Development Of Brain Edema Research Articles

Aquaporins and blood–brain barrier permeability in early edema development after traumatic brain injury

Traumatic brain injury (TBI) is a major contributor to mortality and morbidity. The pathophysiology involves development of brain edema. Therapeutic options are limited as the mechanisms are not fully understood. Changes in the function of the blood–brain barrier (BBB), as well as variations in aquaporin expression, have been proposed to be involved in the development of the edema but the contribution of each factor has not been fully elucidated. In order to evaluate these mechanisms, in a potential window of opportunity, the early dynamic response was studied using an animal model causing a moderate TBI. Sprague-Dawley rats were subjected to blunt controlled head trauma and followed for up to four days by magnetic-resonance-imaging, immunohistofluorescence, immunohistochemistry, and quantitative protein analysis. Non-traumatized animals served as controls. TBI resulted in a midline shift and a decrease in Apparent Diffusion Coefficient, indicating a hemispheric enlargement due to cytotoxic edema. The tight junction protein Zona Occludens-1 was decreased (−25%) and associated with an increased IgG permeability (+20%) in the perilesional brain tissue in accordance with a BBB breakdown. The total amount of AQP4 protein decreased (−20%). The disruption of the BBB lasted for 4 days while the impact on AQP4 levels disappeared between day 1 and 4. Our findings shows that blunt focal brain injury results in an early development of brain edema involving both cytotoxic and vasogenic components, a persistent BBB breakdown and a temporary decrease in AQP4, and indicates that both types of edemas and mechanisms should be targeted in TBI treatment.

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.

Intracellular Na(+) inhibits volume-regulated anion channel in rat cortical astrocytes.

Accumulating evidence indicates that increased intracellular Na(+) concentration ([Na(+) ]i ) in astroglial cells is associated with the development of brain edema under ischemic conditions, but the underlying mechanisms are still elusive. Here, we report that in primary cultured rat cortical astrocytes, elevations of [Na(+) ]i reflecting those achieved during ischemia cause a marked decrease in hypotonicity-evoked current mediated by volume-regulated anion channel (VRAC). Pharmacological manipulations revealed that VRAC inhibition was not due to the reverse mode of the plasma membrane sodium/calcium exchanger. The negative modulation of VRAC was also observed in an astrocytic cell line lacking the predominant astrocyte water channel aquaporin 4, indicating that [Na(+) ]i effect was not mediated by the regulation of aquaporin 4 activity. The inward rectifier Cl(-) current, which is also expressed by cultured astrocytes, was not affected by [Na(+) ]i increase. VRAC depression by high [Na(+) ]i was confirmed in adult astrocytes, suggesting that it was not developmentally regulated. Altogether, these results provide the first evidence that intracellular Na(+) dynamics can modulate astrocytic membrane conductance that controls functional processes linked to cell volume regulation and add further support to the concept that limiting astrocyte intracellular Na(+) accumulation might be a favorable strategy to counteract the development of brain edema.

Aquaporins: Small Proteins with Diverse Functions

It is a well known fact that aquaporins are the small protein channels responsible for the water and salt homeostasis. They are widely distributed in plants, lower organisms and mammals. In addition to the role in water homeostasis they also serve many other important physiological functions and their malfunction may result in many pathological disorders. Present review will add a new dimension to the knowledge of this small protein molecule in various physiological phenomenon such as secretion of glands, neuroexcitation, fat metabolism, cell migration, cell proliferation, hydration of skin, tumor angiogenesis, wound healing and glial scar formation. Transport of water and other molecules such as glycerol and ammonia are responsible for various functions served by aquaporins. Deficiency or absence of aquaporin leads to various pathological disorders such as congenital cataracts and neuromyelitisoptica. They also play role in development of brain edema and obstructive hydrocephalus. Moreover they can be the site of targeted drug therapy in many pathological processes. Disorders such as brain edema, epilepsy, obesity and cancer can be treated by altering the expression of aquaporins on various tissues.

Multimodal MR imaging of acute and subacute experimental traumatic brain injury: Time course and correlation with cerebral energy metabolites.

