CYP2E1*1D regulatory polymorphism: association with alcohol and nicotine dependence

A prospective study of the association between rate of nicotine metabolism and alcohol use in tobacco users in the United States

BACKGROUND

Rate of nicotine metabolism has been identified as a biochemical risk factor for nicotine use and dependence; however, its role in alcohol consumption and related outcomes is not well understood. The current research examined nicotine metabolism rate as a risk factor for alcohol use among current tobacco users. We also examined sex differences in these associations.

METHOD

Data were taken from Waves 1 and 2 of the Population Assessment of Tobacco and Health (PATH) study, a national longitudinal study of tobacco use and associated health outcomes. The nicotine metabolite ratio (NMR) was calculated as the ratio of trans-3' hydroxycotinine to cotinine in urine samples provided at wave 1. Alcohol use outcomes included past 30-day NIAAA-defined hazardous drinking status, total drinks, and alcohol-related consequences. All analyses controlled for alcohol use at Wave 1.

RESULTS

NMR at Wave 1 predicted increased odds of meeting hazardous drinking criteria, adjusted odds ratio (aOR) = 1.14, 95 % CI = 1.06; 1.23, p = 0.001, greater total alcohol consumption amount, adjusted rate ratio (aRR) = 1.21, 95 % CI = 1.12; 1.30, p <  0.001, and more alcohol consequences, aRR = 1.07, 95 % CI = 1.01; 1.13, p =  0.018, at wave 2. No significant sex differences were identified. NMR remained a significant predictor of alcohol use in models controlling for severity of nicotine exposure in cigarette smokers.

CONCLUSIONS

NMR may be a shared risk factor for harmful nicotine and alcohol use that contributes to their co-occurrence.

Reveals of New Candidate Active Components in Hemerocallis Radix and Its Anti-Depression Action of Mechanism Based on Network Pharmacology Approach

The global depression population is showing a significant increase. Hemerocallis fulva L. is a common Traditional Chinese Medicine (TCM). Its flower buds are known to have ability to clear away heat and dampness, detoxify, and relieve depression. Ancient TCM literature shows that its roots have a beneficial effect in calming the spirit and even the temper in order to reduce the feeling of melancholy. Therefore, it is inferred that the root of Hemerocallis fulva L. can be used as a therapeutic medicine for depression. This study aims to uncover the pharmacological mechanism of the antidepressant effect of Hemerocallis Radix (HR) through network pharmacology method. During the analysis, 11 active components were obtained and screened using ADME—absorption, distribution, metabolism, and excretion— method. Furthermore, 267 HR targets and 740 depressive disorder (DD) targets were gathered from various databases. Then protein–protein interaction (PPI) network of HR and DD targets were constructed and cluster analysis was applied to further explore the connection between the targets. In addition, gene ontology (GO) enrichment and pathway analysis was applied to further verify that the biological process related to the target protein is associated with the occurrence of depression disorder. In conclusion, the most important bioactive components—anthraquinone, kaempferol, and vanillic acid—can alleviate depression symptoms by regulating MAOA, MAOB, and ESR1. The proposed network pharmacology strategy provides an integrating method to explore the therapeutic mechanism of multi-component drugs on a systematic level.

No association of CYP2E1 genetic polymorphisms with alcohol dependence in Han Taiwanese population

Cytochrome P450 2E1 (CYP2E1) gene is one of the candidate genes for alcohol dependence (AD). Four single nucleotide polymorphisms (SNPs) of CYP2E1 gene (CYP2E1*1D, *5B, *6 and *1B) have been associated with AD previously in other ethnic populations. To date, only CYP2E1*5B and *6 SNPs have been investigated in relation to AD in our population. The objective of the study was to examine the genetic associations of CYP2E1 covering the four above-noted SNPs conjointly with AD in Han Taiwanese population based on single SNP analysis and haplotype-based approach. We enrolled a total of 340 patients fulfilling DSM-IV-TR diagnostic criteria of AD and 319 healthy controls and genotyped them for the above four SNPs of CYP2E1 gene. By comparing the differences of genotype, allele, and pertinent haplotype frequencies, we did not support a genetic association between CYP2E1 and AD in Han Taiwanese either by single allele tests or haplotype-based analyses.

P450 Pharmacogenetics in Indigenous North American Populations

Indigenous North American populations, including American Indian and Alaska Native peoples in the United States, the First Nations, Métis and Inuit peoples in Canada and Amerindians in Mexico, are historically under-represented in biomedical research, including genomic research on drug disposition and response. Without adequate representation in pharmacogenetic studies establishing genotype-phenotype relationships, Indigenous populations may not benefit fully from new innovations in precision medicine testing to tailor and improve the safety and efficacy of drug treatment, resulting in health care disparities. The purpose of this review is to summarize and evaluate what is currently known about cytochrome P450 genetic variation in Indigenous populations in North America and to highlight the importance of including these groups in future pharmacogenetic studies for implementation of personalized drug therapy.

The Role of CYP2E1 in the Drug Metabolism or Bioactivation in the Brain

Organisms have metabolic pathways that are responsible for removing toxic agents. We always associate the liver as the major organ responsible for detoxification of the body; however this process occurs in many tissues. In the same way, as in the liver, the brain expresses metabolic pathways associated with the elimination of xenobiotics. Besides the detoxifying role of CYP2E1 for compounds such as electrophilic agents, reactive oxygen species, free radical products, and the bioactivation of xenobiotics, CYP2E1 is also related in several diseases and pathophysiological conditions. In this review, we describe the presence of phase I monooxygenase CYP2E1 in regions of the brain. We also explore the conditions where protein, mRNA, and the activity of CYP2E1 are induced. Finally, we describe the relation of CYP2E1 in brain disorders, including the behavioral relations for alcohol consumption via CYP2E1 metabolism.

