Beneficial Properties of Argon After Experimental Subarachnoid Hemorrhage: Early Treatment Reduces Mortality and Influences Hippocampal Protein Expression*

Treatment with inhaled Argon: a systematic review of pre-clinical and clinical studies with meta-analysis on neuroprotective effect

BACKGROUND

Argon (Ar) has been proposed as a potential therapeutic agent in multiple clinical conditions, specifically in organ protection. However, conflicting data on pre-clinical models, together with a great variability in Ar administration protocols and outcome assessments, have been reported. The aim of this study was to review evidence on treatment with Ar, with an extensive investigation on its neuroprotective effect, and to summarise all tested administration protocols.

METHODS

Using the PubMed database, all existing pre-clinical and clinical studies on the treatment with Ar were systematically reviewed (registration: https://doi.org/10.17605/OSF.IO/7983D). Study titles and abstracts were screened, extracting data from relevant studies post full-text review. Exclusion criteria included absence of full text and non-English language. Furthermore, meta-analysis was also performed to assess Ar potential as neuroprotectant agent in different clinical conditions: cardiac arrest, traumatic brain injury, ischemic stroke, perinatal hypoxic-ischemic encephalopathy, subarachnoid haemorrhage. Standardised mean differences for neurological, cognitive and locomotor, histological, and physiological measures were evaluated, through appropriate tests, clinical, and laboratory variables. In vivo studies were evaluated for risk of bias using the Systematic Review Center for Laboratory Animal Experimentation tool, while in vitro studies underwent assessment with a tool developed by the Office of Health Assessment and Translation.

FINDINGS

The systematic review detected 60 experimental studies (16 in vitro, 7 ex vivo, 31 in vivo, 6 with both in vitro and in vivo) investigating the role of Ar. Only one clinical study was found. Data from six in vitro and nineteen in vivo studies were included in the meta-analyses. In pre-clinical models, Ar administration resulted in improved neurological, cognitive and locomotor, and histological outcomes without any change in physiological parameters (i.e., absence of adverse events).

INTERPRETATION

This systematic review and meta-analysis based on experimental studies supports the neuroprotective effect of Ar, thus providing a rationale for potential translation of Ar treatment in humans. Despite adherence to established guidelines and methodologies, limitations in data availability prevented further analyses to investigate potential sources of heterogeneity due to study design.

FUNDING

This study was funded in part by Italian Ministry of Health-Current researchIRCCS and by Ministero della Salute Italiano, Ricerca Finalizzata, project no. RF 2019-12371416.

Conditioning-based therapeutics for aneurysmal subarachnoid hemorrhage - A critical review

Aneurysmal subarachnoid hemorrhage (SAH) carries significant mortality and morbidity, with nearly half of SAH survivors having major cognitive dysfunction that impairs their functional status, emotional health, and quality of life. Apart from the initial hemorrhage severity, secondary brain injury due to early brain injury and delayed cerebral ischemia plays a leading role in patient outcome after SAH. While many strategies to combat secondary brain injury have been developed in preclinical studies and tested in late phase clinical trials, only one (nimodipine) has proven efficacious for improving long-term functional outcome. The causes of these failures are likely multitude, but include use of therapies targeting only one element of what has proven to be multifactorial brain injury process. Conditioning is a therapeutic strategy that leverages endogenous protective mechanisms to exert powerful and remarkably pleiotropic protective effects against injury to all major cell types of the CNS. The aim of this article is to review the current body of evidence for the use of conditioning agents in SAH, summarize the underlying neuroprotective mechanisms, and identify gaps in the current literature to guide future investigation with the long-term goal of identifying a conditioning-based therapeutic that significantly improves functional and cognitive outcomes for SAH patients.

Animal Welfare Aspects in Planning and Conducting Experiments on Rodent Models of Subarachnoid Hemorrhage

Subarachnoid hemorrhage is an acute life-threatening cerebrovascular disease with high socio-economic impact. The most frequent cause, the rupture of an intracerebral aneurysm, is accompanied by abrupt changes in intracerebral pressure, cerebral perfusion pressure and, consequently, cerebral blood flow. As aneurysms rupture spontaneously, monitoring of these parameters in patients is only possible with a time delay, upon hospitalization. To study alterations in cerebral perfusion immediately upon ictus, animal models are mandatory. This article addresses the points necessarily to be included in an animal project proposal according to EU directive 2010/63/EU for the protection of animals used for scientific purposes and herewith offers an insight into animal welfare aspects of using rodent models for the investigation of cerebral perfusion after subarachnoid hemorrhage. It compares surgeries, model characteristics, advantages, and drawbacks of the most-frequently used rodent models-the endovascular perforation model and the prechiasmatic and single or double cisterna magna injection model. The topics of discussing anesthesia, advice on peri- and postanesthetic handling of animals, assessing the severity of suffering the animals undergo during the procedure according to EU directive 2010/63/EU and weighing the use of these in vivo models for experimental research ethically are also presented. In conclusion, rodent models of subarachnoid hemorrhage display pathophysiological characteristics, including changes of cerebral perfusion similar to the clinical situation, rendering the models suited to study the sequelae of the bleeding. A current problem is low standardization of the models, wherefore reporting according to the ARRIVE guidelines is highly recommended. Animal welfare aspects of rodent models of subarachnoid hemorrhage. Rodent models for investigation of cerebral perfusion after subarachnoid hemorrhage are compared regarding surgeries and model characteristics, and 3R measures are suggested. Anesthesia is discussed, and advice given on peri- and postanesthetic handling. Severity of suffering according to 2010/63/EU is assessed and use of these in vivo models weighed ethically.

