A mu opioid receptor gene polymorphism (A118G) and naltrexone treatment response in adherent Korean alcohol-dependent patients

Rationale  Previous studies have demonstrated an association between genetic polymorphisms of the μ opioid receptor gene (OPRM1) and response to naltrexone treatment. The Asp40 variant genotype previously shown to be associated with naltrexone treatment response is known to be relatively common among Koreans. Objectives  This study was conducted to prospectively investigate the relationship between genotype and response to open-label naltrexone treatment in Korean alcohol-dependent subjects. Materials and methods  Sixty-three alcohol-dependent subjects were prescribed naltrexone for 12 weeks in combination with cognitive behavioral therapy. Thirty-two subjects were adherent, taking the medication at least 80% of the treatment days [16 Asn40 (A/A) patients and 16 Asp40 variant (A/G or G/G) patients]. Results  Subjects adherent to naltrexone treatment with one or two copies of the Asp40 allele took a significantly longer time than the Asn40 group to relapse (p = 0.014). Although not significant, the Asn40 group treated with naltrexone had a 10.6 times greater relapse rate than the Asp40 variant group. There was no significant difference between the Asn40 group and the Asp40 variant group treated with naltrexone in rates of abstinence. Conclusions  These results demonstrating a higher therapeutic effect of naltrexone in Korean alcohol-dependent individuals with the Asp40 variant genotype than the Asn40 genotype are consistent with previous study results in individuals of European descent. This is the first study to examine the pharmacogenetics treatment response to naltrexone in non-European subjects.     

The mu-opioid receptor gene polymorphism (A118G) alters HPA axis activation induced by opioid receptor blockade.

An A118G nucleotide exchange in exon 1 of the mu-opioid receptor causes an Asn40Asp substitution polymorphism in the receptor's extracellular domain. In vitro studies show that the Asp40 variant of the mu-opioid receptor binds beta-endorphin three times more avidly than the more common Asn40 variant. Paraventricular corticotropin releasing hormone neurons, which activate the HPA axis, express mu-opioid receptors and are modulated by beta-endorphin neurons. This preliminary study was designed to test the hypothesis that the Asn40Asp substitution polymorphism in the mu-opioid receptor influences HPA axis activation induced by opioid receptor blockade. Thirty-nine healthy men were genotyped (A vs. G) and then underwent opioid receptor blockade with Naloxone. Subjects expressing the A118G receptor variant had greater cortisol responses to opioid receptor blockade. Also, a significant difference in the rate of increase of ACTH (slope) between A/A and A/G was observed between 30-90 minutes as well as a significant difference in the rate of decrease after 90 minutes. Moreover, subjects expressing the variant polymorphism had lower scores on the Conscientiousness Factor and associated subscales of NEO Personality Inventory compared to subjects expressing the common receptor. Because serotonin also modulates the CRF neuron, subjects were genotyped for a functional polymorphism within the serotonin transporter gene. We did not see differences in hormone responses resulting from expression of this functional polymorphism. It is plausible that persons expressing the mu-opioid receptor variant have altered HPA axis dynamics and altered responses to other physiological processes regulated through activation of the mu-opioid receptor.     

The Micro-opioid receptor polymorphism A118G predicts cortisol responses to naloxone and stress.

A polymorphism in the micro-opioid receptor (MOR) (A118G) has been shown to increase beta-endorphin binding affinity, theoretically placing greater inhibitory tone on hypothalamic corticotropin-releasing hormone (CRH) neurons. We hypothesized that the minor allele (G) would predict cortisol responses to both pharmacological (naloxone) and psychological (stress) activation of the hypothalamic-pituitary-adrenal (HPA) axis. Healthy subjects (mean age 25.2 years, SD 9.2 years) completed a naloxone challenge (n=74) and/or the modified Trier Social Stress Test (TSST) (n=86). For the naloxone challenge, two baseline blood samples were obtained. Then, five increasing doses of i.v. naloxone were administered at 30-min intervals and 12 additional blood samples were collected at 15-min intervals. The TSST consisted of 5-min of public speaking and 5-min of mental arithmetic exercises. Three baseline and five post-TSST blood samples were drawn. Both the naloxone and TSST groups had significant adrenocorticotropin (ACTH) and cortisol responses to their respective challenges (P<0.001). There were no differences in baseline ACTH, baseline cortisol, or ACTH response by genotype in either the naloxone or the TSST group. Among subjects expressing a G allele, there was a higher cortisol response to naloxone (P=0.046), but a lower cortisol response to the TSST (P=0.044). In conclusion, the minor allele (G) was associated with a robust cortisol response to naloxone blockade, but a blunted response to psychosocial stress. We speculate that increased opioid avidity of the minor allele receptor contributes to the differential response to naloxone vs stress.     

