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Where Will the Next Generation of Stroke Treatments Come From?

  • D. W. Howells,

    Affiliation: National Stroke Research Institute, Florey Neuroscience Institutes, University of Melbourne, Austin Health, Victoria, Australia

    X
  • G. A. Donnan mail

    gdonnan@unimelb.edu.au

    Affiliation: National Stroke Research Institute, Florey Neuroscience Institutes, University of Melbourne, Austin Health, Victoria, Australia

    X
  • Published: March 02, 2010
  • DOI: 10.1371/journal.pmed.1000224

The Extent of the Problem

Stroke, about 80% of which is ischaemic caused by occlusion of an intracerebral artery and 20% caused by intracerebral bleeding, is the second most common cause of death and disability globally. WHO statistics indicate that stroke and other cerebrovascular diseases kill approximately 5.7 million people each year. In the United States alone it is estimated that the 780,000 symptomatic strokes detected each year may be accompanied by a further 11 million asymptomatic strokes [1]. The need to reduce this burden by better use of existing therapies and identification of new ones is pressing.

Stroke Mechanisms and Pathophysiology: Heterogeneity Is the Key

A unique feature of stroke that creates opportunities for new therapies is the heterogeneity of its mechanisms. These range from large artery to artery embolism, cardiac embolism to in situ small vessel disease and even arterial dissection. Intracerebral haemorrhage may be caused by hypertensive small vessel disease, amyloid angiopathy, or rupture of saccular aneurysms. Risk factors such as atrial fibrillation, hypertension, smoking, diabetes, and disordered lipid metabolism contribute to underlying atherosclerosis or embolus formation [2]. The sequence of events, termed the ischaemic cascade, that follows an ischaemic stroke has also been established [3]. Here, neurons exposed to extreme reductions in blood flow (the “ischaemic core”) lose their membrane potential, undergo irreversible structural damage, and die. In surrounding regions (the “ischaemic penumbra”) the reduction in blood flow is sufficient to compromise neuronal function but not immediately cause neuronal death. A balance between energy supply and consumption exits and tissue survival is determined by the depth and duration of ischaemia [3],[4]. An understanding of this process has led to the concept of reperfusion and neuroprotective therapies.

Twenty Years of Rapid but “Inherited” Advances

Interestingly, many therapeutic advances in stroke have come from research in other disciplines. For example, blood pressure lowering agents such as the ACE inhibitors, developed originally to reduce the risk of vascular injury and myocardial infarction were found to reduce stroke incidence [5],[6]. Similarly for the statins, designed to reduce LDL-cholesterol were found to protect against stroke [7]. Thrombolysis and anti-platelet therapies developed from ischaemic heart disease management [8], and hemicraniectomy to relieve pressure in some cases of ischaemic stroke was used in head trauma [9]. Even some stroke care unit management practices have come from approaches developed in cardiology, oncology, burns, and transplant medicine [10]. We have “inherited” the majority of four categories of acute and five of secondary prevention interventions with level 1 evidence of benefit in stroke since 1978 in this way (see Table 1). As this approach has been successful in the past, abandoning it now would be unwise: we suggest a continued monitoring of other disciplines, while also pursuing novel stroke-specific research. We will address the likely wins from existing classes of intervention and then speculate from where the next therapeutic classes may emerge.

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Table 1. Acute interventions and secondary prevention strategies of proven benefit based on level I evidence.

