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Effect of 1,25,28‐trihydroxyvitamin D 2 and 1,24,25‐trihydroxyvitamin D 3 on intestinal calbindin‐D 9K mRNA and protein: Is there a correlation with intestinal calcium transport?
Author(s) -
Wang Y.Z.,
Li H.,
Bruns M.E.,
Uskokovic M.,
Truitt G.A.,
Horst R.,
Reinhardt T.,
Christakos Sylvia
Publication year - 1993
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.5650081211
Subject(s) - vitamin d dependent calcium binding protein , calcium , calbindin , medicine , endocrinology , vitamin d and neurology , calcium metabolism , vitamin , calcium binding protein , chemistry , receptor , biology
Although analogs and metabolites of vitamin D have been tested for their calciotropic activity, very little information has been available concerning the effects of these compounds on gene expression. In this study one analog of vitamin D, 1,25,28‐trihydroxyvitamin D 2 [1,25,28‐(OH) 3 D 2 ], and one metabolite, 1,24,25‐trihydroxyvitamin D 3 [1,24,25‐(OH) 3 D 3 ], were tested for their effect on intestinal calbindin‐D 9K mRNA and protein as well as for their effect on intestinal calcium absorption and bone calcium mobilization. These compounds were also evaluated for their ability to compete for rat intestinal 1,25‐(OH) 2 D 3 receptor sites and to induce differentiation of human leukemia (HL‐60) cells as indicated by reduction of nitro blue tetrazolium. In vivo studies involved intrajugular injection of 12.5 ng 1,25‐(OH) 2 D 3 or test compound to vitamin D‐deficient rats and sacrifice after 18 h. 1,25,28‐Trihydroxyvitamin D 2 had no effect on intestinal calcium absorption, bone calcium mobilization, or intestinal calbindin‐D 9K protein and mRNA. Competitive binding to 1,25‐(OH) 2 D 3 receptors was 0.8% of that observed using 1,25‐(OH) 2 D 3 . However, 20‐ and 40‐fold higher doses of 1,25,28‐(OH) 3 D 2 (250 and 500 ng) resulted in significant inductions in calbindin‐D 9K protein and mRNA (3.5 to 7.4‐fold), although doses as high as 800 ng were found to have no effect on intestinal calcium absorption or bone calcium mobilization. 1,25,28‐Trihydroxyvitamin D 2 , although lacking in calciotropic activity, was found to induce differentiation of HL‐60 cells at high concentrations [ED 50 = 15 × 10 −8 M compared to ED 50 = 2.5 × 10 −8 M for 1,25‐(OH) 2 D 3 ]. 1,24,25‐Trihydroxyvitamin D 3 was 93% as active as 1,25‐(OH) 2 D 3 in stimulating intestinal calcium transport but was relatively inactive in stimulating bone calcium mobilization. Competitive binding to the 1,25‐(OH) 2 D 3 receptor was 8% of that observed using 1,25‐(OH) 2 D 3 . Although 1,24,25‐(OH) 3 D 3 was 93% as active as 1,25‐(OH) 2 D 3 in stimulating intestinal calcium absorption, this compound was found to be 50% as active as 1,25‐(OH) 2 D 3 in stimulating calbindin‐D 9K protein and mRNA. The lack of a direct correlation between calbindin protein and mRNA and intestinal calcium transport after 1,24,25‐(OH) 3 D 3 administration or after administration of high doses of 1,25,28‐(OH) 3 D 2 suggests that factors in addition to calbindin are involved, at least in part, in vitamin D‐regulated intestinal calcium transport.