Kappa Opioid Research Articles

Brain and molecular mechanisms underlying the nonlinear association between close friendships, mental health, and cognition in children.

Close friendships are important for mental health and cognition in late childhood. However, whether the more close friends the better, and the underlying neurobiological mechanisms are unknown. Using the Adolescent Brain Cognitive Developmental study, we identified nonlinear associations between the number of close friends, mental health, cognition, and brain structure. Although few close friends were associated with poor mental health, low cognitive functions, and small areas of the social brain (e.g., the orbitofrontal cortex, the anterior cingulate cortex, the anterior insula, and the temporoparietal junction), increasing the number of close friends beyond a level (around 5) was no longer associated with better mental health and larger cortical areas, and was even related to lower cognition. In children having no more than five close friends, the cortical areas related to the number of close friends revealed correlations with the density of μ-opioid receptors and the expression of OPRM1 and OPRK1 genes, and could partly mediate the association between the number of close friends, attention-deficit/hyperactivity disorder (ADHD) symptoms, and crystalized intelligence. Longitudinal analyses showed that both too few and too many close friends at baseline were associated with more ADHD symptoms and lower crystalized intelligence 2 y later. Additionally, we found that friendship network size was nonlinearly associated with well-being and academic performance in an independent social network dataset of middle-school students. These findings challenge the traditional idea of 'the more, the better,' and provide insights into potential brain and molecular mechanisms.

Genetic Variation in OPRK1 Gene and Opioid Use Disorder

The OPRK gene encodes the kappa opioid receptor, which is involved in modulating the effects of opioids in the brain. Polymorphisms in the OPRK1 gene have been investigated for their potential association with opioid use disorder (OUD) and related phenotypes. OUD refers to a problematic pattern of opioid use characterized by a loss of control over use, craving, and negative consequences. To evaluate the association between OPRK1 rs963549 and rs997917 and opioid use disorder (OUD) and related phenotypes, Özkan-Kotiloğlu et al conducted a study. A sample of 208 individuals with (n = 100) and without (n = 108) OUD were enrolled. OPRK1 rs963549 and rs997917 were analyzed by PCR-RFLP. Craving, opioid withdrawal, and the intensity of depressive and anxiety symptoms were measured by the appropriate scales. OPRK1 rs963549 variation showed a trend of association with decreased opioid withdrawal. No significant associations were found between OPRK1 rs963549 and rs997917 polymorphisms and craving, depression or anxiety symptoms. Neither single OPRK1 SNPs nor OPRK1 haplotypes were associated with OUD. Their results could be useful for treatment failures of individuals who experience greater opioid withdrawal due to their OPRK1 rs963549 genotypes. Pharmacogenomics. 2023 May 11. doi: 10.2217/pgs-2023-0037. Online ahead of print.

Kappa opioid receptor activation increases thermogenic energy expenditure which drives increased feeding

Opioid receptors, including the kappa opioid receptor (KOR), exert control over thermoregulation and feeding behavior. Notably, activation of KOR stimulates food intake, leading to postulation that KOR signaling plays a central role in managing energy intake. KOR has also been proposed as a target for treating obesity. Herein, we report studies examining how roles for KOR signaling in regulating thermogenesis, feeding, and energy balance may be interrelated using pharmacological interventions, genetic tools, quantitative thermal imaging, and metabolic profiling. Our findings demonstrate that activation of KOR in the central nervous system causes increased energy expenditure via brown adipose tissue activation. Importantly, pharmacologic, or genetic inhibition of brown adipose tissue thermogenesis prevented the elevated food intake triggered by KOR activation. Furthermore, our data reveal that KOR-mediated thermogenesis elevation is reversibly disrupted by chronic high-fat diet, implicating KOR signaling as a potential mediator in high-fat diet-induced weight gain.

Retraction Note: Down-regulation of kappa opioid receptor promotes ESCC proliferation, invasion and metastasis via the PDK1-AKT signaling pathway

This article has been retracted. Please see the Retraction Notice for more detail: https://doi.org/10.1186/s12964-022-00833-3.

