Recent Molecular Insights into Agonist-specific Binding to the Mu-Opioid Receptor

Opioid agonists produce their analgesic effects primarily by acting at the µ-opioid receptor (µOR). µOR agonists with different efficacies exert diverse molecular changes in the µOR which dictate the faith of the receptor’s signaling pathway and possibly it’s the degree of desensitization. Since the development of the active conformations of the µOR, growing data have been published in relation to ligand-specific changes in µOR activation. In this regard, this review summarizes recent data regarding the most studied opioid agonists in in silico µOR activation, including how these ligands are recognized by the µOR, how their binding signal is transmitted toward the intracellular parts of the µOR, and finally, what type of large-scale movements do these changes trigger in the µOR’s domains

Central P2Y12 receptor blockade alleviates inflammatory and neuropathic pain and cytokine production in rodents.

In this study the role of P2Y12 receptors (P2Y12R) was explored in rodent models of inflammatory and neuropathic pain and in acute thermal nociception. In correlation with their activity to block the recombinant human P2Y12R, the majority of P2Y12R antagonists alleviated mechanical hyperalgesia dose-dependently, following intraplantar CFA injection, and after partial ligation of the sciatic nerve in rats. They also caused an increase in thermal nociceptive threshold in the hot plate test. Among the six P2Y12R antagonists evaluated in the pain studies, the selective P2Y12 receptor antagonist PSB-0739 was most potent upon intrathecal application. P2Y12R mRNA and IL-1beta protein were time-dependently overexpressed in the rat hind paw and lumbar spinal cord following intraplantar CFA injection. This was accompanied by the upregulation of TNF-alpha, IL-6 and IL-10 in the hind paw. PSB-0739 (0.3mg/kg i.t.) attenuated CFA-induced expression of cytokines in the hind paw and of IL-1beta in the spinal cord. Subdiaphragmatic vagotomy and the alpha7 nicotinic acetylcholine receptor antagonist MLA occluded the effect of PSB-0739 (i.t.) on pain behavior and peripheral cytokine induction. Denervation of sympathetic nerves by 6-OHDA pretreatment did not affect the action of PSB-0739. PSB-0739, in an analgesic dose, did not influence motor coordination and platelet aggregation. Genetic deletion of the P2Y12R in mice reproduced the effect of P2Y12R antagonists on mechanical hyperalgesia in inflammatory and neuropathic pain models, on acute thermal nociception and on the induction of spinal IL-1beta. Here we report the robust involvement of the P2Y12R in inflammatory pain. The anti-hyperalgesic effect of P2Y12R antagonism could be mediated by the inhibition of both central and peripheral cytokine production and involves alpha7-receptor mediated efferent pathways

A vallásosság szerepe az intenzív osztályon dolgozó orvosok és ápolók véleményének kialakításában az életvégi döntések meghozatalakor

