Aquaporin-4 inhibition attenuates Pentylenetetrazole-induced behavioral seizures and cognitive impairments in kindled rats.

Epilepsy is a neurological condition distinguished by recurrent and unexpected seizures. Astrocytic channels and transporters are essential for maintaining normal neuronal functionality. The astrocytic water channel, aquaporin-4 (AQP4), which plays a pivotal role in regulating water homeostasis, is a potential target for epileptogenesis. In present study, we examined the effect of different doses (10, 50, 100 µM and 5 mM) of AQP4 inhibitor, 2-nicotinamide-1, 3, 4-thiadiazole (TGN-020), during kindling acquisition, on seizure parameters and seizure-induced cognitive impairments. Animals were kindled by injection of pentylenetetrazole (PTZ: 37.5 mg/kg, i.p.). TGN-020 was administered into the right lateral cerebral ventricle 30 min before PTZ every alternate day. Seizure parameters were assessed 20 min after PTZ administration. One day following the last PTZ injection, memory performance was investigated using spontaneous alternation in Y-maze and novel object recognition (NOR) tests. The inhibition of AQP4 during the kindling process significantly decreased the maximal seizure stage and seizure duration (two-way ANOVA, P = 0.0001) and increased the latency of seizure onset and the number of PTZ injections required to induce different seizure stages (one-way ANOVA, P = 0.0001). Compared to kindled rats, the results of the NOR tests showed that AQP4 inhibition during PTZ-kindling prevented recognition memory impairment. Based on these results, AQP4 could be involved in seizure development and seizure-induced cognitive impairment. More investigation is required to fully understand the complex interactions between seizure activity, water homeostasis, and cognitive dysfunction, which may help identify potential therapeutic targets for these conditions.

Toward New AQP4 Inhibitors: ORI-TRN-002.

Cerebral edema is a life-threatening condition that can cause permanent brain damage or death if left untreated. Existing therapies aim at mitigating the associated elevated intracranial pressure, yet they primarily alleviate pressure rather than prevent edema formation. Prophylactic anti-edema therapy necessitates novel drugs targeting edema formation. Aquaporin 4 (AQP4), an abundantly expressed water pore in mammalian glia and ependymal cells, has been proposed to be involved in cerebral edema formation. A series of novel compounds have been tested for their potential inhibitory effects on AQP4. However, selectivity, toxicity, functional inhibition, sustained therapeutic concentration, and delivery into the central nervous system are major challenges. Employing extensive density-functional theory (DFT) calculations, we identified a previously unreported thermodynamically stable tautomer of the recently identified AQP4-specific inhibitor TGN-020 (2-(nicotinamide)-1,3,4-thiadiazol). This novel form, featuring a distinct hydrogen-bonding pattern, served as a template for a COSMOsim-3D-based virtual screen of proprietary compounds from Origenis™. The screening identified ORI-TRN-002, an electronic homologue of TGN-020, demonstrating high solubility and low protein binding. Evaluating ORI-TRN-002 on AQP4-expressing Xenopus laevis oocytes using a high-resolution volume recording system revealed an IC50 of 2.9 ± 0.6 µM, establishing it as a novel AQP4 inhibitor. ORI-TRN-002 exhibits superior solubility and overcomes free fraction limitations compared to other reported AQP4 inhibitors, suggesting its potential as a promising anti-edema therapy for treating cerebral edema in the future.

Trifluoperazine reduces apoptosis and inflammatory responses in traumatic brain injury by preventing the accumulation of Aquaporin4 on the surface of brain cells.

