Xenon preconditioning differently regulates p44/42 MAPK (ERK 1/2) and p46/54 MAPK (JNK 1/2 and 3) in vivo †

Pharmacological Cardioprotection against Ischemia Reperfusion Injury-The Search for a Clinical Effective Therapy

Pharmacological conditioning aims to protect the heart from myocardial ischemia-reperfusion injury (IRI). Despite extensive research in this area, today, a significant gap remains between experimental findings and clinical practice. This review provides an update on recent developments in pharmacological conditioning in the experimental setting and summarizes the clinical evidence of these cardioprotective strategies in the perioperative setting. We start describing the crucial cellular processes during ischemia and reperfusion that drive acute IRI through changes in critical compounds (∆G_ATP, Na⁺, Ca²⁺, pH, glycogen, succinate, glucose-6-phosphate, mitoHKII, acylcarnitines, BH₄, and NAD⁺). These compounds all precipitate common end-effector mechanisms of IRI, such as reactive oxygen species (ROS) generation, Ca²⁺ overload, and mitochondrial permeability transition pore opening (mPTP). We further discuss novel promising interventions targeting these processes, with emphasis on cardiomyocytes and the endothelium. The limited translatability from basic research to clinical practice is likely due to the lack of comorbidities, comedications, and peri-operative treatments in preclinical animal models, employing only monotherapy/monointervention, and the use of no-flow (always in preclinical models) versus low-flow ischemia (often in humans). Future research should focus on improved matching between preclinical models and clinical reality, and on aligning multitarget therapy with optimized dosing and timing towards the human condition.

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.

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.

Effect of Inhaled Xenon on Cardiac Function in Comatose Survivors of Out-of-Hospital Cardiac Arrest-A Substudy of the Xenon in Combination With Hypothermia After Cardiac Arrest Trial

This explorative substudy aimed at determining the effect of inhaled xenon on left ventricular function by echocardiography in comatose survivors of out-of-hospital cardiac arrest.

DESIGN

A randomized two-group single-blinded phase 2 clinical drug trial.

SETTING

A multipurpose ICU in two university hospitals.

PATIENTS

Of the 110 randomized comatose survivors after out-of-hospital cardiac arrest with a shockable rhythm in the xenon in combination with hypothermia after cardiac arrest trial, 38 patients (24-76 yr old) with complete echocardiography were included in this study.

INTERVENTIONS

Patients were randomized to receive either inhaled xenon combined with hypothermia (33°C) for 24 hours or hypothermia treatment alone. Echocardiography was performed at hospital admission and 24 ± 4 hours after hypothermia.

MEASUREMENTS AND MAIN RESULTS

Left ventricular ejection fraction, myocardial longitudinal systolic strain, and diastolic function were analyzed blinded to treatment. There were 17 xenon and 21 control patients in whom echocardiography was completed. Clinical characteristics did not differ significantly between the groups. At admission, ejection fraction was similar in xenon and control patients (39% ± 10% vs 38% ± 11%; p = 0.711) but higher in xenon than control patients after hypothermia (50% ± 10% vs 42% ± 10%; p = 0.014). Global longitudinal systolic strain was similar in xenon and control patients at admission (-9.0% ± 3.8% vs -8.1% ± 3.6%; p = 0.555) but better in xenon than control patients after hypothermia (-14.4.0% ± 4.0% vs -10.5% ± 4.0%; p = 0.006). In patients with coronary artery disease, longitudinal strain improved in the nonischemic myocardial segments in xenon patients. There were no changes in diastolic function between the groups.

CONCLUSIONS

Among comatose survivors of a cardiac cause out-of-hospital cardiac arrest, inhaled xenon combined with hypothermia was associated with greater recovery of left ventricular systolic function in comparison with hypothermia alone.

Perioperative Cardioprotection: General Mechanisms and Pharmacological Approaches

Cardioprotection encompasses a variety of strategies protecting the heart against myocardial injury that occurs during and after inadequate blood supply to the heart during myocardial infarction. While restoring reperfusion is crucial for salvaging myocardium from further damage, paradoxically, it itself accounts for additional cell death-a phenomenon named ischemia/reperfusion injury. Therefore, therapeutic strategies are necessary to render the heart protected against myocardial infarction. Ischemic pre- and postconditioning, by short periods of sublethal cardiac ischemia and reperfusion, are still the strongest mechanisms to achieve cardioprotection. However, it is highly impractical and far too invasive for clinical use. Fortunately, it can be mimicked pharmacologically, for example, by volatile anesthetics, noble gases, opioids, propofol, dexmedetomidine, and phosphodiesterase inhibitors. These substances are all routinely used in the clinical setting and seem promising candidates for successful translation of cardioprotection from experimental protocols to clinical trials. This review presents the fundamental mechanisms of conditioning strategies and provides an overview of the most recent and relevant findings on different concepts achieving cardioprotection in the experimental setting, specifically emphasizing pharmacological approaches in the perioperative context.

