Session 5: Oxidative Stress and Antioxidant Defence Mechanisms

Question 1

What is oxidation?

Answer 1

Oxidation is the loss of electrons.

Question 2

What is reduction?

Answer 2

Reduction is the gain of electrons.

Question 3

What is an oxidising agent?

Answer 3

An oxidising agent (oxidant) oxidises something else.

Question 4

What is a reducing agent?

Answer 4

A reducing agent (reductant) reduces something else.

Question 5

What is oxidative stress?

Answer 5

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

Question 6

What does oxidative stress result in?

Answer 6

Increase in oxidative damage to molecules (proteins, lipids and DNA) leading to cell/tissue damage.

Question 7

What can oxygen gain to form superoxide?

Answer 7

Oxygen can gain an electron to form superoxide.

Question 8

What can superoxide react with to form peroxynitrite?

Answer 8

Superoxide can react with nitric oxide to form peroxynitrite.

Question 9

What radicals are considered the most reactive and damaging?

Answer 9

Hydroxyl radicals are considered the most reactive and damaging free radical as it reacts with anything.

Question 10

What can hydrogen peroxide react with to produce free radicals?

Answer 10

Hydrogen peroxide can react with Fe2+ ions to produce free radicals.

Question 11

What is a free radical?

Answer 11

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

Question 12

What are some examples of endogenous sources of biological oxidants?

Answer 12

Electron transport chain, nitric oxide synthases, NADPH oxidases.

Question 13

What are some examples of exogenous (outside body) sources of biological oxidants?

Answer 13

Radiation (cosmic rays, x-rays, UV light), pollutants, drugs (primaquine, paracetamol), toxins (paraquat herbicide, polonium-210).

Question 14

What are the two main types of ROS damage to DNA?

Answer 14

1) ROS reacts with a base = modified base can lead to mis-pairing & mutation.
2) ROS reacts with a sugar = ribose/deoxyribose causing strand break & mutation.

Question 15

What can failure of repair of DNA damage lead to?

Answer 15

Failure of repair of this damage can lead to mutations which cause cancer.

Question 16

What is lipid peroxidation?

Answer 16

Reaction of unsaturated lipids with ROS is termed lipid peroxidation.

Question 17

What does lipid peroxides do to cell membranes?

Answer 17

Damage.

Question 18

What disease is ROS damage to lipids thought to occur in early stages?

Answer 18

ROS damage to lipids is thought to occur in the early stages of cardiovascular disease.

Question 19

What is produced by the body to protect against oxidative damage?

Answer 19

Glutathione is synthesised by the body to protect against oxidative damage.

Question 20

What are Heinz bodies a clinical sign of?

Answer 20

Glucose-6-Phosphate Dehydrogenase (G6PDH) deficiency.

Question 21

How is superoxide radical produced in the mitochondria?

Answer 21

The superoxide radical is produced by adding an electron to molecular oxygen.

Question 22

Is hydrogen peroxide a free radical?

Answer 22

Hydrogen peroxide is NOT a free radical but it can react with iron ions (Fe2+) to produce free radicals.

Question 23

What is the most damaging free radical?

Answer 23

Hydroxyl free radical (OH*).

Question 24

How is nitrogen oxygen species (NOS) produced?

Answer 24

Superoxide radicals can react with other free radicals such as nitric oxide (NO*) to produce peroxynitrite (ONOO-).

Question 25

What is oxidative stress?

Answer 25

A condition in which the production of oxidants (ROS and RNS) and free radicals exceeds the body's ability to handle them and prevent damage.

Question 26

What can oxidative stress damage?

Answer 26

Proteins, lipids, DNA.

Question 27

What diseases is cellular damage by ROS and RNS indicated in?

Answer 27

CVD, Type 1 Diabetes (T1D), Rheumatoid Arthritis (RA), Crohn's disease, COPD, Ischaemia, Cancer, Pancreatitis, Parkinson's disease (PD), Multiple sclerosis (MS).

Question 28

What are the two forms of DNA damage by ROS and RNS?

Answer 28

1) **Modified base (ROS + base) ** = leading to mispairing and mutation. 2) **Modified pentose sugar (deoxyribose or ribose)** = leading to strand breakage and mutation as result of repair.

Question 29

How does protein damage occur via ROS and RNS?

Answer 29

- **Side chains of amino acids or protein backbone can react with ROS**. - Leads to modification of protein structure. - Loss of protein function.

Question 30

What is one of the most significant types of protein damage by ROS/RNS?

Answer 30

When ROS **takes electron from a cysteine residue** leading to **formation of inappropriate DISULPHIDE bond**.

Question 31

What can result from inappropriate cross-linking of proteins?

Answer 31

Heinz bodies - precipitated haemoglobin within RBC altering their rigidity.

