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Induction of calcium-binding protein in organ-cultured chick intestine by fluoro analogs of vitamin D3
Authors:R A Corradino  N Ikekawa  H F DeLuca
Institution:1. Department of Physical Biology/Section of Physiology, Room 720, Veterinary Research Tower, New York State College of Veterinary Medicine, Cornell University, Ithaca, New York 14853 U.S.A.;2. Tokyo Institute of Technology, O-Okayama Meguro-Ku, Tokyo, Japan;3. Department of Biochemistry, College of Agricultural and Life Sciences, University of Wisconsin, Madison, Wisconsin 53706 U.S.A.
Abstract:Vitamin D-like steroids added to the culture medium induce a specific calcium-binding protein (CaBP) in embryonic chick duodenum maintained in organ culture. This system provides a biologically relevant assay, i.e., a physiological response in a principle target organ, for the study of the relative biopotency of vitamin D metabolites and analogs. A number of fluoro analogs of vitamin D3 (D3) and its metabolites were assayed in the present study. Analogs fluorinated in the lα position (1α-F-D3) or in both the 1α and 25 positions (1α,25-F2-D3) were markedly more potent than vitamin D3 itself although 1α,25-F2-D3 was only 17th as potent as 1α-F-D3. The 25-fluoro analog (25-F-D3) was a very weak inducer; only 145th as potent as vitamin D3. The 25-fluoro analog of 1α-hydroxyvitamin D3 (1α-OH-25-F-D3) was less potent than its nonfluorinated counterpart. Although 25-fluorination reduced biopotency in all other analogs tested, 24R-OH-25-F-D3 was about 15 times more potent than 24R,25-(OH)2-D3. Of considerable interest was the effect of difluorination at the 24-carbon position: both 24,24-F2-25-OH-D3 and 24,24-F2-1α,25-(OH)2-D3 were about four times as potent as their nonfluorinated counterparts. The 24,24-F2-1α,25-(OH)2-D3 is, therefore, the most potent vitamin D3 analog yet tested in this system i.e., it is four times more potent than the most potent naturally occurring vitamin D3 metabolite, 1α,25-(OH)2-D3.
Keywords:To whom correspondence and reprint requests should be addressed  
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