F. et al.,
Bax inhibition protects against free fatty acid-induced lysosomal
permeabilization. Am. J. Physiol. Gastrointest. Liver
Physiol. 2006, 290, G1339–G1346.
[93] Li, Z., Berk, M., McIntyre, T. M., Gores, G. J. et al., The
lysosomal-mitochondrial axis in free fatty acid-induced
hepatic lipotoxicity. Hepatology 2008, 47, 1495–1503.
[94] Li, Z. Z., Berk, M., McIntyre, T. M., Feldstein, A. E., Hepatic
lipid partitioning and liver damage in nonalcoholic
fatty liver disease: role of stearoyl-CoA desaturase. J. Biol.
Chem. 2009, 284, 5637–5644.
[95] Malhi, H., Bronk, S. F., Werneburg, N. W., Gores, G. J., Free
fatty acids induce JNK-dependent hepatocyte lipoapoptosis.
J. Biol. Chem. 2006, 281, 12093–12101.
[96] Barreyro, F. J., Kobayashi, S., Bronk, S. F., Werneburg, N.
W. et al., Transcriptional regulation of Bim by FoxO3A mediates
hepatocyte lipoapoptosis. J. Biol. Chem. 2007, 282,
27141–27154.
[97] Feldstein, A. E., Canbay, A., Angulo, P., Taniai, M. et al.,
Hepatocyte apoptosis and fas expression are prominent
features of human nonalcoholic steatohepatitis. Gastroenterology
2003, 125, 437–443.
[98] Feldstein, A. E., Canbay, A., Guicciardi, M. E., Higuchi, H.
et al., Diet associated hepatic steatosis sensitizes to Fas
mediated liver injury in mice. J. Hepatol. 2003, 39, 978–983.
[99] Inoue, Y., Asanuma, T., Smith, N., Saunders, D. et al., Modulation
of Fas-FasL related apoptosis by PBN in the early
phases of choline deficient diet-mediated hepatocarcinogenesis
in rats. Free Radic. Res. 2007, 41, 972–980.
[100] Malhi, H., Barreyro, F. J., Isomoto, H., Bronk, S. F. et al.,
Free fatty acids sensitise hepatocytes to TRAIL mediated
cytotoxicity. Gut 2007, 56, 1124–1131.
[101] Volkmann, X., Fischer, U., Bahr, M. J., Ott, M. et al., Increased
hepatotoxicity of tumor necrosis factor-related
apoptosis-inducing ligand in diseased human liver. Hepatology
2007, 46, 1498–1508.
[102] Cazanave, S. C., Mott, J. L., Bronk, S. F., Werneburg, N.
W. et al., Death receptor 5 signaling promotes hepatocyte
lipoapoptosis. J. Biol. Chem. 2011, 286, 39336–39348.
[103] Wei, Y., Wang, D., Topczewski, F., Pagliassotti, M. J., Saturated
fatty acids induce endoplasmic reticulum stress and
apoptosis independently of ceramide in liver cells. Am. J.
Physiol. Endocrinol. Metab. 2006, 291, E275–E281.
[104] Wang, D., Wei, Y., Pagliassotti, M. J., Saturated fatty acids
promote endoplasmic reticulum stress and liver injury in
rats with hepatic steatosis. Endocrinology 2006, 147, 943–
951.
[105] Puri, P., Mirshahi, F., Cheung, O., Natarajan, R. et al., Activation
and dysregulation of the unfolded protein response
in nonalcoholic fatty liver disease. Gastroenterology 2008,
134, 568–576.
[106] Rinella, M. E., Siddiqui, M. S., Gardikiotes, K., Gottstein, J.
et al., Dysregulation of the unfolded protein response in
db/db mice with diet-induced steatohepatitis. Hepatology
2011, 54, 1600–1609.
[107] Hotamisligil, G. S., Endoplasmic reticulum stress and the
inflammatory basis of metabolic disease. Cell 2010, 140,
900–917.
[108] Seki, S., Kitada, T., Sakaguchi, H., Clinicopathological significance
of oxidative cellular damage in non-alcoholic fatty
liver diseases. Hepatol. Res. 2005, 33, 132–134.
[109] Madan, K., Bhardwaj, P., Thareja, S., Gupta, S. D. et al.,
Oxidant stress and antioxidant status among patients with
nonalcoholic fatty liver disease (NAFLD). J. Clin. Gastroenterol.
2006, 40, 930–935.
[110] Weltman, M. D., Farrell, G. C., Liddle, C., Increased hepatocyte
CYP2E1 expression in a rat nutritionalmodel of hepatic
steatosis with inflammation. Gastroenterology 1996, 111,
1645–1653.
[111] Weltman, M. D., Farrell, G. C., Hall, P., Ingelman-Sundberg,
M. et al., Hepatic cytochrome P450 2E1 is increased in patients
with nonalcoholic steatohepatitis. Hepatology 1998,
27, 128–133.
[112] Reddy, J. K., Hashimoto, T., Peroxisomal beta-oxidation
and peroxisome proliferator-activated receptor alpha: an
adaptive metabolic system. Annu. Rev. Nutr. 2001, 21,
193–230.
[113] Caldwell, S. H., Swerdlow, R. H., Khan, E. M., Iezzoni, J. C.
et al., Mitochondrial abnormalities in non-alcoholic steatohepatitis.
J. Hepatol. 1999, 31, 430–434.
[114] Perez-Carreras, M., Del, H. P., Martin, M. A., Rubio, J. C.
et al., Defective hepatic mitochondrial respiratory chain
in patients with nonalcoholic steatohepatitis. Hepatology
2003, 38, 999–1007.
