Modulation of AQP4 expression by the protein kinase C activator, phorbol myristate acetate, decreases ischemia-induced brain edema

A hydrogen sulfide donor suppresses pentylenetetrazol-induced seizures in rats via PKC signaling

Epilepsy is a serious neurological disorder. Available antiepileptic drugs are still lacking. Hydrogen sulfide (H2S), a neuron-protective endogenous gasotransmitter, is reported to have effect on epilepsy. But it remains to be determined for its mechanism. In the present study, we found that a novel carbazole-based H2S donor could effectively suppress pentylenetetrazol-induced seizures in rats. The H2S donor could alleviate not only the epileptic behavior of animals but also the hippocampal EEG activity of seizures. The H2S donor down-regulated the expression of aquaporin 4 in the hippocampus of epilepsy rats. The H2S donor also decreased the seizure-induced release of inflammatory cytokines including IL-1β, IL-6 and TNF-α. In addition, the H2S donor increased protein kinase C (PKC) expression in the hippocampus of epilepsy rats. These effects of the H2S donor on epilepsy rats were attenuated after blockade of PKC signaling by Go6983, suggesting that PKC signaling participated in the antiepileptic process of H2S donor. Taken together, the H2S donor has a beneficial effect on epilepsy control in a PKC-dependent manner.

The potential roles of aquaporin 4 in malignant gliomas

Aquaporin 4 (AQP4) is the major water channel expressed in the central nervous system and is primarily expressed in astrocytes. Recently, accumulated evidence has pointed to AQP4 as a key molecule that could play a critical role in glioma development. Discoveries of the role of AQP4 in cell migration suggest that AQP4 could be a significant factor regarding glioma malignancies. However, the AQP4 expression levels in glioma have not been fully elucidated; furthermore, the correlation of AQP4 expression with glioma malignancy remains controversial. Here, we review the expression pattern and predictive significance of AQP4 in malignant glioma. The molecular mechanism of AQP4 as it pertains to the migration and invasion of human glioma cells has been summarized. In addition, the important roles of AQP4 in combating drug resistance as well as potential pharmacological blockers of AQP4 have been systematically discussed. More research should be conducted to elucidate the potential roles of AQP4 in malignant glioma for identifying the tumor type, progression stages and optimal treatment strategies. The observed experimental results strongly emphasize the importance of this topic for future investigations.

Hydrocephalus: the role of cerebral aquaporin-4 channels and computational modeling considerations of cerebrospinal fluid

Aquaporin-4 (AQP4) channels play an important role in brain water homeostasis. Water transport across plasma membranes has a critical role in brain water exchange of the normal and the diseased brain. AQP4 channels are implicated in the pathophysiology of hydrocephalus, a disease of water imbalance that leads to CSF accumulation in the ventricular system. Many molecular aspects of fluid exchange during hydrocephalus have yet to be firmly elucidated, but review of the literature suggests that modulation of AQP4 channel activity is a potentially attractive future pharmaceutical therapy. Drug therapy targeting AQP channels may enable control over water exchange to remove excess CSF through a molecular intervention instead of by mechanical shunting. This article is a review of a vast body of literature on the current understanding of AQP4 channels in relation to hydrocephalus, details regarding molecular aspects of AQP4 channels, possible drug development strategies, and limitations. Advances in medical imaging and computational modeling of CSF dynamics in the setting of hydrocephalus are summarized. Algorithmic developments in computational modeling continue to deepen the understanding of the hydrocephalus disease process and display promising potential benefit as a tool for physicians to evaluate patients with hydrocephalus.

