Hypertonic saline ameliorates cerebral edema through downregulation of aquaporin-4 expression in the astrocytes

MicroRNA-mediated regulation of reactive astrocytes in central nervous system diseases

Astrocytes (AST) are abundant glial cells in the human brain, accounting for approximately 20-50% percent of mammalian central nervous system (CNS) cells. They display essential functions necessary to sustain the physiological processes of the CNS, including maintaining neuronal structure, forming the blood-brain barrier, coordinating neuronal metabolism, maintaining the extracellular environment, regulating cerebral blood flow, stabilizing intercellular communication, participating in neurotransmitter synthesis, and defending against oxidative stress et al. During the pathological development of brain tumors, stroke, spinal cord injury (SCI), neurodegenerative diseases, and other neurological disorders, astrocytes undergo a series of highly heterogeneous changes, which are called reactive astrocytes, and mediate the corresponding pathophysiological process. However, the pathophysiological mechanisms of reactive astrocytes and their therapeutic relevance remain unclear. The microRNAs (miRNAs) are essential for cell differentiation, proliferation, and survival, which play a crucial role in the pathophysiological development of CNS diseases. In this review, we summarize the regulatory mechanism of miRNAs on reactive astrocytes in CNS diseases, which might provide a theoretical basis for the diagnosis and treatment of CNS diseases.

A novel association of osmotic demyelination in Sjögren's syndrome prompts revisiting role of aquaporins in CNS demyelinating diseases: A literature review

BACKGROUND

Primary Sjögren's syndrome (SS) is a chronic systemic autoimmune disease with varied neurological manifestations. SS is associated with anti-aquaporin-4 antibody (AQP4-IgG)-positive neuromyelitis optica spectrum disorder (NMOSD), a demyelinating autoimmune disorder of the central nervous system (CNS). Intriguingly, there are reports of osmotic demyelinating syndrome (ODS), a supposedly non-inflammatory disorder, in the context of SS and renal tubular acidosis (RTA), both of which are not yet established risk factors for ODS.

METHODS

A literature search was undertaken to identify case reports of ODS in patients with SS. Details of the clinical and laboratory features of these patients were compiled. Additionally, we searched for NMOSD in patients with SS. We looked for co-existing RTA in patients with SS-ODS as well as SS-NMOSD. We also screened for reports of ODS in RTA without underlying SS.

RESULTS & DISCUSSION

We identified 15 patients (all women, median age 40 years) with ODS in SS, and all of these patients had comorbid RTA. There were only three reported cases of ODS in RTA without underlying SS. We identified a total of 67 patients with SS-NMOSD, of whom only 3 (4.5%) had RTA. Hence, unlike NMOSD, the development of ODS in SS requires a prolonged osmotic or electrolyte abnormality caused by the comorbid RTA. The 15 patients with ODS and SS -RTA, showed heterogeneous clinical manifestations and outcomes. The most common symptom was quadriparesis, seen in 14 of the 15 patients. Eleven of the 15 patients had one of the following features, either alone or in combination: worsening of the sensorium, extensor plantar response, dysphagia/dysarthria, and facial palsy. The latter four manifestations were present at the onset in 7 patients and later in the course of the illness in the remaining 4 patients. Ocular palsy was seen in only four of the 15 patients and was a late manifestation. One patient who had extensive long-segment myelitis and subsequent ODS died, but most patients recovered without significant sequelae. None had hyponatremia, while all patients had hypokalemia and/or hypernatremia. Hypokalemia causing nephrogenic diabetes insipidus (NDI) followed by rapid rise in sodium and the resultant osmotic stress could potentially explain the occurrence of ODS in SS-RTA. Aquaporin (AQP) in astrocytes is implicated in ODS, and renal AQP is downregulated in NDI. Antibodies against AQPs are present in some patients with SS. Defective AQP is therefore a common link underlying all the connected diseases, namely SS, NDI, and ODS, raising the possibility of immune-mediated AQP dysfunction in the pathogenesis.

CONCLUSION

The hitherto unreported association between SS-RTA and ODS may implicate SS and/or RTA in the development of ODS. In the setting of SS-RTA, ODS must be suspected when a patient with flaccid quadriparesis does not respond to the correction of potassium or develops additional neurological features along with a rise in sodium. Defective functions of AQPs may be a possible mechanism linking demyelinating CNS lesions, SS, and RTA. Studies evaluating AQP functions and serum antibodies against AQPs in these conditions are warranted.

