The two pathophysiologies of focal brain ischemia: implications for translational stroke research.

Brain injury after focal ischemia evolves along two basically different pathophysiologies, depending on the severity of the primary flow reduction and the dynamics of postischemic recirculation. In permanent and gradually reversed focal ischemia as after thromboembolic occlusion, primary core injury is irreversible but the expansion of the core into the penumbra can be alleviated by hemodynamic and molecular interventions. Such alleviation can only be achieved within 3 hours after the onset of ischemia because untreated core injury expands to near maximum size during this interval. In promptly reversed transient ischemia as after mechanical vascular occlusion, primary core injury may recover but a secondary delayed injury evolves after a free interval of as long as 6 to 12 hours. This injury can be alleviated throughout the free interval but the longer window is without clinical relevance because transient mechanical vascular occlusion is not a model of naturally occurring stroke. As this difference is widely ignored in stroke research, most clinical trials have been designed with a far too long therapeutic window, which explains their failure. Transient mechanical vascular occlusion models should, therefore, be eliminated from the repertoire of preclinical stroke research.

Pathophysiological basis of translational stroke research.

The high incidence and the devastating consequences of stroke call for efficient therapies but despite extensive experimental evidence of neuroprotective improvements, most clinical treatments have failed. The poor translational success is attributed to the inappropriate selection of clinically irrelevant animal models, the inappropriate focus on clinically irrelevant injury pathways and the inappropriate estimation of the length of therapeutic windows. To substantiate this conclusion, the pathophysiology of experimental stroke is reviewed. Particular emphasis is placed on the importance of collateral pathways, the penumbra concept and the viability thresholds of ischaemia, the haemodynamic and molecular mechanisms of injury evolution and the effect of secondary complications, notably inflammation and brain oedema. The comparison of permanent and transient focal ischaemia, on the one hand, and between mechanical and thrombolytic reperfusion, on the other, reveal basic differences in the mechanisms and dynamics of injury evolution which are of paramount importance for the proper targeting and time window of therapeutic interventions. These differences must be considered for adequate modelling of preclinical stroke studies to avoid unsuccessful translation of experimental data to the clinical setting.

Induction of cerebral arteriogenesis leads to early-phase expression of protease inhibitors in growing collaterals of the brain.

Cerebral arteriogenesis constitutes a promising therapeutic concept for cerebrovascular ischaemia; however, transcriptional profiles important for therapeutic target identification have not yet been investigated. This study aims at a comprehensive characterization of transcriptional and morphologic activation during early-phase collateral vessel growth in a rat model of adaptive cerebral arteriogenesis. Arteriogenesis was induced using a three-vessel occlusion (3-VO) rat model of nonischaemic cerebral hypoperfusion. Collateral tissue from growing posterior cerebral artery (PCA) and posterior communicating artery (Pcom) was selectively isolated avoiding contamination with adjacent tissue. We detected differential gene expression 24 h after 3-VO with 164 genes significantly deregulated. Expression patterns contained gene transcripts predominantly involved in proliferation, inflammation, and migration. By using scanning electron microscopy, morphologic activation of the PCA endothelium was detected. Furthermore, the PCA showed induced proliferation (PCNA staining) and CD68+ macrophage staining 24 h after 3-VO, resulting in a significant increase in diameter within 7 days after 3-VO, confirming the arteriogenic phenotype. Analysis of molecular annotations and networks associated with differentially expressed genes revealed that early-phase cerebral arteriogenesis is characterised by the expression of protease inhibitors. These results were confirmed by quantitative real-time reverse transcription-PCR, and in situ hybridisation localised the expression of tissue inhibitor of metalloproteinase-1 (TIMP-1) and kininogen to collateral arteries, showing that TIMP-1 and kininogen might be molecular markers for early-phase cerebral arteriogenesis.

Cerebral ischemia: models, methods and outcomes.

Experimental research into brain ischemia contributes substantially to the understanding of ischemic injury mechanisms but suffers from its limited relevance for clinical treatment strategies. One of the reasons is the use of experimental models and methods that do not or only partially replicate the pathophysiology of naturally occurring brain ischemia. To facilitate the understanding and interpretation of experimental data, the most widely used experimental models and analytical methods of brain ischemia are reviewed. Particular emphasis is given to the pathophysiological particularities of the various ischemia models, the application of imaging methods for the reliable differentiation between infarct core, penumbra, benign oligemia and normal tissue, as well as to the final outcome of experimental interventions. Based on this analysis, recommendations are given to improve the translational power of brain ischemia-related experimental research.

