O2 saturation of hemoglobin is mainly controlled by?
Ventilation
p(O2) is?
O2 partial pressure
p(O2) in tissues is mainly controlled by?
Blood flow
p(O2) damage can be caused by?
Too high or low p(O2)
Oxygen containing molecules can be?
Very reactive
ROS stands for?
Reactive oxygen species
ROS are?
Free radicals or their precursors
What is ROS?
Oxygen-containing molecules that oxidize substrates (lipids, proteins, DNA, etc.) to alter their function
What are free radicals?
Molecule, atom or ion containing an unpaired electron → want to find a partner (very reactive)
4 free radicals
- Superoxide
- Nitric oxide
- Hydroxyl radical
- Nitrite radical
2 very aggressive free radicals (cause most damage)
- Hydroxyl radical
2. Nitrite radical
2 free radical precursors
- Hydrogen peroxide
2. Hypochlorite ion
Fenton reaction
very important to know
2 hydrogen peroxide in presence of iron →
water + peroxide radical + hydroxyl radical
Haber-weiss reaction
Hydrogen peroxide + superoxide radical →
O2 + OH- + hydroxyl radical
Hydroxyl radical
●OH
Superoxide-NO reaction
H+ + superoxide radical + nitric oxide →
hydroxyl radical + nitrite radical
Hydrogen peroxide
H2O2
Hypochlorite anion
OCl-
Superoxide
O2●-
Nitrite radical
●NO2
MPO stands for?
Myeloperoxidase
MPO reaction
Hydrogen peroxide + chloride anion →MPO→
hypochlorite anion + water
Hypochlorite-iron reaction
H+ + OCl- + Fe2+ →
Fe3+ + Cl- + hydroxyl radical
Hypochlorite-superoxide reaction
H+ + OCl- + superoxide radical →
O2 + Cl- + hydroxyl radical
Free radical chain reaction
R1● donates unpaired electron to substrate R2 → forms free radical R2●
Free radical chain reaction speeds up when?
Highly reactive radicals formed
Free radical chain reaction slows down when?
Unreactive radicals are formed
Free radical terminal reaction
R1● (macromolecule radical) + R2● (aggressive radical) →oxidation or nitration→ R1-R2
5 sources of ROS
- Ionizing radiation
- Metal catalysts
- ROS reactions
- Metabolism
- Enzymatic catalysts
3 ways ionizing radiation causes ROS
- Radon disintegration
- X-ray
- Cosmic rays
Example of metal catalyst which can cause ROS
Fe2+
Enzymatic catalysts which can form ROS
- NADPH oxidases
- Myeloperoxidase (MPO)
- Nitric oxide synthase
NADPH oxidases found in?
- Neutrophils
2. Macrophages
Myeloperoxidases found in?
Neutrophils
NO synthase found in?
Endothelial cells
Mitochondria generates superoxide as byproduct of?
Electron transport by ubiquinon-cycle (UQ)
What injury is mediated by free radicals?
Ischemia / reperfusion
What does mitochondria generate after ischemia?
ROS burst
NOX stands for?
NADPH-oxidase
Initial activation of neutrophil leads to?
Fusion of vesicles containing NOX
NOX associates with?
Required accessory proteins including RAC
What is RAC?
Small G-protein
Completely assembled NOX-RAC complex uses ____ to generate ___ from?
Uses NADPH to generate superoxide radical from O2
Superoxide radical dimutates to?
Hydrogen peroxide (spontaneous or facilitated by SOD)
SOD stands for?
Superoxide dismutase
Further activation of neutrophil leads to?
Fusion of vesicles containing MPO
MPO makes?
Hydrogen peroxide + chloride anion → hypochlorite
Hypochlorite
OCl- (bleach)
Superoxide radical + hypochlorite forms?
Hydroxyl radical
Hydroxyl radical and superoxide radical do what?
Kill bacteria
SOD catalyzes?
Superoxide radical → hydrogen peroxidation
How do ROS damage lipids?
Damage membranes → ionic gradients collapse and enzymes spill
How do ROS damage proteins?
- Failing enzymes
- Failing transporters
- Failing cell function
- Failing cell signaling
How do ROS damage DNA?
