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

Oxidative Stress and Anti-Oxidants Flashcards

1
Q

What causes cellular damage?

A

ROS and RNS

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2
Q

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

A

A wide range of disease states

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3
Q

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

A
  • Cardiovascular disease
  • Alzheimers disease
  • Rheumatoid arthritis
  • Crohn’s disease
  • COPD
  • Ischaemia / reperfusion injury
  • Cancer
  • Pancreatitis
  • Parkinson’s disease
  • MI
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4
Q

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

A

In pairs

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5
Q

How does each pair of electrons move?

A

Within a defined region of space- an orbital

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6
Q

What is a free radical?

A

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

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7
Q

What is used to denote a free radical?

A

A superscript dot

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8
Q

Are free radicals reactive or inert?

A

Yes, usually very reactive

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9
Q

What do free radicals tend to do?

A

Acquire electrons from other atoms, molecules or ions

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10
Q

Why are free radicals damaging?

A

Because they want to get electrons from another molecule

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11
Q

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

A

A second radical

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12
Q

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

A

It propagates damage

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13
Q

What does ROS stand for?

A

Reactive oxygen species

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14
Q

What are the ROS?

A
  • Molecular oxygen
  • Superoxide
  • Hydrogen peroxide
  • Hydroxyl radical
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15
Q

Regarding radicals, what is molecular oxygen?

A

Biradical

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16
Q

What is meant by molecular oxygen being biradical?

A

It has 2 unpaired electrons in different orbitals

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17
Q

What is superoxide?

A

O 2 º -

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18
Q

When is superoxide produced?

A

When one electron is added to molecular oxygen

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19
Q

Why is superoxide important?

A

It’s an important source of other ROS

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20
Q

What is hydrogen peroxide?

A

H 2 O 2 -

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21
Q

How is hydrogen peroxide formed?

A

Adding 2H + and e - to superoxide

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22
Q

Is hydrogen peroxide a free radical?

A

No, but can react to produce free radicals

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23
Q

Is hydrogen peroxide readily diffusible?

A

Yes

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24
Q

What is the most reactive and damaging free radical?

A

Hydroxyl radical

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25
Q

What is the hydroxyl radical?

A

OHº

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26
Q

How is the hydroxyl radical formed?

A

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

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27
Q

Why is the hydroxyl radical so damaging?

A

It reactions with anything

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28
Q

How is the hydroxyl radical removed?

A

By adding e - and H + , which produces water

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29
Q

What are the two reactive nitrogen species?

A

NAME?

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30
Q

What is nitric oxide?

A

NOº

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31
Q

Where is nitric oxide important?

A

Signalling molecule

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32
Q

What happens when nitric oxide is in high concentrations?

A

It plays a role in the immune system

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33
Q

What role does nitric acid play in the immune system?

A

It can produce free radicals that damage pathogens

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34
Q

What is peroxynitrate?

A

ONOO -

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35
Q

When is peroxynitrate formed?

A

When superoxide reacts with nitric oxide

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36
Q

Is peroxynitrate a free radical?

A

No, but powerful oxidant that can damage cells

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37
Q

What effect does ROS have on DNA?

A

It damages them by taking electrons away

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38
Q

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

A

NAME?

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39
Q

What can the modified base caused by ROS lead to?

A

Mispairing and mutation

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40
Q

Does ROS react with ribose or deoxyribose sugar?

A

Either

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41
Q

What can ROS reacting with the sugar in DNA cause?

A

The strand to break, or mutation on repair

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42
Q

What can be used as a measurement of oxidative damage?

A

The amount of 8-oxo-dG

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43
Q

What can failure to repair DNA damage lead to?

A

Mutation, which can lead to cancer

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44
Q

What happens when ROS react with proteins?

A

Can change backbone or side-chain

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45
Q

What can ROS reaction with side chain lead too?

A

Modified amino acids

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46
Q

How can ROS modify amino acids?

A
  • Carbonyls
  • Hydroxylated adducts
  • Ring opened species
  • Dimers (e.g. di-tyrosine)
  • Disulphide bonds
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47
Q

What can modified amino acids in proteins lead to?

A

Change in protein structure

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48
Q

What could a change in protein structure lead to?

A
  • Gain of function
  • Loss of function
  • Protein degradation
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49
Q

What can ROS reacting with backbones of protein lead to?

A

Fragmentation

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50
Q

What could fragmentation of the protein backbone lead to?

A

Protein degradation

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51
Q

Where do disulphide bonds play an important role?

A

In folding and stability of some proteins

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52
Q

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

A
  • Secreted proteins

- Extracellular domain of membrane proteins

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53
Q

Where are disulphide bonds formed?

