Objective: To investigate the relationships between the serum levels of osteoprotegerin (OPG), receptor activator of nuclear factor-kappa B ligand (RANKL) with age, menopause, bone biochemical markers and bone mineral densities (BMDs) in pre- and postmenopausal women and to determine the contributing factors for serum OPG and RANKL.
Methods: 504 pre- and postmenopausal women aged between 20 and 75 years were enrolled in this study. BMDs at lumbar spine and proximal femur were measured with dual-energy X-ray absorption meter. The serum osteocalcin (BGP), OPG, RANKL and urinary type I collagen (NTx) were also tested.
Results: Age was positively related with serum OPG (r = 0.442, P < 0.001) and was negatively in association with serum RANKL (r = -0.263, P < 0.001). Postmenopausal women showed higher levels of serum OPG [(107.6 +/- 3.0) ng/L], while their serum concentrations of RANKL [(4.7 +/- 0.4) ng/L] and RANKL/OPG ratios (0.045 +/- 0.004) were significantly lower than those of premenopausal women [(72.0 +/- 1.8) ng/L, (5.8 +/- 0.3) ng/L and 0.099 +/- 0.008]. Neither serum OPG nor RANKL or RANKL/OPG was in association with BMDs at lumbar spine or proximal femur after adjustment of age, years-since-menopause (YSM) and body mass index. Serum OPG was positively related with urinary NTx/creatinine. Serum RANKL was negatively related with serum BGP. Serum OPG, RANKL and RANKL/OPG showed no differences among normal, osteopenic and osteoporotic postmenopausal women. In multiple regression analysis, YSM, age and bone markers were the independent contributors to OPG-RANKL system.
Conclusions: The elevation of serum OPG along with age might be a compensatary mechanism against the accelerated bone resorption, while the decreased level of serum RANKL might be helpful for restoring the reduced bone formation in postmenopausal women. YSM, age, together with bone tune-over markers were the main factors affecting serum concentrations of OPG and RANKL.