Effects of cyclosporin A on bone turnover and on resorption of demineralized bone matrix.

The effects of the immunosuppressive drug Cyclosporin A on orthotopic bone turnover and on the resorption of demineralized bone matrix were studied. In the first experiment, rats were labeled with 3H-proline and 45Calcium and treated with Cyclosporin A 2 mg/kg/day or placebo for 2 weeks. Cyclosporin A treatment resulted in an early transient increase in matrix and mineral turnover in the metaphyseal region of the tibia. Furthermore, Cyclosporin A increased mineral turnover in the diaphyseal part of the tibia, but the matrix turnover was unaffected. No osteopenia was seen after 2 weeks. In the second experiment, prelabeled (3H-proline) demineralized bone matrix from rats and rabbits was implanted in the abdominal walls of growing rats that were treated with Cyclosporin A or placebo. After 4 weeks there was no difference in the remaining activity in the implants from Cyclosporin A or placebo treated rats. Cyclosporin A treatment increased mineral content in demineralized allogenic bone matrix implants by 1/3. In the demineralized xenogenic bone matrix implants, mineral content was 4 times higher in the cyclosporin A treated implants.