Metabolic Disease
Ketosis: the convergence of
CHO and Lipid metabolism
Lipid Metabolism Control
• What regulates nutrient partitioning?
– Oxidation/catabolism vs. synthesis/anabolism
• What ensures lipolysis and lipogenesis are
coordinated…instead of competing?
Controllers of Nutrient Partitioning
Insulin
Glucagon
Epinephrine
Growth Hormone
Lipogenesis/Lipolysis
Glycolysis/ Gluconeogenesis & Glycogenolysis
Protein Synthesis/Proteolysis
Ketogenesis
Insulin
• Secreted from pancreas
– Stimulated by the presence of glucose
• Stimulates glycolysis
• Stimulates glycogen synthesis
• Prevents glycogen breakdown
(Glycogenolysis)
• Stimulates lipogenesis (fat synthesis)
• Potent antilipolytic (prevents lipolysis)
• Actions primarily counter balanced by
glucagon
• “I’m full” hormone



Insulin Action
Insulin binding to the insulin receptor induces a signal transduction cascade which
allows the glucose transporter (GLUT4) to transport glucose into the cell.
Glucagon
• Secreted by the pancreas
– Low blood sugar
• Stimulates gluconeogenesis
• Slows down glycolysis
• Stimulates glycogenolysis (glycogen
breakdown)
• Helps stimulate lipolysis
• “I’m hungry” hormone
Epinephrine
• A catecholamine typically present at most
sympathetic synaptic clefts
• Also synthesized and secreted by the adrenal
medulla
• Metabolic Actions
–
–
–
–
 Liver and muscle glycogenolysis
 Lipolysis
 Blood lactate
 Cardiac output
Somatotropin (aka growth hormone)
• Produced by the anterior pituitary
• Protein hormone (~190 amino acids)
• Lipid metabolism:
– During positive energy balance:
• Reduces lipogenesis ( LPL, ACC and FAS)
– During negative energy balance:
• Increases adipose sensitivity to lipolytic signals
Insulin vs. Glucagon
pancreas
muscle
Normal glucose regulation
Liver
Insulin/glucagon
IGF-I
Adrenal gland
Epinephrine
Pituitary
Growth Hormone
Amino acids
Liver
Nutrient Directors/Governors
Glucose
gluconeogenesis & glycogenolysis
fat
Fatty acids
Amino acids
Glucose
Fatty acids
GIT
Circulating Nutrient
Pool
Post-absorptive metabolic regulation
muscle
insulin
fat
Liver
insulin
pancreatic islet
b cells
Nutrients:
glucose
fatty acids
amino acids
GIT
meal
Glucagon
Glucose
Insulin
Meal
Reciprocity in Lipogenic and Liplolyctic
absorption
Lipogenesis
Time after feeding (h)
Lipolysis
Regulation of lipid metabolism
• Well fed:
–
–
–
–
 Insulin   lipogenesis &  lipolysis (also  protein synthesis &  proteolysis)
 glucagon
 epinephrine
 somatotropin
• Starving:
–  epinephrine, glucagon, somatotropin   lipolysis (also  proteolysis)
–  Insulin   lipolysis and  proteolysis
• Very Low CHO, high PTN diet:
– No  Insulin   lipogenesis
– No  Insulin   lipolysis
Adipose Lipogenesis vs. Lipolyis
• Both regulated primarily by phosphorylation
• ACC and HSL
– ACC-P = deactivated
– HSL-P = activated
• Ensures coordination
Epinephrine and Glucagon
Somatotropin
Adipocyte
NEFA
Epi
NEFA
Insulin
TG
Mammary
Gland
ATP
Ketones
Milk Fat
Intracellular triglyceride review
lipogenesis
Lipolysis
Lipoprotein lipase
Fatty acid oxidation
• Sites: Muscle and Liver
– Especially important for muscles under aerobic
conditions
– All cells except for RBCs and brain can use fatty
acids for energy
• Rate of oxidation is proportional to plasma NEFA
concentration
• Takes place in mitochrondia and peroxisomes
– Discovered in 1949 by Kennedy and Lehninger
• Don’t diffuse through mitochrondia membrane
• Need transport system
ß-oxidation of fatty acids involves successive cleavage with release of
acetyl-CoA. Fatty acid oxidase’s are found in the mitochondrial matrix or
inner membrane adjacent to the respiratory chain in the inner membrane.
Oxidation of Palmitate
FADH = 2 ATP
NADH = 3 ATP
Acetyl CoA = 12 ATP
1. CPT I transfers LCFA to carnitine
2. Acyltranslocase transfers LCFA across
innner membrane
3. CPT II re-esterfies LCFA into LCFA-acyl
CoA

Control of CPT
• Fed state: plasma NEFA low,  low oxidation
• Fed state: insulin, ACC, malonyl-CoA
• Malonyl-CoA potent allosteric inhibitor of CPT
• Minimizes futile cycle
Peroxisomes oxidize very long chain
fatty acids:
• Very long chain acyl-CoA synthetase facilitates
the oxidation of very long chain fatty acids (e.g.,
C20, C22).
