Apoptosis and cell proliferation are involved in the initiation of liver carcinogenesis by a subnecrogenic dose of diethylnitrosamine in refed rats.

We investigated whether changes in apoptosis and cell proliferation induced by starvation and refeeding in rat liver may contribute to the initiation mechanism of liver cancer by 20 mg/kg of diethylnitrosamine (DENA). Rats were starved for 4 d, then refed and given 20 mg/kg of DENA after 1 d of refeeding. Rat livers were examined before and after DENA treatment to measure DNA loss and synthesis, the number of the placental form of glutathione S-transferase (P-GST) positive cells and their turnover. Four days of starvation depressed cell replication, as indicated by the labeling index (LI), and induced apoptosis, as shown by the decay of total DNA radioactivity and apoptotic index (AI, TUNEL technique). After 1 d of refeeding, AI significantly decreased and LI remained low, indicating that a high percentage of S phase cells was not required for the DNA damage due to 20 mg/kg of DENA. DENA induced apoptosis and the AI after 20 mg/kg of DENA was 3% in refed rats vs. 1% in fully-fed rats 5 d after DENA (P </= 0.05). Putative-initiated P-GST-positive hepatocytes appeared after administration of 20 mg/kg in refed rats, and they showed a higher LI (6%) than the surrounding P-GST-negative cells 3 d after DENA (LI = 2%; P </= 0.01), while very few P-GST-positive cells were found in fully-fed rats. These data indicate that starvation-induced cell loss and the subsequent refeeding trigger cell proliferation that gives a selective advantage to the cells initiated by 20 mg/kg of DENA to grow in the livers of refed rats.