Paul M. George

Novel Stroke Therapeutics: Unraveling Stroke Pathophysiology and Its Impact on Clinical Treatments

Stroke remains a leading cause of death and disability in the world. Over the past few decades our understanding of the pathophysiology of stroke has increased, but greater insight is required to advance the field of stroke recovery. Clinical treatments have improved in the acute time window, but long-term therapeutics remain limited. Complex neural circuits damaged by ischemia make restoration of function after stroke difficult. New therapeutic approaches, including cell transplantation or stimulation, focus on reestablishing these circuits through multiple mechanisms to improve circuit plasticity and remodeling. Other research targets intact networks to compensate for damaged regions. This review highlights several important mechanisms of stroke injury and describes emerging therapies aimed at improving clinical outcomes.

Three-dimensional conductive constructs for nerve regeneration.

The unique electrochemical properties of conductive polymers can be utilized to form stand-alone polymeric tubes and arrays of tubes that are suitable for guides to promote peripheral nerve regeneration. Noncomposite, polypyrrole (PPy) tubes ranging in inner diameter from 25 microm to 1.6 mm as well as multichannel tubes were fabricated by electrodeposition. While oxidation of the pyrrole monomer causes growth of the film, brief subsequent reduction allowed mechanical dissociation from the electrode mold, creating a stand-alone, conductive PPy tube. Conductive polymer nerve guides made in this manner were placed in transected rat sciatic nerves and shown to support nerve regeneration over an 8-week time period.

Validation and comparison of imaging-based scores for prediction of early stroke risk after transient ischaemic attack: a pooled analysis of individual-patient data from cohort studies

BACKGROUND Identification of patients at highest risk of early stroke after transient ischaemic attack has been improved with imaging based scores. We aimed to compare the validity and prognostic utility of imaging-based stroke risk scores in patients after transient ischaemic attack. METHODS We did a pooled analysis of published and unpublished individual-patient data from 16 cohort studies of transient ischaemic attack done in Asia, Europe, and the USA, with early brain and vascular imaging and follow up. All patients were assessed by stroke specialists in hospital settings as inpatients, in emergency departments, or in transient ischaemic attack clinics. Inclusion criteria were stroke-specialist confirmed transient ischaemic attack, age of 18 years or older, and MRI done within 7 days of index transient ischaemic attack and before stroke recurrence. Multivariable logistic regression was done to analyse the predictive utility of abnormal diffusion-weighted MRI, carotid stenosis, and transient ischaemic attack within 1 week of index transient ischaemic attack (dual transient ischaemic attack) after adjusting for ABCD2 score. We compared the prognostic utility of the ABCD2, ABCD2-I, and ABCD3-I scores using discrimination, calibration, and risk reclassification. FINDINGS In 2176 patients from 16 cohort studies done between 2005 and 2015, after adjusting for ABCD2 score, positive diffusion-weighted imaging (odds ratio [OR] 3·8, 95% CI 2·1-7·0), dual transient ischaemic attack (OR 3·3, 95% CI 1·8-5·8), and ipsilateral carotid stenosis (OR 4·7, 95% CI 2·6-8·6) were associated with 7 day stroke after index transient ischaemic attack (p<0·001 for all). 7 day stroke risk increased with increasing ABCD2-I and ABCD3-I scores (both p<0·001). Discrimination to identify early stroke risk was improved for ABCD2-I versus ABCD2 (2 day c statistic 0·74 vs 0·64; p=0·006). However, discrimination was further improved by ABCD3-I compared with ABCD2 (2 day c statistic 0·84 vs 0·64; p<0·001) and ABCD2-I (c statistic 0·84 vs 0·74; p<0·001). Early stroke risk reclassification was improved by ABCD3-I compared with ABCD2-I score (clinical net reclassification improvement 33% at 2 days). INTERPRETATION Although ABCD2-I and ABCD3-I showed validity, the ABCD3-I score reliably identified highest-risk patients at highest risk of a stroke after transient ischaemic attack with improved risk prediction compared with ABCD2-I. Transient ischaemic attack management guided by ABCD3-I with immediate stroke-specialist assessment, urgent MRI, and vascular imaging should now be considered, with monitoring of safety and cost-effectiveness. FUNDING Health Research Board of Ireland, Irish Heart Foundation, Irish Health Service Executive, Irish National Lottery, National Medical Research Council of Singapore, Swiss National Science Foundation, Bangerter-Rhyner Foundation, Swiss National Science Foundation, Swisslife Jubiläumsstiftung for Medical Research, Swiss Neurological Society, Fondazione Dr Ettore Balli (Switzerland), Clinical Trial Unit of University of Bern, South Koreas Ministry for Health, Welfare, and Family Affairs, UK Wellcome Trust, Wolfson Foundation, UK Stroke Association, British Heart Foundation, Dunhill Medical Trust, National Institute of Health Research (NIHR), Medical Research Council, and the NIHR Oxford Biomedical Research Centre.