doi:10.1371/journal.pmed.1000224.t001

The Next Generation of Treatments: New Twists on Existing Therapies

Primary and Secondary Prevention

The greatest early gains are likely to come from enhancing existing strategies. Declines in stroke incidence and mortality in developed countries are most likely due to better risk factor control [11]. However, not all of the reduction in stroke mortality may have come from better blood pressure control. Benefits may have accrued from the recently recognised anti-inflammatory effects of ACE inhibitors and statins [12], and an inflammatory genesis of atherosclerosis may create opportunities for new therapeutic targets. Better recognition of atrial fibrillation (AF), the risk factor that is often overlooked in spite of its high age-specific attributable risk [13], is necessary and may lead to new opportunities. Prevention of stroke in AF with new classes of drugs such as the thrombin inhibitors is a reality [14]. With the growing impact of metabolic syndrome [15], incretin-based therapies, which help control hyperglycaemia and hyperlipidemia [16], combined with better lifestyle management may also be useful in the future. Anti-platelet agents have been a mainstay of secondary stroke prevention (Table 1). However, a ceiling may have been reached of about 20% relative risk reduction, and further anti-platelet effects may cause unacceptable bleeding [17]. Compounds with actions “beyond the platelet” need to be identified, such as thromboxane receptor antagonists.

Can imaging and other biomarkers assist in the search for new therapies? Although currently little evidence indicates that this would be cost effective, screening to detect asymptomatic aneurysms, variations in Circle of Willis anatomy [18] and arterial collateralization [19] may ultimately prove useful. For example, patients with reduced capacity to redistribute cerebral blood flow and thus maintain perfusion above ischemic thresholds are likely to be susceptible to larger strokes. Reports that variation in expression of molecules such as thrombin activatable fibrinolysis inhibitor (TAFI) [20] and plasminogen activator inhibitor-1 (PAI-1) [21] might define risk in specific stroke subsets needs evaluation in the general population. Bioinformatics may help assess panels of protein or mRNA biomarkers to assess stroke risk. Systems controlling clotting and fibrinolysis and regulating inflammation or oxidative stress may be particularly informative.

Acute Stroke

Novel approaches to thrombolysis.

Recanalisation and restoration of blood flow by thrombolysis with tissue plasminogen activator (tPA) benefits only a small proportion of stroke patients [22]. The narrow 3-hour time window and the risk of bleeding limit its use [23]. The time window has now been extended to 4.5 hours, and penumbral imaging with MR or CT may extend this further [24],[25]. The development of biomarker assays for stroke duration or individual risk of bleeding may increase the proportion of eligible patients. Biomarker assays may also be used to improve the toxicity profile of thrombolytic agents and help develop ways to make thrombolytics safer, for example by using the platelet-derived growth factor receptor, alpha (PDGFR-α) antagonist imatinib to reduce tPA-induced bleeding [26]. Another possibility is TAFI, with a genotype associated with stroke risk [27], circulating activity that modifies outcome after thrombolytic therapy [28] and the capacity to make clots resistant to heparins [29]. With the potential to reduce time to artery opening by up to 90 minutes [30], TAFI inhibitors might be effective and safe profibrinolytic agents for use with existing thrombolytic therapies [31].

Mechanical clot removal/disruption.

The use of mechanical devices to remove clots after the acute stroke event is a logical approach but it is highly labour- and capital-intensive. Early recanalisation success was demonstrated with the MERCI Retriever embolectomy device [32] and has been followed by a number of others, most recently the Penumbra device [33]. While it remains to be proved that clinical benefit accrues, based on the shift from thrombolysis to more direct catheter-based intervention in acute myocardial ischemia management, a similar pattern for acute stroke is likely. Opportunities exist to develop improved clot-retrieval devices and, more importantly, health care system changes to allow deployment effectively in a timely manner.

Neuroprotection.