A Cre Driver Line for Genetic Targeting of Kappa Opioid Receptor Expressing Cells.

Here we describe the generation and characterization of a Cre knock-in mouse line that harbors a Cre insertion in the 3'UTR of the κ opioid receptor gene (Oprk1) locus and provides genetic access to populations of κ opioid receptor (KOR)-expressing neurons throughout the brain. Using a combination of techniques including RNA in situ hybridization and immunohistochemistry, we report that Cre is expressed with high fidelity in KOR-expressing cells throughout the brain in this mouse line. We also provide evidence that Cre insertion does not alter basal KOR function. Baseline anxiety-like behaviors and nociceptive thresholds are unaltered in Oprk1-Cre mice. Chemogenetic activation of KOR-expressing cells in the basolateral amygdala (BLAKOR cells) resulted in several sex-specific effects on anxiety-like and aversive behaviors. Activation led to decreased anxiety-like behavior on the elevated plus maze and increased sociability in female but not in male Oprk1-Cre mice. Activation of BLAKOR cells also attenuated KOR agonist-induced conditioned place aversion (CPA) in male Oprk1-Cre mice. Overall, these results suggest a potential role for BLAKOR cells in regulating anxiety-like behaviors and KOR-agonist mediated CPA. In summary, these results provide evidence for the utility of the newly generated Oprk1-Cre mice in assessing localization, anatomy, and function of KOR circuits throughout the brain.

197-OR: Dynorphin, a Novel Paracrine Factor That Regulates Insulin Secretion

Within the pancreatic islet, the crosstalk between different islet cells through paracrine signals orchestrates a hormonal response that controls glucose levels. The dysregulation of these signals contributes to impaired glucose homeostasis and diabetes. Therefore, understanding intra-islet communication is imperative for developing new strategies for diabetes management. Here, we show that intra-islet dynorphin (Dyn) stimulates somatostatin (SST) secretion and is a novel factor regulating islet function and insulin secretion in human and mouse islets. Dyn, an opioid peptide involved in stress response, pain, and addiction is synthesized in human and mouse β-cells and secreted in response to glucose. Dyn acts mainly through the k-opioid receptor (KOR) expressed in all islet cells with the highest expression in δ-cells. Using perifusion and static incubation studies, we show that Dyn induces SST secretion and decreases insulin secretion in mouse and human islets and that Dyn fails to induce SST secretion in islets from mice with KOR deletion in δ-cells, thereby providing a mechanism for feedback control of insulin secretion (β- to δ-cell Dyn/KOR negative feedback loop). Our data also show that Dyn is increased in islets from HFD-fed mice (8-fold) and in human β-cells from T2D donors. Remarkably, dynorphin mRNA is one of the top ten most upregulated genes in islets from HFD-fed mice, higher than several critical β-cell genes, including pdx1 or ucn3. We demonstrate that the β- to δ-cell Dyn/KOR negative feedback loop is upregulated in diabetes and pharmacological inhibition or genetic deletion of KOR in δ-cells improves glucose homeostasis in high-fat diet (HFD)-fed mice, demonstrating the therapeutic potential of this system. The novel role of the Dyn/KOR axis in islet function in healthy and diabetogenic conditions can have profound implications for glucose homeostasis and serve to develop potential targets for T2D. Disclosure M.Blandino-rosano: None. J.Panzer: None. E.Bernal-mizrachi: None.

The Kappa Opioid Receptor Agonist 16-Bromo Salvinorin A Has Anti-Cocaine Effects without Significant Effects on Locomotion, Food Reward, Learning and Memory, or Anxiety and Depressive-like Behaviors.

