Pharmacogenetics and Human Molecular Genetics of Opiate and Cocaine Addictions and Their Treatments

Impact of OPRM1 (Mu-opioid Receptor Gene) A112G Polymorphism on Dual Oxycodone and Cocaine Self-administration Behavior in a Mouse Model

The use of mu-opioid receptor (MOP-r) agonists such as oxycodone together with cocaine is prevalent, and deaths attributed to using these combinations have increased.

RATIONALE

It is unknown if functional single nucleotide polymorphisms (SNPs), such as the OPRM1 (MOP-r gene) SNP A118G, can predispose individuals to more dual opioid and psychostimulant intake. The dual self-administration (SA) of MOP-r agonists and cocaine has not been thoroughly examined, especially with regard to neurobiological changes.

OBJECTIVES

We examined oxycodone SA and subsequent dual oxycodone and cocaine SA in male and female A112G (A/G and G/G, heterozygote and homozygote, respectively) mice, models of human A118G carriers, versus wild-type (A/A) mice.

METHODS

Adult male and female A/G, G/G and A/A mice self-administered oxycodone (0.25 mg/kg/infusion, 4hr/session, FR 1.) for 10 consecutive days (sessions 1-10). Mice then self-administered cocaine (2 hr) following oxycodone SA (4 hr, as above) in each session for a further 10 consecutive days (sessions 11-20). Message RNA transcripts of 24 reward-related genes were examined in the dorsal striatum.

RESULTS

Male and female A/G and G/G mice had greater oxycodone SA than A/A mice did in the initial 10 days and in the last 10 sessions. Further, A/G and G/G mice showed greater cocaine intake than A/A mice. Dorsal striatal mRNA levels of Pdyn, Fkbp5, Oprk1, and Oprm1 were altered following oxycodone and cocaine SA.

CONCLUSIONS

These studies demonstrated that this functional genetic variation in Oprm1 affected dual opioid and cocaine SA and altered specific gene expression in the striatum.

Comparison of the Effects of OPRM1 A118G Polymorphism Using Different Opioids: A Prospective Study

CONTEXT

μ-opioid receptor gene (OPRM1) A118G polymorphism (rs1799971) causes loss of N-glycosylation sites at the extracellular domain of μ-opioid receptors. G-allele carriers show a limited response to morphine; however, studies investigating the impact of A118G polymorphism on the efficacy of opioids other than morphine are limited.

OBJECTIVE

To compare the impact of A118G polymorphism on the efficacy of various opioids.

METHODS

This prospective cohort study enrolled 222 in-patients administered one of the following opioid therapies for cancer pain as part of an opioid introduction or rotation strategy: tapentadol extended-release tablets, methadone tablets, hydromorphone controlled-release tablets, oxycodone controlled-release tablets, or transdermal fentanyl patches. The impact of A118G polymorphism on the difference in the Brief Pain Inventory-Short Form score on days three, seven, and 14 from baseline was compared among the groups.

RESULTS

Overall, 81, 74, and 67 patients had the AA, AG, and GG genotypes, respectively, with an OPRM1 A118G G-allele variant frequency of 0.47. The reduction in the Brief Pain Inventory-Short Form score after opioid therapy initiation did not differ significantly among the patients with the three A118G genotypes treated with tapentadol (p = 0.84) or methadone (p = 0.97), whereas it was significantly smaller in G-allele carriers than that in AA homozygous patients treated with hydromorphone (p < 0.001), oxycodone (p = 0.031), or fentanyl (p < 0.001).

CONCLUSION

Tapentadol and methadone may be more suitable than hydromorphone, oxycodone, and fentanyl for G-allele carriers due to their dual mechanism of action and low susceptibility to OPRM1 A118G polymorphism.

[Bronchial diseases and heroin use. A systematic review]

INTRODUCTION

Heroin use can cause respiratory complications including asthma, chronic obstructive pulmonary disease (COPD) and bronchiectasis (BD).

OBJECTIVES

A general review of the literature presenting the data on the relationships between heroin consumption and bronchial complications, while underlining the difficulties of diagnosis and management.

DOCUMENTARY SOURCES

Medline, 1980-2022, keywords "asthma" or "bronchospasm" or "COPD" or "bronchiectasis" and "heroin" or "opiate" or "opiates", with limits pertaining to "Title/Abstract". Concerning asthma, 26 studies were included, as were 16 for COPD and 5 for BD.

RESULTS

Asthma and COPD are more prevalent among heroin addicts, who are less compliant than other patients with their treatment. The authors found a positive association between frequency of asthma exacerbations, admission to intensive care and heroin inhalation. Late diagnosis of COPD worsens the course of the disease; emphysema and BD are poor prognostic factors.

CONCLUSION

Bronchial diseases in heroin users can be identified by means of respiratory function exploration and chest CT scans. These tests should be performed frequently in view of optimizing their care, which includes their weaning themselves from addictive substances.

Endocannabinoid-dependent decrease of GABAergic transmission on dopaminergic neurons is associated with susceptibility to cocaine stimulant effects in pre-adolescent male MAOA hypomorphic mice exposed to early life stress

Vulnerability to cocaine use disorder depends upon a combination of genetic and environmental risk factors. While early life adversity is a critical environmental vulnerability factor for drug misuse, allelic variants of the monoamine oxidase A (MAOA) gene have been shown to moderate its influence on the risk of drug-related problems. However, data on the interactions between MAOA variants and early life stress (ES) with respect to predisposition to cocaine abuse are limited. Here, we show that a mouse model capturing the interaction of genetic (low-activity alleles of the Maoa gene; MAOA^Neo) and environmental (i.e., ES) vulnerability factors displays an increased sensitivity to repeated in vivo cocaine psychomotor stimulant actions associated with a reduction of GABAA receptor-mediated inhibition of dopamine neurons of the ventral tegmental area (VTA). Depolarization-induced suppression of inhibition (DSI), a 2-arachidonoylglycerol (2AG)-dependent form of short-term plasticity, also becomes readily expressed by dopamine neurons from male MAOA^Neo ES mice repeatedly treated with cocaine. The activation of either dopamine D2 or CB1 receptors contributes to cocaine-induced DSI expression, decreased GABA synaptic efficacy, and hyperlocomotion. Next, in vivo pharmacological enhancement of 2AG signaling during repeated cocaine exposure occludes its actions both in vivo and ex vivo. This data extends our knowledge of the multifaceted sequelae imposed by this gene-environment interaction in VTA dopamine neurons of male pre-adolescent mice and contributes to our understanding of neural mechanisms of vulnerability for early onset cocaine use.

The Influence of Mediators on the Relationship Between Antenatal Opioid Agonist Exposure and the Severity of Neonatal Opioid Withdrawal Syndrome

OBJECTIVES

(1) To evaluate the direct (un-mediated) and indirect (mediated) relationship between antenatal exposure to opioid agonist medication as treatment for opioid use disorder (MOUD) and the severity of neonatal opioid withdrawal syndrome (NOWS), and (2) to understand the degree to which mediating factors influence the direct relationship between MOUD exposure and NOWS severity.