Currently, no specific and standard treatment for traumatic brain injury (TBI) has been developed. Therefore, studies on new therapeutic drugs for TBI treatment are urgently needed. Trifluoperazine (TFP) is a therapeutic agent for the treatment of psychiatric disorders that reduces edema of the central nervous system. However, the specific working mechanism of TFP is not fully understood in TBI. In this study, the immunofluorescence co-localization analysis revealed that the area and intensity covered by Aquaporin4 (AQP4) on the surface of brain cells (astrocyte endfeet) increased significantly after TBI. In contrast, TFP treatment reversed these phenomena. This finding showed that TFP inhibited AQP4 accumulation on the surface of brain cells (astrocyte endfeet). The tunel fluorescence intensity and fluorescence area were lower in the TBI+TFP group compared to the TBI group. Additionally, the brain edema, brain defect area, and modified neurological severity score (mNSS) were lower in the TBI+TFP. The RNA-seq was performed on the cortical tissues of rats in the Sham, TBI, and TBI+TFP groups. A total of 3774 genes differently expressed between the TBI and the Sham group were identified. Of these, 2940 genes were up-regulated and 834 genes were down-regulated. A total of 1845 differently expressed genes between the TBI+TFP and TBI group were also identified, in which 621 genes were up-regulated and 1224 genes were down-regulated. Analysis of the common differential genes in the three groups showed that TFP could reverse the expression of apoptosis and inflammation genes. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis revealed that the differentially expressed genes (DEGs) were highly enriched in the signaling pathways regulating inflammation. In conclusion, TFP alleviates brain edema after TBI by preventing the accumulation of AQP4 on the surface of brain cells. Generally, TFP alleviates apoptosis and inflammatory response induced by TBI, and promotes the recovery of nerve function in rats after TBI. Thus, TFP is a potential therapeutic agent for TBI treatment.

Inhibition of HIF-1α-AQP4 axis ameliorates brain edema and neurological functional deficits in a rat controlled cortical injury (CCI) model.

Traumatic brain injury (TBI) is an important cause of death in young adults and children. Till now, the treatment of TBI in the short- and long-term complications is still a challenge. Our previous evidence implied aquaporin 4 (AQP4) and hypoxia inducible factor-1α (HIF-1α) might be potential targets for TBI. In this study, we explored the roles of AQP4 and HIF-1α on brain edema formation, neuronal damage and neurological functional deficits after TBI using the controlled cortical injury (CCI) model. The adult male Sprague Dawley rats were randomly divided into sham and TBI group, the latter group was further divided into neutralized-AQP4 antibody group, 2-methoxyestradiol (2-ME2) group, and their corresponding control, IgG and isotonic saline groups, respectively. Brain edema was examined by water content. Hippocampal neuronal injury was assessed by neuron loss and neuronal skeleton related protein expressions. Spatial learning and memory deficits were evaluated by Morris water maze test and memory-related proteins were detected by western blot. Our data showed that increased AQP4 protein level was closely correlated with severity of brain edema after TBI. Compared with that in the control group, both blockage of AQP4 with neutralized-AQP4 antibody and inhibition of HIF-1α with 2-ME2 for one-time treatment within 30-60 min post TBI significantly ameliorated brain edema on the 1st day post-TBI, and markedly alleviated hippocampal neuron loss and spatial learning and memory deficits on the 21st day post-TBI. In summary, our preliminary study revealed the short-term and long-term benefits of targeting HIF-1α-AQP4 axis after TBI, which may provide new clues for the selection of potential therapeutic targets for TBI in clinical practice.

Xinshuitong Capsule extract attenuates doxorubicin-induced myocardial edema via regulation of cardiac aquaporins in the chronic heart failure rats.

