Drug development in targeting ion channels for brain edema

Alterations in brain fluid physiology during the early stages of development of ischaemic oedema

Oedema occurs when higher than normal amounts of solutes and water accumulate in tissues. In brain parenchymal tissue, vasogenic oedema arises from changes in blood-brain barrier permeability, e.g. in peritumoral oedema. Cytotoxic oedema arises from excess accumulation of solutes within cells, e.g. ischaemic oedema following stroke. This type of oedema is initiated when blood flow in the affected core region falls sufficiently to deprive brain cells of the ATP needed to maintain ion gradients. As a consequence, there is: depolarization of neurons; neural uptake of Na+ and Cl- and loss of K+; neuronal swelling; astrocytic uptake of Na+, K+ and anions; swelling of astrocytes; and reduction in ISF volume by fluid uptake into neurons and astrocytes. There is increased parenchymal solute content due to metabolic osmolyte production and solute influx from CSF and blood. The greatly increased [K+]isf triggers spreading depolarizations into the surrounding penumbra increasing metabolic load leading to increased size of the ischaemic core. Water enters the parenchyma primarily from blood, some passing into astrocyte endfeet via AQP4. In the medium term, e.g. after three hours, NaCl permeability and swelling rate increase with partial opening of tight junctions between blood-brain barrier endothelial cells and opening of SUR1-TPRM4 channels. Swelling is then driven by a Donnan-like effect. Longer term, there is gross failure of the blood-brain barrier. Oedema resolution is slower than its formation. Fluids without colloid, e.g. infused mock CSF, can be reabsorbed across the blood-brain barrier by a Starling-like mechanism whereas infused serum with its colloids must be removed by even slower extravascular means. Large scale oedema can increase intracranial pressure (ICP) sufficiently to cause fatal brain herniation. The potentially lethal increase in ICP can be avoided by craniectomy or by aspiration of the osmotically active infarcted region. However, the only satisfactory treatment resulting in retention of function is restoration of blood flow, providing this can be achieved relatively quickly. One important objective of current research is to find treatments that increase the time during which reperfusion is successful. Questions still to be resolved are discussed.

Inhibition of EphA4 reduces vasogenic edema after experimental stroke in mice by protecting the blood-brain barrier integrity

Cerebral vasogenic edema, a severe complication of ischemic stroke, aggravates neurological deficits. However, therapeutics to reduce cerebral edema still represent a significant unmet medical need. Brain microvascular endothelial cells (BMECs), vital for maintaining the blood-brain barrier (BBB), represent the first defense barrier for vasogenic edema. Here, we analyzed the proteomic profiles of the cultured mouse BMECs during oxygen-glucose deprivation and reperfusion (OGD/R). Besides the extensively altered cytoskeletal proteins, ephrin type-A receptor 4 (EphA4) expressions and its activated phosphorylated form p-EphA4 were significantly increased. Blocking EphA4 using EphA4-Fc, a specific and well-tolerated inhibitor shown in our ongoing human phase I trial, effectively reduced OGD/R-induced BMECs contraction and tight junction damage. EphA4-Fc did not protect OGD/R-induced neuronal and astrocytic death. However, administration of EphA4-Fc, before or after the onset of transient middle cerebral artery occlusion (tMCAO), reduced brain edema by about 50%, leading to improved neurological function recovery. The BBB permeability test also confirmed that cerebral BBB integrity was well maintained in tMCAO brains treated with EphA4-Fc. Therefore, EphA4 was critical in signaling BMECs-mediated BBB breakdown and vasogenic edema during cerebral ischemia. EphA4-Fc is promising for the treatment of clinical post-stroke edema.

MRI of cerebral oedema in ischaemic stroke and its current use in routine clinical practice

Currently, with the knowledge of the role of collateral circulation in the development of cerebral ischaemia, traditional therapeutic windows are being prolonged, with time not being the only criterion. Instead, a more personalised approach is applied to select additional patients who might benefit from active treatment. This review briefly describes the current knowledge of the pathophysiology of the development of early ischaemic changes, the capabilities of MRI to depict such changes, and the basics of the routinely used imaging techniques broadly available for the assessment of individual phases of cerebral ischaemia, and summarises the possible clinical use of routine MR imaging, including patient selection for active treatment and assessment of the outcome on the basis of imaging.

Intravenous Injection of Na Ions Aggravates Ang II-Induced Hypertension-Related Vascular Endothelial Injury by Increasing Transmembrane Osmotic Pressure

Introduction

Extracellular protein nanoparticles (PNs) and ions perform synergistical functions in the control of transmembrane osmotic pressure (OP) under isotonic conditions. Intravenous injection may disrupt the ion balance and alter PN levels in blood plasma, changing transmembrane OP and damaging vascular endothelial cells.