METHODS

This cross-sectional study includes data abstracted from the medical records of 1294 opioid-exposed infants (859 MOUD exposed and 435 non-MOUD exposed) born at or admitted to one of 30 US hospitals from July 1, 2016, to June 30, 2017. Regression models and mediation analyses were used to evaluate the relationship between MOUD exposure and NOWS severity (i.e., infant pharmacologic treatment and length of newborn hospital stay (LOS)) to identify potential mediators of this relationship in analyses adjusted for confounding factors.

RESULTS

A direct (un-mediated) association was found between antenatal exposure to MOUD and both pharmacologic treatment for NOWS (aOR 2.34; 95%CI 1.74, 3.14) and an increase in LOS (1.73 days; 95%CI 0.49, 2.98). Delivery of adequate prenatal care and a reduction in polysubstance exposure were mediators of the relationship between MOUD and NOWS severity and as thus, were indirectly associated with a decrease in both pharmacologic treatment for NOWS and LOS.

CONCLUSIONS FOR PRACTICE

MOUD exposure is directly associated with NOWS severity. Prenatal care and polysubstance exposure are potential mediators in this relationship. These mediating factors may be targeted to reduce the severity of NOWS while maintaining the important benefits of MOUD during pregnancy.

Pharmacological data science perspective on fatal incidents of morphine treatment

Morphine prescribed for analgesia has caused drug-related deaths at an estimated incidence of 0.3% to 4%. Morphine has pharmacological properties that make it particularly difficult to assess the causality of morphine administration with a patient's death, such as its slow transfer between plasma and central nervous sites of action and the existence of the active metabolite morphine-6-glucuronide with opioid agonistic effects, Furthermore, there is no well-defined toxic dose or plasma/blood concentration for morphine. Dosing is often adjusted for adequate pain relief. Here, we summarize reported deaths associated with morphine therapy, including associated morphine exposure and modulating patient factors such as pharmacogenetics, concomitant medications, or comorbidities. In addition, we systematically analyzed published numerical information on the stability of concentrations of morphine and its relevant metabolites in biological samples collected postmortem. A medicolegal case is presented in which the causality of morphine administration with death was in dispute and pharmacokinetic modeling was applied to infer the administered dose. The results of this analytical review suggest that (i) inference from postmortem blood concentrations to the morphine dose administered has low validity and (ii) causality between a patient's death and the morphine dose administered remains a highly context-dependent and collaborative assessment among experts from different medical specialties.

PPL-103: A mixed opioid partial agonist with desirable anti-cocaine properties

Cocaine use disorder (CUD) is a persistent public health problem for which no effective medications are available. PPL-103 is an opioid receptor ligand with partial agonist activity at mu, kappa and delta opioid receptors, with a greater efficacy for kappa and low efficacy at mu receptors. Because chronic cocaine use induces changes in the kappa opioid receptor/dynorphin system, we hypothesized that a kappa partial agonist, such as PPL-103, would attenuate the aversive properties of the upregulated kappa system, resulting in effective treatment approach for CUD. We tested the effects of PPL-103 on cocaine self-administration models that recapitulate core aspects of CUD in humans. We found that PPL-103 reduced both long and short access cocaine self-administration, motivation to respond for cocaine, and binge-like cocaine taking, in rats. Operant responding for food, fentanyl and locomotor behavior were not altered at doses that decreased cocaine infusions. Repeated PPL-103 treatment did not lead to tolerance development. PPL-103 also reduced both priming- and cue-induced reinstatement of cocaine seeking, being more effective in the former. Surprisingly, PPL-103 reduced self-administration parameters and reinstatement in rats previously treated with the long-acting kappa receptor antagonist JDTic more potently than in non-JDTic treated animals, whereas naltrexone injected to rats subsequent to JDTic administration increased self-administration, suggesting that the partial mu agonist activity, rather than kappa agonism is important for reduction in cocaine taking and seeking. However, partial kappa activation seems to increase safety by limiting dysphoria, tolerance and addiction development. PPL-103 displays a desirable profile as a possible CUD pharmacotherapy.

Expression of stable and reliable preference and aversion phenotypes following place conditioning with psychostimulants

RATIONALE AND OBJECTIVES

Drug-seeking behavior occurs more readily in some individuals than others. This phenomenon is considered in studies of drug self-administration in which high drug-seeking/taking individuals can be identified. In contrast, studies of conditioned place preference (CPP) often involve a random sample of drug-naïve rodents that includes phenotypes not considered relevant to addiction. The main objective of the current studies was to determine if a priori identification of different conditioning phenotypes could improve the validity and sensitivity of CPP expression as a preclinical test for vulnerability to addiction.

METHODS AND RESULTS

Analysis of cocaine place conditioning data from 443 Swiss-Webster mice revealed a trimodal distribution with peaks corresponding to means of k = 3 clusters. The cluster means occurred at high, low, or negative preference scores, the latter suggesting a phenotype acquiring conditioned place aversion (CPA). The same clusters were identified in mice conditioned with methamphetamine, MDPV, or amphetamine, and these clusters remained stable and reliable during three additional expression tests spaced at 24 h. A meta-analysis of effect sizes obtained from CPP literature revealed a positively skewed distribution affected by sample size, consistent with the existence of a CPA phenotype within the populations tested. A dopamine receptor antagonist, flupentixol, blocked cocaine CPP expression in a group containing all phenotypes, but sensitivity improved markedly when CPA phenotypes were excluded from the dataset.

CONCLUSIONS

These studies suggest that taking phenotype into consideration when designing place conditioning studies will improve their application as a preclinical tool in addiction biology and drug discovery.

A study on methylation of two CpG islands of MAOA gene promoter among opium-addicted males undergoing methadone treatment

The association between methylation of MAOA gene promoter and alcohol and nicotine dependence has been demonstrated in women but not in men yet. Antisocial personality disorder (ASPD) and substance use disorders (SUD) are two types of disorders that could highly be influenced by methylation-induced changes in MAOA function. The aim of the current study is to investigate the effect of opioid addiction on methylation of MAOA gene promoter in males. DNA was extracted from the whole blood of all samples (29 opium-addicted individuals undergoing methadone treatment and 28 healthy people) according to the extraction protocol, followed by treating these samples with bisulfite kits. The investigated region including two CpG islands in the promoter region of MAOA gene contained 35 CpG dinucleotides investigated through Sanger sequencing method. The frequency of methylation at two CpG islands of MAOA gene promoter regions was equal to zero among addicted individuals undergoing methadone treatment and healthy peoples. Then, comparing methylation levels among the study group is not applicable. In conclusion, there was no association between opium addiction and methylation of the MAOA promoter regions in opium-addicted male undergoing methadone treatment.

Knock-In Mouse Models to Investigate the Functions of Opioid Receptors in vivo

Due to their low expression levels, complex multi-pass transmembrane structure, and the current lack of highly specific antibodies, the assessment of endogenous G protein-coupled receptors (GPCRs) remains challenging. While most of the research regarding their functions was performed in heterologous systems overexpressing the receptor, recent advances in genetic engineering methods have allowed the generation of several unique mouse models. These animals proved to be useful to investigate numerous aspects underlying the physiological functions of GPCRs, including their endogenous expression, distribution, interactome, and trafficking processes. Given their significant pharmacological importance and central roles in the nervous system, opioid peptide receptors (OPr) are often referred to as prototypical receptors for the study of GPCR regulatory mechanisms. Although only a few GPCR knock-in mouse lines have thus far been generated, OPr are strikingly well represented with over 20 different knock-in models, more than half of which were developed within the last 5 years. In this review, we describe the arsenal of OPr (mu-, delta-, and kappa-opioid), as well as the opioid-related nociceptin/orphanin FQ (NOP) receptor knock-in mouse models that have been generated over the past years. We further highlight the invaluable contribution of such models to our understanding of the in vivo mechanisms underlying the regulation of OPr, which could be conceivably transposed to any other GPCR, as well as the limitations, future perspectives, and possibilities enabled by such tools.