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.

The Potential Role of Hypoxia-Inducible Factor-1 in the Progression and Therapy of Central Nervous System Diseases

Hypoxia-inducible factor-1 (HIF-1) is a heterodimer protein composed of an oxygenregulated functional subunit, HIF-1α, and a structural subunit, HIF-1β, belonging to the basic helixloop- helix family. Strict regulation of HIF-1 protein stability and subsequent transcriptional activity involves various molecular interactions and is primarily controlled by post-transcriptional modifications. Hypoxia, owing to impaired cerebral blood flow, has been implicated in a range of central nervous system (CNS) diseases by exerting a deleterious effect on brain function. As a master oxygen- sensitive transcription regulator, HIF-1 is responsible for upregulating a wide spectrum of target genes involved in glucose metabolism, angiogenesis, and erythropoiesis to generate the adaptive response to avoid, or at least minimize, hypoxic brain injury. However, prolonged, severe oxygen deprivation may directly contribute to the role-conversion of HIF-1, namely, from neuroprotection to the promotion of cell death. Currently, an increasing number of studies support the fact HIF-1 is involved in a variety of CNS-related diseases, such as intracranial atherosclerosis, stroke, and neurodegenerative diseases. This review article chiefly focuses on the effect of HIF-1 on the pathogenesis and mechanism of progression of numerous CNS-related disorders by mediating the expression of various downstream genes and extensive biological functional events and presents robust evidence that HIF-1 may represent a potential therapeutic target for CNS-related diseases.

Timely and Appropriate Administration of Inhaled Argon Provides Better Outcomes for tMCAO Mice: A Controlled, Randomized, and Double-Blind Animal Study

BACKGROUND

Inhaled argon (iAr) has shown promising therapeutic efficacy for acute ischemic stroke and has exhibited impressive advantages over other inert gases as a neuroprotective agent. However, the optimal dose, duration, and time point of iAr for acute ischemic stroke are unknown. Here, we explored variable iAr schedules and evaluated the neuroprotective effects of acute iAr administration on lesion volume, brain edema, and neurological function in a mouse model of cerebral ischemic/reperfusion injury.

METHODS

Adult ICR (Institute of Cancer Research) mice were randomly subjected to sham, moderate (1.5 h), or severe (3 h) transient middle cerebral artery occlusion (tMCAO). One hour after tMCAO, the mice were randomized to variable iAr protocols or air. General and focal deficit scores were assessed during double-blind treatment. Infarct volume, overall recovery, and brain edema were analyzed 24 h after cerebral ischemic/reperfusion injury.

RESULTS

Compared with those in the tMCAO-only group, lesion volume (p < 0.0001) and neurologic outcome (general, p < 0.0001; focal, p < 0.0001) were significantly improved in the group administered iAr 1 h after stroke onset (during ischemia). Short-term argon treatment (1 or 3 h) significantly improved the infarct volume (1 vs. 24 h, p < 0.0001; 3 vs. 24 h, p < 0.0001) compared with argon inhalation for 24 h. The concentration of iAr was confirmed to be a key factor in improving focal neurological outcomes relative to that in the tMCAO group, with higher concentrations of iAr showing better effects. Additionally, even though ischemia research has shown an increase in cerebral damage proportional to the ischemia time, argon administration showed significant neuroprotective effects on infarct volume (p < 0.0001), neurological deficits (general, p < 0.0001; focal, p < 0.0001), weight recovery (p < 0.0001), and edema (p < 0.0001) in general, particularly in moderate stroke.

CONCLUSIONS

Timely iAr administration during ischemia showed optimal neurological outcomes and minimal infarct volumes. Moreover, an appropriate duration of argon administration was important for better neuroprotective efficacy. These findings may provide vital guidance for using argon as a neuroprotective agent and moving to clinical trials in acute ischemic stroke.

Three-Hour Argon Inhalation Has No Neuroprotective Effect after Open Traumatic Brain Injury in Rats

In vivo studies of the therapeutic effects of argon in traumatic brain injury (TBI) are limited, and their results are contradictory. The aim of this study was to evaluate the effect of a three-hour inhalation of argon (70%Ar/30%O2) after an open TBI on the severity of the neurological deficit and the degree of brain damage in rats. The experiments were performed on male Wistar rats (n = 35). The TBI was simulated by the dosed open brain contusion injury. The animals were divided into three groups: sham-operated (SO, n = 7); TBI + 70%N2/30%O2 (TBI, n = 14); TBI + 70%Ar/30%O2 (TBI + iAr, n = 14). The Neurological status was assessed over a 14-day period (using the limb-placing and cylinder tests). Magnetic resonance imaging (MRI) scans and a histological examination of the brain with an assessment of the volume of the lesions were performed 14 days after the injury. At each of the time points (days 1, 7, and 14), the limb-placing test score was lower in the TBI and TBI + iAr groups than in the SO group, while there were no significant differences between the TBI and TBI + iAr groups. Additionally, no differences were found between these groups in the cylinder test scores (day 13). The volume of brain damage (tissue loss) according to both the MRI and histological findings did not differ between the TBI and TBI + iAr groups. A three-hour inhalation of argon (70%Ar/30%O2) after a TBI had no neuroprotective effect.

