Kappa Opioid Research Articles

A Combination of a Dopamine Receptor 2 Agonist and a Kappa Opioid Receptor Antagonist Synergistically Reduces Weight in Diet-Induced Obese Rodents.

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.

Effects of kappa-opioid agonist U-50488 and p38 MAPK inhibitor SB203580 on the spike activity of pyramidal neurons in the basolateral amygdala

Introduction: Kappa-opioid receptor (KOR) signaling in the basolateral amygdala (BLA) underlies KOR agonist-induced aversion. In this study, we aimed to understand the individual and combined effects of KOR agonist U-50488 and p38 MAPK inhibitor SB203580 on the spiking activity of pyramidal neurons in the BLA to shed light on the complex interplay between KORs, the p38 MAPK, and neuronal excitability. Materials and Methods: Electrophysiological experiments were performed using the patch-clamp technique in the whole-cell configuration. Rat brain slices containing the amygdala were prepared, and pyramidal neurons within the BLA were visually patched and recorded in the current clamp mode. The neurons were identified by their accommodation properties and neural activity signals were amplified and analyzed. Using local perfusion, we obtained three dose-response curves for: (a) U-50488 (0.001–10 μM); (b) U-50488 (0.001–10 μM) in the presence of SB203580 (1 μM); and (c) U-50488 (0.01–10 μM) in the presence of SB203580 (5 μM). Results: After the application of U-50488, pyramidal neurons had a higher action potential firing rate in response to a current injection than control neurons (p<0.001). The dose-dependent curves we obtained indicate that the combination of U-50488 and SB203580 results in non-competitive antagonism. This conclusion is supported by the observed change in the curve’s slope with reduction in the maximum effect of U-50488. Thus, it can be assumed that the increase in spike activity of pyramidal neurons of the amygdala is mediated through the beta-arrestin pathway. When this pathway is blocked, the spike activity reverts to its baseline level. Conclusion: Our study found that the KOR agonist-induced spiking activity of the BLA pyramidal neurons is mediated by the beta-arrestin pathway and can be suppressed by the application of the p38 MAPK inhibitor SB203580.

Neurobiology of Stress-Induced Nicotine Relapse.

Tobacco smoking is the leading cause of preventable death and disease. Although there are some FAD-approved medicines for controlling smoking, the relapse rate remains very high. Among the factors that could induce nicotine relapse, stress might be the most important one. In the last decades, preclinical studies have generated many new findings that lead to a better understanding of stress-induced relapse of nicotine-seeking. Several molecules such as α3β4 nicotinic acetylcholine receptor, α2-adrenergic receptors, cannabinoid receptor 1, trace amine-associated receptor 1, and neuropeptide systems (corticotropin-releasing factor and its receptors, dynorphine and kappa opioid receptor) have been linked to stress-induced nicotine relapse. In this review, we discuss recent advances in the neurobiology, treatment targets, and potential therapeutics of stress-induced nicotine relapse. We also discuss some factors that may influence stress-induced nicotine relapse and that should be considered in future studies. In the final section, a perspective on some research directions is provided. Further investigation on the neurobiology of stress-induced nicotine relapse will shed light on the development of new medicines for controlling smoking and will help us understand the interactions between the stress and reward systems in the brain.

Identification and In Vivo Evaluation of Myelination Agent PIPE-3297, a Selective Kappa Opioid Receptor Agonist Devoid of β-Arrestin-2 Recruitment Efficacy.

