What tissue compartments do stroke pathology involved?
The tissue compartments involved are: the vascular endothelium, astrocytes as well as neurones. A stroke begins as an occlusion to a cerebral artery due to a thrombus or tromboembolism.
What is the role of inflammatory cells in stroke pathology?
Inflammatory cells such as neutrophils, monocytes and macrophages have a role early on. Neutrophils enter the brain within 30 minutes of ischaemic stroke. They are able to enter the parenchyma because of the disrupted BBB and cell adhesion molecules on the endothelial cells.
These cells cause harm and further damage by releasing oxygen free radicals and proteolytic enzymes. Inflammatory cells also activate proteases such as MMP (matrix metalloproteinases) as well as endogenous tPA (tissue plasminogen activator).
5-7 days later, lymphocytes initiate a prolonged inflammatory response, and also promote damage. They promote inflammation by releasing IL-1B, TNFa and PAP (Platelet Activating Factor). They also promote the experession of adhesion molecules on endothelial cells such as ICAM-1 and E-selectins.
The effect of the inflammatory cells tend to be detrimental to the patient.
Describe the concept of the ischaemic core and penumbra
Stroke involves an ischaemic core and the ischaemic penumbra. The core is usually unsalvageable, whereas the penumbra has collateral blood supply, and thus can be salvaged at the onset of stroke and if treatment is administered on time.
Penumbra represents tissue at risk of infarction where perfusion is adequate to maintain cell viability but not adequate for normal neuronal function. This is the area we are trying to save with new therapies.
Lo et al 2003 showed that saving the penumbra with tPA resulted in a low overall damage.
What are normal, and stroke cerebral blood flow rates?
Normal cerebral blood flow is > 50 ml/100g/min
• > 22 < 50 ml/100g/min - Hypoperfusion but likely to survive depending on factors such as collateral flow
• < 22 ml/100g/min - Misery perfusion likely to progress to infarction - this is what is experienced by the penumbra.
• < 10 ml/100g/min rapid cell death - Effect of focal ischaemic on brain metabolism.
What are the metabolic effects of decreasing cerebral blood flow?
The decrease in cerebral blood flow has a range of metabolic effects. The diagram shows that as ml/100g/min (perfusion) decreases:
• ATP stores deplete rapidly at less than 20ml/100g/min
• Glucose utilisation decreases
• Protein synthesis decreases rapidly (conservation of energy)
• Intracellular water content (Na+/K+ uptake) increases
• HSP 70 (Heat Shock Protein 70) up-regulation
• Lactic acidosis
Describe the concept of therapeutic window in stroke
Penumbra represents tissue at risk of infarction where perfusion is adequate to maintain cell viability but not adequate for normal neuronal function.
The window where treatment can have any sort of beneficial effect is around 3h. However, the earlier the administration of treatment, the lower the overall infarct size.
What are the time-dependent stages in stroke pathophysiology?
1. Energy failure (minutes) - very rapidly uses ATP
2. Excitotoxicity (minutes) - due to buildup of glutamate
3. Induction of immediate early genes (hours) - transcriptional upregulation
4. Inflammation (hours/ days) - long-term and delated
5. Programmed cell death / apoptosis (days)
6. Late stage repair
Explain how energy failure contributes to stroke pathophysiology.
Reduced blood flow reduces the amount of ATP that can be generated. Remember the brain uses 20% of total O2 consumption used by the brain which is ~ 2% body weight). This interferes with ion gradients. The Na+ pump fails and hence membrane potential NOT maintained.
Extracellular glutamate (GLU) is elevated - this is usually maintained at very low levels in the synapse through energy dependent GLU transporters. These mechanisms are energy dependent, therefore ATP depletion leads to elevated GLU. Under 20ml/100g/min, extracellular GLU rises, which is dangerous as it activates GLU receptors. Same for GABA and Adenosine.
These changes can even be found in the plasma in the rest of the body (which is far away from the local brain tissue) - in quite a short timescale, only 6 hours.
Ability of GLU to cause damage is mostly via NMDA receptor - this is the crucial one because it is the Na/Ca channel that is the mediator of the next stage of cell death.
Explain how excitotoxicity contributes to stroke pathophysiology.
Excitotoxicity is the pathological process by which nerve cells are damaged or killed by excessive stimulation by neurotransmitters such as glutamate and similar substances. This occurs when receptors for the excitatory neurotransmitter glutamate such as the NMDA receptor and AMPA receptor are overactivated by glutamatergic storm. Glutamate excess is dangerous as it causes cell death by over-exciting neurones.
