Two-pore-domain K+ channels are a novel target for the anesthetic gases xenon, nitrous oxide, and cyclopropane

Neurological Effects of Stimulants and Hallucinogens

In this article, we will discuss the history, pharmacodynamics, and neurotoxicity of psychostimulants and hallucinogens. The drugs discussed are widely used and have characteristic toxidromes and potential for neurological injuries with which the practicing clinician should be familiar. Psychostimulants are a class of drugs that includes cocaine, methamphetamine/amphetamines, and cathinones, among others, which produce a crescendoing euphoric high. Seizures, ischemic and hemorrhagic strokes, rhabdomyolysis, and a variety of movement disorders are commonly encountered in this class. Hallucinogens encompass a broad class of drugs, in which the user experiences hallucinations, altered sensorium, distorted perception, and cognitive dysfunction. The experience can be unpredictable and dysphoric, creating a profound sense of anxiety and panic in some cases. Recognizing the associated neurotoxicities and understanding the appropriate management is critical in caring for these patient populations. Several of these agents are not detectable by standard clinical laboratory analysis, making identification and diagnosis an even greater challenge.

Gasotransmitters and noble gases in cardioprotection: unraveling molecular pathways for future therapeutic strategies

Despite recent progress, ischemic heart disease poses a persistent global challenge, driving significant morbidity and mortality. The pursuit of therapeutic solutions has led to the emergence of strategies such as ischemic preconditioning, postconditioning, and remote conditioning to shield the heart from myocardial ischemia/reperfusion injury (MIRI). These ischemic conditioning approaches, applied before, after, or at a distance from the affected organ, inspire future therapeutic strategies, including pharmacological conditioning. Gasotransmitters, comprising nitric oxide, hydrogen sulfide, sulfur dioxide, and carbon monoxide, play pivotal roles in physiological and pathological processes, exhibiting shared features such as smooth muscle relaxation, antiapoptotic effects, and anti-inflammatory properties. Despite potential risks at high concentrations, physiological levels of gasotransmitters induce vasorelaxation and promote cardioprotective effects. Noble gases, notably argon, helium, and xenon, exhibit organ-protective properties by reducing cell death, minimizing infarct size, and enhancing functional recovery in post-ischemic organs. The protective role of noble gases appears to hinge on their modulation of molecular pathways governing cell survival, leading to both pro- and antiapoptotic effects. Among noble gases, helium and xenon emerge as particularly promising in the field of cardioprotection. This overview synthesizes our current understanding of the roles played by gasotransmitters and noble gases in the context of MIRI and cardioprotection. In addition, we underscore potential future developments involving the utilization of noble gases and gasotransmitter donor molecules in advancing cardioprotective strategies.

Effects of nitrous oxide and ketamine on electrophysiological and molecular responses in the prefrontal cortex of mice: A comparative study

Nitrous oxide (N2O; laughing gas) has recently reported to produce rapid antidepressant effects, but little is known about the underlying mechanisms. We performed transcriptomics, in situ hybridization, and electrophysiological studies to examine the potential shared signatures induced by 1 h inhalation of 50% N2O and a single subanesthetic dose of ketamine (10 mg/kg, i.p.) in the medial prefrontal cortex (mPFC) in adult mice. Both treatments similarly affected the transcription of several negative regulators of mitogen-activated protein kinases (MAPKs), namely, dual specificity phosphatases (DUSPs). The effects were primarily located in the pyramidal cells. Notably, the overall effects of N2O on mRNA expression were much more prominent and widespread compared to ketamine. Ketamine caused an elevation of the spiking frequency of putative pyramidal neurons and increased gamma activity (30-100 Hz) of cortical local field potentials. However, N2O produced no such effects. Spiking amplitudes and spike-to-local field potential phase locking of putative pyramidal neurons and interneurons in this brain area showed no uniform changes across treatments. Our findings suggest that N2O and subanesthetic-dose ketamine target MAPK pathway in the mPFC but produce varying acute electrophysiological responses.

Advances in Therapies to Treat Neonatal Hypoxic-Ischemic Encephalopathy

Neonatal hypoxic-ischemic encephalopathy (HIE) is a condition that results in brain damage in newborns due to insufficient blood and oxygen supply during or after birth. HIE is a major cause of neurological disability and mortality in newborns, with over one million neonatal deaths occurring annually worldwide. The severity of brain injury and the outcome of HIE depend on several factors, including the cause of oxygen deprivation, brain maturity, regional blood flow, and maternal health conditions. HIE is classified into mild, moderate, and severe categories based on the extent of brain damage and resulting neurological issues. The pathophysiology of HIE involves different phases, including the primary phase, latent phase, secondary phase, and tertiary phase. The primary and secondary phases are characterized by episodes of energy and cell metabolism failures, increased cytotoxicity and apoptosis, and activated microglia and inflammation in the brain. A tertiary phase occurs if the brain injury persists, characterized by reduced neural plasticity and neuronal loss. Understanding the cellular and molecular aspects of the different phases of HIE is crucial for developing new interventions and therapeutics. This review aims to discuss the pathophysiology of HIE, therapeutic hypothermia (TH), the only approved therapy for HIE, ongoing developments of adjuvants for TH, and potential future drugs for HIE.

The international clinical trials registry platform (ICTRP): data integrity and the trends in clinical trials, diseases, and drugs

Introduction: Clinical trials are the gold standard for testing new therapies. Databases like ClinicalTrials.gov provide access to trial information, mainly covering the US and Europe. In 2006, WHO introduced the global ICTRP, aggregating data from ClinicalTrials.gov and 17 other national registers, making it the largest clinical trial platform by June 2019. This study conducts a comprehensive global analysis of the ICTRP database and provides framework for large-scale data analysis, data preparation, curation, and filtering. Materials and methods: The trends in 689,793 records from the ICTRP database (covering trials registered from 1990 to 2020) were analyzed. Records were adjusted for duplicates and mapping of agents to drug classes was performed. Several databases, including DrugBank, MESH, and the NIH Drug Information Portal were used to investigate trends in agent classes. Results: Our novel approach unveiled that 0.5% of the trials we identified were hidden duplicates, primarily originating from the EUCTR database, which accounted for 82.9% of these duplicates. However, the overall number of hidden duplicates within the ICTRP seems to be decreasing. In total, 689 793 trials (478 345 interventional) were registered in the ICTRP between 1990 and 2020, surpassing the count of trials in ClinicalTrials.gov (362 500 trials by the end of 2020). We identified 4 865 unique agents in trials with DrugBank, whereas 2 633 agents were identified with NIH Drug Information Portal data. After the ClinicalTrials.gov, EUCTR had the most trials in the ICTRP, followed by CTRI, IRCT, CHiCTR, and ISRCTN. CHiCTR displayed a significant surge in trial registration around 2015, while CTRI experienced rapid growth starting in 2016. Conclusion: This study highlights both the strengths and weaknesses of using the ICTRP as a data source for analyzing trends in clinical trials, and emphasizes the value of utilizing multiple registries for a comprehensive analysis.

