Pathogenic role of basic calcium phosphate crystals in destructive arthropathies

PLoS One. 2013;8(2):e57352. doi: 10.1371/journal.pone.0057352. Epub 2013 Feb 28.


Background: basic calcium phosphate (BCP) crystals are commonly found in osteoarthritis (OA) and are associated with cartilage destruction. BCP crystals induce in vitro catabolic responses with the production of metalloproteases and inflammatory cytokines such as interleukin-1 (IL-1). In vivo, IL-1 production induced by BCP crystals is both dependant and independent of NLRP3 inflammasome. We aimed to clarify 1/ the role of BCP crystals in cartilage destruction and 2/ the role of IL-1 and NLRP3 inflammasome in cartilage degradation related to BCP crystals.

Methodology principal findings: synovial membranes isolated from OA knees were analysed by alizarin Red and FTIR. Pyrogen free BCP crystals were injected into right knees of WT, NLRP3 -/-, ASC -/-, IL-1α -/- and IL-1β-/- mice and PBS was injected into left knees. To assess the role of IL-1, WT mice were treated by intra-peritoneal injections of anakinra, the IL-1Ra recombinant protein, or PBS. Articular destruction was studied at d4, d17 and d30 assessing synovial inflammation, proteoglycan loss and chondrocyte apoptosis. BCP crystals were frequently found in OA synovial membranes including low grade OA. BCP crystals injected into murine knee joints provoked synovial inflammation characterized by synovial macrophage infiltration that persisted at day 30, cartilage degradation as evidenced by loss of proteoglycan staining by Safranin-O and concomitant expression of VDIPEN epitopes, and increased chondrocyte apoptosis. BCP crystal-induced synovitis was totally independent of IL-1α and IL-1β signalling and no alterations of inflammation were observed in mice deficient for components of the NLRP3-inflammasome, IL-1α or IL-1β. Similarly, treatment with anakinra did not prevent BCP crystal effects. In vitro, BCP crystals elicited enhanced transcription of matrix degrading and pro-inflammatory genes in macrophages.

Conclusions significance: intra-articular BCP crystals can elicit synovial inflammation and cartilage degradation suggesting that BCP crystals have a direct pathogenic role in OA. The effects are independent of IL-1 and NLRP3 inflammasome.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Apoptosis
  • Arthritis / etiology*
  • Arthritis / pathology
  • Base Sequence
  • Calcium Phosphates / chemistry*
  • Crystallization
  • DNA Primers
  • Female
  • Immunohistochemistry
  • Interleukin-1 / genetics
  • Interleukin-1 / physiology
  • Macrophages / metabolism
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Real-Time Polymerase Chain Reaction
  • Spectroscopy, Fourier Transform Infrared


  • Calcium Phosphates
  • DNA Primers
  • Interleukin-1
  • calcium phosphate

Grant support

This work was supported by the Fonds national suisse de la recherche scientifique (grant 310030-130085/1), from the Fondation Jean and Linette Warnery, from the Fondation pour la Recherche Médicale (FRM DV020081013483, call for bids Vieillissement, 2008-2011), INSERM, University Paris Diderot, Faculty of Medicine (Institut Claude Bernard), the Société Française de Rhumatologie, the Association pour la Recherche en Pathologie Synoviale (ARPS), Prévention et Traitement des Décalcifications - Cristaux et Cartilage, and Rhumatisme et Travail. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.