Dose-response study of DNA and hemoglobin adduct formation by 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone in F344 rats.

Levels of hemoglobin adducts and DNA adducts were measured in F344 rats after 4 consecutive daily i.p. injections of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). The dose range was from 3 to 10,000 micrograms/kg/day. [5(-3)H]NNK and [C3H3]NNK were used to measure pyridyloxobutylation and methylation, in both globin and DNA, respectively. In globin, the level of binding increased linearly with dose. Total binding of [5(-3)H] NNK to globin was 3.2 to 8900 fmol/mg and total binding of [C3H3]NNK was 3.5 to 20,000 fmol/mg. The extents of pyridyloxobutylation of both DNA and globin were determined by measuring the amounts of 4-hydroxy-1-(3-pyridyl)-1-butanone released from each, over the dose range 15-5000 micrograms/kg/day. The levels of 4-hydroxy-1-(3-pyridyl)-1-butanone released were 3.2-650 fmol/mg globin, 18-3400 fmol/mg liver DNA, and 58-2180 fmol/mg lung DNA. The extents of DNA methylation in both lung and liver were greater than pyridyloxobutylation. When the dose range was 3-5000 micrograms/kg/day, the levels of 7-methylguanine were 0.22-246 pmol/mumol guanine (149-167,000 fmol/mg) in liver DNA and 0.23-78 pmol/mumol guanine (160-53,000 fmol/mg) in lung DNA. In the lung, the ratio of methylation to pyridyloxobutylation decreased as the dose decreased. In contrast to globin adduct formation, DNA adduct formation did not increase linearly with dose; adduct formation was greater at lower doses than would have been predicted by extrapolation from higher doses. Thus the results of this study demonstrate that there was not a linear relationship between globin adduct formation, neither pyridyloxobutylation nor methylation, and DNA adduct formation in the liver or the lung of rats treated with NNK.