Oxidative Stress and Anti-Oxidants Flashcards Preview

Z OLD ESA 1- Metabolism > Oxidative Stress and Anti-Oxidants > Flashcards

Flashcards in Oxidative Stress and Anti-Oxidants Deck (163):
1

What causes cellular damage?

ROS and RNS

2

What is cellular damage by ROS and RNS a significant component in?

A wide range of disease states

3

Give 10 disease states that cellular damage caused by ROS and RNS is a significant component in?

- Cardiovascular disease
- Alzheimers disease
- Rheumatoid arthritis 
- Crohn’s disease  
- COPD
- Ischaemia / reperfusion injury
- Cancer
- Pancreatitis 
- Parkinson’s disease
- MI

4

How do the electrons of atoms, molecules and ions usually associate?

In pairs

5

How does each pair of electrons move?

Within a defined region of space- an orbital

6

What is a free radical?

An atom or molecule that contains one or more unpaired electrons, and it capable of independent existence

7

What is used to denote a free radical?

A superscript dot

8

Are free radicals reactive or inert?

Yes, usually very reactive

9

What do free radicals tend to do?

Acquire electrons from other atoms, molecules or ions

10

Why are free radicals damaging?

Because they want to get electrons from another molecule

11

What does a reaction of a radical with a molecule typically generate?

A second radical

12

What is the result of a reaction of a radical with a molecule typically generating a second radical?

It propagates damage

13

What does ROS stand for?

Reactive oxygen species

14

What are the ROS?

- Molecular oxygen
- Superoxide
- Hydrogen peroxide 
- Hydroxyl radical

15

Regarding radicals, what is molecular oxygen?

Biradical

16

What is meant by molecular oxygen being biradical?

It has 2 unpaired electrons in different orbitals

17

What is superoxide?

O 2 º -

18

When is superoxide produced?

When one electron is added to molecular oxygen

19

Why is superoxide important?

It’s an important source of other ROS

20

What is hydrogen peroxide?

H 2 O 2 -

21

How is hydrogen peroxide formed?

Adding 2H +  and e -  to superoxide

22

Is hydrogen peroxide a free radical?

No, but can react to produce free radicals

23

Is hydrogen peroxide readily diffusible?

Yes

24

What is the most reactive and damaging free radical?

Hydroxyl radical

25

What is the hydroxyl radical?

OHº

26

How is the hydroxyl radical formed?

Adding e -  and H +  to hydrogen peroxide (which removes H 2 O)

27

Why is the hydroxyl radical so damaging?

It reactions with anything

28

How is the hydroxyl radical removed?

By adding e -  and H + , which produces water

29

What are the two reactive nitrogen species?

#NAME?

30

What is nitric oxide?

NOº

31

Where is nitric oxide important?

Signalling molecule

32

What happens when nitric oxide is in high concentrations?

It plays a role in the immune system

33

What role does nitric acid play in the immune system?

It can produce free radicals that damage pathogens

34

What is peroxynitrate?

ONOO -

35

When is peroxynitrate formed?

When superoxide reacts with nitric oxide

36

Is peroxynitrate a free radical?

No, but powerful oxidant that can damage cells

37

What effect does ROS have on DNA?

It damages them by taking electrons away

38

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

#NAME?

39

What can the modified base caused by ROS lead to?

Mispairing and mutation

40

Does ROS react with ribose or deoxyribose sugar?

Either

41

What can ROS reacting with the sugar in DNA cause?

The strand to break, or mutation on repair

42

What can be used as a measurement of oxidative damage?

The amount of 8-oxo-dG

43

What can failure to repair DNA damage lead to?

Mutation, which can lead to cancer

44

What happens when ROS react with proteins?

Can change backbone or side-chain

45

What can ROS reaction with side chain lead too?

Modified amino acids

46

How can ROS modify amino acids?

- Carbonyls 
- Hydroxylated adducts 
- Ring opened species 
- Dimers (e.g. di-tyrosine) 
- Disulphide bonds

47

What can modified amino acids in proteins lead to?

Change in protein structure

48

What could a change in protein structure lead to?

- Gain of function 
- Loss of function 
- Protein degradation

49

What can ROS reacting with backbones of protein lead to?

Fragmentation

50

What could fragmentation of the protein backbone lead to?

Protein degradation

51

Where do disulphide bonds play an important role?

In folding and stability of some proteins

52

What kind of proteins do disulphide bonds usually play an important role?

- Secreted proteins 
- Extracellular domain of membrane proteins

53

Where are disulphide bonds formed?

Between thiol groups of cysteine residues

54

When can inappropriate disulphide bond formation occur?

If ROS takes electrons from cysteines

55

What can inappropriate disulphide bond formation lead to?

- Misfolding
- Crosslinking 
- Disruption of function

56

Is inappropriate disulphide bond formation inter-subunit or intra-subunit?

Can be either

57

How can ROS damage lipids?

Free radical can extract hydrogen atom from polyunsaturated fatty acids in membrane lipids

58

What can be formed when a free radical reacts with a lipid?

