Mu-opioid Receptor Research Articles

Multicenter study of OPRM1 A118G and promoter-region DNA methylation associations with opioid outcomes and chronic postsurgical pain after pediatric musculoskeletal surgery

Abstract Introduction: Mu opioid receptor gene (OPRM1) variant rs1799971 introduces a CpG site, which may influence DNA methylation (DNAm) and opioid/pain outcomes. Objectives: In this nested analysis, we investigated both OPRM1 A118G genotype and promoter/immediate downstream blood DNAm sequencing data for associations with opioid effects and chronic postsurgical pain (CPSP) in a surgical cohort. Methods: Prospectively recruited opioid naïve patients undergoing Nuss procedure or spinal fusion with rs1799971 genotypes (Illumina arrays), DNAm (next generation enzymatic methylation sequencing at Chr6:154,039,209-154,039,803) and outcomes—opioid analgesia (integrated opioid use + pain over postoperative days 0 and 1 normalized to surgery type), safety—respiratory depression (RD) in high opioid use groups, and CPSP (Numerical Rating Scale >3/10 2-12 months postsurgery)—were included. Linear and logistic regression were performed to test genetic and epigenetic associations, adjusted for sociodemographics, cell types, and analgesics. Results: In this cohort (N = 112; 15.3 ± 2.0 years, 50% female, 83% White, 55% had CPSP, 13% had RD), DNAm at Chr6:154039216-154039217 was associated with CPSP (odds ratio [OR], 1.26; 95% confidence interval [CI], 1.00-1.57; P = 0.03), Chr6:154039661-154039662 with acute integrated pain (β = −20.9, 95% CI, −40.70 to −1.10, P = 0.04), Chr6:154039520-154039521 (OR, 1.49; 95% CI, 1.09-2.03; P = 0.01), and Chr6:154039571-154039572 (OR, 1.47; 95% CI, 1.08-2.01; P = 0.02) with RD. Significant CpG sites were located in Repressed Polycomb chromatin states. Genotype was not associated with DNAm or outcomes. Conclusion: Our analyses support OPRM1 DNAm as predictors of acute and chronic pain/opioid outcomes in children after painful surgery. Study limitations included absent GG genotype, low sequencing coverage, and lack of correction for multiple testing.

Abstract B042: The impact of opioids on the pancreatic tumor immune microenvironment

Abstract Pancreatic cancer is a highly lethal malignancy with a 5-year survival rate of 12.8%. Due to the high prevalence of cancer-related pain, 75% of pancreatic cancer patients are prescribed opioids. Opioids, which signal through the G protein-coupled receptor (GPCR) mu-opioid receptor (MOR), have peripheral effects outside of their analgesic function. Importantly, several studies have correlated opioids with worsened survival of patients receiving immunotherapy. However, the mechanism behind this is unknown. Immunotherapy is largely ineffective in pancreatic cancer, due in part to the tumor microenvironment (TME) characterized by dense, desmoplastic stroma, with cancer-associated fibroblasts (CAFs) comprising up to 90% of the tumor volume. CAFs play a large role in immunosuppression and therapy resistance, such as through promoting infiltration of immunosuppressive cells, resulting in reduced presence of antitumor immune cells and impaired immunotherapy efficacy. While the role of CAFs in promoting immunosuppression in the tumor microenvironment is well characterized, the effect of opioids on this phenomenon is unknown. We now provide evidence that MOR directly regulates CAF function. Specifically, knockdown of MOR in CAFs reduces gene expression of alpha-smooth muscle actin (aSMA) and leukemia inhibitory factor. MOR knockdown in CAFs also decreases protein expression of aSMA and type 1a collagen. We hypothesize that opioids promote MOR-dependent CAF activation and secretion of pro-inflammatory cytokines, resulting in a more immunosuppressive TME, and thus impaired immunotherapy response. The long-term goal of this work is to determine the role of opioids on CAFs in the pancreatic TME, as well as the role of MOR in promoting immunosuppression and the resulting value of MOR as a target to improve immunotherapy efficacy. This research is clinically significant because it could uncover a novel mechanism driving immunosuppression caused by a medication commonly prescribed to almost all pancreatic cancer patients. Citation Format: Kathryn Maraszek, Michael Feigin. The impact of opioids on the pancreatic tumor immune microenvironment [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor-body Interactions: The Roles of Micro- and Macroenvironment in Cancer; 2024 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(22_Suppl):Abstract nr B042.