BackgroundTraumatic brain injury (TBI) is one of the leading causes of death and permanent disability world-wide. The predominant cause of death after TBI is brain edema which can be quantified by non-invasive diffusion-weighted magnetic resonance imaging (DWI).PurposeTo provide a better understanding of the early onset, time course, spatial development, and type of brain edema after TBI and to correlate MRI data and the cerebral energy state reflected by the metabolite adenosine triphosphate (ATP).Material and MethodsThe spontaneous development of lateral fluid percussion-induced TBI was investigated in the acute (6 h), subacute (48 h), and chronic (7 days) phase in rats by MRI of quantitative T2 and apparent diffusion coefficient (ADC) mapping as well as perfusion was combined with ATP-specific bioluminescence imaging and histology.ResultsAn induced TBI led to moderate to mild brain damages, reflected by transient, pronounced development of vasogenic edema and perfusion reduction. Heterogeneous ADC patterns indicated a parallel, but mixed expression of vasogenic and cytotoxic edema. Cortical ATP levels were reduced in the acute and subacute phase by 13% and 27%, respectively, but were completely normalized at 7 days after injury.ConclusionThe partial ATP reduction was interpreted to be partially caused by a loss of neurons in parallel with transient dilution of the regional ATP concentration by pronounced vasogenic edema. The normalization of energy metabolism after 7 days was likely due to infiltrating glia and not to recovery. The MRI combined with metabolite measurement further improves the understanding and evaluation of brain damages after TBI.

CT imaging and spontaneous behavior analysis after osmotic blood-brain barrier opening in Wistar rat.

In our previous experiments we demonstrated that osmotic opening of the blood brain barrier (BBB) in rats by administration of mannitol into the internal carotid artery leads to cerebral edema. The aim of this study was to confirm objectively the development of brain edema and determine whether it affects spontaneous locomotor activity in rats (SLA). Brain edema was verified by computer tomography (CT) examination of the brain and SLA was observed during open field test. Twenty four adult male rats were divided into four groups of six: (1) control animals (C), (2) controls with anesthesia (CA), (3) controls with sham surgery (CS), (4) experimental - osmotic opening of the BBB (MA). Osmotic BBB disruption manifested by reducing the density of brain tissue (hypodensity), suggesting a higher water content in the brain tissue. SLA was compared between C, CA, CS and MA groups and between MA and CA groups. Significant difference was found only between the control group and MA group. In the first 30 min of the examination, rats after the mannitol administration revealed a marked limitation of spontaneous locomotor activity. Experimental results demonstrated reduction of spontaneous locomotor activity in rats with induced brain edema.

Treatment of malignant brain edema and increased intracranial pressure after stroke.

The management of patients with large territory ischemic strokes and the subsequent development of malignant brain edema and increased intracranial pressure is a significant challenge in modern neurology and neurocritical care. These patients are at high risk of subsequent neurologic decline and are best cared for in an intensive care unit or a comprehensive stroke center with access to neurosurgical support. Risks include hemorrhagic conversion, herniation, poor functional outcome, and death. This review discusses recent advances in understanding the pathophysiology of edema formation, identifying patients at risk, current management strategies, and emerging therapies.

AQP4 tag single nucleotide polymorphisms in patients with traumatic brain injury.

Accumulating evidence suggests that the extent of brain injury and the clinical outcome after traumatic brain injury (TBI) are modulated, to some degree, by genetic variants. Aquaporin-4 (AQP4) is the predominant water channel in the central nervous system and plays a critical role in controlling the water content of brain cells and the development of brain edema after TBI. We sought to investigate the influence of the AQP4 gene region on patient outcome after TBI by genotyping tag single nucleotide polymorphisms (SNPs) along AQP4 gene. A total of 363 patients with TBI (19.6% female) were prospectively evaluated. Data including the Glasgow Coma Scale (GCS) scores at admission, the presence of intracranial hemorrhage, and the 6-month Glasgow Outcome Scale (GOS) scores were collected. Seven tag SNPs across the AQP4 gene were identified based on the HapMap data. Using logistic regression analyses, SNPs and haplotypes were tested for associations with 6-month GOS after adjusting for age, GCS score, and sex. Significant associations with TBI outcome were detected for rs3763043 (OR [95% confidence interval (CI)]: 5.15 [1.60-16.5], p=0.006, for recessive model), rs3875089 (OR [95% CI]: 0.18 [0.07-0.50] p=0.0009, for allele difference model), and a common haplotype of AQP4 tag SNPs (OR [95% CI]: 2.94, [1.34-6.36], p=0.0065). AQP4 tag SNPs were not found to influence the initial severity of TBI or the presence of intracranial hemorrhages. In conclusion, the present study provides evidence for possible involvement of genetic variations in AQP4 gene in the functional outcome of patients with TBI.

