Regulation of cannabinoid and opioid receptor levels by endogenous and pharmacological chaperones.

Cannabinoid and opioid receptor activities can be modulated by a variety of posttranslational mechanisms including the formation of interacting complexes. This study examines the involvement of endogenous and exogenous chaperones in modulating the abundance and activity of cannabinoid CB1 receptor (CB1R), delta opioid receptor (DOR), and CB1R-DOR interacting complexes. Focussing on endogenous protein chaperones namely receptor transporter proteins (RTPs), we examined relative mRNA expression in the mouse spinal cord and found RTP4 to be expressed at higher levels compared to other RTPs. Next, we assessed the effect of RTP4 on receptor abundance by manipulating RTP4 expression in cell lines. Overexpression of RTP4 causes an increase and knock-down causes a decrease in the levels of CB1R, DOR, and CB1R-DOR interacting complexes; this is accompanied by parallel changes in signaling. The ability of small molecule lipophilic ligands to function as exogenous chaperones was examined using receptor-selective antagonists. Long term treatment leads to increases in receptor abundance and activity with no changes in mRNA supporting a role as pharmacological chaperones. Finally, the effect of cannabidiol (CBD), a small molecule ligand and a major active component of Cannabis, on receptor abundance and activity in mice was examined. We find that CBD administration leads to increases in receptor abundance and activity in mouse spinal cord. Together, these results highlight a role for chaperones (proteins and small molecules) in modulating levels and activity of CB1R, DOR, and their interacting complexes potentially through mechanisms including receptor maturation and trafficking. Significance Statement This study highlights a role for chaperones (endogenous and small membrane-permeable molecules) in modulating levels of CB1R, DOR, and their interacting complexes. These chaperones could be developed as therapeutics for pathologies involving these receptors.

Opiorphin: an endogenous human peptide with intriguing application in diverse range of pathologies.

Mammalian zinc ectopeptidases have significant functions in deactivating neurological and hormonal peptide signals on the cell surface. The identification of Opiorphin, a physiological inhibitor of zinc ectopeptidases that inactivate enkephalin, has revealed its strong analgesic effects in both chemical and mechanical pain models. Opiorphin achieves this by increasing the transmission of endogenous opioids, which are dependent on the body's own opioid system. The function of opiorphin is closely linked to the rat sialorphin peptide, which inhibits pain perception by enhancing the activity of naturally occurring enkephalinergic pathways that depend on µ- and δ-opioid receptors. Opiorphin is highly intriguing in terms of its physiological implications within the endogenous opioidergic pathways, particularly in its ability to regulate mood-related states and pain perception. Opiorphin can induce antidepressant-like effects by influencing the levels of naturally occurring enkephalin, which are released in response to specific physical and/or psychological stimuli. This effect is achieved through the modulation of delta-opioid receptor-dependent pathways. Furthermore, research has demonstrated that opiorphin's impact on the cardiovascular system is facilitated by the renin-angiotensin system (RAS), sympathetic ganglia, and adrenal medulla, rather than the opioid system. Hence, opiorphin shows great potential as a solitary candidate for the treatment of several illnesses such as neurodegeneration, pain, and mood disorders.

A dorsal hippocampus-prodynorphinergic dorsolateral septum-to-lateral hypothalamus circuit mediates contextual gating of feeding.

Adaptive regulation of feeding depends on linkage of internal states and food outcomes with contextual cues. Human brain imaging has identified dysregulation of a hippocampal-lateral hypothalamic area (LHA) network in binge eating, but mechanistic instantiation of underlying cell-types and circuitry is lacking. Here, we identify an evolutionary conserved and discrete Prodynorphin (Pdyn)-expressing subpopulation of Somatostatin (Sst)-expressing inhibitory neurons in the dorsolateral septum (DLS) that receives primarily dorsal, but not ventral, hippocampal inputs. DLS(Pdyn) neurons inhibit LHA GABAergic neurons and confer context- and internal state-dependent calibration of feeding. Viral deletion of Pdyn in the DLS mimicked effects seen with optogenetic silencing of DLS Pdyn INs, suggesting a potential role for DYNORPHIN-KAPPA OPIOID RECEPTOR signaling in contextual regulation of food-seeking. Together, our findings illustrate how the dorsal hippocampus has evolved to recruit an ancient LHA feeding circuit module through Pdyn DLS inhibitory neurons to link contextual information with regulation of food consumption.

