title: Effect of vitamin D metabolites on the expression of alkaline phosphatase activity by epiphyseal hypertrophic chondrocytes in primary cell culture.
abstract: The effects of three vitamin D3 metabolites, 25-hydroxyvitamin D3 (25-(OH)D3), 1 alpha,25-dihydroxyvitamin D3 (1 alpha, 25-(OH)2D3), and 24R,25-dihydroxyvitamin D3 (24R,25-(OH)2D3) on the activity of alkaline phosphatase (AP), a key enzyme involved in biomineralization, have been studied in primary cultures of chicken epiphyseal growth plate chondrocytes. Dosages of 1 alpha, 25-(OH)2D3 (10(-12) to 10(-7) M) caused a progressive, dosage- and time-dependent decrease in cellular AP levels, IC50 occurring at approximately 10(-12) M. In contrast, 24R,25-(OH)2D3 at 10(-13) to 10(-10) M stimulated cellular AP activity, half-maximal stimulation occurring at about 10(-13) M. At higher levels (10(-10) to 10(-7) M), 24R,25-(OH)2D3 caused progressive reduction in AP activity. Maximal effects of 24R,25-(OH)2D3 were evident 48 h after administration of the metabolite. 25-(OH)D3 initially (24 h) caused a weak, dosage-dependent decrease in cellular AP activity, but after 48-72 h, low levels (10(-13) to 10(-11) M) caused a dosage-dependent increase in AP activity. Higher levels of 25-(OH)D (greater than 10(-10) M) were clearly inhibitory to AP. These findings reveal that the AP activity of growth plate chondrocytes is exquisitely sensitive to both 1 alpha,25- and 24R,25-(OH)2D3 but the response to each is in opposite directions. The paradoxical response of the cells to 25-(OH)D3 can be explained if the metabolite is slowly metabolized by a 24-hydroxylase to 24R,25-(OH)2D3 leading to stimulation of cellular AP.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D015650:24,25-Dihydroxyvitamin D 3; D000469:Alkaline Phosphatase / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D002112:Calcifediol / Q000494:pharmacology*; D002117:Calcitriol / Q000494:pharmacology*; D002478:Cells, Cultured; D002645:Chickens; D003470:Culture Media; D004100:Dihydroxycholecalciferols / Q000494:pharmacology*; D005786:Gene Expression Regulation; D006132:Growth Plate / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology; D010641:Phenotype
chemical_list: D003470:Culture Media; D004100:Dihydroxycholecalciferols; D015650:24,25-Dihydroxyvitamin D 3; D000469:Alkaline Phosphatase; D002117:Calcitriol; D002112:Calcifediol