The chemopreventive effects of five water-soluble organosulfur compounds,
S-methylcysteine (SMC) and four analogs, were examined on the promotion stage of
diethylnitrosamine hepatocarcinogenesis in male F344 rats, using the medium-term bioassay (Ito test), which is based on the two-step model of hepatocarcinogenesis. In addition, we investigated the modifying effects of SMC and
cysteine on the initiation stage of rat hepatocarcinogenesis. Carcinogenic potential was scored by comparing the numbers and areas of a putative neoplastic lesion,
glutathione S-transferase placental form (GST-P)--positive hepatocellular foci. SMC and
cysteine significantly decreased the number and area of GST-P--positive foci when given in the promotion stage of the Ito test. When given during the initiation stage, these two organosulfur compounds also significantly inhibited focus formation. Liver
ornithine decarboxylase activity after two thirds partial
hepatectomy and the proportion of hepatocytes positive for
proliferating cell nuclear antigen significantly decreased the number of
aberrant crypt foci in the colon in a multiorgan
carcinogenesis bioassay of rats. These results support SMC and
cysteine as chemopreventive agents for hepatocarcinogenesis and colon
carcinogenesis. Their intake may be of importance for
cancer.