Abstract

Gout is one of the most severe and frequent rheumatic diseases. Clinical manifestations of gout arise from uric acid crystal deposition in the musculoskeletal tissue. At high concentrations of uric acid in the body (hyperuricaemia), needle-shaped monosodium urate (MSU) crystals are formed. The structures are ingested by neutrophils and monocytes and thereby trigger robust activation of the inflammasome, an intracellular protein complex mounting an inflammatory response. Inflammasome activation builds interleukin-1, which acts as a proinflammatory mediator and induces vasodilation, recruitment of additional leucocytes and the expression of proinflammatory cytokines and chemokines. This process is associated with the clinical manifestation of an acute gout attack. Such attacks, however, stop rather rapidly and the process of resolution of inflammation in gout is now better defined. Neutrophils having ingested MSU crystals undergo a specific form of cell death called NETosis, which is characterised by the formation of neutrophil extracellular traps (NETs). During this process, DNA is extruded, allowing the dense packaging of MSU crystals as well as the degradation of proinflammatory cytokines, thereby allowing the stopping of the inflammatory process. Reactive oxygen species are essential for forming NETs and for allowing the resolution of inflammation in gout. This process of NETosis is critical for understanding tophaceous gout, since tophi are composed of NETs and densely packed MSU crystals.