Structural Impact Assessment of Cytochrome P450 2A13 Polymorphisms Using Molecular Dynamics Simulations.

One of the members of CYP, a monooxygenase, CYP2A13 is involved in the metabolism of nicotine, coumarin, and tobacco-specific nitrosamine. Genetic polymorphisms have been identified in CYP2A13, with reported loss or reduction in enzymatic activity in CYP2A13 allelic variants. This study aimed to unravel the mechanism underlying the diminished enzymatic activity of CYP2A13 variants by investigating their three-dimensional structures through molecular dynamics (MD) simulations. For each variant, MD simulations of 1000 ns were performed, and the obtained results were compared with those of the wild type. The findings indicated alterations in the interaction with heme in CYP2A13.4, .6, .8, and .9. In the case of CYP2A13.5, observable effects on the helix structure related to the interaction with the redox partner were identified. These conformational changes were sufficient to cause a decrease in enzyme activity in the variants. Our findings provide valuable insights into the molecular mechanisms associated with the diminished activity in the CYP2A13 polymorphisms.

The Use of the Nicotine Metabolite Ratio as a Biomarker to Personalize Smoking Cessation Treatment: Current Evidence and Future Directions.

The nicotine metabolite ratio (NMR), a genetically informed biomarker of rate of nicotine metabolism, has been validated as a tool to select the optimal treatment for individual smokers, thereby improving treatment outcomes. This review summarizes the evidence supporting the development of the NMR as a biomarker of individual differences in nicotine metabolism, the relationship between the NMR and smoking behavior, the clinical utility of using the NMR to personalize treatments for smoking cessation, and the potential mechanisms that underlie the relationship between NMR and smoking cessation. We conclude with a call for additional research necessary to determine the ultimate benefits of using the NMR to personalize treatments for smoking cessation. These future directions include measurement and other methodologic considerations, disseminating this approach to at-risk subpopulations, expanding the NMR to evaluate its efficacy in predicting treatment responses to e-cigarettes and other noncigarette forms of nicotine, and implementation science including cost-effectiveness analyses.See all articles in this Special Collection Honoring Paul F. Engstrom, MD, Champion of Cancer Prevention.

Functional Characterization of 34 CYP2A6 Allelic Variants by Assessment of Nicotine C-Oxidation and Coumarin 7-Hydroxylation Activities.

CYP2A6, a member of the cytochrome P450 (P450) family, is one of the enzymes responsible for the metabolism of therapeutic drugs and such tobacco components as nicotine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, and N-nitrosodiethylamine. Genetic polymorphisms in CYP2A6 are associated with individual variation in smoking behavior, drug toxicities, and the risk of developing several cancers. In this study, we conducted an in vitro analysis of 34 allelic variants of CYP2A6 using nicotine and coumarin as representative CYP2A6 substrates. These variant CYP2A6 proteins were heterologously expressed in 293FT cells, and their enzymatic activities were assessed on the basis of nicotine C-oxidation and coumarin 7-hydroxylation activities. Among the 34 CYP2A6 variants, CYP2A6.2, CYP2A6.5, CYP2A6.6, CYP2A6.10, CYP2A6.26, CYP2A6.36, and CYP2A6.37 exhibited no enzymatic activity, whereas 14 other variants exhibited markedly reduced activity toward both nicotine and coumarin. These comprehensive in vitro findings may provide useful insight into individual differences in smoking behavior, drug efficacy, and cancer susceptibility.

Does ethnic ancestry play a role in smoking?

The higher proportion of smokers among Black people in Brazil has been attributed to socioeconomic disparities, but genetic factors could also contribute for this finding. This study aimed at investigating associations between smoking status with genetically defined ethnic ancestry and socioeconomic features in Brazilians. Blood samples were collected from 448 volunteers (66.7% male; age: 37.1 ± 11.4 years) classified as current smokers (CS: 60.9%), former smokers (FS: 8.9%) and never smokers (NS: 30.1%). Individual interethnic admixtures were determined using a 48 insertion-deletion polymorphisms ancestry-informative-marker panel. CS showed a lower amount of European ancestry than NS (0.837 ± 0.243 X 0.883 ± 0.194, p ≤ 0.05) and FS (0.837 ± 0.243 X 0.864 ± 0.230, p ≤ 0.05), and a higher proportion of African Sub-Saharan ancestry than FS (0.128 ± 0.222 X 0.07 ± 0.174, p ≤ 0.05) and NS (0.128 ± 0.222 X 0.085 ± 0.178, p ≤ 0.05). NS reported a higher number of years in school than CS (11.2 ± 3.7 X 8.9 ± 3.8, p ≤ 0.001). CS were less common in economic Class A (30%) and more common in Class B (56.8%). In multivariate analysis, only lower number of school years and lower economic class were associated with higher chances for CS. The use of genetic molecular markers for characterizing ethnic background confirmed that socioeconomic disparities are the main determinants of higher smoking rates among Blacks in Brazil.