In vivo production of novel vitamin D2 hydroxy-derivatives by human placentas, epidermal keratinocytes, Caco-2 colon cells and the adrenal gland

We investigated the metabolism of vitamin D2 to hydroxyvitamin D2 metabolites ((OH)D2) by human placentas ex-utero, adrenal glands ex-vivo and cultured human epidermal keratinocytes and colonic Caco-2 cells, and identified 20(OH)D2, 17,20(OH)(2)D2, 1,20(OH)(2)D2, 25(OH)D2 and 1,25(OH)(2)D2 as products. Inhibition of product formation by 22R-hydroxycholesterol indicated involvement of CYPIIAI in 20- and 17-hydroxylation of vitamin D2, while use of ketoconazole indicated involvement of CYP27B1 in lot-hydroxylation of products. Studies with purified human CYP11A1 confirmed the ability of this enzyme to convert vitamin D2 to 20(OH)D2 and 17,20(OH)(2)D2. In placentas and Caco-2 cells, production of 20(OH)D2 was higher than 25(OH)D2 while in human keratinocytes the production of 20(OH)D2 and 25(OH)D2 wete comparable. HaCaT keratinocytes showed high accumulation of 1,20(OH)(2)D2 relative to 20(OH)D2 indicating substantial CYP27B1 activity. This is the first in vivo evidence for a novel pathway of vitamin D2 metabolism initiated by CYP11A1 and modified by CYP27B1, with the product profile showing tissue- and cell-type specificity. (C) 2014 Elsevier Ireland Ltd. All rights reserved.