Regarding interactions between pro-inflammatory cytokines and bone metabolism in rheumatoid arthritis (RA), we investigated the relationship between the serum levels of interleukin (IL)-1beta, IL-6, soluble interleukin-2 receptor (sIL-2r), C-reactive protein (CRP), the vitamin D metabolites 25-hydroxyvitamin D3 (25OHD3) and 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], intact parathyroid hormone (iPTH) as well as serum and urinary parameters of bone turnover in 74 post-menopausal women with RA.
SIL-2r correlated negatively with 1,25(OH)2D3 (P < 0.01), whereas IL-6 showed a positive correlation with urinary excretion of deoxypyridinoline collagen cross-links (P < 0.01). 1,25(OH)2D3 (P < 0.01) and iPTH (P < 0.01) were negatively related to CRP, whereas the urinary excretion of pyridinoline (P < 0.01) and deoxypyridinoline (P < 0.01)-collagen cross-links showed a positive correlation with CRP. 1,25(OH)2D3 (P < 0.01) and iPTH (P < 0.05) were positively related to bone alkaline phosphatase as a marker of osteoblast function.
Our data indicate that IL-6 is a critical determinant of increased bone resorption in post-menopausal RA women with high disease activity and that serum levels of 1,25(OH)2D3 are inversely related to T-cell activation.