Involvement of the mu-opioid receptor gene polymorphism A118G in the efficacy of detoxification of alcohol dependent patients

Introduction

The A118G (rs 1799971) polymorphism in the mu-opioid receptor gene (OPRM1) has been reported to be associated with alcohol addiction.

Methods

In this study 109 patients diagnosed with alcohol dependence in accordance with DMS-IV criteria and 95 healthy subjects were enrolled and everyone has been genotyped.

Results

The percentage of alcoholic patients with higher than normal gamma-glutamyl transferase (GGT) levels significantly decreased after six months of standard detoxification treatment, both in patients with A/A genotype and in the other ones with A/G genotype. However, the percentage of alcohol dependent patients with the A/A genotype recorded a slight decrease of the GGT and the mean corpuscolar volume of erythrocytes (MCV) combination marker after six months of therapy (30% vs 12%), while subjects with the A/G genotype showed no variation.

Conclusion

This finding suggests that alcohol dependent patients with the A/A genotype could have a faster restoration of their liver function than those ones with the A/G genotype: it might be possible that the presence of G allele confers on these patients a reduced ability in abstaining from drinking alcohol.     

Association of an Asn40Asp (A118G) polymorphism in the mu-opioid receptor gene with substance dependence: a meta-analysis

INTRODUCTION: The mu-opioid receptor has been implicated in the pathogenesis of dependence on opioids, alcohol, nicotine, and cocaine. Studies examining the association of the mu-opioid receptor gene (genetic locus OPRM1) with substance dependence (SD) have focused on the Asn40Asp (A118G) single nucleotide polymorphism (SNP). METHOD: We used meta-analysis to examine the literature on the association of Asn40Asp with SD. Twenty-two articles describing 28 distinct samples and over 8000 subjects were included. A variety of factors (i.e., ethnicity, type of SD, rigor with which controls were screened, severity of SD among cases) were examined as potential moderators of the association. RESULTS: Four studies showed a significantly higher frequency of the Asp40 allele among SD cases, while three studies showed a significantly higher frequency of the Asp40 allele among controls. There was no significant association between Asn40Asp and SD (OR=1.01, 95%CI=0.86-1.19), nor was there substantial evidence of a moderator effect. CONCLUSION: The Asn40Asp SNP in OPRM1 does not appear to affect risk for SD. Additional research is needed to determine whether these findings reflect no role for OPRM1 in determining risk for SD or whether another polymorphism in the gene influences receptor function and risk for SD.     

Adverse effects associated with non-opioid and opioid treatment in patients with chronic pain

Chronic pain is a debilitating condition that is associated with many common diseases; this places a major burden on the healthcare system. There are currently numerous analgesic agents available for the treatment of chronic pain. In general, the oral non-opioid analgesic, paracetamol, is recommended for the initial treatment of mild to moderate pain. Therapeutic doses of paracetamol do not appear to result in hepatotoxicity, although overdose may lead to acute liver failure. Current data suggest that paracetamol has acceptable gastrointestinal tolerability. Another class of non-opioid analgesic with confirmed efficacy for the treatment of chronic mild to moderate pain are non-steroidal anti-inflammatory drugs (NSAIDs), although this efficacy is offset by the potential of adverse gastrointestinal events. In particular, non-selective NSAIDs, also known as cyclooxygenase (COX) inhibitors, carry an increased risk of serious upper gastrointestinal complications, including ulcers, perforation and bleeding. The introduction of COX-2 inhibitors provided a NSAID-based option with improved gastrointestinal safety, but increased risk of cardiovascular effects. Opioids are powerful analgesic agents used to treat moderate to severe chronic pain. However, treatment with opioids is associated with a number of common adverse effects, including constipation, nausea or vomiting, pruritus, somnolence or cognitive impairment, dry mouth, tolerance or dependence and urinary retention. Although there are multiple strategies in place to manage adverse events that arise from both non-opioid and opioid analgesic therapy, a better understanding of the mechanisms involved in the development of specific drug-related adverse effects is required along with proper prescribing practices and adequate physician/patient education. Balanced against the adverse effects of pain management medications, there is a need to be mindful of the widespread, often serious, adverse consequences of poorly managed pain itself.     