An Update on Fetal Alcohol Syndrome-Pathogenesis, Risks, and Treatment

Alcohol is a well-established teratogen that can cause variable physical and behavioral effects on the fetus. The most severe condition in this spectrum of diseases is known as fetal alcohol syndrome (FAS). The differences in maternal and fetal enzymes, in terms of abundance and efficiency, in addition to reduced elimination, allow for alcohol to have a prolonged effect on the fetus. This can act as a teratogen through numerous methods including reactive oxygen species (generated as by products of CYP2E1), decreased endogenous antioxidant levels, mitochondrial damage, lipid peroxidation, disrupted neuronal cell-cell adhesion, placental vasoconstriction, and inhibition of cofactors required for fetal growth and development. More recently, alcohol has also been shown to have epigenetic effects. Increased fetal exposure to alcohol and sustained alcohol intake during any trimester of pregnancy is associated with an increased risk of FAS. Other risk factors include genetic influences, maternal characteristics, for example, lower socioeconomic statuses and smoking, and paternal chronic alcohol use. The treatment options for FAS have recently started to be explored although none are currently approved clinically. These include prenatal antioxidant administration food supplements, folic acid, choline, neuroactive peptides, and neurotrophic growth factors. Tackling the wider impacts of FAS, such as comorbidities, and the family system have been shown to improve the quality of life of FAS patients. This review aimed to focus on the pathogenesis, especially mechanisms of alcohol teratogenicity, and risks of developing FAS. Recent developments in potential management strategies, including prenatal interventions, are discussed.

[Genetic polymorphism of cytochrome P450 2E1 and the risk of nasopharyngeal carcinoma]

Cytochrome P450 2E1 (CYP2E1) is a detoxifying enzyme that belongs to the phase I metabolism of xenobiotics. This enzyme is encoded by a highly polymorphic gene whose common polymorphism corresponds to the substitution of cytosine (C) and thymine (T) at position -1019 (rs2031920). This polymorphism has been identified in several cancers including nasopharyngeal cancer (NPC). The study involved 124 patients with nasopharyngeal carcinoma, compared with 166 healthy controls. The presence or absence of the polymorphism is determined by PCR-RFLP. The frequency comparison between the two groups is determined by the χ(2) test. The analysis of our results showed a significant difference between the two groups regarding the mutant genotype (C2/C2) (5% vs. 0.5%, P=0.04) and has a risk factor for NPC in Tunisia (OR=8.39; CI 95% [0.99-388.1]). Also, the C2 allele was significantly associated with the group of patients than the control group (6% vs. 2%, P=0.016) and increased three times the risk of NPC in Tunisia (OR=2.99, CI 95% [1.12-8.79]). Our results confirm the results reported in other populations and emphasize the importance of the involvement of this gene in the development of detoxification of the NPC, which seems more and more strongly associated with environmental factors.

Improved drug therapy: triangulating phenomics with genomics and metabolomics

Embracing the complexity of biological systems has a greater likelihood to improve prediction of clinical drug response. Here we discuss limitations of a singular focus on genomics, epigenomics, proteomics, transcriptomics, metabolomics, or phenomics-highlighting the strengths and weaknesses of each individual technique. In contrast, 'systems biology' is proposed to allow clinicians and scientists to extract benefits from each technique, while limiting associated weaknesses by supplementing with other techniques when appropriate. Perfect predictive modeling is not possible, whereas modeling of intertwined phenomic responses using genomic stratification with metabolomic modifications may greatly improve predictive values for drug therapy. We thus propose a novel-integrated approach to personalized medicine that begins with phenomic data, is stratified by genomics, and ultimately refined by metabolomic pathway data. Whereas perfect prediction of efficacy and safety of drug therapy is not possible, improvements can be achieved by embracing the complexity of the biological system. Starting with phenomics, the combination of linking metabolomics to identify common biologic pathways and then stratifying by genomic architecture, might increase predictive values. This systems biology approach has the potential, in specific subsets of patients, to avoid drug therapy that will be either ineffective or unsafe.

Participation of central imidazoline binding sites in antinociceptive effect of ethanol and nicotine in rats

Despite synergistic morbidity and mortality, concomitant consumption of alcohol and tobacco is increasing, and their antinociceptive effect has been linked with co-abuse. Present study was designed to investigate the role of imidazoline binding sites in the antinociceptive effect of nicotine, ethanol, and their combination. Separate group of male Sprague-Dawley rats (200-250 g) were treated with different doses of alcohol (0.50-2 g/kg, i.p.) or nicotine (0.25-1 mg/kg, i.p.), and their combination evaluated in tail flick test. Influence of endogenous imidazoline binding site ligands, agonist, and antagonists were determined by their prior treatment with effective or subeffective doses of either ethanol or nicotine. Ethanol, nicotine, or their subeffective dose combination exhibited significant antinociceptive effects in dose-dependent manner. Antinociceptive effect of ethanol and nicotine was significantly augmented by intracerebroventricular (i.c.v.) administration of endogenous imidazoline receptor ligands, harmane (25 μg/rat, i.c.v.) and agmatine (10 μg/rat, i.c.v.), as well as imidazoline I1 /α2 adrenergic receptor agonist, clonidine (2 μg/rat, i.c.v.), I1 agonist moxonidine (25 μg/rat, i.c.v.), and imidazoline I2 agonist, 2-BFI (10 μg/rat, i.c.v.). Conversely, antinociception elicited by ethanol or nicotine or their subeffective dose combination was antagonized by pretreatment with imidazoline I1 antagonist, efaroxan (10 μg/rat, i.c.v.), and I2 antagonist, idazoxan (4 μg/rat, i.c.v.), at their per se ineffective doses. These findings project imidazoline binding ligands as important therapeutic molecules for central antinociceptive activity as well as may reduce the co-abuse potential of alcohol and nicotine.

