Abstract：
Novel synthetic opioids (NSOs), including both fentanyl and non-fentanyl analogs that act as μ-opioid receptor (MOR) agonists, are associated with serious intoxication and fatal overdose. Previous studies proposed that G-protein-biased MOR agonists are safer pain medications, while other evidence indicates that low intrinsic efficacy at MOR better explains the reduced opioid side effects. Here, we characterized the in vitro functional profiles of various NSOs at the MOR using adenylate cyclase inhibition and β-arrestin2 recruitment assays, in conjunction with the application of the receptor depletion approach. By fitting the concentration-response data to the operational model of agonism, we deduced the intrinsic efficacy and affinity for each opioid in the Gi protein signaling and β-arrestin2 recruitment pathways. Compared to the reference agonist [d-Ala2,N-MePhe4,Gly-ol5]enkephalin, we found that several fentanyl analogs were more efficacious at inhibiting cAMP production, whereas all fentanyl analogs were less efficacious at recruiting β-arrestin2. In contrast, the non-fentanyl 2-benzylbenzimidazole (i.e., nitazene) analogs were highly efficacious and potent in both the cAMP and β-arrestin2 assays. Our findings suggest that the high intrinsic efficacy of the NSOs in Gi protein signaling is a common property that may underlie their high risk of intoxication and overdose, highlighting the limitation of using in vitro functional bias to predict the adverse effects of opioids. In addition, the extremely high potency of many NSOs now infiltrating illicit drug markets further contributes to the danger posed to public health.
摘要：
新型合成阿片类药物（NSO），包括作为μ阿片受体（MOR）激动剂的芬太尼和非芬太尼类似物，与严重中毒和致命过量有关。先前的研究表明，偏向G蛋白的MOR激动剂是更安全的止痛药，而其他证据表明，MOR的低内在疗效更好地解释了阿片类药物副作用的减少。这里,我们使用腺苷酸环化酶抑制和β-arrestin2募集测定法表征了MOR处各种NSO的体外功能概况，结合受体消耗方法的应用。通过将浓度-响应数据拟合到激动作用的操作模型，我们推导了Gi蛋白信号和β-arrestin2募集途径中每种阿片类药物的内在功效和亲和力。与参考激动剂[d-Ala2，N-MePhe4，Gly-ol5]脑啡肽相比，我们发现几种芬太尼类似物在抑制cAMP产生方面更有效，而所有的芬太尼类似物在招募β-arrestin2时都不太有效。相比之下,非芬太尼2-苄基苯并咪唑(即，硝胺）类似物在cAMP和β-arrestin2测定中均非常有效和有效。我们的研究结果表明，NSO在Gi蛋白信号传导中的高内在功效是一个共同的特性，这可能是它们中毒和过量服用的高风险的基础。强调使用体外功能偏倚预测阿片类药物不良反应的局限性。此外,许多国家统计局现在渗透到非法药物市场的极高效力进一步加剧了对公共卫生构成的危险。
