Association of Functional Opioid Receptor Genotypes With Alcohol Dependence in Koreans

Association between opioid and dopamine receptor gene polymorphisms OPRM1 rs1799971, DAT VNTR 9-10 repeat allele, DRD1 rs4532 and DRD2 rs1799732 and alcohol dependence: an ethnicity oriented meta-analysis

OBJECTIVE

We carried out a meta-analysis of four opioid and dopamine candidate gene polymorphisms having conflicting results in prior literature, namely OPRM1 rs1799971, DAT VNTR 9-10 repeat, DRD1 rs4532 and DRD2 rs1799732, to clarify their association with alcohol dependence and further stratified results by ethnicity to analyze possible ethnicity-mediated effects.

METHODS

Inclusion criteria: case-control studies assessing the association between OPRM1 rs1799971, DAT VNTR 9/10 repeat allele, DRD1 rs4532 and DRD2 rs1799732 with alcohol dependence, with sufficient data available to calculate the odds ratio (OR) within a 95% confidence interval. Exclusion criteria: studies of quantitative measures of alcohol consumption, response to medications or analyses of other markers in the candidate genes, studies without controls, animal studies and lack of genotyping data. Information sources were PubMed, Google Scholar and ScienceDirect databases, all of which were searched for articles published till 2021. Heterogeneity between studies and publication bias, subgroup analyses and sensitivity analyses were carried out.

RESULTS

A total of 41 published studies were included in the current meta-analysis. For the OPRM1 gene, there was a statistically significant association in the Asian population with a pooled OR of 1.707 (95% CI, 1.32-2.20 P  < 0.0001) and 1.618 (95% CI, 1.16-2.26 P  = 0.005) in the additive and dominant genetic models. For DAT VNTR 9/10 repeat, a statistically significant association of the risk vs. common allele was observed in AD with a pooled OR of 1.104 (95% CI, 1.00-1.21 P  = 0.046) in the allele model and the additive genetic model in the Caucasian population with pooled OR of 1.152 (95% CI, 1.01-1.31 P  = 0.034).

CONCLUSION

Results indicate that some of the effects may be ethnicity-specific.

OTHER

The meta-analysis has been registered in the CRD PROSPERO (CRD42023411576).

Association of OPRM1 with addiction: a review on drug, alcohol and smoking addiction in worldwide population

Background

Drugs are chemicals which can disrupt the nerve cell functions of the brain. The present study aims to investigate the addiction related gene (OPRM1) in three types of addiction—drugs, alcohol and smoking. Pathway for the addiction was ascertained through KEGG database, and the hotspot mutations for various populations were identified from Gnomad-exomes database. In silico analyses like SIFT, Polyphen, Hope, I-mutant and mutation taster were performed to understand the amino acid substitution, protein function, stability and pathogenicity of the variants.

Main body

Addiction-related variants were found in exons 1, 2 and 3, while the exon 4 did not exhibit any addiction related variation. Among all the variants from this gene, rs1799971 (A118G) polymorphism was the most commonly studied variation for addiction in different populations worldwide. Population-wise allele and genotype frequencies, demographic and epidemiological studies have also been performed from different populations, and the possible association of these variants with addiction was evaluated.

Conclusion

Our findings suggest that OPRM1 polymorphism impact as pharmacogenetic predictor of response to naltrexone and can also address the genetic predisposition related to addiction in human beings.

Differential sensitivity of human neurons carrying μ opioid receptor (MOR) N40D variants in response to ethanol

The acute and chronic effects of alcohol on the brain and behavior are linked to alterations in inhibitory synaptic transmission. Alcohol's most consistent effect at the synaptic level is probably a facilitation of γ-aminobutyric acid (GABA) release, as seen from several rodent studies. The impact of alcohol on GABAergic neurotransmission in human neurons is unknown, due to a lack of a suitable experimental model. Human neurons can also be used to model effects of genetic variants linked with alcohol use disorders (AUDs). The A118G single nucleotide polymorphism (SNP rs1799971) of the OPRM1 gene encoding the N40D (D40 minor allele) mu-opioid receptor (MOR) variant has been linked with individuals who have an AUD. However, while N40D is clearly associated with other drugs of abuse, involvement with AUDs is controversial. In this study, we employed Ascl1-and Dlx2-induced inhibitory neuronal cells (AD-iNs) generated from human iPS cell lines carrying N40D variants, and investigated the impact of ethanol acutely and chronically on GABAergic synaptic transmission. We found that N40 AD-iNs display a stronger facilitation (versus D40) of spontaneous and miniature inhibitory postsynaptic current frequency in response to acute ethanol application. Quantitative immunocytochemistry of Synapsin 1+ synaptic puncta revealed a similar synapse number between N40 and D40 iNs, suggesting an ethanol modulation of presynaptic GABA release without affecting synapse density. Interestingly, D40 iNs exposed to chronic intermittent ethanol application caused a significant increase in mIPSC frequency, with only a modest enhancement observed in N40 iNs. These data suggest that the MOR genotype may confer differential sensitivity to synaptic output, which depends on ethanol exposure time and concentration for AD-iNs and may help explain alcohol dependence in individuals who carry the MOR D40 SNPs. Furthermore, this study supports the use of human neuronal cells carrying risk-associated genetic variants linked to disease, as in vitro models to assay the synaptic actions of alcohol on human neuronal cells.

Addiction associated N40D mu-opioid receptor variant modulates synaptic function in human neurons

The OPRM1 A118G single nucleotide polymorphism (SNP rs1799971) gene variant encoding the N40D µ-opioid receptor (MOR) has been associated with dependence on opiates and other drugs of abuse but its mechanism is unknown. The frequency of G-allele carriers is ~40% in Asians, ~16% in Europeans, and ~3% in African-Americans. With opioid abuse-related deaths rising at unprecedented rates, understanding these mechanisms may provide a path to therapy. Here we generated homozygous N40D subject-specific induced inhibitory neuronal cells (iNs) from seven human-induced pluripotent stem (iPS) cell lines from subjects of European descent (both male and female) and probed the impact of N40D MOR regulation on synaptic transmission. We found that D40 iNs exhibit consistently stronger suppression (versus N40) of spontaneous inhibitory postsynaptic currents (sIPSCs) across multiple subjects. To mitigate the confounding effects of background genetic variation on neuronal function, the regulatory effects of MORs on synaptic transmission were recapitulated in two sets of independently engineered isogenic N40D iNs. In addition, we employed biochemical analysis and observed differential N-linked glycosylation of human MOR N40D. This study identifies neurophysiological and molecular differences between human MOR variants that may predict altered opioid responsivity and/or dependence in this subset of individuals.

The association between the OPRM1 A118G polymorphism and addiction in a Turkish population

Susceptibility to addiction has a complex genetic basis that includes genes associated with the action and metabolism of drugs of abuse. One important gene in that respect is OPRM1, which codes for the μ-opioid receptor and has an important role in mediating the rewarding effects of addiction substances. The aim of our study was to assess the prevalence of the OPRM1 A118G polymorphism (rs1799971) in Turkish population and to investigate its association with opioid and other substance addiction. In addition, we examined the association of rs1799971 in addicted patients who were also diagnosed with psychiatric disorders. The study included 103 patients addicted to opioids, cocaine, ecstasy, alcohol, lysergic acid diethylamide (LSD), cannabis, and sedative/hypnotic substances and 83 healthy volunteers with similar demographic features as controls. rs1799971 polymorphisms were identified with the polymerase chain reaction restriction fragment length polymorphism method (PCR-RFLP). The genotype frequencies were significantly higher in the addicted patients than controls (32.0 % vs 16.9 %, respectively; p=0.027). The prevalence of the G allele was 16.1 % in the addicted group and 8.4 % in the control group (p=0.031). Our study confirmed the association between the rs1799971(G) allele frequency and opioid and other substance addiction, but not with psychiatric disorders.

Associations among the opioid receptor gene (OPRM1) A118G polymorphism, psychiatric symptoms, and quantitative EEG in Korean males with gambling disorder: A pilot study

BACKGROUND AND AIMS

A single nucleotide polymorphism of A118G (SNP; rs1799971) in the opioid receptor μ-1 (OPRM1) gene is a missense variant that influences the affinity of μ-opioid receptors. This study aimed to investigate the associations among the A118G polymorphism in the OPRM1 gene, psychiatric symptoms, and quantitative electroencephalography (qEEG) findings in patients with gambling disorder.