Fabrication of screen-printed carbon electrode arrays for sensing neuronal messengers

Deciphering the methods of communication between neurons and ensembles of neurons in the brain is a major area of interest in the field of neuroscience. An array of sensors designed to sense specific neuronal messengers or neurotransmitters should provide a better method to study their spatial and temporal activity across a tissue. Screen-printing is a simple and inexpensive technique for fabricating arrays of sensors that can be used to monitor neurotransmitter activity in the brain. One important neuronal messenger known to actively modulate neuronal excitability is nitric oxide (NO). Carbon has been shown to interact with NO in an oxidation-reduction reaction that produces a current proportional to the amount of NO present. The proposed design uses carbon polymer inks screen printed onto aluminum traces to form the sensors. A thick, photodefineable epoxy resin, known as SU-8, serves as an insulator and a mold for the carbon ink. A potentiostat is used to apply a 900 mV voltage between the carbon sensor and a reference electrode positioned in the bath of the experimental setup. The current produced indicates the concentration of NO in close proximity to the carbon site. The screen-printing technique provides an elegant way to produce an array of individual carbon sensors. The carbon sensor array promises a novel approach to mapping the distribution of neurotransmitters in brain tissue.

Inter-rater agreement analysis of the Precise Diagnostic Score for suspected transient ischemic attack

Background No definitive criteria are available to confirm the diagnosis of transient ischemic attack. Inter-rater agreement between physicians regarding the diagnosis of transient ischemic attack is low, even among vascular neurologists. We developed the Precise Diagnostic Score, a diagnostic score that consists of discrete and well-defined clinical and imaging parameters, and investigated inter-rater agreement in patients with suspected transient ischemic attack. Methods Fellowship-trained vascular neurologists, blinded to final diagnosis, independently reviewed retrospectively identical history, physical examination, routine diagnostic studies, and brain magnetic resonance imaging (diffusion and perfusion images) from consecutive patients with suspected transient ischemic attack. Each patient was rated using the 8-point Precise Diagnostic Score score, composed of a clinical score (0–4 points) and an imaging score (0–4 points). The composite Precise Diagnostic Score determines a Precise Diagnostic Score Likelihood of Brain Ischemia Scale: 0–1 = unlikely, 2 = possible, 3 = probable, 4–8 = very likely. Results Three raters reviewed data from 114 patients. Using Precise Diagnostic Score, all three raters scored a similar percentage of the clinical events as being “probable” or “very likely” caused by brain ischemia: 57, 55, and 58%. Agreement was high for both total Precise Diagnostic Score (intraclass correlation coefficient of 0.94) and for the Likelihood of Brain Ischemia Scale (agreement coefficient of 0.84). Conclusions Compared with prior studies, inter-rater agreement for the diagnosis of transient brain ischemia appears substantially improved with the Precise Diagnostic Score scoring system. This score is the first to include specific criteria to assess the clinical relevance of diffusion-weighted imaging and perfusion lesions and supports the added value of magnetic resonance imaging for assessing patients with suspected transient ischemic attack.

Beneficial effects of a semi-intensive stroke unit are beyond the monitor.

Background and Purpose: Precise mechanisms underlying the effectiveness of the stroke unit (SU) are not fully established. Studies that compare monitored stroke units (semi-intensive type, SI-SU) versus an intensive care unit (ICU)-based mobile stroke team (MST-ICU) are lacking. Although inequalities in access to stroke unit care are globally improving, acute stroke patients may be admitted to Intensive Care Units for monitoring and followed by a mobile stroke team in hospitals lacking an SU with continuous cardiovascular monitoring. We aimed at comparing the stroke outcome between SI-SU and MST-ICU and hypothesized that the benefits of SI-SU are driven by additional elements other than cardiovascular monitoring, which is equally offered in both care systems. Methods: In a single-center setting, we compared the unfavorable outcomes (dependency and mortality) at 3 months in consecutive patients with ischemic stroke or spontaneous intracerebral hemorrhage admitted to a stroke unit with semi-intensive monitoring (SI-SU) to a cohort of stroke patients hospitalized in an ICU and followed by a mobile stroke team (MST-ICU) during an equal observation period of 27 months. Secondary objectives included comparing mortality and the proportion of patients with excellent outcomes (modified Rankin Score (mRS) 0-1). Equal cardiovascular monitoring was offered in patients admitted in both SI-SU and MST-ICU. Results: 458 patients were treated in the SI-SU and compared to the MST-ICU (n = 370) cohort. The proportion of death and dependency after 3 months was significantly improved for patients in the SI-SU compared to MST-ICU (p < 0.001; aOR = 0.45; 95% CI: 0.31-0.65). The shift analysis of the mRS distribution showed significant shift to the lower mRS in the SI-SU group, p < 0.001. The proportion of mortality in patients after 3 months also differed between the MST-ICU and the SI-SU (p < 0.05), but after adjusting for confounders this association was not significant (aOR = 0.59; 95% CI: 0.31-1.13). The proportion of patients with excellent outcome was higher in the SI-SU (59.4 vs. 44.9%, p < 0.001) but the relationship was no more significant after adjustment (aOR = 1.17; 95% CI: 0.87-1.5). Conclusions: Our study shows that moving from a stroke team in a monitored setting (ICU) to an organized stroke unit leads to a significant reduction in the 3 months unfavorable outcome in patients with an acute ischemic or hemorrhagic stroke. Cardiovascular monitoring is indispensable, but benefits of a semi-intensive Stroke Unit are driven by additional elements beyond intensive cardiovascular monitoring. This observation supports the ongoing development of Stroke Centers for efficient stroke care.

