Search Results (83)

The presence and function of the opioidergic system in sensory dorsal root ganglia (DRG) was demonstrated in various animal models of pain. To endorse recent functional and transcriptional evidence of opioid receptors in human DRG, this study compared morphological and transcriptional evidence in human and rat DRG using immunofluorescence confocal microscopy and mRNA transcript analysis. Specifically, it examined the neuronal expression of mu (MOR), delta (DOR), and kappa (KOR) opioid receptors, opioid peptide precursors (POMC, PENK, and PDYN), and key pain-signaling molecules. The results demonstrate abundant immunoreactivity in human DRG for key pain transduction receptors, including the thermosensitive ion channels TRPV1, TRPV4 and TRPA1, mechanosensitive PIEZO1 and PIEZO2, and the nociceptive-specific Nav1.8. They colocalized with calcitonin gene-related peptide (CGRP), a marker for peptidergic sensory neurons. Within this same subpopulation, we identified MOR, DOR, and KOR, while their ligand precursors were less abundant. Notably, the mRNA transcripts of MOR and PENK in human DRG were highest among the opioid-related genes; however, they were considerably lower than those of key pain-signaling molecules. These findings were corroborated by functional evidence in demonstrating the fentanyl-induced inhibition of voltage-gated calcium currents in rat DRG, which was antagonized by naloxone. The immunohistochemical and transcriptional demonstration of opioid receptors and their endogenous ligands in both human and rat DRG support recent electrophysiologic and in situ hybridization evidence in human DRG and confirms their potential as analgesic targets. This peripherally targeted approach has the advantage of mitigating central opioid-related side effects, endorsing the potential of future translational pain research from rodent models to humans. Full article

Background/Objectives: Hemorphins, considered to be bioactive atypical oligopeptides, are products of hemoglobin metabolism. Recently, our team reported the synthesis and characterization of three N-modified analogs of hemorphin-4 (H4) with rhodamine B (Rh). In the present study, the Rh-1, Rh-2, and Rh-3 compounds were intracerebroventricularly infused at doses of 1, 2.5, 5, and 10 µg/5 µL, respectively, and evaluated for their antiseizure activity in 6-Hz and maximal electroshock (MES) tests and in a pentylenetetrazol (PTZ)-induced kindling model in mice. Phenytoin and diazepam were used as the reference drugs. The role of opioid receptors (ORs) underlying their mechanism of action was also evaluated in silico and pharmacologically. Results: The three Rh-H4 compounds showed a good safety profile at a concentration of 100 µg/mL in the mouse embryonic fibroblasts. They suppressed psychomotor seizures and seizure spreading as follows: Rh-1 at doses of 5 and 10 µg/5 µL, Rh-2 at the highest dose, and Rh-3 at doses of 1–10 µg/5 µL, respectively. Administered at doses of 5 µg/5 µL (Rh-1 and Rh-3) and 10 µg/5 µL (Rh-2), the compounds suppressed clonic seizures in the kindled mice comparable to the reference drug diazepam. A combination of selective delta (DOR), kappa (KOR), and mu (MOR) OR antagonists with the highest doses of the Rh-1, Rh-2, and Rh-3 compounds was used to elucidate the possible role of ORs in the underlying mechanism related to their protective activity against seizure spread. Only the selective DOR antagonist, natrindole, suppressed the effect of the Rh-1 peptide analog on seizures. The OR antagonist naloxone prevented the antiseizure activity of Rh-1 in the kindled mice. The results of docking analysis also showed the model-specific interaction of the three Rh-H4 compounds with the OR. Conclusions: Our results suggest that the antiseizure activity of Rh-1 is mediated by the OR, and in particular by the DOR, while the mechanism underlying the antiseizure effect of Rh-3 is more complex and may involve other receptors. Full article

