Increased Brain Water Research Articles

Fluid-percussion brain injury induces changes in aquaporin channel expression

Edema, the accumulation of excess fluid, is a major pathological change in the brain that contributes significantly to pathology and mortality after moderate to severe brain injury. Edema is regulated by aquaporin (AQP) channels which transport water across cellular membranes. Six AQPs are found in the brain (1, 3, 4, 5, 8, and 9), and previous studies have found that AQP4 is regulated after traumatic brain injury (TBI). To further understand how AQPs contribute to brain edema, we investigated whether expression of AQP1, 3, and 9 are also regulated after TBI. Adult male Sprague Dawley rats received moderate parasagittal fluid-percussion brain injury (FPI) or sham surgery. After induction of FPI, the injured, ipsilateral parietal cortex and hippocampus were dissected and analyzed by Western blotting. We observed a small decrease in AQP3 and 4 levels at 7 days after FPI in the ipsilateral, parietal cortex. Both AQP1 and 9 significantly increased within 30 min post-injury and remained elevated for up to 6 h in the ipsilateral, parietal cortex. Aqp1 and 9 mRNA levels were also significantly increased at 30 min post-FPI. Administration of an AQP1 and 4 antagonist, AqB013, non-significantly increased brain water content in sham, non-injured animals, and did not prevent edema formation 24 h after trauma in either the parietal cortex or hippocampus. These results indicate that Aqp1 and 9 mRNA and protein levels increase after moderate parasagittal FPI and that an inhibitor of AQP1 and 4 does not decrease edema after moderate parasagittal FPI.

Effects of ketamine combined with moderate hypothermia on brain ischemia-reperfusion injury in a rat model of asphyxial cardiac arrest

Objective To investigate the effects of ketamine combined with moderate hypothermia on brain ischemia-reperfusion (I/R) injury in a rat model of asphyxial cardiac arrest. Methods Fifty healthy Wistar rats of both sexes aged 4.0-4.5 months, weighing 410-510 g were randomly allocated into 5 groups (n = 10each): group Ⅰ sham operation (group S), group Ⅱ asphyxial cardiac arrest (group ACA), group Ⅲ ketamine (group K), group Ⅳ moderate hypothermia (group MH) and group Ⅴ K + MH. The animals were anesthetized with intraperitoneal (IP) phenobarbital 20 mg/100 g, tracheostomized and mechanically ventilated (RR 60 bpm,FiO2 50%), PaCO2 was maintained at 35-45 mm Hg. Cardiac arrest was induced by clamping tracheal tube until ECG activity disappeared and MAP ＜ 15 mm Hg. Resuscitated was started 5 min later. MAP ＞ 60 mm Hg and HR ＞ 250 bpm were considered to be signs of successful resuscitation. Dead animals and animals in which resuscitation time was longer than 5 min were excluded from the study. In group K ketamine 100 mg/kg was administered IP at 5 min before asphyxia. In group MH hypothermia was started as soon as asphyxia was started and body temperature was maintained at 30-35 ℃. After successful resuscitation, the animals were sacrificed. Their brains were removed for determination of brain water content and p-caspase-3 expression in hippocampus. Results Brain I/Rsignificantly increased brain water content and p-caspase-3 expression in group ACA. MH alone significantly attenuated 1/R-induced brain edema and decreased p-caspase-3 expression, while ketamine alone only significantly decreased p-caspase-3 expression but did not decrease I/R-induced brain edema. MH + K decreased p-caspase-3expression further but did not reduce brain edema further as compared with MH alone. Conclusion Ketamine combined with moderate hypothermia provides better protection against brain I/R injury. Key words: Ketamine; Hypothermia, induced; Asphyxia; Heart arrest; Reperfusion injury; Brain