Kappa opioid receptor (KOR) agonists have preclinical antipsychostimulant effects; however, adverse side effects have limited their therapeutic development. In this preclinical study, conducted in Sprague Dawley rats, B6-SJL mice, and non-human primates (NHPs), we evaluated the G-protein-biased analogue of salvinorin A (SalA), 16-bromo salvinorin A (16-BrSalA), for its anticocaine effects, side effects, and activation of cellular signaling pathways. 16-BrSalA dose-dependently decreased the cocaine-primed reinstatement of drug-seeking behavior in a KOR-dependent manner. It also decreased cocaine-induced hyperactivity, but had no effect on responding for cocaine on a progressive ratio schedule. Compared to SalA, 16-BrSalA had an improved side effect profile, with no significant effects in the elevated plus maze, light-dark test, forced swim test, sucrose self-administration, or novel object recognition; however, it did exhibit conditioned aversive effects. 16-BrSalA increased dopamine transporter (DAT) activity in HEK-293 cells coexpressing DAT and KOR, as well as in rat nucleus accumbens and dorsal striatal tissue. 16-BrSalA also increased the early phase activation of extracellular-signal-regulated kinases 1 and 2, as well as p38 in a KOR-dependent manner. In NHPs, 16-BrSalA caused dose-dependent increases in the neuroendocrine biomarker prolactin, similar to other KOR agonists, at doses without robust sedative effects. These findings highlight that G-protein-biased structural analogues of SalA can have improved pharmacokinetic profiles and fewer side effects while maintaining their anticocaine effects.

Discovery of a Potent Highly Biased MOR Partial Agonist among Diastereomeric C9-Hydroxyalkyl-5-phenylmorphans.

All possible diastereomeric C9-hydroxymethyl-, hydroxyethyl-, and hydroxypropyl-substituted 5-phenylmorphans were synthesized to explore the three-dimensional space around the C9 substituent in our search for potent MOR partial agonists. These compounds were designed to lessen the lipophilicity observed with their C9-alkenyl substituted relatives. Many of the 12 diastereomers that were obtained were found to have nanomolar or subnanomolar potency in the forskolin-induced cAMP accumulation assay. Almost all these potent compounds were fully efficacious, and three of those chosen for in vivo evaluation, 15, 21, and 36, were all extremely G-protein biased; none of the three compounds recruited beta-arrestin2. Only one of the 12 diastereomers, 21 (3-((1S,5R,9R)-9-(2-hydroxyethyl)-2-phenethyl-2-azabicyclo[3.3.1]nonan-5-yl)phenol), was a MOR partial agonist with good, but not full, efficacy (Emax = 85%) and subnanomolar potency (EC50 = 0.91 nM) in the cAMP assay. It did not have any KOR agonist activity. This compound was unlike morphine in that it had a limited ventilatory effect in vivo. The activity of 21 could be related to one or more of three well-known theories that attempt to predict a dissociation of the desired analgesia from the undesirable opioid-like side-effects associated with clinically used opioids. In accordance with the theories, 21 was a potent MOR partial agonist, it was highly G-protein biased and did not attract beta-arrestin2, and it was found to have both MOR and DOR agonist activity. All the other diastereomers that were synthesized were either much less potent than 21 or had either too little or too much efficacy for our purposes. It was also noted that a C9-methoxymethyl compound with 1R,5S,9R stereochemistry (41) was more potent than the comparable C9-hydroxymethyl compound 11 (EC50 = 0.65 nM for 41 vs. 2.05 nM for 11). Both 41 and 11 were fully efficacious.

#5584 FIRST EXPERIENCES IN REAL LIFE WITH DIFELIKEFALIN IN GABAPENTIN RESISTANT UREMIC PRURITUS (CKDAP)

