Characterization of new conjugated metabolites in bile of rats administered 24,25-dihydroxyvitamin D3 and 25-hydroxyvitamin D3

The characterization of new conjugated vitamin D metabolites in rat bile was performed using HPLC, liquid chromatography/tandem mass spectrometry combined derivatization, and GC-MS. After the administration of 24,25-dihydroxyvitamin D-3 to rats, 23,25-dihydroxy-24-oxovitamin D-3 23-glucuronide, 3-epi-24,25-dihydroxyvitamin D-3 24-glucuronide, and 24,25-dihydroxyvitamin D-3 3-sulfate were obtained as new biliary metabolites together with 24,25-dihydroxyvitamin D-3 3- and 24-glucuronides. The above metabolites, except 24,25-dihydroxyvitamin D-3 3-glucuronide, were obtained from rats dosed with 25-hydroxyvitamin D-3. 23,25-Dihydroxyvitamin D-3 23-glucuronide was also obtained from the bile of rats administered 25-hydroxyvitamin D-3 in addition to its 3-glucuronide, 25-glucuronide, and 3-sulfate. Thus, it was found that 24,25-dihydroxyvitamin D-3 and 25-hydroxyvitamin D-3 were directly conjugated as glucuronide and sulfate, whereas at the C-23 position, they were hydroxylated and then conjugated. Furthermore, we found that the C-3 epimerization acts as one of the important pathways in vitamin D metabolism. (C) 2000 Elsevier Science Inc. All rights reserved.