Cytochrome P450 2E1: its clinical aspects and a brief perspective on the current research scenario

Research on Cytochrome P450 2E1 (CYP2E1), a key enzyme in alcohol metabolism has been very well documented in literature. Besides the involvement of CYP2E1 in alcohol metabolism as illustrated through the studies discussed in the chapter, recent studies have thrown light on several other aspects of CYP2E1 i.e. its extrahepatic expression, its involvement in several diseases and pathophysiological conditions; and CYP2E1 mediated carcinogenesis and modulation of drug efficacy. Studies involving these interesting facets of CYP2E1 have been discussed in the chapter focusing on the recent observations or ongoing studies illustrating the crucial role of CYP2E1 in disease development and drug metabolism.

The role of CYP2E1 in alcohol metabolism and sensitivity in the central nervous system

Ethanol consumption has effects on the central nervous system (CNS), manifesting as motor incoordination, sleep induction (hypnosis), anxiety, amnesia, and the reinforcement or aversion of alcohol consumption. Acetaldehyde (the direct metabolite of ethanol oxidation) contributes to many aspects of the behavioral effects of ethanol. Given acetaldehyde cannot pass through the blood brain barrier, its concentration in the CNS is primarily determined by local production from ethanol. Catalase and cytochrome P450 2E1 (CYP2E1) represent the major enzymes in the CNS that catalyze ethanol oxidation. CYP2E1 is expressed abundantly within the microsomes of certain brain cells and is localized to particular brain regions. This chapter focuses on the discussion of CYP2E1 in ethanol metabolism in the CNS, covering topics including how it is regulated, where it is expressed and how it influences sensitivity to ethanol in the brain.

Multi-ethnic cytochrome-P450 copy number profiling: novel pharmacogenetic alleles and mechanism of copy number variation formation

To determine the role of CYP450 copy number variation (CNV) beyond CYP2D6, 11 CYP450 genes were interrogated by MLPA and qPCR in 542 African-American, Asian, Caucasian, Hispanic, and Ashkenazi Jewish individuals. The CYP2A6, CYP2B6 and CYP2E1 combined deletion/duplication allele frequencies ranged from 2% to 10% in these populations. High-resolution microarray-based comparative genomic hybridization (aCGH) localized CYP2A6, CYP2B6 and CYP2E1 breakpoints to directly-oriented low-copy repeats. Sequencing localized the CYP2B6 breakpoint to a 529 bp intron 4 region with high homology to CYP2B7P1, resulting in the CYP2B6*29 partial deletion allele and the reciprocal, and novel, CYP2B6/2B7P1 duplicated fusion allele (CYP2B6*30). Together, these data identified novel CYP450 CNV alleles (CYP2B6*30 and CYP2E1*1Cx2) and indicate that common CYP450 CNV formation is likely mediated by non-allelic homologous recombination resulting in both full gene and gene-fusion copy number imbalances. Detection of these CNVs should be considered when interrogating these genes for pharmacogenetic drug selection and dosing.

Zebrafish: a model for the study of addiction genetics

Drug abuse and dependence are multifaceted disorders with complex genetic underpinnings. Identifying specific genetic correlates is challenging and may be more readily accomplished by defining endophenotypes specific for addictive disorders. Symptoms and syndromes, including acute drug response, consumption, preference, and withdrawal, are potential endophenotypes characterizing addiction that have been investigated using model organisms. We present a review of major genes involved in serotonergic, dopaminergic, GABAergic, and adrenoreceptor signaling that are considered to be directly involved in nicotine, opioid, cannabinoid, and ethanol use and dependence. The zebrafish genome encodes likely homologs of the vast majority of these loci. We also review the known expression patterns of these genes in zebrafish. The information presented in this review provides support for the use of zebrafish as a viable model for studying genetic factors related to drug addiction. Expansion of investigations into drug response using model organisms holds the potential to advance our understanding of drug response and addiction in humans.

Gender-specific interactions between alcohol metabolism genes and severity of quantitative alcohol-related-traits in a Tibetan population

Association between genes influencing alcohol metabolism and alcohol use disorders (AUD) has been extensively studied, but the effect of interactions between these genes and AUD have rarely been tested. Our previous case-control study in a Tibetan population noted that the positive association between c2 allele of cytochrome P4502E1 (CYP2E1) gene and AUD might only exist in males who are homozygotes for 1 alleles of aldehyde dehydrogenase-2 (ALDH2) and alcohol dehydrogenase-1B (ADH1B) genes, but this interaction did not reach statistical significance. Using the same set of data, the present study was aimed at exploring interactions between these genes and quantitative alcohol-related-trait scores (QARTs), and whether these are influenced by gender. The sample included 383 AUD cases with the alcohol use disorders identification test (AUDIT) score ≥10 and 350 normal controls with the AUDIT score ≤5. QARTs were measured using three factors from AUDIT. Possible associations of QARTs with interactions among genotypes of ALDH2 1/ 2, ADH1B1/2 and CYP2E1 c1/c2 and sex were analyzed in AUD cases and normal controls separately. The subjects with 2 alleles of ALDH2 or/and ADH1B had significantly lower scores of alcohol intake among controls but had significantly higher scores of alcohol related problems among cases. The score of alcohol intake in male cases who are homozygous for ALDH2 1 and ADH1B 1 and with CYP2E1 c2 allele was significantly higher than that of other cases. These findings suggest that interactions between genes influencing alcohol metabolism are influenced by gender and might affect QARTs differently between the milder-/non-drinkers and AUD cases.

Pharmacogenetics of drug dependence: role of gene variations in susceptibility and treatment

Drug dependency is a highly prevalent mental health disorder that imposes a significant burden on those directly affected, health care systems, and society in general. There is substantial heritability in the susceptibility to drug addiction, which indicates that there are genetic risk factors. Variation in the human genome is abundant and can directly affect drug dependency phenotypes, for example, by altering the function of a gene product or by altering gene expression. Pharmacogenetic studies can assess the effects of genetic variation on the risk for a particular phenotype (e.g., being an alcoholic). In addition, pharmacogenetic variability in treatment efficacy and adverse reactions can be investigated to identify particular genetic variants associated with altered responses. This review highlights examples of genetic variations that are important in the development and maintenance of specific drug dependencies as well as those that affect the response to treatment.

