Xenon Up-regulates Several Genes That are not Up-regulated by Nitrous Oxide

Enhanced Cerebroprotection of Xenon-Loaded Liposomes in Combination with rtPA Thrombolysis for Embolic Ischemic Stroke

Xenon (Xe) has shown great potential as a stroke treatment due to its exceptional ability to protect brain tissue without inducing side effects. We have previously developed Xe-loaded liposomes for the ultrasound-activated delivery of Xe into the cerebral region and demonstrated their therapeutic efficacy. At present, the sole FDA-approved thrombolytic agent for stroke treatment is recombinant tissue plasminogen activator (rtPA). In this study, we aimed to investigate the potential of combining Xe-liposomes with an intravenous rtPA treatment in a clinically relevant embolic rat stroke model. We evaluated the combinational effect using an in vitro clot lysis model and an in vivo embolic middle cerebral artery occlusion (eMCAO) rat model. The treatment groups received intravenous administration of Xe-liposomes (20 mg/kg) at 2 h post-stroke onset, followed by the administration of rtPA (10 mg/kg) at either 2 or 4 h after the onset. Three days after the stroke, behavioral tests were conducted, and brain sections were collected for triphenyltetrazolium chloride (TTC) and TUNEL staining. Infarct size was determined as normalized infarct volume (%). Both in vitro and in vivo clot lysis experiments demonstrated that Xe-liposomes in combination with rtPA resulted in effective clot lysis comparable to the treatment with free rtPA alone. Animals treated with Xe-liposomes in combination with rtPA showed reduced TUNEL-positive cells and demonstrated improved neurological recovery. Importantly, Xe-liposomes in combination with late rtPA treatment reduced rtPA-induced hemorrhage, attributing to the reduction of MMP9 immunoreactivity. This study demonstrates that the combined therapy of Xe-liposomes and rtPA provides enhanced therapeutic efficacy, leading to decreased neuronal cell death and a potential to mitigate hemorrhagic side effects associated with late rtPA treatment.

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.

Repetitive xenon treatment improves post-stroke sensorimotor and neuropsychiatric dysfunction

Stroke is a life-changing event as stroke survivors experience changes in personality, emotions and mood. We investigated the effect of xenon gas encapsulated in liposomes on stroke-generated sensorimotor impairments, and anxiety- and depression-like phenotypes. Ischemic stroke was created by the intraluminal middle cerebral artery occlusion (MCAO) for 6 h followed by reperfusion in rats. Xenon-liposome (6 mg/kg, intravenous) treatment was given multiple times starting at 2 h post-ischemia through 6 h (5X), and once-daily for next 3 days. Rats underwent ischemic injury displayed sensorimotor deficits in the adhesive removal, vibrissae-evoked forelimb placement and rotarod tests. These animals also made lesser entries and spent less time on open arms of the elevated-plus maze and swam more in passive mode in the forced swimming test, indicating anxiety- and depression-like behaviors at 28- and 35-days post-injury, respectively. Repeated intravenous treatment with xenon-liposomes ameliorated these behavioral aberrations (p < 0.05). Gut microbiome analysis (16S ribosomal-RNA gene sequencing) showed a decrease in the Clostridium clusters XI, XIVa, XVIII and Lactobacillus bacterium, and increase of the Prevotella in the xenon-liposome group. No microbiota communities were majorly affected across the treatments. Moreover, xenon treatment group showed augmented plasma levels of IL-6 cytokines (∼5 fold) on day-35 post-ischemia, while no change was noticed in the IL-1β, IL-4, IL-10, IL-13 and MCP-1 levels. Our data highlights the safety, behavioral recovery and reversal of post-stroke brain injury following xenon-liposome treatment in an extended ischemic model. These results show the potential for this treatment strategy to be translated to patients with stroke.

Activation of NLR family, domain of pyrin containing 3 inflammasome by nitrous oxide through thioredoxin-interacting protein to induce nerve cell injury

Nitrous Oxide (N₂O) has been shown to be neurotoxic, but its specific mechanism is still unclear. The purpose of this work is to probe into the impact of N₂O on nerve cell injury through regulating thioredoxin-interacting protein (TXNIP)/the NOD-like receptor domain of pyrin containing 3 (NLRP3) pathway. The results indicated that, N₂O exposure elevated TXNIP/NLRP3 expression in vivo and in vitro, led to declined learning and memory capabilities in mice, reduced apoptosis rate in hippocampal neuron and Nissl bodies, elevated inflammatory factors TNF-α, IL-1β and IL-6 levels, as well as cleaved caspase-3 and Bax expressions, and reduced Bcl-2 expression. Overexpressing TXNIP or NLRP3 further aggravated these injuries, but knocking down TXNIP or NLRP3 improved them. CO-IP indicated that TXNIP and NLRP3 can be combined, with interaction relationship. All in all, the results manifested that N₂O is available to promote nerve cell inflammation and apoptosis through activating the TXNIP/NLRP3 pathway that can be used as a potential target for N₂O-induced nerve damage in the future.