METHODS

Fifty-five male patients with gambling disorder aged between 18 and 65 years old participated in the study. The A118G polymorphism was genotyped into the AA, GA, and GG groups by the polymerase chain reaction/restriction fragment length polymorphism method. Resting-state qEEG was recorded with the eyes closed, and the absolute power of the delta (1-4 Hz), theta (4-8 Hz), alpha (8-12 Hz), and beta (12-30 Hz) frequency bands was analyzed. Psychiatric symptoms, including depression, anxiety, impulsivity and severity of gambling, were assessed by a self-rating scale.

RESULTS

There were no significant differences in psychiatric symptoms among the three genotype groups (AA, GA, and GG). However, the frequency band power of qEEG showed significant differences among the three genotype groups. The absolute power of the beta and theta bands in the frontal lobe was higher in G allele carriers.

DISCUSSION AND CONCLUSION

Based on the findings of this study, the polymorphism in the OPRM1 gene might affect the neurophysiological process in patients with gambling disorder.

Association of opioid receptor gene polymorphisms with drinking severity and impulsivity related to alcohol use disorder in a Korean population

Aims

Recent evidence suggests that the opioid system is implicated in the pathophysiology of alcohol use disorder (AUD). We aimed to examine the genetic influence of opioid receptors on susceptibility to AUD and its clinical and psychological characteristics including harmful drinking behavior and various aspects of impulsivity in AUD patients.

Methods

Three μ‐opioid receptor gene (OPRM1) variants and two κ‐opioid receptor gene (OPRK1) variants were examined in 314 male patients with AUD and 324 male controls. We applied the Alcohol Use Disorders Identification Test (AUDIT), Obsessive Compulsive Drinking Scale (OCDS), and Alcohol Dependence Scale. AUD patients also completed the stop‐signal task, delay discounting task, balloon analogue risk task, and the Barratt Impulsiveness Scale version 11 (BIS‐11).

Results

No significant differences in genotype distributions or haplotype frequencies were found between AUD patients and controls. However, OPRK1 SNP rs6473797 was significantly related to the severity of alcohol‐related symptoms as measured by AUDIT and OCDS and a haplotype containing rs6473797 was also related to OCDS scores in AUD patients. For other psychological traits, OPRM1 SNP rs495491 was significantly associated with scores on the motor subfactor of the BIS‐11.

Conclusion

Genetic variations in opioid receptors may contribute to symptom severity and impulsivity in AUD patients.

Binge-Like Eating Is Not Influenced by the Murine Model of OPRM1 A118G Polymorphism

Impairments in opioid receptor signaling have been implicated in disordered eating. A functional variant of the OPRM1 gene is a guanine (G) substitution for adenine (A) at the 118 position of exon 1 (A118G). The influence of the A118G variant on binge eating behaviors and the effectiveness of pharmacotherapies used to treat binge eating have not been characterized. Mice were generated with A to G substitution at the 112 position on exon 1 to produce a murine equivalent of the human A118G variant. Homozygous female mice (AA or GG) were exposed to intermittent access to a highly palatable sweet-fat food with or without prior calorie deprivation to promote dietary-induced binge eating. There were no genotype-dependent differences in the dietary-induced binge eating. However, GG mice exposed to intermittent calorie restriction (Restrict) had higher body weights compared with GG mice exposed to intermittent sweet fat-food (Binge) and ad libitum feeding (Naive). Acute oral dosing of lisdexamfetamine (0.15, 0.5, and 1.5 mg/kg) or sibutramine (0.3, 1, and 3 mg/kg) did not produce genotype-dependent differences in binge-like eating. In addition, no genotype-dependent differences in binge-like eating were observed with chronic (14-day) dosing of lisdexamfetamine (1.5 mg/kg/day) or sibutramine (3 mg/kg/day). In the chronic dosing, body weights were higher in the GG Restrict compared with AA Restrict. Our findings suggest that the A112G polymorphism does not influence binge eating behaviors or pharmacotherapies for treating binge eating.

Implication of OPRM1 A118G Polymorphism in Opioids Addicts in Pakistan: In vitro and In silico Analysis

Single nucleotide polymorphism in OPRM1 gene is associated with hedonic and reinforcing consequences of opioids. Risk and protective alleles may vary in different populations. One hundred healthy controls and 100 opioids (predominantly heroin) addicts from Pakistani origin were genotyped for A118G (N40D) polymorphism in OPRM1. Structural and functional impact of the polymorphism on encoded protein was predicted by in silico analysis. Results show significant association between homozygous GG genotype and opioid addiction in Pakistani population (p value = 0.016). In silico analysis by SIFT (TI = 0.61), PolyPhen (PISC = 0.227), PANTHER (subPSEC = -1.7171), and SNP effect predicted this SNP benign for encoded protein. Superimposing wild-type and mutated proteins by MODELLER shows no change (RMSD = 0.1) in extracellular ligand binding domain of μ-opioid receptor. However, Haploreg and RegulomeDB predicted OPRM1 gene repression by chromatin condensation and increased binding affinity of RXRA transcription factor that may reduce protein translation and hence the number of available receptors to bind with drugs, which may trigger underlying mechanisms for opioids addiction. Thus, this study outlines causal relationship between opioids addiction and genetic predisposition in Pakistani population.

Lack of associations of the opioid receptor mu 1 (OPRM1) A118G polymorphism (rs1799971) with alcohol dependence: review and meta-analysis of retrospective controlled studies

Background

Studies have sought associations of the opioid receptor mu 1 (OPRM1) A118G polymorphism (rs1799971) with alcohol-dependence, but findings are inconsistent. We summarize the information as to associations of rs1799971 (A > G) and the alcohol-dependence.

Methods

Systematically, we reviewed related literatures using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guideline. Embase, PubMed, Web of Knowledge, and Chinese National Knowledge Infrastructure (CNKI) databases were searched using select medical subject heading (MeSH) terms to identify all researches focusing on the present topic up to September 2016. Odds ratios (ORs) along with the 95% confidence interval (95% CI) were estimated in allele model, homozygote model, heterozygote model, dominant model and recessive model. Ethnicity-specific subgroup-analysis, sensitivity analysis, heterogeneity description, and publication-bias assessment were also analyzed.

Results

There were 17 studies, including 9613 patients in the present meta-analysis. The ORs in the 5 genetic-models were 1.037 (95% CI: 0.890, 1.210; p = 0.64), 1.074 (95% CI: 0.831, 1.387; p = 0.586), 1.155 (95% CI: 0.935, 1.427; p = 0.181), 1.261 (95% CI: 1.008, 1.578; p = 0.042), 0.968 (95% CI: 0.758, 1.236; p = 0.793), respectively. An association is significant in the dominant model, but there is no statistical significance upon ethnicity-specific subgroup analysis.

Conclusion

The rs1799971 (A > G) is not strongly associated with alcohol-dependence. However, there are study heterogeneities and limited sample sizes.

Review: Pharmacogenetics of alcoholism treatment: Implications of ethnic diversity

BACKGROUND AND OBJECTIVES

Pharmacogenetic studies of alcohol use disorder (AUD) have suggested that the efficacy of treatments for AUD is, in part, influenced by the genetic background of an individual. Since the frequency of alleles associated with pharmacotherapy for AUD varies by ancestral background, the effectiveness of medications used to treat AUD may vary among different populations. The purpose of this review is to summarize the existing pharmacogenetic studies of treatments for AUD in individuals of European, East Asian, African, and American Indian/Alaska Native ancestry.

METHODS

Electronic databases were searched for pharmacogenetic studies of AUD treatment that included individuals of diverse ancestral backgrounds.

RESULTS

Pharmacogenetic studies of AUD reviewed here have primarily investigated genetic variation thought to play a role in the response to naltrexone, ondansetron, and topiramate. There is support that the A118G polymorphism should be further investigated in individuals of East Asian ancestry.

DISCUSSION AND CONCLUSIONS

Given the lack of pharmacogenetic research on response to AUD medication in ethnic minority populations and the mixed results, there is a critical need for future studies among individuals of different ancestries. More efforts should be devoted to standardizing procedures such that results can be more readily integrated into a body of literature that can directly inform clinical practice.

SCIENTIFIC SIGNIFICANCE

This review highlights the importance for future research to aim for inclusiveness in pharmacogenetic studies of AUD and increase diversity of clinical trials in order to provide the best treatment outcomes for individuals across different racial and ethnic groups. (Am J Addict 2017;26:516-525).

