Polymorphisms in the A118G SNP of the OPRM1 gene produce different experiences of opioids: A human laboratory phenotype-genotype assessment.

Allelic variations in the A118G SNP of the OPRM1 gene change opioid signaling; however, evaluations of how allelic differences may influence opioid effects are lacking. This human laboratory paradigm examined whether the AA versus AG/GG genotypes determined opioid response profiles. Individuals with limited opioid exposure (N = 100) completed a five-day within-subject, double-blind, placebo-controlled, residential study. Participants were admitted (Day 1), received 4 mg hydromorphone (Day 2) and 0 mg, 2 mg and 8 mg hydromorphone in randomized order (Days 3-5) and completed self-reported visual analog scale (VAS) ratings and Likert scales, observed VAS, and physiological responses at baseline and for 6.5 h post-dose. Outcomes were analysed as peak/nadir effects over time as a function of genotype (available for N = 96 individuals; AG/GG = 13.5%, AA = 86.4%). Participants with AG/GG rated low and moderate doses of hydromorphone as significantly more positive (e.g., Good Effects VAS, coasting, drive, friendly, talkative, stimulation) with fewer negative effects (e.g., itchy skin, nausea, sleepiness), and were also observed as being more talkative and energetic relative to persons with AA. Persons with AG/GG were less physiologically reactive as determined by diastolic blood pressure and heart rate, but had more changes in core temperature compared with those with AA. Persons with AA also demonstrated more prototypic agonist effects across doses; persons with AG/GG showed limited response to 2 mg and 4 mg. Data suggest persons with AG/GG genotype experienced more pleasant and fewer unpleasant responses to hydromorphone relative to persons with AA. Future studies should replicate these laboratory findings in clinical populations to support a precision medicine approach to opioid prescribing.

Pharmacogenetic Guided Opioid Therapy Improves Chronic Pain Outcomes and Comorbid Mental Health: A Randomized, Double-Blind, Controlled Study.

Interindividual variability in analgesic response is at least partly due to well-characterized polymorphisms that are associated with opioid dosing and adverse outcomes. The Clinical Pharmacogenetics Implementation Consortium (CPIC) has put forward recommendations for the CYP2D6 phenotype, but the list of studied drug-gene pairs continues to grow. This clinical trial randomized chronic pain patients (n = 60), referred from primary care to pain unit care into two opioid prescribing arms, one guided by CYP2D6, µ-opioid receptor (OPRM1), and catechol-O-methyl transferase (COMT) genotypes vs. one with clinical routine. The genotype-guided treatment reduced pain intensity (76 vs. 59 mm, p < 0.01) by improving pain relief (28 vs. 48 mm, p < 0.05), increased quality of life (43 vs. 56 mm p < 0.001), and lowered the incidence of clinically relevant adverse events (3 [1-5] vs. 1 [0-2], p < 0.01) and 42% opioid dose (35 [22-61] vs. 60 [40-80] mg/day, p < 0.05) as opposed to usual prescribing arm. The final health utility score was significantly higher (0.71 [0.58-0.82] vs. 0.51 [0.13-0.67] controls, p < 0.05) by improving sleepiness and depression comorbidity, with a significant reduction of 30-34% for headache, dry mouth, nervousness, and constipation. A large-scale implementation analysis could help clinical translation, together with a pharmaco-economic evaluation.

Assessment of structure-activity relationships and biased agonism at the Mu opioid receptor of novel synthetic opioids using a novel, stable bio-assay platform.

