Effect of purified allicin, the major ingredient of freshly crushed garlic, on cancer cell proliferation

The diverse health benefit effects of garlic include its anticancer activit y. However, very little is known about such activity of isolated garlic com pounds, among which allicin (the major ingredient of crushed garlic) has be en the least studied. The aim of this work was to determine whether pure al licin exhibits the antiproliferative effect reported for garlic in in vitro models. Allicin, but not its precursor alliin, inhibited proliferation of human mammary (MCF-7), endometrial (Ishikawa), and colon (HT-29) cancer cel ls (50% inhibitory concentration = 10-25 muM). Two of three tested primary lines of human fibroblasts displayed a similar response to allicin (50% inh ibitory concentration = 16-40 muM), whereas the third line was almost unaff ected by this compound. The pure allicin and water extract of garlic powder with equivalent allicin concentrations displayed a similar potency, sugges ting that allicin is responsible for the antiproliferative effect of the ex tract. The growth inhibition was accompanied by accumulation of cells in th e G(0)/G(1) and G(2)/M phases of the cell cycle (MCF-7 cells) and not by a significant increase in cell death. Allicin caused a transient drop in the intracellular glutathione (GSH) level, the magnitude and kinetics of which significantly varied depending on cell type. The extent of the decrease in GSH levels correlated well (r = 0.75) with the growth inhibitory activity o f allicin. On the basis of these findings, we suggest that allicin plays a major role in the antiproliferative effect of water-soluble garlic preparat ions and that this effect may be attributed to the ability of allicin to tr ansiently deplete the intracellular GSH level.