EVIDENCE SUPPORTING THE ROLE OF DNA PYRIDYLOXOBUTYLATION IN RAT NASALCARCINOGENESIS BY TOBACCO-SPECIFIC NITROSAMINES

The tobacco-specific nitrosamines 4-(methylnitrosamino)-1-(3-pyridyl)- 1-butanone (NNK) and N'-nitrosonornicotine (NNN) both induce nasal tum ors in rats and have a common metabolic activation pathway leading to pyridyloxobutylation of DNA. The role of DNA pyridyloxobutylation in r at nasal carcinogenesis has not been evaluated previously. In this stu dy, we used gas chromatography-mass spectrometry to compare levels of 4-hydroxy-1-(3-pyridyl)-1-butanone-releasing adducts formed by pyridyl -oxobutylation of rat nasal mucosa DNA after treatment with either NNK , NNN, or deuterated analogues of NNK. The latter were [4,4-D-2]NNK, a stronger nasal cavity carcinogen than NNK, and [CD3]NNK, which has ca rcinogenic activity equivalent to NNK. We also investigated toxicity t o the nasal mucosa and levels of O-6-methylguanine in the DNA of this tissue in rats treated with NNK and its deuterated analogues. Rats wer e given three times weekly s.c. injections of the respective nitrosami nes for 4 weeks and then sacrificed 24 h after the final injection. Th e nasal mucosa was separated into the olfactory and respiratory portio ns. In the rats treated with [4,4-D-2]NNK, levels of O-6-methylguanine in DNA from bath the olfactory and respiratory portions of the nasal mucosa were significantly lower and levels of 4-hydroxy-1-(3-pyridyl)- 1-butanone-releasing DNA adducts higher than in the rats treated with equivalent doses of the less carcinogenic compounds NNK or [CD3]NNK. 4 -Hydroxy-1-(3-pyridyl)-1-butanone-releasing adducts were also detected in the nasal mucose DNA of the rats treated with NNN. In the comparat ive study of NNK and its deuterated analogues, the histology of the na sal mucosa did not appear to be markedly different among these groups. Collectively, the results of this study provide strong evidence that DNA pyridyloxobutylation is important in rat nasal cavity carcinogenes is by NNK and NNN.