ROS, ischemia and apoptosis Flashcards
How are ROS made?
Partial reduction of oxygen
Superoxide radical
O2.-
Hydroxyl radicals
OH.
Hypochlorous acid
HOCL
How are RNS formed?
reaction of superoxide with NO
Peroxynitrite
ONOO-
Is NO reactive?
No but the intermediates are
Symptoms of too many RNS
Ischemia, IBD, arthritis
Why is NO a co-oxidant?
reacts with super-oxide to form peroxynitrite which is cytotoxic to tissues, generated at inflammation
Why are ROS bad?
At high levels = mitochondrial dysfunction
When are RNS produced?
Metabolic byproducts of inflammatory diseases
How is hydrogen peroxide formed
Dismutation of O2.-
Where are free radicals made?
Mitochondria - outer/inner membrane and matrix
NADPH oxidase
- Free radical generation in neutrophils and macrophages during phagocytosis releases reactive species
- NADPH oxidases (NOX enzymes 1-5) and DUOX1 and 2 convert oxygen to superoxide
What is apoptosis?
programmed cell death
What is autophagy?
Eukaryotic cells degrade cytoplasmic material - lysosomes. Stimulated by lack of nutrients
What is necrosis?
Unregulated cell death
Apoptosis
- Tightly controlled
- Loss of intercellular junctions
- Chromatin condenses
- Cytoplasm shrinks
- Components recycled
- Phagocytosis of apoptotic bodies by neighbouring cells and macrophages
- No release of intracellular content
- Apoptotic bodies are phagocytosed
- Surface markers cause cells that ingest them to secrete anti-inflammatory cytokines
- No inflammation
Necrosis
- Results due to trauma
- Autolysis
- Loss of cell membrane integrity and losing cellular components into intercellular space
- Stimulates leukocytes etc to come and destroy cells
- Neutrophils enter site and then monocytes
- Early necrosis is reversible
- Oncosis - mitochondria damaged beyond recovery so no ATP made which disrupts ionic concentrations
- Lack of cellular homeostasis - water enters cells - cell membranes and organelles swell - autodigestion - lytic enzymes destroy content - content released into extracellular space
- Debridement removes necrotic tissue
- Infarction
- Coagulative necrosis - build up of fluid but architecture of tissue maintained - albumin forms firm state
Ischemia
- Occlusion of coronary artery
- Hypoxia: oxygen supply insufficient for demand, cause is low oxygen conc, leads to pulmonary oedema and cerebral oedema
- Ischaemia: reduction of blood supply damages oxygen sensitive tissues, caused by problems with circulatory system, leads to MI, stroke, reperfusion injury and arrythmias
- Stops Krebs cycle = lots of lactic acid = intracellular pH falls
- Na+/K+ pump causes influx of sodium
- Myocardial contraction ceases within a minute of ischemia
Reperfusion
- Re-opening of coronary artery
- Cardiomyocytes have lots of mitochondria
- Cardiolipin - lots of unsaturated fatty acids, make compound vulnerable to peroxidation
- NADPH oxidases in neutrophils, make lots of superoxide
- When ischaemia tissue reperfused, influx of oxygen catalyses xanthine oxidase to degrade hypoxanthine to uric acid and releases superoxide anion
- Hydroxide radicals = lipid peroxidation
- Influx of calcium causes cell death by hypercontracture of heart cells
What is PTP?
Depolarisation of mitochondrial membrane
Mitochondrial permeability transition pores
- PTP = depolarisation of mitochondrial membrane
- Reverses ATP synthesis to maintain membrane potential
- Activated fatty acids accumulate in myocardium
Inflammation
- During reperfusion, neutrophils adhere to endothelium and extravasate into tissue, resulting in degradation of basement membranes
- Neutrophils generate ROS = tissue degradation
- Lots of neutrophils = lots of ROS via NADPH
O2 can undergo 4 consecutive reductions
Is NO a free radical?
No
Is H2O2 a free radical?
Yes