FLT3 signaling inhibition abrogates opioid tolerance and hyperalgesia while preserving analgesia

Navigating the duality of opioids’ potent analgesia and side effects, including tolerance and hyperalgesia, is a significant challenge in chronic pain management, often prompting hazardous dose escalation to maintain analgesic effects. The peripheral mu-opioid receptor (MOR) is known to mediate these contradictory effects. Here, we show that the fms-like tyrosine kinase receptor 3 (FLT3) in peripheral somatosensory neurons drives morphine tolerance and hyperalgesia in a male rodent model. We found that chronic morphine treatment increases FLT3 and MOR co-expression, and that inhibiting FLT3 represses MOR-induced hyperactivation of the cyclic adenosine monophosphate (cAMP) signaling pathway, mitigating maladaptive excitatory processes engaged after chronic morphine treatment. Furthermore, in postsurgical or inflammatory models of chronic pain, co-administering morphine with a FLT3-specific inhibitor not only prevents or suppresses tolerance and hyperalgesia but also potentiates the analgesic efficacy of morphine, without aggravating other morphine-induced adverse effects. Our findings suggest that pairing morphine with FLT3 inhibitors could become a promising avenue for chronic pain management to safely harness the power of opioids, without the risk of dose escalation. By enhancing morphine analgesic potency through FLT3 inhibition, this approach could minimize opioid dosage, thereby curtailing the risk of addiction and other opioid-related side effects.

Improving Diagnosis and Management of Opioid-Induced Constipation (OIC) in Clinical Practice: An Italian Expert Opinion

Opioid-induced constipation (OIC) is a very common and troublesome gastrointestinal side effect following the use of opioids. Despite existing international guidelines, OIC is largely underdiagnosed and undertreated. ECHO OIC is a European project designed to improve the diagnosis and management of OIC at the primary care level. The next phase of the ECHO OIC project is to review and adapt the proposed European pathway at national level, considering the local patient journey and clinical practice. A multidisciplinary group of 12 Italian experts reviewed and discussed the European path and formulated a seven-step guide for the practical management of OIC that is also easily applicable in primary care: 1. When prescribing long-term opioids, the physician should inform the patient of the possibility of the onset of OIC; 2. At opioid prescription, doctors should also prescribe a treatment for constipation, preferably macrogol or stimulant laxatives; 3. The patient should be evaluated for OIC within the second week of initiating opioid treatment, by clinical history and Rome IV criteria; 4. In the presence of constipation despite laxatives, prescription of a PAMORA (Peripherally Acting Mu Opioid Receptor Antagonist) should be considered; 5. When prescribing a PAMORA, prescribing information should be carefully reviewed, and patients should be accurately instructed for appropriate use; 6. Efficacy and tolerability of the PAMORA should be monitored regularly by Bowel Function Index, considering a cut-off of 30 for the possible step-up of OIC treatment; 7. After 4 weeks of treatment, if the efficacy of PAMORA is deemed inadequate, discontinuation of the PAMORA, addition of an anti-constipation drugs, change of opioid type, or referral to a specialist should be considered. Spreading knowledge about the OIC problem as much as possible to the health community is crucial to obtain not only an early treatment of the condition but also to promote its prevention.

Activated microglia secretome and proinflammatory cytokines increase neuronal mu-opioid receptor signalling and expression

Due to its potential role in processes which rely on mu-opioid receptor function, investigating the relationship between Mu-Opioid receptors (MORs), neuroinflammation, and glial cells has gained momentum. Traditionally, MOR activation has been associated with immunosuppression, but recent findings suggest a more nuanced, bidirectional relationship with the immune system. To further investigate this relationship, herein, we investigated the role of the activated microglia secretome and proinflammatory cytokines in neuronal MOR expression and signalling. Our results show that both microglial secretome and specific cytokines increase neuronal MOR expression and enhance the [D-Ala2, N-MePhe4, Gly-ol]-enkephalin (DAMGO)-induced MOR activation. We also show that DAMGO-induced neuroinflammation increases neuronal MOR expression, activation, and regulation. Our findings suggest a feedback loop between microglial activation, cytokine release, and neuronal MOR dynamics. Future research should delve into the temporal dynamics and functional implications of this relationship, particularly concerning clinically relevant opioids like morphine and fentanyl and pain management.

