Novel COMP Neoepitopes Identified in Synovial Fluids from Patients with Joint Diseases using Affinity Chromatography and Mass Spectrometry.

To identify patients at risk for progressive joint damage there is a need for early diagnostic tools to detect molecular events leading to cartilage destruction. Isolation and characterization of distinct cartilage oligomeric matrix protein (COMP) fragments derived from cartilage and released into synovial fluid will allow discrimination between different pathological conditions and monitoring of disease progression. Early detection of disease and processes in the tissue as well as an understanding of the pathologic mechanisms will also open for novel treatment strategies. Disease specific COMP fragments were isolated by affinity chromatography of synovial fluids from patients with rheumatoid arthritis (RA), osteoarthritis (OA) or acute trauma (AT). Enriched COMP fragments were separated by SDS-PAGE followed by in-gel digestion and mass spectrometric identification and characterization. Using the enzymes trypsin, chymotrypsin and Asp-N for the digestions an extensive analysis of the enriched fragments could be accomplished. Twelve different neoepitopes were identified and characterized within the enriched COMP fragments. For one of the neoepitopes, S77, an inhibition ELISA was developed. This ELISA quantifies COMP fragments clearly distinguishable from total COMP. Furthermore, fragments containing the neoepitope S77 were released into the culture medium of cytokine (TNF-α and IL-6/sIL-6R) stimulated human cartilage explants. The identified neoepitopes provide a complement to the currently available commercial assays for cartilage markers. Through neoepitope assays, tools to pin-point disease progression, evaluation methods for therapy and means to elucidate disease mechanisms will be provided.