Despite disappointments in the area of neuroprotection, the rhetoric “neuroprotection is dead” seems premature. Systematic reviews and meta-analyses have revealed deficiencies in experimental designs. Failure to consider bias [34] and comorbidities common in human stroke [35] all lead to over-optimistic interpretations of preclinical animal testing. A more rational approach is needed in the sequence of animal to human studies. The heterogeneity of stroke supports the breadth of preclinical evaluation recommended by the Stroke Therapy Academic Industry Roundtable (STAIR) [36], while the fundamentals of good science demand careful bias avoidance [34]. In addition it would seem desirable to have evidence that new drugs reach their hypothesised targets and elicit at least a surrogate response once there. Hypothermia does tick all the appropriate preclinical boxes [37] and has been found to be effective in protecting against the neurological sequelae of cardiac arrest [38]; a large-scale Phase III trial in stroke is needed in spite of logistical difficulties. Also, compounds that directly depress body temperature should perhaps be considered. For example, improgan, a member of a new class of nonopioid analgesics, can reduce core temperature in rodents by 1°C within 10 minutes [39], and hydrogen sulphide can rapidly induce a suspended animation-like state [40]. Drugs that alter the thermoregulatory set-point and make hypothermia more tolerable by reducing shivering are already being considered [41]. We should also entertain alternative mechanisms of action of hypothermia such as control of oedema and local compression.

Timing of treatment following stroke is critical. It may be that neuroprotection is of value only if reperfusion ultimately occurs. In other disciplines, graft ischaemia times for renal, cardiac, and lung transplantation due to developments in effective cold storage and preservative fluids are impressive. Hence “freezing” the penumbra with neuroprotectants may be a realistic goal while waiting for reperfusion. An example is with normobaric oxygen, which increases penumbral oxygen partial pressure and reduces infarct volume in animals [42]. Prolongation of penumbral survival has been inferred in Phase II MR-based studies and pilots of therapy performed in humans [43].

Where May the Next New Class of Therapies Come From?

Although a number of avenues of research may bring rewards in terms of completely new classes of intervention for the prevention and treatment of stroke, we believe two areas are most likely to generate completely new classes of therapeutic targets.

Stimulation of Plasticity

One of the most important advances in neuroscience has been the recognition of activity-dependent plasticity. Synapses, the base units of connectivity, form and disappear depending upon activity and experience, and axons and dendrites can reach out to and withdraw from new targets [44]. Although it had become established that astrocytes and microglia respond rapidly to injury, the realisation that new neurons and supporting oligodendroglia could be generated from pools of neural stem cells and progenitors was a paradigm shift in neurology [45],[46]. These processes offer new and exciting therapeutic opportunities. At the simplest level, we can use observations of benefit after enriching the environment or increasing motor activity to improve traditional rehabilitation strategies [47]. Effective delivery of growth-promoting factors, including the nerve growth factor and glial cell line-derived neurotrophic factor families of proteins, to enhance plasticity and regeneration may also prove effective. Alternatively, mobilization and activation of endogenous neurogenesis/plasticity with drugs such as granulocyte colony-stimulating factor (G-CSF) may be attractive [48]. Although stem cell implants into the brain may currently deliver only a supportive or plastic environment that aids recovery, these cells can mature and integrate into the host neural circuitry [49]. Given that repopulation of connective tissue scaffolds by stem cells can reconstitute a beating animal heart [50], the same may ultimately be possible for regions of damaged brain.

Importantly, evidence is emerging that neural recovery and immune function are intimately linked [51]. Neural outputs seem to regulate bone marrow and spleen activity, while cytokines and related molecules act both locally and systemically to facilitate neuroimmune communication. While this interaction provides considerable scope for clinical intervention, for example by using G-CSF to mobilise neural stem cells [48] or manipulating microglial or macrophage mediated axonal plasticity [52], it is a double-edged sword. Many of the candidate molecular targets directly influence both acute injury development and later neurovascular remodelling [53]. Our approaches need to be sophisticated enough to deal with these critical temporal issues.

