ABSTRACT
Objective To investigate the role of RANKL/RANK/OPG system in bone metabolism of ankylosing spondylitis (AS) by detecting bone mineral density, bone metabolism factors such as osteoprotegerin (OPG), soluble receptor activator of nuclear factors-κB ligand (sRANKL) and the expression of membrane-bound (mb) RANKL in the peripheral blood T lymphocytes. Methods Bone mineral density of AS patients were measured by dual-energy X-ray absorptiometry (DEXA) and serum levels of OPG, sRANKL,tartrate resistant acid phosphatase 5b (TRACP-5b) and bone alkaline phosphatase (BALP) were determined by enzyme-linked immunosorbent assay (ELISA). The percentages of CD4+/RANKL+ and CD8+/RANKL+ in the peripheral blood were detected with flow cytometry. T-test, x2-test were used for statisical analysis. Results ① The incidence of osteopenia and osteoporosis in AS was 47% and 37% respectively. ② Serum RANKL,TRACP-5b levels and RANKL/OPG ratio were higher in AS patients than those in normal controls (P<0.05).But there was no significant difference in OPG and BALP between AS patients and normal controls. ③There were positive linear correlation between serum levels of RANKL and OPG, sRANKL and TRACP-5b, OPG and TRACP-5b in AS (P<0.01). ④ The prevalence of CD4+/RANKL+ cells in the peripheral blood of AS patients was significantly higher than that in the normal controls (P<0.05). Conclusion There is a high incidence of bone loss in AS patients. Increased bone resorbtion is the feature of bone metabolism in AS.RANKL/RANK/OPG system may play an important role. The imbalance of RANKL/RANK/OPG system may be one of the bone loss mechanisms of AS. CD4 + T lymphocyte may play an important role in osteoclasts differentiation and bone resorption in AS by up-regulating the expression of RANKL.
ABSTRACT
BACKGROUND: To determine the bone mineral density (BMD), serum soluble receptor activator of the nuclear factors kappa B ligand (sRANKL) and the osteoprotegerin (OPG) levels in patients with ankylosing spondylitis (AS), and to determine their relationship with disease activity indexes. METHODS: The disease activity was evaluated by the Bath Ankylosing Spondylitis Disease Activity Score Index (BASDAI), Bath Ankylosing Spondylitis Functional Index (BASFI), Bath Ankylosing Spondylitis Metrology Index (BASMI) and Bath Ankylosing Spondylitis Patient Global Score (BAS-G). The BMD was measured by dual energy X-ray absorptiometry. Serum levels of sRANKL and OPG were measured by the sandwich enzyme-linked immunosorbent assay. RESULTS: Osteoporosis and osteopenia of the femoral neck were found in 33% and 41%, respectively. BMD of femoral neck showed a negative correlation with disease activities. The serum levels of sRANKL were higher in patients with AS than in controls, and the ratio of sRANKL to OPG was also elevated in AS, but had no correlation with disease activity. The sRANKL/OPG ratio tended to be higher in patients with lower BMD. CONCLUSIONS: BMD was reduced in 79% of AS patients and reflected disease status. The sRANKL/OPG ratio was upregulated in patients with AS and it appears to be related to BMD and radiological changes. These results suggest that the imbalance between RANKL and OPG might be involved in the pathogenesis and clinical courses of AS.