Molecular mechanisms of opioid receptor-dependent signaling and behavior

Pain in comorbid alcohol use disorder and HIV: A network meta-analysis study

Alcohol use is prevalent among people with HIV (PWH). PWH often experience pain (said discomfort) and use alcohol to combat pain. We reported that short-term alcohol exposure exerts analgesic effect. Prolonged exposure is known to result in chronic pain. We hypothesize that alcohol exposure, either in-vivo for macaques or in-silico simulation exposure onto differentially expressed genes (DEGs) from HIV-1Tg rats and HIV patients, exacerbates discomfort in PWH. To substantiate this hypothesis, we analyzed genomic data collected from three brain datasets including the hippocampus of alcohol-exposed Macaca mulatta (GSE69685), HIV-1Tg rats (GSE47474), and post-mortem brain tissue of HIV-positive patients (GSE28160). Ingenuity Pathway Analysis (IPA)-Core Analysis revealed activation of neuroinflammation, neuropathic pain signaling pathways, and the inhibition of opioid signaling as well as in the increase of neuromuscular disease with neuropathy in Macaca mulatta exposed to binge EtOH and SIV infection. IPA-Core Analysis of the DEGs from HIV-1Tg rats, a rat model that mimics HIV patients on cART, possessing 7 of 9 HIV viral proteins, showed activation of neuroinflammation, neuropathic pain signaling pathways. IPA-Core Analysis of the DEGs from HIV patients showed activation of neuroinflammation and inhibition of neuropathic pain and increase in neuromuscular disease with neuropathy. To study the impact of alcohol exposure in HIV-1Tg rats and HIV patients, in-silico simulation of ethanol (EtOH) treatment mimicking exposure of alcohol onto the DEGs in response to HIV viral proteins in HIV-1Tg rats and HIV infection in HIV patients enhanced discomfort and increased neuromuscular diseases. These molecules showed significant modulation by simulated alcohol exposure, further supporting the link between alcohol use and heightened pain in PWH. Taking together, our findings suggest that alcohol consumption and HIV promote pain via modulating signaling pathways including neuroinflammation, and neuropathic pain signaling pathways and by disease like neuromuscular disease with neuropathy.

Acute changes in functional connectivity associated with first osteopathic manual treatment in chronic low back pain spatially overlap with opioid receptor expression

BACKGROUND

Osteopathic Manipulative Treatment (OMT) has emerged as a therapeutic approach for chronic low back pain (cLBP). Previous Magnetic Resonance (MR) studies have demonstrated that four weeks of OMT alter resting-state functional connectivity (rs-FC) in the somatosensory cortex, prefrontal regions, and frontal operculum/insula. However, it remains unclear whether a single session of OMT can immediately affect brain rs-FC.

METHODS

We combined a data-driven approach with a seed-based connectivity analysis to examine the pattern of whole-brain rs-FC in a cohort of thirty cLBP patients before and after a first acute session of OMT (N = 16) or a sham treatment (N = 14). Correlation analyses were performed to explore the relationship between the resulting rs-FC maps and receptor density/gene expression maps derived from in vivo brain atlases, focusing on the opioid and cannabinoid systems.

RESULTS

Data-driven analysis revealed that, compared to the sham group, the OMT increased the intrinsic connectivity of the right dorsolateral prefrontal cortex. Seed-based connectivity analysis showed that this region increased coupling with the right frontal operculum/insula. Notably, no effect of immediate OMT was found in the somatosensory cortex. The topography of these rs-FC changes selectively overlapped with the distribution of mu-opioid receptors.

CONCLUSIONS

Acute OMT in cLBP patients modulates rs-FC across cortical regions primarily involved in top-down cognitive control of pain, as well as in integrating pain intensity perception and related expectations. Spatial comparisons between rs-FC maps and receptor atlases suggest that these neural changes involve opioid, not cannabinoid, neurotransmission.

Serotonin release mediates analgesia via opioidergic system and withdrawal symptoms in chronic kratom extract-treated mice

BACKGROUND

Kratom alleviates pain by activating μu-opioid receptors (MOR), which trigger serotonin release to produce analgesia. Serotonin also interferes drug abuse effect. This study aimed to determine the role of serotonin in kratom-induced pain relief and withdrawal symptoms in mice.

METHODS

The analgesic effect was assessed using the hot-plate test. To induce withdrawal symptoms, mice received naloxone after being treated with kratom extracts for five days at increasing doses. Another group of morphine-dependent mice was treated with kratom extracts to ameliorate their withdrawal symptoms. A molecular docking study and molecular dynamics were conducted to predict the binding target of alkaloid kratom for increasing serotonin levels.

RESULTS

Chronic administration of kratom alkaloid extract (20 mg/kg) produced analgesic effects comparable to morphine (10 mg/kg). In contrast, kratom crude extracts (10 mg/kg and 20 mg/kg) demonstrated lower analgesia activity. This analgesic effect was mediated by MOR activation, leading to decreased intracellular cAMP and increased serotonin transmission. Repeated and increasing doses of crude or alkaloid kratom extracts (8 mg/kg to 45 mg/kg) produced less severe withdrawal symptoms than morphine. Increased dopamine and serotonin levels contributed to the onset of withdrawal symptoms. In the morphine group, treatment with kratom extracts increased serotonin levels while reducing dopamine. Molecular docking and molecular dynamics result revealed that kratom alkaloids interacts more readily with tryptophan hydroxylase, the enzyme responsible for serotonin biosynthesis.

CONCLUSIONS

Kratom extracts have the potential to provide analgesic effects and withdrawal symptoms, both of which are mediated by elevated serotonin release.

HSK21542 in patients with postoperative pain: two phase 3, multicentre, double-blind, randomized, controlled trials

HSK21542, a peripherally restricted kappa opioid receptor agonist, was evaluated for efficacy and safety in patients with postoperative pain following abdominal surgery. This was assessed in two phase 3, multicentre, randomized, double-blind, controlled trials (HSK21542-301 [ClinicalTrials.gov identifier, NCT04738357] and HSK21542-303 [ClinicalTrials.gov identifier, NCT05390905]) in China. HSK21542-301 was a dual-arm study comparing HSK21542 1.0 μg/kg with placebo, while HSK21542-303 involved three arms comparing HSK21542 1.0 μg/kg with tramadol 50 mg/dose and placebo. All treatments were administered intravenously. The primary endpoint was the time-weighted summed pain intensity differences over 24 h (SPID0-24 h). Both HSK21542-301 (least squares [LS] mean [± standard error], -39.1 [1.88] vs -27.4 [1.89]; P < 0.001) and HSK21542-303 (-64.0 [2.25] vs -45.9 [2.25]; P < 0.001) demonstrated superiority of HSK21542 over placebo in terms of SPID0-24 h, while HSK21542-303 showed non-inferiority to tramadol (LS mean difference, -1.1; 95% confidence interval, -7.4 to 5.1; P < 0.001). Furthermore, HSK21542 had a comparable safety profile to placebo, inducing fewer gastrointestinal adverse events compared with tramadol. Grade ≥3 treatment-emergent adverse events occurred in eight (5.9%) and three (2.3%) patients in the HSK21542 arm of HSK21542-301 and HSK21542-303, respectively. In conclusion, HSK21542 showed potent analgesic effect and was well tolerated in patients who underwent abdominal surgery and experienced postoperative pain.

Neurotransmitter modulation of human facial emotion recognition

Human facial emotion recognition (FER) is an evolutionarily preserved process that influences affiliative behaviours, approach/avoidance and fight-or-flight responses in the face of detecting threat cues, thus enhancing adaptation and survival in social groups. Here, we provide a narrative literature review on how human FER is modulated by neurotransmitters and pharmacological agents, classifying the documented effects by central neurotransmitter systems. Synthesising the findings from studies involving functional neuroimaging and FER tasks, we highlight several emerging themes; for example, noradrenaline promotes an overall positive bias in FER, while serotonin, dopamine and gamma-aminobutyric acid modulate emotions relating to self-preservation. Finally, other neurotransmitters including the cholinergic and glutamatergic systems are responsible for rather non-specific pro-cognitive effects in FER. With the ongoing accumulation of evidence further characterising the individual contributions of each neurotransmitter system, we argue that a sensible next step would be the integration of experimental neuropharmacology with computational models to infer further insights into the temporal dynamics of different neurotransmitter systems modulating FER.