Unravelling the Genetic Code to the Heterogeneity of Stroke

There is about a 40% gap in the population attributable risk for stroke when all known risk factors are considered [54]. Much of the gap may consist of genetic contributions to risk in some form. Fortunately, there have been enormous advances in the genetics of stroke. Initial linkage analysis studies identified, rare conditions such as CADASIL (cerebral autosomal dominant arteriopathy with subcortical infarcts and leucoencephalopathy) due to mutations in the NOTCH3 gene [55], which is involved in cell signalling and fate during embryonic development. Subsequently, a candidate gene approach using case-control designs produced a large number of potential gene polymorphisms, many of which could not be replicated and were probably the product of underpowered studies. The emergence of the concept of polygenic contributions to the stroke syndrome, gene chip technology and genome-wide association studies (GWASs) has revolutionized the area. Large international cooperative studies with sample sizes in the thousands have enabled investigators to produce reliable data. For example, by genotyping more than 310,000 single-nucleotide polymorphisms (SNPs) in more than 1,700 intracranial aneurysms and 7,400 controls, SNPs on Chromosomes 2q, 8q, and 9p were associated with aneurysmal presence. The biological implications come from an understanding of the function of these genes as our research effort explores their biology. Chromosomes 8q and 9p both have genes that are associated with progenitor cells and expressed in blood vessels. The main candidate gene on 8q is SOX17, which is required for endothelial formation and maintenance [56]. The implications for the development of gene-based or other therapies are obvious. Similarly, investigators of the International Stroke Genetics Consortium found an association between SNPs in the Chromosome 9p21.3 region and large-artery stroke [57]. GWASs are still in their infancy and are dependent on careful phenotyping and large sample sizes. However, the likelihood that completely novel therapeutic classes emerge from these studies is extremely high.

Summary

Remarkable progress has occurred over the last two decades in stroke interventions. Many have been developed on the basis of their efficacy in other disorders. This “inheritance” approach should continue, but two areas where completely novel therapeutic targets might emerge are the stimulation of neuroplasticity and unraveling the genetic code of stroke heterogeneity (Table 2). For the former, the next steps are to identify small-molecule, nontoxic compounds that most effectively enhance plasticity in animal models, and then subject them to clinical trial in humans. For the latter, more and larger-scale cooperative GWASs in carefully phenotyped stroke populations are required to better understand the polygenic nature of cerebrovascular disease. Then, the physiological relevance of genetic abnormalities can be determined in in vitro and in vivo systems before candidate compounds are developed.

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Table 2. Five key papers in the field of stroke.

doi:10.1371/journal.pmed.1000224.t002

Author Contributions

ICMJE criteria for authorship read and met: DWH GAD. Wrote the first draft of the paper: DWH GAD. Contributed to the writing of the paper: GAD.

