Disruption of ion homeostasis in the neurogliovascular unit underlies the pathogenesis of ischemic cerebral edema

Development of an Infarct Volume Algorithm to Correct for Brain Swelling After Ischemic Stroke in Rats

The primary measure for experimental stroke studies, infarct volume, can be affected by brain swelling. The algorithm by Lin et al. was developed to correct for brain swelling, however, the correction is not adequate. This chapter presents a new infarct volume algorithm that more appropriately corrects for brain hemisphere volume changes (swelling and stunted growth). Fifty-one adult rats were sacrificed 24 h after middle cerebral artery occlusion (MCAO). Forty-four P10 rat pups were sacrificed 48 h after hypoxia-ischemia (HI). Infarct volumes for 2,3,5-triphenyl-2H-tetrazolium chloride (TTC) stained brains were calculated using our algorithm and that of Lin and colleagues. For MCAO animals, the algorithm of Lin et al. computed smaller infarct volumes than those of our algorithm. For HI animals, Lin et al.'s algorithm's infarct volumes were greater than those of our algorithm. For sham animals, Lin et al.'s algorithm's computed infarct volumes were significantly different from those of our algorithm. Our algorithm produces a more robust estimation of infarct volume than Lin et al.'s algorithm because the effects of ipsilesional hemisphere volume changes are minimized. Herein, our algorithm yields an infarct volume that better corrects for brain swelling and stunted brain growth compared with the algorithm of Lin et al.

Cyclooxygenase-2 Inhibition Provides Lasting Protection Following Germinal Matrix Hemorrhage in Premature Infant Rats

Germinal matrix hemorrhage (GMH) is a major cause of brain damage in prematurity and has long-lasting neurological implications. The development of brain inflammation contributes to brain injury, leading to a lifetime of neurologic deficits. PAR-1 and 4 receptors are involved with inflammatory pathways after brain hemorrhage in adult models of stroke, of which cyclooxygenase-2 (COX-2) is a potential mediator. We therefore hypothesized a role for PAR-1, 4/ COX-2 signaling following GMH. Postnatal day 7 Sprague-Dawley rats were subjected to GMH induction, which entailed stereotactic collagenase infusion into the ganglionic eminence. Animals were euthanized at two time points: 72 h (short-term) or 4 weeks (long-term). Short-term COX-2 expression was evaluated in the context of PAR-1 (SCH-79797) and PAR-4 (P4pal10) inhibition. Pups in the long-term group were administered the selective COX-2 inhibitor (NS-398); and the neurobehavioral and pathological examinations were performed 4 weeks later. Pharmacological PAR-1, 4 antagonism normalized COX-2 expression following GMH and reduced hydrocephalus. Early inhibition of COX-2 by NS-398 improved long-term neurobehavioral outcomes. COX-2 signaling plays an important role in brain injury following neonatal GMH, possibly through upstream PAR-1, 4 receptor mechanisms.

Valproic Acid Pretreatment Reduces Brain Edema in a Rat Model of Surgical Brain Injury

Surgically induced brain injury (SBI) results in brain edema and neurological decline. Valproic acid (VA) has been shown to be neuroprotective in several experimental brain diseases. In this study, we investigated the pretreatment effect of VA in a rat model of SBI. A total of 57 male Sprague-Dawley rats were use in four groups: sham, SBI + vehicle, SBI + low dose (100 mg/kg) VA, and SBI + high dose (300 mg/kg) VA. SBI was induced by partially resecting right frontal lobes. Shams underwent identical surgical procedures without brain resection. VA or vehicle was administered subcutaneously 30 min prior to SBI. At 24 and 72 h post SBI, neurobehavior and brain water content were assessed as well as matrix metalloproteinases (MMPs) activities. There was significantly higher brain water content within the right frontal lobe in SBI rats than in shams. Without neurobehavioral improvements, the low-dose but not high-dose VA significantly reduced brain edema at 24 h post SBI. The protection tends to persist to 72 h post SBI. At 24 h post SBI, low-dose VA did not significantly reduce the elevated MMP-9 activity associated with SBI. In conclusion, VA pretreatment attenuated brain edema at 24 h after SBI but lacked MMP inhibition. The single dose VA was not associated with neurobehavioral benefits.