Blood brain barrier is impermeable to solutes and permeable to water after experimental pediatric cardiac arrest

Pediatric asphyxial cardiac arrest (CA) results in unfavorable neurological outcome in most survivors. Development of neuroprotective therapies is contingent upon understanding the permeability of intravenously delivered medications through the blood brain barrier (BBB). In a model of pediatric CA we sought to characterize BBB permeability to small and large molecular weight substances. Additionally, we measured the percent brain water after CA. Asphyxia of 9min was induced in 16–18 day-old rats. The rats were resuscitated and the BBB permeability to small (sodium fluorescein and gadoteridol) and large (immunoglobulin G, IgG) molecules was assessed at 1, 4, and 24h after asphyxial CA or sham surgery. Percent brain water was measured post-CA and in shams using wet-to-dry brain weight. Fluorescence, gadoteridol uptake, or IgG staining at 1, 4h and over the entire 24h post-CA did not differ from shams, suggesting absence of BBB permeability to these solutes. Cerebral water content was increased at 3h post-CA vs. sham. In conclusion, after 9min of asphyxial CA there is no BBB permeability over 24h to conventional small or large molecule tracers despite the fact that cerebral water content is increased early post-CA indicating the development of brain edema. Evaluation of novel therapies targeting neuronal death after pediatric CA should include their capacity to cross the BBB.

Elevated cerebral lactate: Implications in the pathogenesis of hepatic encephalopathy.

Hepatic encephalopathy (HE), a complex neuropsychiatric syndrome, is a frequent complication of liver failure/disease. Increased concentrations of lactate are commonly observed in HE patients, in the systemic circulation, but also in the brain. Traditionally, increased cerebral lactate is considered a marker of energy failure/impairment however alterations in lactate homeostasis may also lead to a rise in brain lactate and result in neuronal dysfunction. The latter may involve the development of brain edema. This review will target the significance of increased cerebral lactate in the pathogenesis of HE.

Upregulation and lysosomal degradation of AQP4 in rat brains with bacterial meningitis

Brain edema is among the major complications in children with bacterial meningitis. Aquaporins are integral membrane pore proteins that form channels to regulate cellular water content. Aquaporin-4 (AQP4), which is enriched in parts of astrocytic membranes that are apposed to pial or perivascular basal laminae, is the predominant aquaporin in the central nervous system. Dystroglycan is among the proteins that are responsible for the site-specific anchorage of AQP4. To elucidate the role of AQP4 in the development of brain edema induced by meningitis, a model of bacterial meningitis was established by injecting group B β-hemolytic Streptococci into the cerebrospinal fluid of three-week-old rats. The brain water content increased in this model compared with that in the control group. The expression of AQP4 and dystroglycan was examined by Western blot and the degradation route of AQP4 was investigated by double immunofluorescence labeling. Western blot results showed that the expression of AQP4 and dystroglycan in rat brain increased in the meningitis model. Meanwhile, AQP4 was co-localized with the marker of lysosome in this model, indicating that the lysosome is involved in AQP4 degradation.

