Garlic cholesterol inhibition

In vitro, allicin and related compounds inhibit HMG-CoA reductase, which is involved in cholesterol biosynthesis (see Chapter 35 Agents Used in Hyperlipidemia). Several clinical trials have investigated the lipid-lowering potential of garlic. Some have shown significant reductions in cholesterol and others no effect. The most recent meta-analysis suggested a minor (5%) reduction of total cholesterol that was insignificant when dietary controls were in place. 

The allyl sulfur compounds of garlic also have an anticoagulant action (by inhibiting platelet coagulability) and inhibit cholesterol synthesis by inactivating HMG-CoA reductase. 

Liu L and Yeh YY (2002) S-alk(en)yl cysteines of garlic inhibit cholesterol synthesis by deactivating HMG-CoA rednctase in cnltnred rat hepatocytes. Journal of Nutrition 132, 1129-34. 

Yeh, Y.Y. and Yeh, S.M. (1994) Garlic reduces plasma lipids by inhibiting hepatic cholesterol and triacylglycerol synthesis. Lipids. 29 189-193. 

Thus, allicin has been found to inhibit a large number of enzymes in vitro if they contain cysteine at the active sites, but otherwise very few (Lawson, in Koch and Lawson, 1996, p. 65). The reference further states that many of the explanations given for the biological effects of garlic focus on the ability of allicin to react with sulfhydryl enzymes, whatever the latter may be. Moreover, allicin was found to act against cholesterol and triglyceride synthesis. 

Preparations of garlic including garlic paste, garlic oil, allicin, and ajoene have been found to significantly reduce cholesterol biosynthesis in rat hepatocytes via inhibiting 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase and... 

Fig. 121.2 Hypolipidemic mechanism of garlic, (a) Inhibit the cholestamtl biosynthesis in liver, (b) Inhibit the rale limiting enzyme HMG-CoA reductase (c) Inhibit intestinal absorption (d) Induces the rate of cholesterol exraetirai...

Evidence from in vitro, in vivo, and clinical studies support the beneficial effects of garlic consumption in various preparations in the prevention of cardiovascular disease. The raw garlic and AGE are the most important among the available preparation and showed maximum pharmacological effect in low dose. The present report suggests that garlic has the ability to prevent excess free radical production, maintain the oxidative balance via increase in antioxidant status and increase in bioavailability of nitric oxide, prevent vascular inflammation, reduce cholesterol content and plaque formation, and inhibit platelet aggregation. 

---