Current pharmacotherapy for osteoarthritis (OA) alleviates pain and inflammation but does not protect the articular cartilage from further damage or affect disease progression. Biological markers such as YKL-40 may provide a snapshot of current events in joint tissues, allowing rapid assessment of treatments. This review discusses recent data regarding YKL-40, with an emphasis on the relationship between YKL-40 and OA. The presence of YKL-40 in cartilage and synovium in OA patients correlates with histopathological changes and may reflect local disease activity. In addition, the levels of YKL-40 in serum and synovial fluid also seem to correlate with disease severity. The functional role of YKL-40 is not yet clear, but its production as part of the inflammatory response in articular chondrocytes may modulate the cellular response to pro-inflammatory cytokines, acting to limit connective tissue degradation. Further elucidation of its roles and relationships may enable YKL-40 to act as a useful biomarker in the development of therapies for OA.
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