A tobacco smoke-derived nitrosamine, 4-(methytnitrosamino)-1-(3-pyridyl)-1-butanone, is activated by multiple human cytocbrome P450s including the polymorphic human cytochrome P4502D6

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Abstract
We have developed a human B-lymphoblastoid cell line, designated 2D6/Hol, which stably expresses human cyto chrome P450 CYP2D6 cDNA. This cell line exhibits bufuralol 11-hydroxylase activity and immunologically detectable CYP2D6 protein. The specific activity of (+)-bufuralol 1'-hydroxylase in microsomes from 2D6/Hol cells was comparable to that observed in human liver microsomes. This cell line was used to examine the mutagemcity activation of three tobacco smoke-derived nitrosamines, N-nltrosonor nicotine (NNN), 1-(N-methyl-N-nitrosamino)-1-(3-pyr-idinyl)-4-butanal) (NNA) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), by CYP2D6. Exposure of 2D6/Hol cells to NNK concentrations of 30–90 μg/ml induced a concentration-dependent decrease in relative survival and increase in mutant fraction at the hypoxanthine guanine phosphoribosyl transferase (hprt) locus. In contrast, NNK was non-mutagenic and non-cytotoxic to control cells at exposure concentrations up to 150 μg/ml. NNK mutagenicity in 2D6/Hol cells was compared to the responses observed in isogenic cell lines expressing human CYP1A2 (1A2/Hol), human CYP2A3 (2A3/Hol) and human CYP2E1 (2E1/Hol). These three additional human cytochrome P450-expressing cell lines were also found to be sensitive to NNK-lnduced mutagenicity and cytotoxicity. We found no evidence for CYP2D6-medlated activation of NNN or NNA. NNN was non-cytotoxic and non-mutagenic to both control and 2D6/Hol cells. NNA was equally cytotoxic and mutagenic to control cells and 2D6/Hol cells. The activation of NNA to a mutagen may have been carried out by P450 native to the AHH-1 TK+/− cell line. The 2D6/Hol cell line, In conjunction with the control cell line and other isogenic cell lines expressing other human cytochrome P450 cDNAs provides a useful system for the examination of the role of the polymorphic CYP2D6 in human procarcinogen activation and drug metabolism.