The role of bioactive lipids in attenuating the neuroinflammatory cascade in traumatic brain injury

Traumatic brain injury (TBI) is a major cause of morbidity, mortality, and economic burden. Despite this, there are no proven medical therapies in the pharmacologic management of TBI. A better understanding of disease pathophysiology might lead to novel approaches. In one area of increasing interest, bioactive lipids known to attenuate inflammation might serve as an important biomarker and mediator of disease after TBI. In this review, we describe the pathophysiology of inflammation following TBI, the actions of endogenous bioactive lipids in attenuating neuroinflammation, and their possible therapeutic role in the management of TBI. In particular, specialized pro‐resolving lipid mediators (SPMs) of inflammation represent endogenous compounds that might serve as important biomarkers of disease and potential therapeutic targets. We aim to discuss the current literature from animal models of TBI and limited human experiences that suggest that bioactive lipids and SPMs are mechanistically important to TBI recovery, and by doing so, aim to highlight the need for further clinical and translational research. Early investigations of dietary and parenteral supplementation of pro‐resolving bioactive lipids have been promising. Given the high morbidity and mortality that occurs with TBI, novel approaches are needed.

Cortical interlaminar astrocytes across the therian mammal radiation

Interlaminar astrocytes (ILA) in the cerebral cortex possess a soma in layer I and extend an interlaminar process that runs perpendicular to the pia into deeper cortical layers. We examined cerebral cortex from 46 species that encompassed most orders of therian mammalians, including 22 primate species. We described two distinct cell types with interlaminar processes that have been referred to as ILA, that we termed pial ILA and supial ILA. ILA subtypes differ in somatic morphology, position in layer I, and presence across species. We further described rudimentary ILA that have short GFAP⁺ processes that do not exit layer I, and "typical" ILA with longer GFAP⁺ processes that exit layer I. Pial ILA were present in all mammalian species analyzed, with typical ILA observed in Primates, Scandentia, Chiroptera, Carnivora, Artiodactyla, Hyracoidea, and Proboscidea. Subpial ILA were absent in Marsupialia, and typical subpial ILA were only found in Primate. We focused on the properties of pial ILA by investigating the molecular properties of pial ILA and confirming their astrocytic nature. We found that while the density of pial ILA somata only varied slightly, the complexity of ILA processes varied greatly across species. Primates, specifically bonobo, chimpanzee, orangutan, and human, exhibited pial ILA with the highest complexity. We showed that interlaminar processes contact neurons, pia, and capillaries, suggesting a potential role for ILA in the blood-brain barrier and facilitating communication among cortical neurons, astrocytes, capillaries, meninges, and cerebrospinal fluid.

miR‑29a ameliorates ischemic injury of astrocytes in vitro by targeting the water channel protein aquaporin 4

Ischemic stroke is the main cause of brain injury and results in a high rate of morbidity, disability and mortality. In the present study, we aimed to determine whether miR-29a played a protective role in oxygen glucose deprivation (OGD) injury via regulation of the water channel protein aquaporin 4 (AQP4). Real-time PCR and western blotting were used to assess miR-29a levels and AQP4 protein levels, respectively. Apoptosis was detected by flow cytometry, and lactate dehydrogenase (LDH) was determined by enzyme-linked immunosorbent assay (ELISA). Overexpression of miR-29a was significantly downregulated in OGD-induced primary astrocytes, and transfection with a miR-29a mimic decreased LDH release and apoptosis, and improved cell health in OGD-induced astrocytes. AQP4 was the target of miR-29a, which suppressed AQP4 expression, and knockdown of AQP4 mitigated OGD-induced astrocyte injury. Furthermore, miR-29a regulated AQP4 expression in OGD-induced astrocytes. AQP4 exacerbated astrocyte injury following ischemic stroke, and knockdown of AQP4 protected OGD/RX-induced primary cultured astrocytes against injury. The effect of miR-29a inhibitor on primary astrocytes was lost following AQP4 knockdown. These findings indicated that miR-29a prevented astrocyte injury in vitro by inhibiting AQP4. Thus, miR-29a may protect primary cultured astrocytes after OGD-induced injury by targeting AQP4, and may be a potential therapeutic target for ischemic injury of astrocytes.

Hypertonic saline regulates microglial M2 polarization via miR-200b/KLF4 in cerebral edema treatment

BACKGROUND

Hypertonic saline (HS) has been used clinically for treatment of cerebral edema for decades. Previously we have demonstrated that HS alleviates cerebral edema via regulating water/ion channel protein and attenuating neuroinflammation. However, whether HS treatment triggers microglia polarization and its regulatory mechanism during this process is unclear.

