scholarly journals Endogenous Opioid Peptides and Alternatively Spliced Mu Opioid Receptor Seven Transmembrane Carboxyl-Terminal Variants

2021 ◽  
Vol 22 (7) ◽  
pp. 3779
Author(s):  
Anna Abrimian ◽  
Tamar Kraft ◽  
Ying-Xian Pan
Keyword(s):  
Opioid Receptor ◽  
Opioid Peptides ◽  
Splice Variants ◽  
Mu Opioid Receptor ◽  
Kappa Opioid Receptor ◽  
Endogenous Opioid Peptides ◽  
Endogenous Opioid ◽  
Mu Opioid ◽  
Protein Activation ◽  
Biased Signaling

There exist three main types of endogenous opioid peptides, enkephalins, dynorphins and β-endorphin, all of which are derived from their precursors. These endogenous opioid peptides act through opioid receptors, including mu opioid receptor (MOR), delta opioid receptor (DOR) and kappa opioid receptor (KOR), and play important roles not only in analgesia, but also many other biological processes such as reward, stress response, feeding and emotion. The MOR gene, OPRM1, undergoes extensive alternative pre-mRNA splicing, generating multiple splice variants or isoforms. One type of these splice variants, the full-length 7 transmembrane (TM) Carboxyl (C)-terminal variants, has the same receptor structures but contains different intracellular C-terminal tails. The pharmacological functions of several endogenous opioid peptides through the mouse, rat and human OPRM1 7TM C-terminal variants have been considerably investigated together with various mu opioid ligands. The current review focuses on the studies of these endogenous opioid peptides and summarizes the results from early pharmacological studies, including receptor binding affinity and G protein activation, and recent studies of β-arrestin2 recruitment and biased signaling, aiming to provide new insights into the mechanisms and functions of endogenous opioid peptides, which are mediated through the OPRM1 7TM C-terminal splice variants.

scholarly journals Positive allosteric modulation of the mu-opioid receptor produces analgesia with reduced side effects

2021 ◽  
Vol 118 (16) ◽  
pp. e2000017118
Author(s):  
Ram Kandasamy ◽  
Todd M. Hillhouse ◽  
Kathryn E. Livingston ◽  
Kelsey E. Kochan ◽  
Claire Meurice ◽  
...  
Keyword(s):  
Side Effects ◽  
G Protein ◽  
Opioid Receptor ◽  
Opioid Peptides ◽  
Chinese Hamster ◽  
Mu Opioid Receptor ◽  
Endogenous Opioid Peptides ◽  
Endogenous Opioid ◽  
Mu Opioid

Positive allosteric modulators (PAMs) of the mu-opioid receptor (MOR) have been hypothesized as potentially safer analgesics than traditional opioid drugs. This is based on the idea that PAMs will promote the action of endogenous opioid peptides while preserving their temporal and spatial release patterns and so have an improved therapeutic index. However, this hypothesis has never been tested. Here, we show that a mu-PAM, BMS-986122, enhances the ability of the endogenous opioid Methionine-enkephalin (Met-Enk) to stimulate G protein activity in mouse brain homogenates without activity on its own and to enhance G protein activation to a greater extent than β-arrestin recruitment in Chinese hamster ovary (CHO) cells expressing human mu-opioid receptors. Moreover, BMS-986122 increases the potency of Met-Enk to inhibit GABA release in the periaqueductal gray, an important site for antinociception. We describe in vivo experiments demonstrating that the mu-PAM produces antinociception in mouse models of acute noxious heat pain as well as inflammatory pain. These effects are blocked by MOR antagonists and are consistent with the hypothesis that in vivo mu-PAMs enhance the activity of endogenous opioid peptides. Because BMS-986122 does not bind to the orthosteric site and has no inherent agonist action at endogenously expressed levels of MOR, it produces a reduced level of morphine-like side effects of constipation, reward as measured by conditioned place preference, and respiratory depression. These data provide a rationale for the further exploration of the action and safety of mu-PAMs as an innovative approach to pain management.

