ROS Flashcards
what Conditions are Implicated by ROS in Pathogenesis?
Alcoholic liver disease Atherosclerosis Cancer Emphysema Inflammatory disease Ischaemia Reperfusion injury Neurological disorders
what is the definition of ROS?
Very reactive oxidant containing oxygen
Often a free radical
what is the definition of oxidant?
Substance that causes oxidation,
i.e. removal of hydrogen atoms or electrons, or addition of oxygen
what is the definition of free radical?
Species with unpaired electron that can exist independently
Often highly reactive
Tend to set up chain reactions
Orbital occupied by a single electron
Very reactive = short lived and hard to detect Independent of charge (-/+/uncharged)
Just because unpaired doesn’t mean it has to be +/-
why are free radicals reactive?
unpaired electron is unstable -> free radical eager to lose it or gain one
how common are free radicals?
Relatively uncommon -> more likely to encounter and react with non-radical than radical
what is the mechanism of reaction of free radicals?
1) Radical + non radical
2) odd electron unable to find partner
3) production of new radical
4) Chain reaction
5) Radical + free radical
6) odd electrons pair up
7) production of non-radicals
how do you quench free radical chain reactions?
Antioxidants (vit c+e)
Vit c = non radical
throws up 2 free and mops up 2 free radicals
how does ionising radiation cause free radicals?
cells 70% water
water a target for radiation
Hydroxyl Radical + Hydrogen Radical
what sources of ROS are there in healthy individuals?
OH radical - the worst kind
what sources of ionising radiation are there?
Natural radioactivity in soil
nuclear tests/accidents
space
why are Hydroxyl radical and hydrogen radicals from ionising radiation dangerous?
attack DNA/proteins in membranes
what Processes are ROS by-products of metabolic activity?
Respiratory chain – electron transport chain. Tendency for electrons to fall off and attach to oxygens = super oxide
Metabolism of xenobiotics
Eicosanoid (prostaglandins etc.) production
what cases of deliberate ROS production are there?
nitric oxide – chemical signalling molecule
Control of vascular tone
what ROS toxins are there?
nitrogen dioxide – motor vehicle exhaust fumes
Chemicals that are metabolised into ROS inside us e.g. carbon tetrachloride.
Metabolism may lead to coincidental ROS production e.g. alcohol (high concentrations)
Cigarette smoke contains chemicals in all 3 chemicals
what is the significance of ROS production in disease?
Overall effect:
General increase in ROS production
Increase in proportion of more dangerous forms
what is the aim of the respiratory burst?
production of microcidal agents
what cells are involved in the respiratory burst?
phagocytes i.e. neutrophils and macrophages
what is the trigger of the respiratory burst?
initiation of phagocytosis, i.e. when cell attempts to ingest foreign material, damaged tissue etc.
what is the process of the respiratory burst?
1) Initiation of phagocytosis
2) NADPH oxidase activated in phagosome membrane
3) release of superoxide ROS into phagosome
4) spontaneous conversion of superoxide
5) hydrogen peroxide (ROS)
Fast enough to go without an enzyme
what are the 2 fates of hydrogen peroxide in the respiratory burst?
Catalase -> water
OR
Myeloperoxidase -> hypochlorous acid (microcidal- bleach)
describe an inherited defect of NADPH oxidase
no bleach – no myeloperoxidase – more susceptible to infection
what further reactions occur in the respiratory burst?
coincidental production of superoxide, hydrogen peroxide and hypochlorous acid
what is the significance of disease processes in ROS production?
presence of increaed levels of substances that react with these ROS, e.g. free iron and nitric oxide
what happens when disease processes increase levels of substances that react with ROS?
potential to generate very dangerous ROS e.g. hydroxyl radicals
what risks/problems are associated with ROS?
- Cant ensure ROS will react with desired target
- Potential for damage to cell components
- Can be inactivated inappropriately e.g. in autoimmune disease
what happens if the vesicle becomes too damaged by ROS?
can release contents into cell cytosol
what happens if the phagocyte is unable to envelope material to be ingested?
process accelerates = overproduction of ROS
what are the risks of the release of free iron and copper?
Fe2+) & (Cu+
react with hydrogen peroxide and lipid peroxides -> hydroxyl radicals and lipid peroxyl radicals respectively
when can iron and copper react to form free radicals?
