Morphological Evidence that Xenon Neuroprotects against N-Methyl-DL-Aspartic Acid-Induced Damage in the Rat Arcuate Nucleus: A Time-Dependent Study

The neuroprotective effect and possible therapeutic application of xenon in neurological diseases

Xenon is an inert gas with stable chemical properties which is used as an anesthetic. Recent in vitro and in vivo findings indicate that xenon also elicits an excellent neuroprotective effect in subanesthetic concentrations. The mechanisms underlying this primarily involve the attenuation of excitotoxicity and the inhibition of N-methyl-d-aspartic acid (NMDA) receptors and NMDA receptor-related effects, such as antioxidative effects, reduced activation of microglia, and Ca²⁺ -dependent mechanisms, as well as the interaction with certain ion channels and glial cells. Based on this strong neuroprotective role, a large number of experimental and clinical studies have confirmed the significant therapeutic effect of xenon in the treatment of neurological diseases. This review summarizes the reported neuroprotective mechanisms of xenon and discusses its possible therapeutic application in the treatment of various neurological diseases.

Protective Effects of Xenon on Propofol-Induced Neurotoxicity in Human Neural Stem Cell-Derived Models

Early life exposure to general anesthetics can have neurotoxic consequences. Evidence indicates that xenon, a rare noble gas with anesthetic properties, may lessen neuronal damage under certain conditions. However, its potential neuroprotective properties, when used alone or in combination with other anesthetics, remain largely unknown. While it is difficult to verify the adverse effects of long duration anesthetic exposure in infants and children, the utilization of relevant non-clinical models (i.e., human-derived neural stem cells) may serve as a "bridging" model for evaluating the vulnerability of the nervous system. Neural stem cells, purchased from PhoenixSongs Biologicals, Inc., were guided to differentiate into neurons, astrocytes, and oligodendrocytes, which were then exposed to propofol (50 μM) for 16 h in the presence or absence of xenon (33%). Differentiation into cells of the neural lineage was confirmed by labelling with cell-specific markers, β-tubulin for neurons, glial fibrillary acidic protein (GFAP) for astrocytes, and galactocerebroside (GALC) for oligodendrocytes after 5 days of differentiation. The presence and severity of neural damage induced by anesthetic exposures were assessed by several methods, including the TUNEL assay, and immuno-histochemical measurements. Our data demonstrate that prolonged exposure to propofol results in a significant increase in the number of TUNEL-positive cells, indicating increased neural apoptosis. No significant changes were detected in the number of GFAP-positive astrocytes or GALC-positive oligodendrocytes. However, the number of β-tubulin-positive neurons was substantially reduced in the propofol-exposed cultures. Co-administration of xenon effectively blocked the propofol-induced neuronal damage/loss. No significant effects were observed when xenon was administered alone. The data indicate that prolonged exposure to propofol during development produces elevated levels of neuronal apoptosis in a human neural stem cell-derived model. However, sub-clinical, non-anesthetic concentrations of xenon, when used in combination with propofol, can prevent or ameliorate the toxic effects associated with prolonged anesthetic exposure. This is important as a more complete understanding of the neurotoxic mechanisms associated with a variety of clinically relevant anesthetic combinations becomes available. Protective approaches are critical for developing sound guidance on best practices for the use of these agents in the pediatric setting.

Effects of xenon gas on human airway epithelial cells during hyperoxia and hypothermia

BACKGROUND

Hypothermia with xenon gas has been used to reduce brain injury and disability rate after perinatal hypoxia-ischemia. We evaluated xenon gas therapy effects in an in vitro model with or without hypothermia on cultured human airway epithelial cells (Calu-3).

METHODS

Calu-3 monolayers were grown at an air-liquid interface and exposed to one of the following conditions: 1) 21% FiO2 at 37°C (control); 2) 45% FiO2 and 50% xenon at 37°C; 3) 21% FiO2 and 50% xenon at 32°C; 4) 45% FiO2 and 50% xenon at 32°C for 24 hours. Transepithelial resistance (TER) measurements were performed and apical surface fluids were collected and assayed for total protein, IL-6, and IL-8. Three monolayers were used for immunofluorescence localization of zonula occludens-1 (ZO-1). The data were analyzed by one-way ANOVA.

RESULTS

TER decreased at 24 hours in all treatment groups. Xenon with hyperoxia and hypothermia resulted in greatest decrease in TER compared with other groups. Immunofluorescence localization of ZO-1 (XY) showed reduced density of ZO-1 rings and incomplete ring-like staining in the 45% FiO2- 50% xenon group at 32°C compared with other groups. Secretion of total protein was not different among groups. Secretion of IL-6 in 21% FiO2 with xenon group at 32°C was less than that of the control group. The secretion of IL-8 in 45% FiO2 with xenon at 32°C was greater than that of other groups.

CONCLUSION

Hyperoxia and hypothermia result in detrimental epithelial cell function and inflammation over 24-hour exposure. Xenon gas did not affect cell function or reduce inflammation.

Intraoperative xenon for prevention of delirium after on-pump cardiac surgery: a randomised, observer-blind, controlled clinical trial

BACKGROUND

Older patients undergoing cardiac surgery have a 40-60% risk of developing postoperative delirium (POD), which is associated with increased morbidity and mortality. In animals, xenon has been found to be neuroprotective. Little is known about its neuroprotective effects in humans. We evaluated whether xenon anaesthesia prevents POD in patients undergoing cardiac surgery.