A New Discovery of Argon Functioning in Plants: Regulation of Salinity Tolerance

Argon, a non-polar molecule, easily diffuses into deeper tissue and interacts with larger proteins, protein cavities, or even receptors. Some of the biological effects of argon, notably its activity as an antioxidant, have been revealed in animals. However, whether and how argon influences plant physiology remains elusive. Here, we provide the first report that argon can enable plants to cope with salinity toxicity. Considering the convenience of the application, argon gas was dissolved into water (argon-rich water (ARW)) to investigate the argon’s functioning in phenotypes of alfalfa seed germination and seedling growth upon salinity stress. The biochemical evidence showed that NaCl-decreased α/β-amylase activities were abolished by the application of ARW. The qPCR experiments confirmed that ARW increased NHX1 (Na⁺/H⁺ antiporter) transcript and decreased SKOR (responsible for root-to-shoot translocation of K⁺) mRNA abundance, the latter of which could be used to explain the lower net K⁺ efflux and higher K accumulation. Subsequent results using non-invasive micro-test technology showed that the argon-intensified net Na⁺ efflux and its reduced Na accumulation resulted in a lower Na⁺/K⁺ ratio. NaCl-triggered redox imbalance and oxidative stress were impaired by ARW, as confirmed by histochemical and confocal analyses, and increased antioxidant defense was also detected. Combined with the pot experiments in a greenhouse, the above results clearly demonstrated that argon can enable plants to cope with salinity toxicity via reestablishing ion and redox homeostasis. To our knowledge, this is the first report to address the function of argon in plant physiology, and together these findings might open a new window for the study of argon biology in plant kingdoms.

Post-stroke treatment with argon preserved neurons and attenuated microglia/macrophage activation long-termly in a rat model of transient middle cerebral artery occlusion (tMCAO)

In a previous study from our group, argon has shown to significantly attenuate brain injury, reduce brain inflammation and enhance M₂ microglia/macrophage polarization until 7 days after ischemic stroke. However, the long-term effects of argon have not been reported thus far. In the present study, we analyzed the underlying neuroprotective effects and potential mechanisms of argon, up to 30 days after ischemic stroke. Argon administration with a 3 h delay after stroke onset and 1 h after reperfusion demonstrated long-term neuroprotective effect by preserving the neurons at the ischemic boundary zone 30 days after stroke. Furthermore, the excessive microglia/macrophage activation in rat brain was reduced by argon treatment 30 days after ischemic insult. However, long-lasting neurological improvement was not detectable. More sensorimotor functional measures, age- and disease-related models, as well as further histological and molecular biological analyses will be needed to extend the understanding of argon’s neuroprotective effects and mechanism of action after ischemic stroke.

Argon treatment after experimental subarachnoid hemorrhage: evaluation of microglial activation and neuronal survival as a subanalysis of a randomized controlled animal trial

Hereinafter, we evaluate argon's neuroprotective and immunomodulatory properties after experimental subarachnoid hemorrhage (SAH) examining various localizations (hippocampal and cortical regions) with respect to neuronal damage and microglial activation 6, 24 and 72 hours after SAH. One hour after SAH (endovascular perforation rat model) or sham surgery, a mixture of gas containing 50% argon (argon group) or 50% nitrogen (control group) was applied for 1 hour. At 6 hours after SAH, argon reduced neuronal damage in the hippocampal regions in the argon group compared to the control group (P < 0.034). Hippocampal microglial activation did not differ between the treatment groups over time. The basal cortical regions did not show a different lesion pattern, but microglial activation was significantly reduced in the argon group 72 hours after SAH (P = 0.034 vs. control group). Whereas callosal microglial activation was significantly reduced at 24 hours in the argon-treated group (P = 0.018). Argon treatment ameliorated only early hippocampal neuronal damage after SAH. Inhibition of microglial activation was seen in some areas later on. Thus, argon may influence the microglial inflammatory response and neuronal survival after SAH; however, due to low sample sizes the interpretation of our results is limited. The study protocol was approved by the Government Agency for Animal Use and Protection (Protocol number: TVA 10416G1; initially approved by the "Landesamt für Natur, Umwelt und Verbraucherschutz NRW," Recklinghausen, Germany, on April 28, 2009).