A lipid radical

59

What can happen to a lipid free radical?

It can react with oxygen to form a lipid peroxyl radical

60

What is formed when lipid peroxyl radicals are made?

A chain reaction

61

Why is a chain reaction formed when a lipid peroxyl radical is made?

Because the lipid peroxyl radical can extract hydrogen from a nearby fatty acid

62

What is the problem with ROS damage to lipid?

#NAME?

63

What are the two types of biological oxidants?

- Endogenous 
- Exogenous

64

What is meant by endogenous?

Within cells

65

What is meant by exogenous?

Outside cells

66

Give 7 endogenous sources of biological oxidants

#NAME?

67

Give 4 examples of exogenous sources of biological oxidants

#NAME?

68

Give 3 sources of radiation

#NAME?

69

How does the electron transport chain produce ROS?

- NADH and FADH 2  supply electrons to complexes I, II, III, and IV from metabolic substrates 
- e -  pass through ETC, reducing oxygen to form water at complex IV
- Occasionally, electrons accidentally escape the chain and react with the dissolved oxygen to form superoxide

70

How does the electron transport chain deal with the ROS formed

Have protective mechanisms to deal with it

71

What protective mechanisms does the e.t.c. have to deal with ROS produced?

Enzymes

72

What are 3 types of nitric oxide synthase (NOS)?

#NAME?

73

What is iNOS?

Inducible nitric oxide synthase

74

What does iNOS do?

Produces high NO concentration in phagocytes for direct toxic effect

75

What is eNOS?

Endothelial nitric oxide synthase?

76

What does eNOS do?

Signalling

77

What is nNOS?

Neuronal nitric oxide synthase

78

What does nNOS do?

Signalling

79

Give the reaction that NOS catalyses

Arginine + NADPH + O 2 →  citrulline + NOº + NADP + + H 2 O

80

Where is NOº used for signalling?

- Vasodilation 
- Neurotransmission
- S-Nitrosylation

81

What is the problem with NOº at high levels?

It has a toxic effect

82

What happens in a respiratory burst?

Rapid release of superoxide and H 2 O 2  from phagocytic cells

83

Give 2 examples of cells that perform respiratory bursts

- Neutrophils 
- Monocytes

84

What is the purpose of the ROS and peroxynitrate in the respiratory burst?

It destroys invading bacteria

85

What is the respiratory burst part of?

The anti-microbal defence system

86

Describe the process of the respiratory burst

- The membrane bound complex NADPH oxidase converts NADPH to NADP +  using oxygen, which is then converted to superoxide
- The superoxide is then converted to hydrogen peroxide
- The hydrogen peroxide is converted to HOClº (bleach), by action of the enzyme myeloperoxidase and the addition of Cl -
- Simultaneously, iNOS produces NOº, which reacts with the superoxide to produce peroxynitrate, which also attacks the bacteria

87

How is the the enzyme myeloperoxidase, required for respiratory burst, released?

Released from phagolysosome into the phagocytic vesicle by secretory granules

88

What is chronic granulomatous disease?

A genetic defect in the NADPH oxidase complex

89

What is the result of the defect in chronic granulomatous disease?

Causes enhanced susceptibility to bacterial infections

90

Why does chronic granulomatous disease cause an increased susceptibility to bacterial infections?

Because of the reduced capacity for the respiratory burst response

91

What are the symptoms of chronic granulomatous disease?

- Atypical infections 
- Pneumonia
- Abscesses 
- Impetigo
- Cellulitis

92

What are the main cellular defences against ROS?

- Superoxide dismutase (SOD) and catalase
- Glutathione 
- Free radical scroungers

93

What does superoxide dismutase do?

Converts superoxide to H 2 O 2  and oxygen

94

Where is SOD expressed?

In mitochondria

95

Why is SOD produced in the mitochondria?

To deal with superoxides produced by accident in the e.t.c.

96

Why is SOD a primary defence?

Because superoxide is a strong inhibitor of chain reactions

97

What are the 3 isoenzymes of SOD?

- Cu + - Zn 2+ cytosolic
- Cu + - Zn 2+ extracellular
- Mn 2+ mitochondrial

98

What does catalase do?

Converts H 2 O 2  to water and oxygen

99

Where is catalase found?

Widespread

100

Where is catalase particularly important?

Immune cells

101

Why is catalase particularly important in immune cells?

To protect against the oxidative burst

102

Why is SOD alone not sufficient protection?

Because H 2 O 2  still damaging

103

What tripeptide is synthesised to protect against oxidative damage?

Glycine-Cysteine-Glutamate ; called GSH (reduced form)

104

What happens when GSH comes into contact with an ROS?

It donates e -

105

What enzyme is required for the glutathione mechanism of protection from oxidative damage?

Glutathione peroxidase

106

What does glutathione peroxidase do?

Causes two GSH molecules to react together to form a a disulphide bond, forming the oxidised form- GSSG

107

What does glutathione peroxidase require?

Selenium

108

What happens when GSH is converted to GSSG?

H 2 O 2 is converted to H 2 O

109

How is GSSG reduced back to GSH?

