Comparative metabolism of N'-nitrosonornicotine and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone by cultured F344 rat oral tissue and esophagus.
The metabolism and DNA binding of N'-nitrosonornicotine (NNN) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) by cultured F344 rat oral tissue and esophagus were investigated over a range of concentrations. The metabolites present in the culture media were separated by high performance liquid chromatography and were identified by comparison to standards. alpha-Hydroxylation of NNN, an esophageal carcinogen, was the major pathway for metabolism of this nitrosamine in both tissues. The metabolites formed from 2'-hydroxylation were between 3.0 and 3.9 times those formed from 5'-hydroxylation. 2'-Hydroxylation results in a pyridyloxobutylating species. DNA from esophagus cultured with [5-3H]NNN contained a pyridyloxobutylated adduct which upon acid hydrolysis released 3.8 pmol [5-3H]-4-hydroxy-1-(3-pyridyl)-1-butanone/mumol guanine. DNA from oral tissue cultured under the same conditions, where the extent of metabolism was the same, contained no measurable [5-3H]NNN DNA adduct. This suggests that factors, as yet unknown, cause the DNA of oral cavity tissue to be protected from pyridyloxobutylation by NNN. The metabolism of NNK by alpha-hydroxylation was as much as 10-fold less than the metabolism of NNN by this pathway in both tissues. alpha-Hydroxylation of NNK results in either a methylating species or a pyridyloxobutylating species. DNA from oral tissue cultured with [C3H3]NNK contained between 1.7 and 4.3 pmol 7-methylguanine/mumol guanine, respectively. No pyridyloxobutylated DNA (less than 0.2 pmol/mumol guanine) was detected in oral tissue incubated with [5-3H]NNK. The DNA from esophagi incubated with [C3H3]NNK contained no 7-methylguanine (less than 0.4 pmol/mumol guanine). The level of pyridyloxobutylation of DNA from esophagi incubated with [5-3H]NNK was 0.17 pmol/mumol guanine. The ability of the esophagus to metabolize NNN to a greater extent than NNK to a reactive species which pyridyloxobutylates DNA may be important in determining the carcinogenicity of NNN in the esophagus. In contrast, the metabolism of NNK to a methylating species by oral cavity tissue suggests that this tobacco-specific nitrosamine is important in tobacco-related oral cavity carcinogenesis.
Murphy
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SE
American Health Foundation, Naylor Dana Institute for Disease Prevention, Valhalla, New York 10595.
Heiblum
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R
Trushin
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N
D000818:Animals; D001711:Biotransformation; D002273:Carcinogens / Q000378:metabolism*; D002478:Cells, Cultured; D004947:Esophagus / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D009055:Mouth / Q000378:metabolism*; D009602:Nitrosamines / Q000378:metabolism*; D051381:Rats; D011916:Rats, Inbred F344; D014316:Tritium
D002273:Carcinogens; D009602:Nitrosamines; D014316:Tritium; C016583:4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone; C008655:N'-nitrosonornicotine