Interaction among genes influencing ethanol metabolism and sex is association with alcohol use disorders in a Tibet population

Associations between alcohol use disorders and polymorphisms of genes influencing ethanol metabolism have been widely reported, but gene-gene and gene-sex interaction studies have rarely been examined. Using a set of samples collected during an epidemiological study of alcohol use disorders AUDs in a Tibetan population in China, we performed a case-control study to investigate the relationship between the functional polymorphisms of genes influencing ethanol metabolism and AUDs. The sample included 383 individuals with an AUDIT score >or=10 and 350 control subjects with the AUDIT score <or=5. All participants were genotyped for ALDH2*1/*2, ADH1B*1/*2, and CYP2E1*c1/c2*. Data were analyzed employing an integrated strategy using MDR, SPSS, and UNPHASED software. The MDR analysis showed that the four-factor model including ADH1B*1/*2, ALDH2*1/*2, and CYP2E1*c1/*c2 polymorphisms, and sex was the most accurate model associated with AUDs with the highest OR 3.299. It also revealed that CYP2E1 *c1/*c2 polymorphism interacted significantly with sex. Independent analysis confirmed that both ADH2*2 and ALDH2*2 allele were significantly associated with AUDs (OR: 0.441 for ADH2*2 and 0.137 for ALDH2*2). CYP2E1*c2 was positively associated with AUDs only in males homozygotic for ALDH2*1 and ADH1B*1 (OR: 2.585). Cumulative association analysis showed the number of protective alleles and genotypes were negatively associated with AUDs. In conclusion, ALDH2*2 and ADH1B*2 alleles were not only independently associated with AUDs but also demonstrated cumulative dosage effects. However the positive association between CYP2E1*c2 allele and AUDs might only exist in males homozygotic for ALDH2*1 and ADH1B*1.

Common and unique biological pathways associated with smoking initiation/progression, nicotine dependence, and smoking cessation

Twin and family studies reveal a significant genetic contribution to the risk of smoking initiation and progression (SI/P), nicotine dependence (ND), and smoking cessation (SC). Further, numerous genes have been implicated in these smoking-related behaviors, especially for ND. However, no study has presented a comprehensive and systematic view of the genetic factors associated with these important smoking-related phenotypes. By reviewing the literature on these behaviors, we identified 16, 99, and 75 genes that have been associated with SI/P, ND, and SC, respectively. We then determined whether these genes were enriched in pathways important in the neuronal and brain functions underlying addiction. We identified 9, 21, and 13 pathways enriched in the genes associated with SI/P, ND, and SC, respectively. Among these pathways, four were common to all of the three phenotypes, that is, calcium signaling, cAMP-mediated signaling, dopamine receptor signaling, and G-protein-coupled receptor signaling. Further, we found that serotonin receptor signaling and tryptophan metabolism pathways were shared by SI/P and ND, tight junction signaling pathway was shared by SI/P and SC, and gap junction, neurotrophin/TRK signaling, synaptic long-term potentiation, and tyrosine metabolism were shared between ND and SC. Together, these findings show significant genetic overlap among these three related phenotypes. Although identification of susceptibility genes for smoking-related behaviors is still in an early stage, the approach used in this study has the potential to overcome the hurdles caused by factors such as genetic heterogeneity and small sample size, and thus should yield greater insights into the genetic mechanisms underlying these complex phenotypes.

Variability in ethanol biodisposition in whites is modulated by polymorphisms in the ADH1B and ADH1C genes

Association between genetic variations in alcohol-related enzymes and impaired ethanol biodisposition has not been unambiguously proven, and the effect of many newly described polymorphisms remains to be explored. The aims of this study are to elucidate the influence of genetic factors in alcohol biodisposition and effects. We analyzed alcohol pharmacokinetics and biodisposition after the administration of 0.5 g/kg ethanol; we measured ethanol effects on reaction time and motor time in response to visual and acoustic signals, and we analyzed 13 single nucleotide polymorphism (SNPs) in the genes coding for ADH1B, ADH1C, ALDH2, and CYP2E1 in 250 healthy white individuals. Variability in ethanol pharmacokinetics and biodisposition is related to sex, with women showing a higher area under the curve (AUC) (P = 0.002), maximum concentration (Cmax) (P < 0.001) and metabolic rate (P = 0.001). Four nonsynonymous SNPs are related to decreased alcohol metabolic rates: ADH1B rs6413413 (P = 0.012), ADH1C rs283413 (P < 0.001), rs1693482 (P < 0.001), and rs698 (P < 0.001). Individuals carrying diplotypes combining these mutations display statistically significant decrease in alcohol biodisposition as compared with individuals lacking these mutations. Alcohol effects displayed bimodal distribution independently of sex or pharmacokinetics. Most individuals had significant delays in reaction and motor times at alcohol blood concentrations under 500 mg/L, which are the driving limits for most countries.

CONCLUSION

Besides the identification of new genetic factors related to alcohol biodisposition relevant to whites, this study provides unambiguous identification of diplotypes related to variability in alcohol biodisposition.

Genetic polymorphism analysis of cytochrome P4502E1 (CYP2E1) in Chinese Han populations from four different geographic areas of Mainland China

CYP2E1 is one of a superfamily of enzymes that play a central role in activating and detoxifying many xenobiotics and endogenous compounds thought to be involved in the development of several human diseases. Among other factors, individual susceptibility to developing these pathologies relies on genetic polymorphisms, which are related to ethnic differences, since the frequency of mutant genotypes varies in different populations. The aim of this study was to investigate the genetic basis of CYP2E1 polymorphisms in the populations of four different geographical locations of China. Twenty-two different CYP2E1 polymorphisms, including six novel variants in promoter regions and a novel nonsense mutation, were identified. The frequencies of some polymorphisms and genotypes demonstrated significant differences among the four populations. Linkage disequilibrium analysis and tag SNP selection were performed. Haplotypes were analyzed within the selected tag SNPs. Tag SNP selection and haplotype distributions showed differences across the four populations.

