The solubility of calcium pyrophosphate dihydrate crystals

Abstract

The solubility of calcium pyrophosphate dihydrate crystals (CPPD crystals), which cause pseudogout, was studied in vitro and in vivo. The in vitro experiment using 0.1 M tris buffer and 0.2 M glycine buffer indicated that changes in pH and pyrophosphatase activity played a major role in the solubility of CPPD crystals. An experiment using the synovial fluid from patients with pseudogout, rheumatoid arthritis, and from those with osteoarthritis suggested that changes in the synovial fluid pH due to inflammation affected the solubility of these crystals. In addition, an experiment using the air pouch in rat showed that inflammation due to the CPPD crystals was maximum at about 9 hours after CPPD injection, and that inflammatory cells appearing at this time then had a major influence on the crystals' solubility. From these results, it appeared that CPPD crystals released into the joint cavity were mostly dissolved by inflammatory cells, but that crystal dissolution was also affected by changes in the synovial fluid itself, particularly by a change in pH.