Body composition, adipokines, FGF23-Klotho and bone in kidney transplantation: Is there a link?

BACKGROUND: Kidney transplantation-associated mineral and bone disorder (KT-MBD) still represents a black box on the long-term due to scarce available data. We aimed to investigate the impact of non-classical bone regulating factors (body composition, adipokines, inflammatory markers, fibroblast growth factor 23-FGF23 and α-Klotho) in long-standing kidney transplant (KT) recipients compared to the general population. METHODS: Our cross-sectional study, enrolling 59 KT patients and age, sex and body mass index-matched healthy general population volunteers, assessed the predictive role of the body composition, serum adipokines (leptin, adiponectin, resistin), inflammatory markers (erythrocyte sedimentation rate, C-reactive protein) and parathyroid hormone (PTH)-FGF23/α-Klotho axis upon bone mineral density (BMD) and osteocalcin, using correlation and linear multiple regression. RESULTS: The 59 KT recipients (mean transplantation span of 57.7 ± 7.2 months) had similar body composition but significantly lower BMD (p < 0.01) compared to the general population group. Total lean mass was independently associated with BMD in both groups. In KT patients, age, time spent on dialysis and PTH were the main negative independent predictors of BMD, after adjusting for possible confounders. Resistin and α-Klotho also negatively predicted lumbar bone density (p < 0.001), while adiponectin and α-Klotho positively predicted osteocalcin levels (p < 0.001) in KT recipients, independently of inflammatory markers. No significant associations were found between FGF23 and bone parameters in any of the groups. CONCLUSIONS: Age, PTH, time on dialysis and lean mass are among the main bone density predictors in long-standing KT patients. The bone impact of adipokine dysregulation and of α-Klotho merits further investigations in KT-MBD. Preserving lean mass for improved bone outcomes should be part of KT-MBD management on the long-term.