Long-term therapy with a new chemically modified tetracycline (CMT-8) inhibits bone loss in femurs of ovariectomized rats.

The effect of a new non-antimicrobial analog of tetracycline (CMT-8) on bone loss in ovariectomized (OVX) rats was examined. Three-month-old female rats were ovariectomized, and one week later, were distributed into 3 groups: sham-operated non-OVX controls, vehicle-treated OVX controls, and CMT-8-treated OVX rats. After 145 days of daily CMT-8 administration, the intact femurs were dissected and examined by several histological and histomorphometric techniques. OVX significantly (p < 0.01) decreased trabecular bone volume by 53.4% in the metaphyses compared with sham-operated controls. CMT-8 therapy produced a significant (p < 0.05) inhibition of trabecular bone loss and also induced bone formation in the OVX rats. Of interest, the newly synthesized bone in the CMT-treated OVX rats was found to increase the "connectivity" of the trabecular "struts" by bridging the adjacent longitudinal bone trabeculae, forming dense, plate-like bone trabeculae. These results strongly suggest that long-term CMT-8 therapy effectively inhibits bone loss after OVX, not only by inhibiting bone resorption but also by inducing new bone formation in the trabecular areas of long bones.