Differential Regulation of NO Availability from Macrophages and Endothelial Cells by the Garlic Component S-allyl Cysteine

Garlic has been used as a traditional medicine for prevention and treatment of cardiovascular diseases. However, the molecular mechanism of garlic's pharmacological action has not been clearly elucidated. We examined here the effect of garlic extract and its major component, S-allyl cysteine (SAC), on nitric oxide (NO) production by macrophages and endothelial cells. The present study demonstrates that these reagents inhibited NO production through the suppression of iNOS mRNA and protein expression in the murine macrophage cell line RAW264.7, which had been stimulated with LPS and IFNgamma. The garlic extract also inhibited NO production in peritoneal macrophages, rat hepatocytes, and rat aortic smooth muscle cells stimulated with LPS plus cytokines, but it did not inhibit NO production in iNOS-transfected AKN-1 cells or iNOS enzyme activity. These reagents suppressed NF-kappaB activation and murine iNOS promoter activity in LPS and IFNgamma-stimulated RAW264.7 cells. In contrast, these reagents significantly increased cGMP production by eNOS in HUVEC without changes in activity, protein levels, and cellular distribution of eNOS. Finally, garlic extract and SAC both suppressed the production of hydroxyl radical, confirming their antioxidant activity. These data demonstrate that garlic extract and SAC, due to their antioxidant activity, differentially regulate NO production by inhibiting iNOS expression in macrophages while increasing NO in endothelial cells. Thus, this selective regulation may contribute to the anti-inflammatory effect and prevention of atherosclerosis by these reagents.