Fentanyl and morphine are agonists of the Mu opioid receptor (MOR), which is a member of the GPCR family. Their analgesic effects are associated with unwanted side effects. On a signaling level downstream from MOR, it has been hypothesized that analgesia may be mediated through the G protein pathway, whereas the undesirable effects of opioids have been linked to the ß-arrestin (ßarr) pathway. Despite being an increasingly debated subject, little is known about a potential 'bias' (i.e. the preferential activation of one pathway over the other) of the novel synthetic opioids (NSO) - including fentanyl analogs - that have emerged on the illegal drug market. We have therefore developed and applied a novel, robust bio-assay platform to study the activity of 21 NSO, to evaluate to what extent these MOR agonists show biased agonism and to investigate the potential correlation with their structure. In addition, we evaluated the functional selectivity of TRV130, a purported G protein-biased agonist. We applied newly established stable bio-assays in HEK293T cells, based on the principle of functional complementation of a split nanoluciferase, to assess MOR activation via recruitment of a mini-Gi protein (GTPase domain of Gαi subunit) or ßarr2. All but two of the tested NSO demonstrated a concentration-dependent response at MOR in both bio-assays. The developed bio-assays allow to gain insight into the ßarr2 or G protein recruitment potential of NSO, which may eventually help to better understand why certain opioids are associated with higher toxicity. Adding to the recent discussion about the relevance of the biased agonism concept for opioids, we did not observe a significant bias for any of the evaluated compounds, including TRV130.

Cost-Effectiveness Analysis of Genotype-Guided Treatment Allocation in Patients with Alcohol Use Disorders Using Naltrexone or Acamprosate, Using a Modeling Approach.

Alcohol use disorders (AUD) are a major contributor to the global burden of disease, and have huge societal impact. Some studies show that AUD patients carrying the G-allele of the OPRM1 variant c.118A>G respond better to naltrexone, resulting in reduced relapse rates compared to carriers of the AA genotype. Genotype-guided treatment allocation of these patients carrying a G-allele to naltrexone could potentially improve the treatment outcome. However, cost-effectiveness of this strategy should be investigated before considering clinical implementation. We, therefore, evaluated costs and Quality-Adjusted Life-Years (QALYs), using a modelling approach, from an European perspective, of genotype-guided treatment allocation (G-allele carriers receiving naltrexone; AA homozygotes acamprosate or naltrexone) compared to standard care (random treatment allocation to acamprosate or naltrexone), by using a Markov model. Genotype-guided treatment allocation resulted in incremental costs of EUR 66 (95% CI -28 to 149) and incremental effects of 0.005 QALYs (95% CI 0.000-0.011) per patient (incremental cost-effectiveness ratio of EUR 13,350 per QALY). Sensitivity analyses showed that the risk ratio to relapse after treatment allocation had the largest impact on the cost-effectiveness. Depending on the willingness to pay for a gain of one QALY, probabilities that the intervention is cost-effective varies between 6 and 79%. In conclusion, pharmacogenetic treatment allocation of AUD patients to naltrexone, based on OPRM1 genotype, can be a cost-effective strategy, and could have potential individual and societal benefits. However, more evidence on the impact of genotype-guided treatment allocation on relapse is needed to substantiate these conclusions, as there is contradictory evidence about the effectiveness of OPRM1 genotyping.

Antinociceptive and respiratory effects following application of transdermal fentanyl patches and assessment of brain µ-opioid receptor mRNA expression in ball pythons.

OBJECTIVE To quantify plasma fentanyl concentrations (PFCs) and evaluate antinociceptive and respiratory effects following application of transdermal fentanyl patches (TFPs) and assess cerebrospinal µ-opioid receptor mRNA expression in ball pythons (compared with findings in turtles). ANIMALS 44 ball pythons (Python regius) and 10 turtles (Trachemys scripta elegans). PROCEDURES To administer 3 or 12 µg of fentanyl/h, a quarter or whole TFP (TFP-3 and TFP-12, respectively) was used. At intervals after TFP-12 application in snakes, PFCs were measured by reverse-phase high-pressure liquid chromatography. Infrared heat stimuli were applied to the rostroventral surface of snakes to determine thermal withdrawal latencies after treatments with no TFP (control [n = 16]) and TFP-3 (8) or TFP-12 (9). Breathing frequency was measured in unrestrained controls and TFP-12-treated snakes. µ-Opioid receptor mRNA expression in brain and spinal cord tissue samples from snakes and turtles (which are responsive to µ-opioid receptor agonist drugs) were quantified with a reverse transcription PCR assay. RESULTS Mean PFCs were 79, 238, and 111 ng/mL at 6, 24, and 48 hours after TFP-12 application, respectively. At 3 to 48 hours after TFP-3 or TFP-12 application, thermal withdrawal latencies did not differ from pretreatment values or control treatment findings. For TFP-12-treated snakes, mean breathing frequency significantly decreased from the pretreatment value by 23% and 41% at the 24- and 48-hour time points, respectively. Brain and spinal cord tissue µ-opioid receptor mRNA expressions in snakes and turtles did not differ. CONCLUSIONS AND CLINICAL RELEVANCE In ball pythons, TFP-12 application resulted in high PFCs, but there was no change in thermal antinociception, indicating resistance to µ-opioid-dependent antinociception in this species.

