Peroxidase-mediated oxygenation and microbicidal activity

Abstract

It is well documented that a peroxidase, H2O2, and a halide form a "cytotoxic triad." As a result of the interactions of the components of the triad, reactive oxygen intermediates (ROI) are formed and these ROI help to destroy various invading pathogens including Candida. The present study was undertaken to determine if equivalent units of peroxidase activity also induced equivalent macrophage-mediated killing of Candida. Peritoneal macrophages were obtained from age matched C57BL/6J mice and exposed to various concentrations of eosinophil peroxidase (EPO), myeloperoxidase (MPO), and horseradish peroxidase (HRP). Equivalent units of peroxidase as determined by oxidation of guaiacol, did not induce equivalent production of ROI. Luminol-dependent chemiluminescence studies indicated that 10 units of EPO induced more ROI than either HRP or MPO. Candidicidal activity and phagocytosis of M(t) was measured using a fluorescence acridine orange phagocytosis assay. The following pattern EPO>MPO>HRP emerged for both assays. Therefore, enzymatic activity does not directly correlate with candidicidal activity. These data indicate a distinct order of peroxidases relative to their ability to stimulate chemiluminescence and macrophage-mediated killing.