Methods

Na ions were injected into AngII-induced HUVECs to simulate cell injury in vitro, and tail vein infusion of Na ions into hypertensive rats was performed to assess vascular damage. Optical measurements using an intermediate filament (IF) tension probe were conducted to detect indicators related to transmembrane OP. Immunofluorescence, Western blotting and small interfering RNA (siRNA) transfection were employed to investigate inflammasomes and the relationship between Abl2 and inflammation.

Results

Electrolyte injections with sodium ions (but not glucose and hydroxyethyl starch) induced the production of ASC and NLRP3 inflammasomes in Ang II-induced HUVECs; this in turn resulted in the disorder of calcium signals, and changes in transmembrane OP and cell permeability. Moreover, injection of Na ions into Ang II-induced HUVECs activated the mechanosensitive protein Abl2, involved in inflammation-induced transmembrane OP changes. A drug combination was identified that could induce OP recovery and block hyperpermeability induced by cytoplasmic inflammatory corpuscles in vivo and in vitro.

Conclusion

Changes in extracellular PNs and ions following chemical stimuli (Ang II) participate in the regulation of transmembrane OP. Furthermore, injection of Na ions causes vascular endothelial injury in Ang II-induced cells in vitro and hypertension rats in vivo, suggesting it is not safe for hypertensive patients, and we propose a new drug combination as a solution.

Synergistic effects of auraptene and 17-β estradiol on traumatic brain injury treatment: oxidant/antioxidant status, inflammatory cytokines and pathology

OBJECTIVE

Despite significant advances that have been made in the treatment of traumatic brain injury (TBI), it remains a global health issue. This study aimed to investigate the synergistic effects of 17-β estradiol (E2) and auraptene (AUR) on TBI treatment.

METHODS

In total, 70 adult male Wistar rats were divided randomly into ten main groups: Sham, TBI, TBI + DMSO, TBI + AUR (4 mg/kg), TBI + AUR (8 mg/kg), TBI + AUR (25 mg/kg), TBI + E2 group, TBI + AUR (4 mg/kg) + E2 group, TBI + AUR (8 mg/kg) + E2 group and TBI + AUR (25 mg/kg) + E2 group. Diffuse TBI was caused by the Marmarou process in male rats. The brain's tissues were harvested to check the parameters of oxidative stress and levels of inflammatory cytokine.

RESULTS

The finding revealed that TBI induced a significant increase in brain edema, pro-inflammatory cytokines and oxidant levels [MDA and NO], and also a decrease in the brain's antioxidant biomarkers [GPx, SOD]. We also found that E2 and AUR (25 mg/kg) significantly preserved the levels of these biomarkers. The combination of AUR concentrations and E2 showed that this treatment efficiently preserved the levels of these biomarkers. Furthermore, the combination of E2 and AUR (25 mg/kg) c could cause the most effective synergistic interaction.

CONCLUSION

AUR could act synergistically with E2 to treat brain injury complications.

High-intensity interval training ameliorates Alzheimer's disease-like pathology by regulating astrocyte phenotype-associated AQP4 polarization

Background: Alzheimer's disease (AD), one of the most common forms of dementia, is a widely studied neurodegenerative disease characterized by Aβ accumulation and tau hyperphosphorylation. Currently, there is no effective cure available for AD. The astrocyte AQP4 polarized distribution-mediated glymphatic system is essential for Aβ and abnormal tau clearance and is a potential therapeutic target for AD. However, the role of exercise on the AQP4 polarized distribution and the association between the AQP4 polarized distribution and astrocyte phenotype polarization are poorly understood. Methods: Using a streptozotocin (STZ)-induced sporadic AD rat model, we investigated the effects of high-intensity interval training on AD pathologies. The Branes maze task was conducted to measure spatial learning and memory. Immunofluorescence staining of NeuN with TUNEL, Fluoro-Jade C, and relative neuronal damage markers was applied to measure neuronal apoptosis, neurodegeneration, and damage. Sholl analysis was carried out to analyze the morphology of microglia. Line-scan analysis, 3D rendering, and the orthogonal view were applied to analyze the colocalization. Western blot analysis and enzyme-linked immunosorbent assay (ELISA) analysis were conducted to examine AQP4 and Aβ, respectively. An APP/PS1 transgenic AD mice model was used to confirm the key findings. Results: High-intensity interval training (HIIT) alleviates cognitive dysfunction in STZ-induced AD-like rat models and provides neuroprotection against neurodegeneration, neuronal damage, and neuronal loss. Additionally, HIIT improved the drainage of abnormal tau and Aβ from the cortex and hippocampus via the glymphatic system to the kidney. Further mechanistic studies support that the beneficial effects of HIIT on AD might be due, in part, to the polarization of glial cells from a neurotoxic phenotype towards a neuroprotective phenotype. Furthermore, an intriguing finding of our study is that the polarized distribution of AQP4 was strongly correlated with astrocyte phenotype. We found A2 phenotype exhibited more evident AQP4 polarization than the A1 phenotype. Conclusion: Our findings indicate that HIIT ameliorates Alzheimer's disease-like pathology by regulating astrocyte phenotype and astrocyte phenotype-associated AQP4 polarization. These changes promote Aβ and p-tau clearance from the brain tissue through the glymphatic system and the kidney.