Comparative Proteomic Analysis Reveals Altered Ciliary Proteins in Sickle Cell Disease

Sickle cell disease (SCD) is an inherited hemoglobinopathy characterized by sickle-shaped red blood cells (RBCs). Primary cilia are mechanosensory organelles and are projected in the lumen of blood vessels to detect blood flow. We previously reported that interaction between microvasculature endothelial cells and sickled RBCs resulted in altered blood flow that can elevate reactive oxygen species, leading to increased deciliation in SCD patients. However, the impact of deciliation mediated by sickled RBCs in the context of the ciliary protein profiles remains unclear. Here, we investigated cell-cilia stability under different physiological shear-stress magnitudes and examined cilia protein profiles in SCD, utilizing mouse models and human participants. Our results demonstrate that subjecting endothelial cilia to sickled RBCs at 5.0 dyn/cm2 led to significant deciliation events. The proteomic and bioinformatic analyses showed different ciliary protein profiles, distinct signaling pathways, and unique post-translational modification processes in the SCD mouse model. Consistent with the SCD mouse model results, our translational studies validated the enrichment of specific proteins, including Transferrin Receptor-1 (TfR1), Glyceraldehyde-3-Phosphate-Dehydrogenase (GAPDH), and ADP Ribosylation Factor Like GTPase-13B (ARL13B) in SCD patients. These findings underscore the clinical relevance of cilia in SCD and suggest that ciliary proteins are potential biomarkers for assessing vascular damage.

The role of the endogenous opioid system in modulating orthodontic-induced neurogenic inflammation of the dental pulp: A comprehensive review of the literature

BACKGROUND

Orthodontic forces may lead to neurogenic inflammation in the dental pulp by triggering the release of somatosensory neuropeptides such as Substance P (SP), Calcitonin gene-related peptide (CGRP) and Neurokinin A (NKA). In the vast majority of patients, acute symptoms are not triggered, probably due to the control of the neurogenic inflammatory process exerted by endogenous opioid systems.

OBJECTIVE

This review aimed to assess the cellular and molecular mechanisms through which the endogenous opioid system modulates the orthodontic-induced neurogenic inflammation of the dental pulp and to identify potential mechanisms for endogenous control of pulp pain.

METHODS

A literature search was conducted in the databases Pubmed, ISI Web of Science and Scopus to find relevant studies using the keywords: "orthodontic movement," "opioids" and "neurogenic inflammation." Following the PRISMA and Amstar recommendations, studies were selected for the literature review.

RESULTS

After removing duplicated and irrelevant articles, and those that does not meet the inclusion criteria, 38 articles were selected and classified according to the opioid peptides analysed in relation to orthodontic movement and dental pulp.

DISCUSSION

Both peripheral and central pathways, via endogenous opioid systems such as somatostatin (SST), dynorphin, β-endorphin, methionine enkephalin, endocannabinoids and anti-inflammatory cytokines, modulate the neurogenic inflammation elicited by orthodontic movements. The bradykinin and monoaminergic systems also appear to display regulatory effects on pain response. These control mechanisms, however, may be insufficient in cases where severe orthodontic forces are applied, thus leading to asymptomatic irreversible pulpitis or necrosis.

CONCLUSION

The opioid system regulates neurogenic pulpal inflammation and pain at the level of the central and peripheral nervous systems by releasing endogenous substances, including SST, opioid peptides, endocannabinoids and anti-inflammatory cytokines.

Strategy for effective analgesia with intravenous buprenorphine in patients with acute postoperative pain

BACKGROUND

Analgesic treatment is the primary method for managing acute postoperative pain. Opioid analgesics are the main class of drugs used to treat moderate to severe pain, whether it is acute or chronic. These opioids differ in various ways, including their pharmacochemical properties, distribution and absorption rates, metabolism, and elimination pathways for the drug and its metabolites. These differences result in varying degrees of analgesic efficacy, which, in clinical practice, allows for the selection of the most effective drug that maximizes pain relief while ensuring safety. Buprenorphine is a semi-synthetic opioid with properties that are not yet fully understood. It has a wide range of applications in treating both acute and chronic pain, including non-cancer and cancer-related pain. One of the most significant clinical advantages of buprenorphine is its safety profile, which includes a ceiling effect on respiratory depression, no immunosuppressive effects, inhibition of hyperalgesia, no cumulative effects in patients with renal failure, and a low risk of constipation following its use.

AIM

This study aims to analyze current reports on the use of intravenous buprenorphine as a first-line opioid analgesic for postoperative pain relief. The paper discusses the pharmacochemical properties of the drug and the mechanisms behind postoperative pain. Additionally, it presents the experiences of the pain management team at Copernicus Hospital in Gdansk regarding administering intravenous buprenorphine.

MATERIAL AND METHODS

The current literature on buprenorphine for treating moderate to severe acute pain has been reviewed, focusing on its effectiveness in managing postoperative pain following surgical procedures. Additionally, the experience of the Copernicus Hospital pain team with buprenorphine is summarized in a brief discussion.

CONCLUSION

After reviewing current literature and recommendations, along with the experiences of the pain management team at Copernicus Hospital in Gdańsk, it can be concluded that buprenorphine is an analgesic that demonstrates a high level of efficacy and safety. When used in combination with non-opioid analgesics, buprenorphine achieves a synergistic effect, resulting in effective pain relief. This approach facilitates early patient rehabilitation and enables a swift return to normal activities, even following extensive surgical procedures.

Exploring the genetic influences on equine analgesic efficacy through genome-wide association analysis of ranked pain responses

Multimodal analgesic administration is a promising strategy for mitigating side effects typically associated with analgesia; nevertheless, variation in analgesic effectiveness still poses a considerable safety concern for both horses and veterinarians. Pharmacogenomic studies have started delving into genetic influences on varying drug effectiveness and related side effects. However, current findings have narrow implications and are limited in their ability to individualize analgesic dosages in horses. Hydromorphone and detomidine were administered to a cohort of 48 horses at standardized time intervals, with dosage rates recorded. Analgesic effectiveness was scored (1-3) based on pain response to dura penetration during cerebrospinal fluid centesis. Genome-wide association (GWA) analyses identified two SNVs passing the nominal significance threshold (P < 1 ×10-5) in association with analgesic effectiveness. One SNV identified on chromosome 27 (rs1142378599) is contained within the LOC100630731 disintegrin and metalloproteinase domain-containing protein 5 gene. The second identified SNV is an intergenic variant located on chromosome 29 (rs3430772468) These SNVs accounted for 26.11 % and 31.72 % of explained variation in analgesic effectiveness respectively, with all eight of the horses with the lowest analgesic effectiveness expressing the A/C genotype at rs3430772468, with six of which also expressing the C/T genotype at rs1142872965. Whilst highlighting the multifactorial nature of analgesic efficacy, this study serves as an important step in the application of genome-wide approaches to better understand genetic factors underpinning commonly observed variation in analgesic effectiveness in horses, with the goal of tailoring analgesic dosage to minimize commonly observed side effects and improve the outcomes of equine pain management.

A patent review of CXCR7 modulators (2019-present)

INTRODUCTION

Atypical chemokine receptor 3 (ACKR3) (formerly CXCR7) regulates various biological processes through its ligands and is closely associated with numerous diseases, including inflammation, cancer, cardiovascular diseases (CVDs), pain, and neurological disorders. Therefore, ACKR3 has emerged as a potential target for disease treatment.

AREAS COVERED

This review summarizes the ACKR3 modulators published in patents from 2019 to 2024 using data from Google Patents, the European Patent Office, and the World Intellectual Property Organization's online databases. This includes information on their chemical structures, syntheses, activities, and developmental stages.

EXPERT OPINION

ACKR3 agonists gained traction as a treatment for cardiovascular and pain conditions. WW-12, which was derived from the chemical modifications of conolidine, became a novel small-molecule pain modulator by activating ACKR3, which in turn boosted endogenous opioid peptides for the classical opioid receptors.ACKR3 antagonist ACT-1004-1239 from Idorsia Pharmaceuticals Ltd. has demonstrated the ability to treat cancer, acute lung injury/ARDS, and autoimmune diseases, including multiple sclerosis. The outcomes of these clinical trials will direct the development and indications of future ACKR3 modulators.

The addictive process of opioids: current and novel interventions in opioid use disorder

The growing epidemic of opioid misuse presents numerous challenges for healthcare practitioners and patients alike as friction exists between ease of use and efficacy, and potential for overuse and addiction. With over 82 000 deaths related to opioid overdose in North America in 2020, it is imperative to gain a better understanding of the underlying mechanisms behind the addiction process, as well as the current methods being used in the arsenal against this disease. The current best pharmacological approaches for mediating opioid use disorder are methadone, buprenorphine, naltrexone, and naloxone, which act on opioid receptors to produce diverse effects based upon the patients' needs. The variety of effects that these drugs produce, which include removing opioid withdrawal, reversing overdose effects, and blocking opioid properties, makes this arsenal of therapeutics a global necessity in addressing the opioid use epidemic. Accordingly, this narrative review provides a summary of the available data regarding the physiological processes by which opioid addiction takes place and discusses the current and future potential of interventional methods used to mitigate opioid use disorder. The mechanisms of action and subsequent functional outcomes must be understood to reduce the number of opioid-related deaths worldwide.