[115] Sanchez-Alcazar, J. A., Schneider, E., Martinez, M. A., Carmona,
P. et al., Tumor necrosis factor-alpha increases the
steady-state reduction of cytochrome b of the mitochondrial
respiratory chain in metabolically inhibited L929 cells.
J. Biol. Chem. 2000, 275, 13353–13361.
C_
2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.mnf-journal.com
Mol. Nutr. Food Res. 2013, 00, 1–25 21
[116] Higuchi, M., Proske, R. J., Yeh, E. T., Inhibition of mitochondrial
respiratory chain complex I by TNF results in
cytochrome c release, membrane permeability transition,
and apoptosis. Oncogene 1998, 17, 2515–2524.
[117] Pan, M., Cederbaum, A. I., Zhang, Y. L., Ginsberg, H. N.
et al., Lipid peroxidation and oxidant stress regulate hepatic
apolipoprotein B degradation and VLDL production. J. Clin.
Invest. 2004, 113, 1277–1287.
[118] Perlemuter, G., vit-Spraul, A., Cosson, C., Conti, M. et al.,
Increase in liver antioxidant enzyme activities in nonalcoholic
fatty liver disease. Liver Int. 2005, 25, 946–953.
[119] Brunt, E. M., Janney, C. G., Di Bisceglie, A. M.,
Neuschwander-Tetri, B. A. et al., Nonalcoholic steatohepatitis:
a proposal for grading and staging the histological
lesions. Am. J. Gastroenterol. 1999, 94, 2467–2474.
[120] Chalasani, N., Wilson, L., Kleiner, D. E., Cummings, O. W.
et al., Relationship of steatosis grade and zonal location
to histological features of steatohepatitis in adult patients
with non-alcoholic fatty liver disease. J. Hepatol. 2008, 48,
829–834.
[121] Schwabe, R. F., Uchinami, H., Qian, T., Bennett, B. L. et al.,
Differential requirement for c-Jun NH2-terminal kinase in
TNFalpha- and Fas-mediated apoptosis in hepatocytes.
FASEB J. 2004, 18, 720–722.
[122] Dela, P. A., Leclercq, I., Field, J., George, J. et al., NF-kappaB
activation, rather than TNF, mediates hepatic inflammation
in amurine dietary model of steatohepatitis. Gastroenterology
2005, 129, 1663–1674.
[123] Schattenberg, J. M., Singh, R., Wang, Y., Lefkowitch, J. H.
et al., JNK1 but not JNK2 promotes the development of
steatohepatitis in mice. Hepatology 2006, 43, 163–172.
[124] Csak, T., Ganz, M., Pespisa, J., Kodys, K. et al., Fatty acid
and endotoxin activate inflammasomes in mouse hepatocytes
that release danger signals to stimulate immune cells.
Hepatology 2011, 54, 133–144.
[125] Wieckowska, A., Papouchado, B. G., Li, Z., Lopez, R. et al.,
Increased hepatic and circulating interleukin-6 levels in human
nonalcoholic steatohepatitis. Am. J. Gastroenterol.
2008, 103, 1372–1379.
[126] Yamaguchi, K., Itoh, Y., Yokomizo, C., Nishimura, T.
et al., Blockade of interleukin-6 signaling enhances hepatic
steatosis but improves liver injury in methionine cholinedeficient
diet-fed mice. Lab. Invest. 2010, 90, 1169–1178.
[127] Dooley, S., ten, D. P., TGF-beta in progression of liver disease.
Cell Tissue Res. 2012, 347, 245–256.
[128] Choudhury, J.,Mirshahi, F.,Murthy, K. S., Yager, D. R. et al.,
Physiologic concentrations of leptin increase collagen production
by non-immortalized human hepatic stellate cells.
Metabolism 2006, 55, 1317–1322.
[129] George, J., Pera, N., Phung, N., Leclercq, I. et al., Lipid peroxidation,
stellate cell activation and hepatic fibrogenesis
in a rat model of chronic steatohepatitis. J. Hepatol. 2003,
39, 756–764.
[130] Teufelhofer, O., Parzefall, W., Kainzbauer, E., Ferk, F. et al.,
Superoxide generation from Kupffer cells contributes to
hepatocarcinogenesis: studies on NADPH oxidase knockout
mice. Carcinogenesis 2005, 26, 319–329.
[131] Gornicka, A., Morris-Stiff, G., Thapaliya, S., Papouchado,
B. G. et al., Transcriptional profile of genes involved in oxidative
stress and antioxidant defense in a dietary murine
model of steatohepatitis. Antioxid. Redox Signal. 2011, 15,
437–445.
[132] Musso, G., Cassader, M., Rosina, F., Gambino, R., Impact
of current treatments on liver disease, glucose metabolism
and cardiovascular risk in non-alcoholic fatty liver disease
(NAFLD): a systematic review and meta-analysis of randomised
trials. Diabetologia 2012, 55, 885–904.
[133] Kim, M. S., Kung, S., Grewal, T., Roufogalis, B. D., Methodologies
for investigating natural medicines for the treatment
of nonalcoholic fatty liver disease (NAFLD). Curr.
Pharm. Biotechnol. 2012, 13, 278–291.
[134] Musso, G., Gambino, R., Cassader, M., Pagano, G., A metaanalysis
of randomized trials for the treatment of nonalcoholic
fatty liver disease. Hepatology 2010, 52, 79–104.
[135] Nissen, S. E.,Wolski, K., Rosiglitazone revisited: an updated
meta-analysis of risk for myocardial infarction and cardiovascularmortality.
Arch. Intern. Med. 2010, 170, 1191–1201.
[136] Bahcecioglu, I. H., Kuzu, N., Metin, K., Ozercan, I. H. et al.,
Lycopene prevents development of steatohepatitis in experimental
nonalcoholic steatohepatitis model induced by
high-fat diet. Vet. Med. Int. 2010, 2010, 1–8.