Cortisol Stress Response in Men and Women Modulated Differentially by the Mu-Opioid Receptor Gene Polymorphism OPRM1 A118G.

Differences in stress reactivity may affect long-term health outcomes, but there is little information on how these differences arise. The stress axis is regulated by, in part, the endogenous opioid, beta-endorphin, acting on mu-opioid receptors. Persons carrying one or two copies of the G allele of the mu-opioid receptor gene (OPRM1 A118G) may have higher receptor binding for beta-endorphin compared with AA homozygotes that may contribute to individual differences in cortisol reactivity to stress, leading to a relative blunting of cortisol stress reactivity in G allele genotypes. We measured cortisol in 251 young adults (69 GA/GG vs 182 AA genotypes) exposed to mental arithmetic plus public speaking stress relative to a resting control day. Women had smaller cortisol responses than men (F=10.2, p=0.002), and women with GA or GG genotypes (N=39) had an absence of cortisol response relative to AA carriers (N=110) (F=18.4, p<0.0001). Male genotypes had no such difference in response (F=0.29). Cortisol response following mu-opioid receptor blockade using naltrexone in 119 of these subjects unmasked a greater tonic opioid inhibition of cortisol secretion in women (N=64), consistent with their blunted stress reactivity. Compared with men, women may have cortisol stress responses that are more heavily regulated by endogenous opioid mechanisms, and the OPRM1 GA/GG genotypes may affect females differentially relative to males. Diminished cortisol responses to stress may have consequences for health behaviors in women with GA/GG genotypes.

Simultaneous genotyping of single-nucleotide polymorphisms in alcoholism-related genes using duplex and triplex allele-specific PCR with two-step thermal cycles.

We developed a time- and cost-effective multiplex allele-specific polymerase chain reaction (AS-PCR) method based on the two-step PCR thermal cycles for genotyping single-nucleotide polymorphisms in three alcoholism-related genes: alcohol dehydrogenase 1B, aldehyde dehydrogenase 2 and µ-opioid receptor. Applying MightyAmp(®) DNA polymerase with optimized AS-primers and PCR conditions enabled us to achieve effective and selective amplification of the target alleles from alkaline lysates of a human hair root, and simultaneously to determine the genotypes within less than 1.5 h using minimal lab equipment.

Assessment of opioid receptor µ1 gene A118G polymorphism and its association with pain intensity in patients with fibromyalgia.

