Modulation by superoxide anions of neutrophil-mediated platelet activation

When polymorphonuclear neutrophil-platelet suspensions were stimulated by 0.5 microM N-formyl-Met-Leu-Phe in the presence of 40 U/mL of superoxide dismutase, a significant reduction of platelet secretion was observed (51.4 +/- 6.3% vs 62.4 +/- 4.6% for control; mean +/- SEM; N = 6; P < 0.01). This was due to the superoxide anion scavenging property of superoxide dismutase since neutrophil degranulation, cathepsin G and elastase enzymatic activities (the two main mediators of this cell-to-cell interaction) and platelet reactivity were not affected. Involvement of superoxide anions was confirmed using leukotriene B4, a neutrophil agonist which induces degranulation with minimal superoxide anion production. Indeed, serotonin release induced by this agonist was unchanged whether superoxide dismutase was added or not.