Yadlapalli Jai Shankar K, Ford Benjamin M, Ketkar Amit, Wan Anqi, Penthala Narasimha R, Eoff Robert L, Prather Paul L, Dobretsov Maxim, Crooks Peter A
Departments of Pharmaceutical Sciences, University of Arkansas for Medical Sciences, Little Rock, AR, 72205, USA.
Pharmacology and Toxicology, University of Arkansas for Medical Sciences, Little Rock, AR, 72205, USA.
Pharmacol Res. 2016 Nov;113(Pt A):335-347. doi: 10.1016/j.phrs.2016.09.012. Epub 2016 Sep 13.
This study determined the antinociceptive effects of morphine and morphine-6-O-sulfate (M6S) in both normal and diabetic rats, and evaluated the comparative role of mu-opioid receptors (mu-ORs) and delta-opioid receptors (delta-ORs) in the antinociceptive action of these opioids. In vitro characterization of mu-OR and delta-OR-mediated signaling by M6S and morphine in stably transfected Chinese hamster ovary (CHO-K1) cells showed that M6S exhibited a 6-fold higher affinity for delta-ORs and modulated G-protein and adenylyl cyclase activity via delta-ORs more potently than morphine. Interestingly, while morphine acted as a full agonist at delta-ORs in both functional assays examined, M6S exhibited either partial or full agonist activity for modulation of G-protein or adenylyl cyclase activity, respectively. Molecular docking studies indicated that M6S but not morphine binds equally well at the ligand binding site of both mu- and delta-ORs. In vivo analgesic effects of M6S and morphine in both normal and streptozotocin-induced diabetic Sprague-Dawley rats utilizing the hot water tail flick latency test showed that M6S produced more potent antinociception than morphine in both normal rats and diabetic rats. This difference in potency was abrogated following antagonism of delta- but not mu- or kappa (kappa-ORs) opioid receptors. During 9days of chronic treatment, tolerance developed to morphine-treated but not to M6S-treated rats. Rats that developed tolerance to morphine still remained responsive to M6S. Collectively, this study demonstrates that M6S is a potent and efficacious mu/delta opioid analgesic with a delayed tolerance profile when compared to morphine in both normal and diabetic rats.
This study demonstrates that M6S acts at both mu- and delta-ORs, and adds to the growing evidence that the use of mixed mu/delta opioid agonists in pain treatment may have clinical benefit.
本研究确定了吗啡和吗啡 - 6 - O - 硫酸盐（M6S）在正常大鼠和糖尿病大鼠中的抗伤害感受作用，并评估了μ - 阿片受体（μ - ORs）和δ - 阿片受体（δ - ORs）在这些阿片类药物抗伤害感受作用中的比较作用。在稳定转染的中国仓鼠卵巢（CHO - K1）细胞中，对M6S和吗啡介导的μ - OR和δ - OR信号进行体外表征，结果显示M6S对δ - ORs的亲和力比吗啡高6倍，并且通过δ - ORs调节G蛋白和腺苷酸环化酶活性的效力比吗啡更强。有趣的是，在两种功能试验中，吗啡在δ - ORs上均表现为完全激动剂，而M6S在调节G蛋白或腺苷酸环化酶活性时分别表现为部分或完全激动剂活性。分子对接研究表明，M6S而非吗啡在μ - ORs和δ - ORs的配体结合位点结合能力相当。利用热水甩尾潜伏期试验，对正常和链脲佐菌素诱导的糖尿病Sprague - Dawley大鼠进行M6S和吗啡的体内镇痛作用研究，结果显示在正常大鼠和糖尿病大鼠中，M6S产生的抗伤害感受作用比吗啡更强。在拮抗δ - 阿片受体而非μ - 或κ（κ - ORs）阿片受体后，这种效力差异消失。在9天的慢性治疗期间，吗啡治疗的大鼠产生了耐受性，而M6S治疗的大鼠未产生耐受性。对吗啡产生耐受性的大鼠对M6S仍有反应。总体而言，本研究表明，与吗啡相比，M6S在正常和糖尿病大鼠中都是一种强效且有效的μ/δ阿片类镇痛药，且耐受性出现延迟。
本研究表明M6S作用于μ - ORs和δ - ORs，进一步证明了在疼痛治疗中使用μ/δ混合阿片类激动剂可能具有临床益处，这一证据越来越多。
