Hypertonic Saline Alleviates Brain Edema After Traumatic Brain Injury via Downregulation of Aquaporin 4 in Rats

Fingolimod improves diffuse brain injury by promoting AQP4 polarization and functional recovery of the glymphatic system

BACKGROUND

Diffuse brain injury (DBI) models are characterized by intense global brain inflammation and edema, which characterize the most severe form of TBI. In a previous experiment, we found that fingolimod promoted recovery after controlled cortical impact injury (CCI) by modulating inflammation around brain lesions. However, it remains unclear whether fingolimod can also attenuate DBI because of its different injury mechanisms. Furthermore, whether fingolimod has additional underlying effects on repairing DBI is unknown.

METHODS

The impact acceleration model of DBI was established in adult Sprague-Dawley rats. Fingolimod (0.5 mg/kg) was administered 0.5, 24, and 48 h after injury for 3 consecutive days. Immunohistochemistry, immunofluorescence analysis, cytokine array, and western blotting were used to evaluate inflammatory cells, inflammatory factors, AQP4 polarization, apoptosis in brain cells, and the accumulation of APP after DBI in rats. To evaluate the function of the glymphatic system (GS), a fluorescent tracer was injected into the cistern. The neural function of rats with DBI was evaluated using various tests, including the modified neurological severity score (mNSS), horizontal ladder-crossing test, beam walking test, and tape sensing and removal test. Brain water content was also measured.

RESULTS

Fingolimod administration for 3 consecutive days could reduce the levels of inflammatory cytokines, neutrophil recruitment, microglia, and astrocyte activation in the brain following DBI. Moreover, fingolimod reduced apoptotic protein expression, brain cell apoptosis, brain edema, and APP accumulation. Additionally, fingolimod inhibited the loss of AQP4 polarization, improved lymphatic system function, and reduced damage to nervous system function. Notably, inhibiting the GS weakened the therapeutic effect of fingolimod on the neurological function of rats with DBI and increased the accumulation of APP in the brain.

CONCLUSIONS

In brief, these findings suggest that fingolimod alleviates whole-brain inflammation and GS system damage after DBI and that inhibiting the GS could weaken the positive effect of fingolimod on nerve function in rats with DBI. Thus, inhibiting inflammation and regulating the GS may be critical for the therapeutic effect of fingolimod on DBI.

Multimodal evaluation of the effects of low-intensity ultrasound on cerebral blood flow after traumatic brain injury in mice

Traumatic brain injury (TBI) is one of the leading causes of death and disability worldwide, and destruction of the cerebrovascular system is a major factor in the cascade of secondary injuries caused by TBI. Laser speckle imaging (LSCI)has high sensitivity in detecting cerebral blood flow. LSCI can visually show that transcranial focused ultrasound stimulation (tFUS) treatment stimulates angiogenesis and increases blood flow. To study the effect of tFUS on promoting angiogenesis in Controlled Cortical impact (CCI) model. tFUS was administered daily for 10 min and for 14 consecutive days after TBI. Cerebral blood flow was measured by LSCI at 1, 3, 7 and 14 days after trauma. Functional outcomes were assessed using LSCI and neurological severity score (NSS). After the last test, Nissl staining and vascular endothelial growth factor (VEGF) were used to assess neuropathology. TBI can cause the destruction of cerebrovascular system. Blood flow was significantly increased in TBI treated with tFUS. LSCI, behavioral and histological findings suggest that tFUS treatment can promote angiogenesis after TBI.

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.

Tackling Neuroinflammation After Traumatic Brain Injury: Complement Inhibition as a Therapy for Secondary Injury

Traumatic brain injury (TBI) is a leading cause of mortality, sensorimotor morbidity, and neurocognitive disability. Neuroinflammation is one of the key drivers causing secondary brain injury after TBI. Therefore, attenuation of the inflammatory response is a potential therapeutic goal. This review summarizes the most important neuroinflammatory pathophysiology resulting from TBI and the clinical trials performed to attenuate neuroinflammation. Studies show that non-selective attenuation of the inflammatory response, in the early phase after TBI, might be detrimental and that there is a gap in the literature regarding pharmacological trials targeting specific pathways. The complement system and its crosstalk with the coagulation system play an important role in the pathophysiology of secondary brain injury after TBI. Therefore, regaining control over the complement cascades by inhibiting overshooting activation might constitute useful therapy. Activation of the complement cascade is an early component of neuroinflammation, making it a potential target to mitigate neuroinflammation in TBI. Therefore, we have described pathophysiological aspects of complement inhibition and summarized animal studies targeting the complement system in TBI. We also present the first clinical trial aimed at inhibition of complement activation in the early days after brain injury to reduce the risk of morbidity and mortality following severe TBI.

