ABSTRACT. Pentosan polysulfate sodium (PPS) has a heparin-like structure and is purificated from the plant of European beech wood. PPS has been used for the treatment of interstitial cystitis for human patients. Recent years, it was newly recognised that PPS reduce pain and inflammation of OA. The molecular biological mechanism of PPS to express its clinical effects is not fully understood. The purpose of the present study is to investigate a mechanism of action of PPS on inflammatory reaction of chondrocytes in vitro. It was evaluated that effects of PPS on interleukin (IL)-1β-induced phosphorylation of mitogen-actiated protein kinases (MAPKs), such as p38, extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK), nuclear translocation of nuclear factor-kappa B (NF-κB), and matrix metalloproteinase (MMP)-3 production in cultured articular chondrocytes. As a result, in the presence of PPS existence, IL-1β-induced phosphorylation of p38 and ERK were certainly inhibited, while JNK phosphorylation was not affected. Nuclear translocation of NF-κB and MMP-3 production were suppressed by PPS pretreatment prior to IL-1β stimulation. In conclusion, it is strongly suggested that PPS treatment prevents inflammatory intracellular responses induced by IL-1 β through inhibition of phosphorylation of certain MAPKs, p38 and ERK and then nuclear translocation of NF-κB in cultured chondrocytes. These PPS properties may contribute to suppressive consequence of catabolic MMP-3 synthesis. These data might translate the clinical efficacy as PPS treatment could inhibit the cartilage catabolism and related clinical symptoms of OA in dogs. KEY WORD: canine, MAP kinase, NF-κB, osteoarthritis, pentosan polysulfate sodium.doi: 10.1292/jvms.11-0511; J. Vet. Med. Sci. 74(6): 707-711, 2012 In the treatment of canine osteoarthritis (OA), multiple therapeutic intervention tools are used for multimodal pain management, including systemic administration of nonsteroidal anti-inflammatory drugs (NSAIDs), intra-articular administration of hyaluronic acid, intravenous or intramuscular administration of disease-modyfying osteoarthritis drugs (DMOADs), the use of oral nutraceutical agents, rehabilitaion and weight management [20]. In particular, DMOADs are most likely to relief pain and other clinical symptoms directly related to joint pathologies [16].It is thought that the pathophysiology of OA is related with the imbalance of reparative and degradation processes leads to loose aggrecans and collagens from extracellular matrix (ECM) of hyaline cartilage, resulted in articular cartilage degeneration [1,15]. As catabolic enzymes of ECM, matrix metalloproteinase (MMP) and a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS) are playing major role in the process and in establishment of OA pathologies, to which DMOADs should target [19].Pentosan polysulfate sodium (PPS) has a heparin-like structure and is extracted from the plant of European beech wood. In North America and Europe, PPS has been used for several ...