Abstract Background and Aims Chronic kidney disease associated pruritus (CKD-aP) has been recognized for over a century. The actual proposed off-label therapeutic option is gabapentin, that showed relevant efficacy in some small trial. Recently difelikefalin (DFK), a k-opioid receptor agonist, has been the first FDA and EMA approved drug for CKD-aP treatment. We report the first three treated patients suffering gabapentin- resistant CKD-aP in our dialysis center. Method Since March 2022, 2 patients have been treated with DFK. Before starting the treatment and every week thereafter until now, the patients completed the following scales: Worst-Itch Numerical rating scale (WI-NRS, 0 = no Itch, 10 = worst itch), and the sleep quality scale (SQS) (from 0 = worse to 10 = best quality). Results Case 1 (Male, 58 years-old). The patient started hemodialysis (HD) 5 years ago. He was suffering gabapentin resistant CKD-aP (WI-NRS 10, SADS = C, SQS = 3). As soon as DFK was available the patient started DFK 0.5 mcg/kg/every HD session. There was immediate and persistent treatment efficacy. After 1 month gabapentin was stopped and after 4 months of DFK therapy, WI-NRS = 0 and SQS = 10, in the absence of side effects. After 6 months DFK was stopped but 4 weeks later CKD-aP returned (WI-NRS 7, SQS = 7). DFK was administered again with immediate response (Fig. 1a).Case 2 (Female, 81 years-old). The patient started HD 5 years ago. Two years ago she started suffering moderate to severe gabapentin-resistant CKD-aP. Before starting DFK 0.5 mcg/kg/every HD WI-NRS = 6 and SQS = 3. In the next weeks we obtained a progressive reduction of CKD-aP. After 3 months WI-NRS = 3, SQS = 6. At 6 month follow up CKD-aP ameliorated significantly (Wi-NRS 0 and SQS = 9) (Fig. 1b). Case 3. (Male, 75-years old). The patient suffer initial dementia. He started hemodialysis 1 year ago. He presented with scratching lesions on his arms and legs and complained of itching. After an initial period treated with Gabapentin without success Difelikefalin was tried. At the first assessment WI-NRS 7 and SQS 5; after an initial apparent benefit the rating scales were particularly fluctuating. There was also a dissociation between the improvement of the scratching lesions and the persistence of high values on the WI-NRS (after 3 months WI-NRS = 8). At 6 months' follow-up the patient presented WI-NRS 9 and SQS 6 (Fig. 1c). The scratching lesions had almost disappeared. Conclusion Our initial experience with DFK in the treatment of CKD-aP in 3 gabapentin-resistant patients seems to recognize a remarkable efficacy of the drug. In particular, Case 1 showed a complete, immediate and lasting response, whereas no other drug had been able to improve very severe CKD-aP. Case 2 showed a slowly reduction but achieved complete response at 6 months. In Case 3 the improvement of the scratching lesions suggests a partial benefit of DFK, but to date no relevant results with the adopted scales has been achieved. In conclusion DFK seems to show promising efficacy particularly in CKD-aP resistant to gabapentin. In older patiants with cognitive problems the actual tools identified to measure CKD-aP seems inadequate.

Iridoids from Morinda lucida, (Benth.) Rubiaceae, produced analgesic and anti-inflammatory activities via agonism at the kappa and delta opioid receptors, inhibition of COX-2 besides elevation of CAT and SOD activities.

Pain and inflammation are the major symptoms of almost every human disease. Herbal preparations from Morinda lucida are used to treat pain and inflammation in traditional medicine. However, the analgesic and anti-inflammatory activities of some of its chemical constituents are not known. The aim of this study is to evaluate the analgesic and anti-inflammatory activities and possible mechanisms of these activities of iridoids from Morinda lucida. The compounds were isolated using column chromatography and characterized by NMR spectroscopy and LC-MS. Anti-inflammatory activity was evaluated using carrageenan-induced paw edema. Whereas, the analgesic activity was assessed in the hot plate and acetic acid-induced writhing assays. Mechanistic studies were conducted using pharmacological blockers, determination of antioxidant enzymes, lipid peroxidation, and docking studies. The iridoid, ML2-2 exhibited inverse dose-dependent anti-inflammatory activity (42.62% maximum at 2 mg/kg p. o). ML2-3 produced dose-dependent anti-inflammatory activity (64.52% maximum at 10 mg/kg p. o.). Anti-inflammatory activity of diclofenac sodium was 58.60% at 10 mg/kg p. o. Furthermore, ML2-2 and ML2-3 produced analgesic activity (P < 0.01) of 44.44 ± 5.84 and 54.18 ± 19.01%. at 10 mg/kg p. o. respectively in the hot plate assay and 64.88 and 67.44% in the writhing assay. ML2-2 significantly elevated catalase activity. However, ML2-3 elevated SOD and catalase activity significantly. In the docking studies, both iridoids formed stable crystal complexes with delta and kappa opioid receptors, and the COX-2 enzyme with very low free binding energies (ΔG) from -11.2 to -14.0 kcal/mol. However, they did not bind with the mu opioid receptor. The lower bound RMSD of most of the poses were found to be ≤ 2. Several amino acids were involved in the interactions through various inter molecular forces. These results indicate that ML2-2 and ML2-3 possessed very significant analgesic and anti-inflammatory activities via acting as both delta and kappa opioid receptor agonist, elevation of anti-oxidant activity and inhibition of COX-2.