Study of the mechanism by which MSCs combined with LITUS treatment improve cognitive dysfunction caused by traumatic brain injury

Traumatic brain injury (TBI) substantially affects the quality of life of patients, and an effective therapy is unavailable. Previous studies have shown that mesenchymal stem cells (MSCs) and low-intensity transcranial ultrasound (LITUS) are effective treatments for neurological damage, inflammation, edema and cognitive impairment caused by TBI. However, it is unclear whether the combination of the two treatments exerts an additive effect. In this study, a rat TBI model was established using the controlled cortical impact (CCI) method. Neurological function was assessed by determining the rat modified neurological score (mNSS), and cognitive function was assessed using the Y-maze. Pathological changes in the injured tissue were observed using hematoxylin-eosin (HE) staining and immunohistochemistry (IHC), and western blot was performed to detect the expression levels of Nestin, neuron-specific enolase (NSE), glial fibrillary acidic protein (GFAP), growth-associated protein-43 (GAP-43), postsynaptic density protein (PSD-95), brain-derived neurotrophic factor (BDNF), tumor necrosis factor-α (TNF-α), and aquaporin-4 (AQP-4). Real-time fluorescence quantitative polymerase chain reaction (RT-PCR) was performed to detect the expression levels of GAP-43, PSD-95, BDNF, TNF-α, and AQP-4 mRNA to investigate whether MSCs combined with LITUS exert an additive therapeutic effect of alleviating the cognitive dysfunction caused by TBI and the possible mechanisms involved. Rats exhibited cognitive dysfunction 28 days after TBI, and MSCs combined with LITUS treatment ameliorated the cognitive deficits caused by TBI via increasing Nestin, NSE, GAP-43, PSD-95, and BDNF expression and attenuating the inflammatory response and edema caused by TBI via reducing TNF-α and AQP-4 expression. According to these results, MSCs combined with LITUS is more effective than MSCs alone for the treatment of TBI, and the mechanism may be the promotion of neuronal proliferation and differentiation, and the attenuation of the inflammatory response and edema, which ameliorates the spatial learning memory impairment caused by TBI. MSCs combined with LITUS treatment represents a new approach for the clinical treatment of patients with TBI.

TNF-α induces AQP4 overexpression in astrocytes through the NF-κB pathway causing cellular edema and apoptosis

Aquaporin 4 (AQP4) is highly expressed on astrocytes and is critical for controlling brain water transport in neurological diseases. Tumor necrosis factor (TNF)-α is a common cytokine found in disease microenvironment. The aim of this study was to determine whether TNF-α can regulate the expression of AQP4 in astrocytes. Primary astrocyte cultures were treated with different concentrations of TNF-α and the cell viability was assessed through cell counting kit-8 assay and AQP4 expression was detected by qPCR, western blots, and immunofluorescence assays. The activation of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) pathway was detected by western blot. Further, dual-luciferase reporting system and chromatin immunoprecipitation were used to detect the transcriptional regulation of AQP4 by p65. These experiments demonstrated that treatment with TNF-α can lead to astrocyte edema and an increase in AQP4 expression. Following TNF-α treatment, the expression levels of P-IKKα/β-IκBα and P-p65 increased significantly over time. The results of the dual-luciferase reporter system and chromatin immunoprecipitation assays revealed that p65 protein and AQP4 promoter had a robust binding effect after TNF-α treatment, and the NF-κB pathway inhibitor, BAY 11-7082 could inhibit these effects of TNF-α. The expression level of AQP4 was significantly decreased upon p65 interference, while the astrocyte viability was significantly increased compared to that in the TNF-α only group. In conclusion, TNF-α activated NF-κB pathway, which promoted the binding of p65 to the AQP4 gene promoter region, and enhanced AQP4 expression, ultimately reducing astrocyte viability and causing cell edema.