Protein Kinase A Is Responsible for the Presynaptic Inhibition of Glycinergic and Glutamatergic Transmissions by Xenon in Rat Spinal Cord and Hippocampal CA3 Neurons

The effects of a general anesthetic xenon (Xe) on spontaneous, miniature, electrically evoked synaptic transmissions were examined using the "synapse bouton preparation," with which we can clearly evaluate pure synaptic responses and accurately quantify pre- and postsynaptic transmissions. Glycinergic and glutamatergic transmissions were investigated in rat spinal sacral dorsal commissural nucleus and hippocampal CA3 neurons, respectively. Xe presynaptically inhibited spontaneous glycinergic transmission, the effect of which was resistant to tetrodotoxin, Cd2+, extracellular Ca2+, thapsigargin (a selective sarcoplasmic/endoplasmic reticulum Ca2+-ATPase inhibitor), SQ22536 (an adenylate cyclase inhibitor), 8-Br-cAMP (membrane-permeable cAMP analog), ZD7288 (an hyperpolarization-activated cyclic nucleotide-gated channel blocker), chelerythrine (a PKC inhibitor), and KN-93 (a CaMKII inhibitor) while being sensitive to PKA inhibitors (H-89, KT5720, and Rp-cAMPS). Moreover, Xe inhibited evoked glycinergic transmission, which was canceled by KT5720. Like glycinergic transmission, spontaneous and evoked glutamatergic transmissions were also inhibited by Xe in a KT5720-sensitive manner. Our results suggest that Xe decreases glycinergic and glutamatergic spontaneous and evoked transmissions at the presynaptic level in a PKA-dependent manner. These presynaptic responses are independent of Ca2+ dynamics. We conclude that PKA can be the main molecular target of Xe in the inhibitory effects on both inhibitory and excitatory neurotransmitter release. SIGNIFICANCE STATEMENT: Spontaneous and evoked glycinergic and glutamatergic transmissions were investigated using the whole-cell patch clamp technique in rat spinal sacral dorsal commissural nucleus and hippocampal CA3 neurons, respectively. Xenon (Xe) significantly inhibited glycinergic and glutamatergic transmission presynaptically. As a signaling mechanism, protein kinase A was responsible for the inhibitory effects of Xe on both glycine and glutamate release. These results may help understand how Xe modulates neurotransmitter release and exerts its excellent anesthetic properties.

The cellular mechanisms associated with the anesthetic and neuroprotective properties of xenon: a systematic review of the preclinical literature

Introduction

Xenon exhibits significant neuroprotection against a wide range of neurological insults in animal models. However, clinical evidence that xenon improves outcomes in human studies of neurological injury remains elusive. Previous reviews of xenon's method of action have not been performed in a systematic manner. The aim of this review is to provide a comprehensive summary of the evidence underlying the cellular interactions responsible for two phenomena associated with xenon administration: anesthesia and neuroprotection.

Methods

A systematic review of the preclinical literature was carried out according to the PRISMA guidelines and a review protocol was registered with PROSPERO. The review included both in vitro models of the central nervous system and mammalian in vivo studies. The search was performed on 27th May 2022 in the following databases: Ovid Medline, Ovid Embase, Ovid Emcare, APA PsycInfo, and Web of Science. A risk of bias assessment was performed utilizing the Office of Health Assessment and Translation tool. Given the heterogeneity of the outcome data, a narrative synthesis was performed.

Results

The review identified 69 articles describing 638 individual experiments in which a hypothesis was tested regarding the interaction of xenon with cellular targets including: membrane bound proteins, intracellular signaling cascades and transcription factors. Xenon has both common and subtype specific interactions with ionotropic glutamate receptors. Xenon also influences the release of inhibitory neurotransmitters and influences multiple other ligand gated and non-ligand gated membrane bound proteins. The review identified several intracellular signaling pathways and gene transcription factors that are influenced by xenon administration and might contribute to anesthesia and neuroprotection.

Discussion

The nature of xenon NMDA receptor antagonism, and its range of additional cellular targets, distinguishes it from other NMDA antagonists such as ketamine and nitrous oxide. This is reflected in the distinct behavioral and electrophysiological characteristics of xenon. Xenon influences multiple overlapping cellular processes, both at the cell membrane and within the cell, that promote cell survival. It is hoped that identification of the underlying cellular targets of xenon might aid the development of potential therapeutics for neurological injury and improve the clinical utilization of xenon.

Systematic review registration

https://www.crd.york.ac.uk/prospero/, identifier: 336871.

Empirical evidence for the neurocognitive effect of nitrous oxide as an adjunctive therapy in patients with treatment resistant depression: A randomized controlled study

Nitrous oxide (N₂O) has demonstrated an antidepressant effect for treatment-resistant depression (TRD), but no studies investigated the effects of N₂O on different cognition domains. This study aimed to test whether N₂O would display pro-cognitive effects. We conducted a double-blinded, placebo-controlled, randomized controlled trial, 44 patients with TRD were randomized to N₂O group (one-hour inhalation of 50% N₂O/50% oxygen) or placebo group (50% air/50% oxygen). Thirty-four patients completed cognitive tests at the pre-treatment phase, 1-week, and 2 weeks post-treatment including subjective cognitive function, processing speed, attention, and executive function. Although the antidepressant effect of N₂O was not significant at 1 week, patients still showed better performance of executive function at 1 week after receiving N₂O compared with the placebo. Moreover, this significant improvement still existed at 1 week after controlling for the change in depressive symptoms over-time. Additionally, no significant difference was observed in subjective cognitive function, processing speed, and attention between these two groups across the 2-week follow-up period. As the first study investigating the treatment effects of N₂O on improving cognitive function in TRD patients, the current study indicated that N₂O has a potential pro-cognitive effect on executive function and this effect might be independent from improvements in depressive symptoms.

Effect of xenon on brain injury, neurological outcome, and survival in patients after aneurysmal subarachnoid hemorrhage-study protocol for a randomized clinical trial

BACKGROUND

Aneurysmal subarachnoid hemorrhage (aSAH) is a neurological emergency, affecting a younger population than individuals experiencing an ischemic stroke; aSAH is associated with a high risk of mortality and permanent disability. The noble gas xenon has been shown to possess neuroprotective properties as demonstrated in numerous preclinical animal studies. In addition, a recent study demonstrated that xenon could attenuate a white matter injury after out-of-hospital cardiac arrest.

METHODS

The study is a prospective, multicenter phase II clinical drug trial. The study design is a single-blind, prospective superiority randomized two-armed parallel follow-up study. The primary objective of the study is to explore the potential neuroprotective effects of inhaled xenon, when administered within 6 h after the onset of symptoms of aSAH. The primary endpoint is the extent of the global white matter injury assessed with magnetic resonance diffusion tensor imaging of the brain.

DISCUSSION

Despite improvements in medical technology and advancements in medical science, aSAH mortality and disability rates have remained nearly unchanged for the past 10 years. Therefore, new neuroprotective strategies to attenuate the early and delayed brain injuries after aSAH are needed to reduce morbidity and mortality.

TRIAL REGISTRATION

ClinicalTrials.gov NCT04696523. Registered on 6 January 2021. EudraCT, EudraCT Number: 2019-001542-17. Registered on 8 July 2020.

Xenon's Sedative Effect Is Mediated by Interaction with the Cyclic Nucleotide-Binding Domain (CNBD) of HCN2 Channels Expressed by Thalamocortical Neurons of the Ventrobasal Nucleus in Mice

Previous studies have shown that xenon reduces hyperpolarization-activated cyclic nucleotide-gated channels type-2 (HCN2) channel-mediated current (I_h) amplitude and shifts the half-maximal activation voltage (V1/2) in thalamocortical circuits of acute brain slices to more hyperpolarized potentials. HCN2 channels are dually gated by the membrane voltage and via cyclic nucleotides binding to the cyclic nucleotide-binding domain (CNBD) on the channel. In this study, we hypothesize that xenon interferes with the HCN2 CNBD to mediate its effect. Using the transgenic mice model HCN2EA, in which the binding of cAMP to HCN2 was abolished by two amino acid mutations (R591E, T592A), we performed ex-vivo patch-clamp recordings and in-vivo open-field test to prove this hypothesis. Our data showed that xenon (1.9 mM) application to brain slices shifts the V1/2 of I_h to more hyperpolarized potentials in wild-type thalamocortical neurons (TC) (V1/2: -97.09 [-99.56--95.04] mV compared to control -85.67 [-94.47--82.10] mV; p = 0.0005). These effects were abolished in HCN2EA neurons (TC), whereby the V1/2 reached only -92.56 [-93.16- -89.68] mV with xenon compared to -90.03 [-98.99--84.59] mV in the control (p = 0.84). After application of a xenon mixture (70% xenon, 30% O₂), wild-type mice activity in the open-field test decreased to 5 [2-10] while in HCN2EA mice it remained at 30 [15-42]%, (p = 0.0006). In conclusion, we show that xenon impairs HCN2 channel function by interfering with the HCN2 CNBD site and provide in-vivo evidence that this mechanism contributes to xenon-mediated hypnotic properties.

