Opioid Receptor Research Articles

Kratom: a primer for pain physicians.

Kratom is used commonly in the United States, usually to mitigate pain, opioid withdrawal, or fatigue. A comprehensive discussion on kratom, tailored to pain management physicians, is needed, given its associated risks and potential interactions. Kratom and its main metabolites, mitragynine and 7-OH-mitragynine, bind to a variety of receptors including mu opioid receptors. Still, kratom cannot be described as a classic opioid. Kratom has been utilized without FDA approval as an alternative to traditional medications for opioid use disorder and opioid withdrawal. Lower doses of kratom typically cause opioid-like effects while higher doses can have sedating effects. Tolerance, dependence and withdrawal still occur, although kratom withdrawal appears to be more moderate than opioid withdrawal. Contamination with heavy metals and biological toxins is concerning and there is potential for serious complications, including seizures and death. The use of kratom as an opioid-sparing alternative as a part of a multimodal pain regimen is not without significant risks. It is of utmost importance for pain physicians to be aware of the risks and adverse effects associated with kratom use.

Aticaprant, a kappa opioid receptor antagonist, and the recovered 'interest and pleasure' in the concept of major depressive disorder.

Lack of positive mood and anhedonia probably are the most specific depressive symptoms. Anhedonia is a multifaceted concept: the clinical language describes anticipatory/consummatory anhedonia and sensory/social anhedonia while the cognitive neuroscience language describes readiness for reward, energy expenditure to attain reward, updating reward presence and value. Mounting evidence supports the potential of kappa-opioid receptor (KOR) antagonists as novel pharmacotherapies for major depressive disorder : aticaprant is a potent, selective, short-acting KOR antagonist. The fast-fail approach evaluated the impact of aticaprant on the brain circuitry hypothesized to mediate anhedonia and significantly increased fMRI activation in the ventral striatal activation during reward anticipation as compared to placebo; the aticaprant induced changes in the self-reported psychological measures of anhedonia were rather inconsistent. The recently reported results of a phase 2a randomized, double-blind, placebo-controlled trial investigating the efficacy and safety of aticaprant, co-administered to an oral SSRI/SNRI antidepressant in depressed patients who had an inadequate response to 1 or 2 antidepressants. The improvement from baseline favoured the co-administration of aticaprant over the co-administration of placebo at all time points (during 6 weeks), and this was confirmed by higher response rates with aticaprant. A mid-split of patients with higher or lower than median anhedonia also showed that the patients with higher baseline anhedonia had the largest decrease on the MADRS. Tolerability and safety were reassuring. These promising results of the co-administration of aticaprant to an SSRI/SNRI in depressed patients with prominent anhedonia support he further investigation of aticaprant in larger trials.

Exposure of Zebrafish Embryos to Morphine and Cocaine Induces Changes in the Levels of Dopamine and of Proteins Related to the Reward Pathway

Morphine, a drug of abuse used to treat moderate-to-severe pain, elicits its actions by binding to the opioid receptors. Cocaine is an example of a recreational drug that inhibits dopamine reuptake. The molecular effects of morphine and cocaine have been described in different specific brain regions. However, the systemic outcome of these drugs on the whole organism has not been fully addressed. The aim of this study is to analyse the global effects of morphine (10 μM) and cocaine (15 μM) in the expression of proteins related to the reward pathway. Zebrafish embryos were exposed to these drugs from 5 hpf (hours post-fertilisation) to 6 dpf (days post-fertilisation). Dopamine levels were determined by ELISA, and the expression of Fos proteins, Creb, its activated form p-Creb and tyrosine hydroxylase (Th) were examined by Western blot. Both drugs decreased Th levels at 72 hpf and 6 dpf and modified the expression of Fos family members, pCreb and Creb in a time-dependent manner. Morphine and cocaine exposure differentially modified dopamine levels in 72 hpf and 6 dpf zebrafish embryos. Our results indicate that drugs of abuse modify the expression of several proteins and molecules related to the activation of the reward pathway.