References

  1. 1. Leary MC, Saver JL (2003) Annual incidence of first silent stroke in the United States: a preliminary estimate. Cerebrovasc Dis 16: 280–285.
  2. 2. Donnan GA, Fisher M, Macleod M, Davis SM (2008) Stroke. Lancet 371: 1612–1623.
  3. 3. Mergenthaler P, Dirnagl U, Meisel A (2004) Pathophysiology of stroke: lessons from animal models. Metab Brain Dis 19: 151–167.
  4. 4. Donnan G, Baron J, Davis S, Sharp F (2006) The Ischaemic Penumbra: history, current status and implications for therapy. New York: Informa Health Care Inc.
  5. 5. PROGRESS Collaborative Group (2001) Randomised trial of a perindopril-based blood-pressure-lowering regimen among 6,105 individuals with previous stroke or transient ischaemic attack. Lancet 358: 1033–1041.
  6. 6. Kizer JR, Dahlof B, Kjeldsen SE, Julius S, Beevers G, et al. (2005) Stroke reduction in hypertensive adults with cardiac hypertrophy randomized to losartan versus atenolol: the Losartan Intervention For Endpoint reduction in hypertension study. Hypertension 45: 46–52.
  7. 7. Amarenco P, Bogousslavsky J, Callahan A 3rd, Goldstein LB, Hennerici M, et al. (2006) High-dose atorvastatin after stroke or transient ischemic attack. N Engl J Med 355: 549–559.
  8. 8. Granger CB, White HD, Bates ER, Ohman EM, Califf RM (1994) A pooled analysis of coronary arterial patency and left ventricular function after intravenous thrombolysis for acute myocardial infarction. Am J Cardiol 74: 1220–1228.
  9. 9. Vahedi K, Hofmeijer J, Juettler E, Vicaut E, George B, et al. (2007) Early decompressive surgery in malignant infarction of the middle cerebral artery: a pooled analysis of three randomised controlled trials. Lancet Neurol 6: 215–222.
  10. 10. Langhorne P, Williams BO, Gilchrist W, Howie K (1993) Do stroke units save lives? Lancet 342: 395–398.
  11. 11. Feigin VL, Lawes CM, Bennett DA, Anderson CS (2003) Stroke epidemiology: a review of population-based studies of incidence, prevalence, and case-fatality in the late 20th century. Lancet Neurol 2: 43–53.
  12. 12. Bonita R, Beaglehole R (1989) Increased treatment of hypertension does not explain the decline in stroke mortality in the United States, 1970–1980. Hypertension 13: I69–73.
  13. 13. Bejot Y, Ben Salem D, Osseby GV, Couvreur G, Durier J, et al. (2009) Epidemiology of ischemic stroke from atrial fibrillation in Dijon, France, from 1985 to 2006. Neurology 72: 346–353.
  14. 14. Connolly SJ, Ezekowitz MD, Yusuf S, Eikelboom J, Oldgren J, et al. (2009) Dabigatran versus warfarin in patients with atrial fibrillation. N Engl J Med 361: 1139–1151.
  15. 15. Kwon HM, Kim BJ, Park JH, Ryu WS, Kim CK, et al. (2009) Significant association of metabolic syndrome with silent brain infarction in elderly people. J Neurol.
  16. 16. Lovshin JA, Drucker DJ (2009) Incretin-based therapies for type 2 diabetes mellitus. Nat Rev Endocrinol 5: 262–269.
  17. 17. Diener HC (2006) Secondary stroke prevention with antiplatelet drugs: have we reached the ceiling? Int J Stroke 1: 4–8.
  18. 18. Hoksbergen AW, Majoie CB, Hulsmans FJ, Legemate DA (2003) Assessment of the collateral function of the circle of Willis: three-dimensional time-of-flight MR angiography compared with transcranial color-coded duplex sonography. AJNR Am J Neuroradiol 24: 456–462.
  19. 19. Miteff F, Levi CR, Bateman GA, Spratt N, McElduff P, et al. (2009) The independent predictive utility of computed tomography angiographic collateral status in acute ischaemic stroke. Brain 132: 2231–2238.