Role of Anesthetics and Their Adjuvants in Neurovascular Protection in Secondary Brain Injury after Aneurysmal Subarachnoid Hemorrhage

Aneurysmal rupture accounts for the majority of subarachnoid hemorrhage and is responsible for most cerebrovascular deaths with high mortality and morbidity. Initial hemorrhage severity and secondary brain injury due to early brain injury and delayed cerebral ischemia are the major determinants of outcomes after aneurysmal subarachnoid hemorrhage. Several therapies have been explored to prevent these secondary brain injury processes after aneurysmal subarachnoid hemorrhage with limited clinical success. Experimental and clinical studies have shown a neuroprotective role of certain anesthetics in cerebrovascular disorders including aneurysmal subarachnoid hemorrhage. The vast majority of aneurysmal subarachnoid hemorrhage patients require general anesthesia for surgical or endovascular repair of their aneurysm. Given the potential impact certain anesthetics have on secondary brain injury after SAH, appropriate selection of anesthetics may prove impactful on overall outcome of these patients. This narrative review focuses on the available evidence of anesthetics and their adjuvants in neurovascular protection in aneurysmal subarachnoid hemorrhage and discusses current impact on clinical care and future investigative directions.

Argon Inhalation for 24 h After Closed-Head Injury Does not Improve Recovery, Neuroinflammation, or Neurologic Outcome in Mice

BACKGROUND/OBJECTIVE

In recent years, the noble gas argon (Ar) has been extensively studied for its organ protection properties. While mounting in vitro and in vivo evidence indicates that argon provides neuroprotection in ischemic brain injury, its neuroprotective potential in traumatic brain injury (TBI) has not been evaluated in vivo. We tested the hypothesis that prolonged inhalation of 70% or 79% argon for 24 h after closed-head injury (CHI) improves neurologic outcome and overall recovery at 36 days post-injury. We also compared effects of the 30% or 21% residual oxygen on argon's potential neuroprotective capacity.

METHODS

Adult male C57/black mice (n = 240) were subjected to closed-head traumatic brain injury, followed by inhalation of 70% argon or nitrogen (30% oxygen), or 79% argon or nitrogen (21% oxygen) for 24 h. Neurologic outcome (rotarod, neuroscore, and Morris water maze) was evaluated for up to 36 days post-injury. Histologic parameters of neurologic degeneration (Fluoro-Jade staining) and inflammation (F4/80 microglia immunostaining) were assessed in subgroups at 24 h and on post-injury day 7.

RESULTS

Our CHI protocol consistently resulted in significant brain injury. After argon inhalation for 24 h at either concentration, mice did not show significant improvement with regard to neuroscores, rotarod performance, Morris water maze performance, or overall recovery (body weight), compared to nitrogen controls, up to 36 days. At 7 days post-injury, histologic markers of neurodegeneration and inflammation, particularly in the hippocampus, consistently demonstrated significant injury. Notably, recovery was reduced in mice treated with the higher oxygen concentration (30%) after CHI compared to 21%.

CONCLUSIONS

Prolonged argon treatment did not improve neurologic outcome, overall recovery (weight), nor markers of neurodegeneration or neuroinflammation after significant CHI compared to nitrogen. While neuroprotective in predominately ischemic injury, argon did not provide protection after TBI in this model, highlighting the crucial importance of assessing argon's strengths and weaknesses in preclinical models to fully understand its organ protective potential in different pathologies and gas mixtures.

Efficacy of acute administration of inhaled argon on traumatic brain injury in mice

BACKGROUND

Whilst there has been progress in supportive treatment for traumatic brain injury (TBI), specific neuroprotective interventions are lacking. Models of ischaemic heart and brain injury show the therapeutic potential of argon gas, but it is still not known whether inhaled argon (iAr) is protective in TBI. We tested the effects of acute administration of iAr on brain oedema, tissue micro-environmental changes, neurological functions, and structural outcome in a mouse model of TBI.

METHODS

Anaesthetised adult C57BL/6J mice were subjected to severe TBI by controlled cortical impact. Ten minutes after TBI, the mice were randomised to 24 h treatments with iAr 70%/O₂ 30% or air (iCtr). Sensorimotor deficits were evaluated up to 6 weeks post-TBI by three independent tests. Cognitive function was evaluated by Barnes maze test at 4 weeks. MRI was done to examine brain oedema at 3 days and white matter damage at 5 weeks. Microglia/macrophages activation and functional commitment were evaluated at 1 week after TBI by immunohistochemistry.

RESULTS

iAr significantly accelerated sensorimotor recovery and improved cognitive deficits 1 month after TBI, with less white matter damage in the ipsilateral fimbria and body of the corpus callosum. Early changes underpinning protection included a reduction of pericontusional vasogenic oedema and of the inflammatory response. iAr significantly reduced microglial activation with increases in ramified cells and the M2-like marker YM1.

CONCLUSIONS

iAr accelerates recovery of sensorimotor function and improves cognitive and structural outcome 1 month after severe TBI in adult mice. Early effects include a reduction of brain oedema and neuroinflammation in the contused tissue.