Putative Pharmacological Depression and Anxiety-Related Targets of Calcitriol Explored by Network Pharmacology and Molecular Docking.

Depression and anxiety disorders, prevalent neuropsychiatric conditions that frequently coexist, limit psychosocial functioning and, consequently, the individual's quality of life. Since the pharmacological treatment of these disorders has several limitations, the search for effective and secure antidepressant and anxiolytic compounds is welcome. Vitamin D has been shown to exhibit neuroprotective, antidepressant, and anxiolytic properties. Therefore, this study aimed to explore new molecular targets of calcitriol, the active form of vitamin D, through integrated bioinformatic analysis. Calcitriol targets were predicted in SwissTargetPrediction server (2019 version). The disease targets were collected by the GeneCards database searching the keywords "depression" and "anxiety". Gene ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) were used to analyze the intersections of targets. Network analyses were carried out using GeneMania server (2023 version) and Cytoscape (V. 3.9.1.) software. Molecular docking predicted the main targets of the network and Ligplot predicted the main intermolecular interactions. Our study showed that calcitriol may interact with multiple targets. The main targets found are the vitamin D receptor (VDR), histamine H3 receptor (H3R), endocannabinoid receptors 1 and 2 (CB1 and CB2), nuclear receptor NR1H3, patched-1 (PTCH1) protein, opioid receptor NOP, and phosphodiesterase enzymes PDE3A and PDE5A. Considering the role of these targets in the pathophysiology of depression and anxiety, our findings suggest novel putative mechanisms of action of vitamin D as well as new promising molecular targets whose role in these disorders deserves further investigation.

P-321 Uterine fibroids secrete vasodilatory factors that induce their response via the opioid pathway

Abstract Study question Do uterine fibroids produce vasoactive factors that could affect vasculature and induce fibroid associated symptoms? Summary answer Ex vivo secretions from uterine fibroids induce a vasodilatory response in rat mesenteric arteries that is mediated via the opioid receptor pathway. What is known already Uterine fibroids (leiomyoma) are a common but clinically neglected gynaecological condition, where benign smooth muscle tumours arise from the myometrium and cause heavy menstrual bleeding (HMB), pain and infertility. Fibroids affect up to one in two women of reproductive age and are the main reason for failure of both medical and surgical treatments in women with HMB. Fibroids are proposed to affect the systemic vasculature system, with angiogenic growth factors and abnormal vasculature implicated in fibroid pathophysiology. However, the precise mechanism of fibroid induced HMB has yet to be fully elucidated. Study design, size, duration Fibroid and myometrium biopsies were prospectively collected from 13 patients undergoing MyoSure, myomectomy or hysterectomy for the treatment of HMB associated with fibroids at Liverpool Women’s Hospital, a tertiary referral centre. The collection and use of human tissue was ethically approved, and all participants gave informed written consent. Tissue biopsies were incubated in a basal medium for 24 hours. Conditioned medium was collected and used for wire myography assays to examine vascular reactivity. Participants/materials, setting, methods Second order mesenteric arteries from female Wistar rats were mounted on a wire myograph system and toned with uridine triphosphate (UTP) before being exposed to control (non-conditioned), normal myometrium (n = 4) or fibroid (n = 9) conditioned medium. Vascular activity was measured relative to UTP induced vasoconstriction. To determine the mediatory factors of observed vasoreactivity, inhibitors of well characterised pathways were systematically tested in the presence of conditioned medium. Main results and the role of chance Fibroid conditioned medium caused a marked dilation of UTP induced vasoconstriction in rat mesenteric arteries, which was significantly greater than that induced by non-conditioned, or control myometrium conditioned medium. Blockage of ATP-sensitive potassium (KATP) channels with PNU37883A completely inhibited fibroid induced vasodilation. However, blockage of other potassium channels did not inhibit dilation, suggesting that a KATP-mediated PKA-dependent pathway is being stimulated. To test the potential involvement of endothelial-derived nitric oxide synthase in vasodilation, vessels were treated with the inhibitor L-NAME, which partially blocked fibroid induced vasodilation. The specificity of nitric oxide synthase inhibition was confirmed by treating vessels with acetylcholine or carbachol, which induced vasodilation via activation of nitric oxide synthase. In the presence of L-NAME, the vasodilatory effects of acetylcholine and carbachol were blocked, thus confirming inhibitor specificity. An adenosine receptor inhibitor, theophylline, had no effect on fibroid induced vasodilation, thus ruling out the adenosine pathway. Blockage of bradykinin and adrenergic receptors also failed to prevent fibroid induced dilation in mesenteric arteries. However, blocking opioid receptors with naloxone completely inhibited vasodilation in the presence of fibroid conditioned medium. These findings suggest that fibroid induced vasodilation is mediated via endothelial nitric oxide synthase and an unknown opioid compound. Limitations, reasons for caution This study was performed using excised tissue in an ex vivo environment, which may not fully simulate the fibroid secretome in vivo. Although rat mesenteric arteries are a well-established model, human uterine arteries may be more appropriate to study fibroid induced vasoreactivity. Wider implications of the findings Fibroids are responsible for up to half of all hysterectomies and healthcare costs run into the billions globally. This study demonstrates that fibroid secreted factors can impact vasoreactivity, which has important connotations for disease pathophysiology regarding HMB. Targeting vasoactive compounds produced by fibroids may be a future novel treatment option. Trial registration number NA