Association of the OPRM1 Variant rs1799971 (A118G) with Non-Specific Liability to Substance Dependence in a Collaborative de novo Meta-Analysis of European-Ancestry Cohorts

The mu1 opioid receptor gene, OPRM1, has long been a high-priority candidate for human genetic studies of addiction. Because of its potential functional significance, the non-synonymous variant rs1799971 (A118G, Asn40Asp) in OPRM1 has been extensively studied, yet its role in addiction has remained unclear, with conflicting association findings. To resolve the question of what effect, if any, rs1799971 has on substance dependence risk, we conducted collaborative meta-analyses of 25 datasets with over 28,000 European-ancestry subjects. We investigated non-specific risk for "general" substance dependence, comparing cases dependent on any substance to controls who were non-dependent on all assessed substances. We also examined five specific substance dependence diagnoses: DSM-IV alcohol, opioid, cannabis, and cocaine dependence, and nicotine dependence defined by the proxy of heavy/light smoking (cigarettes-per-day >20 vs. ≤ 10). The G allele showed a modest protective effect on general substance dependence (OR = 0.90, 95% C.I. [0.83-0.97], p value = 0.0095, N = 16,908). We observed similar effects for each individual substance, although these were not statistically significant, likely because of reduced sample sizes. We conclude that rs1799971 contributes to mechanisms of addiction liability that are shared across different addictive substances. This project highlights the benefits of examining addictive behaviors collectively and the power of collaborative data sharing and meta-analyses.

A heroin addiction severity-associated intronic single nucleotide polymorphism modulates alternative pre-mRNA splicing of the μ opioid receptor gene OPRM1 via hnRNPH interactions

Single nucleotide polymorphisms (SNPs) in the OPRM1 gene have been associated with vulnerability to opioid dependence. The current study identifies an association of an intronic SNP (rs9479757) with the severity of heroin addiction among Han-Chinese male heroin addicts. Individual SNP analysis and haplotype-based analysis with additional SNPs in the OPRM1 locus showed that mild heroin addiction was associated with the AG genotype, whereas severe heroin addiction was associated with the GG genotype. In vitro studies such as electrophoretic mobility shift assay, minigene, siRNA, and antisense morpholino oligonucleotide studies have identified heterogeneous nuclear ribonucleoprotein H (hnRNPH) as the major binding partner for the G-containing SNP site. The G-to-A transition weakens hnRNPH binding and facilitates exon 2 skipping, leading to altered expressions of OPRM1 splice-variant mRNAs and hMOR-1 proteins. Similar changes in splicing and hMOR-1 proteins were observed in human postmortem prefrontal cortex with the AG genotype of this SNP when compared with the GG genotype. Interestingly, the altered splicing led to an increase in hMOR-1 protein levels despite decreased hMOR-1 mRNA levels, which is likely contributed by a concurrent increase in single transmembrane domain variants that have a chaperone-like function on MOR-1 protein stability. Our studies delineate the role of this SNP as a modifier of OPRM1 alternative splicing via hnRNPH interactions, and suggest a functional link between an SNP-containing splicing modifier and the severity of heroin addiction.

Pharmacogenetics of OPRM1

Pharmacogenetic research has the potential to explain the variation in treatment efficacy within patient populations. Understanding the interaction between genetic variation and medications may provide a method for matching patients to the most effective therapeutic options and improving overall patient outcomes. The OPRM1 gene has been a target of interest in a large number of pharmacogenetic studies due to its genetic and structural variation, as well as the role of opioid receptors in a variety of disorders. The mu-opioid receptor (MOR), encoded by OPRM1, naturally regulates the analgesic response to pain and also controls the rewarding effects of many drugs of abuse, including opioids, nicotine, and alcohol. Genetic variants in OPRM1, particularly the non-synonymous polymorphism A118G, have been repeatedly associated with the efficacy of treatments for pain and various types of dependence. This review focuses on the current understanding of the pharmacogenetic impact of OPRM1, primarily with regard to the treatment of pain and addiction.

Opioid system genes in alcoholism: a case-control study in Croatian population

Due to their involvement in dependence pathways, opioid system genes represent strong candidates for association studies investigating alcoholism. In this study, single nucleotide polymorphisms within the genes for mu (OPRM1) and kappa (OPRK1) opioid receptors and precursors of their ligands - proopiomelanocortin (POMC), coding for beta-endorphin and prodynorphin (PDYN) coding for dynorphins, were analyzed in a case-control study that included 354 male alcohol-dependent and 357 male control subjects from Croatian population. Analysis of allele and genotype frequencies of the selected polymorphisms of the genes OPRM1/POMC and OPRK1/PDYN revealed no differences between the tested groups. The same was true when alcohol-dependent persons were subdivided according to the Cloninger's criteria into type-1 and type-2 groups, known to differ in the extent of genetic control. Thus, the data obtained suggest no association of the selected polymorphisms of the genes OPRM1/POMC and OPRK1/PDYN with alcoholism in Croatian population.

Mu opioids and their receptors: evolution of a concept

Opiates are among the oldest medications available to manage a number of medical problems. Although pain is the current focus, early use initially focused upon the treatment of dysentery. Opium contains high concentrations of both morphine and codeine, along with thebaine, which is used in the synthesis of a number of semisynthetic opioid analgesics. Thus, it is not surprising that new agents were initially based upon the morphine scaffold. The concept of multiple opioid receptors was first suggested almost 50 years ago (Martin, 1967), opening the possibility of new classes of drugs, but the morphine-like agents have remained the mainstay in the medical management of pain. Termed mu, our understanding of these morphine-like agents and their receptors has undergone an evolution in thinking over the past 35 years. Early pharmacological studies identified three major classes of receptors, helped by the discovery of endogenous opioid peptides and receptor subtypes-primarily through the synthesis of novel agents. These chemical biologic approaches were then eclipsed by the molecular biology revolution, which now reveals a complexity of the morphine-like agents and their receptors that had not been previously appreciated.

RGS17: an emerging therapeutic target for lung and prostate cancers

Ligands for G-protein-coupled receptors (GPCRs) represent approximately 50% of currently marketed drugs. RGS proteins modulate heterotrimeric G proteins and, thus, GPCR signaling, by accelerating the intrinsic GTPase activity of the Gα subunit. Given the prevalence of GPCR targeted therapeutics and the role RGS proteins play in G protein signaling, some RGS proteins are emerging as targets in their own right. One such RGS protein is RGS17. Increased RGS17 expression in some prostate and lung cancers has been demonstrated to support cancer progression, while reduced expression of RGS17 can lead to development of chemotherapeutic resistance in ovarian cancer. High-throughput screening is a powerful tool for lead compound identification, and utilization of high-throughput technologies has led to the discovery of several RGS inhibitors, thus far. As screening technologies advance, the identification of novel lead compounds the subsequent development of targeted therapeutics appears promising.

μ-Opioid receptor gene (OPRM1) polymorphism A118G: lack of association in Finnish populations with alcohol dependence or alcohol consumption

Aims: The molecular epidemiological studies on the association of the opioid receptor µ-1 (OPRM1) polymorphism A118G (Asn40Asp, rs1799971) and alcohol use disorders have given conflicting results. The aim of this study was to test the possible association of A118G polymorphism and alcohol use disorders and alcohol consumption in three large cohort-based study samples. Methods: The association between the OPRM1 A118G (Asn40Asp, rs1799971) polymorphism and alcohol use disorders and alcohol consumption was analyzed using three different population-based samples: (a) a Finnish cohort study, Health 2000, with 503 participants having a DSM-IV diagnosis for alcohol dependence and/or alcohol abuse and 506 age- and sex-matched controls; (b) a Finnish cohort study, FINRISK (n = 2360) and (c) the Helsinki Birth Cohort Study (n = 1384). The latter two populations lacked diagnosis-based phenotypes, but included detailed information on alcohol consumption. Results: We found no statistically significant differences in genotypic or allelic distribution between controls and subjects with alcohol dependence or abuse diagnoses. Likewise no significant effects were observed between the A118G genotype and alcohol consumption. Conclusion: These results suggest that A118G (Asn40Asp) polymorphism may not have a major effect on the development of alcohol use disorders at least in the Finnish population.

Mu opioid receptor (OPRM1) as a predictor of treatment outcome in opiate-dependent individuals of Arab descent

BACKGROUND

A number of research studies on the genetics of opiate dependence have focused on the μ-opioid receptor (OPRM1), which is a primary target for opiates. This study aims to identify genetic polymorphisms within the OPRM1 gene involved in response to the biopsychosocial treatment in opiate-dependent individuals of Arab descent.

