Xenon reduces neurohistopathological damage and improves the early neurological deficit after cardiac arrest in pigs*:

Xenon ameliorates chronic post-surgical pain by regulating mitophagy in microglia and rats mediated by PINK1/Parkin pathway

Background

Chronic post-surgical pain (CPSP) is one of the important causes of poor postoperative outcomes, the activation of microglia in the spinal cord is closely related to the generation, transmission and maintenance of CPSP. Xenon (Xe), an anesthetic gas, has been reported to be able to significantly reduce intraoperative analgesia and postoperative pain sensation at low doses. However, the mechanism of the regulatory effect of xenon on activated microglia after CPSP remains unclear.

Methods

In this study, CPSP model rats were treated with 50% Xe inhalation for 1 h following skin/muscle incision and retraction (SMIR), once a day for 5 consecutive days, and then the painbehavioraltests (pain behavior indexes paw withdrawal mechanical threshold, PWMT and thermal withdrawal latency, TWL), microglial activation, oxidative stress-related indexes (malondialdehyde, MDA; superoxide dismutase, SOD; hydrogen peroxide, H2O2; and catalase, CAT), mitophagy and PINK1/Parkin pathway were examined.

Results

The present results showed that a single dose of Xe treatment in SMIR rat model could significantly improve PWMT and TWL in the short-term at a single treatment and long-term at multiple treatments. Xe treatment inhibited microglia activation and oxidative stress in the spinal dorsal horn of SMIR rats, as indicated by the decrease of Iba1 and MDA/H2O2 levels and the increase of SOD/CAT levels. Compared with the control group, Xe further increased the CPSP promoted Mito-Tracker (a mitochondrial marker) and LC3 (an autophagy marker) co-localization positive spots and PINK1/Parkin/ATG5/BECN1 (autophagy-related proteins) protein expression levels, and inhibited the Mito-SOX (a mitochondrial reactive oxygen species marker) positive signal, indicating that Xe promoted microglia mitophagy and inhibited oxidative stress in CPSP. Mechanistically, we verified that Xe promoted PINK1/Parkin signaling pathway activation.

Conclusion

Xe plays a role in ameliorating chronic post-surgical pain by regulating the PINK1/Parkin pathway mediated microglial mitophagy and provide new ideas and targets for the prevention and treatment of CPSP.

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.

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.

Alleviation of neurological and cognitive impairments in rat model of ischemic stroke by 0.5 MAC xenon exposure

The majority of stroke patients have cognitive symptoms and about 50% of them live with neurological deficits that critically limit social adaptation capacities even in the absence of significant motor impairments. The aim of this study was to select the optimal length of 0.5 MAC xenon exposure in order to alleviate the neurological and cognitive impairments in experimental stroke. The focal ischemia-reperfusion injury was modeled in rats (n = 70) ising Longa method. The intervention was immediately followed by inhalation of 0.5 MAC xenon for 30, 60 or 120 min. The neurological deficit was assessed using a 'Limb placement' seven-test battery and the cognitive functionalities were assessed by the Morris water maze test. A 30 min 0.5 MAC xenon exposure provided a 40% increase in the limb placement scores and a 17.6% decrease in the Morris water maze test latency compared with the control group (р = 0.055 and р = 0.08, respectively). With a longer 60 min exposure, the trends became significant, the scores improving 2-fold and by 44.4% compared with the control group (р = 0.01 and р = 0.04, respectively), whereas 120 min exposures afforded 2-fold improvements in both tests (р = 0.01). We conclude that, although 30 min post-stroke inhalations provide negligible benefits in terms of neurological status and learning capacity, prolonged exposure times of 60–120 min afford significant improvement in neurological and cognitive indicators and largely alleviate the deteriorating ischemic damage.

Noble Gases Therapy in Cardiocerebrovascular Diseases: The Novel Stars?

Cardiocerebrovascular diseases (CCVDs) are the leading cause of death worldwide; therefore, to deeply explore the pathogenesis of CCVDs and to find the cheap and efficient strategies to prevent and treat CCVDs, these are of great clinical and social significance. The discovery of nitric oxide (NO), as one of the endothelium-derived relaxing factors and its successful utilization in clinical practice for CCVDs, provides new ideas for us to develop drugs for CCVDs: “gas medicine” or “medical gases.” The endogenous gas molecules such as carbon monoxide (CO), hydrogen sulfide (H₂S), sulfur dioxide (SO₂), methane (CH₄), and hydrogen (H₂) have essential biological effects on modulating cardiocerebrovascular homeostasis and CCVDs. Moreover, it has been shown that noble gas atoms such as helium (He), neon (Ne), argon (Ar), krypton (Kr), and xenon (Xe) display strong cytoprotective effects and therefore, act as the exogenous pharmacologic preventive and therapeutic agents for CCVDs. Mechanistically, besides the competitive inhibition of N-methyl-D-aspartate (NMDA) receptor in nervous system by xenon, the key and common mechanisms of noble gases are involved in modulation of cell death and inflammatory or immune signals. Moreover, gases interaction and reduction in oxidative stress are emerging as the novel biological mechanisms of noble gases. Therefore, to investigate the precise actions of noble gases on redox signals, gases interaction, different cell death forms, and the emerging field of gasoimmunology, which focus on the effects of gas atoms/molecules on innate immune signaling or immune cells under both the homeostatic and perturbed conditions, these will help us to uncover the mystery of noble gases in modulating CCVDs.

