title: Metabolism of 25-hydroxydihydrotachysterol3 in bone cells in vitro.
abstract: Dihydrotachysterol3, a reduced (or hydrogenated) analog of vitamin D3 in which the A ring has been rotate through 180 degrees , is, after hepatic 25-hydroxylation, converted in vivo to a dihydroxylated metabolite, termed peak H, which is at present unidentified but with good affinity for the vitamin D receptor. Although peak H is made in relatively large amounts in vivo, it has not yet been possible to synthesize it in vitro. Mass spectrometric evidence suggests that peak H is 25-hydroxylated and the presumption that it is a metabolite of 25-hydroxydihydrotachysterol3 was confirmed by the demonstration that radiolabeled peak H was formed in vivo in the rat after injection of 25-hydroxy-[10,19-3H]dihydrotachysterol3, produced from [10,19-3H]dihydrotachysterol3 in a hepatic cell model. The metabolism of 25-hydroxy-[10,19-3H]dihydrotachysterol3 was also studied in a rat osteosarcoma cell UMR-106, a known target cell for vitamin D, using high (11 microM) and low (10 nM) substrate concentrations. Metabolic products were isolated by lipid extraction, purified by high-performance liquid chromatography, and characterized by direct-probe mass spectrometry and gas chromatography/mass spectrometry. The formation of peak H from 25-hydroxydihydrotachysterol3 could not be demonstrated in UMR-106 cells. However, 25-hydroxydihydrotachysterol3 was metabolized to at least seven side-chain modified metabolites, each of which was extensively characterized and tentatively identified. It is concluded that the vitamin D enzyme system present in UMR-106 cells is able to metabolize dihydrotachysterol3 very efficiently to a series of metabolites but is incapable of producing peak H.
authors.affiliation: Department of Biochemistry, Queen's University, Kingston, Ontario, Canada.
authors.forename: F S
authors.initials: FS
authors.lastname: Qaw
authors.forename: H L
authors.initials: HL
authors.lastname: Makin
authors.forename: G
authors.initials: G
authors.lastname: Jones
mesh_terms: D000818:Animals; D001842:Bone and Bones / Q000378:metabolism*; D006528:Carcinoma, Hepatocellular / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D004097:Dihydrotachysterol / Q000378:metabolism*; D006801:Humans; D006900:Hydroxylation; D008099:Liver / Q000378:metabolism; D008113:Liver Neoplasms / Q000378:metabolism; D008297:Male; D013058:Mass Spectrometry; D012516:Osteosarcoma / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D014407:Tumor Cells, Cultured
chemical_list: D004097:Dihydrotachysterol