Neurosurgical Anesthesia: Optimizing Outcomes with Agent Selection

Anesthesia in neurosurgery embodies a vital element in the development of neurosurgical intervention. This undisputed interest has offered surgeons and anesthesiologists an array of anesthetic selections to utilize, though with this allowance comes the equally essential requirement of implementing a maximally appropriate agent. To date, there remains a lack of consensus and official guidance on optimizing anesthetic choice based on operating priorities including hemodynamic parameters (e.g., CPP, ICP, MAP) in addition to the route of procedure and pathology. In this review, the authors detail the development of neuroanesthesia, summarize the advantages and drawbacks of various anesthetic classes and agents, while lastly cohesively organizing the current literature of randomized trials on neuroanesthesia across various procedures.

Noble gas and neuroprotection: From bench to bedside

In recent years, inert gases such as helium, argon, and xenon have gained considerable attention for their medical value. Noble gases present an intriguing scientific paradox: although extremely chemically inert, they display a remarkable spectrum of clinically useful biological properties. Despite a relative paucity of knowledge about their mechanisms of action, some noble gases have been used successfully in clinical practice. The neuroprotection elicited by these noble gases has been investigated in experimental animal models of various types of brain injuries, such as traumatic brain injury, stroke, subarachnoid hemorrhage, cerebral ischemic/reperfusion injury, and neurodegenerative diseases. Collectively, these central nervous system injuries are a leading cause of morbidity and mortality every year worldwide. Treatment options are presently limited to thrombolytic drugs and clot removal for ischemic stroke, or therapeutic cooling for other brain injuries before the application of noble gas. Currently, there is increasing interest in noble gases as novel treatments for various brain injuries. In recent years, neuroprotection elicited by particular noble gases, xenon, for example, has been reported under different conditions. In this article, we have reviewed the latest in vitro and in vivo experimental and clinical studies of the actions of xenon, argon, and helium, and discuss their potential use as neuroprotective agents.

Neuroprotection by the noble gases argon and xenon as treatments for acquired brain injury: a preclinical systematic review and meta-analysis

BACKGROUND

The noble gases argon and xenon are potential novel neuroprotective treatments for acquired brain injuries. Xenon has already undergone early-stage clinical trials in the treatment of ischaemic brain injuries, with mixed results. Argon has yet to progress to clinical trials as a treatment for brain injury. Here, we aim to synthesise the results of preclinical studies evaluating argon and xenon as neuroprotective therapies for brain injuries.

METHODS

After a systematic review of the MEDLINE and Embase databases, we carried out a pairwise and stratified meta-analysis. Heterogeneity was examined by subgroup analysis, funnel plot asymmetry, and Egger's regression.

RESULTS

A total of 32 studies were identified, 14 for argon and 18 for xenon, involving measurements from 1384 animals, including murine, rat, and porcine models. Brain injury models included ischaemic brain injury after cardiac arrest (CA), neurological injury after cardiopulmonary bypass (CPB), traumatic brain injury (TBI), and ischaemic stroke. Both argon and xenon had significant (P<0.001), positive neuroprotective effect sizes. The overall effect size for argon (CA, TBI, stroke) was 18.1% (95% confidence interval [CI], 8.1-28.1%), and for xenon (CA, TBI, stroke) was 34.1% (95% CI, 24.7-43.6%). Including the CPB model, only present for xenon, the xenon effect size (CPB, CA, TBI, stroke) was 27.4% (95% CI, 11.5-43.3%). Xenon, both with and without the CPB model, was significantly (P<0.001) more protective than argon.

CONCLUSIONS

These findings provide evidence to support the use of xenon and argon as neuroprotective treatments for acquired brain injuries. Current evidence suggests that xenon is more efficacious than argon overall.

The role of voltage-gated calcium channels in the mechanisms of anesthesia and perioperative analgesia

PURPOSE OF REVIEW

A family of neuronal voltage-gated calcium channels (VGCCs) have received only recently a significant consideration regarding the mechanisms of anesthesia because VGCC inhibition may be important in anesthetic action by decreasing neuronal excitability and presynaptic excitatory transmission. The T-type VGCCs channels (T-channels), although rarely involved in synaptic neurotransmitter release, play an important role in controlling neuronal excitability and in generating spontaneous oscillatory bursting of groups of neurons in the thalamus thought to be involved in regulating the state of arousal and sleep. Furthermore, these channels are important regulators of neuronal excitability in pain pathway. This review will provide an overview of historic perspective and the recent literature on the role of VGCCs and T-channel inhibition in particular in the mechanisms of action of anesthetics and analgesics.

RECENT FINDINGS

Recent research in the field of novel mechanisms of hypnotic action of anesthetics revealed significant contribution of the Ca V 3.1 isoform of T-channels expressed in the thalamus. Furthermore, perioperative analgesia can be achieved by targeting Ca V 3.2 isoform of these channels that is abundantly expressed in pain pathways.

SUMMARY

The review summarizes current knowledge regarding the contribution of T-channels in hypnosis and analgesia. Further preclinical and clinical studies are needed to validate their potential for developing novel anesthetics and new perioperative pain therapies.

High-pressure crystallography shows noble gas intervention into protein-lipid interaction and suggests a model for anaesthetic action

In this work we examine how small hydrophobic molecules such as inert gases interact with membrane proteins (MPs) at a molecular level. High pressure atmospheres of argon and krypton were used to produce noble gas derivatives of crystals of three well studied MPs (two different proton pumps and a sodium light-driven ion pump). The structures obtained using X-ray crystallography showed that the vast majority of argon and krypton binding sites were located on the outer hydrophobic surface of the MPs – a surface usually accommodating hydrophobic chains of annular lipids (which are known structural and functional determinants for MPs). In conformity with these results, supplementary in silico molecular dynamics (MD) analysis predicted even greater numbers of argon and krypton binding positions on MP surface within the bilayer. These results indicate a potential importance of such interactions, particularly as related to the phenomenon of noble gas-induced anaesthesia.

Noble gases are known to interact with proteins and can be good anaesthetics in hyperbaric conditions. This study identifies argon and krypton binding sites on membrane proteins and proposes as a hypothesis that noble gases, by altering protein/lipid contacts, may affect protein function.

Discovery of the Xenon-Protein Interactome Using Large-Scale Measurements of Protein Folding and Stability

The intermolecular interactions of noble gases in biological systems are associated with numerous biochemical responses, including apoptosis, inflammation, anesthesia, analgesia, and neuroprotection. The molecular modes of action underlying these responses are largely unknown. This is in large part due to the limited experimental techniques to study protein-gas interactions. The few techniques that are amenable to such studies are relatively low-throughput and require large amounts of purified proteins. Thus, they do not enable the large-scale analyses that are useful for protein target discovery. Here, we report the application of stability of proteins from rates of oxidation (SPROX) and limited proteolysis (LiP) methodologies to detect protein-xenon interactions on the proteomic scale using protein folding stability measurements. Over 5000 methionine-containing peptides and over 5000 semi-tryptic peptides, mapping to ∼1500 and ∼950 proteins, respectively, in the yeast proteome, were assayed for Xe-interacting activity using the SPROX and LiP techniques. The SPROX and LiP analyses identified 31 and 60 Xe-interacting proteins, respectively, none of which were previously known to bind Xe. A bioinformatics analysis of the proteomic results revealed that these Xe-interacting proteins were enriched in those involved in ATP-driven processes. A fraction of the protein targets that were identified are tied to previously established modes of action related to xenon's anesthetic and organoprotective properties. These results enrich our knowledge and understanding of biologically relevant xenon interactions. The sample preparation protocols and analytical methodologies developed here for xenon are also generally applicable to the discovery of a wide range of other protein-gas interactions in complex biological mixtures, such as cell lysates.