Pharmacogenetics of Addiction Therapy

Drug addiction is a serious relapsing disease that has high costs to society and to the individual addicts. Treatment of these addictions is still in its nascency, with only a few examples of successful therapies. Therapeutic response depends upon genetic, biological, social, and environmental components. A role for genetic makeup in the response to treatment has been shown for several addiction pharmacotherapies with response to treatment based on individual genetic makeup. In this chapter, we will discuss the role of genetics in pharmacotherapies, specifically for cocaine, alcohol, and opioid dependences. The continued elucidation of the role of genetics should aid in the development of new treatments and increase the efficacy of existing treatments.

A Randomized Controlled Comparison of Epidural Analgesia Onset Time and Adverse Reactions During Labor With Different Dose Combinations of Bupivacaine and Sufentanil

OBJECTIVES

The purpose was to compare the effects of 3 different dose combinations of bupivacaine and sufentanil on the onset of analgesia and the occurrence of side effects.

MATERIALS AND METHODS

One hundred sixty-nine pregnant women were randomly assigned to 3 groups: the B1S5 group received 0.1% bupivacaine+5 μg sufentanil in 15 mL; the B125S5 group received 0.125% bupivacaine+5 μg sufentanil in 15 mL; and the B1S10 group received 0.1% bupivacaine+10 μg sufentanil in 15 mL. The primary outcome was the analgesic onset time, and the secondary outcomes were mode of delivery, patient satisfaction, maternal and neonatal side effects (pruritus, hypotension, sedation, motor block, decreased fetal heart rate, fever, and interference with breastfeeding).

RESULTS

The median (inter-quartile range) time to achieve effective analgesia was significantly faster in the B125S5 group than in the B1S5 group (10 [11-14 {4-30}] min vs. 15 [17-20 {5-30}] min, P<0.001). There was no significant difference in the analgesia onset time between the B1S10 and B125S5 groups (10 [11-14 {4-30}] min vs. 12 [13-15 {3-30}] min, P=0.202). Pruritus, hypotension, motor block, maternal satisfaction, delivery mode, decreased fetal heart rate, total bupivacaine dose and breastfeeding scores were not significantly different among the 3 groups except the sufentanil dosage and incidence of mild drowsiness and fever (the B1S10 group had significantly higher fever than the other groups).

DISCUSSION

The B125S5 combination may be superior to the B1S5 and B1S10 combinations as an initial dose for epidural analgesia to achieve rapid effective analgesia with minimal side effects.

Association between GABA receptor delta subunit gene polymorphisms and heroin addiction

Evidence suggests that γ-aminobutyric acid (GABA) receptors are involved in the development of drug dependence. Considering its exclusively extrasynaptic localization, GABA receptor delta subunit (GABRD) is likely involved in heroin addiction. The purpose of this study was to explore the association between the single nucleotide polymorphisms (SNPs) of GABRD and heroin addiction. Genotyping of five SNPs (rs13303344, rs4481796, rs2376805, rs2229110, and rs41307846) in GABRD gene was performed by using TaqMan SNP assay. The association between heroin addiction and these SNPs was assessed in 446 heroin dependent patients and 400 normal control subjects of male Han Chinese origin. Only the genotype and allele frequencies at rs13303344 differed significantly between the cases and controls (nominal P values were 0.028 and 0.019, respectively). The C allele of rs13303344 was associated with an increased risk of heroin addiction (OR = 1.281, 95 % CI: 1.042-1.575). After Bonferroni correction, the association lost significance. The frequencies of the haplotype C-C-A and A-C-A at GARBD (rs13303344-rs4481796- rs2376805) differed significantly between the cases and controls. The heroin craving score was significantly higher in patients with CC/AC genotypes at rs13303344 than in those with the AA genotype (nominal P = 0.017). The results suggest that GABRD rs13303344 may contribute to the susceptibility to heroin addiction and is associated with the drug cravings of heroin dependent patients.

The Streetlight Effect: Reappraising the Study of Addiction in Light of the Findings of Genome-wide Association Studies

Drug dependence has long been thought to have a genetic component. Research seeking to identify the genetic basis of addiction has gone through important transitions over its history, in part based upon the emergence of new technologies, but also as the result of changing perspectives. Early research approaches were largely dictated by available technology, with technological advancements having highly transformative effects on genetic research, but the limitations of technology also affected modes of thinking about the genetic causes of disease. This review explores these transitions in thinking about the genetic causes of addiction in terms of the "streetlight effect," which is a type of observational bias whereby people search for something only where it is easiest to search. In this way, the genes that were initially studied in the field of addiction genetics were chosen because they were the most "obvious," and formed current understanding of the biological mechanisms underlying the actions of drugs of abuse and drug dependence. The problem with this emphasis is that prior to the genomic era the vast majority of genes and proteins had yet to be identified, much less studied. This review considers how these initial choices, as well as subsequent choices that were also driven by technological limitations, shaped the study of the genetic basis of drug dependence. While genome-wide approaches overcame the initial biases regarding which genes to choose to study inherent in candidate gene studies and other approaches, genome-wide approaches necessitated other assumptions. These included additive genetic causation and limited allelic heterogeneity, which both appear to be incorrect. Thus, the next stage of advancement in this field must overcome these shortcomings through approaches that allow the examination of complex interactive effects, both gene × gene and gene × environment interactions. Techniques for these sorts of studies have recently been developed and represent the next step in our understanding of the genetic basis of drug dependence.

Pharmacokinetic and pharmacodynamic analyses of cocaine and its metabolites in behaviorally divergent inbred mouse strains

Cocaine (COC) is a psychostimulant with a high potential for abuse and addiction. Risk for COC use disorder is driven, in part, by genetic factors. Animal models of addiction-relevant behaviors have proven useful for studying both genetic and nongenetic contributions to drug response. In a previous study, we examined initial locomotor sensitivity to COC in genetically diverse inbred mouse strains. That work highlighted the relevance of pharmacokinetics (PK) in initial locomotor response to COC but was limited by a single dose and two sampling points. The objective of the present study was to characterize the PK and pharmacodynamics of COC and its metabolites (norcocaine and benzoylecgonine) in six inbred mouse strains (I/LnJ, C57BL/6J, FVB/NJ, BTBR T+ tf/J, LG/J and LP/J) that exhibit extreme locomotor responses to cocaine. Mice were administered COC at one of four doses and concentrations of cocaine, norcocaine and benzoylecgonine were analyzed in both plasma and brain tissue at 5 different time points. Initial locomotor sensitivity to COC was used as a pharmacodynamic endpoint. We developed an empirical population PK model that simultaneously characterizes cocaine, norcocaine and benzoylecgonine in plasma and brain tissues. We observed interstrain variability occurring in the brain compartment that may contribute to pharmacodynamic differences among select strains. Our current work paves the way for future studies to explore strain-specific pharmacokinetic differences and identify factors other than PK that are responsible for the diverse behavioral response to COC across these inbred mouse strains.