Morphine treatment restricts response to immunotherapy in oral squamous cell carcinoma

BackgroundImmune checkpoint inhibitors (ICIs) are becoming the standard of care for recurrent and metastatic cancer. Opioids, the primary treatment for cancer-related pain, are immunosuppressive raising concerns about their potential to interfere with the efficacy of ICIs. We hypothesize that exogenous opioids given for analgesia suppress antitumor immunity via T cell-mediated mu opioid receptor 1 (OPRM1) signaling.MethodsIn silico bioinformatics were used to assess OPRM1 receptor expression on tumor-infiltrating immune cells in patients with head and neck squamous cell carcinoma (HNSCC) and across different cancer types. A syngeneic orthotopic mouse model of oral squamous cell carcinoma was used to study the impact of morphine and OPRM1 antagonism on tumor-infiltrating immune cells, tumor growth and antitumor efficacy of anti-Programmed cell death protein 1 (PD-1) monoclonal antibody treatment.ResultsIn patients with HNSCC, OPRM1 expression was most abundant in CD8+ T cells, particularly in patients who had not been prescribed opioids prior to resection and exhibited increased expression of exhaustion markers. Exogenous morphine treatment in tumor-bearing mice reduced CD4+ and CD8+ T-cell infiltration and subsequently anti-PD1 ICI efficacy. Peripherally acting mu opioid receptor antagonism, when administered in the adjunctive setting, was able to block morphine-induced immunosuppression and recover the antitumor efficacy of anti-PD1.ConclusionsThese findings suggest that morphine acts via a peripheral OPRM1-mediated mechanism to suppress CD8+ T cells, thereby fostering a pro-tumor-impaired immune response. Importantly, peripherally-restricted OPRM1 antagonism can effectively block this morphine-induced immunosuppression while still allowing for centrally-mediated analgesia, indicating a potential therapeutic strategy for mitigating the adverse effects of opioid pain relief in cancer treatment.

Structure-function relationship of dynorphin B variants using naturally occurring amino acid substitutions.

Dynorphins (Dyn) represent the subset of endogenous opioid peptides with the highest binding affinity to kappa opioid receptors (KOPrs). Activation of the G-protein-coupled pathway of KOPrs has strong anticonvulsant effects. Dyn also bind to mu (MOPrs) and delta opioid receptors (DOPrs) with lower affinity and can activate the β-arrestin pathway. To fully exploit the therapeutic potential of dynorphins and reduce potential unwanted effects, increased selectivity for KOPrs combined with reduced activation of the mTOR complex would be favorable. Therefore, we investigated a series of dynorphin B (DynB) variants, substituted in one or two positions with naturally occurring amino acids for differential opioid receptor activation, applying competitive radio binding assays, GTPγS assays, PRESTO-Tango, and Western blotting on single-opioid receptor-expressing cells. Seven DynB derivatives displayed at least 10-fold increased selectivity for KOPrs over either MOPrs or DOPrs. The highest selectivity for KOPrs over MOPrs was obtained with DynB_G3M/Q8H, and the highest selectivity for KOPrs over DOPrs was obtained with DynB_L5S. Increased selectivity for KOPr over MOPr and DOPr was based on a loss of affinity or potency at MOPr and DOPr rather than a higher affinity or potency at KOPr. This suggests that the investigated amino acid exchanges in positions 3, 5, and 8 are of higher importance for binding and activation of MOPr or DOPr than of KOPr. In tests for signal transduction using the GTPγS assay, none of the DynB derivatives displayed increased potency. The three tested variants with substitutions of glycine to methionine in position 3 displayed reduced efficacy and are, therefore, considered partial agonists. The two most promising activating candidates were further investigated for functional selectivity between the G-protein and the β-arrestin pathway, as well as for activation of mTOR. No difference was detected in the respective read-outs, compared to wild-type DynB. Our data indicate that the assessment of affinity to KOPr alone is not sufficient to predict either potency or efficacy of peptidergic agonists on KOPr. Further assessment of downstream pathways is required to allow more reliable predictions of in vivo effects.

