Nicotine metabolism predicted by CYP2A6 genotypes in relation to smoking cessation: A systematic review

Inhibition of soluble epoxide hydrolase by natural isothiocyanates

GOAL

The long-term goal of our research is to develop safe and effective soluble epoxide hydrolase (sEH) inhibitors. The objective of this study is to evaluate the potency and selectivity of six natural isothiocyanates (ITCs) as sEH inhibitors.

METHODS

Molecular docking was used to model likely interactions between the ligands and receptors. The sEH inhibitory activity was tested using a validated fluorescence-based assay and PHOME as a substrate. To evaluate their selectivity as sEH inhibitors, the inhibitory potential of the ITCs was determined on microsomal epoxide hydrolase (mEH) and cytochrome P450 (CYP) enzymes in human liver microsomes. Probe substrates such as styrene oxide (mEH substrate) and established substrates for CYP2A6, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and CYP3A4 were used in this study. The metabolites of these substrates were analyzed using validated LC-MS/MS and HPLC-UV assays.

RESULTS

Molecular Docking revealed significant differences in binding site preference among the ITCs in silico and pointed to important interactions between the ligands and the catalytic residues of the sEH enzyme. In vitro, the ITCs showed varying degrees of sEH inhibition, but sulforaphane (SFN) and phenyl isothiocyanate (PITC) were the most potent inhibitors with IC50 values of 3.65 and 7.5 μM, respectively. mEH was not significantly inhibited by any of the ITCs. Erucin and iberin were the only ITCs that did not inhibit the activity of any of the tested CYP enzymes.

CONCLUSION

Our results demonstrate that natural ITCs have the potential to offer safe, selective, and potent sEH inhibition.

The Association Between Smoking Behavior and the Risk of Hypertension: Review of the Observational and Genetic Evidence

Background

Cigarette smoking is one of the world's largest avoidable risk factors for morbidity and mortality. Numerous studies have investigated the association between smoking and hypertension (HTN). Although observational data and cross-sectional research often exhibit a link between smoking and HTN, establishing causation remains challenging owing to potential confounding variables. Mendelian randomization (MR), a genetic epidemiological technique that employs genetic variants as instrumental variables, offers a more robust approach for evaluating causal links. This review aimed to explore both the observational and causal relationships between smoking and the risk of HTN.

Methodology

A comprehensive literature search across major electronic databases was conducted to identify relevant observational and Mendelian randomization (MR) studies on smoking and HTN risk. Various characteristics were included during study selection, such as study design, exposure assessment, and age range. Standardized processes were used for data retrieval and quality evaluation.

Results

Analysis of observational data revealed a paradoxical association between smoking and the risk of HTN, where a lower risk was observed among current smokers when compared to non-smokers. However, observational analysis also presented a dose-response effect with greater smoking intensity showed a modest linear increase in HTN risk, and older smoking initiation was associated with a slight increase in HTN risk (compared with younger). In contrast, MR-based causal estimates provide inconsistent evidence regarding the causal relationship between smoking behavior and HTN. Some MR analyses indicated a potential causal link between smoking and HTN; but this was not consistent.

Conclusion

Observational studies suggest a paradoxical association between smoking and HTN. However, MR studies do not provide sufficient evidence to establish a causal relationship. Regardless, lifestyle variables remain crucial for overall health. Healthcare professionals should regularly assess smoking status and provide counseling for quitting. Further research is needed to clarify the underlying processes, identify mediators, and evaluate the interventions.

Inhibitory Effect of Two Carbonic Anhydrases Inhibitors on the Activity of Major Cytochrome P450 Enzymes

BACKGROUND AND OBJECTIVES

Both AW-9A (coumarin derivative) and WES-1 (sulfonamide derivative) were designed and synthesized as potential selective carbonic anhydrase inhibitors and were tested for anticancer activity. This study was undertaken to investigate their potential inhibitory effects on the major human cytochrome P450 (CYP) drug-metabolizing enzymes.

