Differences in clot preparation determine outcome of recombinant tissue plasminogen activator treatment in experimental thromboembolic stroke

Sex Differences in the Dual Antiplatelet Therapy Versus Alteplase for Patients with Minor Nondisabling Acute Ischemic Stroke: A Secondary Analysis of the ARAMIS Study

BACKGROUND AND PURPOSE

Sex is associated with clinical outcome in stroke. The present study aimed to determine the effect of sex on efficacy of dual antiplatelet (DAPT) versus alteplase in ischemic stroke based on Antiplatelet versus recombinant tissue plasminogen activator (R-tPA) for Acute Mild Ischemic Stroke (ARAMIS) trial.

METHODS

In this secondary analysis of the ARAMIS study, eligible patients aged 18 years or older with minor nondisabling stroke who received dual antiplatelet therapy or intravenous alteplase within 4.5 h of stroke onset were divided into two groups: men and women. The primary endpoint was an excellent functional outcome, defined as a modified Rankin Scale (mRS) 0-1 at 90 days. Binary logistic regression analyses and generalized linear models were used.

RESULTS

Of the 719 patients who completed the study, 31% (223) were women, and 69% (496) were men. There were no significant sex differences in excellent functional outcome (unadjusted p = 0.304 for men and p = 0.993 for women; adjusted p = 0.376 for men and p = 0.918 for women) and favorable functional outcome (mRS score of 0-2; unadjusted p = 0.968 for men and p = 0.881 for women; adjusted p = 0.824 for men and p = 0.881 for women). But for the secondary outcomes, compared with alteplase, DAPT was associated with a significantly decreased proportion of early neurological deterioration within 24 h in men {unadjusted odds ratio [OR] = 0.440 [95% confidence interval (CI), 0.221-0.878]; p = 0.020; adjusted OR = 0.436 [95% CI, 0.216-0.877]; p = 0.020}, but not in women [unadjusted OR = 0.636 (95% CI, 0.175-2.319), p = 0.490; adjusted OR = 0.687 (95% CI, 0.181-2.609), p = 0.581]. For the safety outcomes, compared with the DAPT group, alteplase was associated with a significantly increased proportion of any bleeding events in men [unadjusted OR = 3.110 (95% CI, 1.103-8.770); p = 0.032], but not in women [unadjusted OR = 5.333 (95% CI, 0.613-46.407), p = 0.129; adjusted OR = 5.394 (95% CI, 0.592-49.112), p = 0.135].

CONCLUSION

Sex did not influence the effect of dual antiplatelet therapy versus intravenous alteplase in minor nondisabling stroke, but more early neurological deterioration and bleeding events occurred in men who received alteplase.

Dynamic Perviousness Has Predictive Value for Clot Fibrin Content in Acute Ischemic Stroke

Dynamic perviousness is a novel imaging biomarker, with clot density measurements at multiple timepoints to allow longer contrast to thrombus interaction. We investigated the correlations between dynamic perviousness and clot composition in the setting of acute ischemic stroke. Thirty-nine patients with large vessel occlusion (LVO) undergoing mechanical thrombectomy (MT) were analyzed. Patients received a three-phase CT imaging pre-thrombectomy and histopathological analysis of retrieved clots. Clot densities for every phase and change in densities between phases were calculated, leading to four patterns of dynamic perviousness: no contrast uptake, early contrast uptake with and without washout and late uptake. Clots were categorized into three groups based on dominant histologic composition: red blood cell (RBC)-rich, fibrin/platelet-rich and mixed. Clot composition was correlated with dynamic perviousness using the Kruskal-Wallis test and Pearson's correlation analysis. The dynamic perviousness categories showed a significant difference between fibrin-rich clots when compared to RBC-rich plus mixed groups. The uptake without washout category had significantly fewer fibrin clots compared to the uptake with washout (p = 0.036), and nearly significantly fewer fibrin clots when compared to the no uptake category (p = 0.057). Contrast uptake with different patterns of contrast washout showed significant differences of the likelihood for fibrin-rich clots.

Machine Learning Analysis of the Cerebrovascular Thrombi Lipidome in Acute Ischemic Stroke

ABSTRACT

OBJECTIVE: The aim of this study was to identify a signature lipid profile from cerebral thrombi in acute ischemic stroke (AIS) patients at the time of ictus. METHODS: We performed untargeted lipidomics analysis using liquid chromatography-mass spectrometry on cerebral thrombi taken from a nonprobability, convenience sampling of adult subjects (≥18 years old, n = 5) who underwent thrombectomy for acute cerebrovascular occlusion. The data were classified using random forest, a machine learning algorithm. RESULTS: The top 10 metabolites identified from the random forest analysis were of the glycerophospholipid species and fatty acids. CONCLUSION: Preliminary analysis demonstrates feasibility of identification of lipid metabolomic profiling in cerebral thrombi retrieved from AIS patients. Recent advances in omic methodologies enable lipidomic profiling, which may provide insight into the cellular metabolic pathophysiology caused by AIS. Understanding of lipidomic changes in AIS may illuminate specific metabolite and lipid pathways involved and further the potential to develop personalized preventive strategies.

Fibrin-Targeted Nanoparticles for Finding, Visualizing and Characterizing Blood Clots in Acute Ischemic Stroke

Recanalization of the occluded artery is the gold standard treatment for acute ischemic stroke, which includes enzymatic fibrinolytic treatment with the use of recombinant tissue plasminogen activators (rtPAs) to disrupt the occluding clot, the use of mechanical thrombectomy to physically remove the clot, or a combination of both. Fibrin is one of the main components of blood clots causing ischemic stroke and is the target of rtPA upon activation of plasminogen in the clot. In addition, fibrin content also influences the efficacy of mechanical thrombectomy. Current imaging methods can successfully identify occlusions in large vessels; however, there is still a need for contrast agents capable of visualizing small thrombi in ischemic stroke patients. In this work, we describe the synthesis and the in vitro characterization of a new diagnostic nanoparticle, as well as the in vivo evaluation in an animal model of thromboembolic stroke. Gd-labeled KCREKA peptides were synthesized and attached onto the surface of PEGylated superparamagnetic nanoparticles. Magnetic resonance imaging (MRI) of blood clots was performed in vitro and in vivo in animal models of thromboembolic stroke. KCREKA-NPs were synthesized by attaching the peptide to the amino (N) termini of the PEG-NPs. The sizes of the nanoparticles, measured via DLS, were similar for both KCREKA-NPs and PEG-NPs (23 ± 4 nm, PDI = 0.11 and 25 ± 8 nm, PDI = 0.24, respectively). In the same line, r2 relaxivities were also similar for the nanoparticles (149 ± 2 mM Fe s−1 and 151 ± 5 mM Fe s−1), whereas the r1 relaxivity was higher for KCREKA-NPs (1.68 ± 0.29 mM Fe s−1 vs. 0.69 ± 0.3 mM Fe s−1). In vitro studies showed that blood clots with low coagulation times were disrupted by rtPA, whereas aged clots were almost insensitive to the presence of rtPA. MRI in vitro studies showed a sharp decrease in the T1 × T2 signals measured for aged clots incubated with KCREKA-NPs compared with fresh clots (47% [22, 80] to 26% [15, 51]). Furthermore, the control blood showed a higher value of the T1 × T2 signal (39% [20, 61]), being the blood clots with low coagulation times the samples with the lowest values measured by MRI. In vivo studies showed a significant T1 × T2 signal loss in the clot region of 24% after i.v. injection of KCREKA-NPs. The thrombus age (2.5% ± 6.1% vs. 81.3% ± 19.8%, p < 0.01) confirmed our ability to identify in vivo fresh blood clots. In this study, we developed and tested a dual MRI nanoparticle, acting as T1 and T2 contrast agents in MRI analyses. The developed KCREKA-NPs showed affinity for the fibrin content of blood clots, and the MRI signals provided by the nanoparticles showed significant differences depending on the clot age. The developed KCREKA-NPs could be used as a tool to predict the efficacy of a recanalization treatment and improve the triage of ischemic stroke patients.