[137] Wang, Y., Ausman, L. M., Greenberg, A. S., Russell, R. M.
et al., Dietary lycopene and tomato extract supplementations
inhibit nonalcoholic steatohepatitis-promoted hepatocarcinogenesis
in rats. Int. J. Cancer 2010, 126, 1788–
1796.
[138] Choi, S. K., Seo, J. S., Lycopene supplementation suppresses
oxidative stress induced by a high fat diet in gerbils.
Nutr. Res. Pract. 2013, 7, 26–33.
[139] Ahn, J., Lee, H., Jung, C. H., Ha, T., Lycopene inhibits hepatic
steatosis viamicroRNA-21-induced downregulation of fatty
acid-binding protein 7 in mice fed a high-fat diet. Mol. Nutr.
Food Res. 2012, 56, 1665–1674.
[140] Gugger, E. T., Bierer, T. L., Henze, T. M., White, W. S.
et al., Beta-carotene uptake and tissue distribution in ferrets
(Mustela putorius furo). J. Nutr. 1992, 122, 115–119.
[141] Kameji, H., Mochizuki, K., Miyoshi, N., Goda, T., betaCarotene accumulation in 3T3-L1 adipocytes inhibits the
elevation of reactive oxygen species and the suppression
of genes related to insulin sensitivity induced by tumor
necrosis factor-alpha. Nutrition 2010, 26, 1151–1156.
[142] Sangeetha, R. K., Bhaskar, N., Baskaran, V., Comparative effects
of beta-carotene and fucoxanthin on retinol deficiency
induced oxidative stress in rats. Mol. Cell. Biochem. 2009,
331, 59–67.
[143] Kim, J. E., Clark, R. M., Park, Y., Lee, J. et al., Lutein decreases
oxidative stress and inflammation in liver and eyes
of guinea pigs fed a hypercholesterolemic diet. Nutr. Res.
Pract. 2012, 6, 113–119.
[144] Woo, M. N., Jeon, S. M., Shin, Y. C., Lee, M. K. et al., Antiobese
property of fucoxanthin is partly mediated by altering
lipid-regulating enzymes and uncoupling proteins of
visceral adipose tissue in mice. Mol. Nutr. Food Res. 2009,
53, 1603–1611.
C_
2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.mnf-journal.com
22 M.-H. Pan et al. Mol. Nutr. Food Res. 2013, 00, 1–25
[145] Maeda, H., Hosokawa, M., Sashima, T., Murakami-
Funayama, K. et al., Anti-obesity and anti-diabetic effects of
fucoxanthin on diet-induced obesity conditions in amurine
model. Mol. Med. Rep. 2009, 2, 897–902.
[146] Woo, M. N., Jeon, S. M., Kim, H. J., Lee, M. K. et al., Fucoxanthin
supplementation improves plasma and hepatic lipid
metabolism and blood glucose concentration in high-fat
fed C57BL/6N mice. Chem. Biol. Interact. 2010, 186, 316–
322.
[147] Hosokawa, M., Miyashita, T., Nishikawa, S., Emi, S. et al.,
Fucoxanthin regulates adipocytokine mRNA expression in
white adipose tissue of diabetic/obese KK-Ay mice. Arch.
Biochem. Biophys. 2010, 504, 17–25.
[148] Beppu, F., Hosokawa, M., Yim, M. J., Shinoda, T. et al.,
Down-regulation of hepatic stearoyl-CoA desaturase-1
expression by fucoxanthin via leptin signaling in diabetic/
obese KK-A(y) mice. Lipids 2013, 48, 449–455.
[149] Zhu, F. S., Liu, S., Chen, X.M., Huang, Z. G. et al., Effects of n3 polyunsaturated fatty acids from seal oils on nonalcoholic
fatty liver disease associated with hyperlipidemia. World J.
Gastroenterol. 2008, 14, 6395–6400.
[150] Janczyk,W., Socha, P., Lebensztejn, D., Wierzbicka, A. et al.,
Omega-3 fatty acids for treatment of non-alcoholic fatty
liver disease: design and rationale of randomized controlled
trial. BMC Pediatr. 2013, 13, 85.
[151] Masterton, G. S., Plevris, J. N., Hayes, P. C., Review article:
omega-3 fatty acids—a promising novel therapy for
non-alcoholic fatty liver disease. Aliment. Pharmacol. Ther.
2010, 31, 679–692.
[152] Kuda, O., Jelenik, T., Jilkova, Z., Flachs, P. et al., n-3 fatty
acids and rosiglitazone improve insulin sensitivity through
additive stimulatory effects on muscle glycogen synthesis
in mice fed a high-fat diet. Diabetologia 2009, 52, 941–951.
[153] Lamaziere, A., Wolf, C., Barbe, U., Bausero, P. et al.,
Lipidomics of hepatic lipogenesis inhibition by omega 3
fatty acids. Prostaglandins Leukot. Essent. Fatty Acids 2013,
88, 149–154.
[154] Tanaka, N., Sano, K., Horiuchi, A., Tanaka, E. et al., Highly
purified eicosapentaenoic acid treatment improves nonalcoholic
steatohepatitis. J. Clin. Gastroenterol. 2008, 42,
413–418.
[155] Oya, J., Nakagami, T., Sasaki, S., Jimba, S. et al., Intake
of n-3 polyunsaturated fatty acids and non-alcoholic fatty
liver disease: a cross-sectional study in Japanese men and
women. Eur. J. Clin. Nutr. 2010, 64, 1179–1185.
