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Background/Purpose: Gout is caused by synovial deposition of monosodium urate (MSU) crystals from supersaturated extracellular fluid, with subsequent neutrophilic synovitis the hallmark of acute gout. The interaction of neutrophils with MSU induces the release of a large number of inflammatory mediators including superoxide (SO) and chemokines such as interleukin-8 (IL-8). While hyperuricemia is the key risk factor for onset of gout, how hyperuricemia may affect neutrophil function in gout is unknown. We hypothesize that variation in neutrophil production of SO and IL-8 in response to MSU may contribute to the risk of gout. To test this we conducted an observational study of neutrophil response to MSU in subjects with gout, asymptomatic hyperuricemia and age-, gender- appropriate normouricemic individuals (normal controls).
Methods: Individuals with gout (ACR criteria 1977) (n=39), asymptomatic hyperuricemia (n=11) and normal controls (n=10) were recruited from the community. Patients with gout were defined as acute gout if they had discrete attacks without tophi and chronic gout if tophi were present. All individuals with gout were seen between attacks of gout. The proportion of neutrophils (CD15+ leucocytes) in blood and neutrophil expression CD11b in blood was determined using flow cytometry. Peripheral blood neutrophils were isolated using a Ficoll gradient centrifugation, with cell viability and purity being >98%. Neutrophils were stimulated with MSU in vitro and production of SO (WST-1 assay) and IL-8 (Luminex) was measured. Serum IL-8 levels in serum were also determined.
Results: There was no difference between individuals with gout and healthy controls in proportion of neutrophils in peripheral blood or neutrophil CD11b expression. Although neutrophils from all subjects exhibited a concentration-dependent increase in SO production, at all MSU concentrations neutrophils from subjects with gout and asymptomatic hyperuricemia produced higher levels of SO compared to normal controls. Neutrophil production of IL-8 in response to MSU did not differ across subject groups. Furthermore no differences in serum IL-8 levels were seen between subject groups.
Conclusions: These preliminary data suggest that there is no difference in neutrophil IL-8 production that associates with the presence of gout, however neutrophils from individuals with hyperuricemia (with or without gout) may be sensitised to MSU exposure resulting in higher levels of SO production across a broad range of MSU concentrations. These findings suggest hyperuricemia itself may contribute directly to risk of gout by priming neutrophils for SO production on exposure to MSU crystals. Further studies are underway to confirm these results and look at other cell types and inflammatory responses.
Methods: Individuals with gout (ACR criteria 1977) (n=39), asymptomatic hyperuricemia (n=11) and normal controls (n=10) were recruited from the community. Patients with gout were defined as acute gout if they had discrete attacks without tophi and chronic gout if tophi were present. All individuals with gout were seen between attacks of gout. The proportion of neutrophils (CD15+ leucocytes) in blood and neutrophil expression CD11b in blood was determined using flow cytometry. Peripheral blood neutrophils were isolated using a Ficoll gradient centrifugation, with cell viability and purity being >98%. Neutrophils were stimulated with MSU in vitro and production of SO (WST-1 assay) and IL-8 (Luminex) was measured. Serum IL-8 levels in serum were also determined.
Results: There was no difference between individuals with gout and healthy controls in proportion of neutrophils in peripheral blood or neutrophil CD11b expression. Although neutrophils from all subjects exhibited a concentration-dependent increase in SO production, at all MSU concentrations neutrophils from subjects with gout and asymptomatic hyperuricemia produced higher levels of SO compared to normal controls. Neutrophil production of IL-8 in response to MSU did not differ across subject groups. Furthermore no differences in serum IL-8 levels were seen between subject groups.
Conclusions: These preliminary data suggest that there is no difference in neutrophil IL-8 production that associates with the presence of gout, however neutrophils from individuals with hyperuricemia (with or without gout) may be sensitised to MSU exposure resulting in higher levels of SO production across a broad range of MSU concentrations. These findings suggest hyperuricemia itself may contribute directly to risk of gout by priming neutrophils for SO production on exposure to MSU crystals. Further studies are underway to confirm these results and look at other cell types and inflammatory responses.
R. Grainger, None; A. Harrison, None; J. Harper, None.