Short-term systemic insulin-like growth factor-1 is unable to prevent cyclosporin A-induced osteopenia in the rat

Immunosuppression with cyclosporin A (CsA) is effective in a number of immune-mediated diseases and in preventing rejection following organ transplantation. We have repeatedly demonstrated that CsA in the rat model produces accelerated bone remodelling with net bone loss, best characterized in trabecular bone. IGF-I holds promise as a treatment for various osteopenic conditions. Although currently a subject of much controversy, various studies have suggested that in vivo it is anabolic to cortical as well as trabecular bone. The purpose of this study was, in part, to further characterize the effects of CsA and IGF-I on trabecular and cortical bone, and to see whether systemic IGF-I is able to modulate CsA's deleterious skeletal effects. Sixty 10 week-old, male, Sprague-Dawley rats were randomized to receive the following daily for 3 weeks: (1) CsA vehicle (veh) per os (po) + recombinant human (rh) IGF-1 veh subcutaneously (sc); (2) CsA 15 mg/kg po + rhIGF-I-veh; (3) CsA-veh + rhIGF-I 200 microg/kg sc; (4) CsA-veh + rhIGF-I 600 microg/kg sc; (5) CsA 15 mg/kg + rhIGF-I 200 microg/kg, and (6) CsA 15 mg/kg + rhIGF-I 600 microg/kg. Rats were weighed and venous blood was sampled serially for determination of glucose, ionized calcium (Ca2+), PTH, vitamin D, and osteocalcin. Following sacrifice on day 20, histomorphometry was performed on double calcein-labeled tibial metaphysis and diaphysis. All rats receiving CsA had elevated levels of blood glucose and osteocalcin by day 9 and vitamin D at day 20. PTH was similar in all groups, and Ca2+ was only raised in the CsA and CsA + IGF-I 200 microg/kg groups. Rats receiving IGF-I 200 microg/kg and IGF-I 600 microg/kg gained more weight than either vehicle- or CsA-treated animals, attesting to IGF-1's anabolic properties. CsA caused severe trabecular bone loss, not prevented by IGF-I; it even further increased the eroded surface. CsA and IGF-I had little effect on cortical bone volume or marrow area. IGF-I increased endocortical matrix synthesis, as evidenced by the increases in the percent endocortical osteoid perimeter, an effect negated by the addition of CsA. This experiment demonstrates that trabecular bone is more susceptible than cortical bone to the deleterious effects of CsA and indicates little role for IGF-1 in the pathophysiology or treatment of CsA-induced bone disease at the given doses and duration of treatment.