Development Of Vasogenic Brain Edema Research Articles

Blood-Brain Barrier Alterations and Edema Formation in Different Brain Mass Lesions.

Differential diagnosis of brain lesion pathologies is complex, but it is nevertheless crucial for appropriate clinical management. Advanced imaging methods, including diffusion-weighted imaging and apparent diffusion coefficient, can help discriminate between brain mass lesions such as glioblastoma, brain metastasis, brain abscesses as well as brain lymphomas. These pathologies are characterized by blood-brain barrier alterations and have been extensively studied. However, the changes in the blood-brain barrier that are observed around brain pathologies and that contribute to the development of vasogenic brain edema are not well described. Some infiltrative brain pathologies such as glioblastoma are characterized by glioma cell infiltration in the brain tissue around the tumor mass and thus affect the nature of the vasogenic edema. Interestingly, a common feature of primary and secondary brain tumors or tumor-like brain lesions characterized by vasogenic brain edema is the formation of various molecules that lead to alterations of tight junctions and result in blood-brain barrier damage. The resulting vasogenic edema, especially blood-brain barrier disruption, can be visualized using advanced magnetic resonance imaging techniques, such as diffusion-weighted imaging and apparent diffusion coefficient. This review presents a comprehensive overview of blood-brain barrier changes contributing to the development of vasogenic brain edema around glioblastoma, brain metastases, lymphomas, and abscesses.

The Contractile Apparatus Is Essential for the Integrity of the Blood-Brain Barrier After Experimental Subarachnoid Hemorrhage

Development of vasogenic brain edema is a key event contributing to mortality after subarachnoid hemorrhage (SAH). The precise underlying mechanisms at the neurovascular level that lead to disruption of the blood-brain barrier (BBB) are still unknown. Activation of myosin light chain kinases (MLCK) may result in change of endothelial cell shape and opening of the intercellular gap with subsequent vascular leakage. Male C57Bl6 mice were subjected to endovascular perforation. Brain water content was determined by wet-dry ratio and BBB integrity by Evans-Blue extravasation. The specific MLCK inhibitor ML-7 was administered to the mice to determine the role of the contractile apparatus of the neurovascular unit in determining brain water content, BBB integrity, neurofunctional outcome, brain damage, and survival at 7 days after SAH. Inhibition of MLCK significantly reduced BBB permeability (Evans Blue extravasation − 28%) and significantly decreased edema formation in comparison with controls (− 2%). MLCK-treated mice showed reduced intracranial pressure (− 53%), improved neurological outcome at 24 h and 48 h after SAH, and reduced 7-day mortality. Tight junction proteins claudin-5 and zonula occludens-1 levels were not influenced by ML-7 at 24 h after insult. The effect of ML-7 on pMLC was confirmed in brain endothelial cell culture (bEnd.3 cells) subjected to 4-h oxygen-glucose deprivation. The present study indicates that MLCK contributes to blood-brain barrier dysfunction after SAH by a mechanism that does not involve modulation of tight junction protein levels, but via activation of the contractile apparatus of the endothelial cell skeleton. This underlying mechanism may be a promising target for the treatment of SAH.

Identification of the Vascular Source of Vasogenic Brain Edema following Traumatic Brain Injury Using In Vivo 2-Photon Microscopy in Mice.

Vasogenic brain edema due to vascular leakage is one of the most important factors determining the clinical outcome of patients following acute brain injury. To date, performing a detailed in vivo quantification of vascular leakage has not been possible. Here, we used in vivo 2-photon microscopy (2-PM) to determine the spatial (3D) and temporal development of vasogenic brain edema following traumatic brain injury (TBI) in mice; in addition, we identified the vessel types involved in vascular leakage. Thirteen male Tie2-GFP mice (6-8 weeks old) were subjected to controlled cortical impact (CCI) or a sham operation; subsequently, a cranial window was prepared adjacent to the injury site, and tetramethylrhodamine-dextran (TMRM, 40 mg/kg, MW 40,000) was injected intravenously to visualize blood plasma leakage. Parenchymal fluorescence intensity was monitored in three regions for 2-4 h post-CCI, reaching from the surface of the brain to a depth of 300 μm, and TMRM leakage was measured as an increase in TMRM fluorescence intensity outside the vessel lumen and in the parenchyma. In the CCI group, vascular leakage was detected in all investigated regions as early as 2.5 h post-injury. This leakage increased over time and was more pronounced proximal to the primary contusion. Both arterioles and venules contributed similarly to brain edema formation and their contribution was independent of vessel size; however, capillaries were the major contributor to leakage. In summary, using 2-PM to perform in vivo 3D deep-brain imaging, we found that TBI induces vascular leakage from capillaries, venules, and arterioles. Thus, all three vessel types are involved in trauma-induced brain edema and should be considered when developing novel therapies for preventing vasogenic brain edema.