Divergent opioid-mediated suppression of inhibition between hippocampus and neocortex across species and development

Within adult rodent hippocampus (HPC), opioids suppress inhibitory parvalbumin-expressing interneurons (PV-INs), disinhibiting local microcircuits. However, it is unknown whether this disinhibitory motif is conserved across cortical regions, species, or development. We observed that PV-IN-mediated inhibition is robustly suppressed by opioids in HPC proper but not primary neocortex in mice and non-human primates, with spontaneous inhibitory tone in resected human tissue also following a consistent dichotomy. This hippocampal disinhibitory motif is established in early development when PV-INs and opioids regulate early population activity. Morphine pretreatment partially occludes this acute opioid-mediated suppression, with implications for the effects of opioids on hippocampal network activity important for learning and memory. Our findings demonstrate that PV-INs exhibit divergent opioid sensitivity across brain regions, which is remarkably conserved over evolution, and highlight the underappreciated role of opioids acting through immature PV-INs in shaping hippocampal development.

Effects of cannabinoids on immune checkpoint inhibitor response: CCTG pooled analysis of individual patient data

BACKGROUND

Immune checkpoint inhibitors (ICIs) benefit patients across various tumor types. ICIs block cancer and T-cell interactions whereas cannabinoids may inhibit T-cell activation, reducing lysis of tumor cells. Interactions between cannabinoid use and dual ICI treatment remain unknown.

METHODS

Individual patient data from 4 Canadian Cancer Trials Group (CCTG) trials of patients treated with dual ICI ± chemotherapy (n = 684) were pooled. Cochran - Mantel - Haenszel and log-rank tests (stratified by trial/treatment arms) correlated cannabinoid use with clinicopathologic characteristics, Best Overall Response (BOR)/iBOR per RECIST 1.1/iRECIST, Progression-Free Survival (PFS)/iPFS, Overall Survival (OS) and immune-related adverse events (irAEs).

RESULTS

Sixty-five (9.5%) patients took cannabinoids at any time on trial, 32 (4.7%) of which were using cannabinoids at baseline. By multivariate analysis, cannabinoid use at baseline was significantly associated with improved iPFS (0.05), but not iBOR (p = 0.15), PFS (p = 0.12), OS (p = 0.35) or incidence of grade 1/2 or 3/4 irAEs (p = 0.96 and 0.65 respectively). Results were not significantly different with cannabinoid use at any time on trial.

CONCLUSION

Improved iPFS with cannabinoid use in patients treated with durvalumab plus tremelimumab ± chemotherapy did not translate into OS benefits. This study supports the safe use of cannabinoids in the context of combination ICI therapy.

Kappa opioid receptor internalisation-induced p38 nuclear translocation suppresses glioma progression

BACKGROUND

Recent studies have implicated a role for perioperative medications in determining patient outcomes after surgery for malignant tumours, including relapse and metastasis.

METHODS

A combined approach spanned molecular, cellular, and organismal levels, including bioinformatics, immunohistochemical staining of clinical and animal samples, RNA sequencing of glioblastoma multiforme (GBM) cells with Ingenuity Pathway Analysis, lentiviral-mediated gene expression modulation, in vitro cell experiments, and in vivo orthotopic tumour transplantation.

RESULTS

We observed a significant correlation between increased kappa opioid receptor (KOP receptor) expression and better prognosis in patients with glioma. Exogenous KOP receptor overexpression in GBM cells in vitro induced cell cycle arrest, suppressed cell growth, and promoted apoptosis. Conversely, reducing KOP receptor expression in GBM cells reduced the proportion of cells in S and G2/M phases, accelerating cell growth. KOP receptor overexpression inhibited glioma cell growth and prolonged survival in mice in vivo, while KOP receptor knockdown had the opposite effect. Mechanistically, internalised KOP receptors were found to bind cytoplasmic p38, facilitating its nuclear translocation and phosphorylation, which influences downstream gene expression. The selective KOP receptor agonist TRK-820 triggered KOP receptor internalisation, activated the p38 pathway, and diminished glioma cell viability in vitro.

CONCLUSIONS

This combined molecular, cellular, and in vivo approach supports use of KOP receptor agonists as potential adjuvant therapeutics for glioma.

Redefining Ketamine Pharmacology for Antidepressant Action: Synergistic NMDA and Opioid Receptor Interactions?

Ketamine is a racemic compound and medication comprised of (S)-ketamine and (R)-ketamine enantiomers and its metabolites. It has been used for decades as a dissociative anesthetic, analgesic, and recreational drug. More recently, ketamine, its enantiomers, and its metabolites have been used or are being investigated for the treatment of refractory depression, as well as for comorbid disorders such as anxiety, obsessive-compulsive, and opioid use disorders. Despite its complex pharmacology, ketamine is referred to as an N-methyl-d-aspartate (NMDA) receptor antagonist. In this review, the authors argue that ketamine's pharmacology should be redefined to include opioid receptors and the endogenous opioid system. They also highlight a potential mechanism of action of ketamine for depression that is attributed to bifunctional, synergistic interactions involving NMDA and opioid receptors.

Effects of kratom alkaloids on mesolimbic dopamine release

Kratom is derived from the leaves of a plant (Mitragyna speciosa) native to Southeast Asia that has been consumed for its complex stimulant-like effects at low doses, opiate-like effects at high doses, to treat mood related issues like anxiety or depression, or to help ameliorate opioid withdrawal symptoms. However, the neural mechanisms of its major psychoactive alkaloids, mitragynine (MG) and 7-hydroxymitragynine (7-HMG), are still not clear. Given that the effects of kratom are often compared to drugs with abuse liabilities, the current study examined the effects of MG and 7-HMG on reward-related neurotransmission. Fixed potential amperometry was used to quantify stimulation-evoked phasic dopamine release in the nucleus accumbens (NAc) of anesthetized male and female mice before and after MG (1, 15, or 30 mg/kg i.p.), 7-HMG (0.5, 1, or 2 mg/kg i.p.), or vehicle. MG reduced dopamine release over the recording period (90 min) in a dose dependent manner, and the low dose of MG significantly increased dopamine autoreceptor functioning in males. Both sexes responded similarly to 7-HMG with the low dose of 7-HMG increasing dopamine release while the high dose decreased dopamine release. 7-HMG did not alter dopamine autoreceptor functioning for either sex. Neither MG nor 7-HMG altered the clearance rate of stimulation-evoked dopamine. Findings suggest that these kratom alkaloids do alter dopamine functioning, although potentially not in a way consistent with classic drugs of abuse. Further investigation of the neural mechanisms of kratom's alkaloids will provide crucial and urgent insight into their therapeutic uses or potential abuse liability.

Delta opioid receptors engage multiple signaling cascades to differentially modulate prefrontal GABA release with input and target specificity

Opioids regulate circuits associated with motivation and reward across the brain. Of the opioid receptor types, delta opioid receptors (DORs) appear to have a unique role in regulating the activity of circuits related to reward without liability for abuse. In neocortex, DORs are expressed primarily in interneurons, including parvalbumin- and somatostatin-expressing interneurons that inhibit somatic and dendritic compartments of excitatory pyramidal cells, respectively. But how DORs regulate transmission from these key interneuron classes is unclear. We found that DORs regulate inhibition from these interneuron classes using different G-protein signaling pathways that both converge on presynaptic calcium channels but regulate distinct aspects of calcium channel function. This imposes different temporal filtering effects, via short-term plasticity, that depend on how calcium channels are regulated. Thus, DORs engage differential signaling cascades to regulate inhibition depending on the postsynaptic target compartment, with different effects on synaptic information transfer in somatic and dendritic domains.

