Pathogenesis of bone loss in heart transplant candidates and recipients

Background: Heart transplantation (HTX) is associated with decreased bone mineral density and changes in bone metabolism. We conducted this study to evaluate the pathophysiology of bone metabolism in HTX candidates and recipients. Methods: Thirty-six HTX recipients were compared with 36 HTX candidates concerning biochemical parameters of bone metabolism and bone mineral density. Results: Osteocalcin, bone-specific alkaline phosphatase, cross-linked-N-telopeptide of type I collagen, estradiol, serum creatinine, and blood urea nitrogen concentrations were significantly higher, whereas the calcium-creatinine ratio, thyrotropin, thyroxine, and bone mineral density were significantly lower in HTX recipients than in HTX candidates. Compared with a control group, HTX candidates had decreased renal function and increased bone resorption, whereas HTX recipients additionally had increased alkaline phosphatase and osteocalcin levels. In HTX recipients, we found positive correlations between creatinine clearance and bone mineral density; daily and cumulative cortisone doses were not associated with bone mineral density. Conclusion: In HTX candidates, disturbances in bone metabolism with increased bone resorption may be caused partly by existing low-grade renal insufficiency, regular intake of loop diuretics, and restriction of mobility. In HTX recipients, immunosuppressive therapy-glucocorticoids and cyclosporine-seem to be responsible for changes in bone metabolism.