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

Diacerein ameliorates thioacetamide-induced hepatic encephalopathy in rats via modulation of TLR4/AQP4/MMP-9 axis

Astrocyte swelling, blood brain barrier (BBB) dissipation and the subsequent brain edema are serious consequences of persistent hyperammonemia in hepatic encephalopathy (HE) in which if inadequately controlled it will lead to brain death. The current study highlights the potential neuroprotective effect of diacerein against thioacetamide (TAA)-induced HE in acute liver failure rat model. HE was induced in male Sprague-Dawley rats via I.P. injection of TAA (200 mg/kg) for three alternative times/week at 3rd week of the experiment. Diacerein (50 mg/kg) was gavaged for 14 days prior to induction of HE and for further 7 days together with TAA injection for an overall period of 21 days. Diacerein attenuated TAA-induced HE in acute liver failure rat model; as proofed by significant lowering of serum and brain ammonia concentrations, serum AST and ALT activities and significant attenuation of both brain and hepatic MDA contents and IL-1β with marked increases in GSH contents (P < 0.0001). The neuroprotective effect of diacerein was demonstrated by marked improvement of motor and cognitive deficits, brain histopathological changes; hallmarks of HE. As shown by immunohistochemical results, diacerein markedly downregulated brain TLR4 expression which in turn significantly increased the GFAP expression, and significantly decreased AQP4 expression; the astrocytes swelling biomarkers (P < 0.0001). Moreover, diacerein preserved BBB integrity via downregulation of MMP-9 mediated digestion of tight junction proteins such as occludin (P < 0.0001). Collectively, diacerein ameliorated cerebral edema and maintained BBB integrity via modulation of TLR4/AQP4/MMP-9 axis thus may decrease the progression of HE induced in acute liver failure.

CB1 Receptor Activation Provides Neuroprotection in an Animal Model of Glutamate-Induced Excitotoxicity Through a Reduction of NOX-2 Activity and Oxidative Stress

BACKGROUND

Excitotoxicity is a process in which NADPH oxidase-2 (NOX-2) plays a pivotal role in the generation of reactive oxygen species (ROS). Oxidative stress influences the expression of Aquaporin 4 (AQP4), a water channel implicated in blood-brain barrier (BBB) permeability and edema formation. The endocannabinoid system is widely distributed in the brain, particularly through the cannabinoid receptor type 1 (CB1) and type 2 (CB2), which have been shown to have a neuroprotective function in brain injury. Given the significant involvement of NOX-2 in ROS production during excitotoxicity, our research aims to assess the participation of NOX-2 in the neuroprotective effect of the cannabinoid receptor agonist WIN55,212-2 against glutamate-induced excitotoxicity damage in the striatum using in vivo model.

METHODS

Wild-type mice (C57BL/6) and NOX-2 KO (gp91Cybbtm1Din/J) were stereotactically injected in the striatum with monosodium glutamate or vehicle. Subsequently, a group of mice was administered an intraperitoneal dose of WIN55,212-2, AM251, or AM251/WIN55,212-2 following the intracerebral injection. Motor activity was assessed, and the lesion was examined through histological sections stained with cresyl violet. Additionally, brain water content and Evans blue assay were conducted. The activity of NOX was quantified, and the protein expression of CB1, gp91phox, AQP4, Iba-1, TNF-α, and NF-κB was analyzed using Western blot. Furthermore, ROS formation was measured through the DHE assay.

RESULTS

The activation of the endocannabinoid receptors demonstrated a neuroprotective response during excitotoxicity, meditated by NOX-2. The reduction in ROS production led to a decrease in neuroinflammation, and AQP4 expression, resulting in reduced edema formation, and BBB permeability.

CONCLUSIONS

During excitotoxic damage, WIN55,212-2 inhibits NOX-2-induced ROS production, reducing brain injury.

Improvement of neuronal and cognitive functions following treatment with 3',4' dihydroxyflavonol in experimental focal cerebral ischemia-reperfusion injury in rats

INTRODUCTION

Ischemia/reperfusion is a pathological condition by the restoration of perfusion and oxygenation following a period of restricted blood flow to an organ. To address existing uncertainty in the literature regarding the effects of 3', 4'-dihydroxy flavonol (DiOHF) on cerebral ischemia/reperfusion injury, our study aims to investigate the impact of DiOHF on neurological parameters, apoptosis (Caspase-3), aquaporin 4 (AQP4), and interleukin-10 (IL-10) levels in an experimental rat model of brain ischemia-reperfusion injury.

MATERIALS/METHODS

A total of 28 Wistar-albino male rats were used in this study. Experimental groups were formed as 1-Control, 2-Sham, 3-Ischemia-reperfusion, 4-Ischemia-reperfusion + DiOHF (10 mg/kg). The animals were anaesthetized, and the carotid arteries were ligated (ischemia) for 30 min, followed by reperfusion for 30 min. Following reperfusion, DiOHF was administered intraperitoneally to the animals at a dose of 10 mg/kg for 1 week. During the one-week period neurological scores and new object recognition tests were performed. Then, caspase 3 and AQP4 levels were determined by PCR method and IL-10 by ELISA method in hippocampus tissue samples taken from animals sacrificed under anaesthesia.

RESULTS

Brain ischemia reperfusion significantly increased both caspase 3 and AQP4 values in the hippocampus tissue, while decreasing IL-10 levels. However, 1-week DiOHF supplementation significantly suppressed increased caspase 3 and AQP4 levels and increased IL-10 values. While I/R also increased neurological score values, it suppressed the ability to recognize new objects, and the administered treatment effectively ameliorated the adverse effects observed, resulting in a positive outcome.

CONCLUSIONS

The results of the study show that brain ischemia caused by bilateral carotid occlusion in rats and subsequent reperfusion causes tissue damage, but 1-week DiOHF application has a healing effect on both hippocampus tissue and neurological parameters.

A role for astrocytic insulin-like growth factor I receptors in the response to ischemic insult

Increased neurotrophic support, including insulin-like growth factor I (IGF-I), is an important aspect of the adaptive response to ischemic insult. However, recent findings indicate that the IGF-I receptor (IGF-IR) in neurons plays a detrimental role in the response to stroke. Thus, we investigated the role of astrocytic IGF-IR on ischemic insults using tamoxifen-regulated Cre deletion of IGF-IR in glial fibrillary acidic protein (GFAP) astrocytes, a major cellular component in the response to injury. Ablation of IGF-IR in astrocytes (GFAP-IGF-IR KO mice) resulted in larger ischemic lesions, greater blood-brain-barrier disruption and more deteriorated sensorimotor coordination. RNAseq detected increases in inflammatory, cell adhesion and angiogenic pathways, while the expression of various classical biomarkers of response to ischemic lesion were significantly increased at the lesion site compared to control littermates. While serum IGF-I levels after injury were decreased in both control and GFAP-IR KO mice, brain IGF-I mRNA expression show larger increases in the latter. Further, greater damage was also accompanied by altered glial reactivity as reflected by changes in the morphology of GFAP astrocytes, and relative abundance of ionized calcium binding adaptor molecule 1 (Iba 1) microglia. These results suggest a protective role for astrocytic IGF-IR in the response to ischemic injury.

Cinnamaldehyde/lactulose combination therapy alleviates thioacetamide-induced hepatic encephalopathy via targeting P2X7R-mediated NLRP3 inflammasome signaling

AIMS

Cinnamaldehyde (CA), the main active constituent of cinnamon oil, is reported to have neuroprotective effects. However, the potential benefits of CA for brain protection in hepatic encephalopathy (HE) are still not understood. Thus, the present study investigates the possible ameliorative effect of CA (70 mg/kg/day, I.P.) either alone or in combination with lactulose (Lac) (5.3 g/kg/day, oral) against thioacetamide (TAA)-induced hepatic encephalopathy in rats.

MATERIALS AND METHODS

For induction of HE, TAA (200 mg/kg) was intraperitoneally administered for 1 week at alternative days. CA, Lac and Lac+CA were administered for 14 days prior to and for further 7 days together with TAA injection.

KEY FINDINGS

CA, Lac and Lac+CA combination effectively attenuated TAA-induced HE; as indicated by the improvement in behavioral tests, mitigation of pathological abnormalities in both liver and brain, the significant reduction in serum hyperammonemia and amelioration in liver function biomarkers; ALT and AST. This was accompanied with a substantial restoration of redox state in liver and brain; MDA and GSH levels. Moreover, CA, Lac and Lac+CA combination reduced neuroinflammation as demonstrated by the notable attenuation of P2X7R, NLRP3, caspase-1, IL-1β, GFAP and Iba1 brain levels, as well as the amelioration of brain edema as manifested by reduction in AQP4 levels in brain.