Discovery of N′-benzyl-3-chloro-N-((1S,3R,4R)-3-((dimethylamino)methyl)-4-hydroxy-4-(3-methoxyphenyl)cyclohexyl)benzenesulfonamide as a novel selective KOR ligand

The effective management of moderate to severe pain often relies on the use of analgesic agents. However, the widespread utility of these medications is hindered by the occurrence of several undesirable side effects. In light of this challenge, there is growing interest in the development of κ opioid receptor (KOR) agonists, which have shown promise in mitigating these adverse effects. In this study, leveraging the structural scaffold of compound D (our previous study), we embarked on the design, synthesis, and evaluation of a series of N′-benzyl-3-chloro-N- ((1S,3R,4R)-3-((dimethylamino)methyl)-4-hydroxy-4-(3-methoxyphenyl)cyclohexyl)benzenesulfonamide derivatives. These compounds were subjected to comprehensive in vitro and in vivo test. Through systematic structure-activity relationship (SAR) exploration, we successfully identified compound 23p (Ki(KOR):1.9 nM) as a highly selective KOR ligand of new chemotype. 23p showed high clearance in vitro PK test, and abdominal contraction test showed potent antinociceptive effect. 23p and its O-demethyl metabolite 25 were both found in the plasma of mouse, 25 also showed potent affinity toward KOR (Ki(KOR): 3.1 nM), both they contribute to the analgesic effect. Moreover, 23p exhibited potent antinociceptive activity in abdominal constriction test, which was effectively abolished by pre-treatment of nor-BNI, a selective KOR antagonist.

A µ-opioid receptor modulator that works cooperatively with naloxone.

The µ-opioid receptor (µOR) is a well-established target for analgesia1, yet conventional opioid receptor agonists cause serious adverse effects, notably addiction and respiratory depression. These factors have contributed to the current opioid overdose epidemic driven by fentanyl2, a highly potent synthetic opioid. µOR negative allosteric modulators (NAMs) may serve as useful tools in preventing opioid overdose deaths, but promising chemical scaffolds remain elusive. Here we screened a large DNA-encoded chemical library against inactive µOR, counter-screening with active, G-protein and agonist-bound receptor to 'steer' hits towards conformationally selective modulators. We discovered a NAM compound with high and selective enrichment to inactive µOR that enhances the affinity of the key opioid overdose reversal molecule, naloxone. The NAM works cooperatively with naloxone to potently block opioid agonist signalling. Using cryogenic electron microscopy, we demonstrate that the NAM accomplishes this effect by binding a site on the extracellular vestibule in direct contact with naloxone while stabilizing a distinct inactive conformation of the extracellular portions of the second and seventh transmembrane helices. The NAM alters orthosteric ligand kinetics in therapeutically desirable ways and works cooperatively with low doses of naloxone to effectively inhibit various morphine-induced and fentanyl-induced behavioural effects in vivo while minimizing withdrawal behaviours. Our results provide detailed structural insights into the mechanism of negative allosteric modulation of the µOR and demonstrate how this can be exploited in vivo.