Compartment-specific opioid receptor signaling is selectively modulated by Dynorphin subtypes

2020 ◽  
Author(s):  
Jennifer M. Kunselman ◽  
Achla Gupta ◽  
Ivone Gomes ◽  
Lakshmi A. Devi ◽  
Manoj A. Puthenveedu
Keyword(s):  
Opioid Receptor ◽  
Opioid Peptides ◽  
Kappa Opioid Receptor ◽  
Endogenous Opioid Peptides ◽  
Endogenous Opioid ◽  
Spatial Profile ◽  
Downstream Signaling ◽  
G Protein Coupled ◽  
Fine Tune ◽  
Signal Transduction Systems

AbstractMany signal transduction systems have an apparent redundancy built into them, where multiple physiological agonists activate the same receptors. Whether this is true redundancy, or whether this provides as-yet unrecognized specificity in downstream signaling, is not well understood. We address this question using the kappa opioid receptor (KOR), a physiologically relevant G protein-coupled receptor (GPCR) that is activated by multiple members of the Dynorphin family of opioid peptides. We show that, although highly related Dynorphins bind and activate KOR to similar extents on the cell surface, they localize KOR to distinct subcellular compartments, dictate different post-endocytic fates of the receptor, and differentially induce KOR signaling from the degradative pathway. Our results show that seemingly redundant endogenous opioid peptides that are often co-released can in fact fine-tune signaling by differentially regulating the subcellular spatial profile of GPCR localization and signaling.

Dilemma of Addiction and Respiratory Depression in the Treatment of Pain: A Prototypical Endomorphin as a New Approach

Pain Medicine ◽  
2019 ◽  
Vol 21 (5) ◽  
pp. 992-1004 ◽  
Author(s):  
Lynn Webster ◽  
William K Schmidt
Keyword(s):  
Side Effects ◽  
Respiratory Depression ◽  
Opioid Receptor ◽  
Severe Pain ◽  
Mu Opioid Receptor ◽  
Endogenous Opioid Peptides ◽  
Endogenous Opioid ◽  
Mu Opioid ◽  
Receptor Agonists ◽  
Opioid Receptor Agonists

Abstract Objective Although mu-opioid receptor agonists have been the mainstay of analgesic regimens for moderate to severe pain, they are associated with serious side effects, risks, and limitations. We evaluate the most serious risks associated with conventional opioids and compare these with the pharmacology of CYT-1010, a prototypical endomorphin and mu-opioid receptor agonist. Results Addiction and respiratory depression are serious risks of traditional mu-opioid analgesics. Mitigation strategies have been inadequate at addressing the opioid crisis and may interfere with the effective treatment of pain. Improved understanding of mu-opioid receptor biology and the discovery in 1997 of an additional and unique family of endogenous opioid peptides (endomorphins) have provided a pathway for dissociating analgesia from opioid-related adverse events and developing new classes of mu-opioid receptor agonists that use biased signaling and/or target novel sites to produce analgesia with reduced side effect liability. Endomorphin-1 and -2 are endogenous opioid peptides highly selective for mu-opioid receptors that exhibit potent analgesia with reduced side effects. CYT-1010 is a cyclized, D-lysine-containing analog of endomorphin-1 with a novel mechanism of action targeting traditional mu- and exon 11/truncated mu-opioid receptor 6TM variants. CYT-1010 preclinical data have demonstrated reduced abuse potential and analgesic potency exceeding that of morphine. In an initial phase 1 clinical study, CYT-1010 demonstrated significant analgesia vs baseline and no respiratory depression at the dose levels tested. Conclusions CYT-1010 and other novel mu-opioid receptor agonists in clinical development are promising alternatives to conventional opioids that may offer the possibility of safer treatment of moderate to severe pain.

scholarly journals Biased signaling at mu opioid receptor full‐length C‐terminal splice variants

2021 ◽  
Vol 35 (S1) ◽  
Author(s):  
Ankita Narayan ◽  
Amanda Hunkele ◽  
Jin Xu ◽  
Daniel Bassoni ◽  
Ying‐Xian Pan
Keyword(s):  
Opioid Receptor ◽  
Splice Variants ◽  
Mu Opioid Receptor ◽  
Full Length ◽  
Mu Opioid ◽  
Biased Signaling

scholarly journals Region Specificity in Endogenous Opioid Peptides and Mu-opioid Receptor Gene Expression in Rat Brain Areas Involved in Addiction After Frequent Morphine Treatment

2022 ◽  
Vol 12 (4) ◽  
Author(s):  
Shamseddin Ahmadi ◽  
Kayvan Masoudi ◽  
Shiva Mohammadi Talvar ◽  
Mohammad Zobeiri ◽  
Amir Khanizad ◽  
...  
Keyword(s):  
Gene Expression ◽  
Opioid Peptides ◽  
Mu Opioid Receptor ◽  
Morphine Treatment ◽  
Endogenous Opioid Peptides ◽  
Gene Expressions ◽  
Endogenous Opioid ◽  
Brain Areas ◽  
Oprm1 Gene ◽  
Mu Opioid