Inhaled gases as novel neuroprotective therapies in the postcardiac arrest period

PURPOSE OF REVIEW

The purpose of this review is to summarize recent advances about inhaled gases as novel neuroprotective agents in the postcardiac arrest period.

RECENT FINDINGS

Inhaled gases, as nitric oxide (NO) and molecular hydrogen (H2), and noble gases as xenon (Xe) and argon (Ar) have shown neuroprotective properties after resuscitation. In experimental settings, the protective effect of these gases has been demonstrated in both in-vitro studies and animal models of cardiac arrest. They attenuate neuronal degeneration and improve neurological function after resuscitation acting on different pathophysiological pathways. Safety of both Xe and H2 after cardiac arrest has been reported in phase 1 clinical trials. A randomized phase 2 clinical trial showed the neuroprotective effects of Xe, combined with targeted temperature management. Xe inhalation for 24 h after resuscitation preserves white matter integrity as measured by fractional anisotropy of diffusion tensor MRI.

SUMMARY

Inhaled gases, as Xe, Ar, NO, and H2 have consistently shown neuroprotective effects in experimental studies. Ventilation with these gases appears to be well tolerated in pigs and in preliminary human trials. Results from phase 2 and 3 clinical trials are needed to assess their efficacy in the treatment of postcardiac arrest brain injury.

Inhaled Gases as Therapies for Post-Cardiac Arrest Syndrome: A Narrative Review of Recent Developments

Despite recent advances in the management of post-cardiac arrest syndrome (PCAS), the survival rate, without neurologic sequelae after resuscitation, remains very low. Whole-body ischemia, followed by reperfusion after cardiac arrest (CA), contributes to PCAS, for which established pharmaceutical interventions are still lacking. It has been shown that a number of different processes can ultimately lead to neuronal injury and cell death in the pathology of PCAS, including vasoconstriction, protein modification, impaired mitochondrial respiration, cell death signaling, inflammation, and excessive oxidative stress. Recently, the pathophysiological effects of inhaled gases including nitric oxide (NO), molecular hydrogen (H₂), and xenon (Xe) have attracted much attention. Herein, we summarize recent literature on the application of NO, H₂, and Xe for treating PCAS. Recent basic and clinical research has shown that these gases have cytoprotective effects against PCAS. Nevertheless, there are likely differences in the mechanisms by which these gases modulate reperfusion injury after CA. Further preclinical and clinical studies examining the combinations of standard post-CA care and inhaled gas treatment to prevent ischemia-reperfusion injury are warranted to improve outcomes in patients who are being failed by our current therapies.

Ventilation With Argon Improves Survival With Good Neurological Recovery After Prolonged Untreated Cardiac Arrest in Pigs

Background

Ventilation with the noble gas argon (Ar) has shown neuroprotective and cardioprotective properties in different in vitro and in vivo models. Hence, the neuroprotective effects of Ar were investigated in a severe, preclinically relevant porcine model of cardiac arrest.

Methods and Results

Cardiac arrest was ischemically induced in 36 pigs and left untreated for 12 minutes before starting cardiopulmonary resuscitation. Animals were randomized to 4‐hour post‐resuscitation ventilation with: 70% nitrogen–30% oxygen (control); 50% Ar–20% nitrogen–30% oxygen (Ar 50%); and 70% Ar–30% oxygen (Ar 70%). Hemodynamic parameters and myocardial function were monitored and serial blood samples taken. Pigs were observed up to 96 hours for survival and neurological recovery. Heart and brain were harvested for histopathology. Ten animals in each group were successfully resuscitated. Ninety‐six‐hour survival was 60%, 70%, and 90%, for the control, Ar 50%, and Ar 70% groups, respectively. In the Ar 50% and Ar 70% groups, 60% and 80%, respectively, achieved good neurological recovery, in contrast to only 30% in the control group (P<0.0001). Histology showed less neuronal degeneration in the cortex (P<0.05) but not in the hippocampus, and less reactive microglia activation in the hippocampus (P=0.007), after Ar compared with control treatment. A lower increase in circulating biomarkers of brain injury, together with less kynurenine pathway activation (P<0.05), were present in Ar‐treated animals compared with controls. Ar 70% pigs also had complete left ventricular function recovery and smaller infarct and cardiac troponin release (P<0.01).

