Case-Controlled, Cross-Sectional Evidence that Spinal Cord Injury Associated with Sympathetic Decentralisation may Alter Osteocalcin Signalling

Objective: Osteocalcin has been shown to exert an endocrine influence on bone and energy metabolism in both animals and humans; recent evidence indicating a regulatory role for osteocalcin in glucose homeostasis and energy metabolism and as a marker for bone metabolism. The aim of this study was to investigate the interaction between osteocalcin, body composition, and blood biomarkers in men with spinal cord injury (SCI) compared with able-bodied male controls. Materials and Methods: Twenty men with SCI were matched for age, height, and weight with 20 able-bodied controls. Body composition, bone density and blood levels of adiponectin, leptin, insulin, glucose, insulin-like growth factor-1 (IGF-1) were undertaken. Total body and regional fat mass (FM), fat free mass (FFM), total body bone mineral density (BMD) and circulating levels of blood biomarkers were compared between the two groups and correlation analyses performed between osteocalcin and all measures. Results: Compared with controls, SCI had lower total and leg FFM (P<0.05), but higher total and regional FM (P<0.05). Osteocalcin negatively correlated with age (P<0.05), and positively with total, trunk and arm FFM, and IGF-1 (P<0.05) in SCI men. Negative correlations between osteocalcin and age (P<0.05) and positive correlations with total and all regional FM depots, leptin, fasting glucose, and IGF-1 (P<0.05) were found for the controls. Conclusions: Crosstalk between fat mass, osteocalcin, glucose metabolism and adipokines is lost with decentralisation in the sympathetic nervous system (SNS). The clinical impact of this decentralisation deserves further investigation. These findings do not imply causality, but should be considered hypothesis generating.