The influence of albumin on vitamin D metabolism in fetal chick osteoblast-like cells.
Incubation of osteoblast-like cells with [3H]25-(OH)D3 and varying bovine serum albumin (BSA) concentrations resulted in a dramatic change in the accumulation of 1,25-(OH)2D3 and 24,25-(OH)2D3 in the medium. At 0.1% BSA 1,25-(OH)2D3 formation was transient and 24,25-(OH)2D3 was the main product after 3 h. At 2% BSA accumulation of 1,25-(OH)2D3 was sustained whereas 24,25-(OH)2D3 formation was suppressed. At low BSA levels added [3H]1,25-(OH)2D3 was rapidly metabolized to 1,24,25-(OH)3D3 and more polar metabolites. The effect of increasing BSA concentrations on 25-(OH)D3 metabolism was mimicked by addition of cycloheximide. This indicates that high BSA levels prevent the induction of 24-hydroxylase activity in this system, probably by lowering of the free 25-(OH)D3 concentration. The accumulation of 1,25-(OH)2D3 from 25-(OH)D3 not only depends on the 1 alpha-hydroxylase activity, but also on the further metabolism of 1,25-(OH)2D3 by 24-hydroxylation.
D015650:24,25-Dihydroxyvitamin D 3; D000818:Animals; D002112:Calcifediol / Q000378:metabolism; D002117:Calcitriol / Q000378:metabolism; D002642:Chick Embryo; D003513:Cycloheximide / Q000494:pharmacology; D004100:Dihydroxycholecalciferols / Q000378:metabolism; D010006:Osteoblasts / Q000378:metabolism*; D012710:Serum Albumin, Bovine / Q000494:pharmacology*; D013997:Time Factors; D014807:Vitamin D / Q000378:metabolism*
D004100:Dihydroxycholecalciferols; D014807:Vitamin D; D012710:Serum Albumin, Bovine; D015650:24,25-Dihydroxyvitamin D 3; D003513:Cycloheximide; D002117:Calcitriol; D002112:Calcifediol