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Two commonly prescribed treatments for opioid addiction are methadone and buprenorphine. Although these drugs show some efficacy in treating opioid dependence, treatment response varies among individuals. It is likely that genetic factors have a role in determining treatment outcome. This study analyses the pharmacogenetic association of six polymorphisms in OPRD1, the gene encoding the delta-opioid receptor, on treatment outcome in 582 opioid addicted European Americans randomized to either methadone or buprenorphine/naloxone (Suboxone) over the course of a 24-week open-label clinical trial. Treatment outcome was assessed as the number of missed or opioid-positive urine drug screens over the 24 weeks. In the total sample, no single-nucleotide polymorphisms (SNPs) in OPRD1 were significantly associated with treatment outcome in either treatment arm. However, sex-specific analyses revealed two intronic SNPs (rs581111 and rs529520) that predicted treatment outcome in females treated with buprenorphine. Females with the AA or AG genotypes at rs581111 had significantly worse outcomes than those with the GG genotype when treated with buprenorphine (P=0.03, relative risk (RR)=1.67, 95% confidence interval (CI) 1.06-2.1). For rs529520, females with the AA genotype had a significantly worse outcome than those with the CC genotype when (P=0.006, RR=2.15, 95% CI 1.3-2.29). No significant associations were detected in males. These findings suggest that rs581111 and rs52920 may be useful when considering treatment options for female opioid addicts, however, confirmation in an independent sample is warranted.

Background: Addiction susceptibility and treatment responsiveness are greatly influenced by genetic factors. Sequence variation in genes involved in the mechanisms of drug action have the potential to influence addiction risk and treatment outcome. The opioid receptor system is involved in mediating the rewarding effects of cocaine and opioids. The μ-opioid receptor (MOR) has traditionally been considered the primary target for opioid addiction. The MOR, however, interacts with and is regulated by many known MOR interacting proteins (MORIPs), including the δ-opioid receptor (DOR).Methods: The present study evaluated the contribution of OPRD1, the gene encoding the DOR, to the risk of addiction to opioids and cocaine. The association of OPRD1 polymorphisms with both opioid addiction (OA) and cocaine addiction (CA) was analyzed in African American (OA n=336, CA n=503) and European American (OA n=1007, CA n=336) populations.Results: The primary finding of this study is an association of rs678849 with cocaine addiction in African Americans (allelic p=0.0086). For replication purposes, this SNP was analyzed in a larger independent population of cocaine addicted African Americans and controls and the association was confirmed (allelic p=4.53 × 10(-5); n=993). By performing a meta-analysis on the expanded populations, the statistical evidence for an association was substantially increased (allelic p=8.5 × 10(-7)) (p-values non-FDR corrected).Conclusion: The present study suggests that polymorphisms in OPRD1 are relevant for cocaine addiction in the African American population and provides additional support for a broad role for OPRD1 variants in drug dependence. [ABSTRACT FROM AUTHOR]

Although buprenorphine and methadone are both effective treatments for opioid dependence, their efficacy can vary significantly among patients. Genetic differences may explain some of the variability in treatment outcome. Understanding the interactions between genetic background and pharmacotherapy may result in more informed treatment decisions. This study is a pharmacogenetic analysis of the effects of genetic variants in OPRD1, the gene encoding the δ-opioid receptor, on the prevalence of opioid-positive urine tests in African-Americans (n=77) or European-Americans (n=566) undergoing treatment for opioid dependence. Patients were randomly assigned to treatment with either methadone or buprenorphine/naloxone (Suboxone) over a 24-week open-label clinical trial, in which illicit opioid use was measured by weekly urinalysis. In African-Americans, the intronic SNP rs678849 predicted treatment outcome for both medications. Methadone patients with the CC genotype were less likely to have opioid-positive urine tests than those in the combined CT and TT genotypes group (relative risk (RR)=0.52, 95% confidence interval (CI)=0.44-0.60, p=0.001). In the buprenorphine treatment group, however, individuals with the CC genotype were more likely to have positive opioid drug screens than individuals in the combined CT and TT genotypes group (RR=2.17, 95% CI=1.95-2.68, p=0.008). These findings indicate that the genotype at rs678849 predicts African-American patient response to two common treatments for opioid dependence, suggesting that matching patients to treatment type based on the genotype at this locus may improve overall treatment efficacy. This observation requires confirmation in an independent population.

Genetic research on cocaine dependence (CD) may help clarify our understanding of the disorder as well as provide insights for effective treatment. As endocannabinoid signaling and dopamine neurotransmission have been shown to be involved in drug reward, genes related to these systems are plausible candidates for susceptibility to CD. The cannabinoid receptor 1 protein regulates both the endocannabinoid and dopaminergic neurobiological systems, and polymorphisms in the cannabinoid receptor gene, CNR1, have been associated previously with substance dependence. In this study, we attempt to replicate findings associating CNR1 with CD in African Americans. Cocaine-addicted individuals (n=860) and unaffected controls (n=334) of African descent were genotyped for two single nucleotide polymorphisms (SNPs) in CNR1 (rs6454674, rs806368). We observed a significant difference in genotype frequencies between cases and controls for both SNPs (P≤0.042). A meta-analysis was also performed combining our data with that of Zuo et al. who also studied these polymorphisms in African American cocaine addicts (total n=1253 cases versus 543 controls). When our data were combined, rs6454674 increased in significance to P=0.027; however, rs806368 was no longer significant. This study confirms the association between rs6454674 and CD. However, because there is considerable co-morbidity of CD with other drugs of abuse, additional studies are necessary to determine whether polymorphisms in CNR1 induce a general susceptibility to substance dependence or are specific to cocaine addiction. Furthermore, as this population consists of American individuals of African descent, the possibility of population stratification should not be excluded., (© 2011 The Authors, Addiction Biology © 2011 Society for the Study of Addiction.)