Intravenous infusion of xenon-containing liposomes generates rapid antidepressant-like effects

AIM

Similar to ketamine, xenon gas acts as a glutamatergic N-methyl-d-aspartate receptor antagonist, but devoid of propensity to cause untoward effects. Herein, we loaded xenon gas into a liposomal carrier called xenon-containing liposomes (Xe-liposome) for systemic delivery, and investigated its effect as an antidepressant and also analyzed synaptic biomarkers including brain-derived neurotrophic factor (BDNF), protein kinase B (AKT), mammalian target of rapamycin (mTOR), protein kinase C (PKC) and extracellular signal-regulated kinase-1/2 (ERK1/2) in blood and brain.

METHODS

Xe-liposomes (15 μl/mg) were prepared by a pressurized freeze-thaw method, and injected via the lateral tail vein (0.6 mL/rat) in male Wistar rats. The uncaging of xenon gas from circulating Xe-liposome was facilitated by continuous ultrasound application externally on the neck over the internal common carotid artery. One-hour after Xe-liposome infusion, animals were assessed for depression-like behaviors using a forced swimming test (FST), and spontaneous locomotor activity. Blood, as well as frontal cortex and hippocampal samples were obtained for immunoblotting and/or enzyme-linked immune sorbent assays.

RESULTS

Acute intravenous infusion of Xe-liposome, at 6 mg/kg, showed an increase in swimming time in the FST (p < 0.006), indicating antidepressant-like phenotypes. Higher doses of Xe-liposomes (9 mg/kg) failed to improve swimming duration. This behavioral discrepancy was not associated with locomotion aberrations, as gross activity of rats remained similar for both doses. In biochemical analyses of frontal cortex, protein levels of BDNF increased by 64%, and enhanced phosphorylation of AKT (43%) and mTOR (93%) was observed at the 6 mg/kg dose level of Xe-liposomes, while these biomarkers and phosphorylated PKC and ERK1/2 levels remained unchanged at the higher dose. Moreover, Xe-liposomal treatment did not change the plasma and protein levels of BDNF, and phosphorylated AKT, mTOR, PKC and ERK1/2 hippocampal expressions.

CONCLUSION

Xe-liposomes mediate a rapid antidepressant-like effect through activation of AKT/mTOR/BDNF signaling pathway.

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.

The effects of xenon and nitrous oxide gases on alcohol relapse

BACKGROUND

In recent years, the glutamate theory of alcoholism has emerged as a major theory in the addiction research field and N-methyl-d-aspartate (NMDA) receptors have been shown to play a major role in alcohol craving and relapse. The NMDA receptors are considered as the primary side of action of the anesthetic gases xenon (Xe) and nitrous oxide (N2 O). Despite the rapid on/off kinetics of these gases on the NMDA receptor, a brief gas exposure can induce an analgesic or antireward effect lasting several days. The aim of this study was to examine the effect of both Xe and N2 O on alcohol-seeking and relapse-like drinking behavior (measured as the alcohol deprivation effect) in Wistar rats.

METHODS

We used 2 standard procedures-the alcohol deprivation model with repeated deprivation phases and the cue-induced reinstatement model of alcohol seeking-to study the effect of 2 brief gas exposures of either Xe, N2 O, or control gas on relapse-like drinking and alcohol-seeking behavior.

RESULTS

Here, we show that exposure to Xe during the last 24 hours of abstinence produced a trend toward reduced ethanol intake during the first alcohol re-exposure days. In addition, Xe gas exposure significantly decreased the cue-induced reinstatement of alcohol-seeking behavior. N2 O had no effect on either behavior.

CONCLUSIONS

Xe reduces alcohol-seeking behavior in rats and may therefore also interfere with craving in human alcoholics.

Therapeutic time window and dose dependence of xenon delivered via echogenic liposomes for neuroprotection in stroke

AIMS

Neurologic impairment following ischemic injury complicates the quality of life for stroke survivors. Xenon (Xe) has favorable neuroprotective properties to modify stroke. Xe delivery is hampered by a lack of suitable administration strategies. We have developed Xe-containing echogenic liposomes (Xe-ELIP) for systemic Xe delivery. We investigated the time window for Xe-ELIP therapeutic effect and the most efficacious dose for neuroprotection. Molecular mechanisms for Xe neuroprotection were investigated.

METHODS

Xenon-containing echogenic liposomes were created by a previously developed pressurization-freezing method. Following right middle cerebral artery occlusion (2 h), animals were treated with Xe-ELIP at 2, 3, or 5 h to determine time window of therapeutic effect. The neuroprotectant dosage for optimal effect was evaluated 3 h after stroke onset. Expression of brain-derived neurotrophic factor (BDNF), protein kinase B (Akt), and mitogen-activated protein kinases (MAPK) was determined.