SIGNIFICANCE

Our study has demonstrated that CA in combination with Lac possesses a superior neuroprotective effect over Lac alone against TAA-induced HE by attenuation of P2X7R/NLRP3 mediated neuroinflammation and relieving brain edema.

(S)-roscovitine, a CDK inhibitor, decreases cerebral edema and modulates AQP4 and α1-syntrophin interaction on a pre-clinical model of acute ischemic stroke

Cerebral edema is one of the deadliest complications of ischemic stroke for which there is currently no pharmaceutical treatment. Aquaporin-4 (AQP4), a water-channel polarized at the astrocyte endfoot, is known to be highly implicated in cerebral edema. We previously showed in randomized studies that (S)-roscovitine, a cyclin-dependent kinase inhibitor, reduced cerebral edema 48 h after induction of focal transient ischemia, but its mechanisms of action were unclear. In our recent blind randomized study, we confirmed that (S)-roscovitine was able to reduce cerebral edema by 65% at 24 h post-stroke (t test, p = .006). Immunofluorescence analysis of AQP4 distribution in astrocytes revealed that (S)-roscovitine decreased the non-perivascular pool of AQP4 by 53% and drastically increased AQP4 clusters in astrocyte perivascular end-feet (671%, t test p = .005) compared to vehicle. Non-perivascular and clustered AQP4 compartments were negatively correlated (R = -0.78; p < .0001), suggesting a communicating vessels effect between the two compartments. α1-syntrophin, AQP4 anchoring protein, was colocalized with AQP4 in astrocyte endfeet, and this colocalization was maintained in ischemic area as observed on confocal microscopy. Moreover, (S)-roscovitine increased AQP4/α1-syntrophin interaction (40%, MW p = .0083) as quantified by proximity ligation assay. The quantified interaction was negatively correlated with brain edema in both treated and placebo groups (R = -.57; p = .0074). We showed for the first time, that a kinase inhibitor modulated AQP4/α1-syntrophin interaction, and was implicated in the reduction of cerebral edema. These findings suggest that (S)-roscovitine may hold promise as a potential treatment for cerebral edema in ischemic stroke and as modulator of AQP4 function in other neurological diseases.

From Homeostasis to Pathology: Decoding the Multifaceted Impact of Aquaporins in the Central Nervous System

Aquaporins (AQPs), integral membrane proteins facilitating selective water and solute transport across cell membranes, have been the focus of extensive research over the past few decades. Particularly noteworthy is their role in maintaining cellular homeostasis and fluid balance in neural compartments, as dysregulated AQP expression is implicated in various degenerative and acute brain pathologies. This article provides an exhaustive review on the evolutionary history, molecular classification, and physiological relevance of aquaporins, emphasizing their significance in the central nervous system (CNS). The paper journeys through the early studies of water transport to the groundbreaking discovery of Aquaporin 1, charting the molecular intricacies that make AQPs unique. It delves into AQP distribution in mammalian systems, detailing their selective permeability through permeability assays. The article provides an in-depth exploration of AQP4 and AQP1 in the brain, examining their contribution to fluid homeostasis. Furthermore, it elucidates the interplay between AQPs and the glymphatic system, a critical framework for waste clearance and fluid balance in the brain. The dysregulation of AQP-mediated processes in this system hints at a strong association with neurodegenerative disorders such as Parkinson's Disease, idiopathic normal pressure hydrocephalus, and Alzheimer's Disease. This relationship is further explored in the context of acute cerebral events such as stroke and autoimmune conditions such as neuromyelitis optica (NMO). Moreover, the article scrutinizes AQPs at the intersection of oncology and neurology, exploring their role in tumorigenesis, cell migration, invasiveness, and angiogenesis. Lastly, the article outlines emerging aquaporin-targeted therapies, offering a glimpse into future directions in combatting CNS malignancies and neurodegenerative diseases.

Cellular and molecular mechanisms in vascular repair after traumatic brain injury: a narrative review

Traumatic brain injury (TBI) disrupts normal brain function and is associated with high morbidity and fatality rates. TBI is characterized as mild, moderate or severe depending on its severity. The damage may be transient and limited to the dura matter, with only subtle changes in cerebral parenchyma, or life-threatening with obvious focal contusions, hematomas and edema. Blood vessels are often injured in TBI. Even in mild TBI, dysfunctional cerebral vascular repair may result in prolonged symptoms and poor outcomes. Various distinct types of cells participate in vascular repair after TBI. A better understanding of the cellular response and function in vascular repair can facilitate the development of new therapeutic strategies. In this review, we analyzed the mechanism of cerebrovascular impairment and the repercussions following various forms of TBI. We then discussed the role of distinct cell types in the repair of meningeal and parenchyma vasculature following TBI, including endothelial cells, endothelial progenitor cells, pericytes, glial cells (astrocytes and microglia), neurons, myeloid cells (macrophages and monocytes) and meningeal lymphatic endothelial cells. Finally, possible treatment techniques targeting these unique cell types for vascular repair after TBI are discussed.

Classification of brain lesions using a machine learning approach with cross-sectional ADC value dynamics

Diffusion-weighted imaging (DWI) and its numerical expression via apparent diffusion coefficient (ADC) values are commonly utilized in non-invasive assessment of various brain pathologies. Although numerous studies have confirmed that ADC values could be pathognomic for various ring-enhancing lesions (RELs), their true potential is yet to be exploited in full. The article was designed to introduce an image analysis method allowing REL recognition independently of either absolute ADC values or specifically defined regions of interest within the evaluated image. For this purpose, the line of interest (LOI) was marked on each ADC map to cross all of the RELs' compartments. Using a machine learning approach, we analyzed the LOI between two representatives of the RELs, namely, brain abscess and glioblastoma (GBM). The diagnostic ability of the selected parameters as predictors for the machine learning algorithms was assessed using two models, the k-NN model and the SVM model with a Gaussian kernel. With the k-NN machine learning method, 80% of the abscesses and 100% of the GBM were classified correctly at high accuracy. Similar results were obtained via the SVM method. The proposed assessment of the LOI offers a new approach for evaluating ADC maps obtained from different RELs and contributing to the standardization of the ADC map assessment.

Alteration of Aquaporins 1 and 4 immunohistochemical and gene expression in the cerebellum of diabetic albino rat

Aquaporins (AQPs) are a family of transmembrane channel proteins. AQP1 and AQP4 are expressed in cerebellum amongst others. This study was designed to assess the effect of diabetes on AQP1 and AQP4 expression in cerebellum of rats. Diabetes was induced by a single intraperitoneal injection of Streptozotocin 45 mg/kg in 24 adult male Sprague Dawley rats. Six rats from control and diabetic groups were sacrificed at one, four, and eight weeks post diabetic confirmation. After eight weeks, measurement of malondialdehyde (MDA), reduced glutathione (GSH) concentrations, and cerebellar mRNA expression for AQP1 and AQP4 genes were performed. Immunohistochemical evaluation of AQP1, AQP4, and glial fibrillary acidic protein (GFAP) for cerebellar sections was performed for all groups. Diabetes caused degenerative changes in Purkinje cells with a significant increase in the cerebellar level of MDA and AQP1 immunoreactivity and a significant decrease in GSH level and AQP4 expression levels. However, the alteration in the AQP1 mRNA level was not statistically significant. GFAP immunoreactivity was increased in 8 W diabetic rats following its decrease in 1 W diabetic rats. Diabetes caused some alteration in the AQPs 1 and 4 expression in the cerebellum of diabetic rats which may contribute to diabetes-induced cerebellar complications.