Different expressions of AQP1, AQP4, eNOS, and VEGF proteins in ischemic versus non-ischemic cerebropathy in rats: potential roles of AQP1 and eNOS in hydrocephalic and vasogenic edema formation

In this study, expressions of aquaporin (AQP) 1, AQP4, endothelial nitric oxide synthase (eNOS), and vascular endothelial growth factor in blood-cerebrospinal fluid (CSF) barrier and blood-brain barrier (BBB) are examined in rat choroid plexus and peri-infarcted hippocampal formation (HF) following systemic hyponatremia (SH) and permanent middle cerebral artery occlusion (pMCAO). These events are thought to cause the development of hydrocephalic and vasogenic edemas. The importance of CSF overproduction and intact blood-CSF barrier during hydrocephalic edema formation is demonstrated by the high expression of AQP1 (329.86±10.2%, n=4 , P<0.01) and trapped plasma immunoglobulin G (IgG) in choroid plexus epithelium after 24 hours of SH. However, the increased eNOS expression in peri-infarcted HF (130±3%, n=4, P<0.01) and extravasation of plasma IgG into the extravascular compartment after 24 hours of pMCAO suggest that increased microvascular permeability, probably due to elevated levels of nitric oxide, leads to development of vasogenic brain edema via BBB breakdown. Based on these findings, the authors suggest that modulation of different protein expression, dependent on the type of brain edema, is required for primary (pMCAO) and secondary (SH) brain injuries to attenuate brain edema and neuronal degeneration.

Comparison Evans Blue injection routes: Intravenous versus intraperitoneal, for measurement of blood–brain barrier in a mice hemorrhage model

AimsIntracerebral hemorrhage is one of the most devastating subtypes of stroke, leaving survivors with severe neurological deficits. Disruption of the blood brain barrier (BBB) following hemorrhage results in the development of vasogenic brain edema, a most life-threatening event after such events as intracerebral hemorrhage (ICH). The Evans Blue assay is a popular method for the quantification of BBB disruption. Although this method is in common use, there are several protocols of the assay in the literature which vary in the route of administration, as well as the circulation time of the stain. In this study, we compared the amounts of accumulated stain in brain tissue following intraperitoneal versus intravenous injection at 0.5, 3 and 24h of circulation time. Methods58 CD-1 mice were used. Animals were divided into ICH (N=42), sham groups (N=6) and naïve (N=10). ICH animals received stereotactic injection of collagenase type VII into the right basal ganglia. Sham animals received only needle trauma. Evans Blue stain was injected 24h after collagenase injection or needle trauma. The consistency of ICH produced was characterized by estimation of hematoma volume via hemoglobin assay and neurological evaluation. ResultsThe produced hematoma and neurological deficits were well comparable between different experimental groups. There was no statistically significant difference in the results of the Evans Blue assay with regard to administration route. ConclusionsThe amount of Evans Blue stain accumulated in the brains of mice after ICH produced by collagenase injection was independent of the stain administration route.

Reoxygenation stress on blood–brain barrier paracellular permeability and edema in the rat

The blood–brain barrier (BBB) serves as a critical regulator of brain homeostasis. Following hypoxia (i.e. 6% oxygen/1 h) and reoxygenation (H/R), the BBB tight junctional complex is disrupted, resulting in increased BBB permeability and the development of vasogenic brain edema. In this study, we examined the effect of H/R on the in vivo rat BBB over a 36 h time course in conjunction with paracellular permeability, gray matter edema, and systemic inflammatory activity. A biphasic increase was observed in the brain uptake of 14C-sucrose, a paracellular permeability marker; with the first increase at the 10 min reoxygenation time point, and the second increase at the 6–18 h time points. Increased brain water weight gain (edema) also showed a biphasic response with the first increase at the 10 min–1 h reoxygenation time points; and the second increase at only the 24 h time point. Analysis of serum derived cytokines (IL-1β, TNFα, IL-6, IL-10, and IFNγ) demonstrated that only IL-1β and IL-6 were at detectable levels, but these levels were similar to controls. White blood cell counts showed significant decreases in lymphocytes (10 min–3 h), increases in monocytes (10 min–3 h and 12 h), and increases in polymorphonuclear cells (1 h and 3 h). We have shown that H/R elicits a biphasic increase in paracellular permeability and edema, which parallel to post-stroke sequelae, despite the lack of occlusion or complete depletion of oxygen.