Ketamine and major ketamine metabolites function as allosteric modulators of opioid receptors.

Ketamine is a glutamate receptor antagonist that was developed over 50 years ago as an anesthetic agent. At subanesthetic doses, ketamine and some metabolites are analgesics and fast-acting antidepressants, presumably through targets other than glutamate receptors. We tested ketamine and its metabolites for activity as allosteric modulators of opioid receptors expressed in recombinant receptors in heterologous systems and native receptors in rodent brain; signaling was examined by measuring GTP binding, b-arrestin recruitment, MAPK activation and neurotransmitter release. While micromolar concentrations of ketamine alone had weak agonist activity at mu opioid receptors, the combination of submicromolar concentrations of ketamine with endogenous opioid peptides produced robust synergistic responses with statistically significant increases in efficacies. All three opioid receptors (mu, delta, and kappa) showed synergism with submicromolar concentrations of ketamine and either Met-enkephalin, Leu-enkephalin, and/or dynorphin A17, albeit the extent of synergy was variable between receptors and peptides. S-ketamine exhibited higher modulatory effect compared to R-ketamine or racemic ketamine with nearly ~100% increase in efficacy. Importantly, the ketamine metabolite 6-hydroxynorketamine showed robust allosteric modulatory activity at mu opioid receptors; this metabolite is known to have analgesic and antidepressant activity but does not bind to glutamate receptors. Ketamine enhanced potency and efficacy of Met-enkephalin signaling both in mouse midbrain membranes and in rat ventral tegmental area neurons, as determined by electrophysiology recordings in brain slices. Taken together, these findings support the hypothesis that some of the therapeutic effects of ketamine and its metabolites are mediated by directly engaging the endogenous opioid system. Significance Statement We found that ketamine and its major biologically-active metabolites function as potent allosteric modulators of mu, delta, and kappa opioid receptors, with submicromolar concentrations of these compounds synergizing with endogenous opioid peptides such as enkephalin and dynorphin. This allosteric activity may contribute to ketamine's therapeutic effectiveness for treating acute and chronic pain and as a fast-acting antidepressant drug.

Single-neuron projectome-guided analysis reveals the neural circuit mechanism underlying endogenous opioid antinociception.

Endogenous opioid antinociception is a self-regulatory mechanism that reduces chronic pain, but its underlying circuit mechanism remains largely unknown. Here, we showed that endogenous opioid antinociception required the activation of mu-opioid receptors (MORs) in GABAergic neurons of the central amygdala nucleus (CEA) in a persistent-hyperalgesia mouse model. Pharmacogenetic suppression of these CEAMOR neurons, which mimics the effect of MOR activation, alleviated the persistent hyperalgesia. Furthermore, single-neuron projection analysis revealed multiple projectome-based subtypes of CEAMOR neurons, each innervating distinct target brain regions. We found that the suppression of axon branches projecting to the parabrachial nucleus (PB) of one subtype of CEAMOR neurons alleviated persistent hyperalgesia, indicating a subtype- and axonal-branch-specific mechanism of action. Further electrophysiological analysis revealed that suppression of a distinct CEA-PB disinhibitory circuit controlled endogenous opioid antinociception. Thus, this study identified the central neural circuit that underlies endogenous opioid antinociception, providing new insight into the endogenous pain modulatory mechanisms.

A novel cinnamic and caffeic acid-conjugated peptide analogs with anticonvulsant and analgesic potency: Comparative analyses of trans/cis isomers.

The novel cinnamic acid (CA) (H4-CA, H5-CA, and H7-CA) and caffeic acid (KA) (H4-KA, H5-KA, and H7-KA) hemorphin analogs have recently been synthesized and their trans isomers have been tested for antiseizure and antinociceptive activity. In the present study, the cis forms of these compounds were tested and compared with their trans isomers in seizure and nociception tests in mice. The cis-H5-CA and H7-CA compounds showed efficacy against psychomotor seizures, whereas the trans isomers were ineffective. Both the cis and trans KA isomers were ineffective in the 6-Hz test. In the maximal electroshock (MES) test, the cis isomers showed superior antiseizure activity to the trans forms of CA and KA conjugates, respectively. The suppression of seizure propagation by cis-H5-CA and the cis-H5-KA was reversed by a kappa opioid receptor (KOR) antagonist. Naloxone and naltrindole were not effective. The cis-isomers of CA conjugates and cis-H7-KA produced significantly stronger antinociceptive effects than their trans-isomers. The cis-H5-CA antinociception was blocked by naloxone in the acute phase and by naloxone and KOR antagonists in the inflammatory phase of the formalin test. The antinociception of the KA conjugates was not abolished by opioid receptor blockade. None of the tested conjugates affected the thermal nociceptive threshold. The results of the docking analysis also suggest a model-specific mechanism related to the activity of the cis-isomers of CA and KA conjugates in relation to opioid receptors. Our findings pave the way for the further development of novel opioid-related antiseizure and antinociceptive therapeutics.

