Nutrition Research, Vol. 20, No. 2, pp. 273-280.2000
Cotwinht 0 2000 Elsevier Science Inc.
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ELSEVIER
PII: SO271-5317(99)00159-l
EFFECT OF FRESH GARLIC (ALLIUM SATIVUM)
ON LIPID METABOLISM IN MALE RATS
R. Aouadi ‘MS, A. Aouidet’ PhD, A. Elkadhi * DTH, Med. C. Ben Rayana 2 DTH,
H. Jaafoura’ MD, B. Tritar 3 PhD & K. Nagati ‘MD.
‘Ecole Superieure des Sciences et Technique de la Sante de Tunis; * Institut National de Nutrition
et de Technologie Alimentaire ; 3Faculte des Sciences de Tunis.
ABSTRACT
The hypocholesterolemic
effect of dietary garlic was studied. 4 experimental
groups were established. The control group (group-C) received a standard diet ;
the second group (group-G) received a supplement with 10% fresh garlic, the third
group (group-Ch) received 2% cholesterol and the forth group (group-ChG)
received 2% cholesterol and 10% fi-esh garlic. The serum cholesterol level was
significantly lower in group-G (63.21 f 7.24) than in group-C (72.00 + 8.32) (p <
0.05). On the other hand, hypercholesterolemia
induced by cholesterol feeding
(group-Ch: 94.33 f 24.50) was significantly reduced by garlic (group-ChG: 65.03
+ 10.57) (p < 0.005). Garlic supplementation increased high density lipoprotein
and decrease low density lipoprotein in normal, and hypercholesterolemic rats. The
reduction in the plasma cholesterol by feeding garlic was in low density
lipoprotein and very low density lipoprotein cholesterol fractions. However, the
liver weight was influenced by supplementation of garlic. Feeding the garlic diet
decreased liver weight in group-G (3.00 +_0.13) compared with group-C (3.33 +
0.26) (p < 0.005) and in group-ChG (3.66 f 0.24) compared with group-Ch (3.35 f
0.15) (p < 0.05). The plasma glucose in rats fed the cholesterol diet supplemented
with garlic was reduced, but not significantly, compared with those fed the
cholesterol diet without garlic. The results demonstrate that garlic exerts
hypocholesterolemic effects in normal or cholesterol-fed rats and reduces the liver
weight.
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Key Word : Garlic, Rats, Liver, Cholesterol, Lipoprotein, Glucose.
INTRODUCTION
Hyperlipidemia or the increased serum cholesterol level is a high risk factor contributing to the
development of coronary heart disease (CHD) (1). Epidemiological studies have shown that there
is a positive correlation between the incidence of CHD and the blood cholesterol level. Garlic has
been known to have medicinal properties in oriental countries ; it has been used as a popular
remedy for various physiological disorders such as hemorrhoids, coughs abdominal pain, loss of
appetite, pneumonia. Among these, particular attention has been focused on the
Address: Pr. AOUIDET Abdallah, Ecole superieure des Sciences et Technique de la Sante de
Tunis - B.P. No176 - Bab Souika; 1006 - Tunis -Tel: 216.1.562.455 - Fax: 216.1.570.062.
273
274
R. AOUADI et al.
cholesterol-lowering
activity of garlic in recent years. There is a widespread search for a drug,
which may control both hypercholesterolemia and hypertriglyceridemic.
Many works (2, 3) have
confirmed the effect of garlic.
Recent study have shown that fresh garlic is an hypotensive agent for a short term (4). Several
studies (5, 6) have also shown that garlic contain active hypocholesterolemic
and hypoglycemic
components, known as diallyl disultide and dipropyl disultide (7, 8). Garlic can be processed
into different products and used. Our primary objective in the study was to know if the garlic,
prepaed in the oven during 45 minutes for 100°C is able to maintain his hypocholesterolemic
effect. We will to determine the effects of fresh garlic on lipid metabolism in normal rats and rats
rendered hypercholesterolemic
including the determination
of each lipoprotein cholesterol
fraction and the plasma glucose.