Acute Hyperglycemia Is Associated with Immediate Brain Swelling and Hemorrhagic Transformation After Middle Cerebral Artery Occlusion in Rats

Hemorrhagic transformation occurs in as many as 48 % of stroke patients and is a major contributor to post-insult morbidity and mortality. Experimental models of hemorrhagic transformation are utilized for understanding the mechanisms behind its development, as well as for investigating potential therapeutics for prevention and reduction of bleeding. Thoroughly studying animal models of hemorrhagic transformation is critically important for testing novel treatments. Thus far, no study has examined the progression of brain swelling and hemorrhagic transformation after transient middle cerebral artery occlusion (MCAO). Herein, we investigate the development of infarction, brain swelling, and hemorrhagic transformation following MCAO in hyperglycemic rats. Twenty-five Sprague-Dawley rats were subjected to either 1.5 h of MCAO or sham surgery 15 min after induction of hyperglycemia. Animals were sacrificed at 0.25, 1, 3, or 24 h after reperfusion for measurement of infarct volume, brain swelling, and hemoglobin volume. Within 15 min of reperfusion, the infarct volume was significantly larger than in sham animals and did not increase in size over the 24 h. However, both brain swelling and hemorrhagic transformation, which began immediately after reperfusion, increase over 24 h after reperfusion.

Acute Hyperglycemia Does Not Affect Brain Swelling or Infarction Volume After Middle Cerebral Artery Occlusion in Rats

Stroke disproportionally affects diabetic and hyperglycemic patients with increased incidence and is associated with higher morbidity and mortality due to brain swelling. In this study, the intraluminal suture middle cerebral artery occlusion (MCAO) model was used to examine the effects of blood glucose on brain swelling and infarct volume in acutely hyperglycemic rats and normo-glycemic controls. Fifty-four rats were distributed into normo-glycemic sham surgery, hyperglycemic sham surgery, normo-glycemic MCAO, and hyperglycemic MCAO. To induce hyperglycemia, 15 min before MCAO surgery, animals were injected with 50 % dextrose. Animals were subjected to 90 min of MCAO and sacrificed 24 h after reperfusion for hemispheric brain swelling and infarct volume calculations using standard equations. While normo-glycemic and hyperglycemic animals after MCAO presented with significantly higher brain swelling and larger infarcts than their respective controls, no statistical difference was observed for either brain swelling or infarct volume between normo-glycemic shams and hyperglycemic shams or normo-glycemic MCAO animals and hyperglycemic MCAO animals. The findings of this study suggest that blood glucose does not have any significant effect on hemispheric brain swelling or infarct volume after MCAO in rats.

Glycogen Fuels Survival During Hyposmotic-Anoxic Stress in Caenorhabditis elegans

Oxygen is an absolute requirement for multicellular life. Animals that are deprived of oxygen for sufficient periods of time eventually become injured and die. This is largely due to the fact that, without oxygen, animals are unable to generate sufficient quantities of energy. In human diseases triggered by oxygen deprivation, such as heart attack and stroke, hyposmotic stress and cell swelling (edema) arise in affected tissues as a direct result of energetic failure. Edema independently enhances tissue injury in these diseases by incompletely understood mechanisms, resulting in poor clinical outcomes. Here, we present investigations into the effects of osmotic stress during complete oxygen deprivation (anoxia) in the genetically tractable nematode Caenorhabditis elegans. Our findings demonstrate that nematode survival of a hyposmotic environment during anoxia (hyposmotic anoxia) depends on the nematode’s ability to engage in glycogen metabolism. We also present results of a genome-wide screen for genes affecting glycogen content and localization in the nematode, showing that nematode survival of hyposmotic anoxia depends on a large number of these genes. Finally, we show that an inability to engage in glycogen synthesis results in suppression of the enhanced survival phenotype observed in daf-2 insulin-like pathway mutants, suggesting that alterations in glycogen metabolism may serve as a basis for these mutants’ resistance to hyposmotic anoxia.

Therapeutic hypothermia for stroke: Where to go?

Ischemic stroke is a major cause of death and long-term disability worldwide. Thrombolysis with recombinant tissue plasminogen activator is the only proven and effective treatment for acute ischemic stroke; however, therapeutic hypothermia is increasingly recognized as having a tissue-protective function and positively influencing neurological outcome, especially in cases of ischemia caused by cardiac arrest or hypoxic-ischemic encephalopathy in newborns. Yet, many aspects of hypothermia as a treatment for ischemic stroke remain unknown. Large-scale studies examining the effects of hypothermia on stroke are currently underway. This review discusses the mechanisms underlying the effect of hypothermia, as well as trends in hypothermia induction methods, methods for achieving optimal protection, side effects, and therapeutic strategies combining hypothermia with other neuroprotective treatments. Finally, outstanding issues that must be addressed before hypothermia treatment is implemented at a clinical level are also presented.