Role of aquaporin-4 in the development of brain oedema in liver failure

Liver failure is associated with progressive cytotoxic brain oedema (astrocyte swelling), which underlies hepatic encephalopathy (HE). Ammonia and superimposed inflammation are key synergistic factors in HE, but the mechanism(s) involved remain unknown. We aimed to determine whether aquaporin-4 (AQP4), an astrocyte endfeet bi-directional water channel, is associated with the brain oedema of HE. Rats (n=60) received sham-operation (sham), 5 days hyperammonaemia-inducing diet (HD), galactosamine (GALN) induced acute liver failure (ALF), 4 weeks bile duct-ligation (BDL) induced cirrhosis, or caecal ligation and puncture (CLP), a 24h model of bacterial peritonitis. Rats from every group (except CLP) were randomised to receive intraperitoneal injections of lipopolysaccharide (LPS; 1mg/kg) or saline, prior to termination 3h later. Brain water, AQP4 protein expression (western blot) and AQP4 localisation by immunogold electron microscopy were investigated. Significant hyperammonaemia was observed in saline-injected BDL (p<0.05), GALN (p<0.01), and HD (p<0.01), compared to sham rats. LPS injection did not affect arterial ammonia or plasma biochemistry in any of the treatment groups. Increased brain water was observed in saline-injected GALN (p<0.05), HD (p<0.01), and CLP (p<0.001) compared to sham rats. Brain water was numerically increased in BDL rats, but this failed to reach significance (p=0.09). LPS treatment further increased oedema significantly in all treatment groups (p<0.05, respectively). AQP4 expression was significantly increased in saline-injected BDL (p<0.05), but not other treatment groups, compared to sham rats. Membrane polarisation was maintained in BDL rats. The results suggest that AQP4 is not directly associated with the development of brain oedema in liver failure, hyperammonaemia, or sepsis. In cirrhosis, there is increased AQP4 protein expression, but membrane polarisation, is maintained, possibly in a compensatory attempt to limit severe brain oedema.

Modern progress in hepatic encephalopathy

Sir, We read with interest the article by Cash et al. 1 reviewing the pathophysiology and management of hepatic encephalopathy (HE). We agree that this condition is understudied and sub-optimally treated, but would suggest that the following points are considered. First, we would suggest that in contrast to the conclusions of the authors, recent research has provided invaluable insight into the cellular pathophysiology of HE. Modern magnetic resonance techniques have confirmed increased brain water content in patients with HE,2 highlighting the importance of the astrocyte-swelling hypothesis and other well-described pathophysiological mechanisms.3 While increased intra-astrocytic glutamine accumulation, driven by ambient …

Protective effect of fluid resuscitation with 6% hydroxyethyl starch 130/0.4 on the brain in a rat model of traumatic head injury complicated with hemorrhagic shock

Objective To investigate the protective effect of 6% hydroxyethyl starch (HES) 130/0.4 on the brain in a rat model of traumatic head injury (THI) complicated with hemorrhagic shock (HS) .Methods Sixty male SD rats weighing 300-350 g were randomized into 5 groups ( n - 12 each): group Ⅰ sham operation (group S);group Ⅱ THI-HS;group Ⅲ normal saline (group NS) ;group Ⅳ 6% HES 130/0.4 and group V HHS (1M mixture of 10% HES 130/0.4 + 7.5% NaCl) . The animals were anesthetized with intraperitoneal 10% chloral hydrate 4 ml/kg. Bilateral femoral arteries and right femoral vein were cannulated for MAP monitoring, blood letting and fluid resuscitation. In group Ⅱ-Ⅴ THI was produced according to the method described by Feeney. HS was induced by blood-letting (modified Wiggers Method) . MAP was reduced to 40 nun Hg which was maintained for 1 h. In group Ⅲ NS 3 times the volume of blood withdrawn was infused. In group Ⅳ 6% HES 130/0.4 equal to the volume of blood withdrawn was infused. Blood samples were taken before THI (T_0,baseline) , 60 min after THI-HS (T_1 ) and at 30, 60 and 180 min after fluid resuscitation (T_(2-4) ) for determination of serum S-100β protein concentration. Six animals in each group were killed at 3 h after resuscitation. Cerebral water and TNF-α and IL-6 contents were measured. Results MAP was restored to the baseline level immediately after resuscitation in group Ⅲ , Ⅳ and Ⅴ and was significantly higher in group Ⅳ(group HES) and Ⅴ (group HHS) than in group Ⅲ(group NS) . THI-HS significantly increased brain water content in group Ⅱ-Ⅴas compared with group I (group S) . Brain water content was significantly higher in the 3 resuscitation groups (group Ⅲ, Ⅳ, Ⅴ) than in group Ⅱ(THI-HS without resuscitation) . Resuscitation with NS induced higher brain water content than resuscitation with HES and HHS (group Ⅳ, Ⅴ). Serum S-100β concentration was increasing after THI-HS. The increase in serum S-100β concentration was attenuated by resuscitation with HES or HHS especially HES in group Ⅳ. The TNF-a and IL-6 contents in the brain tissue were significantly increased by THI-HS. Resuscitation with HES significantly attenuated the increase in TNF-α and IL-6 induced by THI-HS.Conclusion Resuscitation with 6% HES 130/0.4 can restore MAP and decrease brain edema induced by THI-HS by inhibition of inflammatory response. Key words: Brain injuries; Shock; hemorrhagic; Hetastarch; Fluid therapy

