Peroxynitrite mediates neutrophil migration failure in severe polymicrobial sepsis

Background

Sepsis is a systemic inflammatory response resulting from the host inability to restrict local infection. The failure of neutrophil migration to the infectious focus is one of the mechanisms involved in this process. Recently, it was demonstrated that this event is mediated by nitric oxide. The present study addressed the possibility that peroxynitrite (ONOO^-), a nitric oxide-derived powerful oxidizing and nitrating compound, can be also involved in the neutrophil migration failure.

Materials and methods

Male C57Bl/6 mice were pretreated, subcutaneously, with saline or uric acid (UA; 100 mg/kg) 1 hour before induction of severe sepsis injury (SSI) or were treated with Tetrakis (FeTPPS; 5.0 mg/kg) 15 minutes after SSI, induced by cecal ligation and puncture. Intravital microscopy was used to evaluate leukocyte rolling and adhesion in the mesenteric micro-circulation. TNFα and MIP-1α levels were evaluated by ELISA, lung neutrophil influx by myeloperoxidase activity and nitrotyrosine by immunofluorescence.

Results

The mice pretreated with UA (an ONOO^- scavenger) and subjected to SSI did not present failure of neutrophil rolling, adhesion and migration to the infectious focus. As a consequence, they presented low bacteremia, diminished TNFα and MIP-1α levels in circulation and reduced myeloperoxidase activity. Moreover, increased nitrotyrosine labeling detected in leukocytes present in mesenteric tissues and neutrophils obtained from SSI peritoneal exudate were reduced by UA pretreatment. Finally, the UA pretreatment enhanced significantly the survival rate of the SSI mice. Similarly, treatment with Tetrakis (FeTPPs), a more specific ONOO^- scavenger, reestablished neutrophil migration and increased the survival rate.

Conclusion

Together, the results indicate that ONOO^- partially mediates the reduction of neutrophil/endothelium cell interaction and consequently the neutrophil migration failure to the infectious focus and susceptibility in severe sepsis. Therefore, these results identify ONOO^- inhibitors as potential targets for novel sepsis therapies.