Background Epigallocatechin gallate (EGCG) is the most powerful phenolic compound of green tea. Although its antioxidant properties are the most widely known, EGCG is able to affect the activity and expression of many inflammatory substances through specific intracellular mechanisms. We recently demonstrated that EGCG inhibits the production of inflammatory cytokines and chemokines and cell migration in an in vitro model of calcium crystal-induced inflammation.
Objectives The aim of this study was to investigate the effect of EGCG in an in vitro and in vivo model of monosodium urate (MSU) crystal-induced inflammation through the assessment of key inflammatory cytokines involved in gout.
Methods The human leukemic monocytic cell line THP-1 was primed for 3 hours with phorbole myristate acetate (300 ng/ml), re-incubated overnight and treated with MSU 0.05 mg/ml for 24 hours in presence or absence of EGCG (range 10-100 μM). The levels of IL-1β, IL-8, IL-6 and CCL2 were determined in the culture supernatants by enzyme-linked immunosorbent assay (ELISA).
As regard the study in vivo, the effect of EGCG was evaluated in the acute peritonitis model. Twenty-four mice was randomly subdivided into four groups and injected with 0.5 ml phosphate buffered saline containing: 1- MSU crystals 2mg/ml, 2- MSU crystals and EGCG 20mg/kg, 3- EGCG 20mg/kg, 4- the vehicle alone. The animals were sacrificed after 6 h. Peritoneal inflammation was assessed by cell recruitment (total number of leukocytes and neutrophils) and cytokine levels in the peritoneal lavage fluid. Cell populations were analyzed by flow cytometry while the production of IL-1β, IL-6, KC, CCL2 and TNF was determined by ELISA.
Results EGCG inhibited IL-1β, IL-8, IL-6 and CCL2 release by stimulated THP-1 cells in a dose-dependent manner. Intraperitoneal injection of 1 mg of MSU crystals significantly increased leukocyte infiltrate (2.2 x 10e4 control mice vs 74.5 x 10e4 MSU-injected mice, p<0.05), the levels of IL -6 (7.2±11.1 pg/ml vs 87.5.5±93.4 pg/ml, p<0.05) and those of CCL2 (0 pg/ml vs 149.7±86.1 pg/ml, p<0.05). KC and TNF were also higher (3.5 and 10 times, respectively) with respect to controls, although not significantly. The concentrations of IL- 1β were low or undetectable. EGCG significantly decreased the inflammatory infiltrate induced by crystals (1.8x10e4, p<0.01), the number of neutrophils (5800/ml vs 64000/ml, p<0.05) and levels of all cytokines considered. Highly significant correlations were found between the total number of leukocytes and all the studied cytokines with the exception of TNF.
Conclusions The results of this study show that the main catechin of green tea inhibits MSU crystal-induce peritonitis in mice. It is possible that EGCG acts by receptor-mediated mechanisms as shown in other models, or by activating anti- inflammatory signaling pathways. The identification of EGCG as a natural and potentially non toxic substance, capable of affording protection or modulating the inflammatory response to MSU crystals, may have important implications on therapy and prevention of gout and more generally, of all microcrystalline arthropathies.
Disclosure of Interest : None declared