Joint remodeling outcome of serum levels of Dickkopf-1 (DKK1), cartilage oligomeric matrix protein (COMP), and C-telopeptide of type II collagen (CTXII) in rheumatoid arthritis

Introduction
Rheumatoid arthritis (RA) is the most widespread chronic inflammatory rheumatic disease over the world. It is characterized by chronic proliferation of synovium, cartilage destruction, and periarticular erosion/bone loss. We investigated the serum levels of the C-telopeptide of type II collagen (CTX-II), Dickkopf-1 (DKK1), and cartilage oligomeric matrix protein (COMP) in relationship to the disease activity.

Material and methods
Serum COMP, CTX-II, and DKK1 levels were measured in 63 RA patients and 50 person age and gender matched as a healthy controls by ELISA test. Disease activity score (DAS) were calculated.

Results
The mean level of and COMP and CTX-II were significantly higher in patients with RA than in healthy controls (5.71 ±7.04 vs. 2.70 ±1.31 ng/ml, and 0.45 ±0.27 vs. 0.23 ±0.16 ng/ml, respectively; p < 0.001). Also, DKK1 serum levels were significantly higher in patients with RA than in healthy controls (6970.68 ±7566.68 vs. 3276.96 ±1306.77 pg/m; p < 0.001). There was a positive significant correlation between DKK1 and swollen joint (r = 0.42, p < 0.001). There were no significant differences in the number of patients, gender, the duration of RA disease, DAS, and RF. Sensitivity was 58.7% and specificity was 85.7% at a cut-off point (> 3.6 ng/ml) for serum COMP in RA patients, while, sensitivity was 100% and specificity was 52.4% at a cut-off point (> 0.15 ng/ml) for serum CTX-II and sensitivity was 68.3% and specificity was 95.2 % at a cut-off point (> 4876 pg/ml) for serum DKK1.

Conclusions
Measurement of some serological biomarkers such as CTX-II, COMP, and DKK1 that reflect bone and cartilage destruction in RA patients could be used to indicate disease activity and early joint affection.