Pharmacogenomics and prescription opioid use

Genome-wide association studies and candidate gene findings suggest that genetic approaches may help in choosing the most appropriate drug and dosage, while preventing adverse drug reactions. This is the field that addresses precision medicine: to evaluate variations in the DNA sequence that could be responsible for different individual analgesic response. We review potential gene biomarkers with best overall convergent functional evidence, for opioid use, in pain management. Polymorphisms can modify pharmacodynamics (i.e., mu opioid receptor, OPRM1) and pharmacokinetics (i.e., CYP2D6 phenotypes) pathways altering opioid effectiveness, consumption, side effects or additionally, prescription opioid use dependence vulnerability. This review provides a summary of these candidate variants for the translation of genotype into clinically useful information in pain medicine.

Cerebral vasculitis associated with drug abuse

PURPOSE OF REVIEW

To review understand the epidemiology, background, neuropharmacology, and histopathology of literature verified cases, and likely etiopathogenic mechanisms.

RECENT FINDINGS

There are only a handful of histologically confirmed patients in the literature with cerebral vasculitis because of drug abuse.

SUMMARY

There is little justification for invasive laboratory investigation given the ready availability of highly accurate vascular neuroimaging techniques to dictate management, which usually rests upon avoidance of further exposure and minimizing the secondary neurotoxic effects of the abused substances and polypharmacy use.

Spinocerebellar ataxia type 23 (SCA23): a review

Spinocerebellar ataxias (SCAs), formerly known as autosomal dominant cerebellar ataxias (ADCAs), are a group of hereditary heterogeneous neurodegenerative diseases. Gait, progressive ataxia, dysarthria, and eye movement disorder are common symptoms of spinocerebellar ataxias. Other symptoms include peripheral neuropathy, cognitive impairment, psychosis, and seizures. Patients may lose their lives due to out of coordinated respiration and/or swallowing. Neurological signs cover pyramidal or extrapyramidal signs, spasm, ophthalmoplegia, hyperactive deep tendon reflexes, and so on. Different subtypes of SCAs present various clinical features. Spinocerebellar ataxia type 23 (SCA23), one subtype of the SCA family, is characterized by mutant prodynorphin (PDYN) gene. Based on literatures, this review details a series of SCA23, to improve a whole understanding of clinicians and point out the potential research direction of this dysfunction, including a history, pathophysiological mechanism, diagnosis and differential diagnosis, epigenetics, penetrance and prevalence, genetic counseling, treatment and prognosis.

Salivary Cortisol Levels Are Associated with Craving and Cognitive Performance in Cocaine-Abstinent Subjects: A Pilot Study

Cortisol is a glucocorticoid hormone secreted by the adrenal cortex upon the activation of the hypothalamic-pituitary-adrenal (HPA) axis. Assessment of cortisol in saliva has emerged as a reliable way of evaluating HPA function. We examined the relationships between salivary cortisol levels with both craving and cognitive performance, as a possible biomarker of cocaine addiction. Cognitive performance (attention, declarative and working memory, executive functions and recognition of emotions) was assessed in 14 abstinent cocaine-dependent subjects in outpatient treatment and 13 control participants. Three salivary samples were collected at home by all the participants in the morning, afternoon and at bedtime. Patients showed higher levels of cortisol in the morning, as well as higher area under the curve with respect to the ground (AUCg). Regarding cognitive performance, cocaine-abstinent subjects showed worse performance in attention (d2 test), verbal memory (Spanish Complementary Verbal Learning Test, TAVEC) and executive tests (Tower of Hanoi and phonological fluency test) with respect to the control group. Morning cortisol levels and the AUCg index were negatively associated with the age of onset of drug consumption and the AUCg index was also positively associated with craving in our patients' group. Moreover, morning cortisol levels, as well as the AUCg index, were negatively associated with verbal memory performance. Therefore, our pilot study suggests that salivary cortisol measurements could be a good avenue to predict craving level, as well as cognitive status, especially the declarative memory domain.

Opioid and neuroHIV Comorbidity - Current and Future Perspectives

With the current national opioid crisis, it is critical to examine the mechanisms underlying pathophysiologic interactions between human immunodeficiency virus (HIV) and opioids in the central nervous system (CNS). Recent advances in experimental models, methodology, and our understanding of disease processes at the molecular and cellular levels reveal opioid-HIV interactions with increasing clarity. However, despite the substantial new insight, the unique impact of opioids on the severity, progression, and prognosis of neuroHIV and HIV-associated neurocognitive disorders (HAND) are not fully understood. In this review, we explore, in detail, what is currently known about mechanisms underlying opioid interactions with HIV, with emphasis on individual HIV-1-expressed gene products at the molecular, cellular and systems levels. Furthermore, we review preclinical and clinical studies with a focus on key considerations when addressing questions of whether opioid-HIV interactive pathogenesis results in unique structural or functional deficits not seen with either disease alone. These considerations include, understanding the combined consequences of HIV-1 genetic variants, host variants, and μ-opioid receptor (MOR) and HIV chemokine co-receptor interactions on the comorbidity. Lastly, we present topics that need to be considered in the future to better understand the unique contributions of opioids to the pathophysiology of neuroHIV.

Graphical Abstract

Precision therapeutic opioid dosing implications from genetic biomarkers and craving score

Determining the clinically optimal dose in methadone maintenance therapy (MMT) is a time-consuming procedure, which considers clinical signs and symptoms.To perform a quantitative trait locus association for identifying genetic variants for MMT dosage that underlie heroin addiction and methadone metabolism and then integrate several genotypic and phenotypic factors are potential predictors for clinically optimal MMT dose for personalized prescription.In total, 316 heroin-dependent patients undergoing MMT were recruited at the Addiction Center of the China Medical University Hospital. A multinomial logistic regression model was used to assess associations between genetic polymorphisms and MMT dosing. The data were randomly separated into training and testing sets. In order to enhance the prediction accuracy and the reliability of the prediction model, we used areas under the receiver operating characteristic curves to evaluate optimal MMT dose in both training and testing sets.Four single nucleotide polymorphisms, namely rs806368 in CNR1, s1386493 in TPH2, s16974799 in CYP2B6, and rs2229205 in OPRL1, were significantly associated with the maximum MMT dose (P < .05). The genetic risk score (GRS) was associated with maximum MMT dose, and after adjustments for age, sex, and body mass index, the GRS remained independently associated with the maximum MMT dose. The area under the receiver operating characteristic curve of the combined GRS and craving score was 0.77 for maximum MMT dose, with 75% sensitivity and 60% specificity.Integrating the GRS and craving scores may be useful in the evaluation of individual MMT dose requirements at treatment initiation. Optimal dose prediction allows clinicians to tailor MMT to each patient's needs.