METHODS

Unrelated Jordanian Nationals of Arab descent (N = 183) with opiate dependence were selected for this study. These individuals, all males, met the DSM-IV criteria for opiate dependence and were undergoing a voluntary 8-week treatment program at a Jordanian Drug Rehabilitation Centre. All individuals were genotyped for 22 single nucleotide polymorphisms (SNPs) within the OPRM1 gene using the Sequenom MassARRAY(®) system (iPLEX GOLD). Statistical analyses were carried out using the R package.

RESULTS

Patients receiving biopsychosocial treatment showed that there was a significant difference in their OPRM1 SNPs' genotyping distribution between good, moderate, and poor responders to the treatment at two sites (rs6912029 [G-172T], and rs12205732 [G-1510A], P < 0.05, Fisher's exact test).

CONCLUSION

This study is the first report of an association between the OPRM1 G-172T and G-1510A polymorphisms and treatment response for opiate dependence. Specifically, this study demonstrated that the OPRM1 GG-172 and GG-1510 genotypes were more frequent among patients who were nonresponders to the biopsychosocial treatment. However, further pharmacogenetic studies in a larger cohort of opiate-dependent patients of Arab descent are needed to confirm these findings and identify individuals with increased chance of relapse.

Testing multiple levels of influence in the intergenerational transmission of alcohol disorders from a developmental perspective: the example of alcohol use promoting peers and μ-opioid receptor M1 variation

This study examined the interplay between the influence of peers who promote alcohol use and μ-opioid receptor M1 (OPRM1) genetic variation in the intergenerational transmission of alcohol use disorder (AUD) symptoms while separating the "traitlike" components of AUD symptoms from their age-specific manifestations at three ages from emerging adulthood (17-23 years) to adulthood (29-40 years). The results for males were consistent with genetically influenced peer selection mechanisms as mediators of parent alcoholism effects. Male children of alcoholics were less likely to be carriers of the G allele in single nucleotide polymorphism A118G (rs1799971), and those who were homozygous for the A allele were more likely to affiliate with alcohol use promoting peers who increased the risk for AUD symptoms at all ages. There was evidence for women of an interaction between OPRM1 variation and peer affiliations but only at the earliest age band. Peer influences had stronger effects among women who were G-carriers. These results illustrate the complex ways in which the interplay between influences at multiple levels of analysis can underlie the intergenerational transmission of alcohol disorders as well as the importance of considering age and gender differences in these pathways.

Ethnic-specific meta-analyses of association between the OPRM1 A118G polymorphism and alcohol dependence among Asians and Caucasians

BACKGROUND

Many studies have investigated the association between the OPRM1 A118G polymorphism (rs1799971) and alcohol dependence, but the results were inconsistent. To better understand this relationship, ethnicity-specific meta-analyses were conducted.

METHODS

We retrieved all eligible studies published up to April 12, 2011 from the PubMed/MEDLINE, EMBASE, and ISI Web of Science databases. Ethnicity-specific meta-analyses were performed using either fixed- or random-effect models as appropriate.

RESULTS

Twelve independent studies with 1900 cases and 2382 controls were included. Five studies were conducted in Asians and seven in Caucasians. Ethnicity-specific meta-analyses revealed that the A118G polymorphism was significantly associated with alcohol dependence risk in Asians (GA vs. AA: odds ratio [OR], 1.73; 95% confidence interval [CI], 1.33-2.25; GA+GG vs. AA: OR, 1.57; 95% CI, 1.22-2.02), but not in Caucasians (GA vs. AA: OR, 1.05; 95% CI, 0.75-1.49; GA+GG vs. AA: OR, 1.11; 95% CI, 0.79-1.55).

CONCLUSIONS

The OPRM1 A118G polymorphism may contribute to the susceptibility of alcohol dependence in Asians but not in Caucasians.

Variation in regulator of G-protein signaling 17 gene (RGS17) is associated with multiple substance dependence diagnoses

Background

RGS17 and RGS20 encode two members of the regulator of G-protein signaling RGS-Rz subfamily. Variation in these genes may alter their transcription and thereby influence the function of G protein-coupled receptors, including opioid receptors, and modify risk for substance dependence.

Methods

The association of 13 RGS17 and eight RGS20 tag single nucleotide polymorphisms (SNPs) was examined with four substance dependence diagnoses (alcohol (AD), cocaine (CD), opioid (OD) or marijuana (MjD)] in 1,905 African Americans (AAs: 1,562 cases and 343 controls) and 1,332 European Americans (EAs: 981 cases and 351 controls). Analyses were performed using both χ² tests and logistic regression analyses that covaried sex, age, and ancestry proportion. Correlation of genotypes and mRNA expression levels was assessed by linear regression analyses.

Results

Seven RGS17 SNPs showed a significant association with at least one of the four dependence traits after a permutation-based correction for multiple testing (0.003≤P_empirical≤0.037). The G allele of SNP rs596359, in the RGS17 promoter region, was associated with AD, CD, OD, or MjD in both populations (0.005≤P_empirical≤0.019). This allele was also associated with significantly lower mRNA expression levels of RGS17 in YRI subjects (P = 0.002) and non-significantly lower mRNA expression levels of RGS17 in CEU subjects (P = 0.185). No RGS20 SNPs were associated with any of the four dependence traits in either population.

Conclusions

This study demonstrated that variation in RGS17 was associated with risk for substance dependence diagnoses in both AA and EA populations.

Association of µ-opioid receptor (OPRM1) gene polymorphism with response to naltrexone in alcohol dependence: a systematic review and meta-analysis

Previous studies have suggested that the effect of naltrexone in patients with alcohol dependence may be moderated by genetic factors. In particular, the possession of the G allele of the A118G polymorphism of the µ-opioid receptor gene (OPRM1) has been associated with a better response to naltrexone, although controversial results have been reported. The aim of this paper is to combine previous findings by means of a systematic review and a meta-analysis. We retrieved studies on the relationship between A118G polymorphism in OPRM1 gene and response to treatment with naltrexone in patients with alcohol dependence by means of electronic database search. A meta-analysis was conducted using a random-effects model. Calculations of odds ratio (OR) and their confidence intervals (CI) and tests for heterogeneity of the results have been performed. Six previous studies have analyzed the role of A118G polymorphism in response to naltrexone for alcohol dependence. After meta-analysis, we found that naltrexone-treated patients carrying the G allele had lower relapse rates than those who were homozygous for the A allele (OR: 2.02, 95% CI 1.26-3.22; P = 0.003). There were no differences in abstinence rates. Our results support the fact that the G allele of A118G polymorphism of OPRM1 moderates the effect of naltrexone in patients with alcohol dependence. This genetic marker may therefore identify a subgroup of individuals more likely to respond to this treatment.

The genetics of the opioid system and specific drug addictions

Addiction to drugs is a chronic, relapsing brain disease that has major medical, social, and economic complications. It has been established that genetic factors contribute to the vulnerability to develop drug addiction and to the effectiveness of its treatment. Identification of these factors may increase our understanding of the disorders, help in the development of new treatments and advance personalized medicine. In this review, we will describe the genetics of the major genes of the opioid system (opioid receptors and their endogenous ligands) in connection to addiction to opioids, cocaine, alcohol and methamphetamines. Particular emphasis is given to association and functional studies of specific variants. We will provide information on the sample populations and the size of each study, as well as a list of the variants implicated in association with addiction-related phenotypes, and with the effectiveness of pharmacotherapy for addiction.

Pharmacogenomics of the human µ-opioid receptor

The µ-opioid receptor is a primary target for clinically important opioid analgesics, including morphine, fentanyl and methadone. Many genetic variations have been identified in the human µ-opioid receptor MOP gene (OPRM1), and their implications have been reported in the effects of opioid drugs and susceptibility to drug dependence. Interestingly, agonistic and antagonistic opioid effects are inversely associated with the A118G polymorphism genotype. The A118G polymorphism may also be associated with substance dependence and susceptibility to other disorders, including epilepsy and schizophrenia. The IVS1+A21573G, IVS1-T17286C, and TAA+A5359G polymorphisms in the OPRM1 gene may be associated with alcohol, opioid and tobacco dependence, respectively. However, some studies have failed to confirm the correlations between the polymorphisms and opioid effects and substance dependence. Further studies are needed to elucidate the molecular mechanisms underlying the effects of OPRM1 polymorphisms.

A pharmacogenetic model of naltrexone-induced attenuation of alcohol consumption in rhesus monkeys

BACKGROUND

Variation at the human mu-opioid receptor has been associated with alcohol abuse. The A118G (N40D) polymorphism in humans is functionally mimicked by the C77G (P26R) polymorphism in rhesus monkeys; both show similar in vitro influences on ligand binding and in vivo correlations with physiological measures as well as behavioral measures including predilection towards alcohol consumption. Naltrexone, an antagonist at the receptor, has been used to treat alcoholism in humans and has been reported to show differences in effectiveness depending on genotype.