Temporal alteration of microglia to microinfarcts in rat brain induced by the vascular occlusion with fluorescent microspheres

Microglia, the resident immune cells in the central nervous system, can monitor the microenvironment and actively respond to ischemic stroke and other brain injuries. In this procedure, microglia and neurons can cross-talk via transmembrane chemokine, Fractalkine (CX3CL1), to impact one another. We used a rat model of multifocal microinfarcts induced by the injection of fluorescent microspheres into the right common carotid artery and examined the morphological alteration of blood vessels, microglia, astrocytes, and neurons at 6 h, 1, 7, and 14 days after modeling, along with neurobehavioral tests and the staining of CX3CL1 in this study. Our results demonstrated that in the infarcted regions, astrocytes and microglia activated in response to neuronal degeneration and upregulation of cleaved caspase-3, which occurred concurrently with vascular alteration and higher expression of CX3CL1. We provided sequential histological data to shed light on the morphological changes after modeling, which would help in the identification of new targets and the choice of the ideal time window for therapeutic intervention in ischemic stroke.

Precise control of embolic stroke with magnetized red blood cells in mice

Precise embolism control in immature brains can facilitate mechanistic studies of brain damage and repair after perinatal arterial ischemic stroke (PAIS), but it remains a technical challenge. Microhemorrhagic transformation is observed in one-third of infant patients who have suffered PAIS, but the underlying mechanism remains elusive. Building on an established approach that uses magnetic nanoparticles to induce PAIS, we develop a more advanced approach that utilizes magnetized erythrocytes to precisely manipulate de novo and in situ embolus formation and reperfusion in perinatal rodent brains. This approach grants spatiotemporal control of embolic stroke without any transarterial delivery of pre-formed emboli. Transmission electron microscopy revealed that erythrocytes rather than nanoparticles are the main material obstructing the vessels. Both approaches can induce microbleeds as an age-dependent complication; this complication can be prevented by microglia and macrophage depletion. Thus, this study provides an animal model mimicking perinatal embolic stroke and implies a potential therapeutic strategy for the treatment of perinatal stroke.

Measuring the effect of thrombosis, thrombus maturation and thrombolysis on clot mechanical properties in an in-vitro model

Changes in acute ischemic stroke thrombi structure and composition may result in significant differences in treatment responsiveness. Ischemic stroke patients are often treated with a thrombolytic agent to dissolve thrombi, however these patients may subsequently undergo mechanical thrombectomy to remove the occlusive clot. We set out to determine if rt-PA thrombolysis treatment of blood clots changes their mechanical properties, which in turn may impact mechanical thrombectomy. Using a design-of-experiment approach, ovine clot analogues were prepared with varying composition and further exposed to different levels of compaction force to simulate the effect of arterial blood pressure. Finally, clots were treated with three r-tPA doses for different durations. Clot mass and mechanical behaviour was analysed to assess changes due to (i) Platelet driven contraction (ii) Compaction force and (iii) Thrombolysis. Clots that were exposed to r-tPA for longer duration showed significant reduction in clot mass (p < 0.001). Exposure time to r-tPA (p < 0.001) was shown to be an independent predictor of lower clot stiffness. A decrease in energy dissipation ratio during mechanical compression was associated with longer exposure time in r-tPA (p = 0.001) and a higher platelet concentration ratio (p = 0.018). The dose of r-tPA was not a significant factor in reducing clot mass or changing mechanical properties of the clots. Fibrinolysis reduces clot stiffness which may explain increased distal clot migration observed in patients treated with r-tPA and should be considered as a potential clot modification factor before mechanical thrombectomy.

A Novel Thromboplastin-Based Rat Model of Ischemic Stroke

The thromboembolic ischemia model is one of the most applicable for studying ischemic stroke in humans. The aim of this study was to develop a novel thromboembolic stroke model, allowing, by affordable tools, to reproduce cerebral infarction in rats. In the experimental group, the left common carotid artery, external carotid artery, and pterygopalatine branch of maxillary artery were ligated. A blood clot that was previously formed (during a 20 min period, in a catheter and syringe, by mixing with a thromboplastin solution and CaCl₂) was injected into the left internal carotid artery. After 10 min, the catheter was removed, and the incision was sutured. The neurological status of the animals was evaluated using a 20-point scale. Histological examination of brain tissue was performed 6, 24, 72 h, and 6 days post-stroke. All groups showed motor and behavioral disturbances 24 h after surgery, which persisted throughout the study period. A histological examination revealed necrotic foci of varying severity in the cortex and subcortical regions of the ipsilateral hemisphere, for all experimental groups. A decrease in the density of hippocampal pyramidal neurons was revealed. Compared with existing models, the proposed ischemic stroke model significantly reduces surgical time, does not require an expensive operating microscope, and consistently reproduces brain infarction in the area of the middle cerebral artery supply.

Animal models of stroke

Stroke is a devastating disease with high morbidity and mortality. Animal models are indispensable tools that can mimic stroke processes and can be used for investigating mechanisms and developing novel therapeutic regimens. As a heterogeneous disease with complex pathophysiology, mimicking all aspects of human stroke in one animal model is impossible. Each model has unique strengths and weaknesses. Models such as transient or permanent intraluminal thread occlusion middle cerebral artery occlusion (MCAo) models and thromboembolic models are the most commonly used in simulating human ischemic stroke. The endovascular filament occlusion model is characterized by easy manipulation and accurately controllable reperfusion and is suitable for studying the pathogenesis of focal ischemic stroke and reperfusion injury. Although the reproducibility of the embolic model is poor, it is more convenient for investigating thrombolysis. Rats are the most frequently used animal model for stroke. This review mainly outlines the stroke models of rats and discusses their strengths and shortcomings in detail.

Factors Influencing Recanalization After Mechanical Thrombectomy With First-Pass Effect for Acute Ischemic Stroke: A Systematic Review and Meta-Analysis

Background: First-pass effect (FPE) is increasingly recognized as a predictor of good outcome in large vessel occlusion (LVO). This systematic review and meta-analysis aimed to elucidate the factors influencing recanalization after mechanical thrombectomy (MT) with FPE in treating acute ischemic stroke (AIS).

Methods: Main databases were searched for relevant randomized controlled trials (RCTs) and observational studies reporting influencing factors of MT with FPE in AIS. Recanalization was assessed by the modified thrombolysis in cerebral ischemia (mTICI) score. Both successful (mTICI 2b-3) and complete recanalization (mTICI 2c-3) were observed. Risk of bias was assessed through different scales according to study design. The I² statistic was used to evaluate the heterogeneity, while subgroup analysis, meta-regression, and sensitivity analysis were performed to investigate the source of heterogeneity. Visual measurement of funnel plots was used to evaluate publication bias.

Results: A total of 17 studies and 6,186 patients were included. Among them, 2,068 patients achieved recanalization with FPE. The results of meta-analyses showed that age [mean deviation (MD):1.21,95% confidence interval (CI): 0.26–2.16; p = 0.012], female gender [odds ratio (OR):1.12,95% CI: 1.00–1.26; p = 0.046], diabetes mellitus (DM) (OR:1.17,95% CI: 1.01–1.35; p = 0.032), occlusion of internal carotid artery (ICA) (OR:0.71,95% CI: 0.52–0.97; p = 0.033), occlusion of M2 segment of middle cerebral artery (OR:1.36,95% CI: 1.05–1.77; p = 0.019), duration of intervention (MD: −27.85, 95% CI: −42.11–13.58; p < 0.001), time of onset to recanalization (MD: −34.63, 95% CI: −58.45–10.81; p = 0.004), general anesthesia (OR: 0.63,95% CI: 0.52–0.77; p < 0.001), and use of balloon guide catheter (BGC) (OR:1.60,95% CI: 1.17–2.18; p = 0.003) were significantly associated with successful recanalization with FPE. At the same time, age, female gender, duration of intervention, general anesthesia, use of BGC, and occlusion of ICA were associated with complete reperfusion with FPE, but M2 occlusion and DM were not.