Structure-activity relationship studies led to the discovery of PIPE-3297, a fully efficacious and selective kappa opioid receptor (KOR) agonist. PIPE-3297, a potent activator of G-protein signaling (GTPγS EC50 = 1.1 nM, 91% Emax), did not elicit a β-arrestin-2 recruitment functional response (Emax < 10%). Receptor occupancy experiments performed with the novel KOR radiotracer [3H]-PIPE-3113 revealed that subcutaneous (s.c.) administration of PIPE-3297 at 30 mg/kg in mice achieved 90% occupancy of the KOR in the CNS 1 h post dose. A single subcutaneous dose of PIPE-3297 in healthy mice produced a statistically significant increase of mature oligodendrocytes (P < 0.0001) in the KOR-enriched striatum, an effect that was not observed in animals predosed with the selective KOR antagonist norbinaltorphimine. An equivalent dose given to mice in an open-field activity-monitoring system revealed a small KOR-independent decrease in total locomotor activity versus vehicle measured between 60 and 75 min post dose. Daily doses of PIPE-3297 at both 3 and 30 mg/kg s.c. reduced the disease score in the mouse experimental autoimmune encephalomyelitis (EAE) model. Visually evoked potential (VEP) N1 latencies were also significantly improved versus vehicle in both dose groups, and latencies matched those of untreated animals. Taken together, these findings highlight the potential therapeutic value of functionally selective G-protein KOR agonists in demyelinating disease, which may avoid the sedating side effects typically associated with classical nonbiased KOR agonists.

Expression heterogeneity, tumor immune characteristics and the prognosis effects of OPRL1 in patients with tumors: a pan-cancer study combined with bioinformation analyses and in vitro validation

PurposeOpioids are currently the most frequently prescribed analgesics in clinical practice. However, their effect on cancer progression remains a topic of debate. Opioid receptors (ORs) are present in various types of tumor cells and their expression levels vary depending on the type of tumor. This study aims to explore and preliminarily characterize the association between four different ORs (μ, δ, κ, and nociception/orphanin FQ peptide receptor) and the prognosis of different types of tumors for comparison, with a focus on nociception/ orphanin FQ peptide receptor.MethodsThe expression levels of four ORs in normal tissues and immune cells were obtained from Human Protein Atlas (HPA) RNA-seq dataset, Monaco dataset, and Consensus dataset. Pan-cancer analysis was performed using the The Cancer Genome Atlas (TCGA) dataset, which included the expression of four ORs in different cancer types, significant copy-number alterations (sCNA), gene mutations of the four ORs, survival analysis, co-expression genes analysis, functional enrichment analyses, and correlations between ORs and immune cell infiltration levels. Based on the results of bioinformatic analysis, we selected 10 cancer cell lines for validation in vitro using specific agonists for the four ORs.ResultsOPRL1 (opioid related nociceptin receptor 1 gene) exhibited the highest abundance across different types of cancers, while OPRM1 (opioid receptor mu 1 gene) and OPRD1 (opioid receptor delta 1 gene) were barely detectable in multiple cancer types. Pan-cancer survival analysis revealed the overall worse/better prognosis of the four ORs in certain cancer types. Elevated levels of OPRM1 appear to be associated with poorer outcomes in breast invasive carcinoma and kidney renal clear cell carcinoma. Elevated OPRD1 levels are connected to worsen outcomes in kidney renal clear cell carcinoma and liver hepatocellular carcinoma, but better prognosis in bladder urothelial carcinoma. Increased OPRK1 (opioid receptor kappa 1 gene) expression is linked to a poorer prognosis in kidney renal papillary cell carcinoma. Furthermore, high OPRL1 expression relates to worse outcomes in bladder urothelial carcinoma and liver hepatocellular carcinoma, but better outcomes in breast invasive carcinoma and pancreatic adenocarcinoma. Functional enrichment analyses found that immune-related pathways were enriched in OPRK1 and OPRL1, with OPRL1 exhibiting the highest correlation with immune cell infiltration. Different effects on cell growth, migration, and invasion were observed in different cancer types upon the administration of agonists for the four ORs.ConclusionOPRL1 may play a vital role in monocytes and regulating the immune response and tumor-infiltrating macrophages. Due to its high abundance in different types of tumors, it may hold greater clinical significance for oncology patients. OPRK1 also participates in immune-related pathways. OPRL1 could potentially serve as therapeutic targets for different types of cancers.Graphical

