Reduction of ischemic brain damage by nitrous oxide and xenon

Xenon gas as a potential treatment for opioid use disorder, alcohol use disorder, and related disorders

Xenon gas is considered to be a safe anesthetic and imaging agent. Research on its other potentially beneficial effects suggests that xenon may have broad efficacy for treating health disorders. A number of reviews on xenon applications have been published, but none have focused on substance use disorders. Accordingly, we review xenon effects and targets relevant to the treatment of substance use disorders, with a focus on opioid use disorder and alcohol use disorder. We report that xenon inhaled at subsedative concentrations inhibits conditioned memory reconsolidation and opioid withdrawal symptoms. We review work by others reporting on the antidepressant, anxiolytic, and analgesic properties of xenon, which could diminish negative affective states and pain. We discuss research supporting the possibility that xenon could prevent analgesic- or stress-induced opioid tolerance and, by so doing could reduce the risk of developing opioid use disorder. The rapid kinetics, favorable safety and side effect profiles, and multitargeting capability of xenon suggest that it could be used as an ambulatory on-demand treatment to rapidly attenuate maladaptive memory, physical and affective withdrawal symptoms, and pain drivers of substance use disorders when they occur. Xenon may also have human immunodeficiency virus and oncology applications because its effects relevant to substance use disorders could be exploited to target human immunodeficiency virus reservoirs, human immunodeficiency virus protein-induced abnormalities, and cancers. Although xenon is expensive, low concentrations exert beneficial effects, and gas separation, recovery, and recycling advancements will lower xenon costs, increasing the economic feasibility of its therapeutic use. More research is needed to better understand the remarkable repertoire of effects of xenon and its potential therapeutic applications.

Stroke and Translational Research - Review of Experimental Models with a Focus on Awake Ischaemic Induction and Anaesthesia

Animal models are an indispensable tool in the study of ischaemic stroke with hundreds of drugs emerging from the preclinical pipeline. However, all of these drugs have failed to translate into successful treatments in the clinic. This has brought into focus the need to enhance preclinical studies to improve translation. The confounding effects of anaesthesia on preclinical stroke modelling has been raised as an important consideration. Various volatile and injectable anaesthetics are used in preclinical models during stroke induction and for outcome measurements such as imaging or electrophysiology. However, anaesthetics modulate several pathways essential in the pathophysiology of stroke in a dose and drug dependent manner. Most notably, anaesthesia has significant modulatory effects on cerebral blood flow, metabolism, spreading depolarizations, and neurovascular coupling. To minimise anaesthetic complications and improve translational relevance, awake stroke induction has been attempted in limited models. This review outlines anaesthetic strategies employed in preclinical ischaemic rodent models and their reported cerebral effects. Stroke related complications are also addressed with a focus on infarct volume, neurological deficits, and thrombolysis efficacy. We also summarise routinely used focal ischaemic stroke rodent models and discuss the attempts to induce some of these models in awake rodents.

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.

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.

Neuroprotection in aortic arch surgery: untold flaws and future directions

The current paradigm of brain protection in aortic surgery falls short of delivering good outcomes with minimal complications. A renewed understanding of neuroprotective methods and biomarkers to predict brain injury and aortic disease are crucial towards the development of more effective clinical management strategies. A review of current literature was carried out to identify current flaws in our approach to neuroprotection in aortic surgery. Emerging evidence surrounding neuroprotective strategies, biomarkers for brain injury, and biomarkers for predicting aortic disease are evaluated in terms of their impact for future therapeutic approaches. Current literature suggests that the prevailing methods of neuroprotection need renewal. Clinical outcomes associated with deep hypothermic circulatory arrest remain varied. Branch-first and endovascular approaches to aortic repair are particularly promising alternatives. The use of biomarkers to identify and manage brain injury, as well as to diagnose aortic disease in the nonacute and acute settings, would further help to improve our overall paradigm of neuroprotection in aortic surgery. Though much prospective research is still required, the outlook for neuroprotection in aortic surgery is promising. Adopting alternative surgical techniques and exploiting predictive novel biomarkers will help us to gradually eliminate the risk of brain damage in aortic surgery.

Medical Gas Therapy for Tissue, Organ, and CNS Protection: A Systematic Review of Effects, Mechanisms, and Challenges

Gaseous molecules have been increasingly explored for therapeutic development. Here, following an analytical background introduction, a systematic review of medical gas research is presented, focusing on tissue protections, mechanisms, data tangibility, and translational challenges. The pharmacological efficacies of carbon monoxide (CO) and xenon (Xe) are further examined with emphasis on intracellular messengers associated with cytoprotection and functional improvement for the CNS, heart, retina, liver, kidneys, lungs, etc. Overall, the outcome supports the hypothesis that readily deliverable "biological gas" (CO, H2 , H2 S, NO, O2 , O3 , and N2 O) or "noble gas" (He, Ar, and Xe) treatment may preserve cells against common pathologies by regulating oxidative, inflammatory, apoptotic, survival, and/or repair processes. Specifically, CO, in safe dosages, elicits neurorestoration via igniting sGC/cGMP/MAPK signaling and crosstalk between HO-CO, HIF-1α/VEGF, and NOS pathways. Xe rescues neurons through NMDA antagonism and PI3K/Akt/HIF-1α/ERK activation. Primary findings also reveal that the need to utilize cutting-edge molecular and genetic tactics to validate mechanistic targets and optimize outcome consistency remains urgent; the number of neurotherapeutic investigations is limited, without published results from large in vivo models. Lastly, the broad-spectrum, concurrent multimodal homeostatic actions of medical gases may represent a novel pharmaceutical approach to treating critical organ failure and neurotrauma.

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.

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.

Models and methods for conditioning the ischemic brain

BACKGROUND

In the last decades the need to find new neuroprotective targets has addressed the researchers to investigate the endogenous molecular mechanisms that brain activates when exposed to a conditioning stimulus. Indeed, conditioning is an adaptive biological process activated by those interventions able to confer resistance to a deleterious brain event through the exposure to a sub-threshold insult. Specifically, preconditioning and postconditioning are realized when the conditioning stimulus is applied before or after, respectively, the harmul ischemia.