[156] Nemoto, N., Suzuki, S., Kikuchi, H., Okabe, H. et al.,
Ethyl-eicosapentaenoic acid reduces liver lipids and lowers
plasma levels of lipids in mice fed a high-fat diet. In
Vivo 2009, 23, 685–689.
[157] Shiba, S., Tsunoda, N., Wakutsu, M., Muraki, E. et al.,
Regulation of lipid metabolism by palmitoleate and eicosapentaenoic
acid (EPA) in mice fed a high-fat diet. Biosci.
Biotechnol. Biochem. 2011, 75, 2401–2403.
[158] Kajikawa, S., Harada, T., Kawashima, A., Imada, K. et al.,
Suppression of hepatic fat accumulation by highly purified
eicosapentaenoic acid prevents the progression of dgalactosamineinduced hepatitis in mice fed with a highfat/
high-sucrose diet. Biochim. Biophys. Acta 2009, 1791,
281–288.
[159] Matsumoto, T., Terai, S., Oishi, T., Kuwashiro, S. et al.,
Medaka as a model for human nonalcoholic steatohepatitis.
Dis. Model. Mech. 2010, 3, 431–440.
[160] Varela-Rey, M., Embade, N., Ariz, U., Lu, S. C. et al., Nonalcoholic
steatohepatitis and animal models: understanding
the human disease. Int. J. Biochem. Cell Biol. 2009, 41,
969–976.
[161] Kajikawa, S., Imada, K., Takeuchi, T., Shimizu, Y. et al., Eicosapentaenoic
acid attenuates progression of hepatic fibrosis
with inhibition of reactive oxygen species production
in rats fed methionine- and choline-deficient diet. Dig. Dis.
Sci. 2011, 56, 1065–1074.
[162] Kajikawa, S., Harada, T., Kawashima, A., Imada, K. et al.,
Highly purified eicosapentaenoic acid ethyl ester prevents
development of steatosis and hepatic fibrosis in rats. Dig.
Dis. Sci. 2010, 55, 631–641.
[163] Ishii, H., Horie, Y., Ohshima, S., Anezaki, Y. et al., Eicosapentaenoic
acid ameliorates steatohepatitis and hepatocellular
carcinoma in hepatocyte-specific Pten-deficient mice. J.
Hepatol. 2009, 50, 562–571.
[164] Nanthirudjanar, T., Furumoto, H., Hirata, T., Sugawara,
T., Oxidized eicosapentaenoic acids more potently reduce
LXRalpha-induced cellular triacylglycerol via suppression
of SREBP-1c, PGC-1beta and GPA than its intact form. Lipids
Health Dis. 2013, 12, 73.
[165] Nobili, V., Bedogni, G., Alisi, A., Pietrobattista, A. et al.,
Docosahexaenoic acid supplementation decreases liver fat
content in children with non-alcoholic fatty liver disease:
double-blind randomised controlled clinical trial. Arch. Dis.
Child. 2011, 96, 350–353.
[166] Nobili, V., Alisi, A., Della, C. C., Rise, P. et al., Docosahexaenoic
acid for the treatment of fatty liver: randomised controlled
trial in children. Nutr. Metab. Cardiovasc. Dis. 2012,
in press.
[167] Takayama, F., Nakamoto, K., Totani, N., Yamanushi, T. et al.,
Effects of docosahexaenoic acid in an experimental rat
model of nonalcoholic steatohepatitis. J. Oleo. Sci. 2010,
59, 407–414.
[168] Poudyal, H., Panchal, S. K., Ward, L. C., Brown, L., Effects
of ALA, EPA and DHA in high-carbohydrate, high-fat
diet-induced metabolic syndrome in rats. J. Nutr. Biochem.
2013, 24, 1041–1052.
[169] Tang, X., Li, Z. J., Xu, J., Xue, Y. et al., Short term effects
of different omega-3 fatty acid formulation on lipid
metabolism in mice fed high or low fat diet. Lipids Health
Dis. 2012, 11, 70.
[170] Depner, C. M., Philbrick, K. A., Jump, D. B., Docosahexaenoic
acid attenuates hepatic inflammation, oxidative
stress, and fibrosis without decreasing hepatosteatosis in
a Ldlr(−/−) mouse model of western diet-induced nonalcoholic
steatohepatitis. J. Nutr. 2013, 143, 315–323.
[171] Kim, H. J., Lee, K. T., Park, Y. B., Jeon, S. M. et al., Dietary docosahexaenoic
acid-rich diacylglycerols ameliorate hepatic
steatosis and alter hepatic gene expressions in C57BL/6JLep(
ob/ob) mice. Mol. Nutr. Food Res. 2008, 52, 965–973.
C_
2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.mnf-journal.com
Mol. Nutr. Food Res. 2013, 00, 1–25 23
[172] Fedor, D. M., Adkins, Y., Mackey, B. E., Kelley, D. S., Docosahexaenoic
acid prevents trans-10, cis-12-conjugated
linoleic acid-induced nonalcoholic fatty liver disease in
mice by altering expression of hepatic genes regulating
fatty acid synthesis and oxidation. Metab. Syndr. Relat. Disord.
2012, 10, 175–180.
[173] Vemuri, M., Kelley, D. S., Mackey, B. E., Rasooly, R. et al.,
Docosahexaenoic acid (DHA) but not eicosapentaenoic
acid (EPA) prevents trans-10, cis-12 conjugated linoleic
acid (CLA)-induced insulin resistance in mice. Metab.
Syndr.Relat. Disord. 2007, 5, 315–322.
[174] Luo, X., Yang, Y., Shen, T., Tang, X. et al., Docosahexaenoic
acid ameliorates palmitate-induced lipid accumulation and
inflammation through repressing NLRC4 inflammasome
activation in HepG2 cells. Nutr. Metab. (Lond.) 2012, 9, 34.