Epigenetic and sex differences in opioid use disorder in chronic pain: A real-world study linked with OPRM1 DNA methylation.

Opioid use disorder (OUD) is a multifaceted condition influenced by sex, genetic and environmental factors that could be linked with epigenetic changes. Understanding how these factors interact is crucial to understand and address the development and progression of this disorder. Our aim was to elucidate different potential epigenetic and genetic mechanisms between women and men that correlate with OUD under real-world pain unit conditions. Associations between analgesic response and the DNA methylation level of the opioid mu receptor (OPRM1) gene (CpG sites 1-5 selected in the promoter region) were evaluated in 345 long opioid-treated chronic non cancer pain: cases with OUD (n = 67) and controls (without OUD, n = 278). Cases showed younger ages, low employment status and quality of life, but higher morphine equivalent daily dose and psychotropic use, compared to the controls. The patients with OUD showed a significant decrease in OPRM1 DNA methylation, which correlated with clinical outcomes like pain relief, depression and different adverse events. Significant differences were found at the five CpG sites studied for men, and exclusively in women for CpG site 3, in relation to OUD diagnosis. These findings support the importance of epigenetics and sex as biological variables to be considered toward efficient OUD understanding and therapy development.

Molecular docking, molecular dynamics simulation, preparation, and characterization of naltrexone-phospholipid complex: A novel cargo with improved loading into multivesicular liposomes

Naltrexone hydrochloride (NTX), a water-soluble opioid receptor antagonist, is prescribed widely for opioid and alcohol dependence and pain reduction. However, the significant limitations of NTX are low lipophilicity and extensive first-pass metabolism. This study aimed to design and prepare a novel phospholipid complex of NTX and load it into multivesicular liposomes (MVLs). In silico studies, including molecular docking and molecular dynamics (MD) simulation, were performed to determine the interactions between NTX and phospholipid and evaluate their best molar ratio to prepare the complex, respectively. The NTX phospholipid complex was prepared by solvent evaporation technique and characterized by PXRD, SEM, FTIR, 1HNMR, solubility study, and n-octanol/water partition coefficient analyses. NTX-SPC complex-loaded MVLs (NTX-SPC-MVLs) were prepared by the double-emulsion method and characterized by encapsulation efficiency (EE)%, size, PXRD, FTIR, SEM, and release pattern. MD simulation reported the 1:1.5 M ratio of NTX to phospholipid as the best molar ratio. Complexation led to reduced water solubility and enhanced n-octanol/water partition coefficient. Loading of NTX-SPC complex into MVLs enhanced EE and extended the release duration in comparison to NTX MVLs. Thus, the NTX-SPC complex may be an appropriate system to enhance the physicochemical features of NTX and improve the EE in vesicular drug delivery systems like MVLs.

A single exposure to the predator odor 2,4,5-trimethylthiazoline causes long-lasting affective behavioral changes in female mice: Modulation by kappa opioid receptor signaling

The volatile compound 2,4,5-trimethylthiazoline (TMT, a synthetic predator scent) triggers fear, anxiety, and defensive responses in rodents that can outlast the encounter. The receptor systems underlying the development and persistence of TMT-induced behavioral changes remain poorly characterized, especially in females. Kappa opioid receptors regulate threat generalization and fear conditioning and alter basal anxiety, but their role in unconditioned fear responses in females has not been examined. Here, we investigated the effects of the long-lasting kappa opioid receptor antagonist, nor-binalthorphinmine dihydrochloride (nor-BNI; 10mg/kg), on TMT-induced freezing and conditioned place aversion in female mice. We also measured anxiety-like behavior in the elevated plus maze three days after TMT and freezing behavior when returned to the TMT-paired context ten days after the single exposure. We found that 35μl of 10% TMT elicited a robust freezing response during a five-minute exposure in female mice. TMT evoked persistent fear as measured by conditioned place aversion, reduced entries into the open arm of the elevated plus maze, and increased general freezing behavior long after TMT exposure. In line with the known role of kappa-opioid receptors in threat generalization, we found that kappa-opioid receptor antagonism increased basal freezing but reduced freezing during TMT presentation. Together, these findings indicate that a single exposure to TMT causes long-lasting changes in fear-related behavioral responses in female mice and highlights the modulatory role of kappa-opioid receptor signaling on fear-related behavioral patterns in females.