Összefoglaló. Bevezetés: A haldoklást minden korban kulturális és vallási szabályok vették körül, melyek a mai napig hatnak a társadalomban. A 21. században számos beteg a kórházban, az intenzív osztályon fejezi be életét, ahol nem ritkán kerülhet sor életvégi döntés meghozatalára. Célkitűzés: Vizsgálatunk célja annak feltárása volt, milyen hatással van az orvosok és ápolók vallásossága a kezeléskorlátozással kapcsolatos döntésekre az intenzív osztályon. Módszer: Magyarországi intenzív osztályokon dolgozó orvosok és szakdolgozók körében végeztünk kérdőíves felmérést a vallás életvégi döntésekre gyakorolt hatásáról. 189 orvos és 105 ápoló által anonim módon kitöltött kérdőívet elemeztünk. Eredmények: Az intenzív osztályra történő betegfelvételre nem volt hatással a vallásosság, azonban a szabad ágyak száma a vallásos orvosokat erősebben befolyásolta, mint az ateista és választ nem adó orvosokat (<0,0001). A vallásukat gyakorló orvosok szignifikánsan jobban figyelembe vették a hozzátartozó kérését, mint az ateisták (p = 0,0002). A vallásos ápolók gyakrabban folytatnák a beteg kezelését a hozzátartozó kérése ellenére is, ha még látnának esélyt a gyógyulásra, mint a nem vallásosak. Következtetés: Vizsgálatunk alátámasztotta, hogy a világnézet befolyásolja az orvosokat és ápolókat az élet végéről hozott döntésekben. A kezeléskorlátozásról hozott döntés összetett, elengedhetetlen megismerni hozzá a beteg és családjának haldoklással kapcsolatos vallási szokásait, mivel jó életvégi döntés a világnézeti szempontok figyelembevétele nélkül nem hozható. Orv Hetil. 2021; 162(51): 2047-2054.Death has always been surrounded by habits in all ages, influenced by cultural and religious differences. Many patients finish their lives at intensive care units where end-of-life decisions are the part of everyday practice in the 21th century.The goal of our study was to assess how the religious beliefs of physicians and nurses affect their decision on therapy restriction.We have performed questionnaire-based enquiries among physicians and nurses working at intensive care units on how religion affects end-of-life decisions. We have analyzed the anonymous questionnaires filled out by 189 physicians and 105 nurses.Our results have confirmed the hypothesis that religion affects decision making about therapy restriction. Patients' admissions were not affected by religious beliefs, but the number of available patient beds influenced the religious physicians more than the atheists ones or the non-responders (<0.0001). Actively religious physicians complied significantly better with the relatives than atheists (p = 0.0002). Religious nurses would continue patient treatment even against the will of relatives more often than atheists if they see a chance for recovery.The study supports that religion influences physicians and nurses in their end-of-life decisions. Decisions on therapy restriction are complex; it is important to find out religious beliefs and perception of death among patients and families because good end-of-life decision cannot be made disregarding religious considerations. Orv Hetil. 2021; 162(51): 2047-2054

The Acute Antiallodynic Effect of Tolperisone in Rat Neuropathic Pain and Evaluation of Its Mechanism of Action

Current treatment approaches to manage neuropathic pain have a slow onset and their use is largely hampered by side-effects, thus there is a significant need for finding new medications. Tolperisone, a centrally acting muscle relaxant with a favorable side effect profile, has been reported to affect ion channels, which are targets for current first-line medications in neuropathic pain. Our aim was to explore its antinociceptive potency in rats developing neuropathic pain evoked by partial sciatic nerve ligation and the mechanisms involved. Acute oral tolperisone restores both the decreased paw pressure threshold and the elevated glutamate level in cerebrospinal fluid in neuropathic rats. These effects were comparable to those of pregabalin, a first-line medication in neuropathy. Tolperisone also inhibits release of glutamate from rat brain synaptosomes primarily by blockade of voltage-dependent sodium channels, although inhibition of calcium channels may also be involved at higher concentrations. However, pregabalin fails to affect glutamate release under our present conditions, indicating a different mechanism of action. These results lay the foundation of the avenue for repurposing tolperisone as an analgesic drug to relieve neuropathic pain

14-O-Methylmorphine: A Novel Selective Mu-Opioid Receptor Agonist with High Efficacy and Affinity.

14-O-methyl (14-O-Me) group in morphine-6-O-sulfate (M6SU) or oxymorphone has been reported to be essential for enhanced affinity, potency and antinociceptive effect of these opioids. Herein we report on the pharmacological properties (potency, affinity and efficacy) of the new compound, 14-O-methylmorphine (14-O-MeM) in in vitro. Additionally, we also investigated the antinociceptive effect of the novel compound, as well as its inhibitory action on gastrointestinal transit in in vivo. The potency and efficacy of test compound were measured by [35S]GTPgammaS binding, isolated mouse vas deferens (MVD) and rat vas deferens (RVD) assays. The affinity of 14-O-MeM for opioid receptors was assessed by radioligand binding and MVD assays. The antinociceptive and gastrointestinal effects of the novel compound were evaluated in the rat tail-flick test and charcoal meal test, respectively. Morphine, DAMGO, Ile5,6 deltorphin II, deltorphin II and U-69593 were used as reference compounds. 14-O-MeM showed higher efficacy (Emax) and potency (EC50) than morphine in MVD, RVD or [35S]GTPgammaS binding. In addition, 14-O-MeM compared to morphine showed higher affinity for mu-opioid receptor (MOR). In vivo, in rat tail-flick test 14-O-MeM proved to be stronger antinociceptive agent than morphine after peripheral or central administration. Additionally, both compounds inhibited the gastrointestinal peristalsis. However, when the antinociceptive and antitransit doses for each test compound are compared, 14-O-MeM proved to have slightly more favorable pharmacological profile. Our results affirm that 14-O-MeM, an opioid of high efficacy and affinity for MOR can be considered as a novel analgesic agent of potential clinical value