By glutathione reductase

110

What does glutathione reductase do?

Catalyses the transfer of electrons from NADPH to disulphide bond

111

Where does the NADPH needed to reduce GSSG come from?

Pentose phosphate pathway

112

What does the fact that the NADPH required for the reduction of GSSG comes from the pentose phosphate pathway mean?

That the pentose phosphate pathway is essential for protection from free radical damage

113

What do free radical scroungers do?

Takes hit from free radicals to prevent damage to tissues

114

Give 6 examples of free radical scroungers?

- Vitamin E
- Vitamin C
- Carotenoids
- Uric acid
- Flavonoids 
- Melatonin

115

What is vitamin E also known as?

α-tocopherol

116

Is vitamin E water or lipid soluble?

Lipid

117

Where is vitamin E important?

In protection against lipid peroxidation

118

What is vitamin C also known as?

Ascorbic acid

119

Is vitamin C water or lipid soluble?

Water

120

Where is vitamin C important?

In regenerating reduced form of vitamin E

121

How do free radical scroungers reduce free radical damage?

By donating a hydrogen atom (and it’s electron) to free radicals in a non-enzymatic reaction

122

When does oxidative stress occur?

When defences are compromised, or an excessive burden is on antioxidants

123

What is galactosaemia?

A deficiency is galactokinase, uridyl transferase or UDP-galactose epimerase

124

What does deficiency in the 3 enzymes in galactosaemia favour?

Conversion of galactose to galactitol

125

What does increased activity of aldose reductase cause?

An excessive consumption of NADPH

126

What is the result of an excessive consumption of NADPH?

Compromises defences against ROS damage

127

How can galactosaemia cause cataracts?

#NAME?

128

What are the symptoms of galactosaemia?

- Heptomegaly and cirrhosis 
- Renal failure
- Vomiting
- Seizure and brain damage
- Cataracts
- Hypoglycaemia

129

What is the G6PDH enzyme essential for?

The pentose phosphate pathway

130

What does G6PDH deficiency limit?

The amount of NADPH

131

What is NADPH required for?

Reduction of oxidised glutathione (GSSG) back to reduce glutathione (GSH)

132

What does lower GSH mean?

Less protection against damage from oxidative stress

133

What does G6PDH result in a build up of?

H 2 O 2

134

Why does a G6PDH deficiency cause a build up of H 2 O 2 ?

It’s not converted to water

135

What does the build up of H 2 O 2 cause?

- Lipid peroxidation 
- Protein damage

136

What is the result of the lipid peroxidation?

Cell membrane damage

137

What is the result of cell membrane caused by lipid peroxidation?

Lack of deformity leads to mechanical stress

138

What is the result of protein damage caused by H 2 O 2 build up?

Aggregates chains of cross-linked haemoglobin, causing Heinz bodies

139

What can Heinz bodies lead to?

Haemolysis

140

How do Heinz bodies appear on micrographs?

Dark staining within red blood cells

141

What are Heinz bodies made up of?

Precipitated haemoglobin

142

What are the effect of Heinz bodies?

They alter rigidity

143

How do Heinz bodies alter rigidity?

They bind to the cell membrane

144

What is the result in the altered rigidity due to Heinz bodies?

Increased mechanical stress when cells squeeze through small capillaries

145

What removes Heinz bodies?

Spleen

146

What does the removal of bound Heinz bodies by the spleen result in /

Blister cells

147

What is the presence of Heinz bodies a clinical sign of?

G6PDH deficiency

148

Where does metabolism of paracetamol occur?

Hepatocytes

149

How can paracetamol be metabolised at prescribed dosage?

By conjugation with glucuronide or sulphate

150

What happens in a paracetamol overdose?

The normal pathway becomes saturated, and a second pathway has to be used

151

What is the problem with the second pathway of paracetamol metabolism?

The toxic metabolite NAPQI accumulates

152

Why is NAPQI toxic?

#NAME?

153

What are the direct toxic effects of NAPQI?

Oxidative damage to the liver cell

154

Why does NAPQI build up deplete glutathione reserves?

It’s used to protect the cell against damage

155

What is the result of depletion of NAPQI reserves?

Defences are compromised

156

What is the treatment for paracetamol overdose?

Acetylcysteine

157

How does acetylcysteine work?

Replenishing glutathione levels

158

Where is ischaemia reperfusion injury especially relevant?

- Heart
- Brain 
- Organ transplantation

159

What can happen to cells during ischaemia?

They can be reversibly damaged

160

How can cells damaged by ischaemia recover?

Following restoration of blood flow

161

What is the problem with reperfusion following ischaemia?

Can result in more damage than caused by initial ischaemia

162

What is especially sensitive to reperfusion injury?

Mitochondria

163

What causes ischaemic reperfusion injury?

- Incompletely metabolised products produce ROS on re-introduction of oxygen
- Loss of antioxidants during ischaemia means can’t cope with potential oxidative damage
- Influx of calcium ions upon renewed blood flow 
- Recruitment of leukocytes to affected area