Biased Opioid Receptor Agonists: Balancing Analgesic Efficacy and Side-Effect Profiles

Opioids are the most effective option for severe pain. However, it is well documented that the side effects associated with prolonged opioid use significantly constrain dosage in the clinical setting. Recently, researchers have concentrated on the development of biased opioid receptor agonists that preferentially activate the G protein signaling pathway over β-arrestin signaling. This approach is based on the hypothesis that G protein signaling mediates analgesic effects, whereas β-arrestin signaling is implicated in adverse side effects. Although certain studies have demonstrated that the absence or inhibition of β-arrestin signaling can mitigate the incidence of side effects, recent research appears to challenge these earlier findings. In-depth investigations into biased signal transduction of opioid receptor agonists have been conducted, potentially offering novel insights for the development of biased opioid receptors. Consequently, this review elucidates the contradictory roles of β-arrestin signaling in the adverse reactions associated with opioid receptor activation. Furthermore, a comparative analysis was conducted to evaluate the efficacy of the classic G protein-biased agonists, TRV130 and PZM21, relative to the traditional non-biased agonist morphine. This review aims to inform the development of novel analgesic drugs that can optimize therapeutic efficacy and safety, while minimizing adverse reactions to the greatest extent possible.

A New Trick of Old Dogs: Can Kappa Opioid Receptor Antagonist Properties of Antidepressants Assist in Treating Treatment-Resistant Depression (TRD)?

Background/Objectives: Approximately one in five individuals will experience major depressive disorder (MDD), and 30% exhibit resistance to standard antidepressant treatments, resulting in a diagnosis of treatment-resistant depression (TRD). Historically, opium was used effectively to treat depression; however, when other medications were introduced, its use was discontinued due to addiction and other hazards. Recently, kappa opioid receptor (KOR) antagonism has been proposed as a potential mechanism for treating TRD. The main research question is whether commonly used psychotropic medications possess KOR antagonist properties and whether this characteristic could contribute to their efficacy in TRD. Methods: We investigated the antinociceptive effects of many psychotropic medications and their interactions with the opioid system. Mice were tested with a hotplate or tail-flick after being injected with different doses of these agents. Results: The antidepressants mianserin and mirtazapine (separately) induced dose-dependent antinociception, each yielding a biphasic dose-response curve. Similarly, the antidepressant venlafaxine produced a potent effect and reboxetine produced a weak effect. The antipsychotics risperidone and amisulpride exhibited a dose-dependent antinociceptive effect. The sedative-hypnotic zolpidem induced a weak bi-phasic dose-dependent antinociceptive effect. All seven psychotropic medications elicited antinociception, which was reversed by the non-selective opiate antagonist naloxone and, separately, by the kappa-selective antagonist Nor-BNI. Conclusions: Clinical studies are mandatory to establish the potential efficacy of augmentation of the treatment with antidepressants with these drugs in persons with treatment-resistant depression and the optimal dosage of medications prescribed. We suggest a possible beneficial effect of antidepressants with kappa antagonistic properties.

The immunological and pharmacokinetic evaluation of Lipid-PLGA hybrid nanoparticle-based oxycodone vaccines

The current opioid epidemic is one of the most profound public health crises facing the United States. Despite that it has been under the spotlight for years, available treatments for opioid use disorder (OUD) and overdose are limited to opioid receptor ligands such as the agonist methadone and the overdose reversing drugs such as naloxone. Vaccines are emerging as an alternative strategy to combat OUD and prevent relapse and overdose. Most vaccine candidates consist of a conjugate structure containing the target opioid attached to an immunogenic carrier protein. However, conjugate vaccines have demonstrated some intrinsic shortfalls, such as fast degradation and poor recognition by immune cells. To overcome these challenges, we proposed a lipid-PLGA hybrid nanoparticle (hNP)-based vaccine against oxycodone (OXY), which is one of the most frequently misused opioid analgesics. The hNP-based OXY vaccine exhibited superior immunogenicity and pharmacokinetic efficacy in comparison to its conjugate vaccine counterpart. Specifically, the hNP-based OXY vaccine formulated with subunit keyhole limpet hemocyanin (sKLH) as the carrier protein and aluminum hydroxide (Alum) as the adjuvant (OXY-sKLH-hNP(Alum)) elicited the most potent OXY-specific antibody response in mice. The induced antibodies efficiently bound with OXY molecules in blood and suppressed their entry into the brain. In a following dose-response study, OXY-sKLH-hNP(Alum) equivalent to 60 μg of sKLH was determined to be the most promising OXY vaccine candidate moving forward. This study provides evidence that hybrid nanoparticle-based vaccines may be superior vaccine candidates than conjugate vaccines and will be beneficial in treating those suffering from OUD.

Divergent opioid-mediated suppression of inhibition between hippocampus and neocortex across species and development

Within the adult rodent hippocampus, opioids suppress inhibitory parvalbumin-expressing interneurons (PV-INs), thus disinhibiting local micro-circuits. However, it is unknown if this disinhibitory motif is conserved in other cortical regions, species, or across development. We observed that PV-IN mediated inhibition is robustly suppressed by opioids in hippocampus proper but not primary neocortex in mice and nonhuman primates, with spontaneous inhibitory tone in resected human tissue also following a consistent dichotomy. This hippocampal disinhibitory motif was established in early development when PV-INs and opioids were found to regulate early population activity. Acute opioid-mediated modulation was partially occluded with morphine pretreatment, with implications for the effects of opioids on hippocampal network activity important for learning and memory. Together, these findings demonstrate that PV-INs exhibit a divergence in opioid sensitivity across brain regions that is remarkably conserved across evolution and highlights the underappreciated role of opioids acting through immature PV-INs in shaping hippocampal development.

Selective Mu-Opioid Receptor Imaging Using 18F-Labeled Carfentanils

Carfentanil, a highly potent synthetic opioid, paradoxically serves as a crucial positron emission tomography (PET) imaging tool in neurobiological studies of the mu-opioid receptor (MOR) system when labeled with carbon-11 ([11C]CFN). However, its clinical research use is hindered by extreme potency and the limited availability of short-lived carbon-11 (t1/2 = 20.4 min). We present fluorine-18-labeled fluorocarfentanils ([18F]FCFNs), which can be produced at higher molar activity, allowing for lower mass doses and benefiting from the longer half-life of fluorine-18 (t1/2 = 109.8 min), facilitating broader accessibility. Using copper-mediated radiofluorination, we synthesized a small [18F]FCFN library and conducted preclinical imaging evaluations. Two candidates, o-18F-1 and p-18F-2, showed optimal brain uptake, favorable pharmacokinetics, and high MOR-specific binding. Selectivity was confirmed through in vitro binding assays and in vivo PET scans. These [18F]FCFNs are promising for accessible human brain MOR imaging.

A Comprehensive Analysis of Fibromyalgia and the Role of the Endogenous Opioid System

Fibromyalgia represents a chronic pain disorder characterized by musculoskeletal pain, fatigue, and cognitive impairments. The exact mechanisms underlying fibromyalgia remain undefined; as a result, diagnosis and treatment present considerable challenges. On the other hand, the endogenous opioid system is believed to regulate pain intensity and emotional responses; hence, it might be expected to play a key role in the enhanced sensitivity experienced by fibromyalgia patients. One explanation for the emergence of disrupted pain modulation in individuals with fibromyalgia is a significant reduction in opioid receptor activity or an imbalance in the levels of endogenous opioid peptides. Further research is essential to clarify the complex details of the mechanisms underlying this abnormality. This complexity arises from the notion that an improved understanding could contribute to the development of innovative therapeutic strategies aimed at targeting the endogenous opioid system in the context of fibromyalgia. Although progress is being made, a complete understanding of these complexities remains a significant challenge. This paradigm has the potential to revolutionize the complex management of fibromyalgia, although its implementation may experience challenges. The effectiveness of this approach depends on multiple factors, but the implications could be profound. Despite the challenges involved in this transformation, the potential for improving patient care is considerable, as this condition has long been inadequately treated.

Recommended Opioid Receptor Tool Compounds: Comparative In Vitro for Receptor Selectivity Profiles and In Vivo for Pharmacological Antinociceptive Profiles

Opioid agonist ligands bind opioid receptors and stimulate downstream signaling cascades for various biological processes including pain and reward. Historically, before cloning the receptors, muscle contraction assays using isolated organ tissues were used followed by radiolabel ligand binding assays on native tissues. Upon cloning of the opioid G protein-coupled receptors (GPCRs), cell assays using transfected opioid receptor DNA plasmids became the standard practice including 35S-GTPγS functional and cAMP based assays. A number of research laboratories have studied key "tool" reference opioid receptor ligands for decades and used them as control reference compounds. Some, but not all, of these commonly used tool compounds have been characterized and compared side by side in parallel assays for selectivity profiles at the different human opioid receptors isoforms. Herein, we performed the standard FLIPR calcium mobilization assay using HEK293 cells engineered to stably express the GαΔ6qi4myr in parallel, at human MOR, KOR, DOR, and NOP opioid receptors. The following tool compounds: morphine, fentanyl, oxycodone, DAMGO, DPDPE, U69593, deltorphin II, and nociceptin, were examined herein. These included the substance use disorder (SUD) compounds morphine, fentanyl, and oxycodone. Additionally, the antagonist tool compounds naloxone, NTI, norBNI, and β-FNA were assayed in parallel at the human MOR, KOR, DOR, and NOP opioid receptors. Furthermore, the agonist tool compounds were tested in the same in vivo tail-flick antinociception assays via intrathecal injection for ED50 potencies. These data provide both in vitro comparative pharmacology as a reference for cellular activities and in vivo antinociception profiles for these tool compounds.