METHODS AND RESULTS

The Sprague-Dawley (SD) rats that underwent right-sided middle cerebral artery occlusion (MCAO) were used for assessment of neuroinflammation and microglia functions. Treatment of 10% HS not only significantly reduced infarct size and ipsilateral ischemic hemispheric brain water content (BWC) via attenuating ischemia-induction of TNF-α, IL-1β, microglia M1 markers (iNOS, CD86) and miR-200b, but also increased neurotrophic factors such as IL-10 and IL-4, microglia M2 markers (Arg1, CD206) and Krüppel-like factor 4 (KLF4). Similar changes were confirmed in primary microglial cells subjected to hypoxia with/without HS in vitro. Importantly, overexpression of miR-200b was able to induce microglia M1 polarization via directly targeting KLF4. Restoring KLF4 expression abolished this effect. On the contrary, miR-200b inhibitor or KLF4 overexpression led to microglia M2 polarization. Mechanistically, KLF4 directly binds to promoter region of Agr1, thus inducing its transcription. Similar to treatment of HS, experimental overexpression of KLF4 in vivo exerted significant beneficial effects on ischemia-induced cerebral edema. However, knockdown of KLF4 abrogated the benefits of HS.

CONCLUSIONS

Hypertonic saline regulates microglial M2 polarization via miR-200b/KLF4 during its treatment of cerebral edema. This study may provide new insights of HS-related therapy for cerebral edema.

Selective knockout of astrocytic Na+ /H+ exchanger isoform 1 reduces astrogliosis, BBB damage, infarction, and improves neurological function after ischemic stroke

Stimulation of Na⁺ /H⁺ exchanger isoform 1 (NHE1) in astrocytes causes ionic dysregulation under ischemic conditions. In this study, we created a Nhe1^flox/flox (Nhe1^f/f ) mouse line with exon 5 of Nhe1 flanked with two loxP sites and selective ablation of Nhe1 in astrocytes was achieved by crossing Nhe1^f/f mice with Gfap-Cre^ERT2 Cre-recombinase mice. Gfap-Cre^ERT2+/- ;Nhe1^f/f mice at postnatal day 60-90 were treated with either corn oil or tamoxifen (Tam, 75 mg/kg/day, i.p.) for 5 days. After 30 days post-injection, mice underwent transient middle cerebral artery occlusion (tMCAO) to induce ischemic stroke. Compared with the oil-vehicle group (control), Tam-treated Gfap-Cre^ERT2+/- ;Nhe1^f/f (Nhe1 KO) mice developed significantly smaller ischemic infarction, less edema, and less neurological function deficits at 1-5 days after tMCAO. Immunocytochemical analysis revealed less astrocytic proliferation, less cellular hypertrophy, and less peri-lesion gliosis in Nhe1 KO mouse brains. Selective deletion of Nhe1 in astrocytes also reduced cerebral microvessel damage and blood-brain barrier (BBB) injury in ischemic brains. The BBB microvessels of the control brains show swollen endothelial cells, opened tight junctions, increased expression of proinflammatory protease MMP-9, and significant loss of tight junction protein occludin. In contrast, the Nhe1 KO mice exhibited reduced BBB breakdown and normal tight junction structure, with increased expression of occludin and reduced MMP-9. Most importantly, deletion of astrocytic Nhe1 gene significantly increased regional cerebral blood flow in the ischemic hemisphere at 24 hr post-MCAO. Taken together, our study provides the first line of evidence for a causative role of astrocytic NHE1 protein in reactive astrogliosis and ischemic neurovascular damage.

Risk factors and outcome of Shigella encephalopathy in Bangladeshi children

BACKGROUND

Although, Shigella encephalopathy, a serious extra-intestinal complication of shigellosis, significantly increases the risks of death, data are very limited on predicting factors particularly related to electrolyte profiles in children below five years of age with Shigella encephalopathy. Our objective was to determine the clinical as well as laboratory predicting factors and outcome of children with Shigella encephalopathy.

METHODOLOGY/PRINCIPAL FINDINGS

In this unmatched case-control design, children aged 2-59 months having a positive stool culture for Shigella and who had their serum electrolytes been done from July 2012 to June 2015 were studied. Children with Shigella encephalopathy, defined as having abnormal mentation, constituted the cases, and those without encephalopathy constituted the controls. During the study period, we identified a total of 541 children less than five years of age, who had Shigella in their stool culture. Only 139 children fulfilled the study criteria and among them 69 were cases and 70 were controls. The cases more often had fatal outcome compared to the controls (7% vs. 0%, P = 0.02). In logistic regression analysis, the cases were independently associated with shorter duration (1.2 ± 0.4 days) of diarrhea prior to admission, dehydrating diarrhea, sepsis and hyponatremia (p<0.05 for all). Among 139 Shigella isolates, S. flexneri (88/139, 63%) and S. sonnei(34/139, 24%) were the dominant species. S. dysenteriae was not isolated throughout the study period. S.sonnei was more frequently isolated from the cases (24/69, 35%) than the controls (10/70, 14%), whereas the isolation of S. flexneri was comparable between the groups (40/69, 58% vs 48/70, 69%). A total of 94 (67.6%) isolates were resistant to trimethoprim-sulphamethoxazole, 84 (60.4%) to ciprofloxacin, 66/138 (48%) to ampicillin, 5 (3.5%) to ceftriaxone, 17 (12.2%) to mecillinum and 35 (25%) to azithromycin.