Nalbuphine-6-glucuronide is a potent analgesic with superior safety profiles by altering binding affinity and selectivity for mu-/kappa-opioid receptors

Although nalbuphine, a semi-synthetic analgesic compound, is less potent than morphine in terms of alleviating severe pain, our recent findings have revealed that nalbuphine-6-glucuronide (N6G), one of the glucuronide metabolites of nalbuphine, promotes a significantly more robust analgesic effect than its parent drug. Nevertheless, despite these promising observations, the precise mechanisms underlying the analgesic effects of nalbuphine glucuronides have yet to be determined. In this study, we aim to elucidate the mechanisms associated with the analgesic effects of nalbuphine glucuronides. Pharmacokinetic and pharmacodynamic studies were conducted to investigate the relationship between the central and peripheral compartments of nalbuphine and its derivatives. The analgesic responses of these compounds were evaluated based on multiple behavioral tests involving thermal and mechanical stimuli. Radioligand binding assays were also performed to determine the binding affinity and selectivity of these compounds for different opioid receptors. The results of these tests consistently confirmed that the heightened analgesic effects of N6G are mediated through its enhanced binding affinity for both mu- and kappa-opioid receptors, even comparable to those of morphine. Notably, N6G exhibited fewer side effects and did not induce sudden death, thereby highlighting its superior safety profile. Additionally, pharmacokinetic studies indicated that N6G could cross the blood–brain barrier when administered peripherally, offering pain relief. Overall, N6G provides great analgesic efficacy and enhanced safety. These findings highlight the potential value of nalbuphine glucuronides, particularly N6G, as promising candidates for the development of novel analgesic drugs.

In Silico Screening of Compounds Similar to Codeine, Tramadol, and Morphine with Better Pharmacodynamic and Pharmacokinetics Profiles

Introduction: Pain alleviation is the primary intervention in promoting quality of life. Among the compounds used in management of pain are opioids. Codeine is mostly used as antitussive and is commonly present in cough syrups. Tramadol and Morphine are used as analgesics based on severity of pain. Although these drugs provide instant pain relief, they are associated with many side effects and the most worrying once are addiction, respiratory depression and tolerance. Methods: Codeine, Tramadol, and Morphine were used as query compounds to generate similar compounds using SwissSimilarity. Similar compounds were docked to mu, kappa, and delta receptors and those that showed better docking scores to mu receptor and lower scores to kappa and delta were analyzed for toxicity profiles using ProTox II and pharmacokinetics profiles using SwissADME. Results: ZINC13831510; 0.992, ZINC03629718; 0. 995; ZINC03870350; 0.993; ZINC28256912; 0.992; and ZINC71774151; 0.977 showed highest binding score to mu receptors and lower to both kappa and delta. All compounds were predicted to inhibit CYP2D6 enzyme. All compounds permeated Blood Brain Barrier with the exceptions of ZINC04102208; 0.992; and ZINC13831510; 0.992. Tramadol, its zinc compounds and ZINC03629718; 0.995. were not substrates for P-glycoprotein. Tramadol and ZINC03639132; 0.976; were predicted immunoactive. All compounds conformed to Lipinski rule of five. Conclusion: In conclusion, ZINC13831510; 0.992; showed the highest binding score to morphine. ZINC02509756; 0.986; and ZINC26259212; 0.995; were considered the safest as compared to Tramadol and Codeine and their zinc compounds respectively. Further invitro studies are recommended for the following promising compounds ZINC13831510; 0.992, ZINC03629718; 0. 995; ZINC03870350; 0.993; ZINC28256912; 0.992; and ZINC71774151; 0.977 ZINC02509756; 0.986; and ZINC26259212; 0.995;.

GPCR-G protein selectivity revealed by structural pharmacology.