METHODS

Specific CYP probe substrates and validated analytical methods were used to measure the activity of the tested CYP enzymes. Furthermore, in silico simulations were conducted to understand how AW-9A and WES-1 bind to CYP2A6 at a molecular level. Molecular docking experiments were performed using the high-resolution X-ray structure, Protein Data Bank (PDB) ID: 2FDV for CYP2A6.

RESULTS

CYP2E1-catalyzed chlorzoxazone-6'-hydroxylation was strongly inhibited by AW-9A and WES-1 with IC50 values of 0.084 µM and 0.101 µM, respectively. CYP2A6-catalyzed coumarin-7'-hydroxylation was moderately inhibited by AW-9A (IC50 = 4.2 µM). CYP1A2, CYP2C9, CYP2C19, CYP2D6, and CYP3A4 enzymes were weakly or negligibly inhibited by both agents. Docking studies suggest elevated potential to block the catalytic activity of CYP2A6.

CONCLUSIONS

These findings point to the feasibility of utilizing these agents as promising chemopreventive agents (owing to inhibition of CYP2E1), and AW-9A as a smoking cessation aid (owing to inhibition of CYP2A6). Additional in-vivo studies should be conducted to examine the impact of CYP2A6 and CYP2E1 inhibition on drug interactions with probe substrates of these enzymes.

Evidence for sex differences in the impact of cytochrome P450 genotypes on early subjective effects of cannabis

Early positive subjective effects of cannabis predict the development of cannabis use disorder (CUD). Genetic factors, such as the presence of cytochrome P450 genetic variants that are associated with reduced Δ9-tetrahydrocannabinol (THC) metabolism, may contribute to individual differences in subjective effects of cannabis. Young adults (N = 54) with CUD or a non-CUD substance use disorder (control) provided a blood sample for DNA analysis and self-reported their early (i.e., effects upon initial uses) and past-year positive and negative subjective cannabis effects. Participants were classified as slow metabolizers if they had at least one CYP2C9 or CYP3A4 allele associated with reduced activity. Though the CUD group and control group did not differ in terms of metabolizer status, slow metabolizer status was more prevalent among females in the CUD group than females in the control group. Slow metabolizers reported greater past year negative THC effects compared to normal metabolizers; however, slow metabolizer status did not predict early subjective cannabis effects (positive or negative) or past year positive effects. Post-hoc analyses suggested males who were slow metabolizers reported more negative early subjective effects of cannabis than female slow metabolizers. Other sex-by-genotype interactions were not significant. These initial findings suggest that genetic variation in CYP2C9 and CYP3A4 may have sex-specific associations with cannabis-related outcomes. Slow metabolizer genes may serve as a risk factor for CUD for females independent of subjective effects. Male slow metabolizers may instead be particularly susceptible to the negative subjective effects of cannabis.

Relationships Between the Nicotine Metabolite Ratio and Laboratory Assessments of Smoking Reinforcement and Craving Among Adults in a Smoking Cessation Trial

INTRODUCTION

People who metabolize nicotine more quickly are generally less successful at quitting smoking. However, the mechanisms that link individual differences in the nicotine metabolite ratio (NMR), a phenotypic biomarker of the rate of nicotine clearance, to smoking outcomes are unclear. We tested the hypotheses that higher NMR is associated with greater smoking reinforcement, general craving, and cue-induced cigarette craving in a treatment-seeking sample.

METHODS

Participants were 252 adults who smoke cigarettes enrolled in a randomized controlled smoking cessation trial (NCT03262662) conducted in Buffalo, New York, USA. Participants completed the Choice Behavior Under Cued Conditions (CBUCC) paradigm, a laboratory choice procedure, ~1 week before the first cessation treatment visit, at which time a saliva sample was collected for NMR assessment. On each CBUCC trial, participants reported cigarette craving during cue presentation (cigarette, water) and spent $0.01-$0.25 for a chance (5%-95%) to sample the cue (one puff, sip), providing measures of smoking reinforcement (spending for cigarettes vs. water), general cigarette craving (averaged across cigarette and water cues), and cue-specific craving (cigarette craving during cigarette vs. water cues).