AIMS AND RESULTS

The present review will describe the most common methods to induce brain conditioning, with particular regards to surgical, physical exercise, temperature-induced and pharmacological approaches. It has been well recognized that when the subliminal stimulus is delivered after the ischemic insult, the achieved neuroprotection is comparable to that observed in models of ischemic preconditioning. In addition, subjecting the brain to both preconditioning as well as postconditioning did not cause greater protection than each treatment alone.

CONCLUSIONS

The last decades have provided fascinating insights into the mechanisms and potential application of strategies to induce brain conditioning. Since the identification of intrinsic cell-survival pathways should provide more direct opportunities for translational neuroprotection trials, an accurate examination of the different models of preconditioning and postconditioning is mandatory before starting any new project.

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.

Neurologic and cognitive outcomes associated with the clinical use of xenon: a systematic review and meta-analysis of randomized-controlled trials

BACKGROUND

Xenon has been shown to have positive neurologic effects in various pre-clinical models. This study systematically reviewed the randomized-controlled trials (RCTs) investigating neurologic and cognitive outcomes associated with the clinical use of xenon.

METHODS

We searched PubMed, CENTRAL, EMBASE, CINAHL, elibrary.ru (for Russian studies), Google Scholar (for Russian studies), and Wanfang (for Chinese studies) for appropriate RCTs comparing neurologic or cognitive outcomes after clinical use of xenon with control treatment or with other anesthetic agents.

RESULTS

Seventeen RCTs met the inclusion criteria. Two studies investigated the effects of xenon plus therapeutic hypothermia to treat neonatal asphyxia or out-of-hospital cardiac arrest. Compared with therapeutic hypothermia alone, xenon and therapeutic hypothermia reduced cerebral white matter abnormalities after cardiac arrest but had no effect on neurocognitive outcome and mortality. Xenon had no added value when used to treat neonatal asphyxia. Thirteen RCTs compared neurocognitive effects of xenon with other anesthetic agents in surgical patients. While xenon may be associated with improved short-term (< three hours) cognitive outcome, no medium-term (six hours to three months) advantage was observed, and longer-term data are lacking. No differences in biochemical (S-100β, neuron-specific enolase) and neuropsychologic (attentional performance) outcomes were found with xenon compared with other anesthetic drugs. Finally, two studies suggest that brief, intermittent administration of sub-anesthetic doses of xenon to patients during the acute phase of substance withdrawal may improve neurocognitive outcomes.

CONCLUSIONS

Despite promising pre-clinical results, the evidence for positive clinical neurologic and cognitive outcomes associated with xenon administration is modest. Nevertheless, there is some evidence to suggest that xenon may be associated with better neurologic outcomes compared with the standard of care therapy in certain specific clinical situations. More clinical trials are needed to determine any potential benefit linked to xenon administration.

The role of nitrous oxide in stroke

Stroke that is caused by poor blood flow into the brain results in cell death, including ischemia stroke due to lack of blood into brain tissue, and hemorrhage due to bleeding. Both of them will give rise to the dysfunction of brain. In general, the signs and symptoms of stroke are the inability of feeling or moving on one side of body, sometimes loss of vision to one side. Above symptoms will appear soon after the stroke has happened. If the symptoms and signs happen in 1 or 2 hours, we often call them as transient ischemic attack. Moreover, hemorrhagic stroke often leads to severe headache. It is known that neuronal death can happen after stroke, and it depends upon the activation of N-methyl-D-aspartate (NMDA) excitatory glutamate receptor which is the goal for a lot of neuroprotective agents. Nitrous oxide was discovered by Joseph Priestley in 1772, and then he and his friends, including the poet Coleridge and Robert Sauce, experimented with the gas. They found this gas could make patients loss the sense of pain and still maintain consciousness after inhalation. Shortly the gas was used as an anesthetic, especially in the field of dentists. Now, accroding to theme of Helene N. David and other scientists, both of nitrous oxide at 75 vol% and xenon at 50 vol% could reduce ischemic neuronal death in the cortex by 70% and decrease NMDA-induced Ca²⁺ influx by 30%. Therefore, more clinical and experimental studies are important to illuminate the mechanisms of how nitrous oxide protects brain tissue and to explore the best protocol of this gas in stroke treatment.

Delivery of xenon-containing echogenic liposomes inhibits early brain injury following subarachnoid hemorrhage

Xenon (Xe), a noble gas, has promising neuroprotective properties with no proven adverse side-effects. We evaluated neuroprotective effects of Xe delivered by Xe-containing echogenic liposomes (Xe-ELIP) via ultrasound-controlled cerebral drug release on early brain injury following subarachnoid hemorrhage (SAH). The Xe-ELIP structure was evaluated by ultrasound imaging, electron microscopy and gas chromatography-mass spectroscopy. Animals were randomly divided into five groups: Sham, SAH, SAH treated with Xe-ELIP, empty ELIP, or Xe-saturated saline. Treatments were administrated intravenously in combination with ultrasound application over the common carotid artery to trigger Xe release from circulating Xe-ELIP. Hematoma development was graded by SAH scaling and quantitated by a colorimetric method. Neurological evaluation and motor behavioral tests were conducted for three days following SAH injury. Ultrasound imaging and electron microscopy demonstrated that Xe-ELIP have a unique two-compartment structure, which allows a two-stage Xe release profile. Xe-ELIP treatment effectively reduced bleeding, improved general neurological function, and alleviated motor function damage in association with reduced apoptotic neuronal death and decreased mortality. Xe-ELIP alleviated early SAH brain injury by inhibiting neuronal death and bleeding. This novel approach provides a noninvasive strategy of therapeutic gas delivery for SAH treatment.