Decompression Craniotomy in the Complex Intensive Therapy of Malignant Forms of Massive Ischemic Stroke

A group of patients with benign course of massive ischemic stroke (MII) without development of the dislocation syndrome and a group of patients with malignant course with development of the hemispheric brain edema with the following transtentorial herniation were singled out. Risk factors for the development of malignant form of MII and its fatal outcomes were specified as lateral dislocation (>7 mm), more than 70% of ischemia size in frontal and parietal lobes and more than 80% - in temporal lobes, the disturbance of wakefulness up to moderate coma or more. Based on these results, it was selected patients for decompressive craniotomy in the affected hemisphere that allowed to reduce the fatality rate by more than twice compared to patients treated without surgery.

Induction of systemic oxidative stress leads to brain oedema in portacaval shunted rats

The pathogenesis of hepatic encephalopathy (HE) is multifactorial and often associated with the development of brain oedema. In addition to ammonia playing a central role, systemic oxidative stress is believed to aggravate the neuropsychological effects of ammonia in patients with chronic liver disease (CLD). The aim of this study was to (i) induce systemic oxidative stress in hyperammonaemic portacaval anastomosed (PCA) rats by inhibiting the antioxidant glutathione using Dimethyl maleate (DEM) and (ii) investigate whether a synergistic relationship between ammonia and oxidative stress contributes to the pathogenesis of brain oedema in CLD. Four-week PCA and sham-operated rats received DEM (0.4-4 mg/kg/day) for the last 10 days before sacrifice when oxidative stress markers [reactive oxygen species (ROS) and malondialdehyde (MDA)] were assessed in blood and frontal cortex. Brain water content was measured using a specific gravimetric technique. Dimethyl maleate induced an increase in ROS and MDA in the blood, but not in the brain, of the PCA rats, compared with non-treated PCA rats. This was accompanied with an increase in brain water content (PCA+DEM: 78.45 ± 0.13% vs. PCA: 77.38 ± 0.11%, P < 0.001). Higher doses of DEM induced systemic oxidative stress in sham-operated controls, but brain oedema did not develop. Dimethyl maleate provoked systemic, not central, oxidative stress in PCA rats, resulting in the development of brain oedema. Independently, hyperammonaemia and systemic oxidative stress do not precipitate brain oedema; therefore, our findings sustain that a synergistic effect between hyperammonaemia and systemic oxidative stress is responsible for the development of brain oedema in HE.

Aquaporin-4 deletion in mice reduces encephalopathy and brain edema in experimental acute liver failure

Brain edema and associated astrocyte swelling leading to increased intracranial pressure are hallmarks of acute liver failure (ALF). Elevated blood and brain levels of ammonia have been implicated in the development of brain edema in ALF. Cultured astrocytes treated with ammonia have been shown to undergo cell swelling and such swelling was associated with an increase in the plasma membrane expression of aquaporin-4 (AQP4) protein. Further, silencing the AQP4 gene in cultured astrocytes was shown to prevent the ammonia-induced cell swelling. Here, we examined the evolution of brain edema in AQP4-null mice and their wild type counterparts (WT-mice) in different models of ALF induced by thioacetamide (TAA) or acetaminophen (APAP). Induction of ALF with TAA or APAP significantly increased brain water content in WT mice (by 1.6%±0.3 and 2.3±0.4%, respectively). AQP4 protein was significantly increased in brain plasma membranes of WT mice with ALF induced by either TAA or APAP. In contrast to WT-mice, brain water content did not increase in AQP4-null mice. Additionally, AQP4-null mice treated with either TAA or APAP showed a remarkably lesser degree of neurological deficits as compared to WT mice; the latter displayed an inability to maintain proper gait, and demonstrated a markedly reduced exploratory behavior, with the mice remaining in one corner of the cage with its head tilted downwards. These results support a central role of AQP4 in the brain edema associated with ALF.

