EXTRACELLULAR PYROPHOSPHATE METABOLISM OF CHONDROCYTES

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Considerable recent research has revealed abnormally high intra-articular production of inorganic pyrophosphate (PPi) as an important metabolic defect in calcium pyrophosphate dihydrate (CPPD) deposition disease and osteoarthritis. Cartilage has been identified as a probable major source of abnormal PPi production in these diseses. Elevated activity of the PPi generating ecto-enzyme, nucleoside triphosphate pyrophosphohydrolase (NTPPPH) is found in both cartilage and synovial fluid (SF) of patients with CPPD deposition. SF NTPPPH activity correlates with SF PPi concentration in a variety of arthropathies, but it is not known if NTPPPH participates in intra-articular PPi production. Preliminary experiments indicate isolated porcine chondrocytes exhibit ecto-NTPPPH activity and spontaneously elaborate PPi. We have partially purified NTPPPH from deoxycholate extracts of isolated chondrocytes by anion exchange chromatography. We how propose to highly purify porcine chondrocyte NTPPPH by affinity chromatography and prepare antisera in rabbits. A precipitating antiserum would allow immunohistologic determination of NTPPPH distribution in articular tissues. If an antiserum which specifically blocks NTPPPH activity is obtained, we hope to determine if extracellular PPi elaboration by intact chondrocytes is dependent on NTPPPH.