Oxidative Stress

Is normally produced by ________ (s) ■ important & widespread signaling molecule ■ vasodilator, neurotransmitter, role in inflammation, etc.

Nitric Oxide Synthase

________ may increase 8- OH- G levels by 30- 50 %.

Cigarette smoking

○ Has a major role in many (almost all) pathologies ROS: Generation ● ________ has two unpaired electrons ● When O2 picks up another electron → superoxide radical (O2)- ○ Some oxidant activity with limited membrane permeability ● Superoxide production by ETC of Mitochondria ○ Mitochondria (MTC)- Major Source of Intracellular ROS ○ Electron transport chain (ETC)- responsible for 4 e- reduction of O2 to H2O ○ A small quantity of is generated as e- escapes ■- 1- 3 % of e- going through the ETC leak and generate ROS ■ Mainly from Complex I and Complex III of ETC ● Generation of the Hydrogen Peroxide and Hydroxyl Radical ○ O2-

Molecular oxygen

Is converted to the more stable H2O2 via the action of superoxide dismutase (SOD) ○ H2O2 is somewhat lipid soluble and diffuses across cell membranes ○ H2O2 is not a radical but is considered a(n) ________ as it easily generates the hydroxyl radical via two mechanisms ■ Fenton reaction.

ROS

________ may reverse oxidation of methionine ■ Degradation of Modified Proteins by the PROTEASOME ● Oxidation of proteins may expose hydrophobic patches of the protein that target it for destruction ○ Many proteins must be degraded by the cell ■ This degradation might be a part of "normal "protein turnover to regulate amount of protein; OR ■ A defense mechanism to destroy "bad "proteins (e.g.

Enzymatic system

increase in cell size; response to increased demand

hypertrophy

● Free radicals such as ROS are metabolized via antioxidant enzymes and non-enzymatic processes; i.e

UV exposure) ● Your cells know that you produce free radicals and are prepared

cell has mechanisms that attempt repair of free radical-induced damage ● Cell-to-cell variation in how well-equipped they are to handle free radical production ● Free radicals are detrimental when balance is lost and repair mechanisms are not working or overwhelmed → oxidative stress

defense mechanisms ○ If this fails

use oxygen to generate free radicals to kill organism in conjunction with phagocytosis ○ Xanthine Oxidase ■ necessary for final steps of purine catabolism to uric acid ■ In process, molecular oxygen is reduced to O2 free radical ○ Monoamine Oxidase (MAO) ■ Metabolism of catecholamines in nerve terminals and other cells ■ Generates H2O2 ● Environmental Factors that may Increase ROS ○ Ionizing radiation (ultraviolet, X-rays) ■ Pollutants ■ Cig smoke ■ Environmental/Workplace chemicals ■ Drugs Reactive Nitrogen Species (RNS) ● Nitric Oxide (NO

neutrophils, macrophages) ■ Activated as response to invading pathogens ■ "The respiratory/oxidative burst"

a free radical that possesses a single electron ○ NO

)

combines with O2 or to form ○ Reactive Nitrogen Species (RNS) or if also containing an oxygen (RNOS) ■ NO

is usually at low concentrations that do not cause damage ○ High concentrations

Regeneration of active form of Vitamin E ■ May interact with free radicals directly (donates electrons)

■ ○ Vitamin C (Ascorbic Acid) ■ Principal role

● Inhibit free radical producing enzymes (e.g

■ ○ Flavonoids ■ Multiple compounds with a flavone backbone ■ May have multiple mechanisms

● DNA ○ -10,000 DNA assaults/cell/day ○ Usually mediated by OH

xanthine oxidase) ● May chelate Fe2+ and therefore inhibit Fenton rxn ● May act as free radical scavengers ○ Lycopenes ■ Linear unsaturated hydrocarbon ● Red pigment of plants ■ Antioxidant Effects ● Quench free radicals ● Increase expression of antioxidant enzymes Free Radical-Induced Damage ● Free radicals set off chain reactions in which e-are extracted from other molecules

■ Mispairing ■ Strand breaks ■ Excision of bases ■ Cross-linking ○ Certain anti-cancer drugs depend on these mechanisms to produce their tumor cell killing ○ Mitochondrial DNA may be very sensitive to oxidative stress

○ Many regions of DNA molecule are susceptible (bases, deoxyribose backbone) ○ For DNA bases -existing DNA double helix as well as nucleotide pool may be modified ○ Mechanisms of damage include

e.g

○ Defenses ■ Depending on protein or amino acid structure and type of modification there may be a few specific defenses

increase in cell number; response to increased demand

hyperplasia

change in cell type

metaplasia

decrease in cell size; response to decreased nutrients or decreased demand

atrophy

cell injury is __________ especially if the stressor is removed

reversible

when cell death is irreversible, it frequently results in ___________

cell death

molecule with a single unpaired electron

radical

radical atom or molecule capable of independent existence

free radical

oxygen-containing radical species

reactive oxygen species

cellular repair mechanisms are not working/overwhelmed; free radicals are detrimental

oxidative stress

major source of intracellular ROS

mitochondria

O2. is converted to the more stable H2O2 via the action of what enzyme?

superoxide dismutase

conversion of O2.- to H2O2 using iron or copper as an electron donor

fenton reaction

conversion of O2.- to H2O2 using hydroxyl as an electron donor

haber-weiss reaction

enzyme predominant in liver; uses electrons to activate oxygen for reactions & increases ROS

cytochrome p450 enzymes

enzyme that increases ROS in response to invading pathogens

NADPH Oxidase

enzyme that increases ROS that is necessary for the final steps of purine catabolism to uric acid; molecular oxygen is reduced to O2 free radical

xanthine oxidase

enzyme that increases ROS through metabolism of catecholamines in nerve terminals

monoamine oxidase

free radical that is important in vasodilation, neurotransmission, inflammation; also called RNS

nitric oxide free radical

primary defense against oxidative stress

antioxidant dismutase (SOD)

ion expressed in the mitochondria that works with SOD to protect from ROS

Mn 2+

ions expressed in the cytosol that work with SOD to protect from ROS

Cu +, Zn 2+

tripeptide of glutamate-cysteine-glycine

glutathione

enzyme that handles H2O2 outside the peroxisome; contains selenium

glutathione peroxidase

enzyme necessary to cycle GSSG back to reduced form

glutathione reductase

enzyme found in most plant and animal cells that functions as an oxidative catalyst; highest levels in liver and kidney

catalase

transcription factor that regulates the work of antioxidant proteins that can help protect against oxidative damage

NRF2

nonenzymatic antioxidant that breaks chains of lipid peroxidation; obtained via diet

vitamin e

nonenzymatic antioxidant that regenerates the active form of vitamin e; may interact with free radicals directly

vitamin c; ascorbic acid

nonenzymatic antioxidant that inhibits free radical-producing enzymes, inhibit the fenton rxn, and/or act as free radical scavengers

flavonoids

nonenzymatic antioxidant that gives plants red pigment; quenches free radicals, increases expression of antioxidant enzymes

lycopenes

mechanisms of free-radical damage of dna

mispairing, strand breaks, excision of bases, cross linking

certain anti-__________ drugs depend on dna damaging mechanisms to produce their tumor cell killing

cancer

free radical attack of __________ includes attack at the membranes in a chain reaction known as ___________ peroxidation

lipids

free radical attack of __________ causes modifications in fully synthesized _________, peptides, or individual amino acids

protein

loss of dopaminergic neurons in the substantia nigra - functions with other basal ganglia units as it acts as an integration area

parkinson's disease

intraneuronal structures that lack membranes found in substantia nigra of parkinson's patients

lewy bodies