Aquaporin-4 gene silencing protects injured neurons after early cerebral infarction

Aquaporin-4 regulates water molecule channels and is important in tissue regulation and water transportation in the brain. Upregulation of aquaporin-4 expression is closely related to cellular edema after early cerebral infarction. Cellular edema and aquaporin-4 expression can be determined by measuring cerebral infarct area and apparent diffusion coefficient using diffusion-weighted imaging (DWI). We examined the effects of silencing aquaporin-4 on cerebral infarction. Rat models of cerebral infarction were established by occlusion of the right middle cerebral artery and siRNA-aquaporin-4 was immediately injected via the right basal ganglia. In control animals, the area of high signal intensity and relative apparent diffusion coefficient value on T2-weighted imaging (T2WI) and DWI gradually increased within 0.5-6 hours after cerebral infarction. After aquaporin-4 gene silencing, the area of high signal intensity on T2WI and DWI reduced, relative apparent diffusion coefficient value was increased, and cellular edema was obviously alleviated. At 6 hours after cerebral infarction, the apparent diffusion coefficient value was similar between treatment and model groups, but angioedema was still obvious in the treatment group. These results indicate that aquaporin-4 gene silencing can effectively relieve cellular edema after early cerebral infarction; and when conducted accurately and on time, the diffusion coefficient value and the area of high signal intensity on T2WI and DWI can reflect therapeutic effects of aquaporin-4 gene silencing on cellular edema.

The central role of aquaporins in the pathophysiology of ischemic stroke

Stroke is a complex and devastating neurological condition with limited treatment options. Brain edema is a serious complication of stroke. Early edema formation can significantly contribute to infarct formation and thus represents a promising target. Aquaporin (AQP) water channels contribute to water homeostasis by regulating water transport and are implicated in several disease pathways. At least 7 AQP subtypes have been identified in the rodent brain and the use of transgenic mice has greatly aided our understanding of their functions. AQP4, the most abundant channel in the brain, is up-regulated around the peri-infarct border in transient cerebral ischemia and AQP4 knockout mice demonstrate significantly reduced cerebral edema and improved neurological outcome. In models of vasogenic edema, brain swelling is more pronounced in AQP4-null mice than wild-type providing strong evidence of the dual role of AQP4 in the formation and resolution of both vasogenic and cytotoxic edema. AQP4 is co-localized with inwardly rectifying K(+)-channels (Kir4.1) and glial K(+) uptake is attenuated in AQP4 knockout mice compared to wild-type, indicating some form of functional interaction. AQP4-null mice also exhibit a reduction in calcium signaling, suggesting that this channel may also be involved in triggering pathological downstream signaling events. Associations with the gap junction protein Cx43 possibly recapitulate its role in edema dissipation within the astroglial syncytium. Other roles ascribed to AQP4 include facilitation of astrocyte migration, glial scar formation, modulation of inflammation and signaling functions. Treatment of ischemic cerebral edema is based on the various mechanisms in which fluid content in different brain compartments can be modified. The identification of modulators and inhibitors of AQP4 offer new therapeutic avenues in the hope of reducing the extent of morbidity and mortality in stroke.

Ischemic Postconditioning Alleviates Brain Edema After Focal Cerebral Ischemia Reperfusion in Rats Through Down-Regulation of Aquaporin-4

Cerebral edema is a serious complication associated with cerebral ischemia/reperfusion (I/R). Aquaporin-4 (AQP4) plays a role in generating postischemic edema after reperfusion. Recently, ischemic postconditioning (Postcond) has been shown to produce neuroprotective effects and reduce brain edema in rats after cerebral I/R. It is unclear if ischemic Postcond alleviates brain edema injury through regulation of AQP4. In this study, middle cerebral artery occlusion (MCAO) was induced in rats by filament insertion for 2 h following 24-h reperfusion: ischemic Postcond treatment was performed before reperfusion in the experimental group. We used the wet-dry weight ratio and transmission electron microscopy to evaluate brain edema after 24 h of reperfusion. We used immunohistochemistry and Western blot analyses to evaluate the distribution and expression of AQP4. Ischemic Postcond significantly reduced the water content of the brain tissue and swelling of the astrocytic foot processes. AQP4 expression increased in the I/R and Postcond groups compared to the sham group, but it decreased in the Postcond group compared to the I/R group. The results of our study suggest that ischemic Postcond effectively reduces brain edema after reperfusion by inhibiting AQP4 expression. The data in this study support the use of ischemic Postcond for alleviating brain edema after cerebral I/R.

