title: Cell specificity and properties of the C-3 epimerization of Vitamin D3 metabolites.
abstract: It is well documented that Vitamin D3 metabolites and synthetic analogs are metabolized to their epimers of the hydroxyl group at C-3 of the A-ring. We investigated the C-3 epimerization of Vitamin D3 metabolites in various cultured cells and basic properties of the enzyme responsible for the C-3 epimerization. 1alpha,25-Dihydroxyvitamin D3 [1alpha,25(OH)2D3], 25-hydroxyvitamin D3 [25(OH)D3] and 24,25-dihydroxyvitamin D3 [24,25(OH)2D3] were metabolized to the respective C-3 epimers in UMR-106 (rat osteosarcoma), MG-63 (human osteosarcoma), Caco-2 (human colon adenocarcinoma), LLC-PK1 (porcine kidney) and HepG2 (human hepatoblastoma)] cells, although the differences existed in the amount of each C-3 epimer formed with different cell types. In terms of maximum velocity (Vmax) and Michaelis constant (Km) values for the C-3 epimerization in microsome fraction of UMR-106 cells, 25(OH)D3 exhibited the highest specificity for the C-3 epimerization among 1alpha,25(OH)2D3, 25(OH)D3 and 24,25(OH)2D3. C-3 epimerization activity was not inhibited by various cytochrome P450 inhibitors and antiserum against NADPH cytochrome P450 reductase. Neither CYP24, CYP27A1, CYP27B1 nor 3(alpha --> beta) -hydroxysteroid epimerase (HSE) catalyzed the C-3 epimerization in vitro. Based on these results, the enzyme responsible for the C-3 epimerization of Vitamin D3 are thought to be different from already-known cytochrome P450-related Vitamin D metabolic enzymes and HSE.
authors.affiliation: Department of Hygienic Sciences, Kobe Pharmaceutical University, 4-19-1 Motoyamakita-machi, Higashinada-ku, Kobe 658-8558, Japan.
authors.forename: Maya
authors.initials: M
authors.lastname: Kamao
authors.forename: Syuichiro
authors.initials: S
authors.lastname: Tatematsu
authors.forename: Natsumi
authors.initials: N
authors.lastname: Sawada
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Sakaki
authors.forename: Susumi
authors.initials: S
authors.lastname: Hatakeyama
authors.forename: Noboru
authors.initials: N
authors.lastname: Kubodera
authors.forename: Toshio
authors.initials: T
authors.lastname: Okano
mesh_terms: D000818:Animals; D002460:Cell Line; D002762:Cholecalciferol / Q000378:metabolism*; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D006801:Humans; D007536:Isomerism; D051381:Rats
chemical_list: D002762:Cholecalciferol; D003577:Cytochrome P-450 Enzyme System