title: Autoregulation of 1,25-dihydroxyvitamin D synthesis in macrophage mitochondria by nitric oxide.
abstract: Tissue macrophages from patients with granuloma-forming disease, most notably sarcoidosis, express a 25-hydroxyvitamin D-1-hydroxylase which can produce in vivo sufficient quantities of the active vitamin D metabolite 1,25-dihydroxyvitamin D to cause hypercalcemia. In contrast to the NADPH-dependent cytochrome P450-linked mixed function oxidase which is normally only expressed in significant quantity in proximal renal tubular cells and regulated in an endocrine fashion, the mitochondrial-based 1-hydroxylase in the macrophage [1] is stimulated in a paracrine mode by cytokines (i.e., IFN-gamma) and lipopolysaccharide (LPS) [2] requires an extracellular source of L-arginine for full basal expression and [3] can be regulated in an intracrine fashion by nitric oxide (NO). In these experiments we employed inducible nitric oxide synthase (iNOS)-free, intact mitochondria preparations from the avain macrophage-like cell line HD-11, which constitutively express the 1-hydroxylase, and nonenzymatically-generated NO to investigate NO-mediated autoregulation of the macrophage 1-hydroxylase. Sodium nitroprusside (SNP)- or S-nitroso-N-acetyl-penicillamine (SNAP)-induced up-regulation of the 1-hydroxylase required the presence of either NADPH or NADP in the reaction mixture, while NO-induced inhibition of mitochondrial 1,25-(OH)2D3 synthesis was NO-dependent and NADP/NADPH-independent. These data suggest NO has bifunctional effects on the macrophage 1-hydroxylase. At relatively high concentrations NO competes with O2 for enzyme binding, inhibiting hormone synthesis. At lower production levels, NO serves as a source of reducing equivalents for the enzyme by providing for the reduction of NADP to NADPH.
authors.affiliation: Department of Medicine, Burns and Allen Cedars-Sinai Research Institute, UCLA School of Medicine 90048, USA.
authors.forename: J S
authors.initials: JS
authors.lastname: Adams
authors.forename: S Y
authors.initials: SY
authors.lastname: Ren
mesh_terms: D000818:Animals; D001717:Birds; D002460:Cell Line; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006706:Homeostasis; D008264:Macrophages / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism*; D009569:Nitric Oxide / Q000502:physiology*; D009599:Nitroprusside / Q000494:pharmacology; D010396:Penicillamine / Q000031:analogs & derivatives / Q000494:pharmacology; D026423:S-Nitroso-N-Acetylpenicillamine; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000096:biosynthesis
chemical_list: D004791:Enzyme Inhibitors; D014807:Vitamin D; D009599:Nitroprusside; D009569:Nitric Oxide; C097949:1,25-dihydroxyvitamin D; D026423:S-Nitroso-N-Acetylpenicillamine; D010396:Penicillamine