Doxorubicin (Dox), an effective antineoplastic drug, was limited use for cardiotoxicity. Xinshuitong Capsule (XST), a patented herbal formula, showed desirable beneficial effects in the treatment of chronic heart failure (CHF) patients. However, the drug on Dox-induced cardiotoxicity remains unclear. Ninety male Sprague-Dawley rats were randomized into two groups: 15 rats were selected as the normal group and 75 rats were injected intraperitoneally with Dox to establish CHF rat models, the success ones were randomly divided into five groups: low XST (LXST), medium XST (MXST) or high XST (HXST) (4.9, 9.8, or 19.6 g/kg d) administrated intragastrically twice a day for 4 weeks, with the captopril-treated group and the model group as comparison. The model group showed the cardiac functions generally impaired, and CHF mortality rate higher (47%) than those in the XST-treated groups (averaged 24%, P < 0.05). Compared with XST-treated groups, myocardial remodeling, inflammation and desarcomerization, and higher water content more severe in the cardiac tissue in the model group (P < 0.05), which was associated with higher expressions of mRNA or protein levels of AQP1, 4 and 7. Dox-impaired cardiac functions, cardiac remodeling and myocardial edema could be dose-dependently reverted by XST treatment. XST could inhibit AQP1, 4 and 7 at mRNA levels or at protein levels, which was associated with the attenuation of myocardial edema and cardiac remodeling, decreasing the ventricular stiffness and improving the cardiac functions and rats' survival. AQPs is involved in cardiac edema composed one of the mechanisms of Dox-induced cardiotoxicity, XSTvia inhibition of AQPs relieved the Dox-induced side effects.

Aquaporin 4 inhibition alleviates myocardial ischemia-reperfusion injury by restraining cardiomyocyte pyroptosis.

Myocardial injury caused by ischemia-reperfusion is the main pathological manifestation of coronary artery disease (CAD), which is characterized by high mortality and morbidity. Thus, there's an urgent need to develop efficacious strategies and elucidate the underlying mechanisms to prevent or alleviate myocardial ischemia-reperfusion injury to improve the clinical outcomes in patients. In this study, we took advantage of a typical myocardial cell line of mice (HL-1) and cultured with or without an aquaporin 4 inhibitor (TGN-20 denoted as AQP4i) under normal conditions (NC), ischemia (IS) and ischemia reperfusion (IR), respectively. The cytomorphology, ultrastructure, cell vitality and expression pattern of apoptotic proteins were verified with scanning electron microscope (SEM), immunofluorescence staining, flow cytometry, quantitative real-time PCR and western-blotting analysis, respectively. HL-1 under IS or IR condition revealed higher expression of Aquaporin 4 (Aqp4) compared to the NC group, whereas showed similarity in cytomorphology and ultrastructure. Aqp4 inhibition was sufficient to improve the apoptotic cells in HL-1 while showed minimal effects to the other cellular vitality. Furthermore, the expression pattern of apoptotic proteins and anti-apoptotic proteins together with proinflammatory factors in HL-1 was effectively rescued by Aqp4i treatment both at the mRNA level and protein level. Ischemia and ischemia reperfusion caused higher expression of Aqp4 and resultant increase of cardiomyocyte pyroptosis. Myocardial ischemia-reperfusion injury of HL-1 was effectively alleviated by Aqp4 and pyroptosis inhibition. Our findings provided new references for myocardial ischemia-reperfusion injury management via targeting Aqp4-mediated pyroptosis of cardiomyocyte.

Inhibition of CAMK II modulates water permeability by reducing AQP4 expression in astrocytes after oxygen-glucose deprivation.

The predominant form of edema that occurs during the early stage of ischemic stroke is cytotoxic, resulting in neuronal injury during brain ischemia and reperfusion. Intracellular calcium (Ca2+) is elevated following brain ischemia leading to increased cell membrane permeability. Ca2+/calmodulin-dependent protein kinase II (CaMK II), the downstream molecular signal of N-methyl-d-aspartate receptors (NMDARs), is sensitive to elevations in intracellular Ca2+. Aquaporin-4 (AQP4), which is expressed primarily in the brain, is a water-transport protein. However, it is unclear whether CaMK II regulates AQP4 expression to modulate cellular water permeability. We exposed cultured astrocytes to a hypoxic and glucose-free environment to mimic an ischemic environment in vitro. We investigated the effects of oxygen-glucose deprivation (OGD) on astrocytic viability and swelling, as well as CaMK II and AQP4 expression. We also studied the effects of CaMK II inhibition on cell swelling, viability and AQP4 expression. OGD increased astrocytic swelling and expression of CaMK II and AQP4, and it decreased astrocyte viability. Inhibition of CaMK II resulted in reduced astrocyte water permeability and AQP4 expression. We concluded that the upregulation of CaMK II promoted astrocyte swelling by increasing the expression of AQP4 after OGD.