[175] Tsuzuki, T., Kawakami, Y., Suzuki, Y., Abe, R. et al., Intake
of conjugated eicosapentaenoic acid suppresses lipid accumulation
in liver and epididymal adipose tissue in rats.
Lipids 2005, 40, 1117–1123.
[176] Sun, C., Wei, Z. W., Li, Y., DHA regulates lipogenesis and
lipolysis genes in mice adipose and liver. Mol. Biol. Rep.
2011, 38, 731–737.
[177] Gladine, C., Roy, N. C., Rigaudiere, J. P., Laillet, B. et al., Increasing
intake of long-chain n-3 PUFA enhances lipoperoxidation
and modulates hepatic gene expression in a dosedependent
manner. Br. J. Nutr. 2011, 1–20.
[178] Ono, M., Fujimori, K., Antiadipogenic effect of dietary apigenin
through activation of AMPK in 3T3-L1 cells. J. Agric.
Food Chem. 2011, 59, 13346–13352.
[179] Liu, J. F., Ma, Y., Wang, Y., Du, Z. Y. et al., Reduction of
lipid accumulation in HepG2 cells by luteolin is associated
with activation of AMPK and mitigation of oxidative stress.
Phytother. Res. 2011, 25, 588–596.
[180] Kunimasa, K., Kuranuki, S., Matsuura, N., Iwasaki, N. et al.,
Identification of nobiletin, a polymethoxyflavonoid, as an
enhancer of adiponectin secretion. Bioorg. Med. Chem.
Lett. 2009, 19, 2062–2064.
[181] Lee, Y. S., Cha, B. Y., Saito, K., Yamakawa, H. et al., Nobiletin
improves hyperglycemia and insulin resistance in obese
diabetic ob/ob mice. Biochem. Pharmacol. 2010, 79, 1674–
1683.
[182] Lee, Y. S., Cha, B. Y., Choi, S. S., Choi, B. K. et al., Nobiletin
improves obesity and insulin resistance in high-fat dietinduced
obese mice. J. Nutr. Biochem. 2013, 24, 156–162.
[183] Miyata, Y., Tanaka, H., Shimada, A., Sato, T. et al., Regulation
of adipocytokine secretion and adipocyte hypertrophy by
polymethoxyflavonoids, nobiletin and tangeretin. Life Sci.
2011, 88, 613–618.
[184] Pu, P., Wang, X. A., Salim, M., Zhu, L. H. et al., Baicalein,
a natural product, selectively activating AMPKalpha(2) and
ameliorates metabolic disorder in diet-induced mice. Mol.
Cell. Endocrinol. 2012, 362, 128–138.
[185] Panchal, S. K., Poudyal, H., Brown, L., Quercetin ameliorates
cardiovascular, hepatic, and metabolic changes in
diet-induced metabolic syndrome in rats. J. Nutr. 2012, 142,
1026–1032.
[186] Jung, C. H., Cho, I., Ahn, J., Jeon, T. I. et al., Quercetin
reduces high-fat diet-induced fat accumulation in the liver
by regulating lipid metabolism genes. Phytother. Res. 2013,
27, 139–143.
[187] Hoek-van den Hil E. F., Keijer, J., Bunschoten, A., Vervoort,
J. J. et al., Quercetin induces hepatic lipid omega-oxidation
and lowers serum lipid levels in mice. PLoS One 2013, 8,
e51588.
[188] Ying, H. Z., Liu, Y. H., Yu, B., Wang, Z. Y. et al., Dietary
quercetin ameliorates nonalcoholic steatohepatitis induced
by a high-fat diet in gerbils. Food Chem. Toxicol. 2013, 52,
53–60.
[189] Marcolin, E., San-Miguel, B., Vallejo, D., Tieppo, J. et al.,
Quercetin treatment ameliorates inflammation and fibrosis
in mice with nonalcoholic steatohepatitis. J.Nutr. 2012, 142,
1821–1828.
[190] Marcolin, E., Forgiarini, L. F., Rodrigues, G., Tieppo, J.
et al., Quercetin decreases liver damage in mice with nonalcoholic
steatohepatitis. Basic Clin. Pharmacol. Toxicol.
2013, 112, 385–391.
[191] Jeong, S. M., Kang, M. J., Choi, H. N., Kim, J. H. et al.,
Quercetin ameliorates hyperglycemia and dyslipidemia
and improves antioxidant status in type 2 diabetic db/db
mice. Nutr. Res. Pract. 2012, 6, 201–207.
[192] Vidyashankar, S., Sandeep, V. R., Patki, P. S., Quercetin ameliorate
insulin resistance and up-regulates cellular antioxidants
during oleic acid induced hepatic steatosis in HepG2
cells. Toxicol. In Vitro 2013, 27, 945–953.
[193] Crespo, I., Garcia-Mediavilla, M. V., Almar, M., Gonzalez, P.
et al., Differential effects of dietary flavonoids on reactive
oxygen and nitrogen species generation and changes in antioxidant
enzyme expression induced by proinflammatory
cytokines in Chang Liver cells. Food Chem. Toxicol. 2008,
46, 1555–1569.
[194] Kuzu, N., Bahcecioglu, I. H., Dagli, A. F., Ozercan, I. H.
et al., Epigallocatechin gallate attenuates experimental nonalcoholic
steatohepatitis induced by high fat diet. J. Gastroenterol.
Hepatol. 2008, 23, e465–e470.
[195] Bose, M., Lambert, J. D., Ju, J., Reuhl, K. R. et al., The major
green tea polyphenol, (-)-epigallocatechin-3-gallate, inhibits
obesity, metabolic syndrome, and fatty liver disease
in high-fat-fed mice. J. Nutr. 2008, 138, 1677–1683.
