Short communication: Evaluation of the post-initiation effects of oltipraz on aflatoxin b₁-induced preneoplastic foci in a rat model of hepatic tumorigenesis

Previous studies have demonstrated that ingestion of 5-(2-pyimmyl)-4-methyl-1, 2-dithiole-3-thione (oltipraz) during the aflatoxin B¹ (AFB₁) treatment phase completely prevented hepatic cancer. In this study we evaluated the effect of feeding oltipraz during the post-AFB₁ treatment phase. Fifty-five male F344 rats were divided into five groups. All rats were gavaged with 25 μg AFB₁/rat, five times a week for two successive weeks. The rats were fed the oltipraz-supplemented diet according to three different feeding regimes: during the AFB₁ treatment phase (1 week prior to, during and 1 week after the last gavage with AFBj); during the post-treatment phase; or throughout the entire time of the experiment. Phenobarbital-supplemented diet was fed during post-treatment phase to one group and this was used as a positive control for the promotion of AFB₁-induced focal growth. The burden of putative, preneoplastk, hepatic glutathione S-transferase P-positive foci was evaluated at 13 weeks after the AFB₁ treatment phase. As seen previously, oltipraz fed during the AFB₁ treatment phase significantly inhibited focal development, i.e. the volume percent of the liver occupied with foci was reduced by 87%. Oltipraz when fed during the post-treatment phase neither inhibited nor enhanced focal development.