海洛因依赖和μ阿片受体A118G多态性的关联：Meta分析

目的：探讨汉族人群中海洛因依赖和μ阿片受体基因（OPRM1）A118G多态性的关联。方法：检索PubMed，CNKI，维普等数据库，搜集有关汉族人群海洛因依赖和A118G多态性关联研究的相关文献，然后进行Meta分析。结果：A118G基因型G／G在海洛因依赖组和对照组之间的比较中，异质性检验无显著性差异（P=O．49），遂选用固定效应模型，合并OR=0．90（95％CI，0．64—1．25），效应检验结果提示没有显著性差异（P=0．51）；A118G等位基因G在海洛因依赖组和对照组之间的比较中，异质性检验存在显著性差异（P=0．03），则选用随机效应模型，合并OR=0．94（95％CI，0．71—1．23），效应检验结果提示不存在显著性差异（P=0．63）。结论：汉族人群海洛因依赖与A118G多态性的基因型和等位基因不存在关联性。     

Ile118Val genetic polymorphism of CYP3A4 and its effects on lipid-lowering efficacy of simvastatin in Chinese hyperlipidemic patients

Objectives To determine the frequencies of CYP3A4 alleles (CYP3A4*4,*5 and *6) in Chinese hyperlipidemic patients and to observe the impact of CYP3A4*4 (Ile118Val) genetic polymorphism on the lipid-lowering effects of simvastatin and on the activity of CYP3A4.Methods From hospitalized and non-hospitalized patients, 211 unrelated hyperlipidemic patients were recruited for genotyping. CYP3A4 genotypes were determined by means of polymerase chain reaction and restriction fragment length polymorphism analysis. Of the non-hospitalized hyperlipidemic patients, 8 with CYP3A4*1/*1 and 8 with CYP3A4*1/*4 genotypes were selected to be treated with 20 mg simvastatin daily for 4 weeks. Serum triglycerides (TG), cholesterol (CHO) and low-density lipoprotein (LDL) levels were determined using an automated analyzer (Hitachi 747, Boehringer Mannheim, Mannheim, Germany). CYP3A4 activity was determined by the ratio of 6-hydroxycortisol to free cortisol (6-OHC/FC) in the morning spot urine with a high-throughput liquid chromatography–tandem mass spectrometry method.Results Of 211 subjects, 14 (allele frequency 3.32%) were heterozygous for CYP3A4*4 (Ile118Val). Nevertheless, no subjects with a CYP3A4*5 or CYP3A4*6 allele or homozygous for CYP3A4*4 were identified. The ratio of 6-OHC/FC was 9.9±13.7 and 56.6±35.7 in subjects with the Ile118Val variant (n=8) and in CYP3A4 wild-type subjects (n=8), respectively (P=0.0039). After oral intake of simvastatin 20 mg daily for 4 weeks, the change of serum lipids in CYP3A4*1/*1 and CYP3A4*1/*4 groups showed a significant difference, with a mean decrease in triglycerides and total cholesterol of 38.1±7.6% versus 25.1±8.3% (P=0.034) and of 35.8±9.6% versus 22.0±20.4% (P=0.0015) (means ± SD), respectively. We found no statistically significant difference in the reductions of LDL between subjects carrying the *1 and *4 genotypes (29.0±7.4% versus 36.8±8.8%, P=0.0721).Conclusions The allele frequency of CYP3A4*4 was 3.32% among the hyperlipidemic patients from the Chinese mainland. CYP3A4*4 was an allelic variant related to a functional decrease of CYP3A4 activity, and *4 expression seemed to increase the lipid-lowering effects of simvastatin.     

G protein-coupled receptor structural motifs: relevance to the opioid receptors

As a whole, the G protein-coupled receptor (GPCR) superfamily displays no overall sequence homology. Nevertheless, enough short sequences and even individual amino acid residues are shared by these receptors to afford a common three-dimensional structure and a similar signal transduction mechanism. Some of these sequence commonalities, or structural motifs, are dedicated to preserving receptor infrastructure, while others are critical to agonist-mediated signaling. Certain structural motifs common to GPCRs and other signal transducing integral membrane proteins are present in the conventional opioid receptors, although several of the motifs are not well characterized in this receptor family. Here we focus on six structural motifs found in the mu, delta and kappa opioid receptors as well as the opioid like receptor ORL-1. The motifs are discussed in terms of their dynamic roles in the signaling mechanism documented for several Class A GPCRs including the opioid receptors. Clarification of the roles of GPCR structural motifs provides a blueprint for structure-function studies on newly discovered or recently cloned receptors in the superfamily. Characterization of these motifs in the opioid receptors should enhance understanding of what makes an opioid ligand a full, partial or inverse agonist or antagonist at a given receptor, possibly leading to rational design of therapeutics useful for combating opiate dependence or for pain management.     