Cocaine self-administration augments kappa opioid receptor system-mediated inhibition of dopamine activity in the mesolimbic dopamine system.

Prior studies examining the effects of cocaine on the dynorphin/kappa opioid receptor (Dyn/KOR) system primarily focus on non-contingent cocaine exposure, but the effects of self-administration, which more closely reflects human drug-taking behaviors, are not well studied. In this study we characterized the effects of escalated intravenous cocaine self-administration on the functional state of the Dyn/KOR system and its interaction with mesolimbic dopamine signaling. Rats self-administered cocaine in an extended access, limited intake cocaine procedure, in which animals obtained 40 infusions per day (1.5mg/kg/inf) for 5 consecutive days to ensure comparable consumption levels. Following single day tests of cue reactivity and progressive ratio responding, quantitative real-time polymerase chain reaction was used to measure levels of Oprk and Pdyn transcripts in the ventral tegmental area and nucleus accumbens. Additionally, after self-administration, ex vivo fast-scan cyclic voltammetry in the NAc was used to examine the ability of the KOR agonist U50,488 to inhibit dopamine release. We found that KOR-induced inhibition of dopamine release was enhanced in animals that self-administered cocaine compared to controls, suggesting upregulated Dyn/KOR activity after cocaine self-administration. Furthermore, expression levels of Pdyn in the nucleus accumbens and ventral tegmental area, and Oprk in the nucleus accumbens, were elevated in cocaine animals compared to controls. Additionally, Pdyn expression in the nucleus accumbens was negatively correlated with progressive ratio breakpoints, a measure of motivation to self-administer cocaine. Overall, these data suggest that cocaine self-administration elevates KOR/Dyn system activity in the mesolimbic dopamine pathway.

Sex differences in kappa opioid receptor control over monoaminergic transmission along the NAc shell rostral-caudal axis

Sex differences in kappa opioid receptor control over monoaminergic transmission along the NAc shell rostral-caudal axis

Co-Administration of nalbuphine to improve morphine tolerance in mice with bone cancer pain.

Kappa-opioid receptor (KOR) agonists are known for having opposite and/or different effects compared with Mu-opioid receptor (MOR) agonists. This study is aimed at clarifying the analgesic effect and tolerance of nalbuphine combined with morphine, and quantifying the mRNA and protein expression of spinal MOR and KOR in a mouse bone cancer pain (BCP) model treated with nalbuphine and morphine. BCP model was prepared in C3H/HeNCrlVr Mice by implanting the sarcoma cells into the intramedullary space of the femur. The paw withdrawal thermal latency (PWL) measured by thermal radiometer was used to assess thermal hyperalgesia. PWL testing was performed after implantation and drug administration according to the protocol. Hematoxylin-eosin staining in the spinal cord and x-ray in the femoral intramedullary canal was detected. Real-time PCR and western blot analysis played a role in detecting spinal MOR and KOR expression changes. In tumor-implanted mice, the spinal MOR and KOR protein and mRNA expression was down-regulated when compared to that in sham-implanted mice (p < 0.05). Morphine therapy can lead to a decrease in spinal μ receptor expression. Similarly, the nalbuphine therapy can lead to a decrease in the expression of κ receptor protein and mRNA at the spinal cord level (p < 0.05). Morphine, nalbuphine, or nalbuphine co-administration with morphine all can extend the paw withdrawal thermal latency (PWL) to radiant thermal stimulation in tumor-implanted mice (p < 0.05). Compared with the morphine treatment group, nalbuphine co-administration with morphine delayed the reduction of PWL value again (p < 0.05). BCP itself may induce down-regulation of the spinal MOR and KOR expression. A low dose of nalbuphine co-administration with morphine led to the delayed emergence of morphine tolerance. The part of the mechanism may be due to the regulation of spinal opioid receptors expression.

