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Characterization of equine cytochrome P450: role of CYP 3A in the metabolism of diazepam
Author(s) -
Nakayama S. M. M.,
Ikenaka Y.,
Hayami A.,
Mizukawa H.,
Darwish W. S.,
Watanabe K. P.,
Kawai Y. K.,
Ishizuka M.
Publication year - 2016
Publication title -
journal of veterinary pharmacology and therapeutics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.527
H-Index - 60
eISSN - 1365-2885
pISSN - 0140-7783
DOI - 10.1111/jvp.12303
Subject(s) - cytochrome p450 , metabolite , oxazepam , microsome , pharmacology , diazepam , pharmacokinetics , temazepam , drug metabolism , chemistry , metabolism , horse , in vivo , active metabolite , enzyme , biochemistry , biology , benzodiazepine , receptor , genetics , paleontology
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 ( CYP s) are central to drug pharmacokinetics. This study elucidated the characteristics of equine CYP s 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 CYP s. 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 CYP 3A was the main enzyme responsible for DZP metabolism in horse. Four recombinant equine CYP 3A isoforms expressed in Cos‐7 cells showed that CYP 3A96, CYP 3A94, and CYP 3A89 were important for TMZ formation, whereas CYP 3A97 exhibited more limited activity. Phylogenetic analysis suggested diversification of CYP 3As in each mammalian order. Further study is needed to elucidate functional characteristics of each equine CYP 3A isoform for effective use of diazepam in horses.