The Rise of Fentanyl: Molecular Aspects and Forensic Investigations

Fentanyl is a synthetic opioid widely used for its potent analgesic effects in chronic pain management and intraoperative anesthesia. However, its high potency, low cost, and accessibility have also made it a significant drug of abuse, contributing to the global opioid epidemic. This review aims to provide an in-depth analysis of fentanyl's medical applications, pharmacokinetics, metabolism, and pharmacogenetics while examining its adverse effects and forensic implications. Special attention is given to its misuse, polydrug interactions, and the challenges in determining the cause of death in fentanyl-related fatalities. Fentanyl misuse has escalated dramatically, driven by its substitution for heroin and its availability through online platforms, including the dark web. Polydrug use, where fentanyl is combined with substances like xylazine, alcohol, benzodiazepines, or cocaine, exacerbates its toxicity and increases the risk of fatal outcomes. Fentanyl undergoes rapid distribution, metabolism by CYP3A4 into inactive metabolites, and renal excretion. Genetic polymorphisms in CYP3A4, OPRM1, and ABCB1 significantly influence individual responses to fentanyl, affecting its efficacy and potential for toxicity. Fentanyl's side effects include respiratory depression, cardiac arrhythmias, gastrointestinal dysfunction, and neurocognitive impairments. Chronic misuse disrupts brain function, contributes to mental health disorders, and poses risks for younger and older populations alike. Fentanyl-related deaths require comprehensive forensic investigations, including judicial inspections, autopsies, and toxicological analyses. Additionally, the co-administration of xylazine presents distinct challenges for the scientific community. Histological and immunohistochemical studies are essential for understanding organ-specific damage, while pharmacogenetic testing can identify individual susceptibilities. The growing prevalence of fentanyl abuse highlights the need for robust forensic protocols, advanced research into its pharmacogenetic variability, and strategies to mitigate its misuse. International collaboration, public education, and harm reduction measures are critical for addressing the fentanyl crisis effectively.

Diffuse Noxious Inhibitory Controls in Chronic Pain States: Insights from Pre-Clinical Studies

Diffuse noxious inhibitory control (DNIC), also known as conditioned pain modulation (CPM) in humans, is a paradigm wherein the heterotopic application of a noxious stimulus results in the attenuation of another spatially distant noxious input. The pre-clinical and clinical studies show the involvement of several neurochemical systems in DNIC/CPM and point to a major contribution of the noradrenergic, serotonergic, and opioidergic systems. Here, we thoroughly review the latest data on the monoaminergic and opioidergic studies, focusing particularly on pre-clinical models of chronic pain. We also conduct an in-depth analysis of these systems by integrating the available data with the descending pain modulatory circuits and the neurochemical systems therein to bring light to the mechanisms involved in the regulation of DNIC. The most recent data suggest that DNIC may have a dual outcome encompassing not only analgesic effects but also hyperalgesic effects. This duality might be explained by the underlying circuitry and the receptor subtypes involved therein. Acknowledging this duality might contribute to validating the prognostic nature of the paradigm. Additionally, DNIC/CPM may serve as a robust paradigm with predictive value for guiding pain treatment through more effective targeting of descending pain modulation.

Synthetic Methods of Quinoxaline Derivatives and their Potential Anti-inflammatory Properties

Quinoxaline molecule has gathered great attention in medicinal chemistry due to its vide spectrum of biological activities and has emerged as a versatile pharmacophore in drug discovery and development. Its structure comprises a bicyclic ring of benzopyrazine and displays a range of pharmacological properties, including antibacterial, antifungal, antiviral, anticancer, and antiinflammatory. This study aims to summarize the different strategies for the synthesis of quinoxalines and their anti-inflammatory properties acting through different mechanisms. Structure-activity relationships have also been discussed in order to determine the effect of structural modifications on anti-inflammatory potential. These analyses illuminate critical structural features required for optimal activity, driving the design and synthesis of new quinoxaline analogues with better antiinflammatory activities. The anti-inflammatory properties of quinoxalines are attributed to their inhibitory action on the expression of several inflammatory modulators such as cyclooxygenase, cytokines, nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB) and p38α Mitogen Activated Protein Kinase (p38α MAPK). Activators of nuclear factor erythroid 2-related factor 2 (NRF2) and agonistic effect on opioid receptors have also been discussed. Hence, this study may provide a future template for the design and development of novel quinoxaline derivatives acting through different molecular targets as potential anti-inflammatory agents with better efficacy and safety profiles.

Structure-Activity Relationships and Molecular Pharmacology of Positive Allosteric Modulators of the Mu-Opioid Receptor

Positive allosteric modulation of the mu-opioid receptor is a promising strategy to address the ever-growing problem of acute and chronic pain management. Positive allosteric modulators (PAMs) of the mu-opioid receptor could be employed to enhance the efficacy of endogenous opioid peptides to a degree that provides pain relief without the need for traditional opioid drugs. Alternatively, PAMs might be used to enhance the action of opioid drugs and so provide an opioid-sparing effect, allowing for the use of lower doses of opioid agonists and potentially decreasing associated side effects. BMS-986122 (2-(3-bromo-4-methoxyphenyl)-3-[(4-chlorophenyl)-sulfonyl]-thiazolidine) has been previously identified as a PAM of the mu-opioid receptor. In the present work, we have designed and synthesized 33 analogs of BMS-986122 to explore the structure-activity relationships of this scaffold and confirm its allosteric mechanism of action. Among several newly identified modulators, the most promising compound (14b) had improved activity to increase the in vitro potency of the standard mu-opioid agonist DAMGO and showed in vivo activity in mice to enhance the antinociceptive action of morphine.

The jeong and haan of Vincent van Gogh: neuropeptides of bondedness and loss

We introduce two Korean-named yet transcultural feelings, jeong and haan, to fill gaps in neuroscientific understanding of mammalian bondedness, loss, and aggression. Jeong is a visceral sense of connectedness to a person, place, or thing that may arise after proximity, yet does not require intimacy. The brain opioid theory of social attachment (BOTSA) supports the idea that jeong involves increased activity of enkephalins and beta-endorphins. We propose that withdrawal of jeong-related neuropeptides leads to original haan, a sense of "missingness" that is too subtle to be grossly dysphoric. Through narrative, cognitive appraisals, or moral assignments, however, original haan may transform into the feeling of constructed haan-resentment, bitterness, grievance, sorrow, or suppressed anger. In males, the transformation may be driven by arginine vasopressin, an ancient fight-or-flight neurohormone. Constructed haan may also be driven by vasopressin in females, though data is more sparse, and in both sexes it may depend on situational or societal context. Endogenous opioids inhibit vasopressin, so that when jeong diminishes, vasopressin release may become disinhibited. This relationship implies a companion to the BOTSA, which we articulate as the brain opioid and vasopressin theory of original and constructed haan (BOVTOCH). To illustrate, we reflect on borderline personality disorder, and Vincent van Gogh's self-severing of his ear while living and working with Paul Gauguin, and fearing abandonment by him; yet to understand Van Gogh more completely we also present the brain opioid theory of stable euphoric creativity (BOTSEC), to model the subjective "highs" associated with creative flow states. Together these brain opioid theories may help to explain how feelings related to social bondedness can influence a range of phenomena. For example, opioid drug dependence may be, at least partly, a maladaptive response to feelings of isolation or disconnectedness; the health protective effects of social bonds could be related to tonic exposure to endogenous opioids and their anti-inflammatory properties; endogenous opioid-based social relational enhancement may contribute to placebo responding. Finally we conclude by pointing out the possibility of virtuous cycles of social connectedness and creativity, when feelings of bondedness and euphoric flow reinforce one another through endogenous opioid elevation.