METHODS

Here we describe a study in which we a priori selected rhesus monkeys based on genotype at the OPRM1 C77G single nucleotide polymorphism, trained them to self-administer alcohol, and assessed naltrexone responsiveness.

RESULTS

Alcohol intake in rhesus monkeys varied with genotype across a range of alcohol concentrations (0.5-4%, w/v) such that animals with the G/G genotype drank consistently more alcohol than those animals with the C/C genotype. Additionally, naltrexone attenuated alcohol drinking in a dose- and genotype-dependent manner. Animals harboring the G/G genotype were more sensitive to the effects of naltrexone and showed greater reductions in alcohol consumption at lower naltrexone doses compared to animals with a C/G or C/C genotype.

CONCLUSIONS

This preliminary study demonstrates a pharmacogenomic response to naltrexone in rhesus monkeys that parallels that seen in humans. This finding provides a basis for developing a pharmacogenetic animal model for naltrexone effect that can expand further our understanding of the causes and treatments of alcohol use disorders.

OPRM1 SNP (A118G): involvement in disease development, treatment response, and animal models

Endogenous opioids acting at mu-opioid receptors mediate many biological functions. Pharmacological intervention at these receptors has greatly aided in the treatment of acute and chronic pain, in addition to other uses. However, the development of tolerance and dependence has made it difficult to adequately prescribe these therapeutics. A common single nucleotide polymorphism (SNP), A118G, in the mu-opioid receptor gene can affect opioid function and, consequently, has been suggested to contribute to individual variability in pain management and drug addiction. Investigation into the role of A118G in human disease and treatment response has generated a large number of association studies across various disease states as well as physiological responses. However, characterizing the functional consequences of this SNP and establishing if it causes or contributes to disease phenotypes have been significant challenges. In this manuscript, we will review a number of association studies as well as investigations of the functional impact of this gene variant. In addition, we will describe a novel mouse model that was generated to recapitulate this SNP in mice. Evaluation of models that incorporate known human genetic variants into a tractable system, like the mouse, will facilitate the understanding of discrete contributions of SNPs to human disease.

Association of the functional A118G polymorphism of OPRM1 in diabetic patients with foot ulcer pain

BACKGROUND

Diabetic foot ulcer (DFU) patients may experience moderate or severe pain. A single-nucleotide polymorphism, at nucleotide 118 for opioid receptor mu 1 (OPRM1), has been reported to alter the opioid effects to relieve acute or chronic pain. The purpose of this study was to elucidate the correlation between nucleotide 118 variants and foot ulcer pain in DFU patients.

METHODS

Sixty-five DFU patients with Grade 2-5 Wagner-Meggitt classification were enrolled. The occurrence of pain in activities was categorized into five grades. Patients were allocated either into the painless DFU group, with a visual analog scale (VAS) pain score <or=3, or into the painful DFU group, with a VAS pain score >or=4 and Grades 3-5 of occurrence of pain in daily activities. DNA was extracted from blood samples of analyzed patients. Using the polymerase chain reaction-single-strand conformation polymorphism analysis and DNA sequencing of nucleotide 118, we identified the genotype distribution and allelic frequencies in DFU patients. The sequences of the forward and the reverse primer are designed as follows: 5'-TAATACGACTCACTATAGGG-3' and 5'-ACGCACACGATGGAGTAGAG-3', respectively.

RESULTS

Fifteen patients were classified into the painful DFU group and 50 patients were classified into the painless DFU group. The amplified DNA fragments showed 26 homozygous (AA), 34 heterozygous (AG), and 5 mutant homozygous (GG) genotypes, with overall A and G allelic frequencies of 66.2% and 33.8%, respectively. The painful DFU group included 10 AA subjects, 4 AG subjects, and 1 GG subject, while the painless DFU group had 16 AA, 30 AG, and 4 GG subjects (P=.038).

CONCLUSION

The A118G polymorphism of mu-opioid receptor may be closely associated with DFU pain in 34 out of 50 patients in the painless group and in 5 out of 15 patients in the painful group. This indicates that the nucleotide 118 variant patients may suffer less DFU pain.

Polymorphism of the micro-opioid receptor gene (OPRM1 118A>G) affects fentanyl-induced analgesia during anesthesia and recovery

BACKGROUND

There is much variation in the response of both individuals and different ethnic populations to opioids, with genetic differences being responsible for interindividual variation. The micro-opioid receptor single nucleotide polymorphism (rs number 1799971) at nucleotide position 118 (OPRM1 118A>G) affects the analgesic response to opioids.

OBJECTIVE

This study aimed to investigate the association between the OPRM1 118A>G polymorphism and the effects of fentanyl-induced analgesia, respiratory depression, and anesthetic recovery responses in a population of Han Chinese patients.

STUDY DESIGN

The study was a case series in a hospital setting, with 1 year of study and 1 year of follow-up. A total of 189 patients (92 males and 97 females; American Society of Anesthesiologists Physical Status I or II, Glasgow Coma Scale = 15) who were scheduled for laparoscopic abdominal surgery received intravenous midazolam (Versed) 0.08-0.01 mg/kg and fentanyl (Duragesic) 5.0 microg/kg. The main outcome measure was the degree of postoperative pain, as assessed using the Visual Analog Scale (VAS). VAS scores were recorded 5, 15, 30, 45, and 60 minutes after a fentanyl bolus injection in the post-anesthesia care unit (PACU). The minute expiratory volume, end-tidal carbon dioxide concentration (EtCO(2)) and respiratory rate (RR) were measured continuously. The incidence of fentanyl-induced respiratory depression (RR <8/min and EtCO(2) >45 mmHg) was recorded at its appearance and treated with respiratory assistance. Blood gas analysis was done 15, 30, 45, and 60 minutes after extubation. These parameters were correlated with genotyping results of genomic DNA extracted from whole blood.

RESULTS

Patients with the OPRM1 118 AG or GG genotypes had significantly higher VAS pain scores 15 and 30 minutes after a fentanyl bolus injection in the PACU than AA genotype patients (p < 0.05). A small but statistically significant difference was observed between the 118 AA and 118 AG/GG genotypes with regard to the carbon dioxide arterial pressure (PaCO(2)) at 15 and 30 minutes from the fentanyl bolus injection after extubation (p < 0.05); however, no clinically significant difference in the frequency of respiratory depression was seen. Homozygous 118 GG genotype patients had a significantly shorter time to awakening (p = 0.018) and extubation (p = 0.024) than patients with the 118 AA genotype. When the 118 GG and 118 AG genotypes were combined for analysis, a significantly shorter time to awakening (p = 0.011) and extubation (p = 0.010), compared with the 118 AA genotype, was also seen.

CONCLUSION

The OPRM1 118A>G polymorphism lessens the analgesic response to fentanyl and the time to awakening and extubation but has no clinically significant effect on the incidence of respiratory depression.

Single-nucleotide polymorphism (A118G) in exon 1 of OPRM1 gene causes alteration in downstream signaling by mu-opioid receptor and may contribute to the genetic risk for addiction

The opioid receptor mu1 (OPRM1) mediates the action of morphine. Although genetic background plays an important role in the susceptibility toward abuse of drugs as evident from familial, adoption and twin studies, association of specific single-nucleotide polymorphisms of OPRM1 gene with narcotic addiction is to be established. Here, we demonstrate the involvement of A118G polymorphism of exon1 of human OPRM1 gene (hOPRM1), with heroin and alcohol addiction, in a population in eastern India. Statistical analysis exhibited a significant association of G allele with both heroin and alcohol addiction with a risk factor of P(trend) < 0.05. The functional significance of G allele in A118G single-nucleotide polymorphisms was evaluated by studying the regulation of protein kinase A (PKA), pCREB, and pERK1/2 by morphine in Neuro 2A cells, stably transfected with either wild type or A118G mutant hOPRM1. Unlike acute morphine treatment, both chronic morphine exposure and withdrawal precipitated by naloxone were differentially regulated by A118 and G118 receptor isoforms when both PKA and pERK1/2 activities were compared. Results suggest that the association of A118G polymorphism to heroin and alcohol addiction may be because of the altered regulation of PKA and pERK1/2 during opioid and alcohol exposures.