  20. 20. Biswas A, Tiwari AK, Ranjan R, Meena A, Akhter MS, et al. (2009) Prothrombotic polymorphisms, mutations, and their association with pediatric non-cardioembolic stroke in Asian-Indian patients. Ann Hematol 88: 473–478.
  21. 21. Adamski MG, Turaj W, Slowik A, Wloch-Kopec D, Wolkow P, et al. (2009) A-G-4G haplotype of PAI-1 gene polymorphisms −844 G/A, HindIII G/C, and −675 4G/5G is associated with increased risk of ischemic stroke caused by small vessel disease. Acta Neurol Scand 120: 94–100.
  22. 22. Gilligan AK, Thrift AG, Sturm JW, Dewey HM, Macdonell RA, et al. (2005) Stroke Units, Tissue Plasminogen Activator, Aspirin and Neuroprotection: Which Stroke Intervention Could Provide the Greatest Community Benefit? Cerebrovasc Dis 20: 239–244.
  23. 23. Dawson TM, Dawson VL (2006) Taming the clot-buster tPA. Nat Med 12: 993–994.
  24. 24. Bluhmki E, Chamorro A, Davalos A, Machnig T, Sauce C, et al. (2009) Stroke treatment with alteplase given 3.0–4.5 h after onset of acute ischaemic stroke (ECASS III): additional outcomes and subgroup analysis of a randomised controlled trial. Lancet Neurol 8: 1095–1102.
  25. 25. Hacke W, Kaste M, Bluhmki E, Brozman M, Davalos A, et al. (2008) Thrombolysis with alteplase 3 to 4.5 hours after acute ischemic stroke. N Engl J Med 359: 1317–1329.
  26. 26. Su EJ, Fredriksson L, Geyer M, Folestad E, Cale J, et al. (2008) Activation of PDGF-CC by tissue plasminogen activator impairs blood-brain barrier integrity during ischemic stroke. Nat Med 14: 731–737.
  27. 27. Ladenvall C, Gils A, Jood K, Blomstrand C, Declerck PJ, et al. (2007) Thrombin activatable fibrinolysis inhibitor activation peptide shows association with all major subtypes of ischemic stroke and with TAFI gene variation. Arterioscler Thromb Vasc Biol 27: 955–962.
  28. 28. Brouns R, Heylen E, Sheorajpanday R, Willemse JL, Kunnen J, et al. (2009) Carboxypeptidase U (TAFIa) decreases the efficacy of thrombolytic therapy in ischemic stroke patients. Clin Neurol Neurosurg 111: 165–170.
  29. 29. Semeraro F, Ammollo CT, Semeraro N, Colucci M (2009) Tissue factor-expressing monocytes inhibit fibrinolysis through a TAFI-mediated mechanism, and make clots resistant to heparins. Haematologica 94: 819–826.
  30. 30. Bajzar L, Nesheim ME, Tracy PB (1996) The profibrinolytic effect of activated protein C in clots formed from plasma is TAFI-dependent. Blood 88: 2093–2100.
  31. 31. Bird E, Tamura J, Bostwick JS, Steinbacher TE, Stewart A, et al. (2007) Is exogenous tissue plasminogen activator necessary for antithrombotic efficacy of an inhibitor of thrombin activatable fibrinolysis inhibitor (TAFI) in rats? Thromb Res 120: 549–558.
  32. 32. Smith WS, Sung G, Starkman S, Saver JL, Kidwell CS, et al. (2005) Safety and efficacy of mechanical embolectomy in acute ischemic stroke: results of the MERCI trial. Stroke 36: 1432–1438.
  33. 33. Bose A, Henkes H, Alfke K, Reith W, Mayer TE, et al. (2008) The Penumbra System: a mechanical device for the treatment of acute stroke due to thromboembolism. AJNR Am J Neuroradiol 29: 1409–1413.
  34. 34. Macleod MR, Fisher M, O'Collins V, Sena ES, Dirnagl U, et al. (2009) Good laboratory practice: preventing introduction of bias at the bench. Stroke 40: e50–52.
  35. 35. Sena E, van der Worp HB, Howells D, Macleod M (2007) How can we improve the pre-clinical development of drugs for stroke? Trends Neurosci 30: 433–439.
  36. 36. STAIR (1999) Recommendations for standards regarding preclinical neuroprotective and restorative drug development. Stroke 30: 2752–2758.
  37. 37. van der Worp HB, Sena ES, Donnan GA, Howells DW, Macleod MR (2007) Hypothermia in animal models of acute ischaemic stroke: a systematic review and meta-analysis. Brain 130: 3063–3074.