Fibromyalgia may present with widespread pain and tenderness, fatigue, anxiety, and depression and is associated with a low pain threshold. The etiology of fibromyalgia is yet to be ascertained, although both genetic and environmental factors may play a role in the susceptibility of patients to fibromyalgia. Various genetic variations have been investigated to explain fibromyalgia susceptibility and differences in pain sensitivity, pain threshold, and tolerance. The A118G rs1799971 polymorphism in the opioid receptor µ1 gene (OPRM1) is one of the candidate genes. We hypothesized that the OPRM1 polymorphism may play a role in fibromyalgia susceptibility and impact the pain intensity and pain-related symptoms in fibromyalgia patients. This study comprised of 108 patients with fibromyalgia and 100 healthy controls. Overall, the 118G allele frequency was 16.3 % and was significantly lower in patients with fibromyalgia than in the control group (13.9 and 19 %, respectively). No difference was observed between fibromyalgia patients with and without the A118G allele with regard to the Beck Depression Inventory, widespread pain index, symptom severity, and Fibromyalgia Impact Questionnaire scores. All body parts of patients with fibromyalgia demonstrated lower pressure pain thresholds (PPT) compared to controls. The PPTs were higher in the 118 A/A genotype carrier fibromyalgia patients than in 118*/G carriers; however, the differences were not significant. As the A118G polymorphism frequency was lower in fibromyalgia patients, this polymorphism may exert a protective effect against fibromyalgia in Turkish women. However, the OPRM1 polymorphism does not have a significant effect on pressure pain and fibromyalgia severity.

Direct-to-consumer genetic testing for addiction susceptibility: a premature commercialisation of doubtful validity and value.

Genetic research on addiction liability and pharmacogenetic research on treatments for addiction have identified some genetic variants associated with disease risk and treatment. Genetic testing for addiction liability and treatment response has not been used widely in clinical practice because most of the genes identified only modestly predict addiction risk or treatment response. However, many of these genetic tests have been commercialized prematurely and are available direct to the consumer (DTC). The easy availability of DTC tests for addiction liability and lack of regulation over their use raises a number of ethical concerns. Of paramount concern is the limited predictive power and clinical utility of these tests. Many DTC testing companies do not provide the consumer with the necessary genetic counselling to assist them in interpreting and acting on their test results. They may also engage in misleading marketing to entice consumers to purchase their products. Consumers' genetic information may be vulnerable to misuse by third parties, as there are limited standards to protect the privacy of the genetic information. Non-consensual testing and inappropriate testing of minors may also occur. The United States Food and Drug Administration plans to regulate DTC genetic tests. Based on the ethical concerns we discuss below, we believe there is a strong case for regulation of DTC genetic tests for addiction liability and treatment response. We argue that until this occurs, these tests have more potential to cause harm than to contribute to improved prevention and treatment of addiction.

Understanding naltrexone mechanism of action and pharmacogenetics in Asian Americans via behavioral economics: a preliminary study.

A behavioral economic approach to understanding the relative value of alcohol may be useful for advancing medication development for alcoholism. Naltrexone is a heavily researched and moderately effective treatment for alcohol dependence making it a good candidate for a proof-of-concept study of behavioral economics and alcoholism pharmacotherapy. This study examines naltrexone efficacy and pharmacogenetics in terms of the relative value of alcohol, assessed via demand curve analysis. Participants were 35 heavy drinking (AUDIT ≥8) Asian Americans. A within-subjects cross-over medication design was used along with an intravenous alcohol challenge completed after 4 days of both naltrexone and placebo. At baseline and BrAC = 0.06g/dl, participants completed an Alcohol Purchase Task, which assessed estimated alcohol consumption along escalating prices. Behavioral economic demand curve analysis yielded measures of intensity, elasticity, maximum expenditure (O(max)), proportionate price insensitivity (P(max)) and breakpoint. Compared to placebo, naltrexone significantly reduced intensity, O(max) and breakpoint. There were also trend-level medication effects on P(max). BrAC was associated with increases in P(max) and breakpoint. A significant naltrexone × OPRM1 genotype interaction was observed for intensity of demand. The present study extends the literature on naltrexone's mechanisms through the application of a novel behavioral economic paradigm. These results indicate that naltrexone reduces several indices of demand for alcohol. This preliminary report provides further evidence for the effectiveness of naltrexone and supports the utility of a behavioral economic approach to alcoholism pharmacotherapy development.

Chronic methadone treatment shows a better cost/benefit ratio than chronic morphine in mice.