Abstract 5130: Leptin Increases Perihematomal Inflammation in Experimental Hemorrhagic Stroke

Background : Leptin, one of the most alleged adipokines, exerts its tissue-protective effect in ischemic injuries by reducing apoptosis through extracellular signal-regulated kinase pathway. In this context, it may be speculated that leptin also confer beneficial effect on hemorrhagic events. However, few studies have elaborated on the association between exogenous leptin and tissue damage in experimental hemorrhagic stroke model. Methods : After inducing intracerebral hemorrhage in mouse brain via the sterotaxic infusion of collagenase, 4mg/kg or 8mg/kg of recombinant leptin or vehicle (phosphate buffered saline) was administered intraperitoneally. Brain water content, reflecting peri-hematomal edema, and hemorrhage volume were measured at 72 hours after inducing hemorrhage. Inflammatory cells expressing myeloperoxidase (MPO) or OX6 were counted at 48 hours, and western blotting for Akt, pAkt, STAT3, pSTAT3, ERK and pERK was performed at 24 hours. Results : Compared to the vehicle injected mice, exogenous leptin increased brain water contents (80.07±0.29% in vehicle group, 80.74±0.32% in 4mg/kg leptin, and 81.48±0.18% in 8mg/kg leptin; rho=0.525 and p&lt;0.01). Based on this result, all the following experiments were performed with 8mg/kg of leptin. Leptin injection also augmented infiltration of MPO-stained cells (210±8 cells/mm 3 in leptin group and 133±8 cells/mm 3 in vehicle group; p&lt;0.05) and OX6-stained cells (129±13 cells/mm 3 in leptin group and 88±10 cell/mm 3 in vehicle group; p&lt;0.05). Mean hemorrhage volume was also increased in 8mg/kg leptin group (26.83±3.22 mm 3 in leptin group and 17.98±2.73 mm 3 in vehicle group; p&lt;0.05). The expression level of phosphorylated STAT3 was significantly elevated in mice with 8mg/kg leptin injection (p&lt;0.05), however, pAkt and pERK did not augmented by induced hyperleptinemia. Conclusion : Our study documented that peri-hematomal inflammation and hemorrhage volume were increased by exogenous leptin via STAT3 pathway. These results may indicate the potentially detrimental role of leptin on hemorrhagic stroke via augmentation of inflammatory response after tissue damage.