Association of the OPRM1 variant rs1799971 (A118G) and clinical manifestations in tramadol poisoned patients: a cross-sectional study.

INTRODUCTION: The opioid receptor mu1 is a protein coding gene that can have different codes for a protein and may have variations (polymorphisms) affecting how opioids work. The aim of this study was to investigate the prevalence of the most common opioid receptor mu1 polymorphism (A118G) and any relationship between this polymorphism and features following tramadol overdose. MATERIALS AND METHODS: This was a cross-sectional study of patients admitted with tramadol poisoning to an Iranian hospital. These patients were not taking any other drugs or medications and had no history of seizures. RESULTS: The results showed that among the 83 patients included in the study, 57 (69 per cent) had the AA genotype, 25 (30 per cent) had the AG genotype, and one (1 per cent) had the GG genotype for the opioid receptor mu1 A118G polymorphism. Nausea and/or vomiting occurred in nine (11 per cent) patients and dizziness in 38 (46 per cent) patients. Serious adverse events included seizures in 51 (60 per cent) patients and respiratory failure requiring mechanical ventilation in 21 (25 per cent) patients. However, there was no significant association between the opioid receptor mu1 A118G polymorphism and these adverse events. DISCUSSION: In our study, the frequency of the A allele was greater than the G allele, and the AA genotype was more prevalent than AG. The GG genotype was the least common among the polymorphisms of opioid receptor mu1 rs1799971. There was no significant association between the opioid receptor mu1 A118G polymorphism and symptoms in tramadol-poisoned patients. Although these allele proportions are similar to the results reported in other Caucasian populations, they are dissimilar to the findings in Chinese and Singaporean populations. In these Asian studies, the predominant allele was the G allele. It has been suggested that a mutated G allele will decrease the production of opioid receptor mu1-related messenger ribonucleic acid and related proteins, leading to fewer mu-opioid receptors in the brain. CONCLUSIONS: This study found no significant association between the opioid receptor mu1 A118G polymorphism and adverse outcomes in tramadol-poisoned patients. However, more research is needed to draw more definitive conclusions due to the limited evidence and variability of opioid receptor mu1 polymorphisms in different populations.

Effects of Intranasal Naloxone on Hypoglycemia-Associated Autonomic Failure (HAAF) in Susceptible Individuals.

CONTEXT: Hypoglycemia-associated autonomic failure (HAAF), defined as blunting of counter-regulatory hormone and symptom responses to recurrent hypoglycemia, remains a therapeutic challenge in diabetes treatment. The opioid system may play a role in HAAF pathogenesis since activation of opioid receptors induces HAAF. Blockade of opioid receptors with intravenous naloxone ameliorates HAAF experimentally, yet is not feasible therapeutically. OBJECTIVE: To investigate the effects of opioid receptor blockade with intranasal naloxone on experimentally-induced HAAF. DESIGN: Randomized, double-blinded, placebo-controlled crossover study. SETTING: Academic research center. PARTICIPANTS: Healthy non-diabetic volunteers. INTERVENTIONS: Paired two-day studies, 5-10 weeks apart, each consisting of three consecutive hypoglycemic episodes (hyperinsulinemic hypoglycemic clamps, glucose nadir: 54 mg/dL): two on day 1 with administration of intranasal naloxone vs. placebo, followed by the third episode on day 2. MAIN OUTCOME MEASURES: Differences in counter-regulatory hormones responses and hypoglycemia symptoms between first and third hypoglycemic episodes in naloxone vs. placebo studies. RESULTS: Out of 17 participants, 9 developed HAAF, confirming variable inter-individual susceptibility. Among participants susceptible to HAAF, naloxone maintained some hormonal and symptomatic responses to hypoglycemia and prevented the associated requirement for increased glucose infusion. Unexpectedly, naloxone reduced plasma epinephrine and growth hormone responses to the first hypoglycemic episode but prevented further reduction with subsequent hypoglycemia. CONCLUSIONS: This is the first study to report that intranasal naloxone, a widely used opioid receptor antagonist, may ameliorate some features of HAAF. Further investigation is warranted into mechanisms of variable inter-individual susceptibility to HAAF and the effects of intranasal naloxone in people with diabetes at risk for HAAF.