Receptor-G protein promiscuity is frequently observed in class A G protein-coupled receptors (GPCRs). In particular, GPCRs can couple with G proteins from different families (Gαs, Gαq/11, Gαi/o, and Gα12/13) or the same family subtypes. The molecular basis underlying the selectivity/promiscuity is not fully revealed. We recently reported the structures of kappa opioid receptor (KOR) in complex with the Gi/o family subtypes [Gαi1, GαoA, Gαz, and Gustducin (Gαg)] determined by cryo-electron microscopy (cryo-EM). The structural analysis, in combination with pharmacological studies, provides insights into Gi/o subtype selectivity. Given the conserved sequence identity and activation mechanism between different G protein families, the findings within Gi/o subtypes could be likely extended to other families. Understanding the KOR-Gi/o or GPCR-G protein selectivity will facilitate the development of more precise therapeutics targeting a specific G protein subtype.

The Antidepressant Effect of Magnolol on Depression-Like Behavior of CORT-Treated Mice.

Although the antidepressant-like effect of magnolol has been revealed in previous reports, the mechanism remains unclear. In this study, the antidepressant-like effect of magnolol on corticosterone-induced (CORT-induced) mice was investigated in vivo. After 21 days of CORT induction, the mice showed marked depressive-like behaviors, with a decrease in sucrose preference score and an increase in immobility time in the tail suspension test (TST) and forced swimming test (FST). Pretreatment with either magnolol (50 mg/kg, i.p.) or the kappa opioid receptor (KOR) antagonist nor-BNI (10 mg/kg, i.p.) prevented CORT-induced depression-like behavior and reduced CORT-induced dynorphin (DYN A) elevation in the hippocampal ventral DG. However, no depression-like behavior was observed in mice with KOR downregulation in the ventral DG. We further found that upregulation of DYN A in the DG caused depression-like behavior, which was blocked by intraperitoneal injection of nor-BNI and modulated by magnolol. The present study demonstrated that magnolol could ameliorate CORT-induced depression-like behaviors, by modulating the DYN A/KOR system in the ventral DG of the hippocampus.

Coexpressed δ-, μ-, and κ-Opioid Receptors Modulate Voltage-Gated Ca2+ Channels in Gastric-Projecting Vagal Afferent Neurons.

Opioid analgesics are frequently associated with gastrointestinal side effects, including constipation, nausea, dysphagia, and reduced gastric motility. Though it has been shown that stimulation of opioid receptors expressed in enteric motor neurons contributes to opioid-induced constipation, it remains unclear whether activation of opioid receptors in gastric-projecting nodose ganglia neurons contributes to the reduction in gastric motility and emptying associated with opioid use. In the present study, whole-cell patch-clamp recordings were performed to determine the mechanism underlying opioid receptor-mediated modulation of Ca2+ currents in acutely isolated gastric vagal afferent neurons. Our results demonstrate that CaV2.2 channels provide the majority (71% ± 16%) of Ca2+ currents in gastric vagal afferent neurons. Furthermore, we found that application of oxycodone, U-50488, or deltorphin II on gastric nodose ganglia neurons inhibited Ca2+ currents through a voltage-dependent mechanism by coupling to the Gα i/o family of heterotrimeric G-proteins. Because previous studies have demonstrated that the nodose ganglia expresses low levels of δ-opioid receptors, we also determined the deltorphin II concentration-response relationship and assessed deltorphin-mediated Ca2+ current inhibition following exposure to the δ-opioid receptor antagonist ICI 174,864 (0.3 µM). The peak mean Ca2+ current inhibition following deltorphin II application was 47% ± 24% (EC50 = 302.6 nM), and exposure to ICI 174,864 blocked deltorphin II-mediated Ca2+ current inhibition (4% ± 4% versus 37% ± 20%). Together, our results suggest that analgesics targeting any opioid receptor subtype can modulate gastric vagal circuits. SIGNIFICANCE STATEMENT: This study demonstrated that in gastric nodose ganglia neurons, agonists targeting all three classical opioid receptor subtypes (μ, δ, and κ) inhibit voltage-gated Ca2+ channels in a voltage-dependent mechanism by coupling to Gαi/o. These findings suggest that analgesics targeting any opioid receptor subtype would modulate gastric vagal circuits responsible for regulating gastric reflexes.