Conclusions

Post‐resuscitation ventilation with Ar significantly improves neurologic recovery and ameliorates brain injury after cardiac arrest with long no‐flow duration. Benefits are greater after Ar 70% than Ar 50%.

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.

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.

Prospects for Applying Xenon Curative Properties in Pediatrics

The review discusses experimental and clinical trials on applying noble gas Xenon to treat therapeutic conditions in adults, as well as the prospects for its applying in children. Xenon therapeutic effects on the body are based on the healing properties of a noble gas. Xenon is close to the ‘ideal anesthetic’ by its anesthetic properties; but in addition, it possesses organoand neuroprotective as well as anti-stress properties which have been proved in experiment and clinically. Xenon in pediatric practice is an attractive agent because it is non-toxic, effective for the treatment of posthypoxic and traumatic impairments of the central nervous system, pain syndromes and stress conditions at its therapeutic concentration up to 30%.

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.

The future is now: neuroprotection during cardiopulmonary resuscitation

PURPOSE OF REVIEW

Survival with favorable neurological function after cardiac arrest remains low. The purpose of this review is to identify recent advances that focus on neuroprotection during cardiopulmonary resuscitation (CPR).

RECENT FINDINGS

Multiple strategies have been shown to enhance neuroprotection during CPR. Brain perfusion during CPR is increased with therapies such as active compression decompression CPR and intrathoracic pressure regulation that improve cardiac preload and decrease intracranial pressure. Head Up CPR has been shown to decrease intracranial pressure thereby increasing cerebral perfusion pressure and cerebral blood flow. Sodium nitroprusside enhanced CPR increases cerebral perfusion, facilitates heat exchange, and improves neurologic survival in swine after cardiac arrest. Postconditioning has been administered during CPR in laboratory settings. Poloxamer 188, a membrane stabilizer, and ischemic postconditioning have been shown to improve cardiac and neural function after cardiac arrest in animal models. Postconditioning with inhaled gases protects the myocardium, with more evidence mounting for the potential for neural protection.

SUMMARY

Multiple promising neuroprotective therapies are being developed in animal models of cardiac arrest, and are in early stages of human trials. These therapies have the potential to be bundled together to improve rates of favorable neurological survival after cardiac arrest.

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.

Postconditioning effects of argon or xenon on early graft function in a porcine model of kidney autotransplantation

BACKGROUND

Ischaemia-reperfusion injury is inevitable during renal transplantation and can lead to delayed graft function and primary non-function. Preconditioning, reconditioning and postconditioning with argon and xenon protects against renal ischaemia-reperfusion injury in rodent models. The hypothesis that postconditioning with argon or xenon inhalation would improve graft function in a porcine renal autotransplant model was tested.

METHODS

Pigs (n = 6 per group) underwent left nephrectomy after 60 min of warm ischaemia (renal artery and vein clamping). The procured kidney was autotransplanted in a separate procedure after 18 h of cold storage, immediately after a right nephrectomy. Upon reperfusion, pigs were randomized to inhalation of control gas (70 per cent nitrogen and 30 per cent oxygen), argon (70 per cent and 30 per cent oxygen) or xenon (70 per cent and 30 per cent oxygen) for 2 h. The primary outcome parameter was peak plasma creatinine; secondary outcome parameters included further markers of graft function (creatinine course, urine output), graft injury (aspartate aminotransferase, heart-type fatty acid-binding protein, histology), apoptosis and autophagy (western blot, terminal deoxynucleotidyl transferase dUTP nick-end labelling (TUNEL) staining), inflammatory mediators and markers of cell survival/growth (mRNA and tissue protein quantification), and animal survival. Results are presented as median (i.q.r.). ANOVA and Kruskal-Wallis tests were used where indicated.

RESULTS

Peak plasma creatinine levels were similar between the groups: control 20·8 (16·4-23·1) mg/dl, argon 21·4 (17·1-24·9) mg/dl and xenon 19·4 (17·5-21·0) mg/dl (P = 0·607). Xenon was associated with an increase in autophagy and proapoptotic markers. Creatinine course, urine output, injury markers, histology, survival and inflammatory mediators were not affected by the intervention.