Microphysiological system to address the opioid crisis: A novel multi-organ model of acute opioid overdose and recovery

Opioids have been the primary method used to manage pain for hundreds of years, however the increasing prescription rate of these drugs in the modern world has led to a public health crisis of overdose related deaths. Naloxone is the current standard treatment for opioid overdose rescue, but it has not been fully investigated for potential off-target toxicity effects. The current methods for pharmaceutical development do not correlate well with pre-clinical animal studies compared to clinical results, creating a need for improved methods for therapeutic evaluation. Microphysiological systems (MPS) are a rapidly growing field, and the FDA has accepted this area of research to address this concern, offering a promising alternative to traditional animal models. This study establishes a novel multi-organ MPS model of acute opioid overdose and rescue to investigate the efficacy and off-target toxicity of naloxone in combination with opioids. By integrating primary human and human induced pluripotent stem cell (hiPSC)-derived cells, including preBötzinger complex neurons, liver, cardiac, and skeletal muscle components, this study establishes a novel functional multi-organ MPS model of acute opioid overdose and rescue to investigate the efficacy and off-target toxicity of naloxone in combination with opioids, with clinically relevant functional readouts of organ function. The system was able to successfully exhibit opioid overdose using methadone, as well as rescue using naloxone evidenced by the neuronal component activity. In addition to efficacy, the multi-organ platform was able to characterize potential off-target toxicity effects of naloxone, specifically in the cardiac component.

Simultaneous use of venlafaxine and calcium channel blockers on tolerance to morphine: The role of mitochondrial damage and oxidative stress in the brain

BACKGROUND

One of the reasons for tolerance to morphine is increased oxidative stress and dysfunction of cell mitochondria in the hippocampus. Venlafaxine and calcium channel blockers can protect mitochondrial function. The investigation of the role of mitochondrial damage and oxidative stress in the simultaneous use of venlafaxine and calcium channel blockers on the acute analgesic effects of morphine and the induction of tolerance to its effects in mice was assessed.

METHOD

In this experimental study, to induce tolerance to morphine, NMRI mice were treated with 50 mg/kg morphine for three consecutive days and 5 mg/kg morphine on the fourth day. Venlafaxine (20 mg/kg) alone or in combination with calcium channel blockers, nimodipine (10 mg/kg), and diltiazem (40 mg/kg) was administered 30 min before morphine, and the hot plate test was used. Then, hippocampal mitochondria were isolated by differential centrifugation method, and the levels of mitochondrial dehydrogenase activity, mitochondrial membrane potential, mitochondrial ROS production rate, as well as the content of glutathione and malondialdehyde in hippocampal mitochondria, were measured.

RESULTS

The administration of venlafaxine-nimodipine and venlafaxine-diltiazem increased morphine's acute analgesic effects (P < 0.05) and reduced the induction and expression of tolerance to the analgesic effects of morphine (P < 0.05). Morphine significantly decreased MTT and GSH and increased MDA, mitochondrial membrane damage, and ROS compared to the control group (P < 0.01). Injection of venlafaxine-nimodipine and also venlafaxine-diltiazem 30 min before morphine can improve these alterations (P < 0.05).

DISCUSSION AND CONCLUSION

Our data showed that the simultaneous use of venlafaxine with calcium channel blockers could increase the acute analgesic effects of morphine and reduce the induction and expression of tolerance to it. Also, the preventive and protective roles of simultaneous administration of venlafaxine and calcium channel blockers on morphine-induced mitochondrial oxidative stress and damage during the tolerance test were achieved.

New Psychoactive Substances: A Canadian perspective on emerging trends and challenges for the clinical laboratory

The production and use of New Psychoactive Substances (NPS) has skyrocketed over the last decade, causing major challenges for government authorities, public health agencies, and laboratories across the world. NPS are designed to mimic the psychoactive effects of unregulated or controlled drugs, while constantly being modified to evade drug control regulation. Hence, they are referred to as "legal highs", as they are technically legal to sell, possess, and use. NPS can be classified by their pharmacological mechanism of action and include cannabimimetic, depressants, dissociatives, hallucinogens, opioids, and stimulants. There is significant structural diversity within each NPS class, leading to variable detection using traditional clinical laboratory testing and complicating the interpretation of results. In this article, we review each of the NPS classes and summarize their associated mechanism of action, common structures, and metabolic pathways, and provide examples of recent drugs and emerging threats with a focus on Canadian drug trends. We also explore the current analytical advantages and limitations commonly faced by the clinical laboratory and provide insight on how toxicosurveillance can improve detection of NPS in the ever-changing NPS landscape.

BLA KOR inputs to the BNST regulate social stress-escalated alcohol consumption

Background

Aversive social experiences can lead to escalated drug consumption and increase the risk of relapse to drug seeking. Individuals who consume alcohol to alleviate the effects of social stress are more likely to develop an alcohol use disorder (AUD). Repeated social defeat stress (SDS) enhances the rewarding and reinforcing effects of alcohol. However, the neural mechanisms that underlie social stress-escalated alcohol drinking are not well understood. Here we explored the role of the dynorphin/kappa opioid receptor (Dyn/KOR) system in regulating social stress-escalated alcohol consumption.

Methods

Male and female mice were subjected to repeated SDS for 10 days following which they were left undisturbed in their home cages. They were then subject to intermittent access (IA) two-bottle choice alcohol consumption procedure. The effects of systemic and BNST-specific KOR antagonism using the selective KOR antagonist NorBNI on stress-escalated drinking were evaluated. Using chemogenetic approaches in Oprk1-Cre mice, we examined the role of KOR expressing cells in the basolateral amygdala (BLA KORs ) and BLA KOR -BNST pathway in social stress-escalated alcohol consumption.

Results

Repeated SDS increased alcohol consumption and preference in both males and females. Systemic KOR antagonism attenuated SDS-escalated alcohol consumption in both males and females. BNST -specific KOR antagonism also attenuated stress-escalated drinking in males. Finally, selective chemogenetic activation of BLA KORs and BKA KOR -BNST pathway attenuated social stress-escalated alcohol consumption in both sexes.

Conclusion

Our results suggest a significant role for BLA KOR projections to the BNST in regulating social stress-escalated alcohol consumption. Our results provide further evidence that the Dyn/KOR system maybe a viable target for medications development to tareat comorbid stress and AUD.

Exogenous Opioids and the Human Endocrine System: An Endocrine Society Scientific Statement

The use and misuse of opioids are a growing global problem. Although the effects of these drugs on the human endocrine system have been studied for decades, attention on their related clinical consequences, particularly on the hypothalamic-pituitary system and bone health, has intensified over recent years. This Statement appraises research data related to the impact of opioids on the gonadal and adrenal function. Whereas hypogonadism is well recognized as a side effect of opioids, the significance of their inhibitory actions on the hypothalamic-pituitary-adrenal system and the occurrence of clinically relevant adrenal insufficiency is not fully elucidated. The often-inconsistent results of studies investigating how opioids affect the secretion of GH, prolactin, arginine vasopressin, and oxytocin are assessed. The accumulating evidence of opioid actions on bone metabolism and their negative sequelae on bone mineral density and risk of fracture are also reviewed. In each section, available data on diagnostic and management approaches for opioid endocrine sequelae are described. This Statement highlights a plethora of gaps in research associated with the effects and clinical consequences of opioids on the endocrine system. It is anticipated that addressing these gaps will improve the care of people using or misusing opioids worldwide. The Statement is not intended to serve as a guideline or dictate treatment decisions.

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 as recombinant receptors in heterologous systems and with native receptors in rodent brain; signaling was examined by measuring GTP binding, β-arrestin recruitment, MAPK activation, and neurotransmitter release. Although micromolar concentrations of ketamine alone had weak agonist activity at μ 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 (μ, δ, and κ) showed synergism with submicromolar concentrations of ketamine and either methionine-enkephalin (Met-enk), leucine-enkephalin (Leu-enk), and/or dynorphin A17 (Dyn A17), albeit the extent of synergy was variable between receptors and peptides. S-ketamine exhibited higher modulatory effects compared with R-ketamine or racemic ketamine, with ∼100% increase in efficacy. Importantly, the ketamine metabolite 6-hydroxynorketamine showed robust allosteric modulatory activity at μ 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: This study found that ketamine and its major biologically active metabolites function as potent allosteric modulators of μ, δ, and κ 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.

Impact of renal impairment on the pharmacokinetic profile of intravenous difelikefalin, a kappa opioid receptor agonist for the treatment of pruritus

BACKGROUND

Difelikefalin is a selective kappa opioid receptor agonist that is approved for the treatment of moderate-to-severe pruritus associated with chronic kidney disease in adults undergoing hemodialysis (HD). In this study, we assessed the pharmacokinetics (PK) of intravenous (IV) difelikefalin in healthy subjects, in non-dialysis-dependent (NDD) subjects with varying stages of kidney disease, and in subjects with end-stage renal disease (ESRD) undergoing HD.