Underlying mechanisms for psychotropic effects of delta opioid receptor agonists

Underlying mechanisms for psychotropic effects of delta opioid receptor agonists

Assessment of antinociceptive property of Cynara scolymus L. and possible mechanism of action in the formalin and writhing models of nociception in mice.

Cynara scolymus has bioactive constituents and has been used for therapeutic actions. The present study was undertaken to investigate the mechanisms underlying pain-relieving effects of the hydroethanolic extract of C. scolymus (HECS). The antinociceptive activity of HECS was assessed through formalin and acetic acid-induced writhing tests at doses of 50, 100 and 200 mg/kg intraperitoneally. Additionally, naloxone (non-selective opioid receptors antagonist, 2 mg/kg), atropine (non-selective muscarinic receptors antagonist, 1 mg/kg), chlorpheniramine (histamine HH1-receptor antagonist, 20 mg/kg), cimetidine (histamine H2-receptor antagonist, 12.5 mg/kg), flumazenil (GABAA/BDZ receptor antagonist, 5 mg/kg) and cyproheptadine (serotonin receptor antagonist, 4 mg/kg) were used to determine the systis implicated in HECS-induced analgesia. Impact of HECS on locomotor activity was executed by open-field test. Determination of total phenolic content (TPC) and total flavonoid content (TFC) was done. Evaluation of antioxidant activity was conducted iploying 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging assay. HECS (50, 100 and 200 mg/kg) significantly indicated dose dependent antinociceptive activity against pain-related behavior induced by formalin and acetic acid (P < 0.001). Pretreatment with naloxone, atropine and flumazenil significantly reversed HECS-induced analgesia. Antinociceptive effect of HECS riained unaffected by chlorpheniramine, cimetidine and cyproheptadine. Locomotor activity was not affected by HECS. TPC and TFC of HECS were 59.49 ± 5.57 mgGAE/g dry extract and 93.39 ± 17.16 mgRE/g dry extract, respectively. DPPH free radical scavenging activity (IC50) of HECS was 161.32 ± 0.03 μg/mL. HECS possesses antinociceptive activity which is mediated via opioidergic, cholinergic and GABAergic pathways.

Differential roles of serotonin receptor subtypes in regulation of neurotrophin receptor expression and intestinal hypernociception.

Aberrant serotonin (5-hydroxytryptamine, 5-HT) metabolism and neurite outgrowth were associated with abdominal pain in irritable bowel syndrome (IBS). We previously demonstrated that 5-HT receptor subtype 7 (5-HT₇) was involved in visceral hypersensitivity of IBS-like mouse models. The aim was to compare the analgesic effects of a novel 5-HT₇ antagonist to reference standards in mouse models and investigate the mechanisms of 5-HT₇-dependent neuroplasticity. Two mouse models, including Giardia post-infection combined with water avoidance stress (GW) and post-resolution of trinitrobenzene sulfonic acid-induced colitis (PT) were used. Mice were orally administered CYY1005 (CYY, a novel 5-HT₇ antagonist), alosetron (ALN, a 5-HT₃ antagonist), and loperamide (LPM, an opioid receptor agonist) prior to measurement of visceromotor responses (VMR). Levels of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin receptors (NTRs) were assessed. Peroral CYY was more potent than ALN or LPM in reducing VMR values in GW and PT mice. Increased mucosal 5-HT₇-expressing nerve fibers were associated with elevated Gap43 levels in the mouse colon. We observed higher colonic Ntrk2 and Ngfr expression in GW mice, and increased Bdnf expression in PT mice compared with control mice. Human SH-SY5Y cells stimulated with mouse colonic supernatant or exogenous serotonin exhibited longer nerve fibers, which CYY dose-dependently inhibited. Serotonin increased Ntrk1 and Ngfr expression via 5-HT₇ but not 5-HT₃ or 5-HT₄, while Ntrk2 upregulation was dependent on all three 5-HT receptor subtypes. Stronger analgesic effects by peroral CYY were observed compared with reference standards in two IBS-like mouse models. The 5-HT₇-dependent NTR upregulation and neurite elongation may be involved in intestinal hypernociception.

