Enhancement of NO Production From Resident Peritoneal Macrophages by In Vitro γγ-Irradiation and Its Relationship to Reactive Oxygen Intermediates

The functional changes in macrophages (Mφ) following exposure to a high dose (6 Gy) of γ-rays in vitro were investigated. Resident peritoneal Mφ obtained from C57BL/6 mice were irradiated with γ-rays (137Cs, 0.3 Gy/min). High-dose irradiation enhanced nitric oxide (NO) production from Mφ treated with interferon-γ and their cytotoxic activity. The enhancement of NO production by irradiation was attributed to high levels of expression of the inducible nitric oxide synthase. Furthermore, the participation of reactive oxygen intermediates in NO production was examined. Nitric oxide production was not enhanced by treatment with the membrane-oxidizing agent tert-butyl hydroperoxide or the hypoxanthine/xanthine oxidase superoxide (O2radical dot−)-generating system. On the other hand, NO production was enhanced by treatment with a low dose of hydrogen peroxide (H2O2), which can diffuse passively through the cell membrane and can be converted into hydroxyl radicals (HOradical dot) that cause DNA breaks. In addition, treatment with low-dose actinomycin D, which induces DNA strand breaks, enhanced NO production, but hydroxyurea, which stops DNA replication without DNA strand breaks, had no such effect. These findings suggest that DNA strand breaks caused by hydroxyl radicals formed inside the cells by γ-irradiation, or strand breaks caused directly by radiation, plays an important role in the enhancement of NO production, but peroxidation of cell membranes has little effect. Copyright © 1997 Elsevier Science Inc.