Inactivation of Rat Cytochrome P450 2D Enzyme by a Further Metabolite of 4-Hydroxypropranolol, the Major and Active Metabolite of Propranolol

Shizuo NARIMATSU; Takayuki ARAI; Yasuhiro MASUBUCHI; Toshiharu HORIE; Masakiyo HOSOKAWA; Koichi UENO; Hiroyuki KATAOKA; Shigeo YAMAMOTO; Tsutomu ISHIKAWA; Arthur K. CHO

doi:10.1248/bpb.24.988

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Inactivation of Rat Cytochrome P450 2D Enzyme by a Further Metabolite of 4-Hydroxypropranolol, the Major and Active Metabolite of Propranolol

Shizuo NARIMATSU, Takayuki ARAI, Yasuhiro MASUBUCHI, Toshiharu HORIE, Masakiyo HOSOKAWA, Koichi UENO, Hiroyuki KATAOKA, Shigeo YAMAMOTO, Tsutomu ISHIKAWA, Arthur K. CHO

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Shizuo NARIMATSU
Laboratories of Health Chemistry, Faculty of Pharmaceutical Sciences, Okayama University
Takayuki ARAI
Department of Biopharmaceutics, Graduate School of Pharmaceutical Sciences, Chiba University
Yasuhiro MASUBUCHI
Department of Biopharmaceutics, Graduate School of Pharmaceutical Sciences, Chiba University
Toshiharu HORIE
Department of Biopharmaceutics, Graduate School of Pharmaceutical Sciences, Chiba University
Masakiyo HOSOKAWA
Department of Biochemical Pharmacology, Graduate School of Pharmaceutical Sciences, Chiba University
Koichi UENO
Department of Geriatric Pharmacology and Therapeutics, Graduate School of Pharmaceutical Sciences, Chiba University
Hiroyuki KATAOKA
Laboratories of Health Chemistry, Faculty of Pharmaceutical Sciences, Okayama University
Shigeo YAMAMOTO
Laboratories of Biomolecular Sciences, Faculty of Pharmaceutical Sciences, Okayama University
Tsutomu ISHIKAWA
Department of Medicinal Organic Chemistry, Graduate School of Pharmaceutical Sciences, Chiba University
Arthur K. CHO
Department of Molecular and Medical Pharmacology, University of California Los Angeles School of Medicine

Keywords: 4-hydroxypropranolol, enzyme inactivation, rat CYP2D enzyme, bunitrolol, quinine, 1,4-naphthoquinone

JOURNAL FREE ACCESS

2001 Volume 24 Issue 9 Pages 988-994

DOI https://doi.org/10.1248/bpb.24.988

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Abstract

Repetitive administration of propranolol (PL) in rats decreases the activities of cytochrome P450 (CYP) 2D enzyme(s) in hepatic microsomes. We examined the properties of 4-hydroxypropranolol (4-OH-PL) as an inactivator of rat liver microsomal CYP2D enzyme(s) using bunitrolol (BTL) 4-hydroxylation and PL 5- and 7-hydroxylations as indices of CYP2D enzyme activity. Rat microsomal BTL 4-hydroxylase activity was inhibited by the addition of 4-OH-PL to the incubation medium. The inhibition was greater after preincubation of microsomes with 4-OH-PL in the presence of NADPH than in its absence. The type of inhibition kinetics of BTL 4-hydroxylase by 4-OH-PL was changed from a competitive type to a noncompetitive type by the preincubation. The inhibition of rat liver microsomal PL 5- and 7-hydroxylases by 4-OH-PL was blocked efficiently by co-incubation with quinine, a typical inhibitor of rat CYP2D enzyme(s), or to a lesser extent by BTL. However, quinidine, a diastereomer of quinine, did not significantly protect against the enzyme inactivation. The protective capacities of the substrate and inhibitors reflected their affinities for rat CYP2D enzyme(s). BTL hydroxylase was not affected by either 1,4-naphthoquinone or 1,4-dihydroxynaphthalene which are possible metabolites of 4-OH-PL. These results provide further evidence to support the notion that PL is biotransformed by rat CYP2D enzyme(s) to 4-OH-PL, which is further oxidized to a chemically reactive metabolite in the active site. The inactivation of CYP is likely the result of covalent binding of the reactive species to an amino acid residue of the active site.

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