Initial evidence of an association between OPRM1 and adolescent alcohol misuse

BACKGROUND

Considerable research efforts have attempted to identify genes associated with alcoholism among adults, yet few studies have examined adolescents. Identifying genes associated with alcohol misuse in youth is important given that the relative contribution of genetic and environmental influences on alcoholism varies across development. The purpose of this study was to examine the association between a polymorphism of the mu-opioid receptor gene (OPRM1) and alcohol misuse in a sample of youth and to test whether heightened sensitivity to the reinforcing effects of alcohol mediated this relationship.

METHODS

Adolescents (n = 187; mean age = 15.4 years; 47.6% female) were genotyped for A118G (rs1799971), a single-nucleotide polymorphism (SNP) of the OPRM1 gene, and assessed for alcohol use disorder (AUD) diagnoses and other psychopathology. Alcohol misuse was also measured continuously to maximize detection of drinking problems in youth. Drinking motives were used to capture the extent to which youth consumed alcohol to enhance positive affect.

RESULTS

AUD groups differed significantly in terms of allelic distributions of the A118G SNP, such that 51.9% of youth with an AUD carried at least one copy of the G allele compared to 16.3% of non-AUD controls. Those who carried the G allele endorsed drinking to enhance positive affect more strongly than those who were homozygous for the A allele and drinking to enhance positive affect mediated the association between OPRM1 and alcohol-related problems.

CONCLUSIONS

These data build on findings from adult studies and provide the first evidence that a polymorphism of the OPRM1 receptor gene is associated with the development of early-onset alcohol-related problems during adolescence, in part, by heightening sensitivity to the reinforcing effects of alcohol.

A micro opioid receptor gene polymorphism (A118G) and naltrexone treatment response in adherent Korean alcohol-dependent patients

RATIONALE

Previous studies have demonstrated an association between genetic polymorphisms of the mu opioid receptor gene (OPRM1) and response to naltrexone treatment. The Asp40 variant genotype previously shown to be associated with naltrexone treatment response is known to be relatively common among Koreans.

OBJECTIVES

This study was conducted to prospectively investigate the relationship between genotype and response to open-label naltrexone treatment in Korean alcohol-dependent subjects.

MATERIALS AND METHODS

Sixty-three alcohol-dependent subjects were prescribed naltrexone for 12 weeks in combination with cognitive behavioral therapy. Thirty-two subjects were adherent, taking the medication at least 80% of the treatment days [16 Asn40 (A/A) patients and 16 Asp40 variant (A/G or G/G) patients].

RESULTS

Subjects adherent to naltrexone treatment with one or two copies of the Asp40 allele took a significantly longer time than the Asn40 group to relapse (p=0.014). Although not significant, the Asn40 group treated with naltrexone had a 10.6 times greater relapse rate than the Asp40 variant group. There was no significant difference between the Asn40 group and the Asp40 variant group treated with naltrexone in rates of abstinence.

CONCLUSIONS

These results demonstrating a higher therapeutic effect of naltrexone in Korean alcohol-dependent individuals with the Asp40 variant genotype than the Asn40 genotype are consistent with previous study results in individuals of European descent. This is the first study to examine the pharmacogenetics treatment response to naltrexone in non-European subjects.

The opioid peptides enkephalin and beta-endorphin in alcohol dependence

BACKGROUND

Experimental evidence indicates that the endogenous opioid system influences stress responses as well as reinforces effects of addictive drugs. Because stress is an important factor contributing to drug dependence and relapse, we have now studied ethanol preference in enkephalin- and beta-endorphin-deficient mice under baseline conditions and after stress exposure.

METHODS

In the present study we used a two-bottle choice paradigm to study ethanol consumption and stress-induced ethanol preference. To examine alcohol withdrawal symptoms the forced drinking procedure was employed. We performed an association analysis in two case-control samples of alcohol addicts to determine whether these opioid peptides also contribute to ethanol dependence in humans.

RESULTS

Ethanol consumption was significantly reduced in the absence of beta-endorphins, particularly in female knockout animals. Stress exposure results in an increased ethanol consumption in wild-type mice but did not influence ethanol-drinking in beta-endorphin knockouts. Enkephalin-deficient mice showed no difference from wild-type mice in baseline ethanol preference but also showed no stress-induced elevation of ethanol consumption. Interestingly, we found a two-marker haplotype in the POMC gene that was associated with alcohol dependence in females in both cohorts.

CONCLUSIONS

Together these results indicate a contribution of beta-endorphin to ethanol consumption and dependence.

Analgesic requirements after major abdominal surgery are associated with OPRM1 gene polymorphism genotype and haplotype

Aims: The association between SNPs of the human OPRM1 gene encoding the µ-opioid receptor and postoperative analgesic requirements in surgical patients remains controversial. Here, we evaluate whether any of the five tag SNPs (A118G, IVS2+G691C, IVS3+G5953A, IVS3+A8449G and TAA+A2109G) representing the four linkage disequilibrium blocks of the OPRM1 gene influences postoperative analgesic requirements. Materials & methods: We studied 138 adult Japanese patients who underwent major open abdominal surgery under combined general and epidural anesthesia and received continuous postoperative epidural analgesia with opioids. Results: The 118G homozygous (GG) patients required 24-h postoperative analgesics more than 118A homozygous (AA) and heterozygous (AG) patients. Tag SNP haplotypes also were associated with 24-h postoperative analgesic requirements. Conclusions: These results suggest that OPRM1 gene tag SNP genotypes and haplotypes can primarily contribute to prediction of postoperative analgesic requirements in individual patients undergoing major open abdominal surgery.

Pharmacogenetic treatments for drug addiction: alcohol and opiates

AIMS

Psychiatric pharmacogenetics involves the use of genetic tests that can predict the effectiveness of treatments for individual patients with mental illness such as drug dependence. This review aims to cover these developments in the pharmacotherapy of alcohol and opiates, two addictive drugs for which we have the majority of our FDA approved pharmacotherapies.

METHODS

We conducted a literature review using Medline searching terms related to these two drugs and their pharmacotherapies crossed with related genetic studies.

RESULTS

Alcohol's physiological and subjective effects are associated with enhanced beta-endorphin release. Naltrexone increases baseline beta-endorphin release blocking further release by alcohol. Naltrexone's action as an alcohol pharmacotherapy is facilitated by a putative functional single nucleotide polymorphism (SNP) in the opioid mu receptor gene (Al18G) which alters receptor function. Patients with this SNP have significantly lower relapse rates to alcoholism when treated with naltrexone. Caucasians with various forms of the CYP2D6 enzyme results in a 'poor metabolizer' phenotype and appear to be protected from developing opioid dependence. Others with a "ultra-rapid metabolizer" phenotype do poorly on methadone maintenance and have frequent withdrawal symptoms. These patients can do well using buprenorphine because it is not significantly metabolized by CYP2D6.

CONCLUSIONS

Pharmacogenetics has great potential for improving treatment outcome as we identify gene variants that affect pharmacodynamic and pharmacokinetic factors. These mutations guide pharmacotherapeutic agent choice for optimum treatment of alcohol and opiate abuse and subsequent relapse.

The OPRD1 and OPRK1 loci in alcohol or drug dependence: OPRD1 variation modulates substance dependence risk

Eleven single-nucleotide polymorphisms (SNPs) spanning OPRD1 were examined in 1063 European Americans (EAs) (620 cases with substance dependence (SD), including 557 with alcohol dependence (AD), 225 with cocaine dependence (CD) and 111 with opioid dependence (OD), and 443 controls). Nominally significant associations (P<0.05) of five SNPs with SD were observed; only the association of the non-synonymous variant G80T with OD remained significant after correction for multiple testing using SNPSpD. Haplotype analyses with six tag SNPs indicated that a specific haplotype GCAACT, which harbors G80T G-allele and C921T C-allele, was significantly associated with AD (chi(2)=14.82, degrees of freedom (d.f.)=1, P<0.001), CD (chi(2)=9.19, d.f.=1, P=0.002) and OD (chi(2)=20.68, d.f.=1, P<0.001). Logistic regression analyses, with sex and age being considered, demonstrated that this haplotype had a risk effect on AD (P=0.03, beta=1.86, odds ratio (OR)=6.43) and especially on OD (P<0.001, beta=3.92, OR=50.57). Moreover, seven SNPs covering OPRK1 were examined in the majority of the above subjects (390 cases, including 327 AD, 177 CD and 97 OD subjects, and 358 controls). Although no significant differences in allele, genotype or haplotype frequency distributions were seen between cases and controls, a specific OPRK1 haplotype, GGCTTCT, was significantly associated with AD (chi(2)=8.12, d.f.=1, P=0.004). Logistic regression analyses also revealed its risk effect on AD (P=0.009, beta=1.06, OR=2.90). Population stratification artifact was not observed in the sample. Taken together, our findings supported a positive association between OPRD1 variants and SD, and a positive haplotypic association between OPRK1 and AD in EAs.