Plasma from Volunteers Breathing Helium Reduces Hypoxia-Induced Cell Damage in Human Endothelial Cells-Mechanisms of Remote Protection Against Hypoxia by Helium

PURPOSE

Remote ischemic preconditioning protects peripheral organs against prolonged ischemia/reperfusion injury via circulating protective factors. Preconditioning with helium protected healthy volunteers against postischemic endothelial dysfunction. We investigated whether plasma from helium-treated volunteers can protect human umbilical vein endothelial cells (HUVECs) against hypoxia in vitro through release of circulating of factors.

METHODS

Healthy male volunteers inhaled heliox (79% helium, 21% oxygen) or air for 30 min. Plasma was collected at baseline, directly after inhalation, 6 h and 24 h after start of the experiment. HUVECs were incubated with either 5% or 10% of the plasma for 1 or 2 h and subjected to enzymatically induced hypoxia. Cell damage was measured by LDH content. Furthermore, caveolin 1 (Cav-1), hypoxia-inducible factor (HIF1α), extracellular signal-regulated kinase (ERK)1/2, signal transducer and activator of transcription (STAT3) and endothelial nitric oxide synthase (eNOS) were determined.

RESULTS

Prehypoxic exposure to 10% plasma obtained 6 h after helium inhalation decreased hypoxia-induced cell damage in HUVEC. Cav-1 knockdown in HUVEC abolished this effect.

CONCLUSIONS

Plasma of healthy volunteers breathing helium protects HUVEC against hypoxic cell damage, possibly involving circulating Cav-1.

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.

Pretreatment With Argon Protects Human Cardiac Myocyte-Like Progenitor Cells from Oxygen Glucose Deprivation-Induced Cell Death by Activation of AKT and Differential Regulation of Mapkinases

BACKGROUND

The noble gas argon induces cardioprotection in a rabbit model of myocardial ischemia and reperfusion. However, no studies in human primary cells or subjects have been performed so far. We used human cardiac myocyte-like progenitor cells (HCMs) to investigate the protective effect on the cellular level.

METHODS

HCMs were pretreated with 30% or 50% argon before oxygen-glucose deprivation (OGD) and reperfusion. We evaluated apoptotic states by flow cytometry and the activation of mitogen-activated protein kinase (MAPKs) members extracellular signal-regulated kinase (ERK), c-jun N-terminal kinase (JNK), p38 MAPkinase, and protein kinase B (Akt) by Westernblot analysis and by activity assays of downstream transcription factors. Specific inhibitors were used to proof a significant participation of these pathways in the protection by argon. Beneficial effects were further assessed by TdT-mediated dUTP-biotin nick end labeling (TUNEL) assay, lactate dehydrogenase (LDH), mitochondrial deoxyribonucleic acid (mtDNA), and cytokine release.

RESULTS

Pretreatment with 30% or 50% argon for 90 min before OGD resulted in a significant protection of HCMs against apoptosis. This effect was reversed by the application of MAPK and Akt inhibitors during argon exposure. Argon 30% reduced the release of LDH by 33% and mtDNA by 45%. The release of interleukin 1β was reduced by 44% after OGD and more than 90% during reperfusion.

CONCLUSIONS

Pretreatment with argon protects HCMs from apoptosis under ischemic conditions via activation of Akt, Erk, and biphasic regulation of JNK. Argon gas is cheap and easily administrable, and might be a novel therapy to reduce myocardial ischemia-reperfusion injury.

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.

Hypercholesterolemia Abrogates Remote Ischemic Preconditioning-Induced Cardioprotection: Role of Reperfusion Injury Salvage Kinase Signals

Remote ischemic preconditioning (RIPC) is one of the most powerful intrinsic cardioprotective strategies discovered so far and experimental data indicate that comorbidity may interfere with the protection by RIPC. Therefore, we investigate whether RIPC-induced cardioprotection was intact in hypercholesterolemic rat hearts exposed to ischemia reperfusion in vivo. Normal or hypercholesterolemic rat hearts were exposed to 30 min of ischemia and 2 h of reperfusion, with or without RIPC, PI3K inhibitor wortmannin, MEK-ERK1/2 inhibitor PD98059, GSK3β inhibitor SB216763. Infarct size, apoptosis, MG53, PI3K-p85, p-Akt, p-ERK1/2, p-GSK3β, and cleaved Caspase-3 were determined. RIPC reduced infarct size, limited cardiomyocyte apoptosis following IR that was blocked by wortmannin but not PD98059. RIPC triggered unique cardioprotective signaling including MG53, phosphorylation of Akt, and glycogen synthase kinase-3ß (GSK3β) in concert with reduced proapoptotic active caspase-3. In contrast, RIPC failed to reduce myocardial necrosis and apoptosis as well as to increase the phosphorylated Akt and GSK3β in hypercholestorolemic myocardium. Importantly, we found that inhibition of GSK with SB216763 reduced myocardial infarct size in healthy and hypercholesterolemic hearts, but no additional cardioprotective effect was achieved when combined with RIPC. Our results suggest that acute GSK3β inhibition may provide a novel therapeutic strategy for hypercholesterolemic patients during acute myocardial infarction, whereas RIPC is less effective due to signaling events that adversely affect GSK3β.