Delayed xenon post-conditioning mitigates spinal cord ischemia/reperfusion injury in rabbits by regulating microglial activation and inflammatory factors

The neuroprotective effect against spinal cord ischemia/reperfusion injury in rats exerted by delayed xenon post-conditioning is stronger than that produced by immediate xenon post-conditioning. However, the mechanisms underlying this process remain unclear. Activated microglia are the main inflammatory cell type in the nervous system. The release of pro-inflammatory factors following microglial activation can lead to spinal cord damage, and inhibition of microglial activation can relieve spinal cord ischemia/reperfusion injury. To investigate how xenon regulates microglial activation and the release of inflammatory factors, a rabbit model of spinal cord ischemia/reperfusion injury was induced by balloon occlusion of the infrarenal aorta. After establishment of the model, two interventions were given: (1) immediate xenon post-conditioning—after reperfusion, inhalation of 50% xenon for 1 hour, 50% N₂/50%O₂ for 2 hours; (2) delayed xenon post-conditioning—after reperfusion, inhalation of 50% N₂/50%O₂ for 2 hours, 50% xenon for 1 hour. At 4, 8, 24, 48 and 72 hours after reperfusion, hindlimb locomotor function was scored using the Jacobs locomotor scale. At 72 hours after reperfusion, interleukin 6 and interleukin 10 levels in the spinal cord of each group were measured using western blot assays. Iba1 levels were determined using immunohistochemistry and a western blot assay. The number of normal neurons at the injury site was quantified using hematoxylin-eosin staining. At 72 hours after reperfusion, delayed xenon post-conditioning remarkably enhanced hindlimb motor function, increased the number of normal neurons at the injury site, decreased Iba1 levels, and inhibited interleukin-6 and interleukin-10 levels in the spinal cord. Immediate xenon post-conditioning did not noticeably affect the above-mentioned indexes. These findings indicate that delayed xenon post-conditioning after spinal cord injury improves the recovery of neurological function by reducing microglial activation and the release of interleukin-6 and interleukin-10.

Xenon-helium gas mixture at equimolar concentration of 37.5% protects against oxygen and glucose deprivation-induced injury and inhibits tissue plasminogen activator

Xenon (Xe) is considered to be the golden standard neuroprotective gas. However, Xe has a higher molecular weight and lower thermal conductivity and specific heat than those of nitrogen, the main diluent of oxygen in air. These physical characteristics could impair or at least reduce the intrinsic neuroprotective action of Xe by increasing the patient's respiratory workload and body temperature. In contrast, helium (He) is a cost-efficient gas with a lower molecular weight and higher thermal conductivity and specific heat than those of nitrogen, but is far less potent than Xe. In this study, we hypothesized that mixing Xe and He could allow obtaining a neuroprotective gas mixture with advantageously reduced molecular weight and increased thermal conductivity. We found that Xe and He at the equimolar concentration of 37.5% reduced oxygen-glucose deprivation-induced increase in lactate dehydrogenase in brain slices, an ex vivo model of acute ischemic stroke. These results together with the effects of Xe-He on the thrombolytic efficiency of tissue plasminogen activator are discussed.

A method for calculating the gas volume proportions and inhalation temperature of inert gas mixtures allowing reaching normothermic or hypothermic target body temperature in the awake rat

The noble gases xenon (Xe) and helium (He) are known to possess neuroprotective properties. Xe is considered the golden standard neuroprotective gas. However, Xe has a higher molecular weight and lower thermal conductivity and specific heat than those of nitrogen, the main diluent of oxygen (O2) in air, conditions that could impair or at least reduce the intrinsic neuroprotective properties of Xe by increasing the critical care patient's respiratory workload and body temperature. In contrast, He has a lower molecular weight and higher thermal conductivity and specific heat than those of nitrogen, but is unfortunately far less potent than Xe at providing neuroprotection. Therefore, combining Xe with He could allow obtaining, depending on the gas inhalation temperature and composition, gas mixtures with neutral or hypothermic properties, the latter being advantageous in term of neuroprotection. However, calculating the thermal properties of a mixture, whatever the substances - gases, metals, rubbers, etc. - is not trivial. To answer this question, we provide a graphical method to assess the volume proportions of Xe, He and O2 that a gas mixture should contain, and the inhalation temperature to which it should be administered to allow a clinician to maintain the patient at a target body temperature.

Duration of isoflurane-based surgical anesthesia determines severity of brain injury and neurological deficits after a transient focal ischemia in young adult rats

Tremendous efforts and funds invested in discovery of novel drug treatments for ischemic stroke have so far failed to deliver clinically efficacious therapies. The reasons for these failures are not fully understood. An indiscriminate use of isoflurane-based surgical anesthesia with or without nitrous oxide may act as an unconstrained, untraceable source of data variability, potentially causing false-positive or false-negative results. To test this hypothesis, a common transient suture middle cerebral artery occlusion (tMCAO) model of ischemic stroke in young adult male rats was used to determine the impact of a typical range of anesthesia durations required for this model on data variability (i.e., infarct volume and neurological deficits). The animals were maintained on spontaneous ventilation. The study results indicated that: (1) Variable duration of isoflurane anesthesia prior, during and after tMCAO is a significant source of data variability as evidenced by measurements of infarct volume and neurological deficits; and (2) Severity of brain injury and neurological deficits after tMCAO is inversely related to the duration of isoflurane anesthesia: e.g., in our study, a 90min isoflurane anesthesia nearly completely protected brain tissues from tMCAO-induced injury and thus, would be expected to obscure the effects of stroke treatments in pre-clinical trials. To elevate transparency, rigor and reproducibility of stroke research and minimize undesirable effects of isoflurane on the outcome of novel drug testing, we propose to monitor, minimize and standardize isoflurane anesthesia in experimental surgeries and make anesthesia duration a required reportable parameter in pre-clinical studies. Specifically, we propose to adopt 20-30min as an optimal anesthesia duration that both minimizes neuroprotective effects of isoflurane and permits a successful completion of surgical procedures in a suture tMCAO model of ischemic stroke in rodents. As the mechanisms and neuroprotective, metabolic and immune effects of general anesthesia are not fully understood, the results of this study cannot be blindly generalized to other anesthetics, animal species and experimental models.

Modulation by the Noble Gas Helium of Tissue Plasminogen Activator: Effects in a Rat Model of Thromboembolic Stroke

INTERVENTIONS

Helium has been shown to provide neuroprotection in mechanical model of acute ischemic stroke by inducing hypothermia, a condition shown by itself to reduce the thrombolytic and proteolytic properties of tissue plasminogen activator. However, whether or not helium interacts with the thrombolytic drug tissue plasminogen activator, the only approved therapy of acute ischemic stroke still remains unknown. This point is not trivial since previous data have shown the critical importance of the time at which the neuroprotective noble gases xenon and argon should be administered, during or after ischemia, in order not to block tissue plasminogen activator-induced thrombolysis and to obtain neuroprotection and inhibition of tissue plasminogen activator-induced brain hemorrhages.