METHODS

The PK and safety of single IV doses of difelikefalin (3.0 mcg/kg) were initially evaluated in NDD subjects with mild, moderate, or severe renal impairment compared with matched healthy subjects. Based on those data, the PK and safety of 3 dose levels of IV difelikefalin (0.5, 1.0, or 2.5 mcg/kg) were compared with matched placebo in subjects undergoing HD with each dose administered following dialysis, 3 times over a 1-week treatment period).

RESULTS

Single IV dosing of difelikefalin in NDD subjects (N = 36) with mild renal impairment demonstrated comparable exposure to healthy subjects with normal renal function, while subjects with moderate or severe renal impairment had higher total exposure. NDD subjects with severe renal impairment had higher total exposure compared with those with moderate renal impairment (i.e., exposure in severe NDD > moderate NDD > mild NDD ≈ healthy subjects). Clearance of difelikefalin correspondingly decreased with increasing renal impairment. In the multiple-dose study in subjects with ESRD undergoing HD (N = 19), IV difelikefalin demonstrated dose proportionality and was shown to be mostly cleared by dialysis; steady state was achieved with the second dose on day 3. Safety findings for all subjects were consistent with the known profile of IV difelikefalin.

CONCLUSIONS

IV difelikefalin was well tolerated. Similar exposure was observed in NDD subjects with mild renal impairment compared with healthy subjects with normal renal function, with reduced clearance and higher exposure in NDD subjects with moderate or severe renal impairment. Dose proportionality was demonstrated in subjects with ESRD undergoing HD administered IV difelikefalin 3 times per week following dialysis and was shown to be mostly cleared by dialysis.

TRIAL REGISTRATION

Single-dose study: NA; multiple-dose study: ClinicalTrials.gov registration number NCT02229929, first registration 03/09/2014.

Transcriptional reprogramming post-peripheral nerve injury: A systematic review

Neuropathic pain is characterised by periodic or continuous hyperalgesia, numbness, or allodynia, and results from insults to the somatosensory nervous system. Peripheral nerve injury induces transcriptional reprogramming in peripheral sensory neurons, contributing to increased spinal nociceptive input and the development of neuropathic pain. Effective treatment for neuropathic pain remains an unmet medical need as current therapeutics offer limited effectiveness and have undesirable effects. Understanding transcriptional changes in peripheral nerve injury-induced neuropathy might offer a path for novel analgesics. Our literature search identified 65 papers exploring transcriptomic changes post-peripheral nerve injury, many of which were conducted in animal models. We scrutinize their transcriptional changes data and conduct gene ontology enrichment analysis to reveal their common functional profile. Focusing on genes involved in 'sensory perception of pain' (GO:0019233), we identified transcriptional changes for different ion channels, receptors, and neurotransmitters, shedding light on its role in nociception. Examining peripheral sensory neurons subtype-specific transcriptional reprograming and regeneration-associated genes, we delved into downstream regulation of hypersensitivity. Identifying the temporal program of transcription regulatory mechanisms might help develop better therapeutics to target them effectively and selectively, thus preventing the development of neuropathic pain without affecting other physiological functions.

Designed dualsteric modulators: A novel route for drug discovery

Orthosteric and allosteric modulators, which constitute the majority of current drugs, bind to the orthosteric and allosteric sites of target proteins, respectively. However, the clinical efficacy of these agents is frequently compromised by poor selectivity or reduced potency. Dualsteric modulators feature two linked pharmacophores that bind to orthosteric and allosteric sites of the target proteins simultaneously, thereby offering a promising avenue to achieve both potency and specificity. In this review, we summarize recent structures available for dualsteric modulators in complex with their target proteins, elucidating detailed drug-target interactions and dualsteric action patterns. Moreover, we provide a design and optimization strategy for dualsteric modulators based on structure-based drug design approaches.

Aniquinazoline B, a Fungal Natural Product, Activates the μ-Opioid Receptor

The development of new μ-opioid receptor (MOR) agonists without the undesirable side effects, such as addiction or respiratory depression, has been a difficult challenge over the years. In the search for new compounds, we screened our chemical database of over 40.000 substances and further assessed the best 100 through molecular docking. We selected the top 10 compounds and evaluated them for their biological activity and potential to influence cyclic adenosine monophosphate (cAMP) levels. From the tested compounds, compound 7, called aniquinazoline B, belonging to the quinazolinone alkaloids class and isolated from the marine fungus Aspergillus nidulans, showed promising results, by inhibiting cAMP levels and in vitro binding to MOR, verified through microscale thermophoresis. Transcriptomic data investigation profiled the genes affected by compound 7 and discovered activation of different pathways compared to opioids. The western blot analysis revealed compound 7 as a balanced ligand, activating both p-ERK1/2 and β-arrestin1/2 pathways, showing this is a favorable candidate to be further tested.

Identification of Cytisine Derivatives as Agonists of the Human Delta Opioid Receptor by Supercomputer-Based Virtual Drug Screening and Transcriptomics

Delta opioid receptors (DORs) are rising as therapeutic targets, not only for the treatment of pain but also other neurological disorders (e.g., Parkinson's disease). The advantage of DOR agonists compared to μ-opioid receptor agonists is that they have fewer side effects and a lower potential to induce tolerance. However, although multiple candidates have been tested in the past few decades, none have been approved for clinical use. The current study focused on searching for new DOR agonists by screening a chemical library containing 40,000 natural and natural-derived products. The functional activity of the top molecules was evaluated in vitro through the cyclic adenosine monophosphate accumulation assay. Compound 3 showed promising results, and its activity was further investigated through transcriptomic methods. Compound 3 inhibited the expression of TNF-α, prevented NF-κB translocation to the nucleus, and activated the G-protein-mediated ERK1/2 pathway. Additionally, compound 3 is structurally different from known DOR agonists, making it a valuable candidate for further investigation for its anti-inflammatory and analgesic potential.

The Effects of Eating a Traditional High Fat/High Carbohydrate or a Ketogenic Diet on Sensitivity of Female Rats to Morphine

Patients diagnosed with obesity are prescribed opioid medications at a higher rate than the general population; however, it is not known if eating a high fat diet might impact individual sensitivity to these medications. To explore the hypothesis that eating a high fat diet increases sensitivity of rats to the effects of morphine, 24 female Sprague-Dawley rats (n = 8/diet) ate either a standard (low fat) laboratory chow (17% kcal from fat), a high fat/low carbohydrate (ketogenic) chow (90.5% kcal from fat), or a traditional high fat/high carbohydrate chow (60% kcal from fat). Morphine-induced antinociception was assessed using a warm water tail withdrawal procedure, during which latency (in seconds) for rats to remove their tail from warm water baths was recorded following saline or morphine (0.32-56 mg/kg, i.p.) injections. Morphine was administered acutely and chronically (involving 18 days of twice-daily injections, increasing in 1/4 log dose increments every 3 days: 3.2-56 mg/kg, i.p., to induce dependence and assess tolerance). The adverse effects of morphine (i.e., tolerance, withdrawal, and changes in body temperature) were assessed throughout the study. Acute morphine induced comparable antinociception in rats eating different diets, and all rats developed tolerance following chronic morphine exposure. Observable withdrawal signs and body temperature were also comparable among rats eating different diets; however, withdrawal-induced weight loss was less severe for rats eating ketogenic chow. These results suggest that dietary manipulation might modulate the severity of withdrawal-related weight loss in ways that could be relevant for patients.

The effect of intrathecal pethidine on post-spinal anesthesia shivering after cesarean section: a systematic review and meta-analysis

Background

Spinal anesthesia is the most preferred method for cesarean section (C-section). This meta-analysis was performed to determine the effect of low and high intrathecal doses of pethidine on the maternal outcomes after C-section.

Methods

A systematic search of PubMed, Scopus, Cochrane Library, and Google Scholar was performed. Random-effects meta-analysis was performed to derive odds ratios (ORs) from dichotomous data.

Results

Seventeen randomized controlled trials with 1304 C-section patients were included. Patients who had received intrathecal pethidine experienced decreased shivering and intensity of shivering (OR 0.13; P<0.001) and (OR 0.21; P<0.001), respectively. Moreover, vomiting (OR 2.47; P=0.002) and pruritus (OR 5.92; P<0.001) were significantly higher in the pethidine group. There was no statistically significant difference in the incidence of nausea (OR 2.55; P=0.06) and hypotension (OR 0.91; P=0.67).

Conclusions

Intrathecal pethidine can effectively decrease shivering, although it increases the risk of vomiting and pruritus. No significant difference was found both in the maternal hypotension and nausea.

