Ischemia Reperfusion Flashcards
Human brain is _____/______ in terms of energy use
expensive/inefficient
The human brain is only ___% of total body weight but uses ___ % of energy consumed
2%, 20%
ATP consumption per gm/min used in signaling is equal to
energy used by leg muscle to complete a marathon
Approx. ___% of the ATP consumption of the brain is used for signaling, and ____% is used for maintaining essential cellular activity
75%, 25%
Metabolic rates of the brain are higher in ____ matter than in ____ matter
Higher in gray matter than in white matter
energy rich substrates enter the brain from blood via
blood brain barrier
Endothelial cells of Blood brain barrier and brain cells have transporter for uptake of ____ and _____
glucose and moncarboxylic acids
cerebral metabolic rate ______ during early development and ______ after maturation
increases, plateaus
Transporters are unique to _______, and determine specific ____ used by them
different cell types, substrates
Transporters of endothelial cells and brain cells are altered during
development and under pathological conditions
__________ (_________) shows that carbohydrate oxidation is the main source of energy in brain
respiratory quotient (CO2 produced/O2 consumed)
_____, ______, ______ (____) and ______ ( _______ and _____) are utilized by the brain for energy
Glucose, Glycogen, moncarboxylic acids (lactate) and ketone bodies (acetoacetate and betahydroxy butyrate)
Respiratory quotient (CO2 produced / O2 consumed) shows that _______ _______ is the main source of energy in the brain
carbohydrate oxidation
_____ is essentail for brain, most important energy source for adult brain
Glucose
______ is important to brain during immediate post natal period
lactate
_____ are used by brain during suckling due to high fat content of milk
Ketone bodies
______ is actively utilized by nerve cells (2% of total metabolic rate compared to glucose)
Glycogen
______ continuous cerebral circulation is required to sustain brain function
Continuous
Both excitatory and inhibitory neurons consume ________ energy
equivalent
oxygen concentration in cerebral venous blood is _____ than in cerebral arterial blood
lower
high extortion of O2 by brain cells (___-____%) while glucose extracted is only ____%
(50-70%), 10%
What are the metabolic pathways of the brain
- Glycolysis
- Glycogenolysis
- Pentose phosphate shunt
- Malate Aspartate shuttle
- TCA cycle
What is the excitatory neural transmitter in cerebellar granule neurons
glutamate
what is the inhibitory neurotransmitter in cortical neurons
GABA
What are the experimental models for brain research
- Primary neuronal cultures or co-cultures
- Cell lines
- Brian
- Isolated organelles
- Synaptosomes
- Mitochondria
- Cytosol
- Brain slice cultures
- Isolated organelles
- surgical methods performed in live animals
- in vivo imaging techniques (humans)
What are some of the isolated brain organelles used in experimental models
- synaptosomes
- mitochondria
- Cytosol
Examples of surgical methods of experimental model in animals
- Middle cerebral artery occlusion- focal ischemia
- Carotid Artery occlusion- Global occlusion
Carotid artery occlusion is an example of a
global occulsion
Middle cerebral artery occlusion is an example of a
focal ischemia
examples of in vivo imagine techniques used of experimental models of the brain
MRI, CT, PET scan
Metabolic studies in brain: imaging and spectroscopy
- global imaging of whole brain: brain metabolic rates with assays of artery-venous differences
- Glucose and oxygen primary fuels
- Various analogs used
- Useful technique, but effect averages out across various brain structures. Changes in small structures not detectable
What does PET imaging stand for
Positron Emission Tomography
Local rates of glucose and O2 utilization can be measured by
PET imaging (positron emission tomography)
PET imaging uses analogs of _____ (_____, in experimental animals) and _______ (in humans)
glucose (2-deoxy glucose, in experimental animals) and 2-fluoro-deoxy glucose (in humans)
PET imaging rely on
quantitative intracellular trapping of the major phosphorylated metabolite DG-6-phosphate, which enables assays of hexokinase reaction in all regions of the brain in conscious individuals
MRS (Magnetic resonance spectroscopy ) utilizes ____ labeled with radioactive (___, ____, ____) or stable isotope (___)
glucose labeled with radioactive (3H, 14C, 11C) or stable isotope (13C) (note that the numbers before the litters suggest there atomic number)
MRS allows assessment of glucose metabolites as they are
formed in different pathways
MRS is used to determine metabolism of precursors via
specific neuronal and glial pathways
MRS allows for method-NMR spectra to be obtained. each very _____ and ____
characteristic and unique
Brain engr. metabolism has what unique features
- High metabolic rate
- Limited intrinsic energy stores
