Nakayama S M M, Ikenaka Y, Hayami A, Mizukawa H, Darwish W S, Watanabe K P, Kawai Y K, Ishizuka M
Laboratory of Toxicology, Department of Environmental Veterinary Sciences, Graduate School of Veterinary Medicine, Hokkaido University, Kita-ku, Sapporo, Japan.
Water Research Group, Unit for Environmental Sciences and Management, North-West University, Potchefstroom, South Africa.
J Vet Pharmacol Ther. 2016 Oct;39(5):478-87. doi: 10.1111/jvp.12303. Epub 2016 Mar 11.
Research on drug metabolism and pharmacokinetics in large animal species including the horse is scarce because of the challenges in conducting in vivo studies. The metabolic reactions catalyzed by cytochrome P450s (CYPs) are central to drug pharmacokinetics. This study elucidated the characteristics of equine CYPs using diazepam (DZP) as a model compound as this drug is widely used as an anesthetic and sedative in horses, and is principally metabolized by CYPs. Diazepam metabolic activities were measured in vitro using horse and rat liver microsomes to clarify the species differences in enzyme kinetic parameters of each metabolite (temazepam [TMZ], nordiazepam [NDZ], p-hydroxydiazepam [p-OH-DZP], and oxazepam [OXZ]). In both species microsomes, TMZ was the major metabolite, but the formation rate of p-OH-DZP was significantly less in the horse. Inhibition assays with a CYP-specific inhibitors and antibody suggested that CYP3A was the main enzyme responsible for DZP metabolism in horse. Four recombinant equine CYP3A isoforms expressed in Cos-7 cells showed that CYP3A96, CYP3A94, and CYP3A89 were important for TMZ formation, whereas CYP3A97 exhibited more limited activity. Phylogenetic analysis suggested diversification of CYP3As in each mammalian order. Further study is needed to elucidate functional characteristics of each equine CYP3A isoform for effective use of diazepam in horses.
由于在体内进行研究存在挑战，包括马在内的大型动物物种的药物代谢和药代动力学研究很少。细胞色素P450（CYP）催化的代谢反应是药物药代动力学的核心。本研究以地西泮（DZP）为模型化合物，阐明了马CYP的特征，因为该药物在马中广泛用作麻醉剂和镇静剂，并且主要由CYP代谢。使用马和大鼠肝微粒体在体外测量地西泮代谢活性，以阐明每种代谢物（替马西泮[TMZ]、去甲地西泮[NDZ]、对羟基地西泮[p-OH-DZP]和奥沙西泮[OXZ]）的酶动力学参数的物种差异。在两个物种的微粒体中，TMZ都是主要代谢物，但马中p-OH-DZP的形成速率明显较低。用CYP特异性抑制剂和抗体进行的抑制试验表明，CYP3A是马中负责DZP代谢的主要酶。在Cos-7细胞中表达的四种重组马CYP3A同工型表明，CYP3A96、CYP3A94和CYP3A89对TMZ的形成很重要，而CYP3A97的活性则较为有限。系统发育分析表明，每个哺乳动物目中CYP3A都有多样化。需要进一步研究以阐明每种马CYP3A同工型的功能特征，以便在地西泮在马中的有效使用。
