The capacity of the v‐myc‐transformed, chicken myelomonocytic cell line HD‐11 to metabolize 25‐hydroxyvitamin D3 (25‐OHD3) was examined. HD‐11 cells produced and secreted a metabolite of 25‐OHD, that was bound with high affinity by receptor for 1,25‐dihydroxyvitamin D3 [1,25‐(OH)2D3]. On normal‐phase HPLC, this metabolite cochromatographed with authentic 1,25‐(OH)2D3 in both hexane‐ and methylene chloride‐based solvent systems. The 25‐OHD, 1‐hydroxylation reaction was substrate saturable with a Km of 73 nM 25‐OHD3 and a maximal velocity of 167 fmol per 106 cells per h. This reaction was inhibited by keto‐conazole, a recognized inhibitor of cytochrome P450 mixed‐function oxidases including the authentic, renal 25‐OHD3 1‐hydroxylase. On the other hand, HD‐11 cell 1,25‐(OH)2D3 production was not affected by the antioxidant DPPD, a known inhibitor of free radical‐generated 1,25‐(OH)2D3. In addition to synthesizing 1,25‐(OH)2D3, this monocyte‐macrophage cell line also has the potential to be a target for the hormone; HD‐11 cells express high‐affinity receptor for 1,25‐(OH)2D3 (Kin = 0.06 nM). Division of Endocrinology and Metabolism, Cedars‐Sinai Medical Center‐UCLA School of Medicine, Los Angeles, CA 90048.
ASJC Scopus subject areas
- Endocrinology, Diabetes and Metabolism
- Orthopedics and Sports Medicine