Two-dimensional crystal structure of aquaporin-4 bound to the inhibitor acetazolamide

Interaction Between the Glymphatic System and α-Synuclein in Parkinson's Disease

The glymphatic system contributes to the clearance of amyloid-β from the brain and is disrupted in Alzheimer's disease. However, whether the system is involved in the removal of α-synuclein (α-syn) and whether it is suppressed in Parkinson's disease (PD) remain largely unknown. In mice receiving the intranigral injection of recombinant human α-syn, we found that the glymphatic suppression via aquaporin-4 (AQP4) gene deletion or acetazolamide treatment reduced the clearance of injected α-syn from the brain. In mice overexpressing the human A53T-α-syn, we revealed that AQP4 deficiency accelerated the accumulation of α-syn, facilitated the loss of dopaminergic neurons, and accelerated PD-like symptoms. We also found that the overexpression of A53T-α-syn reduced the expression/polarization of AQP4 and suppressed the glymphatic activity of mice. The study demonstrates a close interaction between the AQP4-mediated glymphatic system and parenchymal α-syn, indicating that restoring the glymphatic activity is a potential therapeutic target to delay PD progression.

Combined Effect of Cold Atmospheric Plasma and Curcumin in Melanoma Cancer

Curcumin (CUR) has interesting properties to cure cancer. Cold atmospheric plasma (CAP) is also an emerging biomedical technique that has great potential for cancer treatment. Therefore, the combined effect of CAP and CUR on inducing cytotoxicity and apoptosis of melanoma cancer cells might be promising. Here, we investigated the combined effects of CAP and CUR on cytotoxicity and apoptosis in B16-F10 melanoma cancer cells compared to L929 normal cells using MTT method, acridine orange/ethidium bromide fluorescence microscopic assay, and Annexin V/PI flow cytometry. In addition, the activation of apoptosis pathways was evaluated using BCL2, BAX, and Caspase-3 (CASP3) gene expression and ratio of BAX to BCL2 (BAX/BCL2). Finally, in silico study was performed to suggest the molecular mechanism of this combination therapy on melanoma cancer. Results showed that although combination therapy with CUR and CAP has cytotoxic and apoptotic effects on cancer cells, it did not improve apoptosis rate in melanoma B16-F10 cancer cells compared to monotherapy with CAP or CUR. In addition, evaluation of gene expression in cancer cell line confirmed that CUR and CAP concomitant treatment did not enhance the expression of apoptotic genes. In silico analysis of docked model suggested that CUR blocks aquaporin- (AQP-) 1 channel and prevents penetration of CAP-induced ROS into the cells. In conclusion, combination therapy with CAP and CUR does not improve the anticancer effect of each alone.

Neurofluids-Deep inspiration, cilia and preloading of the astrocytic network

With the advent of real-time MRI, the motion and passage of cerebrospinal fluid can be visualized without gating and exclusion of low-frequency waves. This imaging modality gives insights into low-volume, rapidly oscillating cardiac-driven movement as well as sustained, high-volume, slowly oscillating inspiration-driven movement. Inspiration means a spontaneous or artificial increase in the intrathoracic dimensions independent of body position. Alterations in thoracic diameter enable the thoracic and spinal epidural venous compartments to be emptied and filled, producing an upward surge of cerebrospinal fluid inside the spine during inspiration; this surge counterbalances the downward pooling of venous blood toward the heart. Real-time MRI, as a macroscale in vivo observation method, could expand our knowledge of neurofluid dynamics, including how astrocytic fluid preloading is adjusted and how brain buoyancy and turgor are maintained in different postures and zero gravity. Along with these macroscale findings, new microscale insights into aquaporin-mediated fluid transfer, its sensing by cilia, and its tuning by nitric oxide will be reviewed. By incorporating clinical knowledge spanning several disciplines, certain disorders-congenital hydrocephalus with Chiari malformation, idiopathic intracranial hypertension, and adult idiopathic hydrocephalus-are interpreted and reviewed according to current concepts, from the basics of the interrelated systems to their pathology.

Role of Carbonic Anhydrase in Cerebral Ischemia and Carbonic Anhydrase Inhibitors as Putative Protective Agents

Ischemic stroke is a leading cause of death and disability worldwide. The only pharmacological treatment available to date for cerebral ischemia is tissue plasminogen activator (t-PA) and the search for successful therapeutic strategies still remains a major challenge. The loss of cerebral blood flow leads to reduced oxygen and glucose supply and a subsequent switch to the glycolytic pathway, which leads to tissue acidification. Carbonic anhydrase (CA, EC 4.2.1.1) is the enzyme responsible for converting carbon dioxide into a protons and bicarbonate, thus contributing to pH regulation and metabolism, with many CA isoforms present in the brain. Recently, numerous studies have shed light on several classes of carbonic anhydrase inhibitor (CAI) as possible new pharmacological agents for the management of brain ischemia. In the present review we summarized pharmacological, preclinical and clinical findings regarding the role of CAIs in strokes and we discuss their potential protective mechanisms.

