[A role for lipoproteins in the recovery from CPPD crystal-induced arthritis]

Calcium pyrophosphate dihydrate (CPPD) crystal-induced inflammation subsides spontaneously, and there have been few reports on its mechanism. It has recently been proposed that lipoproteins in the inflammatory synovial fluid played a role in the recovery from crystal-induced arthritis. This study investigated the inhibitory effect of lipoprotein on the inflammation-inducing activity of CPPD crystals in vitro and in vivo. Lipoproteins (very low density lipoprotein--VLDL, and low density lipoprotein-LDL) were isolated from human serum (in vitro) and rat serum (in vivo) by the sequential ultracentrifugal technique. In the in vitro studies, saline with lipoproteins was mixed with CPPD crystals, and co-incubated with isolated polymorphonuclear leukocytes (PMN). The production of superoxide anion (O-(2)) was measured as an index of inflammatory activity. In the in vivo studies, suspensions of CPPD crystals and rat lipoprotein solutions, were injected into the rat air pouch. The total number of white blood cells (WBC), crystal-containing WBCs, and concentrations of beta-glucronidase and prostaglandin (PG) E2, were measured. In the in vitro studies, O-(2) production by PMNs was more significantly suppressed after treating the CPPD crystals with VLDL or LDL than when the crystals were not treated with VLDL or LDL. In the in vivo studies, treatment of the CPPD crystals with lipoproteins significantly decreased the number of WBC and crystal-containing WBC, as well as the concentration of beta-glucronidase, and tended to depress the concentration of PGE2. These findings suggested that lipoproteins, especially LDL in inflammatory synovial fluid played an important role in the recovery from CPPD crystal-induced arthritis.