Conclusion: Age, gender, occlusion site, anesthesia type, and use of BGC were influencing factors for both successful and complete recanalization after first-pass thrombectomy. Further studies with more comprehensive observations indexes are need in the future.

A Narrative Review of Common Uses of Ophthalmic Ultrasound in Emergency Medicine

BACKGROUND

The timely evaluation of ocular conditions in the emergency department (ED) can be difficult due to a general lack of specialized equipment, trained personnel, and the time-sensitive nature of emergent ocular conditions. Recently, the use of ocular point-of-care ultrasound (POCUS) has been shown to be particularly useful in the ED. POCUS can be used to promptly diagnose various ocular pathologies, which include ocular trauma, vitreous hemorrhage, central retinal artery occlusion, and retinal detachment.

OBJECTIVES

This narrative review seeks to inform the reader of current literature regarding the use of POCUS for the assessment of various ocular emergencies in the ED. The goal of this review is to provide the emergency physician with succinct and up-to-date information and instruction regarding the current uses of POCUS for patients presenting with particular ocular emergencies. Ocular pathologies that are common (ocular trauma) or for which ultrasound is particularly useful (such as retinal detachment) are discussed. Other ocular pathologies are also briefly discussed, such as central retinal artery occlusion, which is a promising new application for ultrasound evaluation.

DISCUSSION

There have been many studies that provide evidence for the utility of POCUS in the evaluation of trauma and other ocular pathologies, including vitreous hemorrhage, retinal detachment, and central retinal artery occlusion.

CONCLUSIONS

Ocular POCUS is a useful modality in the evaluation of acute ocular complaints in the ED. Emergency physicians should be aware of these findings and feel confident in the utility of ocular POCUS in the ED.

Using the Retrobulbar Spot Sign to Assist in Diagnosis and Management of Central Retinal Artery Occlusions

Point-of-care ultrasound has become an integral part of the evaluation of monocular vision loss. Most commonly, it has been used to evaluate retinal detachment, vitreous hemorrhage, and posterior vitreous detachment. Point-of-care ultrasound can also be used to evaluate central retinal arterial occlusion, whereby a retrobulbar spot sign is present. We present a case series of 4 patients presenting with monocular vision loss who were found to have central retinal artery occlusion. We describe what a retrobulbar spot sign is and how its presence or absence can assist in the evaluation and treatment of these patients.

Simultaneous R2* and quantitative susceptibility mapping measurement enables differentiation of thrombus hematocrit and age: an in vitro study at 3 T

BACKGROUND

The efficacy of acute ischemic stroke treatment is affected by thrombus composition and age, yet no diagnostic method capable of quantitative thrombus characterization currently exists. This in vitro study evaluates the use of R_2^* , quantitative susceptibility mapping (QSM), and proton density fat fraction (FF) maps derived from a single gradient echo (GRE) MRI acquisition for characterizing clot of various hematocrit, as well as added calcified and lipidic components, throughout aging.

METHODS

Two thrombus phantoms containing porcine clots (10-60% hematocrit, one with added calcium or lard) were scanned serially throughout 6 days of aging. Three-dimensional multi-echo GRE imaging was used to generate R_2^* , QSM, and FF maps, from which mean values for all clots at every time point were obtained. Receiver operating characteristic analysis was used to derive thresholds differentiating acute from chronic clot, and measured R_2^* and QSM were tested for their ability to estimate clot hematocrit.

RESULTS

R_2^* and QSM varied minimally over the first 6 hours of aging (acute), and QSM was found to linearly relate to clot hematocrit. Beyond 6 hours (chronic), R_2^* and QSM increased considerably over time and hematocrit could be estimated from the R_2^* /QSM ratio. R_2^* and QSM thresholds of 22 s^-1 and 0.165 ppm differentiated acute from chronic clots with a sensitivity/specificity of 100%/100% and 85%/92%, respectively. QSM and FF maps definitively distinguished calcium and lipid, respectively, from clots of any hematocrit and age.

CONCLUSIONS

R_2^* , QSM, and FF from a single multi-echo GRE scan discriminated hematocrit and age, and distinguished calcification and lipid withinin vitro clot.

Presence of multi-segment clot sign on dynamic CT angiography: a predictive imaging marker of recanalisation and good outcome in acute ischaemic stroke patients

OBJECTIVE

To investigate the value of multi-segment clot (MSC) sign on dynamic CT angiography (CTA) in predicting recanalisation and outcome after reperfusion therapy in acute ischaemic stroke (AIS) with large artery occlusion (LAO).

METHODS

We retrospectively reviewed data of anterior circulation LAO patients from a prospectively collected database for consecutive AIS patients who underwent perfusion CT (CTP) before treatment. MSC sign was defined as the presence of multiple segments on dynamic CTA derived from CTP data. Good outcome was defined as modified Rankin score 0-3 at 90 days.

RESULTS

A total of 181 LAO patients were enrolled. MSC sign was present in 73 (40.3%) patients. When compared with patients without MSC sign, patients with MSC sign had a significantly higher rate of recanalisation (76.7% versus 56.5%, p = 0.005) and good outcome (67.1% versus 51.0%, p = 0.035). Multivariable logistic regression analyses showed that MSC sign was an independent predictor for both recanalisation (OR [95% CI] = 2.237 [1.069-4.681]; p = 0.033) and good outcome (OR [95% CI] = 2.715 [1.154-6.388]; p = 0.022) after adjustment.

CONCLUSIONS

The MSC sign is a good indicator for recanalisation and good outcome after reperfusion therapy in anterior circulation LAO patients.

KEY POINTS

• MSC sign was present in about 40% acute anterior circulation LAO patients. • MSC sign is a predictor for recanalisation after reperfusion treatment. • Patients with MSC sign have a better outcome.

Role of Hyperintense Acute Reperfusion Marker for Classifying the Stroke Etiology

Purpose

The hyperintense acute reperfusion marker (HARM) is a delayed enhancement of the subarachnoid or subpial space observed on post-contrast fluid-attenuated inversion recovery (FLAIR) images and is associated with permeability changes to the blood–brain barrier in acute stroke. We investigated the relationship between HARM and stroke etiology based on the Trial of ORG 10172 in Acute Stroke Treatment (TOAST) classification. In addition, we evaluated the relationship between HARM and stroke locations with respect to vascular territories and anatomic compartments.

Materials and methods

We recruited 264 consecutive patients (109 women; mean age 68.63 years) who were diagnosed with acute ischemic stroke and underwent brain magnetic resonance imaging (MRI) including post-contrast FLAIR and DWI within 7 days of symptom onset from May 2015 to March 2016 for this retrospective study. Post-contrast FLAIR images were obtained 5 min after gadolinium administration. The mean time interval between the onset of stroke symptoms and MRI acquisition in total included patients was 18 h and 7 min (median 12 h and 57 min, range 2–127 h). We analyzed the overall incidence and distribution patterns of HARM in acute ischemic stroke cases and compared the relative incidence and distribution patterns of HARM between the subgroups of stroke etiology based on conventional TOAST classification. We obtained odds ratio (OR) of HARM in different stroke locations based on vascular territories and anatomical compartments. This study was approved by our institutional review board.