H 2O 2 induces paracellular permeability of porcine brain-derived microvascular endothelial cells by activation of the p44/42 MAP kinase pathway

In vivo, pathological conditions such as ischemia and ischemia/reperfusion are known to damage the blood–brain barrier (BBB) leading to the development of vasogenic brain edema. Using an in vitro model of the BBB, consisting of brain-derived microvascular endothelial cells (BMEC), it was demonstrated that hypoxia-induced paracellular permeability was strongly aggravated by reoxygenation (H/R), which was prevented by catalase suggesting that H 2O 2 is the main mediator of the reoxygenation effect. Therefore, mechanisms leading to H 2O 2-induced hyperpermeability were investigated. N-acetylcysteine and suramin and furthermore usage of a G protein antagonist inhibited H 2O 2 effects suggesting that activation of cell surface receptors coupled to G proteins may mediate signal initiation by H 2O 2. Further, H 2O 2 activated phospholipase C (PLC) and increased the intracellular Ca 2+ release because U73122, TMB-8, and the calmodulin antagonist W7 inhibited H 2O 2-induced hyperpermeability. H 2O 2 did not activate protein kinase C (PKC), nitric-oxide synthase (NOS), and phosphatidyl-inositol-3 kinase (PI3-K/Akt). Inhibition of the extracellular signal-regulated kinase (ERK1/ERK2 or p44/42 MAPK), but not of the p38 and of the c-jun NH 2-terminal kinase (JNK), inhibited hyperpermeability by H 2O 2 and H/R completely. Corresponding to H 2O 2- and H/R-induced permeability changes the phosphorylation of the p44/42 MAP kinase was inhibited by the specific MAP kinase inhibitor PD98059 and by TMB-8 and W7. Paracellular permeability changes by H 2O 2 correlated to changes of the localization of the tight junction (TJ) proteins occludin, zonula occludens 1 (ZO-1), and zonula occludens 2 (ZO-2) which were prevented by blocking the p44/p42 MAP kinase activation. Results suggest that H 2O 2 is the main inducer of H/R-induced permeability changes. The hyperpermeability is caused by activation of PLC via receptor activation leading to the intracellular release of Ca 2+ followed by activation of the p44/42 MAP kinase and paracellular permeability changes mediated by changes of the localization of TJ proteins.

Simultaneous activation of several second messengers in hypoxia‐induced hyperpermeability of brain derived endothelial cells

In vivo, ischemia is known to damage the blood-brain barrier (BBB) leading to the development of vasogenic brain edema. Hypoxia-induced vascular endothelial growth factor (VEGF) has been shown to be a key regulator of these permeability changes. However, the signaling pathways that underlie VEGF-induced hyperpermeability are incompletely understood. In this study, we demonstrate that hypoxia- and VEGF-induced permeability changes depend on activation of phospholipase Cgamma (PLCgamma), phosphatidylinositol 3-kinase/Akt (PI3-K/Akt), and protein kinase G (PKG). Inhibition of mitogen-activated protein kinases (MAPK) and of the protein kinase C (PKC) did not affect permeability at all. Paralleling hypoxia- and VEGF-induced permeability changes, localization of the tight junction proteins occludin, zonula occludens-1 (ZO-1), and ZO-2 along the cell membrane changed from a continuous to a more discontinuous expression pattern during hypoxia. In particular, localization of ZO-1 and ZO-2 expression moved from the cell membrane to the cytoplasm and nucleus whereas occludin expression remained at the cell membrane. Inhibition of PLCgamma, PI3-kinase, and PKG abolished these hypoxia-induced changes. These findings demonstrate that hypoxia and VEGF induce permeability through rearrangement of endothelial junctional proteins which involves activation of the PLCgamma and PI3-K/AKT pathway leading to the activation of PKG.

Hypoxia-Induced Hyperpermeability in Brain Microvessel Endothelial Cells Involves VEGF-Mediated Changes in the Expression of Zonula Occludens-1