Genetic and environmental influences on the ratio of 3'hydroxycotinine to cotinine in plasma and urine

OBJECTIVES

The ratio of trans-3'hydroxycotinine/cotinine (3HC/COT) is a marker of CYP2A6 activity, an important determinant of nicotine metabolism. This analysis sought to conduct a combined genetic epidemiologic and pharmacogenetic investigation of the 3HC/COT ratio in plasma and urine.

METHODS

One hundred and thirty-nine twin pairs [110 monozygotic and 29 dizygotic] underwent a 30-min infusion of stable isotope-labelled nicotine and its major metabolite, cotinine, followed by an 8-h in-hospital stay. Blood and urine samples were taken at regular intervals for analysis of nicotine, cotinine, and metabolites. DNA was genotyped to confirm zygosity and for variation in the gene for the primary nicotine metabolic enzyme, CYP2A6 (variants genotyped: *1B, *1 x 2, *2, *4, *9, *12). Univariate biometric analyses quantified genetic and environmental influences on each measure in the presence and absence of covariates, including measured CYP2A6 genotype.

RESULTS

There was a substantial amount of variation in the free 3HC/COT ratio in plasma (6 h postinfusion) attributable to additive genetic influences (67.4%, 95% confidence interval=55.9-76.2%). The heritability estimate was reduced to 61.0 and 49.4%, respectively, after taking into account the effect of covariates and CYP2A6 genotype. In urine (collected over 8 h), the estimated amount of variation in the 3HC/COT ratio attributable to additive genetic influences was smaller (47.2%, 95% confidence interval=0-67.2%) and decreased to 44.6 and 42.0% after accounting for covariates and genotype.

CONCLUSION

Additive genetic factors are prominent in determining variation in plasma 3HC/COT but less so in determining variation in urine 3HC/COT.

Tobacco addiction and pharmacogenetics of nicotine metabolism

This paper presents a brief overview of several components of tobacco addiction, including: 1) the epidemiology of smoking in the United States and elsewhere around the world; 2) implications of the pharmacogenetic study of nicotine metabolism for understanding tobacco addiction and its treatment; 3) the use of the twin design as an example of one strategy to understand the contribution of genetic and environmental factors to the pharmacokinetics of nicotine metabolism; 4) results from recent genomic studies of tobacco addiction in adults; and 5) a discussion of progress (past and future) toward the development of a comprehensive understanding of the pharmacogenetics of tobacco addiction and its treatment.

Global patterns of variation in allele and haplotype frequencies and linkage disequilibrium across the CYP2E1 gene

Cytochrome P450 2E1, gene symbol CYP2E1, is one of a family of enzymes with a central role in activating and detoxifying xenobiotics and endogenous compounds. Genetic variation at this gene has been reported in different human populations, and some association studies have reported increased risk for cancers and other diseases. To the best of our knowledge, multi-single-nucleotide polymorphism haplotypes and linkage disequilibrium (LD) have not been systematically studied for CYP2E1 in multiple populations. Haplotypes can greatly increase the power both to identify patterns of genetic variation relevant for gene expression as well as to detect disease-related susceptibility mutations. We present frequency and LD data and analyses for 11 polymorphisms and their haplotypes that we have studied on over 2600 individuals from 50 human population samples representing the major geographical regions of the world. The diverse patterns of haplotype variation found in the different populations we have studied show that ethnicity may be an important variable helping to explain inconsistencies that have been reported by association studies. More studies clearly are needed of the variants we have studied, especially those in the 5' region, such as the variable number of tandem repeats, as well as studies of additional polymorphisms known for this gene to establish evidence relating any systematic differences in gene expression that exist to the haplotypes at this gene.

A haplotype analysis of CYP2E1 polymorphisms in relation to alcoholic phenotypes in Mexican Americans

BACKGROUND

Studies regarding the association between the 4 polymorphisms of CYP2E1 (CYP2E1*1D, *5B, *6, and *1B) and alcoholism are inconsistent and inconclusive. The purpose of the present study was to clarify previously discordant studies by haplotype analysis in the Mexican American population.

METHODS

The 4 polymorphisms of CYP2E1 were studied in 334 alcoholics and 365 controls. Genotype, allele, and haplotype frequency comparisons between alcoholics and controls were assessed. Patterns of linkage disequilibrium (LD) at CYP2E1 were determined. Reconstructed haplotypes were tested for associations with clinical phenotypes (age onset of drinking, Maxdrinks, and smoking status).

RESULTS

No significant associations between the 4 polymorphisms of CYP2E1 and alcoholism were revealed by single allele tests. High LD was found between the CYP2E1 c2 and C alleles in Mexican Americans. Eleven haplotypes were present in the 699 participants. The 6 main haplotypes with frequencies higher than 1% made up 97% of the total halpotypes. The frequency of subjects carrying H6 (1C-c2-C-A2) was significantly higher in alcoholics than in controls (p = 0.0001). In contrast, the frequencies of H7 (1C-c2-C-A1) and H10 (1C-c2-D-A1) were significantly lower in alcoholics than in controls (p = 0.0072 for H7 and p = 0.0407 for H10). The frequency of H6 was significantly higher in alcoholics who had late onset of drinking than in nonalcoholic controls. Furthermore, the frequencies of H6 haplotype were also consistently higher in groups who had high number of maximum drinks (9 to 32 drinks) than in controls. When smokers are excluded, the frequencies of H6, H7, and H9 (1C-c2-D-A2) showed statistically significant differences between alcoholics and controls (p < 0.05). Moreover, the association between H6 and alcoholism become more robust when smokers are excluded. Furthermore, the frequency of H1 (1C-c1-D-A2) in alcoholic-smokers was much higher than in alcoholic-nonsmokers (p = 0.0028). In contrast, alcoholic-smokers carried less H2 (1C-c1-D-A1) in comparison with alcoholic-nonsmokers (p = 0.0417). The H3 (1D-c2-C-A2) frequency in alcoholic-smokers was much lower than in alcoholic-nonsmokers (p = 0.0042) and control-smokers (p = 0.0363).

