METABOLISM OF H-3 1-ALPHA,25-DIHYDROXYVITAMIN D-3 IN CULTURED HUMAN KERATINOCYTES

In the present investigation we studied the metabolism of 1 alpha,25-dihydroxy-[1 beta-H-3]vitamin D-3 (H-3-1,25(OH)(2)D-3) in culture-grown human keratinocytes (CHK). Our results showed that the cellular uptake of H-3-1,25(OH)(2)D-3, upon incubation with CHK, occurred very rapidly; and it paralleled a decrease in the concentration of H-3-1,25(OH)(2)D-3 in the medium. The amount of H-3-calcitroic acid, on the other hand, increased slowly in the medium, while the concentration of H-3-calcitroic acid in the cell remained undetectable during the whole period of incubation. When the cells were preincubated with 1,25(OH)(2)D-3 (10(-8)M), conversion of H-3-1,25(OH)(2)D-3 to H-3-calcitroic acid increased almost twofold, indicating that 1,25(OH)(2)D-3 catalyzed its own catabolism. (C) 1995 Wiley-Liss, Inc.