Renal function following xenon anesthesia for partial nephrectomy-An explorative analysis of a randomized controlled study

Background

Perioperative preservation of renal function has a significant impact on morbidity and mortality in kidney surgery. Nephroprotective effects of the anesthetic xenon on ischemia-reperfusion injury were found in several experimental studies.

Objective

We aimed to explore whether xenon anesthesia can reduce renal damage in humans undergoing partial nephrectomy and to gather pilot data of possible nephroprotection in these patients.

Design

A prospective randomized, single-blinded, controlled study.

Setting

Single-center, University Hospital of Aachen, Germany between July 2013-October 2015.

Patients

Forty-six patients with regular renal function undergoing partial nephrectomy.

Interventions

Patients were randomly assigned to receive xenon- (n = 23) or isoflurane (n = 23) anesthesia.

Main outcome measures

Primary outcome was the maximum postoperative glomerular filtration rate (GFR) decline within seven days after surgery. Secondary outcomes included intraoperative and tumor-related data, assessment of further kidney injury markers, adverse events and optional determination of renal function after 3–6 months.

Results

Unexpected radical nephrectomy was performed in 5 patients, thus they were excluded from the per-protocol analysis, but included in the intention-to-treat analysis. The maximum postoperative GFR decline was attenuated by 45% in the xenon-group (10.9 ml min^-1 1.73 cm^-2 versus 19.7 ml min^-1 1.73 cm^-2 in the isoflurane group), but without significance (P = 0.084). Occurrence of adverse events was reduced (P = 0.003) in the xenon group. Renal function was similar among the groups after 3–6 months.

Conclusion

Xenon anesthesia was feasible and safe in patients undergoing partial nephrectomy with regard to postoperative renal function. We found no significant effect on early renal function but less adverse events in the xenon group. Larger randomized controlled studies in more heterogeneous collectives are required, to confirm or refute the possible clinical benefit on renal function by xenon.

Trial registration

ClinicalTrials.gov NCT01839084 and EudraCT 2012-005698-30

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.

Effect of helium pre- or postconditioning on signal transduction kinases in patients undergoing coronary artery bypass graft surgery

BACKGROUND

The noble gas helium induces pre- and postconditioning in animals and humans. Volatile anesthetics induce cardioprotection in humans undergoing coronary artery bypass graft (CABG) surgery. We hypothesized that helium induces pre- and postconditioning in CABG-patients, affecting signaling molecules protein kinase C-epsilon (PKC-ε), p38 mitogen activated protein kinase (p38 MAPK), extracellular signal-regulated kinase 1/2 (ERK-1/2) and heat shock protein 27 (HSP-27) within cardiac tissue, and reducing postoperative troponin levels.

METHODS

After ethical approval and informed consent, 125 elective patients undergoing CABG surgery were randomised into this prospective, placebo controlled, investigator blinded, parallel arm single-centre study. Helium preconditioning (3 × 5 min of 70 % helium and 30 % oxygen) was applied before aortic cross clamping; postconditioning (15 min of helium) was applied before release of the aortic cross clamp. Signaling molecules were measured in right atrial appendix specimens. Troponin-T was measured at 4, 12, 24 and 48 h postoperatively.

RESULTS

Baseline characteristics of all groups were similar. Helium preconditioning did not significantly alter the primary outcome (molecular levels of kinases PKC-ε and HSP-27, ratio of activated p38 MAPK or ERK ½). Postoperative troponin T was 11 arbitrary units [5, 31; area-under-the-curve (interquartile range)] for controls, and no statistically significant changes were observed after helium preconditioning [He-pre: 11 (6, 18)], helium postconditioning [He-post: 11 (8, 15)], helium pre- and postconditioning [He-PP: 14 (6, 20)] and after sevoflurane preconditioning [APC: 12 (8, 24), p = 0.13]. No adverse effects related to study treatment were observed in this study.

CONCLUSIONS

No effect was observed of helium preconditioning, postconditioning or the combination thereof on activation of p38 MAPK, ERK 1/2 or levels of HSP27 and PKC-ε in the human heart. Helium pre- and postconditioning did not affect postoperative troponin release in patients undergoing CABG surgery. Clinical trial number Dutch trial register ( http://www.trialregister.nl/ ) number NTR1226.