The neuroprotective effect and possible therapeutic application of xenon in neurological diseases

Xenon is an inert gas with stable chemical properties which is used as an anesthetic. Recent in vitro and in vivo findings indicate that xenon also elicits an excellent neuroprotective effect in subanesthetic concentrations. The mechanisms underlying this primarily involve the attenuation of excitotoxicity and the inhibition of N-methyl-d-aspartic acid (NMDA) receptors and NMDA receptor-related effects, such as antioxidative effects, reduced activation of microglia, and Ca²⁺ -dependent mechanisms, as well as the interaction with certain ion channels and glial cells. Based on this strong neuroprotective role, a large number of experimental and clinical studies have confirmed the significant therapeutic effect of xenon in the treatment of neurological diseases. This review summarizes the reported neuroprotective mechanisms of xenon and discusses its possible therapeutic application in the treatment of various neurological diseases.

Two-Pore-Domain Potassium (K2P-) Channels: Cardiac Expression Patterns and Disease-Specific Remodelling Processes

Two-pore-domain potassium (K_2P-) channels conduct outward K⁺ currents that maintain the resting membrane potential and modulate action potential repolarization. Members of the K_2P channel family are widely expressed among different human cell types and organs where they were shown to regulate important physiological processes. Their functional activity is controlled by a broad variety of different stimuli, like pH level, temperature, and mechanical stress but also by the presence of lipids or pharmacological agents. In patients suffering from cardiovascular diseases, alterations in K_2P-channel expression and function have been observed, suggesting functional significance and a potential therapeutic role of these ion channels. For example, upregulation of atrial specific K_2P3.1 (TASK-1) currents in atrial fibrillation (AF) patients was shown to contribute to atrial action potential duration shortening, a key feature of AF-associated atrial electrical remodelling. Therefore, targeting K_2P3.1 (TASK-1) channels might constitute an intriguing strategy for AF treatment. Further, mechanoactive K_2P2.1 (TREK-1) currents have been implicated in the development of cardiac hypertrophy, cardiac fibrosis and heart failure. Cardiovascular expression of other K_2P channels has been described, functional evidence in cardiac tissue however remains sparse. In the present review, expression, function, and regulation of cardiovascular K_2P channels are summarized and compared among different species. Remodelling patterns, observed in disease models are discussed and compared to findings from clinical patients to assess the therapeutic potential of K_2P channels.

Effect of Xenon Treatment on Gene Expression in Brain Tissue after Traumatic Brain Injury in Rats

The overactivation of inflammatory pathways and/or a deficiency of neuroplasticity may result in the delayed recovery of neural function in traumatic brain injury (TBI). A promising approach to protecting the brain tissue in TBI is xenon (Xe) treatment. However, xenon's mechanisms of action remain poorly clarified. In this study, the early-onset expression of 91 target genes was investigated in the damaged and in the contralateral brain areas (sensorimotor cortex region) 6 and 24 h after injury in a TBI rat model. The expression of genes involved in inflammation, oxidation, antioxidation, neurogenesis and neuroplasticity, apoptosis, DNA repair, autophagy, and mitophagy was assessed. The animals inhaled a gas mixture containing xenon and oxygen (ϕXe = 70%; ϕO₂ 25-30% 60 min) 15-30 min after TBI. The data showed that, in the contralateral area, xenon treatment induced the expression of stress genes (Irf1, Hmox1, S100A8, and S100A9). In the damaged area, a trend towards lower expression of the inflammatory gene Irf1 was observed. Thus, our results suggest that xenon exerts a mild stressor effect in healthy brain tissue and has a tendency to decrease the inflammation following damage, which might contribute to reducing the damage and activating the early compensatory processes in the brain post-TBI.

Safety and efficacy of an equimolar mixture of oxygen and nitrous oxide: a randomized controlled trial in patients with peripheral neuropathic pain

ABSTRACT

Nitrous oxide (N2O) is an odorless and colorless gas routinely used as an adjuvant of anesthesia and for short-duration analgesia in various clinical settings mostly in the form of an N2O/O2 50%-50% equimolar mixture (EMONO). Experimental studies have suggested that EMONO could also induce long-lasting analgesic effects related to the blockade of N-methyl-D-aspartate receptors. We designed the first international multicenter proof of concept randomized, placebo-controlled study to assess the efficacy and safety of a 1-hour administration of EMONO or placebo (medical air) on 3 consecutive days up to 1 month after the last administration in patients with chronic peripheral neuropathic pain. A total of 240 patients were recruited in 22 centers in France and Germany and randomly assigned to 1 study group (120 per group). Average pain intensity (primary outcome), neuropathic pain characteristics (Neuropathic Pain Symptom Inventory), Patient Global Impression of Change, anxiety, depression, and quality of life were systematically assessed before and after treatment. The changes in average pain intensity between baseline and 7 days after the last administration were not significantly different between the 2 groups. However, evoked pain intensity (predefined secondary endpoint) and Patient Global Impression of Change (exploratory endpoint) were significantly improved in the EMONO group, and these effects were maintained up to 4 weeks after the last treatment administration. Mostly transient side effects were reported during the treatment administration. These encouraging results provide a basis for further investigation of the long-term analgesic effects of EMONO in patients with neuropathic pain.

Structural Insights into the Mechanisms and Pharmacology of K2P Potassium Channels

Leak currents, defined as voltage and time independent flows of ions across cell membranes, are central to cellular electrical excitability control. The K_2P (KCNK) potassium channel class comprises an ion channel family that produces potassium leak currents that oppose excitation and stabilize the resting membrane potential in cells in the brain, cardiovascular system, immune system, and sensory organs. Due to their widespread tissue distribution, K_2Ps contribute to many physiological and pathophysiological processes including anesthesia, pain, arrythmias, ischemia, hypertension, migraine, intraocular pressure regulation, and lung injury responses. Structural studies of six homomeric K_2Ps have established the basic architecture of this channel family, revealed key moving parts involved in K_2P function, uncovered the importance of asymmetric pinching and dilation motions in the K_2P selectivity filter (SF) C-type gate, and defined two K_2P structural classes based on the absence or presence of an intracellular gate. Further, a series of structures characterizing K_2P:modulator interactions have revealed a striking polysite pharmacology housed within a relatively modestly sized (~70 kDa) channel. Binding sites for small molecules or lipids that control channel function are found at every layer of the channel structure, starting from its extracellular side through the portion that interacts with the membrane bilayer inner leaflet. This framework provides the basis for understanding how gating cues sensed by different channel parts control function and how small molecules and lipids modulate K_2P activity. Such knowledge should catalyze development of new K_2P modulators to probe function and treat a wide range of disorders.

A protet-based, protonic charge transfer model of energy coupling in oxidative and photosynthetic phosphorylation

Textbooks of biochemistry will explain that the otherwise endergonic reactions of ATP synthesis can be driven by the exergonic reactions of respiratory electron transport, and that these two half-reactions are catalyzed by protein complexes embedded in the same, closed membrane. These views are correct. The textbooks also state that, according to the chemiosmotic coupling hypothesis, a (or the) kinetically and thermodynamically competent intermediate linking the two half-reactions is the electrochemical difference of protons that is in equilibrium with that between the two bulk phases that the coupling membrane serves to separate. This gradient consists of a membrane potential term Δψ and a pH gradient term ΔpH, and is known colloquially as the protonmotive force or pmf. Artificial imposition of a pmf can drive phosphorylation, but only if the pmf exceeds some 150-170mV; to achieve in vivo rates the imposed pmf must reach 200mV. The key question then is 'does the pmf generated by electron transport exceed 200mV, or even 170mV?' The possibly surprising answer, from a great many kinds of experiment and sources of evidence, including direct measurements with microelectrodes, indicates it that it does not. Observable pH changes driven by electron transport are real, and they control various processes; however, compensating ion movements restrict the Δψ component to low values. A protet-based model, that I outline here, can account for all the necessary observations, including all of those inconsistent with chemiosmotic coupling, and provides for a variety of testable hypotheses by which it might be refined.