Can only react if they are free – not bound to proteins.
what natural defences are there to prevent iron and copper reacting to form free radicals?
Antioxidant defences e.g. ferritin and transferrin– don’t let iron and cu become free
why is free iron and copper related to disease? 3 reasons
1) Tissue injury may release of iron from cell proteins that contain it
2) Low blood pH release of iron and copper from blood transport proteins. pH 7 deigned to hold on, pH5 designed to let go for cells – if pH drops then it will start to let go so free iron and copper
3) Some diseases cause iron overload = more free iron
how does the starvation and restoration of oxygen to tissues affect ROS?
possibility that metabolic changes during period of hypoxia prime cells for ROS production when oxygen supply restored
how does inflammation cause ROS production?
Inflammation= increase in eicosanoids
- potential to leak ROS. Increase in production = increase in ROS
Active phagocytes generate NITRIC OXIDE
how do cytokines cause ROS production?
Cytokines (signalling molecules) and lipopolysaccharide (bacterial product) increase NITRIC OXIDE production by endothelial and smooth muscle cells (line blood vessels)
how do inhibitors of protein degrading enzymes contribute to protein damage?
may contribute to development of emphysema due to failure to block protein breakdown
you need to Keep protein digesting enzymes under control so only digest when needed. ROS attacks can damage inhibitors and stop them working so digestive enzymes get out of hand
what are the consequences of protein damage?
loss of function and/or make protein liable to attack by protein degrading enzymes.
Especially –SH groups – enzyme is dead.
Cell recognises it is damaged. If damage is significant – protein is degraded instead of repaired so leads to loss of function – level of protein goes down
how are extracellular matrix proteins damaged?
may contribute to tissue destruction in inflammatory arthiritis
how are extracellular matrix proteins damaged?
may contribute to tissue destruction in inflammatory arthritis
what is the significance of Apo B-100 in protein damage?
important in development of atherosclerosis.
Ensures cholesterol carried by LDL can get out.
Scavenger cells build up cholesterol and foam cells – lead to an atherosclerotic plaque.
Macrophages take up cholesterol carrying lipoproteins leads to this
what is lipid peroxidation?
When fat is attacked by free radicals
what kind of fat is attacked in lipid peroxidation?
Poly unsaturated. only does it with 2 or more double bonds - not monounsaturated e.g. olive oil.
how does lipid peroxidation occur?
1) Free radical attacks polyunsaturated acid
2) lipid peroxyl radical is formed
3) lipid peroxyl radical reacts with another polyunsaturated fatty acid
4) lipid peroxide + new lipid radical formed
what are the consequences of lipid peroxidation?
Changes nature of what makes up the membrane
Lipid peroxides behave differently to parent polyunsaturated
leads to altered protein behaviour
Ability to transport changes
what determines the extent of lipid peroxidation damage?
length of time of chain reaction
If not much poly in membrane or stopped early then not too bad. Even small lipid peroxide can change fluidity
what happens if lipid peroxidation is generated in large amounts or goes on for a long time?
membrane unstable and breaks which Kills the cell
Cell lyses and dies, contents released into cytosol
what happens if lipid radicals react with membrane rect with membrane proteins or DNA?
more damage
what is the mechanism of damage when ROS attacks DNA base?
- attempted repair
- either successful repair
- altered base (gene mutation)
what is the usual outcome of DNA ROS damage?
successful repair
what is the mechanism of damage when ROS attacks DNA backbone (strand break)?
- attempted repair
- either successful repair
- deletion, inversion, translocation (chromosome mutation)
what would be a reason for being unable to repair DNA damage? and what is a consequence?
lack of repair enzyme (genetic defect)
increase risk of cancer
what is oxidative stress in terms of antioxidants?
Condition where ROS production exceeds capacity of antioxidant defence systems = increase in chance of ROS-mediated damage
what does oxidative stress result from?
increase in ROS production amd/or failure of antioxidant defence systems
what does an increase in ROS do to vitamin c?
depletion of dietary antioxidants, e.g. vitamin C
where in the body are antioxidants?
All tissues, intracellularly, extracellularly, aqueous and lipid phases
what do antioxidants do?
prevent ROS formation, terminate chain reactions, repair damage etc
which antioxidants act directly?
dietary vitamin c and e
which antioxidants act indirectly?
selenium, play key role in function of antioxidant enzymes