CONCLUSIONS

Our data demonstrate that carrying haplotype H6 might enhance susceptibility to developing alcoholism, but possessing the H7 or H10 haplotype appears to decrease this susceptibility. The H6, H7, and H9 haplotypes may play certain roles in different clinical phenotypes in Mexican American alcoholics. In addition, our data suggest that the H1, H2, and H3 haplotypes are associated with alcohol drinking and smoking. These results support that haplotype analysis is much more informative than single allele analysis. Our findings clearly indicate the importance of H6 haplotype in alcohol drinking in Mexican Americans.

Genetics and smoking behavior

Accumulating data support the role of genetic factors in smoking initiation, progression to tobacco dependence, and smoking persistence. This review summarizes current research on the heritability of tobacco use phenotypes and genetic association studies of smoking-related behaviors. Although progress has been made in genetics research on smoking behavior, many studies have methodological limitations, including insufficient samples for detecting gene-gene and gene-environment interactions and use of less refined phenotypes. Pharmacogenetic investigations also are identifying variants in drug-metabolizing enzymes, receptors, and transporters that modify therapeutic response to smoking cessation medications; however, the field is relatively new, and most findings in this area have yet to be replicated. As this research advances, it will be important to study and address practical, economic, ethical, and social barriers to the translation of genetics research on tobacco use to clinical practice.

Effects of selective opioid receptor antagonists on alcohol-induced and nicotine-induced antinociception

BACKGROUND

Despite synergistic increases in risks of various cancers, the incidence of concomitant smoking and drinking remains high. An additive or synergistic analgesic effect of combined alcohol and nicotine may contribute to their coabuse. Recently, we provided evidence that doses of alcohol and nicotine that are ineffective in inducing an antinociceptive effect alone, when combined, can induce such an effect. Moreover, this antinociceptive effect could be attenuated by pretreatment with the nonselective opioid antagonist naloxone. The purpose of this study was to determine the role of selective opioid receptor subtypes (micro, delta, and kappa) in mediating the antinociceptive effects of alcohol, nicotine, and their combination.

METHODS

Adult male Wistar rats were administered selective opioid antagonists, D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH(2) (CTAP, for micro receptor, 1.0 mg/kg), naltrindole (for delta receptors, 10 mg/kg), and norbinaltorphimine (nor-BNI, for kappa receptor, 10 mg/kg) before injection of alcohol, nicotine or their combination. The animals were tested in hot-plate and tail-flick assays, representing nociception mediated predominantly via brain or spinal pathways, respectively. All the injections were administered acutely and the nociceptive tests were carried out 20 minutes after alcohol and 10 minutes after nicotine administration.

RESULTS

In general, the antagonists were more effective in blocking the effects of alcohol, nicotine, or their combination in the tail-flick versus the hot-plate assay. CTAP was most effective in blocking the effects of alcohol alone and nicotine alone in the tail-flick test, whereas in the hot-plate test both CTAP and naltrindole were more effective than nor-BNI. All 3 antagonists had a very similar profile in attenuating the combination of alcohol and nicotine effect in the hot-plate assay. None of the antagonists had a significant effect against the highest alcohol-nicotine dose in this test. In the tail-flick test, however, CTAP and naltrindole were more effective than nor-BNI in attenuating the highest alcohol-nicotine dose.

CONCLUSIONS

The data suggest the utility of all 3 opioid antagonists in blocking the effects of alcohol, nicotine, or their combination in spinally mediated antinociception. Although the supraspinally mediated antinociception was also attenuated by the opioid antagonists, further investigation of combination doses of these antagonists in fully blocking the supraspinal effects or attenuating voluntary alcohol and nicotine intake is warranted.

Application of nicotine enantiomers, derivatives and analogues in therapy of neurodegenerative disorders

This review gives a brief overview over the major aspects of application of the nicotine alkaloid and its close derivatives in the therapy of some neurodegenerative disorders and diseases (e.g. Alzheimer's disease, Parkinson's disease, Tourette's syndrome, schizophrenia etc.). The issues concerning methods of nicotine analysis and isolation, and some molecular aspects of nicotine pharmacology are included. The natural and synthetic analogues of nicotine that are considered for medical practice are also mentioned. The molecular properties of two naturally occurring nicotine enantiomers are compared--the less-common but less-toxic (R)-nicotine is suggested as a natural compound that may find its place in pharmaceutical practice.

Role of the Genetic Polymorphisms in the 5'-Flanking Region for Transcriptional Regulation of the Human CYP2E1 Gene

BACKGROUND

The human cytochrome P-4502E1 (CYP2E1) has been known to be that are associated with alcohol-related diseases and various cancers. Difference in susceptibility in enzyme induction of the CYP2E1 by environmental factors such as ethanol may be associated with the risk of these diseases. In the 5'-flanking region of the human CYP2E1 gene, there were tandem repeat polymorphism (CYP2E1*1C*,1D) and RsaI polymorphism (CYP2E1*5A*,5B), which have been reported to be related to these diseases. Thus, we focused relationship between these polymorphisms and transcriptional regulation. The aim of this study was to determine the role of these polymorphisms for the transcriptional regulation of the human CYP2E1 gene in general transcription and during enzyme induction.

METHODS

To determine the role of these polymorphisms, various constructs of the 5'-flanking region of the human CYP2E1 gene were prepared and transfected into HeLa cells and HepG2 cells treated or not with pyrazine, a well-known CYP2E1 inducer.

RESULTS

The transcriptional activity of CYP2E1*1D was higher than that of CYP2E1*1C in HeLa cells. The -1,306 base pairs (bp) construct (-1,306 to +9) increased transcriptional activity compared with the 2.5 kb full-length construct. The suppressive effect of transcriptional activity by deletion of the region including CYP2E1*1C was greater than that by CYP2E1*1D in HeLa cells. The -580 bp construct (-580 to +9) decreased transcriptional activity compared with the -1,306 bp construct. The -1,306 bp construct also showed a similar tendency during pyrazine treatment.

