Lipoic Acid Attenuates Lipopolysaccharide- and Escherichia coli-Induced Reactive Oxygen Species Production and Neutrophil Extracellular Trap Formation Without Impairing Escherichia coli or Staphylococcus aureus Killing by Human Neutrophils

Neutrophils are essential for antimicrobial defense through reactive oxygen species (ROS) production, tumor necrosis factor-alpha (TNF-α) release, and neutrophil extracellular trap formation. Lipoic acid, a redox-active antioxidant, modulates activation in human neutrophils. Neutrophils isolated from healthy donors were pretreated with lipoic acid and then exposed to lipopolysaccharide (LPS) or whole Escherichia coli, according to the specific assay. ROS production, NET formation, TNF-α release, bacterial killing, metabolic activity, and cell death were assessed using fluorometric assays, enzyme-linked immunosorbent assay, colony-forming unit assays, MTT reduction, and Annexin V-FITC/propidium iodide flow cytometry. Lipoic acid significantly reduced ROS production and NET formation induced by LPS and Escherichia coli. at 0.5 mM, lipoic acid also reduced E. coli-induced NET formation by approximately 50% and attenuated TNF-α release at early stimulation times. In colony-forming unit assays, lipoic acid did not significantly reduce neutrophil-mediated killing of Escherichia coli or Staphylococcus aureus. Although only neutrophil preparations with high baseline viability were used, Escherichia coli challenge markedly reduced cell viability during the assay; under this condition, lipoic acid pretreatment limited bacteria-induced necrosis and preserved a higher proportion of viable neutrophils. These findings indicate that lipoic acid dampens excessive oxidative and inflammatory neutrophil responses while maintaining measurable bactericidal capacity in vitro.