Aquaporin-4 maintains ependymal integrity in adult mice

Ependymal cells form the walls of the ventricles, and take part in the production of cerebrospinal fluid (CSF). Aquaporin-4 (AQP4), a predominant water channel of the brain, is restricted to basolateral plasma membranes of ependymal cells. The highly polarized expression of AQP4 suggests it may be involved in maintaining the structural and functional integrity of the ependyma. This hypothesis was validated by using adult AQP4 knockout mice generated by our laboratory [Fan Y, Zhang J, Sun XL, Gao L, Zeng XN, Ding JH, Cao C, Niu L, Hu G (2005) Sex- and region-specific alterations of basal amino acid and monoamine metabolism in the brain of aquaporin-4 knockout mice. J Neurosci Res 82:458–464]. Histological analysis showed disorganized ependymal layer of the lateral ventricle and aqueduct in AQP4-deficiency mice. A majority (92.7%) of null mice displayed reduced lateral ventricular volume, while a small fraction (7.3%) had enlarged or normal ventricular size with a narrow aqueduct. Immunohistochemistry demonstrated that AQP4 deletion resulted in decreased expression of gap junction protein connexin43 in the ependymal cells. Electron microscopy confirmed junctional complex absence at basolateral membranes of ependymocytes. Moreover, AQP4 knockout mice showed decreased CSF production and increased brain water content compared with wild-type mice. These results highlight a key role of AQP4 in maintaining the structure and function of the ependyma. In addition, variable profiles of ventricle system in adult AQP4 null mice indicate functional AQP4 polymorphisms.

Melatonin reduces experimental subarachnoid hemorrhage‐induced oxidative brain damage and neurological symptoms

Oxidative stress has detrimental effects in several models of neurodegenerative diseases, including subarachnoid hemorrhage (SAH). This study investigated the putative neuroprotective effect of melatonin, a powerful antioxidant, in a rat model of SAH. Male Wistar albino rats were divided as control, vehicle-treated SAH, and melatonin-treated (10 mg/kg, i.p.) SAH groups. To induce SAH, 0.3 mL blood was injected into cisterna magna of rats. Forty-eight hours after SAH induction, neurological examination scores were measured and the rats were decapitated. Brain tissue samples were taken for blood-brain barrier (BBB) permeability, brain water content, histological examination, or determination of malondialdehyde (MDA) and glutathione (GSH) levels, myeloperoxidase (MPO), and Na+-K+-ATPase activities. Formation of reactive oxygen species in brain tissue samples was monitored by using a chemiluminescence (CL) technique. The neurological examination scores were increased in SAH groups on the second day of SAH induction and SAH caused a significant decrease in brain GSH content and Na+-K+-ATPase activity, which was accompanied with significant increases in CL, MDA levels, and MPO activity. On the other hand, melatonin treatment reversed all these biochemical indices as well as SAH-induced histopathological alterations, while increased brain water content and impaired BBB were also reversed by melatonin treatment. This study suggests that melatonin, which can easily cross BBB, alleviates SAH-induced oxidative stress and exerts neuroprotection by preserving BBB permeability and by reducing brain edema.

Conivaptan Bolus Dosing for the Correction of Hyponatremia in the Neurointensive Care Unit

Hyponatremia frequently complicates acute brain injury and may precipitate neurological worsening by promoting cerebral edema. An increase in brain water may be better managed through water excretion than with fluid restriction or hypertonic fluids. Vasopressin-receptor antagonists such as conivaptan, which promote free water excretion, may be ideal agents to treat this common and potentially serious disorder. The efficacy of intermittent bolus doses of conivaptan to correct hyponatremia was examined in a consecutive series of patients treated in our neurointensive care unit. Patients were excluded if baseline sodium was over 135 mEq/l or if another conivaptan dose was given within 12 h. We assessed the proportion responding with a 4 or 6 mEq/l rise in sodium by 12 h, the change in sodium from baseline, and, in those not receiving another dose for at least 72 h, the long-term ability of a single dose to maintain sodium at least 4 mEq/l above baseline. We also recorded the effects of conivaptan on urine output and specific gravity, and noted any adverse events. A total of 25 doses given to 19 patients were included (out of 44 total doses administered in the study period). Sodium rose by 5.8 +/- 3.2 mEq/l within 12 h, with 71% rising by at least 4 mEq/l and 52% manifesting at least a 6 mEq/l increase. In those receiving only a single dose, 69% maintained at least a 4 mEq/l rise up to 72 h. Conivaptan also consistently led to increased urine output and a significant drop in urine specific gravity (i.e., aquaresis). No cases of phlebitis were observed despite administration of conivaptan through peripheral IVs. Intermittent dosing of conivaptan was effective in increasing free water excretion and correcting hyponatremia in neurologically ill patients. This supports its further evaluation for managing hyponatremia in this population.

