Long-term treatment with eldecalcitol (1α, 25-dihydroxy-2β- (3-hydroxypropyloxy) vitamin D3) suppresses bone turnover and leads to prevention of bone loss and bone fragility in ovariectomized rats.

The purpose of this study is to estimate the efficacy of eldecalcitol (1α, 25-Dihydroxy-2β- (3-hydroxypropyloxy) vitamin D3; ELD) on bone metabolism after long-term administration. Six-month-old Wistar-Imamichi rats were ovariectomized (OVX) and administered ELD orally at doses of 7.5, 15, or 30 ng/kg daily. Bone mineral density (BMD), urinary excretion of deoxypyridinoline (DPD), a bone resorption marker, and serum total alkaline phosphatase (ALP), a surrogate marker of bone formation, were assessed after 3, 6, and 12 months of treatment. After 12 months of treatment, the biomechanical strength of the L4 lumbar vertebra and femoral shaft was measured, and bone histomorphometry was performed on the L3 lumbar vertebra and the tibia diaphysis. ELD prevented OVX-induced decreases in BMD of the lumbar vertebrae and femur throughout the treatment period. ELD significantly suppressed OVX-induced increases in urinary DPD excretion throughout the treatment period with minimal effects on ALP. OVX resulted in significant decreases in ultimate load and stiffness of the L4 lumbar vertebra and femoral shaft, and ELD significantly prevented the reduction in these biomechanical parameters. Bone histomorphometry at the L3 lumbar vertebra revealed that OVX induced increases in bone resorption parameters (osteoclast surface and osteoclast number) and bone formation parameters (osteoblast surface, osteoid surface, and bone formation rate), and ELD suppressed these parameters after 12 months treatment. Activation frequency, which was elevated in the OVX/vehicle group, was significantly suppressed to baseline levels in ELD-treated groups, indicating that ELD maintained bone turnover at a normal level. ELD also prevented OVX-induced deterioration of microstructure in trabecular and cortical bone. These results indicated that long-term treatment of OVX rats with ELD suppressed bone turnover, and prevented OVX-induced bone loss, deterioration of bone microstructure, and reduction in bone biomechanical strength.