CONCLUSIONS/SIGNIFICANCE

The case-fatality-rate was significantly higher among the children with Shigella encephalopathy compared to those without encephalopathy. Early identification and aggressive management of simple risk factors for Shigella encephalopathy may help to reduce morbidity and deaths in such children especially in resource-limited settings.

Hypertonic saline alleviates experimentally induced cerebral oedema through suppression of vascular endothelial growth factor and its receptor VEGFR2 expression in astrocytes

BACKGROUND

Cerebral oedema is closely related to the permeability of blood-brain barrier, vascular endothelial growth factor (VEGF) and its receptor vascular endothelial growth factor receptor 2 (VEGFR2) all of which are important blood-brain barrier (BBB) permeability regulatory factors. Zonula occludens 1 (ZO-1) and claudin-5 are also the key components of BBB. Hypertonic saline is widely used to alleviate cerebral oedema. This study aimed to explore the possible mechanisms underlying hypertonic saline that ameliorates cerebral oedema effectively.

METHODS

Middle cerebral artery occlusion (MCAO) model in Sprague-Dawley (SD) rats and of oxygen-glucose deprivation model in primary astrocytes were used in this study. The brain water content (BWC) was used to assess the effect of 10 % HS on cerebral oedema. The assessment of Evans blue (EB) extravasation was performed to evaluate the protective effect of 10 % HS on blood-brain barrier. The quantification of VEGF, VEGFR2, ZO-1 and claudin-5 was used to illustrate the mechanism of 10 % HS ameliorating cerebral oedema.

RESULTS

BWC was analysed by wet-to-dry ratios in the ischemic hemisphere of SD rats; it was significantly decreased after 10 % HS treatment (P < 0.05). We also investigated the blood-brain barrier protective effect by 10 % HS which reduced EB extravasation effectively in the peri-ischemic brain tissue. In parallel to the above notably at 24 h following MCAO, mRNA and protein expression of VEGF and VEGFR2 in the peri-ischemic brain tissue was down-regulated after 10 % HS treatment (P < 0.05). Along with this, in vitro studies showed increased VEGF and VEGFR2 mRNA and protein expression in primary astrocytes under hypoxic condition (P < 0.05), but it was suppressed after HS treatment (P < 0.05). In addition, HS inhibited the down-regulation of ZO-1, claudin-5 effectively.

CONCLUSIONS

The results suggest that 10 % HS could alleviate cerebral oedema possibly through reducing the ischemia induced BBB permeability as a consequence of inhibiting VEGF-VEGFR2-mediated down-regulation of ZO-1, claudin-5.

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.

Reduced brain edema and infarct volume in aquaporin-4 deficient mice after transient focal cerebral ischemia

Aquaporin-4 (AQP4) is a water channel expressed in astrocyte end-feet lining the blood-brain barrier. AQP4 deletion in mice is associated with improved outcomes in global cerebral ischemia produced by transient carotid artery occlusion, and focal cerebral ischemia produced by permanent middle cerebral artery occlusion (MCAO). Here, we investigated the consequences of 1-h transient MCAO produced by intraluminal suture blockade followed by 23 h of reperfusion. In nine AQP4(+/+) and nine AQP4(-/-) mice, infarct volume was significantly reduced by an average of 39 ± 4% at 24h in AQP4(-/-) mice, cerebral hemispheric edema was reduced by 23 ± 3%, and Evans Blue extravasation was reduced by 31 ± 2% (mean ± SEM). Diffusion-weighted magnetic resonance imaging showed greatest reduction in apparent diffusion coefficient around the occlusion site after reperfusion, with remarkably lesser reduction in AQP4(-/-) mice. The reduced infarct volume in AQP4(-/-) mice following transient MCAO supports the potential utility of therapeutic AQP4 inhibition in stroke.