CONCLUSION

Postconditioning with argon or xenon did not improve kidney graft function in this experimental model. Surgical relevance Ischaemia-reperfusion injury is inevitable during renal transplantation and can lead to delayed graft function and primary non-function. Based on mainly small animal experiments, noble gases (argon and xenon) have been proposed to minimize this ischaemia-reperfusion injury and improve outcomes after transplantation. The hypothesis that postconditioning with argon or xenon inhalation would improve graft function was tested in a porcine kidney autotransplantation model. The peak plasma creatinine concentration was similar in the control, argon and xenon groups. No other secondary outcome parameters, including animal survival, were affected by the intervention. Xenon was associated with an increase in autophagy and proapoptotic markers. Despite promising results in small animal models, postconditioning with argon or xenon in a translational model of kidney autotransplantation was not beneficial. Clinical trials would require better results.

Xenon Protects against Blast-Induced Traumatic Brain Injury in an In Vitro Model

The aim of this study was to evaluate the neuroprotective efficacy of the inert gas xenon as a treatment for patients with blast-induced traumatic brain injury in an in vitro laboratory model. We developed a novel blast traumatic brain injury model using C57BL/6N mouse organotypic hippocampal brain-slice cultures exposed to a single shockwave, with the resulting injury quantified using propidium iodide fluorescence. A shock tube blast generator was used to simulate open field explosive blast shockwaves, modeled by the Friedlander waveform. Exposure to blast shockwave resulted in significant (p < 0.01) injury that increased with peak-overpressure and impulse of the shockwave, and which exhibited a secondary injury development up to 72 h after trauma. Blast-induced propidium iodide fluorescence overlapped with cleaved caspase-3 immunofluorescence, indicating that shock-wave–induced cell death involves apoptosis. Xenon (50% atm) applied 1 h after blast exposure reduced injury 24 h (p < 0.01), 48 h (p < 0.05), and 72 h (p < 0.001) later, compared with untreated control injury. Xenon-treated injured slices were not significantly different from uninjured sham slices at 24 h and 72 h. We demonstrate for the first time that xenon treatment after blast traumatic brain injury reduces initial injury and prevents subsequent injury development in vitro. Our findings support the idea that xenon may be a potential first-line treatment for those with blast-induced traumatic brain injury.

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 Reduces Neuronal Hippocampal Damage and Alters the Pattern of Microglial Activation after Experimental Subarachnoid Hemorrhage: A Randomized Controlled Animal Trial

Objective

The neuroprotective properties of the noble gas xenon have already been demonstrated using a variety of injury models. Here, we examine for the first time xenon’s possible effect in attenuating early brain injury (EBI) and its influence on posthemorrhagic microglial neuroinflammation in an in vivo rat model of subarachnoid hemorrhage (SAH).

Methods

Sprague-Dawley rats (n = 22) were randomly assigned to receive either Sham surgery (n = 9; divided into two groups) or SAH induction via endovascular perforation (n = 13, divided into two groups). Of those randomized for SAH, 7 animals were postoperatively ventilated with 50 vol% oxygen/50 vol% xenon for 1 h and 6 received 50 vol% oxygen/50 vol% nitrogen (control). The animals were sacrificed 24 h after SAH. Of each animal, a cerebral coronal section (−3.60 mm from bregma) was selected for assessment of histological damage 24 h after SAH. A 5-point neurohistopathological severity score was applied to assess neuronal cell damage in H&E and NeuN stained sections in a total of four predefined anatomical regions of interest. Microglial activation was evaluated by a software-assisted cell count of Iba-1 stained slices in three cortical regions of interest.

Results

A diffuse cellular damage was apparent in all regions of the ipsilateral hippocampus 24 h after SAH. Xenon-treated animals presented with a milder damage after SAH. This effect was found to be particularly pronounced in the medial regions of the hippocampus, CA3 (p = 0.040), and dentate gyrus (DG p = 0.040). However, for the CA1 and CA2 regions, there were no statistical differences in neuronal damage according to our histological scoring. A cell count of activated microglia was lower in the cortex of xenon-treated animals. This difference was especially apparent in the left piriform cortex (p = 0.017).

Conclusion

In animals treated with 50 vol% xenon (for 1 h) after SAH, a less pronounced neuronal damage was observed for the ipsilateral hippocampal regions CA3 and DG, when compared to the control group. In xenon-treated animals, a lower microglial cell count was observed suggesting an immunomodulatory effect generated by xenon. As for now, these results cannot be generalized as only some hippocampal regions are affected. Future studies should assess the time and localization dependency of xenon’s beneficial properties after SAH.