Aquaporins in Nervous System

Aquaporins (AQPs) mediate water flux between the four distinct water compartments in the central nervous system (CNS). In the present chapter, we mainly focus on the expression and function of the nine AQPs expressed in the CNS, which include five members of aquaporin subfamily: AQP1, AQP4, AQP5, AQP6, and AQP8; three members of aquaglyceroporin subfamily: AQP3, AQP7, and AQP9; and one member of superaquaporin subfamily: AQP11. In addition, AQP1, AQP2, and AQP4 expressed in the peripheral nervous system are also reviewed. AQP4, the predominant water channel in the CNS, is involved both in the astrocyte swelling of cytotoxic edema and the resolution of vasogenic edema and is of pivotal importance in the pathology of brain disorders such as neuromyelitis optica, brain tumors, and neurodegenerative disorders. Moreover, AQP4 has been demonstrated as a functional regulator of recently discovered glymphatic system that is a main contributor to clearance of toxic macromolecule from the brain. Other AQPs are also involved in a variety of important physiological and pathological process in the brain. It has been suggested that AQPs could represent an important target in treatment of brain disorders like cerebral edema. Future investigations are necessary to elucidate the pathological significance of AQPs in the CNS.

Dual-modal in vivo assessment for electrophysical and hemodynamic characteristics of cerebral edema induced by lipopolysaccharide

The pathological features of cerebral edema are complicated. The intracranial pressure (ICP) is regarded as the most important indicator for monitoring cerebral edema. Recently, multi-parameter has been used to explore the types and pathogenesis of cerebral edema and design effective treatment strategies. This research focused on investigating the characteristic of the cerebral edema induced by lipopolysaccharide (LPS) in rats by using simultaneous electrophysical and hemodynamic parameters. The results showed that neurophysiologic parameters (firing rate (FR) and the power spectrum of local field potential (LFP power)) and hemodynamic parameters (relative concentration of oxygenated hemoglobin (ΔCHbO2), relative concentration of deoxyhemoglobin ΔCHbR) and relative cerebral blood flow (rCBF)) were linearly correlated, and the Pearson’s correlation coefficient was changed by pathological progression of cerebral edema induced by LPS. Furtherly, the treatment after two agents were observed successfully through these multi-parameters. Our findings revealed the relationship between neural activity and hemodynamic response during the progression of cerebral edema and provided a multi-parameter solution for cerebral edema functional monitoring and anti-edema drug efficacy evaluation.

Progress on Brain and Ocular Lymphatic System

In recent years, 2 major discoveries have modified the traditional understanding of the brain. First, meningeal lymphatic vessels (MLV) were found in the dural sinus, which may absorb and drain cerebrospinal fluid (CSF). Second, the glymphatic system was discovered, composed of para-arterial CSF influx channel, paravenous interstitial fluid (ISF) efflux channel, and the water channel aquaporin-4 (AQP4) in astrocytes connecting the 2 channels. Accumulating evidence demonstrates that the lymphatic system of the brain plays a vital role within the circulation of CSF and, therefore, in the removal of metabolites. Therefore, it is involved in the incidence and development of some central nervous system (CNS) diseases. The optic nerve and retina are the extension of the CNS in the orbit. Whether they have a lymphatic system and how they clear the metabolites of the optic nerve and retina are still unclear. Recent studies have found that the ocular lymphatic system has a crucial impact on bounding eye diseases, like disorders of the optic nerve and retina. Therefore, here we review the recent research progress concerning the structure and function of MLV and glymphatic system. We also discuss the biomarkers for identification of lymphatic vessels, the composition of ocular lymphatic systems, and the possible association with diseases.

What are we measuring? A refined look at the process of disrupted autoregulation and the limitations of cerebral perfusion pressure in preventing secondary injury after traumatic brain injury

The cerebral perfusion pressure (CPP) and its relationship between intracranial pressure and mean arterial pressure is a concept ubiquitous in caring for the critically ill patient. CPP is often used as a surrogate measure for cerebral blood flow (CBF); however, this view fails to account for changes in cerebral vascular resistance (CVR). Changes in CVR occur due to cerebral autoregulation, which has classically been taught on a sigma shaped curve with a decline and increase at either end of a plateau. Historically, the conceptualized regulation maintains careful homeostatic levels despite external or internal dynamic changes; however, moderate and severe traumatic brain injury (TBI) has been postulated to bring about cerebral autoregulation dysfunction. We review the current application of CPP is limited by the dynamic changes in cerebral autoregulation after TBI. This review highlights CPP's role as a surrogate measure for CBF and the inherent limitations of current clinical management, due to the lack of monitoring capable of capture continuous variables to assist real-time decision making. This review evaluates the known literature and introduces topics for discussion that warrant further investigation via pre-clinical and clinical experimentation.

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

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

Emerging roles for dynamic aquaporin-4 subcellular relocalization in CNS water homeostasis

Aquaporin channels facilitate bidirectional water flow in all cells and tissues. AQP4 is highly expressed in astrocytes. In the CNS, it is enriched in astrocyte endfeet, at synapses, and at the glia limitans, where it mediates water exchange across the blood-spinal cord and blood-brain barriers (BSCB/BBB), and controls cell volume, extracellular space volume, and astrocyte migration. Perivascular enrichment of AQP4 at the BSCB/BBB suggests a role in glymphatic function. Recently, we have demonstrated that AQP4 localization is also dynamically regulated at the subcellular level, affecting membrane water permeability. Ageing, cerebrovascular disease, traumatic CNS injury, and sleep disruption are established and emerging risk factors in developing neurodegeneration, and in animal models of each, impairment of glymphatic function is associated with changes in perivascular AQP4 localization. CNS oedema is caused by passive water influx through AQP4 in response to osmotic imbalances. We have demonstrated that reducing dynamic relocalization of AQP4 to the BSCB/BBB reduces CNS oedema and accelerates functional recovery in rodent models. Given the difficulties in developing pore-blocking AQP4 inhibitors, targeting AQP4 subcellular localization opens up new treatment avenues for CNS oedema, neurovascular and neurodegenerative diseases, and provides a framework to address fundamental questions about water homeostasis in health and disease.

Cerebral Microcirculation, Perivascular Unit, and Glymphatic System: Role of Aquaporin-4 as the Gatekeeper for Water Homeostasis

In the past, water homeostasis of the brain was understood as a certain quantitative equilibrium of water content between intravascular, interstitial, and intracellular spaces governed mostly by hydrostatic effects i.e., strictly by physical laws. The recent achievements in molecular bioscience have led to substantial changes in this regard. Some new concepts elaborate the idea that all compartments involved in cerebral fluid homeostasis create a functional continuum with an active and precise regulation of fluid exchange between them rather than only serving as separate fluid receptacles with mere passive diffusion mechanisms, based on hydrostatic pressure. According to these concepts, aquaporin-4 (AQP4) plays the central role in cerebral fluid homeostasis, acting as a water channel protein. The AQP4 not only enables water permeability through the blood-brain barrier but also regulates water exchange between perivascular spaces and the rest of the glymphatic system, described as pan-cerebral fluid pathway interlacing macroscopic cerebrospinal fluid (CSF) spaces with the interstitial fluid of brain tissue. With regards to this, AQP4 makes water shift strongly dependent on active processes including changes in cerebral microcirculation and autoregulation of brain vessels capacity. In this paper, the role of the AQP4 as the gatekeeper, regulating the water exchange between intracellular space, glymphatic system (including the so-called neurovascular units), and intravascular compartment is reviewed. In addition, the new concepts of brain edema as a misbalance in water homeostasis are critically appraised based on the newly described role of AQP4 for fluid permeation. Finally, the relevance of these hypotheses for clinical conditions (including brain trauma and stroke) and for both new and old therapy concepts are analyzed.

Exploring cell membrane water exchange in aquaporin-4-deficient ischemic mouse brain using diffusion-weighted MRI

BACKGROUND

Aquaporin-4 is a membrane channel protein that is highly expressed in brain astrocytes and facilitates the transport of water molecules. It has been suggested that suppression of aquaporin-4 function may be an effective treatment for reducing cellular edema after cerebral infarction. It is therefore important to develop clinically applicable measurement systems to evaluate and better understand the effects of aquaporin-4 suppression on the living body.

METHODS

Animal models of focal cerebral ischemia were created by surgically occluding the middle cerebral artery of wild-type and aquaporin-4 knockout mice, after which multi-b-value multi-diffusion-time diffusion-weighted imaging measurements were performed. Data were analyzed with both the apparent diffusion coefficient (ADC) model and a compartmental water-exchange model.

RESULTS

ADCs were estimated for five different b value ranges. The ADC of aquaporin-4 knockout mice in the contralateral region was significantly higher than that of wild-type mice for each range. In contrast, aquaporin-4 knockout mice had significantly lower ADC than wild-type mice in ischemic tissue for each b-value range. Genotype-dependent differences in the ADC were particularly significant for the lowest ranges in normal tissue and for the highest ranges in ischemic tissue. The ADCs measured at different diffusion times were significantly different for both genotypes. Fitting of the water-exchange model to the ischemic region data found that the water-exchange time in aquaporin-4 knockout mice was approximately 2.5 times longer than that in wild-type mice.