Results

Among the 264 patients, 67 (25.38%) patients were HARM positive and 197 (74.62%) patients were HARM negative. There was significant difference in HARM incidence among the stroke subgroups (p < 0.001). Small vessel occlusion (SVO) was associated with the HARM-negative group (p < 0.001), while large artery atherosclerosis (LAA) and cardioembolism (CE) were associated with the HARM-positive group (p = 0.001). Also, regional pattern of HARM on the same vascular territory as the acute infarction was dominantly demonstrated regardless of stroke etiology. The OR for HARM from middle cerebral artery (MCA) infarction was 1.868 [95% confidence interval (CI): 1.025–3.401]. The OR for HARM from cortical infarction was 9.475 (95% CI: 4.754–18.883) compared to other anatomic compartments.

Conclusion

The presence of the HARM was significantly associated with embolic infarctions including LAA and CE. Conversely, SVO was exclusively associated with the absence of the HARM. Second, MCA and cortical infarction showed a more pronounced HARM compared to infarctions at other vascular territories and anatomic compartments. According to the results in the current study, we speculate that the presence of HARM on post-contrast FLAIR images was associated with specific stroke causes especially in embolic causes.

From head to toe: Sex and gender differences in the treatment of ischemic cerebral disease

Stroke is a major cause of mortality and morbidity, particularly in the older ages. Women have a longer life expectancy and are more likely to experience stroke than men. Interestingly, the increased risk of ischemic stroke in women seems to be independent from age or classical cardiovascular risk factors. Notwithstanding the fact that stroke outcomes and survival are usually poorer in women, current evidence suggests that thrombolysis, antiplatelet and anticoagulant therapies are more beneficial in women than in men. A possible explanation of this paradox might be that females are often undertreated and they have fewer chances to be submitted to an effective and timely treatment for stroke than the male counterpart. The first step in the attempt to solve this obvious discrimination is surely to emphasize any reasons for differences in the therapeutic approach in relation to gender and then to denounce the lack of a sustainable motivation for them. In this article, we aimed to review the existing literature about gender-related differences on efficacy, administration and side effects of the most common drugs used for the treatment of ischemic stroke. The most striking result was the evidence that the therapeutic approach for stroke is often different according to patients' gender with a clear detrimental prognostic effect for women. A major effort is necessary to overcome this problem in order to ensure equal right to treatment without any sexual discrimination.

Control of cerebral ischemia with magnetic nanoparticles

The precise manipulation of microcirculation in mice can facilitate mechanistic studies of brain injury and repair after ischemia, but this manipulation remains a technical challenge, particularly in conscious mice. We developed a technology that uses micromagnets to induce aggregation of magnetic nanoparticles to reversibly occlude blood flow in microvessels. This allowed induction of ischemia in a specific cortical region of conscious mice of any postnatal age, including perinatal and neonatal stages, with precise spatiotemporal control but without surgical intervention of the skull or artery. When combined with longitudinal live-imaging approaches, this technology facilitated the discovery of a feature of the ischemic cascade: selective loss of smooth muscle cells in juveniles but not adults shortly after onset of ischemia and during blood reperfusion.

Is shorter transient middle cerebral artery occlusion (t-MCAO) duration better in stroke experiments on diabetic female Sprague Dawely rats?

AIM

To determine optimal duration of transient middle cerebral artery occlusion (t-MCAO) for a stroke model in female diabetic Sprague-Dawley (SD) rats.

METHODS

Streptozotocin-induced type-1 diabetic SD female rats (n = 25, 12 weeks old, five groups; n = 5 per group) were subjected to different duration of t-MCAO (20, 30, 45, 60 and 90 minutes) followed by reperfusion. A control group of rats without diabetes (n = 5) was subjected to 30 minutes of t-MCAO followed by reperfusion. Twenty-four hours after reperfusion, infarct volumes were evaluated by 2,3,5-triphenyltetrazolium chloride (TTC) staining.

RESULTS

Intra-ischaemic reductions of regional cerebral blood flow (rCBF) were similar in all groups (68-75% of baseline values). Reperfusion was significantly impaired in the 90-minute ischaemia group (56-62% vs 80-125% in other groups). Twenty minutes of t-MCAO induced a small infarct (3 ± 5% of ischaemic hemisphere). Thirty minutes of ischaemia produced a significantly larger infarct (46 ± 6%). In the 45 and 60 minute groups, ischaemia infarct was 52 ± 5% and 59 ± 3% of the ischaemic hemisphere, respectively. Ischaemia of 90' led to a massive stroke (89 ± 6% of ischaemic hemisphere encompassing the whole striatum (22 ± 3%) and almost the whole MCA irrigated cortex area (67 ± 6%)). Thirty minutes of t-MCAO did not produce stroke in the control group.

CONCLUSION

The diabetic rat stroke model should be different from the non-diabetic, because female type-1 diabetic SD rats are highly sensitive to brain ischaemia and it is necessary to significantly shorten the duration of t-MCAO, optimally to 30 minutes.

High CD3+ Cells in Intracranial Thrombi Represent a Biomarker of Atherothrombotic Stroke

Background and Purpose

Approximately 30% of strokes are cryptogenic despite an exhaustive in-hospital work-up. Analysis of clot composition following endovascular treatment could provide insight into stroke etiology. T-cells already have been shown to be a major component of vulnerable atherosclerotic carotid lesions. We therefore hypothesize that T-cell content in intracranial thrombi may also be a biomarker of atherothrombotic origin.

Materials and Methods

We histopathologically investigated 54 consecutive thrombi retrieved after mechanical thrombectomy in acute stroke patients. First, thrombi were classified as fibrin-dominant, erythrocyte-dominant or mixed pattern. We then performed quantitative analysis of CD3+ cells on immunohistochemically-stained thrombi and compared T-cell content between “atherothrombotic”, “cardioembolism” and “other causes” stroke subtypes.

Results

Fourteen (26%) thrombi were defined as fibrin-dominant, 15 (28%) as erythrocyte-dominant, 25 (46%) as mixed. The stroke cause was defined as “atherothrombotic” in 10 (18.5%), “cardioembolism” in 25 (46.3%), and “other causes” in 19 (35.2%). Number of T-cells was significantly higher in thrombi from the “atherothrombotic” group (53.60 ± 28.78) than in the other causes (21.77 ± 18.31; p<0.0005) or the “cardioembolism” group (20.08 ± 15.66; p<0.0003).

Conclusions

The CD3+ T-cell count in intracranial thrombi was significantly higher in “atherothrombotic” origin strokes compared to all other causes. Thrombi with high content of CD3+ cells are more likely to originate from an atherosclerotic plaque.

The Importance of Considering Sex Differences in Translational Stroke Research

Stroke is the second leading cause of death worldwide, and differences between men and women have been documented in incidence, prevalence, and outcome. Here, we reviewed the literature on sex differences in stroke severity, mortality, functional outcome, and response to therapies after ischemic stroke. Many of the sex differences in stroke severity and mortality are explained by differences in baseline demographics such as older age in women. However, women account for more stroke deaths, consistently suffer from worse stroke outcomes, and are more often institutionalized and permanently disabled than men. These sex differences in functional outcome are equalized after treatment with tissue plasminogen activator (tPA) and women may benefit more from treatment than men. However, this may depend on race, as African-American women have less of a response to tPA than other groups. Regarding endovascular treatments, the few existing studies that have investigated sex differences in stroke outcome point to equal benefit in both sexes; however, many clinical trials are relatively underpowered to detect sex differences. Further, we considered sex-specific effects in animal models of stroke and present recommendations for the performance of stroke studies in female animals. The male-biased use of research animals is distinguished from the clinical situation where there is a disproportionate and growing female stroke population. Stroke in women is greatly understudied, and including both sexes is especially important in both preclinical and clinical studies that evaluate potential stroke therapies.

