We reported previously that garlic cultivated with
selenite fertilization showed powerful chemopreventive activity in the rat dimethylbenz[a]
anthracene (DMBA)-induced mammary
tumor model (
Carcinogenesis 15, 573-576, 1994). In order to ascertain that the efficacy of the high-
selenium garlic in
cancer protection is primarily dependent on the action of
selenium we compared the effects of two batches of garlic
powder with marked differences in their level of
selenium enrichment, 112 or 1355 p.p.m. Se dry weight. Both products were added to the diet to achieve the same final concentration of 2 p.p.m. Se. The supplementation protocol was designed to evaluate the efficacy during either the initiation phase or post-initiation phase of DMBA mammary
carcinogenesis. Significant
tumor reduction was observed with either treatment protocol. Furthermore, the magnitude
tumor suppression, as well as the extent of
DMBA-DNA adduct inhibition, were very similar with the two batches of garlic, even though the amounts of garlic in the diet varied considerably between them (1.8% for the 112 p.p.m. Se garlic versus 0.15% for the 1355 p.p.m. Se garlic). This suggests that the anti-
cancer activity of the high-
selenium garlic was likely to be accounted for by the effect of
selenium, rather than the effect of garlic per se. A continuous feeding of the high-
selenium garlic produced a modest increase in total
selenium in various tissues. In general the profile of
selenium accumulation was comparable in rats ingesting either the 112 or the 1355 p.p.m. Se garlic. Thus, based on the results of several
biological responses, it appears that the ability of the high-
selenium garlic to protect against
tumorigenesis is primarily dependent on increased intake of
selenium provided by the vegetable. Future research will be focused on the chemical form of
selenium in the garlic.