Insula Dynorphin and Kappa Opioid Receptor Systems Regulate Alcohol Drinking in a Sex-Specific Manner in Mice.

Alcohol use disorder is complex and multifaceted, involving the coordination of multiple signaling systems across numerous brain regions. Previous work has indicated that both the insular cortex and dynorphin (DYN)/kappa opioid receptor (KOR) systems contribute to excessive alcohol use. More recently, we identified a microcircuit in the medial aspect of the insular cortex that signals through DYN/KOR. Here, we explored the role of insula DYN/KOR circuit components on alcohol intake in a long-term intermittent access (IA) procedure. Using a combination of conditional knock-out strategies and site-directed pharmacology, we discovered distinct and sex-specific roles for insula DYN and KOR in alcohol drinking and related behavior. Our findings show that insula DYN deletion blocked escalated consumption and decreased the overall intake of and preference for alcohol in male and female mice. This effect was specific to alcohol in male mice, as DYN deletion did not impact sucrose intake. Further, insula KOR antagonism reduced alcohol intake and preference during the early phase of IA in male mice only. Alcohol consumption was not affected by insula KOR knockout in either sex. In addition, we found that long-term IA decreased the intrinsic excitability of DYN and deep layer pyramidal neurons (DLPNs) in the insula of male mice. Excitatory synaptic transmission was also impacted by IA, as it drove an increase in excitatory synaptic drive in both DYN neurons and DLPNs. Combined, our findings suggest there is a dynamic interplay between excessive alcohol consumption and insula DYN/KOR microcircuitry.SIGNIFICANCE STATEMENT The insular cortex is a complex region that serves as an integratory hub for sensory inputs. In our previous work, we identified a microcircuit in the insula that signals through the kappa opioid receptor (KOR) and its endogenous ligand dynorphin (DYN). Both the insula and DYN/KOR systems have been implicated in excessive alcohol use and alcohol use disorder (AUD). Here, we use converging approaches to determine how insula DYN/KOR microcircuit components contribute to escalated alcohol consumption. Our findings show that insula DYN/KOR systems regulate distinct phases of alcohol consumption in a sex-specific manner, which may contribute to the progression to AUD.

Buprenorphine reduces somatic withdrawal in a mouse model of early-life morphine exposure

The rising prevalence of early-life opioid exposure has become a pressing public health issue in the U.S. Neonates exposed to opioids in utero are at risk of experiencing a constellation of postpartum withdrawal symptoms commonly referred to as neonatal opioid withdrawal syndrome (NOWS). Buprenorphine (BPN), a partial agonist at the mu-opioid receptor (MOR) and antagonist at the kappa-opioid receptor (KOR), is currently approved to treat opioid use disorder in adult populations. Recent research suggests that BPN may also be effective in reducing withdrawal symptoms in neonates who were exposed to opioids in utero. We sought to determine whether BPN attenuates somatic withdrawal in a mouse model of NOWS. Our findings indicate that the administration of morphine (10mg/kg, s.c.) from postnatal day (PND) 1–14 results in increased somatic symptoms upon naloxone-precipitated (1mg/kg, s.c.) withdrawal. Co-administration of BPN (0.3mg/kg, s.c.) from PND 12–14 attenuated symptoms in morphine-treated mice. On PND 15, 24h following naloxone-precipitated withdrawal, a subset of mice was examined for thermal sensitivity in the hot plate test. BPN treatment significantly increased response latency in morphine-exposed mice. Lastly, neonatal morphine exposure elevated mRNA expression of KOR, and reduced mRNA expression of corticotropin-releasing hormone (CRH) in the periaqueductal gray when measured on PND 14. Altogether, this data provides support for the therapeutic effects of acute low-dose buprenorphine treatment in a mouse model of neonatal opioid exposure and withdrawal.