Acute Administration of 3,4‐Methylenedioxymethamphetamine Induces Profound Hyperthermia, Blood–Brain Barrier Disruption, Brain Edema Formation, and Cell Injury

The psychostimulant 3,4-,ethylenedioxymethamphetamine (MDMA, "ecstasy") is known to induce hyperthermia and alterations in neurochemical metabolism in the CNS. However, the detailed cellular or molecular mechanisms behind MDMA-induced neurotoxicity are still not well known. Since MDMA induces profound hyperthermia that could lead to intense cellular stress and cause disruption of the blood-brain barrier (BBB), this investigation examined the effects of acute MDMA on BBB dysfunction, brain edema, and cell injury in rats and mice. When MDMA (40 mg/kg, i.p.) was administered to rats or mice, these animals exhibited profound behavioral disturbances (hyperactivity and hyperlocomotion) and hyperthermia (>40 to 41 degrees C) at 4 h. At this time, the leakage of Evans blue dye was evident, particularly in the cerebellum, hippocampus, cortex, thalamus, and hypothalamus. This effect was most pronounced in mice compared to rats. Marked increase in brain water along with Na(+), K(+), and Cl(-) content was also seen in the aforementioned brain regions. Presence of distorted neuronal and glial cells in brain regions associated with leakage of Evans blue is quite common in MDMA-treated animals. Increased albumin immunoreactivity, indicating breakdown of the BBB, and upregulation of glial fibrillary acidic protein (GFAP), suggesting activation of astrocytes, were seen in most brain regions showing edematous changes. Upregulation of heat-shock protein (HSP72) immunoreactivity in the nuclei and cell cytoplasm of the neurons located in the edematous brain regions are quite common. Taken together, these observations are the first to show that MDMA has the capacity to disrupt BBB permeability to proteins and to induce the formation of edema, probably by inducing hyperthermia and cellular stress, as evident with HSP overexpression leading to cell injury.

The perivascular pool of aquaporin-4 mediates the effect of osmotherapy in postischemic cerebral edema*

Osmotherapy with hypertonic saline ameliorates cerebral edema associated with experimental ischemic stroke. We tested the hypothesis that hypertonic saline exerts its antiedema effect by promoting an efflux of water from brain via the perivascular aquaporin-4 pool. We used mice with targeted disruption of the gene encoding alpha-syntrophin (alpha-Syn(-/-)) that lack the perivascular aquaporin-4 pool but retain the endothelial pool of this protein. Prospective laboratory animal study. Research laboratory in a university teaching hospital. Halothane-anesthetized adult male wildtype C57B/6 and alpha-Syn(-/-) mice were subjected to 90 min of transient middle cerebral artery occlusion and treated with either a continuous intravenous infusion of 0.9% saline or 3% hypertonic saline (1.5 mL/kg/hr) for 48 hr. In the first series of experiments (n = 59), increased brain water content analyzed by wet-to-dry ratios in the ischemic hemisphere of wildtype mice was attenuated after hypertonic saline (79.9% +/- 0.5%; mean +/- SEM) but not after 0.9% saline (82.3% +/- 1.0%) treatment. In contrast in alpha-Syn(-/-) mice, hypertonic saline had no effect on the postischemic edema (hypertonic saline: 80.3% +/- 0.7%; 0.9% saline: 80.3% +/- 0.4%). In the second series of experiments (n = 32), treatment with hypertonic saline attenuated postischemic blood-brain barrier disruption at 48 hr in wildtype mice but not in alpha-Syn(-/-) mice; alpha-Syn(-/-) deletion alone had no effect on blood-brain barrier integrity. In the third series of experiments (n = 34), alpha-Syn(-/-) mice treated with either hypertonic saline or 0.9% saline had smaller infarct volume as compared with their wildtype counterparts. These data demonstrate that 1) osmotherapy with hypertonic saline exerts antiedema effects via the perivascular pool of aquaporin-4, 2) hypertonic saline attenuates blood-brain barrier disruption depending on the presence of perivascular aquaporin-4, and 3) deletion of the perivascular pool of aquaporin-4 alleviates tissue damage after stroke, in mice subjected to osmotherapy and in nontreated mice.