Glutamate binds to NMDA (and AMPA) and causes Na+ and Ca2+ influx.
• Na+ influx causes depolarisation and cell swelling (due to osmotic forces).
• Ca2+ influx mediates:
○ Proteases, Nucleases
○ XDH (Xanthine Dehydrogenase)
○ PLA2 (Phospholipase A2 – regulates inflammatory response)
○ NOS (Nitric Oxide Synthase)
This results in formation of reactive oxygen species, which can interact with lipids in cell membrane, leading to loss of membrane integrity.
Increased calcium levels intracellularly causes mitochondrial surface membrane to become more permeable. Leakage of Cytochrome C from mitochondria leads to mediation of programmed cell death - apoptosis.
What are the three different types of NOS?
There are three different forms of NOS. In general only the NOS in endothelial cells are beneficial in the event of CI:
• nNOS (neuronal)- acts as a retrograde messenger - leads to toxic levels of NO free radicals, causing neuronal lesions
• eNOS (endothelial)- vasodilatory action (relaxing smooth muscles) - beneficial - improves cerebral blood flow
• iNOS (inducible) - immune mediator - leads to toxic effects enhanced in ischaemia
What protects against free-radical damage?
There are endogenous antioxidants and free radical scavengers which are important in the ischaemic period and also in the subsequent reperfusion when tissue is exposed to high levels of oxygen (“oxidative stress”) - by NO and O2.
These protective antioxidant and free radical scavengers include:
• Superoxide dismutase (SOD)
• Catalase
• Glutathioneperoxidase
• Alpha-tocopherol
• Ascorbic acid
Explain how glutamate mediated excitotoxicity can influence the extent of necrosis or apoptosis
The severity of the insult influences the extent of apoptosis that occurs in comparison to necrosis. In a severe insult, Ca2+ influx causes free radical generation and uptake into mitochondria. There is severe ATP depletion which causes mitochondrial swelling which causes a necrotic lesion. This happens at the ischaemic core.
At the penumbra there is a more milder insult. Reduced oxygen and thus ATP causes a transient depolarisation. Ca2+ is able to be loaded into the mitochondria reducing formation of ROS (Reactive Oxygen Species). This causes activation of Cytochrome C and therefore apoptosis through the mitochondrial pathway.
Explain how excitotoxicity could be targeted for treatment, and drawbacks.
Glutamate antagonists and ion channel blockers in stroke models
• NMDA, AMPA antagonists - HIGHLY effective up to ~2h after insult BUT have psychotomimetic (NMDA) and respiratory depressive properties. Furthermore, the window of therapeutic opportunity is difficult to translate to application in man.
• Metabotropic receptors: Group 1 receptors antagonists (postsynaptic and associated with NMDAR action) and Group II / III mGluR agonists (presynaptic, inhibit glutamate release) are effective.
• Ca2+ channel (L, P/Q and N), Ca2+-dependent K+, channel and proton activated Ca2+ permeable channel (ASIC1a) blockers reduce brain injury.
Explain how transcriptional cascades contribute to stroke pathophysiology.
Glutamate activates a transcriptional cascade which occurs during normal neuronal activity (but also is a response to noxious insults). Ca2+ influx through NMDAR function, causes the activation of Ca2+-Calmodulin Kinase IV Pathway (CAMKIV). This leads to the phosphorylation of CREB (cAMP Response Element Binding protein). CREB/CREB binding protein (CBP) complex activates transcriptional and neurotrophic factors.
This leads to the activation of the multi-potential early response genes:
• Inducible transcription factors (IEGs) - which activate/repress other genes
• Enzymes such as COX-2 - which underlie developmental and behavioural responses
• Neuroprotective proteins - e.g. HSPs which counter damaging effects This pathway mediates an injury response which can contribute to cell survival or death.
What are some of the genes activated by glutamate mediated transcriptional cascades in the penumbra?
Elevated extracellular K+ and glutamate depolarisation in penumbra leads to upregulation of injury response genes (e.g. c-jun, ATF3, and heat shock proteins HSPs). Transcription of these genes are found all around the area of infarct. The upregulation of these genes is sensitive to glutamate antagonists - providing glutamate antagonists prevents this from happening.
Explain the role of heat-shock proteins in stroke pathophysiology.
Heat Shock Proteins act as protein chaperones facilitating the transfer of proteins between subcellular compartments. Following a noxious stimulus (heat, ischaemia) HSPs are induced which target abnormal proteins for degradation. HSPs are also anti-apoptotic and antioxidant (HSP27).