CONCLUSIONS

Multi-b-value multi-diffusion-time diffusion-weighted imaging may be useful for in vivo research and clinical diagnosis of aquaporin-4-related diseases.

Potentially Detrimental Effects of Hyperosmolality in Patients Treated for Traumatic Brain Injury

Hyperosmotic therapy is commonly used to treat intracranial hypertension in traumatic brain injury patients. Unfortunately, hyperosmolality also affects other organs. An increase in plasma osmolality may impair kidney, cardiac, and immune function, and increase blood-brain barrier permeability. These effects are related not only to the type of hyperosmotic agents, but also to the level of hyperosmolality. The commonly recommended osmolality of 320 mOsm/kg H2O seems to be the maximum level, although an increase in plasma osmolality above 310 mOsm/kg H2O may already induce cardiac and immune system disorders. The present review focuses on the adverse effects of hyperosmolality on the function of various organs.

Cerebral Edema Formation After Stroke: Emphasis on Blood-Brain Barrier and the Lymphatic Drainage System of the Brain

Brain edema is a severe stroke complication that is associated with prolonged hospitalization and poor outcomes. Swollen tissues in the brain compromise cerebral perfusion and may also result in transtentorial herniation. As a physical and biochemical barrier between the peripheral circulation and the central nervous system (CNS), the blood–brain barrier (BBB) plays a vital role in maintaining the stable microenvironment of the CNS. Under pathological conditions, such as ischemic stroke, the dysfunction of the BBB results in increased paracellular permeability, directly contributing to the extravasation of blood components into the brain and causing cerebral vasogenic edema. Recent studies have led to the discovery of the glymphatic system and meningeal lymphatic vessels, which provide a channel for cerebrospinal fluid (CSF) to enter the brain and drain to nearby lymph nodes and communicate with the peripheral immune system, modulating immune surveillance and brain responses. A deeper understanding of the function of the cerebral lymphatic system calls into question the known mechanisms of cerebral edema after stroke. In this review, we first discuss how BBB disruption after stroke can cause or contribute to cerebral edema from the perspective of molecular and cellular pathophysiology. Finally, we discuss how the cerebral lymphatic system participates in the formation of cerebral edema after stroke and summarize the pathophysiological process of cerebral edema formation after stroke from the two directions of the BBB and cerebral lymphatic system.

Function of Astrocytes in Neuroprotection and Repair after Ischemic Stroke

BACKGROUND

Astrocytes are the most numerous cell types within the central nervous system, and many efforts have been put into determining the exact role of astrocytes in neuroprotection and repair after ischemic stroke. Although numerous studies have been done in recent years, there is still no thorough understanding of the exact function of astrocytes in the whole course of the stroke.

SUMMARY

According to the recent literature, there are many structures and factors that play important roles in the process of ischemic stroke, among which blood-brain barrier, various growth factors, gap junctions, AQP4, and glial scars have been studied most comprehensively, and all these factors are closely related to astrocytes. The role of astrocytes in ischemic stroke, therefore, can be analyzed more comprehensively. Key Message: The present review mainly summarized the current knowledge about astrocytes and their potential roles after ischemic stroke.

Ligands of the Neuropeptide Y Y2 Receptors as a Potential Multitarget Therapeutic Approach for the Protection of the Neurovascular Unit Against Acute Ischemia/Reperfusion: View from the Perspective of the Laboratory Bench

Ischemic stroke is the third leading cause of death and disability worldwide, with no available satisfactory prevention or treatment approach. The current treatment is limited to the use of “reperfusion methods,” i.e., an intravenous or intra-arterial infusion of a fibrinolytic agent, mechanical removal of the clot by thrombectomy, or a combination of both methods. It should be stressed, however, that only approximately 5% of all acute strokes are eligible for fibrinolytic treatment and fewer than 10% for thrombectomy. Despite the tremendous progress in understanding of the pathomechanisms of cerebral ischemia, the promising results of basic research on neuroprotection are not currently transferable to human stroke. A possible explanation for this failure is that experiments on in vivo animal models involve healthy young animals, and the experimental protocols seldom consider the importance of protecting the whole neurovascular unit (NVU), which ensures intracranial homeostasis and is seriously damaged by ischemia/reperfusion. One of the endogenous protective systems activated during ischemia and in neurodegenerative diseases is represented by neuropeptide Y (NPY). It has been demonstrated that activation of NPY Y2 receptors (Y2R) by a specific ligand decreases the volume of the postischemic infarction and improves performance in functional tests of rats with arterial hypertension subjected to middle cerebral artery occlusion/reperfusion. This functional improvement suggests the protection of the NVU. In this review, we focus on NPY and discuss the potential, multidirectional protective effects of Y2R agonists against acute focal ischemia/reperfusion injury, with special reference to the NVU.

Role of the noninvasive imaging techniques in monitoring and understanding the evolution of brain edema

Human brain injury elicits accumulation of water within the brain due to a variety of pathophysiological processes. As our understanding of edema emerged two temporally (and cellular) distinct processes were identified, cytotoxic and vasogenic edema. The emergence of both types of edema is reflected by the temporal evolution and is influenced by the underlying pathology (type and extent). However, this two-edema compartment model does not adequately describe the transition between cytotoxic and vasogenic edema. Hence, a third category has been proposed, termed ionic edema, that is observed in the transition between cytotoxic and vasogenic edema. Magnetic resonance neuroimaging of edema today primarily utilizes T2-weighted (T2WI) and diffusion-weighted imaging (DWI). Clinical diagnostics and translational science studies have clearly demonstrated the temporal ability of both T2WI and DWI to monitor edema content and evolution. DWI measures water mobility within the brain reflecting cytotoxic edema. T2WI at later time points when vasogenic edema develops visualizes increased water content in the brain. Clinically relevant imaging modalities, including ultrasound and positron emission tomography, are not typically used to assess edema. In sum, edema imaging is an important cornerstone of clinical diagnostics and translational studies and can guide effective therapeutics manage edema and improve patient outcomes.

The Antiedematous Effect of Exogenous Lactate Therapy in Traumatic Brain Injury: A Physiological and Mechanistic Approach

Background

Sodium lactate (SL) has been described as an efficient therapy in treating raised intracranial pressure (ICP). However, the precise mechanism by which SL reduces intracranial hypertension is not well defined. An antiedematous effect has been proposed but never demonstrated. In this context, the involvement of chloride channels, aquaporins, or K–Cl cotransporters has also been suggested, but these mechanisms have never been assessed when using SL.

Methods

In a rat model of traumatic brain injury (TBI), we compared the effect of SL versus mannitol 20% on ICP, cerebral tissue oxygen pressure, and brain water content. We attempted to clarify the involvement of chloride channels in the antiedematous effects associated with lactate therapy in TBI.

Results

An equimolar single bolus of SL and mannitol significantly reduced brain water content and ICP and improved cerebral tissue oxygen pressure 4 h after severe TBI. The effect of SL on brain water content was much longer than that of mannitol and persisted at 24 h post TBI. Western blot and immunofluorescence staining analyses performed 24 h after TBI revealed that SL infusion is associated with an upregulation of aquaporin 4 and K–Cl cotransporter 2.

Conclusions

SL is an effective therapy for treating brain edema after TBI. This study suggests, for the first time, the potential role of chloride channels in the antiedematous effect induced by exogenous SL.

Potential Therapies for Cerebral Edema After Ischemic Stroke: A Mini Review

Stroke is the leading cause of global mortality and disability. Cerebral edema and intracranial hypertension are common complications of cerebral infarction and the major causes of mortality. The formation of cerebral edema includes three stages (cytotoxic edema, ionic edema, and vasogenic edema), which involve multiple proteins and ion channels. A range of therapeutic agents that successfully target cerebral edema have been developed in animal studies, some of which have been assessed in clinical trials. Herein, we review the mechanisms of cerebral edema and the research progress of anti-edema therapies for use after ischemic stroke.