METHODS AND MATERIALS
Reuartition of the grouns
One month-old young male rats of the Wistar strain in the weight range 70-80 g were used as
experimental animals. The animals were divided into four different groups of 10 animals each. 1)
A group of control rats (Group-C) ; 2) group-G received 10% garlic 3) group-Ch received 2%
cholesterol and 4) group-ChG received 10% garlic + 2% cholesterol. After a short adjustment
period (2 weeks), the rats were kept in stainless-steel cages in a room maintained at 20-22’C
with a 12-hour/dark cycle and about 50% relative humidity. Cholesterol and the contents of
garlic pearls were supplemented in the required proportion to the control.
Exnerimental Design
Our study was carried to examine the effect of garlic given for a relatively long period of time
(12 weeks) on cholesterol, HDL-Cholesterol,
LDL-Cholesterol,
triglycerides and glucose
concentrations in the total blood. The infbtence of garlic on body weight gain, food intake was
also evaluated (the body weight and food consumption were determined weekly).
TABLE 1: The comnosition
Ingredients
Corn starch
Casein
Soya oil
Linoleic acid
L-Methionine + L-Cysteine
Choline
Vitamin mixtures
Mineral mixture
of control diet
Amounts, g/IOOg diet
52.1
35.8
5.7
1.5
0.6
0.2
1.7
1 Vitamin mixture, ner 100 g drv weight diet :
vitamin A palmitate : 1,442 IU ; cholecalciferol : 2,000 IU ; a-tocopherol acetate : 4.1 mg ;
vitamin K3 : 0.1 mg ; thiamin : 1.2 mg ; riboflavin 0.4 mg ; niacin : 7.7 mg ; vitamin B3 : 0.9
mg ; vitamin B 12 : 1.O mg ; pyridoxine : 1.9 mg ; folacin : 5.4 mg.
2 Trace elements. ner g or m&n drv weight diet :
calcium : 7.8 g ; phosphorus : 7.6 g ; sodium : 1.5 g ; choline : 0.35 g ; potassium : 6.9 g ; sulfur :
1.8 g ; magnesium : 1.5 g ; iron : 190 mg ; copper : 7 mg ; zinc : 54 mg ; manganese : 90 mg ;
cobalt : 4 mg ; selenium : 4 mg ; iodine : 1 mg.
HYPOLIPIDEMIC
275
EFFECT OF GARLIC
Prenaration of garlic and diets :
Garlic bulbs were obtained from a commercial source, peeled off, washed and ground by a
blender for 10 minutes. The contents of garlic or cholesterol or garlic plus cholesterol were
supplemented in the required proportion to the control diet (given from PROVITAL -Z.I. 8030 GROMBALIA) which was ground in mill for grains. Diets were prepared by mechanically
mixing the ingredients. An addition of the distilled water (100 ml per 100 g of diet) was made to
form a bread dough. ARerwards, we put the diets in the oven (REGQLATO ELBA type PRB
5540E SER. NR. 9719 ; CAT. II 2H3+ CQn = Kw ; 78&/h - made in Italy) during 45 minutes
for 100°C to make as flat as pancake. The diets were stored at a constant temperature of 4°C and
were weighted and changed daily. The diet of control group (group-C) was prepared similarly to
the other diets, but without supplement of cholesterol or garlic.
Samnle collection
On the 12th week, rats were killed by decapitation at 9:00 after 15 hr fasting and blood was
collected. Liver, aorta, kidney and stomach were removed from each animal washed in saline
solution, weighed and kept in formaldehyde solution.
Plasma analvsis :
Total plasma cholesterol levels
(BIOMERIEUX/France)
(9).
Serum triglycerides
were
determined
by the enzymatic
were determined by enzymatic calorimetric
CHOD-PAP
method
method (10)
The lipoprotein (measured by the Enzymatic Calorimetric Method) VLDL and LDL are
precipitated by addition of phosphotungstic acid and magnesium chloride After centrifugation
the clear supematant contains the HDL (High density lipoproteins) - fraction, which is assayed
for cholesterol with the CHRONOLAB/Suitzerland
test kit (11).
