The dopamine receptor D1 gene is associated with the length of interval between first heroin use and onset of dependence in Chinese Han heroin addicts

Single Nucleotide Variants (SNVs) of the Mesocorticolimbic System Associated with Cardiovascular Diseases and Type 2 Diabetes: A Systematic Review

The mesocorticolimbic (MCL) system is crucial in developing risky health behaviors which lead to cardiovascular diseases (CVDs) and type 2 diabetes (T2D). Although there is some knowledge of the MCL system genes linked to CVDs and T2D, a comprehensive list is lacking, underscoring the significance of this review. This systematic review followed PRISMA guidelines and the Cochrane Handbook for Systematic Reviews of Interventions. The PubMed and Web of Science databases were searched intensively for articles related to the MCL system, single nucleotide variants (SNVs, formerly single nucleotide polymorphisms, SNPs), CVDs, T2D, and associated risk factors. Included studies had to involve a genotype with at least one MCL system gene (with an identified SNV) for all participants and the analysis of its link to CVDs, T2D, or associated risk factors. The quality assessment of the included studies was performed using the Q-Genie tool. The VEP and DAVID tools were used to annotate and interpret genetic variants and identify enriched pathways and gene ontology terms associated with the gene list. The review identified 77 articles that met the inclusion criteria. These articles provided information on 174 SNVs related to the MCL system that were linked to CVDs, T2D, or associated risk factors. The COMT gene was found to be significantly related to hypertension, dyslipidemia, insulin resistance, obesity, and drug abuse, with rs4680 being the most commonly reported variant. This systematic review found a strong association between the MCL system and the risk of developing CVDs and T2D, suggesting that identifying genetic variations related to this system could help with disease prevention and treatment strategies.

High Genetic Addiction Risk Score (GARS) in Chronically Prescribed Severe Chronic Opioid Probands Attending Multi-pain Clinics: an Open Clinical Pilot Trial

Millions of Americans experience pain daily. In 2017, opioid overdose claimed 64,000 lives increasing to 84,000 lives in 2020, resulting in a decrease in national life expectancy. Chronic opioid use results in dependency, drug tolerance, neuroadaptation, hyperalgesia, potential addictive behaviors, or Reward Deficiency Syndrome (RDS) caused by a hypodopaminergia. Evaluation of pain clinic patients with the Genetic Addiction Risk Score (GARS) test and the Addiction Severity Index (ASI- Media Version V) revealed that GARS scores equal to or greater than 4 and 7 alleles significantly predicted drug and alcohol severity, respectively. We utilized RT-PCR for SNP genotyping and multiplex PCR/capillary electrophoresis for fragment analysis of the role of eleven alleles in a ten-reward gene panel, reflecting the activity of brain reward circuitry in 121 chronic opioid users. The study consisted of 55 males and 66 females averaging ages 54 and 53 years of age, respectively. The patients included Caucasians, African Americans, Hispanics, and Asians. Inclusion criteria mandated that the Morphine Milligram Equivalent (MME) was 30-600 mg/day (males) and 20 to 180 mg/day (females) for treatment of chronic pain over 12 months. Ninety-six percent carried four or more risk alleles, and 73% carried seven or more risk alleles, suggesting a high predictive risk for opioid and alcohol dependence, respectively. These data indicate that chronic, legally prescribed opioid users attending a pain clinic possess high genetic risk for drug and alcohol addiction. Early identification of genetic risk, using the GARS test upon entry to treatment, may prevent iatrogenic induced opioid dependence.

Heroin delay discounting and impulsivity: Modulation by DRD1 genetic variation

BACKGROUND

Dopamine D1 receptors (encoded by DRD1) are implicated in drug addiction and high-risk behaviors. Delay discounting (DD) procedures measure decisional balance between choosing smaller/sooner rewards vs larger/later rewards. Individuals with higher DD (rapid discounting) are prone to maladaptive behaviors that provide immediate reinforcement (eg, substance use). DRD1 variants have been linked with increased DD (in healthy volunteers) and opioid abuse. This study determined whether four dopaminergic functional variants modulated heroin DD and impulsivity.

METHODS

Substance use, DD, and genotype data (DRD1 rs686 and rs5326, DRD3 rs6280, COMT rs4680) were obtained from 106 current heroin users. Subjects completed an array of DD choices during two imagined conditions: heroin satiation and withdrawal. Rewards were expressed as $10 heroin bag units, with maximum delayed amount of 30 bags. Delays progressively increased from 3 to 96 hours.