Regulation and Function of AQP4 in the Central Nervous System

Aquaporin 4 (AQP4) is the predominant water channel in the mammalian brain and is mainly expressed in the perivascular glial endfeet at the brain-blood interface. Based on studies on AQP4(-/-) mice, AQP4 has been assigned physiological roles in stimulus-induced K(+) clearance, paravascular fluid flow, and brain edema formation. Conflicting data have been presented on the role of AQP4 in K(+) clearance and associated extracellular space shrinkage and on the stroke-induced alterations of AQP4 expression levels during edema formation, raising questions about the functional importance of AQP4 in these (patho)physiological aspects. Phosphorylation-dependent gating of AQP4 has been proposed as a regulatory mechanism for AQP4-mediated osmotic water transport. This paradigm was, however, recently challenged by experimental evidence and molecular dynamics simulations. Regulatory patterns and physiological roles for AQP4 thus remain to be fully explored.

Selective vasopressin-1a receptor antagonist prevents brain edema, reduces astrocytic cell swelling and GFAP, V1aR and AQP4 expression after focal traumatic brain injury

A secondary and often lethal consequence of traumatic brain injury is cellular edema that we posit is due to astrocytic swelling caused by transmembrane water fluxes augmented by vasopressin-regulated aquaporin-4 (AQP4). We therefore tested whether vasopressin 1a receptor (V1aR) inhibition would suppress astrocyte AQP4, reduce astrocytic edema, and thereby diminish TBI-induced edematous changes. V1aR inhibition by SR49059 significantly reduced brain edema after cortical contusion injury (CCI) in rat 5h post-injury. Injured-hemisphere brain water content (n=6 animals/group) and astrocytic area (n=3/group) were significantly higher in CCI-vehicle (80.5±0.3%; 18.0±1.4 µm(2)) versus sham groups (78.3±0.1%; 9.5±0.9 µm(2)), and SR49059 blunted CCI-induced increases in brain edema (79.0±0.2%; 9.4±0.8µm(2)). CCI significantly up-regulated GFAP, V1aR and AQP4 protein levels and SR49059 suppressed injury induced up regulation (n=6/group). In CCI-vehicle, sham and CCI-SR49059 groups, GFAP was 1.58±0.04, 0.47±0.02, and 0.81±0.03, respectively; V1aR was 1.00±0.06, 0.45±0.05, and 0.46±0.09; and AQP4 was 2.03±0.34, 0.49±0.04, and 0.92±0.22. Confocal immunohistochemistry gave analogous results. In CCI-vehicle, sham and CCI-SR49059 groups, fluorescence intensity of GFAP was 349±38, 56±5, and 244±30, respectively, V1aR was 601±71, 117.8±14, and 390±76, and AQP4 was 818±117, 158±5, and 458±55 (n=3/group). The results support that edema was predominantly cellular following CCI and documented that V1aR inhibition with SR49059 suppressed injury-induced up regulation of GFAP, V1A and AQP4, blunting edematous changes. Our findings suggest V1aR inhibitors may be potential therapeutic tools to prevent cellular swelling and provide treatment for post-traumatic brain edema.

Real-time monitoring of changes in brain extracellular sodium and potassium concentrations and intracranial pressure after selective vasopressin-1a receptor inhibition following focal traumatic brain injury in rats