A Review on Bioactive Phytochemical Constituents and Pharmacological Activities of Aegiceras corniculatum: A Pharmaceutically Important Mangrove Plant

Aegiceras corniculatum, commonly referred to as Khalsi, is a member of the mangrove Myrsinaceae family. The various parts of this plant have been used in traditional medicinal systems for their potential therapeutic effects in conditions such as asthma, microbial infections, diabetes, pain relief, inflammation, cancer, and arthritis. A diverse array of bioactive phytochemicals such as flavonoids, benzoquinones, triterpenes, polyphenolic acids, stilbenes, tannins, and macrolides have been identified in different parts of this plant. The aim of this review was to summarize the bioactive phytoconstituents reported from this plant that are accountable for the observed different pharmacological effects of the plant and further elucidate the possible underlying mechanisms by which these chemicals exert their actions. The search was conducted on various widely used database platforms, including Google Scholar, Scopus, Web of Science, SciFinder, and PubMed. Articles published until July 2023 were extracted and all the information was sorted based on the inclusion and exclusion criteria. The data revealed that anti-inflammatory compounds from this plant suppress iNOS, myeloperoxidase, COX, LOX, and cytokines (like TNF-alpha, IL-1ß, LTB4, IL-12, and IL-6) to reduce inflammation. 5-O-Butyl-embelin, 2-hydroxy-5-ethoxy-3-nonyl1, 4-benzoquinone, 5-O-methylembelin, 5-O-methyl-rapanone, s-saponin, and 5-O-ethylembelin are some phytochemicals of A. corniculatum with anticancer properties, although their mechanism is unclear. A. corniculatum has antibacterial, parasitic, and antifungal effects, but no antiviral effects were reported. The plant-isolated coumaric acid and fatty acids interact with bacterial DNA/RNA and limit protein formation, making them antibacterial. Gallocatechin, epicatechin, epigallocatechin-3-O-gallate, epigallocatechin, and other tannins, as well as flavonoids like kaempferol, quercetin, and isorhamnetin, are some of the compounds in A. corniculatum that may depolarize and change bacterial membranes, showing antibacterial effect. These phenolic chemicals also reduce oxidative stress and help treat cancer and other inflammatory diseases. The extract of this plant activates the κ-opioid receptor, causing central antinociception. Catechol components, such as epigallocatechin-3-O-gallate, protect against CNS illnesses including Parkinson’s disease and amnesia. Despite numerous studies demonstrating various pharmacological advantages of this plant and its constituents, the number of clinical trials conducted on humans remains significantly limited.

Endogenous Opioid Activity as the Mechanism of Action for Mitragyna speciosa (Kratom): The Current State of the Evidence.

Kratom (Mitragyna speciosa) is a substance derived from botanical compounds native to Southeast Asia. This substance has been cultivated predominantly in Thailand, Malaysia, Vietnam, and Myanmar, where it has historically been used in traditional medicine as a near panacea for several health problems. Such ritualistic use of kratom has been present for centuries; however, recreational use appears to have increased globally, especially in the United States. Pharmacodynamic and pharmacokinetic studies have found that kratom demonstrates a unique parabolic, dose-dependent pattern of effects ranging from stimulation to opioid and analgesic effects. Pharmacological research indicates that kratom is both a mu opioid receptor (μ-OR; MOR) and a kappa opioid receptor (κ-OR; KOR) agonist, which mediates its analgesic effects. Other research suggests that kratom may simultaneously act on dopaminergic and serotonergic receptors, which mediate its stimulant effects. This chapter reviews the literature related to the structural, functional, and cultural characteristics of kratom use. We begin with an overview of current and historical patterns of kratom, followed by a review of data on the pharmacodynamics and pharmacokinetics of kratom thus far.