• These enzymes are induced by high-fat diets
and by hypolipidemic drugs such as Clofibrate.
Peroxisome Oxidation
Only ½ has efficient as mitochrondia
FADH = energy is lost as heat
NADH, can diffuse out and enter mictochrondia
And contribute to the ETC
Doesn’t go to completion: just shortens so the FA
can enter the mitochondria
Fate of acetyl-CoA isn’t known
10% of all fatty acid oxidation
Excessive fatty acid catabolism in the liver.
Conditions that lead to ketone body synthesis:
1) Uncontrolled diabetes mellitus
reduced insulin action results in uncontrolled
lipolysis
2) Starvation
3) Early lactation
4) High protein/low CHO diet
Hormonal environment:
1) Insulin levels are low (or ineffective)
2) Glucagon levels are high
Acetyl-CoA formed
from fatty acid ßoxidation is either:
1) oxidized in TCA
2) repackaged
3) forms ketones
KETOGENESIS
• It occurs when there is a high rate of fatty acid
oxidation in the liver
• Directly proportional
to b- oxidation
• These three substances are collectively known as the
ketone bodies (also called acetone bodies or
acetone). Enzymes responsible for ketone bodies
formation are associated with mitochondria.
Ketosis
• Ketones can be oxidized by most tissues
• Formed in the liver from fat oxidation
– Most tissues can directly oxidize fatty acids
– Red blood cells and the CNS ca not
• Require the fatty acids to be converted into ketones
– Can provide 75% of CNS energy supply during starvation
• Very important in the conversion of adipose
tissue into available energy
– Not as much energy in ketones as from fatty acids
• Costs ATP to convert ketones into usable energy
• Occurs during:
–
–
–
–
Starvation
Diabetes
Low carbohydrate diet
Early lactation
Fatty Acid Oxidation/Gluconeogenesis and
Ketone Synthesis
• FA oxidation generates a lot of acetyl CoA
• An animal oxidizing fatty acids is in need of
energy… also  need for gluconeogenesis
•  oxaloacetate leaves TCA
• No carbon molecule for acetyl CoA to
combine with in order to enter TCA
• Acetyl CoA build up
NADH
Gluconeogenesis
Glucose
GAP
Pyruvate
Glycerol
Lactate
Acetyl CoA
OAA
TCA
Cycle
Amino Acids
Propionate
(from rumen fermentation)
Ketones Fate
•
Conversion of ketone bodies to acetyl-CoA requires ATP
–
–
•
 not as efficient as just oxidizing fatty acids
But, this is tolerated as the alternative is death.
Taken up by tissues and catabolized for energy
–
–
Rates of their metabolism is directly related to plasma concentration
Liver doesn’t oxidize ketones
•
Lacks succinyl CoA:3 ketoacid transferace
–
Necessary to activate acetoacetat to acetoacetyl CoA
•
Exhaled by the lungs
•
Secreted in sweat
•
Secreted in urine
–
Causes the loss of Na+
KETOGENESIS IS REGULATED AT
THREE CRUCIAL STEPS:
1.
Adipose tissue:
Factors regulating
mobilization of free fatty acids from adipose
tissue are important in controlling ketogenesis
2. Liver: After acylation, fatty acids undergo ßoxidation or esterified to triacylglycerol or
ketone bodies.
a. CPT-1 regulates entry of long-chain acyl
groups into mitochondria prior to ß-oxidation.
Its activity is low in the fed state, and high in
starvation.
2 a) continued
Fed state: Malonyl-CoA formed in the fed state is a potent
inhibitor of CPT-1. Under these conditions, free fatty acids enter
the liver cell in low concentrations and are nearly all esterified to
acylglycerols and transported out as VLDL.
Starvation:
Free fatty acid concentration increases with
starvation, acetyl-CoA carboxylase is inhibited and malonyl-CoA
decreases releasing the inhibition of CPT-I and allowing more ßoxidation.
These events are reinforced in starvation by decrease in
insulin/glucagon ratio. This causes inhibition of ACC in the liver
by phosphorylation.
In short, ß-oxidation from free fatty acids is controlled by the
CPT-I gateway into the mitochondria, and the balance of free
fatty acid uptake not oxidized is esterified.
3. Acetyl-CoA formed
from ß-oxidation of
fatty acids is either
oxidized in TCA
cycle or it forms
ketone bodies.
