Risk reduction strategies in ischaemic stroke : the role of antiplatelet therapy

Targeted delivery of nanomedicines for promoting vascular regeneration in ischemic diseases

Ischemic diseases, the leading cause of disability and death, are caused by the restriction or blockage of blood flow in specific tissues, including ischemic cardiac, ischemic cerebrovascular and ischemic peripheral vascular diseases. The regeneration of functional vasculature network in ischemic tissues is essential for treatment of ischemic diseases. Direct delivery of pro-angiogenesis factors, such as VEGF, has demonstrated the effectiveness in ischemic disease therapy but suffering from several obstacles, such as low delivery efficacy in disease sites and uncontrolled modulation. In this review, we summarize the molecular mechanisms of inducing vascular regeneration, providing the guidance for designing the desired nanomedicines. We also introduce the delivery of various nanomedicines to ischemic tissues by passive or active targeting manner. To achieve the efficient delivery of nanomedicines in various ischemic diseases, we highlight targeted delivery of nanomedicines and controllable modulation of disease microenvironment using nanomedicines.

The effect of age, sex and strains on the performance and outcome in animal models of stroke

Stroke is one of the leading causes of death worldwide, and the majority of cerebral stroke is caused by occlusion of cerebral circulation, which eventually leads to brain infarction. Although stroke occurs mainly in the aged population, most animal models for experimental stroke in vivo almost universally rely on young-adult rodents for the evaluation of neuropathological, neurological, or behavioral outcomes after stroke due to their greater availability, lower cost, and fewer health problems. However, it is well established that aged animals differ from young animals in terms of physiology, neurochemistry, and behavior. Stroke-induced changes are more pronounced with advancing age. Therefore, the overlooked role of age in animal models of stroke could have an impact on data quality and hinder the translation of rodent models to humans. In addition to aging, other factors also influence functional performance after ischemic stroke. In this article, we summarize the differences between young and aged animals, the impact of age, sex and animal strains on performance and outcome in animal models of stroke and emphasize age as a key factor in preclinical stroke studies.

Ischemic stroke: experimental models and reality

The vast majority of cerebral stroke cases are caused by transient or permanent occlusion of a cerebral blood vessel (“ischemic stroke”) eventually leading to brain infarction. The final infarct size and the neurological outcome depend on a multitude of factors such as the duration and severity of ischemia, the existence of collateral systems and an adequate systemic blood pressure, etiology and localization of the infarct, but also on age, sex, comorbidities with the respective multimedication and genetic background. Thus, ischemic stroke is a highly complex and heterogeneous disorder. It is immediately obvious that experimental models of stroke can cover only individual specific aspects of this multifaceted disease. A basic understanding of the principal molecular pathways induced by ischemia-like conditions comes already from in vitro studies. One of the most frequently used in vivo models in stroke research is the endovascular suture or filament model in rodents with occlusion of the middle cerebral artery (MCA), which causes reproducible infarcts in the MCA territory. It does not require craniectomy and allows reperfusion by withdrawal of the occluding filament. Although promptly restored blood flow is far from the pathophysiology of spontaneous human stroke, it more closely mimics the therapeutic situation of mechanical thrombectomy which is expected to be increasingly applied to stroke patients. Direct transient or permanent occlusion of cerebral arteries represents an alternative approach but requires craniectomy. Application of endothelin-1, a potent vasoconstrictor, allows induction of transient focal ischemia in nearly any brain region and is frequently used to model lacunar stroke. Circumscribed and highly reproducible cortical lesions are characteristic of photothrombotic stroke where infarcts are induced by photoactivation of a systemically given dye through the intact skull. The major shortcoming of this model is near complete lack of a penumbra. The two models mimicking human stroke most closely are various embolic stroke models and spontaneous stroke models. Closeness to reality has its price and goes along with higher variability of infarct size and location as well as unpredictable stroke onset in spontaneous models versus unpredictable reperfusion in embolic clot models.

Comparison of carotid atherosclerotic plaque characteristics between patients with first-time and recurrent acute ischaemic stroke using B-mode ultrasound

OBJECTIVES

The differences between initial and recurrent stroke plaques are not defined. Hence, a nested case-control study was conducted to evaluate the association of stroke recurrence with the echogenic characteristics of carotid plaques in patients with ischaemic stroke.

METHODS

One hundred and four patients with 1-year recurrent acute ischaemic stroke were enrolled and compared with 104 control patients (first-time ischaemic stroke) matched for age, gender, stroke severity and treatment allocation. Based on the Mannheim Carotid Intima-Media Thickness Consensus (2004-2006), the number of carotid plaques and echogenicity between the two groups of patients were compared.