Non-pharmacological factors that determine drug use and addiction

Based on their pharmacological properties, psychoactive drugs are supposed to take control of the natural reward system to finally drive compulsory drug seeking and consumption. However, psychoactive drugs are not used in an arbitrary way as pure pharmacological reinforcement would suggest, but rather in a highly specific manner depending on non-pharmacological factors. While pharmacological effects of psychoactive drugs are well studied, neurobiological mechanisms of non-pharmacological factors are less well understood. Here we review the emerging neurobiological mechanisms beyond pharmacological reinforcement which determine drug effects and use frequency. Important progress was made on the understanding of how the character of an environment and social stress determine drug self-administration. This is expanded by new evidence on how behavioral alternatives and opportunities for drug instrumentalization generate different patterns of drug choice. Emerging evidence suggests that the neurobiology of non-pharmacological factors strongly determines pharmacological and behavioral drug action and may, thus, give rise for an expanded system's approach of psychoactive drug use and addiction.

Pharmacogenomics of Pain Management: The Impact of Specific Biological Polymorphisms on Drugs and Metabolism

PURPOSE OF REVIEW

Pain is multifactorial and complex, often with a genetic component. Pharmacogenomics is a relative new field, which allows for the development of a truly unique and personalized therapeutic approach in the treatment of pain.

RECENT FINDINGS

Until recently, drug mechanisms in humans were determined by testing that drug in a population and calculating response averages. However, some patients will inevitably fall outside of those averages, and it is nearly impossible to predict who those outliers might be. Pharmacogenetics considers a patient's unique genetic information and allows for anticipation of that individual's response to medication. Pharmacogenomic testing is steadily making progress in the management of pain by being able to identify individual differences in the perception of pain and susceptibility and sensitivity to drugs based on genetic markers. This has a huge potential to increase efficacy and reduce the incidence of iatrogenic drug dependence and addiction. The streamlining of relevant polymorphisms of genes encoding receptors, transporters, and drug-metabolizing enzymes influencing the pain phenotype can be an important guide to develop safe new strategies and approaches to personalized pain management. Additionally, some challenges still prevail and preclude adoption of pharmacogenomic testing universally. These include lack of knowledge about pharmacogenomic testing, inadequate standardization of the process of data handling, questionable benefits about the clinical and financial aspects of pharmacogenomic testing-guided therapy, discrepancies in clinical evidence supporting these tests, and doubtful reimbursement of the tests by health insurance agencies.

Association between three common genetic polymorphisms of XPC and susceptibility to heroin dependency

As heroin and morphine produce reactive oxygen species and down-regulate several genes involved in cellular detoxification and DNA repair pathways, neurons experience DNA damage. Xeroderma pigmentosum complementation group C (XPC, OMIM: 613208) gene, which is expressed in the brain, is one of the central genes in the nucleotide excision repair pathway. Three common XPC polymorphisms (Lys939Gln, Ala499Val and PAT) are associated with reduced DNA repair capacity. In this study, the relationship between these polymorphisms and the risk of heroin dependency (HD), as well as, age of first use (AFU) for illegal drugs was investigated on 795 healthy individuals and 442 heroin dependent patients. Statistical analyses indicated that there was no significant association between the XPC polymorphisms and the risk of HD. The haplotypic frequencies of the polymorphisms showed significant difference between HD patients and healthy controls (χ² = 16.38, df = 6, P = 0.012). Analysis indicated that the "Ala + Gln" haplotype increased the HD risk more than the "Ala + Lys" haplotype (OR = 4.21, 95% CI = 1.29-13.7, P = 0.017). In Cox proportional model, there was significant association between AFU and the Ala499Val polymorphism (Hazard ratio = 1.53, 95% CI: 1.02-2.92, P = 0.036). To investigate the effect of the linkage between the polymorphic sites, we compared the AFU among two common diplotypes ("Ala - Lys/Ala - Lys" and "Val - Lys/Val - Lys"). Statistical analysis indicated that AFU was significantly lower in "Val - Lys/Val - Lys" diplotype (t = 2.63, df = 49, P = 0.011). The present findings suggest that the XPC is a candidate polymorphic locus for AFU.

The Effect of OPRM1 rs648893 Gene Polymorphism on Opioid Addiction in an Iranian population in Zabol: A Case-Control Study

Introduction: Opioid addiction (OA) is a neurologically life-threatening challenge associated with socioeconomic and health concerns for individuals and society. The addictive drugs trigger neuromodulators and neurotransmitters through the opioid receptors and corresponding endogenous peptide ligands. In addition, drug addiction is reportedly related to the mu-opioid receptor (OPRM1) encoding gene and its variants. According to the role of the rs648893 polymorphism of the OPRM1 gene in numerous disorders, it has been suggested as a candidate associated with drug addiction. The present case-control study was conducted to evaluate the role of OPRM1 rs648893 polymorphism in the OA risk. Methods: To this end, the rs648893 polymorphism was genotyped by tetra amplification refractory mutation system-polymerase chain reaction among 160 Iranian subjects consisting of 105 OA cases and 155 controls. Results: According to our findings, there was no significant association between OA and the OPRM1 rs648893 gene polymorphism. Moreover, a marginally insignificant difference was found between OA cases and controls in accordance with the allelic frequencies (P=0.05) Conclusion: In general, our results reported no association between OPRM1 rs648893 gene polymorphism and OA although further research among various ethnicities with larger sample sizes is needed to draw a definite conclusion on the association of rs648893 polymorphism and other OPRM1 intronic variants with opioid and other addictions.

OPRM1 A118G Polymorphisms and Its Role in Opioid Addiction: Implication on Severity and Treatment Approaches

The epidemic of opioid addiction is shaping up as the most serious clinical issues of current times. Opioids have the greatest propensity to develop addiction after first exposure. Molecular, genetic variations, epigenetic alterations, and environmental factors are also implicated in the development of opioid addiction. Genetic and epigenetic variations in candidate genes have been identified for their associations with opioid addiction. OPRM1 nonsynonymous single nucleotide polymorphism rs1799971 (A118G) is the most prominent candidate due to its significant association with onset and treatment of opioid addiction. Marked inter-individual variability in response to available maintenance pharmacotherapies is the common feature observed in individuals with opioid addiction. Several therapies are only effective among subgroups of opioid individuals which indicate that ethnic, environmental factors and genetic polymorphism including rs1799971 may be responsible for the response to treatment. Pharmacogenetics has the potential to enhance our understanding around the underlying genetic, epigenetic and molecular mechanisms responsible for the heterogeneous response of maintenance pharmacotherapies in opioid addiction. A more detailed understanding of molecular, epigenetic and genetic variants especially the implication of OPRM1 A118G polymorphism in an individual may serve as the way forward to address the opioid epidemic. Personalized medicine, which involves developing targeted pharmacotherapies in accordance with individual genetic and epigenetic makeup, are required to develop safe and effective treatments for opioid addiction.