Selective delta opioid receptor agonists for inflammatory and neuropathic pain

In the last decade a number of selective and potent non-peptidic agents became available to explore the usefulness of the delta-opioid receptor in modulation of pain of different origins. As a continuing effort in this field, potent and selective delta-opioid agonists based on the pyrrolomorphinan framework have been designed, synthesised and characterised biologically in our laboratories. In animal models, a selected compound of interest, SB 235863, has proved the concept that selective delta-opioid agonists may have great potential as pain relief agents in inflammatory and neuropathic pain conditions. Importantly, such a compound was free of the unwanted side effects usually associated with narcotic analgesics such as morphine.     

Altered levels of basal cortisol in healthy subjects with a 118G allele in exon 1 of the Mu opioid receptor gene.

The mu opioid receptor is centrally involved in the development of the addictive diseases. It also modulates the stress responsive hypothalamic-pituitary-adrenal axis. Receptors encoded by the variant 118G polymorphism in exon 1 of the mu opioid receptor gene have a threefold increase in beta-endorphin binding and beta-endorphin is three times more potent in receptor-mediated activation of G protein-coupled inwardly rectifying potassium channels. Humans with this variant have increased stress response following opioid antagonism. Here, we study basal levels of adrenocorticotropic hormone and cortisol in subjects with this variant. In all, 59 healthy adults were genotyped and had morning levels of adrenocorticotropic hormone and cortisol measured following intravenous administration of saline placebo. Subjects with a 118G allele had significantly greater levels of cortisol than subjects with the prototype gene. Groups did not differ in levels of adrenocorticotropic hormone. A planned comparison revealed significantly greater cortisol in females with at least one copy of the 118G allele compared to females with the prototype gene. There was no significant effect of gender alone, nor was there a significant interaction between gender and genotype, on ACTH or cortisol. Subjects with at least one copy of the 118G allele have increased basal levels of cortisol, which may influence the susceptibility to and treatment of the stress responsive dyscrasia.     

Pharmacokinetics of parenteral paracetamol and its analgesic effects in post-operative dental pain

Summary A double-blind, randomised, crossover trial was undertaken to compare the analgesic effects of a single dose of paracetamol (1000 mg i. v.) with placebo in the immediate post-operative period following removal of impacted lower third molars. There was no significant difference in the pain relief between paracetamol and placebo in the first hour following injection. Thereafter, there was significantly less pain (P<0.05) after treatment with paracetamol than after placebo. Plasma concentrations of paracetamol were measured and pharmacokinetic variables were determined. Over the four hour period of investigation there was no clear relationship between analgesia and paracetamol concentration in either central or peripheral compartments.     

The effects of receptor selective opioid peptides on morphine-induced analgesia

Utilizing the mouse tail-flick assay, four opioid peptides, which have been reported to be selective for either μ- or δ-opioid receptors, were examined for their analgesic potency and for their ability to modify morphine-induced analgesia. [D-Ala²,D-Leu⁵]enkephalin and [D-Ser²,Thr⁶]leucine-enkephalin, putative δ-receptor selective peptides, produced a potent analgesic response and at subanalgesic doses potentiated morphine-induced analgesia. Morphiceptin and [D-Ala²,Pro⁵]enkephalinamide, putative μ-receptor selective peptides, were similarly found to produce analgesia. However, in contrast to the δ-receptor selective peptides, three μ-receptor selective peptides were unable to alter the potency of morphine. Thus, it would appear that the potentiation of morphine analgesia is a unique property of δ-receptor selective peptides.     

Analgesic activity of metabotropic glutamate receptor 1 antagonists on spontaneous post-operative pain in rats

Activation of metabotropic glutamate (mGlu) receptors has previously been shown to play a role in inflammatory or neuropathic pain states. However, the role of mGlu type 1 receptors in post-operative pain remains to be investigated. In the present study, effects of potent and selective mGlu₁ receptor antagonists A-841720, A-794282, A-794278, and A-850002 were evaluated in a skin incision-induced post-operative pain model in rats. Post-operative pain was examined 2 h following surgery using weight-bearing difference between injured and uninjured paws as a measure of spontaneous pain. In this model, A-841720, A-794282, A-794278, and A-850002 induced significant attenuation of spontaneous post-operative pain behavior, with ED_50s of 10, 50, 50, and 65 μmol/kg i.p., respectively. Depending on the compound, significant motor side effects were also observed at 3 to 10 fold higher doses. These results support the notion that mGlu₁ receptor activation plays a significant role in nociceptive transmission in post-operative pain, though motor impairment may be a limiting factor in developing mGlu₁ receptor antagonists as novel analgesics.     