Aquaporins-2 and -4 regulate glycogen metabolism and survival during hyposmotic-anoxic stress in Caenorhabditis elegans

Periods of oxygen deprivation can lead to ion and water imbalances in affected tissues that manifest as swelling (edema). Although oxygen deprivation-induced edema is a major contributor to injury in clinical ischemic diseases such as heart attack and stroke, the pathophysiology of this process is incompletely understood. In the present study we investigate the impact of aquaporin-mediated water transport on survival in a Caenorhabditis elegans model of edema formation during complete oxygen deprivation (anoxia). We find that nematodes lacking aquaporin water channels in tissues that interface with the surrounding environment display decreased edema formation and improved survival rates in anoxia. We also find that these animals have significantly reduced demand for glycogen as an energetic substrate during anoxia. Together, our data suggest that reductions in membrane water permeability may be sufficient to induce a hypometabolic state during oxygen deprivation that reduces injury and extends survival limits.

What's New in Traumatic Brain Injury: Update on Tracking, Monitoring and Treatment

Traumatic brain injury (TBI), defined as an alteration in brain functions caused by an external force, is responsible for high morbidity and mortality around the world. It is important to identify and treat TBI victims as early as possible. Tracking and monitoring TBI with neuroimaging technologies, including functional magnetic resonance imaging (fMRI), diffusion tensor imaging (DTI), positron emission tomography (PET), and high definition fiber tracking (HDFT) show increasing sensitivity and specificity. Classical electrophysiological monitoring, together with newly established brain-on-chip, cerebral microdialysis techniques, both benefit TBI. First generation molecular biomarkers, based on genomic and proteomic changes following TBI, have proven effective and economical. It is conceivable that TBI-specific biomarkers will be developed with the combination of systems biology and bioinformation strategies. Advances in treatment of TBI include stem cell-based and nanotechnology-based therapy, physical and pharmaceutical interventions and also new use in TBI for approved drugs which all present favorable promise in preventing and reversing TBI.

Correcting for Brain Swelling's Effects on Infarct Volume Calculation After Middle Cerebral Artery Occlusion in Rats

Evaluating infarct volume is the primary outcome for experimental ischemic stroke studies and is a major factor in determining translation of a drug into clinical trials. Numerous algorithms are available for evaluating this critical value, but a major limitation of current algorithms is that brain swelling is not appropriately considered. The model by Lin et al. is widely used, but overestimates swelling within the infarction, yielding infarct volumes which do not reflect the true infarct size. Herein, a new infarct volume algorithm is developed to minimize the effects of both peri-infarct and infarct core swelling on infarct volume measurement. 2,3,5-Triphenyl-2H-tetrazolium chloride-stained brain tissue of adult rats subjected to middle cerebral artery occlusion was used for infarct volume analysis. When both peri-infarct swelling and infarction core swelling are removed from infarct volume calculations, such as accomplished by our algorithm, larger infarct volumes are estimated than those of Lin et al.'s algorithm. Furthermore, the infarct volume difference between the two algorithms is the greatest for small infarcts (<10% of brain volume) when peri-infarct swelling is the greatest. Finally, using data from four published studies, our algorithm is compared to Lin et al.'s algorithm. Our algorithm offers a more reliable estimation of the infarct volume after ischemic brain injury, and thus may provide the foundation for comparing infarct volumes between experimental studies and standardizing infarct volume quantification to aid in the selection of the best candidates for clinical trials.

Neuroinflammation in hepatic encephalopathy: mechanistic aspects

Hepatic encephalopathy (HE) is a major neurological complication of severe liver disease that presents in acute and chronic forms. While elevated brain ammonia level is known to be a major etiological factor in this disorder, recent studies have shown a significant role of neuroinflammation in the pathogenesis of both acute and chronic HE. This review summarizes the involvement of ammonia in the activation of microglia, as well as the means by which ammonia triggers inflammatory responses in these cells. Additionally, the role of ammonia in stimulating inflammatory events in brain endothelial cells (ECs), likely through the activation of the toll-like receptor-4 and the associated production of cytokines, as well as the stimulation of various inflammatory factors in ECs and in astrocytes, are discussed. This review also summarizes the inflammatory mechanisms by which activation of ECs and microglia impact on astrocytes leading to their dysfunction, ultimately contributing to astrocyte swelling/brain edema in acute HE. The role of microglial activation and its contribution to the progression of neurobehavioral abnormalities in chronic HE are also briefly presented. We posit that a better understanding of the inflammatory events associated with acute and chronic HE will uncover novel therapeutic targets useful in the treatment of patients afflicted with HE.