In Situ Microparticles Loaded with S-Nitrosoglutathione Protect from Stroke

Treatment of stroke, especially during the first hours or days, is still lacking. S-nitrosoglutathione (GSNO), a cerebroprotective agent with short life time, may help if administered early with a sustain delivery while avoiding intensive reduction in blood pressure. We developed in situ forming implants (biocompatible biodegradable copolymer) and microparticles (same polymer and solvent emulsified with an external oily phase) of GSNO to lengthen its effects and allow cerebroprotection after a single subcutaneous administration to Wistar rats. Arterial pressure was recorded for 3 days (telemetry, n = 14), whole-blood platelet aggregation up to 13 days (aggregometry, n = 58), and neurological score, cerebral infarct size and edema volume for 2 days after obstruction of the middle cerebral artery by autologous blood clots (n = 30). GSNO-loaded formulations (30 mg/kg) induced a slighter and longer hypotension (-10 vs. -56 ± 6 mmHg mean arterial pressure, 18 h vs. 40 min) than free GSNO at the same dose. The change in pulse pressure (-50%) lasted even up to 42 h for microparticles. GSNO-loaded formulations (30 mg/kg) prevented the transient 24 h hyper-aggregability observed with free GSNO and 7.5 mg/kg-loaded formulations. When injected 2 h after stroke, GSNO-loaded microparticles (30 mg/kg) reduced neurological score at 24 (-62%) and 48 h (-75%) vs. empty microparticles and free GSNO 7.5 mg/kg and, compared to free GSNO, divided infarct size by 10 and edema volume by 8 at 48 h. Corresponding implants reduced infarct size and edema volume by 2.5 to 3 times. The longer (at least 2 days) but slight effects on arterial pressures show sustained delivery of GSNO-loaded formulations (30 mg/kg), which prevent transient platelet hyper-responsiveness and afford cerebroprotection against the consequences of stroke. In conclusion, in situ GSNO-loaded formulations are promising candidates for the treatment of stroke.

Tissue Plasminogen Activator for preclinical stroke research: Neither "rat" nor "human" dose mimics clinical recanalization in a carotid occlusion model

Tissue plasminogen activator (tPA) is the only approved thrombolytic therapy for acute ischemic stroke, yet many patients do not recanalize. Enhancing thrombolytic efficacy of tPA is a major focus of stroke research. Traditionally, a “rat dose” of 10 mg/kg has been used in rodent models. Recent studies suggested that the clinical “human” dose (0.9 mg/kg) may better mimic clinical recanalization. These studies only compared the rat and clinical doses, and so we aimed to test recanalization efficacy of multiple tPA doses ranging from 0.9 to 10 mg/kg in a model of endothelial injury and vessel stenosis. The common carotid artery of rats was crushed and stenosed to allow in-situ occlusive thrombus formation (Folt’s model of ‘physiological’ thrombus). Intravenous tPA was administered 60 minutes post-occlusion (n = 6-7/group). Sustained recanalization rates were 0%, 17%, 67% and 71%, for 0.9, 1.8, 4.5, and 10 mg/kg, respectively. Median time to sustained recanalization onset decreased with increasing dosage. We conclude that 10 mg/kg of tPA is too effective, whereas 0.9 mg/kg is ineffective for lysis of occlusive thrombi formed in situ. Neither dose mimics clinical tPA responses. A dose of 2x the clinical dose is a more appropriate mimic of clinical tPA recanalization in this model.

A Thrombotic Stroke Model Based On Transient Cerebral Hypoxia-ischemia

Stroke research has endured many setbacks in translating neuroprotective therapies into clinical practice. In contrast, the real-world therapy (tPA thrombolysis) rarely produces benefits in mechanical occlusion-based experimental models, which dominate preclinical stroke research. This split between the bench and bedside suggests the need to employ tPA-responsive models in preclinical stroke research. To this end, a simple and tPA-reactive thrombotic stroke model is invented and described here. This model consists of transient occlusion of the unilateral common carotid artery and delivery of 7.5% oxygen through a face mask in adult mice for 30 min, while maintaining the animal rectal temperature at 37.5 ± 0.5 °C. Although reversible ligation of the unilateral carotid artery or hypoxia each suppressed cerebral blood flow only transiently, the combination of both insults caused lasting reperfusion deficits, fibrin and platelet deposition, and large infarct in the middle cerebral artery-supplied territory. Importantly, tail-vein injection of recombinant tPA at 0.5, 1, or 4 hr post-tHI (10 mg/kg) provided time-dependent reduction of the mortality rate and infarct size. This new stroke model is simple and can be standardized across laboratories to compare experimental results. Further, it induces thrombosis without craniectomy or introducing pre-formed emboli. Given these unique merits, the tHI model is a useful addition to the repertoire of preclinical stroke research.

Animal models of ischemic stroke and their application in clinical research

This review outlines the most frequently used rodent stroke models and discusses their strengths and shortcomings. Mimicking all aspects of human stroke in one animal model is not feasible because ischemic stroke in humans is a heterogeneous disorder with a complex pathophysiology. The transient or permanent middle cerebral artery occlusion (MCAo) model is one of the models that most closely simulate human ischemic stroke. Furthermore, this model is characterized by reliable and well-reproducible infarcts. Therefore, the MCAo model has been involved in the majority of studies that address pathophysiological processes or neuroprotective agents. Another model uses thromboembolic clots and thus is more convenient for investigating thrombolytic agents and pathophysiological processes after thrombolysis. However, for many reasons, preclinical stroke research has a low translational success rate. One factor might be the choice of stroke model. Whereas the therapeutic responsiveness of permanent focal stroke in humans declines significantly within 3 hours after stroke onset, the therapeutic window in animal models with prompt reperfusion is up to 12 hours, resulting in a much longer action time of the investigated agent. Another major problem of animal stroke models is that studies are mostly conducted in young animals without any comorbidity. These models differ from human stroke, which particularly affects elderly people who have various cerebrovascular risk factors. Choosing the most appropriate stroke model and optimizing the study design of preclinical trials might increase the translational potential of animal stroke models.

Factors affecting clinical outcome in large-vessel occlusive ischemic strokes

Clinical outcome after large-vessel occlusive strokes depends on admitting clinical condition, successful recanalization, and robust collateral circulation. However, predicting successful recanalization and quantifying collateral status in the acute setting remain elusive. Successful recanalization has many predictive factors. Strong evidence supports increasing clot length being associated with poor recanalization. Current imaging techniques completed in the acute setting suggest that clot length can be estimated with a clot burden score. In vitro evidence suggests that clots with more red blood cells and less thrombin lyse more easily after systemic fibrinolysis. Clinical correlations with clot composition have been mixed, although one study suggested that clot composition could be predicted with computed tomography and correlate with successful recanalization. Finally, overwhelming proof shows that robust collateral circulation correlates with improved clinical outcome. Imaging modalities in the acute setting remain promising, with studies suggesting that collaterals can be quantified with computed tomography angiography and perfusion studies. Patients with large-vessel occlusive strokes have variable clinical responses to fibrinolysis and thrombectomy. Independent predictive variables that can possibly alter clinical outcome appear to be successful recanalization and robust collateral circulation. Future studies that allow for better prediction of successful recanalization and quantification of collateral status may help clinical decision-making when evaluating large-vessel occlusions.

Animal models of stroke: translational potential at present and in 2050

Translation from basic science bench research in ischemic stroke to bedside treatment of patients suffering ischemic stroke remains a difficult challenge. Despite literally hundreds of compounds and interventions that provide benefit in experimental models of cerebral ischemia, efficacy in humans remains to be demonstrated. The reasons for failure to translate the extensive positive basic science findings to successful clinical trials have been the focus of discussion for years. Some attribute the failure to flaws in clinical trial design, others question the predictive value of current animal models and some question the quality of preclinical data. It is likely that a combination of all these shortcomings have ultimately led to the failure. The purpose of this review is to analyze the commonly used animal models used in the field today, provide a framework for understanding the current state of basic science research in the ischemic stroke field and discuss a path forward.

