Bisphosphonates clodronate and etidronate in the prevention of ovariectomy-induced osteopenia in growing rats.

The aim of this study was to evaluate the ability of the bisphosphonate compounds clodronate and etidronate to prevent ovariectomy-induced bone changes. Three-month-old Sprague-Dawley rats were either ovariectomized (OVX) or sham-operated (SHAM) and further divided into groups receiving either vehicle (n = 30), 25 mg/kg/week of clodronate (n = 25) or 25 mg/kg/week of etidronate (n = 25). The subcutaneous drug administration was started immediately after the surgery and was continued for 12 weeks. OVX rats had accelerated bone turnover rates compared with the SHAM animals, as indicated by the results of dynamic histomorphometry and biochemical markers in serum and urine. Femoral and vertebral mineralized trabecular bone volume and maximum loads in compressions of the femoral neck and lumbar vertebra were lower after OVX compared with the SHAM operation. Both clodronate and etidronate prevented the decrease in trabecular bone volume and suppressed the increase in the bone turnover rate. Clodronate and etidronate also blocked the loss of bone strength in the femoral neck and lumbar vertebra of OVX rats. Both compounds resulted in an absence of double fluorochrome labels on the endocortical surface of the femoral metaphysis, which seemed, however, to be a dose-dependent response. Furthermore, etidronate also lowered serum osteocalcin and diaphyseal endocortical bone formation below the vehicle level both in the OVX and SHAM rats. In conclusion, clodronate and etidronate were effective in preventing the estrogen deficiency-induced decreases in trabecular bone volume and bone strength in rats. Treatment with a high dose of clodronate induced minor signs of abnormally low bone formation but not any impairment of bone mineralization, whereas both of these events were seen with high-dose etidronate administration.

Long-term effects of clodronate on growing rat bone.

For evaluating the long-term effects of the bisphosphonate compound clodronate on the rat skeleton, 100 female rats were given subcutaneous injections of clodronate at doses of 0 (vehicle), 4 (low), or 12 (high) mg/kg per week, or 50 mg/kg every fourth week (cyclical). The treatment was started at 3 months of age and was continued for 6 months. The mechanical strength of bones was studied by torsion of the tibia, three-point bending of the femur, axial compression of the femoral neck, and compression of a lumbar vertebra. Quantitative histomorphometric variables were determined from distal femur and lumbar vertebra, and variables reflecting bone metabolism were measured in serum and urine. Bone mass, indicated by ash weight of the tibia, was increased with the low and high clodronate doses compared with the vehicle. The maximum load in vertebra compression was increased with the low dose of clodronate compared with the vehicle, whereas changes in other variables concerning bone strength were not significant. In bone histomorphometry, clodronate treatment induced more pronounced changes in cancellous bone volume in distal femur than in lumbar vertebra, the differences not being statistically significant between the groups at either site, however. The longitudinal growth rate of the femur, measured by double-fluorochrome labeling for 1 week at the end of the treatment period, was significantly decreased in the high-dose clodronate group compared with the other groups. Serum values for calcium, tartrate-resistant acid phosphatase, and alkaline phosphatase did not differ between the groups. However, serum osteocalcin was significantly lower in the high-dose group compared with the vehicle group. Urinary calcium, hydroxyproline, and hydroxylysylpyridinoline were decreased at all the clodronate doses administered. In conclusion, the beneficial effects of long-term clodronate treatment on bone mass and strength were observed at the lowest dose used. A high dose of clodronate decreased bone growth rate, which was, however, not reflected in the mechanical quality of bone.