Chronic olanzapine treatment leads to increased opioid receptor expression and changes in feeding regulating neurons in the female rat hypothalamus

Opioid receptor antagonists have shown increasing promise as an adjunct therapy to psychotropic medication. The goal is to reduce the weight gain and metabolic adverse effects that are associated with certain second-generation antipsychotics, such as olanzapine and clozapine. In this study, female rats were treated for 4 weeks with a long-acting injectable formulation of olanzapine to assess effects on hypothalamic feeding regulation. Using quantitative spatial in situ hybridization and receptor autoradiography, expression levels of the mu, kappa and delta opioid receptors were defined in the five hypothalamic areas: paraventricular nucleus (PVN), arcuate nucleus (ARC), ventromedial nucleus (VMN), dorsomedial nucleus (DMN) and lateral hypothalamus (LH). In addition, hypothalamic neuron number and size were estimated using the unbiased optical fractionator and spatial rotator methods. Hyperphagia was observed after only 24 hours of olanzapine treatment, with continued weight gain throughout the duration of the study. In contrast, the observed food intake reversed to control levels after 2 weeks of olanzapine treatment. Chronic olanzapine treatment increased expression of kappa opioid receptor mRNA and receptor availability in the PVN, as well as increased mu opioid receptor availability in the PVN, ARC and VMN. These changes were accompanied by fewer anorexigenic proopiomelanocortin-expressing neurons of the ARC and corticotropin-releasing hormone expressing neurons of the PVN. This study links olanzapine-driven metabolic effects to increased opioid receptor expression in the hypothalamus, thus providing a rationale for the positive effects of using opioid receptor antagonists to relieve olanzapine adverse effects.

Peripheral opioid receptor antagonism alleviates fentanyl-induced cardiorespiratory depression and is devoid of aversive effects.

In this study, we compare the central versus peripheral components underlying fentanyl-induced cardiorespiratory depression to prevent overdose deaths. Our data indicate that these effects are, at least partially, due to the activation of mu opioid receptors present in peripheral sites. These findings provide insight into peripheral contributions to fentanyl-induced overdoses and could potentially lead to the development of treatments selectively targeting the peripheral system, sparing individuals from the CNS-driven acute opioid withdrawal generally observed with the use of naloxone.

Mu and Delta Opioid Receptors Modulate Inhibition within the Prefrontal Cortex Through Dissociable Cellular and Molecular Mechanisms.

The endogenous opioid system regulates behaviors that rely on prefrontal cortex (PFC) function. Previous studies have described Mu and Delta opioid receptor expression within cortical GABAergic interneurons, but a detailed understanding of how opioids regulate different interneuron subtypes and cortical microcircuits has not been reported. We use whole-cell patch-clamp electrophysiology, genetically engineered mice, and optogenetics to assess MOR and DOR regulation of PFC inhibitory transmission, demonstrating that MOR and DOR inhibition of interneurons display qualitative and quantitative variation across GABAergic circuits within mouse prelimbic PFC.

Intravenous Bolus Injection of Fentanyl Triggers an Immediate Central and Upper Airway Obstructive Apnea via Activating Vagal Sensory Afferents.

Intravenous bolus (IVb) injection of fentanyl induces an immediate apnea, but the characteristics of the apnea and relevant mechanism remain unclear. Here, we tested whether IVb injection of fentanyl induced an immediate central and upper airway obstructive apnea associated with chest wall rigidity via activating vagal C-fibers (VCFs) and vagal afferent opioid receptors (ORs). Cardiorespiratory and electromyography of external and internal intercostal, thyroarytenoid and superior pharyngeal constrictor muscles (EMGEI, EMGII, EMGTA and EMGSPC) responses to IVb injection of fentanyl were recorded in anesthetized and spontaneously breathing rats with or without bilateral peri-vagal capsaicin treatment or intra-vagal microinjection of naloxone. Immunohistochemical approach was employed to define the presence of opioid mu-receptor (MOR) expression in vagal C-neurons and a patch clamp technique utilized to determine the evoked current responses of vagal C-neurons to fentanyl in vitro. Fentanyl induced an immediate apnea and subsequent respiratory depression. The apnea was characterized by cessation of EMGEI activity and augmentation of tonic discharges of EMGII, EMGTA, and EMGSPC, i.e., central expiratory apnea, laryngeal closure and pharyngeal constriction/collapse accompanied with chest wall rigidity. The apneic response was abolished by blockade of VCF signal conduction and largely attenuated by antagonism of vagal afferent ORs. The latter significantly alleviated the initial (within 5 min post injection), but not the later, respiratory depression. Vagal C-neurons expressed MORs and were activated by fentanyl. We conclude that IVb injection of fentanyl causes a VCF- and vagal afferent OR-mediated immediate central apnea, upper airway obstruction and chest wall rigidity.