Characterization of a new model of thromboembolic stroke in C57 black/6J mice

This study characterizes a new model of thromboembolic stroke of the middle cerebral artery in C57 black/6J mice, thus offering an opportunity to use the model for studying ischemic stroke in transgenic mice. Thromboembolic stroke was induced by local injection of either 1.5 or 3.0 UI of thrombin directly into the right MCA of C57 black/6J mice. Cerebral blood flow (CBF) velocity was measured continuously by laser Doppler flowmetry, which allowed documentation of both MCA occlusion and of spontaneous recanalization. After 24 h, all animals were euthanized. Cryosections were cut at 400-μm intervals and silver stained with the high-contrast method for volumetric assessment of infarct size. Interleukin (IL)-6, tumor necrosis factor-alpha (TNF-α), caspase-3 and hsp 70 protein levels were investigated by immunofluorescence. Thrombin injection resulted in clot formation in all animals. Cortical infarction occurred in 63% of the mice while 37% had a spontaneous MCA recanalization during the first 20 min following thrombin injection. In cases of successful MCA occlusion with consequent infarction, the clot was stable up to 2 h after formation. Subsequently, 20% recanalized spontaneously. Infarctions were restricted to the cortex with a mean lesion volume of 36 ± 5 for 1.5 UI and 56 ± 8 for 3.0 UI thrombin. Protein levels of IL-6, TNF-α, caspase-3, and hsp 70 were significantly increased after MCAO. The results demonstrate that the mouse thromboembolic stroke model produces cortical infarctions of consistent size in C57 black/6J mice, which is dependent upon the amount of thrombin used for clot formation. Spontaneous MCA recanalization occurs after 2 h of ischemia in 20% of mice. Thus, the thromboembolic model is an applicable stroke model for C57 black/6J mice, which mimics many of the features of human stroke, including spontaneous recanalization. However, strain differences between Swiss and C57 black/6J mice must be taken into account when using the model.

Synergy of combined tPA-edaravone therapy in experimental thrombotic stroke

Edaravone, a potent antioxidant, may improve thrombolytic therapy because it benefits ischemic stroke patients on its own and mitigates adverse effects of tissue plasminogen activator (tPA) in preclinical models. However, whether the combined tPA-edaravone therapy is more effective in reducing infarct size than singular treatment is uncertain. Here we investigated this issue using a transient hypoxia-ischemia (tHI)-induced thrombotic stroke model, in which adult C57BL/6 mice were subjected to reversible ligation of the unilateral common carotid artery plus inhalation of 7.5% oxygen for 30 min. While unilateral occlusion of the common carotid artery suppressed cerebral blood flow transiently, the addition of hypoxia triggered reperfusion deficits, endogenous thrombosis, and attenuated tPA activity, leading up to infarction. We compared the outcomes of vehicle-controls, edaravone treatment, tPA treatment at 0.5, 1, or 4 h post-tHI, and combined tPA-edaravone therapies with mortality rate and infarct size as the primary end-points. The best treatment was further compared with vehicle-controls in behavioral, biochemical, and diffusion tensor imaging (DTI) analyses. We found that application of tPA at 0.5 or 1 h – but not at 4 h post-tHI – significantly decreased infarct size and showed synergistic (p<0.05) or additive benefits with the adjuvant edaravone treatment, respectively. The acute tPA-edaravone treatment conferred >50% reduction of mortality, ∼80% decline in infarct size, and strong white-matter protection. It also improved vascular reperfusion and decreased oxidative stress, inflammatory cytokines, and matrix metalloproteinase activities. In conclusion, edaravone synergizes with acute tPA treatment in experimental thrombotic stroke, suggesting that clinical application of the combined tPA-edaravone therapy merits investigation.

Impact of the neutrophil response to granulocyte colony-stimulating factor on the risk of hemorrhage when used in combination with tissue plasminogen activator during the acute phase of experimental stroke

Background

Granulocyte colony-stimulating factor (G-CSF) is a pharmacologic agent inducing neutrophil mobilization and a new candidate for neuroprotection and neuroregeneration in stroke. Its effects when used in combination with tissue plasminogen activator (tPA) were explored during the acute phase of ischemic stroke.

Methods

We used a middle cerebral artery occlusion (MCAO) model of cerebral ischemia, associated with treatment with tPA, in male spontaneously hypertensive rats (SHR). Granulocyte colony-stimulating factor (G-CSF; 60 μg/kg) was injected just before tPA. Neutrophil response in peripheral blood and in the infarct area was quantified in parallel to the infarct volume. Protease matrix metallopeptidase 9 (MMP-9) release from circulating neutrophils was analyzed by immunochemistry and zymography. Vascular reactivity and hemorrhagic volume in the infarct area was also assessed.

Results

Twenty four hours after ischemia and tPA, G-CSF administration induced a significant increase of neutrophils in peripheral blood (P <0.05). At 72 hours post-ischemia, G-CSF was significantly associated with an increased risk of hemorrhage in the infarct area (2.5 times more likely; P <0.05) and significant cerebral endothelium-dependent dysfunction. Ex vivo, an increased MMP-9 release from neutrophils after tPA administration correlated to the increased hemorrhagic risk (P <0.05). In parallel, G-CSF administration was associated with a decreased neutrophil infiltration in the infarct area (-50%; P <0.05), with a concomitant significant neuroprotective effect (infarct volume: -40%; P <0.05).

Conclusions

We demonstrate that G-CSF potentiates the risk of hemorrhage in experimental stroke when used in combination with tPA by inducing neutrophilia. This effect is concomitant to an increased MMP-9 release from peripheral neutrophils induced by the tPA treatment. These results highlight the potential hemorrhagic risk of associating G-CSF to thrombolysis during the acute phase of stroke.

Clot injection technique affects thrombolytic efficacy in a rat embolic stroke model: implications for translaboratory collaborations

Current recommendations encourage the use of embolic stroke (ES) models and replication of results across laboratories in preclinical research. Since such endeavors employ different surgeons, we sought to ascertain the impact of injection technique on outcome and response to thrombolysis in an ES model. Embolic stroke was induced in Male Wistar Kyoto rats (n=166) by a fast or a slow clot injection (CI) technique. Saline or recombinant tissue plasminogen activator (rtPA) was given at 1 hour after stroke. Flow rate curves were assessed in 24 animals. Cerebral perfusion was assessed using laser Doppler flowmetry. Edema corrected infarct volume, hemispheric swelling, hemorrhagic transformation, and neurologic outcome were assessed at 24 hours after stroke. Clot burden was estimated in a subset of animals (n=40). Slow CI resulted in significantly smaller infarct volumes (P=0.024) and better neurologic outcomes (P=0.01) compared with fast CI at 24 hours. Unexpectedly, rtPA treatment attenuated infarct size in fast (P<0.001) but not in slow CI experiments (P=0.382), possibly related to reperfusion injury as indicated by greater hemorrhagic transformation (P<0.001) and hemispheric swelling (P<0.05). Outcome and response to thrombolysis after ES are operator dependent, which needs to be considered when comparing results obtained from different laboratories.

Thrombus composition in acute ischemic stroke: a histopathological study of thrombus extracted by endovascular retrieval

BACKGROUND AND PURPOSE

The composition of occlusive thrombus in acute ischemic stroke may affect treatment success. Neuroimaging characteristics may correlate with thrombus composition. In this study we aimed to investigate the relationship between the hyperdense artery sign (HAS) on imaging and thrombus composition.

MATERIALS AND METHODS

Acute ischemic stroke patients who underwent endovascular thrombus retrieval from 2010-2012 were prospectively recruited. One blinded pathologist prepared the histology sections of retrieved thrombi whereby staining with haematoxylin and eosin and CD34 immunostain were performed. Histology sections were categorised into 4 phases of thrombus formation: red blood cell (RBC) dominant, RBC proportion equal to fibrin, fibrin dominant and organised fibrin. Computed tomography (CT) brain scans were assessed for HAS. Fisher's exact test was performed to identify an association between HAS and thrombus composition.

