Allyl mercaptan, a major metabolite of garlic compounds, reduces cellular cholesterol synthesis and its secretion in Hep-G2 cells☆

Abstract 

The cytotoxicity, cellular cholesterol synthesis, and secretion of allyl mercaptan, a major metabolite of garlic compounds, were studied in Hep-G2 cells. The cells were grown in Dulbecco’s modified Eagle’s medium supplemented with 10% fetal bovine serum and treated with 5, 25, 50, 100, 125, 250, and 500 μg of allyl mercaptan/mL for 4, 12, and 24 hours. At concentrations up to 125 μg, no significant cytotoxic effect was noted during those incubation periods. However, at a concentration of 250 μg, cell viability decreased approximately 50% compared with the control (P < 0.05) in all three incubation times. At a concentration of 500 μg, allyl mercaptan was highly toxic, causing extensive cell death. The treatment of cells with 5, 10, 25, 50, or 100 μg (noncytotoxic concentration) of allyl mercaptan resulted in a marked inhibition of ³H-acetate incorporation into cholesterol. At concentrations between 5 and 100 μg, the cholesterol synthesis was inhibited 20 to 80% in cells and the cholesterol secretion into the medium decreased 20 to 50% compared with the control (P < 0.05). The concentration of allyl mercaptan required to suppress cholesterol synthesis by 50% was approximately 25 μg/mL. Allyl mercaptan treatment of cells incubated with 1 mM of oleic acid also resulted in a significant decrease in the cholesterol synthesis compared with the cells incubated with oleic acid alone (19.5 ± 1.2 × 10³ dpm/mg protein/4 h vs. 30.0 ± 2.6 × 10³ dpm/mg protein/4 h; P < 0.05). The present study demonstrates that allyl mercaptan is effective in inhibiting cholesterol synthesis at concentrations as low as 5 μg, and its inhibition is concentration dependent.

Keywords:  : allyl mercaptan, cholesterol synthesis, cholesterol secretion, cytotoxicity, Hep-G2 cell