A Small-molecule Antagonist Radiotracer for Positron Emission Tomography Imaging of the Mu Opioid Receptor.

The opioid crisis is a catastrophic health emergency catalyzed by the misuse of opioids that target and activate the mu opioid receptor. Traditional radioligands used to study the mu opioid receptor are often tightly regulated owing to their abuse and respiratory depression potential. In the present study, we sought to design and characterize a library of 24 non-agonist ligands for the mu opioid receptor. Ligands were evaluated for the binding affinity, intrinsic activity, and predicted blood-brain barrier permeability. Several ligands demonstrated single-digit nM binding affinity for the mu opioid receptor while also demonstrating selectivity over the delta and kappa opioid receptors. The antagonist behavior of 1A and 3A at the mu opioid receptor indicate that these ligands would likely not induce opioid-dependent respiratory depression. Therefore, these ligands can enable a safer means to interrogate the endogenous opioid system. Based on binding affinity, selectivity, and potential off-target binding, [ 11 C] 1A was prepared via metallophotoredox of the aryl-bromide functional group to [ 11 C]methyl iodide. The nascent radiotracer demonstrated brain uptake in a rhesus macaque model and accumulation in the caudate and putamen. Naloxone was able to reduce [ 11 C] 1A binding, though the interactions were not as pronounced as naloxone's ability to displace [ 11 C]carfentanil. These results suggest that GSK1521498 and related congeners are amenable to radioligand design and can offer a safer way to query opioid neurobiology.

Classics in Chemical Neuroscience: Tianeptine.

Tianeptine (1) is an unusual antidepressant in that its mechanism of action appears to be independent from any activity at serotonin receptors or monoamine transporters. In fact, tianeptine has been shown to be a moderately potent agonist for the mu opioid receptor (MOR) and to a lesser extent the delta opioid receptor (DOR). Additionally, tianeptine's efficacy may be related to its action on glutamate-mediated pathways of neuroplasticity. Regardless of which neurotransmitter system is primarily responsible for the observed efficacy, the MOR agonist activity is problematic with respect to abuse liability. Increasing numbers of case reports have demonstrated that tianeptine is indeed being used recreationally at doses far beyond what are considered therapeutically relevant or safe, and scheduling reclassifications or outright bans on tianeptine products are ongoing around the world. It is the aim of this review to discuss the medicinal chemistry and pharmacology of tianeptine and to summarize this intriguing discrepancy between tianeptine's historical use as a safe and effective antidepressant and its emerging potential for abuse.

Serum cytokines and inflammatory proteins in individuals with heroin use disorder: potential mechanistically based biomarkers for diagnosis

Opioid use disorders cause major morbidity and mortality, and there is a pressing need for novel mechanistic targets and biomarkers for diagnosis and prognosis. Exposure to mu-opioid receptor (MOR) agonists causes changes in cytokine and inflammatory protein networks in peripheral blood, and also in brain glia and neurons. Individuals with heroin use disorder (iHUD) show dysregulated levels of several cytokines in the blood. However, there is limited data on a comprehensive panel of such markers in iHUD versus healthy controls (HC), especially considered as a multi-target biomarker. We used a validated proximity extension assay for the relative quantification of 92 cytokines and inflammatory proteins in the serum of iHUD on medication-assisted therapy (MAT; n = 21), compared to HC (n = 24). Twenty-nine targets showed significant group differences (primarily iHUD>HC), surviving multiple comparison corrections (p = 0.05). These targets included 19 members of canonical cytokine families, including specific chemokines, interleukins, growth factors, and tumor necrosis factor (TNF)-related proteins. For dimensionality reduction, data from these 19 cytokines were entered into a principal component (PC) analysis, with PC1 scores showing significant group differences (iHUD > HC; p < 0.0001). A receiver-operating characteristic (ROC) curve analysis yielded an AUROC = 91.7% (p < 0.0001). This PC1 score remained a positive predictor of being in the HUD group in a multivariable logistic regression, that included select demographic/clinical variables. Overall, this study shows a panel of cytokines that differ significantly between iHUD and HC, providing a multi-target “cytokine biomarker score” for potential diagnostic purposes, and future examination of disease severity.