A

Between thiol groups of cysteine residues

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54
Q

When can inappropriate disulphide bond formation occur?

A

If ROS takes electrons from cysteines

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55
Q

What can inappropriate disulphide bond formation lead to?

A
  • Misfolding
  • Crosslinking
  • Disruption of function
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56
Q

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

A

Can be either

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57
Q

How can ROS damage lipids?

A

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

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58
Q

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

A

A lipid radical

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59
Q

What can happen to a lipid free radical?

A

It can react with oxygen to form a lipid peroxyl radical

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60
Q

What is formed when lipid peroxyl radicals are made?

A

A chain reaction

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61
Q

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

A

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

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62
Q

What is the problem with ROS damage to lipid?

A

NAME?

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63
Q

What are the two types of biological oxidants?

A
  • Endogenous

- Exogenous

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64
Q

What is meant by endogenous?

A

Within cells

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65
Q

What is meant by exogenous?

A

Outside cells

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66
Q

Give 7 endogenous sources of biological oxidants

A

NAME?

67
Q

Give 4 examples of exogenous sources of biological oxidants

A

NAME?

68
Q

Give 3 sources of radiation

A

NAME?

69
Q

How does the electron transport chain produce ROS?

A
  • 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
Q

How does the electron transport chain deal with the ROS formed

A

Have protective mechanisms to deal with it

71
Q

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

A

Enzymes

72
Q

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

A

NAME?

73
Q

What is iNOS?

A

Inducible nitric oxide synthase

74
Q

What does iNOS do?

A

Produces high NO concentration in phagocytes for direct toxic effect

75
Q

What is eNOS?

A

Endothelial nitric oxide synthase?

76
Q

What does eNOS do?

A

Signalling

77
Q

What is nNOS?

A

Neuronal nitric oxide synthase

78
Q

What does nNOS do?

A

Signalling

79
Q

Give the reaction that NOS catalyses

A

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

80
Q

Where is NOº used for signalling?

A
  • Vasodilation
  • Neurotransmission
  • S-Nitrosylation
81
Q

What is the problem with NOº at high levels?

A

It has a toxic effect

82
Q

What happens in a respiratory burst?

A

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

83
Q

Give 2 examples of cells that perform respiratory bursts

A
  • Neutrophils

- Monocytes

84
Q

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

A

It destroys invading bacteria

85
Q

What is the respiratory burst part of?

A

The anti-microbal defence system

86
Q

Describe the process of the respiratory burst

A
  • 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
Q

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

A

Released from phagolysosome into the phagocytic vesicle by secretory granules

88
Q

What is chronic granulomatous disease?

A

A genetic defect in the NADPH oxidase complex

89
Q

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

A

Causes enhanced susceptibility to bacterial infections

90
Q

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

A

Because of the reduced capacity for the respiratory burst response

91
Q

What are the symptoms of chronic granulomatous disease?

A
  • Atypical infections
  • Pneumonia
  • Abscesses
  • Impetigo
  • Cellulitis
92
Q

What are the main cellular defences against ROS?

A
  • Superoxide dismutase (SOD) and catalase
  • Glutathione
  • Free radical scroungers
93
Q

What does superoxide dismutase do?

A

Converts superoxide to H 2 O 2 and oxygen

94
Q

Where is SOD expressed?

A

In mitochondria

95
Q

Why is SOD produced in the mitochondria?

A

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

96
Q

Why is SOD a primary defence?

A

Because superoxide is a strong inhibitor of chain reactions

97
Q

What are the 3 isoenzymes of SOD?

A
  • Cu + - Zn 2+ cytosolic
  • Cu + - Zn 2+ extracellular
  • Mn 2+ mitochondrial
98
Q

What does catalase do?

A

Converts H 2 O 2 to water and oxygen

99
Q

Where is catalase found?

A

Widespread

100
Q

Where is catalase particularly important?

A

Immune cells

101
Q

Why is catalase particularly important in immune cells?

A

To protect against the oxidative burst

102
Q

Why is SOD alone not sufficient protection?

A

Because H 2 O 2 still damaging

103
Q

What tripeptide is synthesised to protect against oxidative damage?

A

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

104
Q

What happens when GSH comes into contact with an ROS?

A

It donates e -

105
Q

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

A

Glutathione peroxidase

106
Q

What does glutathione peroxidase do?

A

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

107
Q

What does glutathione peroxidase require?

A

Selenium

108
Q

What happens when GSH is converted to GSSG?

A

H 2 O 2 is converted to H 2 O

109
Q

How is GSSG reduced back to GSH?