Brain swelling and increased intracranial pressure (ICP) following traumatic brain injury (TBI) contribute to poor outcome. Vasopressin-1a receptors (V1aR) and aquaporin-4 (AQP4) regulate water transport and brain edema formation, perhaps in part by modulating cation fluxes. After focal TBI, V1aR inhibitors diminish V1aR and AQP4, reduce astrocytic swelling and brain edema. We determined whether V1aR inhibition with SR49059 after lateral controlled-cortical-impact (CCI) injury affects extracellular Na(+) and K(+) concentrations ([Na(+)]e; [K(+)]e). Ion-selective Na(+) and K(+) electrodes (ISE) and an ICP probe were implanted in rat parietal cortex, and [Na(+)]e, [K(+)]e, and physiological parameters were monitored for 5 h post-CCI. Sham-vehicle-ISE, CCI-vehicle-ISE and CCI-SR49059-ISE groups were studied, and SR49059 was administered 5 min to 5 h post-injury. We found a significant injury-induced decrease in [Na(+)]e to 80.1 ± 15 and 87.9 ± 7.9 mM and increase in [K(+)]e to 20.9 ± 3.8 and 13.4 ± 3.4 mM at 5 min post-CCI in CCI-vehicle-ISE and CCI-SR49059-ISE groups, respectively (p<0.001 vs. baseline; ns between groups). Importantly, [Na(+)]e in CCI-SR49059-ISE was reduced 5-20 min post-injury and increased to baseline at 25 min, whereas recovery in CCI-vehicle-ISE required more than 1 hr, suggesting SR49059 accelerated [Na(+)]e recovery. In contrast, [K(+)]e recovery took 45 min in both groups. Further, ICP was lower in the CCI-SR49059-ISE group. Thus, selective V1aR inhibition allowed faster [Na(+)]e recovery and reduced ICP. By augmenting the [Na(+)]e recovery rate, SR49059 may reduce trauma-induced ionic imbalance, blunting cellular water influx and edema after TBI. These findings suggest SR49059 and V1aR inhibitors are potential tools for treating cellular edema post-TBI.

Combustion smoke-induced inflammation in the cerebellum and hippocampus of adult rats

AIMS

The effect of combustion smoke inhalation on the respiratory system is widely reported but its effects on the central nervous system remain unclear. Here, we aimed to determine the effects of smoke inhalation on the cerebellum and hippocampus which are areas vulnerable to hypoxia injury.

METHODS

Adult male Sprague-Dawley rats were subjected to combustion smoke inhalation and sacrificed at 0.5, 3, 24 and 72 h after exposure. The cerebellum and hippocampus were subjected to Western analysis for VEGF, iNOS, eNOS, nNOS and AQP4 expression; ELISA analysis for cytokine and chemokine levels; and immunohistochemistry for GFAP/AQP4, RECA-1/RITC and TUNEL. Aminoguanidine (AG) was administered to determine the effects of iNOS after smoke inhalation.

RESULTS

Both the cerebellum and hippocampus showed a significant increase in VEGF, iNOS, eNOS, nNOS and AQP4 expression with corresponding increases in inflammatory cytokines and chemokines and increased AQP4 expression and RITC permeability after smoke exposure. AG was able to decrease the expression of iNOS, followed by VEGF, eNOS, nNOS, RITC and AQP4 after smoke exposure. There was also a significant increase in TUNEL+ cells in the cerebellum and hippocampus which were not significantly reduced by AG. Beam walk test revealed immediate deficits after smoke inhalation which was attenuated with AG.

CONCLUSION

The findings suggest that iNOS plays a major role in the central nervous system inflammatory pathophysiology after smoke inhalation exposure with concomitant increase in proinflammatory molecules, vascular permeability and oedema, for which the cerebellum appears to be more vulnerable to smoke exposure than the hippocampus.

Foxo3a transcriptionally upregulates AQP4 and induces cerebral edema following traumatic brain injury

Increased cranial pressure due to development of edema contributes significantly to the pathology of traumatic brain injury (TBI). Induction of an astrocytic water channel protein, Aquaporin 4 (AQP4), is known to predominantly contribute to cytotoxic edema following TBI. However, the mechanism for the increase in AQP4 following 24 h of TBI is poorly understood. Here we show that transcriptional activation of a ubiquitously expressed mammalian forkhead transcription factor, Foxo3a, induces cerebral edema by increasing the AQP4 level in the controlled cortical impact model of TBI in mice. TBI stimulates nuclear translocation of Foxo3a in astrocytes and subsequently augments its binding to AQP4 promoter in pericontusional cortex. Nuclear accumulation of Foxo3a is augmented by a decrease in phosphorylation at its Ser256 residue due to inactivation of Akt after TBI. Depletion of Foxo3a in mice rescues cytotoxic edema by preventing induction of AQP4 as well as attenuates memory impairment after TBI in mice.

