Reactive Oxygen Species Flashcards
What are reactive oxygen species?
Highly reactive metabolites of molecular oxygen
How are reactive oxygen species produced?
Primarily a by-product of the incomplete reduction of oxygen in the respiratory chain
How are reactive oxygen species produced?
They are a by-product of the incomplete reduction of oxygen in the respiratory chain
Examples of reactive oxygen species
Superoxide anion
Hydrogen peroxide
Hydroxyl radical
Peroxinitrite
What are NADPH oxidases?
Major source of ROS in the cell
NADPH oxidases contain how many enzymes?
They are multimeric enzymes
True or false:
There is only one isoform of the NOX catalytic subunit
False - there are many (Nox1-5, Duox1/2)
Is NOX2 active or inactive?
It exists in both active and inactive states
What ROS does NOX2 produce?
Superoxide
Is NOX4 active or inactive?
Constituently active
What ROS does NOX4 produce?
Hydrogen peroxide
NOX2 and NOX4 produce high/low levels of ROS
Low
What roles does NOX2 play in CVD?
Atherosclerotic lesion formation
Determining size of infarct after ischaemic reperfusion injury
Calcium release from SR
What does NOX4 protect the vasculature against?
Inflammatory stress
How are ROS generated from NOX2?
Physiological stretch activates activates NOX2 generating ROS
Where does ROS production take place?
Sarcolemmal and T-tubule membranes
True or false:
ROS production triggers the release of calcium sparks?
True, they are mediated via RyR in the SR
Stretch increases/decreases the frequency of sparks?
Increases
Is the activity of the RyR redox sensitive?
Yes
How is the LTCC inhibited?
By oxidation as it is redox sensitive
Free radicals inhibit/potentiate LTCC?
Inhibit
What is the effect of chemical oxidation of sodium channels?
It impairs their rapid inactivation, meaning there is a longer depolarising current, a longer action potential and this can lead to arrhythmogenesis and sodium overload
Effect of oxidants such as H2O2 on SERCA and the NCX
Inhibit SERCA
Activate NCX
How does H2O2 reduce the size of the calcium transient?
H2O2 enhances removal of calcium from cells and reduces calcium re-uptake into SR
Calcium content of SR becomes more and more empty, leading to the reduction in size of the calcium transient
What is glutathionylation?
Post-translational modification in which glutathione reversibly binds to thiol groups on proteins via disulphide bonds
What is glutathione?
A cellular reducing agent
Which subunit of the Na pump undergoes glutathionylation under oxidative stress to reduce its activity
The beta subunit
ROS are positively/negatively inotropic?
Negatively inotropic, depress cardiac contractility
How does ROS reduce the size of the calcium current?
By activating the RyR, depleting the SR of Ca
Inhibits the LTCC
How does ROS prolong the AP?
Slows the inactivation of LTCC
Which type of PKA is redox active?
Type I PKA
How is PKA I activated?
Activated by hydrogen peroxide which promotes the formation of disulphide bond between 2 regulatory subunits
Voltage gated calcium channels:
What are they phosphorylated by?
What is the effect of the phosphorylation?
Phosphorylated of Rad by PKA
Increases trigger calcium and increases CACR
RyR:
What are they phosphorylated by?
What is the effect of the phosphorylation?
Phosphorylated by PKA
Increases calcium release from SR
SERCA2a/PLB:
What is it phosphorylated by?
What is the effect of the phosphorylation?
PLB phosphorylated by PKA
Increases SERCA activity, increasing Ca reuptake into SR, increasing Ca store and gives rise to bigger calcium transients
Sodium pump:
What is it phosphorylated by?
What is the effect of the phosphorylation?
PLM phosphorylated by PKA
Increases Na efflux, preventing Na overload
Troponin I:
What is it phosphorylated by?
What is the effect of the phosphorylation?
TnI phosphorylated by PKA
Reduced affinity of TnC for Ca, reduction in contraction of cardiac muscle and accelerates relaxation
Biochemical changes ischaemia
Switch to anaerobic ATP production
Metabolite accumulation
Which metabolites accumulate in ischaemia?
Protons (cause acidosis)
Phosphate
Free radicals
Potassium
Oxidised lipids
What happens in the baroreceptor reflex?
Increased sympathetic stimulation
Increased contractility
Increased oxygen demand
How does impaired pumping accelerate glycolysis?
Briefly increases glucose uptake into myocyte
Inhibits glycogen synthetase
Activates phosphofructokinase reaction
Why does glycolysis fail under ischaemic conditions?
Lack of substrate to metabolise
Lack of oxidised NAD
Metabolic acidosis
Consequences of metabolic acidosis in ischaemica
Inhibition of NCX and RyR (this is protective)
Reduces action potential velocity
Protons compete with Ca for binding to specific sites on proteins
Acidosis occurs quickly/slowly after the onset of ischaemia
Very quickly
Acidosis occurs quickly/slowly after the onset of ischaemia
It occurs extremely rapidly
What is the primary explanation for impaired heart contractility in ischaemia?
Acidosis reduces calcium affinity, maximum tension and contractility of myofilaments
Function of NCX
Regulates intracellular pH through exchange of intracellular H+ for extracellular Na
What is HNE?
A major lipid peroxidation product formed during oxidative stress
What does HNE do?
Reacts with thiol groups on proteins altering their activities
What is the garden hose effect?
Perfusion of the intracoronary vessels has a distending effect on the cardiac muscle, distension of the cardiac muscle is positively inotropic
How does impaired relaxation arise in early and late ischaemia?
Early - inhibition of Ca efflux
Late - formation of rigor bonds
Changes to the cardiac action potential in ischaemia
Delayed activation
Slower to rise (due to less Na channels in resting state)
Slower to trigger Ca channels
Reaches threshold more slowly
AP propagates more slowly
What causes cells to die in ischaemia?
Calcium activated proteases degrade proteins and long chain AcylCoA disrupts sarcolemma
What is reperfusion injury?
Restoration of blood flow following ischaemia results in a substantial increase in number of cardiomocytes that die
What causes reperfusion injury?
Abnormal calcium handling
Oxidative stress
Mitochondrial dysfunction
Mitochondrial Permeability Transition Pore (mPTP) opening is acclelerated/decelerated by Ca and Ros
Accelerated
Myocytes appear to be ___ years younger than the person they’re from?
10 years younger
