oxidative stress and atherosclerosis. objectives: what is „free radical“? reactive oxygen and...
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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 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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