The effects of garlic preparations against human tumor cell proliferation

Epidemiological studies in China provide reason to suspect that a rich garl ic content in the diet might reduce the proliferation of tumors in humans. We conducted experiments on human tumor cell lines and determined the influ ence of a garlic powder preparation, a garlic extract (reported as 8-10% L( +)-alliin enriched), and a combination thereof, on cellular proliferation i n cell cultures, employing the widely used indirect neutral red procedure. Garlic powder failed to inhibit the growth of human hepatoma HepG2 or human colorectal carcinoma Caco2 cells at concentrations of up to 1000 mu g/ml. Garlic extract, in which the alliin content was highly enriched was also un able to inhibit the growth of these cells. However, when the garlic extract was supplemented with garlic powder (to 10% final concentration) there was a concentration-dependent clear inhibition of tumor cell growth (IC50 valu es of 330 mu g/ml for HepG2 and 480 mu g/ml for Caco-2 cells). The growth o f the human lymphatic leukemia cell line CCRF CEM was significantly inhibit ed in a dose-dependent manner by both garlic powder and garlic extract at c oncentrations as low as 30 mu g/ml. However, no potentiation of this effect occured upon mixing of the two preparations. Our results suggest that the antiproliferative effects of garlic may be due to breakdown products of all iin, such as allicin or polysulfides, rather than alliin itself, since the addition of an alliinase system (garlic powder) to an alliin enriched prepa ration without alliinase (garlic extract) potentiated the effects observed with the two preparations alone.