Hypertonic saline alleviates cerebral edema by inhibiting microglia-derived TNF-α and IL-1β-induced Na-K-Cl Cotransporter up-regulation

Background

Hypertonic saline (HS) has been successfully used clinically for treatment of various forms of cerebral edema. Up-regulated expression of Na-K-Cl Cotransporter 1 (NKCC1) and inflammatory mediators such as tumor necrosis factor alpha (TNF-α) and interleukin-1 beta (IL-1β) has been demonstrated to be closely associated with the pathogenesis of cerebral edema resulting from a variety of brain injuries. This study aimed to explore if alleviation of cerebral edema by 10% HS might be effected through down-regulation of inflammatory mediator expression in the microglia, and thus result in decreased NKCC1 expression in astrocytes in the cerebral cortex bordering the ischemic core.

Methods

The Sprague-Dawley (SD) rats that underwent right-sided middle cerebral artery occlusion (MCAO) were used for assessment of NKCC1, TNF-α and IL-1β expression using Western blotting, double immunofluorescence and real time RT-PCR, and the model also was used for evaluation of brain water content (BWC) and infarct size. SB203580 and SP600125, specific inhibitors of the p38 and JNK signaling pathways, were used to treat primary microglia cultures to determine whether the two signaling pathways were required for the inhibition of HS on microglia expressing and secreting TNF-α and IL-1β using Western blotting, double immunofluorescence and enzyme-linked immunosorbent assay (ELISA). The effect of TNF-α and IL-1β on NKCC1 expression in primary astrocyte cultures was determined. In addition, the direct inhibitory effect of HS on NKCC1 expression in primary astrocytes was also investigated by Western blotting, double immunofluorescence and real time RT-PCR.

Results

BWC and infarct size decreased significantly after 10% HS treatment. TNF-α and IL-1β immunoexpression in microglia was noticeably decreased. Concomitantly, NKCC1 expression in astrocytes was down-regulated. TNF-α and IL-1β released from the primary microglia subjected to hypoxic exposure and treatment with 100 mM HS were decreased. NKCC1 expression in primary astrocytes was concurrently and progressively down-regulated with decreasing concentration of exogenous TNF-α and IL-1β. Additionally, 100 mM HS directly inhibited NKCC1 up-regulation in astrocytes under hypoxic condition.

Conclusions

The results suggest that 10% HS alleviates cerebral edema through inhibition of the NKCC1 Cotransporter, which is mediated by attenuation of TNF-α and IL-1β stimulation on NKCC1.

Variable change in renal function by hypertonic saline

AIM: To investigate the effects of hypertonic saline in the neurocritical care population.

METHODS: We retrospectively reviewed our hospital’s use of hypertonic saline (HS) since March of 2005, and prospectively since October 2010. Comparisons were made between admission diagnoses, creatinine change (Cr), and HS formulation (3% NaCl, 3% NaCl/sodium acetate mix, and 23.4% NaCl) to patients receiving normal saline or lactated ringers. The patients (n = 1329) of the retrospective portion were identified. The data presented represents the first 230 patients with data.

RESULTS: Significant differences in Acute Physiology and Chronic Health Evaluation II scores and Glasgow Coma Scale scores occurred between different saline formulations. No significant correlation of Cl^- or Na⁺ with Cr, nor with saline types, occurred. When dichotomized by diagnosis, significant correlations appear. Traumatic brain injury (TBI) patients demonstrated moderate correlation between Na⁺ and Cr of 0.45. Stroke patients demonstrated weak correlations between Na⁺ and Cr, and Cl^- and Cr (0.19 for both). Patients receiving HS and not diagnosed with intracerebral hemorrhage, stroke, subarachnoid hemorrhage, or TBI demonstrated a weak but significant correlation between Cl^- and Cr at 0.29.

CONCLUSION: Cr directly correlates with Na⁺ or Cl^- in stroke, Na⁺ in TBI, and Cl^- in other populations. Prospective comparison of HS and renal function is needed.

Rapamycin alleviates brain edema after focal cerebral ischemia reperfusion in rats

Brain edema is a major consequence of cerebral ischemia reperfusion. However, few effective therapeutic options are available for retarding the brain edema progression after cerebral ischemia. Recently, rapamycin has been shown to produce neuroprotective effects in rats after cerebral ischemia reperfusion. Whether rapamycin could alleviate this brain edema injury is still unclear. In this study, the rat stroke model was induced by a 1-h left transient middle cerebral artery occlusion using an intraluminal filament, followed by 48 h of reperfusion. The effects of rapamycin (250 μg/kg body weight, intraperitoneal; i.p.) on brain edema progression were evaluated. The results showed that rapamycin treatment significantly reduced the infarct volume, the water content of the brain tissue and the Evans blue extravasation through the blood-brain barrier (BBB). Rapamycin treatment could improve histological appearance of the brain tissue, increased the capillary lumen space and maintain the integrity of BBB. Rapamycin also inhibited matrix metalloproteinase 9 (MMP9) and aquaporin 4 (AQP4) expression. These data imply that rapamycin could improve brain edema progression after reperfusion injury through maintaining BBB integrity and inhibiting MMP9 and AQP4 expression. The data of this study provide a new possible approach for improving brain edema after cerebral ischemia reperfusion by administration of rapamycin.

