Synovial fluid potentially contains markers for early diagnosis and
disease progression in degenerative
joint diseases such as
osteoarthritis. Here, a method is described for profiling endogenous
peptides in human synovial fluid, using ultrafiltration, solid-phase extraction, nanoscale liquid chromatography, and high-resolution mass spectrometry. Synovial fluid is characterized by its high viscosity, caused by the presence of the
lubricant hyaluronic acid. The method proved to be capable of eliminating the high concentrations of
hyaluronic acid, which appeared to be necessary to obtain satisfactory analytical performance, that is, within-day relative standard deviations of 5-15%, between-day relative standard deviations of 6-16%, a linear response of R2=0.994, a limit of detection in the femtomole range, and reproducible recoveries of 14-67%. With the developed method, in a synovial fluid sample from an
osteoarthritis patient and a healthy control, in total, 501
peptides originating from 40
proteins were identified.
Peptide cleavage products from six
proteins that have been associated with
osteoarthritis in earlier studies (
collagen II, proteoglcycan 4,
serum amyloid A,
tubulin,
vimentin, and Matrix Gla) could also be identified with our profiling method. The robustness of the method indicates that it can be applied in systems biology approaches for further studies on degenerative
joint disease, eventually leading to a better understanding of the disease and its
therapy, as well as the development of novel
biomarkers to monitor these processes.