Metabolism of 1α,25-dihydroxyvitamin D3 and its C-3 epimer 1α,25-dihydroxy-3-epi-vitamin D3 in neonatal human keratinocytes

We previously reported that 1 alpha ,25-dihydroxyvitamin D-3 [1 alpha ,25(OH)(2)D-3] is metabolized into 1 alpha ,25-dihydroxy-3-epi-vitamin D-3 [1 alpha ,25(OH)(2)-3-epi-D-3] in primary cultures of neonatal human keratinocytes. We now report that 1 alpha ,25(OH)(2)-3-epi-D-3 itself is further metabolized in human keratinocytes into several polar metabolites. One of the polar metabolite was unequivocally identified as 1 alpha ,23,25-trihydroxy-3-epi-vitamin D-3 by mass spectrometry and its sensitivity to sodium periodate. Three of the polar metabolites were identified as 1 alpha ,24,25-trihydroxy-3-epi-vitamin D-3, 1 alpha ,25-dihydroxy-24-oxo-3-epi-vitamin D-3 and 1 alpha ,23,25-trihydroxy-24-oxo-3-epi-vitamin D-3 by comigration with authentic standards on both straight and reverse phase HPLC systems. In addition to the polar metabolites, 1 alpha ,25(OH)(2)-3-epi-D-3 was also metabolized into two less polar metabolites. A possible structure of either 1 alpha OH-3-epi-D-3-20,25-cyclic ether or 1 alpha OH-3-epi-D-3-24,25-epoxide was assigned to one of the less polar metabolites through mass spectrometry. Thus, we indicate for the first time that 1 alpha ,25(OH)(2)-3-epi-D-3 is metabolized in neonatal human keratinocytes not only via the same C-24 and C-23 oxidation pathways like its parent, 1 alpha ,25(OH)(2)D-3; but also is metabolized into a less polar metabolite via a pathway that is unique to 1 alpha ,25(OH)(2)-3-epi-D-3. (C) 2001 Elsevier Science Inc. All rights reserved.