CONCLUSIONS

The region including the tandem repeat polymorphism was suggested to regulate transcription suppressively. Besides, it was speculated that the transcriptional activity of CYP2E1*1D was higher than that of CYP2E1*1C because transcriptional suppression of CYP2E1*1D was weaker than that of CYP2E1*1C. Also, it was confirmed that the region including RsaI polymorphism was associated with the promotion of transcription.

Metabolic and genetic factors contributing to alcohol induced effects and fetal alcohol syndrome

Alcohol-related damages on newborns and infants include a wide variety of complications from facial anomalies to neurodevelopmental delay, known as fetal alcohol syndrome (FAS). However, only less than 10% of women drinking alcohol during pregnancy have children with FAS. Understanding the risk factors increasing the probability for newborn exposed in utero to alcohol to develop FAS is therefore a key issue. The involvement of genetics as a one risk factor in FAS has been suggested by animal models and by molecular epidemiological studies on different populations, bearing allelic variants for those enzymes, such as ADH e CYP2E1, involved in ethanol metabolism. Indeed, one of the major factors determining the peak blood alcohol exposure to the fetus is the metabolic activity of the mother, in addition to placental and fetal metabolism, explaining, at least partially, the risk of FAS. The different rates of ethanol metabolism may be the result of genetic polymorphisms, the most relevant of which have been described in the paper.

Smoking comorbidity in alcoholism: neurobiological and neurocognitive consequences

Considerable research attests to the adverse effects of chronic smoking on cardiac, pulmonary, and vascular function as well as on increased risk for various cancers. However, comparatively little is known about the effects of chronic smoking on brain function. Although smoking rates have decreased in the developed world (they have increased in the developing world), smoking rates have been at a persistently high level in individuals with alcohol use disorders. Despite the high prevalence of comorbid chronic smoking and alcohol dependence, very few studies have addressed the separate and interactive effects that smoking and alcoholic drinking may have on neurobiology and brain function. This symposium, which took place at the annual meeting of the Research Society on Alcoholism in Santa Barbara, California, on June 29, 2005, postulates that the neurobiologic and neurocognitive abnormalities commonly described in studies of alcohol-dependent individuals are modulated by concurrent abuse of tobacco products and that brain recovery in abstinent alcoholic individuals is affected by chronic smoking. Four expert speakers and a discussant from different research disciplines focus in this symposium on the description of neurobiological and neurobehavioral effects because of concomitant drinking and smoking. Understanding the potential separate effects and interactions of chronic nicotine/smoking and alcohol consumption promotes a better understanding of specific mechanisms and neurocognitive consequences of brain injury and brain recovery with abstinence. The material presented contributes useful information to ongoing discussions about treatment strategies for these comorbid disorders and valuable educational material that can be used to affect public perception about smoking and perhaps health policy.

Molecular cloning and expression of novel alternatively spliced cytochrome P450 2E1 mRNAs in humans

Human cytochrome P450 2E1 (CYP2E1) is a phase I metabolizing enzyme. It is involved in the biotransformation of xenobiotics and endogenous substrates. Inter-individual genetic polymorphisms of the CYP2E1 gene are associated with different cancer diseases as well as alcohol and nicotine dependence. We report here for the first time three novel alternative spliced mRNA transcripts which are more frequently present in lung carcinoma cell lines as in hepatocyte cell lines. They are unexpected detectable in blood leukocytes from healthy volunteers but not in normal and cancerous lung tissue. The full-length wildtype transcript of CYP2E1 is described to be concomitant to an alternatively spliced mRNA transcript. Stimulation with CYP2E1-inducing agents did not change the splicing transcript pattern. The three splicing variants should lead to truncated non-functional proteins. Thus the genetic diversity of CYP2E1 is additionally extended at the transcriptional level of gene expression. The physiological role of the splicing variants is not known, yet, but they seem to be related to the carcinogenic property of the cell lines.

Ethnic variation in CYP2A6*7, CYP2A6*8 and CYP2A6*10 as assessed with a novel haplotyping method

Cytochrome P450 2A6 is the main human nicotine metabolizing enzyme coded for by a highly polymorphic gene, CYP2A6. CYP2A6*7, CYP2A6*8 and CYP2A6*10 are variant alleles common to Asian ethnicities. The CYP2A6*7 and CYP2A6*8 alleles each contain a non-synonymous single nucleotide polymorphism (SNP) 6558T>C and 6600G>T, respectively, whereas the CYP2A6*10 haplotype allele contains both. We have developed the first haplotyping assay; it can unambiguously distinguish the CYP2A6*7, CYP2A6*8 and CYP2A6*10 alleles. The allele frequencies of these three variants were assessed using the novel haplotyping assay in Chinese-Canadian (n=112), Chinese-American (n=221), Taiwanese (n=319), Korean-American (n=207) and Japanese-Canadian (n=64) populations, as well as in Caucasian (n=110) and African-Canadian (n=113) populations. Our new method demonstrated higher frequencies of CYP2A6*7 and CYP2A6*10, and a lower frequency of CYP2A6*8 in Asian populations, but no significant change of allele frequencies in Caucasian or African-Canadian populations.

Metabolism and Disposition Kinetics of Nicotine

Nicotine is of importance as the addictive chemical in tobacco, pharmacotherapy for smoking cessation, a potential medication for several diseases, and a useful probe drug for phenotyping cytochrome P450 2A6 (CYP2A6). We review current knowledge about the metabolism and disposition kinetics of nicotine, some other naturally occurring tobacco alkaloids, and nicotine analogs that are under development as potential therapeutic agents. The focus is on studies in humans, but animal data are mentioned when relevant to the interpretation of human data. The pathways of nicotine metabolism are described in detail. Absorption, distribution, metabolism, and excretion of nicotine and related compounds are reviewed. Enzymes involved in nicotine metabolism including cytochrome P450 enzymes, aldehyde oxidase, flavin-containing monooxygenase 3, amine N-methyltransferase, and UDP-glucuronosyltransferases are represented, as well as factors affecting metabolism, such as genetic variations in metabolic enzymes, effects of diet, age, gender, pregnancy, liver and kidney diseases, and racial and ethnic differences. Also effects of smoking and various inhibitors and inducers, including oral contraceptives, on nicotine metabolism are discussed. Due to the significance of the CYP2A6 enzyme in nicotine clearance, special emphasis is given to the effects and population distributions of CYP2A6 alleles and the regulation of CYP2A6 enzyme.

