Differences in MSU-induced superoxide responses by neutrophils from gout subjects compared to healthy controls and a role for environmental inflammatory cytokines and hyperuricemia in neutrophil function and survival.

OBJECTIVE

To determine whether monosodium urate (MSU) crystal-induced superoxide production is greater for neutrophils from patients with gout compared to asymptomatic hyperuricemic and healthy controls, and whether neutrophil functions are altered by an MSU crystal-induced inflammatory environment.

METHODS

Neutrophils were purified from the whole blood of study participants, restimulated with 500 mg MSU crystals ex vivo, and superoxide production measured using the colorimetric dye WST-1. Purified neutrophils were exposed to conditioned media from MSU crystal-activated blood monocyte cultures with and without neutralizing antibodies for interleukin 1ss (IL-1ss), IL-8 (CXCL8), IL-6, and tumor necrosis factor-alpha (TNF-alpha). Neutrophil superoxide production was measured and neutrophil apoptosis and IL-8 production were determined by flow cytometry. Serum samples were collected from participants and analyzed by Lincoplex bead array for IL-1ss, IL-8, IL-6, and TNF-alpha.

RESULTS

Neutrophils from gout and asymptomatic hyperuricemic subjects produced higher levels of MSU crystal-induced superoxide, and a weak trend toward elevated serum cytokines was observed compared to healthy controls. A correlation between serum uric acid and elevated neutrophil superoxide production was also observed. Neutrophils exposed to media from MSU crystal-activated monocytes exhibited enhanced superoxide production to MSU-crystal stimulation, increased IL-8 production, and extended cell survival that was predominantly dependent on IL-8, TNF-alpha and IL-6, respectively.

CONCLUSION

Neutrophils from gout and asymptomatic hyperuricemic individuals are primed for enhanced MSU crystal-induced superoxide production that may be driven by a subclinical inflammatory cytokine environment combined with hyperuricemia. This inflammatory environment likely contributes to elevated neutrophil IL-8 production and survival in the absence of direct crystal stimulation. Asymptomatic hyperuricemia is not associated with suppressed neutrophil function.