Molecular Genetics and New Medication Strategies for Opioid Addiction

OPRM1 rs2075572 has potential to affect plasma buprenorphine level in opioid users, but not OPRM1 rs562859

OPRM1 gene encoding mu-opioid receptor (MOR) is the primary candidate gene for buprenorphine (BUP) pharmacogenetics. OPRM1 undergoes alternative splicing leading to multiple MOR subtypes. Thus, in the current study 2 SNPs (rs1799972 and rs562859) were selected due to evidence for their contribution to alternative splicing of OPRM1. The effects of 2 SNPs of OPRM1 gene on plasma buprenorphine and norbuprenorphine levels in a sample of 233 OUD patients receiving BUP/naloxone were examined. Polymorphisms were analyzed by PCR and RFLP. BUP and norbuprenorphine concentrations in plasma were measured by LC-MS/MS. OPRM1 rs2075572 GC + CC (0.12 ng/ml) had significantly higher plasma BUP level compared to GG (0.084 ng/ml) (p = 0.043). Although there was not a statistically significant difference between OPRM1 rs562859 genotypes (p = 0.46), patients with OPRM1 rs562859 CT + TT had higher plasma BUP and BUP-related values as compared to those with CC. In conclusion, the effect of OPRM1 rs2075572 on BUP levels in opioid users' plasma was shown in a Caucasian population for the first time. On the other hand, OPRM1 rs562859 seems not to influence the BUP pharmacology.

OPRM1 Gene Polymorphism in Women with Alcohol Use Disorder

The main aims of the present study were to explore the relationship of the OPRM1 gene rs1074287 polymorphism in alcohol-dependent women with their personality traits and to try to find out whether any specific features may influence alcohol cravings and be a prognostic for alcohol dependency and treatment in AUD women. Our study found a notable correlation between openness and the interaction of the ORIM1 gene and AUD. The alcohol use disorder subjects with genotype AG showed a higher level of openness compared to the control group with genotypes AG (p = 0.0001) and AA (p = 0.0125). The alcohol use disorder subjects with the AA genotype displayed higher levels of openness than the control group with genotype AG (p = 0.0271). However, the alcohol use disorder subjects with the AA genotype displayed lower levels of openness than the control group with genotype GG (p = 0.0212). Our study indicates that openness as a personality trait is correlated with the OPRM1 gene rs1074287 polymorphism in alcohol-dependent women. These are the first data and results exploring such a relationship between opioid and alcohol pathways and the mental construction of AUD women. Personality traits such as openness to experience and neuroticism might play major roles in the addiction mechanism, especially in genetically predisposed females, independent of the reward system involved in the emotional disturbances that coexist with anxiety and depression.

A novel tetra-primer ARMS-PCR for genotyping of the OPRM1 gene rs1799971 variant associated with opioid use disorders

OBJECTIVES

A SNV is a single nucleotide change that can occur at any point in the genome. SNVs are the most common genetic variants that occur in the human genome, and a number of SNVs have been found to be associated with human traits and disease. Researchers genotype SNVs using TaqMan technology, DNA microarray, MALDI-TOF mass spectrometry, and automated sequencing, which are expensive and time-consuming. The OPRM1 gene rs1799971 (A118G) has been identified for its association with Opioid use disorder (OUD). The present study focused on developing a single step identification test using Tetra-Primer Amplification Refractory Mutation System-PCR (T-ARMS-PCR) to detect the presence of SNV OPRM1 rs1799971 (A118G). This study was performed to optimize the protocol for the designed four primers and validate it using a total of 52 buccal samples from volunteers who are currently under rehabilitation for the drug abuse disorder.

RESULTS

Utilizing 52 DNA samples, a novel T-ARMS-PCR assay was successfully developed, tested, and validated. The products of the T-ARMS PCR for rs1799971 contained 395 bp as the control band, 186 bp as G allele (variant) and 257 bp as A allele (wild type), which were observed in the gel image. The genotype frequencies for the OPRM1 gene rs1799971 (A118G) were 44% (22/52) of homozygous variant type (GG), 28.9% (15/52) of homozygous wild type (AA) and 28.9% (15/22) of heterozygous (AG). The G allele frequency was 56.7% and A allele frequency was 43.3%.