Exploring the antinociceptive potential of homoeriodictyol in nociception models

Context: Homoeriodictyol is a flavonoid with known antioxidant, anti-inflammatory, and anti-tumor properties found in various plants. However, its potential analgesic effects have not been explored. Aims: To investigate the pain-relieving properties of homoeriodictyol using different mouse models of nociception. Methods: Various doses of homoeriodictyol (50, 100, 150, and 200 µg/kg) were administered to mice and evaluated using the acetic acid-induced writhing test, the hot plate test, and the formalin-induced paw licking assay. These effects were compared with those of mice treated with acetylsalicylic acid or morphine, both with and without naloxone, an opioid receptor antagonist. Additionally, capsaicin- and glutamate-induced paw-licking tests were conducted to assess the involvement of the vanilloid and glutamatergic systems, respectively. Results: Homoeriodictyol demonstrated a significant and dose-dependent reduction in nociceptive behavior in the acetic acid-induced writhing test, achieving a 52.4% inhibition at a dose of 200 µg/kg. It also substantially increased the latency period in response to the hot plate test (65.8% at 200 µg/kg) and significantly suppressed both the neurogenic and inflammatory phases in the formalin-induced paw-licking test. Notably, the effects of homoeriodictyol in the hot plate test and formalin-induced paw-licking test were significantly reversed by naloxone. Furthermore, homoeriodictyol effectively reduced neurogenic nociception induced by intraplantar injections of glutamate and capsaicin (57.8% and 76.9%, respectively, at a dose of 200 µg/kg). Conclusions: This study concludes that homoeriodictyol exhibits antinociceptive activity in mice, acting through both central and peripheral pathways.

Recent advances in treatment of prurigo nodularis

Abstract Prurigo nodularis is a chronic skin condition which has significant negative impacts on the psychosocial function and quality of life of affected patients. It is a heterogeneous disease with complex underlying pathogenic mechanisms, and the clinical efficacy of traditional treatment options is often limited. Recently, great advances have been made in the pathogenesis of prurigo nodularis, which have enabled the development of novel targeted therapies for this disease. Various clinical trials have investigated the therapeutic efficacy of biologics which target the Th2 pathway. Dupilumab, a monoclonal antibody targeting interleukin 4 (IL-4) receptor α, has shown clinical efficacy and obtained United States Food and Drug Administration approval for prurigo nodularis. In addition, nemolizumab (IL-31 receptor A antagonist) and vixarelimab (oncostatin M receptor β antagonist) have shown therapeutic efficacy in clinical trials for prurigo nodularis. Small-molecule inhibitors with clinical promise which are currently under investigation include nalbuphine (opioid receptor modulator), Janus kinase inhibitors, and aprepitant and serlopitant (neurokinin-1 receptor antagonists). The recent development of new biologics and small-molecule inhibitors targeting various immunological and neurological signaling pathways have provided great hope that we are entering a new era of targeted therapies for this challenging clinical condition. In addition, recent advances in RNA sequencing technology may enable the identification of unique signaling pathways and the development of novel treatments for this disease in the future. In this review article, we summarize the current knowledge of the pathogenesis of prurigo nodularis, and discuss recent advances in treatment for this challenging clinical condition.

A Bicyclic Analog of the Linear Peptide Arodyn Is a Potent and Selective Kappa Opioid Receptor Antagonist.