A complete review of preclinical and clinical uses of the noble gas argon: Evidence of safety and protection

The noble gas argon (Ar) is a "biologically" active element and has been extensively studied preclinically for its organ protection properties. This work reviews all preclinical studies employing Ar and describes the clinical uses reported in literature, analyzing 55 pertinent articles found by means of a search on PubMed and Embase. Ventilation with Ar has been tested in different models of acute disease at concentrations ranging from 20% to 80% and for durations between a few minutes up to days. Overall, lesser cell death, smaller infarct size, and better functional recovery after ischemia have been repeatedly observed. Modulation of the molecular pathways involved in cell survival, with resulting anti-apoptotic and pro-survival effects, appeared as the determinant mechanism by which Ar fulfills its protective role. These beneficial effects have been reported regardless of onset and duration of Ar exposure, especially after cardiac arrest. In addition, ventilation with Ar was safe both in animals and humans. Thus, preclinical and clinical data support future clinical studies on the role of inhalatory Ar as an organ protector.

Recent advances in the neuroprotective effects of medical gases

Central nervous system injuries are a leading cause of death and disability worldwide. Although the exact pathophysiological mechanisms of various brain injuries vary, central nervous system injuries often result in an inflammatory response, and subsequently lead to brain damage. This suggests that neuroprotection may be necessany in the treatment of multiple disease models. The use of medical gases as neuroprotective agents has gained great attention in the medical field. Medical gases include common gases, such as oxygen, hydrogen and carbon dioxide; hydrogen sulphide and nitric oxide that have been considered toxic; volatile anesthetic gases, such as isoflurane and sevoflurane; and inert gases like helium, argon, and xenon. The neuroprotection from these medical 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. Nevertheless, the transition into the clinical practice is still lagging. This delay could be attributed to the contradictory paradigms and the conflicting results that have been obtained from experimental models, as well as the presence of inconsistent reports regarding their safety. In this review, we summarize the potential mechanisms underlying the neuroprotective effects of medical gases and discuss possible candidates that could improve the outcomes of brain injury.

Argon Inhalation for 24 Hours After Onset of Permanent Focal Cerebral Ischemia in Rats Provides Neuroprotection and Improves Neurologic Outcome

OBJECTIVES

We tested the hypothesis that prolonged inhalation of 70% argon for 24 hours after in vivo permanent or temporary stroke provides neuroprotection and improves neurologic outcome and overall recovery after 7 days.

DESIGN

Controlled, randomized, double-blinded laboratory study.

SETTING

Animal research laboratories.

SUBJECTS

Adult Wistar male rats (n = 110).

INTERVENTIONS

Rats were subjected to permanent or temporary focal cerebral ischemia via middle cerebral artery occlusion, followed by inhalation of 70% argon or nitrogen in 30% oxygen for 24 hours. On postoperative day 7, a 48-point neuroscore and histologic lesion size were assessed.

MEASUREMENTS AND MAIN RESULTS

After argon inhalation for 24 hours immediately following "severe permanent ischemia" induction, neurologic outcome (neuroscore, p = 0.034), overall recovery (body weight, p = 0.02), and infarct volume (total infarct volume, p = 0.0001; cortical infarct volume, p = 0.0003; subcortical infarct volume, p = 0.0001) were significantly improved. When 24-hour argon treatment was delayed for 2 hours after permanent stroke induction or until after postischemic reperfusion treatment, neurologic outcomes remained significantly improved (neuroscore, p = 0.043 and p = 0.014, respectively), as was overall recovery (body weight, p = 0.015), compared with nitrogen treatment. However, infarct volume and 7-day mortality were not significantly reduced when argon treatment was delayed.

CONCLUSIONS

Neurologic outcome (neuroscore), overall recovery (body weight), and infarct volumes were significantly improved after 24-hour inhalation of 70% argon administered immediately after severe permanent stroke induction. Neurologic outcome and overall recovery were also significantly improved even when argon treatment was delayed for 2 hours or until after reperfusion.

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

Background

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

Methods

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

Results

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

Conclusions

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

The role and therapeutic potential of heat shock proteins in haemorrhagic stroke

Heat shock proteins (HSPs) are induced after haemorrhagic stroke, which includes subarachnoid haemorrhage (SAH) and intracerebral haemorrhage (ICH). Most of these proteins function as neuroprotective molecules to protect cerebral neurons from haemorrhagic stroke and as markers to indicate cellular stress or damage. The most widely studied HSPs in SAH are HSP70, haeme oxygenase-1 (HO-1), HSP20 and HSP27. The subsequent pathophysiological changes following SAH can be divided into two stages: early brain injury and delayed cerebral ischaemia, both of which determine the outcome for patients. Because the mechanisms of HSPs in SAH are being revealed and experimental models in animals are continually maturing, new agents targeting HSPs with limited side effects have been suggested to provide therapeutic potential. For instance, some pharmaceutical agents can block neuronal apoptosis signals or dilate cerebral vessels by modulating HSPs. HO-1 and HSP70 are also critical topics for ICH research, which can be attributed to their involvement in pathophysiological mechanisms and therapeutic potential. However, the process of HO-1 metabolism can be toxic owing to iron overload and the activation of succedent pathways, for example, the Fenton reaction and oxidative damage; the overall effect of HO-1 in SAH and ICH tends to be protective and harmful, respectively, given the different pathophysiological changes in these two types of haemorrhagic stroke. In the present study, we focus on the current understanding of the role and therapeutic potential of HSPs involved in haemorrhagic stroke. Therefore, HSPs may be potential therapeutic targets, and new agents targeting HSPs are warranted.

