Toxicity of oxygen from naturally occurring redox-active pro-oxidants.

The survival of all aerobic life forms requires the ground-state of molecular oxygen, O2. However, the activation of O2 to reactive oxygen species (ROS) is responsible for universal toxicity. ROS are responsible in deleterious intracellular reactions associated with oxidative stress including membrane lipid peroxidation, and the oxidation of proteins and DNA. Redox-active allelochemicals such as quinones and phenolic compounds are involved in activating O2 to its deleterious forms including superoxide anion free radical, O2.-, hydrogen peroxide, H2O2, and hydroxyl radical, OH. Molecular oxygen is also activated in biologically relevant photosensitizing reactions to the singlet form, 1O2. The insect lifestyle exposes them to a broad diversity of pro-oxidant allelochemicals and, like mammalian species, they have developed an elaborate antioxidant system comprised of chemical antioxidants and a bank of anti-oxidant enzymes. We have found that an insect's antioxidant adaptation to a particular food correlates well with its risk of exposure to potential pro-oxidants.