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Effect of vitamin D metabolites on the expression of alkaline phosphatase activity by epiphyseal hypertrophic chondrocytes in primary cell culture
Author(s) -
Hale Laura V.,
Kemick Mary Lynn S.,
Wuthier Roy E.
Publication year - 1986
Publication title -
journal of bone and mineral research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.882
H-Index - 241
eISSN - 1523-4681
pISSN - 0884-0431
DOI - 10.1002/jbmr.5650010602
Subject(s) - alkaline phosphatase , metabolite , endocrinology , medicine , chemistry , vitamin d and neurology , stimulation , cholecalciferol , vitamin , active metabolite , cell culture , calcitriol , ic50 , enzyme , biochemistry , biology , in vitro , genetics
The effects of three vitamin D 3 metabolites, 25‐hydroxyvitamin D 3 (25‐(OH)D 3 ), 1α,25‐dihydroxyvitamin D 3 (1α,25‐(OH) 2 D 3 ), and 24 R ,25‐dihydroxyvitamin D 3 (24 R ,25‐(OH) 2 D 3 ) 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 1α,25‐(OH) 2 D 3 (10 −12 to 10 −7 M ) caused a progressive, dosage‐and time‐dependent decrease in cellular AP levels, IC 50 occurring at approximately 10 −12 M. In contrast, 24 R ,25‐(OH) 2 D 3 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 ), 24 R ,25‐(OH) 2 D 3 caused progressive reduction in AP activity. Maximal effects of 24 R ,25‐(OH) 2 D 3 were evident 48 h after administration of the metabolite. 25‐(OH)D 3 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 (> 10 −10 M ) were clearly inhibitory to AP. These findings reveal that the AP activity of growth plate chondrocytes is exquisitely sensitive to both 1α,25‐ and 24 R ,25‐(OH) 2 D 3 but the response to each is in opposite directions. The paradoxical response of the cells to 25‐(OH)D 3 can be explained if the metabolite is slowly metabolized by a 24‐hydroxylase to 24 R ,25‐(OH) 2 D 3 leading to stimulation of cellular AP. The inhibitory effects of all metabolites at higher levels (10 −8 to 10 −7 M ) may be explained if both 25‐(OH)D 3 and 24 R ,25‐(OH) 2 D 3 act as weak agonists for the 1α,25‐(OH) 2 D 3 receptor, mimicking its inhibitory action. The data show that vitamin D metabolites exert a direct effect on the growth plate chondrocytes. Studies are in progress to elucidate the mechanism of this AP response.