The role of mu-opioid receptors in pancreatic islet α-cells.

Diabetes is a complex disease that impacts more than 500 million people across the world. Many of these individuals will develop diabetic neuropathy as a comorbidity, which is historically treated with exogenous opioids like morphine, oxycodone, or tramadol. Although these opioids are effective analgesics, growing evidence indicates that they may directly impact the endocrine pancreas function in patients. One common feature of these exogenous opioid ligands is their preference for the mu opioid receptor (MOPR), so we aimed to determine if endogenous MOPRs directly regulate pancreatic islet metabolism and hormone secretion. We show that pharmacological antagonism of MOPRs enhances glucagon secretion, but not insulin secretion, from human islets under high glucose conditions. This increased secretion is accompanied by increased cAMP signaling. mRNA expression of MOPRs is robust in non-diabetic human islets, but downregulated in islets from T2D donors, suggesting a link between metabolism and MOPR expression. Conditional genetic knockout of MOPRs in murine α-cells increases glucagon secretion under high glucose conditions without increasing glucagon content. Consistent with downregulation of MOPRs during metabolic disease, conditional MOPR knockout mice treated with a high fat diet show impaired glucose tolerance, increased glucagon secretion, increased insulin content, and increased islet size. Together, these results demonstrate a direct mechanism of action for endogenous opioid regulation of endocrine pancreas.

Dihydrokoumine, a dual-target analgesic with reduced side effects isolated from a traditional Chinese medicine

IntroductionOpioids are the most common antinociceptive drugs, but long-term administration causes serious adverse side effects. Gelsemium elegans Benth. is traditionally used as an analgesic agent and mainly contains indole alkaloids with structures different from those in common opioids, indicating distinct pharmacological properties. This work aims to find a new analgesic from Gelsemium elegans Benth. and evaluate it in vitro and in vivo. MethodsDihydrokoumine was purified from Gelsemium elegans Benth. Binding to mu opioid receptor (MOR), M3 receptor (M3R) and other 15 G protein-coupled receptors were evaluated in vitro combined with molecular docking analysis. Analgesic efficacy and side effects were measured in vivo using hot-plate, formalin paw, and rotarod tests in mice. Cytotoxicity, acute toxicity in mice and pharmacokinetics were assessed. ResultsA MOR agonist, dihydrokoumine, was first identified from Gelsemium elegans Benth. Further investigations showed that dihydrokoumine exhibited selective partial agonist action on the MOR and antagonist action on the M3R among other 15 GPCRs. In in vivo mouse models, dihydrokoumine could relieve acute pain and chronic inflammatory pain without drug tolerance and sedative side effects. Additionally, we observed a good safety profile and favorable pharmacokinetic properties. ConclusionA MOR partial agonist/M3R antagonist analgesic with reduced side effects was isolated from a traditional Chinese medicine. This study bestows dihydrokoumine as a new dual-target analgesic and as a potential lead compound in long-term pain management.

Inadequate management of opioid-induced constipation in European cancer pain patients: results of a real-world, multicentre, observational study ("E-StOIC").

The objectives of the study were to determine the prevalence of (uncontrolled) OIC, relevant medications / interventions employed by healthcare professionals, and the additional strategies utilised by patients, amongst European patients with cancer pain. This study was a prospective observational study conducted at 24 research sites in ten European countries. Cancer patients receiving opioid analgesics for at least a week were recruited, and asked to complete a questionnaire including background information, single question (Are you constipated?), Rome IV diagnostic criteria for OIC, Bowel Function Index (BFI), and Patient Assessment of Constipation Quality of Life questionnaire (PAC-QOL). Participants were characterised as having / not having OIC on the basis of the Rome IV diagnostic criteria. 1200 participants completed the study. 59.5% met the Rome IV diagnostic criteria for OIC: only 61.5% that met these criteria self-reported constipation. 72% participants were prescribed a regular conventional laxative / peripherally acting mu-opioid receptor antagonist (PAMORA). However, only 66% took their prescribed laxatives every day. Many participants had utilised other strategies / interventions to manage their OIC. Furthermore, 27% had needed to use suppositories, 26.5% had needed to use an enema, and 8% had had a manual evacuation. The use of PAMORAs, and other novel effective medications, was relatively uncommon. The results of this study suggest that management in Europe is often inadequate, and this undoubtedly relates to a combination of inadequate assessment, inappropriate treatment, and inadequate reassessment.