- Altered expression
- Failure to protect
- Failure to repair
CAT stands for?
Catalase
GSH is?
Reduced glutathione
GSSG is?
Oxidized glutathione
CAT catalyzes?
2 hydrogen peroxide → O2 + H2O
SOD / CAT defense
SOD converted superoxide radical to hydrogen peroxide → CAT converts hydrogen peroxide to oxygen and water
Glutathione cycle
Hydrogen peroxide + 2 GSH → GSSG + 2 H2O
GSSG regenerated
How is GSSG regenerated?
GSSG + 2 NADPH → 2 GSH + 2 NADP+
What catalyzes hydrogen peroxide + 2 GSH → GSSG
Glutathione peroxidase
What catalyzes GSSG → 2 GSH
Glutathione reductase
Iron is bound to?
Transferrin
2 transferrins store?
2 iron atoms
Iron uptake into cell is guarded by?
Transferrin receptor
Iron is stored how?
Ferritin
Asc stands for?
Ascorbic acid
Asc cycle against free radicals
R● + Asc → Asc● + R
Asc● + Asc● → Asc + DH-Asc
DH-ASc stands for?
Non-toxic dehydro-ascorbate
1st step of Asc cycle
Asc reacts with R● and becomes free radical Asc●
2nd step of Asc cycle
2 Asc● combine → break down unevenly into Asc and DH-Asc
4 defenses against ROS
- SOD/CAT (Superoxide dismutase / Catalase)
- Glutathione cycle
- Iron control
- Antioxidants (ex: Asc)
2 types of oxygen sensing
- Central sensors
2. Peripheral sensors
Central sensors are located in?
Brain
Peripheral sensors are located in?
- Carotid bodies
2. Aortic bodies
Control center of oxygen sensing
Brain stem (medulla)
Effectors
Respiratory mm. control depth and frequency of breathing
Peripheral sensory cells are called?
Glomus cells
Glomus cells are innervated by?
CN IX afferent dendrites
3 sensors for p(O2)
- Cell membrane heme-protein
- ATP production in mitochondria maintains low AMP in cytosol
- Superoxide radical production by cytosolic NOX
Heme-protein at normal p(O2)
Bound to O2, keeps K+ channels open
Heme-protein at low p(O2)
Empty, closes K+ channels
ATP production in mitochondria at normal p(O2)
Low AMP keeps AMP-kinase inactive
ATP production in mitochondria at low p(O2)
High AMP via AMP-kinase cause K+ channels to close
Superoxide radical production by cytosolic NOX at normal p(O2)
Superoxide radical oxidizes K+ channels (keeps channels open)
Superoxide radical production by cytosolic NOX at low p(O2)
Less superoxide radical causes K+ channels closed
Inhibition of K+ channels causes?
Depolarization of membrane potential
Depolarization of membrane potential causes?
Opens voltage-gated Ca2+ channel
Open voltage-gated Ca+ channel allows?
Influx of Ca2+
Elevation of Ca2+ initiates?
Release of neurotransmitters Ach and dopamine
Released neurotransmitters do what?
Activate afferent dendrites of CN IX
Activated CN IX activates?
Respiratory center in medulla of brainstem
HIF-1 stands for?
Hypoxia inducible factor
HIF-1 senses?
O2
Under hypoxia, HIF-1 does what?
Upregulates expression of genes that help cells return to normoxia
Examples of genes HIF-1 upregulates under hypxoia
- Lactate DHN
- GLUT1
- EPO
- VEGF
Lactate DHN is involved in what process?
Glycolysis
GLUT1 is involved in what process?
Glucose uptake
EPO is involved in what process?
Erythropoiesis
VEGF is involved in what process?
Angiogenesis (making new vessels)
In presence of O2, what happens to HIF-1alpha?
HIF-1alpha hydroxylated by prolyl-hydroxylases
What happens to hydroxylated HIF-1alpa?
Ubiquinated → marked for destruction in proteosomes
Under hypoxia, HIF-1alpha survives and does what?
Moves to nucleus → interacts with accessory subunit HIF-1beta and transcription factors → initiates gene transcription
Transcription factors involved with HIF-1
- p300
2. CBP