{"title":"Activation of μ receptors by SR-17018 through a distinctive mechanism","authors":"","doi":"10.1016/j.neuropharm.2024.110093","DOIUrl":null,"url":null,"abstract":"<div><p>Agonists at μ opioid receptors relieve acute pain, however, their long-term use is limited by side effects, which may involve β-arrestin2. Agonists biased against β-arrestin2 recruitment may be advantageous. However, the classification of bias may be compromised by assays utilising overexpressed μ receptors which overestimate efficacy for G-protein activation. There is a need for re-evaluation with restricted receptor availability to determine accurate agonist efficacies. We depleted μ receptor availability in PathHunter CHO cells using the irreversible antagonist, β-funaltrexamine (β-FNA), and compared efficacies and apparent potencies of twelve agonists, including several previously reported as biased, in β-arrestin2 recruitment and cAMP assays. With full receptor availability all agonists had partial efficacy for stimulating β-arrestin2 recruitment relative to DAMGO, while only TRV130 and buprenorphine were partial agonists as inhibitors of cAMP accumulation. Limiting receptor availability by prior exposure to β-FNA (100 nM) revealed morphine, oxycodone, PZM21, herkinorin, U47700, tianeptine and U47931e are also partial agonists in the cAMP assay. The efficacies of all agonists, except SR-17018, correlated between β-arrestin2 recruitment and cAMP assays, with depleted receptor availability in the latter. Furthermore, naloxone and cyprodime exhibited non-competitive antagonism of SR-17018 in the β-arrestin2 recruitment assay. Limited antagonism by naloxone was also non-competitive in the cAMP assay, while cyprodime was competitive. Furthermore, SR-17018 only negligibly diminished β-arrestin2 recruitment stimulated by DAMGO (1 μM), whereas fentanyl, morphine and TRV130 all exhibited the anticipated competitive inhibition. The data suggest that SR-17018 achieves bias against β-arrestin2 recruitment through interactions with μ receptors outside the orthosteric agonist site.</p></div>","PeriodicalId":19139,"journal":{"name":"Neuropharmacology","volume":null,"pages":null},"PeriodicalIF":4.6000,"publicationDate":"2024-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Neuropharmacology","FirstCategoryId":"3","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0028390824002624","RegionNum":2,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"NEUROSCIENCES","Score":null,"Total":0}
引用次数: 0
Abstract
Agonists at μ opioid receptors relieve acute pain, however, their long-term use is limited by side effects, which may involve β-arrestin2. Agonists biased against β-arrestin2 recruitment may be advantageous. However, the classification of bias may be compromised by assays utilising overexpressed μ receptors which overestimate efficacy for G-protein activation. There is a need for re-evaluation with restricted receptor availability to determine accurate agonist efficacies. We depleted μ receptor availability in PathHunter CHO cells using the irreversible antagonist, β-funaltrexamine (β-FNA), and compared efficacies and apparent potencies of twelve agonists, including several previously reported as biased, in β-arrestin2 recruitment and cAMP assays. With full receptor availability all agonists had partial efficacy for stimulating β-arrestin2 recruitment relative to DAMGO, while only TRV130 and buprenorphine were partial agonists as inhibitors of cAMP accumulation. Limiting receptor availability by prior exposure to β-FNA (100 nM) revealed morphine, oxycodone, PZM21, herkinorin, U47700, tianeptine and U47931e are also partial agonists in the cAMP assay. The efficacies of all agonists, except SR-17018, correlated between β-arrestin2 recruitment and cAMP assays, with depleted receptor availability in the latter. Furthermore, naloxone and cyprodime exhibited non-competitive antagonism of SR-17018 in the β-arrestin2 recruitment assay. Limited antagonism by naloxone was also non-competitive in the cAMP assay, while cyprodime was competitive. Furthermore, SR-17018 only negligibly diminished β-arrestin2 recruitment stimulated by DAMGO (1 μM), whereas fentanyl, morphine and TRV130 all exhibited the anticipated competitive inhibition. The data suggest that SR-17018 achieves bias against β-arrestin2 recruitment through interactions with μ receptors outside the orthosteric agonist site.
期刊介绍:
Neuropharmacology publishes high quality, original research and review articles within the discipline of neuroscience, especially articles with a neuropharmacological component. However, papers within any area of neuroscience will be considered. The journal does not usually accept clinical research, although preclinical neuropharmacological studies in humans may be considered. The journal only considers submissions in which the chemical structures and compositions of experimental agents are readily available in the literature or disclosed by the authors in the submitted manuscript. Only in exceptional circumstances will natural products be considered, and then only if the preparation is well defined by scientific means. Neuropharmacology publishes articles of any length (original research and reviews).