Cryo-EM structure of small-molecule agonist bound delta opioid receptor-Gi complex enables discovery of biased compound

Delta opioid receptor (δOR) plays a pivotal role in modulating human sensation and emotion. It is an attractive target for drug discovery since, unlike Mu opioid receptor, it is associated with low risk of drug dependence. Despite its potential applications, the pharmacological properties of δOR, including the mechanisms of activation by small-molecule agonists and the complex signaling pathways it engages, as well as their relation to the potential side effects, remain poorly understood. In this study, we use cryo-electron microscopy (cryo-EM) to determine the structure of the δOR-Gi complex when bound to a small-molecule agonist (ADL5859). Moreover, we design a series of probes to examine the key receptor-ligand interaction site and identify a region involved in signaling bias. Using ADL06 as a chemical tool, we elucidate the relationship between the β-arrestin pathway of the δOR and its biological functions, such as analgesic tolerance and convulsion activities. Notably, we discover that the β-arrestin recruitment of δOR might be linked to reduced gastrointestinal motility. These insights enhance our understanding of δOR’s structure, signaling pathways, and biological functions, paving the way for the structure-based drug discovery.

The Role of the Rat Prefrontal Cortex and Sex Differences in Decision-Making.

The prefrontal cortex is critical for decision-making across species, with its activity linked to choosing between options. Drift diffusion models (DDMs) are commonly employed to understand the neural computations underlying this behavior. Studies exploring the specific roles of regions of the rodent prefrontal cortex in controlling the decision process are limited. This study explored the role of the prelimbic cortex (PLC) in decision-making using a two-alternative forced-choice task. Rats first learned to report the location of a lateralized visual stimulus. The brightness of the stimulus indicated its reward value. Then, the rats learned to make choices between pairs of stimuli. Sex differences in learning were observed, with females responding faster and more selectively to high-value stimuli than males. DDM analysis found that males had decreased decision thresholds during initial learning, whereas females maintained a consistently higher drift rate. Pharmacological manipulations revealed that PLC inactivation reduced the decision threshold for all rats, indicating that less information was needed to make a choice in the absence of normal PLC processing. μ-Opioid receptor stimulation of the PLC had the opposite effect, raising the decision threshold and reducing bias in the decision process toward high-value stimuli. These effects were observed without any impact on the rats' choice preferences. Our findings suggest that PLC has an inhibitory role in the decision process and regulates the amount of evidence that is required to make a choice. That is, PLC activity controls "when," but not "how," to act.

Preparation, Evaluation and Optimization of Polymeric Nanoparticles of Eluxadoline for the Treatment of Irritable Bowel Syndrome

ABSTRACT Eluxadoline, exhibits potential as an irritable bowel syndrome treatment and management strategy. Eluxadoline, a muopioid receptor agonist and delta-opioid receptor antagonist, has shown efficacy in relieving IBS symptoms. However, its applications have been limited due to low water solubility, which causes a low dissolution rate and oral bioavailability. In this study, we aimed to enhance the therapeutic efficacy of eluxadoline by formulating polymeric nanoparticles of eluxadoline. Polymeric nanoparticles of chitosan loaded with eluxadoline were prepared using the ionic gelation method. The formulation parameters including concentration of chitosan, concentration of tripolyphosphate and volume of tripolyphosphate were systematically optimized using a Box-Behnken design to achieve nanoparticles (CNP1-CNP17) with optimal physicochemical properties. The optimized formulation based on particle size of (300.4 nm) with a low PDI value (0.305), zeta potential (41.2mV) and % entrapment efficacy (76.89%). The efficiency of the drug release from optimised formulation was studied in vitro by using a dialysis bag diffusion technique in buffer condition pH 6.8 intestinal condition and showed a sustained release behaviour with maximum drug release 80.23%. Thus, the findings demonstrated that the formulated chitosan-based polymeric nanoparticles present a promising strategy for efficiently delivering eluxadoline via oral administration, offering a potential solution for treating irritable bowel syndrome.