Plasma glucose levels were determined by the enzymatic calorimetric method (GOD-PAP ;
CHRONOLAB / Suitzerland ; cat n”lOl-0083). The glucose is determined after enzymatic
oxidation in the presence of glucose oxidase (GOD). The formed Hz02 reacts under catalysis of
peroxidase (POD) with phenol and 4-amino-antipyrine
to form quinoneimine. The intensity of
the color is proportional to the glucose concentration in the sample.
Statistical analysis :
Results have been expressed as the mean f SD.
Statistical analysis was performed using a two-tailed Student’s t-test.
The difference was considered significant at p < 0.05.
RESULTS
Feeding the cholesterol the rats of group-Ch, when compared to group-C, increased significantly
their levels plasma cholesterol (p < 0.005) and plasma triglycerides (p < 0.05). The plasma
cholesterol level in the group-C was significantly reduced (p < 0.05) by feeding garlic (group-G).
Whereas hypercholesterolemia
induced in group-Ch was significantly reduced (p < 0.005) by
feeding garlic (group-ChG). However, Hypertriglyceridemia was not changed neither in group-G
nor in group ChG, compared with the group-C and the group-Ch respectively.
Rats fed the diet supplemented with garlic (group-G and group-ChG), compared with group-C
and Ch respectively,
increased significantly
(p < 0.05) high density lipoprotein (HDL)
R. AOUAPI et al.
276
cholesterol and decreased (but not significantly) low density lipoprotein (LDL) (figurel). The
plasma cholesterol was divided into each lipoprotein cholesterol and the percentage of each
lipoprotein cholesterol to the plasma total is given in figurel. The proportion of low density
lipoprotein (LDL) cholesterol was lower in rats fed the garlic than in animals fed the control diet,
Just opposite results were obtained in the proportion of high-density lipoprotein .(HDL)
cholesterol to the plasma total cholesterol, Rats fed the cholesterol diet showed an increase in the
LDL-cholesterol level but the supplementation of garlic to the cholesterol diet reduced that.
T
G
=
5
35
=
5
30
2
.f
25
z
h
20
.g
15
5
s
10
T
5
0
LDL
HDL
VLDL
Figure 1 : Effects of garlic on the percentage of each plasma lipoprotein cholesterolfraction to the total cholesterol
in male rats. C : control ; G: control + 10% fresh garlic ; Ch: control + 2% cholesterol ; ChG: control + 10% fresh
garlic + 2% cholesterol. * : p < 0.05
Each bar representsthe mean f standarddeviation.(SD)Compamisonswere made between C, G or ch and chG.
Body weight gain was not significantly different between all the groups. Feeding the garlic diet
decreased liver weight. Rats fed the cholesterol diet showed greater liver weight than control
rats. The supplementation of garlic to the cholesterol diet decreased this parameter (table 2).
The plasma glucose concentration was reduced in rats fed garlic (group-G) by 6.7%, but this was
not significant.The concentration of plasma glucose in rats fed the cholesterol diet supplemented
with garlic was decreased significantly (p < 0.05) compared with controls but not when
compared with those fed the cholesterol diet without garlic. On the other hand, the same
parameter was decreased in rats fed the cholesterol compared with controls.
DISCUSSION
The decrease of plasma cholesterol level in garlic fed animals indicated that the excretion of
cholesterol and cholesterol metabolites can be changed by garlic feeding. The other possible
mechanism of garlic action may be direct or indirect inhibition of endogenous cholesterol
synthesis as suggested in previous reports (12, 13). The importance of plasma levels of
cholesterol and lipoprotein in the pathogenesis of atherosclerosis has been noted by a number of
studies. Increased levels of total plasma cholesterol and LDL or VLDL associated with increased
risks of developing high concentration coronary diseases (12, 14).
!
. . ..
2% cholesterol
2% cholesterol
+
10% garlic
Ch : Cholesterol
ChG : Cholesterol
+
garlic
.
.
