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Department of Biological Sciences, Faculty of Science, Kuwait University, 13060 Safat, Kuwait
4 To whom correspondence should be addressed. E-mail: martha{at}kuc01.kuniv.edu.kw.
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ABSTRACT |
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 TOP ABSTRACT MATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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KEY WORDS: • cholesterol • garlic • glucose • triglycerides
Hyperlipidemia is a major risk factor involved in ischemic heart disease. During the last few decades, the hypolipidemic effect of garlic and onion has been confirmed by many investigators (1–5). There are many drugs in the market that control hypercholesterolemia and hypertriglyceridemia. Garlic and onion are said to lower serum cholesterol, enhance fibrinolytic activity, and inhibit platelet aggregation and thromboxane formation (6–11). There have also been reports on the beneficial effects of garlic extract and oil (12–14) in controlling hyperlipidemia in animals. Adding garlic to sucrose and cholesterol in the diet of rats prevents an increase in serum and liver cholesterol, triglycerides, and free fatty acids (15,16). Moreover, the addition of garlic decreases blood sugar with a concomitant increase in liver glycogen. These effects were attributed to the presence of sulfur compounds in the garlic (17).
High doses of garlic (1 g/kg) have been reported to have beneficial effects in reducing hyperlipidemia (18). The aim of this investigation was to study the efficacy of an aqueous extract of raw garlic in controlling levels of sugar, cholesterol, and triglycerides in the blood of normal rats treated orally and intraperitoneally daily for 4 wk. Because there have been many inconsistent reports about the use of different preparations of garlic, we decided to use the aqueous extract of garlic.
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MATERIALS AND METHODS |
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TOPABSTRACTMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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The animals were given 0.5 mL aqueous extract of garlic every d for 4 wk. After the 4-wk treatment, the rats were killed using urethane anesthesia. The blood was collected by cardiac puncture and allowed to clot, and the clotted blood was then centrifuged at 3500 x g for 30 min. The serum was separated and stored at –80°C for cholesterol and triglyceride analysis. Serum glucose was determined immediately by the glucose oxidase method using kits supplied by Randox. Cholesterol and triglyceride levels in the serum were measured using enzymatic kits also supplied by Randox.
Aqueous extract of raw garlic was prepared as described previously (19). Boiled extract of the bulbs was obtained by heating the raw extract for 10 min in a boiling water bath. Both extracts were stored in aliquots at –20°C and thawed daily for administering to animals. The experimental data are expressed as means ± SEM and were analyzed by two-tailed Student's t test. A level of P < 0.05 was considered to be significant.
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RESULTS AND DISCUSSION |
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TOPABSTRACTMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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Our studies with rats receiving daily oral or intraperitoneal injections of the aqueous extract of raw garlic for a period of 4 wk produced consistent results. Garlic, when used in either low (50 mg/kg) or high (500 mg/kg) doses, caused a significant reduction in serum cholesterol and triglyceride levels (Figs. 1 and 2). The effect was more pronounced at the high dose of garlic (Fig. 1). In contrast, when boiled-garlic extracts were used in high concentration (500 mg/kg), cholesterol and triglyceride levels were significantly reduced (Fig. 3). However, the percentage of reduction was less than that observed with raw garlic at this dose (Figs 1 and 2).
The results of this study confirm the earlier hypolipidemic effects reported for garlic (18,20). A similar hypocholesterolemic effect of garlic was observed previously in rats fed a high-cholesterol diet in the presence of garlic oil (23).
The results show that an aqueous extract of raw garlic taken in small amounts has a profound effect in lowering cholesterol and triglyceride levels. In contrast, blood-glucose levels do not decrease in rats receiving a low dose of fresh garlic extract. However, high doses of this herb have a significant effect in lowering blood-glucose levels. This study also shows that the effects on triglyceride and cholesterol levels are lowered but not abolished upon boiling the garlic extract. In contrast, the boiled garlic extract lost all effectiveness in lowering serum-glucose levels.
