Download Oxidative Stress

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

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
R3C. Carbon-centered
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 biomoleculs are not radicals
Radicals are highly reactive species
Non-Radicals:
 Species that have strong oxidizing
potential
 Species that favor the formation of
strong oxidants (e.g., transition
metals)
R3N. Nitrogen-centered
R-O. Oxygen-centered
R-S. Sulfur-centered
H2O2 Hydrogen peroxide
HOCl- Hypochlorous acid
O3
Ozone
1O
2
Singlet oxygen
ONOO- Peroxynitrite
Men+
Transition metals
Reactive Oxygen Species (ROS)
Radicals:
O2.-
Superoxide
Non-Radicals:
.OH
Hydroxyl
H2O2
Hydrogen peroxide
HOCl-
Hypochlorous acid
.
RO2 Peroxyl
RO. Alkoxyl
HO2. Hydroperoxyl
Reactive Nitrogen Species (RNS)
Radicals as:
NO. Nitric Oxide
NO2. Nitrogen dioxide
Non-Radicals as:
Peroxynitrite
Oxidative Stress
Antioxidants
Oxidants
“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
Endogenous sources of ROS and RNS
Microsomal Oxidation,
Flavoproteins, CYP enzymes
Xanthine Oxidase,
NOS isoforms
Myeloperoxidase
(phagocytes)
Transition
metals
Endoplasmic Reticulum
Cytoplasm
Lysosomes
Fe
Cu
Oxidases,
Flavoproteins
Peroxisomes
Mitochondria
Plasma Membrane
Lipoxygenases,
Prostaglandin synthase
NADPH oxidase
Electron transport
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
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
Selinium
In RBCS
Nitric Oxide (NO)

NO:
Free radical gas
Very short half-life (seconds)
Metabolized into nitrates & nitrites and
perooxynitrite


Synthesis:
Enzyme: NO synthase
Precursor: L-Arginine
Effects:
Relaxes vascular smooth muscle
Prevents platelet aggregation
Bactricidal & Tumoricidal effects
Neurotransmitter 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
NO• signaling in physiology
Nitric Oxide Synthase
O2-•
NO•
ONOO-
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, phosphodiesterases, ion
channels)
Physiological response
(relaxation of smooth
muscles, inhibition of
platelet aggregation,
etc.)
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
Oxidation of
vitamin E
Lipid peroxidation
Membrane damage
Proteins
Thiol oxidation
Carbonyl formation
Damage to Ca2+ and
other ion transport
systems
Disruption of normal
ion gradients
DNA
DNA damage
Altered gene
expression
Depletion of ATP
and NAD(P)H
Activation/deactivation
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:
Altered
vascular tone
Increased 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 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
LDL-Receptor
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