Na(+)/H(+) exchanger in the regulation of platelet activation and paradoxical effects of cariporide

Platelets are anucleated cell fragments derived from mature megakaryocytes and function in hemostasis when the endothelium is injured. Hemostasis involving platelets can be divided into four phases: adhesion, activation, secretion, and aggregation. Platelet activation requires a rise in intracellular Ca(2+) concentrations and results in both a morphological change and the secretion of platelet granule contents. Na(+)/H(+) exchanger isoform 1 (NHE1) regulates the intracellular pH (pHi) and the volume of platelets. In addition, NHE1 plays a large role in platelet activation. Thrombus generation involves NHE1 activation and an increase in [Ca(2+)]i, which results from NHE1-mediated Na(+) overload and the reversal of the Na(+)/Ca(2+) exchanger. Cariporide (HOE-642), a potent NHE1 inhibitor, has inhibitory effects on the degranulation of human platelets, the formation of platelet-leukocyte-aggregates, and the activation of the GPIIb/IIIa receptor (PAC-1). However, despite the demonstrated protection against myocardial infarction as mediated by cariporide in patients undergoing coronary artery bypass graft surgery, the EXPEDITION clinical trial revealed that cariporide treatment increased mortality due to thromboembolic stroke. These findings suggest that a better understanding of NHE1 and its effect on platelet function and procoagulant factor regulation is warranted in order to develop therapies using NHE inhibitors.

Antagonists of the Vasopressin V1 Receptor and of the β(1)-Adrenoceptor Inhibit Cytotoxic Brain Edema in Stroke by Effects on Astrocytes - but the Mechanisms Differ

Brain edema is a serious complication in ischemic stroke because even relatively small changes in brain volume can compromise cerebral blood flow or result in compression of vital brain structures on account of the fixed volume of the rigid skull. Literature data indicate that administration of either antagonists of the V1 vasopressin (AVP) receptor or the β1-adrenergic receptor are able to reduce edema or infarct size when administered after the onset of ischemia, a key advantage for possible clinical use. The present review discusses possible mechanisms, focusing on the role of NKCC1, an astrocytic cotransporter of Na(+), K(+), 2Cl(-) and water and its activation by highly increased extracellular K(+) concentrations in the development of cytotoxic cell swelling. However, it also mentions that due to a 3/2 ratio between Na(+) release and K(+) uptake by the Na(+),K(+)-ATPase driving NKCC1 brain extracellular fluid can become hypertonic, which may facilitate water entry across the blood-brain barrier, essential for development of edema. It shows that brain edema does not develop until during reperfusion, which can be explained by lack of metabolic energy during ischemia. V1 antagonists are likely to protect against cytotoxic edema formation by inhibiting AVP enhancement of NKCC1-mediated uptake of ions and water, whereas β1-adrenergic antagonists prevent edema formation because β1-adrenergic stimulation alone is responsible for stimulation of the Na(+),K(+)-ATPase driving NKCC1, first and foremost due to decrease in extracellular Ca(2+) concentration. Inhibition of NKCC1 also has adverse effects, e.g. on memory and the treatment should probably be of shortest possible duration.

Ammonia, like K(+), stimulates the Na(+), K(+), 2 Cl(-) cotransporter NKCC1 and the Na(+),K(+)-ATPase and interacts with endogenous ouabain in astrocytes

Brain edema during hepatic encephalopathy or acute liver failure as well as following brain ischemia has a multifactorial etiology, but it is a dangerous and occasionally life-threatening complication because the brain is enclosed in the rigid skull. During ischemia the extracellular K(+) concentration increases to very high levels, which when energy becomes available during reperfusion stimulate NKCC1, a cotransporter driven by the transmembrane ion gradients established by the Na(+),K(+)-ATPase and accumulating Na(+), K(+) and 2 Cl(-) together with water. This induces pronounced astrocytic swelling under pathologic conditions, but NKCC1 is probably also activated, although to a lesser extent, during normal brain function. Redistribution of ions and water between extra- and intracellular phases does not create brain edema, which in addition requires uptake across the blood-brain barrier. During hepatic encephalopathy and acute liver failure a crucial factor is the close resemblance between K(+) and NH4(+) in their effects not only on NKCC1 and Na(+),K(+)-ATPase but also on Na(+),K(+)-ATPase-induced signaling by endogenous ouabains. These in turn activate production of ROS and nitrosactive agents which slowly sensitize NKCC1, explaining why cell swelling and brain edema generally are delayed under hyperammonemic conditions, although very high ammonia concentrations can cause immediate NKCC1 activation.