Evidence for a conditioning effect of inhalational anesthetics on angiographic vasospasm after aneurysmal subarachnoid hemorrhage

OBJECTIVE

Delayed cerebral ischemia (DCI) after aneurysmal subarachnoid hemorrhage (SAH) is characterized by large-artery vasospasm, distal autoregulatory dysfunction, cortical spreading depression, and microvessel thrombi. Large-artery vasospasm has been identified as an independent predictor of poor outcome in numerous studies. Recently, several animal studies have identified a strong protective role for inhalational anesthetics against secondary brain injury after SAH including DCI-a phenomenon referred to as anesthetic conditioning. The aim of the present study was to assess the potential role of inhalational anesthetics against cerebral vasospasm and DCI in patients suffering from an SAH.

METHODS

After IRB approval, data were collected retrospectively for all SAH patients admitted to the authors' hospital between January 1, 2010, and December 31, 2013, who received general anesthesia with either inhalational anesthetics only (sevoflurane or desflurane) or combined inhalational (sevoflurane or desflurane) and intravenous (propofol) anesthetics during aneurysm treatment. The primary outcomes were development of angiographic vasospasm and development of DCI during hospitalization. Univariate and logistic regression analyses were performed to identify independent predictors of these endpoints.

RESULTS

The cohort included 157 SAH patients whose mean age was 56 ± 14 (± SD). An inhalational anesthetic-only technique was employed in 119 patients (76%), while a combination of inhalational and intravenous anesthetics was employed in 34 patients (22%). As expected, patients in the inhalational anesthetic-only group were exposed to significantly more inhalational agent than patients in the combination anesthetic group (p < 0.05). Multivariate logistic regression analysis identified inhalational anesthetic-only technique (OR 0.35, 95% CI 0.14-0.89), Hunt and Hess grade (OR 1.51, 95% CI 1.03-2.22), and diabetes (OR 0.19, 95% CI 0.06-0.55) as significant predictors of angiographic vasospasm. In contradistinction, the inhalational anesthetic-only technique had no significant impact on the incidence of DCI or functional outcome at discharge, though greater exposure to desflurane (as measured by end-tidal concentration) was associated with a lower incidence of DCI.

CONCLUSIONS

These data represent the first evidence in humans that inhalational anesthetics may exert a conditioning protective effect against angiographic vasospasm in SAH patients. Future studies will be needed to determine whether optimized inhalational anesthetic paradigms produce definitive protection against angiographic vasospasm; whether they protect against other events leading to secondary brain injury after SAH, including microvascular thrombi, autoregulatory dysfunction, blood-brain barrier breakdown, neuroinflammation, and neuronal cell death; and, if so, whether this protection ultimately improves patient outcome.

Post-stroke treatment with argon attenuated brain injury, reduced brain inflammation and enhanced M2 microglia/macrophage polarization: a randomized controlled animal study

BACKGROUND

In recent years, argon has been shown to exert neuroprotective effects in an array of models. However, the mechanisms by which argon exerts its neuroprotective characteristics remain unclear. Accumulating evidence imply that argon may exert neuroprotective effects via modulating the activation and polarization of microglia/macrophages after ischemic stroke. In the present study, we analyzed the underlying neuroprotective effects of delayed argon application until 7 days after reperfusion and explored the potential mechanisms.

METHODS

Twenty-one male Wistar rats underwent transient middle cerebral artery occlusion or sham surgery randomly for 2 h using the endoluminal thread model. Three hours after transient middle cerebral artery occlusion induction and 1 h after reperfusion, animals received either 50% vol Argon/50% vol O2 or 50% vol N2/50% vol O2 for 1 h. The primary outcome was the 6-point neuroscore from 24 h to d7 after reperfusion. Histological analyses including infarct volume, survival of neurons (NeuN) at the ischemic boundary zone, white matter integrity (Luxol Fast Blue), microglia/macrophage activation (Iba1), and polarization (Iba1/Arginase1 double staining) on d7 were conducted as well. Sample size calculation was performed using nQuery Advisor + nTerim 4.0. Independent t test, one-way ANOVA and repeated measures ANOVA were performed, respectively, for statistical analysis (SPSS 23.0).

RESULTS

The 6-point neuroscore from 24 h to d7 after reperfusion showed that tMCAO Ar group displayed significantly improved neurological performance compared to tMCAO N2 group (p = 0.026). The relative numbers of NeuN-positive cells in the ROIs of tMCAO Ar group significantly increased compared to tMCAO N2 group (p = 0.010 for cortex and p = 0.011 for subcortex). Argon significantly suppressed the microglia/macrophage activation as revealed by Iba1 staining (p = 0.0076) and promoted the M2 microglia/macrophage polarization as revealed by Iba1/Arginase 1 double staining (p = 0.000095).

