Contribution of Genetic Polymorphisms and Haplotypes in DRD2, BDNF, and Opioid Receptors to Heroin Dependence and Endophenotypes Among the Han Chinese

Methylation and expression quantitative trait loci rs1799971 in the OPRM1 gene and rs4654327 in the OPRD1 gene are associated with opioid use disorder

Opioid use disorder (OUD) is a chronic and relapsing brain disease that results in significant mortality worldwide. Genetic factors are estimated to contribute to 40%-60% of the liability, with polymorphisms of opioid receptor genes implicated in this disorder. However, the mechanisms underlying these associations are not yet fully understood. In the present study, we first examined the methylation levels in the promoter region of the OPRM1, OPRD1, and OPRK1 genes in 111 healthy controls (HCs) and 120 patients with OUD, and genotyped three tag SNPs in these genes. Correlations between these SNPs and the methylation levels of the CpG sites and expression levels of the genes were analyzed. After identifying the mQTLs and eQTLs, we determined the associations between the mQTLs/eQTLs and susceptibility to and characteristics of OUD in 930 HCs and 801 patients with OUD. Our results demonstrated that SNPs rs1799971 in the OPRM1 gene and rs4654327 in the OPRD1 gene were both mQTLs and eQTLs. We observed unique correlations between mQTLs and methylation levels of several CpG sites in the OUD group compared to the HC group. Interestingly, both the two mQTLs and eQTLs were associated with the susceptibility to OUD. In conclusion, we suppose that mQTLs and eQTLs in genes may underlie the associations between certain risk genetic polymorphisms and OUD. These mQTLs and eQTLs could potentially serve as promising biomarkers for better management of opioid misuse.

Associated and intermediate factors between genetic variants of the dopaminergic D2 receptor gene and harmful alcohol use in young adults

Dopamine receptor D2 (DRD2) and ankyrin repeat and kinase domain-containing protein 1 (ANKK1) genes have received considerable attention for their involvement in alcohol use disorder (AUD), but many questions remain on their exact role. We conducted a population-based case-control and genetic association study in a large sample of young adults. Our aim was to assess the association between DRD2 and ANKK1 single nucleotide polymorphisms (SNPs) and harmful alcohol use, disentangling associated and possible intermediate factors. A total of 1841 college students from the French region Champagne-Ardennes, aged between 18 and 21 years and who reported at least one lifetime alcohol consumption, were included in this study. Allele frequencies were analysed according to harmful alcohol use (assessed through the Alcohol Use Disorder Identification Test [AUDIT] questionnaire). Different substance use disorders, including nicotine and cannabis dependences, were also assessed through questionnaires, as was a list of potential associated factors (e.g., major depressive episode, conduct disorder, attention-deficit/hyperactivity disorder [ADHD], school failure, sugar consumption, sexual trauma, parents' use of alcohol, tobacco or cannabis). We found that DRD2 rs1800498 was associated with harmful alcohol use. Many factors were detected, but a global path analysis revealed that DRD2 rs1800498 had a significant direct effect on harmful alcohol use and that early age at first alcohol consumption and depressive symptoms moderated this effect. This study suggests an interplay between harmful alcohol use, DRD2 genotypes and other risk factors that, with a full understanding, could be useful for preventive purposes.

Effects of OPRM1 and DRD2 on brain structure in drug-naïve adolescents: Genetic and neural vulnerabilities to substance use

Genetic variants in the opioid receptor mu 1 (OPRM1) and dopamine receptor d2 (DRD2) genes are implicated in behavioral phenotypes related to substance use disorders (SUD). Despite associations among OPRM1 (rs179971) and DRD2 (rs6277) genes and structural alterations in neural reward pathways implicated in SUDs, little is known about the contribution of risk-related gene variants to structural neurodevelopment. In a 3-year longitudinal study of initially SU-naïve adolescents (N = 129; 70 females; 11-14 years old), participants underwent an MRI structural scan at baseline and provided genetic assays for OPRM1 and DRD2 with SU behavior assessed during follow-up visits. Baseline differences in key reward-related brain regions (i.e., bilateral caudate and cingulate cortex) were detected in those with genetic liability for SU in OPRM1 who went onto engage in SU at subsequent waves of data collection. In addition, main effects of OPRM1, DRD2, and SU were related to variability in structure of the putamen, anterior cingulate, and nucleus accumbens, respectively. These data provide preliminary evidence that genetic risk factors interact with future SU to confer structural variability prior to SU in regions commonly implicated in risk for SU and the development of SUDs.