- Critical dependence on circulation to provide glucose and other fuels
_______ techniques are useful for studying brain metabolism in humans
in Vivo imaging
According to WHO, ___ million people has stroke each year, ____ million of whom die
15, 6
Ischemia and brain infarct is the ___ leading cause of death and disabilities worldwide
2nd
___ good treatments for stroke available
No
Outcome of brain infarct depends on
which particular part of the brain and which cell types affected
What are the two types of ischemia
Focal cerebral ischemia
Global cerebral ischemia
Focal cerebral ischemia
focal disruption of blood flow to a part of the brain (e.g. due to occlusion of an artery by an embolus)
Global cerebral ischemia
Transient impairment of blood flow to whole brain (e.g. during cardiac arrest)
What kind of ischemia accounts for the majority of strokes
Focal cerebral ischemia
The are of infarction in a focal ischemia is typically ____ than the entire distribution of the occluded artery due to what factor
less, due to collateral circulation
Injury of a focal ischemia depend on
duration and degree of vascular occlusion and the magnitude of collateral blood supply
What is the ischemic core or umbra seen in focal ischemia
injury grows over time-electrophysiological, molecular, metabolic, and perfusion disturbances in the area
What is the rim/area surrounding ischemic core (umbra) is ________. What are its characteristics
penumbra
an area of reduced cerebral flow, impaired protein synthesis, preserved energy metabolism
Prompt restoration of perfusion in penumbra by injection of ________ agents is key to minimizing damage in this region
thrombolytic
In actue case of focal ischemia the focus is on saving the ______
penumbra
The window of opportunity to save the penumbra is
short
if adequate blood supply is not established within ___ hours necrosis extends to penumbra ( area of reversible damage )
3 hours
Transient loss of blood flow to the entire brain as in cardiac arrest followed by resuscitation
Global ischemia
neurons are ____ sensitive than glial cells to global ischemia
more
Neurons present within same vascular position and juxtaposed to each other may be selectively ______ or _______ to insult
vulnerable or resistance
What cells have the highest vulnerability to global ischemia
- Hippocampal pyramidal cells of CA 1 region
- Pyramidal neocortical neurons (layer 3,5, and 6)
- Purkinje cells
- Striatal neurons
What cells are most resistant to global ischemia
- CA3 in hippocampus
- Granule cells
biochemistry of ischemia
- Disruption of blood flow
- Reduction or absence of O2 and glucose supply to brain
- Impaired energy metabolism
- Reduction of ATP metabolism
- Ion pump dysfunction (pumps need ATP)
- Disruption of ion gradients
- Membrane depolarization
- Opening of voltage-gated channels
- Cascade of subsequent signaling events
- Cell death in a given brain region
Fall in _____ leads to enhanced lactate production (Pasteur effect)
PO2
What is the pasteur effect
fall in PO2 leads to enhanced lactate production
During an ischemic episode cells move from _____ metabolism to _____
Aerobic metabolism, glycolysis
lactic acidosis caused by ischemic episode reduces pH of cells from ___ to ___-____-
7.3 to 6.8-6.2
During ischemic episode there is an efflux of ___ through __ channels
potassium through potassium channels
During an ischemic episode ____ or ____ propagates in brain tissue
cellular depolarization or ‘spreading depression’
During an ischemic episode ____ and ____ gradients collapse
Na+ and Ca2+
during an ischemic episode Voltage gated _____ channels open allowing influx of ___ into the cell
Ca2+, Ca2+
The influx of Ca2+ into a cell after an ischemic episode leads to
release of NT
Both ____ and ____/_____ over activation contribute to excitotoxicity
NMDA and AMPA/Kainate
In excitotoxic injury loss of ion gradients leads to
build up of extracellular glutamate
During an excitotoxic injury the activation of glutamate receptors causes an ______ and ____
influx of calcium, Zn2+
During an excitotoxic injury elevated intracellular Ca2+ causes release of ___ thus leading to
Neurotransmitters- levels of extracellular neurotransmitters rise
The increased levels of extracellular neurotransmitters leads to
impaired glutamate uptake and excess release
The influx of Ca2+ and Zn2+ due to excitotoxic injury activates
cytotoxic intracellular pathways
Mechanisms of excitotoxic injury
- Prolonged availability of glutamate
- Lethal derangements of ions
- Sustained elevation in intracellular calcium
- Activation of Calpain-Degrades cytoskeleton
- Damage to mitochondria, impaired energy
- Activation of NOS-Generation of NO and ROS (reactive oxygen species) (these lead to neuronal necrosis)
- Activation of Phospholipase A2, formation of arachidonic acid, cyclooxygenases, lipoxygenases
- Formation of lipid free radicals
- membrane damage
DAPK1 is linked with ____ receptor toxicity in stroke damage. explain
NMDA.
