The Role of Testosterone in Cyclosporine‐Induced Osteopenia

• Published in: Journal of bone and mineral research Vol. 12; no. 4; pp. 607 - 615
• Main Authors: Bowman, A. R., Sass, D. A., Dissanayake, I. R., Ma, Y. F., Liang, H., Yuan, Z., Jee, W. S. S., Epstein, S.
• Format: Journal Article
• Language: English
• Published: Washington, DC John Wiley and Sons and The American Society for Bone and Mineral Research (ASBMR) 01.04.1997; American Society for Bone and Mineral Research
• Subjects: Animals; Biological and medical sciences; Blood Urea Nitrogen; Body Weight; Bone Diseases, Metabolic - chemically induced; Bone Diseases, Metabolic - drug therapy; Calcium - blood; Creatinine - blood; Cyclosporine - adverse effects; Drug Synergism; Humans; Immunomodulators; Immunosuppressive Agents - adverse effects; Male; Medical sciences; Organ Transplantation - adverse effects; Osteocalcin - blood; Osteoporosis - drug therapy; Osteoporosis - etiology; Pharmacology. Drug treatments; Rats; Rats, Sprague-Dawley; Tacrolimus - adverse effects; Tacrolimus - blood; Testosterone - blood; Testosterone - therapeutic use; Androgen; Rat; Controlled release form; Rodentia; Diseases of the osteoarticular system; Bone disease; Testosterone; Vertebrata; Mammalia; Tacrolimus; Ciclosporin; Testicular hormone; Immunosuppressive agent; Bone; Sex steroid hormone; Morphometry; Osteopenia; Pellet(dosage form)
• ISSN: 0884-0431; 1523-4681
• DOI: 10.1359/jbmr.1997.12.4.607

Our laboratory has demonstrated that the immunosuppressants Cyclosporin A (CsA) and tacrolimus (FK506), in vivo in the rat, produce a high‐turnover osteopenia. CsA is known to decrease serum testosterone (Test) levels both in the rat and in human transplant patients. Less is known of FK506's effect on androgens. CsA‐induced hypogonadism may contribute to the aforementioned bone loss because hypogonadism itself is a risk factor for osteoporosis and fracture. The aim of this study was to assess serum androgen levels following CsA and FK506 therapy and to see whether Test replacement therapy, in the form of 28‐day controlled release subcutaneous pellet implants, could prevent CsA‐induced osteopenia. Two experiments were conducted. In experiment I, four groups of 6‐month‐old male Sprague‐Dawley rats received the following: (A) CsA vehicle and placebo pellet, (B) Test 15 mg pellet and CsA vehicle, (C) CsA 10 mg/kg and placebo pellet, (D) Test 15 mg pellet and CsA 10 mg/kg. In experiment II, two groups of rats received (E) FK506 vehicle and (F) FK506 4 mg/kg. CsA, FK506, and vehicles were given for 28 days by daily oral gavage. The rats were weighed and bled on days 0, 14, and 28. All rats received double fluorescent labeling, and on day 28 the tibiae were removed for histomorphometry. Whole blood was assayed for CsA and FK506 levels. Serum was assayed for total and free Test as well as for osteocalcin (BGP), blood urea nitrogen (BUN), creatinine, and calcium. Whole blood monoclonal CsA levels measured by fluorescent immunoassay were in the therapeutic range, while a drug concentration profile showed good absorption of FK506. Those rats receiving Test and FK506 lost weight, while those receiving CsA remained constant. BUN was only marginally elevated in the CsA‐treated groups on day 28 (p < 0.05), while creatinine was unchanged. On day 28, total and free Test was significantly reduced in the CsA‐treated rats versus control (p < 0.05), while Test replacement therapy maintained total Test levels above vehicle (p < 0.01) and free Test levels similar to vehicle on day 28. FK506 did not lower total or free Test levels. BGP levels were significantly increased in the CsA (p < 0.01) and FK506 (p < 0.001) groups on day 28. BGP in the groups receiving Test alone and in combination with CsA remained similar to vehicle. Histomorphometry confirmed CsA‐ and FK506‐induced high‐turnover osteopenia. The Test alone group marginally increased bone formation. Test replacement failed to prevent the CsA‐induced bone loss. In conclusion, immunosuppressive doses of CsA, but not FK506, lowers serum total and free Test. Hypoandrogenemia does not seem to be a major factor in CsA‐induced osteopenia because bone loss occurs despite Test replacement.