A new mechanistic approach for the treatment of chronic neuropathic pain with nitrous oxide integrated from a systems biology narrative review

The limitations of the currently available treatments for chronic neuropathic pain highlight the need for safer and more effective alternatives. The authors carried out a focused review using a systems biology approach to integrate the complex mechanisms of nociception and neuropathic pain, and to decipher the effects of nitrous oxide (N2O) on those pathways, beyond the known effect of N2O on N-methyl-D-aspartate receptors. This review identified a number of potential mechanisms by which N2O could impact the processes involved in peripheral and central sensitization. In the ascending pathway, the effects of N2O include activating TWIK-related K+ channel 1 potassium channels on first-order neurons, blocking voltage-dependent calcium channels to attenuate neuronal excitability, attenuating postsynaptic glutamatergic receptor activation, and possibly blocking voltage-dependent sodium channels. In the descending pathway, N2O induces the release of endogenous opioid ligands and stimulates norepinephrine release. In addition, N2O may mediate epigenetic changes by inhibiting methionine synthase, a key enzyme involved in DNA and RNA methylation. This could explain why this short-acting analgesic has shown long-lasting anti-pain sensitization effects in animal models of chronic pain. These new hypotheses support the rationale for investigating N2O, either alone or in combination with other analgesics, for the management of chronic neuropathic pain.

Mechanistic insights into volatile anesthetic modulation of K2P channels

K2P potassium channels are known to be modulated by volatile anesthetic (VA) drugs and play important roles in clinically relevant effects that accompany general anesthesia. Here, we utilize a photoaffinity analog of the VA isoflurane to identify a VA-binding site in the TREK1 K2P channel. The functional importance of the identified site was validated by mutagenesis and biochemical modification. Molecular dynamics simulations of TREK1 in the presence of VA found multiple neighboring residues on TREK1 TM2, TM3, and TM4 that contribute to anesthetic binding. The identified VA-binding region contains residues that play roles in the mechanisms by which heat, mechanical stretch, and pharmacological modulators alter TREK1 channel activity and overlaps with positions found to modulate TASK K2P channel VA sensitivity. Our findings define molecular contacts that mediate VA binding to TREK1 channels and suggest a mechanistic basis to explain how K2P channels are modulated by VAs.

Xenon treatment after severe traumatic brain injury improves locomotor outcome, reduces acute neuronal loss and enhances early beneficial neuroinflammation: a randomized, blinded, controlled animal study

BACKGROUND

Traumatic brain injury (TBI) is a major cause of morbidity and mortality, but there are no clinically proven treatments that specifically target neuronal loss and secondary injury development following TBI. In this study, we evaluate the effect of xenon treatment on functional outcome, lesion volume, neuronal loss and neuroinflammation after severe TBI in rats.

METHODS

Young adult male Sprague Dawley rats were subjected to controlled cortical impact (CCI) brain trauma or sham surgery followed by treatment with either 50% xenon:25% oxygen balance nitrogen, or control gas 75% nitrogen:25% oxygen. Locomotor function was assessed using Catwalk-XT automated gait analysis at baseline and 24 h after injury. Histological outcomes were assessed following perfusion fixation at 15 min or 24 h after injury or sham procedure.

RESULTS

Xenon treatment reduced lesion volume, reduced early locomotor deficits, and attenuated neuronal loss in clinically relevant cortical and subcortical areas. Xenon treatment resulted in significant increases in Iba1-positive microglia and GFAP-positive reactive astrocytes that was associated with neuronal preservation.

CONCLUSIONS

Our findings demonstrate that xenon improves functional outcome and reduces neuronal loss after brain trauma in rats. Neuronal preservation was associated with a xenon-induced enhancement of microglial cell numbers and astrocyte activation, consistent with a role for early beneficial neuroinflammation in xenon's neuroprotective effect. These findings suggest that xenon may be a first-line clinical treatment for brain trauma.

Administration of inhaled noble and other gases after cardiopulmonary resuscitation: A systematic review

OBJECTIVE

Inhalation of noble and other gases after cardiac arrest (CA) might improve neurological and cardiac outcomes. This article discusses up-to-date information on this novel therapeutic intervention.

DATA SOURCES

CENTRAL, MEDLINE, online published abstracts from conference proceedings, clinical trial registry clinicaltrials.gov, and reference lists of relevant papers were systematically searched from January 1960 till March 2019.

STUDY SELECTION

Preclinical and clinical studies, irrespective of their types or described outcomes, were included.

DATA EXTRACTION

Abstract screening, study selection, and data extraction were performed by two independent authors. Due to the paucity of human trials, risk of bias assessment was not performed DATA SYNTHESIS: After screening 281 interventional studies, we included an overall of 27. Only, xenon, helium, hydrogen, and nitric oxide have been or are being studied on humans. Xenon, nitric oxide, and hydrogen show both neuroprotective and cardiotonic features, while argon and hydrogen sulfide seem neuroprotective, but not cardiotonic. Most gases have elicited neurohistological protection in preclinical studies; however, only hydrogen and hydrogen sulfide appeared to preserve CA1 sector of hippocampus, the most vulnerable area in the brain for hypoxia.

CONCLUSION

Inhalation of certain gases after CPR appears promising in mitigating neurological and cardiac damage and may become the next successful neuroprotective and cardiotonic interventions.

PLD2-PI(4,5)P2 interactions in fluid phase membranes: Structural modeling and molecular dynamics simulations

Interaction of phospholipase D2 (PLD2) with phosphatidylinositol (4,5)-bisphosphate (PIP2) is regarded as the critical step of numerous physiological processes. Here we build a full-length model of human PLD2 (hPLD2) combining template-based and ab initio modeling techniques and use microsecond all-atom molecular dynamics (MD) simulations of the protein in contact with a complex membrane to determine hPLD2-PIP2 interactions. MD simulations reveal that the intermolecular interactions preferentially occur between specific PIP2 phosphate groups and hPLD2 residues; the most strongly interacting residues are arginine at the pbox consensus sequence (PX) and pleckstrin homology (PH) domain. Interaction networks indicate formation of clusters at the protein-membrane interface consisting of amino acids, PIP2, and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidic acid (POPA); the largest cluster was in the PH domain.

Two-Pore Domain Potassium Channels as Drug Targets: Anesthesia and Beyond

Two-pore domain potassium (K2P) channels stabilize the resting membrane potential of both excitable and nonexcitable cells and, as such, are important regulators of cell activity. There are many conditions where pharmacological regulation of K2P channel activity would be of therapeutic benefit, including, but not limited to, atrial fibrillation, respiratory depression, pulmonary hypertension, neuropathic pain, migraine, depression, and some forms of cancer. Up until now, few if any selective pharmacological regulators of K2P channels have been available. However, recent publications of solved structures with small-molecule activators and inhibitors bound to TREK-1, TREK-2, and TASK-1 K2P channels have given insight into the pharmacophore requirements for compound binding to these sites. Together with the increasing availability of a number of novel, active, small-molecule compounds from K2P channel screening programs, these advances have opened up the possibility of rational activator and inhibitor design to selectively target K2P channels.

Studies on the mechanism of general anesthesia

Anesthetics are used every day in thousands of hospitals to induce loss of consciousness, yet scientists and the doctors who administer these compounds lack a molecular understanding for their action. The chemical properties of anesthetics suggest that they could target the plasma membrane. Here the authors show anesthetics directly target a subset of plasma membrane lipids to activate an ion channel in a two-step mechanism. Applying the mechanism, the authors mutate a fruit fly to be less sensitive to anesthetics and convert a nonanesthetic-sensitive channel into a sensitive one. These findings suggest a membrane-mediated mechanism will be an important consideration for other proteins of which direct binding of anesthetic has yet to explain conserved sensitivity to chemically diverse anesthetics.