Inhibitory effect of vasopressin receptor antagonist OPC-31260 on experimental brain oedema induced by global cerebral ischaemia

The effects of the non-peptide vasopressin V(2) receptor antagonist 5-dimethylamino-1-[4-(2-methylbenzoylamino)benzoyl]-2,3,4,5-tetrahydro-1H-benzazepine hydrochloride (OPC-31260) on the cerebral oedema induced by general cerebral hypoxia were studied in rats. The general cerebral hypoxia was produced by bilateral common carotid ligation in Sprague-Dawley rats of the CFY strain. By 6 h after the ligation, half of the rats had died, but the survival rate was significantly higher following OPC-31260 administration. Electron microscopic examinations revealed typical ischaemic changes after the carotid ligation. The carotid ligation increased the brain contents of water and Na(+) and enhanced the plasma vasopressin level. The increased brain water and Na(+) accumulation was prevented by OPC-31260 administration, but the plasma vasopressin level was further enhanced by OPC-31260. These results demonstrate the important role of vasopressin in the development of the disturbances in brain water and electrolyte balance in response to general cerebral hypoxia. The carotid ligation-induced cerebral oedema was significantly reduced following oral OPC-31260 administration. The protective mechanism exerted by OPC-31260 stems from its influence on the renal vasopressin V(2) receptors. These observations might suggest an effective approach to the treatment of global hypoxia-induced cerebral oedema in humans.

MATRIX METALLOPROTEINASE INHIBITION ATTENUATES BRAIN EDEMA IN AN IN VIVO MODEL OF SURGICALLY-INDUCED BRAIN INJURY

Neurosurgical procedures can result in brain injury by various means, including direct trauma, hemorrhage, retractor stretch, and electrocautery. This surgically-induced brain injury (SBI) can cause postoperative complications such as brain edema after blood-brain barrier (BBB) disruption. The present study seeks to test a matrix metalloproteinase (MMP) inhibitor for preventing postoperative brain edema and BBB disruption in an in vivo model of surgically-induced brain injury. A rodent model of SBI was used which involves resection of a part of the right frontal lobe. A total of 89 Sprague-Dawley male rats (weight, 300-350 g) were randomly divided into four groups: 1) SBI with vehicle treatment (0.1% dimethyl sulfoxide), 2) SBI with single treatment of MMP inhibitor-1 (an inhibitor of MMP-9 and MMP-2), 3) SBI treated daily (total 3 times) with MMP inhibitor-1, and 4) sham surgical group. Postoperative assessment at different time periods included evaluation of BBB permeability, brain water content (brain edema), neurological scoring, histology, immunohistochemistry, and zymography for MMP enzymatic activity. Temporal magnetic resonance imaging studies were also performed to assess postoperative edema. The results indicate that SBI caused increased brain water content (ipsilateral frontal lobe) and BBB permeability compared with sham animals. Treatment with MMP inhibitor-1 attenuated MMP-9 and MMP-2 activity and decreased brain water content with preservation of the BBB. Inhibition of MMP-9 and MMP-2 attenuates brain edema and BBB disruption after SBI. The study suggests a potential role for MMP inhibition as preoperative therapy before neurosurgical procedures.

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.