Kappa opioid receptor (KOR) antagonists have potential therapeutic applications in the treatment of stress-induced relapse to substance abuse and mood disorders. The dynorphin A analog arodyn (Ac[Phe1,2,3,Arg4,D-Ala8]dynorphin A-(1-11)-NH2) exhibits potent and selective kappa opioid receptor antagonism. Multiple cyclizations in longer peptides, such as dynorphin and its analogs, can extend the conformational constraint to additional regions of the peptide beyond what is typically constrained by a single cyclization. Here, we report the design, synthesis, and pharmacological evaluation of a bicyclic arodyn analog with two constraints in the opioid peptide sequence. The peptide, designed based on structure-activity relationships of monocyclic arodyn analogs, was synthesized by solid-phase peptide synthesis and cyclized by sequential ring-closing metathesis (RCM) in the C- and N-terminal sequences. Molecular modeling studies suggest similar interactions of key aromatic and basic residues in the bicyclic peptide with KOR as found in the cryoEM structure of KOR-bound dynorphin, despite substantial differences in the backbone conformations of the two peptides. The bicyclic peptide's affinities at KOR and mu opioid receptors (MOR) were determined in radioligand binding assays, and its KOR antagonism was determined in the [35S]GTPγS assay in KOR-expressing cells. The bicyclic analog retains KOR affinity and selectivity (Ki = 26 nM, 97-fold selectivity over MOR) similar to arodyn and exhibits potent KOR antagonism in the dynorphin-stimulated [35S]GTPγS assay. This bicyclic peptide represents a promising advance in preparing cyclic opioid peptide ligands and opens avenues for the rational design of additional bicyclic opioid peptide analogs.

Identification and biophysical characterization of a novel domain-swapped camelid antibody specific for fentanyl

Opioid use disorders (OUD) and overdoses are ever-evolving public health threats that continue to grow in incidence and prevalence in the United States and abroad. Current treatments consist of opioid receptor agonists and antagonists, which are safe and effective but still suffer from some limitations. Murine and humanized monoclonal antibodies (mAb) have emerged as an alternative and complementary strategy to reverse and prevent opioid-induced respiratory depression. To explore antibody applications beyond traditional heavy-light chain mAbs, we identified and biophysically characterized a novel single-domain antibody specific for fentanyl from a camelid variable-heavy-heavy (VHH) domain phage display library. Structural data suggested that VHH binding to fentanyl was facilitated by a unique domain-swapped dimerization mechanism, which accompanied a rearrangement of complementarity-determining region loops leading to the formation of a fentanyl-binding pocket. Structure-guided mutagenesis further identified an amino acid substitution that improved the affinity and relaxed the requirement for dimerization of the VHH in fentanyl binding. Our studies demonstrate VHH engagement of an opioid and inform on how to further engineer a VHH for enhanced stability and efficacy, laying the groundwork for exploring the invivo applications of VHH-based biologics against OUD and overdose.

Exploratory study of associations between monetary reward anticipation brain responses and mu-opioid signalling in alcohol dependence, gambling disorder and healthy controls

Alcohol dependence (AD) and gambling disorder (GD) are common addiction disorders with significant physical and mental health consequences. AD and GD are associated with dysregulated responses to reward which could be due to a common mechanism of dysregulated endogenous opioid signalling. We explored associations between reward anticipation responses, using the Monetary Incentive Delay (MID) functional magnetic resonance imaging (fMRI) task, and mu-opioid receptor (MOR) availability and endogenous opioid release capacity using [11C]carfentanil positron emission tomography (PET), in 13 AD, 15 GD and 14 heathy control (HC) participants. We also examined differences in MID task reward anticipation responses between AD, GD and HC participants. These were secondary exploratory analysis of data collected to examine differences in MOR PET in addiction. We did not find significant differences in MID win > neutral anticipation BOLD responses compared between participant groups in a priori ROIs (ventral striatum, putamen, caudate) or whole brain analyses. We found no significant correlations between MID win > neutral anticipation BOLD responses and [11C]carfentanil PET measures, except for limited negative correlations between putamen MOR availability and MID win > neutral anticipation BOLD response in AD participants. Previous research has suggested a limited role of endogenous opioid signalling on MID task reward anticipation responses in AD and HCs as these responses are not modulated by opioid receptor blockade and this may explain our lack of significant correlations in HC and AD or GD participants. Our results, particularly the lack of differences in MID win > neutral anticipation BOLD responses across participants groups, may be limited due to only including AD or GD participants who are abstinent or in active treatment.