DRD2 and ANKK1 genes associate with late-onset heroin dependence in men

Objectives: Dopamine plays an important role in reward system of heroin dependence (HD), and dopaminergic D2 receptor (DRD2) gene is a candidate for the aetiology of HD. Ankyrin repeat and kinase domain containing 1 (ANKK1) gene is proximal to DRD2 and may influence its expression. We explored whether DRD2 and ANKK1 associate with occurrence of HD, and whether the genetic variants influence personality traits in male patients with HD.Methods:DRD2/ANKK1 polymorphisms were analysed in 950 unrelated Han Chinese male participants (601 HD patients and 349 healthy controls). All participants were screened using the same assessment tools and all patients met the diagnostic criteria of HD. Personality traits were assessed in 274 patients and 142 controls using the Tridimensional Personality Questionnaire.Results: According to the allele, genotype and haplotype frequency analysis, we observed an association between HD and several DRD2/ANKK1 polymorphisms (rs1800497, rs1800498, rs1079597 and rs4648319); this was most notable in the late-onset HD subgroup. However, these DRD2/ANKK1 polymorphisms did not associate with specific personality traits in HD patients and controls.Conclusions:DRD2/ANKK1 may play an important role in occurrence of late-onset HD, but does not mediate the relationship between personality traits and HD in Han Chinese male population.

Coevolution of Residues Provides Evidence of a Functional Heterodimer of 5-HT2AR and 5-HT2CR Involving Both Intracellular and Extracellular Domains

Serotonin is a neurotransmitter that plays a role in regulating activities such as sleep, appetite, mood and substance abuse disorders; serotonin receptors 5-HT2AR and 5-HT2CR are active within pathways associated with substance abuse. It has been suggested that 5-HT2AR and 5-HT2CR may form a dimer that affects behavioral processes. Here we study the coevolution of residues in 5-HT2AR and 5-HT2CR to identify potential interactions between residues in both proteins. Coevolution studies can detect protein interactions, and since the thus uncovered interactions are subject to evolutionary pressure, they are likely functional. We assessed the significance of the 5-HT2AR/5-HT2CR interactions using randomized phylogenetic trees and found the coevolution significant (p-value = 0.01). We also discuss how co-expression of the receptors suggests the predicted interaction is functional. Finally, we analyze how several single nucleotide polymorphisms for the 5-HT2AR and 5-HT2CR genes affect their interaction. Our findings are the first to characterize the binding interface of 5-HT2AR/5-HT2CR and indicate a correlation between this interface and location of SNPs in both proteins.

Gene Variants in Hepatic Metabolism, Gamma-Aminobutyric Acid-ergic Reward, and Prostaglandin Pathways in Opioid-Consuming and Opioid-Naïve Patients Presenting for Lower Extremity Total Joint Replacement

Gene variants may contribute to individual differences in the experience of pain and the efficacy and reward of treatments. We explored gene variation in opioid-naïve and opioid-consuming patients undergoing elective lower extremity total joint replacement. We focused on 3 gene pathways including prostaglandin, gamma-aminobutyric acid (GABA)-ergic reward, and hepatic metabolism pathways. We report that for genes with possible or probable deleterious impact in these 3 pathways, opioid consumers had more gene variants than opioid-naïve patients (median 3 vs 1, P = .0092). We conclude that chronic opiate users may have genetic susceptibility to altered responses in reward/dependency and pain/inflammation pathways.

A Genetic Model of Impulsivity, Vulnerability to Drug Abuse and Schizophrenia-Relevant Symptoms With Translational Potential: The Roman High- vs. Low-Avoidance Rats

The bidirectional selective breeding of Roman high- (RHA) and low-avoidance (RLA) rats for respectively rapid vs. poor acquisition of active avoidant behavior has generated two lines/strains that differ markedly in terms of emotional reactivity, with RHA rats being less fearful than their RLA counterparts. Many other behavioral traits have been segregated along the selection procedure; thus, compared with their RLA counterparts, RHA rats behave as proactive copers in the face of aversive conditions, display a robust sensation/novelty seeking (SNS) profile, and show high impulsivity and an innate preference for natural and drug rewards. Impulsivity is a multifaceted behavioral trait and is generally defined as a tendency to express actions that are poorly conceived, premature, highly risky or inappropriate to the situation, that frequently lead to unpleasant consequences. High levels of impulsivity are associated with several neuropsychiatric conditions including attention-deficit hyperactivity disorder, obsessive-compulsive disorder, schizophrenia, and drug addiction. Herein, we review the behavioral and neurochemical differences between RHA and RLA rats and survey evidence that RHA rats represent a valid genetic model, with face, construct, and predictive validity, to investigate the neural underpinnings of behavioral disinhibition, novelty seeking, impulsivity, vulnerability to drug addiction as well as deficits in attentional processes, cognitive impairments and other schizophrenia-relevant traits.

Significant association of DRD2 enhancer variant rs12364283 with heroin addiction in a Pakistani population

The dopamine D2 receptor encoded by DRD2 has been implicated in multiple psychiatric disorders, mediated at least in part by two intronic variants affecting mRNA splicing, rs1076560 and rs2283265, and a less frequent enhancer variant, rs12364283, which increases DRD2 mRNA expression. This study tests whether these functionally validated variants confer susceptibility toward heroin addiction in a Pakistani population. A total of 540 heroin addicts and 467 healthy controls were genotyped, basic allele and genotype tests were performed. Neither rs1076560 nor rs2283265 significantly associated with heroin addiction. The enhancer rs12364283 occurs more frequently in heroin-dependent cases than controls (MAF 13% vs. 7%, respectively), revealing significant association with heroin addiction (p = 3.0E-06, OR 2.1). This study identifies rs12364283 of DRD2 as a potential risk factor for heroin addiction in the Pakistani study population. This enhancer variant had been shown to increase DRD2 mRNA expression, a possible factor in increased vulnerability to heroin addiction. Further studies are needed to validate this association of rs12364283.

VMAT2 gene (SLC18A2) variants associated with a greater risk for developing opioid dependence

Aim: To determine if selected serotonergic and noradrenergic gene variants are associated with heroin addiction. Subjects & methods: A total of 126 variants in 19 genes in subjects with Dutch European ancestry from The Netherlands. Subjects included 281 opioid-dependent volunteers in methadone maintenance or heroin-assisted treatment, 163 opioid-exposed but not opioid-dependent volunteers who have been using illicit opioids but never became opioid-dependent and 153 healthy controls. Results: Nominal associations were indicated for 20 variants in six genes including an experiment-wise significant association from the combined effect of three SLC18A2 SNPs (rs363332, rs363334 and rs363338) with heroin dependence (p_final = 0.047). Conclusion: Further studies are warranted to confirm and elucidate the role of these variants in the vulnerability to opioid addiction.

Central Nervous System Vasculitis Due to Substance Abuse

Illicit drug abuse is a common differential diagnosis of acquired central nervous system vasculitis even though there are only a handful of histopathologically confirmed patients in the literature from among the many potential classes of abused drugs traditionally implicated in this disease. This article considers the major classes of illicit drugs in those with and without human immunodeficiency virus type-1 infection and acquired immune deficiency syndrome.