New morphine analogues produce peripheral antinociception within a certain dose range of their systemic administration

Growing data support the peripheral opioid antinociceptive effect, particularly, in inflammatory pain models. Here, we examined the antinociceptive effects of the subcutaneously (s.c.) administered, recently synthesized 14-O-Methylmorphine-6-O-sulfate (14-O-MeM6SU) compared to morphine-6-O-sulfate (M6SU) in a rat model of inflammatory pain, induced by an injection of Complete Freund's Adjuvant (CFA) and a mouse model of visceral pain evoked by acetic acid. The s.c. doses of 14-O-MeM6SU and M6SU up to 126 and 547 nmol/kg, respectively produced significant and s.c. or intraplantar (i.pl.) naloxone methiodide (NAL-M) reversible antinociception in inflamed paws compared to non-inflamed paws. These certain doses neither of them affected significantly the thiobutabarbital's sleeping time or rat pulmonary parameters. However, the antinociceptive effects of higher doses were only partially reversed by NAL-M indicating CNS contribution. In mouse writhing test, 14-O-MeM6SU was more potent than M6SU after s.c. or intracerebroventricular (i.c.v.) injections. Both displayed high s.c./i.c.v. ED50 ratios. The antinociceptive effects of s.c. 14-O-MeM6SU and M6SU up to 136 and 3043 nmol/kg, respectively were fully antagonized by s.c. NAL-M. In addition, the test compounds inhibit the mouse gastrointestinal transit in antinociceptive doses. Taken together, these findings suggest that the systemic administration of the novel compound 14-O-MeM6SU similar to M6SU in specific dose ranges showed peripheral antinociception in rat and mouse inflammatory pain models without central adverse effects. These findings apply for male animals, and need to be confirmed in females. Therefore titration of systemic doses of opioid compounds with limited access to the brain might offer peripheral antinociception of clinical importance

New opioid receptor antagonist: naltrexone-14-O-sulfate synthesis and pharmacology.

Opioid antagonists, naloxone and naltrexone have long been used in clinical practice and research. In addition to their low selectivity, they easily pass through the blood-brain barrier. Quaternization of the amine group in these molecules, (e.g. methylnaltrexone) results in negligible CNS penetration. In addition, zwitterionic compounds have been reported to have limited CNS access. The current study, for the first time gives report on the synthesis and the in vitro [competition binding, G-protein activation, isolated mouse vas deferens (MVD) and mouse colon assay] pharmacology of the zwitterionic compound, naltrexone-14-O-sulfate. Naltrexone, naloxone, and its 14-O-sulfate analogue were used as reference compounds. In competition binding assays, naltrexone-14-O-sulfate showed lower affinity for micro, delta or kappa opioid receptor than the parent molecule, naltrexone. However, the mu/kappa opioid receptor selectivity ratio significantly improved, indicating better selectivity. Similar tendency was observed for naloxone-14-O-sulfate when compared to naloxone. Naltrexone-14-O-sulfate failed to activate GTPgammaS-binding but inhibit the activation evoked by opioid agonists (DAMGO, Ile5,6deltorphin II and U69593), similarly to the reference compounds. Schild plot constructed in MVD revealed that naltrexone-14-O-sulfate acts as a competitive antagonist. In mouse colon, naltrexone-14-O-sulfate antagonized the inhibitory effect of morphine with lower affinity compared to naltrexone and higher affinity when compared to naloxone or naloxone-14-O-sulfate. In vivo (mouse tail-flick test), subcutaneously injected naltrexone-14-O-sulfate antagonized morphine's antinociception in a dose-dependent manner, indicating it's CNS penetration, which was unexpected from such zwitter ionic structure. Future studies are needed to evaluate it's pharmacokinetic profile