Oxidative Stress Flashcards
Define free radicals
An atom or molecule that contains one or more unpaired electron and is capable of ‘free’ existence.
Which molecules is the free radical exception?
The molecular oxygen that we breathe. Has 2 unpaired electrons but not highly reactive to the same extent.
Name the reactive nitrogen species
nitric oxide (NO.) and peroxynitrite (ONOO-)
What is nitric oxide used for?
vasodilation and immune response in high concs
What is the most reactive and damaging free radical?
Hydroxyl radical (OH.)
Why is hydrogen peroxide dangerous?
readily diffusible and can react to produce very damaging free radicals
How can ROS damage DNA?
react with base: mispairing and mutation
react with sugar: strand break and mutation on repair
What is 8-oxo-dG used for?
Measurement of oxidative damage within the cell
How can ROS damage proteins?
damage backbone: fragmentation and degradation
react with side chain: modified amino acids
What can a change in protein structure cause?
gain of function, loss of function and degradation
Where do disulfide bonds form?
Between thiol groups of cysteine residues
What can inappropriate disulfide bond formation lead to?
misfolding, cross-linking, disruption of function
How does ROS damage lipids?
free radical extract hydrogen atom from unsaturated FA, lipid radical formed, react with oxygen to produce a lipid peroxyl radical, chain reaction disrupts hydrophobic environment
Name the endogenous oxidant sources
electron transport chain, nitric oxide synthases and NADPH oxidases
Name the exogenous sources of oxidants
radiation, pollutants, drugs and toxins
How many types of nitric oxide synthases are there and which one is most important?
3 types, iNOS is most important: oxidative burst in phagocytes
What is an oxidative burst?
The rapid released of ROS and RNS from phagocytic cells to destroy invading bacteria.
Which enzymes are important in oxidative burst?
NADPH oxidase, iNOS, myeloperoxidase
Which enzymes work together as a cellular defence against oxidative damage?
superoxide dismutase and catalase
What is the function of superoxide dismutase?
converts superoxide to hydrogen peroxide and oxygen and stops superoxide initiating a chain reaction
Where is SOD expressed most?
In mitochondria to mop of superoxides from ETC
What is the function of catalase?
converts hydrogen peroxide to water and oxygen and protects against oxidative burst
How does glutathione work?
thiol group of Cys residue donates electron to ROS, two GSHs react to form GSSG via the enzyme glutathione peroxidase
How is GSSG reduced back to GSH?
glutathione reductase, transfers electrons from NADPH to disulfide bond to break it
Which vitamins are free radical scavengers?
vitamin E and vitamin C
How do vitamins protect against oxidative damage?
vitamin E is oxidised to prevent lipids being oxidised and vitamin C regenerates the reduced formed of vitamin E
Do for vitamins require enzymes to protect against oxidative damage?
No
The reactions are non-enzymatic
Name 2 other free radical scavengers
uric acid and melatonin
What happens in galactosaemia that makes the patient susceptible to oxidative damage?
increased activity of aldose reductase, more NADPH consumed, less NADPH available to reduce glutathione (GSSG), compromised defence against ROS
Which enzymes can be deficient in galactosaemia?
galactokinase, galactose-1-P uridyl transferase, UDP-galactose-epimerase
How could G6PDH deficiency affect oxidative stress?
less pentose phosphate pathway, limits amount of NADPH produced, less NADPH available for reducing glutathione, more susceptible to oxidative damage
How is paracetamol normally metabolised?
Safely metabolised through conjugation with sulphate or glucuronide
What usually reduces the effects of NAPQI?
Glutathione
How does N-acetylcysteine work?
It boosts glutathione levels so cells are less susceptible to oxidative damage and levels of NAPQI can be reduced.
What is ischaemia reperfusion injury?
Reperfusion of oxygenated blood after ischaemia that results in more damage.
Why does the reperfusion injury occur?
ROS are produced due to incomplete metabolism and antioxidants are lost in ischaemia
Name some diseases that can result from oxidative stress
multiple sclerosis, Parkinson’s, cancer, rheumatoid arthritis, COPD, pancreatitis