SPARC-like 1 (SC1) is a diversely expressed and developmentally regulated matricellular protein that does not compensate for the absence of SPARC in the CNS

SPARC-like 1 (SC1) is a member of the SPARC family of matricellular proteins that has been implicated in the regulation of processes such as cell migration, proliferation, and differentiation. Here we show that SC1 exhibits remarkably diverse and dynamic expression in the developing and adult nervous system. During development, SC1 localizes to radial glia and pial-derived structures, including the vasculature, choroid plexus, and pial membranes. SC1 is not downregulated in postnatal development, but its expression shifts to distinct time windows in subtypes of glia and neurons, including astrocytes, large projection neurons, Bergmann glia, Schwann cells, and ganglionic satellite cells. In addition, SC1 expression levels and patterns are not altered in the SPARC null mouse, suggesting that SC1 does not compensate for the absence of SPARC. We conclude that SC1 and SPARC may share significant homology, but are likely to have distinct but complementary roles in nervous system development.

PRO: osmotherapy for the treatment of acute intracranial hypertension

Persisting severe brain edema causes intracranial hypertension and is associated with poor patient outcome. The treatment of acute intracranial hypertension is complex and multimodal. The most important options for medical treatment include controlled ventilation and osmotherapy, maintenance of brain and body homeostasis, and sedation. Osmotherapy is recommended in all relevant guidelines. The 2 osmotic agents most frequently used are mannitol and hypertonic saline. Both reduce intracranial pressure and improve cerebral perfusion and cerebral oxygen delivery. However, hypertonic saline seems advantageous over mannitol in many situations. In multitrauma patients, hypertonic saline contributes to hemodynamic stabilization and to the prevention of secondary insults. In addition, hypertonic saline has neurohumoral and immunologic effects, which may be beneficial in cerebral resuscitation.

Intravenous hypertonic saline use in the pediatric emergency department

OBJECTIVES

The objective of this study was to describe the use, dosing, and administration of intravenous hypertonic saline (IHS) use in a pediatric emergency department.

METHODS

This was a retrospective chart review of patients 0 to 18 years receiving IHS as part of their management in a pediatric ED with an annual volume of more than 50,000 visits.

RESULTS

Over 4 years, 56 patients received IHS as part of their management in the emergency department. Clinical scenarios for IHS administration included traumatic brain injury with concern for increased intracranial pressure in 19 patients (34%), diabetic ketoacidosis with altered mental status in 18 (32%), hyponatremia without seizure activity in 6 (10.7%), hyponatremic seizure in 3 (5.4%), and altered mental status secondary to a nontraumatic, non-diabetic ketoacidosis cause in 10 (17.9%). The median age of the patients was 11.3 years (interquartile range, 6-13.9 years) receiving a median dose of 4.1 mL/kg (interquartile range, 3.08-5 mL/kg) of IHS. The median time for administration of the IHS was 17 minutes, with 87% of doses given via peripheral intravenous catheters. Approximately one fourth (26.8%) of patients received their dose in 10 minutes or less, with 7.2% of patients receiving a bolus of IHS in 3 minutes or less. We found no evidence of adverse effects.

CONCLUSIONS

Intravenous hypertonic saline use is increasing within the pediatric emergency department. Within this institution, it is most frequently used at a dosing range of 3 to 5 mL/kg and does not require central venous access for rapid infusion.

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.

Potential contribution of hypoxia-inducible factor-1α, aquaporin-4, and matrix metalloproteinase-9 to blood-brain barrier disruption and brain edema after experimental subarachnoid hemorrhage

The current research aimed to investigate the role of hypoxia-inducible factor-1α (HIF-1α), aquaporin-4 (AQP-4), and matrix metalloproteinase-9 (MMP-9) in blood-brain barrier (BBB) dysfunction and cerebral edema formation in a rat subarachnoid hemorrhage (SAH) model. The SAH model was induced by injection of 0.3 ml fresh arterial, non-heparinized blood into the prechiasmatic cistern in 20 s. Anti-AQP-4 antibody, minocycline (an inhibitor of MMP-9), or 2-methoxyestradiol (an inhibitor of HIF-1α), was administered intravenously at 2 and 24 h after SAH. Brain samples were extracted at 48 h after SAH and examined for protein expressions, BBB impairment, and brain edema. Following SAH, remarkable edema and BBB extravasations were observed. Compared with the control group, the SAH animals have significantly upregulated expressions of HIF-1α, AQP-4, and MMP-9, in addition to decreased amounts of laminin and tight junction proteins. Brain edema was repressed after inhibition of AQP-4, MMP-9, or HIF-1α. Although BBB permeability was also ameliorated after inhibition of either HIF-1α or MMP-9, it was not modulated after inhibition of AQP-4. Inhibition of MMP-9 reversed the loss of laminin. Finally, inhibition of HIF-1α significantly suppressed the level of AQP-4 and MMP-9, which could induce the expression of laminin and tight junction proteins. Our results suggest that HIF-1α plays a role in brain edema formation and BBB disruption via a molecular signaling pathway involving AQP-4 and MMP-9. Pharmacological intervention of this pathway in patients with SAH may provide a novel therapeutic strategy for early brain injury.

