Advances in understanding calcium-containing crystal disease.

PURPOSE OF REVIEW: Calcium pyrophosphate dihydrate and basic calcium phosphate crystals are the two most common calcium-containing crystals involved in rheumatic diseases. Recent literature concerning their role in the pathogenesis of osteoarthritis is reviewed.

RECENT FINDINGS: In some instances, these calcium crystals might worsen osteoarthritis cartilage destruction. Laboratory investigations have identified determinants of cartilage calcification, especially a better characterization of matrix vesicle content and a better understanding of the regulation of inorganic pyrophosphate and phosphate concentration. In-vitro studies have highlighted new pathogenic mechanisms of calcium crystal-induced cell activation. Several intracellular signalling pathways are activated by calcium crystals. Recent studies suggested the implication of the inflammasome complex and a pivotal role for IL-1 in pseudogout attacks and chondrocyte apoptosis in basic calcium phosphate crystal-related arthropathies.

SUMMARY: Animal models of osteoarthritis and in-vitro studies using calcium pyrophosphate dihydrate and basic calcium phosphate crystals will improve our knowledge of these common crystals and could suggest new targets for drugs, as these common diseases are 'orphan' with respect to therapy.