[Animal models of cerebral ischemia--testing therapeutic strategies in vivo]. / Agyi ischaemiás állatmodellek--terápiás stratégiák in vivo tesztelése.

Acute cerebral ischemia is one of the leading causes of mortality and chronic disability worldwide. Animal models of focal (stroke-type) and global (cardiac arrest-type) ischemia have been established to investigate the morphological, functional and molecular consequences and to design therapeutic strategies for the improvement of ischemic injury. Despite highly beneficial effects in experimental studies, most human clinical trials were disappointing, suggesting inefficacies in the design and/or translation of animal experiments. In this review the pathophysiologically relevant specifics of ischemia models will be discussed to provide a rational basis for the proper selection of animal models for testing therapeutic strategies under experimental conditions.

Pathophysiology and therapy of experimental stroke.

1. Stroke is the neurological evidence of a critical reduction of cerebral blood flow in a circumscribed part of the brain, resulting from the sudden or gradually progressing obstruction of a large brain artery. Treatment of stroke requires the solid understanding of stroke pathophysiology and involves a broad range of hemodynamic and molecular interventions. This review summarizes research that has been carried out in many laboratories over a long period of time, but the main focus will be on own experimental research. 2. The first chapter deals with the hemodynamics of focal ischemia with particular emphasis on the collateral circulation of the brain, the regulation of blood flow and the microcirculation. In the second chapter the penumbra concept of ischemia is discussed, providing a detailed list of the physiological, biochemical and structural viability thresholds of ischemia and examples of how these thresholds can be applied for imaging the penumbra. The third chapter summarizes the pathophysiology of infarct progression, focusing on the role of peri-infarct depolarisation, the multitude of putative molecular injury pathways, brain edema and inflammation. Finally, the fourth chapter provides an overview of currently discussed therapeutic approaches, notably the effect of mechanical or thrombolytic reperfusion, arteriogenesis, pharmacological neuroprotection, ischemic preconditioning and regeneration. 3. The main emphasis of the review is placed on the balanced differentiation between hemodynamic and molecular factors contributing to the manifestation of ischemic injury in order to provide a rational basis for future therapeutic interventions.

Establishing a photothrombotic 'ring' stroke model in adult mice with late spontaneous reperfusion: quantitative measurements of cerebral blood flow and cerebral protein synthesis.

This study sought to establish the photothrombotic 'ring' stroke model with late spontaneous reperfusion in adult mice. By applying a 3.0-mm diameter laser ring-beam (514 nm, 0.21 mm thick, 0.65 W/cm2) onto the exposed skull for 60 secs with concurrent erythrosin B (4.25 mg/kg) intravenous infusion for 15 secs, the centrally located cortical region within the ring locus was progressively encroached by an annular ring-shaped perfusion deficit. In this region, local cerebral blood flow (lCBF) measured by laser-Doppler flowmetry declined promptly after irradiation to 43% of the baseline value at 30 mins poststroke. Using double tracer autoradiography, quantitative lCBF measured with [14C]iodoantipyrine was 46 to 17 to 58 ml/100 g/mins at 4 h to 48 h to 7 days postischemia in this area. Cerebral protein synthesis (CPS), as detected by [3H]leucine incorporation into protein, transiently decreased to 57% to 38% to 112% at 4 h to 48 h to 7 days postischemia in the center region. Morphologically, some neurons in the center region appeared swollen at 4 h. At 48 h, the majority of neurons were severely swollen with eosinophilia and pyknosis, whereas at 7 days poststroke' the tissue morphology became partly restored. The center within the mouse photothrombotic ring lesion thus exhibits reversible alterations of local CBF, CPS and tissue morphology that are reminiscent of the cortical penumbra in other models of focal cerebral ischemia.

Granulocyte-macrophage colony-stimulating factor as an arteriogenic factor in the treatment of ischaemic stroke.