The role of aquaporin 4 in the brain

Emerging evidence suggests that aquaporin (AQP) 4 water channels play an important role in water homeostasis in the brain. These water channels are most abundant in the cell membrane of astrocytes, but are also present within ependymal cell membranes and in osmosensory areas of the hypothalamus. Water transport through AQP4 depends on concentration gradients across the membrane, but the rate of transport is determined by the capacity of astrocytes to up- and down-regulate AQP4 numbers, their location within the membrane, and the overall permeability of the channel. Other functions of brain AQP4 involve potassium uptake and release by astrocytes, migration of glial cells, glial scarring, and astrocyte-to-astrocyte cell communication. AQP water channels are involved in formation and control of edema in the brain and in multiple disease processes in the brain, such as seizures and tumors. There is abundant scientific literature on AQP4 describing its structure, function, location, and role in water homeostasis and edema in the brain. Investigation of AQP expression in the canine and feline brain should be pursued so that clinically relevant comparisons between findings in mice, rats, and people and animal patients can be made.

Bolus injection of hypertonic solutions for cerebral edema in rats: challenge of homeostasis of healthy brain

Hypertonic solutions are mainstay of osmotherapy to cerebral edema. How hypertonic solutions affect healthy brain homeostasis, however, is not fully understood. Using rat model of cerebral edema induced by local cryoinjury, we found with immunohistochemistry that less microglial activation in healthy hemishere 24 h after hypertonic saline (HS, 3% NaCl) administration, compared to mannitol (20%, the same osmotic concentration of 3% NaCl) while dehydrating the brain tissue. To see whether blood-brain barrier (BBB) or aquaporin-4 (AQP4) contribute to this difference, HS or mannitol was intra-arterially injected to normal rats, and BBB opening, ultrastructure and AQP4 immunoreactivity were examined. Evans blue extravasation indicated that BBB was opened much lighter in HS group than mannitol group at the same time points. Electron microscopy also showed edema around the capillaries slightly lighter in HS than mannitol group 24 h after injection. Meanwhile, HS injection led to AQP4 down regulation in expression similarly as mannitol, compared with NS group. These data suggested that bolus injection of hypertonic agents may lead to microglia activation in healthy brain in different extent, due to BBB compromise, instead of water movement or AQP4 expression. Hence in clinical application, BBB of healthy brain should be considered in perspective to maintain the brain homeostasis.

Water, water, everywhere: sodium and water balance and the injured brain

PURPOSE OF REVIEW

This review focuses on water shift and oedema in acute brain injury, with particular aspects on pathophysiology of water movements, the role of aquaporins and the potential of new therapies. This review reports on update of both significant experimental and clinical findings on factors implicated in oedema formation.

RECENT FINDINGS

The main inputs came from the demonstrated role of aquaporins (especially AQP4) in brain oedema control. The absence of aquaporin agonist or antagonist does not help to clarify the net effect of aquaporins on brain oedema. The clinical practice of osmotherapy, especially with hypertonic saline failed to improve neurological outcome in a large randomized clinical trial. Colloid treatment was not proven efficient and potentially dangerous. Some hopes might come from targeting inflammatory cascade and neurogenic mediators to reduce lesion severity and to limit the blood-brain barrier dysrupture.

SUMMARY

Water content control and partition can be better assessed in clinic with NMR helping to make decisions, but with limited proven therapies. The timing for such interventions might be crucial and future biomarkers might be very helpful.

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.

A comparative study on the efficacy of 10% hypertonic saline and equal volume of 20% mannitol in the treatment of experimentally induced cerebral edema in adult rats

Background

Hypertonic saline and mannitol are commonly used in the treatment of cerebral edema and elevated intracranial pressure (ICP) at present. In this connection, 10% hypertonic saline (HS) alleviates cerebral edema more effectively than the equal volume of 20% mannitol. However, the exact underlying mechanism for this remains obscure. This study aimed to explore the possible mechanism whereby 10% hypertonic saline can ameliorate cerebral edema more effectively than mannitol.

