24-25-dihydroxyvitamin-d-3 and Tibial-Fractures

The effect(s) of 24R,25-dihydroxyvitamin D3 [24R,25(OH)2D3] on fracture healing was studied in a vitamin D-depleted chick model. 24R,25(OH)2D3, together with another hormonally active vitamin D metabolite, 1alpha,25-dihydroxyvitamin D3 [1alpha,25(OH)2D3], improved bone mechanical strength parameters (torsional strength, angular deformation, and stiffness) and the ash content. The synthetic epimer 24S,25-dihydroxyvitamin D3 [24S,25(OH)2D3] was not as potent as the natural 24R,25(OH)2D3. In light of the ability of the fracture-healing callus to discriminate between 24R,25(OH)2D3 and 24S,25(OH)2D3, a search was initiated in fracture-healing callus tissue for the presence of a specific 24R,25(OH)2D3 receptor. No evidence was obtained for a classical nuclear/cytosol receptor for 24R,25(OH)2D3 in the fracture-healing callus. A specific receptor/binding protein for 24R,25(OH)2D3 was found in the callus membrane fraction, which showed different ligand binding affinities [KD = 18.3 +/- 1.9 nmol/L, Bmax = 43.9 +/- 6.0 fmol/mg; relative competitive index (RCI) for 24R,25(OH)2D3/24S,25(OH)2D3/25(OH)D3/1alpha,25(OH)2D3 = 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 1alpha,25(OH)2D3 was detected with a KD = 0.83 +/- 0.35 nmol/L and a Bmax = 35.5 +/- 5.2 fmol/mg. Thus, we have demonstrated a biological role for 24R,25(OH)2D3 in fracture healing and described the presence of its receptor/binding protein in a callus membrane fraction.

Topics: 24,25-Dihydroxyvitamin D 3; Animals; Bony Callus; Calcifediol; Calcitriol; Chickens; Fracture Healing; Male; Receptors, Calcitriol; Stereoisomerism; Structure-Activity Relationship; Tibial Fractures; Vitamin D Deficiency

To investigate the possible biological actions of 24,25-dihydroxyvitamin D3 (24,25(OH)2D3), a tibial fracture-healing model was established in White Leghorn chicks. Three-week-old White Leghorn chicks fed a vitamin D3-replete diet were divided into four groups (control, anesthetized, sham, and fractured). On varying days after tibial fracture (F) or sham manipulation (S), renal 25(OH)D3-1 alpha-hydroxylase and 25(OH)D3-24-hydroxylase (24-hydroxylase) activities and serum Ca2+ concentrations were measured. Metofane anesthesia was found to have no effect on the activity of either of the hydroxylases; the activities of the hydroxylases in the control, anesthetized, and sham-operated birds were similar. By 10 days after tibial fracture, the renal 24-hydroxylase activity increased more than 3-fold in F (1.33 +/- 0.07 pmol/mg of protein) as compared with S (0.42 +/- 0.03 pmol/mg of protein) (p < 0.0001). A time-dependent study of the renal 24-hydroxylase activity during the fracture repair process revealed a slow increase from the first day after fracture, a higher activity at 8 days, which peaked at 10-11 days, which is consistent with the formation of the callus. The 24-hydroxylase activity then returned to the same level as the sham group 14 days after fracture. There was no significant difference in serum Ca2+ levels between the F and S groups over the 3-week postfracture period. Serum levels of vitamin D3 metabolites were also measured during the fracture healing process: a 3.4x increase of the 24,25(OH)2D3 level in the fractured group (3.64 +/- 1.16 nM) was observed as compared with the control groups (1.08 +/- 0.49 nM) at 10 days after fracture (p = 0.068). No significant differences were observed in the plasma levels of 25(OH)D3 or 1 alpha, 25(OH)2D3 between the group with a fracture and the controls. Exposure of primary chick kidney cells in culture to serum obtained from chicks with a tibial fracture for 20 h resulted in an approximately 40% increase in the activity of the 24-hydroxylase as compared with cells exposed to serum from control birds. These results suggest that 24,25(OH)2D3 is involved in the early process of fracture repair and that there is some form of physiological communication between the fractured bone and the kidney so as to increase the renal 24-hydroxylase and the circulating concentration of this metabolite.