The role of vasopressin V1A receptors in cytotoxic brain edema formation following brain injury

BACKGROUND

The hormone and neuropeptide arginine-vasopressin is designated to the maintenance of osmotic homoeostasis and blood pressure regulation. While experimental data show vasopressin V(1A) receptors to regulate aquaporin (AQP)4 water channel dependent brain water movement, the specific role in vasogenic and cytotoxic edema formation remains unclear. The present study was designed to quantify the V(1A) receptor mediated regional brain edema formation in two clinically relevant experimental models, brain injury combined with secondary insult and focal ischemia.

METHODS

Male Sprague-Dawley rats were randomly assigned to a continuous infusion of vehicle (1 % DMSO) or the selective non-peptide V(1A) antagonist SR49059 (83nM = 1 mg/kg) starting before controlled cortical impact (CCI) injury plus hypoxia and hypotension (HH, 30 min), or middle cerebral artery (MCA) occlusion (2 h + 2 h reperfusion).

RESULTS

A global analysis of brain water content by the wet/dry weight method allowed optimizing the SR49059 dosage, and demonstrated the down-regulation of brain AQP4 expression by immunoblotting. Microgravimetrical quantification in 64 one mm(3) samples per animal (n = 6 per group) from bregma +2.7 to -6.3 mm analysis demonstrated brain edema to be reduced at 4 h by SR49059 treatment in the injured and contralateral cortex following CCI + HH (p = 0.007, p < 0.001) and in the infarct area following MCA occlusion (p = 0.013, p = 0.002, p = 0.004).

CONCLUSIONS

Our findings demonstrate that an early cytotoxic brain edema component following brain injury plus secondary insult or focal ischemia results from a vasopressin V(1A) receptor mediated response, and occurs most likely through AQP4 up-regulation. The V(1A) antagonist SR49059 offers a new avenue in brain edema treatment and prompts further study into the role of vasopressin following brain injury.

Hypertonic saline reduces lipopolysaccharide-induced mouse brain edema through inhibiting aquaporin 4 expression

INTRODUCTION

Three percent sodium chloride (NaCl) treatment has been shown to reduce brain edema and inhibited brain aquaporin 4 (AQP4) expression in bacterial meningitis induced by Escherichia coli. Lipopolysaccharide (LPS) is the main pathogenic component of E. coli. We aimed to explore the effect of 3% NaCl in mouse brain edema induced by LPS, as well as to elucidate the potential mechanisms of action.

METHODS

Three percent NaCl was used to treat cerebral edema induced by LPS in mice in vivo. Brain water content, IL-1β, TNFα, immunoglobulin G (IgG), AQP4 mRNA and protein were measured in brain tissues. IL-1β, 3% NaCl and calphostin C (a specific inhibitor of protein kinase C) were used to treat the primary astrocytes in vitro. AQP4 mRNA and protein were measured in astrocytes. Differences in various groups were determined by one-way analysis of variance.

RESULTS

Three percent NaCl attenuated the increase of brain water content, IL-1β, TNFα, IgG, AQP4 mRNA and protein in brain tissues induced by LPS. Three percent NaCl inhibited the increase of AQP4 mRNA and protein in astrocytes induced by IL-1β in vitro. Calphostin C blocked the decrease of AQP4 mRNA and protein in astrocytes induced by 3% NaCl in vitro.

CONCLUSIONS

Osmotherapy with 3% NaCl ameliorated LPS-induced cerebral edema in vivo. In addition to its osmotic force, 3% NaCl exerted anti-edema effects possibly through down-regulating the expression of proinflammatory cytokines (IL-1β and TNFα) and inhibiting the expression of AQP4 induced by proinflammatory cytokines. Three percent NaCl attenuated the expression of AQP4 through activation of protein kinase C in astrocytes.

