Presentation on OXIDATIVE STRESS SHAILY MEHRA M.PHARM
Presentation on OXIDATIVE STRESS
SHAILY MEHRA M.PHARM
Contents Introduction
Causes of oxidative stress Free radicals Free radicals nomenclature Types of free radicals Roles of free radicals in biological system Effect of oxidative stress Molecular Vascular
Common diseases caused by Oxidative stress
Measurement of Oxidative stress
Protective measures for Oxidative stress
What is oxidative stress?A disturbance in the balance between reactive species or free radicals and antioxidants.
Under normal conditions, cells are able to balance the production of oxidants and antioxidants.
Oxidative stress occurs when there is imbalance in our cells due to either an increase in free radicals or a decrease in antioxidants.
Oxidative stress leads to the structural changes of the cell
wall and hamper the process of maturation of cellular
structures. Its also lead to the change in the function and
death eventually.
ENDOGENOUS SOURCEBody's normal use of oxygen such as respiration and
some cell mediated immune functions Immune cell activationInflammationMental stress etc.
EXOGENOUS SOURCEEnvironmental pollutantsCigarette smoke Radiations etc.
Free Radicals any species capable of independent existent that contains
one or more unpaired electrons.
These are highly reactive chemical entities that have a single unpaired electron in their outer most orbit.
Under certain conditions can be highly toxic to the cells.
Generally unstable and try to become stable, either by accepting or donating an electron.
Example of free radicals
Radicals can be formed by…
1. The loss of a single electron from a non-radical, or by the gain of a single electron by a non-radical.
2. The breakage of covalent bond ‘hemolytic fission’.
Free Radical Nomenclature
A free radical is denoted by a superscript dot to the oxygen (or carbon)
e.g., HO, NO, CH3
If a free radical is a charged species, the dot is put and then the charge
e.g., O2-
TYPES OF FREE RADICALS Superoxide radical
Hydroxide radical
Nitric oxide radical
Peroxide radicals
H2O2(non radical)..etc.
SUPEROXIDE RADICAL Generation of superoxide (O2
- )
• The addition a single electron to the ground-state molecule (O2 + e- O2
- )
Biological generation of O2-
• Mitochondrial electron transport chain
• Enzymatic reduction of oxygen (O2)
• Xenobiotic metabolisms (redox cycling)
• Respiratory burst (phagocytes)
Biological Generation of Superoxide Enzymatic reduction of oxygen Xanthine/hypoxanthine Uric acid
Redox cycling : Paraquat (Xenobiotic)
XOD
N • N CH3H3C+
N N CH3H3C+
Oxidizedcytochomre P450 reductase
Reducedcytochomre P450 reductase
NADPH
NADP
O2
O2 -
Paraquate -
+
Respiratory Burst Myeloperoxidase
• Oxidizes Cl- to hypochlorous acid• Chronic granulomatous disease
NADPH oxidase enzyme.
• •NADPH
NADP+
O2
O2-
NADPH
NADP+O2
O2-
outside inside
....
Phagocytic vacuole (phagosome)
Hydrogen Peroxide Not a free radical but ROS(reactive oxygen species)
Formed in the cell by dismutation reactions by :• Spontaneously during respiratory burst.• By enzymes e.g. : Superoxide dismutase.
Hydroxyl Radical (HO) Highly reactive oxygen radicals
Formation of hydroxyl radicals in biological systems :
• Ionizing radiation
• Reaction of metal ions with hydrogen peroxide
(Fenton reaction)
Formation of hydroxyl radical from ozone (O3)
Fenton Reaction
Discovered by Fenton (1894) “A mixture of hydrogen peroxide and an iron(II) salts
causes the formation of hydroxyl radical”
Fe2+ + H2O2 intermediate complex Fe3+ + OH-
+ HO
Fe3+ + H2O2 intermediate complex Fe2+ + O2 -
+ 2H+
Haber-Weiss reaction
Fe2+ + H2O2 Fe3+ + OH- + HO
Fe3+ + O2 - Fe2+ + O2
Net : O2- + H2O2 O2 + HO + OH-
Nitrogen-Centered Radicals Nitric oxide (NO)
• Endothelial derived-relaxing factor (EDRF)• Generated from the catalysis of L-arginine by nitric oxide
synthase (NOS) enzymes• Functions
• Vascular function, platelet aggregation, immune response, neurotransmitter, signal transduction
• Cytotoxicity.NO + O2
- ONOO- (highly toxic)
L- arginine L-citrulline + NO
NOS
In the absence of L-arginine and BH4(tetrahydrobiopterin),
the activation of molecular by NOS results in a divalent reduction of O2 to yield superoxide anions and hydrogen peroxide.
BH4
Roles of Free Radicals in Biological Systems
• Enzyme-catalyzed reactions• Electron transport in mitochondria• Signal transduction & gene expression• Activation of nuclear transcription factors• Oxidative damages of molecules, cells, tissues• Antimicrobial actions• Aging & diseases
Molecular effects of oxidative stress
• Lipid peroxidation• DNA damage• Protein oxidation• Inactivation of enzymes• Release of ca ions from intracellular stores• Cytoskeletal damage • Chemotaxis
Vascular effects
• altered vascular tone
• increased endothelial permeability
Common diseases caused by oxidative stress
Measurement of Oxidative Stress
Oxygen consumption
Oxidative markers
• Lipid peroxidation products (TBARs, lipid
hydroperoxides, etc.)
• DNA hydroxylation products
• Protein hydroxylation products (nitration products)
Free radical detection
• Single photon counting
• Chemiluminescence
• Fluorescent probe
• Electron paramagnetic resonance spectroscopy (EPR)
Protection Against ROS Damage Direct protection against ROS
• Superoxide dismutase, Glutathione peroxidase, Catalase
Non-specific reduction system
• Glutathione, Vitamin C
Protection against lipid peroxidation
• Glutathione peroxidase, Vitamin E, -Carotene
Sequestration of metals
• Transferrin, Lactoferrin, Ferritin, Metallothionein
Repair systems
• DNA repair enzymes, Macroxyproteinases, Glutathione
transferase