MEASUREMENTS AND MAIN RESULTS

We show that helium of 25-75 vol% inhibits in a concentration-dependent fashion the catalytic and thrombolytic activity of tissue plasminogen activator in vitro and ex vivo. In vivo, in rats subjected to thromboembolic brain ischemia, we found that intraischemic helium at 75 vol% inhibits tissue plasminogen activator-induced thrombolysis and subsequent reduction of ischemic brain damage and that postischemic helium at 75 vol% reduces ischemic brain damage and brain hemorrhages.

CONCLUSIONS

In a clinical perspective for the treatment of acute ischemic stroke, these data suggest that helium 1) should not be administered before or together with tissue plasminogen activator therapy due to the risk of inhibiting the benefit of tissue plasminogen activator-induced thrombolysis; and 2) could be an efficient neuroprotective agent if given after tissue plasminogen activator-induced reperfusion.

Paradigms and mechanisms of inhalational anesthetics mediated neuroprotection against cerebral ischemic stroke

Cerebral ischemic stroke is a leading cause of serious long-term disability and cognitive dysfunction. The high mortality and disability of cerebral ischemic stroke is urging the health providers, including anesthesiologists and other perioperative professioners, to seek effective protective strategies, which are extremely limited, especially for those perioperative patients. Intriguingly, several commonly used inhalational anesthetics are recently suggested to possess neuroprotective effects against cerebral ischemia. This review introduces multiple paradigms of inhalational anesthetic treatments that have been investigated in the setting of cerebral ischemia, such as preconditioning, proconditioning and postconditioning with a variety of inhalational anesthetics. The pleiotropic mechanisms underlying these inhalational anesthetics-afforded neuroprotection against stroke are also discussed in detail, including the common pathways shared by most of the inhalational anesthetic paradigms, such as anti-excitotoxicity, anti-apoptosis and anti-inflammation. There are also distinct mechanisms involved in specific paradigms, such as preserving blood brain barrier integrity, regulating cerebral blood flow and catecholamine release. The ready availability of these inhalational anesthetics bedside and renders them a potentially translatable stroke therapy attracting great efforts for understanding of the underlying mechanisms.

Anesthesia in Experimental Stroke Research

Anesthetics have enabled major advances in development of experimental models of human stroke. Yet, their profound pharmacologic effects on neural function can confound the interpretation of experimental stroke research. Anesthetics have species-, drug-, and dose-specific effects on cerebral blood flow and metabolism, neurovascular coupling, autoregulation, ischemic depolarizations, excitotoxicity, inflammation, neural networks, and numerous molecular pathways relevant for stroke outcome. Both preconditioning and postconditioning properties have been described. Anesthetics also modulate systemic arterial blood pressure, lung ventilation, and thermoregulation, all of which may interact with the ischemic insult as well as the therapeutic interventions. These confounds present a dilemma. Here, we provide an overview of the anesthetic mechanisms of action and molecular and physiologic effects on factors relevant to stroke outcomes that can guide the choice and optimization of the anesthetic regimen in experimental stroke.

Xenon-mediated neuroprotection in response to sustained, low-level excitotoxic stress

Noble gases such as xenon and argon have been reported to provide neuroprotection against acute brain ischemic/anoxic injuries. Herein, we wished to evaluate the protective potential of these two gases under conditions relevant to the pathogenesis of chronic neurodegenerative disorders. For that, we established cultures of neurons typically affected in Alzheimer's disease (AD) pathology, that is, cortical neurons and basal forebrain cholinergic neurons and exposed them to L-trans-pyrrolidine-2,4-dicarboxylic acid (PDC) to generate sustained, low-level excitotoxic stress. Over a period of 4 days, PDC caused a progressive loss of cortical neurons which was prevented substantially when xenon replaced nitrogen in the cell culture atmosphere. Unlike xenon, argon remained inactive. Xenon acted downstream of the inhibitory and stimulatory effects elicited by PDC on glutamate uptake and efflux, respectively. Neuroprotection by xenon was mimicked by two noncompetitive antagonists of NMDA glutamate receptors, memantine and ketamine. Each of them potentiated xenon-mediated neuroprotection when used at concentrations providing suboptimal rescue to cortical neurons but most surprisingly, no rescue at all. The survival-promoting effects of xenon persisted when NMDA was used instead of PDC to trigger neuronal death, indicating that NMDA receptor antagonism was probably accountable for xenon’s effects. An excess of glycine failed to reverse xenon neuroprotection, thus excluding a competitive interaction of xenon with the glycine-binding site of NMDA receptors. Noticeably, antioxidants such as Trolox and N-acetylcysteine reduced PDC-induced neuronal death but xenon itself lacked free radical-scavenging activity. Cholinergic neurons were also rescued efficaciously by xenon in basal forebrain cultures. Unexpectedly, however, xenon stimulated cholinergic traits and promoted the morphological differentiation of cholinergic neurons in these cultures. Memantine reproduced some of these neurotrophic effects, albeit with less efficacy than xenon. In conclusion, we demonstrate for the first time that xenon may have a therapeutic potential in AD.

Structural Basis for Xenon Inhibition in a Cationic Pentameric Ligand-Gated Ion Channel

GLIC receptor is a bacterial pentameric ligand-gated ion channel whose action is inhibited by xenon. Xenon has been used in clinical practice as a potent gaseous anaesthetic for decades, but the molecular mechanism of interactions with its integral membrane receptor targets remains poorly understood. Here we characterize by X-ray crystallography the xenon-binding sites within both the open and "locally-closed" (inactive) conformations of GLIC. Major binding sites of xenon, which differ between the two conformations, were identified in three distinct regions that all belong to the trans-membrane domain of GLIC: 1) in an intra-subunit cavity, 2) at the interface between adjacent subunits, and 3) in the pore. The pore site is unique to the locally-closed form where the binding of xenon effectively seals the channel. A putative mechanism of the inhibition of GLIC by xenon is proposed, which might be extended to other pentameric cationic ligand-gated ion channels.