Results

Adult male Sprague-Dawley (SD) rats were subjected to permanent right-sided middle cerebral artery occlusion (MCAO) and treated with a continuous intravenous infusion of 10% HS, 20% mannitol or D-[1-³H(N)]-mannitol. Brain water content (BWC) as analyzed by wet-to-dry ratios in the ischemic hemisphere of SD rats decreased more significantly after 10% HS treatment compared with 20% mannitol. Concentration of serum Na⁺ and plasma crystal osmotic pressure of the 10% HS group at 2, 6, 12 and 18 h following permanent MCAO increased significantly when compared with 20% mannitol treated group. Moreover, there was negative correlation between the BWC of the ipsilateral ischemic hemisphere and concentration of serum Na⁺, plasma crystal osmotic pressure and difference value of concentration of serum Na⁺ and concentration of brain Na⁺ in ipsilateral ischemic hemisphere in the 10% HS group at the various time points after MCAO. A remarkable finding was the progressive accumulation of mannitol in the ischemic brain tissue.

Conclusions

We conclude that 10% HS is more effective in alleviating cerebral edema than the equal volume of 20% mannitol. This is because 10% HS contributes to establish a higher osmotic gradient across BBB and, furthermore, the progressive accumulation of mannitol in the ischemic brain tissue counteracts its therapeutic efficacy on cerebral edema.

Perspectives on neonatal hypoxia/ischemia-induced edema formation

Neonatal hypoxia/ischemia (HI) is the most common cause of developmental neurological, cognitive and behavioral deficits in children, with hyperoxia (HHI) treatment being a clinical therapy for newborn resuscitation. Although cerebral edema is a common outcome after HI, the mechanisms leading to excessive fluid accumulation in the brain are poorly understood. Given the rigid nature of the bone-encased brain matter, knowledge of edema formation in the brain as a consequence of any injury, as well as the importance of water clearance mechanisms and water and ion homeostasis is important to our understanding of its detrimental effects. Knowledge of the pathological process underlying the appearance of dysfunctional outcomes after development of cerebral edema after neonatal HI in the developing brain and the molecular events triggered will allow a rational assessment of HHI therapy for neonatal HI and determine whether this treatment is beneficial or harmful to the developing infant.

Immunohistochemical examination of intracerebral aquaporin-4 expression and its application for differential diagnosis between freshwater and saltwater drowning

Human brain samples were collected from 70 autopsy cases including 22 freshwater drowning (FWD), 26 saltwater drowning (SWD), and 22 non-drowning cases as controls. Then, immunohistochemical study combined with morphometry was carried out in order to examine the differential expression of AQP1 and AQP4 in the brain samples. Immunohistochemically, star-shaped cells bearing highly branched processes, often surrounding blood vessels, showed positive reactions for AQP1 and AQP4 in FWD, SWD, as well as control groups. Additionally, with double-color immunofluorescence analysis, AQP1- or AQP4-positive cells could be identified as GFAP-positive astrocytes. Moreover, AQP1-positive reaction was also observed in blood vessels. Morphometrically, there were no significant differences in AQP1 expression in astrocytes or in blood vessels among the three groups. In contrast, the average value of AQP4-positive astrocytes was significantly higher in FWD cases than in SWD and control groups. Moreover, AQP4 expression was significantly lower in SWD than in the control group (p < 0.05). Moreover, there was no significant correlation between post-submerged interval and AQP expression in drowning cases. Therefore, immunohistochemical analysis of intracerebral AQP4 expression would be forensically useful for differentiation between FWD and SWD.

Aquaporins: relevance to cerebrospinal fluid physiology and therapeutic potential in hydrocephalus

The discovery of a family of membrane water channel proteins called aquaporins, and the finding that aquaporin 1 was located in the choroid plexus, has prompted interest in the role of aquaporins in cerebrospinal fluid (CSF) production and consequently hydrocephalus. While the role of aquaporin 1 in choroidal CSF production has been demonstrated, the relevance of aquaporin 1 to the pathophysiology of hydrocephalus remains debated. This has been further hampered by the lack of a non-toxic specific pharmacological blocking agent for aquaporin 1. In recent times aquaporin 4, the most abundant aquaporin within the brain itself, which has also been shown to have a role in brain water physiology and relevance to brain oedema in trauma and tumours, has become an alternative focus of attention for hydrocephalus research. This review summarises current knowledge and concepts in relation to aquaporins, specifically aquaporin 1 and 4, and hydrocephalus. It also examines the relevance of aquaporins as potential therapeutic targets in hydrocephalus and other CSF circulation disorders.