CONCLUSIONS

Argon administration with a 3 h delay after stroke onset and 1 h after reperfusion significantly alleviated neurological deficit within the first week and preserved the neurons at the ischemic boundary zone 7 days after stroke. Moreover, argon reduced the excessive microglia/macrophage activation and promoted the switch of microglia/macrophage polarization towards the anti-inflammatory M2 phenotype. Studies making efforts to further elucidate the protective mechanisms and to benefit the translational application are of great value.

Argon reduces the pulmonary vascular tone in rats and humans by GABA-receptor activation

Argon exerts neuroprotection. Thus, it might improve patients' neurological outcome after cerebral disorders or cardiopulmonary resuscitation. However, limited data are available concerning its effect on pulmonary vessel and airways. We used rat isolated perfused lungs (IPL) and precision-cut lung slices (PCLS) of rats and humans to assess this topic. IPL: Airway and perfusion parameters, oedema formation and the pulmonary capillary pressure (Pcap) were measured and the precapillary and postcapillary resistance (Rpost) was calculated. In IPLs and PCLS, the pulmonary vessel tone was enhanced with ET-1 or remained unchanged. IPLs were ventilated and PCLS were gassed with argon-mixture or room-air. IPL: Argon reduced the ET-1-induced increase of Pcap, Rpost and oedema formation (p < 0.05). PCLS (rat): Argon relaxed naïve pulmonary arteries (PAs) (p < 0.05). PCLS (rat/human): Argon attenuated the ET-1-induced contraction in PAs (p < 0.05). Inhibition of GABAB-receptors abolished argon-induced relaxation (p < 0.05) in naïve or ET-1-pre-contracted PAs; whereas inhibition of GABAA-receptors only affected ET-1-pre-contracted PAs (p < 0.01). GABAA/B-receptor agonists attenuated ET-1-induced contraction in PAs and baclofen (GABAB-agonist) even in pulmonary veins (p < 0.001). PLCS (rat): Argon did not affect the airways. Finally, argon decreases the pulmonary vessel tone by activation of GABA-receptors. Hence, argon might be applicable in patients with pulmonary hypertension and right ventricular failure.

Argon Mitigates Impaired Wound Healing Process and Enhances Wound Healing In Vitro and In Vivo

Diabetic foot ulcers are associated with significant morbidity and mortality, and current treatments are far from optimal. Chronic wounds in diabetes are characterised by impaired angiogenesis, leukocyte function, fibroblast proliferation, and keratinocyte migration and proliferation.

Methods: We tested the effect of exposure to argon gas on endothelial cell, fibroblast, macrophage and keratinocyte cell cultures in vitro and in vivo of a streptozotocin-induced diabetic mouse model.

Results: Exposure to normobaric argon gas promotes multiple steps of the wound healing process. Argon accelerated angiogenesis, associated with upregulation of pro-angiogenic Angiopoietin-1 and vascular endothelial growth factor (VEGF) signalling in vitro and in vivo. Treatment with argon enhanced expression of transforming growth factor (TGF)-β, early recruitment of macrophages and keratinocyte proliferation. Argon had a pro-survival effect, inducing expression of cytoprotective mediators B-cell lymphoma 2 and heme oxygenase 1. Argon was able to accelerate wound closure in a diabetic mouse model.

Conclusion: Together these findings indicate that argon gas may be a promising candidate for clinical use in treatment of diabetic ulcers.

Argon attenuates multiorgan failure following experimental aortic cross-clamping

AIMS

Argon has been shown to prevent ischaemic injuries in several scenarios of regional ischaemia. We determined whether it could provide a systemic effect in a model of multiorgan failure (MOF) induced by aortic cross-clamping.

METHODS

Anaesthetized rabbits were submitted to aortic cross-clamping (30 min) and subsequent reperfusion (300 min). They were either ventilated with oxygen-enriched air throughout the protocol [fraction of inspired oxygen (FiO₂ ) = 30%; control group) or with a mixture of 30% oxygen and 70% argon (argon groups). In a first group treated with argon ('Argon-Total'), its administration was started 30 min before ischaemia and maintained throughout the protocol. In the two other groups, the administration was started either 30 min before ischaemia ('Argon-Pre') or at the onset of reperfusion ('Argon-Post'), for a total duration of 2 h. Cardiovascular, renal and inflammatory endpoints were assessed throughout protocol.

RESULTS

Compared with control, shock was significantly attenuated in Argon-Total and Argon-Pre but not Argon-Post groups (e.g. cardiac output = 62±5 vs. 29 ± 5 ml min^-1 kg^-1 in Argon-Total and control groups at the end of the follow-up). Shock and renal failure were reduced in all argon vs. control groups. Histopathological examination of the gut showed attenuation of ischaemic lesions in all argon vs. control groups. Blood transcription levels of interleukin (IL) 1β, IL-8, IL-10 and hypoxia-inducible factor 1α were not significantly different between groups.

CONCLUSION

Argon attenuated clinical and biological modifications of cardiovascular, renal and intestinal systems, but not the inflammatory response, after aortic cross-clamping. The window of administration was crucial to optimize organ protection.