Backgrounds: Molecular mechanisms involved in adverse effects of morphine, including tolerance and dependence, have remained elusive. We examined possible alterations in the gene expression of proenkephalin (Penk), prodynorphin (Pdyn), and mu-opioid receptor (Oprm1) in reward brain areas following frequent morphine treatment. Methods: Two groups of male Wistar rats were used. The groups received either saline (1 mL/kg) or morphine (10 mg/kg) twice daily for eight days. On day 8, rats were decapitated, brain areas involved in addiction were dissected, including the midbrain, striatum, prefrontal cortex (PFC), hippocampus, and hypothalamus, and gene expression was evaluated with real-time PCR. Results: Prolonged morphine treatment decreased Penk, Pdyn, and Oprm1 gene expressions in the midbrain but upregulated them in the striatum compared to the control group treated with saline. Significant increases in Pdyn and Oprm1 gene expressions were detected in the PFC, but there was no significant difference in Penk gene expression between the two groups. Besides, Pdyn gene expression was decreased in the hippocampus and hypothalamus; however, no significant differences in Penk and Oprm1 gene expressions were detected between the groups in these areas. Conclusions: The expression of endogenous opioid peptides and receptors after frequent use of morphine follows a region specificity in brain areas involved in addiction. These alterations may result in new physiological setpoints outside the normal range, which need to be considered when using morphine in medicine.

scholarly journals 6,5-Fused Ring, C2-Salvinorin Ester, Dual Kappa and Mu Opioid Receptor Agonists as Analgesics Devoid of Anxiogenic Effects

2021 ◽  
Author(s):  
Nicholas S. Akins ◽  
Nisha Mishra ◽  
Hannah M. Harris ◽  
Narendar Dudhipala ◽  
Seong Jong Kim ◽  
...  
Keyword(s):  
Opioid Receptor ◽  
Opioid Receptors ◽  
Analgesic Activity ◽  
Mu Opioid Receptor ◽  
Kappa Opioid Receptor ◽  
Mu Opioid ◽  
Receptor Agonists ◽  
Opioid Receptor Agonists

Analgesia is commonly mediated through the mu or kappa opioid receptor agonism. Unfortunately, selective mu or kappa receptor agonists often cause harmful side effects. Recently, ligands exhibiting dual agonism to the opioid receptors, such as to mu and kappa, or to mu and delta, have been suggested to temper undesirable adverse effects while retaining analgesic activity. Herein we report an introduction of various 6,5-fused rings to C2 of the salvinorin scaffold <i>via</i> an ester linker. <i>In vitro</i> studies showed that some of these compounds have dual agonism on kappa and mu opioid receptors, while some have triple agonism on kappa, mu, and delta. <i>In vivo </i>studies on the lead dual kappa and mu opioid receptor agonist, compound <b>10</b>, showed that it<b> </b>produced analgesic activity while avoiding anxiogenic effects in murine models, thus providing further strong evidence for the therapeutic advantages of dual opioid receptor agonists over selective opioid receptor agonists.

In major depression, increased kappa and mu opioid receptor levels are associated with immune activation

2020 ◽  
Vol 32 (2) ◽  
pp. 99-108 ◽  
Author(s):  
Hussein Kadhem Al-Hakeim ◽  
Suhaer Zeki Al-Fadhel ◽  
Arafat Hussein Al-Dujaili ◽  
Michael Maes
Keyword(s):  
Opioid Receptor ◽  
Immune Activation ◽  
Mu Opioid Receptor ◽  
Kappa Opioid Receptor ◽  
Receiver Operating Curve ◽  
Primary Immune Response ◽  
Mu Opioid ◽  
Simultaneous Activation ◽  
Drug Free ◽  
Inflammatory System

AbstractObjective:This study was carried out to delineate differences between major depressive disorder (MDD) and healthy controls in dynorphin and kappa opioid receptor (KOR) levels in association with changes in the β-endorphin – mu opioid receptor (MOR) and immune-inflammatory system.Methods:The present study examines dynorphin, KOR, β-endorphin, MOR, interleukin (IL)-6 and IL-10 in 60 drug-free male participants with MDD and 30 age-matched healthy males.Results:Serum dynorphin, KOR, β-endorphin and MOR are significantly higher in MDD as compared to controls. The increases in the dynorphin/KOR system and β-endorphin/MOR system are significantly intercorrelated and are both strongly associated with increased IL-6 and IL-10 levels. Dynorphin, β-endorphin, KOR and both cytokines showed a good diagnostic performance for MDD versus controls with a bootstrapped (n = 2000) area under the receiver operating curve of 0.972. The dynorphin/KOR system is significantly decreased in depression with comorbid nicotine dependence.Conclusion:Our findings suggest that, in MDD, immune activation is associated with a simultaneous activation of dynorphin/KOR and β-endorphin/MOR signaling and that these opioid systems may participate in the pathophysiology of depression by (a) exerting immune-regulatory activities attenuating the primary immune response and (b) modulating reward responses and mood as well as emotional and behavioural responses to stress.

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