μ阿片受体激动剂缓解急性疼痛,然而,它们的长期使用受到副作用的限制,可能涉及β-arrestin2。偏向β-arrestin2募集的激动剂可能是有利的。然而,偏倚的分类可能会受到使用过表达的μ受体的测定的影响,这些μ受体高估了G蛋白激活的功效。需要用受限的受体可用性重新评估以确定准确的激动剂效力。我们使用不可逆拮抗剂耗尽了PathHunterCHO细胞中μ受体的可用性,β-福纳曲胺(β-FNA),并比较了12种激动剂的疗效和表观效力,包括一些以前报道的偏见,在β-arrestin2募集和cAMP测定中。相对于DAMGO,由于受体完全可用,所有激动剂对刺激β-arrestin2募集具有部分功效,而只有TRV130和丁丙诺啡是部分激动剂作为cAMP积累的抑制剂。通过先前暴露于β-FNA(100nM)限制受体的可用性显示吗啡,羟考酮,PZM21,Herkinorin,U47700、tianeptine和U47931e也是cAMP测定中的部分激动剂。所有参与者的功效,除SR-17018外,β-arrestin2募集与cAMP测定相关,后者的受体可用性耗尽。此外,在β-arrestin2募集试验中,纳洛酮和环丙地姆表现出SR-17018的非竞争性拮抗作用。纳洛酮的有限拮抗作用在cAMP测定中也是非竞争性的,而环丙肽是有竞争力的。此外,SR-17018仅可忽略地减少DAMGO(1μM)刺激的β-arrestin2募集,而芬太尼,吗啡和TRV130均表现出预期的竞争性抑制。数据表明,SR-17018通过与正位激动剂位点外部的μ受体相互作用,实现了对β-arrestin2募集的偏见。
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. This article is part of the Special Issue on \"Ligand Bias\".