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Crystals in arthritis: new age nonsense or novel therapeutic target?

Apatite crystals are present in up to 70% of fluids from degenerated joints.1 Their presence correlates strongly with radiographic evidence of cartilage degeneration and is associated with larger joint effusions when compared with joints without crystals.2 3 Whether the presence of apatite crystals is a cause of cartilage damage or an effect of cartilage damage is unclear.4 Several lines of evidence suggest that apatite crystals cause joint destruction. For example, apatite crystals induce both mitogenesis and prostaglandin synthesis in synovial fibroblasts and chondrocytes in vitro.5 They also induce matrix metalloprotease (MMP) synthesis and secretion, thus promoting tissue damage.6 7 The cellular mechanisms whereby apatite crystals induce such responses are currently under investigation. Like many other growth promoting agents, apatite crystals induce a variety of transcription factors such as nuclear factor κB (NF-κB) and activator protein 1 (AP-1).8 They also …