In vivo, hypoxia is known to damage the blood–brain barrier (BBB) leading to the development of vasogenic brain edema. Primary cultures of porcine brain derived microvascular endothelial cells were used as an in vitro BBB model to evaluate the mechanisms by which hypoxia regulates paracellular permeability. Paracellular passage across endothelial cell monolayers is regulated by specialized intercellular structures like the tight junctions (TJ). Zonula occludens-1 (ZO-1), a protein of the TJ, lines the cytoplasmic face of intact TJ. The continuity of the ZO-1 expression was disrupted during 24 h of hypoxia which correlated with a decrease of the protein level to 32 ± 8% and with a twofold increase in the phosphorylation of ZO-1 in comparison to values determined at the start of the experiment. The localization and expression level of ZO-1 were maintained during hypoxia in the presence of a polyclonal antibody to vascular endothelial growth factor (VEGF) demonstrating that hypoxia-induced changes of the ZO-1 expression are mediated by VEGF. The effect of hypoxia on the ZO-1 distribution probably is not tissue- or cell-specific because similar changes of ZO-1 distribution were observed when the rat brain endothelial cell line RBE4 or the murine epithelial cell line CSG was used. Furthermore, ZO-1 changes correlated with small changes in actin distribution. These results suggest that hypoxia increases the paracellular flux across the cell monolayer via the release of VEGF, which in turn leads to the dislocalization, decreased expression, and enhanced phosphorylation of ZO-1.

Mild hypothermia prevents the occurrence of cytotoxic brain edema in rats.

Hypothermia maintains the impermeability of the blood-brain barrier to proteins and, therefore, presumably the development of vasogenic brain edema after brain ischemia. We intended to determine whether mild hypothermia would have a protective effect against cytotoxic brain edema, the early stage of ischemic brain edema. Two groups of Wistar rats (37 degrees C and 35 degrees C body temperature) were subjected to 6 h of moderate decrease of cerebral blood flow (CBF) by means of permanent bilateral carotid artery ligation, and compared to a third group of unaffected animals. Carotid artery ligation induced a local cerebral blood flow (LCBF) reduction to 50-80% of baseline values. LCBF in the frontal cortex was restored to a higher level in hypothermic animals than in normothermic ones (P < 0.05). In normothermic animals, an increase of brain water content was detected in the frontoparietal and occipital cortex as well as in the hippocampus (P < 0.05), but only in one region of the frontoparietal cortex in hypothermic animals. The impermeability of the blood-brain barrier to proteins was shown by the absence of staining with Evans blue as an indicator of vasogenic brain edema. We conclude that mild hypothermia offers protection against the development of cytotoxic brain edema.

Amino acids in extracellular fluid in vasogenic brain edema.

We have investigated if changes in brain dialysate, reflecting alterations in brain extracellular composition, can be detected during the development of vasogenic brain edema. The blood-brain barrier was opened by intracarotid infusion of 5 or 10 mg protamine sulphate. The rats were killed two hours after opening of the BBB when the brains were macroscopically edematous, after 10 mg but not 5 mg protamine sulphate. No significant alterations in the amino acid concentration in the dialysate were observed after the lower dose. 40 min after infusion of 10 mg protamine, the level of glutamate was significantly increased in the dialysate followed by that of aspartate, glycine, phosphoethanolamine and taurine 10 min later and a further delayed increase in GABA. We conclude that the development of vasogenic brain edema is associated with significant increases in extracellular concentration of excitatory amino acids, of taurine, and of phosphoethanolamine and GABA.

Cerebrovascular permeability and brain edema after cortical photochemical infarcts in the rat.

The importance of protein extravasation for the development of vasogenic brain edema is still controversial. We, therefore, assessed the cerebrovascular permeability to serum proteins in relation to the development and resolution of brain edema in a photochemical cortical lesion in the rat. Cortical infarction was induced by in situ thrombosis using an argon laser beam aimed at the exposed parietal bone in animals given rose bengal i.v. The histology and the cerebrovascular permeability to serum proteins were scrutinized from 2 h to 3 weeks after the insult. The presence of serum proteins was demonstrated by an immunoperoxidase technique. The cerebral water content was estimated by specific gravity measurements of the cortical tissue in a kerosene-monobromobenzene gradient column from 2 h to 7 days after infarction. The blood-brain barrier was permeable to proteins at 2 h following the insult and proteins spread into the medial and lateral tissue reaching a maximum at 24 h. The specific gravity did not deviate from control values at 2 h. After 8 h the specific gravity of the lesion decreased with smaller decreases in the immediately adjacent tissue. At 24 h the changes in specific gravities reached a maximum in all regions except the immediately lateral area. The edema was generally worse in tissue medial to rather than lateral to the infarct. The degradation of serum proteins and the resolution of the brain edema followed the same time course with partial resolution of 72 h. By 1 week serum proteins and edema were confined to the central necrotic core. The results suggest a relationship between cerebrovascular permeability and cerebral edema in photochemical cortical infarction.