Inhaled anesthetics are a chemically diverse collection of hydrophobic molecules that robustly activate TWIK-related K⁺ channels (TREK-1) and reversibly induce loss of consciousness. For 100 y, anesthetics were speculated to target cellular membranes, yet no plausible mechanism emerged to explain a membrane effect on ion channels. Here we show that inhaled anesthetics (chloroform and isoflurane) activate TREK-1 through disruption of phospholipase D2 (PLD2) localization to lipid rafts and subsequent production of signaling lipid phosphatidic acid (PA). Catalytically dead PLD2 robustly blocks anesthetic TREK-1 currents in whole-cell patch-clamp recordings. Localization of PLD2 renders the TRAAK channel sensitive, a channel that is otherwise anesthetic insensitive. General anesthetics, such as chloroform, isoflurane, diethyl ether, xenon, and propofol, disrupt lipid rafts and activate PLD2. In the whole brain of flies, anesthesia disrupts rafts and PLD^null flies resist anesthesia. Our results establish a membrane-mediated target of inhaled anesthesia and suggest PA helps set thresholds of anesthetic sensitivity in vivo.

Ketamine and nitrous oxide: The evolution of NMDA receptor antagonists as antidepressant agents

N-methyl-d-aspartate receptor (NMDAR) antagonists, including ketamine and nitrous oxide, are currently intensely studied as rapid-acting antidepressant agents. Interestingly, both of these compounds are also drugs of abuse. Intravenous ketamine, a dissociative anesthetic that induces complex downstream effects via NMDARs, rapidly reduces depressive and suicidal symptoms in treatment-resistant depression (TRD), as demonstrated by several trials. Recently, the United States Food and Drug Administration (FDA) approved an intranasal version of ketamine (esketamine) for TRD. The United States Drug Enforcement Agency (DEA) lists ketamine as a Class III scheduled drug (moderate-low potential for physical and psychological abuse). The FDA has established a Risk Evaluation and Management Strategy (REMS) program to ensure proper drug storage, handling, dispensing, and monitoring intranasal esketamine to minimize misuse/abuse opportunities. Nitrous Oxide is a colorless, odorless, gas that has been in medical use for over 150 years. The mechanisms of action of nitrous oxide are not fully understood; however, it is known to act as a non-competitive inhibitor of NMDA-type glutamate receptors. Currently, nitrous oxide is used for inhalational general anesthesia and analgesia for short procedures. Inhaled nitrous oxide is also used recreationally, primarily by teens and young adults, but is not believed to have strong addiction potential. In contrast to ketamine, nitrous oxide is not a controlled substance and can be legally purchased without a prescription. A recent double-blind, prospective, cross-over study demonstrated that nitrous oxide reduced depressive symptoms in a group of severely ill TRD patients. Though this is a promising initial study, further investigation is needed.

Update of the organoprotective properties of xenon and argon: from bench to beside

The growth of the elderly population has led to an increase in patients with myocardial infarction and stroke (Wajngarten and Silva, Eur Cardiol 14: 111–115, 2019). Patients receiving treatment for ST-segment-elevation myocardial infarction (STEMI) highly profit from early reperfusion therapy under 3 h from the onset of symptoms. However, mortality from STEMI remains high due to the increase in age and comorbidities (Menees et al., N Engl J Med 369: 901–909, 2013). These factors also account for patients with acute ischaemic stroke. Reperfusion therapy has been established as the gold standard within the first 4 to 5 h after onset of symptoms (Powers et al., Stroke 49: e46-e110, 2018). Nonetheless, not all patients are eligible for reperfusion therapy. The same is true for traumatic brain injury patients. Due to the complexity of acute myocardial and central nervous injury (CNS), finding organ protective substances to improve the function of remote myocardium and the ischaemic penumbra of the brain is urgent. This narrative review focuses on the noble gases argon and xenon and their possible cardiac, renal and neuroprotectant properties in the elderly high-risk (surgical) population. The article will provide an overview of the latest experimental and clinical studies. It is beyond the scope of this review to give a detailed summary of the mechanistic understanding of organ protection by xenon and argon.

Closed circuit xenon delivery for 72h in neonatal piglets following hypoxic insult using an ambient pressure automated control system: Development, technical evaluation and pulmonary effects

BACKGROUND

Therapeutic hypothermia (TH) for 72h is the standard treatment following neonatal encephalopathy (NE). However, one-third do not benefit and adjunctive therapies are urgently needed. Xenon enhances neuroprotection with TH when administered at 50% concentration within 5hours of hypoxia in experimental studies. Delayed initiation (~10 hours of age) of 30% xenon for 24 hours during TH did not improve early adverse biomarkers in a clinical trial of Xenon+TH vs TH. After hypoxia-ischemia, excitotoxic injury via N-methyl-D-aspartate receptor overactivation lasts days. Since xenon partially inhibits this receptor, we hypothesised that giving 50% xenon throughout the entire 72h TH and rewarming periods would enhance neuroprotection. Xenon costs $30/litre, so a closed-circuit breathing system is desirable with automated fresh gas delivery.

METHODS

Seven mechanically ventilated newborn pigs were randomized to receive 50% inhaled xenon for 72h during hypothermia (rectal-temperature 35°C) and subsequent rewarming following a global hypoxic-ischemic insult (XeHT, N = 4) or under normothermia for 72h (rectal-temperature 38.5°C) following sham insult (XeNT, N = 3). An automated fresh gas delivery system injected oxygen/air/xenon boluses into a closed-circuit based on measured gas concentrations.

RESULTS AND DISCUSSION

Median (IQR) xenon consumption was 0.31 L/h (0.18, 0.50) and 0.34L/h (0.32, 0.49) for hypothermic and normothermic groups respectively, 0.34L/h (0.25, 0.53) overall. 92% of 9626 xenon and 69% of 9635 oxygen measurements were within 20% variation from targets. For xenon concentration, the median absolute performance errors for the XeHT and XeNT groups were 6.14% and 3.84% respectively and 4.31% overall. For oxygen these values were 13.42%, 15.05% and 12.4% respectively. There were no adverse pulmonary pathophysiology findings. Clinical problems over the total period included three related to sensors, seven breathing system leaks, ten partial and one complete tracheal tube occlusion episodes.

CONCLUSION

The automated controller functioned as intended maintaining an inhaled xenon concentration close to the 50% target for 72-78h at a xenon cost of $11.1/h.

Disruption of palmitate-mediated localization; a shared pathway of force and anesthetic activation of TREK-1 channels

TWIK related K+ channel (TREK-1) is a mechano- and anesthetic sensitive channel that when activated attenuates pain and causes anesthesia. Recently the enzyme phospholipase D2 (PLD2) was shown to bind to the channel and generate a local high concentration of phosphatidic acid (PA), an anionic signaling lipid that gates TREK-1. In a biological membrane, the cell harnesses lipid heterogeneity (lipid compartments) to control gating of TREK-1 using palmitate-mediated localization of PLD2. Here we discuss the ability of mechanical force and anesthetics to disrupt palmitate-mediated localization of PLD2 giving rise to TREK-1's mechano- and anesthetic-sensitive properties. The likely consequences of this indirect lipid-based mechanism of activation are discussed in terms of a putative model for excitatory and inhibitory mechano-effectors and anesthetic sensitive ion channels in a biological context. Lastly, we discuss the ability of locally generated PA to reach mM concentrations near TREK-1 and the biophysics of localized signaling. Palmitate-mediated localization of PLD2 emerges as a central control mechanism of TREK-1 responding to mechanical force and anesthetic action. This article is part of a Special Issue entitled: Molecular biophysics of membranes and membrane proteins.

