Specificity of a porcine 127‐kd nucleotide pyrophosphohydrolase for articular tissues

Abstract

Objective. To determine the tissue specificity of a porcine 127-kd nucleotide pyrophosphohydrolase (NTPPHase) found in vesicles derived from hyaline articular cartilage (ACV).Methods. Homogenates of porcine brain, lung, liver, kidney, urinary bladder, pancreas, spleen, skin, vena cava, marrow, bone (cells), tendon (Achilles), ligament (anterior cruciate), elastic cartilage, meniscus, and hyaline cartilage were analyzed for NTPPHase activity (thymidine monophosphate paranitrophenyl ester substrate) and by Western blot using polyclonal antibodies against 127-kd NTPPHase and against recombinant PC-1, another ecto-NTPPHase.Results. All tissues contained NTPPHase activity; the highest specific activity was found in hyaline articular cartilage, the lowest in brain. ACV-associated 127-kd NTPPHase was expressed in cartilage, ligament, and tendon. PC-1 was also expressed in those tissues and in skin, kidney, bone cells, and (probably) in liver and muscle.Conclusion. The 127-kd NTPPHase appears to be highly specific for articular tissues.Successful pharmacologic control of inorganic pyrophosphate (PPi) production by articular tissues could prevent calcium pyrophosphate dihydrate (CPPD) crystal deposition and its biologic consequences of acute inflammatory attacks and accelerated joint tissue degeneration. This goal has stimulated _.

Extracellular Nucleotides Block Bone Mineralization in Vitro: Evidence for Dual Inhibitory Mechanisms Involving Both P2Y2 Receptors and Pyrophosphate

“…Compared with other tissues, bone and cartilage exhibit high levels of ENPP activity (32), most of which is attributed to ENPP-1 (33) and ENPP-3 (or B10) (23). The expression and specific activities of ENPP-1 and ENPP-3 in primary osteoblasts are reported to be approximately equal, but ENPP-1 may play a more important role in the regulation of mineralization because it is preferentially targeted to the plasma membrane and matrix vesicles after translation, whereas ENPP-3 remains intracellular (34).…”

Extracellular nucleotide metabolism and signaling in the pathophysiology of articular cartilage

“…A DNA probe coding for the 61-kd porcine protein hybridizes with human articular chondrocyte mRNA (54). In contrast to the widespread NPP1, this enzyme is restricted to articular tissues (50). Both 61-kd and 127-kd proteins are detected by Western blot in human synovial fluid (55).…”

“…Articular chondrocytes constitutively elaborate large amounts of ePPi (48,49) and possess the highest known NTPPH activity (50). Several tissues that synthesize collagenous extracellular matrices express NPP1, NPP2␣, and NPP3 (36,41,48,51).…”

New developments in the pathogenesis of articular cartilage calcification

“…These enzymes hydrolyze the phosphodiester I bond in purine and pyrimidine nucleoside triphosphates (designated as NTPPPH activity) [9,32]. Chondrocytes and osteoblasts have particularly specific activity of NTPPPH [33]. Moreover, cartilage NTPPPH activity and PPi elaboration are both markedly increased in idiopathic chondrocalcinosis of the elderly [9].…”