Effect of PDYN and OPRK1 polymorphisms on the risk of alcohol use disorder and the intensity of depressive symptoms.

The dynorphin (DYN)/Kappa Opioid Receptor (KOR) system has been suggested to be involved in both negative affective states and the action of alcohol. The present study was undertaken to explore whether the DYN/KOR system genes, PDYN and OPRK1, influence on individual differences in the intensity of depressive symptoms at admission as well as the risk of alcohol use disorder (AUD) risk in a sample of 101 individuals with AUD and 100 controls. PDYN (rs2281285, rs2225749 and rs910080) and OPRK1 (rs6473797, rs963549 and rs997917) polymorphisms were analyzed by PCR-RFLP. The intensity of depressive and anxiety symptoms and craving were measured by the Beck Depression Inventory-II (BDI-II), Beck Anxiety Inventory (BAI), and Penn Alcohol Craving Scale, respectively. A significant association between the risk of AUD and OPRK1 rs6473797 (P < 0.05) at the gene level. OPRK1 rs6473797 CC genotype was found to lead to a 3.11 times greater alcohol dependence risk. In addition, the BDI-II score of the OPRK1 rs963549 CC genotype was found to be significantly lower (20.9 ± 11.2, min: 1.0, max: 48.0) than that of the CT + TT genotypes (27.04 ± 12.7, min: 0.0, max: 49.0) (t: -2.332, P = 0.022). None of the PDYN polymorphisms were associated with BDI-II score. Variations in the KOR are associated with the risk of AUD and the intensity of depressive symptoms at admission at the gene level in Turkish males. On the other hand, PDYN gene seemed not to be associated with AUD, depression, anxiety, and craving.

Assessment of the physical dependence potential of difelikefalin: randomized placebo-controlled study in patients receiving hemodialysis.

Difelikefalin is a selective kappa opioid receptor agonist approved for treating moderate-to-severe pruritus in adults undergoing hemodialysis (HD). Difelikefalin is not a controlled substance under the Controlled Substances Act. This study assessed the potential for developing physical dependence on difelikefalin in patients undergoing HD. Eligible patients received open-label difelikefalin after each dialysis session for 3 weeks before entering a 2-week double-blind phase, when they were randomized to either continue difelikefalin or to switch to receiving placebo. Signs of physical withdrawal were assessed using the Clinical Opiate Withdrawal Scale (COWS), several patient-reported scales, and physiological measures. The primary endpoint was the between-group difference in mean maximum COWS total scores during the double-blind phase; the mean difference (placebo - difelikefalin) was compared against a pre-defined noninferiority limit (+4). Thirty-five patients (57.1% male; 91.4% Black or African American; median [range] age 58 [28-77] years) were included, of which 30 were randomized (placebo, n=14; difelikefalin, n=16). The least square mean difference in maximum COWS total scores was 0.52 (95% confidence interval [CI]: -0.56, 1.59). The upper CI limit (1.59) was below +4, indicating that patients who discontinued difelikefalin (placebo group) had similar withdrawal scores to patients who continued difelikefalin. Additional assessments supported the COWS results, showing no meaningful differences between groups in physiological measures or in patient-reported measures of sleep or physical withdrawal. These results demonstrate that abruptly discontinuing chronic difelikefalin treatment in patients undergoing HD does not produce signs or symptoms of physical withdrawal.

Deuterated buprenorphine retains pharmacodynamic properties of buprenorphine and resists metabolism to the active metabolite norbuprenorphine in rats.