Endotoxemia produces coma and brain swelling in bile duct ligated rats

This study explores the hypothesis that the inflammatory response induced by administration of lipopolysaccharide (LPS) exacerbates brain edema in cirrhotic rats; and if so whether this is associated with altered brain metabolism of ammonia or anatomical disturbance of the blood-brain barrier. Adult Sprague-Dawley rats 4 weeks after bile duct ligation (BDL)/Sham-operation, or naïve rats fed a hyperammonemic diet (HD), were injected with LPS (0.5 mg/kg, intraperitoneally) or saline, and killed 3 hours later. LPS administration increased brain water in HD, BDL, and sham-operated groups significantly (P < 0.05), but this was associated with progression to pre-coma stages only in BDL rats. LPS induced cytotoxic brain swelling and maintained anatomical integrity of the blood-brain barrier. Plasma/brain ammonia levels were higher in HD and BDL rats than in sham-operated controls and did not change with LPS administration. Brain glutamine/myoinositol ratio was increased in the HD group but reduced in the BDL animals. There was a background pro-inflammatory cytokine response in the brains of cirrhotic rats, and plasma/brain tumor necrosis factor alpha (TNF-alpha) and IL-6 significantly increased in LPS-treated animals. Plasma nitrite/nitrate levels increased significantly in LPS groups compared with non-LPS controls; however, frontal cortex nitrotyrosine levels only increased in the BDL + LPS rats (P < 0.005 versus BDL controls). Injection of LPS into cirrhotic rats induces pre-coma and exacerbates cytotoxic edema because of the synergistic effect of hyperammonemia and the induced inflammatory response. Although the exact mechanism of how hyperammonemia and LPS facilitate cytotoxic edema and pre-coma in cirrhosis is not clear, our data support an important role for the nitrosation of brain proteins.

Bilobalide prevents ischemia-induced edema formation in vitro and in vivo

EGb761, a standardized extract of Ginkgo biloba, has neuroprotective properties in animal models of ischemia, an activity that is partially attributed to its constituent, bilobalide. EGb761 has also been reported to inhibit edema formation induced by toxins such as triethyltin. The goal of this study was to test the activity of pure bilobalide to prevent edema formation in models of ischemia. Oxygen-glucose deprivation (OGD) in rat hippocampal slices served as a model of in vitro-ischemia. OGD caused cellular edema formation as indicated by an increase of slice water contents in 30 min. Bilobalide (1–10 μM) reduced slice water contents in ischemic slices in a concentration-dependent manner. As a model of in vivo-ischemia, we performed middle cerebral artery occlusion (MCAO) in mice. Permanent MCAO caused cell death and swelling of the ischemic hemisphere within 24 h. Pretreatment of the mice with bilobalide (10 mg/kg i.p.) reduced infarct area by 43% (as judged by 2,3,5-triphenyl-tetrazolium chloride (TTC) staining) and edema formation by 70% (as judged by hemispheric enlargement). In parallel experiments, pretreatment with bilobalide also reduced forebrain water contents in the ischemic hemisphere by 57%. As an alternative model of brain edema formation, we used water intoxication to increase brain water content; bilobalide, was, however, inactive in this model. We conclude that bilobalide strongly and specifically attenuates edema formation in models of brain ischemia in vitro and in vivo. Bilobalide may be therapeutically effective in brain edema which occurs secondarily to large hemispheric stroke and traumatic brain injury in humans.

Predominance of cellular edema in traumatic brain swelling in patients with severe head injuries

The edema associated with brain swelling after traumatic brain injury (TBI) has been thought to be vasogenic in origin, but the results of previous laboratory studies by the authors have shown that a cellular form of edema is mainly responsible for brain swelling after TBI. In this study the authors used magnetic resonance (MR) imaging techniques to identify the type of edema that occurs in patients with TBI. Diffusion-weighted MR imaging was used to evaluate the apparent diffusion coefficient (ADC) in 44 patients with TBI (Glasgow Coma Scale Score < 8) and in eight healthy volunteers. Higher ADC values have been associated with vasogenic edema, and lower ADC values with a predominantly cellular form of edema. Regional measurements of ADC in patients with focal and diffuse injury were computed. The water content of brain tissue was also assessed in absolute terms by using MR imaging to measure the percentage of water per gram of tissue. Cerebral blood flow (CBF) was measured using stable Xe-computerized tomography (CT) studies to rule out ischemia as a cause of cellular edema. The mean ADC value in the healthy volunteers was 0.82 +/- 0.05 x 10(-3) mm2/second. The ADC values in the patients with diffuse brain injury without swelling were close to the mean for the healthy volunteers. In contrast, the patients with brain swelling had increased brain water content and low ADC values (mean 0.74 +/- 0.05 x 10(-3) mm2/second). The ADC values correlated with CT classifications. In all patients with low ADC values, the CBF values were outside the range for ischemia. The brain swelling observed in patients with TBI appears to be predominantly cellular, as signaled by low ADC values in brain tissue with high levels of water content.