Aquaporin 4 in Traumatic Brain Injury: From Molecular Pathways to Therapeutic Target

Traumatic brain injury (TBI) is known as an acute degenerative pathology of the central nervous system, and has been shown to increase brain aquaporin 4 (AQP4) expression. Various molecular mechanisms affect AQP4 expression, including neuronal high mobility group box 1, forkhead box O3a, vascular endothelial growth factor, hypoxia-inducible factor-1 α (HIF-1 α) sirtuin 2, NF-κB, Malat1, nerve growth factor and Angiotensin II receptor type 1. In addition, inhibition of AQP4 with FK-506, MK-801 (indirectly by targeting N-methyl-D-aspartate receptor), inactivation of adenosine A2A receptor, levetiracetam, adjudin, progesterone, estrogen, V1aR inhibitor, hypertonic saline, erythropoietin, poloxamer 188, brilliant blue G, HIF-1alpha inhibitor, normobaric oxygen therapy, astaxanthin, epigallocatechin-3-gallate, sesamin, thaliporphine, magnesium, prebiotic fiber, resveratrol and omega-3, as well as AQP4 gene silencing lead to reduced edema upon TBI. This review summarizes current knowledge and evidence on the relationship between AQP4 and TBI, and the potential mechanisms involved.

Genetic variations of toll-like receptors: Impact on susceptibility, severity and prognosis of bacterial meningitis

Bacterial meningitis (BM) is a serious infectious disease of the central nervous system，which is mainly caused by Streptococcus pneumoniae, Neisseria meningitidis, Haemophilus influenzae, Group B Streptococcus and Listeria monocytogenes. Throughout the world, BM has become one of the most lethal diseases that commonly occurs in children. Toll like receptors (TLRs) are one of the most important immune defense lines in infectious diseases, and play an essential role in host defense. Accumulating evidence shows that genetic variations in TLRs are associated with host responses in BM. This review aims to summarize the role of different TLRs and their genetic variations in the susceptibility, severity and prognosis of BM and discuss the identified risk factors for better treatment and improvement of the course and outcome of BM.

Serum cytokine profile of pediatric patients with laboratory confirmed pneumococcal meningitis

BACKGROUND

Streptococcus pneumoniae infection is a leading cause of bacterial meningitis in children with severe sequelae. Cytokines are important molecules in regulating of host inflammatory and anti-inflammatory responses. So far, the cytokine profile of bacterial meningitis caused by single pathogen has been rarely reported. The aim of this study was to explore serum cytokine profile in pediatric patients with pneumococcal meningitis (PM) and its clinical relevance which could be considered as a valuable tool for differential diagnosis of PM.

METHODS

During 2015-2018, 95 children with laboratory-confirmed PM were included. Of them, 63 had serum samples at admission. Ten cytokines including TNF-α, IL-12p40, IL-17A, IL-1β, IFN-γ, GM-CSF, IL-10, CXCL-1, IL-8 and IL-13 were measured by multiplex immunoassay in sera of 63 PM patients and 55 age-matched healthy controls (HCs). Level of serum cytokines was compared with different clinical features of patients.

RESULTS

Significantly higher level of IL-10 was observed in patients than HCs (median, 2.19 vs. 1.92 pg/mL, p = 0.017). Significantly lower levels of serum IL-12p40, IL-17A and IL-1β were observed in patients than HCs (median, 0.68 vs. 10.12 pg/mL, p < 0.0001; 1.14 vs. 1.14 pg/mL, p = 0.004; 1.00 vs. 5.09 pg/mL, p < 0.0001, respectively). No difference was found in levels of other cytokines between patients and controls. A negative correlation was noticed between percentages of blood neutrophils and concentrations of IL-10 (p = 0.048, r = -0.25). Significantly lower levels of IL-12p40 and CXCL-1 were observed in PM patients with sepsis than those without (median 0.68 vs. 1.64 pg/mL, p = 0.026; 7.25 vs. 12.84 pg/mL, p = 0.043, respectively).

CONCLUSIONS

Our results suggested that there might be significant changes in serum pro-inflammatory and anti-inflammatory cytokines in PM children and that the determination of these cytokines may have limited value for evaluation of clinical outcome of pediatric PM.

Effect of Low Intensity Transcranial Ultrasound (LITUS) on Post-traumatic Brain Edema in Rats: Evaluation by Isotropic 3-Dimensional T2 and Multi-TE T2 Weighted MRI

Background: Brain edema is one of the important factors affecting the prognosis of traumatic brain injury (TBI). Low-intensity transcranial ultrasound (LITUS) has significant anti-cerebral edema effect. T2-weighted image-based volume and T2 value measurements can sensitively reflect tissue edema.