Overexpression of HSP70 and HSP27 reduces the infarct size in mice after MCAO (Middle Cerebral Artery Occlusion).
Sulindac is an NSAID which increases HSP27 and reduces infarct size [Modi et al 2014].
Heat shock proteins play a role in ischaemic preconditioning (IPC). IPC is a process in which brief exposure to ischaemia (such as after TIA) provides robust protection/tolerance to subsequent prolonged ischaemia. HSP involvement in IPC has been demonstrated in cardiac and cerebral ischaemia [Sun et al 2010] mediated through the NF-kB* pathway [Tranter et al 2010] .
Explain the role of cytokines in the pathophysiology of stroke.
Cytokines are produced by a range of activated cell types (endothelial cells, microglia, neurones, astrocytes, platelets, leukocytes, fibroblast) within the first few hours after ischaemia.
• IL-1 and TNFa upregulate adhesion molecules promoting neutrophil migration
○ CSF levels of IL-1, IL-6 and TNFa at 24h correlate with infarct size • Chemokines (e.g. CINC and MCP-1)* detected in the brain between 6 and 24h attract neutrophils & infiltration.
However, some cytokines are neuroprotective. IGFb and IL-10 produced by lymphocytes limit leukocyte invasion and reduce immune responses Complex protective/harmful effects are seen due to multiple sites of action
Describe how cytokines have been studied as a potential therapeutic target for stroke.
• IL-1b receptor antagonists are protective.
• TNFa neutralising antibodies and antisense nucleotides are protective.
• Preliminary studies suggested that neutrophil infiltration is correlated with infarct size.
However, Phase III anti-neutrophil drugs failed to improve stroke outcome and anti-ICAM (n=625) increased mortality (Becker et al 2002)
Describe the role of apoptosis in stroke pathophysiology.
This is most relevant to damage in the penumbra (e.g. delayed cell death). Damage in the core is primarily by necrotic pathways.
Apoptosis is triggered by free radicals, death receptor, DNA damage, protease action and ion imbalance. Release of cytochrome c from mitochondria activates the formation of an apoptosome complex (APAF1 + procaspase 9) and caspase 3 activation (detected at ~8h) leading to DNA fragmentation.
Describe how apoptosis have been studied as a potential therapeutic target for stroke.
• Caspase 3 selective inhibitors (zDEVD.FMK) are effective up to 9h after reversible ischaemia. Broad specificity caspase inhibitors (zVAD)/ caspase 1 deletion protects against ischaemia.
• Viral mediated gene transfer of Bcl-2 and Bcl-XL are neuroprotective
Explain the role of late-stage repair in stroke.
• Growth factors are secreted by neurones, astrocytes, microglia, macrophages, vascular and peripheral cells e.g. IGF1, and erythropoietin.
• Glutamate-mediated synaptic activity increases BDNF [Brain-derived neurotrophic factor] transcription and secretion.
• Neuronal sprouting occurs in an attempt to form contacts.
Explain the role of tPA in stroke treatment.
Restoration of blood flow by thrombolysis with tPA has had the greatest impact on stroke treatment. It is the most effective procedure for SALVAGING ischaemic brain tissue. BUT rapid administration is ESSENTIAL together with rapid assessment of risk. Not everyone benefits as there is a significant haemorrhage risk. Furthermore tPA has no effect on mortality.
Define Stroke
Definition of stroke: acute-onset neurological symptoms or signs indicative of focal central nervous system dysfunction, due to vascular cause (ischemia/ haemorrhage), lasting >24 hours. • If<24hours,it is a TIA. • You can get occlusions in the spinal cord and retina as well as the brain.
Describe the causal classification of stroke
There are two main types of stroke: ischaemic (80%) and haemorrhagic (20%). Ischaemic stroke can be: • Arterial: ○ AIS (Acute Ischaemic Stroke) - classically thought of stroke. Most common cause of stroke. ○ Lacunar - small vessel blockage. • Venous: ○ CVST (cerebral venous sinus thrombosis) - thrombus in the veins causing backpressure and oedema. Haemorrhagic stroke can also be: • Arterial: ○ Aneurysm - balloon-like bulge in the blood vessel. Most common cause of haemorrhagic stroke. ○ PICH (primary intracerebral haemorrhage) - within the brain tissue (not related to meninges). Also most common cause of haemorrhagic stroke. ○ AVM (arteriovenous malformation) ○ EDH (extradural haemorrhage) - usually in young patients after trauma ○ AIS transformed to haemorrhagic stroke with or without thrombolysis. • Venous: ○ SDH (subdural haemorrhage) - due to sheer forces; can be acute in young people, but often chronic in elderly patients. ○ CVST (cerebral venous sinus thrombosis) ○ Cavernoma
What are the categories of causes of ischaemic stroke?