Early hyperbaric oxygen therapy inhibits aquaporin 4 and adrenocorticotropic hormone expression in the pituitary gland of rabbits with blast-induced craniocerebral injury

In the present study, rabbits were treated with hyperbaric oxygen for 1 hour after detonator-blast- induced craniocerebral injury. Immunohistochemistry showed significantly reduced aquaporin 4 expression and adrenocorticotropic hormone expression in the pituitary gland of rabbits with craniocerebral injury. Aquaporin 4 expression was positively correlated with adrenocorticotropic hormone expression. These findings indicate that early hyperbaric oxygen therapy may suppress adrenocorticotropic hormone secretion by inhibiting aquaporin 4 expression.

ATP-P2X7 receptor signaling controls basal and TNFα-stimulated glial cell proliferation

Activation and proliferation of glial cells and their progenitors is a key process of neuroinflammation associated with many neurodegenerative disorders. Under neuropathological conditions where glial cell activation and proliferation is evident, controlling the population of glia might be of therapeutic importance. The proliferative action of the cytokine tumor necrosis factor alpha (TNFα) on microglia has been reported, but the molecular mechanism of TNFα regulation of glial cell proliferation is largely unknown. Using a model of organotypic hippocampal-entorhinal cortex (HEC) slice culture, we investigated the role of ATP-P2X(7) receptor signaling in glial proliferation by TNFα. Populations of proliferating cells in HEC culture were labeled with 5-bromo-2'-deoxyuridine (BrdU). Treatment with TNFα induced strong expression of P2X(7) receptor mRNA and immunoreactivity in BrdU+ cells while markedly increasing proliferation of BrdU+ cells. In addition, TNFα increased aquaporin 4 (AQP4) expression, an ion channel involved in glial proliferation. The proliferative action of TNFα was attenuated by blocking the P2X(7) receptors with the specific antagonists oxATP, BBG, and KN62, or by lowering extracellular ATP with ATP hydrolysis apyrase. Basal proliferation of BrdU+ cells was also sensitive to blockade of ATP-P2X(7) signaling. Furthermore, TNFα activation of P2X(7) receptors appear to regulate AQP4 expression through protein kinase C cascade and down regulation of AQP4 expression can reduce TNFα-stimulated BrdU+ cell proliferation. Taken together, these novel findings demonstrate the importance of ATP-P2X(7) signaling in controlling proliferation of glial progenitors under the pathological conditions associated with increased TNFα.

Aquaporins in cerebrovascular disease: a target for treatment of brain edema?

In cerebrovascular disease, edema formation is frequently observed within the first 7 days and is characterized by molecular and cellular changes in the neurovascular unit. The presence of water channels, aquaporins (AQPs), within the neurovascular unit has led to intensive research in understanding the underlying roles of each of the AQPs under normal conditions and in different diseases. In this review, we summarize some of the recent knowledge on AQPs, focusing on AQP4, the most abundant AQP in the central nervous system. Several experimental models illustrate that AQPs have dual, complex regulatory roles in edema formation and resolution. To date, no specific therapeutic agents have been developed to inhibit water flux through these channels. However, experimental results strongly suggest that this is an important area for future investigation. In fact, early inhibition of water channels may have positive effects in the prevention of edema formation. At later time points during the course of disease, AQP is important for the clearance of water from the brain into blood vessels. Thus, AQPs, and in particular AQP4, have important roles in the resolution of edema after brain injury. The function of these water channel proteins makes them an excellent therapeutic target.

