Lecture 5.2: Antioxidants and Oxidative Stress

Question 1

What is a REDOX reaction?

Answer 1

Redox reactions are reactions where both oxidation and reduction are taking place

Question 2

Oxidative Stress

Answer 2

Condition in which the rate of generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS) exceeds the body’s ability to protect itself against them

Results in an increase in oxidative damage to molecules (proteins, lipids and DNA) leading to cell/tissue damage

Question 3

Oxidative Stress: Possible Disease

Answer 3

• Cardiovascular disease
• Type 1 diabetes
• Alzheimer’s disease
• Rheumatoid arthritis
• Crohn’s disease
• COPD
• Ischaemia/reperfusion injury
• Cancer
• Pancreatitis
• Parkinson’s disease
• Multiple sclerosis

Question 4

Reactive Oxygen Species

Answer 4

Oxygen —-> Super Oxide Radical
Super Oxide Radical —-> Hydrogen Peroxide
Hydrogen Peroxide (reacts with Fe2+) —-> Water + Hydroxyl Radical

Hydroxyl Radical is the most damaging free radical, it reacts with anything!
Super Oxide is an important source of other ROS

Question 5

Reactive Nitrogen Species

Answer 5

Nitric Oxide Radical + Super Oxide Radical —-> Peroxynitrite (ONOO-)

Peroxynitrite is not itself a free radical, but is a powerful oxidant that can damage cells

Question 6

Free Radicals

Answer 6

A free radical is an atom, molecule or ion that contains one or more unpaired electrons, capable of independent (“free”) existence

Free radicals are usually very reactive and tend to acquire electrons from
other atoms, molecules or ions

A superscript dot is used to denote a free radical

Question 7

The Electron Transport Chain as A Source of ROS

Answer 7

• NADH and FADH2 donate electrons (e−)

• e − pass through electron transport chain onto oxygen to form H2O

• Occasionally electrons can accidentally escape the chain and react with
dissolved O2 to form superoxide

• Superoxide gives rise to other ROS

Question 8

Sources of Biological Oxidants: Endogenous (7)

Answer 8

• Electron transport chain
• Peroxidases
• Nitric oxide synthases
• Lipooxygenases
• NADPH oxidases
• Xanthine oxidase
• Monoamine oxidase

Question 9

Sources of Biological Oxidants: Exogenous (8/9)

Answer 9

• Radiation: Cosmic rays, UV light, X-rays
• Pollutants
• Drugs: Primaquine (anti-malarial), paracetamol
• Toxins: Paraquat (herbicide), Polonium-210

Question 10

ROS Damage to DNA

Answer 10

ROS reacts with base: Modified base can lead to mis-pairing and mutation

ROS reacts with sugar (ribose or deoxyribose): Can cause strand break and mutation as a result of repair

Failure in repair can lead to mutation, which could lead to cancer

Question 11

How to measure ROS Damage to DNA

Answer 11

The amount of 8-oxo-dG (product of DNA oxidation) present in cells can be used as measurement of oxidative damage

Question 12

ROS Damage to Proteins (2)

Answer 12

Damage to Backbone
Damage to Side-R Chain

Question 13

ROS Damage to Proteins: Damage to Backbone

Answer 13

Leads to Fragmentation
Thus Protein Degradation

Question 14

ROS Damage to Proteins: Damage to Side-R Chain

Answer 14

Modified amino acid:
• Carbonyls
• Hydroxylated adducts
• Ring opened species
• Dimers (e.g. di-tyrosine)
• Disulphide bond (Cys)

Leads to change in protein structure, thus loss/gain of function, (thus maybe protein degradation)

Question 15

ROS Damage to Lipids (4)

Answer 15

• Reaction of unsaturated lipids with ROS is termed lipid peroxidation
• Lipid peroxides are formed (ROS)
• Causes damage to cell membranes
• Thought to be involved in the early stage of cardiovascular disease

Question 16

Nitric Oxide Synthase (NOS): 3 Types

Answer 16

iNOS: Inducible nitric oxide synthase, produces high NO concentrations in phagocytes for direct toxic effect

eNOS: Endothelial nitric oxide synthase (Signalling)

nNOS: Neuronal nitric oxide synthase (Signalling)

Question 17

Arginine to Nitric Oxide Radical Reaction + Effects of NO radical

Answer 17

Arginine + NOS enzyme —> Citrulline + Nitric Oxide Radical (NO)

Toxic effects at high level

Signalling molecule
• Vasodilation
• Neurotransmission
• S-Nitrosylation

Question 18

Cellular Defence Mechanisms against Superoxide Radicals

Answer 18

Superoxide dismutase SOD converts superoxide into hydrogen peroxide

Catalase converts H2O2 into H20 and O2

Question 19

Cellular Defence Mechanisms- GSH

Answer 19

FIND WAY SUMMARISE SLIDE 19 LECTURE 5.3

Question 20

Heinz Bodies

Answer 20

• Dark staining within red blood cells from
resulting precipitations of damaged
haemoglobin attached to your red blood cells
• Bind to cell membrane altering rigidity
• Increased mechanical stress when cells
squeeze through small capillaries
• Spleen removes bound Heinz bodies resulting in
“blister cells”
• Clinical sign of G6PDH deficiency

Question 21

Cellular Defences: Vitamin E

Answer 21

Lipid soluble antioxidant

Important for protection against lipid peroxidation

Question 22

Cellular Defences: Vitamin C

Answer 22

Water soluble antioxidant

Important role in regenerating reduced form of Vitamin E

Question 23

Cellular Defences: Other

Answer 23

• Carotenoids
• Flavonoids
• Selenium
• Uric acid
• Melatonin
• Zinc

Question 24

How do Free Radical Scavengers reduce free radical damage?

Answer 24

Free radical scavengers reduce free radical damage by donating hydrogen atom (and its electron) to free radicals in a nonenzymatic reaction

Question 25

Respiratory Burst

Answer 25

• Rapid release of superoxide and H2O2 from phagocytic cells (e.g. neutrophils
and monocytes)
• ROS and peroxynitrite destroy invading bacteria
• Part of antimicrobial defence system

Question 26

Chronic Granulomatous Disease: what is it?

Answer 26

Genetic defect in NADPH oxidase complex causes enhanced susceptibility to bacterial infections

Question 27

Chronic Granulomatous Disease: Symptoms + Signs

Answer 27

• Atypical Infections
• Pneumonia
• Abscesses
• Impetigo
• Cellulitis