Aortic Arch Atheroma A Plaque of a Different Color or More of the Same

See related article, p 1248. Despite the common occurrence of aortic arch atherosclerosis in patients with stroke, evidence-based treatment for this disease has remained fundamentally uncharted territory. After Winter1 first described this phenomena in 1957 from autopsy cases, the association between aortic atheroma and stroke has been a topic of great interest. A strong association with cerebral ischemic events was established by a landmark postmortem study of 500 patients with neurological symptoms; aorta atherosclerotic disease was present in 28% of the patients who perished from a cerebrovascular insult compared with 5% in patients who died from another neurological process.2 Subsequent studies, including prospective cohorts evaluated with transesophageal echocardiography,3 established the presence of aortic arch atheroma (especially plaques >4 mm or mobile plaques) as a risk factor for cerebrovascular disease and a high risk factor for recurrent stroke.4 Until now, however, retrospective studies and subgroup analysis of larger trials have provided the sole source of guidance for treating patients with severe aortic arch disease and cryptogenic stroke.5 In fact, the latest guidelines from the American College of Cardiology Foundation and the American Heart Association state that for significant aortic atherosclerosis (>4 mm) there is no definitive therapeutic regimen for this high-risk patient group because no randomized trial has been completed.6 These guidelines proceed to state that either oral anticoagulation or antiplatelet therapy is a reasonable option for antithrombotic therapy. In this issue of Stroke , Amarenco et al7 describe the first prospective randomized trial addressing …

Stroke as a Complication of General Medical Disorders

Stroke is a leading cause of death and morbidity throughout the world. Numerous medical conditions are associated with stroke and predispose individuals to cerebrovascular disease. Hematologic disorders are a frequent cause. Several important disorders that involve the coagulation cascade, including protein C and S deficiencies, antithrombin III deficiency, and protein C resistance, are examined. Additionally, the relationship between the immune system and stroke is considered. Various circulating proteins such as homocysteine, lipoprotein (a), and cryoglobulins are linked to stroke and are discussed, as also are sickle cell disease, conditions that perturb coagulation such as malignancy, and medication use and the risk of stroke. The relationship between genetics and stroke is considered with regard to stroke evaluation and therapies in the future.

Electrically Conductive Scaffold to Modulate and Deliver Stem Cells

Stem cell therapy has emerged as an exciting stroke therapeutic, but the optimal delivery method remains unclear. While the technique of microinjection has been used for decades to deliver stem cells in stroke models, this technique is limited by the lack of ability to manipulate the stem cells prior to injection. This paper details a method of using an electrically conductive polymer scaffold for stem cell delivery. Electrical stimulation of stem cells using a conductive polymer scaffold alters the stem cells genes involved in cell survival, inflammatory response, and synaptic remodeling. After electrical preconditioning, the stem cells on the scaffold are transplanted intracranially in a distal middle cerebral artery occlusion rat model. This protocol describes a powerful technique to manipulate stem cells via a conductive polymer scaffold and creates a new tool to further develop stem cell-based therapy.

Engineered stem cell mimics to enhance stroke recovery

Currently, no medical therapies exist to augment stroke recovery. Stem cells are an intriguing treatment option being evaluated, but cell-based therapies have several challenges including developing a stable cell product with long term reproducibility. Since much of the improvement observed from cellular therapeutics is believed to result from trophic factors the stem cells release over time, biomaterials are well-positioned to deliver these important molecules in a similar fashion. Here we show that essential trophic factors secreted from stem cells can be effectively released from a multi-component hydrogel system into the post-stroke environment. Using our polymeric system to deliver VEGF-A and MMP-9, we improved recovery after stroke to an equivalent degree as observed with traditional stem cell treatment in a rodent model. While VEGF-A and MMP-9 have many unique mechanisms of action, connective tissue growth factor (CTGF) interacts with both VEGF-A and MMP-9. With our hydrogel system as well as with stem cell delivery, the CTGF pathway is shown to be downregulated with improved stroke recovery.