Effect of secondary insults upon aquaporin-4 water channels following experimental cortical contusion in rats

Although secondary insults of hypoxia and hypotension (HH) are generally considered to cause fulminant brain edema in traumatic brain injury (TBI), the combined effect of TBI with HH on brain edema and specifically the expression of aquaporin-4 (AQP4) have not been fully elucidated. The goal of this study was to document the effect of secondary insults on brain water, AQP4 expression, electrolytes, and blood-brain barrier (BBB) permeability during the acute stage of edema development. We measured brain water content and electrolytes (series 1); BBB permeability based on Evans blue (EB) dye extravasation (series 2); and AQP4 expression using immunoblotting (series 3) at 1 h and 5 h following cortical contusion injury (CCI). Secondary insults significantly worsened BBB function at 5 h post injury. Moreover, a significant reduction of upregulation on AQP4 expression was observed in trauma, coupled with a mild secondary insult of hypoxia hypotension. These findings indicate that a secondary insult following CCI at 5 h post injury worsens brain edema, disrupts ionic homeostasis, and blunts the normal upregulation of AQP4 that occurs after trauma, suggesting that the blunting of AQP4 may contribute to the detrimental effects of secondary insults.

Curcumin attenuates cerebral edema following traumatic brain injury in mice: a possible role for aquaporin-4?

Traumatic brain injury is a devastating neurological injury associated with significant morbidity and mortality. Medical therapies to limit cerebral edema, a cause of increased intracranial hypertension and poor clinical outcome, are largely ineffective, emphasizing the need for novel therapeutic approaches. In the present study, pre-treatment with curcumin (75, 150 mg/kg) or 30 min post-treatment with 300 mg/kg significantly reduced brain water content and improved neurological outcome following a moderate controlled cortical impact in mice. The protective effect of curcumin was associated with a significant attenuation in the acute pericontusional expression of interleukin-1beta, a pro-inflammatory cytokine, after injury. Curcumin also reversed the induction of aquaporin-4, an astrocytic water channel implicated in the development of cellular edema following head trauma. Notably, curcumin blocked IL-1beta-induced aquaporin-4 expression in cultured astrocytes, an effect mediated, at least in part, by reduced activation of the p50 and p65 subunits of nuclear factor kappaB. Consistent with this notion, curcumin preferentially attenuated phosphorylated p65 immunoreactivity in pericontusional astrocytes and decreased the expression of glial fibrillary acidic protein, a reactive astrocyte marker. As a whole, these data suggest clinically achievable concentrations of curcumin reduce glial activation and cerebral edema following neurotrauma, a finding which warrants further investigation.

The modulation of aquaporin-4 by using PKC-activator (phorbol myristate acetate) and V1a receptor antagonist (SR49059) following middle cerebral artery occlusion/reperfusion in the rat

BACKGROUND

We have pursued the concept that traumatic brain edema is predominantly cellular and that water entry is modulated in part by aquaporins. Aquaporin-4 (AQP4) has been shown to play a significant role in cellular edema formation. Phorbol myristate acetate (PMA) is a potent PKC activator; purportedly involved in modulation of AQP4 activity. Alternatively, AQP4 may be regulated by arginine-vasopressin. Administration of the vasopressin antagonist (SR49059) reduced brain water content and sodium shift following MCAo. To investigate if edema formation is affected by the reduction of AQP4 expression, we utilized PMA and SR49059 following middle cerebral artery occlusion model (MCAo), and measured AQP4 expression by Western-Blot (WB) techniques.

METHODS

Male Sprague Dawley rats were randomly assigned to sham (n=4) or MCAo groups (vehicle, PMA or SR49059 infusion; n=6 each). Each solution was infused for 5 hours, starting 1 hour before injury. After a two-hour period of ischemia and two-hour reperfusion, animals were sacrificed and brain regions of interest were processed by WB to quantify the effect of treatment on AQP4 expression.

RESULTS

These studies demonstrate that MCAo results in a significant up-regulation of AQP4 on the ischemic zone when compared to the contralateral un-injured hemisphere (p < 0.05) and that PMA and SR49059 treatment significantly down-regulated AQP4 expression compared to the vehicle group (p < 0.05).

CONCLUSIONS

These studies support the hypotheses that PMA and SR49059 may be useful in reducing cerebral water accumulation by modulating AQP4 expression and that pharmacological manipulation of AQP4 may emerge as a viable strategy for the reduction of fulminating edema following ischemic injury.

