Translation in Stroke Research

• Translation in Stroke Research
• 1. Background
• 2. Ongoing projects
• 3. Methods
• 4. Cooperation
• Selected references

Translation in Stroke Research

Ischemic and hemorrhagic stroke are major causes of morbidity and mortality. Presently, the medical means to prevent cerebral lesion progression in-hospital are very limited. Clinical trials of neuroprotectants have mostly failed and clearly a  better understanding of the mechanisms of in-hospital lesion progression is required. Cortical spreading depolarizations  (CSD, synonyms: cortical spreading depression, peri-infarct depolarization) were proven in the 1990’s to be a mechanism of ischemic lesion development in animals. Our recent work has shown that ‘inverse’ neurovascular coupling to CSD is a critical determinant of this effect in the animal (Dreier et al., 1998; Dreier et al., 2000; Windmüller et al., 2005) and human (Dreier et al., 2006, 2009) brain. Due to neurovascular dysfunction, severe microvascular spasm is coupled to CSD instead of the vasodilation that occurs with CSD in healthy cortex (Dreier et al., 1998; Dreier et al., 2000; Windmüller et al., 2005). As a result, CSD induces a prolonged spreading perfusion deficit, or cortical spreading ischemia (CSI).

1. Background

1.1. 'Normal' and 'inverse' neurovascular coupling to CSD

The term 'cortical spreading depolarization' (CSD) describes the loss of function in the brain’s gray matter that is triggered when passive  cation influx across the cellular membranes exceeds ATP-dependent Na+ and Ca2+ pump activity. Depolarization of neurons and astrocytes results, followed by cellular swelling and cessation of neuronal function. This mass tissue depolarization propagates through gray matter as a wave, or ‘brain tsunami’, at ~3 mm/min, and is measured as a slow negative shift, 10-20 mV in amplitude, of the extracellular direct current (DC) potential – the largest extracellular signal generated by the brain.  

CSD is a passive process, driven by electrical and diffusion forces. Subsequent repolarization, however, increases energy consumption because additional Na+ and Ca2+ pumps are recruited to correct their harmful intracellular surge. Thus, even in healthy tissue where full repolarization of cellular membranes is achieved within 1-2 min, ATP falls ~50%. To increase oxygen and glucose availability, CSD induces dilation of resistance vessels in healthy tissue. Hence, regional cerebral blood flow (rCBF) increases in response to CSD resulting in cortical spreading hyperemia (CSH), a process which is termed 'normal' neurovascular coupling.  

The opposite of the 'normal' neurovascular  response, termed 'inverse' neurovascular coupling, occurs when there is local dysfunction of the microvasculature. With 'inverse' coupling, severe microvascular spasm instead of vasodilation is coupled to CSD, resulting in CSI. The perfusion deficit of CSI in turn  prolongs the neuronal depolarization since the oxygen-/glucose deprivation further reduces ATP availability (Dreier et al., 1998; Dreier et al., 2000; Windmüller et al., 2005). This is reflected by a prolongation of both the negative DC potential shift and the silencing of neuronal activity. Pharmacologically induced CSI was sufficient  to produce widespread focal necrosis in absence of a preceding significant perfusion deficit in rats.2 This suggested that 'inverse' neurovascular coupling is (i) a sufficient condition for CSD to induce cell death, and, thus (ii) a promising target for therapeutic intervention.

1.2. Lesion progression in acute brain injury

The concept of lesion progression originates with the discovery of the ischemic penumbra, the region bordering a core cerebral infarct with  rCBF reductions sufficient to depress synaptic activity, but adequate to initially maintain membrane polarization. The penumbra is progressively recruited into the core infarction over time, as shown in clinical imaging studies, and is therefore the target for tissue salvage  through early restoration of blood flow or neuroprotective drugs. Without intervention, terminal depolarization in the core gives rise to spontaneous depolarization waves (CSD) that propagate through the penumbra and beyond, causing progressive step-wise expansion of the ischemic core. This effect of CSD is proven to be causal. Accordingly, pharmacological treatments which inhibit CSD also reduce infarct volumes. Unfortunately, however, CSDs become increasingly pharmacoresistant with energy depletion. Recently it has been found that CSDs in the ischemic penumbra of both cats and mice are associated with CSI. This result, together with the finding that CSI alone is sufficient to cause cortical pannecrosis, suggests that  the vascular response manifested in CSI, rather than the electrochemical phenomenon of CSD itself, is the critical mechanism of lesion
progression.