RESULTS

Forty patients were included. The mean age was 65.6±12.9 years and 67.5% were male. Atrial fibrillation was detected in 19 (47.5%) patients, diabetes mellitus in 6 (15.0%), hypercholesterolaemia in 11 (27.5%), hypertension in 20 (50.0%) and previous stroke or transient ischemic attack in 8 (20.0%) patients. Of the retrieved thrombi, 11 (27.5%) were RBC dominant, 11 (27.5%) RBC proportion was equal to fibrin, 7 (17.5%) fibrin dominant and 11 (27.5%) organised fibrin pathology. HAS was present in 29 (72.5%) patients and was significantly associated with thrombus early phase pathology (P<0.05).

CONCLUSION

HAS was significantly associated with early phase thrombus composition. This may enable the prediction of thrombus composition and allow for targeted selection of therapeutic modality.

Experimental models of brain ischemia: a review of techniques, magnetic resonance imaging, and investigational cell-based therapies

Stroke continues to be a significant cause of death and disability worldwide. Although major advances have been made in the past decades in prevention, treatment, and rehabilitation, enormous challenges remain in the way of translating new therapeutic approaches from bench to bedside. Thrombolysis, while routinely used for ischemic stroke, is only a viable option within a narrow time window. Recently, progress in stem cell biology has opened up avenues to therapeutic strategies aimed at supporting and replacing neural cells in infarcted areas. Realistic experimental animal models are crucial to understand the mechanisms of neuronal survival following ischemic brain injury and to develop therapeutic interventions. Current studies on experimental stroke therapies evaluate the efficiency of neuroprotective agents and cell-based approaches using primarily rodent models of permanent or transient focal cerebral ischemia. In parallel, advancements in imaging techniques permit better mapping of the spatial-temporal evolution of the lesioned cortex and its functional responses. This review provides a condensed conceptual review of the state of the art of this field, from models and magnetic resonance imaging techniques through to stem cell therapies.

Histopathologic composition of cerebral thrombi of acute stroke patients is correlated with stroke subtype and thrombus attenuation

Introduction

We related composition of cerebral thrombi to stroke subtype and attenuation on non-contrast CT (NCCT) to gain more insight in etiopathogenesis and to validate thrombus attenuation as a new imaging biomarker for acute stroke.

Methods

We histopathologically investigated 22 thrombi retrieved after mechanical thrombectomy in acute stroke patients. First, thrombi were classified as fresh, lytic or organized. Second, percentages of red blood cells (RBCs), platelets and fibrin and number of red, white (respectively RBCs or platelets outnumbering other components with ≥15%) or mixed thrombi were compared between large artery atherosclerosis (LAA), cardioembolism, dissection and unknown subtype. Third, correlation between attenuation and RBCs, platelets and fibrin was calculated using Pearson's correlation coefficients (r).

Results

Thrombi were fresh in 73% (n = 16), lytic in 18% (n = 4) and organized in 9% (n = 2). The stroke cause was LAA in eight (36%), cardioembolism in six (27%), dissection in three (14%), and unknown in five (23%) patients. LAA thrombi showed the highest percentage RBCs (median 50 (range 35–90)), followed by dissection (35 (20–40), p = 0.05), cardioembolism (35 (5–45), p = 0.013) and unknown subtype (25 (2–40), p = 0.006). No differences in platelets (p = 0.16) and fibrin (p = 0.52) between subtypes were found. LAA thrombi were classified as red or mixed (both n = 4), cardioembolisms as mixed (n = 5) or white (n = 1) and dissection as mixed (n = 3). There was a moderate positive correlation between attenuation and RBCs (r = 0.401, p = 0.049), and weak negative correlations with platelets (r = −0.368, p = 0.09) and fibrin (r = −0.073, p = 0.75).

Conclusions

The majority of cerebral thrombi is fresh. There are no differences in age of thrombi between subtypes. LAA thrombi have highest percentages RBCs, cardioembolism and unknown subtype lowest. No relationship exists between subtype and platelets or fibrin percentages. We found a correlation between the RBC-component and thrombus attenuation, which improves validation of thrombus attenuation on NCCT as an imaging biomarker for stroke management.

Clinical outcomes after intravenous fibrinolysis in cryptogenic strokes with or without patent foramen ovale

BACKGROUND

Pivotal clinical trials suggest that intravenous (IV) recombinant tissue plasminogen activator (rt-PA) benefits stroke patients regardless of the underlying etiology. Paradoxical strokes, presumed to be caused by fibrin-rich clots originating in the venous circulation, may respond better to fibrinolysis than other ischemic stroke subtypes. In this study, we compared the response with IV rt-PA in paradoxical stroke patients and other stroke subtypes.

METHODS

In total, 486 patients treated with IV rt-PA at a single institution were retrospectively reviewed. Adjudication of stroke mechanism was based on chart review. Five major stroke mechanisms--cardioembolic, artery-to-artery emboli, lacunar, cryptogenic, and paradoxical--were identified by final diagnosis from chart reviews. Mimics, undefined etiology, and defined etiology not falling into the major mechanisms were excluded. Analysis of variance and general linear model were used to assess the differences between groups.

RESULTS

A total of 323 patients were analyzed. We found significant differences in clinical outcome between stroke mechanisms, including discharge National Institutes of Health Stroke Scale (NIHSS) (P=.007), discharge Rankin (P=.011), discharge disposition (P=.000), and infarct volume (P=.007). Post hoc analysis showed that cardioembolic patients had the worst outcomes (discharge NIHSS score 11.12±12.26), whereas paradoxical strokes had the best outcomes (discharge NIHSS score 3.67±4.90), but these did not approach statistical significance. However, regression analysis showed that 4 variables--congestive heart failure, admission NIHSS, age, and mean infarct volume--rather than stroke mechanism were the true predictors of poor outcome.

CONCLUSIONS

Paradoxical strokes had better outcomes after IV fibrinolysis than other ischemic stroke subtypes, but this difference is attributable to younger age and milder stroke severity on presentation.

An endovascular canine stroke model: middle cerebral artery occlusion with autologous clots followed by ipsilateral internal carotid artery blockade

Stroke is one of the leading causes of death worldwide and the main reason for long-term disability. An appropriate animal model of stroke is urgently required for understanding the exact pathophysiological mechanism of stroke and testing any new therapeutic regimen. Our work aimed to establish a canine stroke model occluding the middle cerebral artery (MCA) and blocking the ipsilateral internal carotid artery (ICA), and to assess the infarct lesions by magnetic resonance imaging. The stroke model was generated by injecting two autologous clots into each MCA, followed by 2-h ipsilateral ICA blockade (ilICAB) using a catheter in 15 healthy adult beagles. Outcome measurements included 24-h and 7-day postocclusion T2-weighted imaging (T2WI)-based infarct volume calculation. In addition, pial collateral score, canine neurobehavioral score and histopathologic results were documented. Out of 15 dogs, 12 with successful MCA occlusion (MCAO) and ilICAB survived 7 days without complications or casualties and MCA were reperfused at 7 days after occlusion. High signal intensity in the basal ganglia and cerebral cortex on T2WI was initially observed in each dog at 6 h after the procedure. The mean percentage hemispherical infarct volume corrected for edema in all dogs on T2WI at 24 h after occlusion was 12.99±1.57%, and the degree of variability was 12.08%. The infarct volumes at 24 h after occlusion correlated with pial collateral scores and canine neurobehavioral scores well. This canine stroke model with combined MCAO and ilICAB reported here were proven to be highly feasible and reproducible.

Individual lytic efficacy of recombinant tissue plasminogen activator in an in vitro human clot model: rate of "nonresponse"

OBJECTIVES

Recombinant tissue plasminogen activator (rt-PA) is a lytic medication widely used in the emergency department to treat acute thrombotic disorders such as ischemic stroke and myocardial infarction. It is known in the clinical use of this drug that it can be less effective in approximately 25% of individuals receiving such treatment. However, there are no data on the variation of lytic efficacy of rt-PA in decreasing individuals' clot size over time. In this study, in vitro lytic efficacy was determined by measuring the decrease in clot diameter after 30 minutes of drug exposure. The authors sought to explore whether there are individuals who do not respond to this lytic therapy and to estimate the rate of nonresponse.