The use of race variables in genetic studies of complex traits and the goal of reducing health disparities: A transdisciplinary perspective

The use of racial variables in genetic studies has become a matter of intense public debate, with implications for research design and translation into practice. Using research on smoking as a springboard, the authors examine the history of racial categories, current research practices, and arguments for and against using race variables in genetic analyses. The authors argue that the sociopolitical constructs appropriate for monitoring health disparities are not appropriate for use in genetic studies investigating the etiology of complex diseases. More powerful methods for addressing population structure exist, and race variables are unacceptable as gross proxies for numerous social/environmental factors that disproportionately affect minority populations. The authors conclude with recommendations for genetic researchers and policymakers, aimed at facilitating better science and producing new knowledge useful for reducing health disparities.

The Unique Regulation of Brain Cytochrome P450 2 (CYP2) Family Enzymes by Drugs and Genetics

Cytochrome P450 (CYP) enzymes in the brain may have a role in the activation or inactivation of centrally acting drugs, in the metabolism of endogenous compounds, and in the generation of damaging toxic metabolites and/or oxygen stress. CYPs are distributed unevenly among brain regions, and are found in neurons, glial cells and at the blood-brain interface. They have been observed in mitochondrial membranes, in neuronal processes and in the plasma membrane, as well as in endoplastic reticulum. Brain CYPs are inducible by many common hepatic inducers, however many compounds affect liver and brain CYP expression differently, and some CYPs which are constitutively expressed in liver are inducible in brain. CYP induction is isozyme-, brain region-, cell type- and inducer-specific. While it is unlikely that brain CYPs contribute to overall clearance of xenobiotics, their punctate, region- and cell-specific expression suggests that CNS CYPs may create micro-environments in the brain with differing drug and metabolite levels (not detected or predicted by plasma drug monitoring). Coupled with the sensitivity of CNS CYPs to induction, this may in part account for inter-individual variation in response to centrally acting drugs and neurotoxins, and may have implications for individual variation in receptor adaptation and cross-tolerance to different drugs. In addition, genetic variation in brain CYPs, depending on the type of polymorphism (structural versus regulatory), will alter enzyme activity. These aspects of brain CYP expression regulation and genetic influences are illustrated in this review using mRNA, protein, and enzyme activity data for CYP2D1/6, CYP2E1 and CYP2B1/6 in rat and human brain. The role of CYP-mediated metabolism in the brain, a highly heterogeneous and complex organ, is a new and relatively unexplored field of scientific enquiry. It holds promise for furthering our undestanding of inter-individual variability in response to centrally acting drugs as well as risk for neurological diseases and pathogies.

Cyp1a2 protects against reactive oxygen production in mouse liver microsomes

H(2)O(2) production was evaluated in liver microsomes prepared from Cyp1a1/1a2(+/+) wild-type and Cyp1a1(-/-) and Cyp1a2(-/-) knockout mice pretreated with 5 microg dioxin (TCDD)/kg body wt or vehicle alone. NADPH-dependent H(2)O(2) production in TCDD-induced microsomes from wild-type mice was about one-third of that in noninduced microsomes. In Cyp1a2(-/-) mice, H(2)O(2) production was the same for induced and noninduced microsomes, with levels significantly higher than those in wild-type mice. Cyp1a1(-/-) microsomes displayed markedly lower levels of H(2)O(2) production in both induced and noninduced microsomes, compared with those in wild-type and Cyp1a2(-/-) microsomes. The CYP1A2 inhibitor furafylline in vitro exacerbated microsomal H(2)O(2) production proportional to the degree of CYP1A2 inhibition, and the CYP2E1 inhibitor diethyldithiocarbamate decreased H(2)O(2) production proportional to the degree of CYP2E1 inhibition. Microsomal H(2)O(2) production was strongly correlated to NADPH-stimulated production of thiobarbituric acid-reactive substances, as well as to decreases in microsomal membrane polarization anisotropy, indicative of peroxidation of unsaturated membrane lipids. Our results suggest that possibly acting as an "electron sink," CYP1A2 might decrease CYP2E1-and CYP1A1-mediated H(2)O(2) production and oxidative stress. In this regard, CYP1A2 may be considered an antioxidant enzyme.

Suppression of cytochrome P450 2E1 promoter activity by interferon-gamma and loss of response due to the -71G>T nucleotide polymorphism of the CYP2E1*7B allele

The CYP2E1*7B allele is defined by two nucleotide sequence polymorphisms, -71G>T and -333T>A. The CYP2E1 promoter sequence flanking the -71G nucleotide is consistent with a gamma-interferon activated sequence. Inflammation and interferon (IFN)-gamma suppress expression of CYP2E1 in vivo; however, the exact mechanism is not known. The objectives of this study were to determine whether the CYP2E1 promoter is regulated by IFN-gamma and to examine the influence of the nucleotide substitutions on this function. Treatment of HepG2 cells with IFN-gamma, after transient transfection with a luciferase reporter gene bearing the native CYP2E1 (-71G) promoter sequence resulted, in a dose-dependent reduction of luciferase activity. In contrast, no suppression was observed in cells transfected with the *7B allele promoter (-333A and -71T) nor a CYP2E1 plasmid containing only the -71T polymorphism. These data indicate that IFN-gamma suppresses native CYP2E1 promoter activity and that the -71G is critical for this response.