Helium postconditioning regulates expression of caveolin-1 and -3 and induces RISK pathway activation after ischaemia/reperfusion in cardiac tissue of rats

Caveolae, lipid enriched invaginations of the plasma membrane, are epicentres of cellular signal transduction. The structural proteins of caveolae, caveolins, regulate effector pathways in anaesthetic-induced cardioprotection, including the RISK pathway. Helium (He) postconditioning (HePoc) is known to mimic anaesthetic conditioning and to prevent damage from myocardial infarction. We hypothesize that HePoc regulates caveolin-1 and caveolin-3 (Cav-1 and Cav-3) expression in the rat heart and activates the RISK pathway. Male Wistar rats (n=8, each group) were subjected to 25min of cardiac ischaemia followed by reperfusion (I/R) for 5, 15 or 30min (I/R 5/15/30). The HePoc groups underwent I/R with 70% helium ventilation during reperfusion (IR+He 5/15/30min). Sham animals received surgical treatment without I/R. After each protocol blood and hearts were retrieved. Tissue was obtained from the area-at-risk (AAR) and non-area-at-risk (NAAR) and processed for western blot analyses and reverse-transcription-real-time-polymerase-chain-reaction (RT-qPCR). Protein analyses revealed increased amounts of Cav-1 and Cav-3 in the membrane of I/R+He15 (AAR: Cav-1, P<0.05; Cav-3, P<0.05; both vs. I/R15). In serum, Cav-3 was found to be elevated in I/R+He15 (P<0.05 vs. I/R15). RT-qPCR showed increased expression of Cav-1 in IR+He15 in AAR tissue (P<0.05 vs. I/R15). Phosphorylation of RISK pathway proteins pERK1/2 (AAR: P<0.05 vs. I/R15) and pAKT (AAR: P<0.05; NAAR P<0.05; both vs. I/R15) was elevated in the cytosolic fraction of I/R+He15. These results suggest that 15min of HePoc regulates Cav-1 and Cav-3 and activates RISK pathway kinases ERK1/2 and AKT. These processes might be crucially involved in HePoc mediated cardioprotection.

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

BACKGROUND

Oxidative stress is the predominant pathogenic mechanism of ischaemia-reperfusion (IR) injury. The noble gas argon has been shown to alleviate oxidative stress-related myocardial and cerebral injury. The risk of lung IR injury is increased in some major surgeries, reducing clinical outcome. However, no study has examined the lung-protective efficacy of argon preconditioning. The present study investigated the protective effects of argon preconditioning on airway epithelial cells exposed to hydrogen peroxide (H2O2) to induce oxidative stress.

METHODS

A549 airway epithelial cells were treated with a cytotoxic concentration of H2O2 after exposure to standard air or 30 or 50% argon/21% oxygen/5% carbon dioxide/rest nitrogen for 30, 45 or 180 min. Cells were stained with annexin V/propidium iodide, and apoptosis was evaluated by fluorescence-activated cell sorting. Protective signalling pathways activated by argon exposure were identified by Western blot analysis for phosphorylated candidate molecules of the mitogen-activated protein kinase and protein kinase B (Akt) pathways.

RESULTS

Preconditioning with 50% argon for 30, 45 and 180 min and 30% argon for 180 min caused significant protection of A549 cells against H2O2-induced apoptosis, with increases in cellular viability of 5-47% (p < 0.0001). A small adverse effect was also observed, which presented as a 12-15% increase in cellular necrosis in argon-treated groups. Argon exposure resulted in early activation of c-Jun N-terminal kinase (JNK) and p38, peaking 10- 30 min after the start of preconditioning, and delayed activation of the extracellular signal-regulated kinase 1/2 (ERK1/2) pathway, peaking after 60-90 min.

CONCLUSIONS

Argon preconditioning protects airway epithelial cells from H2O2-induced apoptotic cell death. Argon activates the JNK, p38, and ERK1/2 pathways, but not the Akt pathway. The cytoprotective properties of argon suggest possible prophylactic applications in surgery-related IR injury of the lungs.