Preclinical neuroprotective actions of xenon and possible implications for human therapeutics: a narrative review

PURPOSE

The purpose of this report is to facilitate an understanding of the possible application of xenon for neuroprotection in critical care settings. This narrative review appraises the literature assessing the efficacy and safety of xenon in preclinical models of acute ongoing neurologic injury.

SOURCE

Databases of the published literature (MEDLINE® and EMBASE™) were appraised for peer-reviewed manuscripts addressing the use of xenon in both preclinical models and disease states of acute ongoing neurologic injury. For randomized clinical trials not yet reported, the investigators' declarations in the National Institutes of Health clinical trials website were considered.

PRINCIPAL FINDINGS

While not a primary focus of this review, to date, xenon cannot be distinguished as superior for surgical anesthesia over existing alternatives in adults. Nevertheless, studies in a variety of preclinical disease models from multiple laboratories have consistently shown xenon's neuroprotective properties. These properties are enhanced in settings where xenon is combined with hypothermia. Small randomized clinical trials are underway to explore xenon's efficacy and safety in clinical settings of acute neurologic injury where hypothermia is the current standard of care.

CONCLUSION

According to the evidence to date, the neuroprotective efficacy of xenon in preclinical models and its safety in clinical anesthesia set the stage for the launch of randomized clinical trials to determine whether these encouraging neuroprotective findings can be translated into clinical utility.

Xenon Blocks Neuronal Injury Associated with Decompression

Despite state-of-the-art hyperbaric oxygen (HBO) treatment, about 30% of patients suffering neurologic decompression sickness (DCS) exhibit incomplete recovery. Since the mechanisms of neurologic DCS involve ischemic processes which result in excitotoxicity, it is likely that HBO in combination with an anti-excitotoxic treatment would improve the outcome in patients being treated for DCS. Therefore, in the present study, we investigated the effect of the noble gas xenon in an ex vivo model of neurologic DCS. Xenon has been shown to provide neuroprotection in multiple models of acute ischemic insults. Fast decompression compared to slow decompression induced an increase in lactate dehydrogenase (LDH), a well-known marker of sub-lethal cell injury. Post-decompression administration of xenon blocked the increase in LDH release induced by fast decompression. These data suggest that xenon could be an efficient additional treatment to HBO for the treatment of neurologic DCS.

Argon blocks the expression of locomotor sensitization to amphetamine through antagonism at the vesicular monoamine transporter-2 and mu-opioid receptor in the nucleus accumbens

We investigated the effects of the noble gas argon on the expression of locomotor sensitization to amphetamine and amphetamine-induced changes in dopamine release and mu-opioid neurotransmission in the nucleus accumbens. We found (1) argon blocked the increase in carrier-mediated dopamine release induced by amphetamine in brain slices, but, in contrast, potentiated the decrease in KCl-evoked dopamine release induced by amphetamine, thereby suggesting that argon inhibited the vesicular monoamine transporter-2; (2) argon blocked the expression of locomotor and mu-opioid neurotransmission sensitization induced by repeated amphetamine administration in a short-term model of sensitization in rats; (3) argon decreased the maximal number of binding sites and increased the dissociation constant of mu-receptors in membrane preparations, thereby indicating that argon is a mu-receptor antagonist; (4) argon blocked the expression of locomotor sensitization and context-dependent locomotor activity induced by repeated administration of amphetamine in a long-term model of sensitization. Taken together, these data indicate that argon could be of potential interest for treating drug addiction and dependence.

Adding 5 h delayed xenon to delayed hypothermia treatment improves long-term function in neonatal rats surviving to adulthood

BACKGROUND

We previously reported that combining immediate hypothermia with immediate or 2 h delayed inhalation of an inert gas, xenon, gave additive neuroprotection in rats after a hypoxic-ischemic insult, compared to hypothermia alone. Defining the therapeutic time window for this new combined intervention is crucial in clinical practice when immediate treatment is not always feasible. The aim of this study is to investigate whether combined hypothermia and xenon still provide neuroprotection in rats after a 5 h delay for both hypothermia and xenon.

METHODS

Seven-day-old Wistar rat pups underwent a unilateral hypoxic-ischemic insult. Pups received 5 h of treatment starting 5 h after the insult randomized between normothermia, hypothermia, or hypothermia with 50% xenon. Surviving pups were tested for fine motor function through weeks 8-10 before being euthanized at week 11. Their hemispheric and hippocampal areas were assessed.

RESULTS

Both delayed hypothermia-xenon and hypothermia-only treated groups had significantly less brain tissue loss than those which underwent normothermia. The functional performance after 1 wk and adulthood was significantly better after hypothermia-xenon treatment as compared to the hypothermia-only or normothermia groups.

CONCLUSION

Adding 50% xenon to 5 h delayed hypothermia significantly improved functional outcome as compared to delayed hypothermia alone despite similar reductions in brain area.

Rewarming from therapeutic hypothermia induces cortical neuron apoptosis in a swine model of neonatal hypoxic-ischemic encephalopathy

The consequences of therapeutic hypothermia for neonatal hypoxic-ischemic encephalopathy are poorly understood. Adverse effects from suboptimal rewarming could diminish neuroprotection from hypothermia. Therefore, we tested whether rewarming is associated with apoptosis. Piglets underwent hypoxia-asphyxia followed by normothermic or hypothermic recovery at 2 hours. Hypothermic groups were divided into those with no rewarming, rewarming at 0.5 °C/hour, or rewarming at 4 °C/hour. Neurodegeneration at 29 hours was assessed by hematoxylin and eosin staining, TUNEL assay, and immunoblotting for cleaved caspase-3. Rewarmed piglets had more apoptosis in motor cortex than did those that remained hypothermic after hypoxia-asphyxia. Apoptosis in piriform cortex was greater in hypoxic-asphyxic, rewarmed piglets than in naive/sham piglets. Caspase-3 inhibitor suppressed apoptosis with rewarming. Rapidly rewarmed piglets had more caspase-3 cleavage in cerebral cortex than did piglets that remained hypothermic or piglets that were rewarmed slowly. We conclude that rewarming from therapeutic hypothermia can adversely affect the newborn brain by inducing apoptosis through caspase mechanisms.

