Differential association of the N-propeptide of collagen IIA (PIIANP) and collagen II C-telopeptide (CTX-II) with synovitis and erosions in early and longstanding rheumatoid arthritis.

OBJECTIVES: To determine the N-terminal propeptide of collagen IIA (PIIANP) in early and established rheumatoid arthritis (RA) and to study the association with collagen II degradation assessed by its C-telopeptide (CTX-II), x-ray status and disease activity measures.

METHODS: Two cohorts of RA patients were included: A) a one-year prospective cohort including 45 patients with early, untreated RA and B) a cross-sectional study comprising 50 RA patients with advanced disease. Blood donors and healthy volunteers served as controls. PIIANP in serum and urine CTX-II were measured by ELISA.

RESULTS: PIIANP did not differ from control levels at any time in patients with early RA (p=0.16 and p=0.89), but at one-year follow-up, PIIANP was decreased compared with baseline (p=0.046). In patients with longstanding RA, PIIANP was lower than in controls (p=0.002) and RA patients with a 12-month disease (p=0.01). PIIANP was unrelated to joint counts and CRP in both cohorts, but baseline PIIANP was lower among x-ray progressors than in non-progressors (p=0.04). CTX-II was persistently increased in both cohorts (p<0.001 and p<0.001). CTX-II was positively associated with joint counts and CRP but not with x-ray progression (p=0.84). There was no correlation between PIIANP and CTX-II.

CONCLUSION: Declining PIIANP with increasing RA duration and persistently increased CTX-II indicate that cartilage anabolic and degradative pathways are unbalanced from clinical RA onset. Furthermore, that collagen II depletion in RA is both mediated by anti-anabolic effects unassociated with synovitis (decreased PIIANP) and by excess collagen II degradation linked to synovitis (increased CTX-II).