title: In vivo metabolism of 24R,25-dihydroxyvitamin D3: structure of its major bile metabolite.
abstract: In vivo metabolism of 24R,25-dihydroxyvitamin D3 (24,25-(OH)2D3) in female dogs has been studied thoroughly, and its major bile metabolite identified. After single oral administration of 24,25-(OH)2 [6,19,19-3H]D3 the plasma concentrations of radioactive metabolites were monitored for 504 h, and the metabolites in the bile collected and analyzed. The concentration of 24,25-(OH)2D3 in plasma reached a maximum after 6 h and decayed in two distinct phases; a fast-phase with a half-life of 17 h, followed by a slow-phase with a 17-day half-life. The area under the concentration/time curve (AUC) was 78-84% (0-504 h). The only detectable metabolite in the plasma was 25-hydroxy-24-oxovitamin D3 whose AUC was less than 5%. At 504 h, about 50% of administered radioactivity has been excreted, of which about 90% was found in the feces, indicating most of the administered 24,25-(OH)2D3 to be excreted in bile. A major metabolite, which constituted 23% of the total bile radioactivity at 504 h, was found in the bile. This metabolite was efficiently deconjugated by beta-glucuronidase to afford an aglycone which was identified as 23S,25-dihydroxy-24-oxovitamin D3 (23S,25-(OH)2-24-oxo-D3), by co-chromatography on HPLC with synthetic standards. The glucuronide was isolated from the bile of dogs given large doses of 24,25-(OH)2D3, and the structure determined being 23-(beta-glucuronide) of 23S,25-(OH)2-24-oxo-D3, by analyzing its negative ion mass spectrum and the positive ion mass spectrum of its derivatives. Thus it was concluded that, in dogs, 24,25-(OH)2D3 is a long lasting vitamin D metabolite, is mainly excreted in bile when metabolized to 23S,25-(OH)2-24-oxo-D3 and is conjugated at 23-OH as glucuronide.
authors.affiliation: Institute for Medical and Dental Engineering, Tokyo Medical and Dental University, Kanda, Chiyoda-ku, Japan.
authors.forename: A
authors.initials: A
authors.lastname: Shimoyamada
authors.forename: S
authors.initials: S
authors.lastname: Tomiyama
authors.forename: M
authors.initials: M
authors.lastname: Shimizu
authors.forename: K
authors.initials: K
authors.lastname: Yamamoto
authors.forename: S
authors.initials: S
authors.lastname: Kunii
authors.forename: S
authors.initials: S
authors.lastname: Yamada
mesh_terms: D015650:24,25-Dihydroxyvitamin D 3 / Q000378:metabolism* / Q000493:pharmacokinetics; D000818:Animals; D001192:Arylsulfatases / Q000378:metabolism; D001646:Bile / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid; D004100:Dihydroxycholecalciferols / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D004285:Dogs; D004872:Ergocalciferols / Q000737:chemistry / Q000378:metabolism; D005260:Female; D005965:Glucuronates / Q000737:chemistry / Q000378:metabolism; D005966:Glucuronidase / Q000378:metabolism; D013058:Mass Spectrometry; D015394:Molecular Structure
chemical_list: D004100:Dihydroxycholecalciferols; D004872:Ergocalciferols; D005965:Glucuronates; D015650:24,25-Dihydroxyvitamin D 3; C037780:23,25-dihydroxy-24-oxovitamin D3; D001192:Arylsulfatases; D005966:Glucuronidase