title: Two novel metabolic pathways of 22-oxacalcitriol (OCT). C-25 dehydration and C-3 epimerization and biological activities of novel OCT metabolites.
abstract: 22-Oxacalcitriol (OCT) is an analog of calcitriol, characterized by potent differentiation-inducing activity and low calcemic liability. The metabolism of OCT has been studied and its polar metabolites, such as 24/26-hydroxylated-OCT and hexanor-1 alpha,20-dihydroxyvitamin D(3) (1 alpha,20(OH)(2)D(3)), have been identified. In contrast, little is known about the less polar metabolites of OCT, which have been found in relatively large amounts. In this study, the in vitro metabolism of OCT was studied in UMR 106, Caco-2, and LLC-PK(1) cells to identify the less polar metabolites and to assess their biological activity. OCT was initially metabolized to three less polar metabolites, 3-epi-OCT and two dehydrates, 25-dehydroxy- 25-ene-22-oxa-1 alpha(OH)D(3) (25-ene-22-oxa-1 alpha(OH)D(3)) and 25-dehydroxy-24-ene-22-oxa-1 alpha(OH)D(3) (24-ene-22-oxa-1 alpha(OH)D(3)). We also observed further metabolites, the two C-3 epimers of the C-25 dehydrates, 25-ene-3-epi-22-oxa-1 alpha(OH)D(3) and 24-ene-3-epi-22-oxa-1 alpha(OH)D(3). The structures of these metabolites were successfully assigned by (1)H NMR and LC-MS analyses. The three cell lines differ in their ability to metabolize OCT through the C-3 epimerization or the C-25 dehydration pathway. The biological activity of the OCT metabolites assessed by a luciferase reporter gene transcriptional activation system, binding assays for the vitamin D receptor (VDR) and vitamin D-binding protein (DBP), and assays for regulatory activities of cell differentiation and proliferation was found to be lower than that of OCT. Thus, both the C-3 epimerization and C-25 dehydration may work to reduce the biological activity of OCT.
authors.affiliation: Department of Hygienic Sciences, Kobe Pharmaceutical University, Kobe 658-8558, Japan.
authors.forename: Maya
authors.initials: M
authors.lastname: Kamao
authors.forename: Syuichiro
authors.initials: S
authors.lastname: Tatematsu
authors.forename: Susumi
authors.initials: S
authors.lastname: Hatakeyama
authors.forename: Keiichi
authors.initials: K
authors.lastname: Ozono
authors.forename: Noboru
authors.initials: N
authors.lastname: Kubodera
authors.forename: G Satyanarayana
authors.initials: GS
authors.lastname: Reddy
authors.forename: Toshio
authors.initials: T
authors.lastname: Okano
mesh_terms: D000818:Animals; D002117:Calcitriol / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology; D002454:Cell Differentiation / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D002851:Chromatography, High Pressure Liquid; D006801:Humans
chemical_list: D002117:Calcitriol; C051883:maxacalcitol