Influence of argon on temperature modulation and neurological outcome in hypothermia treated rats following cardiac arrest

AIM OF THE STUDY

Combining xenon and mild therapeutic hypothermia (MTH) after cardiac arrest (CA) confers a degree of protection that is greater than either of the two interventions alone. However, xenon is very costly which might preclude a widespread use. We investigated whether the inexpensive gas argon would enhance hypothermia induced neurologic recovery in a similar manner.

METHODS

Following nine minutes of CA and three minutes of cardiopulmonary resuscitation 21 male Sprague-Dawley rats were randomized to receive MTH (33°C for 6h), MTH plus argon (70% for 1h), or no treatment. A first day condition score assessed behaviour, motor activity and overall condition. A neurological deficit score (NDS) was calculated daily for seven days following the experiment before the animals were killed and the brains harvested for histopathological analysis.

RESULTS

All animals survived. Animals that received MTH alone showed best overall neurologic function. Strikingly, this effect was abolished in the argon-augmented MTH group, where animals showed worse neurologic outcome being significant in the first day condition score and on day one to three and five in the NDS in comparison to MTH treated rats. Results were reflected by the neurohistopathological analysis.

CONCLUSION

Our study demonstrates that argon augmented MTH does not improve functional recovery after CA in rats, but may even worsen neurologic function in this model.

Emulsified isoflurane postconditioning improves survival and neurological outcomes in a rat model of cardiac arrest

Emulsified isoflurane (EIso) has a protective effect against ischemia/reperfusion (I/R) injury in animal models. However, the protective effects of EIso on global cerebral I/R injury remain unclear. The present study aimed to investigate whether EIso postconditioning was able to improve survival and neurological outcomes in a rat model of cardiac arrest (CA). Rats were randomly divided into five groups, namely the control, EIso-2ml, EIso-4ml, isoflurane (Iso) and emulsion (E) groups. All rats were resuscitated by a standardized method following 6 min of asphyxia. Furthermore, all interventions were administered immediately following the return of spontaneous circulation (ROSC). The animal survival was recorded daily, and evaluations of behavioral and brain morphology were assessed at 1 and 7 days after ROSC. The results showed that EIso treatment increased the survival rate 7 days after ROSC, with a 41.7% 7-day survival in the EIso-2ml group, 66.7% in the EIso-4ml group and 50% in the Iso group compared with 33.3% survival in the control and E groups. Moreover, the neural deficit score and memory function were improved in the EIso-4ml group, and this treatment also ameliorated brain hippocampal cell injury and apoptosis. In addition, a better brain protective effect was observed in the EIso-4ml group compared with the EIso-2ml, Iso and E groups. In summary, the data of the present study suggest that EIso postconditioning improved the survival and neurological outcomes following CA in a dose-dependent manner.

Gas chromatography/mass spectrometry measurement of xenon in gas-loaded liposomes for neuroprotective applications

RATIONALE

We have produced a liposomal formulation of xenon (Xe-ELIP) as a neuroprotectant for inhibition of brain damage in stroke patients. This mandates development of a reliable assay to measure the amount of dissolved xenon released from Xe-ELIP in water and blood samples.

METHODS

Gas chromatography/mass spectrometry (GC/MS) was used to quantify xenon gas released into the headspace of vials containing Xe-ELIP samples in water or blood. In order to determine blood concentration of xenon in vivo after Xe-ELIP administration, 6 mg of Xe-ELIP lipid was infused intravenously into rats. Blood samples were drawn directly from a catheterized right carotid artery. After introduction of the samples, each vial was allowed to equilibrate to 37°C in a water bath, followed by 20 minutes of sonication prior to headspace sampling. Xenon concentrations were calculated from a gas dose-response curve and normalized using the published xenon water-gas solubility coefficient.

RESULTS

The mean corrected percent of xenon from Xe-ELIP released into water was 3.87 ± 0.56% (SD, n = 8), corresponding to 19.3 ± 2.8 μL/mg lipid, which is consistent with previous independent Xe-ELIP measurements. The corresponding xenon content of Xe-ELIP in rat blood was 23.38 ± 7.36 μL/mg lipid (n = 8). Mean rat blood xenon concentration after intravenous administration of Xe-ELIP was 14 ± 10 μM, which is approximately 15% of the estimated neuroprotective level.

CONCLUSIONS

Using this approach, we have established a reproducible method for measuring dissolved xenon in fluids. These measurements have established that neuroprotective effects can be elicited by less than 20% of the calculated neuroprotective xenon blood concentration. More work will have to be done to establish the protective xenon pharmacokinetic range. Copyright © 2016 John Wiley & Sons, Ltd.

