oxidative stress

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