METHODS

Human whole blood clots were made from blood drawn from 22 adult volunteers. The only exclusion criterion was the use of aspirin within 72 hours of the blood draw. Blood clots were allowed to spontaneously form at room temperature and were then incubated at 37°C for 3 hours to ensure complete clot retraction. Sample clots from the same individuals were then exposed to human fresh-frozen plasma (hFFP) control or rt-PA in hFFP (rt-PA) at a concentration of 3.15 μg/mL. All clots were exposed at 37°C for 30 minutes, and clot diameter was measured as a function of time, using a microscopic imaging technique. The fractional clot loss (FCL), which is the percentage decrease in clot diameter at 30 minutes, was used as a measure of lytic efficacy.

RESULTS

Means with standard deviation (SD) FCL values were 8.6% (±3.0%) for control and 20.6% (±9.3%) for rt-PA-treated clots. The mean (±SD) difference in FCL values was 12.0% (±8.8%) and was significant (p < 0.05, paired t-test). Five of the 22 subjects (23%) were "rt-PA nonresponders," in that their FCL (rt-PA) values fell within that of the FCL control values.

CONCLUSIONS

Overall, rt-PA does not produce clot lysis in vitro in clots from a substantial minority of the population, likely due to individual variations in clot composition and structure.

Density of thrombus on admission CT predicts revascularization efficacy in large vessel occlusion acute ischemic stroke

BACKGROUND AND PURPOSE

Can lysability of large vessel thrombi in acute ischemic stroke be predicted by measuring clot density on admission nonenhanced CT (NECT), postcontrast enhanced CT, or CT angiogram (CTA)?

METHODS

We retrospectively studied 90 patients with acute large vessel ischemic strokes treated with intravenous (IV) tPA, intra-arterial (IA) tPA, and/or mechanical thrombectomy devices. Clot density [in Hounsfield unit (HU)] was measured on NECT, postcontrast enhanced CT, and CTA. Recanalization was assessed by the Thrombolysis in Cerebral Infarction grading system (TICI) on digital subtraction angiography.

RESULTS

Thrombus density on preintervention NECT correlated with postintervention TICI grade regardless of pharmacological (IV tPA r=0.69, IA tPA r=0.72, P<0.0001) or mechanical treatment (r=0.73, P<0.0001). Patients with TICI≥2 demonstrated higher HU on NECT (mean corrected HU IV tPA=1.58, IA tPA=1.66, mechanical treatment=1.7) compared with patients with TICI<2 (IV tPA=1.39, IA tPA=1.4, mechanical treatment=1.3) (P=0.01, 0.006, <0.0001 respectively). There was no association between recanalization and age, sex, baseline National Institute of Health Stroke Scale, treatment method, time to treatment, or clot volume.

CONCLUSIONS

Thrombi with lower HU on NECT appear to be more resistant to pharmacological lysis and mechanical thrombectomy. Measuring thrombus density on admission NECT provides a rapid method to analyze clot composition, a potentially useful discriminator in selecting the most appropriate reperfusion strategy for an individual patient.

Embolic middle cerebral artery occlusion model using thrombin and fibrinogen composed clots in rat

Ischemic stroke accounts for over 80% in total human stroke which mostly affect middle cerebral artery (MCA) territory. Embolic stroke models induced by injection of homologous clots into the internal carotid artery and MCA closely mimic human stroke and have been commonly used in stroke research. Studies indicate that the size and composition of clots are critical for the reproducibility of the stroke model. In the present study, we modified the homologous clots formation by addition of thrombin and fibrinogen which produced even distribution of fibrin with tight cross linkage of red blood cells. We optimized the embolic MCA occlusion model in rats using different size of the mixed clots. A precise lodgment of the clots at the MCA bifurcation and highly reproducible ischemic lesion in the MCA territory were demonstrated in the embolic MCA occlusion model induced by injection of 10 pieces of 1-mm long mixed clots made in PE-60 catheter. We further tested the effect of recombinant tissue plasminogen activator (rtPA) in this embolic MCA occlusion model. rtPA induced thrombolysis, improved neurological outcome, and significantly reduced ischemic lesion volume when administered at 1h after embolism as compared with control. In summary, we have established a reproducible embolic MCA occlusion model using clots made of homologous blood, thrombin and fibrinogen. The mixed clots enable precise lodgment at the MCA bifurcation which is responsive to thrombolytic therapy of rtPA.

Combined systemic thrombolysis with alteplase and early hyperbaric oxygen therapy in experimental embolic stroke in rats: relationship to functional outcome and reduction of structural damage

INTRODUCTION

The only causal therapy in ischemic stroke is thrombolysis with recombinant tissue plasminogen activator (rtPA), but it is feasible only for few patients, and new therapies are needed. This study investigates the effects of systemic thrombolysis with rtPA combined with hyperbaric oxygen therapy (HBOT) in embolic stroke in rats.

METHODS

In 22 male Wistar rats, an embolic ischemic stroke was induced. The animals were randomized to one of four groups: control, thrombolysis alone, HBOT sequential or HBOT parallel with thrombolysis. HBOT (2.4 ATA, 1 h) started 45 min (sequential) or 120 min (parallel) after stroke. rtPA was given intravenously 120 min after stroke onset. Functional tests were performed after stroke induction and after treatment. After 6 h infarct volume and intracerebral hemorrhagic complications were assessed.

RESULTS

Compared to the control group only the combination of HBOT and thrombolysis significantly improved the functional outcome (p=0.03) and reduced the infarct volume (p=0.01), whereas thrombolysis alone did not show a significant benefit. In all treatment groups there was a trend towards fewer hemorrhagic transformations.

CONCLUSION

Hyperbaric oxygen in combination with thrombolysis shows neuroprotection in acute ischemic stroke in rats by reducing infarct volume and improving functional outcome in the early poststroke period.

A mouse model of hemorrhagic transformation by delayed tissue plasminogen activator administration after in situ thromboembolic stroke

BACKGROUND AND PURPOSE

thrombolytic treatment with tissue plasminogen activator (tPA) improves outcome of patients with stroke who can be treated within 3 hours of symptom onset. However, delayed treatment with tPA leads to increased risk of hemorrhagic transformation and can result in enhanced brain injury. The purpose of this study is to validate a reproducible mouse model of hemorrhagic transformation associated with delayed administration of tPA.

METHODS

mice were anesthetized and thrombin was injected into the middle cerebral artery to induce the formation of a clot as described by Orset et al. To induce reperfusion, tPA (10 mg/kg) was intravenously administered 20 minutes or 3 hours after thrombin injection.

RESULTS

thrombin produced a clot in 83.1% of the animals, which caused focal ischemia determined 24 hours after the injection. Different degrees of bleeding were found in the middle cerebral artery occlusion group, including hemorrhagic infarction type 1 (HI-1) in 46.2%, hemorrhagic infarction type 2 (HI-2) in 30.8% and parenchymal hemorrhage type 1 in 23.0%. Administration of tPA 20 minutes after the occlusion produced an effective reperfusion in 62.5% of the animals and reduced both infarct volume and appearance of severe hemorrhage (10% nonhemorrhage, 80% HI-1 and 10% HI-2). However, administration of tPA 3 hours after the occlusion led to effective reperfusion in 47.1% of the animals, did not reduce infarct volume, caused hemorrhagic transformation (25% HI-1, 37.5% HI-2, and 37.5% parenchymal hemorrhage type 1), and increased hemorrhage and brain swelling.

CONCLUSIONS

we have set up a reproducible mouse model of hemorrhagic transformation associated with delayed administration of tPA similar to that observed in humans.