Purpose: To evaluate the effect and possible mechanisms of LITUS on brain edema by iso-voxel 3-dimensional T2WI (iso-3D T2WI) and multi-TE T2WI. Methods: Forty-five rats were randomly divided into sham control, TBI and TBI + LITUS groups (n = 15, respectively). Iso-voxel 3-dimensional T2WI and multi-TE T2WI sequences at 3.0T to obtain T2 value and edema volume of the injury cortex. T2 values were obtained on days 1, 7, 14, 21, 28, 35, and 42 after TBI and brain edema volume were obtained on days 7 and 14.

Results: The T2 values of the damaged cortex in the TBI group showed a slow decreasing trend after a significant increase. For TBI+LITUS group, T2 values decreased with continuous LITUS treatment. At day 28, the T2 values were not significantly longer than the control group (adjusted P = 0.0535), but were significantly shorter than the TBI group at day 42 (adjusted P = 0.0003). The edema volume at day 7 and 14 in the LITUS group was significantly lower than the TBI group (P = 0.0004 and P < 0.0001, respectively). AQP-4 and β-APP protein staining showed a strong positive reaction near the CCI point, TBI+LITUS group showed a medium positive reaction, and the sham control group showed a weak positive reaction.

Conclusion: The therapeutic effect of LITUS on post-traumatic brain edema was confirmed through T2 value and edema volume, and the mechanism may be related to inhibiting the expression of AQP-4 and promoting the removal of β-APP.

The impact of hypertonic saline on cerebrovascular reactivity and compensatory reserve in traumatic brain injury: an exploratory analysis

Background

Intravenous hypertonic saline is utilized commonly in critical care for treatment of acute or refractory elevations of intracranial pressure (ICP) in traumatic brain injury (TBI) patients. Though there is a clear understanding of the general physiological effects of a hypertonic saline solution over long periods of time, smaller epoch effects of hypertonic saline (HTS) have not been thoroughly analyzed. The aim of this study was to perform a direct evaluation of the high-frequency response of HTS on the cerebrovascular physiological responses in TBI.

Methods

We retrospectively reviewed our prospectively maintained adult TBI database for those with archived high-frequency cerebral physiology and available HTS treatment information. We evaluated different epochs of physiology around HTS bolus dosing, comparing pre- with post-HTS. We assessed for changes in slow fluctuations in ICP, pulse amplitude of ICP (AMP), cerebral perfusion pressure (CPP), mean arterial pressure (MAP), cerebrovascular reactivity (as measured through pressure reactivity index (PRx)), and cerebral compensatory reserve (correlation (R) between AMP (A) and ICP (P)). Comparisons of mean measures and percentage time above clinically relevant thresholds for the physiological parameters were compared pre- and post-HTS using descriptive statistics and Mann-Whitney U testing. We assessed for subgroups of physiological responses using latent profile analysis (LPA).

Results

Fifteen patients underwent 69 distinct bolus infusions of hypertonic saline. Apart from the well-documented decrease in ICP, there was also a reduction in AMP. The analysis of cerebrovascular reactivity response to HTS solution had two main effects. For patients with grossly impaired cerebrovascular reactivity pre-HTS (PRx > + 0.30), HTS bolus led to improved reactivity. However, for those with intact cerebrovascular reactivity pre-HTS (PRx < 0), HTS bolus demonstrated a trend towards more impaired reactivity. This indicates that HTS has different impacts, dependent on pre-bolus cerebrovascular status. There was no significant change in metrics of cerebral compensatory reserve. LPA failed to demonstrate any subgroups of physiological responses to HTS administration.

Conclusions

The direct decrease in ICP and AMP confirms that a bolus dose of a HTS solution is an effective therapeutic agent for intracranial hypertension. However, in patients with intact autoregulation, hypertonic saline may impair cerebral hemodynamics. These findings regarding cerebrovascular reactivity remain preliminary and require further investigation.

Electronic supplementary material

The online version of this article (10.1007/s00701-020-04579-0) contains supplementary material, which is available to authorized users.