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.

Protein nanoparticle-induced osmotic pressure gradients modify pulmonary edema through hyperpermeability in acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS), caused by noncardiogenic pulmonary edema (PE), contributes significantly to Coronavirus 2019 (COVID-19)-associated morbidity and mortality. We explored the effect of transmembrane osmotic pressure (OP) gradients in PE using a fluorescence resonance energy transfer-based Intermediate filament (IF) tension optical probe. Angiotensin-II- and bradykinin-induced increases in intracellular protein nanoparticle (PN)-OP were associated with inflammasome production and cytoskeletal depolymerization. Intracellular protein nanoparticle production also resulted in cytomembrane hyperpolarization and L-VGCC-induced calcium signals, which differed from diacylglycerol-induced calcium increment via TRPC6 activation. Both pathways involve voltage-dependent cation influx and OP upregulation via SUR1-TRPM4 channels. Meanwhile, intra/extracellular PN-induced OP gradients across membranes upregulated pulmonary endothelial and alveolar barrier permeability. Attenuation of intracellular PN, calcium signals, and cation influx by drug combinations effectively relieved intracellular OP and pulmonary endothelial nonselective permeability, and improved epithelial fluid absorption and PE. Thus, PN-OP is pivotal in pulmonary edema in ARDS and COVID-19, and transmembrane OP recovery could be used to treat pulmonary edema and develop new drug targets in pulmonary injury.

Graphical Abstract

The short form of the SUR1 and its functional implications in the damaged brain

Sulfonylurea receptor (SUR) belongs to the adenosine 5′-triphosphate (ATP)-binding cassette (ABC) transporter family; however, SUR is associated with ion channels and acts as a regulatory subunit determining the opening or closing of the pore. Abcc8 and Abcc9 genes code for the proteins SUR1 and SUR2, respectively. The SUR1 transcript encodes a protein of 1582 amino acids with a mass around 140–177 kDa expressed in the pancreas, brain, heart, and other tissues. It is well known that SUR1 assembles with Kir6.2 and TRPM4 to establish K_ATP channels and non-selective cation channels, respectively. Abbc8 and 9 are alternatively spliced, and the resulting transcripts encode different isoforms of SUR1 and SUR2, which have been detected by different experimental strategies. Interestingly, the use of binding assays to sulfonylureas and Western blotting has allowed the detection of shorter forms of SUR (~65 kDa). Identity of the SUR1 variants has not been clarified, and some authors have suggested that the shorter forms are unspecific. However, immunoprecipitation assays have shown that SUR2 short forms are part of a functional channel even coexisting with the typical forms of the receptor in the heart. This evidence confirms that the structure of the short forms of the SURs is fully functional and does not lose the ability to interact with the channels. Since structural changes in short forms of SUR modify its affinity to ATP, regulation of its expression might represent an advantage in pathologies where ATP concentrations decrease and a therapeutic target to induce neuroprotection. Remarkably, the expression of SUR1 variants might be induced by conditions associated to the decrease of energetic substrates in the brain (e.g. during stroke and epilepsy). In this review, we want to contribute to the knowledge of SUR1 complexity by analyzing evidence that shows the existence of short SUR1 variants and its possible implications in brain function.

Pharmacological Modulation and (Patho)Physiological Roles of TRPM4 Channel-Part 2: TRPM4 in Health and Disease

Transient receptor potential melastatin 4 (TRPM4) is a unique member of the TRPM protein family and, similarly to TRPM5, is Ca²⁺ sensitive and permeable for monovalent but not divalent cations. It is widely expressed in many organs and is involved in several functions; it regulates membrane potential and Ca²⁺ homeostasis in both excitable and non-excitable cells. This part of the review discusses the currently available knowledge about the physiological and pathophysiological roles of TRPM4 in various tissues. These include the physiological functions of TRPM4 in the cells of the Langerhans islets of the pancreas, in various immune functions, in the regulation of vascular tone, in respiratory and other neuronal activities, in chemosensation, and in renal and cardiac physiology. TRPM4 contributes to pathological conditions such as overactive bladder, endothelial dysfunction, various types of malignant diseases and central nervous system conditions including stroke and injuries as well as in cardiac conditions such as arrhythmias, hypertrophy, and ischemia-reperfusion injuries. TRPM4 claims more and more attention and is likely to be the topic of research in the future.