Chronic Δ9-tetrahydrocannabinol impact on plasticity, and differential activation requirement for CB1-dependent long-term depression in ventral tegmental area GABA neurons in adult versus young mice

The ventral tegmental area (VTA) mediates incentive salience and reward prediction error through dopamine (DA) neurons that are regulated by local VTA GABA neurons. In young mice, VTA GABA cells exhibit a form of synaptic plasticity known as long-term depression (LTD) that is dependent on cannabinoid 1 (CB1) receptors preceded by metabotropic glutamate receptor 5 (mGluR5) signaling to induce endocannabinoid production. This LTD was eliminated following chronic (7-10 consecutive days) exposure to the marijuana derived cannabinoid Δ9 -tetrahydrocannabinol (THC). We now examine the mechanism behind THC-induced elimination of LTD in adolescents as well as plasticity induction ability in adult versus young male and female mice using whole-cell electrophysiology experiments of VTA GABA cells. Chronic THC injections in adolescents resulted in a loss of CB1 agonist-mediated depression, illustrating chronic THC likely desensitizes or removes synaptic CB1. We noted that seven days withdrawal from chronic THC restored LTD and CB1 agonist-induced depression, suggesting reversibility of THC-induced changes. Adult mice continue to express functional mGluR5 and CB1, but require a doubling of the synaptic stimulation compared to young mice to induce LTD, suggesting a quantitative difference in CB1-dependent plasticity between young and adult mice. One potential rationale for this difference is changes in AMPA and NMDA glutamate receptors. Indeed, AMPA/NMDA ratios were increased in in adults compared to young mice. Lastly, we performed quantitative reverse-transcription PCR and identified that CB1, DAGLα, and GluA1 levels increased following chronic THC exposure. Collectively, our data demonstrate the first age-dependent GABA neuron plasticity in the VTA, which could have implications for decreased THC dependence capacity in adults, as well as the mechanism behind chronic THC-induced synaptic alterations in young mice.

New Approaches in Drug Dependence: Opioids

Purpose of Review

This article aims to provide an overview of standard and adjunctive treatment options in opioid dependence in consideration of therapy-refractory courses. The relevance of oral opioid substitution treatment (OST) and measures of harm reduction as well as heroin-assisted therapies are discussed alongside non-pharmacological approaches.

Recent Findings

Currently, recommendation can be given for OST with methadone, buprenorphine, slow-release oral morphine (SROM), and levomethadone. Heroin-assisted treatment using diamorphine shall be considered as a cost-effective alternative for individuals not responding to the afore-mentioned opioid agonists in order to increase retention and reduce illicit opioid use. The modalities of application and the additional benefits of long-acting formulations of buprenorphine should be sufficiently transferred to clinicians and the eligible patients; simultaneously methods to improve planning of actions and self- management need to be refined. Regarding common primary outcomes in research on opioid treatment, evidence of the effectiveness of adjunctive psychological interventions is scarce.

Summary

Maintaining a harm reduction approach in the treatment of opioid addiction, a larger range of formulations is available for the prescribers. Embedding the pharmacological, ideally individualized treatment into a holistic, structure-giving concept also requires a reduction of fragmentation of ancillary services available, drug policies, and treatment philosophies on a global scale.

Can Src protein tyrosine kinase inhibitors be combined with opioid analgesics? Src and opioid-induced tolerance, hyperalgesia and addiction

The clinical application of opioids may be accompanied by a series of adverse consequences, such as opioid tolerance, opioid-induced hyperalgesia, opioid dependence or addiction. In view of this issue, clinicians are faced with the dilemma of treating various types of pain with or without opioids. In this review, we discuss that Src protein tyrosine kinase plays an important role in these adverse consequences, and Src inhibitors can solve these problems well. Therefore, Src inhibitors have the potential to be used in combination with opioids to achieve synergy. How to combine them together to maximize the analgesic effect while avoiding unnecessary trouble provides a topic for follow-up research.

Prenatal opioid exposure and vulnerability to future substance use disorders in offspring

The heightened incidence of opioid use during pregnancy has resulted in unprecedented rates of neonates prenatally exposed to opioids. Prenatal opioid exposure (POE) results in significantly adverse medical, developmental, and behavioral outcomes in offspring. Of growing interest is whether POE contributes to future vulnerability to substance use disorders. The effects of POE on brain development is difficult to assess in humans, as the timing, dose, and route of drug exposure together with complex genetic and environmental factors affect susceptibility to addiction. Preclinical models of POE have allowed us to avoid methodological difficulties and confounding factors of POE in humans. Here, we review the effects of maternal opioid exposure on the developing brain with an emphasis on the neurobiological basis of drug addiction and on preclinical models of POE and their limitations. These studies have indicated that POE increases self-administration of drugs, reward-driven behaviors in the conditioned place paradigm, and locomotor sensitization. While addiction is multifaceted and vulnerability to drug addiction is still inconclusive in human studies of prenatally exposed infants, animal studies do provide a noteworthy corroboration of negative behavioral outcomes.

