I | Excess O2 (oxygen therapy) |
II | Absorption of radiant energy (ultraviolet light) or ionizing radiation (radiotherapy) |
III | Exposure to toxins: carbon tetrachloride, dioxin, alloxan and streptozotocin to name just a few |
IV | Reduction-oxidation (redox) reactions during normal physiologic processes (cellular respiration) |
A. Respiratory chain enzymes and oxygen | |
B. Xanthine oxidase | |
C. Cytochrome P450 monooxygenase activity | |
D. NAD(P)H / NADH oxidase | |
E. Fenton reaction: Fe++ + H2O2 → Fe+++ + OH + OH- | |
F. Haber-Weiss Reaction H2O2 + O2- → -OH- + O2 +OH- | |
V | Ischemia – Ischemia reperfusion injury |
VI | Inflammatory processes. Acute and chronic |
VII | Once free ROS radicals form, they can react with membrane lipids, proteins and nucleic acid to initiate auto-catalytic reactions (ROS beget ROS) [9] |