Noncirrhotic portal vein thrombosis exhibits neuropsychological and MR changes consistent with minimal hepatic encephalopathy†

Hepatic encephalopathy can arise from portal-systemic shunting in the absence of intrinsic liver disease. However, there are few descriptions of this form of encephalopathy. Portal vein thrombosis is an infrequent disease that causes portal-systemic shunting. Episodic hepatic encephalopathy has been described in patients with portal vein thrombosis, but it is not known if these patients develop minimal hepatic encephalopathy. We designed a study to investigate the neurological consequences of portal vein thrombosis in patients without cirrhosis and no clinical signs of encephalopathy. For this purpose, 10 patients underwent neuropsychological tests, an oral glutamine challenge test, and brain magnetic resonance (MR) imaging. The results were compared with those obtained in 10 healthy controls. Patients with portal vein thrombosis exhibited abnormalities in the results of neuropsychological tests, oral glutamine challenge test, and MR similar to those described in hepatic encephalopathy associated with cirrhosis. MR spectroscopy revealed a decrease in myo-inositol and an increase in glutamine. The increase in glutamine correlated with an increase in ammonia following the oral glutamine challenge test, signs of increased brain water (decrease in magnetization transfer ratio), and impairment of attention tests. In conclusion, patients with noncirrhotic portal vein thrombosis develop subclinical neurological abnormalities compatible with minimal hepatic encephalopathy. These disturbances, which include signs of increase in brain water and a compensatory osmotic response (decrease in brain myo-inositol), appear to be secondary to brain exposure to ammonia induced by portal-systemic shunting.

Aquaporin-4 Gene Disruption in Mice Reduces Brain Swelling and Mortality in Pneumococcal Meningitis

The astroglial water channel aquaporin-4 (AQP4) facilitates water movement into and out of brain parenchyma. To investigate the role of AQP4 in meningitis-induced brain edema, Streptococcus pneumoniae was injected into cerebrospinal fluid (CSF) in wild type and AQP4 null mice. AQP4-deficient mice had remarkably lower intracranial pressure (9 +/- 1 versus 25 +/- 5 cm H2O) and brain water accumulation (2 +/- 1 versus 9 +/- 1 microl) at 30 h, and improved survival (80 versus 0% survival) at 60 h, through comparable CSF bacterial and white cell counts. Meningitis produced marked astrocyte foot process swelling in wild type but not AQP4 null mice, and slowed diffusion of an inert macromolecule in brain extracellular space. AQP4 protein was strongly up-regulated in meningitis, resulting in a approximately 5-fold higher water permeability (P(f)) across the blood-brain barrier compared with non-infected wild type mice. Mathematical modeling using measured P(f) and CSF dynamics accurately simulated the elevated lower intracranial pressure and brain water produced by meningitis and predicted a beneficial effect of prevention of AQP4 upregulation. Our findings provide a novel molecular mechanism for the pathogenesis of brain edema in acute bacterial meningitis, and suggest that inhibition of AQP4 function or up-regulation may dramatically improve clinical outcome.

Changes in neuropsychological function following hyperammonemia induced by a simulated bleed is mediated by increase in brain water: Rajiv Jalan, University College London Medical School, London United Kingdom; Sherzad Balata, Royal Infirmary, Edinburgh United Kingdom; Steven W Olde Damink, Maastricht University, Maastricht Netherlands; Karen Ferguson, Ian Marshall, Neuroradiology, Western General Hospital, Edinburgh United Kingdom; Dharmesh Kapoor, University College London, London

Changes in neuropsychological function following hyperammonemia induced by a simulated bleed is mediated by increase in brain water: Rajiv Jalan, University College London Medical School, London United Kingdom; Sherzad Balata, Royal Infirmary, Edinburgh United Kingdom; Steven W Olde Damink, Maastricht University, Maastricht Netherlands; Karen Ferguson, Ian Marshall, Neuroradiology, Western General Hospital, Edinburgh United Kingdom; Dharmesh Kapoor, University College London, London