BMS 531.10 Reactive Oxygen Species PDF Spring 2025

Reactive Oxygen Species BMS 531.10 SPRING 2025  Objectives OVERALL: Evaluate oxygen free radicals and reactive 6. Summarize the steps involved in the generation of oxygen species in human metabolism and disease reactive nitrogen-oxygen species 1. Identif...

Reactive Oxygen Species BMS 531.10 SPRING 2025  Objectives OVERALL: Evaluate oxygen free radicals and reactive 6. Summarize the steps involved in the generation of oxygen species in human metabolism and disease reactive nitrogen-oxygen species 1. Identify the reactive oxygen species generated by 7. Describe the role of ROS and RNOS in the following normal metabolic processes human systems, conditions, and diseases: inflammation, phagocytosis, diabetes with impacts 2. List the steps involved in the generation of oxygen on vasculature, ischemia-reperfusion events, and free radicals in terms of the specific free radicals vitamin deficiencies generated and summarize the Haber-Weiss and Fenton reactions 8. Summarize the mechanisms of cellular defenses against oxidative damage and the role of the 3. List the reactive oxygen species and reactive following in protection against oxidative damage: nitrogen-oxygen species that are generated by vitamin C, vitamin E, GSH, superoxide dismutase, metabolic processes catalase, and copper 4. Summarize the steps involved in lipid peroxidation 5. Critique lipid peroxidation in terms of its localization and consequences for the cell and explain the role of the mitochondria in ROS production Overall LO1, LO2, LO3 Terminology Radical = molecule that has a single unpaired electron in an orbital Free Radical= molecule with unpaired electron; also capable of independent existence Adducts = two components united together via covalent bond ◦ Affects both form and function and can lead to inappropriate accumulation (i.e. vascular accumulation contributing to atherosclerosis) Overall LO1, LO2, LO3 Reduction of O2 Oxygen as part of the NORMAL metabolic processes can accept single electrons ◦ Typically from reduced electron carriers of the Electron Transport Chain ◦ Generates Oxygen Radicals ◦ Oxygen is a biradical molecule with 2 unpaired electrons in different orbitals spinning with the same spin (parallel thus ANTIBONDING) ◦ Highly reactive ◦ 3-5% of all oxygen consumed is converted to free radicals Generates: ◦ Superoxide (O2-) ◦ Hydrogen peroxide (H2O2) ◦ Hydroxyl radical (OH) Mailloux 2015 Overall LO1, LO2, LO3 Oxygen Free Radicals and Reactive Oxygen Species Reactive Oxygen Species ◦ Free radicals can be oxygen alone or in compounds ◦ Can be generated via enzymatic or nonenzymatic processes Hydroxyl ◦ Accidental byproducts OR major products Radicals ◦ Initiate chain reactions as they steal electrons to +H+ complete orbitals ◦ Can be deadly to cells H2O ◦ Damage proteins and DNA ◦ Forms lipid peroxides and malondialdehyde ◦ Exacerbate effects of cellular damage caused by other processes ◦ Can directly cause a disease state as well (i.e. tissue damage from ionizing radiation exposure) Or Cu+ Mailloux 2015 Adapted from Baynes et al Medical Biochemistry 2015 Overall LO1, LO2, LO3 Oxidative Stress Managing reactive oxygen is a careful balance Multiple factors increase and decrease ROS Oxidative stress = imbalance of factors Several normal biological processes result in ROS Overall LO4, LO5 Lipid Peroxidation Common Lipid Peroxide Degradation Products Chain reactions in membranes that form lipid free radicals and lipid peroxides Major contributor to ROS injury ◦ Increases cellular permeability leading to further mitochondrial damage ◦ Cysteine sulfhydryl groups and other aa residues are oxidized leading to degradation ◦ Oxidation of DNA causes damage (i.e. strand breaks) Produce aldehydes which easily react with proteins, are more stable and can attack distant targets Gashler and Stockwell 2017; Barrera et al 2018 Overall LO1, LO2, LO3 Mitochondria and ROS Mitochondria function in electron transport as part of ATP production Essentially, a series of redox reactions involving single electrons A side reaction of this activity generates semiquinone radical that ultimately leads to generation of superoxide radicals Overall LO3, LO6 Additional Free Radicals and ROS Hypochlorous Acid (HOCl) ◦ ROS that is a powerful oxidizing agent ◦ Produced by phagocytes Reactive Nitrogen-Oxygen Species (RNOS) ◦ Involved in neurodegenerative diseases and chronic inflammatory diseases ◦ Nitric Oxide (NO) ◦ RNOS that binds metal ions and can combine with O2 to produce additional RNOS ◦ NO + O2 or NO+ O2- ◦ Examples of other RNOS ◦ Peroxynitrite ◦ Strong oxidizing agent capable of producing radical nitrogen dioxide ◦ Nitrogen dioxide ◦ Environmental or Generated in Cells Lieberman and Peet Medical Biochemistry 2018 Overall LO7 Free Radicals and Inflammation Deliberate generation of toxic free radicals occurs during inflammatory response Rapid consumption of O2 in phagocytes = respiratory burst ◦ Major source of ROS NO production along with NADPH oxidase activation leads to RNOS production and damage to surrounding tissues Inflammation at ischemic areas (i.e. following myocardial infarction) may increase damage Davies et al 2018 Overall LO7 ROS in Phagocytosis Superoxide is critical to the process of phagocytosis Defects in NADPH oxidase result in defects in this process ◦ Chronic granulomatous disease (CGD) ◦ Life-threatening, chronic bacterial and fungal infections result Overall LO7 Reactive Oxygen Species in Disease ROS can exacerbate preexisting problems or cause additional effects in disease states In Diabetes, ROS are a major cause of vascular endothelial dysfunction Increased production of xanthine oxidase in ischemia-reperfusion leads to increased ROS and damage ◦ Return to normal O2 after ischemia causes xanthine oxidase to generate H2O2 and O2- at the site of injury Ito et al 2019; Sasaki and Joh 2007 Overall LO7, LO8 Cellular Defense Against Oxygen Toxicity Antioxidant Defense Enzymes ◦ Superoxide Dismutase, Catalase, Glutathione Peroxidase and Glutathione Reductase Dietary Antioxidants/Free-Radical Scavengers ◦ Vitamin E, Ascorbic Acid, Carotenoids Endogenous Antioxidants/Free-Radical Scavengers ◦ Uric acid, protein thiols, melatonin Cellular Compartmentalization Metal Sequestration Repair of Damage Traber et al 2020 Overall LO7, LO8 Ascorbate (Vitamin C) Enolate anion is the form of Vitamin C at physiological pH This anion spontaneously interacts with free radicals including superoxide The resulting new radical may dismutate ◦ Regenerates ascorbate ◦ Generates dehydroascorbate which can be recycled by dehydroascorbate reductase The enzyme dehydroascorbate reductase is GSH dependent and found in all cells Overall LO7, LO8 Glutathione (GSH) Components of electron transport that are known to generate ROS Enzymatic reactions known to generate ROS Main non-protein thiol in cells Cofactor for many anti-oxidant enzymes Found in both the mitochondria and cytosol thus can be transported into mitochondria via transporter proteins Ribas et al 2014 Overall LO7, LO8 Copper Activity against ROS SOD = superoxide dismutase Requires covalent incorporation of key ions such as copper and zinc for function The Copper/Zinc Superoxide Dismutase has been found to increase after radiation There is also evidence that Copper/Zinc Superoxide dismutase can function as a transcription factor that turns on key genes needed for repair and recovery from oxidative damage Altobelli et al 2020 Overall LO7, LO8 Superoxide Dismutase and Catalase