A Differential Effect of Hydrogen Peroxide on the Ability of Macrophages to Phagocytose Microorganisms
Richard Lockshin, Department of Biology, St. John’s College of Liberal Arts and Sciences
Lin L Mantell, Department of Pharmaceutical Sciences, College of Pharmacy and Health Sciences
Binh Phan, Tahereh Entezari-Zaher, Cardiopulmonary Research, Department of Surgery, Feinstein Institute for Medical Research
Prolonged exposure to hyperoxia during mechanical ventilation causes acute proinflammatory responses. Nosocomial pneumonia in patients receiving mechanical ventilation is a related problem and one of the major causes for mortality and morbidity in Intensive Care Units. Hydrogen peroxide, generated by phagocytes during inflammation to kill the invading microorganisms, impairs the macrophage’s ability to phagocytose. However, hydrogen peroxide exhibits differential effects on cell proliferation and cell death in a concentration-dependent manner. In this study, we tested whether the impairment of macrophage phagocytosis by hydrogen peroxide depends on its concentration in cultured macrophages. RAW 264.7 cells were exposed to various concentrations of hydrogen peroxide from 1mM to 1 µM for up to 3 hours. Consistent with the previous studies, hydrogen peroxide significantly reduced macrophage phagocytosis of microbeads at concentrations higher than 500 µM. In addition, loss of mitochondria dehydrogenase activity, as evidenced by the MTT assay, and reduced total actin polymerization were observed in these cells. In contrast, the ability of RAW cells to phagocytose was significantly (>50%) increased when the cells were treated with <200 µM hydrogen peroxide. Furthermore, actin polymerization was markedly more pronounced in cells treated with low concentrations of hydrogen peroxide. These results suggest that a moderate amount of hydrogen peroxide can stimulate actin polymerization and improve phagocytosis in macrophages although high concentrations of hydrogen peroxide are detrimental to macrophage functions.