Calcitroic acid is a major catabolic metabolite in the metabolism of 1 alpha-dihydroxyvitamin D-2

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 de activation of 1 alpha ,25-dihydroxyvitamin D-3. This deactivation process i nvolves a series of oxidation reactions at C-24 and C-23 leading to side-ch ain cleavage and, ultimately, formation of the calcitroic acid. Like 1 alph a ,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 evidenc e suggesting that 1 alpha ,25-dihydroxyvitamin D-2 undergoes side-chain cle avage. To investigate this possibility, we studied 1 alpha ,25-dihydroxyvit amin D-2 metabolism in HPK1A-ras cells as well as the well characterized pe rfused rat kidney system. Lipid and aqueous-soluble metabolites were prepar ed for characterization. Aqueous-soluble metabolites were subjected to reve rse-phase HPLC analysis. The major aqueous-soluble metabolite from both the kidney and cell incubations comigrated with authentic calcitroic acid on t wo reverse-phase HPLC columns of different chemistry. The putative calcitro ic acid from the cell and kidney incubations was methylated and found to co migrate with methylated authentic standard on straight-phase and reverse-ph ase HPLC columns. The identity of the methylated metabolite from cell incub ations was also confirmed by mass spectral analysis. These data show, for t he first time, that calcitroic acid is a major terminal product for the dea ctivation of 1 alpha ,25-dihydroxyvitamin D-2. Intermediates leading to the formation of the calcitroic acid in the 1 alpha ,25-dihydroxyvitamin D-2 m etabolism pathway are currently being studied. (C) 2001 Academic Press.