OPRD1 SNPs associated with opioid addiction are cis-eQTLs for the phosphatase and actin regulator 4 gene, PHACTR4, a mediator of cytoskeletal dynamics

Several OPRD1 intronic variants were associated with opioid addiction (OD) in a population-specific manner. This follow-up study aims to further characterize the OPRD1 haplotype pattern of the risk variants in different populations and apply in silico analysis to identify potential causal variants. A population-specific haplotype pattern was revealed based on six OPRD1 eQTL SNPs and five common haplotypes were identified in a sample of European ancestry (CEU). A European-specific haplotype ('Hap 3') that includes SNPs previously associated with OD and is tagged by SNP rs2236861 is more common in subjects with OD. It is quite common (10%) in CEU but is absent in the African sample (YRI) and extends upstream of OPRD1. SNP rs2236857 is most probably a non-causal variant in LD with the causal SNP/s in a population-specific manner. The study provides an explanation for the lack of association in African Americans, despite its high frequency in this population. OD samples homozygous for 'Hap 3' were reanalyzed using a denser coverage of the region and revealed at least 25 potentially regulatory SNPs in high LD. Notably, GTEx data indicate that some of the SNPs are eQTLs for the upstream phosphatase and actin regulator 4 (PHACTR4), in the cortex, and others are eQTLs for OPRD1 and the upstream lncRNA ENSG00000270605, in the cerebellum. The study highlights the limitation of single SNP analysis and the sensitivity of association studies of OPRD1 to a genetic background. It proposes a long-range functional connection between OPRD1 and PHACTR4. PHACTR4, a mediator of cytoskeletal dynamics, may contribute to drug addiction by modulating synaptic plasticity.

AddictGene: An integrated knowledge base for differentially expressed genes associated with addictive substance

Addiction, a disorder of maladaptive brain plasticity, is associated with changes in numerous gene expressions. Nowadays, high-throughput sequencing data on addictive substance-induced gene expression have become widely available. A resource for comprehensive annotation of genes that show differential expression in response to commonly abused substances is necessary. So, we developed AddictGene by integrating gene expression, gene-gene interaction, gene-drug interaction and epigenetic regulatory annotation for over 70,156 items of differentially expressed genes associated with 7 commonly abused substances, including alcohol, nicotine, cocaine, morphine, heroin, methamphetamine, and amphetamine, across three species (human, mouse, rat). We also collected 1,141 addiction-related experimentally validated genes by techniques such as RT-PCR, northern blot and in situ hybridization. The easy-to-use web interface of AddictGene (http://159.226.67.237/sun/addictgedb/) allows users to search and browse multidimensional data on DEGs of their interest: 1) detailed gene-specific information extracted from the original studies; 2) basic information about the specific gene extracted from NCBI; 3) SNP associated with substance dependence and other psychiatry disorders; 4) expression alteration of specific gene in other psychiatric disorders; 5) expression patterns of interested gene across 31 primary and 54 secondary human tissues; 6) functional annotation of interested gene; 7) epigenetic regulators involved in the alteration of specific genes, including histone modifications and DNA methylation; 8) protein-protein interaction for functional linkage with interested gene; 9) drug-gene interaction for potential druggability. AddictGene offers a valuable repository for researchers to study the molecular mechanisms underlying addiction, and might provide valuable insights into potential therapies for drug abuse and relapse.

