© 1992 Oxford University Press
research-article |
Alkylation of rodent tissue DNA induced by N-nitrosobis(2-hydroxypropyl)amine
Department of Pathology, Northwestern University Medical School 303 E. Chicago Avenue, Chicago, IL 60611, USA
Levels of methyl and hydroxypropyl adducts induced by single s.c. injections of various doses of tritium-labeled N-nitrosobis(2-hydroxypropyl}amine ([1-3H]BHP) were determined in the liver, pancreas, kidney and lung of hamsters and rats. At doses of BHP used in carcinogenesis studies (100–500 mg/kg), methylation of DNA was more extensive than its hydroxypropylation; however, it did not increase proportionally with the dose and gradually became secondary to hydroxypropylation at higher doses of the carcinogen. Ratios of hydroxypropyl versus methyl adducts also varied significantly depending on the tissue and species. In both species ratios of N7-hydroxypropylguanine (N7 -HpG) versus N7 -methylguanine (N7 -MeG) were greater in kidney and pancreas than in liver or lung. Due to apparent differences in the repair of O6-methylguanine (N7-MeG) and O6-hydroxypropylguanine (O6-HpG), and the propensity of 2-hydroxypropylating as compared to methylating agents to yield a greater percentage of oxygen adducts, ratios of O6-HpG versus O6-MeG were markedly greater than those of N7-HpG versus N7-MeG. Levels of O6-HpG were greater than those of O6-MeG in rat liver, pancreas and kidney and also in hamster kidney, while such levels were similar in rat lung and also in hamster liver, pancreas and lung. Like N-nitrosobis(2-oxopropyl)amine (BOP) and N-nitroso(2-hydroxypropyl)(2-oxopropyl)amine (HPOP), BHP was activated primarily in the liver and induced substantially greater DNA damage in this than in any other tissue examined. However, unlike BOP and HPOP, which induced similar levels of hepatic DNA damage in the above two species, BHP methylated and hydroxypropylated hamster liver DNA more extensively than that of the rat. Differences between BOPand BHP were also observed regarding levels and distribution of DNA adducts in extrahepatic tissues. In rats, BHP induced greater levels of methylation and hydroxypropylation in lung than in kidney, while the reverse was observed with BOP. Apparently reduction of the ß-carbon of pancreas-specific nitrosamine carcinogens results in a shift of alkylation from kidney to the lung. Excretion of HPOP in the urine of BHP-treated animals and the observed saturation ofDNA methylation at high doses of BHP, supported the hypothesis that the BHP-induced methylation of DNA proceeded via the intermediate formation of HPOP. This was further supported by the observation that both excretion of HPOP and levels of methyl adducts were greater in hamsters than in rats. Based on levels of adducts in hepatic tissue, it was estimated that at a dose of 100 mg/kg 39 and 24% of the BHP activated in the liver of hamsters and rats respectively was firstoxidized to yield HPOP.