Oxidative Stress and Anti-Oxidants Flashcards
(163 cards)
1
Q
What causes cellular damage?
A
ROS and RNS
2
Q
What is cellular damage by ROS and RNS a significant component in?
A
A wide range of disease states
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
4
Q
How do the electrons of atoms, molecules and ions usually associate?
A
In pairs
5
Q
How does each pair of electrons move?
A
Within a defined region of space- an orbital
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
7
Q
What is used to denote a free radical?
A
A superscript dot
8
Q
Are free radicals reactive or inert?
A
Yes, usually very reactive
9
Q
What do free radicals tend to do?
A
Acquire electrons from other atoms, molecules or ions
10
Q
Why are free radicals damaging?
A
Because they want to get electrons from another molecule
11
Q
What does a reaction of a radical with a molecule typically generate?
A
A second radical
12
Q
What is the result of a reaction of a radical with a molecule typically generating a second radical?
A
It propagates damage
13
Q
What does ROS stand for?
A
Reactive oxygen species
14
Q
What are the ROS?
A
- Molecular oxygen
- Superoxide
- Hydrogen peroxide
- Hydroxyl radical
15
Q
Regarding radicals, what is molecular oxygen?
A
Biradical
16
Q
What is meant by molecular oxygen being biradical?
A
It has 2 unpaired electrons in different orbitals
17
Q
What is superoxide?
A
O 2 º -
18
Q
When is superoxide produced?
A
When one electron is added to molecular oxygen
19
Q
Why is superoxide important?
A
It’s an important source of other ROS
20
Q
What is hydrogen peroxide?
A
H 2 O 2 -
21
Q
How is hydrogen peroxide formed?
A
Adding 2H + and e - to superoxide
22
Q
Is hydrogen peroxide a free radical?
A
No, but can react to produce free radicals
23
Q
Is hydrogen peroxide readily diffusible?
A
Yes
24
Q
What is the most reactive and damaging free radical?
A
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