Objective: To narratively review currently available antidepressants and future potential antidepressants as monotherapy for the treatment of depressive disorders. Methods: Selective serotonin reuptake inhibitors (SSRIs), serotonin norepinephrine reuptake inhibitors (SNRIs), dopamine reuptake inhibitor (bupropion), tricyclic antidepressants (TCAs), and monoamine oxidase inhibitors (MAOIs) were reviewed according to the results from Sequenced Treatment Alternatives to Relieve Depression (STAR*D) Study and systematic reviews. For the rest of the antidepressants, a PubMed/Medline search was conducted with priority for systematic reviews. For drugs in development for depressive disorders, PubMed, Google, and Clinicaltrials.gov databases were used. Results: The STAR*D Study demonstrated that sertraline, venlafaxine, and bupropion monotherapy had similar efficacy in patients with major depressive disorder (MDD) who failed citalopram. A network meta-analyses of randomized, placebo-controlled trials found that SSRIs, SNRIs, bupropion, TCAs, mirtazapine, and agomelatine had similar relative efficacy compared to placebo, but had different acceptability. Gepirone had more failed/negative studies and smaller effect size relative to placebo compared to other antidepressants. The combination of dextromethorphan and bupropion, ketamine infusion, and intranasal esketamine had faster onset of action but similar effect size compared to monoamine-based antidepressants as monotherapy. Brexanolone and zuranolone are effective in postpartum depression (PPD), but the effect size of zuranolone in MDD as monotherapy or adjunctive therapy was very small. Psychedelics, glutamate receptor-related agents, kappa opioid receptor antagonists, orexin receptor antagonists, new anti-inflammatory agents, and biomarker-based antidepressant therapy have been under investigation for depressive disorders. Psychedelics showed faster onset of action, large effect size, and long durability. Conclusions: Monoamine-based antidepressants likely continue to be the mainstream antidepressants for depressive disorder. NMDA receptor antagonists and neurosteroid antidepressants will play a bigger role with the improvement of accessibility. Psychedelics may become a game changer if phase III studies validate their efficacy and safety in depressive disorders. Full article

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. Full article

Kappa opioid receptor (KOR) agonists have well-established antinociceptive effects. However, many KOR agonists have negative side effects, which limit their therapeutic potential. Some researchers have suggested that the development of biased agonists that preferentially stimulate KOR G-protein pathways over β-arrestin pathways may yield drugs with fewer adverse side effects. This was investigated in the current study. We describe the synthesis and characterization of three U50,488 analogues, 1, 2, and 3. We evaluated the acute and chronic antinociceptive effects of these compounds in mice using the warm-water tail flick assay and in a paclitaxel-induced neuropathic pain model. Side effects were investigated using open-field, passive wire hang, rotarod, elevated zero maze, conditioned place aversion, and whole-body plethysmography, with some tests being conducted in KOR or β-arrestin2 knock out mice. All compounds were highly potent, full agonists of the KOR, with varying signaling biases in vitro. In the warm-water tail withdrawal assay, these agonists were ~10 times more potent than U50,488, but not more efficacious. All KOR agonists reversed paclitaxel-induced neuropathic pain, without tolerance. Compound 3 showed no significant side effects on any test. Signaling bias did not correlate with the antinociceptive or side effects of any compounds and knockout of β-arrestin2 had no effect on U50,488-induced sedation or motor incoordination. These findings highlight the therapeutic potential of 3, with its lack of side effects typically associated with KOR agonists, and also suggest that G-protein signaling bias is a poor predictor of KOR agonist-induced side effects. Full article

Bipolar disorder’s etiology involves genetics, environmental factors, and gene–environment interactions, underlying its heterogeneous nature and treatment complexity. In 2020, Forstner and colleagues catalogued 378 sequence variants co-segregating with familial bipolar disorder. A notable candidate was an R59Q missense mutation in the PDZ (PSD-95/Dlg1/ZO-1) domain of RGS12. We previously demonstrated that RGS12 loss removes negative regulation on the kappa opioid receptor, disrupting basal ganglia dopamine homeostasis and dampening responses to dopamine-eliciting psychostimulants. Here, we investigated the R59Q variation in the context of potential PDZ domain functional alterations. We first validated a new target for the wildtype RGS12 PDZ domain—the SAPAP3 C-terminus—by molecular docking, surface plasmon resonance (SPR), and co-immunoprecipitation. While initial molecular dynamics (MD) studies predicted negligible effects of the R59Q variation on ligand binding, SPR showed a significant reduction in binding affinity for the three peptide targets tested. AlphaFold2-generated models predicted a modest reduction in protein–peptide interactions, which is consistent with the reduced binding affinity observed by SPR, suggesting that the substituted glutamine side chain may weaken the affinity of RGS12 for its in vivo binding targets, likely through allosteric changes. This difference may adversely affect the CNS signaling related to dynorphin and dopamine in individuals with this R59Q variation, potentially impacting bipolar disorder pathophysiology. Full article