Neuroprotection and neurotoxicity in the developing brain: an update on the effects of dexmedetomidine and xenon

Growing and consistent preclinical evidence, combined with early clinical epidemiological observations, suggest potentially neurotoxic effects of commonly used anesthetic agents in the developing brain. This has prompted the FDA to issue a safety warning for all sedatives and anesthetics approved for use in children under three years of age. Recent studies have identified dexmedetomidine, the potent α2-adrenoceptor agonist, and xenon, the noble gas, as effective anesthetic adjuvants that are both less neurotoxic to the developing brain, and also possess neuroprotective properties in neonatal and other settings of acute ongoing neurologic injury. Dexmedetomidine and xenon are effective anesthetic adjuvants that appear to be less neurotoxic than other existing agents and have the potential to be neuroprotective in the neonatal and pediatric settings. Although results from recent clinical trials and case reports have indicated the neuroprotective potential of xenon and dexmedetomidine, additional randomized clinical trials corroborating these studies are necessary. By reviewing both the existing preclinical and clinical evidence on the neuroprotective effects of dexmedetomidine and xenon, we hope to provide insight into the potential clinical efficacy of these agents in the management of pediatric surgical patients.

[Neuroprotection by noble gases: New developments and insights]

Noble gases are chemically inert elements, some of which exert biological activity. Experimental neuroprotection in particular has been widely shown for xenon, argon and helium. The underlying mechanisms of action are not yet fully understood. Besides an interference with neuronal ion-gated channels and cellular signaling pathways as well as anti-apoptotic effects, the modulation of neuroinflammation seems to play a crucial role. This review presents the current knowledge on neuroprotection by noble gases with a focus on interactions with the neuronal-glial network and neuroinflammation and the perspectives on clinical applications.

[Xenon: From rare gaz to doping product]

Doping is defined as the use of processes or substances to artificially increase physical or mental performance. Xenon is a noble gas used as an anesthetic and recently as a doping agent. Xenon is neuroprotective as an antagonist of NMDA glutamate receptors. Xenon stimulates the synthesis of erythropoietin (EPO) by increase of hypoxia inducible factor (HIF). Xenon would be a new doping product, maintaining doping methods ahead of detection.

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.

Inhaled nitric oxide improves transpulmonary blood flow and clinical outcomes after prolonged cardiac arrest: a large animal study

Introduction

The probability to achieve a return of spontaneous circulation (ROSC) after cardiac arrest can be improved by optimizing circulation during cardiopulomonary resuscitation using a percutaneous left ventricular assist device (iCPR). Inhaled nitric oxide may facilitate transpulmonary blood flow during iCPR and may therefore improve organ perfusion and outcome.

Methods

Ventricular fibrillation was electrically induced in 20 anesthetized male pigs. Animals were left untreated for 10 minutes before iCPR was attempted. Subjects received either 20 ppm of inhaled nitric oxide (iNO, n = 10) or 0 ppm iNO (Control, n = 10), simultaneously started with iCPR until 5 hours following ROSC. Animals were weaned from the respirator and followed up for five days using overall performance categories (OPC) and a spatial memory task. On day six, all animals were anesthetized again, and brains were harvested for neurohistopathologic evaluation.

Results

All animals in both groups achieved ROSC. Administration of iNO markedly increased iCPR flow during CPR (iNO: 1.81 ± 0.30 vs Control: 1.64 ± 0.51 L/min, p < 0.001), leading to significantly higher coronary perfusion pressure (CPP) during the 6 minutes of CPR (25 ± 13 vs 16 ± 6 mmHg, p = 0.002). iNO-treated animals showed significantly lower S-100 serum levels thirty minutes post ROSC (0.26 ± 0.09 vs 0.38 ± 0.15 ng/mL, p = 0.048), as well as lower blood glucose levels 120–360 minutes following ROSC. Lower S-100 serum levels were reflected by superior clinical outcome of iNO-treated animals as estimated with OPC (3 ± 2 vs. 5 ± 1, p = 0.036 on days 3 to 5). Three out of ten iNO-treated, but none of the Control animals were able to successfully participate in the spatial memory task. Neurohistopathological examination of vulnerable cerebral structures revealed a trend towards less cerebral lesions in neocortex, archicortex, and striatum in iNO-treated animals compared to Controls.

Conclusions

In pigs resuscitated with mechanically-assisted CPR from prolonged cardiac arrest, the administration of 20 ppm iNO during and following iCPR improved transpulmonary blood flow, leading to improved clinical neurological outcomes.

Toxic and protective effects of inhaled anaesthetics on the developing animal brain: systematic review and update of recent experimental work

BACKGROUND

Accumulating preclinical data indicate that neonatal exposure to general anaesthetics is detrimental to the central nervous system. Some studies, however, display potential protective effects of exactly the same anaesthetic agents on the immature brain. The effects of inhaled anaesthetics on the developing brain have received close attention from researchers, clinicians and the public in recent decades.