SEVERE Malnutrition:
KB
ketonuria
ketosis
ketoacidosis
coma
Tissue Fuel Usage in Fed and Fasting
States in Humans
Fed
Tissue
Liver
Kidney
GIT
used
released
used
released
Glucose (glycogen)
AA & FA
FA, Glucose
AA, Lactate
FA, Glycerol
Glucose,
ketone bodies
AA, Lactate,
FA, glycerol
glucose
glucose
Glucose, Aspartate,
Glutamate
Asparagine &
glutamine
Adipose
Glucose
Muscle
Glucose, Glycogen,
BCAA
Brain
Fasting
Glucose
FA, AA, CHO’s
FA, Glycerol
Lactate,
Alanine,
&Glutamine
FA, Ketones,
BCAA
Glucose &
Ketones
AA, but not
BCAA
Metabolic Disorders
Energy-Related Disorders
1- Fatty Liver Syndrome
2- Ketosis (Acetonemia)
3- Rumen Acidosis
4- Laminitis
5- Displaced Abomasum
6- Milk Fat Depression (rumen lipid issues)
Minerals & Vitamins-Related Disorders
1- Hypocalcemia (Milk Fever)
2- Udder edema (protein problem?)
3- Retained Placenta
Ketosis
Hypoclycemia and insulin insensitivity are primary reasons for
ketosis:
Body reserve: ~500 g
Intake during
Dry period: ~0 g/d
Lactation: ~0 g/d
Glucose lost in
feces: ~0 g/d
Glucose secretion in milk (as lactose): 2.3 kg/d
(for 45 kg/d of milk)
Occurrence:
Ketosis
• Occurs 2 to 4 weeks after calving (peak incidence is about 3 week)
• Affect most high producing cows (sub-clinically) in early lactation
Symptoms:
• “Typical” ketone (acetone) smell in the breath;
• Lack of appetite
– Decreased rumen mobility and production of “dry feces”
• Loss of weight, gaunt appearance, and dullness
Detection:
• Two changes in the blood related to liver functions
– Drop in blood glucose (<50 mg/dl)
– Rise in b-hydroxy butyrate (>14.4 mg/dl)
• Presence of ketones in urine (“Ketostick”):
– b-hydroxy butyrate; Acetone; Aceto-acetic acid.
Transition Period
Calving
Late Lactation
Dry Period
Gestation
Early Lactation
Uterine Involution
Lactogenesis
When Cows Leave the Herd
Health Costs = 5x
0.24%
624,614 Cows Leaving
5,749Herds
10%
0.20%
Average Risk per Day of Leaving In a
Period
% Cows Leaving That Left In the Period
12%
~25% of culling occurs prior to 600.16%
DIM
8%
6%
0.12%
4%
0.08%
2%
0.04%
0%
0.00%
20 41 62 83 104 125 146 167 188 209 230 251 272 293 314 335 356 377 398 419 440
21- Day Period Ending Day
Percent of Cows Leaving
Risk of Leaving
Source: 2002, Steve Stewart, DVM, Dipl.-ABVP, Univ. of Minnesota, College of Vet. Med.
Days Open Phenotypic Trend
Days open
160
Parity
1
2
3
4
5
140
120
USA Holstein
100
65
70
75
80
85
90
95
00
Year
H.D. NORMAN 2004 USDA
Energy Balance
EBAL = Feed Intake – (Maintenance (BW0.75) + Milk Production (yield and composition))
Especially fat!
OUTPUT
ENERGY BALANCE
INPUT
Estimated Energy Balance
Around Calving
Balance NEl, Mcal/day
(NEl intake - NEl expanded)Drop in
DMI
5
Colostrum & milk
synthesis
0
-5
-10
-15
-21
Grummer, 1995
-14
-7
0
7
14
Days Relative to Calving
21
DMI, lb/d
Feed Intake and Adipose Mobilization
During the Transition Period
50
1000
40
800
30
600
20
400
DMI (lbs)
NEFA
10
0
-29 -22 -15 -8
-1
6
200
0
13 20 27
Day relative to calving
Burhans and Bell, 1998
Plasma NEFA and fat mobilization increases
during negative energy balance
Dunshea et al (1990b)
Plasma GH (g/L)
80
40
25
Dry matter intake
(kg/d)
18
Time, P < 0.001
120
Time, P = 0.07
20
16
Time, P < 0.001
14
12
10
8
6
15
4
10
280
5
0
40
Time, P < 0.001
20
0
-20
Plasma insulin (pmol/L)
Plasma IGF-I
(g/L)
160
Time, P < 0.001
210
140
70
-40
-60
-21
-14
-7
0
+7
+14
+21 +28
Day relative to parturition
-21
-14
-7
0
+7
+14
+21
Day relative to parturition
+28
Well Fed….Mid Lactation
Baumgard and Rhoads, 2007
Transition Cow
Metabolic Flexibility:
Decreased Insulin Sensitivity
Baumgard and Rhoads, 2007