Synthesis and function of 8 alpha,25-dihydroxy-3-oxoneocholecalciferol in liver.
25-Hydroxycholecalciferol (25-OHD3) is converted to 8 alpha,25-dihydroxy-3-oxoneocholecalciferol [8,25-(OH)2-3-oxoneo-D3] by liver microsomes, alveolar macrophages and myeloid leukemia cells. The characteristics of this reaction in liver microsomes have been determined. Omission of an NADPH-generating system or NADH resulted in a greater than 75% reduction in the production of 8,25-(OH)2-3-oxoneo-D3. In the absence of the cytosolic fraction, 25-OHD3 was converted to products that comigrated with 8,25-(OH)2-3-oxoneo-D3 on a silica column developed with hexane-isopropanol, thereby preventing quantitation. Production of 8,25-(OH)2-3-oxoneo-D3 was unaffected by EDTA and was stimulated by N,N'-diphenyl-p-phenylenediamine. Both progesterone and pregnenolone inhibited production of 8,25-(OH)2-3-oxoneo-D3; inhibition by progesterone was greater than that by pregnenolone. 8,25-(OH)2-3-Oxoneo-D3 did not bind the thymus receptor for 1,25-dihydroxycholecalciferol [1,25-(OH)2D3] at concentrations 10-fold higher than that of 1,25-(OH)2D3. The lack of affinity of 8,25-(OH)2-3-oxoneo-D3 for the 1,25-(OH)2D3 receptor suggests that this metabolite is a degradative product of 25-OHD3, which might be produced when 25-OHD3 concentrations in the liver are excessive. Synthesis of this metabolite in the liver may be catalyzed by enzymes that also metabolize other steroids.
Richardson
K A
KA
Department of Biochemistry, Morehouse School of Medicine, Atlanta, GA 30310.
Thierry-Palmer
M
M
D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D002782:Cholestenes; D002855:Chromatography, Thin Layer; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects / Q000378:metabolism*; D009243:NAD / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D010655:Phenylenediamines / Q000494:pharmacology; D011284:Pregnenolone / Q000494:pharmacology; D011374:Progesterone / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains
D000975:Antioxidants; D002782:Cholestenes; D010655:Phenylenediamines; D009243:NAD; C053021:8,25-dihydroxy-9,10-seco-4,6,10(19)-cholestatrien-3-one; D011374:Progesterone; D009249:NADP; D011284:Pregnenolone; C004845:N,N'-diphenyl-4-phenylenediamine