Conversion of vitamin D3 to 1alpha,25-dihydroxyvitamin D3 in human skin equivalents.
These results demonstrate for the first time that human keratinocytes under in vivo-like conditions have the capacity of the enzymatic hydroxylation of vitamin D3 to hormonally active calcitriol (1alpha,25(OH)2D3). Supplementation of the culture medium with bovine serum albumin (BSA) up to 1.5%) (w/v) amplifies the conversion of vitamin D3 to 1alpha,25(OH)2D3. The maximum turnover rate of this reaction at 780 nM vitamin D3 in presence of 1.0% (w/v) BSA amounts to approximately 3 pmol 1alpha,25(OH)2D3 per 10(6) cells after 6 h of incubation. The hydroxylation of vitamin D3 to 1alpha,25(OH)2D3 is inhibited by the P-450 oxidase inhibitor ketoconazole. The generation of 1alpha,25(OH)2D3 from vitamin D3 has an apparent Michaelis constant (Km) of 2.3x10(-6) M. The intrinsic conversion of vitamin D3 to biologically active 1alpha,25(OH)2D3 may be of importance for the regulation of proliferation and differentiation of keratinocytes.
Lehmann
B
B
Department of Dermatology, Carl Gustav Carus Medical School, Dresden University of Technology, Germany.
Rudolph
T
T
Pietzsch
J
J
Meurer
M
M
D002478:Cells, Cultured; D002762:Cholecalciferol / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D006900:Hydroxylation / Q000187:drug effects; D015603:Keratinocytes / Q000187:drug effects / Q000378:metabolism*; D007654:Ketoconazole / Q000494:pharmacology; D007700:Kinetics; D009247:NADH, NADPH Oxidoreductases / Q000037:antagonists & inhibitors; D009251:NADPH-Ferrihemoprotein Reductase; D012710:Serum Albumin, Bovine / Q000494:pharmacology; D013997:Time Factors; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000378:metabolism
D004791:Enzyme Inhibitors; C118756:dihydroxy-vitamin D3; D014807:Vitamin D; D002762:Cholecalciferol; D012710:Serum Albumin, Bovine; D009247:NADH, NADPH Oxidoreductases; D009251:NADPH-Ferrihemoprotein Reductase; D007654:Ketoconazole