Identification of a sex-stratified genetic algorithm for opioid addiction risk

The opioid epidemic has had a devastating impact on our country, with wide-ranging effects on healthcare, corrections, employment, and social systems. Programs have been put in place for monitoring prescriptions, initiating and expanding medications for opioid use disorder, and harm reduction (i.e., naloxone distribution, needle exchanges). However, opportunities for personalization of opioid therapy based on addiction risk have been limited. The goal of the present study was to develop an objective risk assessment algorithm based on genetic markers that are correlated with opioid use disorder (OUD). A total of 180 single-nucleotide polymorphisms (SNPs) were tested in patients with and without OUD. SNPs selected for testing were associated with opioid metabolism and drug reward pathways based on previous studies. Of the 394 patients recruited, 200 had OUD and 194 served as controls without OUD but with prior opioid exposure. Logistic regression analyses stratified by sex identified ten unique SNPs in females and nine unique SNPs in males that were significantly associated with OUD. A Genetics Opioid Risk Score (GenORs) was calculated by counting the number of OUD risk-associated SNPs/genotypes for each patient. To evaluate the discrimination of the GenORs, a receiver operating characteristic (ROC) curve for each sex was generated and determined to be sensitive and specific. This represents the first published example of a sex-based genetic risk score with potential to predict OUD, and the first OUD algorithm to include opioid-associated pharmacokinetic genes.

Expression of Dopamine-Related Genes in Four Human Brain Regions

A better understanding of dopaminergic gene expression will inform future treatment options for many different neurologic and psychiatric conditions. Here, we utilized the National Institutes of Health’s Genotype-Tissue Expression project (GTEx) dataset to investigate genotype by expression associations in seven dopamine pathway genes (ANKK1, DBH, DRD1, DRD2, DRD3, DRD5, and SLC6A3) in and across four human brain tissues (prefrontal cortex, nucleus accumbens, substantia nigra, and hippocampus). We found that age alters expression of DRD1 in the nucleus accumbens and prefrontal cortex, DRD3 in the nucleus accumbens, and DRD5 in the hippocampus and prefrontal cortex. Sex was associated with expression of DRD5 in substantia nigra and hippocampus, and SLC6A3 in substantia nigra. We found that three linkage disequilibrium blocks of SNPs, all located in DRD2, were associated with alterations in expression across all four tissues. These demographic characteristic associations and these variants should be further investigated for use in screening, diagnosis, and future treatment of neurological and psychiatric conditions.

The opioid crisis: a contextual, social-ecological framework

The prevalence of opioid use and misuse has provoked a staggering number of deaths over the past two and a half decades. Much attention has focused on individual risks according to various characteristics and experiences. However, broader social and contextual domains are also essential contributors to the opioid crisis such as interpersonal relationships and the conditions of the community and society that people live in. Despite efforts to tackle the issue, the rates of opioid misuse and non-fatal and fatal overdose remain high. Many call for a broad public health approach, but articulation of what such a strategy could entail has not been fully realised. In order to improve the awareness surrounding opioid misuse, we developed a social-ecological framework that helps conceptualise the multivariable risk factors of opioid misuse and facilitates reviewing them in individual, interpersonal, communal and societal levels. Our framework illustrates the multi-layer complexity of the opioid crisis that more completely captures the crisis as a multidimensional issue requiring a broader and integrated approach to prevention and treatment.

Genomics testing and personalized medicine in the preoperative setting: Can it change outcomes in postoperative pain management?

Postoperative pain and opioid use are major challenges in perioperative medicine. Pain perception and its response to opioid use are multi-faceted and include pharmacological, psychological, and genetic components. Precision medicine is a unique approach to individualized health care in which decisions in management are based on genetics, lifestyle, and environment of each person. Genetic variations can have an impact on the perception of pain and response to treatment. This can have an effect on pain management in both acute and chronic settings. Although there is currently not enough evidence for making recommendations about genetic testing to guide pain management in the acute care setting, there are some known polymorphisms that play a role in surgical pain and opioid-related postoperative adverse outcomes. In this review, we describe the potential use of pharmacogenomics (PGx) for improving perioperative pain management. We first review a number of genotypes that have shown correlations with pain and opioid use and then describe the importance of PGx-guided analgesic protocols and implementation of screening in a preoperative evaluation clinical setting.