Introduction: An active metabolite of buprenorphine (BUP), called norbuprenorphine (NorBUP), is implicated in neonatal opioid withdrawal syndrome when BUP is taken during pregnancy. Therefore, reducing or eliminating metabolism of BUP to NorBUP is a novel strategy that will likely lower total fetal exposure to opioids and thus improve offspring outcomes. Precision deuteration alters pharmacokinetics of drugs without altering pharmacodynamics. Here, we report the synthesis and testing of deuterated buprenorphine (BUP-D2). Methods: We determined opioid receptor affinities of BUP-D2 relative to BUP with radioligand competition receptor binding assays, and the potency and efficacy of BUP-D2 relative to BUP to activate G-proteins via opioid receptors with [35S]GTPγS binding assays in homogenates containing the human mu, delta, or kappa opioid receptors. The antinociceptive effects of BUP-D2 and BUP were compared using the warm-water tail withdrawal assay in rats. Blood concentration versus time profiles of BUP, BUP-D2, and NorBUP were measured in rats following intravenous BUP-D2 or BUP injection. Results: The synthesis provided a 48% yield and the product was ≥99% deuterated. Like BUP, BUP-D2 had sub-nanomolar affinity for opioid receptors. BUP-D2 also activated opioid receptors and induced antinociception with equal potency and efficacy as BUP. The maximum concentration and the area under the curve of NorBUP in the blood of rats that received BUP-D2 were over 19- and 10-fold lower, respectively, than in rats that received BUP. Discussion: These results indicate that BUP-D2 retains key pharmacodynamic properties of BUP and resists metabolism to NorBUP and therefore holds promise as an alternative to BUP.

Ligand and G-protein selectivity in the κ-opioid receptor

The κ-opioid receptor (KOR) represents a highly desirable therapeutic target for treating not only pain but also addiction and affective disorders1. However, the development of KOR analgesics has been hindered by the associated hallucinogenic side effects2. The initiation of KOR signalling requires the Gi/o-family proteins including the conventional (Gi1, Gi2, Gi3, GoA and GoB) and nonconventional (Gz and Gg) subtypes. How hallucinogens exert their actions through KOR and how KOR determines G-protein subtype selectivity are not well understood. Here we determined the active-state structures of KOR in a complex with multiple G-protein heterotrimers—Gi1, GoA, Gz and Gg—using cryo-electron microscopy. The KOR–G-protein complexes are bound to hallucinogenic salvinorins or highly selective KOR agonists. Comparisons of these structures reveal molecular determinants critical for KOR–G-protein interactions as well as key elements governing Gi/o-family subtype selectivity and KOR ligand selectivity. Furthermore, the four G-protein subtypes display an intrinsically different binding affinity and allosteric activity on agonist binding at KOR. These results provide insights into the actions of opioids and G-protein-coupling specificity at KOR and establish a foundation to examine the therapeutic potential of pathway-selective agonists of KOR.

The Pharmacokinetics of Subcutaneous Methylnaltrexone Bromide in Rhesus Macaques (Macaca mulatta).

Opioids are an integral component of pain management for nonhuman primates. These potent analgesics also adverse gastrointestinal (GI) effects that include constipation, bloating, and delayed gastric emptying. Methylnaltrexone bromide (MNTX) is a selective, peripherally acting μ- and κ-opioid receptor antagonist that can be used to mitigate the GI effects associated with opioid administration. Unlike naltrexone, a similar drug in this class, MNTX possesses an N-methyl-quaternary amine group that prevents it from crossing the blood brain barrier. This blockage allows inhibition of peripheral GI opioid receptors without affecting opioid-mediated analgesia in the central nervous system. We conducted a pharmacokinetic analysis of MNTX in serum and CSF of 6 healthy juvenile male rhesus macaques after subcutaneous administration of a 0.15-mg/kg dose. We hypothesized that the macaques would demonstrate a Tmax of 0.5 h, similar to that of humans, and that no MNTX would be detected in the CSF. This treatment resulted in a peak serum concentration of 114 ± 44 ng/mL at 0.25 ± 0.00 h; peak CSF at concentrations were 0.34 ± 0.07 ng/mL at the Tmax. These data show that subcutaneous administration of MNTX to rhesus macaques may block peripheral adverse effects of opioids without interfering with their central analgesic effects.