Neuroprotective Effect of Maternal Resveratrol Supplementation in a Rat Model of Neonatal Hypoxia-Ischemia

Neonatal hypoxia-ischemia (nHI) is a major cause of death or subsequent disabilities in infants. Hypoxia-ischemia causes brain lesions, which are induced by a strong reduction in oxygen and nutrient supply. Hypothermia is the only validated beneficial intervention, but not all newborns respond to it and today no pharmacological treatment exists. Among possible therapeutic agents to test, trans-resveratrol is an interesting candidate as it has been reported to exhibit neuroprotective effects in some neurodegenerative diseases. This experimental study aimed to investigate a possible neuroprotection by resveratrol in rat nHI, when administered to the pregnant rat female, at a nutritional dose. Several groups of pregnant female rats were studied in which resveratrol was added to drinking water either during the last week of pregnancy, the first week of lactation, or both. Then, 7-day old pups underwent a hypoxic-ischemic event. Pups were followed longitudinally, using both MRI and behavioral testing. Finally, a last group was studied in which breastfeeding females were supplemented 1 week with resveratrol just after the hypoxic-ischemic event of the pups (to test the curative rather than the preventive effect). To decipher the molecular mechanisms of this neuroprotection, RT-qPCR and Western blots were also performed on pup brain samples. Data clearly indicated that when pregnant and/or breastfeeding females were supplemented with resveratrol, hypoxic-ischemic offspring brain lesions were significantly reduced. Moreover, maternal resveratrol supplementation allowed to reverse sensorimotor and cognitive deficits caused by the insult. The best recoveries were observed when resveratrol was administered during both gestation and lactation (2 weeks before the hypoxic-ischemic event in pups). Furthermore, neuroprotection was also observed in the curative group, but only at the latest stages examined. Our hypothesis is that resveratrol, in addition to the well-known neuroprotective benefits via the sirtuin’s pathway (antioxidant properties, inhibition of apoptosis), has an impact on brain metabolism, and more specifically on the astrocyte-neuron lactate shuttle (ANLS) as suggested by RT-qPCR and Western blot data, that contributes to the neuroprotective effects.

An Integrated Transcriptome Analysis Reveals IGFBP7 Upregulation in Vasculature in Traumatic Brain Injury

Vasculature plays critical roles in the pathogenesis and neurological repair of traumatic brain injury (TBI). However, how vascular endothelial cells respond to TBI at the molecular level has not been systematically reviewed. Here, by integrating three transcriptome datasets including whole cortex of mouse brain, FACS-sorted mouse brain endothelial cells, and single cell sequencing of mouse brain hippocampus, we revealed the key molecular alteration of endothelial cells characterized by increased Myc targets and Epithelial-Mesenchymal Transition signatures. In addition, immunofluorescence staining of patients’ samples confirmed that IGFBP7 was up-regulated in vasculature in response to TBI. TGFβ1, mainly derived from microglia and endothelial cells, sufficiently induces IGFBP7 expression in cultured endothelial cells, and is significantly upregulated in response to TBI. Our results identified IGFBP7 as a potential biomarker of vasculature in response to TBI, and indicate that TGFβ signaling may contribute to the upregulation of IGFBP7 in the vasculature.

Comparison of equiosmolar doses of 10% hypertonic saline and 20% mannitol for controlling intracranial hypertention in patients with large hemispheric infarction

OBJECTIVE

We conducted this prospective self-crossover controlled trial to compare the efficacy and safety of 10 % hypertonic saline (HS) and 20 % mannitol in doses of similar osmotic burden for the treatment of increased intracranial pressure (ICP) in patients with large hemispheric infarction (LHI).

PATIENTS AND METHODS

Patients with LHI were enrolled from January 2017 to January 2018. We used an alternating treatment protocol to compare the effects of HS with mannitol given for episodes of increased ICP in patients with LHI. Indicators such as ICP, mean arterial pressure (MAP) and cerebral perfusion pressure (CPP) were continuously monitored at regular intervals for 240 min after initiation of infusion. Electrolytes, plasma osmolality and renal functions were measured before and 240 min after initiation of infusion to compare the efficacy and safety of the two drugs.

RESULTS

A total of 49 episodes of increased ICP occurred in 14 patients with LHI, of which 24 were infused with 10 % HS and 25 with 20 % mannitol. Both the treatments were equally effective in reducing ICP (P < 0.01). The differences in the duration and degree of reduction were not significant between the groups (P > 0.05). Although both the osmolar agents decreased MAP, the degree was greater in the mannitol group (P < 0.05) at T120. The increase in CPP was greater in the HS group compared with the mannitol group (P < 0.05) at T120. However, HS was associated with faster heart rate (HR) and higher serum chloride levels (P < 0.05). Changes in serum sodium levels and osmolality were not significant between the groups in spite of being higher in the HS group.

CONCLUSIONS

Both the drugs can serve as first-line agents for treating intracranial hypertension caused by LHI and should be selected rationally according to the differences in efficacy and adverse effects.

Neuroprotective Methodologies of Co-Enzyme Q10 Mediated Brain Hemorrhagic Treatment: Clinical and Pre-Clinical Findings

Cerebral brain hemorrhage is associated with the highest mortality and morbidity despite only constituting approximately 10-15% of all strokes classified into intracerebral and intraventricular hemorrhage where most of the patients suffer from impairment in memory, weakness or paralysis in arms or legs, headache, fatigue, gait abnormality and cognitive dysfunctions. Understanding molecular pathology and finding the worsening cause of hemorrhage will lead to explore the therapeutic interventions that could prevent and cure the disease. Mitochondrial ETC-complexes dysfunction has been found to increase neuroinflammatory cytokines, oxidative free radicals, excitotoxicity, neurotransmitter and energy imbalance that are the key neuropathological hallmarks of cerebral hemorrhage. Coenzyme Q10 (CoQ10), as a part of the mitochondrial respiratory chain can effectively restore these neuronal dysfunctions by preventing the opening of mitochondrial membrane transition pore, thereby counteracting cell death events as well as exerts an anti-inflammatory effect by influencing the expression of NF-kB1 dependent genes thus preventing the neuroinflammation and energy restoration. Due to behavior and biochemical heterogeneity in post cerebral brain hemorrhagic pattern different preclinical autologous blood injection models are required to precisely investigate the forthcoming therapeutic strategies. Despite emerging pre-clinical research and resultant large clinical trials for promising symptomatic treatments, there are very less pharmacological interventions demonstrated to improve post operative condition of patients where intensive care is required. Therefore, in current review, we explore the disease pattern, clinical and pre-clinical interventions under investigation and neuroprotective methodologies of CoQ10 precursors to ameliorate post brain hemorrhagic conditions.

HUCBC Treatment Improves Cognitive Outcome in Rats With Vascular Dementia

Background and purpose: Vascular dementia (VaD) is the second common cause of dementia after Alzheimer's disease in older people. Yet, there are no FDA approved drugs specifically for VaD. In this study, we have investigated the therapeutic effects of human umbilical cord blood cells (HUCBC) treatment on the cognitive outcome, white matter (WM) integrity, and glymphatic system function in rats subject to a multiple microinfarction (MMI) model of VaD. Methods: Male, retired breeder rats were subjected to the MMI model (800 ± 100 cholesterol crystals/300 μl injected into the internal carotid artery), and 3 days later were treated with phosphate-buffered saline (PBS) or HUCBC (5 × 10⁶, i.v.). Sham rats were included as naïve control. Following a battery of cognitive tests, rats were sacrificed at 28 days after MMI and brains extracted for immunohistochemical evaluation and Western blot analysis. To evaluate the glymphatic function, fluorescent tracers (Texas Red dextran, MW: 3 kD and FITC-dextran, MW: 500 kD) was injected into the cisterna magna over 30 min at 14 days after MMI. Rats (3-4/group/time point) were sacrificed at 30 min, 3 h, and 6 h, and the tracer movement analyzed using laser scanning confocal microscopy. Results: Compared to control MMI rats, HUCBC treated MMI rats exhibit significantly improved short-term memory and long-term memory exhibited by increased discrimination index in novel object recognition task with retention delay of 4 h and improved novel odor recognition task with retention delay of 24 h, respectively. HUCBC treatment also improves spatial learning and memory as measured using the Morris water maze test compared to control MMI rats. HUCBC treatment significantly increases axon and myelin density increases oligodendrocyte and oligodendrocyte progenitor cell number and increases Synaptophysin expression in the brain compared to control MMI rats. HUCBC treatment of MMI in rats significantly improves glymphatic function by reversing MMI induced delay in the penetration of cerebrospinal fluid (CSF) into the brain parenchyma via glymphatic pathways and reversing delayed clearance from the brain. HUCBC treatment significantly increases miR-126 expression in serum, aquaporin-4 (AQP4) expression around cerebral vessels, and decreases transforming growth factor-β (TGF-β) protein expression in the brain which may contribute to HUCBC induced improved glymphatic function. Conclusions: HUCBC treatment of an MMI rat model of VaD promotes WM remodeling and improves glymphatic function which together may aid in the improvement of cognitive function and memory. Thus, HUCBC treatment warrants further investigation as a potential therapy for VaD.