Argon prevents the development of locomotor sensitization to amphetamine and amphetamine-induced changes in mu opioid receptor in the nucleus accumbens

Systemic administration of γ-amino-butyric acid type A (GABA-A) and benzodiazepine receptor agonists has been reported to block the development of locomotor sensitization to amphetamine. Here, we investigated whether the non-anesthetic noble gas argon, shown to possess agonistic properties at these receptors, may block the acquisition of amphetamine-induced locomotor sensitization and mu opioid receptor activation in the nucleus accumbens. Rats were pretreated with saline solution or amphetamine (1 mg/kg) from day 1 to day 3 and then exposed, immediately after injection of amphetamine, to medicinal air or argon at 75 vol% (with the remainder being oxygen). After a 3-day period of withdrawal, rats were challenged with amphetamine on day 7. Rats pretreated with amphetamine and argon had lower locomotor activity (U = 5, P < 0.005) and mu opioid receptor activity in the nucleus accumbens (U = 0, P < 0.001) than rats pretreated with amphetamine and air. In contrast, argon had effect on locomotor and mu receptor activity neither in rats pretreated with saline and challenged with amphetamine (acute amphetamine) nor in rats pretreated and challenged with saline solution (controls). These results indicate that argon inhibits the development of both locomotor sensitization and mu opioid receptor activation induced by repeated administration of amphetamine.

Combination of therapeutic hypothermia and other neuroprotective strategies after an ischemic cerebral insult

Abrupt deprivation of substrates to neuronal tissue triggers a number of pathological events (the “ischemic cascade”) that lead to cell death. As this is a process of delayed neuronal cell death and not an instantaneous event, several pharmacological and non-pharmacological strategies have been developed to attenuate or block this cascade. The most promising neuroprotectant so far is therapeutic hypothermia and its beneficial effects have inspired researchers to further improve its protective benefit by combining it with other neuroprotective agents. This review provides an overview of all neuroprotective strategies that have been combined with therapeutic hypothermia in rodent models of focal cerebral ischemia. A distinction is made between drugs interrupting only one event of the ischemic cascade from those mitigating different pathways and having multimodal effects. Also the combination of therapeutic hypothermia with hemicraniectomy, gene therapy and protein therapy is briefly discussed. Furthermore, those combinations that have been studied in a clinical setting are also reviewed.

Crystallographic Studies with Xenon and Nitrous Oxide Provide Evidence for Protein-dependent Processes in the Mechanisms of General Anesthesia

Background:

The mechanisms by which general anesthetics, including xenon and nitrous oxide, act are only beginning to be discovered. However, structural approaches revealed weak but specific protein–gas interactions.

Methods:

To improve knowledge, we performed x-ray crystallography studies under xenon and nitrous oxide pressure in a series of 10 binding sites within four proteins.

Results:

Whatever the pressure, we show (1) hydrophobicity of the gas binding sites has a screening effect on xenon and nitrous oxide binding, with a threshold value of 83% beyond which and below which xenon and nitrous oxide, respectively, binds to their sites preferentially compared to each other; (2) xenon and nitrous oxide occupancies are significantly correlated respectively to the product and the ratio of hydrophobicity by volume, indicating that hydrophobicity and volume are binding parameters that complement and oppose each other’s effects; and (3) the ratio of occupancy of xenon to nitrous oxide is significantly correlated to hydrophobicity of their binding sites.

Conclusions:

These data demonstrate that xenon and nitrous oxide obey different binding mechanisms, a finding that argues against all unitary hypotheses of narcosis and anesthesia, and indicate that the Meyer–Overton rule of a high correlation between anesthetic potency and solubility in lipids of general anesthetics is often overinterpreted. This study provides evidence that the mechanisms of gas binding to proteins and therefore of general anesthesia should be considered as the result of a fully reversible interaction between a drug ligand and a receptor as this occurs in classical pharmacology.

Anesthetics, cerebral protection and preconditioning

BACKGROUND AND OBJECTIVES

Several studies demonstrate that cerebral preconditioning is a protective mechanism against a stressful situation. Preconditioning determinants are described, as well as the neuroprotection provided by anesthetic and non-anesthetics agents.

CONTENT

Review based on the main articles addressing the pathophysiology of ischemia-reperfusion and neuronal injury and pharmacological and non-pharmacological factors (inflammation, glycemia, and temperature) related to the change in response to ischemia-reperfusion, in addition to neuroprotection induced by anesthetic use.

CONCLUSIONS

The brain has the ability to protect itself against ischemia when stimulated. The elucidation of this mechanism enables the application of preconditioning inducing substances (some anesthetics), other drugs, and non-pharmacological measures, such as hypothermia, aimed at inducing tolerance to ischemic lesions.

The neurotoxicity of nitrous oxide: the facts and "putative" mechanisms

Nitrous oxide is a widely used analgesic agent, used also in combination with anaesthetics during surgery. Recent research has raised concerns about possible neurotoxicity of nitrous oxide, particularly in the developing brain. Nitrous oxide is an N-methyl-d-aspartate (NMDA)-antagonist drug, similar in nature to ketamine, another anaesthetic agent. It has been linked to post-operative cardiovascular problems in clinical studies. It is also widely known that exposure to nitrous oxide during surgery results in elevated homocysteine levels in many patients, but very little work has investigated the long term effect of these increased homocysteine levels. Now research in rodent models has found that homocysteine can be linked to neuronal death and possibly even cognitive deficits. This review aims to examine the current knowledge of mechanisms of action of nitrous oxide, and to describe some pathways by which it may have neurotoxic effects.

[Hyperbaric oxygen therapy and inert gases in cerebral ischemia and traumatic brain injury]

Cerebral ischemia is a common thread of acute cerebral lesions, whether vascular or traumatic origin. Hyperbaric oxygen (HBO) improves tissue oxygenation and may prevent impairment of reversible lesions. In experimental models of cerebral ischemia or traumatic brain injury, HBO has neuroprotective effects which are related to various mechanisms such as modulation of oxidative stress, neuro-inflammation or cerebral and mitochondrial metabolism. However, results of clinical trials failed to prove any neuroprotective effects for cerebral ischemia and remained to be confirmed for traumatic brain injury despite preliminary encouraging results. The addition of inert gases to HBO sessions, especially argon or xenon which show neuroprotective experimental effects, may provide an additional improvement of cerebral lesions. Further multicentric studies with a strict methodology and a better targeted definition are required before drawing definitive conclusions about the efficiency of combined therapy with HBO and inert gases in acute cerebral lesions.

