A NOVEL SERUM ELISA FOR II COLLAGEN HELICAL DOMAIN DEGRADATION (S-HELIX-II) TO ASSESS CARTILAGE DAMAGE IN PATIENTS WITH RHEUMATOID ARTHRITIS

Background: The hallmark of rheumatoid arthritis (RA) is cartilage degradation. Biochemical markers of type II collagen degradation, the most abundant protein of cartilage matrix, are promising diagnostic tests to assess joint damage in RA. Recent studies have shown that the urinary excretion of fragments arising from the degradation of the helical (u-Helix-II) or the C-telopeptide (u-CTX-II) region of type II collagen are increased in patients with RA and associated with disease progression. Developing serum based assays for type II collagen degradation markers may improve measurement precision and consequently the diagnostic sensitivity of the test.Objectives: To develop an ELISA for serum Helix-II and compare its clinical performance with urinary Helix-II in patients with RAMethods: We developed a competitive polyclonal antibody-based ELISA for serum Helix-II using the 622-632 peptide from human type II collagen sequence (Helix-II) as immunogen and standard. Serum (s-Helix-II), and urinary Helix-II (u-Helix-II) levels were measured in 50 patients with early RA (disease duration < 5 years, mean 2.3 years) and in 34 healthy controls.Results: The ELISA for serum HELIX-II demonstrated intra and inter-assay variability below 15% and recovery of diluted serum samples ranged from 90 to 119%.As shown on the table, median serum Helix-II levels were increased by 2 fold compared to healthy controls (p<0.0001). Using the 95 percentile of healthy controls as the upper limit of normals, 98% of RA patients were identified at increased type II collagen degradation, whereas 40% had increased urinary Helix-II levels. When healthy controls and RA patients were considered together serum Helix-II correlated significantly but modestly to urinary Helix-II (r =0.318, p=0.0052). Groups Serum levels of HELIX-II (ng/ml) p vs controls Median 5- 95 th percentile Controls (n=34) 0.56 0.25-1.02 RA (n=50) 1.67 1.12-5.18 <0.0001 Conclusion: The assay for serum Helix-II has adequate technical performances and is highly sensitive to detect increased type II collagen degradation in early RA. The value of serum Helix-II to predict disease progression in RA and others arthritis diseases should be investigated.Citation: Ann Rheum Dis, volume 65, supplement II, year 2006, page 145Session: Rheumatic arthritis – prognosis and predictors