Ischaemic stroke is ultimately caused by dysregulated haemostasis. Disruption of Virchow’s triad leads to haemostasis, and vessel occlusion. Virchow's triad involves: • Hypercoagulability • Blood stasis (turbulence, atrial fibrillation) • Vessel wall injury
What are the specific hypercoagulability causes of stroke?
• Vascular: Polycythaemia and other haematological conditions such as thrombocytopaenia and paroxysmal nocturnal haemoglobinuria. • Infection: systemic TB, chlamydia, sepsis • Trauma: fracture, sympathetic stress response. • Autoimmune: antiphospholipid syndrome, Behcet's syndrome • Metabolic: oestrogen (HRT, OCP), testosterone, diabetes hyperomolar hyperglycamic state (HHS), nephrotic syndrome, volume depletion • Iatrogenic: chemotherapy, COX-2 inhibitors • Neoplastic: adenocarcinoma, AML, head-neck carcinoma • Congenital: Factor V Leiden, prothombin mutations.
What are the specific stasis causes of stroke?
Stasis cause venous thrombosis or closures. These causes include: • Operation, particularly orthopaedic or obstetric • Obesity • Flights • Reduced circulating volume due to hypovolemia • Right-sided heart failure • Atrial fibrillation • Cardiomyopathy
What are the specific vessel wall causes of stroke?
Vessel wall defects cause arterial thrombosis or closures. These causes include: • Atherosclerosis • Hypertension • Dissection • Vasculitis - autoimmune, sarcoid, infection • Injury - iatrogenic, radiation, catheter • Spasm - migraine • Embolism or compression.
List the main clinical syndromes of stroke
• MCA (Middle Cerebral Artery) Infarcts • Anterior cerebral artery infarcts (ACA) • PCA (Posterior Cerebral Artery) infarcts • Brainstem-Cerebellar Infarcts • Lacunar Infarcts • Primary intra-cerebral Haemorrhage • Subarachnoid Haemorrhage • Subdural Haemorrhage • Extradural Haemorrhage
Describe the syndrome of MCA Infarct.
The commonest manifestation of ischaemic stroke is due to blockage of the middle cerebral artery. You can get: • Blockage of the lenticulo-stiate arteries - which supplies the basal ganglia and internal capsule produce symptoms of weakness and hemiparesis. Because they are end arteries, there are no collateral supplies, so blocking these are unsalvageable • Blockage of cortical segments, but these have other collateral supplies?
Describe the syndrome of non-MCA arterial infarcts.
• Anterior cerebral artery infarcts cause paralysis in feet and legs – this can fool doctors who may think it is a black problem, e.g. slipped disc, but is actually an ACA infarct. • Posterior cerebral artery infarcts cause problems with vision – e.g. homonymous hemianopia
Describe the syndrome of Brainstem-cerebellar Infarct.
These are due to posterior circulation. • One example of this kind of infarct is PICA infarct = posterior inferior cerebellar artery – medullar dorsolateral syndrome. It is the most common type of brainstem stroke. • When weakness/symptoms on same side of the face and opposite side of the body – whenever you have this crossed pattern of paralysis (opposite face and body), you know it is a brain stem infarct. • Can also affect swallowing because it affects nucleus ambiguous – CN IX and X • Infarction of pons bilaterally can lead to locked-in syndrome – due to blockage of basillar artery
Describe the symptoms of Lacunar infarcts.
These lacunar infarcts cause progressive, cumulative problems – leading to dementia and Parkinsonism (not Parkinson's disease itself, but parkinsonism). Vascular dementia is one of the main causes of age-related cognitive decline. • Acute Syndromes: ○ Pure motor ○ Pure sensory ○ Ataxia-hemiparesis ○ Dysarthria-Clumsy hand • Chronic Syndromes: ○ Executive cognitive impairment, bradyphrenia ○ Lower body parkinsonism, gait apraxia
What are the main tests requested in investigating an ischaemic (after haemorrhagic ruled out) stroke?
Arterial: • Carotid Doppler – Looking for obvious stenosis/clot • MR Angiogram – Assessing the carotids/circle of Willis • Bubble Echocardiogram [of heart] – Look for Mural Thrombus, valve vegetations (aortic), inter-atrial shunt, endocarditis • 24 hour ECG - to look for AF, especially paroxysmal AF Venous: • CT-V – Contrast scan of cranial sinuses, especially Sagittal and Coronal views
What causes a primary intra-cerebral haemorrhage?
