Background: There is growing evidence of a correlation between fat and bone metabolism at both the clinical and molecular levels, although the systemic regulators have not been clearly identified. The receptor activator of nuclear factor kB ligand (RANKL) and its soluble decoy receptor, osteoprotegerin (OPG), are involved in bone resorption and vascular calcification. OPG levels has been related with insulin resistance in adult obese subjects.
Objective and hypotheses: i) To evaluate RANKL and OPG serum levels in obese subjects and healthy lean controls; ii) to investigate correlation between metabolic alteration and OPG levels; iii) to correlate OPG and RANKL levels with bone status assessed by QUS.
Method: Twenty-five subjects (16 males, median age 10.8±2.6), BMI for age and sex >95th centile, were enrolled. Waist circumference was assessed in all subjects. As control group were recruited 28 non-obese subjects (18 males, median age of 10.8±2.6 years), age- and sex-matched. Bone status was assessed by QUS through BTT-Z-score and Ad-Sos-Z-score evaluation.
Results: Obese children have higher RANKL (P=0.01) and lower OPG (P<0.006) serum levels compared with controls; thus, RANKL to OPG ratio was significantly higher in patients than controls (P<0.001). However, these serum levels did not correlate with BTT-Z-score and Ad-Sos-Z-score, although obese patients had significantly reduced QUS parameters compared to the controls (P<0.01). Interestingly, in patients BTT-Z-score and Ad-Sos-Z-score inversely correlated with serum LDL levels (P<0.04 and P<0.01 respectively) whereas RANKL and RANKL to OPG ratio correlated with serum cholesterol levels (P<0.05). Parallel results demonstrated that OPG serum concentrations significantly correlate with waist circumference (P<0.05), SDS-BMI (P<0.05), insulin levels and HOMA-IR (P<0.04).
Conclusion: Our results pointed out to a complex alteration in obese children involving adipose tissue, bone and glucose metabolism, which is orchestrated by RANKL and OPG, two cytokines which function is cell-tissue specific.
20 - 22 Sep 2014
European Society for Paediatric Endocrinology