Nitrous oxide and perioperative outcomes

There is emerging evidence related to the effects of nitrous oxide on important perioperative patient outcomes. Proposed mechanisms include metabolic effects linked to elevated homocysteine levels and endothelial dysfunction, inhibition of deoxyribonucleic acid and protein formation, and depression of chemotactic migration by monocytes. Newer large studies point to possible risks associated with the use of nitrous oxide, although data are often equivocal and inconclusive. Cardiovascular outcomes such as stroke or myocardial infarction were shown to be unchanged in previous studies, but the more recent Evaluation of Nitrous Oxide in the Gas Mixture for Anesthesia I trial shows possible associations between nitrous oxide and increased cardiovascular and pulmonary complications. There are also possible effects on postoperative wound infections and neuropsychological function, although the multifactorial nature of these complications should be considered. Teratogenicity linked to nitrous oxide use has not been firmly established. The use of nitrous oxide for routine anesthetic care may be associated with significant costs if complications such as nausea, vomiting, and wound infections are taken into consideration. Overall, definitive data regarding the effect of nitrous oxide on major perioperative outcomes are lacking. There are ongoing prospective studies that may further elucidate its role. The use of nitrous oxide in daily practice should be individualized to each patient's medical conditions and risk factors.

Levosimendan limits reperfusion injury in a rat middle cerebral artery occlusion (MCAO) model

Background

Neuroprotective strategies in ischemic stroke are an important challenge in clinical and experimental research as an adjunct to reperfusion therapy that may reduce neurologic injury and improve outcome. The neuroprotective properties of levosimendan in traumatic brain injury in vitro, transient global brain ischemia and focal spinal cord ischemia suggest the potential for similar effects in transient brain ischemia.

Methods

Transient brain ischemia was induced for 60 min by intraluminal occlusion of the middle cerebral artery in 40 male Wistar rats under general anesthesia with s-ketamine and xylazine and with continuous monitoring of their blood pressure and cerebral perfusion. Five minutes before inducing reperfusion, a levosimendan bolus (24 μg kg ^-1) was administered over a 20 minute period. Infarct size, brain swelling, neurological function and the expression of inflammatory markers were quantified 24 hours after reperfusion.

Results

Although levosimendan limited the infarct size and brain swelling by 40% and 53%, respectively, no effect on neurological outcome or mortality could be demonstrated. Upregulation of tumor necrosis factor α and intercellular adhesion molecule 1 was significantly impeded. Cerebral blood flow during reperfusion was significantly reduced as a consequence of sustained autoregulation.

Conclusions

Levosimendan demonstrated significant neuroprotective properties in a rat model of transient brain ischemia by reducing reperfusion injury.

Anesthetics, cerebral protection and preconditioning

BACKGROUND AND OBJECTIVES

Several studies demonstrate that cerebral preconditioning is a protective mechanism against a stressful situation. Preconditioning determinants are described, as well as the neuroprotection provided by anesthetic and non-anesthetics agents.

CONTENT

Review based on the main articles addressing the pathophysiology of ischemia-reperfusion and neuronal injury and pharmacological and non-pharmacological factors (inflammation, glycemia, and temperature) related to the change in response to ischemia-reperfusion, in addition to neuroprotection induced by anesthetic use.

CONCLUSIONS

The brain has the ability to protect itself against ischemia when stimulated. The elucidation of this mechanism enables the application of preconditioning inducing substances (some anesthetics), other drugs, and non-pharmacological measures, such as hypothermia, aimed at inducing tolerance to ischemic lesions.

Modulation by the noble gas argon of the catalytic and thrombolytic efficiency of tissue plasminogen activator

Argon has been shown to provide cortical as well as, under certain conditions, subcortical neuroprotection in all models so far (middle cerebral artery occlusion, trauma, neonatal asphyxia, etc.). This has led to the suggestion that argon could be a cost-efficient alternative to xenon, a metabolically inert gas thought to be gold standard in gas pharmacology but whose clinical development suffers its little availability and excessive cost of production. However, whether argon interacts with the thrombolytic agent tissue plasminogen activator, which is the only approved therapy of acute ischemic stroke to date, still remains unknown. This latter point is not trivial since previous data have clearly demonstrated the inhibiting effect of xenon on tPA enzymatic and thrombolytic efficiency and the critical importance of the time at which xenon is administered, during or after ischemia, in order not to block thrombolysis and to obtain neuroprotection. Here, we investigated the effect of argon on tPA enzymatic and thrombolytic efficiency using in vitro methods shown to provide reliable prediction of the in vivo effects of both oxygen and the noble inert gases on tPA-induced thrombolysis. We found that argon has a concentration-dependent dual effect on tPA enzymatic and thrombolytic efficiency. Low and high concentrations of argon of 25 and 75 vol% respectively block and increase tPA enzymatic and thrombolytic efficiency. The possible use of argon at low and high concentrations in the treatment of acute ischemic stroke if given during ischemia or after tPA-induced reperfusion is discussed as regards to its neuroprotectant action and its inhibiting and facilitating effects on tPA-induced thrombolysis. The mechanisms of argon-tPA interactions are also discussed.

Post-conditioning by xenon reduces ischaemia-reperfusion injury of the spinal cord in rats

BACKGROUND

The neuroprotective effects of xenon post-conditioning following spinal cord injury remain unknown. We monitored the effect of xenon post-conditioning on the spinal cord following ischaemia-reperfusion injury and determined its mechanism of action.

METHODS

Spinal cord ischaemia was induced following balloon occlusion of the thoracic aorta in male Sprague-Dawley rats. Rats were divided into three groups (n = 30 in each group). The control group underwent ischaemia-reperfusion injury and immediately inhaled 50% (v/v) nitrogen at the time of reperfusion for 60 min continuously. The xenon-post-conditioning group underwent the same surgical procedure and immediately inhaled 50% (v/v) xenon at the time of reperfusion for 60 min continuously. The sham operation group underwent the same surgical procedure without aortic catheter occlusion and inhaled the same gas as that in control rats. Neurologic function was assessed using the Basso, Beattie, and Bresnahan score at 4, 24, and 48 h after reperfusion. Histological changes were observed using Nissl staining, the ultrastructure of the spinal cord was examined using transmission electron microscopy, and apoptosis was monitored using terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labelling.

