interstingly,the same study demonstrated a catabolic role of leptin treatment on chondrocytes as judged by reduced proliferation accompanied by an induction of IL-1beta production and MMP-9 and MMP-13 protein expression.furthermore, another study showed the protein of leptin as a therapeutic target for OA as it suggested a correlation between leptin expression and DNA methylation in osteoarthritic cartilage and primary chondrocytes(65).more specifically, it was demonstrated that leptin silencing by small interference RNA (si RNA) dramatically inhibited MMP-13 expression in osteoarthritic chondrocytes which is a desirable effect in OA therapy as it inhibits cartilage degradation(65).moreover,that level of leptin in the synovial fluid of the joint was recently shown to be much higher in OA patients comparate to control individuals with no history of OA.in fact, leptin levels in the synovial fluid were much more elevated than in serum (59) and were stongly associated with the radiographic severity of OA (66),indicating a local effect of leptin in articular cartilage and further suggesting that leptin levels in the synovial fluid could be used as an effective quantitative marker for detection of OA.last but not least, at the genetic level, an association was recently revealed between leptin gene single nucleotide polymorphisms and knee OA susceptibility providing in vivo human evidence for the link between leptin, obesity and osteoarthritis(67).together these studies on adipokines and their connection to OA and obesity suggest that they may comprise a critical metabolic link between obesity and OA which further proposes the existence of a metabolic compound in OA.