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Studies on 24R,25-dihydroxyvitamin D3: evidence for a nonnuclear membrane receptor in the chick tibial fracture-healing callus

Publication Date
DOI: 10.1016/s8756-3282(98)00085-4
  • 24R
  • 25-Dihydroxyvitamin D3
  • 25-Dihydroxyvitamin D3
  • Fracture Healing
  • Bone Strength
  • Membrane Receptor/Binding Protein
  • Biology


Abstract The effect(s) of 24R,25-dihydroxyvitamin D 3 [24R,25(OH) 2D 3] on fracture healing was studied in a vitamin D-depleted chick model. 24R,25(OH) 2D 3, together with another hormonally active vitamin D metabolite, 1α,25-dihydroxyvitamin D 3 [1α,25(OH) 2D 3], improved bone mechanical strength parameters (torsional strength, angular deformation, and stiffness) and the ash content. The synthetic epimer 24S,25-dihydroxyvitamin D 3 [24S,25(OH) 2D 3] was not as potent as the natural 24R,25(OH) 2D 3. In light of the ability of the fracture-healing callus to discriminate between 24R,25(OH) 2D 3 and 24S,25(OH) 2D 3, a search was initiated in fracture-healing callus tissue for the presence of a specific 24R,25(OH) 2D 3 receptor. No evidence was obtained for a classical nuclear/cytosol receptor for 24R,25(OH) 2D 3 in the fracture-healing callus. A specific receptor/binding protein for 24R,25(OH) 2D 3 was found in the callus membrane fraction, which showed different ligand binding affinities [ K D = 18.3 ± 1.9 nmol/L, B max = 43.9 ± 6.0 fmol/mg; relative competitive index (RCI) for 24R,25(OH) 2D 3/24S,25(OH) 2D 3/25(OH)D 3/1α,25(OH) 2D 3 = 100/37/401/2.0] compared with the ubiquitous serum vitamin D-binding protein (RCI = 100/99/219/5). Also, a callus membrane-binding protein/receptor for 1α,25(OH) 2D 3 was detected with a K D = 0.83 ± 0.35 nmol/L and a B max = 35.5 ± 5.2 fmol/mg. Thus, we have demonstrated a biological role for 24R,25(OH) 2D 3 in fracture healing and described the presence of its receptor/binding protein in a callus membrane fraction.

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