This is caused by a ruptured vessel leads to bleed directly into the parenchyma. Caused by hypertension, amyloid angiopathy or AVM.
What causes a subarachnoid haemorrhage?
A bleed into the space between arachnoid and pia mater. Can cause a secondary vasospasm (leading to ischaemic stroke downstream). Caused by Aneurysm (e.g. Berry Aneurysm in PKD [polycystic kidney disease])/ Dissection/ Trauma
What type of haemorrhage is characterised by a slow bleed, gradual dementia, spreads across brain surface.
A bleed into space between arachnoid and Dura mater. - Subdural Haemorrhage
Describe the causes and main symptoms of an extradural haemorrhage.
• Bleed into space between skull and Dura mater • Usually rupture of Meningeal artery (e.g. MMA damage in pterion injury) • Fast bleed, acute headache and rapid deterioration, convex bleed shape
What is the mortality for all strokes?
20-30% die within 1 year. Most survive with considerable disability.
What are the most common causes of death in stroke?
- Cerebral oedema - Aspiration Pneumonia due to weak swallowing muscles - Pulmonary embolism due to patients in bed for a long period of time
How do you manage any type of stroke?
Rapid recognition and reaction to stroke symptoms. → Immediate call of emergency service → Priority transport with pre-announcement to target hospital (specifically trained and equipped to deal with acute stroke) → Rapid and targeted diagnostic work-up and therapy in hospital. The aim is to deliver thrombolysis within 30 minutes of entering the door. This involves taking vitals, performing examinations and a CT scan. Emergency room: In the emergency room four things are done: • Medical history - Stroke suspected? ○ Time since symptoms-onset/last seen well ○ Do symptoms correspond to a vascular territory (ischaemia)? • Vital signs ○ Vigilance → clinical ○ Respiration → clinical, plusoximetry ○ Circulation → BP,HR,ECG • Laboratory (CBC, coagulation) • Neuro exam: NIHSS stroke scale to grade severity Imaging is always necessary The modality of choice is CT, as it is fast and widely available. Imaging is important to tell the difference between ischaemic and haemorrhagic stroke.
How is ischaemic stroke treated?
After ICH has been ruled out with CT scan we can operate knowing it is ischaemic in nature. Important to rule out haemorrhage as treatments for ischaemic stroke would deteriorate the hemorrhaging patient. If the onset of the persisting deficit is <4.5h or CCT early infarct signs <1/3: • Intravenous thrombolysis (intravenous recannulisation) • Mechanical thrombectomy (a type of interventional recannulisation) Unfortunately for a significant proportion of patients, there is unknown symptom onset: • Multimodal MRI/CT based thrombolysis? • New therapies within trials?
How is intravenous thrombolysis administered?
rtPA is the only licensed medical therapy of acute ischaemic stroke - in 4.5 hour time window. • 0.9 mg/kg over 60 min (max. dose 90 mg) • With a bolus of 10% over 1 min Important to be aware of the eligibility criteria
How are novel imaging modalities being used to replace the symptom-time based criteria for tPA administration?
As mentioned a significant proportion of patients have an unknown time of symptom onset for various reasons, meaning they will miss out on thrombolysis treatment. To overcome this, we are trying to substitute the clock with pathophysiology, using imaging modalities. There’s a mismatch between the small area of infarct and the large area of generalised reduced perfusion. The difference is the penumbra, which is at risk and should be salvaged. We can use diffusion weighted imaging (DWI) to image the ischaemic core, and perfusion weighted imaging (PWI) to image the area of reduced perfusion (core + penumbra). By subtracting the two, you can image the penumbra to see how much tissue can be salvaged, informing whether to use thrombolysis. There are new trials to select suitable patients according to various imaging techniques. ECASS-4/EXTEND trial was a phase III RCT showing rtPA with selection via MRI-mismatch had a 4.5-9h time window. Similar phase III EU funded trial called Wake-up trial currently ongoing.
What Interventional recanalisation methods are used?
Interventional recanalisation is carried out by different devices: • Ultrasound (EKOS) • Shockwave/vacuum • Angiojet • Retrieval devices (MERCI, penumbra) • Laser devices (EPAR) • Stent retrievers
What are the benefits and limitations of interventional recanalisation methods
These endovascular treatments have been shown to be more effective than rtPA alone by randomised control trials. With mechanical thrombectomy, again faster is better in producing patients with a good clinical outcome. A 30% delay translates to 12% less chance of good clinical outcome. Unlike rtPA, you need a specialised team to carry out endovascular treatment, so this presents a challenge for the chronically underfunded NHS.