Voluntary Exercise Ameliorates Chronic Ethanol Withdrawal-Induced Adaptations of Opioid Receptor Expression in the Nucleus Accumbens, Dopamine Release, and Ethanol Consumption.

Exercise has increasingly been recognized as an adjunctive therapy for alcohol-use disorder (AUD), yet our understanding of its underlying neurological mechanisms remains limited. This knowledge gap impedes the development of evidence-based exercise guidelines for AUD treatment. Chronic ethanol (EtOH) exposure has been shown to upregulate and sensitize kappa opioid receptors (KORs) in the nucleus accumbens (NAc), which is innervated by dopamine (DA) neurons in the midbrain ventral tegmental area (VTA), which may contribute to AUD-related behaviors. In this study, we investigated the impact of voluntary exercise in EtOH-dependent mice on EtOH consumption, KOR and delta opioid receptor (DOR) expression in the NAc and VTA, and functional effects on EtOH-induced alterations in DA release in the NAc. Our findings reveal that voluntary exercise reduces EtOH consumption, reduces KOR and enhances DOR expression in the NAc, and modifies EtOH-induced adaptations in DA release, suggesting a competitive interaction between exercise-induced and EtOH-induced alterations in KOR expression. We also found changes to DOR expression in the NAc and VTA with voluntary exercise but no significant changes to DA release. These findings elucidate the complex interplay of AUD-related neurobiological processes, highlighting the potential for exercise as a therapeutic intervention for AUD.

Interactions Between Endogenous Opioids and the Immune System.

The endogenous opioid system, which consists of opioid receptors and their ligands, is widely expressed in the nervous system and also found in the immune system. As a part of the body's defense machinery, the immune system is heavily regulated by endogenous opioid peptides. Many types of immune cells, including macrophages, dendritic cells, neutrophils, and lymphocytes are influenced by endogenous opioids, which affect cell activation, differentiation, proliferation, apoptosis, phagocytosis, and cytokine production. Additionally, immune cells also synthesize and secrete endogenous opioid peptides and participate peripheral analgesia. This chapter is structured into two sections. Part one focuses on immunoregulatory functions of central endogenous opioids; and part two describes how opioid peptide-containing immune cells participate in local analgesia.

The Role of Endogenous Opioids in Cardioprotection.

The opioid system involves opioid receptors (OPRs) and endogenous opioid peptides.This chapter will focus on the distribution of OPRs in the cardiovascular system, the expression pattern in the heart, the activation by opioid peptides, and the effects of OPRs activation with potential relevance in cardiovascular performance. In the heart, OPRs are co-expressed with beta adrenergic receptors (ß-ARs) in the G-protein-coupled receptor (GPCR) superfamily, functionally cross-talk with ß-Ars and modify catecholamine-induced effects. They are involved in cardiac contractility, energy metabolism, myocyte survival or death, vascular resistance. The effects of the opioid system in the regulation of systemic circulation at both the central and peripheral level are presented. The pathways are discussed under physiological (i.e., aging) and pathological conditions (atherosclerosis, heart failure, essential hypertension, ischemic stress). Stimulation of OPRs not only inhibits cardiac excitation-contraction coupling, but also protects the heart against hypoxic and ischemic injury. An enhanced sensitivity to opioids of endocrine organs and neuronal systems is operative in hypertensive patients. The opioid system can be pharmacologically engaged to selectively mimic these responses via cardiac and nervous signaling. The clinical opportunities for the use of cardioprotective effects of opioids require future investigations to provide more specific details of the impact on cardiac performance and electrophysiological properties.

BNT12, a novel hybrid peptide of opioid and neurotensin pharmacophores, produces potent central antinociception with limited side effects.

