Human pulmonary biotransformation of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone and impact of genetic polymorphisms on cytochrome P450 1A1-related activities in human lung.

摘要

Studies described in this thesis were intended: (i) to characterize the human pulmonary biotransformation of the carcinogenic tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK); (ii) to determine the abilities of different potential human lung target cell types to bioactivate and detoxify NNK; (iii) to assess the roles of different enzymes in human pulmonary NNK biotransformation; and (iv) to determine the functional significance of genetically determined alterations (polymorphisms) on cytochrome P4501 Al (CYP1A1)-related activities in human lung.; Intact, alveolar type II (i.e. surfactant-secreting) cells, alveolar macrophages, and polymorphonuclear leukocytes (PMNs) freshly isolated from human lung, all were capable of bioactivating NNK, with marked inter-individual and inter-cellular variability observed. Chemical inhibition implicated a role for cytochromes P450 (P450 or CYP) in NNK bioactivation, particularly in type II cells, which may be progenitors of adenocarcinomas. In whole human lung microsomes, inhibition by; carbon monoxide, absence of an NADPH-generating system, specific antibodies, and selective chemical inhibitors, indicated the presence of both P450 and non-P450-mediated processes for NNK bioactivation, with CYP2A6 and/or CYP2A13 being particularly implicated. Enzymes sensitive to inhibition by 1-aminobenzotriazole were major contributors to whole lung microsomal NNK metabolism. In isolated, intact cells, contributions of specific P450 enzymes could not be ascribed to specific cell types, suggesting roles for multiple enzymes in NNK metabolism in intact lung cells.; Mean 7-ethoxyresorufin O-deethylase (i.e. EROD), which is indicative of CYP1A1 catalytic activity, was 15-fold higher in whole lung microsomes from reported current smokers than in microsomes from non/former smokers. Some atypical EROD activities could be attributed to specific disease states or chemical exposures. However, CYPIA1*1/2A, CYP1A1*1 /2B, CYP1A1*1/4, and AHR 554 Arg/Lys variants did not significantly affect EROD activities. Furthermore, no association between EROD activity and the GSTM1-null polymorphism was observed. The results suggest that the reported association of certain CYP1A1 genotypes and the GSTM1-null genotype with differential susceptibilities to lung cancer, is not occurring as a result of altered CYP1A1 activities. Furthermore, both heterozygote and homozygote CYP1B1*3 variants of cytochrome P4501B1(CYP1B1) do not appear to significantly effect EROD activities inhuman lung microsomes.