RESULTS

Compared with the control group, the xenon-post-conditioning group showed improved neurologic outcomes (11.3 ± 1.6 vs. 15.7 ± 3.1, respectively) and had more morphologically normal neurons (6 ± 2 vs. 12 ± 3) at 48 h after reperfusion. Moreover, apoptotic cell death in xenon-treated rats was reduced when compared with control rats (18.29 ± 3.06 vs. 27.34 ± 3.63, P < 0.05, respectively).

CONCLUSIONS

Xenon post-conditioning exerts a neuroprotective effect on the spinal cord following ischaemia-reperfusion injury via its anti-apoptotic role.

Combining xenon and mild therapeutic hypothermia preserves neurological function after prolonged cardiac arrest in pigs

OBJECTIVE

Despite the introduction of mild therapeutic hypothermia into postcardiac arrest care, cerebral and myocardial injuries represent the limiting factors for survival after cardiac arrest. Administering xenon may confer an additional neuroprotective effect after successful cardiopulmonary resuscitation due to its ability to stabilize cellular calcium homeostasis via N-methyl-D-aspartate-receptor antagonism.

DESIGN

In a porcine model, we evaluated effects of xenon treatment in addition to therapeutic hypothermia on neuropathologic and functional outcomes after cardiopulmonary resuscitation.

SETTING

Prospective, randomized, laboratory animal study.

SUBJECTS

Fifteen male pigs.

INTERVENTIONS

Following 10 mins of cardiac arrest and 6 mins of cardiopulmonary resuscitation, ten pigs were randomized to receive either mild therapeutic hypothermia (33°C for 16 hrs) or mild therapeutic hypothermia 1 xenon (70% for 1 hr). Five animals served as normothermic controls.

MEASUREMENTS AND MAIN RESULTS

Gross hemodynamic variables were measured using right-heart catheterization. Neurocognitive performance was evaluated for 5 days after cardiopulmonary resuscitation using a neurologic deficit score before the brains were harvested for histopathological analysis. All animals survived the observation period in the mild therapeutic hypothermia 1 xenon group while one animal in each of the other two groups died. Mild therapeutic hypothermia 1 xenon preserved cardiac output during the induction of mild therapeutic hypothermia significantly better than did mild therapeutic hypothermia alone (4.6 6 0.6 L/min vs. 3.2 6 1.6 L/min, p # .05). Both treatment groups showed significantly fewer necrotic lesions in the cerebral cortex, caudate nucleus, putamen, and in hippocampal sectors CA1 and CA3/4. However, only the combination of mild therapeutic hypothermia and xenon resulted in reduced astrogliosis in the CA1 sector and diminished microgliosis and perivascular inflammation in the putamen. Clinically, only the mild therapeutic hypothermia 1 xenon-treated animals showed significantly improved neurologic deficit scores over time (day 1 = 59.0 6 27.0 vs. day 5 = 4.0 6 5.5, p ø .05) as well as in comparison to the untreated controls on days 3 through 5 after cardiopulmonary resuscitation.

CONCLUSIONS

These results demonstrate that even a short exposure to xenon during induction of mild therapeutic hypothermia results in significant improvements in functional recovery and ameliorated myocardial dysfunction.

Prothrombolytic action of normobaric oxygen given alone or in combination with recombinant tissue-plasminogen activator in a rat model of thromboembolic stroke

The potential benefit of 100 vol% normobaric oxygen (NBO) for the treatment of acute ischemic stroke patients is still a matter of debate. To advance this critical question, we studied the effects of intraischemic normobaric oxygen alone or in combination with recombinant tissue-plasminogen activator (rtPA) on cerebral blood flow and ischemic brain damage and swelling in a clinically relevant rat model of thromboembolic stroke. We show that NBO provides neuroprotection by achieving cerebral blood flow restoration equivalent to 0.9 mg/kg rtPA through probable direct interaction and facilitation of the fibrinolytic properties of endogenous tPA. In contrast, combined NBO and rtPA has no neuroprotective effect on ischemic brain damage despite producing cerebral blood flow restoration. These results 1) by providing a new mechanism of action of NBO highlight together with previous findings the way by which intraischemic NBO shows beneficial action; 2) suggest that NBO could be an efficient primary care therapeutic intervention for patients eligible for rtPA therapy; 3) indicate that NBO could be an interesting alternative for patients not eligible for rtPA therapy; and 4) caution the use of NBO in combination with rtPA in acute stroke patients.

Ex vivo and in vivo neuroprotection induced by argon when given after an excitotoxic or ischemic insult

In vitro studies have well established the neuroprotective action of the noble gas argon. However, only limited data from in vivo models are available, and particularly whether postexcitotoxic or postischemic argon can provide neuroprotection in vivo still remains to be demonstrated. Here, we investigated the possible neuroprotective effect of postexcitotoxic-postischemic argon both ex vivo in acute brain slices subjected to ischemia in the form of oxygen and glucose deprivation (OGD), and in vivo in rats subjected to an intrastriatal injection of N-methyl-D-aspartate (NMDA) or to the occlusion of middle-cerebral artery (MCAO). We show that postexcitotoxic-postischemic argon reduces OGD-induced cell injury in brain slices, and further reduces NMDA-induced brain damage and MCAO-induced cortical brain damage in rats. Contrasting with its beneficial effect at the cortical level, we show that postischemic argon increases MCAO-induced subcortical brain damage and provides no improvement of neurologic outcome as compared to control animals. These results extend previous data on the neuroprotective action of argon. Particularly, taken together with previous in vivo data that have shown that intraischemic argon has neuroprotective action at both the cortical and subcortical level, our findings on postischemic argon suggest that this noble gas could be administered during but not after ischemia, i.e. before but not after reperfusion has occurred, in order to provide cortical neuroprotection and to avoid increasing subcortical brain damage. Also, the effects of argon are discussed as regards to the oxygen-like chemical, pharmacological, and physical properties of argon.