Conclusions
Our study suggests that there are significant differences in bone metabolism between postmenopausal women with OA and OP and provides evidence for the inverse relationship between OA and OP. Differential levels of bone remodeling markers, leptin, FLI, and OPG may partly contribute to the proposed inverse relationship. Roles of leptin and its soluble receptor in bone metabolism regulation should be explored further.
Methods
A total of 120 postmenopausal women with OA and OP (n = 60, respectively) were included in this comparative study. Anthropometric parameters and BMD at the spine and the proximal femur were measured. Serum leptin, soluble leptin receptor (sLR), osteoprotegerin (OPG), and bone remodeling markers, including bone-specific alkaline phosphatase (BALP), osteocalcin (OC), deoxypyridinoline cross-links (DPD), and cross-linked N-telopeptides of type I collagen (NTX), were quantified with commercial ELISA or EIA kits. Free leptin index (FLI) was also calculated by the ratio between serum leptin and sLR levels.
Results
Postmenopausal women with OA had higher body weight, body mass index, fat mass, and percentage of fat than those suffered from OP. Compared with the patients in OP group, the patients in OA group had significantly higher BMD values at all sites measured. Higher serum leptin and FLI and lower OPG levels were shown in the OA group (leptin: 31.22 +/- 6.4 versus 26.50 +/- 9.27 ng/ml, p < 0.001; FLI: 3.20 +/- 1.02 versus 2.50 +/- 0.95, p < 0.05; OPG: 4.75 +/- 1.97 versus 6.96 +/- 2.75 pM, p < 0.001), whereas lower serum OC and higher urine DPD were noted in the OP group (OC: 16.45 +/- 8.45 versus 13.06 +/- 6.25 ng/ml, p < 0.05; DPD: 10.83 +/- 7.12 versus 15.29 +/- 6.65 nM BCE/mM Cr, p < 0.001). Serum OPG levels negatively correlated with BMD at all sites assessed. However, no correlation was found between leptin and BMD. Only in the OA group di positive correlations exist between FLI and Z-score at the femoral neck and Ward's triangle region. After stepwise regression analysis, it was found that differential factors were able to predict the variance of BMD at different sites to a certain extent. Conclusions: Our study suggests that there are significant differences in bone metabolism between postmenopausal women with OA and OP and provides evidence for the inverse relationship between OA and OP. Differential levels of bone remodeling markers, leptin, FLI, and OPG may partly contribute to the proposed inverse relationship. Roles of leptin and its soluble receptor in bone metabolism regulation should be explored further.