Comparative Analysis of Infarct-Limiting Activity of Peptide and Non-Peptide δ- and κ-Opioid Receptor Agonists during Heart Reperfusion In Vivo.

A comparative analysis of the infarct-limiting activity of δ- and κ-opioid receptors (OR) agonists was carried out on a model of coronary occlusion (45 min) and reperfusion (120 min) in male Wistar rats. We used selective δ2-OR agonist deltorphin II (0.12 mg/kg), δ-OR agonists BW373U86 and p-Cl-Phe DPDPE (0.1 and 1 mg/kg), selective agonists of δ1-OR DPDPE (0.1 and 0.969 mg/kg), κ1-OR U-50,488 (0.1 and 1 mg/kg), κ2-OR GR-89696 (0.1 mg/kg), and κ-OR ICI-199,441 (0.1 mg/kg). All drugs were administered intravenously 5 min before reperfusion. Deltorphin II, BW373U86 (1 mg/kg), p-Cl-Phe DPDPE (1 mg/kg), U-50,488 (1 mg/kg), and ICI-199,441 had a cardioprotective effect. The most promising compounds for drug development are ICI-199,441 and deltorphin II.

Hair Loss in a Hemodialysis Patient after Repetitive Use of the Antipruritic Drug Nalfurafine: Implications of Impaired Angiogenesis for Hair Loss.

A 47-year-old man who presented with scalp hair loss was transferred to our dialysis facility 3 months after hemodialysis initiation. He noticed systemic hair loss one month after the initiation of dialysis. Because the antipruritic drug nalfurafine was the only drug that had been newly added to his regular medication after he started hemodialysis, we stopped its prescription. His hair loss was completely ameliorated for the next five months. We speculated that κ-opioid receptor activation by nalfurafine caused blood capillary regression around the hair follicles, leading to cessation of hair growth and subsequent hair fallout.

Copaifera langsdorffii Desf. tree oleoresin-induced antinociception recruits µ1- and κ -opioid receptors in the ventrolateral columns of the periaqueductal gray matter

Popular medicine has been using oleoresin from several species of copaíba tree for the treatment of various diseases and its clinical administration potentially causes antinociception. Electrical stimulation of ventrolateral (vlPAG) and dorsolateral (dlPAG) columns of the periaqueductal gray matter also causes antinociception. The aim this study was to verify the antinociceptive effect of oleoresin extracted from Copaifera langsdorffii tree and to test the hypothesis that oleoresin-induced antinociception is mediated by µ1- and κ-opioid receptors in the vlPAG and dlPAG. Nociceptive thresholds were determined by the tail-flick test in Wistar rats. The copaíba tree oleoresin was administered at different doses (50, 100 and 200 mg/kg) through the gavage technique. After the specification of the most effective dose of copaíba tree oleoresin (200 mg/kg), rats were pretreated with either the µ1-opioid receptor selective antagonist naloxonazine (at 0.05, 0.5 and 5 µg/ 0.2 µl in vlPAG, and 5 µg/ 0.2 µl in dlPAG) or the κ-opioid receptor selective antagonist nor-binaltorphimine (at 1, 3 and 9 nmol/ 0.2 µl in vlPAG, and 9 nmol/ 0.2 µl in dlPAG). The blockade of µ1 and κ opioid receptors of vlPAG decreased the antinociception produced by copaíba tree oleoresin. However, the blockade of these receptors in dlPAG did not alter copaíba tree oleoresin-induced antinociception. These data suggest that vlPAG µ1 and κ opioid receptors are critically recruited in the antinociceptive effect produced by oleoresin extracted from Copaifera langsdorffii.

Safety, tolerability, pharmacokinetics, and pharmacodynamics of a novel kappa opioid receptor agonist ZYKR1: a randomized double-blind placebo-control phase 1 study in healthy adult human participants.