Argon Induces Protective Effects in Cardiomyocytes during the Second Window of Preconditioning

Increasing evidence indicates that argon has organoprotective properties. So far, the underlying mechanisms remain poorly understood. Therefore, we investigated the effect of argon preconditioning in cardiomyocytes within the first and second window of preconditioning. Primary isolated cardiomyocytes from neonatal rats were subjected to 50% argon for 1 h, and subsequently exposed to a sublethal dosage of hypoxia (<1% O₂) for 5 h either within the first (0–3 h) or second window (24–48 h) of preconditioning. Subsequently, the cell viability and proliferation was measured. The argon-induced effects were assessed by evaluation of mRNA and protein expression after preconditioning. Argon preconditioning did not show any cardioprotective effects in the early window of preconditioning, whereas it leads to a significant increase of cell viability 24 h after preconditioning compared to untreated cells (p = 0.015) independent of proliferation. Argon-preconditioning significantly increased the mRNA expression of heat shock protein (HSP) B1 (HSP27) (p = 0.048), superoxide dismutase 2 (SOD2) (p = 0.001), vascular endothelial growth factor (VEGF) (p < 0.001) and inducible nitric oxide synthase (iNOS) (p = 0.001). No difference was found with respect to activation of pro-survival kinases in the early and late window of preconditioning. The findings provide the first evidence of argon-induced effects on the survival of cardiomyocytes during the second window of preconditioning, which may be mediated through the induction of HSP27, SOD2, VEGF and iNOS.

Noble gases as cardioprotectants - translatability and mechanism

Several noble gases, although classified as inert substances, exert a tissue-protective effect in different experimental models when applied before organ ischaemia as an early or late preconditioning stimulus, after ischaemia as a post-conditioning stimulus or when given in combination before, during and/or after ischaemia. A wide range of organs can be protected by these inert substances, in particular cardiac and neuronal tissue. In this review we summarize the data on noble gas-induced cardioprotection, focusing on the underlying protective mechanisms. We will also look at translatability of experimental data to the clinical situation.

Xenon and isoflurane reduce left ventricular remodeling after myocardial infarction in the rat

BACKGROUND

Xenon and isoflurane are known to have cardioprotective properties. We tested the hypothesis that these anesthetics positively influence myocardial remodeling 28 days after experimental perioperative myocardial infarction and compared their effects.

METHODS

A total of 60 male Sprague-Dawley rats were subjected to 60 min of coronary artery occlusion and 120 min of reperfusion. Prior to ischemia, the animals were randomized for the different narcotic regimes (0.6 vol% isoflurane, 70 vol% xenon, or intraperitoneal injection of s-ketamine). Acute injury was quantified by echocardiography and troponin I. After 4 weeks, left ventricular function was assessed by conductance catheter to quantify hemodynamic compromise. Cardiac remodeling was characterized by quantification of dilatation, hypertrophy, fibrosis, capillary density, apoptosis, and expression of fetal genes (α/β myosin heavy chains, α-skeletal actin, periostin, and sarco/endoplasmic reticulum Ca2+-ATPase).

RESULTS

Whereas xenon and isoflurane impeded the acute effects of ischemia-reperfusion on hemodynamics and myocardial injury at a comparable level, differences were found after 4 weeks. Xenon in contrast to isoflurane or ketamine anesthetized animals demonstrated a lower remodeling index (0.7 ± 0.1 vs. 0.9 ± 0.3 and 1.0 ± 0.3g/ml), better ejection fraction (62 ± 9 vs. 49 ± 7 and 35 ± 6%), and reduced expression of β-myosin heavy chain and periostin. The effects on hypertrophy, fibrosis, capillary density, and apoptosis were comparable.

CONCLUSIONS

Compared to isoflurane and s-ketamine, xenon limited progressive adverse cardiac remodeling and contractile dysfunction 28 days after perioperative myocardial infarction.

Hypercholesterolemia blocked sevoflurane-induced cardioprotection against ischemia-reperfusion injury by alteration of the MG53/RISK/GSK3β signaling

BACKGROUND

Recent studies have demonstrated that volatile anesthetic preconditioning confers myocardial protection against ischemia-reperfusion (IR) injury through activation of the reperfusion injury salvage kinase (RISK) pathway. As RISK has been shown to be impaired in hypercholesterolemia, we investigate whether anesthetic-induced cardiac protection was maintained in hypercholesterolemic rats.

METHODS

Normocholesteolemic or hypercholesterolemic rat hearts were subjected to 30 min of ischemia and 2 h of reperfusion. Animals received 2.4% sevoflurane during three 5 min periods with and without PI3K antagonist wortmannin (10 μg/kg, Wort) or the ERK inhibitor PD 98059 (1 mg/kg, PD). The infarct size, apoptosis, p-Akt, p-ERK1/2, p-GSK3β were determined.

RESULTS

Two hundred and six rats were analyzed in the study. In the healthy rats, sevoflurane significantly reduced infarct size by 42%, a phenomenon completely reversed by wortmannin and PD98059 and increased the phosphorylation of Akt, ERK1/2 and their downstream target of GSK3β. In the hypercholesterolemic rats, sevoflurane failed to reduce infarct size and increase the phosphorylated Akt, ERK1/2 and GSK3β. In contrast, GSK inhibitor SB216763 conferred cardioprotection against IR injury in healthy and hypercholesterolemic hearts.