Topics: 24,25-Dihydroxyvitamin D 3; Animals; Calcium; Chickens; Cytochrome P-450 Enzyme System; Enzyme Induction; Fracture Healing; Kidney; Parathyroid Glands; Steroid Hydroxylases; Tibial Fractures; Vitamin D3 24-Hydroxylase

We tested the hypothesis that 24R,25-dihydroxyvitamin D3 [24R,25-(OH)2D3] is an essential vitamin D metabolite for the development of normal bone integrity and the healing of fractures. The natural 24R,25-(OH)2D3 and its synthetic epimer 24S,25-dihydroxyvitamin D3 [24S,25-(OH)2D3] were tested alone or in combination with 1alpha,25-dihydroxyvitamin D3 [1alpha,25-(OH)2D3], on normal bone development and other related variables of the Ca2+ homeostasis system [serum Ca2+, 25-hydroxyvitamin D3 (25OHD3), 24,25-(OH)2D3, and 1alpha,25-(OH)2D3 levels] in chicks. Mechanical testing of torsional strength was carried out on the femur. 24R,25-(OH)2D3 (80 nmol/kg diet) alone was sufficient for normal bone growth and integrity similar to that achieved by the vitamin D3-replete controls. Next, chicks were fed a 25OHD3-replete diet (75 nmol/kg diet) for 8 days after hatching, and then 25OHD3 was withdrawn to minimize any residual circulating metabolites before the imposition of standardized tibial fractures 14 days later. Vitamin D metabolites were administered for 2 weeks to determine their effects on the mechanical properties of healed tibia. 24S,25-(OH)2D3 combined with 1alpha,25-(OH)2D3 or 1alpha,25-(OH)2D3 alone resulted in poor healing [strength values of 0.158 +/- 0.011 and 0.123 +/- 0.009 Nm (Newton x meter), respectively] compared with that in the 25OHD3-treated control group (0.374 +/- 0.029 Nm). In contrast, the fractured tibia of the birds fed 24R,25-(OH)2D3 in combination with 1alpha,25-(OH)2D3 showed healing equivalent to that in the control group, with strength values of 0.296 +/- 0.043 Nm. These results suggest that when 24R,25-(OH)2D3 is present at normal physiological concentrations, it is an essential vitamin D3 metabolite for both normal bone integrity and healing of fracture in chicks.

Topics: 24,25-Dihydroxyvitamin D 3; Animals; Biomechanical Phenomena; Bone and Bones; Bone Development; Calcium; Chickens; Fracture Healing; Tensile Strength; Tibial Fractures

In vitamin D-fed chicks 1,25-dihydroxyvitamin D3 and 24,25-dihydroxyvitamin D3 were implanted into experimentally-produced fractures of the mid-tibia. The mechanical and biochemical properties of the tibia were evaluated for two weeks, including torsion tests, measurement of alkaline phosphatase activity, 45Ca incorporation, and Ca2+ content. Both dihydroxylated metabolites of vitamin D3 had a direct effect on endochondral bone formation. 24,25(OH)2D3 strengthened the callus, and raised alkaline phosphate activity in the first seven days after fracture. 1,25(OH)2D3 decreased the strength of the callus concomitant with a reduction in 45Ca incorporation. It is suggested that local application of 24,25(OH)2D3 into fractures may accelerate healing and prevent non-union.

Topics: 24,25-Dihydroxyvitamin D 3; Alkaline Phosphatase; Animals; Biomechanical Phenomena; Bony Callus; Calcitriol; Calcium; Chickens; Drug Implants; Male; Stress, Mechanical; Tibial Fractures

Topics: 24,25-Dihydroxyvitamin D 3; Animals; Bone Development; Chickens; Dihydroxycholecalciferols; Female; Growth Plate; Rickets; Tibia; Tibial Fractures

One-day-old chicks were depleted of vitamin D. At 3 weeks their right tibiae, and those of a control group given vitamin D3, were fractured and pinned. After fracture the controls were kept on vitamin D3. Another group was left vitamin D-deficient. The remaining depleted chicks, divided into four groups, were given vitamin D3, 24,25-dihydroxyvitamin D3 [24,25(OH)2D3], 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] or a combination of 24,25(OH)2D3 and 1,25(OH)2D3. The callus obtained after 9 and 14 days was subjected to torsional stress. The callus of chicks given vitamin D continuously showed the greatest resistance, whereas that of vitamin D-deficient chicks showed the smallest resistance. Repletion with either vitamin D3 or its metabolites increased the strength of the callus. Repletion with the combination of 24,25(OH)2D3 and 1,25(OH)2D3 produced the most marked results, in that the callus was even stronger than that of chicks replete with vitamin D3. It is concluded that 24,25(OH)2D3 is essential for bone formation in addition to the known active vitamin D metabolite 1,25(OH)2D3, and the possible clinical implications of these findings are discussed.

Topics: 24,25-Dihydroxyvitamin D 3; Animals; Body Weight; Bony Callus; Calcitriol; Calcium; Chickens; Cholecalciferol; Dihydroxycholecalciferols; Male; Phosphates; Stress, Mechanical; Tibial Fractures; Wound Healing