A new bisphosphonate, BM 21.0955, prevents bone loss associated with cessation of ovarian function in experimental dogs.

We previously found that bone loss occurs as soon as 1 month after ovariohysterectomy (OHX) in beagle dogs. Indirect evidence pointed to an early dramatic increase in bone resorption. To verify this hypothesis and evaluate the effects of a newly developed bisphosphonate, BM 21.0955 (Boehringer Mannheim), 36 beagle dogs were subjected to OHX and 12 dogs were sham operated (Sham). OHX dogs were divided into six groups (n = 6 each) and received subcutaneous injections of vehicle or BM 21.0955 at various doses (0.1, 0.3, 1, 10, and 100 micrograms/kg/day) for 1 month. Sham dogs were given vehicle (n = 6) or BM 21.0955 (1 microgram/kg/day, n = 6). Iliac crest biopsies and blood drawings were done at baseline and at month 1. OHX dogs given vehicle exhibited a decrease in cancellous bone volume associated with an increase in erosion depth and a decrease in serum levels of 1,25-dihydroxyvitamin D. BM 21.0955 prevented the bone loss at a dose > or = 1 microgram/kg and the increase in erosion depth and the decrease in serum levels of 1,25-(OH)2D at a dose > or = 0.3 microgram/kg. No osteomalacia was observed at any dose of BM 21.0955. Bone turnover was reduced only when BM 21.0955 was administered at doses of 10 or 100 micrograms/kg. There were no changes in body weight or serum levels of calcium, phosphorus, creatinine, parathyroid hormone, or osteocalcin in all groups. The increase in erosion depth in OHX dogs given vehicle proves that the early rapid bone loss after cessation of ovarian function is related to an increase in osteoclastic activity. The antiosteoclastic activity of BM 21.0955 at a dose > or = 1 microgram/kg prevents this increase and preserves bone volume. The absence of any signs of osteomalacia at any dose confers a relatively wide therapeutic margin to BM 21.0955. BM 21.0955 at a dose > or = 10 micrograms/kg also acts as an inhibitor of bone turnover. This is not observed at a dose of 1 microgram/kg, at least after 1 month of administration.