Beneficial effects of xenon inhalation on behavioral changes in a valproic acid-induced model of autism in rats

BACKGROUND

Xenon (Xe) is a noble gas that has been used for the last several decades as an anesthetic during surgery. Its antagonistic effect on glutamate subtype of NMDA (N-methyl-D-aspartate) receptors resulted in evaluation of this gas for treatment of CNS pathologies, including psychoemotional disorders. The aim of this study was to assess the behavioral effects of acute inhalation of subanesthetic concentrations of Xe and to study the outcomes of Xe exposure in valproic acid (VPA)-induced rodent model of autism.

METHODS

We have conducted two series of experiments with a battery of behavioral tests aimed to evaluate locomotion, anxiety- and depression-like behavior, and social behavior in healthy, VPA-treated and Xe-exposed young rats.

RESULTS

We have shown that in healthy animals Xe exposure resulted in acute and delayed decrease of exploratory motivation, partial decrease in risk-taking and depressive-like behavior as well as improved sensorimotor integration during the negative geotaxis test. Acute inhalations of Xe in VPA-exposed animals led to improvement in social behavior, decrease in exploratory motivation, and normalization of behavior in forced-swim test.

CONCLUSION

Behavioral modulatory effects of Xe are probably related to its generalized action on excitatory/inhibitory balance within the CNS. Our data suggest that subanesthetic short-term exposures to Xe have beneficial effect on several behavioral modalities and deserves further investigation.

Neuroprotection Strategies for Term Encephalopathy

Brain injury in the full-term and near-term neonates is a significant cause of mortality and long-term morbidity, resulting in injury patterns distinct from that seen in premature infants and older patients. Therapeutic hypothermia improves long-term outcomes for many of these infants, but there is a continued search for therapies to enhance the plasticity of the newborn brain, resulting in long-term repair. It is likely that a combination strategy utilizing both early and late interventions may have the most benefit, capitalizing on endogenous mechanisms triggered by hypoxia or ischemia. Optimizing care of these critically ill newborns in the acute setting is also vital for improving both short- and long-term outcomes.

Effects of Xenon-Based Anesthetic Exposure on the Expression Levels of Polysialic Acid Neural Cell Adhesion Molecule (PSA-NCAM) on Human Neural Stem Cell-Derived Neurons

Numerous studies suggest a long duration of anesthesia during the late gestation period and infancy is associated with an increased risk of neuronal damage and neurocognitive impairment. The noble gas xenon is an anesthetic that is reported to have neuroprotective effects in some circumstances at certain concentrations. Currently, the effects of xenon on the brain and its potential neuroprotective properties, and/or the effects of xenon used in combination with other anesthetics, are not clearly understood and some reported data appear contradictory. In the present study, human neural stem cells were employed as a human-relevant model to evaluate the effects of xenon when it was co-administered with propofol, a frequently used anesthetic in pediatric anesthesia, and to understand the mechanism(s). The expression of polysialic acid (PSA) neural cell adhesion molecule (NCAM) on human neural stem cell-differentiated neurons was investigated as a key target molecule. PSA is a specific marker of developing neurons. It is essential for neuronal viability and plasticity. Human neural stem cells were maintained in neural differentiation medium and directed to differentiate into neuronal and glial lineages, and were exposed to propofol (50 μM) for 16 h in the presence or absence of xenon (33%). The neural stem cell-derived neurons were characterized by labelling cells with PSA-NCAM, after 5 days of differentiation. Propofol- and/or xenon-induced neurotoxicities were determined by measuring PSA immunoreactivity. A time course study showed that neuronal cell surface PSA was clearly cleaved off from NCAM by endoneuraminidase N (Endo-N), and eliminated PSA immunostaining was not re-expressed 4, 8, or 16 h after Endo-N washout. However, in the presence of 33% xenon, intense PSA staining on neuronal cell surface and processes was evident 16 h after Endo-N washout. In addition, prolonged (16 h) propofol exposure significantly decreased the positive rate of PSA-labeled neurons. When combined with xenon, propofol's adverse effects on neurons were attenuated. This work, conducted on the human neural stem cell-derived models, has provided evidence of the beneficiary effects of xenon on neurons and helps develop xenon-based anesthesia regimens in the pediatric population.

Noble gas neuroprotection: xenon and argon protect against hypoxic-ischaemic injury in rat hippocampus in vitro via distinct mechanisms

Background

Noble gases may provide novel treatments for neurological injuries such as ischaemic and traumatic brain injury. Few studies have evaluated the complete series of noble gases under identical conditions in the same model.

Methods

We used an in vitro model of hypoxia–ischaemia to evaluate the neuroprotective properties of the series of noble gases, helium, neon, argon, krypton, and xenon. Organotypic hippocampal brain slices from mice were subjected to oxygen-glucose deprivation, and injury was quantified using propidium iodide fluorescence.

Results

Both xenon and argon were equally effective neuroprotectants, with 0.5 atm of xenon or argon reducing injury by 96% (P<0.0001), whereas helium, neon, and krypton were devoid of any protective effect. Neuroprotection by xenon, but not argon, was reversed by elevated glycine.

Conclusions

Xenon and argon are equally effective as neuroprotectants against hypoxia–ischaemia in vitro, with both gases preventing injury development. Although xenon's neuroprotective effect may be mediated by inhibition of the N-methyl-d-aspartate receptor at the glycine site, argon acts via a different mechanism. These findings may have important implications for their clinical use as neuroprotectants.

Ketamine Action in the In Vitro Cortical Slice Is Mitigated by Potassium Channel Blockade

BACKGROUND

Ketamine is a general anesthetic thought to act by antagonizing N-methyl-D-aspartate receptors. However, ketamine acts on multiple channels, many of which are potential targets-including hyperpolarization-activated cyclic nucleotide-gated and potassium channels. In this study we tested the hypothesis that potassium leak channels contribute to the anesthetic action of ketamine.

METHODS

Adult mouse cortical slices (400 µm) were exposed to no-magnesium artificial cerebrospinal fluid to generate seizure-like event activity. The reduction in seizure-like event frequency after exposure to ketamine (n = 14) was quantified as a signature of anesthetic effect. Pharmacologic manipulation of hyperpolarization-activated cyclic nucleotide-gated and potassium channels using ZD7288 (n = 11), cesium chloride (n = 10), barium chloride (n = 10), low-potassium (1.5 mM) artificial cerebrospinal fluid (n = 10), and urethane (n = 7) were investigated.

RESULTS

Ketamine reduced the frequency of seizure-like events (mean [SD], -62 [22]%, P < 0.0001). Selective hyperpolarization-activated cyclic nucleotide-gated channel block with ZD7288 did not significantly alter the potency of ketamine to inhibit seizure-like event activity. The inhibition of seizure-like event frequency by ketamine was fully antagonized by the potassium channel blockers cesium chloride and barium chloride (8 [26]% and 39 [58%] increase, respectively, P < 0.0001, compared to ketamine control) and was facilitated by the potassium leak channel opener urethane (-93 [8]%, P = 0.002 compared to ketamine control) and low potassium artificial cerebrospinal fluid (-86 [11]%, P = 0.004 compared to ketamine control).

CONCLUSIONS

The results of this study show that mechanisms additional to hyperpolarization-activated cyclic nucleotide-gated channel block are likely to explain the anesthetic action of ketamine and suggest facilitatory action at two-pore potassium leak channels.