Chronic treatment of pain with opiate drugs can lead to analgesic tolerance and drug dependence. Although all opiate drugs can promote tolerance and dependence in practice, the severity of those unwanted side effects differs depending on the drug used. Although each opiate drug has its own unique set of pharmacological profiles, methadone is the only clinically used opioid drug that produces substantial receptor endocytosis at analgesic doses. Here, we examined whether moderate doses of methadone carry any benefits over chronic use of equianalgesic morphine, the prototypical opioid. Our data show that chronic administration of methadone produces significantly less analgesic tolerance than morphine. Furthermore, we found significantly reduced precipitated withdrawal symptoms after chronic methadone treatment than after chronic morphine treatment. Finally, using a novel animal model with a degrading µ-opioid receptor we showed that, although endocytosis seems to protect against tolerance development, endocytosis followed by receptor degradation produces a rapid onset of analgesic tolerance to methadone. Together, these data indicated that opioid drugs that promote receptor endocytosis and recycling, such as methadone, may be a better choice for chronic pain treatment than morphine and its derivatives that do not.

Assessment of nociceptin/orphanin FQ and micro-opioid receptor mRNA in the human right atrium.

BACKGROUND: The expression of micro (mu: MOP) and nociceptin/orphanin FQ (NOP) receptors in the human myocardium is controversial. In this polymerase chain reaction (PCR)-based study using human right atrial biopsies, we have (i) probed for mRNA encoding NOP receptor and its endogenous peptide precursor, ppN/OFQ, and mRNA encoding MOP and (ii) attempted to correlate expression with cardiac function. METHODS: mRNA encoding MOP, NOP, and the precursor for NOP (ppN/OFQ) was assessed by quantitative real-time PCR (Q-PCR) using validated TaqMan primers and compared with a housekeeper (glyceraldehyde-3-phosphate dehydrogenase, GAPDH). Q-PCR data are expressed as the difference in cycle threshold (DeltaC(t)=C(tGene of interest)-C(tGAPDH): high value, low expression) and patients were grouped according to left ventricular ejection fraction (LVEF). RESULTS: Forty patients were recruited; NOP, MOP, and ppN/OFQ mRNA were measured in 38, 29, and 10 patients, respectively. DeltaC(t) (median and range) values for NOP and MOP were 10.9 (7.8-13.7) and 16.0 (12.3-18.9), respectively, representing low expression of MOP and approximately 34-fold more NOP. MOP mRNA was not detected in seven samples and with DeltaC(t) values of approximately 20, ppN/OFQ was considered absent. When patients were grouped into normal (>50%) and impaired (<50%) LVEF, there was no difference between the groups for either NOP or MOP. In some patients, intraoperative LVEF was estimated using transoesophageal echocardiography, and there was no correlation with either NOP or MOP. CONCLUSIONS: The human right atrium of patients with coronary artery disease and heart failure expresses mRNA encoding NOP and possibly low levels of MOP. This does not correlate with degree of cardiac dysfunction. In addition, the atrium does not express ppN/OFQ mRNA.

Gene polymorphisms of the mu opioid receptor in methamphetamine abusers.

In drug addiction, the opioid system is thought to mediate motivational effects through dopamine-independent mechanisms. We have investigated associations of the mu-opioid receptor gene (OPRM) variations with methamphetamine (MAP) dependence/psychosis. The allelic frequency of A118G (Asn40Asp) in exon 1 of ORPM was 45.3% in our control subjects, but only 7.5-25.8% in the Caucasian or African-American population of previous studies. We have identified several novel polymorphisms in intron 1 and the 5' untranslated region (5'UTR) of OPRM. Polymorphisms in the functionally relevant 5' regulatory region of OPRM were different in our Japanese population from Caucasian or African-American populations. No significant differences between controls and MAP abusers were found in either genotype or allele frequency at any single nucleotide polymorphism (SNP) or (AC)n dinucleotide repeat in intron 1. A subdivision of our MAP group revealed that A118G of OPRM shows a significant association with MAP psychosis having latency less than three years. Further analysis should be capable of identifying associations between the OPRM variations and MAP dependence/psychosis.