Repeated morphine exposure activates synaptogenesis and other neuroplasticity-related gene networks in the dorsomedial prefrontal cortex of male and female rats

BACKGROUND

Opioid abuse is a chronic disorder likely involving stable neuroplastic modifications. While a number of molecules contributing to these changes have been identified, the broader spectrum of genes and gene networks that are affected by repeated opioid administration remain understudied.

METHODS

We employed Next-Generation RNA-sequencing (RNA-seq) followed by quantitative chromatin immunoprecipitation to investigate changes in gene expression and their regulation in adult male and female rats' dorsomedial prefrontal cortex (dmPFC) after a regimen of daily injection of morphine (5.0 mg/kg; 10 days). Ingenuity Pathway Analysis (IPA) was used to analyze affected molecular pathways, gene networks, and associated regulatory factors. A complementary behavioral study evaluated the effects of the same morphine injection regimen on locomotor activity, pain sensitivity, and somatic withdrawal signs.

RESULTS

Behaviorally, repeated morphine injection induced locomotor hyperactivity and hyperalgesia in both sexes. 90 % of differentially expressed genes (DEGs) in morphine-treated rats were upregulated in both males and females, with a 35 % overlap between sexes. A substantial number of DEGs play roles in synaptic signaling and neuroplasticity. Chromatin immunoprecipitation revealed enrichment of H3 acetylation, a transcriptionally activating chromatin mark. Although broadly similar, some differences were revealed in the gene ontology networks enriched in females and males.

CONCLUSIONS

Our results cohere with findings from previous studies based on a priori gene selection. Our results also reveal novel genes and molecular pathways that are upregulated by repeated morphine exposure, with some common to males and females and others that are sex-specific.

Recent Advances in the Treatment of Opioid Use Disorder

PURPOSE OF REVIEW

Opioid use disorder (OUD) remains a national epidemic with an immense consequence to the United States' healthcare system. Current therapeutic options are limited by adverse effects and limited efficacy.

RECENT FINDINGS

Recent advances in therapeutic options for OUD have shown promise in the fight against this ongoing health crisis. Modifications to approved medication-assisted treatment (MAT) include office-based methadone maintenance, implantable and monthly injectable buprenorphine, and an extended-release injectable naltrexone. Therapies under investigation include various strategies such as heroin vaccines, gene-targeted therapy, and biased agonism at the G protein-coupled receptor (GPCR), but several pharmacologic, clinical, and practical barriers limit these treatments' market viability. This manuscript provides a comprehensive review of the current literature regarding recent innovations in OUD treatment.

Evolution of regulatory signatures in primate cortical neurons at cell-type resolution

The human cerebral cortex contains many cell types that likely underwent independent functional changes during evolution. However, cell-type-specific regulatory landscapes in the cortex remain largely unexplored. Here we report epigenomic and transcriptomic analyses of the two main cortical neuronal subtypes, glutamatergic projection neurons and GABAergic interneurons, in human, chimpanzee, and rhesus macaque. Using genome-wide profiling of the H3K27ac histone modification, we identify neuron-subtype-specific regulatory elements that previously went undetected in bulk brain tissue samples. Human-specific regulatory changes are uncovered in multiple genes, including those associated with language, autism spectrum disorder, and drug addiction. We observe preferential evolutionary divergence in neuron subtype-specific regulatory elements and show that a substantial fraction of pan-neuronal regulatory elements undergoes subtype-specific evolutionary changes. This study sheds light on the interplay between regulatory evolution and cell-type-dependent gene-expression programs, and provides a resource for further exploration of human brain evolution and function.

Is marijuana use associated with decreased use of prescription opioids? Toxicological findings from two US national samples of drivers

Background

State governments in the United States are increasingly viewing marijuana legalization as a policy option for controlling the opioid epidemic under the premise that marijuana is a less harmful substitute for opioids. The purpose of this study is to assess whether marijuana use is associated with decreased odds of prescription opioid use.

Methods

A cross-sectional study design was applied to toxicological testing data from two national samples of drivers: 1) the 2011–2016 Fatality Analysis Reporting System (FARS) and 2) the 2013–2014 National Roadside Survey of Alcohol and Drug Use by Drivers (NRS). Adjusted odds ratios (ORs) and 95% confidence intervals (CIs) estimated from multivariable logistic regression models were used to assess the associations of marijuana use with prescription opioid use and alcohol use.

