Modulation of diethylnitrosamine-initiated placental glutathione S-transferase positive preneoplastic and neoplastic lesions by clofibrate, a hepatic peroxisome proliferator.

The effect of clofibrate (CF) on proliferation of diethylnitrosamine (DEN)-initiated glutathione S-transferase placental form (GST-P)-positive preneoplastic and neoplastic lesions as studied in male F344 rats. Animals were given a single i.p. injection of 200 mg/kg body weight of DEN, and then from 2 weeks later were given a diet containing 0.3% CF (group 1), or no supplement (group 2) until week 64. Group 3 received an injection of 0.9% NaCl instead of DEN and then a diet containing 0.3% CF, like group 1. Animals in all groups were subjected to partial hepatectomy at week 3 and killed at weeks 8, 20, 32, 49 or 64. The results showed that development of GST-P-positive lesions was significantly less in group 1 than in group 2 from week 8 (P less than 0.05). However, in group 1, morphologically distinguishable GST-P-negative preneoplastic lesions increased from week 20 (P less than 0.05), and the total number of GST-P-positive and -negative lesions was significantly greater than that in group 2 from week 32 (P less than 0.05). The induction of hepatocellular carcinoma (HCC) was greater in group 1 than in group 2 from week 49. All the HCCs induced in group 2 were GST-P-positive, whereas 38.9% (7/18) of those in group 1 were GST-P-negative. In group 3, only a few GST-P-positive and/or -negative preneoplastic lesions developed by week 64. These results suggest that CF has tumor-promoting activity, and that GST-P-positive cells induced by DEN changed to GST-P-negative cells on subsequent treatment with CF.