Chen Chongguang, Huang Peng, Bland Kathryn, Li Mengchu, Zhang Yan, Liu-Chen Lee-Yuan
Center for Substance Abuse Research and Department of Neural Sciences, Temple University Lewis Katz School of Medicine, Philadelphia, PA, United States.
Department of Medicinal Chemistry, School of Pharmacy, Virginia Commonwealth University, Richmond, VA, United States.
Front Pharmacol. 2022 May 16;13:835809. doi: 10.3389/fphar.2022.835809. eCollection 2022.
Selective kappa opioid receptor (KOR) agonists are promising antipruritic agents and analgesics. However, clinical development of KOR agonists has been limited by side effects, including psychotomimetic effects, dysphoria, and sedation, except for nalfurafine, and recently. CR845 (difelikefalin). Activation of KOR elicits G protein- and β-arrestin-mediated signaling. KOR-induced analgesic and antipruritic effects are mediated by G protein signaling. However, different results have been reported as to whether conditioned place aversion (CPA) induced by KOR agonists is mediated by β-arrestin signaling. In this study, we examined in male mice if there was a connection between agonist-promoted CPA and KOR phosphorylation and internalization, proxies for β-arrestin recruitment using four KOR agonists. Herein, we demonstrated that at doses producing maximal effective analgesic and antiscratch effects, U50,488H, MOM-SalB, and 42B, but not nalfurafine, promoted KOR phosphorylation at T363 and S369 in mouse brains, as detected by immunoblotting with phospho-KOR-specific antibodies. In addition, at doses producing maximal effective analgesic and antiscratch effects, U50,488H, MOM-SalB, and 42B, but not nalfurafine, caused KOR internalization in the ventral tegmental area of a mutant mouse line expressing a fusion protein of KOR conjugated at the C-terminus with tdTomato (KtdT). We have reported previously that the KOR agonists U50,488H and methoxymethyl salvinorin B (MOM-SalB) cause CPA, whereas nalfurafine and 42B do not, at doses effective for analgesic and antiscratch effects. Taken together, these data reveal a lack of connection between agonist-promoted KOR-mediated CPA with agonist-induced KOR phosphorylation and internalization in male mice.
选择性κ阿片受体（KOR）激动剂是很有前景的止痒剂和镇痛药。然而，除了纳呋拉啡和最近的CR845（地氟来法林）外，KOR激动剂的临床开发受到副作用的限制，包括拟精神病效应、烦躁不安和镇静作用。KOR的激活引发G蛋白和β-抑制蛋白介导的信号传导。KOR诱导的镇痛和止痒作用由G蛋白信号传导介导。然而，关于KOR激动剂诱导的条件性位置厌恶（CPA）是否由β-抑制蛋白信号传导介导，已有不同的报道。在本研究中，我们使用四种KOR激动剂，在雄性小鼠中研究了激动剂促进的CPA与KOR磷酸化和内化之间是否存在联系，KOR磷酸化和内化是β-抑制蛋白募集的指标。在此，我们证明，通过使用磷酸化KOR特异性抗体进行免疫印迹检测，在产生最大有效镇痛和抗抓挠作用的剂量下，U50,488H、MOM-SalB和42B可促进小鼠大脑中KOR在T363和S369位点的磷酸化，但纳呋拉啡不能。此外，在产生最大有效镇痛和抗抓挠作用的剂量下，U50,488H、MOM-SalB和42B可导致在表达C末端与tdTomato（KtdT）缀合的KOR融合蛋白的突变小鼠品系的腹侧被盖区中KOR内化，但纳呋拉啡不能。我们之前曾报道，KOR激动剂U50,488H和甲氧基甲基Salvinorin B（MOM-SalB）在产生有效镇痛和抗抓挠作用的剂量下会导致CPA，而纳呋拉啡和42B则不会。综上所述，这些数据揭示了在雄性小鼠中，激动剂促进的KOR介导的CPA与激动剂诱导的KOR磷酸化和内化之间缺乏联系。
