INHIBITION OF CALCIUM PYROPHOSPHATE DIHYDRATE CRYSTAL-FORMATION IN ARTICULAR-CARTILAGE VESICLES AND CARTILAGE BY PHOSPHOCITRATE

Articular cartilage vesicles (ACV), isolated by differential centrifug ation of adult hyaline articular cartilage collagenase digests, minera lized in the presence of calcium and ATP. Mineral analysis by microsco py, chemical analysis, energy-dispersive analysis, and infrared spectr oscopy revealed crystals resembling calcium pyrophosphate dihydrate (C PPD). Adult articular cartilage also underwent ATP-dependent mineraliz ation, supporting the contention that vesicles in situ fostered adult articular cartilage mineralization. Phosphocitrate (PC) is a recognize d in vitro inhibitor of hydroxyapatite and calcium oxalate monohydrate crystal formation, but it is not known whether PC can similarly restr ict CPPD crystal development. In the present study we examine the effe ct of PC, citrate, and n-sulfo-2-amino-tricarballylate (SAT, a PC anal ogue) on the ATP-induced CPPD crystal formation in both ACV and articu lar cartilage models. Only PC (10-1000 mu M) blocked both the ATP-depe ndent and -independent mineralization in ACV in a dose-dependent fashi on, At 1 mM, SAT and citrate blocked the ATP-independent mineralizatio n. Similarly, only PC blocked both the ATP- and non-ATP-dependent mine ralization in native articular cartilage slices, PC, SAT, and citrate had no effect on ACV nucleoside triphosphate pyrophosphohydrolase acti vity, suggesting that none of these agents blocked mineralization thro ugh the inhibition of nucleoside triphosphate pyrophosphohydrolase act ivity, which generates inorganic pyrophosphate from ATP.