Oxidative stress Flashcards
What is Oxidative stress
Oxidative stress reflects an imbalance between reactive oxygen species and a biological systems ability to detoxify them or to repair the resulting damage
More ROS than the cell can tolerate
What are ROS?
ROS are damaging chemical entities, often very reactive and short lived, that react with and damage other biological molecules
How is the cellular state of oxidative stress described?
Increased generation of free radicals, and ROS in excess of antioxidant defences
Why is an increase in free radicals and ROS bad?
They can potentially damage macromolecules including DNA, proteins and lipids
What are free radicals?
Are molecules with one or more unpaired electrons —-> highly unstable and reactive
Their types include ROS and RNS
What are some examples of free radicals?
- Superoxide radical
- Hydrogen peroxide
- Hydroxyl radical
- Nitric oxide radical
What are the sources of ROS?
Some are inevitable/accidental by products of chemical reactions involving oxygen
What have cells adapted in regards to producing ROS?
Cells have evolved enzymes to produce ROS with specific biochemical purposes
e.g. NADPH oxidase to kill microbes
What are the endogenous sources of ROS?
- Some ROS- inevitable/accidental by products (mitochondria)
- Evolved specifically to produce ROS (NADPH oxidase)
What type of cells generate large amounts of ROS?
Phagocytes (Neutrophils and Macrophages)- white blood cells generating ROS to kill microbes trapped/eaten by the phagocytes
How are ROS usually removed?
Inside of most cells = high concentration of passive redox buffers and active antioxidant defences which in combination use energy to remove ROS
Why is it hard to experiment with ROS?
If biological molecules are removed from the cellular reducing environment, it is hard to stop them rapidly oxidising in the lab before analyzing them
Typically, how are ROS measured?
Localised ROS probes with rapid kinetics can show where in cells ROS are generated
How are free radicals produced from mitochondria?
If electrons leak during aerobic respiration then 0.2% of total daily oxygen consumption is converted to ROS
What happens during phagocytosis with regards to ROS?
There is a large increase in oxygen uptake by neutrophils and most macrophages through activation of an NDPH-oxidase that reduces oxygen to superoxide (oxidative burst)
What happens to the individuals with a defect in the NADPH-oxidase?
granulomatous disease (chronic)
Often die as a result of recurrent bacterial infection
Almost all cells have an active NADPH-oxidase complex
What is the problem with ROS during phagocytosis?
ROS are secreted into the phagosome to kill bacteria. However, many ROS freely diffuse through membranes
What cellular biomolecules do ROS damage?
Damaged lipids and proteins must be re-synthesised
DNA is less reactive and resistant to damage and is repaired
However, unrepaired damage can lead to mutations
How common is oxidative DNA damage?
estimated at 10,000 events per cell per day
slow accumulation of mutations = aging
How do ROS damage proteins?
Cysteine oxidation: a sulphur switch
The sulphur in a cysteine amino acid can be oxidised to several higher oxidation states, so cysteine can be reversibly oxidised to many forms
This changes protein function
What is Cysteine?
Cysteine is a naturally occurring amino acids incorporated into most proteins
Contains a sulphur containing sidechain making it sensitive to oxidation
What’s the difference between reversible and irreversible?
Reversible- regulation
Irreversible- Probably damage
What diseases are associated with protein oxidative damage?
-Neurodegenerative diseases
-Muscular dystrophy
-Rheumatoid arthritis
What are the exogenous sources of free radicals?
-Air pollution
-Radiation
-Cigarette smoke
-UV exposure
-Alcohol consumption
-Anticancer drugs
-Exposure to heavy metals
What are antioxidants?
The first line of defence against free radical-induced cellular damage
Categorized into enzymatic and non enzymatic
What are the non-enzymatic Antioxidants (redox buffers)?
Glutathione- most important intracellular defence against ROS
Vitamin E- Major lipid soluble antioxidant
What are the enzymatic antioxidants?
Superoxide Dismutase- superoxide into oxygen and hydrogen peroxide
Catalase- hydrogen peroxide into water and oxygen
Glutathione Peroxidase- Hydrogen peroxide to water