To analyze serum concentrations of interleukin 6 (IL-6), osteocalcin, intact parathyroid hormone (PTH), and type 1 collagen carboxyterminal telopeptide (ICTP) as well as the urinary concentrations of crosslinked N-telopeptides of type 1 collagen (NTx) and deoxypyridinoline (Dpd) in patients with rheumatoid arthritis (RA) to investigate their role in the etiology of the osteopenia in this disease.
Using ELISA and radioimmunoassay methods, we estimated serum concentrations of IL-6, osteocalcin, ICTP, intact PTH, and spot urine concentrations of NTx and Dpd in 25 female patients with active RA, 25 female patients with suppressed disease, and 25 age matched healthy female controls.
Patients with active RA had significantly higher (p < 0.001) concentrations of IL-6 (94.0+/-12.1 pg/ml) compared to patients with suppressed disease (13.2+/-0.8 pg/ml) and healthy controls (12.3+/-0.8 pg/ml). Serum osteocalcin was significantly lower (p < 0.001) in patients with active RA (1.9+/-0.2 ng/ml) compared to patients with suppressed disease (2.7+/-0.2 ng/ml) and the controls (2.9+/-0.2 ng/ml). Similarly, serum intact PTH was significantly lower (p < 0.001) in patients with active disease (29.9+/-1.5 ng/ml) compared to patients with suppressed RA (38.0+/-1.6 ng/ml) and controls (49.8+/-2.4 ng/ml). Serum ICTP was also significantly higher (p < 0.01) in patients with active RA (9.5+/-0.3 microg/l) versus patients with suppressed disease (4.1+/-0.2 microg/l) and controls (3.4+/-0.2 microg/l). In patients with active disease, spot urine concentrations of NTx (123.1+/-5.1 nmol bone collagen equivalent/mmol creatinine) and Dpd (15.1+/-0.7 nmol/mmol creatinine) were significantly higher (p < 0.001) than in patients with suppressed disease (58.4+/-2.5 nmol bone collagen equivalent/mmol creatinine and 10.1+/-0.5 nmol/mmol creatinine, respectively) and healthy controls (53.4+/-2.1 nmol bone collagen equivalent/mmol creatinine and 9.7+/-0.5 nmol/mmol creatinine, respectively). There were no significant correlations between serum IL-6 and serum ICTP (r = 0.2357, p = 0.257) or urinary NTx (r = 0.1436, p = 0.494) or between serum intact PTH and ICTP (r = 0.0206, p = 0.922) in patients with active RA.
There are no significant correlations between bone resorption markers and serum IL-6 and intact PTH in patients with RA.