OBJECTIVES

To summarise the preclinical evidence reported in the last 5 years on both the deleterious effects and the neuroprotective potential in special indications, of inhaled anaesthetics on the developing brain.

DESIGN

A systematic review.

DATA SOURCES

PubMed search performed in June 2013.

ELIGIBILITY CRITERIA

Search terms included brain, development, inhaled anaesthetic, toxicity and protection within the scope of the last 5 years with animals. The reference lists of relevant articles and recent reviews were also hand-searched for additional studies. The type, dose and exposure duration of anaesthetics, species and age of animals, histopathologic indicators, outcomes and affected brain areas, neuro developmental test modules and outcomes, as well as other outcomes and comments were summarised.

RESULTS

Two hundred and nineteen relevant titles were initially revealed. In total, 81 articles were identified, with 68 articles assessing the detrimental effects induced by inhaled anaesthetics in the immature brain along with possible treatments. The remaining 13 articles focused on the protective profile of inhaled anaesthetics on perinatal hypoxic-ischaemic brain injury. Administration of inhaled anaesthetic agents to the immature brain was shown to be deleterious in several preclinical studies. In perinatal hypoxic-ischaemic brain injury models, pre- and postconditioning of inhalational anaesthetics exerted neuroprotective effects.

CONCLUSION

The majority of studies have linked inhaled anaesthetics to toxic effects in the neonatal brain of rodents, piglets and primates. Only a few studies, however, could demonstrate long-lasting cognitive impairment. The results of inhalational anaesthetic-induced neuroprotection in perinatal hypoxic-ischaemic brain injury are a promising basis for more research in this field. In general, prospective clinical trials are needed to further differentiate the effects of inhaled anaesthetics on the immature brain.

Xenon improves neurologic outcome and reduces secondary injury following trauma in an in vivo model of traumatic brain injury

OBJECTIVES

To determine the neuroprotective efficacy of the inert gas xenon following traumatic brain injury and to determine whether application of xenon has a clinically relevant therapeutic time window.

DESIGN

Controlled animal study.

SETTING

University research laboratory.

SUBJECTS

Male C57BL/6N mice (n = 196).

INTERVENTIONS

Seventy-five percent xenon, 50% xenon, or 30% xenon, with 25% oxygen (balance nitrogen) treatment following mechanical brain lesion by controlled cortical impact.

MEASUREMENTS AND MAIN RESULTS

Outcome following trauma was measured using 1) functional neurologic outcome score, 2) histological measurement of contusion volume, and 3) analysis of locomotor function and gait. Our study shows that xenon treatment improves outcome following traumatic brain injury. Neurologic outcome scores were significantly (p < 0.05) better in xenon-treated groups in the early phase (24 hr) and up to 4 days after injury. Contusion volume was significantly (p < 0.05) reduced in the xenon-treated groups. Xenon treatment significantly (p < 0.05) reduced contusion volume when xenon was given 15 minutes after injury or when treatment was delayed 1 or 3 hours after injury. Neurologic outcome was significantly (p < 0.05) improved when xenon treatment was given 15 minutes or 1 hour after injury. Improvements in locomotor function (p < 0.05) were observed in the xenon-treated group, 1 month after trauma.

CONCLUSIONS

These results show for the first time that xenon improves neurologic outcome and reduces contusion volume following traumatic brain injury in mice. In this model, xenon application has a therapeutic time window of up to at least 3 hours. These findings support the idea that xenon may be of benefit as a neuroprotective treatment in patients with brain trauma.

A systematic review of neuroprotective strategies after cardiac arrest: from bench to bedside (Part I - Protection via specific pathways)

Neurocognitive deficits are a major source of morbidity in survivors of cardiac arrest. Treatment options that could be implemented either during cardiopulmonary resuscitation or after return of spontaneous circulation to improve these neurological deficits are limited. We conducted a literature review of treatment protocols designed to evaluate neurologic outcome and survival following cardiac arrest with associated global cerebral ischemia. The search was limited to investigational therapies that were utilized to treat global cerebral ischemia associated with cardiac arrest. In this review we discuss potential mechanisms of neurologic protection following cardiac arrest including actions of several medical gases such as xenon, argon, and nitric oxide. The 3 included mechanisms are: 1. Modulation of neuronal cell death; 2. Alteration of oxygen free radicals; and 3. Improving cerebral hemodynamics. Only a few approaches have been evaluated in limited fashion in cardiac arrest patients and results show inconclusive neuroprotective effects. Future research focusing on combined neuroprotective strategies that target multiple pathways are compelling in the setting of global brain ischemia resulting from cardiac arrest.