Lesion progression is also a well-defined clinical entity in aneurysmal subarachnoid hemorrhage (aSAH). Delayed ischemic neurologic deficits (DIND) occur in 33-38% of patients with a peak occurrence around day 7, and  10-13% develop delayed computed tomography (CT)-proven infarcts. The assumed mechanism of DIND is proximal vasospasm resulting from subarachnoid breakdown products of erythrocytes, although the positive predictive value of
digital subtraction angiography for the development of DIND is only between 30-50%. A complementary explanation for DIND is the occurrence of CSD, which  in the presence of erythrocyte breakdown products, exhibits ‘inverse’ neurovascular coupling with microarterial spasm arresting microcirculation for minutes to hours (Dreier et al., 1998, 2000, 2006, 2009; Windmüller et al., 2005). Importantly, aSAH is a model disease for the study of lesion progression, since patients can be monitored prior to and throughout the
whole period of delayed infarct development.

2. Ongoing projects

DFG DR 323/5-1  Depolarizations in  ISCHaemia after subARachnoid haemorrhaGE
(DISCHARGE-1)  
DISCHARGE-1 is a prospective, clinical, multicenter, ISRCTN-registered, diagnostic trial (Berlin [PIs: Dreier, Vajkoczy], Heidelberg, Frankfurt, Cologne, Beer-Sheva) of the COSBID study group (www.cosbid.org).
Hypothesis: recording of CSDs allows real time detection of delayed ischemia after aSAH at the bedside, thus, it becomes possible to stratify the population of aSAH patients into two groups at  the earliest possible time point: (1) the group
developing delayed ischemia and (2) the group not developing delayed ischemia.
Implications:  This clinical trial will provide: (1) an  immediate value in the near future for neurointensive care patients with aSAH in whom clinical assessment is often limited because of reduced consciousness (analgo-sedation etc.) since aggressive treatment of delayed ischemia with the currently established standard regimen (triple-H-therapy, see below) can be selectively started earlier; (2) the basis for future proof of concept studies on neuroprotective
strategies that allows for (a) selective treatment allocation to those patients developing ischemia while ischemic stroke is still in the phase of early development plus (b) the option for aggressive neuroprotection that interferes with consciousness or even respiratory drive since delayed strokes develop on the intensive care unit under the eyes of the treating intensivist; (3) the basis to develop automated detection systems for CSD and CSD-induced depression
of high-frequency electrocorticographic (ECoG)  activity in collaboration with physicists and mathematicians; (4) a strong argument to target prolonged CSDs or disturbed neurovascular coupling between CSD and rCBF in the future development of novel neuroprotective strategies; (5) the translation of the CSD concept from experimental research into clinical practice with implications far beyond aSAH for  the whole class of neurological diseases that are characterized by development of cytotoxic edema in the brain including ischemic and hemorrhagic stroke, traumatic brain injury and hypoxia that place the highest health burden on our society in terms of mortality, morbidity and economic costs.

DFG SFB Tr3 D10 A possible role of cortical spreading depolarization for cellular damage in status epilepticus and subsequent development of temporal lobe epilepsy (CSD as a mediator of damage during status epilepticus in animals) Contact: Janos Lückl
 
DFG DR 323/3-1 Cortical spreading ischaemia in hypoxia and global ischaemia (animal study to dissect the mechanisms underlying CSI in hypoxia and global ischemia) Contact: Nikolas Offenhauser
 
German-Israeli Foundation for Scientific Research and Development (G.I.F.)No. I –833-134.2/2004 Spreading Depression under blood-brain barrier disruption: characteristics and underlying mechanisms (animal and brain slice study)
6-8
 
Endothelin-1 as a potent inducer of CSD9,10

3. Methods

Clinical trials

Design and conduction of diagnostic and interventional mono-/and multicentric trials in patients with aSAH, stroke or migraine.
Invasive and non-invasive analysis of clinical ECoG, rCBF

Animal models

Cranial window models using imaging and microelectrodes Human and animal brain slice models Histology, immunohistochemistry

