Superoxide Anion Chemistry—Its Role at the Core of the Innate Immunity

Abstract

Classically, superoxide anion O2•− and reactive oxygen species ROS play a dual role. At the physiological balance level, they are a by-product of O2 reduction, necessary for cell signalling, and at the pathological level they are considered harmful, as they can induce disease and apoptosis, necrosis, ferroptosis, pyroptosis and autophagic cell death. This revision focuses on understanding the main characteristics of the superoxide O2•−, its generation pathways, the biomolecules it oxidizes and how it may contribute to their modification and toxicity. The role of superoxide dismutase, the enzyme responsible for the removal of most of the superoxide produced in living organisms, is studied. At the same time, the toxicity induced by superoxide and derived radicals is beneficial in the oxidative death of microbial pathogens, which are subsequently engulfed by specialized immune cells, such as neutrophils or macrophages, during the activation of innate immunity. Ultimately, this review describes in some depth the chemistry related to O2•− and how it is harnessed by the innate immune system to produce lysis of microbial agents.

Pathophysiological Impact of the MEK5/ERK5 Pathway in Oxidative Stress

“…ROS production relies on both enzymatic and non-enzymatic reactions. The superoxide radical (O 2 •− ) can be generated from the mitochondrial electron transport chain, which is the main source of O 2 •− and many enzymes, including nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, xanthine oxidase, lipoxygenase, cyclooxygenase and cytochrome P450 reductase [ 9 ]. Once formed, O 2 •− is involved in several reactions, which, in turn, may generate other ROS/RNS such as hydrogen peroxide (H 2 O 2 ), hydroxyl radical ( • OH), peroxynitrite (ONOO − ) and hypochlorous acid (HOCl).…”

Enhanced Antibacterial Activity in Cellulose Acetate Films with Surface Defect-Rich MgO Nanoparticles for Sustainable Active Packaging Applications

“…51 Nevertheless, the detection of H • or hydrated electrons could possibly indicate the further reduction of oxygen to superoxide anions. 52 Thus, the results of NBT and EPR proved the higher ROS production capability of our MgO NPs than commercial MgO NPs.…”

“…No O 2 ·– adducts being detected by EPR could be attributed to the higher rate constant of H · or e – aq with DMPO than for superoxide anions with DMPO . Nevertheless, the detection of H · or hydrated electrons could possibly indicate the further reduction of oxygen to superoxide anions . Thus, the results of NBT and EPR proved the higher ROS production capability of our MgO NPs than commercial MgO NPs.…”

Engineered Multifunctional Zinc–Organic Framework-Based Aggregation-Induced Emission Nanozyme for Accelerating Spinal Cord Injury Recovery

“…Additionally, the SOD-like activity of Zn@MOF-TPD nanozymes was quantified at a concentration of 874.89 U/mg using a commercial SOD assay kit (Figure S11). Although the nanozymes exhibited relatively SOD-like activity, they may effectively alleviate oxidative stress because superoxide anions are easily converted into other types of ROS , and the nanozymes have excellent ROS-scavenging activity. Besides, the gallic acid-based MOF can not only act like superoxide dismutase and catalase to eliminate ROS, but also possess considerably good stability and large specific area with reaction sites, which was similar to the properties of nanozymes.…”