Results

Among the 47,602 drivers from the FARS, 15.7% tested positive for marijuana and 6.9% positive for prescription opioids. Compared with drivers testing negative for marijuana, those testing positive for marijuana were 28% more likely to test positive for prescription opioids (adjusted OR = 1.28, 95% CI = 1.15–1.42). Among the 7881 drivers from the NRS, 7.9% tested positive for marijuana and 4.5% positive for prescription opioids. Relative to drivers testing negative for marijuana, those testing positive for marijuana were twice as likely to test positive for prescription opioids (adjusted OR = 2.03, 95% CI = 1.29–3.20). In both study samples, marijuana use was associated with significantly increased odds of alcohol positivity.

Conclusions

Drivers who test positive for marijuana are significantly more likely to test positive for prescription opioids. Longitudinal studies with rigorous designs and toxicological testing data are needed to further address the substitution hypothesis between marijuana and prescription opioids.

Pharmacokinetic and pharmacodynamic considerations in developing a response to the opioid epidemic

Introduction: Opioids continue to be used widely for pain management. Widespread availability of prescription opioids has led to opioid abuse and addiction. Besides steps to reduce inappropriate prescribing, exploiting opioid pharmacology to make their use safer is important.Areas covered: This article discusses the pathology and factors underlying opioid abuse. Pharmacokinetic and pharmacodynamic properties affecting abuse liability of commonly abused opioids have been highlighted. These properties inform the development of ideal abuse deterrent products. Mechanisms and cost-effectiveness of available abuse deterrent products have been reviewed in addition to the pharmacology of medications used to treat addiction.Expert opinion: The opioid crisis presents unique challenges to managing pain effectively given the limited repertoire of strong analgesics. The 5-point strategy to combat the opioid crisis calls for better preventive, treatment, and recovery services, better data, better pain management, better availability of overdose-reversing drugs and better research. There is an urgent need to decrease the cost of abuse deterrent opioids which deters their cost-effectiveness. In addition, discovery of novel analgesics, further insight into central and peripheral pain mechanisms, understanding genomic risk profiles for efficient targeted efforts, and education will be key to winning this fight against the opioid crisis.

Clinical Trials for Opioid Use Disorder

This chapter describes recent clinical trials for opioid use disorder (OUD), an area that has rapidly accelerated in response to the opioid overdose crisis in the USA and newly appropriated funding. Trials involve a wide range of compounds including cannabinoids and psychedelics, new and existing compounds targeting domains emerging from addiction neuroscience, agents repurposed from other indications, and novel strategies including vaccines, enzymes, and other biologicals. In parallel, new formulations of existing compounds offer immediate promise, as do a variety of web-based interventions and smartphone-delivered apps. Trials focused on implementing existing effective interventions in mainstream healthcare settings, and others focused on special populations, e.g., adolescents, criminal justice, pregnant women, native Americans, etc., have the potential to vastly expand treatment in the near term. Given the range of ongoing and recent trials, this chapter is not intended to be an exhaustive review but rather to present an overview of approaches within the framework of the opioid treatment cascade and the context of current OUD pharmacotherapies.

Improving naltrexone compliance and outcomes with putative pro- dopamine regulator KB220, compared to treatment as usual

A recent analysis from Stanford University suggested that without any changes in currently available treatment, prevention, and public health approaches, we should expect to have 510,000 deaths from prescription opioids and street heroin from 2016 to 2025 in the US. In a recent review, Mayo Clinic Proceedings (October 2019), Gold and colleagues at Mayo Clinic reviewed the available medications used in opioid use disorders and concluded that in private and community practice adherence is more important as a limiting factor to retention, relapse, and repeat overdose. It is agreed that the primary utilization of known opioid agonists like methadone, buprenorphine and naloxone combinations, while useful as a way of reducing societal harm, is limited by 50% of more discontinuing treatment within 6 months, their diversion, and addiction liability. Opioid agonists may have other unintended consequences, like continuing the down regulation of dopamine systems. While naltrexone would be expected to have opposite effects, adherence is also low even after detoxification and long acting naltrexone injections. Recent studies have shown Naltrexone is beneficial by attenuation of craving via “psychological extinction” and reducing relapse. Buprenorphine is the MAT of choice currently but injectable Naltrexone plus an agent to improve dopaminergic function and tone may renew interest amongst addiction physicians and patients. Understanding this dilemma there is increasing movement to opt for the non-addicting narcotic antagonist Naltrexone. Even with extended injectable option there is still poor compliance. As such, we describe an open label investigation in humans showing improvement of naltrexone compliance and outcomes with dopamine augmentation with the pro- dopamine regulator KB220 (262 days) compared to naltrexone alone (37days). This well studied complex consists of amino-acid neurotransmitter precursors and enkephalinase inhibitor therapy compared to treatment as usual. Consideration of this novel paradigm shift may assist in not only addressing the current opioid epidemic but the broader question of reward deficiency in general.

