Dose-dependent inhibition of glutathione S-transferase placental form-positive hepatocellular foci induction in the rat by methyl propyl disulfide and propylene sulfide from garlic and onions.

Two organosulfur compounds, methyl propyl disulfide (MPD) and propylene sulfide (PS) from garlic and onions, were studied for their modifying effects on hepatocarcinogenesis in the F344 rats. Modifying potential was scored by comparing the number and area per cm2 of induced glutathione S-transferase placental form (GST-P)-positive foci in the liver. MPD and PS significantly reduced both these parameters of GST-P-positive foci in a dose-dependent manner. To investigate possible mechanisms of inhibition, ornithine decarboxylase (ODC) and spermidine/spermine N1-acetyltransferase (SAT) activities were measured. In MPD and PS-high dose-treated liver tissue there was a tendency for their decrease, albeit non-significant, which suggested that the inhibitory effect might have been caused by decreased cell proliferation associated with decreased polyamine biosynthesis. In evaluating relationships between diet and cancer, it is thus necessary to consider various effects in assessing possible protective roles of garlic and onions.