Methylation status of DNA cytosine during the course of induction of liver cancer in hamsters by hydrazine sulfate

'To whom correspondence should be addressed Hydrazine, which is toxic and carcinogenic to rodent liver, has been shown to react with endogenous formaldehyde in the liver to form formaldehyde hydrazone (CH2 = N-NH2), an alkylating intermediate that methylates DNA guanine at the Nl- and Oppositions. Studies were conducted to investigate the role of chronic hydrazine-induced hepato-toxicity on DNA maintenance methylation (formation of 5-methyldeoxycytosine) and the development of liver cancer. Male Syrian golden hamsters were given hydrazine sulfate (0, 170, 340 and 510 mg/1) in drinking water for 21 months (average dose 0, 4.2, 6.7 and 9.8 mg/kg body wt hydrazine as the free base). Hepatotoxicity was evaluated histologically, and regenerative DNA synthesis and main-tenance methylation were measured as the incorporation of [methyl-14C]thymidine into DNA and the methyl moiety of [methyl-3H]methionine into 5-methyldeoxycytosine in DNA, respectively. Methylguanines were detected in liver DNA at the first observation time of 6 months of treatment; levels of these aberrant bases decreased or became undetect-able at 14 months, and increased in a dose-related manner for the remainder of the study. DNA adducts persisted in the highest dose group throughout the study, repeating the results of a similar study previously reported by this laboratory (Bosan et al, Carcinogenesis, 8, 439-444, 1987). Linear regression analysis of thymidine and methionine methyl moiety incorporation into liver DNA suggested impairment of maintenance methylation of DNA (5-methyl-deoxycytosine) in the middle and high exposure animals. Hepatic adenomas and hepatocellular carcinomas developed in a dose-related manner and were highly correlated to decreased uptake of radiolabel from methion-ine into DNA 5-methylcytosine. These results are part of a continuing study on alteration of maintenance methylation during hydrazine induction of liver cancer