RESULTS

Xenon-containing echogenic liposomes administration for up to 5 h after stroke onset reduced infract size. Treatment groups given 7 and 14 mg/kg of Xe-ELIP reduced infarct size. Behavioral outcomes corresponded to changes in infarct volume. Xe-ELIP treatment reduced ischemic neuronal cell death via activation of both MAPK and Akt. Elevated BDNF expression was shown following Xe-ELIP delivery.

CONCLUSION

This study demonstrates the therapeutic efficacy of Xe-ELIP administered within 5 h after stroke onset with an optimal dosage range of 7-14 mg/kg for maximal neuroprotection.

Xenon preconditioning: molecular mechanisms and biological effects

Xenon is one of noble gases and has been recognized as an anesthetic for more than 50 years. Xenon possesses many of the characteristics of an ideal anesthetic, but it is not widely applied in clinical practice mainly because of its high cost. In recent years, numerous studies have demonstrated that xenon as an anesthetic can exert neuroprotective and cardioprotective effects in different models. Moreover, xenon has been applied in the preconditioning, and the neuroprotective and cardioprotective effects of xenon preconditioning have been investigated in a lot of studies in which some mechanisms related to these protections are proposed. In this review, we summarized these mechanisms and the biological effects of xenon preconditioning.

Xenon Upregulates Hypoxia Inducible Factor 1 Alpha in Neonatal Rat Brain under Normoxic Conditions

Xenon can induce cell and organ protection through different molecular mechanisms related to oxygen level. We explored the effect of xenon on oxygen-related signalling in the central nervous system via hypoxia inducible factor 1 alpha (HIF-1α) and mammalian target of rapamycin (mTOR). Methods. Postnatal day 7 (P7) Sprague Dawley rats were exposed to 25% oxygen/75% nitrogen (air group) or 25% oxygen/75% xenon (treatment group) for 120 min. Brains were collected immediately (transcript analysis—relative real-time polymerase chain reaction) or 24 hours (protein analysis—immunohistochemistry) after the 120-minute exposure period; peak anesthetic preconditioning has been previously identified at 24 hours post-exposure. Results. HIF-1α transcript and protein levels were found to be increased in xenon-exposed compared to air-exposed brains. Sustained nuclear translocation of the protein, accounting for an increased activity of HIF-1α, was also noted. mTOR transcript analysis revealed no significant difference between xenon-exposed and air-exposed brains immediately after the 120-minute exposure. Conclusion. Our data suggest that xenon induces the upregulation of HIF-1α transcription and translation, which may contribute to xenon's neuroprotective preconditioning effect. However, given that xenon exposure did not affect mTOR transcription, further investigation into other signalling cascades mediating xenon’s effects on HIF-1α in developing brain is warranted.

Xenon anesthesia improves respiratory gas exchanges in morbidly obese patients

Background. Xenon-in-oxygen is a high density gas mixture and may improve PaO2/FiO2 ratio in morbidly obese patients uniforming distribution of ventilation during anesthesia. Methods. We compared xenon versus sevoflurane anesthesia in twenty adult morbidly obese patients (BMI > 35) candidate for roux-en-Y laparoscopic gastric bypass and assessed PaO2/FiO2 ratio at baseline, at 15 min from induction of anaesthesia and every 60 min during surgery. Differences in intraoperative and postoperative data including heart rate, systolic and diastolic pressure, oxygen saturation, plateau pressure, eyes opening and extubation time, Aldrete score on arrival to the PACU were compared by the Mann-Whitney test and were considered as secondary aims. Moreover the occurrence of side effects and postoperative analgesic demand were assessed. Results. In xenon group PaO2-FiO2 ratio was significantly higher after 60 min and 120 min from induction of anesthesia; heart rate and overall remifentanil consumption were lower; the eyes opening time and the extubation time were shorter; morphine consumption at 72 hours was lower; postoperative nausea was more common. Conclusions. Xenon anesthesia improved PaO2/FiO2 ratio and maintained its distinctive rapid recovery times and cardiovascular stability. A reduction of opioid consumption during and after surgery and an increased incidence of PONV were also observed in xenon group.

NAP protects against cytochrome c release: inhibition of the initiation of apoptosis

NAPVSIPQ (NAP), an 8 amino acid peptide derived from activity-dependent neuroprotective protein (ADNP), provides neuroprotection through interaction with microtubules. Previous results have demonstrated NAP protection against oxygen-glucose deprivation in hippocampal cells in culture. Furthermore, in vivo studies have shown that NAP reduces caspase 3 activation in rats subjected to permanent mid-cerebral artery occlusion (a rat model of stroke). Oxygen-glucose deprivation (ischemia) has been associated with microtubule breakdown and cytochrome c release from mitochondria leading to apoptosis. Here, NAP in concentrations ranging from 10(-14)M to 10(-8)M completely blocked cytochrome c release in cortical neurons subjected to oxygen-glucose deprivation. Furthermore, quantitative microscopy coupled to microtubule immunocytochemistry suggested that NAP prevented microtubule degradation under oxidative stress. As cytochrome c release is a known initiator of the apoptotic pathway, it is suggested that NAP inhibits the early events of apoptosis.