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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 stres s

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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

Basics of Redox Chemistry

Term Definition

Oxidation Gain in oxygen

Loss of hydrogen

Loss of electrons

Reduction Loss of oxygen

Gain of hydrogen

Gain of electrons

Oxidant Oxidizes another chemical by taking

electrons, hydrogen, or by adding oxygen

Reductant Reduces another chemical by supplying

electrons, hydrogen, or by removing oxygen

Reactive Species





  • Free 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 biomoleculsare not radicals

H2O2Hydrogen peroxide

HOCl- Hypochlorous acid


1O2 Singlet oxygen

ONOO- Peroxynitrite

Men+ Transition metals

Radicals are highlyreactivespecies

  • Non-Radicals:

  • Species that have strong oxidizing potential

  • Species that favor the formation of strong oxidants (e.g., transition metals)

Reactive Oxygen Species (ROS)


O2.- Superoxide

.OH Hydroxyl

RO2. Peroxyl

RO. Alkoxyl



H2O2Hydrogen peroxide

HOCl- Hypochlorous acid

Reactive Nitrogen Species (RNS)

Radicals as:

NO. Nitric Oxide

NO2.Nitrogen dioxide

Non-Radicals as:


Oxidative Stress



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

Oxidative 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

Microsomal Oxidation,

Flavoproteins, CYP enzymes



Xanthine Oxidase,

NOS isoforms

Endoplasmic Reticulum

Transition metals









Plasma Membrane

Electron transport


Prostaglandin synthase

NADPH oxidase

Endogenous sources of ROS and RNS

Reactive Oxygen Species (ROS)

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

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

Non-free radical: Hydrogen peroxide



Superoxide dismutase


Glutathione system(glutathione, NADPH, reductase, peroxidase & selenium)


Vitamin C (ascorbic acid)

Vitamin A and β-carotenes

Vitamin E

Trace elements:


Nitric oxide no
Nitric Oxide (NO)

NO: Freeradicalgas Very short half-life (seconds) Metabolized into nitrates&nitrites and perooxynitrite

Synthesis: Enzyme: NO synthasePrecursor: L-Arginine

Effects:Relaxes vascular smooth muscle Prevents platelet aggregation Bactricidal & Tumoricidal effects Neurotransmitter in brain

Nos nitric oxide synthase
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

NO• signaling in physiology

Nitric Oxide Synthase


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.)



Oxidative stress role of nitric oxide no
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

Oxidative Stress

Lipids Proteins DNA

Oxidation of

vitamin E

Thiol oxidation

Carbonyl formation

DNA damage

Altered gene


Damage to Ca2+ and

other ion transport


Lipid peroxidation

Membrane damage

Disruption of normal

ion gradients

Depletion of ATP

and NAD(P)H


of various enzyme systems

Cell Injury

Adapted from: Kehrer JP, 1993

Consequences of lipid peroxidation

(polyunsaturated fatty acids)

  • Structural changes in membranes

    • alter fluidity and channels

    • alter membrane-bound signaling proteins

    • increases 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
Vascular effects of ROS:

  • Altered vascular tone

  • Increased endothelial cell permeability

Pathologicalconditions 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 receptor

  • Un-regulated receptor

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

  • Atherosclerotic plaque formation

Athersclerotic Plaque Formation

Un-regulated LDL Uptake

Regulated LDL Uptake

high-affinity, specific & tightly regulated