Association of variants of prodynorphin promoter 68-bp repeats in caucasians with opioid dependence diagnosis: Effect on age trajectory of heroin use

The dynorphin/kappa opioid receptor (Dyn/KOR) system is involved in reward processing and dysphoria/anhedonia. Exposure to mu-opioid receptor agonists such as heroin increases expression of the prodynorphin gene (PDYN) in the brain. In this study in a Caucasian cohort, we examined the association of the functional PDYN 68-bp repeat polymorphism with opioid use disorders. In this case-control study, 554 subjects with Caucasian ancestry (142 healthy controls, 153 opioid-exposed, but never opioid dependent, NOD, and 259 with an opioid dependence diagnosis, OD) were examined for association of the PDYN 68-bp repeats with the diagnosis of opioid dependence (DSM-IV criteria), with a dimensional measure of heroin exposure (KMSK scale), and age trajectory parameters of heroin use (age of heroin first use, and age of onset of heaviest use). The PDYN 68-bp repeat genotype (classified as: "short-short" [SS], "long-long" [LL], and "short-long" [SL], based on the number of repeats) was not associated with categorical opioid dependence diagnoses. However, the LL genotype was associated with later age of first heroin use than the SS + SL genotype (19 versus 18 years; p < 0.01). This was also confirmed by a significant positive correlation between the number of repeats and the age of first use of heroin, in volunteers with OD (Spearman r = 0.16; p = 0.01). This suggests that the functional PDYN 68-bp repeat genotype is associated with the age of first use of heroin in Caucasians diagnosed with opioid dependence.

Polydrug use patterns and their impact on relapse among heroin-dependent patients in Shanghai, China

AIMS

To describe the polysubstance use patterns of heroin-dependent patients and to understand the impact of polysubstance use patterns on relapse during the 5 years after completing compulsory rehabilitation programmes.

DESIGN

In this secondary analysis, the baseline data of 503 heroin-dependent patients were linked with their 5-year follow-up data from official records.

SETTING

Four compulsory rehabilitation centres in Shanghai, China.

PARTICIPANTS

A total of 564 heroin-dependent patients who were discharged from Shanghai compulsory rehabilitation facilities in 2007 and 2008 were recruited. Among these, 503 patients with available follow-up records were included in this analysis.

MEASUREMENTS

The baseline measurements included the Addiction Severity Index, the Temperament and Character Inventory and the Medical Outcomes Study Social Support Scale. Relapses after discharge from the compulsory rehabilitation centres were extracted monthly from the official electronic record system. Latent class analysis was used to identify different polysubstance use patterns. Associations between the identified latent classes and heroin use and the factors related to relapse during the 5-year follow-up were analysed with the Cox regression model.

FINDINGS

Three latent classes were identified in this cohort: (1) alcohol polydrug users (APU; 13.7%), (2) low polydrug users (LPU; 76.5%) and (3) amphetamine-type stimulant polydrug users (ASPU; 9.7%). During the 5-year follow-up, 298 heroin patients relapsed, and the three groups showed different relapse rates (ASPU 69.4 versus LPU 60.5 versus APU 44.9%, P = 0.02). The average durations of abstinence for the three groups differed (ASPU 31.27 ± 3.41 months versus LPU 36.77 ± 1.19 months versus APU 42.46 ± 2.81 months, P = 0.02). Multivariate Cox regression analyses found that the LPU [hazard ratio (HR) = 1.63, 1.06-2.51] and ASPU (HR = 2.10, 1.24-3.56) classes were positively associated with the risk of heroin relapse.

CONCLUSION

Polydrug use patterns differ among heroin-dependent patients in compulsory rehabilitation programmes in China. A history of polydrug use may predict heroin relapse risk among patients in those compulsory rehabilitation programmes.

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.

Neurobiology of Opioid Use Disorder and Comorbid Traumatic Brain Injury

IMPORTANCE

Treating patients with opioid use disorder (OUD) and traumatic brain injury illustrates 6 neurobiological principles about the actions of 2 contrasting opioid analgesics, morphine and fentanyl, as well as pharmacotherapies for OUD, methadone, naltrexone, and buprenorphine.

OBSERVATIONS

This literature review focused on a patient with traumatic brain injury who developed OUD from chronic morphine analgesia. His treatment is described in a neurobiological framework of 6 opioid action principles.

CONCLUSIONS AND RELEVANCE

The 6 principles are (1) coactivation of neuronal and inflammatory immune receptors (Toll-like receptor 4), (2) 1 receptor activating cyclic adenosine monophosphate and β-arrestin second messenger systems, (3) convergence of opioid and adrenergic receptor types on 1 second messenger, (4) antagonist (eg, naltrexone)-induced receptor trafficking, (5) genetic μ-opioid receptor variants influencing analgesia and tolerance, and (6) cross-tolerance vs receptor antagonism as the basis of OUD pharmacotherapy with methadone or buprenorphine vs naltrexone.

The impact of OPRM1's genetic polymorphisms on methadone maintenance treatment in opioid addicts: a systematic review

Aim: Methadone is a long-acting opioid receptor agonist. It is prescribed to patients with opioid-related use disorders. The OPRM1 gene encodes for methadone's main receptor. It appears that polymorphisms in OPRM1 may affect the efficacy of methadone maintenance treatment (MMT). Objective: Our purpose was to identify all relevant published papers dealing with the impact ofOPRM1's SNPs  on MMT's efficacy and to summarize results in order to evaluate the relevance of conducting pretherapeutic genotyping in opioid addicts prior to the onset of MMT. Methods: MEDLINE, PsychINFO and Scopus databases were systematically searched up to 1 January  2018 with no year restrictions using the following keyword combination (MMT) AND (mu or OPRM or mu opioid receptors or SNP or polymorphism or gene). Endpoint of the included studies had to be the impact of OPRM1 gene polymorphisms on the efficacy of MMT and/or methadone required doses during MMT. All abstracts were reviewed to assess papers’ relevance. Studies conducted on animals and duplicate papers were excluded. Results: Our literature search identified 438 articles. Eight of them were included in our systematic review. The total number of included participants was equal to 2170, of whom 1718 underwent MMT. One study reported results of a randomized controlled trial. Three were designed as case–control studies and four as cross-sectional studies. rs1799971 (A118G) was the most studied allele. Results were divergent. Other SNPs might affect MMT's efficacy, however they were scarcely studied. Conclusion: Genotyping patients with opioid-related use disorders is a promising way to reach a better outcome in patients willing to be on MMT. Focusing on OPRM1 solely should be balanced since polymorphisms in other genes implicated in methadone pharmacodynamics and/or pharmacokinetics may conjunctly affect the efficacy of MMT. Recommendations cannot be enunciated for the moment.

Pharmacogenetics in Pain Treatment

Pain is an unpleasant feeling usually resulting from tissue damage that can persist along weeks, months, or even years after the injury, turning into pathological chronic pain, the leading cause of disability. Currently, pharmacology interventions are usually the first-line therapy but there is a highly variable analgesic drug response. Pharmacogenetics (PGx) offers a means to identify genetic biomarkers that can predict individual analgesic response opening doors to precision medicine. PGx analyze the way in which the presence of variations in the DNA sequence (single-nucleotide polymorphisms, SNPs) could be responsible for portions of the population reaching different levels of pain relief (phenotype) due to gene interference in the drug mechanism of action (pharmacodynamics) and/or its concentration at the place of action (pharmacokinetics). SNPs in the cytochrome P450 enzymes genes (CYP2D6) influence metabolism of codeine, tramadol, hydrocodone, oxycodone, and tricyclic antidepressants. Blood concentrations of some NSAIDs depend on CYP2C9 and/or CYP2C8 activity. Additional candidate genes encode for opioid receptors, transporters, and other molecules important for pharmacotherapy in pain management. However, PGx studies are often contradictory, slowing the uptake of this information. This is likely due, in large part, to a lack of robust evidence demonstrating clinical utility and to its polygenic response modulated by other exogenous or epigenetics factors. Novel therapies, including targeting of epigenetic changes and gene therapy-based approaches, broaden future options to improve understanding of pain and the treatment of people who suffer it.