CONCLUSIONS

Hyperchoesterolemia abrogated sevoflurane-induced cardioprotection against IR injury by alteration of upstream signaling of GSK3β and acute GSK inhibition may provide a novel therapeutic strategy to protect hypercholesterolemic hearts against IR injury.

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.

Helium-induced cardioprotection of healthy and hypertensive rat myocardium in vivo

Helium protects healthy myocardium against ischemia/reperfusion injury by early and late preconditioning (EPC, LPC) and postconditioning (PostC). We investigated helium-induced PostC of the hypertensive heart and enhancement by addition of LPC and EPC. We also investigated involvement of signaling kinases glycogen synthase kinase 3 beta (GSK-3β) and protein kinase C-epsilon (PKC-ε). To assess myocardial cell damage, we performed infarct size measurements in healthy Wistar Kyoto (WKY rats, n=8-9) and Spontaneous Hypertensive rats (SHR, n=8-9) subjected to 25 min ischemia and 120 min reperfusion. Rats inhaled 70% helium for 15 min after index ischemia (PostC), combined with 15 min helium 24h prior to index ischemia (LPC+PostC), a triple intervention with additional 3 short cycles of 5 min helium inhalation shortly before ischemia (EPC+LPC+PostC), or no further treatment. In WKY rats, PostC reduced infarct size from 46 ± 2% (mean ± S.E.M) in the control group to 29 ± 2%. LPC+PostC or EPC+LPC+PostC reduced infarct sizes to a similar extent (30 ± 3% and 32 ± 2% respectively). In SHR, EPC+LPC+PostC reduced infarct size from 53 ± 3% in control to 39 ± 3%, while PostC or LPC+PostC alone were not protective; infarct size 48 ± 4% and 44 ± 4%, respectively. Neither PostC in WKY rats nor EPC+LPC+PostC in SHR was associated with an increase in phosphorylation of GSK-3β and PKC-ε after 15 min of reperfusion. Concluding, a triple intervention of helium conditioning results in cardioprotection in SHR, whereas a single intervention does not. In WKY rats, the triple intervention does not further augment protection. Helium conditioning is not associated with a mechanism involving GSK-3β and PKC-ε.

Application of medical gases in the field of neurobiology

Medical gases are pharmaceutical molecules which offer solutions to a wide array of medical needs. This can range from use in burn and stroke victims to hypoxia therapy in children. More specifically however, gases such as oxygen, helium, xenon, and hydrogen have recently come under increased exploration for their potential theraputic use with various brain disease states including hypoxia-ischemia, cerebral hemorrhages, and traumatic brain injuries. As a result, this article will review the various advances in medical gas research and discuss the potential therapeutic applications and mechanisms with regards to the field of neurobiology.

Postconditioning by xenon and hypothermia in the rat heart in vivo

BACKGROUND AND OBJECTIVE

Hypothermia protects against myocardial reperfusion injury. However, inducing hypothermia takes time, which makes it unsuitable as an emergency treatment. Combining mild hypothermia with low-dose xenon, applied either simultaneously or one after the other, protects the neonatal rat brain against reperfusion injury. We investigated whether xenon, administered prior to hypothermia or simultaneously with hypothermia, also protects the rat heart from reperfusion injury.

METHODS

Anaesthetized rats (chloralose, ketamine, diazepam) were randomly allocated to five groups and subjected to 25 min coronary artery occlusion, followed by 120 min reperfusion. At the onset of reperfusion, controls received no intervention and inhaled oxygen in air with an inspired oxygen fraction of 0.8 (Con80). Further groups received either 1 h of mild hypothermia of 34 degrees C (Hypo34) or 30 min of xenon 20% (Xe20). Additional groups received xenon 20% and hypothermia 34 degrees C simultaneously (Xe20 + Hypo34) or in succession (Xe20-->Hypo34). Infarct sizes were assessed by triphenyltetrazolium chloride staining.

RESULTS

The combination of xenon 20% and hypothermia 34 degrees C significantly reduced infarct size [Xe20 + Hypo34: 55(22)%, mean (SD)] compared with control [Con80: 76(12)%, P = 0.03]. Xenon and hypothermia in succession produced no infarct size reduction.

CONCLUSION

The combination of xenon 20% and hypothermia of 34 degrees C, applied during early reperfusion, reduces infarct size in the rat heart in vivo.

The effect of xenon on isoflurane protection against experimental myocardial infarction

OBJECTIVES

To investigate if the protective effects of xenon and isoflurane against myocardial ischemia-reperfusion damage would be additive.

DESIGN

A prospective, randomized laboratory investigation.

SETTING

An animal laboratory of a university hospital.

PARTICIPANTS

Thirty-six pigs (female German landrace).