The opioid receptor family is involved in the development and maintenance of drug addiction. The mu-opioid receptor (MOR) mediates the rewarding effects of multiple drugs, including opiates and cocaine. A number of proteins interact with MOR, potentially modulating MOR function and altering the physiological consequences of drug use. These mu-opioid receptor interacting proteins (MORIPs) are potential therapeutic targets for the treatment of addiction. The Wntless (WLS) protein was recently identified as a MORIP in a yeast two-hybrid screen. In this study, we conducted a case-control association analysis of 16 WLS genetic variants in opioid and cocaine addicted individuals of both African-American (opioid n=336, cocaine n=908) and European-American (opioid n=335, cocaine n=336) ancestry. Of the analyzed SNPs, three were nominally associated with opioid addiction and four were nominally associated with cocaine addiction. None of these associations were significant following multiple testing correction. These data suggest that the common variants of WLS analyzed in this study are not associated with opioid or cocaine addiction. However, this study does not exclude the possibilities that rare variants in WLS may affect susceptibility to drug addiction, or that common variants with small effect size may fall below the detection level of our analysis., (Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.)

The rewarding properties of drugs of abuse are mediated by the mu-opioid receptor (MOR). Genetic variations in MOR and MOR interacting proteins (MORIPs) involved in MOR signaling may increase the risk for drug dependence. The MORIP β-arrestin plays an important role in the regulation of MOR trafficking, thereby highlighting it as a candidate gene for addiction phenotypes. In this case-control association study, DNA samples from cocaine-dependent (n=336) and opioid-dependent (n=335) patients and controls (n=656) were genotyped for seven single nucleotide polymorphisms (rs11868227, rs3786047, rs4522461, rs1045280, rs2271167, rs2036657, and rs4790694) across ARRB2, the gene encoding the β-arrestin 2 protein. No significant differences were observed in genotype or allele frequency between drug-dependent and control individuals for any of the single nucleotide polymorphisms analyzed. Haplotype analysis was similarly negative. Further studies are needed to determine whether variations in ARRB2 (or other MORIPs) are relevant to cocaine or opioid dependence in different ethnic populations or whether they confer a risk that is specific to dependence on other drugs of abuse.

Sex differences in cocaine addiction warrants further research focused on examining the growing population of female cocaine addicts. As demonstrated in both clinical and preclinical research, females are more susceptible to drug relapse with anxiety being a contributing factor. In support of this, a recent clinical study from our laboratory highlights the importance of menstrual cycle phase and anxiety at treatment admission for cocaine addiction on treatment retention. In support of these trends in the clinical population, the purpose of the present study was to design an animal model to directly test the role of circulating hormone levels during cocaine withdrawal. To directly measure the influence of estrogen on anxiety-like behavior during early stages of withdrawal, both ovariectomized and intact female rodent models were employed. The elevated-plus maze and elevated-zero maze were used to assess anxiety-like behavior. Recent evidence in male rodents highlights a potential role for the delta opioid-receptor (DOR) system in the modulation of cocaine withdrawal-induced anxiety. In addition to the evaluation of hormonal effects, a potential anxiolytic specific for DOR was tested for its efficacy in females withdrawn from cocaine. Our results support the use of DOR agonists as a potential anxiolytic in females and highlight the importance of estrogen and other circulating hormones during all phases of cocaine addiction.

Drug abuse among women is a societal health problem which has received greater attention in recent years. Studies examining sex differences in drug abuse have shown consistent differences between males and females. In the current study, we retrospectively examined 75 treatment-seeking females to determine the relationships between intake measurements of psychopathology, intake urinalysis, menstrual cycle phase at admission, and treatment compliance. Our results support a relationship among these variables and a potential relationship between menstrual cycle phase and anxiety level is discussed. These results support the need for the development of individually tailored treatment programs.

Interactions between the opioidergic and dopaminergic systems in the nucleus accumbens (NAcb) play a critical role in mediating cocaine withdrawal-induced effects on cell signaling and behavior. In support of this, increased activation of striatal dopamine-D1 receptors (D1R) results in desensitization of delta-opioid receptor (DOR) signaling through adenylyl cyclase during early cocaine withdrawal. A potential cellular substrate underlying receptor desensitization is receptor internalization. The present study examined the effect of cocaine withdrawal on subcellular localization of DOR in dendrites of the NAcb core (NAcbC) and shell (NAcbS) using immunoelectron microscopy. Female and male rats received binge-pattern cocaine or saline for 14 days and subsequently underwent 48 h withdrawal. Animals were transcardially perfused and tissue sections were processed for immunogold-silver localization of DOR. Semi-quantitative analysis revealed that cocaine withdrawal caused an increase in the percentage of DOR localized intracellularly in the NAcbS of male and female rats and the NAcbC of male rats compared to saline controls. In contrast, in the NAcbC of female rats, there was an increase in DOR associated with the plasma membrane following cocaine withdrawal. To determine whether modulation of D1R could directly impact DOR containing neurons, the hypothesis that DOR and D1R co-exist in common neurons of the NAcb was examined in naïve rats. Semi-quantitative analysis revealed a subset of profiles containing both DOR and D1R immunoreactivities. The present findings demonstrate a redistribution of DOR in the NAcb following cocaine withdrawal and provide anatomical evidence supporting D1R regulation of DOR function in a subset of NAcb neurons.