Anesthetics: from modes of action to unconsciousness and neurotoxicity

Modern anesthetic compounds and advanced monitoring tools have revolutionized the field of medicine, allowing for complex surgical procedures to occur safely and effectively. Faster induction times and quicker recovery periods of current anesthetic agents have also helped reduce health care costs significantly. Moreover, extensive research has allowed for a better understanding of anesthetic modes of action, thus facilitating the development of more effective and safer compounds. Notwithstanding the realization that anesthetics are a prerequisite to all surgical procedures, evidence is emerging to support the notion that exposure of the developing brain to certain anesthetics may impact future brain development and function. Whereas the data in support of this postulate from human studies is equivocal, the vast majority of animal research strongly suggests that anesthetics are indeed cytotoxic at multiple brain structure and function levels. In this review, we first highlight various modes of anesthetic action and then debate the evidence of harm from both basic science and clinical studies perspectives. We present evidence from animal and human studies vis-à-vis the possible detrimental effects of anesthetic agents on both the young developing and the elderly aging brain while discussing potential ways to mitigate these effects. We hope that this review will, on the one hand, invoke debate vis-à-vis the evidence of anesthetic harm in young children and the elderly, and on the other hand, incentivize the search for better and less toxic anesthetic compounds.

Xenon improves long-term cognitive function, reduces neuronal loss and chronic neuroinflammation, and improves survival after traumatic brain injury in mice

Background

Xenon is a noble gas with neuroprotective properties that can improve short and long-term outcomes in young adult mice after controlled cortical impact. This follow-up study investigates the effects of xenon on very long-term outcomes and survival.

Methods

C57BL/6N young adult male mice (n=72) received single controlled cortical impact or sham surgery and were treated with either xenon (75% Xe:25% O₂) or control gas (75% N₂:25% O₂). Outcomes measured were: (i) 24 h lesion volume and neurological outcome score; (ii) contextual fear conditioning at 2 weeks and 20 months; (iii) corpus callosum white matter quantification; (iv) immunohistological assessment of neuroinflammation and neuronal loss; and (v) long-term survival.

Results

Xenon treatment significantly reduced secondary injury (P<0.05), improved short-term vestibulomotor function (P<0.01), and prevented development of very late-onset traumatic brain injury (TBI)-related memory deficits. Xenon treatment reduced white matter loss in the contralateral corpus callosum and neuronal loss in the contralateral hippocampal CA1 and dentate gyrus areas at 20 months. Xenon's long-term neuroprotective effects were associated with a significant (P<0.05) reduction in neuroinflammation in multiple brain areas involved in associative memory, including reduction in reactive astrogliosis and microglial cell proliferation. Survival was improved significantly (P<0.05) in xenon-treated animals compared with untreated animals up to 12 months after injury.

Conclusions

Xenon treatment after TBI results in very long-term improvements in clinically relevant outcomes and survival. Our findings support the idea that xenon treatment shortly after TBI may have long-term benefits in the treatment of brain trauma patients.

Role of TREK-1 in Health and Disease, Focus on the Central Nervous System

TREK-1 is the most studied background K_2P channel. Its main role is to control cell excitability and maintain the membrane potential below the threshold of depolarization. TREK-1 is multi-regulated by a variety of physical and chemical stimuli which makes it a very promising and challenging target in the treatment of several pathologies. It is mainly expressed in the brain but also in heart, smooth muscle cells, endocrine pancreas, and prostate. In the nervous system, TREK-1 is involved in many physiological and pathological processes such as depression, neuroprotection, pain, and anesthesia. These properties explain why many laboratories and pharmaceutical companies have been focusing their research on screening and developing highly efficient modulators of TREK-1 channels. In this review, we summarize the different roles of TREK-1 that have been investigated so far in attempt to characterize pharmacological tools and new molecules to modulate cellular functions controlled by TREK-1.

Tandem pore TWIK-related potassium channels and neuroprotection

TWIK-related potassium channels (TREK) belong to a subfamily of the two-pore domain potassium channels family with three members, TREK1, TREK2 and TWIK-related arachidonic acid-activated potassium channels. The two-pore domain potassium channels is the last big family of channels being discovered, therefore it is not surprising that most of the information we know about TREK channels predominantly comes from the study of heterologously expressed channels. Notwithstanding, in this review we pay special attention to the limited amount of information available on native TREK-like channels and real neurons in relation to neuroprotection. Mainly we focus on the role of free fatty acids, lysophospholipids and other neuroprotective agents like riluzole in the modulation of TREK channels, emphasizing on how important this modulation may be for the development of new therapies against neuropathic pain, depression, schizophrenia, epilepsy, ischemia and cardiac complications.

TREK-1 channels regulate pressure sensitivity and calcium signaling in trabecular meshwork cells

The trabecular meshwork (TM) plays a fundamental role in intraocular pressure regulation, but its mechanotransduction pathway is poorly understood. Yarishkin et al. show that the mechanosensing channel TREK-1 regulates TM membrane potential, pressure sensitivity, calcium homeostasis, and impedance.

Mechanotransduction by the trabecular meshwork (TM) is an essential component of intraocular pressure regulation in the vertebrate eye. This process is compromised in glaucoma but is poorly understood. In this study, we identify transient receptor potential vanilloid isoform 4 (TRPV4) and TWIK-related potassium channel-1 (TREK-1) as key molecular determinants of TM membrane potential, pressure sensitivity, calcium homeostasis, and transcellular permeability. We show that resting membrane potential in human TM cells is unaffected by “classical” inhibitors of voltage-activated, calcium-activated, and inwardly rectifying potassium channels but is depolarized by blockers of tandem-pore K⁺ channels. Using gene profiling, we reveal the presence of TREK-1, TASK-1, TWIK-2, and THIK transcripts in TM cells. Pressure stimuli, arachidonic acid, and TREK-1 activators hyperpolarize these cells, effects that are antagonized by quinine, amlodipine, spadin, and short-hairpin RNA–mediated knockdown of TREK-1 but not TASK-1. Activation and inhibition of TREK-1 modulates [Ca²⁺]_TM and lowers the impedance of cell monolayers. Together, these results suggest that tensile homeostasis in the TM may be regulated by balanced, pressure-dependent activation of TRPV4 and TREK-1 mechanotransducers.

Xenon: An Emerging Neuroprotectant With Potential Application for Cardiac Arrest Care

Xenon is an inert, highly polarizable noble gas with demonstrated safety and application in general anesthesia for over 50 years. A potent inhibitor of the N-methyl-D-aspartate subtype of glutamate receptors, xenon has a well-documented ameliorating effect on excitotoxic neuronal injury in numerous cellular and animal models of hypoxic-ischemic brain injury. The most important determinant of overall survival and morbidity in out-of-hospital cardiac arrest is the severity of neurological injury. The only approved neuroprotective strategy in this setting is mild therapeutic hypothermia, which has demonstrated significant, albeit modest, improvements in mortality. The combination therapy of therapeutic hypothermia and xenon in porcine models of cardiac arrest has shown a greater improvement in functional outcomes than either intervention alone, thereby prompting the study of combination therapy in randomized clinical trials. The treatment of postarrest patients with xenon and mild hypothermia is safe and demonstrates favorable cardiovascular features, including a reduced heart rate, a reduction in troponin elevations, and a decreased need for vasopressors. Combination therapy is superior in protecting white matter integrity than hypothermia alone, but did not significantly impact neurological outcomes at 6-month follow-up. Despite an abundance of preclinical evidence supporting xenon's neuroprotective properties, its translational potential in postcardiac arrest care is indeterminate due to a lack of adequately-powered studies.

Potential application value of xenon in stroke treatment

Stroke is an acute disease with extremely high mortality and disability, including ischemic stroke and hemorrhagic stroke. Currently only limited drugs and treatments have been shown to have neuroprotective effects in stroke. As a medical gas, xenon has been proven to have neuroprotective effect in considerable amount of previous study. Its unique properties are different from other neuroprotective agents, making it is promising to play a special therapeutic role in stroke, either alone or in combination with other treatments. In this article, we aim to review the role of xenon in the treatment of stroke, and summarize the mechanism of using xenon to produce therapeutic effects after stroke according to the existing research. Moreover, we intend to explore and demonstrate the feasibility and safety of xenon for clinical treatment of stroke. Despite the disadvantages of difficulty in obtaining and being expensive, as long as the use of reasonable methods, xenon can play an important role in the treatment of stroke.