To perform first-in-human single-dose escalation trial of ZYKR1, which is a potent, selective, and peripherally-restricted kappa opioid receptor agonist, is the purpose of this study. This randomized, double-blind, placebo-controlled single ascending dose study conducted at Zydus Research Centre, Ahmedabad, India included healthy male participants aged 18-55years and weighing > 50kg. The primary objective was to evaluate the safety and tolerability of ZYKR1. The secondary objective was to evaluate the pharmacokinetics and pharmacodynamics (PD) of ZYKR1. Participants received ZYKR1 (0.5 - 6 mcg/kg) or placebo infused intravenously in 15 ± 1min. Of total five dose groups (0.5 - 6 mcg/kg), each group included eight participants with six and two randomized to ZYKR1 and placebo, respectively. Three participants experienced six treatment-emergent adverse events (TEAEs); two were gastrointestinal disorders (nausea and vomiting at 2 mcg/kg); and four were related to the nervous system (headache (at 2 mcg/kg) and facial tingling, facial numbness and paresthesia (at 6 mcg/kg)); all TEAEs were mild and resolved without sequelae. The Cmax of ZYKR1 was achieved after 15 - 20min of start of infusion. The mean exposures (Cmax and AUC0 - t) increased in a dose-proportional manner. The mean t1/2 ranged from 2.20 to 2.98h across the dose range. Increase in the mean prolactin level was significantly higher in treatment groups compared with that in the placebo group. Intravenous ZYKR1 at doses up to 6 mcg/kg showed acceptable safety and tolerability and demonstrated a short half-life with principal route of excretion as renal. ZYKR1 displayed a potent PD effect reflected by increased prolactin levels, supporting further study in patients. Trial registration Clinical Trial Registry of India: CTRI/2018/07/014927. Date of registration: 18/07/2018.

Chronic intermittent ethanol exposure-induced m6A modifications around mRNA stop codons of opioid receptor genes

ABSTRACT Chronic alcohol consumption may alter mRNA methylation and expression levels of genes related to addiction and reward in the brain, potentially contributing to alcohol tolerance and dependence. Neuron-like (SH-SY5Y) and non-neuronal (SW620) cells were utilized as models to examine chronic intermittent ethanol (CIE) exposure-induced global m6A RNA methylation changes, as well as m6A mRNA methylation changes around the stop codon of three opioid receptor genes (OPRM1, OPRD1, and OPRK1), which are known to regulate pain, reward, and addiction behaviours. CIE exposure for three weeks significantly increased global RNA methylation levels in both SH-SY5Y (t = 3.98, P = 0.007) and SW620 (t = 2.24, P = 0.067) cells. However, a 3-week CIE exposure resulted in hypomethylation around mRNA stop codon regions of OPRM1 and OPRD1 in both cell lines [OPRM1 (SH-SY5Y): t = -5.05, P = 0.0005; OPRM1 (SW620): t = -3.19, P = 0.013; OPRD1 (SH-SY5Y): t = -13.43, P < 0.00001; OPRD1 (SW620): t = -4.00, P = 0.003]. Additionally, mRNA expression levels of OPRM1, OPRD1, and OPRK1 were downregulated (corresponding to mRNA hypomethylation) in both SH-SY5Y and SW620 cells after a 3-week CIE exposure. The present study demonstrated that chronic ethanol exposure altered global RNA methylation levels, as well as mRNA methylation and expression levels of opioid receptor genes in both neuron-like and non-neuronal cells. Our findings suggest a potential epitranscriptomic mechanism by which chronic alcohol consumption remodels the expression of reward-related and alcohol responsive genes in the brain, thus increasing the risk of alcohol use disorder development. Abbreviations: OPRM1: the μ-opioid receptor; OPRD1: the δ-opioid receptor; OPRK1: the κ-opioid receptor; CIE: chronic intermittent ethanol exposure; CIE+WD: chronic intermittent ethanol exposure followed by a 24-hr withdrawal; SH-SY5Y: human neuroblastoma cell Line; SW620: human colon carcinoma cell line; RT-qPCR: reverse transcription followed by quantitative polymerase reaction; MazF-RT-qPCR: MazF digestion followed by RT-qPCR