[196] Chen, Y. K., Cheung, C., Reuhl, K. R., Liu, A. B. et al., Effects
of green tea polyphenol (-)-epigallocatechin-3-gallate
on newly developed high-fat/Western-style diet-induced
obesity and metabolic syndrome in mice. J. Agric. Food
Chem. 2011, 59, 11862–11871.
[197] Xiao, J., Ho, C. T., Liong, E. C., Nanji, A. A. et al., Epigallocatechin
gallate attenuates fibrosis, oxidative stress, and
inflammation in non-alcoholic fatty liver disease rat model
through TGF/SMAD, PI3 K/Akt/FoxO1, and NF-kappa B pathways.
Eur. J. Nutr. 2013, in press.
[198] Klaus, S., Pultz, S., Thone-Reineke, C., Wolfram, S., Epigallocatechin
gallate attenuates diet-induced obesity in mice
by decreasing energy absorption and increasing fat oxidation.
Int. J. Obes. (Lond.) 2005, 29, 615–623.
[199] Friedrich, M., Petzke, K. J., Raederstorff, D., Wolfram, S.
et al., Acute effects of epigallocatechin gallate from green
C_
2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.mnf-journal.com
24 M.-H. Pan et al. Mol. Nutr. Food Res. 2013, 00, 1–25
tea on oxidation and tissue incorporation of dietary lipids
in mice fed a high-fat diet. Int. J. Obes. (Lond.) 2012, 36,
735–743.
[200] Lin, C. L., Huang, H. C., Lin, J. K., Theaflavins attenuate hepatic
lipid accumulation through activating AMPK in human
HepG2 cells. J. Lipid Res. 2007, 48, 2334–2343.
[201] Luo, X. Y., Takahara, T., Hou, J., Kawai, K. et al., Theaflavin
attenuates ischemia-reperfusion injury in a mouse fatty
liver model. Biochem. Biophys. Res. Commun. 2012, 417,
287–293.
[202] Huong, D. T., Takahashi, Y., Ide, T., Activity and mRNA levels
of enzymes involved in hepatic fatty acid oxidation in mice
fed citrus flavonoids. Nutrition 2006, 22, 546–552.
[203] Mulvihill, E. E., Allister, E. M., Sutherland, B. G., Telford, D.
E. et al., Naringenin prevents dyslipidemia, apolipoprotein
B overproduction, and hyperinsulinemia in LDL receptornull
mice with diet-induced insulin resistance. Diabetes
2009, 58, 2198–2210.
[204] Assini, J.M., Mulvihill, E. E., Sutherland, B. G., Telford, D. E.
et al., Naringenin prevents cholesterol-induced systemic inflammation,
metabolic dysregulation, and atherosclerosis
in Ldlr(−)/(−) mice. J. Lipid Res. 2013, 54, 711–724.
[205] Cha, J. Y., Cho, Y. S., Kim, I., Anno, T. et al., Effect of hesperetin,
a citrus flavonoid, on the liver triacylglycerol content
and phosphatidate phosphohydrolase activity in orotic
acid-fed rats. Plant Foods Hum. Nutr. 2001, 56, 349–358.
[206] Iwatsuka, H., Shino, A., Suzuoki, Z., General survey of diabetic
features of yellow KK mice. Endocrinol. Jpn. 1970, 17,
23–35.
[207] Guo, H., Li, D., Ling,W., Feng, X. et al., Anthocyanin inhibits
high glucose-induced hepatic mtGPAT1 activation and prevents
fatty acid synthesis through PKCzeta. J. Lipid Res.
2011, 52, 908–922.
[208] Guo, H., Xia,M., Zou, T., Ling,W. et al., Cyanidin 3-glucoside
attenuates obesity-associated insulin resistance and hepatic
steatosis in high-fat diet-fed and db/db mice via the
transcription factor FoxO1. J. Nutr. Biochem. 2012, 23, 349–
360.
[209] Zhu, W., Jia, Q., Wang, Y., Zhang, Y. et al., The anthocyanin
cyanidin-3-O-beta-glucoside, a flavonoid, increases hepatic
glutathione synthesis and protects hepatocytes against reactive
oxygen species during hyperglycemia: involvement
of a cAMP-PKA-dependent signaling pathway. Free Radic.
Biol. Med. 2012, 52, 314–327.
[210] Guo, H., Liu, G., Zhong, R., Wang, Y. et al., Cyanidin-3-Obetaglucoside regulates fatty acidmetabolism via an AMPactivated
protein kinase-dependent signaling pathway in
human HepG2 cells. Lipids Health Dis. 2012, 11, 10.
[211] Kim, M. H., Park, J. S., Jung, J. W., Byun, K. W. et al.,
Daidzein supplementation prevents non-alcoholic fatty
liver disease through alternation of hepatic gene expression
profiles and adipocytemetabolism. Int. J. Obes.(Lond.)
2011, 35, 1019–1030.
[212] Crespillo, A., Alonso, M., Vida, M., Pavon, F. J. et al., Reduction
of body weight, liver steatosis and expression of
stearoyl-CoA desaturase 1 by the isoflavone daidzein in
diet-induced obesity. Br. J. Pharmacol. 2011, 164, 1899–
1915.
[213] Takahashi, Y., Odbayar, T. O., Ide, T., A comparative analysis
of genistein and daidzein in affecting lipid metabolism in
rat liver. J. Clin. Biochem. Nutr. 2009, 44, 223–230.
[214] Shin, E. S., Cho, S. Y., Lee, E. H., Lee, S. J. et al., Positive
regulation of hepatic carnitine palmitoyl transferase
1A (CPT1A) activities by soy isoflavones and L-carnitine.