Give two examples of stroke causes you would not treat with tPA.
- Basilar Artery Thrombosis - Space-Occupying Middle Cerebral Artery
How would you treat a Space-Occupying Middle Cerebral Artery Stroke?
A hemicraniectomy is vital in reducing brainstem death. In the DESIRE trial, patients showed much better outcomes with surgery compared to conservative treatment.
What additional therapies can be given to stroke patients (not revascularisation)?
Only a minority of patients are able to benefit from revascularisation by thombolysis or endovascular therapy. There are hundred of studies suggesting potential molecular targets for neuroprotective drugs. However, none so far have made it into clinics :( An essential part of stroke treatment is provided by the infrastructure of stroke units.
What is a stroke unit comprised of?
The stroke unit is not just a ward, it is an interdisciplinary team formed of ICU, A&E, neurovascular surgery, neuroradiology, discharge to home, neurology ward, inpatient rehabilitation, physiotherapy, SALT, long-term care and home care.
What are stroke units used for?
They are used to: • Monitor patients with acute stroke (>24g, unstable phase) • Immediate diagnostic work-up for cause of stroke • Immediate specific therapy and secondary prevention (very important also) • Continuous monitoring of vital signs and aims for homeostasis • Prevention of secondary complications • Stay therefore rarely exceeds 5 days.
How effective are stroke unit?
? Stroke units are the most effective ?treatment. Level 1 evidence shows: • Reduced morbidity and mortality independent of sex, age, severity • Shorten inpatient treatment • Lower number of patients surviving with severe disability and needing long-term care • Increase proportion of patients with complete recovery.
What is the epidemiology of an intracerebral haemorrhage?
• Causes 8-15% of all strokes • 1 year mortality is 37-47% - 2/3 X higher than ischaemic stroke • 1/3 of survivors remain severely disabled (dependent on nursing)
What are the main causes of an intracerebral haemorrhage?
• Hypertensive arteriolopathy (70%) [Hypertension is number 1 risk factor] • Cerebral amyloid angiopathy (5-20%) related to Alzheimer's disease Other causes: • Anticoagulants (15%) • Tumour (5%) • Vascular malformations (1-2%)
What feature of ICH is closely related to prognosis?
Early haematoma enlargement is frequent and is associated with clinical deterioration. In fact, size of the haematoma is one of the best indicators of prognosis. The dynamic nature of ICH during the first several hours represents an opportunity and a challenge to physicians. If one could stop the bleeding during the first few hours and remove the accumulated blood without significant additional brain trauma from the operation, neurological deterioration and poor outcome could be prevented in some patients but this is extremely rare at present.
What are the types of therapy for ICH?
• Haemostatic therapy for ICH • Anticoagulation reversal for OAC-ICH • Antihypertensive therapy in acute ICH • Surgery
Describe the use of, and evidence surrounding haemostatic therapy for ICH
Recombinant factor VIIa can help push the clotting process so that bleeding does not occur. In the FAST trial, you could see that there was a volume reduction of the bleeding, but no improvement of death and disability, and also there was increased risk of thromboembolic events. Maybe we need to improve patient selection by finding out who is likely to continue bleeding and who is not. Generally, administration of haemostatic drugs is not recommended in spontaneous ICH
Describe how anticoagulation reversal is achieved for OAC-ICH.
Recommendations are to stop Vit K antagonists and give vitamin K/prothrombin concentrate. Evidence for positive effect of fast anticoagulation reversal on haematoma growth in VKA-ICH (Vit K Antagonist). For NOAC: Idarucizumab is a humanised Fab fragment. Highly specific antagonisation of dabigatran activity (binding affinity for dabigatran ~300x higher than dabigatran to thrombin) • i.v. administration, immediate onset of action • Short half-life (terminal HL about 10h) • Small distribution volume (about 8-9l) • No intrinsic pro-anticoagulatory effect expected Idarucizumab also prevents excess haematoma expansion and Idarucizumab reduces mortality. Andexanet-alpha - recombinant modified human factor Xa • Designed to reverse anticoagulant effects of factor Xa inhibitors • Acts as factor Xa decoy to bind molecules that inhibit factor Xa
Describe the use of, and evidence surrounding antihypertensive therapy for ICH
• In the INTERACT-2 trial, researchers used intensive BP lowering drugs <140mmHg in 1 hour versus standard care • Made sure to have exclusion criteria, excluding people with a structural cause of haematoma, coma, massive haematoma with bad prognosis or planned early surgery • They found that there was no effect on early haematoma volume but: ○ Lowering BP below 140mmHg in acute phase of ICH is safe ○ It reduces the likelihood of unfavourable outcome ○ The time to reaching BP target could be shorter ○ But it’s still unclear why the risk of bad outcomes was reduced • In the ATACH-2 trial, they went even further and lowered BP to <120mmHg. They found no effect of very intensive therapy on outcome .