Dopamine Receptor DRD2 Gene rs1076560, Personality Traits and Anxiety in the Polysubstance Use Disorder

Development of an addiction is conditioned by many factors. The dopaminergic system has been shown to be the key element in this process. In this paper, we analyzed the influence of dopamine receptor 2 polymorphism rs1076560 in two groups—polysubstance-dependent male patients (n = 299) and the controls matched for age (n = 301). In both groups, we applied the same questionnaires for testing—Mini-international neuropsychiatric interview, the NEO Five-Factor Inventory, and the State–Trait Anxiety Inventory. The real-time PCR method was used for genotyping. When we compared the controls with the case group subjects, we observed significantly higher scores in the second group on both the state and trait scales of anxiety, as well as on the Neuroticism and Openness scales of the NEO-FFI; and lower scores on the scales of Extraversion and Agreeability of the NEO-FFI. The model 2 × 3 factorial ANOVA of the addicted subjects and controls was performed, and the DRD2 rs1076560 variant interaction was found for the anxiety state and trait scales, and for the NEO-FFI Neuroticism scale. The observed associations allow noticing that analysis of psychological factors in combination with genetic data opens new possibilities in addiction research.

Endogenous opiates and behavior: 2017

This paper is the fortieth consecutive installment of the annual anthological review of research concerning the endogenous opioid system, summarizing articles published during 2017 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides and receptors as well as effects of opioid/opiate agonists and antagonists. The review is subdivided into the following specific topics: molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors (1), the roles of these opioid peptides and receptors in pain and analgesia in animals (2) and humans (3), opioid-sensitive and opioid-insensitive effects of nonopioid analgesics (4), opioid peptide and receptor involvement in tolerance and dependence (5), stress and social status (6), learning and memory (7), eating and drinking (8), drug abuse and alcohol (9), sexual activity and hormones, pregnancy, development and endocrinology (10), mental illness and mood (11), seizures and neurologic disorders (12), electrical-related activity and neurophysiology (13), general activity and locomotion (14), gastrointestinal, renal and hepatic functions (15), cardiovascular responses (16), respiration and thermoregulation (17), and immunological responses (18).

Genetic polymorphisms in the opioid receptor delta 1 (OPRD1) gene are associated with methadone dose in methadone maintenance treatment for heroin dependence

Delta opioid receptor (DOR) is well known to be involved in heroin dependence. This study tested the hypothesis that single nucleotide polymorphisms (SNPs) in the opioid receptor delta 1 (OPRD1) gene coding region are associated with treatment responses in a methadone maintenance therapy (MMT) cohort in Taiwan. Three hundred forty-four MMT patients were recruited. Diastolic/systolic blood pressure, heart rate, methadone dosage, and plasma concentrations of methadone were recorded. Twenty-five SNPs located within the OPRD1 genetic region were selected and genotyped from the genomic DNA of all 344 participants. After pairwise tagger analyses, tagger SNP rs204047 showed a significant association with methadone dosage (P = 0.0019), and tagger SNPs rs204047 and rs797397 were significantly associated with plasma R, S-methadone concentrations (P < 0.0006) in patients tested negative in the urine morphine test, which indicated patients with a better response to MMT. The major genotype carriers showed a higher methadone dosage and higher plasma concentrations of R, S-methadone than the minor genotype carriers. The results indicated that OPRD1 genetic variants were associated with methadone dosage and methadone plasma concentration in MMT patients with a negative morphine test result.

Members of the same pharmacological family are not alike: Different opioids, different consequences, hope for the opioid crisis?

Pain management is the specialized medical practice of modulating pain perception and thus easing the suffering and improving the life quality of individuals suffering from painful conditions. Since this requires the modulation of the activity of endogenous systems involved in pain perception, and given the large role that the opioidergic system plays in pain perception, opioids are currently the most effective pain treatment available and are likely to remain relevant for the foreseeable future. This contributes to the rise in opioid use, misuse, and overdose death, which is currently characterized by public health officials in the United States as an epidemic. Historically, the majority of preclinical rodent studies were focused on morphine. This has resulted in our understanding of opioids in general being highly biased by our knowledge of morphine specifically. However, recent in vitro studies suggest that direct extrapolation of research findings from morphine to other opioids is likely to be flawed. Notably, these studies suggest that different opioid analgesics (opioid agonists) engage different downstream signaling effects within the cell, despite binding to and activating the same receptors. This recognition implies that, in contrast to the historical status quo, different opioids cannot be made equivalent by merely dose adjustment. Notably, even at equianalgesic doses, different opioids could result in different beneficial and risk outcomes. In order to foster further translational research regarding drug-specific differences among opioids, here we review basic research elucidating differences among opioids in pharmacokinetics, pharmacodynamics, their capacity for second messenger pathway activation, and their interactions with the immune system and the dopamine D2 receptors.