Increased brain lactate is central to the development of brain edema in rats with chronic liver disease

The pathogenesis of brain edema in patients with chronic liver disease (CLD) and minimal hepatic encephalopathy (HE) remains undefined. This study evaluated the role of brain lactate, glutamine and organic osmolytes, including myo-inositol and taurine, in the development of brain edema in a rat model of cirrhosis. Six-week bile-duct ligated (BDL) rats were injected with (13)C-glucose and de novo synthesis of lactate, and glutamine in the brain was quantified using (13)C nuclear magnetic resonance spectroscopy (NMR). Total brain lactate, glutamine, and osmolytes were measured using (1)H NMR or high performance liquid chromatography. To further define the interplay between lactate, glutamine and brain edema, BDL rats were treated with AST-120 (engineered activated carbon microspheres) and dichloroacetate (DCA: lactate synthesis inhibitor). Significant increases in de novo synthesis of lactate (1.6-fold, p<0.001) and glutamine (2.2-fold, p<0.01) were demonstrated in the brains of BDL rats vs. SHAM-operated controls. Moreover, a decrease in cerebral myo-inositol (p<0.001), with no change in taurine, was found in the presence of brain edema in BDL rats vs. controls. BDL rats treated with either AST-120 or DCA showed attenuation in brain edema and brain lactate. These two treatments did not lead to similar reductions in brain glutamine. Increased brain lactate, and not glutamine, is a primary player in the pathogenesis of brain edema in CLD. In addition, alterations in the osmoregulatory response may also be contributing factors. Our results suggest that inhibiting lactate synthesis is a new potential target for the treatment of HE.

Occludin and connexin 43 expression contribute to the pathogenesis of traumatic brain edema.

The experimental model of traumatic brain injury was established in Sprague-Dawley rats according to Feeney's free falling method. The brains were harvested at 2, 6 and 24 hours, and at 3 and 5 days after injury. Changes in brain water content were determined using the wet and dry weights. Our results showed that water content of tissue significantly increased after traumatic brain injury, and reached minimum at 24 hours. Hematoxylin-eosin staining revealed pathological impairment of brain tissue at each time point after injury, particularly at 3 days, with nerve cell edema, degenera-tion, and necrosis observed, and the apoptotic rate significantly increased. Immunohistochemistry and western blot analysis revealed that the expression of occludin at the injured site gradually de-creased as injury time advanced and reached a minimum at 3 days after injury; the expression of connexin 43 gradually increased as injury time advanced and reached a peak at 24 hours after in-jury. The experimental findings indicate that changes in occludin and connexin 43 expression were consistent with the development of brain edema, and may reflect the pathogenesis of brain injury.

Roles of Changes in Active Glutamine Transport in Brain Edema Development During Hepatic Encephalopathy: An Emerging Concept

Excessive glutamine (Gln) synthesis in ammonia-overloaded astrocytes contributes to astrocytic swelling and brain edema, the major complication of hepatic encephalopathy (HE). Much of the newly formed Gln is believed to enter mitochondria, where it is recycled to ammonia, which causes mitochondrial dysfunction (a “Trojan horse” mode of action). A portion of Gln may increase osmotic pressure in astrocytes and the interstitial space, directly and independently contributing to brain tissue swelling. Here we discuss the possibility that altered functioning of Gln transport proteins located in the cellular or mitochondrial membranes, modulates the effects of increased Gln synthesis. Accumulation of excess Gln in mitochondria involves a carrier-mediated transport which is activated by ammonia. Studies on the expression of the cell membrane N-system transporters SN1 (SNAT3) and SN2 (SNAT5), which mediate Gln efflux from astrocytes rendered HE model-dependent effects. HE lowered the expression of SN1 at the RNA and protein level in the cerebral cortex (cc) in the thioacetamide (TAA) model of HE and the effect paralleled induction of cerebral cortical edema. Neither SN1 nor SN2 expression was affected by simple hyperammonemia, which produces no cc edema. TAA-induced HE is also associated with decreased expression of mRNA coding for the system A carriers SAT1 and SAT2, which stimulate Gln influx to neurons. Taken together, changes in the expression of Gln transporters during HE appear to favor retention of Gln in astrocytes and/or the interstitial space of the brain. HE may also affect arginine (Arg)/Gln exchange across the astrocytic cell membrane due to changes in the expression of the hybrid Arg/Gln transporter y+LAT2. Gln export from brain across the blood–brain barrier may be stimulated by HE via its increased exchange with peripheral tryptophan.