The role of glymphatic system in the cerebral edema formation after ischemic stroke.

Cerebral edema following ischemic stroke is predictive of the severity of the eventual stroke related damage, however the effective treatment is limited. The glymphatic system is a recently identified waste clearance pathway in the brain, found in the paravascular space and mainly composed of astrocytes and their aquaporin-4 (AQP4) water channels. In this review, we primarily focus on the role of the glymphatic system in the formation of cerebral edema after ischemic stroke. There is still no definite conclusion whether the influx of cerebrospinal fluid (CSF) in the glymphatic system is increased or not after ischemic stroke. However, the reduced interstitial fluid (ISF) clearance after ischemic stroke is definite. Additionally, AQP4 as the most important part of glymphatic system plays a complex bimodal in cerebral edema after ischemic stroke. Most of the research has found that AQP4 deletion in animals reduces cerebral edema after acute ischemic stroke compared with wild type animal models. The mislocalization of astrocytic AQP4 was also presented after ischemic stroke. As the cerebral edema after ischemic stroke is difficult to treat, we discuss several potential treatment targets related to glymphatic system. More studies are needed to explore the role of glymphatic system in the formation of cerebral edema after ischemic stroke and develop probable treatment strategies.

Astrocytic Modulation of Supraoptic Oxytocin Neuronal Activity in Rat Dams with Pup-Deprivation at Different Stages of Lactation.

Appropriate interactions between astrocytes and oxytocin neurons in the hypothalamo- neurohypophysial system are essential for normal lactation. To further explore the mechanisms underlying astrocytic modulation of oxytocin neuronal activity, we observed astrocytic plasticity in the supraoptic nucleus of lactating rats with intermittent pup-deprivation (PD, 20 h/day) at early (day 1-5) and middle (day 8-12) stages of lactation. PD at both stages decreased suckling duration and litter's body weight gain. They also significantly increased the expression of glial fibrillary acidic protein (GFAP) in Western blots while increased GFAP filaments and the colocalization of GFAP filaments with aquaporin 4 (AQP4) puncta in astrocyte processes surrounding oxytocin neuronal somata in immunohistochemistry in the supraoptic nucleus. Suckling between adjacent milk ejections but not shortly after them decreased molecular association between GFAP and AQP4. In hypothalamic slices from male rats, oxytocin treatment (0.1 nmol/L, 10 min) significantly reduced the length of GFAP filaments and AQP4 puncta in the processes but increased GFAP staining in the somata. These oxytocin effects were blocked by pretreatment of the slices with N-(1,3,4-Thiadiazolyl) nicotinamide (TGN-020, inhibitor of AQP4, 10 µmol/L, 5 min before oxytocin). In addition, inhibition of AQP4 with TGN-020 blocked excitation in oxytocin neurons evoked by prostaglandin E2, a downstream signal of oxytocin receptor and mediator of oxytocin-evoked burst firing, in whole-cell patch-clamp recordings. These results indicate that AQP4-associated astrocytic plasticity is essential for normal oxytocin neuronal activity during lactation and that PD-evoked hypogalactia is associated with astrocytic process expansion following increased GFAP and AQP4 expressions.

Methylene blue ameliorates brain edema in rats with experimental ischemic stroke via inhibiting aquaporin 4 expression.

