Soluble receptor activator of NFkappa B-ligand and osteoprotegerin in rheumatoid arthritis - relationship with bone mineral density,disease activity and bone turnover

The aim of our study was to investigate determinants of bone mineral density (BMD) measured by dual X-ray absorptiometry at the lumbar spine (BMD-LS) and at the femoral neck (BMD-FN) in patients with rheumatoid arthritis (RA) with special respect to bone resorbing proinflammatory cytokines and their physiological antagonists. In 142 RA patients the following parameters were measured in parallel with BMD: serum levels of soluble receptor activator of nuclear factor kappa-B-ligand (sRANKL), osteoprotegerin (OPG), interleukin (IL)-6, soluble glycoprotein 130 (sgp130), 25-hydroxyvitamin D3 (25OHD₃), 1,25-dihydroxyvitamin D3 (1,25OH]₂D₃), intact parathyroid hormone, osteocalcin, ionized calcium, renal excretion of pyridinolin and deoxypyridinolin, C-reactive protein, and erythrocyte sedimentation rate (ESR). No significant differences of sRANKL, OPG, IL-6, and spg130 were found between patients with osteoporosis (47.9% of patients), osteopenia (36.6%), and normal BMD (15.5%). However, total sRANKL was significantly higher in postmenopausal women with osteoporosis at FN than in those without (p < 0.05) and showed a negative correlation with BMD-LS in patients older than 60 years (p = 0.01). BMD-LS and BMD-FN (p < 0.001) and total sRANKL (p < 0.01) were negatively related with the age of the patients. Only IL-6 (positive correlation, p < 0.001) and 1,25(OH)₂D₃ (negative correlation, p < 0.001) but not sRANKL, OPG, and sgp130 were related to disease activity. Using multiple linear regression analysis, menopause was identified as the crucial negative determinant of BMD-LS (R ² = 0.94, p = 0.001), whereas cumulative glucocorticoid dose (β = −0.80, p = 0.001) and ESR (β = −0.44, p = 0.016) were the negative determinants of BMD-FN (R ² = 0.86, p = 0.001). The results indicate that influences of age and gender must be considered in investigations on the relationship between BMD and sRANKL in RA and that high serum levels of sRANKL seems to be associated with osteoporosis only in subgroups of RA patients.