Association between single nucleotide polymorphisms in the mu opioid receptor gene (OPRM1) and self-reported responses to alcohol in American Indians

BACKGROUND

Variation in response to the hedonic and adverse effects of a substance is in part an inherited factor that may influence its use, abuse and dependence. The mu opioid receptor is the primary site of action for opiates and individuals with polymorphisms in this receptor appear to have variation in the CNS effects of opiates. Several studies have suggested that this receptor may also mediate some of the effects of non-opioid drugs, such as alcohol. The purpose of this study was to investigate associations between 13 single nucleotide polymorphisms in the mu opioid receptor gene (OPRM1) with self-reported responses to alcohol, an endophenotype associated with the development of alcohol dependence, in American Indians living on eight contiguous reservations.

METHODS

Each participant gave a blood sample and completed a structured diagnostic interview. Additionally, response to alcohol was indexed using the expectation version of the subjective high assessment scale (SHAS-E). SNPs were genotyped in 251 participants and data analyses were conducted using SOLAR.

RESULTS

The estimated heritability (h2) for the SHAS-E phenotypes ranged from 0.01 to 0.28. Endorsing the expectation of a more intense response on one or more of the following items from the SHAS-E: buzzed, clumsy, dizzy, drunk, effects, high, nausea, sleepy, talkative, terrible, and/or uncomfortable after imbibing 2-3 drinks was significantly associated with having at least one minor allele for at least one of 7 SNPs (p < 0.01) in the OPRM1 receptor gene.

CONCLUSION

These studies provide data to suggest that the minor allele, for most of the polymorphisms in the OPRM1 receptor gene investigated, was found to be associated with a more intense, and/or more adverse, response to alcohol, traits that are significantly correlated with lowered quantity of alcohol consumption and less susceptibility to dependence in this Indian population. These data further suggest that making conclusions on the role of the mu opiod receptor gene in the development of alcohol dependence may be limited if only one polymorphism in the gene is evaluated in isolation.

An evaluation of mu-opioid receptor (OPRM1) as a predictor of naltrexone response in the treatment of alcohol dependence: results from the Combined Pharmacotherapies and Behavioral Interventions for Alcohol Dependence (COMBINE) study

CONTEXT

Naltrexone hydrochloride treatment for alcohol dependence works for some individuals but not for everyone. Asn40Asp, a functional polymorphism of the mu-opioid receptor gene (OPRM1), might predict naltrexone response.

OBJECTIVE

To evaluate whether individuals with alcoholism who are heterozygous (Asp40/Asn40) or homozygous (Asp40/Asp40) for the OPRM1 Asp40 allele respond better to naltrexone.

DESIGN

Pharmacogenetic analysis conducted between January 1, 2001, and January 31, 2004.

SETTING

Eleven academic sites in the COMBINE Study.

PARTICIPANTS

Recently abstinent volunteers who met all 3 of the following conditions: (1) DSM-IV criteria for primary alcohol dependence; (2) participation in the COMBINE Study; and (3) availability of DNA.

INTERVENTIONS

Alcoholic subjects were treated for 16 weeks with 100 mg of naltrexone hydrochloride (234 Asn40 homozygotes and 67 with at least 1 copy of the Asp40 allele) or placebo (235 Asn40 homozygotes and 68 with at least 1 copy of the Asp40 allele). All participants received medical management (MM) alone or with combined behavioral intervention (CBI).

MAIN OUTCOME MEASURES

Time trends in percentage of days abstinent, percentage of heavy drinking days, and rates of good clinical outcome.

RESULTS

Alcoholic subjects with an Asp40 allele receiving MM alone (no CBI) had an increased percentage of days abstinent (P = .07) and a decreased percentage of heavy drinking days (P = .04) if treated with naltrexone vs placebo, while those with the Asn40/Asn40 genotype showed no medication differences. If treated with MM alone and naltrexone, 87.1% of Asp40 carriers had a good clinical outcome, compared with only 54.8% of individuals with the Asn40/Asn40 genotype (odds ratio, 5.75; confidence interval, 1.88-17.54), while, if treated with placebo, 48.6% of Asp40 carriers and 54.0% of individuals with the Asn40/Asn40 genotype had a good clinical outcome (interaction between medication and genotype, P = .005). No gene x medication interactions were observed in those treated with both MM and CBI.

CONCLUSIONS

These results confirm and extend the observation that the functionally significant OPRM1 Asp40 allele predicts naltrexone treatment response in alcoholic individuals. This relationship might be obscured, however, by other efficacious treatments. OPRM1 genotyping in alcoholic individuals might be useful to assist in selecting treatment options.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00006206.

The single nucleotide polymorphism A118G alters functional properties of the human mu opioid receptor

The most common single nucleotide polymorphism in the coding region of the human mu opioid receptor gene is the A118G variant, an adenine to guanine transition at nucleotide position 118 of the coding sequence of the gene. This polymorphism codes for an asparagine to aspartic acid substitution at amino acid 40 in the amino-terminus, thereby removing a potential extracellular glycosylation site. Using in vitro cellular expression assays, this variant has been reported to change binding of the endogenous agonist beta-endorphin and signaling of the receptor following binding of beta-endorphin. Three clinical studies report that A118G genotype affects opioid antagonist-mediated increases in cortisol levels. These studies demonstrate a functional role of this variant in responses to endogenous and exogenous opioids. To further characterize function, we expressed the prototype and variant receptors in two types of cells (human 293 embryonic kidney cells and Syrian hamster adenovirus-12-induced tumor cells). Stable expression of variant and prototype receptors was characterized by differences in levels of cell surface binding capacity (B(max)), forskolin-induced cAMP accumulation, as well as agonist-induced accumulation of cAMP (EC(50)) for several agonists, but not for beta-endorphin. In contrast, transiently expressed variant receptors showed only a minor difference in cell surface binding capacity compared to the prototype, and no differences in cAMP EC(50) values.

The opioid system in alcohol and drug dependence: family-based association study

Opioid receptors and their endogenous peptide ligands play important roles in neurotransmission and neuromodulation in response to addictive drugs such as heroin, cocaine, and alcohol. In an earlier study, we reported that variation in the genes encoding the kappa-opioid receptor (OPRK1) and its peptide ligand (PDYN) were associated with the risk for alcoholism. We continued our investigation of the role of the opioid system in alcohol dependence by analyzing the genes encoding the micro- and delta-opioid receptors and their peptide ligands. We analyzed 18 OPRM1 SNPs, 18 OPRD1 SNPs, 7 PENK SNPs, and 7 POMC SNPs in a sample of 1923 European Americans from 219 multiplex alcohol dependent families. Employing a family-based test of association, we found no evidence that these four genes were significantly associated with alcohol dependence. We also did not find association between these genes and illicit drug dependence. Secondary analyses employing the narrower phenotype of opioid dependence (83 affected individuals) demonstrated association with SNPs in PENK and POMC, but not in OPRM1 or OPRD1. Haplotype analyses provided further support for the association of PENK and POMC with opioid dependence. Therefore, our data provide no support for the idea that variations in OPRM1, OPRD1, PENK and POMC are associated with alcohol dependence or general illicit drug dependence, but variations in PENK and POMC appear to be associated with the narrower phenotype of opioid dependence in these families.

Polymorphisms in the µ-opioid receptor gene (OPRM1) and the implications for alcohol dependence in humans

Twin and adoption studies have shown that alcohol dependence contains a substantial genetic component. In attempts to identify the genetic factors involved, association studies have linked the opioid system to alcohol dependence, with a main focus on the OPRM1 gene encoding the μ-opioid receptor. Our aim was to conduct a systematic review of the literature on the associations between polymorphisms in OPRM1 and alcohol dependence. We addressed findings of 12 studies that met our inclusion criteria. All studies employed a case–control design and included alcohol dependence as a dependent outcome measure. Our review showed that clinical studies do not unequivocally support an association between polymorphisms in OPRM1 and alcohol dependence. Factors that complicate genetic research on alcohol dependence, such as gene–environment interaction, and genetic and clinical heterogeneity, are discussed.