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. Full article

We recently developed a series of nalfurafine analogs (TK10, TK33, and TK35) that may serve as non-addictive candidate analgesics. These compounds are mixed-action agonists at the kappa and delta opioid receptors (KOR and DOR, respectively) and produce antinociception in a mouse warm-water tail-immersion test while failing to produce typical mu opioid receptor (MOR)-mediated side effects. The warm-water tail-immersion test is an assay of pain-stimulated behavior vulnerable to false-positive analgesic-like effects by drugs that produce motor impairment. Accordingly, this study evaluated TK10, TK33, and TK35 in a recently validated assay of pain-related behavioral depression in mice that are less vulnerable to false-positive effects. For comparison, we also evaluated the effects of the MOR agonist/analgesic hydrocodone (positive control), the neurokinin 1 receptor (NK1R) antagonist aprepitant (negative control), nalfurafine as a selective KOR agonist, SNC80 as a selective DOR agonist, and a nalfurafine/SNC80 mixture. Intraperitoneal injection of dilute lactic acid (IP lactic acid) served as a noxious stimulus to depress vertical and horizontal locomotor activity in male and female ICR mice. IP lactic acid-induced locomotor depression was alleviated by hydrocodone but not by aprepitant, nalfurafine, SNC80, the nalfurafine/SNC80 mixture, or the KOR/DOR agonists. These results suggest that caution is warranted in advancing mixed-action KOR/DOR agonists as candidate analgesics. Full article

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

The opioid epidemic continues to be a major public health issue that includes millions of people who inject drugs (PWID). PWID have increased incidence of serious infections, including HIV as well as metabolic and inflammatory sequelae. We sought to discern the extent of systemic alterations in humoral immunity associated with injection drug use, including alterations in the plasma proteome and its regulation of B cell responsiveness. Comprehensive plasma proteomics analysis of HIV negative/hepatitis C negative individuals with a history of recent injection heroin use was performed using mass spectrometry and ELISA. The effects of plasma from PWID and healthy controls on the in vitro proliferation and transcriptional profile of B cell responses to stimulation were determined by flow cytometry and RNA-Seq. The plasma proteome of PWID was distinct from healthy control individuals, with numerous immune-related analytes significantly altered in PWID, including complement (C3, C5, C9), immunoglobulin (IgD, IgM, kappa light chain), and other inflammatory mediators (CXCL4, LPS binding protein, C-reactive protein). The plasma of PWID suppressed the in vitro proliferation of B cells. Transcriptome analysis indicated that PWID plasma treatment increased B cell receptor and CD40 signaling and shifted B cell differentiation from plasma cell-like toward germinal center B cell-like transcriptional profiles. These results indicate that the systemic inflammatory milieu is substantially altered in PWID and may impact their B cell responses. Full article

Neuroplasticity in the central nucleus of the amygdala (CeA) plays a key role in the modulation of pain and its aversive component. The dynorphin/kappa opioid receptor (KOR) system in the amygdala is critical for averse-affective behaviors in pain conditions, but its mechanisms are not well understood. Here, we used chemogenetic manipulations of amygdala KOR-expressing neurons to analyze the behavioral consequences in a chronic neuropathic pain model. For the chemogenetic inhibition or activation of KOR neurons in the CeA, a Cre-inducible viral vector encoding Gi-DREADD (hM4Di) or Gq-DREADD (hM3Dq) was injected stereotaxically into the right CeA of transgenic KOR-Cre mice. The chemogenetic inhibition of KOR neurons expressing hM4Di with a selective DREADD actuator (deschloroclozapine, DCZ) in sham control mice significantly decreased inhibitory transmission, resulting in a shift of inhibition/excitation balance to promote excitation and induced pain behaviors. The chemogenetic activation of KOR neurons expressing hM3Dq with DCZ in neuropathic mice significantly increased inhibitory transmission, decreased excitability, and decreased neuropathic pain behaviors. These data suggest that amygdala KOR neurons modulate pain behaviors by exerting an inhibitory tone on downstream CeA neurons. Therefore, activation of these interneurons or blockade of inhibitory KOR signaling in these neurons could restore control of amygdala output and mitigate pain. Full article