We can therefore conclude that raw garlic is more beneficial than the cooked form in reducing blood lipid and glucose levels, and could potentially play an important role in preventing atherosclerosis or diabetes. Of significance is that one of the chronic complications of diabetes is the increased prevalence of cardiovascular disease (24). Therefore, any agent that has the ability to both lower blood-lipid and glucose levels is a potential preventive agent for diabetics. It is clear from the present results that garlic extracts in modest doses could have a beneficial effect on blood lipids and glucose in health and disease.
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FOOTNOTES |
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2 Author disclosure: No relationships to disclose.
3 This research was supported by Kuwait University research grant SB 030.
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LITERATURE CITED |
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TOPABSTRACTMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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1. Jain RC. Effect of garlic on serum lipids, coagulability and fibrinolytic activity. Am J Clin Nutr. 1977;30:1380–1.
2. Sainani GS, Desai DB, Gorhe NH, Natu SM, Pise DV, Sainani PG. Effect of dietary garlic and onion on serum lipid profile in Jain commmunity. Indian J Med Res. 1979;69:776–80.[Medline]
3. Sainani GS, Desai DB, Natu MN, Katrodia KM, Valame VP, Sainani PG. Onion, garlic, and experimental atherosclerosis. Jpn Heart J. 1979;20:351–7.[Medline]
4. Bordia A. Effect of garlic on blood lipids in patients with coronary heart disease. Am J Clin Nutr. 1981;34:2100–3.
5. Chetty KN, Calahan L, Harris KC, Dorsey W, Hill D, Chetty S, Jain SK. Garlic attenuates hypercholesterolemic risk factors in olive oil fed rats and high cholesterol fed rats. Pathophysiology. 2003;9:127–32.[Medline]
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12. Bordia AK, Bansal HC, Arora SK, Rathore AS, Ranawat RVS, Singh SV. Effect of essential oil of garlic on serum cholesterol, plasma fibrinogen, whole blood coagulation time and fibrinolytic activity in alimentary lipaemia. J. Assoc. Physicians India 1974;22:267–70.[Medline]
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15. Adamu I, Joseph PK, Augusti KT. Hypolipidemic action of onion and garlic unsaturated oils in sucrose fed rats over a two month period. Experientia. 1982;38:899–901.[Medline]
16. Chang ML, Johnson MA. Effect of garlic on carbohydrate metabolism and lipid synthesis in rats. J Nutr. 1980;110:931–6.
17. Augusti KT, Mathew PT. Lipid lowering effect of allicin (Diallyl Diasulfideoxide) on long term feeding to normal rats. Experientia. 1974;30:468–70.[Medline]
18. Bordia AK, Sodhya SK, Rathore AS, Bhu N. Essential oil of garlic on blood lipids and fibrinolyitc activity in patients of coronary artery disease. J. Asso. Physicians India. 1978;26:327–31.
19. Ali M, Mohammed SY. Selective suppression of platelet thromboxane formation with sparing of vascular prostacyclin synthesis by aqueous extract of garlic in rabbits. Prostaglandins Leukot Med. 1986;25:139–46.[Medline]
20. Augusti KT. Hypocholesterolemic effect of garlic, Allium sativum Linn. Indian J Exp Biol. 1977;15:489–90.[Medline]
21. Arora RC, Arora S. Comparative effects of colfibrate, garlic and onion on alimentary hyperlipemia. Atherosclerosis. 1981;39:447–52.[Medline]
22. Luley C, Lehmann-Leo W, Moller B, Martin T, Schwartzkopff W. Lack of efficacy of dried garlic in patients with hyperlipoproteinemia. Arzneimittelforschung. 1986;36:766–8.[Medline]
23. Sodimu O, Joseph PK, Augusti KT. Certain biochemical effects of garlic oil on rats maintained on high fat - high cholesterol diet. Experientia. 1984;40:78–80.[Medline]
24. White DA, Baxter M. Diabetes mellitus. In: White DA, Middleton B, Baxter M, editors. Hormones and metabolic control. 2nd edition. London: E. Arnold; 1984. p. 79–92.
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