Effect of Antioxidant Supplementation on NET Formation Induced by LPS In Vitro; the Roles of Vitamins E and C, Glutathione, and N-acetyl Cysteine

Neutrophil extracellular traps (NETs) require reactive oxygen species (ROS) to eliminate pathogens by inducing oxidative stress. However, this process can also cause tissue damage to the host. Neutrophils contain high concentrations of vitamin C (1.5 mM) compared to the bloodstream (0.1 mM), and this antioxidant can interact with vitamin E and glutathione (GSH) inside the cell to maintain the redox balance. Previous studies have investigated the effect of vitamins E or C and N-acetyl cysteine (NAC) on NET formation, but the interactions of these molecules in neutrophils remain unknown. In this study, we investigated the effect of antioxidants alone and two combinations on NET formation and oxidative stress. Neutrophils were pre-loaded with GSH + NAC or vitamin E + vitamin C + GSH + NAC (termed ALL), and LPS-induced NET formation was assessed using fluorometry and immunofluorescence. Antioxidant effects were evaluated by measuring the total antioxidant capacity (TAC), GSH/GSSG ratio, ROS production, nitrite + nitrate levels, and lipid peroxidation. Our results showed that even low doses of antioxidants are capable of decreasing NETs. Furthermore, the combinations augmented TAC and GSH/GSSG ratio and decreased ROS, nitrites + nitrates, and malondialdehyde (MDA) levels in supplemented neutrophils in vitro.

Physiological concentrations of short-chain fatty acids induce the formation of neutrophil extracellular traps in vitro

Neutrophils represent the first line of host cellular defense against various pathogens. The most recently described microbicidal mechanism of these cells is the release of neutrophil extracellular traps (NET). Currently, a wide range of chemical and biological stimuli are known to induce this response; however, the effect of short-chain fatty acids (SCFAs) on the induction of NET is still unknown. SCFAs are produced mainly by bacterial fermentation of dietary fiber and are found in host tissues and blood. This study aimed to determine whether physiological levels of SCFAs can induce the formation of NET. Previously reported concentrations of SCFAs (as found in the colonic lumen and peripheral blood in postprandial and basal states) were used to stimulate the neutrophils. In order to determine the signaling pathway utilized by SCFAs, we tested the inhibition of the Free Fatty Acid 2 Receptor (FFA2R) expressed in neutrophils using CATPB, the inhibitor of FFA2R, genistein, an inhibitor of the downstream Gα/q11 proteins and DPI, an inhibitor of the NADPH oxidase complex. The SCFAs at colonic intestinal lumen concentrations were able to induce the formation of NET, and when tested at concentrations found in the peripheral blood, only acetic acid at 100 μM (fasting equivalent) and 700 μM (postprandial equivalent) was found to induce the formation of NET. The administration of the competitive inhibitor against the receptor or blockade of relevant G protein signaling and the inhibition of NADPH oxidase complex decreased NET release. SCFAs stimulate NET formation in vitro and this effect is mediated, in part, by the FFA2R.