Drug development in targeting ion channels for brain edema

Cerebral edema is a pathological hallmark of various central nervous system (CNS) insults, including traumatic brain injury (TBI) and excitotoxic injury such as stroke. Due to the rigidity of the skull, edema-induced increase of intracranial fluid significantly complicates severe CNS injuries by raising intracranial pressure and compromising perfusion. Mortality due to cerebral edema is high. With mortality rates up to 80% in severe cases of stroke, it is the leading cause of death within the first week. Similarly, cerebral edema is devastating for patients of TBI, accounting for up to 50% mortality. Currently, the available treatments for cerebral edema include hypothermia, osmotherapy, and surgery. However, these treatments only address the symptoms and often elicit adverse side effects, potentially in part due to non-specificity. There is an urgent need to identify effective pharmacological treatments for cerebral edema. Currently, ion channels represent the third-largest target class for drug development, but their roles in cerebral edema remain ill-defined. The present review aims to provide an overview of the proposed roles of ion channels and transporters (including aquaporins, SUR1-TRPM4, chloride channels, glucose transporters, and proton-sensitive channels) in mediating cerebral edema in acute ischemic stroke and TBI. We also focus on the pharmacological inhibitors for each target and potential therapeutic strategies that may be further pursued for the treatment of cerebral edema.

Regulation of AQP4 in the Central Nervous System

Aquaporin-4 (AQP4) is the main water channel protein expressed in the central nervous system (CNS). AQP4 is densely expressed in astrocyte end-feet, and is an important factor in CNS water and potassium homeostasis. Changes in AQP4 activity and expression have been implicated in several CNS disorders, including (but not limited to) epilepsy, edema, stroke, and glioblastoma. For this reason, many studies have been done to understand the various ways in which AQP4 is regulated endogenously, and could be regulated pharmaceutically. In particular, four regulatory methods have been thoroughly studied; regulation of gene expression via microRNAs, regulation of AQP4 channel gating/trafficking via phosphorylation, regulation of water permeability using heavy metal ions, and regulation of water permeability using small molecule inhibitors. A major challenge when studying AQP4 regulation is inter-method variability. A compound or phosphorylation which shows an inhibitory effect in vitro may show no effect in a different in vitro method, or even show an increase in AQP4 expression in vivo. Although a large amount of variability exists between in vitro methods, some microRNAs, heavy metal ions, and two small molecule inhibitors, acetazolamide and TGN-020, have shown promise in the field of AQP4 regulation.

Possible Role of Glymphatic System of the Brain in the Pathogenesis of High-Altitude Cerebral Edema

In this article, we suggest that the glymphatic system of the brain can play an important role in the pathogenesis of high-altitude cerebral edema (HACE). Water enters the intercellular space of the brain primarily through aquaporin-4 (AQP-4) water channels, the main component of the glymphatic system, whereas acetazolamide, pharmacological agent used in the prevention of HACE, is the blocker of the AQP-4 molecule. In animal experiments, cerebral edema caused by hypobaric hypoxia was associated with an increased expression of AQP-4 by astrocytes. Also, the glymphatic system is primarily active during sleep, although sleep at high altitude is a well-known risk factor of developing HACE. All these findings support our hypothesis. We suggest that future research on the prevention and treatment of HACE should involve factors that are already known to modify activity of the glymphatic system, such as angiotensin-converting enzyme inhibitors or other pharmaceutical agents affecting noradrenergic system of the brain, body posture during sleep, anatomy of the veins draining the cranial cavity, and the influence of physical activity before and during exposure to high altitude, especially in relation to sleep.

Carbonic anhydrase inhibition selectively prevents amyloid β neurovascular mitochondrial toxicity

Mounting evidence suggests that mitochondrial dysfunction plays a causal role in the etiology and progression of Alzheimer's disease (AD). We recently showed that the carbonic anhydrase inhibitor (CAI) methazolamide (MTZ) prevents amyloid β (Aβ)-mediated onset of apoptosis in the mouse brain. In this study, we used MTZ and, for the first time, the analog CAI acetazolamide (ATZ) in neuronal and cerebral vascular cells challenged with Aβ, to clarify their protective effects and mitochondrial molecular mechanism of action. The CAIs selectively inhibited mitochondrial dysfunction pathways induced by Aβ, without affecting metabolic function. ATZ was effective at concentrations 10 times lower than MTZ. Both MTZ and ATZ prevented mitochondrial membrane depolarization and H2 O2 generation, with no effects on intracellular pH or ATP production. Importantly, the drugs did not primarily affect calcium homeostasis. This work suggests a new role for carbonic anhydrases (CAs) in the Aβ-induced mitochondrial toxicity associated with AD and cerebral amyloid angiopathy (CAA), and paves the way to AD clinical trials for CAIs, FDA-approved drugs with a well-known profile of brain delivery.

