Nitric oxide donors release extracellular traps from human neutrophils by augmenting free radical generation

High availability of NO, oxidative stress and neutrophil extracellular trap (NETs) contents are often noticed at the site of inflammation/infection. Studies from this lab and others have reported NO mediated free radical generation from neutrophils; role of NO in NETs formation however remains undefined so far. The present study was therefore undertaken to explore the effect of NO donors on NET release from human neutrophils (PMNs), using confocal/scanning microscopy, measuring the extracellular DNA content and NET-bound elastase activity. Addition of NO donors (SNAP and SNP) to adhered PMNs led to a time and concentration dependent NETs release, which was blocked by N-acetyl cysteine, suggesting involvement of free radicals in NETs formation. Free radical formation by NO donors was assessed by using DCF-DA, DMPO-nitrone antibody and by p47 phox migration to the neutrophils membrane. NO mediated formation of free radicals and NETs was significantly reduced by the pretreatment of neutrophils with diphenyleneiodonium (DPI), a NADPH-oxidase inhibitor and 4-aminobenzoic acid hydrazide (ABAH), a myeloperoxidase inhibitor, suggesting role of enzymatic free radical generation by NO donors. We thus demonstrate that NO by augmenting free radical formation in human neutrophils mediates NETs release.