Modulation of Ca2+ Channels by Heterologously Expressed Wild-Type and Mutant Human μ-Opioid Receptors (hMORs) Containing the A118G Single-Nucleotide Polymorphism

The most common single-nucleotide polymorphism (SNP) of the human μ-opioid receptor (hMOR) gene occurs at position 118 (A118G) and results in substitution of asparagine to aspartate at the N-terminus. The purpose of the present study was to compare the pharmacological profile of several opioid agonists to heterologously expressed hMOR and N-type Ca2+ channels in sympathetic neurons. cDNA constructs coding for wild-type and mutant hMOR were microinjected in rat superior cervical ganglion neurons and N-type Ca2+ channel modulation was investigated using the whole cell variant of the patch-clamp technique. Concentration–response relationships were generated with the following selective MOR agonists: DAMGO, morphine, morphine-6-glucuronide (M-6-G), and endomorphin I. The estimated maximal inhibition for the agonists ranged from 52 to 64% for neurons expressing either hMOR subtype. The rank order of potencies for estimated EC50 values (nM) in cells expressing wild-type hMOR was: DAMGO (31) ≫ morphine (76) ≅ M-6-G (77) ≅ endomorphin I (86). On the other hand, the rank order in mutant-expressing neurons was: DAMGO (14) ≫ morphine (39) ≫ endomorphin I (74) ≅ M-6-G (82), with a twofold leftward shift for both DAMGO and morphine. The DAMGO-mediated Ca2+ current inhibition was abolished by the selective MOR blocker, CTAP, and by pertussis toxin pretreatment of neurons expressing either hMOR subtype. These results suggest that the A118G variant MOR exhibits an altered signal transduction pathway and may help explain the variability of responses to opiates observed with carriers of the mutant allele.

Association of mu-opioid receptor gene polymorphism A118G with alcohol dependence in a Japanese population

Ethanol is considered to activate the brain reward system by increasing the release of an endogenous opioid receptor ligand, beta-endorphin. The polymorphism A118G in the mu-opioid receptor gene (OPRM1) causes the amino acid change Asn40Asp and has been reported to affect the affinity of the ligand for the receptor. The association of this polymorphism with the vulnerability to alcohol dependence has been studied in many populations, but not yet in Japanese people. In the present study, we compared the frequencies of the polymorphism OPRM1 A118G between patients with alcohol dependence and healthy control subjects living in a Japanese provincial prefecture. We also genotyped a polymorphism, G1510A, in the acetaldehyde dehydrogenase 2 gene (ALDH2), in which the A allele causes poor metabolism of acetaldehyde, a major metabolite of alcohol. Both OPRM1 118G and ALDH2 1510G were significantly associated with alcohol dependence. These results suggest that OPRM1 118G in addition to ALDH2 1510G might be one of the risk factors for alcohol dependence in Japanese people.

Targeting treatments for alcohol dependence: the pharmacogenetics of naltrexone

Alcohol dependence is one of the leading causes of morbidity worldwide, yet only a minority of those afflicted engages in treatment. While increasing access to treatment is an important public health approach, increasing the success of treatment is also likely to lead to greater engagement. However, alcohol dependence is a complex disorder likely to consist of several biological subtypes. Recent evidence from a number of different studies has suggested that genetic variation in the mu-opioid receptor has a significant influence on clinical presentation of alcohol problems and response to treatment with an opioid antagonist. Most notably, the A118G polymorphism of the mu-receptor gene has been demonstrated to predict clinical response to naltrexone in alcohol-dependent individuals. This article reviews the biological correlates and outlines a scientific agenda for better understanding the role of opioid neurotransmission in the etiology, maintenance and treatment of alcohol dependence.

Association of an Asn40Asp (A118G) polymorphism in the mu-opioid receptor gene with substance dependence: a meta-analysis

INTRODUCTION

The mu-opioid receptor has been implicated in the pathogenesis of dependence on opioids, alcohol, nicotine, and cocaine. Studies examining the association of the mu-opioid receptor gene (genetic locus OPRM1) with substance dependence (SD) have focused on the Asn40Asp (A118G) single nucleotide polymorphism (SNP).

METHOD

We used meta-analysis to examine the literature on the association of Asn40Asp with SD. Twenty-two articles describing 28 distinct samples and over 8000 subjects were included. A variety of factors (i.e., ethnicity, type of SD, rigor with which controls were screened, severity of SD among cases) were examined as potential moderators of the association.

RESULTS

Four studies showed a significantly higher frequency of the Asp40 allele among SD cases, while three studies showed a significantly higher frequency of the Asp40 allele among controls. There was no significant association between Asn40Asp and SD (OR=1.01, 95%CI=0.86-1.19), nor was there substantial evidence of a moderator effect.

CONCLUSION

The Asn40Asp SNP in OPRM1 does not appear to affect risk for SD. Additional research is needed to determine whether these findings reflect no role for OPRM1 in determining risk for SD or whether another polymorphism in the gene influences receptor function and risk for SD.

New findings on the genetic influences on alcohol use and dependence

PURPOSE OF REVIEW

Alcohol dependence is a complex disorder with a well documented highly hereditary nature. This article reviews the recent advances in our understanding of the direct and indirect genetic influences on alcohol use and dependence.

RECENT FINDINGS

Recent findings can be summarized as follows: (a) twin studies have defined and estimated the risks of general and specific alcohol-related vulnerabilities. (b) Linkage studies have provided largely inconsistent findings, though several chromosomal regions have been implicated. (c) Quantitative trait loci analyses in animals have identified that the Mpdz gene predisposes to alcohol dependence and withdrawal. (d) Examination of family-based samples has identified several genes including GABRA2 and CHRM2 thought to be associated with alcohol dependence.

SUMMARY

Despite great advances in understanding of genetic vulnerability in alcohol use disorders, only two gene complexes, ADH and ALDH2, have been identified as having defined effects on alcohol use and liability to dependence in humans. New genes associated with increased risks for the disorder will certainly be added to this list in the near future. Neurobiological analyses of the effects of these genes will surely contribute to further understanding of the cause of alcohol dependence and the interindividual differences in risks.

Pharmacotherapy for alcohol dependence: anticraving medications for relapse prevention

Alcohol dependence is a chronic disorder that results from a variety of genetic, psychosocial, and environmental factors. Relapse prevention for alcohol dependence has traditionally involved psychosocial and psychotherapeutic interventions. Pharmacotherapy, however, in conjunction with behavioral therapy, is generating interest as another modality to prevent relapse and enhance abstinence. Naltrexone and acamprosate are at the forefront of the currently available pharmacological options. Naltrexone is an opioid receptor antagonist and is thought to reduce the rewarding effect of alcohol. Acamprosate normalizes the dysregulation of N-methyl-D- aspartate (NMDA)-mediated glutamatergic excitation that occurs in alcohol withdrawal and early abstinence. These different mechanisms of action and different target neurotransmitter systems may endow the two drugs with efficacy for different aspects of alcohol use behavior. Since not all patients seem to benefit from naltrexone and acamprosate, there are ongoing efforts to improve the treatment outcomes by examining the advantages of combined pharmacotherapy and exploring the variables that might predict the response of the medications. In addition, novel medications are being investigated to assess their efficacy in preventing relapse and increasing abstinence.

Association between two mu-opioid receptor gene (OPRM1) haplotype blocks and drug or alcohol dependence

We examined 13 single nucleotide polymorphisms (SNPs) spanning the coding region of the mu-opioid receptor gene (OPRM1), among 382 European Americans (EAs) affected with substance dependence [alcohol dependence (AD) and/or drug dependence (DD)] and 338 EA healthy controls. These SNPs delineated two haplotype blocks. Genotype distributions for all SNPs were in Hardy-Weinberg equilibrium (HWE) in controls, but in cases, four SNPs in Block I and three SNPs in Block II showed deviation from HWE. Significant differences were found between cases and controls in allele and/or genotype frequencies for six SNPs in Block I and two SNPs in Block II. Association of SNP4 in Block I with DD (allele: P=0.004), SNP5 in Block I with AD and DD (allele: P< or =0.005 for both) and two SNPs in Block II with AD (SNP11 genotype: P=0.002; SNP12 genotype: P=0.001) were significant after correction for multiple testing. Frequency distributions of haplotypes (constructed by five tag SNPs) differed significantly for cases and controls (P<0.001 for both AD and DD). Logistic regression analyses confirmed the association between OPRM1 variants and substance dependence, when sex and age of subjects and alleles, genotypes, haplotypes or diplotypes of five tag SNPs were considered. Population structure analyses excluded population stratification artifact. Additional supporting evidence for association between OPRM1 and AD was obtained in a smaller Russian sample (247 cases and 100 controls). These findings suggest that OPRM1 intronic variants play a role in susceptibility to AD and DD in populations of European ancestry.