RESULTS

As observed in prior work, the NMR was significantly higher among White and female participants. As expected, both spending and cigarette craving were significantly greater on cigarette compared to water trials. However, contrary to our hypotheses, higher NMR was not associated with greater smoking reinforcement, general craving, or cue-specific craving.

CONCLUSIONS

The present data do not support that smoking reinforcement or craving is related to nicotine metabolism among individuals seeking to quit smoking.

IMPLICATIONS

Though greater smoking reinforcement, general craving, and cue-specific craving are hypothesized to be linked to faster nicotine metabolism, there was no evidence of such relationships in the present sample of adults seeking to quit smoking. Further research, including replication and consideration of alternate hypotheses, is warranted to elucidate the mechanisms by which the NMR is related to smoking cessation.

The Role of Nicotine Metabolic Rate on Nicotine Dependence and Rewarding: Nicotine Metabolism in Chinese Male Smokers and Male Mice

The exact relationship between nicotine metabolism and dependence is not fully understood but is known to be influenced at a molecular level by genetic factors. A sample comprising 274 Chinese adult male smokers was categorized into groups based on their metabolic rates, namely fast, intermediate, and slow metabolizers. We then measured their smoking topography, evaluated their nicotine dependence, and assessed the rewarding effects. Based on these findings, we proposed the hypothesis that the rate of nicotine metabolism could influence the level of dopamine release which in turn had repercussions on the pleasurable and rewarding effects. To test this hypothesis, male mice were selected with different nicotine metabolic rates that closely resembled in the smoker group. We evaluated their nicotine dependence and rewarding effects through conditioned place preference and withdrawal symptom tests, supplemented with dopamine release measurements. In both animal and human, the slow metabolism group (SMG) required less nicotine to maintain a comparable level of dependence than the fast metabolism group (FMG). The SMG could achieve similar rewarding effects to FMG despite consuming less nicotine. Comparable dopamine levels released were therefore critical in setting the nicotine acquisition behavior in this animal model and also for the smokers tested. Our findings suggested that even within the same ethnicity of established smokers (Chinese Han), differences in nicotine metabolism were an important parameter to modulate the degree of nicotine dependence.

Early developmental risks for tobacco addiction: A probabilistic epigenesis framework

Considerable progress has been made in elucidating the relationships between early life psychobiological and environmental risk factors and the development of tobacco addiction. However, a comprehensive understanding of the heterogeneity in tobacco addiction phenotypes requires integrating research findings. The probabilistic epigenesis meta-theory offers a valuable framework for this integration, considering systemic, multilevel, developmental, and evolutionary perspectives. In this paper, we critically review relevant research on early developmental risks associated with tobacco addiction and highlight the integrative heuristic value of the probabilistic epigenesis framework for this research. For this, we propose a four-level systems approach as an initial step towards integration, analyzing complex interactions among different levels of influence. Additionally, we explore a coaction approach to examine key interactions between early risk factors. Moreover, we introduce developmental pathways to understand interindividual differences in tobacco addiction risk during development. This integrative approach holds promise for advancing our understanding of tobacco addiction etiology and informing potentially effective intervention strategies.

Effect of changes in metabolic enzymes and transporters on drug metabolism in the context of liver disease: Impact on pharmacokinetics and drug-drug interactions