Combustion smoke exposure induces up-regulated expression of vascular endothelial growth factor, aquaporin 4, nitric oxide synthases and vascular permeability in the retina of adult rats

Retinal cells respond to various experimental stimuli including hypoxia, yet it remains to be investigated whether they react to smoke inhalation. We show here that retinal cells in rats, notably the ganglion cells, Müller cells, astrocytes and blood vessels responded vigorously to a smoke challenge. The major changes included up-regulated expression of vascular endothelial growth factor (VEGF), aquaporin 4 (AQP4) and nitric oxide synthase (NOS). VEGF expression was localized in the ganglion cells, Müller cells, astrocytes and associated blood vessels. AQP4 was markedly enhanced in both astrocytes and Müller cells. Increase in vascular permeability after smoke exposure was evidenced by extravasation of serum derived rhodamine isothiocyanate which was internalized by Müller cells and ganglion cells. The tracer leakage was attenuated by aminoguanidine and N(G)-nitro-L-arginine methyl ester (L-NAME) treatment which suppressed retinal tissue NOS and nitric oxide (NO) levels concomitantly. It is suggested that VEGF, AQP4 and NO are involved in increased vascular permeability following acute smoke exposure in which hypoxia was ultimately implicated as shown by blood gases analysis. NOS inhibitors effectively reduced the vascular leakage and hence may ameliorate possible retinal edema in smoke inhalation.

Progesterone exerts neuroprotective effects after brain injury

Progesterone, although still widely considered primarily a sex hormone, is an important agent affecting many central nervous system functions. This review assesses recent, primarily in vivo, evidence that progesterone can play an important role in promoting and enhancing repair after traumatic brain injury and stroke. Although many of its specific actions on neuroplasticity remain to be discovered, there is growing evidence that this hormone may be a safe and effective treatment for traumatic brain injury and other neural disorders in humans.

Aquaporin-4 in hepatic encephalopathy

Brain edema is a critical component of hepatic encephalopathy (HE) associated with acute liver failure and such edema appears to be principally due to astrocyte swelling (cytotoxic edema). Ammonia is believed to represent a major factor responsible for astrocyte swelling, although the mechanisms by which ammonia causes such swelling are not completely understood. Recent studies have implicated potential role of oxidative stress, and the mitochondrial permeability transition (mPT). While it is not known how oxidative stress and the mPT cause astrocyte swelling, it is reasonable to suggest that these events may affect one or more plasma membrane proteins involved in water and ion homeostasis in astrocytes. One such protein strongly implicated in brain edema in other neurological conditions is the water channel protein aquaporin-4 (AQP-4), which is abundantly expressed in astrocytes. This article summarizes the potential role of AQP-4 in brain edema in in vivo models of HE, as well as in ammonia-induced cell swelling in cultured astrocytes. The involvement of AQP-4 in the effects of manganese, another toxin implicated in HE, will also be discussed.

A review of progress in understanding the pathophysiology and treatment of brain edema

Object

Brain edema resulting from traumatic brain injury (TBI) or ischemia if uncontrolled exhausts volume reserve and leads to raised intracranial pressure and brain herniation. The basic types of edema—vasogenic and cytotoxic—were classified 50 years ago, and their definitions remain intact.

Methods

In this paper the author provides a review of progress over the past several decades in understanding the pathophysiology of the edematous process and the success and failures of treatment. Recent progress focused on those manuscripts that were published within the past 5 years.

Results

Perhaps the most exciting new findings that speak to both the control of production and resolution of edema in both trauma and ischemia are the recent studies that have focused on the newly described “water channels” or aquaporins. Other important findings relate to the predominance of cellular edema in TBI.

Conclusions

Significant new findings have been made in understanding the pathophysiology of brain edema; however, less progress has been made in treatment. Aquaporin water channels offer hope for modulating and abating the devastating effects of fulminating brain edema in trauma and stroke.