INTERVENTIONS

In an open-chest preparation with thiopental anesthesia, the left anterior descending artery was occluded to produce ischemia for 60 minutes. One hour previously, ischemic preconditioning, isoflurane (0.55 minimum alveolar concentration [MAC]) alone, or isoflurane together with xenon (0.55 MAC each) were started in the respective groups. A fourth (control) group received no protective intervention. Myocardial ischemia was followed by 2 hours of reperfusion.

MEASUREMENTS AND MAIN RESULTS

Hearts were excised and stained (Evans Blue/TTC) to measure infarct size as related to the area at risk. Myocardial infarct size was reduced (means +/- standard deviation) from 64% +/- 9% of the area at risk in the control group to 19% +/- 12% with ischemic preconditioning to 46% +/- 12% with isoflurane and to 39% +/- 13% with isoflurane and xenon. All intervention groups were significantly different from the control (p < 0.05), and both anesthetic groups were significantly different from ischemic preconditioning (p < 0.05).

CONCLUSION

Combined isoflurane/xenon anesthesia reduced infarct size but not more than isoflurane alone. Ischemic preconditioning was more effective than the anesthetics.

Xenon preconditioning: the role of prosurvival signaling, mitochondrial permeability transition and bioenergetics in rats

BACKGROUND

Similar to volatile anesthetics, the anesthetic noble gas xenon protects the heart from ischemia/reperfusion injury, but the mechanisms responsible for this phenomenon are not fully understood. We tested the hypothesis that xenon-induced cardioprotection is mediated by prosurvival signaling kinases that target mitochondria.

METHODS

Male Wistar rats instrumented for hemodynamic measurements were subjected to a 30 min left anterior descending coronary artery occlusion and 2 h reperfusion. Rats were randomly assigned to receive 70% nitrogen/30% oxygen (control) or three 5-min cycles of 70% xenon/30% oxygen interspersed with the oxygen/nitrogen mixture administered for 5 min followed by a 15 min memory period. Myocardial infarct size was measured using triphenyltetrazolium staining. Additional hearts from control and xenon-pretreated rats were excised for Western blotting of Akt and glycogen synthase kinase 3 beta (GSK-3beta) phosphorylation and isolation of mitochondria. Mitochondrial oxygen consumption before and after hypoxia/reoxygenation and mitochondrial permeability transition pore opening were determined.

RESULTS

Xenon significantly (P < 0.05) reduced myocardial infarct size compared with control (32 +/- 4 and 59% +/- 4% of the left ventricular area at risk; mean +/- sd) and enhanced phosphorylation of Akt and GSK-3beta. Xenon pretreatment preserved state 3 respiration of isolated mitochondria compared with the results obtained in the absence of the gas. The Ca(2+) concentration required to induce mitochondrial membrane depolarization was larger in the presence compared with the absence of xenon pretreatment (78 +/- 17 and 56 +/- 17 microM, respectively). The phosphoinositol-3-kinase-kinase inhibitor wortmannin blocked the effect of xenon on infarct size and respiration.

CONCLUSIONS

These results indicate that xenon preconditioning reduces myocardial infarct size, phosphorylates Akt, and GSK-3beta, preserves mitochondrial function, and inhibits Ca(2+)-induced mitochondrial permeability transition pore opening. These data suggest that xenon-induced cardioprotection occurs because of activation of prosurvival signaling that targets mitochondria and renders them less vulnerable to ischemia-reperfusion injury.

Blockade of anaesthetic-induced preconditioning in the hyperglycaemic myocardium: the regulation of different mitogen-activated protein kinases

Preconditioning by volatile anaesthetics is blocked by hyperglycaemia. The regulation of mitogen-activated protein kinases during this effect has yet not been investigated. For infarct size measurements, anaesthetized rats were subjected to 25 min coronary artery occlusion followed by 120 min reperfusion. Control animals were not further treated. One group was preconditioned by two 5-min periods of desflurane inhalation (desflurane preconditioning, Des-preconditioning, 1MAC), each followed by 10-min washout. Four groups received glucose 50% in order to achieve blood glucose concentrations between 22.2 and 33.3 mM/l. Glucose infusion started 40 min before ischaemia (early hyperglycaemia, EH) and stopped with the onset of artery occlusion with (EH+Des-preconditioning) or without (EH) preconditioning. The other two groups received glucose during ischaemia (late hyperglycaemia, LH), again with (LH+Des-preconditioning) or without (LH) preconditioning. Additional hearts were excised for Western blot of mitogen-activated protein kinases. Infarct size was reduced from 51.7+/-9.0% in controls to 28.8+/-11.8% after Des-preconditioning (P<0.01 vs Con). Hyperglycaemia alone did not affect infarct size (EH, 51.5+/-9.0%, LH, 44.3+/-16.9%), but EH as well as LH blocked Des-preconditioning (49.1+/-12.3%, P<0.01, 48.1+/-17.6%, P<0.05 vs Des-preconditioning). All three mitogen-activated protein kinases showed a similar time course pattern of phosphorylation in the Des-preconditioning, EH and EH+Des-preconditioning group. Despite the lack of cardioprotection, mitogen-activated protein kinases are activated in hyperglycaemic myocardium. Therefore, it can be assumed that the hyperglycaemic induced blockade of Des-preconditioning is situated downstream or in parallel of these mitogen-activated protein kinases or involves different signal transduction pathways.

