The anti-oxidative, anti-inflammatory, and protective effect of S100A8 in endotoxemic mice

Polymorphonuclear neutrophils (PMNs) produce and release copious amounts of reactive oxygen species (ROS) which target potential bacterial invaders but also contribute to the inflammation-associated organ injuries seen in sepsis. Calprotectin is an immune regulatory protein complex made of S100A8 and S100A9 that inhibits the oxidative metabolism of PMNs in vitro, an effect that can be potentiated by the controlled activation of the protease activated receptor-2 (PAR2). The aim of this study was to test the use of a dual strategy of calprotectin and PAR2 administration to mitigate the deleterious inflammation seen in sepsis. We hypothesized that exogenous calprotectin would protect against the injuries produced by lipopolysaccharides (LPS)-induced endotoxemia and that the controlled activation of PAR2 would potentiate this beneficial effect. Exogenous S100A8 and/or a PAR2 activating peptide (PAR2 AP) were administered in a mouse model of LPS induced endotoxemia. The survival rates as well as markers of inflammation and oxidative damage were measured in the lungs, kidneys, and livers of endotoxemic mice. Mice treated with S100A8 following LPS had less PMN infiltration and less severe histological changes in their lungs, kidneys, and livers. A significantly lower score of oxidative damage in the livers and lungs of S100A8/LPS treated mice was also noted when compared to mice treated with LPS alone. This protective and anti-inflammatory effect of S100A8 was potentiated by the controlled activation of PAR2. Finally, in further support to our hypothesis, the survival rate was almost doubled from 33% to 65% and 63% in mice treated by, respectively, S100A8 and PAR2 AP, whereas 85% of the mice treated with both PAR2 AP and S100A8 survived, a statistically significant higher rate. These results support an anti-inflammatory, anti-oxidative, and protective effect of S100A8 in sepsis, and warrant further studies on the role of PAR2.