Characterizing the glymphatic influx by utilizing intracisternal infusion of fluorescently conjugated cadaverine

AIMS

Accumulating evidence supports that cerebrospinal fluid (CSF) in the subarachnoid space (SAS) could reenter the brain parenchyma via the glymphatic influx. The present study was designed to characterize the detailed pathway of subarachnoid CSF influx by using a novel CSF tracer.

MAIN METHODS

Fluorescently conjugated cadaverine (A488-ca), for the first time, was employed to investigate CSF movement in the brain. Following intracisternal infusion of CSF tracers, mice brain was sliced and prepared for fluorescence imaging. Some brain sections were immunostained in order to observe tracer distribution and cellular uptake.

KEY FINDINGS

A488-ca moved into the brain parenchyma rapidly, and the influx was time and region dependent. A488-ca entered the mice brain more readily and spread more widely than another commonly used CSF tracer-fluorescently conjugated ovalbumin (OA-45). Furthermore, A488-ca could enter the brain parenchyma either along the paravascular space or across the pial surface. Suppression of glymphatic transport by administration with acetazolamide strikingly reduced the influx of A488-ca. More importantly, relative to OA-45 largely remained in the extracellular space, A488-ca exhibited obvious cellular uptake by astrocytes surrounding the blood vessels and neurons in the cerebral cortex.

SIGNIFICANCE

Subarachnoid CSF could flow into the brain parenchyma via the glymphatic influx, in which the transcellular pathway was faithfully traced by intracisternal infusion with fluorescently conjugated cadaverine. These observations extend our comprehension on the glymphatic influx pathway.

Substantial role for carbonic anhydrase in latitudinal variation in mesophyll conductance of Populus trichocarpa Torr. & Gray

In Populus trichocarpa (black cottonwood), net photosynthesis (A_n ) varies with latitude and, in northern genotypes, is supported by higher stomatal conductance (g_s ). We report here a parallel cline in mesophyll conductance (g_m ) and link this variation to carbonic anhydrase (CA) activity. Using concurrent carbon isotope discrimination and chlorophyll fluorescence methods, we examined the effects of acetazolamide, an inhibitor of CA, on g_m in six representative genotypes (three from either end of the north-south cline). Acetazolamide reduced CA activity, g_m , g_s , chloroplast CO₂ concentration (C_c ) and A_n at normal CO₂ (400 μmol mol^-1 ), the latter being reversible at saturating CO₂ . Absolute reductions in A_n , g_m and CA activity were greater in northern genotypes than in southern genotypes (P < 0.025) but percent reductions were similar. In contrast, northern genotypes showed lower percent reduction in C_c compared to southern genotypes (P < 0.025). The northern genotypes had greater CA activity relative to both leaf area (two-fold) and mass (1.8-fold) (P < 0.016). The relationship between CA activity and g_m was similar whether the variation was inherent or inhibitor induced. We suggest that greater CA activity contributes to higher g_m in northern P. trichocarpa genotypes, but other diffusion pathway components may also be involved.

Acetazolamide Mitigates Astrocyte Cellular Edema Following Mild Traumatic Brain Injury

Non-penetrating or mild traumatic brain injury (mTBI) is commonly experienced in accidents, the battlefield and in full-contact sports. Astrocyte cellular edema is one of the major factors that leads to high morbidity post-mTBI. Various studies have reported an upregulation of aquaporin-4 (AQP4), a water channel protein, following brain injury. AZA is an antiepileptic drug that has been shown to inhibit AQP4 expression and in this study we investigate the drug as a therapeutic to mitigate the extent of mTBI induced cellular edema. We hypothesized that mTBI-mediated astrocyte dysfunction, initiated by increased intracellular volume, could be reduced when treated with AZA. We tested our hypothesis in a three-dimensional in vitro astrocyte model of mTBI. Samples were subject to no stretch (control) or one high-speed stretch (mTBI) injury. AQP4 expression was significantly increased 24 hours after mTBI. mTBI resulted in a significant increase in the cell swelling within 30 min of mTBI, which was significantly reduced in the presence of AZA. Cell death and expression of S100B was significantly reduced when AZA was added shortly before mTBI stretch. Overall, our data point to occurrence of astrocyte swelling immediately following mTBI, and AZA as a promising treatment to mitigate downstream cellular mortality.