Brain edema is a common and serious complication of ischemic stroke with limited effective treatment. We previously reported that methylene blue (MB) attenuated ischemic brain edema in rats, but the underlying mechanisms remained unknown. Aquaporin 4 (AQP4) in astrocytes plays a key role in brain edema. We also found that extracellular signal-regulated kinase 1/2 (ERK1/2) activation was involved in the regulation of AQP4 expression in astrocytes. In the present study, we investigated whether AQP4 and ERK1/2 were involved in the protective effect of MB against cerebral edema. Rats were subjected to transient middle cerebral artery occlusion (tMCAO), MB (3 mg/kg, for 30 min) was infused intravenously through the tail vein started immediately after reperfusion and again at 3 h after ischemia (1.5 mg/kg, for 15 min). Brain edema was determined by MRI at 0.5, 2.5, and 48 h after tMCAO. The decreases of apparent diffusion coefficient (ADC) values on diffusion-weighted MRI indicated cytotoxic brain edema, whereas the increase of T2 MRI values reflected vasogenic brain edema. We found that MB infusion significantly ameliorated cytotoxic brain edema at 2.5 and 48 h after tMCAO and decreased vasogenic brain edema at 48 h after tMCAO. In addition, MB infusion blocked the AQP4 increases and ERK1/2 activation in the cerebral cortex in ischemic penumbra at 48 h after tMCAO. In a cell swelling model established in cultured rat astrocyte exposed to glutamate (1 mM), we consistently found that MB (10 µM) attenuated cell swelling, AQP4 increases and ERK1/2 activation. Moreover, the ERK1/2 inhibitor U0126 (10 µM) had the similar effects as MB. These results demonstrate that MB improves brain edema and astrocyte swelling, which may be mediated by the inhibition of AQP4 expression via ERK1/2 pathway, suggesting that MB may be a potential choice for the treatment of brain edema.

Recurrent optic neuritis in a patient with Sjogren syndrome and neuromyelitis optica spectrum disorder: A case report.

RATIONALE: Neuromyelitis optica spectrum disorder (NMOSD) patients, especially those with anti-aquaporin-4 antibody positivity, a water channel expressed on astrocytes, is often accompanied by autoimmune diseases (ADs) including Sjogren syndrome (SS). Here, we report a case of a young Chinese woman with recurrent optic neuritis who was diagnosed with asymptomatic SS and NMOSD. PATIENT CONCERNS: A 22-year-old Chinese woman suffered from optic neuritis for 3 years. The main manifestation was recurrent loss of vision. The anti-aquaporin-4 antibody was positive in the cerebrospinal fluid, and she was diagnosed with NMOSD. Other laboratory tests revealed positive anti-SSA and anti-SSB antibodies, and labial gland biopsy showed lymphocytic infiltration. She also fulfilled the international criteria for SS. DIAGNOSIS: On the basis of recurrent vision loss and laboratory examination, we defined the patient with SS accompanied by NMOSD. INTERVENTIONS: When the patient first experienced vision loss, the corticosteroid treatment in the external hospital was effective, and her visual acuity improved significantly. However, in several later attacks, such treatment was no longer obviously effective. Considering the patient's condition, she was treated with corticosteroids, cyclophosphamide, and immunoglobulin therapy on admission. OUTCOMES: The patient's visual acuity was increased to the right eye 20/800 and left eye finger counting when she was discharged from the hospital. LESSONS: SS accompanied with NMOSD is common in clinical practice, and always with the positive Anti-AQP4 antibody as a potential biomarker. Patients with SS and NMOSD showed significant neurological symptoms and had a worse prognosis than SS patients with negative anti-AQP4 antibody because of cross-immunity between anti-SSA antibody and anti-AQP4 antibody. Rheumatologists and ophthalmologists should pay attention to this and perform appropriate tests.

Alleviation of Cerebral Infarction of Rats With Middle Cerebral Artery Occlusion by Inhibition of Aquaporin 4 in the Supraoptic Nucleus.

