5. Oxidative Damage

• What are some reasons why free radicals might form and what is the result?

• What is the interplay between a stable molecule, free radical and anti-oxidant

• Free radicals may form due to UV light, Ionic radiation, pollution, smoking, inflammation and metabolism —> They result in DNA damage

• Free radicals are molecules with uneven #e that steal an electron from stable molecules that have an even #e; Antioxidants take one electron from free radicals in order to make them stable

Name the Oxidative species (5)

• Categorize in bad and good groups

• BAD

  • Superoxide Radical —> O₂-

  • Peroxide Radical —> ROOR

  • Hydroxyl Radical —> OH_^*

• GOOD

  • Nitric oxide —> NO- (neuro signaling molecule)

  • Peroxynitrite —> ONOO-

Oxidant Enzymes (these are good)

• Cytochromes (in heme or P450

• NADPH oxidase (e- transport complex), Myeloperoxidase ( from macrophages), Tryptophan oxygenase, thyroid peroxidase

• Nitric oxide synthase (for cell signaling)

Name all the implications of Oxidation by free radicals as applied to biomolecules

• Hemoglobin Oxidation: conversion from ferrous (Fe2+) hemoglobin to ferric (Fe3+) forms a superoxide (O2-)

• Uncoupled Cytochrome P450: gets rid of unwanted substances by reacting oxygen and NADPH, but uncoupling results in creation of hydrogen peroxide

• Macrophages: can generate superoxide and hydrogen peroxide and myeloperoxidase

• Fenton reaction: peroxide and Fe2+ react to form Fe3+ and hydroxyl radical

Antioxidant Enzymes and their function

• Superoxide dismutase: turns superoxide into hydrogen peroxide

• Catalase: turns hydrogen peroxide into water

• Peroxiredoxin: Reduces peroxides

• Thioredoxin reductase: reduces thioredoxin

• Methionine reductase: reduces and restores methionine

• Glutathione peroxidase: uses glutathione to reduce peroxides

• Glutathione reductase: reduces glutathione

Antioxidant molecules

• Glutathione

• Thioredoxin

• Vitamin C

• Vitamin E

Where do electrons causing free radicals come from?

They come from the e- transport chain in the mitochondria

NO2- is found where?

In processed meats

How do these oxygen/nitrogen species cause damage to biological molecules?

• Affects proteins folding and aggregation: aromatic rings and sulfur most likely to be affected

• Polysaccharides: oxidants depolymerize mucins and destroy their lubricant properties —> synovial fluid

• Nucleic Acid: broken chains and altered bases —> mitochondrial DNA more susceptible

• Lipid bilayer: conjugation of unsaturated bonds is affected