Eur. J. Nutr. 2006, 45, 159–164.
[215] Kim, S., Shin, H. J., Kim, S. Y., Kim, J. H. et al., Genistein
enhances expression of genes involved in fatty acid
catabolism through activation of PPARalpha. Mol. Cell. Endocrinol.
2004, 220, 51–58.
[216] Shin, E. S., Lee, H. H., Cho, S. Y., Park, H.W. et al., Genistein
downregulates SREBP-1 regulated gene expression by inhibiting
site-1 protease expression in HepG2 cells. J. Nutr.
2007, 137, 1127–1131.
[217] Kim, M. H., Kang, K. S., Lee, Y. S., The inhibitory effect of
genistein on hepatic steatosis is linked to visceral adipocyte
metabolism in mice with diet-induced non-alcoholic fatty
liver disease. Br. J. Nutr. 2010, 104, 1333–1342.
[218] Yalniz, M., Bahcecioglu, I. H., Kuzu, N., Poyrazoglu, O. K.
et al., Preventive role of genistein in an experimental nonalcoholic
steatohepatitis model. J. Gastroenterol. Hepatol.
2007, 22, 2009–2014.
[219] Lee, Y. M., Choi, J. S., Kim, M. H., Jung, M. H. et al., Effects
of dietary genistein on hepatic lipid metabolism and
mitochondrial function in mice fed high-fat diets. Nutrition
2006, 22, 956–964.
[220] Huang, C., Qiao, X., Dong, B., Neonatal exposure to genistein
ameliorates high-fat diet-induced non-alcoholic steatohepatitis
in rats. Br. J. Nutr. 2011, 106, 105–113.
[221] Ji, G., Yang, Q., Hao, J., Guo, L. et al., Anti-inflammatory
effect of genistein on non-alcoholic steatohepatitis rats induced
by high fat diet and its potential mechanisms. Int.
Immunopharmacol. 2011, 11, 762–768.
[222] Mohamed, S. S., Nallasamy, P., Muniyandi, P., Periyasami,
V. et al., Genistein improves liver function and attenuates
non-alcoholic fatty liver disease in a rat model of insulin
resistance. J. Diabetes 2009, 1, 278–287.
[223] Arunkumar, E., Karthik, D., Anuradha, C. V., Genistein
sensitizes hepatic insulin signaling and modulates lipid
regulatory genes through p70 ribosomal S6 kinase-1 inhibition
in high-fat-high-fructose diet-fed mice. Pharm. Biol.
2013, 51, 815–824.
[224] Ae, P. S., Choi, M. S., Cho, S. Y., Seo, J. S. et al., Genistein
and daidzeinmodulate hepatic glucose and lipid regulating
enzyme activities in C57BL/KsJ-db/db mice. Life Sci. 2006,
79, 1207–1213.
[225] Lei, H., Lu, F., Dong, H., Xu, L. et al., Genistein reverses free
fatty acid-induced insulin resistance in HepG2 hepatocytes
through targeting JNK. J. Huazhong Univ. Sci. Technolog.
Med. Sci. 2011, 31, 185–189.
[226] Shang, J., Chen, L. L., Xiao, F. X., Sun, H. et al., Resveratrol
improves non-alcoholic fatty liver disease by activating
AMP-activated protein kinase. Acta Pharmacol. Sin. 2008,
29, 698–706.
[227] Jeon, B. T., Jeong, E. A., Shin, H. J., Lee, Y. et al., Resveratrol
attenuates obesity-associated peripheral and central
C_
2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.mnf-journal.com
Mol. Nutr. Food Res. 2013, 00, 1–25 25
inflammation and improves memory deficit in mice fed a
high-fat diet. Diabetes 2012, 61, 1444–1454.
[228] Cho, I. J., Ahn, J. Y., Kim, S., Choi, M. S. et al., Resveratrol
attenuates the expression of HMG-CoA reductase mRNA
in hamsters. Biochem. Biophys. Res. Commun. 2008, 367,
190–194.
[229] Gomez-Zorita, S., Fernandez-Quintela, A., Macarulla, M. T.,
Aguirre, L. et al., Resveratrol attenuates steatosis in obese
Zucker rats by decreasing fatty acid availability and reducing
oxidative stress. Br. J. Nutr. 2012, 107, 202–210.
[230] Alberdi, G., Rodriguez, V. M., Macarulla, M. T., Miranda, J.
et al., Hepatic lipid metabolic pathways modified by resveratrol
in rats fed an obesogenic diet. Nutrition 2013, 29,
562–567.
[231] Cho, S. J., Jung, U. J., Choi, M. S., Differential effects
of low-dose resveratrol on adiposity and hepatic steatosis
in diet-induced obese mice. Br. J. Nutr. 2012, 108,
2166–2175.
[232] Ahn, J., Cho, I., Kim, S., Kwon, D. et al., Dietary resveratrol
alters lipid metabolism-related gene expression of mice on
an atherogenic diet. J. Hepatol. 2008, 49, 1019–1028.
[233] Poulsen, M. M., Larsen, J. O., Hamilton-Dutoit, S., Clasen,
B. F. et al., Resveratrol up-regulates hepatic uncoupling
protein 2 and prevents development of nonalcoholic fatty
liver disease in rats fed a high-fat diet. Nutr. Res. 2012, 32,
701–708.
[234] Bagul, P. K., Middela, H., Matapally, S., Padiya, R. et al.,
Attenuation of insulin resistance, metabolic syndrome and
hepatic oxidative stress by resveratrol in fructose-fed rats.
Pharmacol. Res. 2012, 66, 260–268.
[235] Bujanda, L., Hijona, E., Larzabal, M., Beraza, M. et al.,
Resveratrol inhibits nonalcoholic fatty liver disease in rats.