- after a stroke, the increased extracellular concentration of glutamate causes overflow of synaptic glutamate and excitotoxic activation of extra-synaptic NMDARs. The increase in Ca2+ influx through NR2B-containing activates DAPK1 (death-associated protein kinase 1) and sequentially ing to NMDA receptor NR2B subunit, leading to neuronal cell death
Injected _____ intravenously 2 hours after a stoke can protect against brain damage and improve neurological functions by inhibiting the binding of DAPK1 to NR2B subunit
NR2B CT
What are some examples of injuries of reperfusion
- ROS (reactive oxygen species)
- Microvascular injury and Edema
- Ischemic Apoptosis
How are reactive oxygen species formed after ischemic episode
- High amounts of polyunsaturated fatty acids (PUFA) in neuronal membrane
- Presence of high concentration of iron in certain brain regions (ex. substantial nigra)
- sensitive to lipid peroxidation
- Mitochondria donate electrons to O2
- forms ROS such as superoxide free radicals and hydroxyl free radicals , H2O2, and ONOO-
Unpaired electrons are very
reactive
Unpaired electrons (such as in ROS) react with
proteins, lipids, and DNA
ROS cause _____ and _____ changes in biomolecules thus leading to cellular _____ and eventually cell ____
structural and functional, dysfunction and eventually cell death
Blood brain barrier permeability increased at ____ min after reperfusion
15 min
Acute disruption of blood brain barrier occurs after ____ post reperfusion
3-5 hours
Damage to BBB (blood brain barrier) caused by reperfusion can lead to _____ cell death and promotes adhesion of ______ thus leading to
endothelial cell death, promotes adhesion of leukocytes thus leading to vessel plugging
____ ________ also contribute to BBB damage after reperfusion
matrix metalloproteinases
The damage to the BBB caused by reperfusion promotes _____ transformation and entry of _____ and _____ factors thus leading to _____ further secondary injury
hemorrhagic transformation, cytokines and pro-inflammatory factors
edema
After microvascular injury due to reperfusion what is the secondary injury
Edema
Ischemic apoptosis
- programmed cell death
- Deprivation of growth factor support
- Oxidative stress
- Exposure of inflammatory cytokines
- Damage to micochondria
What is the extrinsic pathway for apoptosis
- Activation of death receptor (Fas) promotes formation of multi protein DISC that includes the receptor adaptor (FADD)
- DISC is the site of activation for Procaspase-8
- Propaspase-8 Becomes active by oligomerization (active form Caspase-8)
- Caspase-8 can directly activate capase-3, an effector caspase
- Caspase-8 aslo cleaves proapoptotic BID into tBID, which translocates to mitochondria to execute apoptosis
What is the intrinsic pathway for apoptosis
- Excessive influx of calcium into cytoplasm causes disruption of normal homeostasis
- Affects the function of mitochondria and ER
- Altered activity of protein phosphatase (e.g. calcineurin) causes translocation of BAD to promote mitochondria apoptotic pathway
- The release of cytochrome C from mitochondrial inter membrane space results in caspase-3 activation via apoptosome complex
- The AIF is released form mitochondria and is translocated to the nucleus
- ER undergoes stress upon depletion of calcium form its lumen. ER stress induces activation of capsize 12, capsize-9, and capsize-3
- Moreover, efflux of calcium form ER might trigger secondary activation of mitochondria. Anti- and pro- apoptotic Bcl-2 family members are localized to both the mitochondria and the ER
- Caspases cleave key structural components of the cytoskeleton and nucleus, a characteristic feature of apoptosis
Neuroprotective strategies: Multiprong approach
- Thrombolytics
- NMDA receptor antagonists
- GABA agonists
- Protein synthesis inhibitors (e.x. cycloheximide)
- Caspase inhibitors
- Omega 3 fatty acids (DHA)
- Heat shock response (bind proteins and keep them form being harmed)
- Antioxidants- free radical scavengers, e.x. Spin traps
- Growth factors- basic fibroblast growth factor
- Neurotrophins
risks of tPA
may cause fatal edema or intracranial hemorhage
DHA is an
omega 3 fatty acid
DHA is involved in ____ and ____ development
brain and retinal
DHA functions in important in memory and synaptic function
True
DHA treatment has been beneficial for patients with
CAD, cancer, and RA
DHA is protective in ____ and ____
ischemia and spinal cord injury
DHA is a precursor of ____
NPD1
a docosanoid called neuropectin or NPD1 acts functions
acts against apoptosis, promotes cell survival, inhibits brain ischemia, inhibits reperfusion mediated leukocyte infiltration and pro-inflammatory gene expression
reduces stroke volume, if administered within 48 hours after MCAO (middle cerebral artery occlusion)
DHA has potent ______ activity
anti-infammatory
DHA is found in
cold water fatty fish