  38. 38. Bernard S (2006) Therapeutic hypothermia after cardiac arrest: now a standard of care. Crit Care Med 34: 923–924.
  39. 39. Salussolia CL, Nalwalk JW, Hough LB (2007) Improgan-induced hypothermia: a role for cannabinoid receptors in improgan-induced changes in nociceptive threshold and body temperature. Brain Res 1152: 42–48.
  40. 40. Aslami H, Schultz MJ, Juffermans NP (2009) Potential applications of hydrogen sulfide-induced suspended animation. Curr Med Chem 16: 1295–1303.
  41. 41. Sessler DI (2009) Defeating normal thermoregulatory defenses: induction of therapeutic hypothermia. Stroke 40: e614–621.
  42. 42. Henninger N, Bouley J, Nelligan JM, Sicard KM, Fisher M (2007) Normobaric hyperoxia delays perfusion/diffusion mismatch evolution, reduces infarct volume, and differentially affects neuronal cell death pathways after suture middle cerebral artery occlusion in rats. J Cereb Blood Flow Metab 27: 1632–1642.
  43. 43. Singhal AB, Benner T, Roccatagliata L, Koroshetz WJ, Schaefer PW, et al. (2005) A pilot study of normobaric oxygen therapy in acute ischemic stroke. Stroke 36: 797–802.
  44. 44. Holtmaat A, Svoboda K (2009) Experience-dependent structural synaptic plasticity in the mammalian brain. Nat Rev Neurosci 10: 647–658.
  45. 45. Curtis MA, Eriksson PS, Faull RL (2007) Progenitor cells and adult neurogenesis in neurodegenerative diseases and injuries of the basal ganglia. Clin Exp Pharmacol Physiol 34: 528–532.
  46. 46. Kuhlmann T, Miron V, Cuo Q, Wegner C, Antel J, et al. (2008) Differentiation block of oligodendroglial progenitor cells as a cause for remyelination failure in chronic multiple sclerosis. Brain 131: 1749–1758.
  47. 47. Johansson BB (2000) Brain plasticity and stroke rehabilitation. The Willis lecture. Stroke 31: 223–230.
  48. 48. Minnerup J, Heidrich J, Wellmann J, Rogalewski A, Schneider A, et al. (2008) Meta-analysis of the efficacy of granulocyte-colony stimulating factor in animal models of focal cerebral ischemia. Stroke 39: 1855–1861.
  49. 49. Daadi MM, Maag AL, Steinberg GK (2008) Adherent self-renewable human embryonic stem cell-derived neural stem cell line: functional engraftment in experimental stroke model. PLoS One 3: e1644.
  50. 50. Ott HC, Matthiesen TS, Goh SK, Black LD, Kren SM, et al. (2008) Perfusion-decellularized matrix: using nature's platform to engineer a bioartificial heart. Nat Med 14: 213–221.
  51. 51. Dirnagl U, Schwab JM (2009) Brain-immune interactions in acute and chronic brain disorders. Neuroscience 158: 969–971.
  52. 52. Batchelor PE, Liberatore GT, Wong JY, Porritt MJ, Frerichs F, et al. (1999) Activated macrophages and microglia induce dopaminergic sprouting in the injured striatum and express brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor. J Neurosci 19: 1708–1716.
  53. 53. Lo EH (2008) A new penumbra: transitioning from injury into repair after stroke. Nat Med 14: 497–500.
  54. 54. Whisnant J (1997) Modeling of risk factors for ischemic stroke. The Willis Lecture. Stroke 28: 1840–1844.
  55. 55. Louvi A, Arboleda-Velasquez JF, Artavanis-Tsakonas S (2006) CADASIL: a critical look at a Notch disease. Dev Neurosci 28: 5–12.
  56. 56. Bilguvar K, Yasuno K, Niemela M, Ruigrok YM, von Und Zu Fraunberg M, et al. (2008) Susceptibility loci for intracranial aneurysm in European and Japanese populations. Nat Genet 40: 1472–1477.
  57. 57. Gschwendtner A, Bevan S, Cole JW, Plourde A, Matarin M, et al. (2009) Sequence variants on chromosome 9p21.3 confer risk for atherosclerotic stroke. Ann Neurol 65: 531–539.