A

By glutathione reductase

110
Q

What does glutathione reductase do?

A

Catalyses the transfer of electrons from NADPH to disulphide bond

111
Q

Where does the NADPH needed to reduce GSSG come from?

A

Pentose phosphate pathway

112
Q

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

A

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

113
Q

What do free radical scroungers do?

A

Takes hit from free radicals to prevent damage to tissues

114
Q

Give 6 examples of free radical scroungers?

A
  • Vitamin E
  • Vitamin C
  • Carotenoids
  • Uric acid
  • Flavonoids
  • Melatonin
115
Q

What is vitamin E also known as?

A

α-tocopherol

116
Q

Is vitamin E water or lipid soluble?

A

Lipid

117
Q

Where is vitamin E important?

A

In protection against lipid peroxidation

118
Q

What is vitamin C also known as?

A

Ascorbic acid

119
Q

Is vitamin C water or lipid soluble?

A

Water

120
Q

Where is vitamin C important?

A

In regenerating reduced form of vitamin E

121
Q

How do free radical scroungers reduce free radical damage?

A

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

122
Q

When does oxidative stress occur?

A

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

123
Q

What is galactosaemia?

A

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

124
Q

What does deficiency in the 3 enzymes in galactosaemia favour?

A

Conversion of galactose to galactitol

125
Q

What does increased activity of aldose reductase cause?

A

An excessive consumption of NADPH

126
Q

What is the result of an excessive consumption of NADPH?

A

Compromises defences against ROS damage

127
Q

How can galactosaemia cause cataracts?

A

NAME?

128
Q

What are the symptoms of galactosaemia?

A
  • Heptomegaly and cirrhosis
  • Renal failure
  • Vomiting
  • Seizure and brain damage
  • Cataracts
  • Hypoglycaemia
129
Q

What is the G6PDH enzyme essential for?

A

The pentose phosphate pathway

130
Q

What does G6PDH deficiency limit?

A

The amount of NADPH

131
Q

What is NADPH required for?

A

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

132
Q

What does lower GSH mean?

A

Less protection against damage from oxidative stress

133
Q

What does G6PDH result in a build up of?

A

H 2 O 2

134
Q

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

A

It’s not converted to water

135
Q

What does the build up ofH 2 O 2 cause?

A
  • Lipid peroxidation

- Protein damage

136
Q

What is the result of the lipid peroxidation?

A

Cell membrane damage

137
Q

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

A

Lack of deformity leads to mechanical stress

138
Q

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

A

Aggregates chains of cross-linked haemoglobin, causing Heinz bodies

139
Q

What can Heinz bodies lead to?

A

Haemolysis

140
Q

How do Heinz bodies appear on micrographs?

A

Dark staining within red blood cells

141
Q

What are Heinz bodies made up of?

A

Precipitated haemoglobin

142
Q

What are the effect of Heinz bodies?

A

They alter rigidity

143
Q

How do Heinz bodies alter rigidity?

A

They bind to the cell membrane

144
Q

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

A

Increased mechanical stress when cells squeeze through small capillaries

145
Q

What removes Heinz bodies?

A

Spleen

146
Q

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

A

Blister cells

147
Q

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

A

G6PDH deficiency

148
Q

Where does metabolism of paracetamol occur?

A

Hepatocytes

149
Q

How can paracetamol be metabolised at prescribed dosage?

A

By conjugation with glucuronide or sulphate

150
Q

What happens in a paracetamol overdose?

A

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

151
Q

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

A

The toxic metabolite NAPQI accumulates

152
Q

Why is NAPQI toxic?

A

NAME?

153
Q

What are the direct toxic effects of NAPQI?

A

Oxidative damage to the liver cell

154
Q

Why does NAPQI build up deplete glutathione reserves?

A

It’s used to protect the cell against damage

155
Q

What is the result of depletion of NAPQI reserves?

A

Defences are compromised

156
Q

What is the treatment for paracetamol overdose?

A

Acetylcysteine

157
Q

How does acetylcysteine work?

A

Replenishing glutathione levels

158
Q

Where is ischaemia reperfusion injury especially relevant?

A
  • Heart
  • Brain
  • Organ transplantation
159
Q

What can happen to cells during ischaemia?

A

They can be reversibly damaged

160
Q

How can cells damaged by ischaemia recover?

A

Following restoration of blood flow

161
Q

What is the problem with reperfusion following ischaemia?

A

Can result in more damage than caused by initial ischaemia

162
Q

What is especially sensitive to reperfusion injury?

A

Mitochondria

163
Q

What causes ischaemic reperfusion injury?

A
  • 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

Z OLD ESA 1- Metabolism (17 decks)

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