Beneficial Effects on Brain Micro-Environment by Caloric Restriction in Alleviating Neurodegenerative Diseases and Brain Aging

Aging and neurodegenerative diseases are frequently associated with the disruption of the extracellular microenvironment, which includes mesenchyme and body fluid components. Caloric restriction (CR) has been recognized as a lifestyle intervention that can improve long-term health. In addition to preventing metabolic disorders, CR has been shown to improve brain health owing to its enhancing effect on cognitive functions or retarding effect on the progression of neurodegenerative diseases. This article summarizes current findings regarding the neuroprotective effects of CR, which include the modulation of metabolism, autophagy, oxidative stress, and neuroinflammation. This review may offer future perspectives for brain aging interventions.

Sulfonylurea Receptor 1 in Central Nervous System Injury: An Updated Review

Sulfonylurea receptor 1 (SUR1) is a member of the adenosine triphosphate (ATP)-binding cassette (ABC) protein superfamily, encoded by Abcc8, and is recognized as a key mediator of central nervous system (CNS) cellular swelling via the transient receptor potential melastatin 4 (TRPM4) channel. Discovered approximately 20 years ago, this channel is normally absent in the CNS but is transcriptionally upregulated after CNS injury. A comprehensive review on the pathophysiology and role of SUR1 in the CNS was published in 2012. Since then, the breadth and depth of understanding of the involvement of this channel in secondary injury has undergone exponential growth: SUR1-TRPM4 inhibition has been shown to decrease cerebral edema and hemorrhage progression in multiple preclinical models as well as in early clinical studies across a range of CNS diseases including ischemic stroke, traumatic brain injury, cardiac arrest, subarachnoid hemorrhage, spinal cord injury, intracerebral hemorrhage, multiple sclerosis, encephalitis, neuromalignancies, pain, liver failure, status epilepticus, retinopathies and HIV-associated neurocognitive disorder. Given these substantial developments, combined with the timeliness of ongoing clinical trials of SUR1 inhibition, now, another decade later, we review advances pertaining to SUR1-TRPM4 pathobiology in this spectrum of CNS disease—providing an overview of the journey from patch-clamp experiments to phase III trials.

TRPM4 Expression During Postnatal Developmental of Mouse CA1 Pyramidal Neurons

TRPM4 is a non-selective cation channel activated by intracellular calcium and permeable to monovalent cations. This channel participates in the control of neuronal firing, neuronal plasticity, and neuronal death. TRPM4 depolarizes dendritic spines and is critical for the induction of NMDA receptor-dependent long-term potentiation in CA1 pyramidal neurons. Despite its functional importance, no subcellular localization or expression during postnatal development has been described in this area. To examine the localization and expression of TRPM4, we performed duplex immunofluorescence and patch-clamp in brain slices at different postnatal ages in C57BL/6J mice. At P0 we found TRPM4 is expressed with a somatic pattern. At P7, P14, and P35, TRPM4 expression extended from the soma to the apical dendrites but was excluded from the axon initial segment. Patch-clamp recordings showed a TRPM4-like current active at the resting membrane potential from P0, which increased throughout the postnatal development. This current was dependent on intracellular Ca²⁺ (I_CAN) and sensitive to 9-phenanthrol (9-Ph). Inhibiting TRPM4 with 9-Ph hyperpolarized the membrane potential at P14 and P35, with no effect in earlier stages. Together, these results show that TRPM4 is expressed in CA1 pyramidal neurons in the soma and apical dendrites and associated with a TRPM4-like current, which depolarizes the neurons. The expression, localization, and function of TRPM4 throughout postnatal development in the CA1 hippocampal may underlie an important mechanism of control of membrane potential and action potential firing during critical periods of neuronal development, particularly during the establishment of circuits.

An update on the pharmacological management and prevention of cerebral edema: current therapeutic strategies

Introduction: Cerebral edema is a common complication of multiple neurological diseases and is a strong predictor of outcome, especially in traumatic brain injury and large hemispheric infarction.Areas Covered: Traditional and current treatments of cerebral edema include treatment with osmotherapy or decompressive craniectomy at the time of clinical deterioration. The authors discuss preclinical and clinical models of a variety of neurological disease states that have identified receptors, ion transporters, and channels involved in the development of cerebral edema as well as modulation of these receptors with promising agents.Expert opinion: Further study is needed on the safety and efficacy of the agents discussed. IV glibenclamide has shown promise in preclinical and clinical trials of cerebral edema in large hemispheric infarct and traumatic brain injury. Consideration of underlying pathophysiology and pharmacodynamics is vital, as the synergistic use of agents has the potential to drastically mitigate cerebral edema and secondary brain injury thusly transforming our treatment paradigms.