Transient Blood Brain Barrier Disruption Induced by Oleic Acid is Mediated by Nitric Oxide

The blood brain barrier (BBB) maintains cerebral microenvironmental homeostasis. Transient disruption of the BBB after brain fat embolism in clinical cases and animal models has been reported but the precise mechanism underlying this occurrence is unclear. In the present study, we investigated BBB alterations in rats treated oleic acid (OA) delivered intra-arterially. Following OA treatment, transient brain edema, extravasation of Evans blue and Fluorescein isothiocyanate (FITC)-labeled dextran, and loss of laminin in the affected brain area were observed. Activation of matrix metalloproteinase (MMP)-2, -3, and -13 was found in the cerebral vessels 2 h after OA administration. Expression of intercellular adhesion molecule (ICAM)-1 in the vessels and neutrophil infiltration into the brain tissue was also observed. Inducible nitric oxide synthase (iNOS) was expressed in the neutrophils and nitrotyrosine was produced mainly in the vessels. Inhibitor of iNOS activity suppressed the loss of laminin, leakage of FITC-labeled dextran and Evans blue, and activation of MMP-2 and -13. Protein level of aquaporin (AQ)-4 was increased after OA administration but was not affected by treatment with iNOS inhibitor. In conclusion, we suggest that nitric oxide (NO) contributes to OA-induced MMP activation, BBB disruption and the development of transient brain edema.

Brain magnetic resonance in experimental acute‐on‐chronic liver failure

Acute-on-chronic liver failure is the term that refers to sustained liver injury with acute decompensation, usually induced by a precipitating factor. A common link between ensuing failures of various organs is impairment of the vascular supply, which may also induce vasogenic oedema in the brain. The aim of this study was to perform magnetic resonance (MR) study of the brain in a rat model combining bile duct ligation (BDL) and lipopolysaccharide (LPS) administration to investigate brain oedema in liver failure. Bile duct-ligated rats underwent in vivo brain MR imaging at 4, 5 and 6 weeks, and after superimposed administration of LPS. The MR techniques applied enabled assessment of brain metabolites, and intra- or extracellular water distribution. Brain water content was assessed by gravimetry. MR spectroscopy showed an increase in brain glutamine and a decrease in myo-inositol and choline in relation to progression of liver disease. BDL rats showed a slight, progressive increase in the amount of cortical brain water that was significant after LPS injection. These changes did not modify the apparent diffusion coefficient, supporting a mixed origin of brain oedema (vasogenic and cytotoxic). The mechanisms leading to the development of brain oedema in an experimental liver disease model were related to the time course of liver failure and to pro-inflammatory stimuli. MR findings support the presence of cytotoxic and vasogenic mechanisms in induced brain oedema in BDL rats exposed to LPS.

Pathophysiology of cerebral oedema in acute liver failure

Cerebral oedema is a devastating consequence of acute liver failure (ALF) and may be associated with the development of intracranial hypertension and death. In ALF, some patients may develop cerebral oedema and increased intracranial pressure but progression to life-threatening intracranial hypertension is less frequent than previously described, complicating less than one third of cases who have proceeded to coma since the advent of improved clinical care. The rapid onset of encephalopathy may be dramatic with the development of asterixis, delirium, seizures and coma. Cytotoxic and vasogenic oedema mechanisms have been implicated with a preponderance of experimental data favouring a cytotoxic mechanism. Astrocyte swelling is the most consistent neuropathological finding in humans with ALF and ammonia plays a definitive role in the development of cytotoxic brain oedema. The mechanism(s) by which ammonia induces astrocyte swelling remains unclear but glutamine accumulation within astrocytes has led to the osmolyte hypothesis. Current evidence also supports an alternate 'Trojan horse' hypothesis, with glutamine as a carrier of ammonia into mitochondria, where its accumulation results in oxidative stress, energy failure and ultimately astrocyte swelling. Although a complete breakdown of the blood-brain barrier is not evident in human ALF, increased permeation to water and other small molecules such as ammonia has been demonstrated resulting from subtle alterations in the protein composition of paracellular tight junctions. At present, there is no fully efficacious therapy for cerebral oedema other than liver transplantation and this reflects our incomplete knowledge of the precise mechanisms underlying this process which remain largely unknown.