Granulocyte-macrophage colony-stimulating factor (GM-CSF) induces arteriogenic growth of collateral vessels after occlusion of cardiac or peripheral arteries. Recently, evidence has been provided that arteriogenesis also occurs in the brain under conditions of reduced arterial blood supply. Hemispheric hypoperfusion induced by unilateral carotid and bilateral vertebral artery occlusion (three-vessel occlusion, [3-VO]) led to the growth of the anterior and posterior segments of the circle of Willis, which is the main collateral pathway between the origins of the anterior, middle and posterior cerebral arteries. GM-CSF applied subcutaneously at daily doses of 40 microg.kg(-1) resulted in the marked acceleration of this process. Within one week after the onset of treatment, the diameter of the posterior segment of the circle of Willis enlarged to 170% of control, blood flow and the haemodynamic reserve capacity of the brain returned to normal, and haemodynamic stroke, induced after 3-VO by systemic hypotension, was greatly alleviated. GM-CSF-induced stimulation of arteriogenesis in the hypoperfused brain thus provides powerful protection against ischaemic stroke.

Granulocyte-macrophage colony-stimulating factor-induced arteriogenesis reduces energy failure in hemodynamic stroke.

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a powerful arteriogenic factor in the hypoperfused rat brain. To test the pathophysiological relevance of this response, the influence of GM-CSF on brain energy state was investigated in a model of hemodynamic stroke. Sprague-Dawley rats were submitted to three-vessel (bilateral vertebral and unilateral common carotid artery) occlusion (3-VO) to induce unilaterally accentuated brain hypoperfusion. One week later, hemodynamic stroke was induced by additional lowering of arterial blood pressure. Experiments were terminated by in situ freezing of the brain. ATP was measured in cryostat sections by using a bioluminescence method. The use of 3-VO, in combination with 15 min of hypotension of 50, 40, or 30 mmHg, did not produce disturbances of energy metabolism, however, focal areas of ATP depletion were unilaterally detected after 3-VO, in combination with 15 min of hypotension of 20 mmHg. Treating such animals with GM-CSF (40 microg.kg(-1).d(-1)) during the 1-week interval between 3-VO and induced hypotension significantly reduced the hemispheric volume of energy depletion from 48.8 +/- 44.2% (untreated group, n = 10) to 15.8 +/- 17.4% (treated group, n = 8, P = 0.033). GM-CSF-induced arteriogenesis is another approach to protect the brain against ischemic injury.

Time course of circulatory and metabolic recovery of cat brain after cardiac arrest assessed by perfusion- and diffusion-weighted imaging and MR-spectroscopy.

Brain recovery after cardiac arrest (CA) was assessed in cats using arterial spin tagging perfusion-weighted imaging (PWI), diffusion-weighted imaging (DWI), and 1H-spectroscopy (1H-MRS). Cerebral reperfusion and metabolic recovery was monitored in the cortex and in basal ganglia for 6 h after cardiopulmonary resuscitation (CPR). Furthermore, the effects of an hypertonic/hyperoncotic solution (7.5% NaCl/6% hydroxyl ethyl starch, HES) and a tissue-type plasminogen activator (TPA), applied during CPR, were assessed on brain recovery. CA and CPR were carried out in the MR scanner by remote control. CA for 15-20 min was induced by electrical fibrillation of the heart, followed by CPR using a pneumatic vest. PWI after successful CPR revealed initial cerebral hyperperfusion followed by delayed hypoperfusion. Initial cerebral recirculation was improved after osmotic treatment. Osmotic and thrombolytic therapy were ineffective in ameliorating delayed hypoperfusion. Calculation of the apparent diffusion coefficient (ADC) from DWI demonstrated complete recovery of ion and water homeostasis in all animals. 1H-MRS measurements of lactate suggested an extended preservation of post-ischaemic anaerobic metabolism after TPA treatment. The combination of noninvasive MR techniques is a powerful tool for the evaluation of therapeutical strategies on circulatory and metabolic cerebral recovery after experimental cerebral ischaemia.

Therapeutic induction of arteriogenesis in hypoperfused rat brain via granulocyte-macrophage colony-stimulating factor.