RESULTS

As compared to patients with first-time stroke, those with recurrent stroke showed significantly higher prevalence of heart disease (13.46 vs 28.85%, P = 0.0066) and presence of intracranial stenosis (55.77 vs 89.90%, P < 0.0001). During the 1-year follow-up, patients with recurrent stroke had a significantly higher rate of unstable plaques (80.41%) than patients with first-time stroke (64.21%, P = 0.036). Also, patients with recurrent stroke had a significantly larger number of plaques than patients with first-time stroke (P = 0.0152). Multivariate conditional logistic regression analysis (after adjustment for heart disease and intracranial stenosis) identified an association between 1-year stroke recurrence and the presence of unstable plaques (hazard ratio 3.077; 95% CI: 1.133-8.355).

CONCLUSION

Stroke recurrence is related to advanced atherosclerosis defined by carotid plaque and its characteristics.

Platelet-mediated vascular dysfunction during acute lung injury

CONTEXT

Platelets have significant roles in initiating and mediating reduced alveolar blood flow, microvascular leak, and ventilation/perfusion mismatch caused by metabolic changes and altered signal transduction caused by ischemia-reperfusion.

OBJECTIVE

This review focuses on platelet mechanisms of vascular dysfunction in the lung and presents a hypothesis for interplay between platelet activation, endothelial damage and fibrinogen. The purpose is to discuss current knowledge regarding mechanisms of platelet-mediated endothelial injury and implications for new strategies to treat vascular dysfunction associated with acute lung injury (ALI).

METHODS

Literature from a number of fields was searched using Medline and Google Scholar.

RESULTS

Activated platelets contribute to redox imbalance through reactive oxygen species production, pro-leak molecules such as PAF and serotonin, and recruitment of inflammatory cytokines and leukocytes to the damaged endothelium.

CONCLUSION

Platelets are a critical component of pulmonary ALI, acting in conjunction with fibrinogen to mediate endothelial damage through multiple signal transduction pathways.

Comparison of carotid atherosclerotic plaque characteristics by high-resolution black-blood MR imaging between patients with first-time and recurrent acute ischemic stroke

BACKGROUND AND PURPOSE

It has been shown that patients with a first ischemic stroke are at high risk of developing recurrent stroke due to carotid atherosclerotic plaque rupture. However, no one has defined the difference in plaques between initial and recurrent stroke. This study sought to investigate the characteristics of carotid plaque between patients with first-time and recurrent acute ischemic stroke by using MR imaging.

MATERIALS AND METHODS

Eighty-nine patients with recent acute ischemic stroke were recruited. All subjects underwent carotid high-resolution black-blood MR imaging. The index carotid arteries, defined as the arteries responsible for the ipsilateral stroke, were analyzed quantitatively and qualitatively. Carotid plaque burden and compositional features between patients with first-time and recurrent ischemic stroke were compared.

RESULTS

Of 89 recruited patients, 51 had first-time stroke and 38 had recurrent stroke. The mean WA, WT, and PWV were greater in patients with recurrent stroke than in patients with first-time stroke (all, P < .05). Compared with patients with first-time stroke, those with recurrent stroke showed significantly higher prevalence of calcification (44.7% versus 23.5%, P = .035) as well as a larger volume of LRNC (179.14 ± 254.81 mm(2) versus 71.65 ± 111.15 mm(2), P = .027). IPH or fibrous cap rupture or both were observed in 15.8% of patients with recurrent stroke and 3.9% of patients with first-time stroke.

CONCLUSIONS

Carotid plaques in patients with recurrent ischemic stroke are significantly aggravated compared with those in patients with first-time stroke, and monitoring carotid plaques in patients with initial stroke by MR imaging may be helpful for secondary stroke prevention.

Different strokes for different folks: the rich diversity of animal models of focal cerebral ischemia

No single animal model is able to encompass all of the variables known to affect human ischemic stroke. This review highlights the major strengths and weaknesses of the most commonly used animal models of acute ischemic stroke in the context of matching model and experimental aim. Particular emphasis is placed on the relationships between outcome and underlying vascular variability, physiologic control, and use of models of comorbidity. The aim is to provide, for novice and expert alike, an overview of the key controllable determinants of experimental stroke outcome to help ensure the most effective application of animal models to translational research.

Inducing stroke in aged, hypertensive, diabetic rats

Animal models of ischemic stroke often neglect comorbidities common in patients. This study shows the feasibility of inducing stroke by 2 h of thread occlusion of the middle cerebral artery in aged (56 week old) spontaneously hypertensive rats (SHRs) with both acute (2 weeks) and chronic (36 weeks) diabetes. After modifying the streptozotocin dosing regimen to ensure that old SHRs survived the induction of diabetes, few died after induction of stroke. Induction of stroke is feasible in rats with multiple comorbidities. Inclusion of such comorbid animals may improve translation from the research laboratory to the clinic.