[en] OBJECTIVE: This study was undertaken to identify new biomarkers of osteoarthritis (OA) by proteomics analysis and to develop specific immunoassays to detect and quantify them. METHODS: Proteomics analysis was performed in urine samples from 10 women (mean+/-SD age 76.0+/-5.0 years) undergoing knee replacement surgery due to severe OA and 5 healthy women (mean+/-SD age 25.6+/-2.6 years). Protein content was analyzed by 2-dimensional differential gel electrophoresis. Protein spots that exhibited an OA:control abundance ratio of >/=1.5 were identified by mass spectrometry. Specific enzyme-linked immunosorbent assays were developed and validated in serum obtained from 236 healthy subjects ages 20-64 years and from 76 patients with severe radiologic knee OA (mean+/-SD age 68.8+/-11.9 years). Immunohistochemical analysis was performed on articular cartilage from tibial plateaus. RESULTS: Thirteen proteins within spots that were significantly modified between groups were identified. Two peptides of fibulin 3, named Fib3-1 and Fib3-2, were of particular interest. Two antisera directed against these peptides were used to develop immunoassays. Compared with age-matched healthy subjects, median levels of serum Fib3-1 and Fib3-2 were elevated in OA patients (54.6 pM versus 85.1 pM [P<0.0001] and 144.4 pM versus 191.4 pM [P<0.0001], respectively). Using area under the receiver operating characteristic curve analysis, we demonstrated that Fib3-1 and Fib3-2 levels discriminate between OA and normal populations. Immunostaining revealed the presence of Fib3-1 and Fib3-2 in chondrocytes and in the extracellular matrix of the superficial layer of the fibrillated cartilage. CONCLUSION: Our findings indicate that Fib3-1 and Fib3-2 are potential biochemical markers for the diagnosis of OA.