Opioid Receptors Gene Polymorphism and Heroin Dependence in Iran

Introduction:

Genes often have multiple polymorphisms that interact with each other and the environment in different individuals. Variability in the opioid receptors can influence opiate withdrawal and dependence. In humans, A118G Single Nucleotide Polymorphisms (SNP) on μ-Opioid Receptor (MOR), 36 G>T in κ-Opioid Receptor (KOR), and T921C in the δ-Opioid Receptor (DOR) have been found to associate with substance dependence.

Methods:

To investigate the association between opioid receptors gene polymorphism and heroin addiction, 100 control subjects with no history of opioid use, and 100 heroin addicts (50% males and 50% females) in Tehran (capital of Iran), were evaluated. A118G, 36 G>T, and T921C SNPs on the MOR, KOR, DOR genes, respectively, were genotyped by sequencing.

Results:

We found no differences in either allele or genotype frequency for MOR, KOR and DOR genes SNPs between controls and subjects addicted to heroin.

Conclusion:

The relationships among polymorphisms may be important in determining the risk profile for complex diseases such as addiction, but opioid addiction is a multifactorial syndrome which is partially hereditary and partially affected by the environment.

Enkephalin as a Pivotal Player in Neuroadaptations Related to Psychostimulant Addiction

Enkephalin expression is high in mesocorticolimbic areas associated with psychostimulant-induced behavioral and neurobiological effects, and may also modulate local neurotransmission in this circuit network. Psychostimulant drugs, like amphetamine and cocaine, significantly increase the content of enkephalin in these brain structures, but we do not yet understand the specific significance of this drug-induced adaptation. In this review, we summarize the neurochemical and molecular mechanism of psychostimulant-induced enkephalin activation in mesocorticolimbic brain areas, and the contribution of this opioid peptide in the pivotal neuroadaptations and long-term behavioral changes underlying psychostimulant addiction. There is evidence suggesting that adaptive changes in enkephalin content in the mesocorticolimbic circuit, induced by acute and chronic psychostimulant administration, may represent a key initial step in the long-term behavioral and neuronal plasticity induced by these drugs.

Oprm1 A112G, a single nucleotide polymorphism, alters expression of stress-responsive genes in multiple brain regions in male and female mice

BACKGROUND

OPRM1 A118G, a functional human mu-opioid receptor (MOR) polymorphism, is associated with drug dependence and altered stress responsivity in humans as well as altered MOR signaling. MOR signaling can regulate many cellular processes, including gene expression, and many of the long-term, stable effects of drugs and stress may stem from changes in gene expression in diverse brain regions. A mouse model bearing an equivalent polymorphism (Oprm1 A112G) was previously generated and studied. Mice homozygous for the G112 allele show differences in opioid- and stress-related phenotypes.

APPROACH

The current study examines the expression of 24 genes related to drug and stress responsivity in the caudoputamen, nucleus accumbens, hypothalamus, hippocampus, and amygdala of drug-naïve, stress-minimized, male and female mice homozygous for either the G112 variant allele or the wild-type A112 allele.

RESULTS

We detected nominal genotype-dependent changes in gene expression of multiple genes. We also detected nominal sex-dependent as well as sex-by-genotype interaction effects on gene expression. Of these, four genotype-dependent differences survived correction for multiple testing: Avp and Gal in the hypothalamus and Oprl1 and Cnr1 in the hippocampus.

CONCLUSIONS

Changes in the regulation of these genes by mu-opioid receptors encoded by the G112 allele may be involved in some of the behavioral and molecular consequences of this polymorphism observed in mice.

Pharmacogenomics in pain treatment

The experience of chronic pain is one of the commonest reasons for seeking medical attention, being a major issue in clinical practice. While pain is a universal experience, only a small proportion of people who felt pain develop pain syndromes. In addition, painkillers are associated with wide inter-individual variability in the analgesic response. This may be partly explained by the presence of single nucleotide polymorphisms in genes encoding molecular entities involved in pharmacodynamics and pharmacokinetics. However, uptake of this information has been slow due in large part to the lack of robust evidences demonstrating clinical utility. Furthermore, novel therapies, including targeting of epigenetic changes and gene therapy-based approaches are further broadening future options for the treatment of chronic pain. The aim of this article is to review the evidences behind pharmacogenetics (PGx) to individualize therapy (boosting the efficacy and minimizing potential toxicity) and genes implicated in pain medicine, in two parts: (i) genetic variability with pain sensitivity and analgesic response; and (ii) pharmacological concepts applied on PGx.

Pharmacoepigenomics of opiates and methadone maintenance treatment: current data and perspectives

Current treatments of opioid addiction include primarily maintenance medications such as methadone. Chronic exposure to opiate and/or long-lasting maintenance treatment induce modulations of gene expression in brain and peripheral tissues. There is increasing evidence that epigenetic modifications underlie these modulations. This review summarizes published results on opioid-induced epigenetic changes in animal models and in patients. The epigenetic modifications observed with other drugs of abuse often used by opiate abusers are also outlined. Specific methadone maintenance treatment induced epigenetic modifications at different treatment stages may be combined with the ones resulting from patients’ substance use history. Therefore, research comparing groups of addicts with similar history and substances use disorders but contrasting for well-characterized treatment phenotypes should be encouraged.

Genetic Variation of the Mu Opioid Receptor (OPRM1) and Dopamine D2 Receptor (DRD2) is Related to Smoking Differences in Patients with Schizophrenia but not Bipolar Disorder

It is not known why mentally ill persons smoke excessively. Inasmuch as endogenous opioid and dopaminergic systems are involved in smoking reinforcement, it is important to study mu opioid receptor (OPRM1) A118G (rs1799971), dopamine D2 receptor (DRD2) Taq1A (rs1800497) genotypes, and sex differences among patients with schizophrenia or bipolar disorder. Smokers and nonsmokers with schizophrenia (n=177) and bipolar disorder (n=113) were recruited and genotyped. They were classified into three groups: current smoker, former smoker, and never smoker by tobacco smoking status self-report. The number of cigarettes smoked per day was used as the major tobacco smoking parameter. In patients with schizophrenia, tobacco smoking prevalence was greater in males than in females as expected, but women had greater daily cigarette consumption (p<0.01). Subjects with schizophrenia who had the OPRM1 *G genotype smoked more cigarettes per day than the AA allele carriers with schizophrenia (p<0.05). DRD2 Taq1A genotype differences had no effect on the number of cigarettes smoked per day. However, female smokers with schizophrenia who were GG homozygous of the DRD2 receptor smoked more than the *A male smokers with schizophrenia (p<0.05). In bipolar patients, there were no OPRM1 and DRD2 Taq1A genotype differences in smoking status. There also were no sex differences for smoking behavior among the bipolar patients. The results of this study indicate that single nucleotide polymorphism (SNP) of the less functional mu opioid receptor increases tobacco smoking in patients with schizophrenia. Alteration of DRD2 receptor function also increased smoking behavior in females with schizophrenia.