Diverse chemical and pharmacological strategies are currently being explored to minimize the unwanted side effects of currently used opioid analgesics while achieving effective pain relief. The use of multitarget ligands with activity at more than one receptor represents a promising therapeutic approach. We recently reported a bifunctional peptide-based hybrid LENART01 combining dermorphin and ranatensin pharmacophores, which displays activity to the mu-opioid receptor (MOR) and dopamine D2 receptor (D2R) in rat brains and spinal cords. In this study, we investigated the in vitro binding and functional activities to the human MOR and the in vivo pharmacology of LENART01 in mice after subcutaneous administration. In vitro binding assays showed LENART01 to bind and be selective to the human MOR over the other opioid receptor subtypes and delta, kappa and nociceptin receptors. In the [³⁵S]GTPγS binding assay, LENART01 acted as a potent and full agonist to the human MOR. In mice, LENART01 produced dose-dependent antinociceptive effects in formalin-induced inflammatory pain, with increased potency than morphine. Antinociceptive effects were reversed by naloxone, indicating MOR activation in vivo. Behavioral studies also demonstrated LENART01’s properties to induce less adverse effects without locomotor dysfunction and withdrawal syndrome compared to conventional opioid analgesics, such as morphine. LENART01 is the first peptide-based MOR-D2R ligand known to date and the first dual MOR-dopamine D2R ligand for which in vivo pharmacology is reported with antinociceptive efficacy and reduced opioid-related side effects. Our current findings may pave the way to new pain therapeutics with limited side effects in acute and chronic use. Full article

Decades of drug development research have explored a vast chemical space for highly active compounds. The exponential growth of virtual libraries enables easy access to billions of synthesizable molecules. Computational modeling, particularly molecular docking, utilizes physics-based calculations to prioritize molecules for synthesis and testing. Nevertheless, the molecular docking process often yields docking poses with favorable scores that prove to be inaccurate with experimental testing. To address these issues, several approaches using machine learning (ML) have been proposed to filter incorrect poses based on the crystal structures. However, most of the methods are limited by the availability of structure data. Here, we propose a new pose classification approach, PECAN2 (Pose Classification with 3D Atomic Network 2), without the need for crystal structures, based on a 3D atomic neural network with Point Cloud Network (PCN). The new approach uses the correlation between docking scores and experimental data to assign labels, instead of relying on the crystal structures. We validate the proposed classifier on multiple datasets including human mu, delta, and kappa opioid receptors and SARS-CoV-2 Mpro. Our results demonstrate that leveraging the correlation between docking scores and experimental data alone enhances molecular docking performance by filtering out false positives and false negatives. Full article

Knowing that biomolecules, such as β-amyrin and α-amyrin, have some pharmacological effects, the aim of this study was directed towards exploring the protective effect of Tomato Peel and Seed Extract (TPSE) for its soothing function but also for its capacity to modulate the adrenal axis, which is involved in stress response. Ex vivo tests were carried out on skin explants to evaluate the effectiveness of TPSE formulated at 0.5% on Calcitonin Gene-Related Peptide (CGRP) and IL-10 release, Kappa Opioid Receptor (KOR), and Caspase 14 expression. An in vivo study combined a clinical evaluation of skin homogeneity and psychological parameters as well as an analysis of salivary cortisol and dehydroepiandrosterone concentrations. All measurements were carried out at the beginning and after 28 days of applying a TPSE face cream. TPSE regulated not only the release of CGRP, IL-10, and the expression of Caspase 14, reflecting anti-neurogenic and anti-inflammatory properties, but also modulated KORs. Twenty-eight days of TPSE application induced a significant decrease in intensity and extent erythrosis, a lower output of salivary cortisol, and a significant increase in pleasant emotions when compared to placebo. These results provide encouragement to continue exploring the impact of cosmetic ingredients on psychophysiological parameters to improve skin health and well-being. Full article

As the global obesity rate increases, so does the urgency to find effective anti-obesity drugs. In the search for therapeutic targets, central nervous system (CNS) mechanisms engaged in the regulation of energy expenditure and food intake, such as the opioid and dopamine systems, are crucial. In this study, we examined the effect on body weight of two drugs: bromocriptine (BC), a D2R receptor agonist, and PF-04455242, a selective κ opioid receptor (KOR) antagonist. Using diet-induced obese (DIO) rats, we aimed to ascertain whether the administration of BC and PF-04455242, independently or in combination, could enhance body weight loss. Furthermore, the present work demonstrates that the peripheral coadministration of BC and PF-04455242 enhances the reduction of weight in DIO rats and leads to a decrease in adiposity in a food-intake-independent manner. These effects were based on heightened energy expenditure, particularly through the activation of brown adipose tissue (BAT) thermogenesis. Overall, our findings indicate that the combination of BC and PF-04455242 effectively induces body weight loss through increased energy expenditure by increasing thermogenic activity and highlight the importance of the combined use of drugs to combat obesity. Full article