Argon Preconditioning Protects Airway Epithelial Cells against Hydrogen Peroxide-Induced Oxidative Stress

Candidate Signature miRNAs from Secreted miRNAome of Human Lung Microvascular Endothelial Cells in Response to Different Oxygen Conditions: A Pilot Study

Oxygen conditions in the lung determine downstream organ functionality by setting the partial pressure of oxygen, regulating the redox homeostasis and by activating mediators in the lung that can be propagated in the blood stream. Examples for such mediators are secreted soluble or vesicle-bound molecules (proteins and nucleic acids) that can be taken up by remote target cells impacting their metabolism and signaling pathways. MicroRNAs (miRNAs) have gained significant interest as intercellular communicators, biomarkers and therapeutic targets in this context. Due to their high stability in the blood stream, they have also been attributed a role as "memory molecules" that are able to modulate gene expression upon repeated (stress) exposures. In this study, we aimed to identify and quantify released miRNAs from lung microvascular endothelial cells in response to different oxygen conditions. We combined next-generation sequencing (NGS) of secreted miRNAs and cellular mRNA sequencing with bioinformatic analyses in order to delineate molecular events on the cellular and extracellular level and their putative interdependence. We show that the identified miRNA networks have the potential to co-mediate some of the molecular events, that have been observed in the context of hypoxia, hyperoxia, intermittent hypoxia and intermittent hypoxia/hyperoxia.

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.

Effects of Hyperoxia and Hyperoxic Oscillations on the Proteome of Murine Lung Microvascular Endothelium

Patients presenting with insufficient tissue oxygenation and impaired lung function as in acute respiratory distress syndrome (ARDS) frequently require mechanical ventilation with supplemental oxygen. Despite the lung being used to experiencing the highest partial pressure of oxygen during healthy breathing, the organ is susceptible to oxygen-induced injury at supraphysiological concentrations. Hyperoxia-induced lung injury (HALI) has been regarded as a second hit to pre-existing lung injury and ventilator-induced lung injury (VILI) attributed to oxidative stress. The injured lung has a tendency to form atelectasis, a cyclic collapse and reopening of alveoli. The affected lung areas experience oxygen conditions that oscillate between hyperoxia and hypoxia rather than remaining in a constant hyperoxic state. Mechanisms of HALI have been investigated in many animal models previously. These studies provided insights into the effects of hyperoxia on the whole organism. However, cell type-specific responses have not been dissected in detail, but are necessary for a complete mechanistic understanding of ongoing pathological processes. In our study, we investigated the effects of constant and intermittent hyperoxia on the lung endothelium from a mouse by an in vitro proteomic approach. We demonstrate that these oxygen conditions have characteristic effects on the pulmonary endothelial proteome that underlie the physiological (patho)mechanisms.

Argon preconditioning protects neuronal cells with a Toll-like receptor-mediated effect

The noble gas argon has the potential to protect neuronal cells from cell death. So far, this effect has been studied in treatment after acute damage. Preconditioning using argon has not yet been investigated. In this study, human neuroblastoma SH-SY5Y cells were treated with different concentrations of argon (25%, 50%, and 74%; 21% O₂, 5% CO₂, balance nitrogen) at different time intervals before inflicting damage with rotenone (20 µM, 4 hours). Apoptosis was determined by flow cytometry after annexin V and propidium iodide staining. Surface expressions of Toll-like receptors 2 and 4 were also examined. Cells were also processed for analysis by western blot and qPCR to determine the expression of apoptotic and inflammatory proteins, such as extracellular-signal regulated kinase (ERK1/2), nuclear transcription factor-κB (NF-κB), protein kinase B (Akt), caspase-3, Bax, Bcl-2, interleukin-8, and heat shock proteins. Immunohistochemical staining was performed for TLR2 and 4 and interleukin-8. Cells were also pretreated with OxPAPC, an antagonist of TLR2 and 4 to elucidate the molecular mechanism. Results showed that argon preconditioning before rotenone application caused a dose-dependent but not a time-dependent reduction in the number of apoptotic cells. Preconditioning with 74% argon for 2 hours was used for further experiments showing the most promising results. Argon decreased the surface expression of TLR2 and 4, whereas OxPAPC treatment partially abolished the protective effect of argon. Argon increased phosphorylation of ERK1/2 but decreased NF-κB and Akt. Preconditioning inhibited mitochondrial apoptosis and the heat shock response. Argon also suppressed the expression of the pro-inflammatory cytokine interleukin-8. Immunohistochemistry confirmed the alteration of TLRs and interleukin-8. OxPAPC reversed the argon effect on ERK1/2, Bax, Bcl-2, caspase-3, and interleukin-8 expression, but not on NF-κB and the heat shock proteins. Taken together, argon preconditioning protects against apoptosis of neuronal cells and mediates its action via Toll-like receptors. Argon may represent a promising therapeutic alternative in various clinical settings, such as the treatment of stroke.