Mechanisms of Blood-Brain Barrier Dysfunction in Traumatic Brain Injury

Traumatic brain injuries (TBIs) account for the majority of injury-related deaths in the United States with roughly two million TBIs occurring annually. Due to the spectrum of severity and heterogeneity in TBIs, investigation into the secondary injury is necessary in order to formulate an effective treatment. A mechanical consequence of trauma involves dysregulation of the blood–brain barrier (BBB) which contributes to secondary injury and exposure of peripheral components to the brain parenchyma. Recent studies have shed light on the mechanisms of BBB breakdown in TBI including novel intracellular signaling and cell–cell interactions within the BBB niche. The current review provides an overview of the BBB, novel detection methods for disruption, and the cellular and molecular mechanisms implicated in regulating its stability following TBI.

Traumatic Brain Injury and Blood-Brain Barrier (BBB): Underlying Pathophysiological Mechanisms and the Influence of Cigarette Smoking as a Premorbid Condition

Traumatic brain injury (TBI) is among the most pressing global health issues and prevalent causes of cerebrovascular and neurological disorders all over the world. In addition to the brain injury, TBI may also alter the systemic immune response. Thus, TBI patients become vulnerable to infections, have worse neurological outcomes, and exhibit a higher rate of mortality and morbidity. It is well established that brain injury leads to impairments of the blood-brain barrier (BBB) integrity and function, contributing to the loss of neural tissue and affecting the response to neuroprotective drugs. Thus, stabilization/protection of the BBB after TBI could be a promising strategy to limit neuronal inflammation, secondary brain damage, and acute neurodegeneration. Herein, we present a review highlighting the significant post-traumatic effects of TBI on the cerebrovascular system. These include the loss of BBB integrity and selective permeability, impact on BBB transport mechanisms, post-traumatic cerebral edema formation, and significant pathophysiological factors that may further exacerbate post-traumatic BBB dysfunctions. Furthermore, we discuss the post-traumatic impacts of chronic smoking, which has been recently shown to act as a premorbid condition that impairs post-TBI recovery. Indeed, understanding the underlying molecular mechanisms associated with TBI damage is essential to better understand the pathogenesis and progression of post-traumatic secondary brain injury and the development of targeted treatments to improve outcomes and speed up the recovery process. Therapies aimed at restoring/protecting the BBB may reduce the post-traumatic burden of TBI by minimizing the impairment of brain homeostasis and help to restore an optimal microenvironment to support neuronal repair.

Evolutionary Adaptation of Aquaporin-4 in Yak (Bos grunniens) Brain to High-Altitude Hypoxia of Qinghai-Tibetan Plateau

Background: In high-altitude animals, brain cell resilience against hypoxia stress is one critical evolutionary step that has promoted individual survival and species adaptation to the environment. Aquaporin-4 (AQP4) is implicated in a number of physiopathological processes, particularly in the development of brain edema, and other functions such as the regulation of extracellular space volume, potassium buffering, waste clearance, and calcium signaling. Still, the role of AQP4 in the adaptation to high-altitude hypoxia remains unknown. The yak (Bos grunniens) is the only large mammal that is currently known to have adapted to the high-altitude hypoxic environment of the Qinghai-Tibet Plateau (>4000 m above sea level). Methods: In this study, we cloned the complementary DNA (cDNA) for yak AQP4 and analyzed structural differences of AQP4 between yak and cattle. We used reverse transcription quantitative polymerase chain reaction and western blot to investigate whether the expression of AQP4 mRNA and protein was different in brain of yak and cattle. In addition, immunohistochemistry was use to analyze the localization and expression of AQP4 in brain of yak and cattle. Results: Immunohistochemical results have shown that AQP4 is expressed in many regions of the yak brain, and both protein and messenger RNA (mRNA) levels are significantly lower than those of low-altitude cattle (Bos taurus). Phylogenetic analysis revealed that yak AQP4 is evolutionarily conserved. Interestingly, a substitution of Ala (cattle) to Ser in position 82, and eight additional amino acid residues composing an α-helix region are present in yak AQP4 protein. These sequence modifications potentially modulate the function of AQP4 in distinct environments. Conclusions: Our findings suggest that AQP4 may have an important role in the resistance to cerebral edema through low expression and maintenance of normal physiological function in the yak brain.

Vasopressin V1a Receptors Regulate Cerebral Aquaporin 1 after Traumatic Brain Injury

Brain edema formation contributes to secondary brain damage and unfavorable outcome after traumatic brain injury (TBI). Aquaporins (AQP), highly selective water channels, are involved in the formation of post-trauma brain edema; however, their regulation is largely unknown. Because vasopressin receptors are involved in AQP-mediated water transport in the kidney and inhibition of V1a receptors reduces post-trauma brain edema formation, we hypothesize that cerebral AQPs may be regulated by V1a receptors. Cerebral Aqp1 and Aqp4 messenger ribonucleic acid (mRNA) and AQP1 and AQP4 protein levels were quantified in wild-type and V1a receptor knockout (V1a-/-) mice before and 15 min, 1, 3, 6, 12, or 24 h after experimental TBI by controlled cortical impact. In non-traumatized mice, we found AQP1 and AQP4 expression in cortical neurons and astrocytes, respectively. Experimental TBI had no effect on Aqp4 mRNA or AQP4 protein expression, but increased Aqp1 mRNA (p < 0.05) and AQP1 protein expression (p < 0.05) in both hemispheres. The Aqp1 mRNA and AQP1 protein regulation was blunted in V1a receptor knockout mice. The V1a receptors regulate cerebral AQP1 expression after experimental TBI, thereby unraveling the molecular mechanism by which these receptors may mediate brain edema formation after TBI.

Maternal consumption of piceatannol: A nutritional neuroprotective strategy against hypoxia-ischemia in rat neonates

Hypoxia-ischemia (HI) remains a major cause of perinatal mortality and chronic disability in newborns worldwide (1-6 for 1000 births) with a high risk of future motor, behavioral and neurological deficits. Keeping newborns under moderate hypothermia is the unique therapeutic approach but is not sufficiently successful as nearly 50% of infants do not respond to it. In a 7-day post-natal rat model of HI, we used pregnant and breastfeeding female nutritional supplementation with piceatannol (PIC), a polyphenol naturally found in berries, grapes and passion fruit, as a neuroprotective strategy. Maternal supplementation led to neuroprotection against neonate brain damage and reversed their sensorimotor deficits as well as cognitive impairments. Neuroprotection of per os maternal supplementation with PIC is a preventive strategy to counteract brain damage in pups induced by HI. This nutritional approach could easily be adopted as a preventive strategy in humans.

Noninvasive magnetic resonance imaging stratifies injury severity in a rodent model of male juvenile traumatic brain injury

Age and severity are significant predictors of traumatic brain injury (TBI) outcomes in the immature brain. TBI studies have segregated TBI injury into three severity groups: mild, moderate, and severe. While mild TBI is most frequent form in children and adults, there is debate over the indicators used to denote mild injury. Clinically, magnetic resonance imaging (MRI) and computed tomography (CT) are used to diagnose the TBI severity when medically warranted. Herein, we induced mild, moderate, and severe TBI in juvenile rats (jTBI) using the controlled cortical impact model. We characterized the temporal and spatial injury after graded jTBI in vivo using high-field MRI at 0.25 (6 hr), 1 and 3 days post-injury (dpi) with comparative histology. Susceptibility-weighted imaging (SWI) for blood and T2-weighted imaging (T2WI) for edema were quantified over the 0.25-3 dpi. Edema volumes increased linearly with severity at 0.25 dpi that slowly continued to decrease over the 3 dpi. In contrast, blood volumes did not decrease over time. Mild TBI had the least amount of blood visible on SWI. Fluoro-jade B (FJB) staining for cell death confirmed increased cellular death with increasing severity and increased FJB + cells in the corpus callosum (CC). Interestingly, the strongest correlation was observed for cell death and the presence of extravascular blood. A clear understanding of acute brain injury (jTBI) and how blood/edema contribute to mild, moderate, and severe jTBI is needed prior to embarking on therapeutic interventions. Noninvasive imaging should be used in mild jTBI to verify lack of overt injury.