The development of multitarget opioid drugs has emerged as an attractive approach for innovative pain management with reduced side effects. In the present study, a novel hybrid peptide BNT12 containing the opioid and neurotensin (NT)-like fragments was synthesized and pharmacologically characterized. In acute radiant heat paw withdrawal test, intracerebroventricular (i.c.v.) administration of BNT12 produced potent antinociception in mice. The central antinociceptive activity of BNT12 was mainly mediated by µ-, δ-opioid receptor, neurotensin receptor type 1 (NTSR1) and 2 (NTSR2), supporting a multifunctional agonism of BNT12 in the functional assays. BNT12 also exhibited significant antinociceptive effects in spared nerve injury (SNI)-neuropathic pain, complete Freund's adjuvant (CFA)-induced inflammatory pain, acetic acid-induced visceral and formalin-induced pain after i.c.v. administration. Furthermore, BNT12 exhibited substantial reduction of acute antinociceptive tolerance, shifted the dose-response curve to the right by only 1.3-fold. It is noteworthy that BNT12 showed insignificant chronic antinociceptive tolerance at the supraspinal level. In addition, BNT12 exhibited reduced or no opioid-like side effects on conditioned place preference (CPP) response, naloxone-precipitated withdrawal response, acute hyperlocomotion, motor coordination, gastrointestinal transit, and cardiovascular responses. The present investigation demonstrated that the novel hybrid peptide BNT12 might serve as a promising analgesic candidate with limited opioid-like side effects.

Cebranopadol, a novel long-acting opioid agonist with low abuse liability, to treat opioid use disorder: Preclinical evidence of efficacy.

Maintenance therapy with buprenorphine and methadone is the gold standard pharmacological treatment for opioid use disorder (OUD). Despite these compounds demonstrating substantial efficacy, a significant number of patients do not show optimal therapeutic responses. The abuse liability of these medications is also a concern. Here we used rats to explore the therapeutic potential of the new long-acting pan-opioid agonist Cebranopadol in OUD. We tested the effect of cebranopadol on heroin self-administration and yohimbine-induced reinstatement of heroin seeking. In addition, we evaluated the abuse liability potential of cebranopadol in comparison to that of heroin under fixed ratio 1 (FR1) and progressive ratio (PR) operant self-administration contingencies. Oral administration of cebranopadol (0, 25, 50 µg/kg) significantly attenuated drug self-administration independent of heroin dose (1, 7, 20, 60µg/inf). Cebranopadol also reduced the break point for heroin (20 µg/inf). Finally, pretreatment with cebranopadol significantly attenuated yohimbine-induced reinstatement of drug seeking. In abuse liability experiments under FR1 contingency, rats maintained responding for heroin (1, 7, 20, 60µg/inf) to a larger extent than cebranopadol (0.03, 0.1, 0.3, 1.0, 6.0µg/inf). Under PR contingency, heroin maintained responding at high levels at all except the lowest dose, while the break point (BP) for cebranopadol did not differ from that of saline. Together, these data indicate that cebranopadol is highly efficacious in attenuating opioid self-administration and stress-induced reinstatement, while having limited abuse liability properties. Overall, the data suggest clinical potential of this compound for OUD treatment.

Delta opioid receptor expression correlates to skin ageing and melanin expression in Asian women.

While the evidence for the implication of opioid receptors (OPr) in ageing is growing, there is, to our knowledge, no study focusing directly on changes in vivo cutaneous OPr expression with increasing age. We thus investigated OPr expression in 30 healthy female Asian volunteers in Southern China whose ages range from the early 20s to the early 60s. Excisional biopsies were taken from the sun-exposed extensor area of the lower arm and the photo-protected area of the upper inner arm. The thickness of the epidermal layers, melanin content, as well as expression of mu-opioid receptors (MOPr) and delta-opioid receptors (DOPr) were compared between different age ranges and photo-exposure status. Significant increased epidermal hypertrophy on the extensor surface was observed. There was significant reduction of DOPr in the epidermis with increasing age, independent of photo-ageing. The increase of melanin was significantly correlated with epidermal DOPr expression, not with MOPr expression. DOPr expression could thus serve as a marker for real biological ageing unaffected by chronic photo-exposure. Additionally, DOPr expression was inversely correlated with the deposition of melanin. Based on these results, we hypothesise that regulation of DOPr expression could be used to improve aged skin, including hyperpigmentation.

Neuroprotective effects of naltrexone in a mouse model of post-traumatic seizures.