Describe the use of, and evidence surrounding surgery for ICH.
• In a meta analysis for mortality in prospective studies of haematoma evacuation, there was a favourable outcome • In the STICH trial, researchers compared surgery vs. conservative treatment and looked after favourable outcomes .They found that there was no difference regarding survival but in a subgroup of patients who had haematomas less than 1 cm from the cortical surface, there was a favourable outcome of surgery • So in the STICH II trial, they focused on lobar ICH less than 1cm from the brain surface, and found that there was increased survival and better outcomes for that specific group of patients • Decompressive surgery might be useful if there is oedema • In general, we do not recommend surgery for patients with haematoma
What are the general uses of animal models in stroke?
• Insight into pathophysiology: Selective neuronal loss, cortical spreading depression, neuroinflammation, "ischaemic penumbra", etc. • Validation of clinical observations and concepts: Brain imaging (e.g. DWI, PWI), tPA-toxicity, immunodepression, hypothermia, etc. • Drug development
List the types of models used for ischaemic stroke
80% of animal models in stroke are rodents. There are a variety of techniques used to cause ischaemic stroke in the animal models (in order of most popular): 1. Intraluminal filament - a filament is advanced via the carotid artery into the skull to occlude the MCA. 2. Coaugulation/cauterisation/transection 3. Clip/ligation 4. Emboli: autologous clot/microsphere/macrosphere 5. Photochemical 6. Endothelin 7. Compression/balloon/torniquet - often used in big animals
Describe the Intraluminal filament model, and it's opportunities and limitations.
Filament placed into MCA to cause occlusion. Can vary length of time before removal (and hence reperfusion) - so you can get different levels of ischaemia. Most commonly used method - 45-90 min occlusion time Pros: ○ Relatively easy operation ○ No craniectomy ○ Can simulate reperfusion • Cons: ○ Hypothermia ○ Weight loss ○ High mortality ○ Short observation period
Describe the animal models of stroke requiring surgery, and it's opportunities and limitations.
• Transient occlusion can be modeled using Clip or Ligation • Permanent occlusion can be modeled using Coagulation or Ligation Pros of using these surgical methods: • Suitable also for large animal models • High proportion of successful procedures • High reproducibility • No hypothermia, low mortality • Long-term observation possible Cons: • Skull opened (dura incision, CSF leakage, surgical trauma) • Usually permanent MCAo • Does not model recanalisation • Surgical skill required
Describe the embolic stroke models, and it's opportunities and limitations.
One method is to inject an externally produced emboli, similar to using the filament model. Another method is to inject thrombin. Both can by lysed by rt-PA Pros: • Models most common cause of human stroke • Allows analysis of thrombolysis • No craniectomy (except thrombin injection) • No hypothermia • Lower mortality compared to filament MCAo Cons: • Low rate of successful MCAo • Little control over site of clot lodgement • Certainty of occlusion versus effective reperfusion • Excellent surgical skills needed (clot emboli; thrombin injection)
Describe the photothrombosis model, and it's opportunities and limitations.
This is done by inject agent called rose bengal, then apply laser at certain wavelength, which via reactive oxygen species causes very small strokes within the brain. This produces very small, precisely defined lesions. Lesions can be induced stereotactically in predefined anatomical regions. Pros: • Precise localisation of infarction • Targeting functionally defined regions • High reproducibility • Dura not opened • Minimal mortality Cons: • Additional direct effects on brain function o Endothelial lesion • Expensive material / difficult method • Useful only for specific study aims
Describe the opportunities and limitations of stroke models in larger animals
Pros: • Closer to human brain anatomy and function • Imaging techniques (PET, MRI) easier • Better monitoring of physiology Cons: • Intensive in cost and labour • Large variability • High mortality • Limitations by animal welfare • Public and ethical concerns
What are the limitations of using rodents as human brain models?