Bursting at the Seams: Molecular Mechanisms Mediating Astrocyte Swelling

Brain swelling is one of the most robust predictors of outcome following brain injury, including ischemic, traumatic, hemorrhagic, metabolic or other injury. Depending on the specific type of insult, brain swelling can arise from the combined space-occupying effects of extravasated blood, extracellular edema fluid, cellular swelling, vascular engorgement and hydrocephalus. Of these, arguably the least well appreciated is cellular swelling. Here, we explore current knowledge regarding swelling of astrocytes, the most abundant cell type in the brain, and the one most likely to contribute to pathological brain swelling. We review the major molecular mechanisms identified to date that contribute to or mitigate astrocyte swelling via ion transport, and we touch upon the implications of astrocyte swelling in health and disease.

The Expanding Role of Vesicles Containing Aquaporins

In animals and plants, membrane vesicles containing proteins have been defined as key for biological systems involving different processes such as trafficking or intercellular communication. Docking and fusion of vesicles to the plasma membrane occur in living cells in response to different stimuli, such as environmental changes or hormones, and therefore play an important role in cell homeostasis as vehicles for certain proteins or other substances. Because aquaporins enhance the water permeability of membranes, their role as proteins immersed in vesicles formed of natural membranes is a recent topic of study. They regulate numerous physiological processes and could hence serve new biotechnological purposes. Thus, in this review, we have explored the physiological implications of the trafficking of aquaporins, the mechanisms that control their transit, and the proteins that coregulate the migration. In addition, the importance of exosomes containing aquaporins in the cell-to-cell communication processes in animals and plants have been analyzed, together with their potential uses in biomedicine or biotechnology. The properties of aquaporins make them suitable for use as biomarkers of different aquaporin-related diseases when they are included in exosomes. Finally, the fact that these proteins could be immersed in biomimetic membranes opens future perspectives for new biotechnological applications.

Neurovascular unit transport responses to ischemia and common coexisting conditions: smoking and diabetes

Transporters at the neurovascular unit (NVU) are vital for the regulation of normal brain physiology via ion, water, and nutrients movement. In ischemic stroke, the reduction of cerebral blood flow causes several complex pathophysiological changes in the brain, one of which includes alterations of the NVU transporters, which can exacerbate stroke outcome by increased brain edema (by altering ion, water, and glutamate transporters), altered energy metabolism (by altering glucose transporters), and enhanced drug toxicity (by altering efflux transporters). Smoking and diabetes are common risk factors as well as coexisting conditions in ischemic stroke that are also reported to change the expression and function of NVU transporters. Coexistence of these conditions could cause an additive effect in terms of the alterations of brain transporters that might lead to worsened ischemic stroke prognosis and recovery. In this review, we have discussed the effects of ischemic stroke, smoking, and diabetes on some essential NVU transporters and how the simultaneous presence of these conditions can affect the clinical outcome after an ischemic episode. Further scientific investigations are required to elucidate changes in NVU transport in cerebral ischemia, which can lead to better, personalized therapeutic interventions tailor-made for these comorbid conditions.

Aquaporin-4 deletion ameliorates hypoglycemia-induced BBB permeability by inhibiting inflammatory responses

Background

Severe hypoglycemia induces brain edema by upregulating aquaporin-4 (AQP4) expression and by degrading tight junctions. Acute severe hypoglycemia induces a proinflammatory environment that may contribute to a disruption in the epithelial barrier by decreasing tight junction protein expression. Interestingly, the altered AQP4 expression has been considered to play a critical role in neuroinflammation during acute brain injury. It has been shown that AQP4 deletion reduces brain inflammation in AQP4-null mice after intracerebral LPS injection. However, the effect of AQP4 deletion regarding protection against hypoglycemia-induced blood-brain barrier (BBB) breakdown is unknown.

Methods

An acute severe hypoglycemic stress model was established via injection of 4 unit/kg body weight of insulin. Evans blue (EB) staining and water measurement were used to assess BBB permeability. Western blot, reverse transcription polymerase chain reaction, and immunofluorescence were used to detect the expression of related proteins. The production of cytokines was assessed via enzyme-linked immunosorbent assay.

Results

Hypoglycemia-induced brain edema and BBB leakage were reduced in AQP4^−/− mice. AQP4 deletion upregulated PPAR-γ and inhibited proinflammatory responses. Moreover, knockdown of aquaporin-4 by small interfering RNA in astrocytes co-cultured with endothelial cells effectively reduced transendothelial permeability and degradation of tight junctions. Treatment with PPAR-γ inhibitors showed that upregulation of PPAR-γ was responsible for the protective effect of AQP4 deletion under hypoglycemic conditions.

Conclusions

Our data suggest that AQP4 deletion protects BBB integrity by reducing inflammatory responses due to the upregulation of PPAR-γ expression and attenuation of proinflammatory cytokine release. Reduction in AQP4 may be protective in acute severe hypoglycemia.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1203-8) contains supplementary material, which is available to authorized users.

Interstitial ion homeostasis and acid-base balance are maintained in oedematous brain of mice with acute toxic liver failure

Acute toxic liver failure (ATLF) rapidly leads to brain oedema and neurological decline. We evaluated the ability of ATLF-affected brain to control the ionic composition and acid-base balance of the interstitial fluid. ATLF was induced in 10-12 weeks old male C57Bl mice by single intraperitoneal (i.p.) injection of 100 μg/g azoxymethane (AOM). Analyses were carried out in cerebral cortex of precomatous mice 20-24 h after AOM administration. Brain fluid status was evaluated by measuring apparent diffusion coefficient [ADC] using NMR spectroscopy, Evans Blue extravasation, and accumulation of an intracisternally-injected fluorescent tracer. Extracellular pH ([pH]_e) and ([K⁺]_e) were measured in situ with ion-sensitive microelectrodes. Cerebral cortical microdialysates were subjected to photometric analysis of extracellular potassium ([K⁺]_e), sodium ([Na⁺]_e) and luminometric assay of extracellular lactate ([Lac]_e). Potassium transport in cerebral cortical slices was measured ex vivo as ⁸⁶Rb uptake. Cerebral cortex of AOM-treated mice presented decreased ADC supporting the view that ATLF-induced brain oedema is primarily cytotoxic in nature. In addition, increased Evans blue extravasation indicated blood brain barrier leakage, and increased fluorescent tracer accumulation suggested impaired interstitial fluid passage. However, [K⁺]_e, [Na⁺]_e, [Lac]_e, [pH]_e and potassium transport in brain of AOM-treated mice was not different from control mice. We conclude that in spite of cytotoxic oedema and deregulated interstitial fluid passage, brain of mice with ATLF retains the ability to maintain interstitial ion homeostasis and acid-base balance. Tentatively, uncompromised brain ion homeostasis and acid-base balance may contribute to the relatively frequent brain function recovery and spontaneous survival rate in human patients with ATLF.

Recombinant PEP-1-SOD1 improves functional recovery after neural stem cell transplantation in rats with traumatic brain injury

The transplantation of neural stem cells (NSCs) has been demonstrated as a potential treatment strategy for traumatic brain injury (TBI). Cu, Zn-superoxide dismutase (SOD1) is an important antioxidant enzyme that detoxifies intracellular reactive oxygen species, thereby protecting cells from oxidative damage. PEP-1, a peptide carrier, is able to deliver full-length native peptides or proteins into cells. Therefore, the current study investigated the effect of the transplantation of NSCs in combination with PEP-1-SOD1 for the treatment of experimental TBI in rats. Initially, the effect of PEP-1-SOD1 on the proliferation of NSCs was evaluated by MTT assay. PEP-1-SOD1 (0.5, 2.5 and 4.5 µM) significantly increased the proliferation rates of NSCs at 24, 48 and 72 h in a dose-dependent manner. PEP-1-SOD1 also promoted the differentiation of NSCs in vitro. The in vivo experiment showed that PEP-1-SOD1 in combination with NSC transplantation significantly improved the functional recovery of rats following TBI compared with NSC transplantation alone. A significant increase in brain aquaporin-4 (AQP4) mRNA and protein expression levels was observed 4 days post-TBI in PEP-1-SOD1, NSCs and PEP-1-SOD1 + NSCs groups compared with the saline group. The PEP-1-SOD1 + NSCs group showed a further increase of AQP4 mRNA and protein expression levels compared with the NSCs and PEP-1-SOD1 groups. In conclusion, the current data suggests that PEP-1-SOD1 may promote the proliferation and differentiation of NSCs, and thereby improve the functional recovery of TBI model rats following NSCs transplantation through upregulating the expression of AQP4.