Central glucagon-like peptide 1 receptor activation inhibits Toll-like receptor agonist-induced inflammation

Glucagon-like peptide-1 receptor agonists (GLP-1RAs) exert anti-inflammatory effects relevant to the chronic complications of type 2 diabetes. Although GLP-1RAs attenuate Tcell-mediated gut and systemic inflammation directly through the gut intraepithelial lymphocyte GLP-1R, how GLP-1RAs inhibit systemic inflammation in the absence of widespread immune expression of the GLP-1R remains uncertain. Here, we show that GLP-1R activation attenuates the induction of plasma tumor necrosis factor alpha (TNF-α) by multiple Toll-like receptor agonists. These actions are not mediated by hematopoietic or endothelial GLP-1Rs but require central neuronal GLP-1Rs. In a cecal slurry model of polymicrobial sepsis, GLP-1RAs similarly require neuronal GLP-1Rs to attenuate detrimental responses associated with sepsis, including sickness, hypothermia, systemic inflammation, and lung injury. Mechanistically, GLP-1R activation leads to reduced TNF-α via α1-adrenergic, δ-opioid, and κ-opioid receptor signaling. These data extend emerging concepts of brain-immune networks and posit a new gut-brain GLP-1R axis for suppression of peripheral inflammation.

Preclinical Models of Attention Deficit Hyperactivity Disorder: Neurobiology, Drug Discovery, and Beyond

Objective: We offer an overview of ADHD research using mouse models of nicotine exposure. Method: Nicotine exposure of C57BL/6 or Swiss Webster mice occurred during prenatal period only or during the prenatal and the pre-weaning periods. Behavioral, neuroanatomical and neurotransmitter assays were used to investigate neurobiological mechanisms of ADHD and discover candidate ADHD medications. Results: Our studies show that norbinaltorphimine, a selective kappa opioid receptor antagonist is a candidate novel non-stimulant ADHD treatment and that a combination of methylphenidate and naltrexone has abuse deterrent potential with therapeutic benefits for ADHD. Other studies showed transgenerational transmission of ADHD-associated behavioral traits and demonstrated that interactions between untreated ADHD and repeated mild traumatic brain injury produced behavioral traits not associated with either condition alone. Conclusion: Preclinical models contribute to novel insights into ADHD neurobiology and are valuable tools for drug discovery and translation to benefit humans with ADHD.

Design and structural validation of peptide–drug conjugate ligands of the kappa-opioid receptor

Despite the increasing number of GPCR structures and recent advances in peptide design, the development of efficient technologies allowing rational design of high-affinity peptide ligands for single GPCRs remains an unmet challenge. Here, we develop a computational approach for designing conjugates of lariat-shaped macrocyclized peptides and a small molecule opioid ligand. We demonstrate its feasibility by discovering chemical scaffolds for the kappa-opioid receptor (KOR) with desired pharmacological activities. The designed De Novo Cyclic Peptide (DNCP)-β-naloxamine (NalA) exhibit in vitro potent mixed KOR agonism/mu-opioid receptor (MOR) antagonism, nanomolar binding affinity, selectivity, and efficacy bias at KOR. Proof-of-concept in vivo efficacy studies demonstrate that DNCP-β-NalA(1) induces a potent KOR-mediated antinociception in male mice. The high-resolution cryo-EM structure (2.6 Å) of the DNCP-β-NalA–KOR–Gi1 complex and molecular dynamics simulations are harnessed to validate the computational design model. This reveals a network of residues in ECL2/3 and TM6/7 controlling the intrinsic efficacy of KOR. In general, our computational de novo platform overcomes extensive lead optimization encountered in ultra-large library docking and virtual small molecule screening campaigns and offers innovation for GPCR ligand discovery. This may drive the development of next-generation therapeutics for medical applications such as pain conditions.