Argon inhibits reactive oxygen species oxidative stress via the miR-21-mediated PDCD4/PTEN pathway to prevent myocardial ischemia/reperfusion injury

The objective of this study was to explore the effect of argon preconditioning on myocardial ischemia reperfusion (MI/R) injury and its mechanism. Cardiomyocytes H2C9 were pre-treated with 50% argon, and a cell model of oxygen-glucose deprivation (OGD) was established. CCK-8 and cytotoxicity detection kits were used to detect cell viability and lactate dehydrogenase (LDH) release. The miR-21 expression was detected using quantitative real-time polymerase chain reaction. Western blot analysis was performed to detect the expression of programmed cell death protein 4 (PDCD4) and homologous phosphatase and tensin homolog (PTEN) proteins. The levels of inflammatory factors (IL-1β, IL-6, and IL-8) and oxidative stress factors (reactive oxygen species ROS], malondialdehyde [MDA], and superoxide dismutase [SOD]) were measured using an enzyme-linked immunosorbent assay. The effect of argon on cell apoptosis was detected using flow cytometry. Argon increased the proliferation of cardiomyocytes induced by OGD, decreased the release of LDH in cell culture medium, increased miR-21 expression in cells, decreased the expression of miR-21 target proteins PDCD4 and PTEN, decreased the levels of inflammatory factors (interleukin-1β [IL-1β], interleukin-6 [IL-6], and interleukin-8 [IL-8]) and oxidative stress factors (ROS and MDA), increased the SOD content, and decreased the cell apoptosis rate. Our results suggest that argon preconditioning inhibited the PDCD4/PTEN pathway via miR-21, thereby inhibiting ROS oxidative stress and preventing MI/R injury.

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.

Oxygen conditions oscillating between hypoxia and hyperoxia induce different effects in the pulmonary endothelium compared to constant oxygen conditions

The pulmonary endothelium is an immediate recipient of high oxygen concentrations upon oxygen therapy and mediates down-stream responses. Cyclic collapse and reopening of atelectatic lung areas during mechanical ventilation with high fractions of inspired oxygen result in the propagation of oxygen oscillations in the hypoxic/hyperoxic range. We used primary murine lung endothelial cell cultures to investigate cell responses to constant and oscillating oxygen conditions in the hypoxic to hyperoxic range. Severe constant hyperoxia had pro-inflammatory and cytotoxic effects including an increase in expression of ICAM1, E-selectin, and RAGE at 24 hr exposure. The coagulative/fibrinolytic system responded by upregulation of uPA, tPA, and vWF and PAI1 under constant severe hyperoxia. Among antioxidant enzymes, the upregulation of SOD2, TXN1, TXNRD3, GPX1, and Gstp1 at 24 hr, but downregulation of SOD3 at 72 hr constant hyperoxia was evident. Hypoxic/hyperoxic oscillating oxygen conditions induced pro-inflammatory cytokine release to a lesser extent and later than constant hyperoxia. Gene expression analyses showed upregulation of NFKB p65 mRNA at 72 hr. More evident was a biphasic response of NOS3 and ACE1 gene expression (downregulation until 24 hr and upregulation at 72 hr). ACE2 mRNA was upregulated until 72 hr, but shedding of the mature protein from the cell surface favored ACE1. Oscillations resulted in severe production of peroxynitrite, but apart from upregulation of Gstp1 at 24 hr responses of antioxidative proteins were less pronounced than under constant hyperoxia. Oscillating oxygen in the hypoxic/hyperoxic range has a characteristical impact on vasoactive mediators like NOS3 and on the activation of the renin-angiotensin system in the lung endothelium.

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.

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.

A new ocotillol-type ginsenoside from stems and leaves of Panax quinquefolium L. and its anti-oxidative effect on hydrogen peroxide exposed A549 cells

A new ocotillol-type ginsenoside, namely 12-one-pseudoginsenoside F₁₁ (12-one-PF₁₁), was isolated from stems and leaves of Panax quinquefolium, whose structure was elucidated 6-O-[α-L-rhamnopyranosyl-(1-2)-β-D-glucopyranosyl]-dammar-12-one-20S,24R-epoxy-3β,6α,25-triol. 12-one-PF₁₁ significantly suppressed hydrogen peroxide induced oxidative stress in human lung carcinoma A549 cells. As compared with model group, 12-one-PF₁₁ improved cell viability of A549 cells in a dose-dependent manner, and significantly decreased the generation of malondialdehyde (MDA) and increased production of superoxide dismutase (SOD) and glutathione (GSH) and protein expression levels of nuclear related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) in A549 cells.

Intermittent Hypoxia Activates Duration-Dependent Protective and Injurious Mechanisms in Mouse Lung Endothelial Cells

Intermittent hypoxia is a major factor in clinical conditions like the obstructive sleep apnea syndrome or the cyclic recruitment and derecruitment of atelectasis in acute respiratory distress syndrome and positive pressure mechanical ventilation. In vivo investigations of the direct impact of intermittent hypoxia are frequently hampered by multiple co-morbidities of patients. Therefore, cell culture experiments are important model systems to elucidate molecular mechanisms that are involved in the cellular response to alternating oxygen conditions and could represent future targets for tailored therapies. In this study, we focused on mouse lung endothelial cells as a first frontier to encounter altered oxygen due to disturbances in airway or lung function, that play an important role in the development of secondary diseases like vascular disease and pulmonary hypertension. We analyzed key markers for endothelial function including cell adhesion molecules, molecules involved in regulation of fibrinolysis, hemostasis, redox balance, and regulators of gene expression like miRNAs. Results show that short-time exposure to intermittent hypoxia has little impact on vitality and health of cells. At early timepoints and up to 24 h, many endothelial markers are unchanged in their expression and some indicators of injury are even downregulated. However, in the long-term, multiple signaling pathways are activated, that ultimately result in cellular inflammation, oxidative stress, and apoptosis.