Cold‐induced brain edema and infarction are reduced in transgenic mice overexpressing CuZn‐Superoxide dismutase

It has been proposed that oxygen-derived radicals, superoxide in particular, are involved in the alteration of blood-brain barrier permeability and the pathogenesis of brain edema following trauma, ischemia, and reperfusion injury. Using transgenic mice that overexpress the human gene for copper-zinc-superoxide dismutase, we studied the role of superoxide radicals in the blood-brain permeability changes, edema development, and delayed infarction resulting from cold-trauma brain injury. At 2 hours after a 30-second cold injury, cerebral water and Evans blue contents were reduced, respectively, from 80 +/- 0.2% and 132.7 +/- 12.9 micrograms/gm of dry weight for nontransgenic mice to 78.5 +/- 0.3% and 87.1 +/- 9.9 micrograms/gm of dry weight for transgenic mice. Infarction, as measured by 2,3,5-triphenyltetrazolium chloride staining, was reduced by 52% in transgenic brains. These data indicate that an increased level of superoxide dismutase activity in the brain reduces the development of vasogenic brain edema and infarction. Superoxide radicals play an important role in the pathogenesis of these lesions in cold-traumatized brain.

Protective effects of liposome-entrapped superoxide dismutase on posttraumatic brain edema.

Oxygen-derived free radicals and membrane lipid peroxidation have been postulated to be involved in brain edema and cell death, secondary to ischemia and traumatic injury. Using a model of brain edema induced by cold-induced injury, we have demonstrated an early elevation of superoxide radicals followed by permeability changes in the blood-brain barrier and development of edema in injured brain. Intravenous injection of liposome-entrapped copper-zinc-superoxide dismutase 5 minutes before the injury-enhanced entry of the enzyme into endothelial cells of the blood-brain barrier of injured brain reduced the brain level of superoxide radicals and ameliorated blood-brain barrier permeability changes and brain edema. Identical treatment 5 minutes after injury was also effective. These data demonstrate that superoxide radicals play an important role in the delayed development of vasogenic brain edema following brain injury.

Effects of dexamethasone on brain edema induced by kainic acid seizures

The histopathological alterations developing in the hippocampus, pirifonn cortex and thalamus of the rat brain, the blood-brain barrier damage, and the effects of dexamethasone pretreatment on the brain edema were investigated 4 h following intraperitoneal kainic acid administration. The most pronounced Evans Blue extravasation accompanied by increases in the water and sodium contents and a decrease in the potassium content, were observed in the thalamus. Dexamethasone, injected in a dose of 5 mg/kg 2 h before kainic acid administration, reduced considerably the vasogenic edema and neuronal damage in the thalamus, but the cytotoxic edema of the hippocampus and pirifonn cortex remained unaltered. Kainic acid-induced seizures lead to the development of vasogenic brain edema mainly in the thalamus, as well as to cytotoxic edema in the hippocampus and pirifonn cortex. The vasogenic edema seems to contribute to the cell damage in the thalamus. Dexamethasone reduces the vasogenic edema and cell damage in the thalamus, possibly by inducing the synthesis of certain protein(s) with antiphospholipase A 2 activity.

Kainic acid neurotoxicity: Characterization of blood-brain barrier damage

The alterations in the water, sodium (Na) and potassium (K) contents of the frontoparietal cortex, hippocampus and thalamus as well as the protein permeability of the blood-brain barrier were investigated in rats 4 h after systemic kainic acid administration. Increases in the water and Na contents and a decrease in the K content were observed together with Evans blue extravasation in the thalamus area indicating the development of vasogenic brain edema. Changes observed in the ion contents of the frontoparietal cortex and hippocampus may be due to a general cell membrane permeability damage but are not caused by a primary disturbance of the blood-brain barrier.

Disturbances of the blood-brain barrier in cerebrovascular disorders.

The disturbances of the BBB in cerebrovascular disorders may affect adversely an underlying basic pathological condition. Breakdown of the barrier associated with extravasation of serum proteins leads to development of vasogenic edema in the brain tissue. An abnormal passage of pharmacologically active substances, such as biogenic amines, may significantly affect cerebral blood flow and metabolism and activate neurons equipped with receptors for these substances. Also, a barrier dysfunction related to faulty out-transport of metabolites may contribute to edema and tissue damage. In cerebral ischemia, following release of arterial occlusion there can be two separate openings of the barrier: the first - occurring promptly after recirculation and related to ensuing reactive hyperemia, the second - after some delay and related to pathological changes in the brain tissue. In some circumstances, such as epileptic seizures, both "hemodynamic" and "tissue" factors may be operative at the same time. The selective features of BBB changes are related to multiplicity of barrier systems residing in cerebral endothelium. These selective features are demonstrable during development and during reversibility of postichemic barrier disturbances. Intermittent openings of the barrier observed in chronic hypertension may lead to accumulation of extravasated serum proteins and be responsible for frequently observed edematous changes in this condition.