Monosodium urate crystals-induced joint hypernociception in mice: the participation of 5-lipoxygenase pathway and neutrophils in an experimental model of articular acute gout

Flavio Amaral1, Vivian Costa2, Fernanda Coelho1, Daniela Sachs1, Carolina Rezende2, Caio Fagundes1, Tarcilia Silva3, Mauro Teixeira1, Danielle Souza2. 1Department of Biochemistry and Immunology, Universidade Federal de Minas Gerais, Brazil, 2Department of Microbiology, Universidade Federal de Minas Gerais, Brazil, 3Department of Oral Pathology, Universidade Federal de Minas Gerais, Brazil.

Gout arthritis is characterized by precipitation of uric acid crystals (UAC), mainly in articular cavity, leading to an intense local inflammation. The basic mechanism of this inflammatory response is the intense neutrophil recruitment, with the release of cytokines, chemokines, arachidonic acid metabolites, proteases, and oxygen radicals. Our aim was to set up a new animal model of acute gout disease and to evaluate the role of 5-lipoxygenase (5-LO) metabolites and of neutrophils in its pathogenesis. Wild type male C57/BL6 mice (WT) and 5-lipoxygenase knock-out (5-LO-/-) SV129 mice were used. Treatment with MK886 [5LO-activating protein (FLAP) inhibitor] and the compound CP105696 (LTB4 receptor 1 (BLT1) antagonist) were used. To access the role of neutrophil migration, mice were treated with CXCR2 antagonist and fucoidan. UAC were prepared by precipitation of the crystals after addition of uric acid in borate buffer solution (pH 8.5). A dose of 100μg/10 μl of UAC was injected in the tibio-femoral joint. Hypernociception was measured by a digital analgesimeter (EFF-301). Samples of the periarticular tissue were collected for cytokine analysis (ELISA) and neutrophil quantification (MPO). A lavage of the joint was made to evaluate the cell infiltration on articular space. The time-points chosen were 6 and 15 hours after injection, where there was an increase in all parameters evaluated, as compared to vehicle-treated mice. All strategies used to block the action of the metabolites of 5-LO pathway decreased the inflammatory parameters after UAC injection when compared to vehicle-treated mice. In fact, UAC injection in 5-LO-/- mice, MK 886-treated mice, and CP105696-treated mice elicited reduced articular cell infiltration when compared to WT vehicle-treated ones. Similarly, administration of the CXCR2 receptor antagonists or fucoidan lead to reduced cell influx, MPO activity and inhibited production of IL-1β and MIP-2 after UAC injection. Our data point out the present model as an interesting animal model of acute gout due to a direct injection of UAC on articular joint, as well as the measurement of the hypernociception in these mice. Furthermore, the reduced inflammatory response observed in 5-LO-/- mice and in MK 886-treated, CP105696-treated and CXCR2 antagonists-treated mice suggest an important role of the 5-LO pathway and neutrophils in this model of articular acute gout.

Financial Support: CNPq, CAPES.