Hypertonic saline improves brain edema resulting from traumatic brain injury by suppressing the NF-κB/IL-1β signaling pathway and AQP4

Although hypertonic saline (HS) has been extensively applied to treat brain edema in the clinic, the precise mechanism underlying its function remains poorly understood. Therefore, the aim of the present study was to investigate the therapeutic mechanism of HS in brain edema in terms of aquaporins and inflammatory factors. In the present study, traumatic brain injury (TBI) was established in male adult Sprague-Dawley rats, which were continuously administered 10% HS by intravenous injection for 2 days. In addition, brain edema and brain water content were detected by MRI and wet/dry ratio analysis and histological examination, respectively. Immunohistochemical staining for albumin and western blotting for occludin, zonula occludens-1 and claudin-5 was performed to evaluate the integrity of the blood-brain barrier. Aquaporin 4 (AQP4) expression was also analyzed using western blotting and reverse transcription-quantitative PCR, whilst interleukin (IL)-1β and NF-κB levels were measured using ELISA. It was demonstrated that HS treatment significantly reduced brain edema in TBI rats and downregulated AQP4 expression in cerebral cortical tissues around the contusion site. In addition, IL-1β and NF-κB levels were found to be downregulated after 10% HS treatment. Therefore, results from the present study suggested that HS may protect against brain edema induced by TBI by modulating the expression levels of AQP4, NF-κB and IL-1β.

Interferon-Gamma and Interleukin-1Beta Enhance the Secretion of Brain-Derived Neurotrophic Factor and Promotes the Survival of Cortical Neurons in Brain Injury

Neuro-inflammation is associated with the production of cytokines, which influence neuronal and glial functions. Although the proinflammatory cytokines interferon-γ (IFN-γ) and interleukin-1Beta (IL-1β) are thought to be the major mediators of neuro-inflammation, their role in brain injury remains ill-defined. The objective of this study was to examine the effect of IFN-γ and IL-1β on survival of cortical neurons in stab wound injury in mice. A stab wound injury was made in the cortex of male BALB/c mice. Injured mice (I) were divide into IFN-γ and IL-1β treatment experiments. Mice in I + IFN-γ group were treated with IFN-γ (ip, 10 µg/kg/day) for 1, 3 and 7 days and mice in I + IL-1β group were treated with 5 IP injection of IL-1β (0.5 µg /12 h). Appropriate control mice were maintained for comparison. Immunostaining of frozen brain sections for astrocytes (GFAP), microglia (Iba-1) and Fluoro-Jade B staining for degenerating neurons were used. Western blotting and ELISA for brain-derived neurotrophic factor (BDNF) were done on the tissues isolated from the injured sites. Results showed a significant increase in the number of both astrocytes and microglia in I + IFN-γ and I + IL-1β groups. There were no significant changes in the number of astrocytes or microglia in noninjury groups (NI) treated with IFN-γ or IL-1β. The number of degenerating neurons significantly decreased in I + IFN-γ and I + IL-1β groups. GFAP and BDNF levels were significantly increased in I + IFN-γ and I + IL-1β groups. Interferon-γ and IL-1β induce astrogliosis, microgliosis, enhance the secretion of BDNF, one of the many neurotrophic factors after brain injury, and promote the survival of cortical neurons in stab wound brain injury.

Hypertonic saline mediates the NLRP3/IL-1β signaling axis in microglia to alleviate ischemic blood-brain barrier permeability by downregulating astrocyte-derived VEGF in rats

Introduction

The aim of this study was to explore whether the antibrain edema of hypertonic saline (HS) is associated with alleviating ischemic blood‐brain barrier (BBB) permeability by downregulating astrocyte‐derived vascular endothelial growth factor (VEGF), which is mediated by microglia‐derived NOD‐like receptor protein 3 (NLRP3) inflammasome.

Methods

The infarct volume and BBB permeability were detected. The protein expression level of VEGF in astrocytes in a transient focal brain ischemia model of rats was evaluated after 10% HS treatment. Changes in the NLRP3 inflammasome, IL‐1β protein expression, and the interleukin‐1 receptor (IL1R1)/pNF‐кBp65/VEGF signaling pathway were determined in astrocytes.

Results

HS alleviated the BBB permeability, reduced the infarct volume, and downregulated the expression of VEGF in astrocytes. HS downregulates IL‐1β expression by inhibiting the activation of the NLRP3 inflammasome in microglia and then downregulates VEGF expression by inhibiting the phosphorylation of NF‐кBp65 mediated by IL‐1β in astrocytes.

Conclusions

HS alleviated the BBB permeability, reduced the infarct volume, and downregulated the expression of VEGF in astrocytes. HS downregulated IL‐1β expression via inhibiting the activation of the NLRP3 inflammasome in microglia and then downregulated VEGF expression through inhibiting the phosphorylation of NF‐кBp65 mediated by IL‐1β in astrocytes.