AN ENPP1-SPECIFIC INHIBITOR ATTENUATES EXTRACELLULAR ECTO-PYROPHOSPHATASE ACTIVITY IN HUMAN OSTEOARTHRITIC CARTILAGE

Background: Calcium pyrophosphate deposition (CPPD) is associated with osteoarthritis (OA) and is the cause of a common inflammatory articular disease (1). Nucleotide pyrophosphatase/phosphodiesterase1 (eNPP1) is the major ecto-pyrophosphatase (NTPPPH) in chondrocytes and chondrocyte-derived matrix vesicles (MVs) (2). Thus, eNPP1 is a principle contributor to extracellular pyrophosphate levels and a potential target for interventions aimed at preventing CPPD. Recently, we synthesized and described a novel eNPP1 inhibitor (3). Objectives: To evaluate whether the eNPP1-specific inhibitor, SK4A, attenuates NTPPPH activity in human OA articular cartilage. Methods: Cartilage tissue, primary chondrocytes and cartilage-derived MVs were obtained from donors with osteoarthritis undergoing knee replacement surgery.The effect of SK4A on cell viability was assayed by the XTT method. eNPP1 expression was evaluated by Western blot. NTPPPH activity was measured by a colorimetric assay with thymidine 5'-monophosphate p-nitrophenyl ester as a substrate and by HPLC analysis of ATP levels. Results: Primary OA chondrocytes express eNPP1 in early passages, but this expression is subsequently lost upon further passaging. Similarly, significant NTPPPH activity can only be detected in early-passage human chondrocytes. The eNPP1 inhibitor, SK4A, does not affect chondrocyte viability at concentrations of up to 1mM. SK4A effectively inhibits the ex vivo NTPPPH activity in whole cartilage tissue, in isolated primary chondrocytes and in cartilage-derived MVs. Conclusions: SK4A inhibits NTTTPH activity in human OA cartilage and may prevent extracellular pyrophosphate accumulation and calcium pyrophosphate deposition. References: 1. Zhang W, Doherty M, Bardin T, et al. Ann Rheum Dis. 2011;70(4):563-70. 2. Johnson K, Terkeltaub R. Front Biosci. 2005; 10:988-97. 3. Nadel Y, Lecka J, Gilad Y, et al. J Med Chem. 2014; 57(11): 4677-91. Disclosure of Interest: None declared DOI: 10.1136/annrheumdis-2015-eular.2707Citation: Annals of the Rheumatic Diseases, volume 74, supplement 2, year 2015, page 662Session: Cartilage, synovium and osteoimmunology (Poster Presentations )