4. Cooperation

COSBID study group (www.cosbid.org)
Prof. Gabriel Curio, Charité Berlin, Germany
Dr. Markus Dahlem, TU Berlin, Germany
Prof. Ulrich Dirnagl, Charité Berlin, Germany
Prof. Wolfram Döhner, Charité Berlin, Germany
Prof. Matthias Endres, Charité Berlin, Germany
Prof. Alon Friedman, Beer-Sheva, Israel
Dr. Georg Bohner, Charité Berlin, Germany
Prof. Uwe Heinemann, Charité Berlin, Germany
Prof. Peter Heuschmann, Charité Berlin, Germany
Prof. Eric Jüttler, Charité Berlin, Germany
PD Dr. Randolf Klingebiel, Charité Berlin, Germany
Prof. Golo Kronenberg, Charité Berlin, Germany
Prof. Ute Lindauer, Munich, Germany
Prof. Andreas Meisel, Charité Berlin, Germany
Prof. Christian Meisel, Charité Berlin, Germany
Dr. Christoph Melzer-Gartzke, Charité Berlin, Germany
PD Dr. Gabor Petzold, Charité Berlin, Germany
Dr. Ryszard Pluta, NINDS, Washington, USA
Prof. Josef Priller, Charité Berlin, Germany
Dr. Harald Prüss, Charité Berlin, Germany
PD Dr. Asita Sarrafzadeh, Genf, Switzerland
Prof. Eckehard Schöll, TU Berlin, Germany
Dr. Ilan Shelef, Beer-Sheva, Israel
Prof. Jan Sobesky, Charité Berlin, Germany
Prof. Peter Vajkoczy, Charité Berlin, Germany
Prof. Johannes Woitzik, Charité Berlin, Germany

Selected references

1  Dreier JP, Körner K, Ebert N, Görner A, Rubin I, Back T, Lindauer U, Wolf T, Villringe A, Einhäupl KM, Lauritzen M, Dirnagl U (1998) Nitric oxide scavenging by hemoglobin or nitric oxide synthase inhibition by  N-nitro-L-arginine induce cortical spreading ischemia when K+ is increased in the subarachnoid space. J Cereb Blood Flow Metab 18:978-990

2  Dreier JP, Ebert N, Priller J, Megow D, Lindauer U, Klee R, Reuter U, Imai Y, Einhäup KM, Victorov I, Dirnagl U (2000) Products of hemolysis in the subarachnoid space induce cortical spreading ischemia and focal necrosis in rats, a model for delayed ischemic neurological deficits after subarachnoid hemorrhage? J Neurosurg 93:668 676

3  Windmüller O, Lindauer U, Foddis M, Einhäupl KM, Dirnagl U, Heinemann U, Dreier JP (2005) Ion changes of spreading ischaemia induce rat middle cerebral arter constriction in absence of NO. Brain 128:2042-2051

4  Dreier JP, Woitzik J, Fabricius M, Bhatia R, Major S, Drenckhahn C, Lehmann T-N, Sarrafzadeh A, Willumsen L, Hartings JA,  Sakowitz OW, Seemann JH, Thieme A, Lauritzen M, Strong AJ (2006) Delayed  ischaemic neurological deficits afte subarachnoid haemorrhage are associated with clusters of spreading depolarisations Brain 129:3224-3237

5   Dreier JP, Major S, Manning A, Woitzik J, Drenckhahn C, Steinbrink J, Tolias C, Oliveira-Ferreira AI, Fabricius M, Hartings JA, Vajkoczy P, Lauritzen M, Dirnagl U, Bohner G, Strong AJ (2009) Cortical spreading ischaemia is a novel process involved in ischaemic damage in patients with aneurysmal subarachnoid haemorrhage. Brain in press

6  Seiffert E, Dreier JP, Ivens S, Bechmann I, Tomkins O, Heinemann U, Friedman A (2004) Lasting blood-brain barrier disruption induces epileptic focus in the rat somatosensory cortex. J Neurosci 24:7829 - 7836

7  Dreier JP, Jurkat-Rott K, Petzold GC, Tomkins O, Klingebiel R, Kopp UA, Lehmann-Horn F, Friedman A, Dichgans M (2005) Opening of the blood-brain barrier preceding a cortical edema in a severe attack of FHM type II. Neurology 64:2145-2147

8  Tomkins O, Friedman O, Ivens S, Reiffurth C, Major S, Dreier JP, Heinemann U, Friedman A (2007) Blood–brain barrier disruption results in delayed functional and structural alterations in the rat neocortex. Neurobiol Dis 25:367-377

9   Dreier JP, Kleeberg J, Petzold G, Priller J, Windmüller O, Orzechowski H-D, Lindauer U, Heinemann U, Einhäupl KM, Dirnagl U (2002) Endothelin-1 potently induces Leão’s cortical spreading depression in vivo in the rat: A model for an endothelial trigger of migrainous aura? Brain 125:102-112

10  Dreier JP, Kleeberg J, Alam M, Major  S, Kohl-Bareis M, Petzold GC, Victorov I, Dirnagl U, Obrenovitch TP, Priller J (2007) Endothelin-1-induced spreading depression in rats is associated with a micro area of selective neuronal necrosis. Exp Biol Med
(Maywood) 232:204-213