BACKGROUND: Colony-stimulating factors (CSFs) have been shown to effectively induce arteriogenesis in the hindlimb. Moreover, clinical trials demonstrated positive effects of CSFs on arteriogenesis in patients with coronary artery disease. However, patients with cerebrovascular disease have not yet profited from treatments aimed at the growth of brain vessels. Thus far, angiogenesis studies have failed to demonstrate improvement of stroke outcome. Arteriogenesis differs from angiogenesis in that it substitutes arterial collaterals for the occluded artery. METHODS AND RESULTS: We tested in a novel brain arteriogenesis rat model (occlusion of vertebral plus left carotid artery [3-VO]) the application of CSFs or saline over 7 or 21 days. On 3-VO postmortem, latex perfusion demonstrated a time- and treatment-dependent arteriogenesis of the posterior cerebral artery (PCA). In saline-treated animals, the PCA diameter increased by 39%; in granulocyte-macrophage (GM)-CSF-treated animals, this increase was significantly faster (72% after 1 week). Functionally, saline-treated animals exhibited a decline of CO2 reactivity (mm Hg) from 1.48% to 0.1% compared with GM-CSF-treated animals (1.43% arterial pCo2 change after 1 week). This difference remained significant after 3 weeks. This functional improvement correlated with increased numbers of CD68-positive macrophages in histological sections of the PCA in GM-CSF--treated animals and only a few macrophages in saline-treated animals. CONCLUSIONS: To the best of our knowledge, this is the first report of stimulation of arteriogenesis in the brain. The subcutaneous application of GM-CSF led to functional improvement of brain hemodynamic parameters.

Effect of mild hypothermia on focal cerebral ischemia. Review of experimental studies.

The purposes of this review are to clarify the effect of hypothermia therapy on focal cerebral ischemia in rats, and to consider the relevancy of its application to human focal cerebral ischemia. Since 1990, 26 reports confirming the brain-protecting effect of hypothermia in rat focal cerebral ischemia models have been published. Seventy-four experimental groups in these 26 reports were classified as having transient middle cerebral arterial occlusion (MCAO) with mild hypothermia (group A; 43 groups), permanent MCAO with mild hypothermia (group B; 14 groups), permanent MCAO with deep hypothermia (group C; 8 groups) and transient or permanent MCAO with mild hyperthermia (group D; 9 groups). The results were evaluated as the % infarct volume change caused by hypothermia or hyperthermia compared with the infarct volume in normothermic animals. The effectiveness was confirmed in 36 (83%) of the 43 groups in group A, 10 (71%) of the 14 in group B, and six (75%) of the eight in group C. The infarct volume of eight of the nine groups in group D was markedly aggravated. The percent infarct volume change was 55.3% +/- 27.1% in group A, 57.6% +/- 24.7% in group B, 60.8% +/- 45.5% in group C, and 189.7% +/- 89.4% in group D. For effective reduction of the infarct volume, hypothermia should be started during ischemia or within 1 h, at latest, after the beginning of reperfusion in the rat transient MCAO model. However, it is not clear whether this neuroprotective effect of hypothermia can also be observed in the chronic stage, such as several months later. Keeping the body temperature normothermic in order to avoid mild hyperthermia seems to be rather important for not aggravating cerebral infarction. Clinical randomized studies on the efficacy of mild hypothermia for focal cerebral ischemia and sophisticated mild hypothermia therapy techniques are mandatory.

Arteriogenesis in hypoperfused rat brain.

Experimental and clinical studies have provided evidence for spontaneous and therapeutically induced arteriogenesis after occlusion of major peripheral or cardiac vessels. Such evidence is lacking for the cerebrovascular system. In halothane-anesthetized rats, different degrees of brain hypoperfusion were induced by one- to four-vessel occlusion, that is, one or both common carotid arteries in combination with or without bilateral vertebral artery occlusion. The flow decline was monitored by laser Doppler flowmetry, the residual hemodynamic reserve by testing flow reactivity to ventilation with 6% CO(2) and arteriogenesis by intravascular latex infusion and immunohistochemistry of vascular proliferation and monocyte adhesion. The optimum condition for induction of arteriogenesis was three-vessel (one carotid plus both vertebral arteries) occlusion, which led to reduction of blood flow to about 50% and complete suppression of CO(2) reactivity, but no histologic injury. One week after three-vessel occlusion, the ipsilateral posterior cerebral artery significantly enlarged by 39%, and after 3 weeks by 72%, paralleled by the partial return of CO(2) reactivity and the appearance of immunohistochemical markers of arteriogenesis. Three-vessel occlusion is a reliable model for the induction of arteriogenesis in the adult brain and is a new approach for exploring the potentials of arteriogenesis for the prevention of progressing brain ischemia.