Four single nucleotide polymorphisms in genes involved in neuronal signaling are associated with Opioid Use Disorder in West Virginia

Objective

Pilot study to assess utility in opioid use disorder (OUD) of a panel of single nucleotide polymorphisms in genes previously related to substance use disorder (SUD) and/or phenotypes that predispose individuals to OUD/SUD.

Design

Genetic association study.

Setting

West Virginia University's Chestnut Ridge Center Comprehensive Opioid Abuse Treatment (COAT) clinic for individuals diagnosed with OUD.

Patients

Sixty patients 18 years of age or older with OUD undergoing medication (buprenorphine/naloxone)-assisted treatment (MAT); all sixty patients recruited contributed samples for genetic analysis.

Outcome Measures

Minor allele frequencies for single nucleotide polymorphisms.

Results

Four of the fourteen single nucleotide polymorphisms examined were present at frequencies that are statistically significantly different than in a demographically-matched general population.

Conclusions

For the purposes of testing WV individuals via genetic means for predisposition to OUD, at least four single nucleotide polymorphisms in three genes are likely to have utility in predicting susceptibility. Additional studies with larger populations will need to be conducted to confirm these results before use in a clinical setting.

OPRD1 gene affects disease vulnerability and environmental stress in patients with heroin dependence in Han Chinese

Exposure to stress not only increases the vulnerability to heroin dependence (HD) but also provokes relapse. The etiology of HD and the role of life stress remain unclear, but prior studies suggested that both genetic and environmental factors are important. Opioid related genes, including OPRM1, OPRD1, OPRK1, and POMC, are obvious candidates for HD. Therefore, this study was conducted to explore whether the genetic polymorphisms of the candidates could affect vulnerability to HD and response to life stress in patients with HD. Ten polymorphisms of the opioid related genes were analyzed in 801 patients and 530 controls. The Life Event Questionnaire was used to assess the perspective and response to life stress in the past year. The genotype distribution and allelic frequency analyses showed that the minor C allele of rs2234918 in OPRD1 is over-represented in the HD group (P = .006 and P = .002, respectively). This finding was further confirmed by logistic regression analysis, showing that C allele carriers have a 1.42 times greater risk for HD compared to T/T homozygotes. A subgroup of 421 patients and 135 controls were eligible for life stress assessment. Patients with HD have a higher occurrence of negative events (No), negative events score (Ns), and average negative event score (Na) than those of controls (all P < .001), but there was no difference regarding positive recent events between the two groups. Gene-stress assessment in the HD group showed that T/T homozygotes of OPRD1 rs2236857 have more severe stress than C allele carriers (Ns, P = .004 and Na, P = .047). Our results indicate that the OPRD1 gene may not only play a role in the pathogenesis of HD but also affect the response to life stress among patients with HD in our Han Chinese population. Patients with the risk genotype may need additional psychosocial intervention for relapse prevention.

Molecular Imaging of Opioid and Dopamine Systems: Insights Into the Pharmacogenetics of Opioid Use Disorders

Opioid use in the United States has steadily risen since the 1990s, along with staggering increases in addiction and overdose fatalities. With this surge in prescription and illicit opioid abuse, it is paramount to understand the genetic risk factors and neuropsychological effects of opioid use disorder (OUD). Polymorphisms disrupting the opioid and dopamine systems have been associated with increased risk for developing substance use disorders. Molecular imaging studies have revealed how these polymorphisms impact the brain and contribute to cognitive and behavioral differences across individuals. Here, we review the current molecular imaging literature to assess how genetic variations in the opioid and dopamine systems affect function in the brain's reward, cognition, and stress pathways, potentially resulting in vulnerabilities to OUD. Continued research of the functional consequences of genetic variants and corresponding alterations in neural mechanisms will inform prevention and treatment of OUD.