The effects of morphine administration on the central nervous system (CNS): advantages and disadvantages

Morphine, a potent opioid analgesic, plays a critical role in pain management but elicits complex effects on the central nervous system (CNS), demonstrating both beneficial and detrimental outcomes. This paper reviews preclinical studies to examine morphine's interactions with the CNS, notably via binding to opioid receptors, leading to analgesia as well as a series of adverse effects, including addiction, tolerance, and neurological impairments. Acute exposure to morphine alters neurotransmitter activity, gene expression, and neuronal firing rates. In contrast, chronic use results in significant neuronal damage, altered memory functions, increased pain sensitivity, and neuroinflammation, highlighting the drug's impact on neurogenesis and neural cell viability. Additionally, morphine's protective properties against neurotoxic insults are discussed, alongside its potential to disrupt cellular and molecular pathways, culminating in neurotoxicity and cognitive deficits. Given the dual nature of morphine's impact on the CNS - protective vs. harmful, depending on specific conditions such as dosage, disease type, and administration frequency - this paper underscores the necessity for further research to untangle this complex interplay to leverage morphine's pain management benefits while minimizing its risks. A thorough evaluation of morphine administration practices can help reconcile these conflicting results.

Dexketoprofen Trometamol and Tramadol Hydrochloride Fixed-Dose Combination in Moderate to Severe Acute Low Back Pain: A Phase IV, Randomized, Parallel Group, Placebo, Active-Controlled Study (DANTE).

Dexketoprofen/tramadol 25/75 mg (DKP/TRAM) is a fixed-dose combination of a cyclooxygenase inhibitor and opioid receptor agonist. To better understand the efficacy and safety of DKP/TRAM in the treatment of moderate to severe acute lower back pain (LBP) with or without radiculopathy, we carried out a large explorative phase IV international, multicenter, prospective, randomized, double-blind, parallel group, placebo-controlled study (DANTE). A total of 538 patients with or without a history of LBP and experiencing acute LPB of moderate to severe intensity [Numerical Rating Scale-Pain Intensity (NRS-PI) score > 5] were randomized 4:4:1:1 to DKP/TRAM 25/75 mg every 8 h (n = 211), tramadol (TRAM) 100 mg (n = 207), placebo-matched DKP/TRAM (n = 59), or placebo-matched TRAM (n = 61). The proportion of patients achieving the primary endpoint, defined as the time to first achieve NRS-PI score < 4 or pain intensity reduction ≥ 30% from drug intake up to 8 h after the first dose, was higher in the DKP/TRAM arm than in the placebo group, but the difference was not statistically significant (46.1% vs. 42.6%, respectively; hazard ratio 1.11; 95% confidence interval 0.775, 1.595; p = 0.566). DKP/TRAM achieved superiority over TRAM in total pain relief at 4, 6, and 8 h (p < 0.05). Conversely, in relation to the secondary endpoints, a significantly greater reduction in NRS-PI score was seen with DKP/TRAM versus placebo starting from 1 h, and this reduction remained numerically lower throughout 8 h. Summed pain intensity difference values were also significantly lower at 4, 6, and 8 h with DKP/TRAM compared to TRAM (p < 0.05). Overall, DKP/TRAM was well tolerated. Although the primary endpoint was not met, secondary efficacy analyses suggest the superiority of DKP/TRAM over placebo and TRAM alone in terms of total pain relief. DKP/TRAM can be considered to be an effective and safe option for the treatment of moderate to severe acute LBP. EudraCT number: 2019-003656-37; ClinicalTrials.gov Identifier: NCT05170841.