Preconditioning, but not postconditioning, with Sevoflurane reduces pulmonary neutrophil accumulation after lower body ischaemia/reperfusion injury in rats

BACKGROUND AND OBJECTIVES

Aortic ischaemia and reperfusion may induce pulmonary sequestration of neutrophil granulocytes. Preconditioning and postconditioning with volatile anaesthetics confer protection against reperfusion injury in various organs, such as heart, kidneys or brain. We tested the hypothesis that pre- or postconditioning with Sevoflurane attenuates pulmonary neutrophil accumulation after ischaemia/reperfusion injury of the aorta.

METHODS

Anaesthetized and mechanically ventilated Wistar rats underwent laparotomy and were randomly assigned to one of the following groups: Sham (n = 10), ischaemia/reperfusion (n = 8, lower body ischaemia by clamping of the infrarenal aorta for 2 h followed by 3 h of reperfusion), preconditioning (n = 10, 2.0% Sevoflurane administered over 30 min prior to ischaemia) and postconditioning (n = 9, 2.0% Sevoflurane during reperfusion). Following reperfusion, the lungs were removed for microscopic determination of neutrophil accumulation.

RESULTS

Ischaemia/reperfusion induced a significant increase in pulmonary neutrophil accumulation (mean +/- SD, 29.9 +/- 7.4 vs. 15.8 +/- 6.6 neutrophils per microscopic field in ischaemia/reperfusion vs. Sham, respectively, P < 0.001). Sevoflurane preconditioning resulted in a lower neutrophil count (20.3 +/- 7.1 neutrophils, P < 0.001 vs. ischaemia/reperfusion), while postconditioning showed no effects (25.8 +/- 9.8 neutrophils vs. ischaemia/reperfusion, not significant).

CONCLUSIONS

Preconditioning, but not postconditioning, with Sevoflurane reduces pulmonary neutrophil accumulation after ischaemia/reperfusion injury of the lower body. Since neutrophil accumulation plays a major role in the pathophysiology of acute lung injury, our data suggest a protective effect of Sevoflurane preconditioning on remote pulmonary ischaemia/reperfusion injury.

Noble gases without anesthetic properties protect myocardium against infarction by activating prosurvival signaling kinases and inhibiting mitochondrial permeability transition in vivo

BACKGROUND

The anesthetic noble gas, xenon, produces cardioprotection. We hypothesized that other noble gases without anesthetic properties [helium (He), neon (Ne), argon (Ar)] also produce cardioprotection, and further hypothesized that this beneficial effect is mediated by activation of prosurvival signaling kinases [including phosphatidylinositol-3-kinase, extracellular signal-regulated kinase, and 70-kDa ribosomal protein s6 kinase] and inhibition of mitochondrial permeability transition pore (mPTP) opening in vivo.

METHODS

Rabbits (n = 98) instrumented for hemodynamic measurement and subjected to a 30-min left anterior descending coronary artery (LAD) occlusion and 3 h reperfusion received 0.9% saline (control), three cycles of 70% He-, Ne-, or Ar-30% O2 administered for 5 min interspersed with 5 min of 70% N2-30% O2 before LAD occlusion, or three cycles of brief (5 min) ischemia interspersed with 5 min reperfusion before prolonged LAD occlusion and reperfusion (ischemic preconditioning). Additional groups of rabbits received selective inhibitors of phosphatidylinositol-3-kinase (wortmannin; 0.6 mg/kg), extracellular signal-regulated kinase (PD 098059; 2 mg/kg), or 70-kDa ribosomal protein s6 kinase (rapamycin; 0.25 mg/kg) or mPTP opener atractyloside (5 mg/kg) in the absence or presence of He pretreatment.

RESULTS

He, Ne, Ar, and ischemic preconditioning significantly (P < 0.05) reduced myocardial infarct size [23% +/- 4%, 20% +/- 3%, 22% +/- 2%, 17% +/- 3% of the left ventricular area at risk (mean +/- sd); triphenyltetrazolium chloride staining] versus control (45% +/- 5%). Wortmannin, PD 098059, rapamycin, and atractyloside alone did not affect infarct size, but these drugs abolished He-induced cardioprotection.

CONCLUSIONS

The results indicate that noble gases without anesthetic properties produce cardioprotection by activating prosurvival signaling kinases and inhibiting mPTP opening in rabbits.