Synergistic cytolysis mediated by hydrogen peroxide combined with peptide defensins

Possible cytolytic interactions between hydrogen peroxide (H2O2) and neutrophil granule proteins were studied. Preliminary experiments demonstrated synergistic cytolysis when erythro-leukemia targets were exposed to H2O2 combined with a low molecular weight (approximately 3900) granule extract that was predominantly composed of peptide defensins. The synergistic interaction was confirmed when sublytic concentrations of H2O2 were combined with defensin preparations that had been purified to homogeneity. Synergy was concentration dependent in regard to both molecules and could not be explained by trace contamination of defensin preparations with myeloperoxidase. Sequential addition experiments suggested that synergistic lysis required a simultaneous exposure to both cytotoxins. In the presence of sublytic concentrations of H2O2, the binding of iodinated defensin to targets was significantly increased, providing a possible explanation for the observed synergy. Since both molecules are concurrently secreted by activated neutrophils, this interaction may be important during leukocyte-mediated anti-tumor effects or inflammatory tissue injury.