The preventive and interventional effects of raloxifene analog (LY117018 HCL) on osteopenia in ovariectomized rats

The effects of LY117018 HCL (LY) treatment on bone metabolism, spine bone mineral density (BMD), bone mineral content (BMC), and serum cholesterol were studied in ovariectomized (OVX) rats. Experiment 1 was designed to observe the preventive effects of LY on bone loss due to ovariectomy (OVX; prevention study). The rats were divided into three groups: sham group, OVX + vehicle, and OVX + LY. LY was administrated at the same time of OVX. Experiment 2 was designed to investigate the interventional effects of LY on OVX rats with osteopenia (intervention study). The rats were divided into the sham and OVX groups, first. The OVX rats were allowed to lose bone for 6 weeks. At 6 weeks post-OVX, the OVX rats were divided into two groups: OVX + vehicle and OVX + LY. The longitudinal effects of LY on bone were studied by dual-energy X-ray absorptiometry and biochemical markers including urinary pyridinoline (Pyr), deoxypyridinoline (Dpyr), and serum osteocalcin. Urinary Pyr and Dpyr increased maximally at 6 weeks post-OVX, decreased at 12 and 18 weeks post-OVX, although the OVX rats had significantly higher levels of Pyr and Dpyr than the sham group during the experiment. LY was a very potent inhibitor of Pyr and Dpyr excretion while at the same time only partially reducing the bone loss in the high turnover phase at 6 weeks postovariectomy. However, at the later time points at 12 and 18 weeks, no further bone loss occurred in rats treated with LY, while the vehicle-treated group lost another 10% in spine BMD and BMC. LY also completely blocked further bone loss when used in an intervention protocol. LY significantly reduced serum cholesterol levels in OVX rats. The results suggest that LY is not fully protective during the early rapid bone loss phase, but the compound is fully protective during the later slow phase of bone loss in both the protocols.