Biological Activities–Protection of the cardiovascular system
Inhibition of cholesterol synthesis
Garlic and garlic-derived organosulfur compounds have been found to decrease the synthesis of cholesterol by hepatocytes. Several garlic-derived organosulfur compounds, including S-allylcysteine and ajoene, have been found to inhibit 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase (HMG-CoA reductase), a critical enzyme in the cholesterol biosynthesis pathway. Garlic-derived compounds may also inhibit other enzymes in this pathway, including sterol 4α-methyl oxidase.
Inhibition of platelet aggregation
An increase in the ability of platelets to aggregate has been linked to the narrowing of blood vessels and the occurrence of acute thrombotic events. A variety of garlic-derived organosulfur compounds have been found to inhibit platelet aggregation in the test tube. Aged garlic extract was found to inhibit chemically stimulated platelet aggregation by downregulating the fibrinogen binding activity of glycoprotein IIb/IIIa fibrinogen receptor found on platelets and/or by preventing intraplatelet calcium mobilization.
Inhibition of vascular smooth muscle cell (VSMC) proliferation
The proliferation and migration of normally quiescent VSMCs are central features of vascular diseases, including atherosclerosis and coronary restenosis (when treated arteries become blocked again). Although the significance of these findings for human cardiovascular disease is not yet clear, limited cell culture research suggested that organosulfur compounds from garlic could inhibit the proliferation and migration of VSMCs .
Inhibition of vascular cell adhesion molecules
An elevation of oxidized low-density lipoprotein (LDL) concentration in plasma has been involved in the pathogenesis of atherosclerosis. Oxidized LDL may stimulate the recruitment of inflammatory white blood cells from the blood to the arterial wall by inducing the expression of vascular cell adhesion molecules. DADS and DATS inhibited the expression of adhesion molecules, E-selectin and vascular cell adhesion molecule-1 (VCAM-1), on endothelial cell surface by reversing oxidized LDL-induced inhibition of PI3K/Akt and cAMP responsive element binding protein (CREB) signaling pathways.
Hydrogen sulfide-mediated vasodilatory activity
The preservation of normal arterial function plays an important role in cardiovascular disease prevention. Hydrogen sulfide (H2S), a gaseous signaling molecule produced by some cells within the body, acts as a vasodilator (relaxes blood vessels) and thus may have cardioprotective properties. H2S production may be involved in vascular smooth muscle cell relaxation through regulating the opening/closing of potassium channels and/or enhancing NO-dependent signaling pathway. A study found that garlic-derived compounds are converted to hydrogen sulfide by red blood cells in vitro. However, human consumption of a high dose of raw garlic does not increase breath hydrogen sulfide levels, suggesting that significant metabolism of garlic compounds to hydrogen sulfide does not occur in vivo.
Note that the potential benefits of garlic consumption/supplementation on cardiovascular health may also be attributed to antioxidant and anti-inflammatory activities described above.