Traumatic Brain Injury (TBI) induces neuroinflammatory response that can initiate epileptogenesis, which develops into epilepsy. Recently, we identified anti-convulsive effects of naltrexone, a mu-opioid receptor (MOR) antagonist, used to treat drug addiction. While blocking opioid receptors can reduce inflammation, it is unclear if post-TBI seizures can be prevented by blocking MORs. Here, we tested if naltrexone prevents neuroinflammation and/or seizures post-TBI. TBI was induced by a modified Marmarou Weight-Drop (WD) method on 4-week-old C57BL/6J male mice. Mice were placed in two groups: non-telemetry assessing the acute effects or in telemetry monitoring for interictal events and spontaneous seizures both following TBI and naltrexone. Molecular, histological and neuroimaging techniques were used to evaluate neuroinflammation, neurodegeneration and fiber track integrity at 8 days and 3 months post-TBI. Peripheral immune responses were assessed through serum chemokine/cytokine measurements. Our results show an increase in MOR expression, nitro-oxidative stress, mRNA expression of inflammatory cytokines, microgliosis, neurodegeneration, and white matter damage in the neocortex of TBI mice. Video-EEG revealed increased interictal events in TBI mice, with 71% mice developing post-traumatic seizures (PTS). Naltrexone treatment ameliorated neuroinflammation, neurodegeneration, reduced interictal events and prevented seizures in all TBI mice, which makes naltrexone a promising candidate against PTS, TBI-associated neuroinflammation and epileptogenesis in a WD model of TBI.

Activation of Cardiac δ2-Opioid Receptors Increases Heart Tolerance to Reperfusion.

Coronary occlusion (45 min) and reperfusion (120 min) in male Wistar rats in vivo, as well as total ischemia (45 min) of an isolated rat heart followed by reperfusion (30 min) were reproduced. The selective δ2-opioid receptor agonist deltorphin II (0.12 mg/kg and 152 nmol/liter) was administered intravenously 5 min before reperfusion in vivo or added to the perfusion solution at the beginning of reperfusion of the isolated heart. The peripheral opioid receptor antagonist naloxone methiodide and δ2-opioid receptor antagonist naltriben were used in doses of 5 and 0.3 mg/kg, respectively. It was found that the infarct-limiting effect of deltorphin II is associated with the activation of δ2-opioid receptors. We have demonstrated that deltorphin II can improve the recovery of the contractility of the isolated heart after total ischemia.

Total-body imaging of mu-opioid receptors with [11C]carfentanil in non-human primates.

PURPOSE: Mu-opioid receptors (MORs) are widely expressed in the central nervous system (CNS), peripheral organs, and immune system. This study measured the whole body distribution of MORs in rhesus macaques using the MOR selective radioligand [11C]carfentanil ([11C]CFN) on the PennPET Explorer. Both baseline and blocking studies were conducted using either naloxone or GSK1521498 to measure the effect of the antagonists on MOR binding in both CNS and peripheral organs. METHODS: The PennPET Explorer was used for MOR total-body PET imaging in four rhesus macaques using [11C]CFN under baseline, naloxone pretreatment, and naloxone or GSK1521498 displacement conditions. Logan distribution volume ratio (DVR) was calculated by using a reference model to quantitate brain regions, and the standard uptake value ratios (SUVRs) were calculated for peripheral organs. The percent receptor occupancy (%RO) was calculated to establish the blocking effect of 0.14 mg/kg naloxone or GSK1521498. RESULTS: The %RO in MOR-abundant brain regions was 75-90% for naloxone and 72-84% for GSK1521498 in blocking studies. A higher than 90% of %RO were observed in cervical spinal cord for both naloxone and GSK1521498. It took approximately 4-6 min for naloxone or GSK1521498 to distribute to CNS and displace [11C]CFN from the MOR. A smaller effect was observed in heart wall in the naloxone and GSK1521498 blocking studies. CONCLUSION: [11C]CFN total-body PET scans could be a useful approach for studying mechanism of action of MOR drugs used in the treatment of acute and chronic opioid use disorder and their effect on the biodistribution of synthetic opioids such as CFN. GSK1521498 could be a potential naloxone alternative to reverse opioid overdose.

Amelioration of Anxiety Associated with Opioid Withdrawal by Activation of Spinal Mechanoreceptors Via Novel Heterodyned Whole Body Vibration.