In ischemic stroke, vasopressin hypersecretion is a critical factor of cerebral swelling and brain injury. To clarify neural mechanisms underlying ischemic stroke-evoked vasopressin hypersecretion, we observed the effect of unilateral permanent middle cerebral artery occlusion (MCAO) in rats on astrocytic plasticity and vasopressin neuronal activity in the supraoptic nucleus (SON) as well as their associated cerebral injuries. MCAO for 8 hr caused cerebral infarction in the MCAO side where water contents also increased. Immunohistochemical examination revealed that the percentage of phosphorylated extracellular signal-regulated protein kinase 1/2 (pERK1/2)-positive vasopressin neurons in the SON of MCAO side was significantly higher than that in non-MCAO side and in sham group. In the cortex, pERK1/2 and aquaporin 4 expressions increased significantly in the infarction area, while glial fibrillary acidic protein (GFAP) reduced significantly compared with the noninfarction side in brain cortex. Microinjection of N-(1,3,4-Thiadiazolyl)nicotinamide-020 [TGN-020, a specific blocker of aquaporin 4] into the SON blocked MCAO-evoked increases in pERK1/2 in the SON as well as the reduction of GFAP and the increase in pERK1/2 and aquaporin 4 in the infarction area of the cortex. Finally, oxygen and glucose deprivation reduced GFAP expression and the colocalization and molecular association of GFAP with aquaporin 4 in the SON in brain slices. These effects were blocked by TGN-020 and/or phloretin, a blocker of astrocytic volume-regulated anion channels. These findings indicate that blocking aquaporin 4 in the SON may reduce the activation of vasopressin neurons and brain injuries elicited by vasopressin during ischemic stroke.

Inhibition of Aquaporin 4 Decreases Amyloid Aß40 Drainage Around Cerebral Vessels.

Aquaporin-4 (AQP4) is located mainly in the astrocytic end-feet around cerebral blood vessels and regulates ion and water homeostasis in the brain. While deletion of AQP4 is shown to reduce amyloid-ß (Aß) clearance and exacerbate Aß peptide accumulation in plaques and vessels of Alzheimer's disease mouse models, the mechanism and clearing pathways involved are debated. Here, we investigated how inhibiting the function of AQP4 in healthy male C57BL/6 J mice impacts clearance of Aß40, the more soluble Aß isoform. Using two-photon in vivo imaging and visualizing vessels with Sulfurodamine 101 (SR101), we first showed that Aß40 injected as a ≤ 0.5-µl volume in the cerebral cortex diffused rapidly in parenchyma and accumulated around blood vessels. In animals treated with the AQP4 inhibitor TGN-020, the perivascular Aß40 accumulation was significantly (P < 0.001) intensified by involving four times more vessels, thus suggesting a generalized clearance defect associated with vessels. Increasing the injecting volume to ≥ 0.5 ≤ 1 µl decreased the difference of Aß40-positive vessels observed in non-treated and AQP4 inhibitor-treated animals, although the difference was still significant (P = 0.001), suggesting that larger injection volumes could overwhelm intramural vascular clearance mechanisms. While both small and large vessels accumulated Aß40, for the ≤ 0.5-µl volume group, the average diameter of the Aß40-positive vessels tended to be larger in control animals compared with TGN-020-treated animals, although the difference was non-significant (P = 0.066). Using histopathology and ultrastructural microscopy, no vascular structural change was observed after a single massive dose of TGN-020. These data suggest that AQP4 deficiency is directly involved in impaired Aß brain clearance via the peri-/para-vascular routes, and AQP4-mediated vascular clearance might counteract blood-brain barrier abnormalities and age-related vascular amyloidopathy.

Inebilizumab: First Approval.

