title: Calcitroic acid is a major catabolic metabolite in the metabolism of 1 alpha-dihydroxyvitamin D(2).
abstract: Calcitroic acid (1 alpha-hydroxy-23 carboxy-24,25,26,27-tetranorvitamin D(3)) is known to be the major water-soluble metabolite produced during the deactivation of 1 alpha,25-dihydroxyvitamin D(3). This deactivation process involves a series of oxidation reactions at C(24) and C(23) leading to side-chain cleavage and, ultimately, formation of the calcitroic acid. Like 1 alpha,25-dihydroxyvitamin D(3), 1 alpha,25-dihydroxyvitamin D(2) is also known to undergo side-chain oxidation; however, to date there has been no evidence suggesting that 1 alpha,25-dihydroxyvitamin D(2) undergoes side-chain cleavage. To investigate this possibility, we studied 1 alpha,25-dihydroxyvitamin D(2) metabolism in HPK1A-ras cells as well as the well characterized perfused rat kidney system. Lipid and aqueous-soluble metabolites were prepared for characterization. Aqueous-soluble metabolites were subjected to reverse-phase HPLC analysis. The major aqueous-soluble metabolite from both the kidney and cell incubations comigrated with authentic calcitroic acid on two reverse-phase HPLC columns of different chemistry. The putative calcitroic acid from the cell and kidney incubations was methylated and found to comigrate with methylated authentic standard on straight-phase and reverse-phase HPLC columns. The identity of the methylated metabolite from cell incubations was also confirmed by mass spectral analysis. These data show, for the first time, that calcitroic acid is a major terminal product for the deactivation of 1 alpha,25-dihydroxyvitamin D(2). Intermediates leading to the formation of the calcitroic acid in the 1 alpha,25-dihydroxyvitamin D(2) metabolism pathway are currently being studied.
authors.affiliation: Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, Iowa 50011, USA.
authors.forename: D R
authors.initials: DR
authors.lastname: Zimmerman
authors.forename: T A
authors.initials: TA
authors.lastname: Reinhardt
authors.forename: R
authors.initials: R
authors.lastname: Kremer
authors.forename: D C
authors.initials: DC
authors.lastname: Beitz
authors.forename: G S
authors.initials: GS
authors.lastname: Reddy
authors.forename: R L
authors.initials: RL
authors.lastname: Horst
mesh_terms: D000818:Animals; D002117:Calcitriol / Q000031:analogs & derivatives / Q000737:chemistry / Q000378:metabolism*; D002460:Cell Line; D002851:Chromatography, High Pressure Liquid; D004872:Ergocalciferols / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D007668:Kidney / Q000378:metabolism; D013058:Mass Spectrometry; D010084:Oxidation-Reduction; D010477:Perfusion; D051381:Rats; D012995:Solubility
chemical_list: D004872:Ergocalciferols; C003564:1,25-dihydroxyergocalciferol; C021640:calcitroic acid; D002117:Calcitriol