Objectives: Opioid use disorder (OUD)-associated overdose deaths have reached epidemic proportions worldwide. An important driving force for relapse is anxiety associated with opioid withdrawal. We hypothesized that our new technology, termed heterodyned whole-body vibration (HWBV) would ameliorate anxiety associated with OUD. Methods: Using a randomized, placebo (sham)-controlled, double-blind study design in an NIH-sponsored Phase 1 trial, we evaluated 60 male and 26 female participants diagnosed with OUD and undergoing treatment at pain and rehabilitation clinics. We utilized the Hamilton Anxiety Scale (HAM-A) and a daily visual analog scale anxiety rating (1-10) to evaluate anxiety. Subjects were treated for 10 min 5X/week for 4 weeks with either sham vibration (no interferential beat or harmonics) or HWBV (beats and harmonics). The participants also completed a neuropsychological test battery at intake and discharge. Results: In OUD subjects with moderate anxiety, there was a significant improvement in daily anxiety scores in the HWBV group compared to the sham treatment group (p=3.41 × 10-7). HAM-A scores in OUD participants at intake showed moderate levels of anxiety in OUD participants (HWBV group: 15.9 ± 1.6; Sham group: 17.8 ± 1.6) and progressively improved in both groups at discharge, but improvement was greater in the HWBV group (p=1.37 × 10-3). Furthermore, three indices of neuropsychological testing (mental rotations, spatial planning, and response inhibition) were significantly improved by HWBV treatment. Conclusions: These findings support HWBV as a novel, non-invasive, non-pharmacological treatment for anxiety associated with OUD.

Low doses of acetaminophen produce antidepressive-like effects through the opioid system in mice.

Acetaminophen (paracetamol) is one of the most popular analgesics for the management of fever and pain but few reports have investigated its antidepressant-like effect. Moreover, the role of the opioidergic pathway has been indicated in depression pathophysiology. This study aimed to examine the involvement of the opioid receptors in the antidepressant-like effect of acetaminophen after acute and sub-chronic administration using mice forced swimming test (FST). Our finding showed that administration of acetaminophen (50 and 100 mg/kg, i.p.) 30 min before the FST produced an antidepressant effect which was reduced by naloxone (1 mg/kg, i.p., a nonselective opioid receptor antagonist). Moreover, we observed that acetaminophen in higher doses (200 and 400 mg/kg) was ineffective. Also, the response of the non-effective dose of acetaminophen (25 mg/kg) was potentiated by the non-effective dose of morphine (0.1 mg/kg) in the FST that was antagonized by naloxone. Also, in contrast to morphine (10 mg/kg), acetaminophen (100 mg/kg, i.p.) induced neither tolerance to the anti-immobility behavior nor withdrawal syndrome after repeated administration. In addition, RT-PCR showed that hippocampal mu- and kappa-opioid receptor mRNA expression increased in mice after repeated administration of acetaminophen; however, morphine therapy for 6 days did not affect kappa-opioid receptor expression. Our findings demonstrated that acetaminophen in lower doses but not high doses revealed an antidepressant-like activity without inducing tolerance and withdrawal syndromes. Moreover, the observed effect of acetaminophen may be via altering the opioid system, particularly hippocampal mu- and kappa-receptors.

Bivalent and bitopic ligands of the opioid receptors: The prospects of a dual approach.

Opioid receptors belonging to the class A G-protein coupled receptors (GPCRs) are the targets of choice in the treatment of acute and chronic pain. However, their on-target side effects such as respiratory depression, tolerance and addiction have led to the advent of the 'opioid crisis'. In the search for safer analgesics, bivalent and more recently, bitopic ligands have emerged as valuable tool compounds to probe these receptors. The activity of bivalent and bitopic ligands rely greatly on the allosteric nature of the GPCRs. Bivalent ligands consist of two pharmacophores, each binding to the individual orthosteric binding site (OBS) of the monomers within a dimer. Bitopic or dualsteric ligands bridge the gap between the OBS and the spatially distinct, less conserved allosteric binding site (ABS) through the simultaneous occupation of these two sites. Bivalent and bitopic ligands stabilize distinct conformations of the receptors which ultimately translates into unique signalling and pharmacological profiles. Some of the interesting properties shown by these ligands include improved affinity and/or efficacy, subtype and/or functional selectivity and reduced side effects. This review aims at providing an overview of some of the bivalent and bitopic ligands of the opioid receptors and, their pharmacology in the hope of inspiring the design and discovery of the next generation of opioid analgesics.