Changes in the pharmacokinetic and resulting pharmacodynamic properties of drugs are common in many chronic liver diseases, leading to adverse effects, drug interactions and increased risk of over- or underdosing of medications. Structural and functional hepatic impairment can have major effects on drug metabolism and transport. This review summarizes research on the functional changes in phase I and II metabolic enzymes and in transport proteins in patients with metabolic diseases such as type 2 diabetes, metabolic dysfunction-associated steatotic liver disease, metabolic dysfunction-associated steatohepatitis and cirrhosis, providing a clinical perspective on how these changes affect drug uptake and metabolism. Generally, a decrease in expression and/or activity of many enzymes of the cytochrome P450 family (e.g. CYP2E1 and CYP3A4), and of influx and efflux transporters (e.g. organic anion-transporting polypeptide [OATP]1B1, OATP2B1, OAT2 and bile salt export pump), has been recently documented in patients with liver disease. Decreased enzyme levels often correlate with increased severity of chronic liver disease. In subjects with hepatic impairment, there is potential for strong alterations of drug pharmacokinetics due to reduced absorption, increased volume of distribution, metabolism and extraction. Due to the altered pharmacokinetics, specific drug-drug interactions are also a potential issue to consider in patients with liver disease. Given the huge burden of liver disease in western societies, there is a need to improve awareness among all healthcare professionals and patients with liver disease to ensure appropriate drug prescriptions.

Mendelian randomization analyses of smoking and Alzheimer's disease in Chinese and Japanese populations

Background

Previous epidemiological studies have reported controversial results on the relationship between smoking and Alzheimer's disease (AD). Therefore, we sought to assess the association using Mendelian randomization (MR) analysis.

Methods

We used single nucleotide polymorphisms (SNPs) associated with smoking quantity (cigarettes per day, CPD) from genome-wide association studies (GWAS) of Japanese population as instrumental variables, then we performed two-sample MR analysis to investigate the association between smoking and AD in a Chinese cohort (1,000 AD cases and 500 controls) and a Japanese cohort (3,962 AD cases and 4,074 controls), respectively.

Results

Genetically higher smoking quantity showed no statistical causal association with AD risk (the inverse variance weighted (IVW) estimate in the Chinese cohort: odds ratio (OR) = 0.510, 95% confidence interval (CI) = 0.149-1.744, p = 0.284; IVW estimate in the Japanese cohort: OR = 1.170, 95% confidence interval CI = 0.790-1.734, p = 0.434).

Conclusion

This MR study, for the first time in Chinese and Japanese populations, found no significant association between smoking and AD.

A systematic review of genetic variation within nicotinic acetylcholine receptor genes and cigarette smoking cessation

BACKGROUND

Nicotine produces its effects by binding to nicotinic acetylcholine receptors (nAChRs). Variants of genes encoding properties of nAChRs are candidates for affecting likelihood of smoking cessation.

METHODS

A systematic review was conducted summarizing evidence of associations between single nucleotide polymorphisms (SNPs) of nAChR genes and smoking cessation. From 24 articles meeting inclusion criteria, summary odds ratios (ORs) for associations between nine SNPs and smoking cessation were calculated from 26 studies (N = 233-29,072) stratified by gene, ancestry, study design, and pharmacotherapy; SNPs in linkage disequilibrium were pooled. Results for a tenth SNP from two GWAS were summarized.

RESULTS

People of European ancestry with minor alleles of CHRNA5 rs16969968 and CHRNA3 rs1051730 had longer time to cessation [HR = 0.90, 95 % CI 0.88 - 0.92 (n = 2 studies)] and lower odds of cessation [OR = 0.88, 95 % CI 0.80 - 0.97 (n = 5 cohort studies), OR = 0.64, 95 % CI 0.45 - 0.90 (n = 4 placebo arms)]. Risk of persistent smoking associated with these alleles was attenuated in smokers receiving nicotine replacement therapy (NRT). Recipients of bupropion alone or with NRT with these alleles had higher, though not statistically significant, odds of cessation. Results for CHRNA5 rs588765 and rs680244 were similar to rs16969968/rs1051730 findings. Evidence was limited for other SNPs.

CONCLUSION

Evidence consistently indicates the minor alleles of four SNPs within CHRNA3 or CHRNA5 are risk alleles for cessation failure. Analysis by pharmacotherapy revealed bupropion may be the most efficacious intervention for people with these alleles.