Inebilizumab (Uplizna™; inebilizumab-cdon in the USA) is a humanised anti-CD19 monoclonal antibody being developed by Viela Bio for the treatment of a range of autoimmune diseases associated with CD19-expressing B cells. Inebilizumab targets and depletes CD19-expressing B cells through antibody-dependent cell-mediated cytotoxicity. In June 2020, inebilizumab received its first global approval in the USA for the treatment of neuromyelitis optica spectrum disorder (NMOSD) in adult patients who are seropositive for immunoglobulin G autoantibodies against aquaporin-4 (AQP4-IgG). The drug is also undergoing clinical evaluation for kidney transplant desensitization, myasthenia gravis, and IgG4-related disease. This article summarizes the milestones in the development of inebilizumab leading to this first approval for the treatment of AQP4-IgG seropositive NMOSD.

Diffusion MRI reveals in vivo and non-invasively changes in astrocyte function induced by an aquaporin-4 inhibitor.

The Glymphatic System (GS) has been proposed as a mechanism to clear brain tissue from waste. Its dysfunction might lead to several brain pathologies, including the Alzheimer's disease. A key component of the GS and brain tissue water circulation is the astrocyte which is regulated by acquaporin-4 (AQP4), a membrane-bound water channel on the astrocytic end-feet. Here we investigated the potential of diffusion MRI to monitor astrocyte activity in a mouse brain model through the inhibition of AQP4 channels with TGN-020. Upon TGN-020 injection, we observed a significant decrease in the Sindex, a diffusion marker of tissue microstructure, and a significant increase of the water diffusion coefficient (sADC) in cerebral cortex and hippocampus compared to saline injection. These results indicate the suitability of diffusion MRI to monitor astrocytic activity in vivo and non-invasively.

Differential effects of aquaporin-4 channel inhibition on BOLD fMRI and diffusion fMRI responses in mouse visual cortex.

The contribution of astrocytes to the BOLD fMRI and DfMRI responses in visual cortex of mice following visual stimulation was investigated using TGN-020, an aquaporin 4 (AQP4) channel blocker, acting as an astrocyte function perturbator. Under TGN-020 injection the amplitude of the BOLD fMRI response became significantly higher. In contrast no significant changes in the DfMRI responses and the electrophysiological responses were observed. Those results further confirm the implications of astrocytes in the neurovascular coupling mechanism underlying BOLD fMRI, but not in the DfMRI responses which remained unsensitive to astrocyte function perturbation.

Aquaporin 4 inhibition alters chemokine receptor expression and T cell trafficking.

Aquaporins (AQPs) are water channels that mediate a variety of biological processes. However, their role in the immune system is poorly understood. We recently reported that AQP4 is expressed by naïve and memory T cells and that AQP4 blockade with a small molecule inhibitor prolongs murine heart allograft survival at least partially through diminishing T cell activation, proliferation and trafficking. The goal of this study was to determine how AQP4 function impacts T cells in the absence of antigen stimulation. AQP4 inhibition transiently reduced the number of circulating CD4+ and CD8+ T cells in naïve non-transplanted mice in the absence of systemic T cell depletion. Adoptive transfer studies demonstrated T cell intrinsic effect of AQP4 inhibition. AQP4 blockade altered T cell gene and protein expression of chemokine receptors S1PR1 and CCR7, and their master regulator KLF-2, and reduced chemotaxis toward S1P and CCL21. Consistent with the in vitro data, in vivo AQP4 inhibition reduced T lymphocyte numbers in the lymph nodes with simultaneous accumulation in the liver. Our findings indicate that blocking AQP4 reversibly alters T lymphocyte trafficking pattern. This information can be explored for the treatment of undesirable immune responses in transplant recipients or in patients with autoimmune diseases.

Aquaporin 4 Blockade Attenuates Acute Lung Injury Through Inhibition of Th17 Cell Proliferation in Mice.