Influence of opioid receptor antagonists on motor-impairing effects of benzodiazepines

The influence of naloxone and naltrexone on the motor-impairing effects of diazepam, chlordiazepoxide, clonazepam and estazolam were studied in the aerial righting reflex test (mice, rats), and the first two drugs were examined in the rota-rod test (mice). Benzodiazepine-induced motor incoordination was significantly decreased by naloxone and naltrexone (4-16 mg/kg) in mice and rats in aerial righting reflex test. The motor-impairing effects of diazepam and chlordiazepoxide observed in rota-rod test were significantly diminished only by naltrexone (8-16 mg/kg). These data seem to confirm some interactions between benzodiazepines and opioid system.     

Influence of the OPRM1 A118G polymorphism on alcohol-induced euphoria, risk for alcoholism and the clinical efficacy of naltrexone

Alcohol-use disorders are thought to be heterogeneous in etiology, pathophysiology and response to treatment. One hypothesized contributor to this variability is the common A118G polymorphism of the μ-opioid receptor gene, OPRM1. This article critically evaluates the evidence that the A118G substitution affects subjective, behavioral and neurobiological responses to alcohol and the opioid receptor antagonist, naltrexone. Although screening of patients in a clinical setting remains premature, results suggest the A118G substitution may influence one etiological pathway to alcoholism, for which naltrexone pharmacotherapy is more effective.     

The polymorphism A118G of the human mu-opioid receptor gene decreases the pupil constrictory effect of morphine-6-glucuronide but not that of morphine.

Large individual differences in the clinical response to morphine therapy have been known for a long time by clinicians. The recent advances in genomic research encourage the search for pharmacogenetic causes of that variability. As a measure of central opioid effects, pupil diameters were assessed every 20 min for 18 h after administration of morphine or its active metabolite morphine-6-glucuronide (M6G) in a two-way crossover study. The opioid effects were compared between six subjects with a single-nucleotide polymorphism (SNP) A118G in the mu-opioid receptor gene (five heterozygous, one homozygous) and six control subjects. Non-parametric pharmacokinetic-pharmacodynamic modelling was employed to identify the influence of the A118G SNP on the concentration-response relationship of M6G and morphine, which was described by a sigmoid Emax model. As a measure of potency, the EC50 of the pupil constrictory effects of M6G was 714 +/- 197 nmol/l in wild-type and 1475 +/- 424 nmol/l in heterozygous carriers of the A118G SNP. In the homozygous carrier of the SNP, it had an EC50 of 3140 nmol/l. In addition, the dose-response relationship was flatter in the A118G carriers than in control subjects (shape factor of the sigmoid Emax model: gamma = 3.3 +/- 1.2, 1.7 +/- 0.5 and 1.6 for wild-type, heterozygous and the homozygous A118G carriers, respectively). In contrast, the concentration-response relationship of morphine was not affected by this specific SNP. The A118G SNP in the mu-receptor gene significantly reduces the potency of M6G in humans.     

Activation of G protein by opioid receptors: role of receptor number and G-protein concentration

The collision-coupling model for receptor-G-protein interaction predicts that the rate of G-protein activation is dependent on receptor density, but not G-protein levels. C6 cells expressing mu- or delta-opioid receptors, or SH-SY5Y cells, were treated with beta-funaltrexamine (mu) or naltrindole-5'-isothiocyanate (delta) to decrease receptor number. The time course of full or partial agonist-stimulated ?35SGTPgammaS binding did not vary in C6 cell membranes containing <1-25 pmol/mg mu-opioid receptor, or 1. 4-4.3 pmol/mg delta-opioid receptor, or in SHSY5Y cells containing 0. 16-0.39 pmol/mg receptor. The association of ?35SGTPgammaS binding was faster in membranes from C6mu cells than from C6delta cells. A 10-fold reduction in functional G-protein, following pertussis toxin treatment, lowered the maximal level of ?35SGTPgammaS binding but not the association rate. These data indicate a compartmentalization of opioid receptors and G protein at the cell membrane.