Pathophysiology, treatment, and animal and cellular models of human ischemic stroke

Abstract

Stroke is the world's second leading cause of mortality, with a high incidence of severe morbidity in surviving victims. There are currently relatively few treatment options available to minimize tissue death following a stroke. As such, there is a pressing need to explore, at a molecular, cellular, tissue, and whole body level, the mechanisms leading to damage and death of CNS tissue following an ischemic brain event. This review explores the etiology and pathogenesis of ischemic stroke, and provides a general model of such. The pathophysiology of cerebral ischemic injury is explained, and experimental animal models of global and focal ischemic stroke, and in vitro cellular stroke models, are described in detail along with experimental strategies to analyze the injuries. In particular, the technical aspects of these stroke models are assessed and critically evaluated, along with detailed descriptions of the current best-practice murine models of ischemic stroke. Finally, we review preclinical studies using different strategies in experimental models, followed by an evaluation of results of recent, and failed attempts of neuroprotection in human clinical trials. We also explore new and emerging approaches for the prevention and treatment of stroke. In this regard, we note that single-target drug therapies for stroke therapy, have thus far universally failed in clinical trials. The need to investigate new targets for stroke treatments, which have pleiotropic therapeutic effects in the brain, is explored as an alternate strategy, and some such possible targets are elaborated. Developing therapeutic treatments for ischemic stroke is an intrinsically difficult endeavour. The heterogeneity of the causes, the anatomical complexity of the brain, and the practicalities of the victim receiving both timely and effective treatment, conspire against developing effective drug therapies. This should in no way be a disincentive to research, but instead, a clarion call to intensify efforts to ameliorate suffering and death from this common health catastrophe. This review aims to summarize both the present experimental and clinical state-of-the art, and to guide future research directions.

Figure 1

Major cellular patho-physiological mechanisms of ischemic stroke. Ischemia-induced energy failure leads to the depolarization of neurons. Activation of specific glutamate receptors dramatically increases intracellular Ca²⁺, and Na⁺, and K⁺ is released into the extracellular space. Edema results from water shifts to the intracellular space. Increased levels of intracellular messenger Ca²⁺ activates proteases, lipases and endonucleases. Free radicals are generated which damage membranes, mitochondria and DNA, in turn triggering cell death and inducing the formation of inflammatory mediators, which then induce JNK, p-38, NFκB and AP-1 activation in glial cells, endothelial cells, and infiltrating leukocytes. This culminates in pro-inflammatory cytokine and chemokine secretion and leads to the invasion of leukocytes via up-regulation of endothelial adhesion molecules.

Figure 2

Surgical technique for inducing global or focal cerebral ischemia in mouse. Schematic illustration of arteries demonstrating the three points of occlusion (black arrows) for global ischemia (3-VO) and red arrows for focal ischemia. MCA: middle cerebral artery; ICA: internal carotid artery; ECA: external carotid artery; BA: basilar artery; CCA: common carotid artery.

Figure 3

Representative coronal brain section from a mouse that had been subjected to MCA occlusion-reperfusion. This mouse had a one hour MCA occlusion and 72 hours reperfusion. The red staining indicates healthy brain tissue and the white indicates damaged tissue.

Figure 4

Representative images of leukocyte interactions in pial microcirculation of a sham-operated mouse and in mice which underwent 1-hour MCA occlusion and 12 or 24-hour reperfusion. Sham-operated animals show minimal leukocyte adhesion. Scale bar 50 μm.

Figure 5

Representative images of neuronal cell death following 12 h oxygen and glucose deprivation (OGD). Dead cells have altered membrane permeability, thereby facilitating the entry of trypan blue (yellow arrow) into the cell and staining the cytoplasm blue, whereas the live cells have a clear cytoplasm.