RESULTS

DRD1 rs686 (A/A, n = 25; G/A, n = 56; G/G, n = 25) was linearly related to the difference in heroin DD (area under the curve; AUC) between the heroin satiation and withdrawal conditions; specifically, G/G homozygotes had a significantly smaller (satiation minus withdrawal) AUC difference score had higher drug-use impulsivity questionnaire scores, relative to A/A homozygotes, with G/A intermediate. DRD3 and COMT variants were not associated with these DD and impulsivity outcomes.

CONCLUSION

DRD1 rs686 modulated the difference in heroin DD score between pharmacological states and was associated with drug-use impulsivity. These data support a role of DRD1 in opioid DD and impulsive behaviors.

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.

Methadone Dosage and Plasma Levels, SNPs of OPRM1 Gene and Age of First Drug Use Were Associated With Outcomes of Methadone Maintenance Treatment

Objective: To explore the association between methadone dosage, plasma drug concentration, SNPs of μ-opioid receptor gene (OPRM1), ATP-binding cassette subfamily B member 1 gene (ABCB1), and methadone maintenance treatment (MMT) response.

Method: A total of 240 Chinese Han participants receiving MMT were recruited from Shanghai. Nine single nucleotide polymorphisms (SNPs) of the OPRM1 gene and three SNPs of the ABCB1 gene were genotyped, plasma methadone concentration was detected, and a morphine urine test was taken from all subjects.

Results: Methadone dosage, plasma methadone concentration, and negative rate of morphine urine test of retention participants were significantly higher, although the addiction severity index (ASI) was not significantly different between the two groups. A allele and AA genotype carriers of rs562859 (OPRM1 gene) had better compliance of MMT, and AA genotype carriers had a higher negative rate of morphine urine test. However, the difference was not significant after adjusting influence factors (age, sex, and methadone dosage). GG genotype carriers of rs3192723 (OPRM1 gene) had a significantly lower negative rate of morphine urine test, and the difference was still significant after adjusting influence factors. Logistic regression analysis showed that methadone-free trough concentration (OR = 0.910, p = 0.023) and AA genotype of rs526859 (OR = 0.580, p = 0.037) were associated with better compliance of MMT. After Bonferroni correction, only free trough concentration of methadone was negatively correlated with MMT compliance. The SNPs rs6912029 (OR = 0.021, p = 0.066) and rs6902403 (OR = 0.910, p = 0.007) of the OPRM1 gene, age at first use (OR = 1.118, p = 0.005), and average methadone dosage (OR = 1.033, p = 0.045) were associated with MMT effect. After Bonferroni correction, average methadone dosage was no longer correlated with MMT effect.

Conclusion: Dosage of methadone, plasma methadone concentration, several SNPs (rs3192723, rs6912029, rs6902403) of the OPRM1 gene, and age of first drug use were associated with better MMT outcomes.

Dopamine receptor D4 promoter hypermethylation increases the risk of drug addiction

Heroin and methylamphetamine (METH) are two addictive drugs that cause serious problems for society. Dopamine receptor D4 (DRD4), a key receptor in the dopaminergic system, may facilitate the development of drug addiction. The aim of the present study was to investigate the association between the promoter methylation level of DRD4 gene and drug addiction. Bisulfite pyrosequencing technology was used to measure the methylation levels of DRD4 promoter in 60 drug addicts and 52 matched controls. Significantly higher levels of DRD4 CpG1 and CpG4 methylation were detected in METH and heroin drug addicts compared with controls (P<0.05). Male METH addicts exhibited significantly higher DRD4 CpG1, CpG2 and CpG4 methylation levels compared with sex-matched controls (P<0.05). In heroin addicts, a positive correlation was observed between depression-dejection and DRD4 CpG5 methylation (r=0.537, P=0.039) whereas there was a negative correlation between drug usage frequency and CpG1 methylation (r=-0.632, P=0.011). In METH addicts, methylation levels were not significantly associated with depression-dejection and drug usage frequency. In addition, luciferase assays demonstrated that the target sequence of the DRD4 promoter upregulates gene expression. The results of the present study suggest that DNA methylation of DRD4 may be responsible for the pathophysiology of drug addiction.