Neurobehavioral testing in subarachnoid hemorrhage: A review of methods and current findings in rodents

The most important aspect of a preclinical study seeking to develop a novel therapy for neurological diseases is whether the therapy produces any clinically relevant functional recovery. For this purpose, neurobehavioral tests are commonly used to evaluate the neuroprotective efficacy of treatments in a wide array of cerebrovascular diseases and neurotrauma. Their use, however, has been limited in experimental subarachnoid hemorrhage studies. After several randomized, double-blinded, controlled clinical trials repeatedly failed to produce a benefit in functional outcome despite some improvement in angiographic vasospasm, more rigorous methods of neurobehavioral testing became critical to provide a more comprehensive evaluation of the functional efficacy of proposed treatments. While several subarachnoid hemorrhage studies have incorporated an array of neurobehavioral assays, a standardized methodology has not been agreed upon. Here, we review neurobehavioral tests for rodents and their potential application to subarachnoid hemorrhage studies. Developing a standardized neurobehavioral testing regimen in rodent studies of subarachnoid hemorrhage would allow for better comparison of results between laboratories and a better prediction of what interventions would produce functional benefits in humans.

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.

Argon attenuates the emergence of secondary injury after traumatic brain injury within a 2-hour incubation period compared to desflurane: an in vitro study

Despite years of research, treatment of traumatic brain injury (TBI) remains challenging. Considerable data exists that some volatile anesthetics might be neuroprotective. However, several studies have also revealed a rather neurotoxic profile of anesthetics. In this study, we investigated the effects of argon 50%, desflurane 6% and their combination in an in vitro TBI model with incubation times similar to narcotic time slots in a daily clinical routine. Organotypic hippocampal brain slices of 5- to 7-day-old mice were cultivated for 14 days before TBI was performed. Slices were eventually incubated for 2 hours in an atmosphere containing no anesthetic gas, argon 50% or desflurane 6% or both. Trauma intensity was evaluated via fluorescent imagery. Our results show that neither argon 50% nor desflurane 6% nor their combination could significantly reduce the trauma intensity in comparison to the standard atmosphere. However, in comparison to desflurane 6%, argon 50% displayed a rather neuroprotective profile within the first 2 hours after a focal mechanical trauma (P = 0.015). A 2-hour incubation in an atmosphere containing both gases, argon 50% and desflurane 6%, did not result in significant effects in comparison to the argon 50% group or the desflurane 6% group. Our findings demonstrate that within a 2-hour incubation time neither argon nor desflurane could affect propidium iodide-detectable cell death in an in vitro TBI model in comparison to the standard atmosphere, although cell death was less with argon 50% than with desflurane 6%. The results show that within this short time period processes concerning the development of secondary injury are already taking place and may be manipulated by argon.

A porcine ex vivo lung perfusion model with maximal argon exposure to attenuate ischemia-reperfusion injury

Argon (Ar) is a noble gas with known organoprotective effects in rodents and in vitro models. In a previous study we failed to find a postconditioning effect of Ar during ex vivo lung perfusion (EVLP) on warm-ischemic injury in a porcine model. In this study, we further investigated a prolonged exposure to Ar to decrease cold ischemia-reperfusion injury after lung transplantation in a porcine model with EVLP assessment. Domestic pigs (n = 6/group) were pre-conditioned for 6 hours with 21% O₂ and 79% N₂ (CONTR) or 79% Ar (ARG). Subsequently, lungs were cold flushed and stored inflated on ice for 18 hours inflated with the same gas mixtures. Next, lungs were perfused for 4 hours on EVLP (acellular) while ventilated with 12% O₂ and 88% N₂ (CONTR group) or 88% Ar (ARG group). The perfusate was saturated with the same gas mixture but with the addition of CO₂ to an end-tidal CO₂ of 35-45 mmHg. The saturated perfusate was drained and lungs were perfused with whole blood for an additional 2 hours on EVLP. Evaluation at the end of EVLP did not show significant effects on physiologic parameters by prolonged exposure to Ar. Also wet-to-dry weight ratio did not improve in the ARG group. Although in other organ systems protective effects of Ar have been shown, we did not detect beneficial effects of a high concentration of Ar on cold pulmonary ischemia-reperfusion injury in a porcine lung model after prolonged exposure to Ar in this porcine model with EVLP assessment.

The Molecular Pathway of Argon-Mediated Neuroprotection

The noble gas argon has attracted increasing attention in recent years, especially because of its neuroprotective properties. In a variety of models, ranging from oxygen-glucose deprivation in cell culture to complex models of mid-cerebral artery occlusion, subarachnoid hemorrhage or retinal ischemia-reperfusion injury in animals, argon administration after individual injury demonstrated favorable effects, particularly increased cell survival and even improved neuronal function. As an inert molecule, argon did not show signs of adverse effects in the in vitro and in vivo model used, while being comparably cheap and easy to apply. However, the molecular mechanism by which argon is able to exert its protective and beneficial characteristics remains unclear. Although there are many pieces missing to complete the signaling pathway throughout the cell, it is the aim of this review to summarize the known parts of the molecular pathways and to combine them to provide a clear insight into the cellular pathway, starting with the receptors that may be involved in mediating argons effects and ending with the translational response.