Question 32

How does lipid damage occur by ROS and RNS?

Answer 32

- **ROS reacts with lipids in lipid peroxidation**. - **Lipid peroxides (lipid peroxyl radicals) formed**. - Lipid peroxyl radicals react with nearby fatty acids & hydrophobic environment of bilayer disrupting its integrity. - Damage to cell membrane integrity.

Question 33

What is the name of the process which describes oxidative damage by ROS in lipids?

Answer 33

Lipid peroxidation.

Question 34

What process of oxidative damage is significant in the aetiology of atherosclerosis?

Answer 34

Lipid peroxidation is significant in the aetiology of atherosclerosis.

Question 35

Outline the two antioxidant defense systems.

Answer 35

1) **Enzymatic defense systems** = superoxide dismutase (SOD), catalase (CAT) 2) **Non-enzymatic defense system** = glutathione (GSH).

Question 36

What does the enzymatic defense system do?

Answer 36

Superoxide radicals are converted to hydrogen peroxide by superoxide dismutase enzyme.

Question 37

What does catalase do?

Answer 37

Hydrogen peroxide is converted to water and molecular oxygen by catalase enzyme.

Question 38

What does glutathione (GSH) do?

Answer 38

Helps to prevent damage by reactive oxygen species generated in the course of metabolism.

Question 39

Which vitamins are the 'free radical scavengers'?

Answer 39

Vitamins A, C and E (ACE).

Question 40

What trace elements are considered to be 'free radical scavengers'?

Answer 40

Melatonin, Selenium, Carotenoids, Polyphenols, Flavonoids.

Question 41

What capacity do free radical scavengers have?

Answer 41

Free radical scavengers have a high oxygen radical absorbance capacity (ORAC).

Question 42

What do free radical scavengers like vitamins A, C and E reduce the risk of?

Answer 42

Chronic degenerative disorders.

Question 43

How do free radical scavengers protect the cell?

Answer 43

By donating a H+ atom and its electron to free radicals in a non-enzymatic reaction.

Question 44

What is respiratory burst?

Answer 44

Some phagocytic immune cells (neutrophils & monocytes) release ROS & RNS when stimulated. This is part of the antimicrobial defense system.

Question 45

Which phagocytic immune cells carry out respiratory burst?

Answer 45

Neutrophils and monocytes.

Question 46

What membrane-bound enzyme is involved in respiratory burst process?

Answer 46

NADPH oxidase.

Question 47

Give an example of a disorder which arises from oxidative damage to proteins in the cell.

Answer 47

* **Heinz bodies** form due to **cross-linked haemoglobin aggregation**, often caused by oxidative stress (e.g., G6PD deficiency). * These damaged red blood cells become **fragile**, **leading to haemolysis** (RBC destruction) and **haemolytic anaemia**.

Question 48

What is Vitamin E?

Answer 48

Lipid-soluble antioxidant, **protection against lipid peroxidation**.

Question 49

What is Vitamin C (ascorbic acid)?

Answer 49

Water-soluble antioxidant, important role in regenerating reduced form of Vitamin E.

Question 50

How is the Electron Transport Chain considered to be an endogenous source of ROS?

Answer 50

NADH and FADH2 donate electrons which pass through transport chain onto oxygen to form H2O. Occasionally these electrons can escape the chain and react with dissolved oxygen to form superoxide radicals.

Question 51

What is a free radical?

Answer 51

Atom, molecule or ion that contains one or more unpaired electrons, capable of independent 'free' existence.

Question 52

What is oxidative stress?

Answer 52

Refers to a cellular state at which cells do NOT have a sufficient antioxidant power to cope with ROS.

Question 53

What is ROS?

Answer 53

Reactive oxygen species.

Question 54

What are Heinz bodies?

Answer 54

Inclusions of the red blood cells which form as a result of oxidative damage to haemoglobin.

Question 55

What are the three key antioxidant vitamins?

Answer 55

A, C, E.

Question 56

Which one of the following is ROS? A) All of the above except hydrogen B) Hydrogen C) Hydroxyl radical D) Hydrogen peroxide E) All of the above F) Superoxide radical

Answer 56

A) All of the above except hydrogen.

Question 57

Which cellular component is MOST affected by ROS?

Answer 57

D) Mitochondria.

Question 58

Which key enzyme catalyses the conversion of superoxide to hydrogen peroxide and oxygen?

Answer 58

Superoxide dismutase.

Question 59

What disease is associated with oxidative stress and deficiency of an enzyme involved in carbohydrate metabolism?

Answer 59

Galactosaemia.

Question 60

What happens to GSH levels in people with G6PDH deficiency?

Answer 60

They produce lower GSH, meaning less protection against oxidative damage from oxidative stress.