• Rodents have greater capillary density • Lesser inter-capillary diffusion distance • Greater CSF turnover • Gyral complexity much more defined in man • Grey:White matter ratio: Rodent brains are 90% grey matter, whereas for humans it is the white matter tracts that are especially important for function
What are the limitations in translating the knowledge gained in the laboratory into new clinical approaches?
Animal studies • Used only young, healthy animals • Statistical problems: Randomization, blinded analysis, power, sample size • No clinically relevant time point of treatment • Physiological parameters not controlled Clinical studies • Adequate drug levels were not reached • Time window was not used based on preclinical data • Inclusion of patients to study not adjusted for mode of drug action
What are the models of Intracerebral Haemorrhage?
Either inject something that makes the blood vessel wall break down (collagenase), or inject blood directly. Collagenase-injection model: Bacterial collagenase destroys the basal lamina of cerebral blood vessels dose-dependently. This causes bleeding in the surrounding tissue. Blood injection model Direct injection of blood into the striatum. Here there is no vessel damage.
What are the seemingly opposing functions of the immune system after stroke?
There are two sides to the immune system's involvement: • Evidence for increased susceptibility to infections due to suppression of peripheral immune system. • Ischaemic CNS damage leads to secondary neuroinflammation, which can cause infarct growth Two effects that are opposite to each other
Describe the phenomena of immune system susceptibility to infection after stroke
30 % of all stroke patients develop infections (Pneumonia: 10%, UTI: 10%) with pneumonia being the most important cause of death (subacute phase). Some people are calling this Stroke-Induced Immunodeficiency Syndrome. This is characterised by: • Spontaneous bacteraemia and pneumonia in murine stroke model • Lymphocytopenia (blood, lymphatic organs: apoptosis) • Reduced responsiveness of innate and adaptive immune cells to in vitro stimulation
What causes immune system depression following stroke?
Mainly mediated by stress hormones (e.g. NA, glucocorticoids, ACh) • Immune cells have receptors for these hormones, leading to immunodepression • Breakdown on immunological barriers This makes them more susceptible to infection
Describe the neuroinflammatory response to stroke
Following ischaemia, there is activation of microglia, which secrete pro-inflammatory cytokines, which makes the BBB more permeable and leads to infiltration of systemic immune cells (also with increased adhesion molecules). As a result, you get systemic immune cells in the brain which release cytokines and chemokines themselves, which are also cytotoxic. Inflammatory cascades in acute phase of ischemia predominantly deleterious and lead to infarct enlargement. Pro-inflammatory T-cells are increasingly recognized as an important deleterious systemic immune cell populations.
Describe the immune system modulator targeted for use in stroke.
Are T-cells a suitable target for protective therapeutic approaches? Anti-inflammatory therapy by blocking leukocyte adhesion - Anti-CD49d therapy is used in MS. Natalizumab is humanised, monoclonal antibody against α4-Integrin (=CD49d) which blocks CNS-migration, but does not destroy lymphocytes. • Phase III Studies: > 70% Reduction of episodes in MS Natalizumab was shown to minimise immune cell infiltration around the lesion site. While this had no effect on the acute inflammatory phase, it did prevent infarct growth.
How has natalizumab performed in stroke model experiments?
Experimental Design: • Permanent occlusion of middle cerebral artery (MCAO) by electro-coagulation after trepanation • Infarct volumetry [imaging] by silver staining of coronary sections • Blockade of integrin alpha4 (CD49d) on leukocytes by monoclonal antibody Experiment results: • Substantial reduction of infiltrating cells around infarct • No change in infarct size at 1 day • But significant decrease in infarct size by 7 days
Describe the translation of Natalizumab to the Clinical Settling
Protection in several experimental stroke models → Proof-of-concept by complementary methodology approach → Confirmation in multicentre preclinical RCT → Phase 2 RCT with proof-of-concept approach → (Currently in planning:) Phase 2b/3 efficacy and safety Study design of the Phase 2 - Randomised, double blind, placebo-controlled trial of natalizumab in acute ischemic stroke: Primary Endpoint - change in infarct volume: • Natalizumab did not affect infarct volume growth compared to placebo! • I.e. it wasn't like it was in the animal models Clinical outcomes in Natalizumab- and placebo- treated patients: • At days 30 and 90, natalizumab showed a meaningful benefit over placebo treatment on global clinical and cognitive function, but not NIHSS [National Institutes of Health Stroke Scale] score • The likelihood of an excellent outcome on the mRS [modified ranking score] (score ≤1) was analysed in patient subgroups stratified by baseline infarct size, treatment time window, and tPA use