  58. 58. (1995) Tissue plasminogen activator for acute ischemic stroke. The National Institute of Neurological Disorders and Stroke rt-PA Stroke Study Group. N Engl J Med 333: 1581–1587.
  59. 59. (1997) The International Stroke Trial (IST): a randomised trial of aspirin, subcutaneous heparin, both, or neither among 19435 patients with acute ischaemic stroke. International Stroke Trial Collaborative Group. Lancet 349: 1569–1581.
  60. 60. Mayer SA, Brun NC, Begtrup K, Broderick J, Davis S, et al. (2005) Recombinant activated factor VII for acute intracerebral hemorrhage. N Engl J Med 352: 777–785.
  61. 61. Mendelow AD, Gregson BA, Fernandes HM, Murray GD, Teasdale GM, et al. (2005) Early surgery versus initial conservative treatment in patients with spontaneous supratentorial intracerebral haematomas in the International Surgical Trial in Intracerebral Haemorrhage (STICH): a randomised trial. Lancet 365: 387–397.
  62. 62. Hacke W, Albers G, Al-Rawi Y, Bogousslavsky J, Davalos A, et al. (2005) The Desmoteplase in Acute Ischemic Stroke Trial (DIAS): a phase II MRI-based 9-hour window acute stroke thrombolysis trial with intravenous desmoteplase. Stroke 36: 66–73.
  63. 63. Alexandrov AV, Molina CA, Grotta JC, Garami Z, Ford SR, et al. (2004) Ultrasound-enhanced systemic thrombolysis for acute ischemic stroke. N Engl J Med 351: 2170–2178.
  64. 64. (2006) Glyceryl trinitrate vs. control, and continuing vs. stopping temporarily prior antihypertensive therapy, in acute stroke: rationale and design of the Efficacy of Nitric Oxide in Stroke (ENOS) trial (ISRCTN99414122). Int J Stroke 1: 245–249.
  65. 65. Lees KR, Zivin JA, Ashwood T, Davalos A, Davis SM, et al. (2006) NXY-059 for acute ischemic stroke. N Engl J Med 354: 588–600.
  66. 66. (1978) A randomized trial of aspirin and sulfinpyrazone in threatened stroke. The Canadian Cooperative Study Group. N Engl J Med 299: 53–59.
  67. 67. Diener HC, Cunha L, Forbes C, Sivenius J, Smets P, et al. (1996) European Stroke Prevention Study. 2. Dipyridamole and acetylsalicylic acid in the secondary prevention of stroke. J Neurol Sci 143: 1–13.
  68. 68. CAPRIE Steering Committee (1996) A randomised, blinded, trial of clopidogrel versus aspirin in patients at risk of ischaemic events (CAPRIE). Lancet 348: 1329–1339.
  69. 69. (1993) Secondary prevention in non-rheumatic atrial fibrillation after transient ischaemic attack or minor stroke. EAFT (European Atrial Fibrillation Trial) Study Group. Lancet 342: 1255–1262.
  70. 70. (1991) Beneficial effect of carotid endarterectomy in symptomatic patients with high-grade carotid stenosis. North American Symptomatic Carotid Endarterectomy Trial Collaborators. N Engl J Med 325: 445–453.
  71. 71. (1991) MRC European Carotid Surgery Trial: interim results for symptomatic patients with severe (70–99%) or with mild (0–29%) carotid stenosis. European Carotid Surgery Trialists' Collaborative Group. Lancet 337: 1235–1243.
  72. 72. (2001) Randomised trial of a perindopril-based blood-pressure-lowering regimen among 6,105 individuals with previous stroke or transient ischaemic attack. Lancet 358: 1033–1041.
  73. 73. Amarenco P, Bogousslavsky J, Callahan A, Goldstein LB, Hennerici M, et al. (2006) High-dose atorvastatin after stroke or transient ischemic attack. New England Journal of Medicine 355: 549–559.
  74. 74. Yadav JS, Wholey MH, Kuntz RE, Fayad P, Katzen BT, et al. (2004) Protected carotid-artery stenting versus endarterectomy in high-risk patients. N Engl J Med 351: 1493–1501.