Ischemia induces a translocation of the splicing factor tra2-beta 1 and changes alternative splicing patterns in the brain.

Alternative splice-site selection is regulated by the relative concentration of individual members of the serine-arginine family of proteins and heterogeneous nuclear ribonucleoproteins. Most of these proteins accumulate predominantly in the nucleus, and a subset of them shuttles continuously between nucleus and cytosol. We demonstrate that in primary neuronal cultures, a rise in intracellular calcium concentration induced by thapsigargin leads to a translocation of the splicing regulatory protein tra2-beta1 and a consequent change in splice-site selection. To investigate this phenomenon under physiological conditions, we used an ischemia model. Ischemia induced in the brain causes a cytoplasmic accumulation and hyperphosphorylation of tra2-beta1. In addition, several of the proteins binding to tra2-beta1, such as src associated in mitosis 68 and serine/arginine-rich proteins, accumulate in the cytosol. Concomitant with this subcellular relocalization, we observed a change in alternative splice-site usage of the ICH-1 gene. The increased usage of its alternative exons is in agreement with previous studies demonstrating its repression by a high concentration of proteins with serine/arginine-rich domains. Our findings suggest that a change in the calcium concentration associated with ischemia is part of a signaling event, which changes pre-mRNA splicing pathways by causing relocalization of proteins that regulate splice-site selection.

Magnetic resonance angiography of thromboembolic stroke in rats: indicator of recanalization probability and tissue survival after recombinant tissue plasminogen activator treatment.

Magnetic resonance angiography (MRA) was performed in a thromboembolic stroke model of the rat to characterize intracranial vessel occlusion patterns and to test its predictive power for tissue recovery after recombinant tissue plasminogen activator (rt-PA) treatment. After rt-PA-treated selective middle cerebral artery (MCA) occlusion, full recanalization was observed in two of three animals, whereas additional occlusion of the circle of Willis (CW) resulted in full vascular flow restitution in only one of six rats. Tissue reperfusion markedly lagged the onset of treatment, and the delay correlated with the pattern of vessel occlusion (20 to 23 minutes for selective MCA occlusion vs. 71 to 79 minutes for combined MCA/CW occlusion). In lateral cortex and striatum the apparent diffusion coefficient decreased to 78 +/- 15% of control after embolization, recovered to 80% to 85% after rt-PA treatment of selective MCA occlusion, but further declined to 66% to 69% after combined MCA/CW occlusion. Correspondingly, T2 relaxation time increased to 107% to 118% of control after selective MCA occlusion and to 112% to 124% after combined MCA/CW occlusion in these regions. The present investigation shows that MRA provides valuable information on the severity of thromboembolic stroke and has the power to predict, before the initiation of treatment, the functional tissue outcome after rt-PA-induced thrombolysis.

Biochemical changes and gene expression following traumatic brain injury: Role of spreading depression.

The effects of spreading depression-like DC depolarizations on biochemical changes and gene expression were examined following trau-matic neocortical lesions, as induced by transcranial cold injury. The surrounding of traumatic cold lesions was characterized by increased glu-cose and lactate contents, without major disturbances of protein synthesis or energy state. A transient pH decrease by 0.4 units was noticed 1 h post-injury, which shifted towards alkaline values by 3 h. These changes were similar in animals with spontaneous spreading depression-like DC shifts (n = 14) and those without spreading depressions (n = 7), but there was a marked difference in the gene response. In injured animals without SD, only a short-lasting response of c-fos, junB, c-jun and MKP-1 mRNAs as well as c-Fos protein was bilaterally found in the piri-form cortex, and - with ipsilateral dominance - the dentate gyrus and hippocampal CA3/4 fields at 1 h after lesioning. In injure d animals with spreading depressions, on the contrary, a strong elevation was seen in layers II-IV and VI of the injury-remote ipsilateral cerebral cortex, which persisted over as long as 6 h. The expression of c-fos, junB and MKP-1 mRNAs was closely related to the time interval between the last spreading depression and the end of the experiments. Levels were highest shortly after transient DC shifts, and decreased thereafter mono-exponentially with half-lives of 48, 75 and 58 min for c-fos, junB and MKP-1 mRNAs, respectively. Thus, spreading depression is a prominent factor influencing the trauma-related gene response, but - in contrast to focal ischemia - it does not aggravate the metabolic dysfunction.