ENVIRONMENTAL HYDRAZINES AND METHYLATION OF DNA GUANINE

联氨是一种具有肝毒性和神经毒性的环境污染物

Hydrazine is an environmental contaminant which is hepato- and neurotoxic and weakly hepatocarcinogenic. Administration of toxic doses of hydrazine to rodents results in formation of 7-methylguanine and O6-methylguanine in target organ DNA. It is proposed that hydrazine and hydrazine-generating derivatives are carcinogenic because hydrazine reacts with endogenous formaldehyde to form tetraformyltrisazine and/or formalazine which in turn are metabolized to methylation agents. Environmentally important hydrazino compounds will be tested in vivo for their ability to induce methylation of DNA guanine and their ability to release hydrazine as the free base; maleic hydrazide, 3-amino-1,2,4-triazole, methylformylhydrazine, 2-hydroxyethylhydrazine, iproniazid, isocarboxazid, nialamide, phenelzine, sulfamethizole, sulfamethoxypyridazine, sulfaphenazole, furazolidone, nitrofurantoin, nitrofurazone, isoniazid, hydralazine, acetazolamide, and phenylhydrazine will be administered orally to Sprague Dawley rats. Hydrazinecarboxamide, hydrazinohistidine, formalazine, and tetraformyltrisazine will also be tested. Twenty-four hours later methylguanines will be quantitatively determined from neutral thermal and mild acid hydrolysates of liver, kidney, and lung DNA fractionated by high performance liquid chromatography (hlpc) with fluorescence spectrophotometric detection. Hydrazine will be measured by hplc as phthalhydrazine from acid extracts of tissue. Formation of azomethane, azoxymethane, methylazomethanol and methylazoxymethanol will be determined by hplc in in vitro and in vivo rodent systems as an initial step in the elucidation of biochemical pathways for the activation of hydrazine to a methylating agent. Kinetics of formation of condensation products of hydrazine and formaldehyde will be studied in in vivo and in vitro rodent systems, with particular attention given to the role of alcohol and aldehyde dehydrogenases in the metabolic activation of these products. DNA methylation by the monomethylhydrazine-formaldehyde condensation product, 1,4-dimethylhexahydro-1,2,4,5-tetrazine, will be determined. Environmental sources of formaldehyde and the hepatotoxins (dimethylnitrosamine, diethylnitrosamine, carbon tetrachloride, and phosphorus) will be studied for their ability to raise tissue formaldehyde levels and augment hydrazine-induced methylation of DNA guanine. Formaldehyde will be measured by hplc. The effect of hydrazine-induced methylation on the distribution of 5-methylcytosine in DNA and on maintenance methylation in liver of newborn and partially hepatectomized rats will be investigated; 5-methylcytosine will be determined from enzymic hydrolysates of DNA by hplc. The proposed studies will provide experimental evidence to evaluate environmental hydrazine compounds as potential DNA damaging agents and the carcinogenic hazard they may present to human health.