Acute lung injury (ALI) is a syndrome characterized by damage to the alveolar-capillary wall, pulmonary edema and recruitment of inflammatory cells. Previous studies have indicated that aquaporin 4 (AQP4) plays a key role in brain edema formation and resolution. However, the role of AQP4 in the development and progression of ALI is not clear and needs to be resolved. In our current study, mouse ALI was induced by intratracheal instillation of lipopolysaccharide (LPS) at a concentration of 30 mg/kg. For the inhibition of AQP4, 200 mg/kg of TGN-020 (Sigma, USA) was administered intraperitoneally every 6 h starting at 30 min before intratracheal instillation of LPS. The results of the present work indicate, for the first time, that mice treated with the AQP4 inhibitor TGN-020 had attenuated LPS-induced lung injury, reduced proinflammatory cytokine release (including IL-1α, IL-1ß, IL-6, TNF-α, IL-23, and IL-17A), and an improved survival rate. Additionally, we found that the attenuated lung injury scores, increased survival rate, and decreased BALF total protein concentration in TGN-020-treated mice were all abrogated by rIL-17A administration. Furthermore, TGN-020 treatment downregulated the phosphorylation of PI3K and Akt, increased the expression of SOCS3, and decreased the expression of p-STAT3 and RORγt. In conclusion, inhibition of AQP4 by TGN-020 has a detectable protective effect against lung tissue injury induced by LPS, and this effect is associated with inhibition of IL-17A through the downregulation of the PI3K/Akt signaling pathway and upregulation of SOCS3 protein.

Functionalized Phenylbenzamides Inhibit Aquaporin-4 Reducing Cerebral Edema and Improving Outcome in Two Models of CNS Injury.

Cerebral edema in ischemic stroke can lead to increased intracranial pressure, reduced cerebral blood flow and neuronal death. Unfortunately, current therapies for cerebral edema are either ineffective or highly invasive. During the development of cytotoxic and subsequent ionic cerebral edema water enters the brain by moving across an intact blood brain barrier and through aquaporin-4 (AQP4) at astrocyte endfeet. Using AQP4-expressing cells, we screened small molecule libraries for inhibitors that reduce AQP4-mediated water permeability. Additional functional assays were used to validate AQP4 inhibition and identified a promising structural series for medicinal chemistry. These efforts improved potency and revealed a compound we designated AER-270, N-[3,5-bis (trifluoromethyl)phenyl]-5-chloro-2-hydroxybenzamide. AER-270 and a prodrug with enhanced solubility, AER-271 2-{[3,5-Bis(trifluoromethyl) phenyl]carbamoyl}-4-chlorophenyl dihydrogen phosphate, improved neurological outcome and reduced swelling in two models of CNS injury complicated by cerebral edema: water intoxication and ischemic stroke modeled by middle cerebral artery occlusion.

The aquaporin-4 inhibitor AER-271 blocks acute cerebral edema and improves early outcome in a pediatric model of asphyxial cardiac arrest.

BACKGROUND: Cerebral edema after cardiac arrest (CA) is associated with increased mortality and unfavorable outcome in children and adults. Aquaporin-4 mediates cerebral water movement and its absence in models of ischemia improves outcome. We investigated early and selective pharmacologic inhibition of aquaporin-4 in a clinically relevant asphyxial CA model in immature rats in a threshold CA insult that produces primarily cytotoxic edema in the absence of blood-brain barrier permeability. METHODS: Postnatal day 16-18 Sprague-Dawley rats were studied in our established 9-min asphyxial CA model. Rats were randomized to aquaporin-4 inhibitor (AER-271) vs vehicle treatment, initiated at return of spontaneous circulation. Cerebral edema (% brain water) was the primary outcome with secondary assessments of the Neurologic Deficit Score (NDS), hippocampal neuronal death, and neuroinflammation. RESULTS: Treatment with AER-271 ameliorated early cerebral edema measured at 3 h after CA vs vehicle treated rats. This treatment also attenuated early NDS. In contrast to rats treated with vehicle after CA, rats treated with AER-271 did not develop significant neuronal death or neuroinflammation as compared to sham. CONCLUSION: Early post-resuscitation aquaporin-4 inhibition blocks the development of early cerebral edema, reduces early neurologic deficit, and blunts neuronal death and neuroinflammation post-CA.