Evidence of CNIH3 involvement in opioid dependence

Opioid dependence, a severe addictive disorder and major societal problem, has been demonstrated to be moderately heritable. We conducted a genome-wide association study in Comorbidity and Trauma Study data comparing opioid-dependent daily injectors (N=1167) with opioid misusers who never progressed to daily injection (N=161). The strongest associations, observed for CNIH3 single-nucleotide polymorphisms (SNPs), were confirmed in two independent samples, the Yale-Penn genetic studies of opioid, cocaine and alcohol dependence and the Study of Addiction: Genetics and Environment, which both contain non-dependent opioid misusers and opioid-dependent individuals. Meta-analyses found five genome-wide significant CNIH3 SNPs. The A allele of rs10799590, the most highly associated SNP, was robustly protective (P=4.30E-9; odds ratio 0.64 (95% confidence interval 0.55-0.74)). Epigenetic annotation predicts that this SNP is functional in fetal brain. Neuroimaging data from the Duke Neurogenetics Study (N=312) provide evidence of this SNP's in vivo functionality; rs10799590 A allele carriers displayed significantly greater right amygdala habituation to threat-related facial expressions, a phenotype associated with resilience to psychopathology. Computational genetic analyses of physical dependence on morphine across 23 mouse strains yielded significant correlations for haplotypes in CNIH3 and functionally related genes. These convergent findings support CNIH3 involvement in the pathophysiology of opioid dependence, complementing prior studies implicating the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) glutamate system.

Overlapping dopaminergic pathway genetic susceptibility to heroin and cocaine addictions in African Americans

Drugs of abuse activate the mesolimbic dopaminergic pathway. Genetic variations in the dopaminergic system may contribute to drug addiction. Several processes are shared between cocaine and heroin addictions but some neurobiological mechanisms may be specific. This study examined the association of 98 single nucleotide polymorphisms in 13 dopamine-related genes with heroin addiction (OD) and/or cocaine addiction (CD) in a sample of 801 African Americans (315 subjects with OD ± CD, 279 subjects with CD, and 207 controls). Single-marker analyses provided nominally significant evidence for associations of 24 SNPs) in DRD1, ANKK1/DRD2, DRD3, DRD5, DBH, DDC, COMT and CSNK1E. A DRD2 7-SNPs haplotype that includes SNPs rs1075650 and rs2283265, which were shown to alter D2S/D2L splicing, was indicated in both addictions. The Met allele of the functional COMT Val158Met was associated with protection from OD. None of the signals remained significant after correction for multiple testing. The study results are in accordance with the results of previous studies, including our report of association of DRD1 SNP rs5326 with OD. The findings suggest the presence of an overlap in genetic susceptibility for OD and CD, as well as shared and distinct susceptibility for OD in subjects of African and European descent.

Genetic Addiction Risk Score (GARS): molecular neurogenetic evidence for predisposition to Reward Deficiency Syndrome (RDS)

We have published extensively on the neurogenetics of brain reward systems with reference to the genes related to dopaminergic function in particular. In 1996, we coined “Reward Deficiency Syndrome” (RDS), to portray behaviors found to have gene-based association with hypodopaminergic function. RDS as a useful concept has been embraced in many subsequent studies, to increase our understanding of Substance Use Disorder (SUD), addictions, and other obsessive, compulsive, and impulsive behaviors. Interestingly, albeit others, in one published study, we were able to describe lifetime RDS behaviors in a recovering addict (17 years sober) blindly by assessing resultant Genetic Addiction Risk Score (GARS™) data only. We hypothesize that genetic testing at an early age may be an effective preventive strategy to reduce or eliminate pathological substance and behavioral seeking activity. Here, we consider a select number of genes, their polymorphisms, and associated risks for RDS whereby, utilizing GWAS, there is evidence for convergence to reward candidate genes. The evidence presented serves as a plausible brain-print providing relevant genetic information that will reinforce targeted therapies, to improve recovery and prevent relapse on an individualized basis. The primary driver of RDS is a hypodopaminergic trait (genes) as well as epigenetic states (methylation and deacetylation on chromatin structure). We now have entered a new era in addiction medicine that embraces the neuroscience of addiction and RDS as a pathological condition in brain reward circuitry that calls for appropriate evidence-based therapy and early genetic diagnosis and that requires further intensive investigation.