BMC Gastroenterol. 2008, 8, 40.
[236] Kang, W., Hong, H. J., Guan, J., Kim, D. G. et al., Resveratrol
improves insulin signaling in a tissue-specific manner
under insulin-resistant conditions only: in vitro and in vivo
experiments in rodents. Metabolism 2012, 61, 424–433.
[237] Chen, S., Li, J., Zhang, Z., Li, W. et al., Effects of resveratrol
on the amelioration of insulin resistance in KKAymice. Can.
J. Physiol. Pharmacol. 2012, 90, 237–242.
[238] Wang, G. L., Fu, Y. C., Xu,W. C., Feng, Y. Q. et al., Resveratrol
inhibits the expression of SREBP1 in cellmodel of steatosis
via Sirt1-FOXO1 signaling pathway. Biochem. Biophys. Res.
Commun. 2009, 380, 644–649.
[239] Hou, X., Xu, S., Maitland-Toolan, K. A., Sato, K. et al., SIRT1
regulates hepatocyte lipid metabolism through activating
AMP-activated protein kinase. J. Biol. Chem. 2008, 283,
20015–20026.
[240] Jung, T. W., Lee, K. T., Lee, M. W., Ka, K. H., SIRT1 attenuates
palmitate-induced endoplasmic reticulum stress and
insulin resistance in HepG2 cells via induction of oxygenregulated
protein 150. Biochem. Biophys. Res. Commun.
2012, 422, 229–232.
[241] Shapiro, H., Bruck, R., Therapeutic potential of curcumin
in non-alcoholic steatohepatitis. Nutr. Res. Rev. 2005, 18,
212–221.
[242] Kuo, J. J., Chang, H. H., Tsai, T. H., Lee, T. Y., Positive effect of
curcumin on inflammation and mitochondrial dysfunction
in obese mice with liver steatosis. Int. J. Mol. Med. 2012,
30, 673–679.
[243] Zeng, C. H., Zeng, P., Deng, Y. H., Shen, N. et al., The effects
of curcumin derivative on experimental steatohepatitis.
Zhonghua Gan. Zang. Bing. Za Zhi 2011, 19, 454–459.
[244] Weisberg, S. P., Leibel, R., Tortoriello, D. V., Dietary curcumin
significantly improves obesity-associated inflammation
and diabetes in mouse models of diabesity. Endocrinology
2008, 149, 3549–3558.
[245] Ramirez-Tortosa, M. C., Ramirez-Tortosa, C. L., Mesa, M. D.,
Granados, S. et al., Curcumin ameliorates rabbits’s steatohepatitis
via respiratory chain, oxidative stress, and TNFalpha.
Free Radic. Biol. Med. 2009, 47, 924–931.
[246] Qu, X. B., Zhao, S. P., Xu, J., Dong, L. N., Effects of curcumin
on secretion of adiponectin and interleukin-6 in human adipose
tissues: an in vitro study. Zhong. Xi. Yi. Jie. He. Xue.
Bao. 2008, 6, 711–715.
[247] Mouzaoui, S., Rahim, I., Djerdjouri, B., Aminoguanidine and
curcumin attenuated tumor necrosis factor (TNF)-alphainduced
oxidative stress, colitis and hepatotoxicity inmice.
Int. Immunopharmacol. 2012, 12, 302–311.
[248] Kuo, J. J., Chang, H. H., Tsai, T. H., Lee, T. Y., Curcumin ameliorates
mitochondrial dysfunction associated with inhibition
of gluconeogenesis in free fatty acid-mediated hepatic
lipoapoptosis. Int. J. Mol. Med. 2012, 30, 643–649.
[249] Messner, D. J., Rhieu, B. H., Kowdley, K. V., Iron overload
causes oxidative stress and impaired insulin signaling in
AML-12 hepatocytes. Dig. Dis. Sci. 2013, 58, 1899–1908.
[250] Lin, J., Zheng, S., Chen, A., Curcumin attenuates the effects
of insulin on stimulating hepatic stellate cell activation
by interrupting insulin signaling and attenuating oxidative
stress. Lab. Invest. 2009, 89, 1397–1409.
[251] Lin, J., Chen, A., Curcumin diminishes the impacts of hyperglycemia
on the activation of hepatic stellate cells by
suppressing membrane translocation and gene expression
of glucose transporter-2. Mol. Cell. Endocrinol. 2011, 333,
160–171.
[252] Tang, Y., Chen, A., Curcumin prevents leptin raising glucose
levels in hepatic stellate cells by blocking translocation
of glucose transporter-4 and increasing glucokinase.
Br. J. Pharmacol. 2010, 161, 1137–1149.
[253] Tang, Y., Chen, A., Curcumin protects hepatic stellate cells
against leptin-induced activation in vitro by accumulating
intracellular lipids. Endocrinology 2010, 151, 4168–4177.
[254] Kang, Q., Chen, A., Curcumin eliminates oxidized LDL roles
in activating hepatic stellate cells by suppressing gene expression
of lectin-like oxidized LDL receptor-1. Lab. Invest.
2009, 89, 1275–1290.
[255] Kang, Q., Chen, A., Curcumin suppresses expression of
low-density lipoprotein (LDL) receptor, leading to the inhibition
of LDL-induced activation of hepatic stellate cells.
Br. J. Pharmacol. 2009, 157, 1354–1367.
[256] Garcea, G., Jones, D. J., Singh, R., Dennison, A. R. et al.,
Detection of curcumin and its metabolites in hepatic tissue
and portal blood of patients following oral administration.
Br. J. Cancer 2004, 90, 1011–1015.
C_
2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.mnf-journal.com