Unlocking opioid neuropeptide dynamics with genetically encoded biosensors

Neuropeptides are ubiquitous in the nervous system. Research into neuropeptides has been limited by a lack of experimental tools that allow for the precise dissection of their complex and diverse dynamics in a circuit-specific manner. Opioid peptides modulate pain, reward and aversion and as such have high clinical relevance. To illuminate the spatiotemporal dynamics of endogenous opioid signaling in the brain, we developed a class of genetically encoded fluorescence sensors based on kappa, delta and mu opioid receptors: κLight, δLight and µLight, respectively. We characterized the pharmacological profiles of these sensors in mammalian cells and in dissociated neurons. We used κLight to identify electrical stimulation parameters that trigger endogenous opioid release and the spatiotemporal scale of dynorphin volume transmission in brain slices. Using in vivo fiber photometry in mice, we demonstrated the utility of these sensors in detecting optogenetically driven opioid release and observed differential opioid release dynamics in response to fearful and rewarding conditions.

Neural circuit-selective, multiplexed pharmacological targeting of prefrontal cortex-projecting locus coeruleus neurons drives antinociception

Selective manipulation of neural circuits using optogenetics and chemogenetics holds great translational potential but requires genetic access to neurons. Here, we demonstrate a general framework for identifying genetic tool-independent, pharmacological strategies for neural circuit-selective modulation. We developed an economically accessible calcium imaging-based approach for large-scale pharmacological scans of endogenous receptor-mediated neural activity. As a testbed for this approach, we used the mouse locus coeruleus due to the combination of its widespread, modular efferent neural circuitry and its wide variety of endogenously expressed GPCRs. Using machine learning-based action potential deconvolution and retrograde tracing, we identified an agonist cocktail that selectively inhibits medial prefrontal cortex-projecting locus coeruleus neurons. In vivo, this cocktail produces synergistic antinociception, consistent with selective pharmacological blunting of this neural circuit. This framework has broad utility for selective targeting of other neural circuits under different physiological and pathological states, facilitating non-genetic translational applications arising from cell type-selective discoveries.

L-asparaginase induces IP3R-mediated ER Ca2+ release by targeting µ-OR1 and PAR2 and kills acute lymphoblastic leukemia cells

L-asparaginase is a standard therapeutic option for acute lymphoblastic leukemia (aLL), a hematologic cancer that claims the most lives of pediatric cancer patients. Previously, we demonstrated that L-asparaginase kills aLL cells via a lethal rise in [Ca2+]i due to IP3R-mediated ER Ca2+ release followed by calpain-1-Bid-caspase-3/12 activation (Blood, 133, 2222-2232). However, upstream targets of L-asparaginase that trigger IP3R-mediated ER Ca2+ release remain elusive. Here, we show that L-asparaginase targets µ-OR1 and PAR2 and induces IP3R-mediated ER Ca2+ release in aLL cells. In doing so, µ-OR1 plays a major role while PAR2 plays a minor role. Utilizing PAR2- and µ-OR1-knockdown cells, we demonstrate that L-asparaginase stimulation of µ-OR1 and PAR2 relays its signal via Gαi and Gαq, respectively. In PAR2-knockdown cells, stimulation of adenylate cyclase with forskolin or treatment with 8-CPT-cAMP reduces L-asparaginase-induced µ-OR1-mediated ER Ca2+ release, suggesting that activation of µ-OR1 negatively regulates AC and cAMP. In addition, the PKA inhibitor 14-22 amide (myr) alone evokes ER Ca2+ release, and subsequent L-asparaginase treatment does not induce further ER Ca2+ release, indicating the involvement of PKA inhibition in L-asparaginase-induced µ-OR1-mediated ER Ca2+ release, which can bypass the L-asparaginase-µ-OR1-AC-cAMP loop. This coincides with (a) the decreases in PKA-dependent inhibitory PLCβ3 Ser1105 phosphorylation, which prompts PLCβ3 activation and ER Ca2+ release, and (b) BAD Ser118 phosphorylation, which leads to caspase activation and apoptosis. Thus, our findings offer new insights into the Ca2+-mediated mechanisms behind L-asparaginase-induced aLL cell apoptosis and suggest that PKA may be targeted for therapeutic intervention for aLL.

Sex differences in sensitivity to fentanyl effects in mice: Behavioral and molecular findings during late adolescence

PURPOSE

Sex differences play a crucial role in understanding vulnerability to opioid addiction, yet there have been limited preclinical investigations of this effect during the transition from adolescence to adulthood. The present study compared the behaviors of male and female rodents in response to fentanyl treatment and targeted molecular correlates in the striatum and medial prefrontal cortex.

MATERIALS AND METHODS

Thirty adolescent C57BL/6J mice underwent a 1-week fentanyl treatment with an escalating dose. In addition to evaluating locomotor activity and anxiety-related parameters, we also assessed naloxone-induced fentanyl acute withdrawal jumps. We employed real-time quantitative PCR (qPCR) to assess overall gene expression of dopaminergic receptors (Drd1, Drd2, Drd4 and Drd5) and the μ-opioid receptor Oprm1. The levels of epigenetic base modifications including 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC) were assessed on CpG islands of relevant genes.

RESULTS

Females had higher locomotor activity than males after chronic fentanyl treatment, and they exhibited higher fentanyl withdrawal jumping behavior induced by naloxone. Females also presented lower Drd4 gene expression and DNA methylation (5mC + 5hmC) in the striatum. We found that locomotor activity and fentanyl withdrawal jumps were negatively correlated with Drd4 methylation and gene expression in the striatum, respectively.

CONCLUSIONS

The findings suggested that female mice displayed heightened sensitivity to the effects of fentanyl treatment during the transition from adolescence to adulthood. This effect may be associated with molecular alterations related to the Drd4 gene.

Nanotechnology-Enhanced Naloxone and Alternative Treatments for Opioid Addiction

Opioids are commonly prescribed to address intense, ongoing pain associated with cancer, as well as long-lasting noncancer-related pain when alternative methods have proven ineffective. Individuals who exhibit both chronic pain and misuse of opioids face a significant danger of experiencing adverse health outcomes and the potential loss of life related to opioid use. Thus, there is a current movement to prescribe naloxone to those considered high-risk for opioid overdose. Naloxone has been explored as an antidote to reverse acute respiratory depression. Conversely, naloxone can give rise to other problems, including hypertension and cardiac arrhythmias. Thus, the importance of nanotechnology-enabled drug delivery strategies and their role in mitigating naloxone side-effects are significant. In this review, we explore the latest advancements in nanotechnology-enabled naloxone and alternative methods for addressing the opioid crisis through the utilization of non-opioid natural alternatives for chronic pain management.

Delta opioid receptors engage multiple signaling cascades to differentially modulate prefrontal GABA release with input and target specificity

Opioids regulate circuits associated with motivation and reward across the brain. Of the opioid receptor types, delta opioid receptors (DORs) appear to have a unique role in regulating the activity of circuits related to reward without a liability for abuse. In neocortex, DORs are expressed primarily in interneurons, including parvalbumin- and somatostatin-expressing interneurons that inhibit somatic and dendritic compartments of excitatory pyramidal cells, respectively. But how DORs regulate transmission from these key interneuron classes is unclear. We found that DORs regulate inhibition from these interneuron classes using different G-protein signaling pathways that both converge on presynaptic calcium channels, but regulate distinct aspects of calcium channel function. This imposes different temporal filtering effects, via short-term plasticity, that depend on how calcium channels are regulated. Thus, DORs engage differential signaling cascades to regulate inhibition depending on the postsynaptic target compartment, with different effects on synaptic information transfer in somatic and dendritic domains.

Integrating mechanistic-based and classification-based concepts into perioperative pain management: an educational guide for acute pain physicians

Chronic pain begins with acute pain. Physicians tend to classify pain by duration (acute vs chronic) and mechanism (nociceptive, neuropathic and nociplastic). Although this taxonomy may facilitate diagnosis and documentation, such categories are to some degree arbitrary constructs, with significant overlap in terms of mechanisms and treatments. In clinical practice, there are myriad different definitions for chronic pain and a substantial portion of chronic pain involves mixed phenotypes. Classification of pain based on acuity and mechanisms informs management at all levels and constitutes a critical part of guidelines and treatment for chronic pain care. Yet specialty care is often siloed, with advances in understanding lagging years behind in some areas in which these developments should be at the forefront of clinical practice. For example, in perioperative pain management, enhanced recovery protocols are not standardized and tend to drive treatment without consideration of mechanisms, which in many cases may be incongruent with personalized medicine and mechanism-based treatment. In this educational document, we discuss mechanisms and classification of pain as it pertains to commonly performed surgical procedures. Our goal is to provide a clinical reference for the acute pain physician to facilitate pain management decision-making (both diagnosis and therapy) in the perioperative period.