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.

Fentanyl overdoses and pharmacogenetics

Fentanyl has been implicated as a major contributor to the increased number of opioid overdose deaths. Surprisingly, little is known about the pharmacogenetic influences on fentanyl pharmacokinetics or pharmacodynamics. Pharmacogenetic studies of fentanyl are based largely on small sample sizes and have examined the potential association of only a small number of high frequency variants in selected candidate genes primarily with postoperative pain. Few data are available on low frequency variants, variants from racially/ethnically diverse populations, or on other phenotypes. Given the genetic diversity of low frequency variants, DNA sequencing may be needed to determine whether pharmacogenetic differences may contribute to lethal opioid overdoses.

Do human subject safeguards matter to potential participants in psychiatric genetic research?

Despite longstanding concerns about the adequacy of human research protections in mental illness investigations, minimal work has focused on the perspectives of key stakeholders regarding these safeguards. This investigation examined the perspectives of potential research participants regarding safeguards for psychiatric genetic research. Individuals with mental illness (n = 71), first-degree family members of individuals with mental illness (n = 54), and individuals with no personal or close family history of mental illness (n = 57) provided responses to items regarding perceptions of: 1) protectiveness of a range of research safeguards in genetic research on mental illness; 2) influence of these safeguards on research participation decision-making; and 3) importance of these safeguards depending on the nature of the research (i.e., genetic vs. non-genetic mental illness research; and genetic research on mental illness vs. physical illness). Potential research participants perceived existing safeguard procedures as generally protective. The three groups did not differ in their ratings of protectiveness, with the exception of the safeguard domain of "Informed Consent or Alternative Decision-Making Procedures," which was viewed as more protective by family members of people with mental illness than by individuals with mental illness or comparison participants. Safeguard procedures were perceived as strongly influential with respect to willingness to enroll in psychiatric genetic research. These findings suggest that the presence of safeguards positively influences enrollment decision-making by research volunteers and indicate that potential psychiatric genetic research participants find safeguards to be protective, underscoring the responsibility to implement safeguard practices conscientiously.

Risk Factors and Prevention Strategies for Postoperative Opioid Abuse

Worldwide, 80% of patients who undergo surgery receive opioid analgesics as the fundamental agent for pain relief. However, the irrational use of opioids leads to excessive drug dependence and drug abuse, resulting in an increased mortality rate and huge economic loss. The crisis of opioid overuse remains a great challenge. In this review, we summarize several key factors in opioid abuse, including race, region, income, genetic factors, age and gender, smoking and alcohol abuse, history of chronic pain and analgesic drug abuse, surgery, neuropsychiatric illness, depression and antidepressant use, human factors, national policies, hospital regulations, and health insurance under treatment of pain. Furthermore, we present several prevention strategies, such as perioperative measures, opioid substitutes, treatment of the primary illness, emotional regulation, use of opioid antagonists, efforts of the state, hospitals, doctors and pharmacy benefit managers, gene therapy, and vaccines. Greater understanding and better assessment are required of the risks associated with opioid abuse to ensure the safety and analgesic effects of pain treatment after surgery.

Management of opioid use disorder in the USA: present status and future directions

Opioid use disorder is characterised by the persistent use of opioids despite the adverse consequences of its use. The disorder is associated with a range of mental and general medical comorbid disorders, and with increased mortality. Although genetics are important in opioid use disorder, younger age, male sex, and lower educational attainment level and income, increase the risk of opioid use disorder, as do certain psychiatric disorders (eg, other substance use disorders and mood disorders). The medications for opioid use disorder, which include methadone, buprenorphine, and extended-release naltrexone, significantly improve opioid use disorder outcomes. However, the effectiveness of medications for opioid use disorder is limited by problems at all levels of the care cascade, including diagnosis, entry into treatment, and retention in treatment. There is an urgent need for expanding the use of medications for opioid use disorder, including training of health-care professionals in the treatment and prevention of opioid use disorder, and for development of alternative medications and new models of care to expand capabilities for personalised interventions.

Positron emission tomography probes targeting bromodomain and extra-terminal (BET) domains to enable in vivo neuroepigenetic imaging

Novel PET radiotracer of BET proteins enable in vivo neuroepigenetic imaging.