title: Metabolism of 25-hydroxyvitamin D3 by microsomal and mitochondrial vitamin D3 25-hydroxylases (CYP2D25 and CYP27A1): a novel reaction by CYP27A1.
abstract: The metabolism of 25-hydroxyvitamin D(3) was studied with a crude mitochondrial cytochrome P450 extract from pig kidney and with recombinant human CYP27A1 (mitochondrial vitamin D(3) 25-hydroxylase) and porcine CYP2D25 (microsomal vitamin D(3) 25-hydroxylase). The kidney mitochondrial cytochrome P450 catalyzed the formation of 1alpha,25-dihydroxyvitamin D(3), 24,25-dihydroxyvitamin D(3) and 25,27-dihydroxyvitamin D(3). An additional metabolite that was separated from the other hydroxylated products on HPLC was also formed. The formation of this 25-hydroxyvitamin D(3) metabolite was dependent on NADPH and the mitochondrial electron transferring protein components. A monoclonal antibody directed against purified pig liver CYP27A1 immunoprecipitated the 1alpha- and 27-hydroxylase activities towards 25-hydroxyvitamin D(3) as well as the formation of the unknown metabolite. These results together with substrate inhibition experiments indicate that CYP27A1 is responsible for the formation of the unknown 25-hydroxyvitamin D(3) metabolite in kidney. Recombinant human CYP27A1 was found to convert 25-hydroxyvitamin D(3) into 1alpha,25-dihydroxyvitamin D(3), 25,27-dihydroxyvitamin D(3) and a major metabolite with the same retention time on HPLC as that formed by kidney mitochondrial cytochrome P450. Gas chromatography-mass spectrometry (GC-MS) analysis of the unknown enzymatic product revealed it to be a triol different from other known hydroxylated 25-hydroxyvitamin D(3) metabolites such as 1alpha,25-, 23,25-, 24,25-, 25,26- or 25,27-dihydroxyvitamin D(3). The product had the mass spectrometic properties expected for 4beta,25-dihydroxyvitamin D(3). Recombinant porcine CYP2D25 converted 25-hydroxyvitamin D(3) into 1alpha,25-dihydroxyvitamin D(3) and 25,26-dihydroxyvitamin D(3). It can be concluded that both CYP27A1 and CYP2D25 are able to carry out multiple hydroxylations of 25-hydroxyvitamin D(3).
authors.affiliation: Division of Biochemistry, Department of Pharmaceutical Biosciences, University of Uppsala, Box 578, Husargatan 3, S-751 23 Uppsala, Sweden.
authors.forename: Zufan
authors.initials: Z
authors.lastname: Araya
authors.forename: Fardin
authors.initials: F
authors.lastname: Hosseinpour
authors.forename: Karl
authors.initials: K
authors.lastname: Bodin
authors.forename: Kjell
authors.initials: K
authors.lastname: Wikvall
mesh_terms: D000325:Adrenodoxin / Q000378:metabolism; D000818:Animals; D000911:Antibodies, Monoclonal / Q000378:metabolism; D002112:Calcifediol / Q000378:metabolism*; D002461:Cell Line, Transformed; D003577:Cytochrome P-450 Enzyme System / Q000302:isolation & purification / Q000378:metabolism*; D005287:Ferredoxin-NADP Reductase / Q000378:metabolism; D006801:Humans; D006900:Hydroxylation; D007668:Kidney / Q000166:cytology; D007700:Kinetics; D008862:Microsomes, Liver / Q000201:enzymology*; D008928:Mitochondria / Q000201:enzymology*; D008930:Mitochondria, Liver / Q000201:enzymology; D011994:Recombinant Proteins / Q000302:isolation & purification / Q000378:metabolism; D013379:Substrate Specificity; D013552:Swine; D013997:Time Factors
chemical_list: D000911:Antibodies, Monoclonal; D011994:Recombinant Proteins; D000325:Adrenodoxin; D003577:Cytochrome P-450 Enzyme System; D005287:Ferredoxin-NADP Reductase; D002112:Calcifediol