Changes in the Expression of AQP4 and AQP9 in the Hippocampus Following Eclampsia-Like Seizure

Eclampsia is a hypertensive disorder of pregnancy that is defined by the new onset of grand mal seizures on the basis of pre-eclampsia. Until now, the mechanisms underlying eclampsia were poorly understood. Brain edema is considered a leading cause of eclamptic seizures; aquaporins (AQP4 and AQP9), the glial water channel proteins mainly expressed in the nervous system, play an important role in brain edema. We studied AQP4 and AQP9 expression in the hippocampus of pre-eclamptic and eclamptic rats in order to explore the molecular mechanisms involved in brain edema. Using our previous animal models, we found several neuronal deaths in the hippocampal CA1 and CA3 regions after pre-eclampsia and that eclampsia induced more neuronal deaths in both areas by Nissl staining. In the current study, RT-PCR and Western blotting data showed significant upregulation of AQP4 and AQP9 mRNA and protein levels after eclamptic seizures in comparison to pre-eclampsia and at the same time AQP4 and AQP9 immunoreactivity also increased after eclampsia. These findings showed that eclamptic seizures induced cell death and that upregulation of AQP4 and AQP9 may play an important role in this pathophysiological process.

Cardiac output changes after osmotic therapy in neurosurgical and neurocritical care patients: a systematic review of the clinical literature

AIM

Osmotherapy constitutes a first-line intervention for intracranial hypertension management. However, hyperosmolar solutes exert various systematic effects, among which their impact on systemic haemodynamics is poorly clarified. This review aims to appraise the clinical evidence of the effect of mannitol and hypertonic saline (HTS) on cardiac performance in neurosurgical and neurocritical care patients.

METHOD

A database search was conducted to identify randomized clinical trials and observational studies reporting HTS or mannitol use in acute brain injury setting. The primary end-points were alterations of cardiac output (CO) and other haemodynamic variables, while the impact of osmotic agents on intracranial pressure, brain relaxation, plasma osmolality, electrolyte levels and urinary output constituted secondary outcomes.

RESULTS

Eight studies, enrolling 182 patients in total, were included. HTS exerted a more profound cardiac output augmentation than mannitol, but no distinct difference between groups occurred. Central venous pressure, stroke volume and stroke volume variation were favourably affected by both osmotic agents, whilst the reported changes in blood pressure were inconclusive. HTS infusion yielded a larger intracranial pressure reduction than mannitol but had an equivalent effect on brain relaxation. Mannitol presented a more potent diuretic effect than HTS. Effect on serum osmolality was alike in both osmotic agents, but contrary to HTS-promoted hypernatraemia, mannitol use induced transient hyponatraemia.

CONCLUSIONS

Mannitol or HTS administration seems to induce an enhancement of cardiac performance; being more prominent after HTS infusion. This effect combined with mannitol-induced enhancement of diuresis and HTS-promoted increase of plasma sodium concentration could partially explain the effects of osmotherapy on cerebral haemodynamics.

Oncotic Cell Death in Stroke

Oncotic cell death or oncosis represents a major mechanism of cell death in ischaemic stroke, occurring in many central nervous system (CNS) cell types including neurons, glia and vascular endothelial cells. In stroke, energy depletion causes ionic pump failure and disrupts ionic homeostasis. Imbalance between the influx of Na⁺ and Cl^- ions and the efflux of K⁺ ions through various channel proteins and transporters creates a transmembrane osmotic gradient, with ensuing movement of water into the cells, resulting in cell swelling and oncosis. Oncosis is a key mediator of cerebral oedema in ischaemic stroke, contributing directly through cytotoxic oedema, and indirectly through vasogenic oedema by causing vascular endothelial cell death and disruption of the blood-brain barrier (BBB). Hence, inhibition of uncontrolled ionic flux represents a novel and powerful strategy in achieving neuroprotection in stroke. In this review, we provide an overview of oncotic cell death in the pathology of stroke. Importantly, we summarised the therapeutically significant pathways of water, Na⁺, Cl^- and K⁺ movement across cell membranes in the CNS and their respective roles in the pathobiology of stroke.

Mechanism of aquaporin 4 (AQP 4) up-regulation in rat cerebral edema under hypobaric hypoxia and the preventative effect of puerarin

AIM

We aim to investigate the mechanism of aquaporin 4 (AQP 4) up-regulation during high-altitude cerebral edema (HACE) in rats under hypobaric hypoxia and preventative effect of puerarin.

METHODS

Rats were exposed to a hypobaric chamber with or without the preventative treatment of puerarin or dexamethasone. Morriz water maze was used to evaluate the spatial memory injury. HE staining and W/D ratio were used to evaluate edema injury. Rat astrocytes and microglia were co-cultured under the condition of hypoxia with the administration of p38 inhibitor, NF-κB inhibitor or puerarin. Interleukin 6 (IL-6) and tumor necrosis factor α (TNF α) of cortex and culture supernatant were measured with ELISA. AQP4, phosphorylation of MAPKs, NF-κB pathway of cortex and astrocytes were measured by Western blot.

KEY FINDINGS

Weakened spatial memory and cerebral edema were observed after hypobaric hypoxia exposure. AQP4, phosphorylation of NF-κB and MAPK signal pathway of cortex increased after hypoxia exposure and decreased with preventative treatment of puerarin. Hypoxia increased TNF-α and IL-6 levels in cortex and microglia and puerarin could prevent the increase of them. AQP4 of astrocytes increased after co-cultured with microglia when both were exposed to hypoxia. AQP4 showed a decrease after administered with p38 inhibitor, NF-κB inhibitor or puerarin.

SIGNIFICANCE

Hypoxia triggers inflammatory response, during which AQP4 of astrocytes can be up regulated through the release of TNF-α and IL-6 from microglia. Puerarin can exert a preventative effect on the increase of AQP4 through inhibiting the release of TNF-α and phosphorylation of NF-κB, MAPK pathway.

Role of NADPH Oxidase as a Mediator of Oxidative Damage in Low-Dose Irradiated and Hindlimb-Unloaded Mice

The purpose of this study was to determine whether nicotinamide adenine dinucleotide phosphate (NADPH) oxidase-derived stress can account for unloading- and radiation-induced endothelial damage and neurovascular remodeling in a mouse model. Wild-type (WT, Nox2^+/+) C57BL/6 mice or Nox2^-/- (B6.129S6-CYBBM) knockout (KO) mice were placed into one of the following groups: age-matched control; hindlimb unloading (HLU); low-dose/low-dose-rate radiation (LDR); or HLU with LDR simultaneously for 21 days. The mice were then sacrificed one month later. Anti-orthostatic tail suspension was used to model the unloading, fluid shift and physiological stress aspects of microgravity. The LDR was delivered using ⁵⁷Co plates (0.04 Gy at 0.01 cGy/h) to the simulate whole-body irradiation, similar to that experienced while in space. Brains were isolated for characterization of various oxidative stress markers and vascular topology. The level of 4-hydroxynonenal (4-HNE) protein, a specific marker for lipid peroxidation, was measured. Expression of aquaporin-4 (AQP4), a water channel protein expressed in astrocyte end-feet, was quantified. Thirty days after simulated spaceflight, KO mice showed decreased apoptosis (P < 0.05) in the brain compared to WT counterparts. The HLU-dependent increase in apoptosis in WT mice was not observed in KO mice. The level of 4-HNE protein was significantly elevated in the hippocampus of the LDR with HLU treatment group compared to WT controls (P < 0.05). However, there were no significant differences among groups of Nox2-KO mice at the one-month time point. In contrast to findings in the WT animals, superoxide dismutase (SOD) level and expression of AQP4 were similar among all KO groups. In summary, for most of the parameters, the oxidative response to HLU and LDR was suppressed in Nox2-KO mice. This suggests that Nox2-containing NADPH oxidase may contribute to spaceflight environment-induced oxidative stress.