Novelties in pharmacological management of cardiopulmonary resuscitation

PURPOSE OF REVIEW

The ultimate goal of cardiopulmonary resuscitation is long-term neurologically intact survival. Despite numerous well-designed studies, the medications currently used in advanced cardiac life support have not demonstrated success in this regard. This review describes the novel therapeutics under investigation to improve functional recovery and survival.

RECENT FINDINGS

Whereas current medications focus on achieving return of spontaneous circulation and improved hemodynamics, novel therapies currently in development are focused on improving cellular survival and function by preventing metabolic derangement, protecting mitochondria, and preventing cell death caused by cardiac arrest. Improved cardiac and neurologic function and survival benefits have been observed using animal models of cardiopulmonary arrest.

SUMMARY

Although substantial data have shown benefits using robust animal models, further human studies are necessary to investigate the potential long-term benefits of these therapies.

Timing of xenon-induced delayed postconditioning to protect against spinal cord ischaemia-reperfusion injury in rats

BACKGROUND

This study was designed to assess the neuroprotective effect of xenon-induced delayed postconditioning on spinal cord ischaemia-reperfusion injury (IRI) and to determine the time of administration for best neuroprotection in a rat model of spinal cord IRI.

METHODS

Fifty male rats were randomly divided equally into a sham group, control group, and three xenon postconditioning groups (n=10 per group). The control group underwent spinal cord IRI and immediately inhaled 50% nitrogen/50% oxygen for 3 h at the initiation of reperfusion. The three xenon postconditioning groups underwent the same surgical procedure and immediately inhaled 50% xenon/50% oxygen for 3 h at the initiation of reperfusion or 1 and 2 h after reperfusion. The sham operation group underwent the same surgical procedure without aortic occlusion, and inhaled 50% nitrogen/50% oxygen. Neurological function was assessed using the Basso, Beattie, and Bresnahan score at 4, 24, and 48 h of reperfusion. Histological examination was performed using Nissl staining and immunohistochemistry, and apoptosis was detected by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end-labelling staining.

RESULTS

Compared with the control group, the three xenon postconditioning groups showed improvements in neurological outcomes, and had more morphologically normal neurones at 48 h of reperfusion. Apoptotic cell death was reduced and the ratio of Bcl-2/Bax immunoreactivity increased in xenon-treated rats compared with controls.

CONCLUSIONS

Xenon postconditioning up to 2 h after reperfusion provided protection against spinal cord IRI in rats, but the greatest neuroprotection occurred with administration of xenon for 1 h at reperfusion.

Neuroprotection against Traumatic Brain Injury by Xenon, but Not Argon, Is Mediated by Inhibition at the N-Methyl-d-Aspartate Receptor Glycine Site

Background:

Xenon, the inert anesthetic gas, is neuroprotective in models of brain injury. The authors investigate the neuroprotective mechanisms of the inert gases such as xenon, argon, krypton, neon, and helium in an in vitro model of traumatic brain injury.

Methods:

The authors use an in vitro model using mouse organotypic hippocampal brain slices, subjected to a focal mechanical trauma, with injury quantified by propidium iodide fluorescence. Patch clamp electrophysiology is used to investigate the effect of the inert gases on N-methyl-d-aspartate receptors and TREK-1 channels, two molecular targets likely to play a role in neuroprotection.

Results:

Xenon (50%) and, to a lesser extent, argon (50%) are neuroprotective against traumatic injury when applied after injury (xenon 43 ± 1% protection at 72 h after injury [N = 104]; argon 30 ± 6% protection [N = 44]; mean ± SEM). Helium, neon, and krypton are devoid of neuroprotective effect. Xenon (50%) prevents development of secondary injury up to 48 h after trauma. Argon (50%) attenuates secondary injury, but is less effective than xenon (xenon 50 ± 5% reduction in secondary injury at 72 h after injury [N = 104]; argon 34 ± 8% reduction [N = 44]; mean ± SEM). Glycine reverses the neuroprotective effect of xenon, but not argon, consistent with competitive inhibition at the N-methyl-d-aspartate receptor glycine site mediating xenon neuroprotection against traumatic brain injury. Xenon inhibits N-methyl-d-aspartate receptors and activates TREK-1 channels, whereas argon, krypton, neon, and helium have no effect on these ion channels.

Conclusions:

Xenon neuroprotection against traumatic brain injury can be reversed by increasing the glycine concentration, consistent with inhibition at the N-methyl-d-aspartate receptor glycine site playing a significant role in xenon neuroprotection. Argon and xenon do not act via the same mechanism.