Objective: Posttransplant bone disease and bone metabolism markers were investigated in primary kidney transplant recipients receiving calcineurin inhibitor (CNI) based triple immunosuppression. We examined the safety profile and independent potential of CNIs on bone formation and bone resorption. The study also attempted to correct for modifiable and nonmodifiable factors that impact on posttransplantation bone metabolism, such as age, renal function, rejection, steroid dosage, and secondary hyperparathyroidism.
Materials and methods: Serum alkaline phosphatase and osteocalcin were used as indices of bone formation and urinary deoxypyridinoline as a marker for bone resorption. Bone mineral density (BMD) data were assessed in all patients. Osteocalcin and deoxypyridinoline data were correlated with BMD scores to predict the clinical utility and sensitivity of these tests. Sixty-six patients among 300 kidney transplant recipients were enrolled as eligible candidates based upon more than 12 months' posttransplantation follow-up excellent graft function (GFR values >60 mL/min), and intact parathormone levels <100 pg/mL.
Results: Mean follow-up was 1395.3 +/- 179.3 days and 1488.9 +/- 225.1 days for cyclosporine (CsA) and FK506 groups, respectively. Mean values for alkaline phosphatase and osteocalcin were 108.8 +/- 6.0 versus 98.4 +/- 9.7 U/L and 10.1 +/- 1.2 versus 9.8 +/- 1.5 ng/mL for the CsA and FK506 groups, respectively. Both CsA and FK506 caused mild osteoblastic proliferation and matrix mineralization activity, as reflected by increased osteocalcin and alkaline phosphatase levels in 22.6% and 12.5% of patients, respectively. This bone formation activity was counterbalanced by a three-fold increase in urine deoxypyridinoline levels in both groups. Mean deoxypyridinoline levels were, respectively, 13.8 +/- 4.4 versus 11.3 +/- 2.1 nM/mMCr in the CsA and FK506 groups. Thirty-four (68%) patients in the CsA and 10 (62.5%) in the FK506 groups had elevated deoxypyridinoline levels. A strong correlation existed between deoxypyridinoline levels and BMD scores for the CsA group (P < .0001). Despite the presence of relatively greater elevations in deoxypyridinoline and BMD values among CsA-treated patients, there was no significant difference in terms of bone resorption potential of both groups. No correlation existed between iPTH values (<65 pg/mL or among 65 to 98.2 pg/mL) at any time versus osteocalcin, alkaline phosphatase, deoxypyridinoline, or BMD levels. The symptomatic bone disease and fracture rates were 0% in this series.
Conclusion: Calcineurin inhibitor-based immunosuppression with low maintenance doses of glucocorticoids induces slight bone formation but relatively potent, clinically relevant bone resorption.