Oxidative Stress and Atherosclerosis

Oxidative Stress and Atherosclerosis

Objectives:

What is „free radical“? Reactive oxygen and nitrogen species

(RONS) Are the RONS always dangerous? Well known term „oxidative stress“ - what is

it? Antioxidants - types Disorders Associated with Oxidative stress Oxidative stress and atherosclerosis

Term Definition

Oxidation Gain in oxygenLoss of hydrogenLoss of electrons

Reduction Loss of oxygenGain of hydrogenGain of electrons

Oxidant Oxidizes another chemical by takingelectrons, hydrogen, or by adding oxygen

Reductant Reduces another chemical by supplyingelectrons, hydrogen, or by removing

oxygen

Basics of Redox ChemistryBasics of Redox Chemistry

Free RadicalsFree Radicals: A molecule with an unpaired

electron in an outer valence shell• tend to reach equilibrium, plucks

an electron from the nearest intact molecule.

• most of biomoleculs are not radicals

R3C. Carbon-centered

R3N. Nitrogen-centered

R-O. Oxygen-centered

R-S. Sulfur-centered

Reactive SpeciesReactive Species

Non-RadicalsNon-Radicals: Species that have strong oxidizing

potential Species that favor the formation of

strong oxidants (e.g., transition metals)

H2O2 Hydrogen peroxide

HOCl- Hypochlorous acid

O3 Ozone

1O2 Singlet oxygen

ONOO- Peroxynitrite

Men+ Transition metals

Radicals are highly reactive species

Reactive Oxygen Species (ROS)Reactive Oxygen Species (ROS)

Radicals:

O2.- Superoxide

.OH Hydroxyl

RO2. Peroxyl

RO. Alkoxyl

HO2. Hydroperoxyl

Non-Radicals:

H2O2 Hydrogen peroxide

HOCl- Hypochlorous acid

Reactive Nitrogen Species (RNS)Reactive Nitrogen Species (RNS)

Radicals as:

NO. Nitric Oxide

NO2. Nitrogen dioxide

Non-Radicals as:Peroxynitrite

“An imbalance favoring (pro)oxidants and/or disfavoring antioxidants, potentially leading to damage” -H. Sies

Antioxidants

Oxidants

Oxidative StressOxidative Stress

Oxidative StressOxidative Stress

It is a state in the cells in which there is increased concentration of reactive species which is not counterbalanced by increased levels of antioxidants.

This imbalance was implicated in production of different diseases as atherosclerosis

Endogenous sources of ROS and RNSEndogenous sources of ROS and RNS

Mitochondria

Lysosomes

Peroxisomes

Endoplasmic Reticulum

Cytoplasm

Microsomal Oxidation, Flavoproteins, CYP enzymes Myeloperoxidase

(phagocytes)

Electron transport

Oxidases,Flavoproteins

Plasma Membrane

Lipoxygenases,Prostaglandin synthase

NADPH oxidase

Xanthine Oxidase,NOS isoforms

FeCu

Transition metals

Reactive Oxygen Species (ROS)

Oxygen-derived Free radicals: e.g., Superoxide and hydroxyl radicals

Non-free radical: Hydrogen peroxide

O2. , H2O2 , OH. By partial reduction of molecular oxygen in electron transport chain in mitochondria

Antioxidants Enzymes:

Superoxide dismutase Catalase Glutathione system (glutathione, NADPH, reductase,

peroxidase & selenium)

• Vitamins: Vitamin C (ascorbic acid) Vitamin A and β-carotenes Vitamin E

Trace elements: Selenium

Antioxidant Mechanisms

Glutathione System

SeliniumSelinium

In RBCS

Nitric Oxide (NO)

NO: Free radical gasVery short half-life (seconds)Metabolized into nitrates & nitrites and

perooxynitrite Synthesis:

Enzyme: NO synthasePrecursor: L-Arginine

Effects:Relaxes vascular smooth musclePrevents platelet aggregationBactricidal & Tumoricidal effectsNeurotransmitter in brain

NOS ( nitric oxide synthase)

2 constitiutive NOS: are calcium-calmodulin dependent and constantly produce low level of NO ( primarly in endothelium=eNOS, neural=nNOS).

1 inducible NOS : calcium independent can be expressed in many cells including hepatocytes,

macrophages and neutrophils. The inducers include bacterial toxins, tumor-necrosis

factor and inflammatory cytokines It can produce large amounts of NO over hours or even

days

Nitric Oxide Synthase

NO•

Binds to heme moiety of guanylate cyclase

Conformational change of the enzyme

Increased activity (production of cGMP)

Modulation of activity of other proteins (protein

kinases, phospho-diesterases, ion

channels)

Physiological response (relaxation of smooth muscles, inhibition of platelet aggregation,

etc.)

NO• signaling in physiology

O2-• ONOO-

Oxidative Stress: Role of Nitric Oxide (NO)

NO produced by endothelial NOS (eNOS) improving vascular dilation and perfusion (i.e., beneficial).

Vasodilators such as nitroglycerin is metabolized into NO and causes vasodilatation

Increased iNOS activity is generally associated with inflammatory processes

Lipids Proteins DNA

Oxidation of vitamin E

Lipid peroxidation

Membrane damage

Thiol oxidationCarbonyl formation

Damage to Ca2+ andother ion transport

systems

DNA damage

Cell Injury

Disruption of normalion gradients

Activation/deactivationof various enzyme systems

Altered gene expression

Depletion of ATPand NAD(P)H

Adapted from: Kehrer JP, 1993

Oxidative Stress

Consequences of lipid peroxidation(polyunsaturated fatty acids)

• Structural changes in membranesalter fluidity and channelsalter membrane-bound signaling proteinsincreases ion permeability

• Lipid peroxidation products form adducts/crosslinks with non lipids

e.g., proteins and DNA• Cause direct toxicity of lipid peroxidation

products Disruptions in membrane-dependent

signaling

Vascular effects of ROS:

Altered vascular toneIncreased endothelial

cell permeability

Pathological conditions that involve oxidative stress

•Inflammation

•Atherosclerosis

•Ischemia/reperfusion injury

•Cancer

•Aging

•Obesity

Pathogenesis of Atherosclerosis

• Modified (oxidized) LDL … Oxidative stress(imbalance between oxidants and antioxidants)

• Endothelial injury of arterial wall

• Adherence of monocytes to endothelial cells and their movement into intima where it becomes macrophages

• Uptake of oxLDL by macrophage scavenger receptor:Scavenger receptor class A (SR-A)

Low-affinity, non-specific receptorUn-regulated receptor

•Foam cell transformation: Accumulation of excess lipids inside the cells (unregulated receptor)

• Atherosclerotic plaque formation

Athersclerotic Plaque FormationUn-regulated LDL Uptake

Regulated LDL Uptake high-affinity, specific & tightly regulated LDL-Receptor

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