20.80 + 1.47 (9)
21.48 f 1.66 (8)
19.80 k 1.52 (9)
20.01 f 1.79 (8)
(g/day)
Food
Consumption
21.21 f4.5 (9)
22.48 k 5.6 (8)
20.8 + 6.5 (9)
22.01 f 5.79 (8)
Weight Gain
(g/week)
3.35” + 0.15*(9)
3.66 f 0.24b (8)
3.00 + 0.13’ (9)
3.33 f 0.26’(8)
(8)
70.65 f 10.43b
50.25 k 4.40” (8)
59.89 k6.55’ (8)
65.03 k10.574b (7) 72.97 Z!I11.02b
L
94.33 f 24.50’ (8)
63.21 + 7.24b (8)
72.00 zk8.32’ (8)
116.38 f 11.8b
(7)
‘Means + SD
* : Liver weight in g/l 00 g body weight
< 0.05).
made between groups-G and C ; Ch and C and ChG and Ch. nbcMeans in the same row with different superscripts differ significantly
(p
114.58 f 8.5b (8)
121.6 f 10.7’ (8)
130.37 It 13.9’ (8)
Liver Weight
Plasma Glucose
Plasma
Triglycerides
mg/dl
Cholesterol
(g/lOOg)
mg/dl
.........
.............
....................
................
...... ........
.......
.........
.......
............
...............
..................................
................
...
(mk!!!!!)
in male normal rats and rats fed cholesterol ’
* : The composition of the control diet is given in materials and methods ; number of rats is given in parentheses, Comparisons were
10% garlic
Supplement to
Control Diet *
(“~)
. .
G : Garlic
C : Control
Group
Effect of garlic on weight gain and plasma components
TABLE 2
R. AOUADI et al.
278
In our experiment, rats fed cholesterol diets (group-Ch) increased significantly their serum
triglycerides. The increase in circulatory cholesterol and triglycerides levels observed in our
results may be due to endogenous synthesis (15). A supplementation of 10% of fresh garlic in the
diet caused a marked reduction in the serum cholesterol levels (12.2%). About the absence of an
hypotriglyceridemic
effect of the garlic, we think that requires a longer period.Thus 10% fresh
garlic in the equivalent to 2 - 3% powder garlic was sufficient to have an hypocholesterolemic
effect. Garlic fed rats (group-ChG) showed an increase in HDL cholesterol compared with those
fed the cholesterol diet (group-Ch) when expressed as a percentage to total plasma cholesterol.
The increase of plasma cholesterol in animals fed the cholesterol diet was in mostly LDL
fraction ; garlic feeding (group-ChG) reduced the increased LDL cholesterol fraction. The results
suggest that one reason of preventive effect of garlic against the atherosclerotic process may be
the changes in the portions of lipoprotein cholesterol fractions. But, The groups-G and ChG can
have their lipid metabolism altered by the restriction of nutrient/energy
since these groups
consumed less protein, vitamin, minerals etc. when compared with groups-C or group-Ch. This
is why in our mtur experiments, we have interest to verify this hypothesis in rats which should
receive the same ratios nutrient.
Previous studies have shown that ingestion of garlic appear to inhibit hepatic fatty acid synthesis
(12) by lowering key enzymes activities in supplying substrates and consequently reduced the
lipid accumulation in the liver and the triglycerides level in the plasma. However, this dose of
1. lg - 1.3g body weight is comparable to the dosage of 1.2 - 1.6g body weight found to be
effective in rats (16). The results of the present study, however, clearly confirm the previous
clinical studies about the hypocholesterolemic effect of garlic (5).
Unlike the previous reports (17, 18) there was no influence of garlic on the plasma glucose
concentration in the present study. The hypoglycemic effect of garlic was suggested by
increasing the plasma insulin level (14,18). Unfortunately the plasma concentration of insulin
was not determined in this study and the discrepancy between our results and others on the
hypoglycemic effect of garlic is not known. For the reduction of plasma glucose in group-Ch and
group-ChG, we think that there is a cholesterol effect on plasma glucose, or an overall effects,
but the mechanism is unknown. The same results were obseved with Myung S and ~011.(19)
ACKNOWLEDGEMENTS
The authors thank HAOUARI M., SFAXI A. (Ecole Superieure des Sciences et Techniques de la
Sante de Tunis) And ALGUEMI C (Institut National de Nutrition) and MAALOUL A. (Institut
de Sante et de Securite au Travail) for their excellent technical assistance and supports during the
course of this study.
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Accepted
for
publication
June
30,
1999.
in rats fed