METHODS

We conducted a randomised, observer-blind, controlled trial in which 190 patients 65 yr or older undergoing on-pump cardiac surgery were randomly allocated to xenon or sevoflurane anaesthesia. During cardiopulmonary bypass, propofol infusion was used for anaesthetic maintenance. Subjects were screened for POD daily during the first 5 postoperative days using the 3-Minute Diagnostic Interview for Confusion Assessment Method (CAM) or with a CAM version for patients in ICU (CAM-ICU). Other methods to detect delirium, such as chart review, were also used. Secondary outcomes included the duration and severity of POD, and postoperative cognitive function.

RESULTS

The overall incidence of POD was 41% (78/190). There was no statistically significant difference in the POD incidence between the xenon and sevoflurane groups (42.7% [41/96] vs 39.4% [37/94], P=0.583). The odds ratio for POD when comparing xenon with sevoflurane was 1.18 (95% confidence interval, 0.65-2.16).

CONCLUSIONS

In older patients undergoing cardiac surgery, xenon anaesthesia did not result in a significant reduction in POD. Based on these results alone, use of xenon cannot be recommended for this purpose.

CLINICAL TRIAL REGISTRATION

EudraCT: 2014-005370-11 (May 13, 2015; https://www.clinicaltrialsregister.eu/ctr-search/search?query=2014-005370-11).

Inhaled Gases for Neuroprotection of Neonates: A Review

Importance: Hypoxic-ischemic encephalopathy (HIE) is a significant cause of morbidity and mortality in neonates. The incidence of HIE is 1-8 per 1,000 live births in developed countries. Whole-body hypothermia reduces the risk of disability or death, but 7 infants needed to be treated to prevent death or major neurodevelopmental disability. Inhalational gases may be promising synergistic agents due to their rapid onset and easy titratability. Objective: To review current data on different inhaled gases with neuroprotective properties that may serve as adjunct therapies to hypothermia. Evidence review: Literature review was performed using the PubMed database, google scholar, and ClinicalTrials.Gov. Results focused on articles published from January 1, 2005, through December 31, 2017. Articles published earlier than 2005 were included when appropriate for historical perspective. Our review emphasized preclinical and clinical studies relevant to the use of inhaled agents for neuroprotection. Findings: Based on the relevance to our topic, 111 articles were selected pertaining to the incidence of HIE, pathophysiology of HIE, therapeutic hypothermia, and emerging therapies for hypoxic-ischemic encephalopathy in preclinical and clinical settings. Supplemental tables summarizes highly relevant 49 publications that were included in this review. The selected publications emphasize the emergence of promising inhaled gases that may improve neurologic survival and alleviate neurodevelopmental disability when combined with therapeutic hypothermia in the future. Conclusions: Many inhaled agents have neuroprotective properties and could serve as an adjunct therapy to whole-body hypothermia. Inhaled agents are ideal due to their easy administration, titrability, and rapid onset and offset.

Prospects for Applying Xenon Curative Properties in Pediatrics

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

Xenon Combined With Hypothermia in Perinatal Hypoxic-Ischemic Encephalopathy: A Noble Gas, a Noble Mission

Perinatal hypoxia-ischemia is a major cause of neonatal morbidity. It generates primary neuronal damage of the neonatal brain and later secondary damage when reperfusion of the ischemic brain tissue causes a surge of oxygen free radicals and inflammation. This post-hypoxic-ischemic brain damage is a leading cause of motor and intellectual disabilities in survivors. Research worldwide has focused on mitigating this injury. Mild or moderate hypothermia is the standard treatment in many centers. However, its benefit is modest and the search for combinatorial effective neuroprotectants continues. This review focuses on xenon as one such agent. The use of mild to moderate hypothermia is reviewed first. Then promising results on the use of xenon to potentiate the effect of hypothermia in in vitro and in vivo animal experiments are discussed. In the first feasibility study on human neonates, researchers found a significant benefit of using 50% xenon for 18 hours in addition to 72 hours of hypothermia. Yet, this additional benefit of xenon was lacking in a larger cohort study, potentially because xenon was used beyond six hours of birth. The future of using xenon is promising, but further clinical studies are awaited to confirm the feasibility of its routine use and its optimal timing, concentration, and duration, for human neonatal hypoxia-ischemia.

Modulation by the Noble Gas Helium of Tissue Plasminogen Activator: Effects in a Rat Model of Thromboembolic Stroke

INTERVENTIONS

Helium has been shown to provide neuroprotection in mechanical model of acute ischemic stroke by inducing hypothermia, a condition shown by itself to reduce the thrombolytic and proteolytic properties of tissue plasminogen activator. However, whether or not helium interacts with the thrombolytic drug tissue plasminogen activator, the only approved therapy of acute ischemic stroke still remains unknown. This point is not trivial since previous data have shown the critical importance of the time at which the neuroprotective noble gases xenon and argon should be administered, during or after ischemia, in order not to block tissue plasminogen activator-induced thrombolysis and to obtain neuroprotection and inhibition of tissue plasminogen activator-induced brain hemorrhages.

MEASUREMENTS AND MAIN RESULTS

We show that helium of 25-75 vol% inhibits in a concentration-dependent fashion the catalytic and thrombolytic activity of tissue plasminogen activator in vitro and ex vivo. In vivo, in rats subjected to thromboembolic brain ischemia, we found that intraischemic helium at 75 vol% inhibits tissue plasminogen activator-induced thrombolysis and subsequent reduction of ischemic brain damage and that postischemic helium at 75 vol% reduces ischemic brain damage and brain hemorrhages.

CONCLUSIONS

In a clinical perspective for the treatment of acute ischemic stroke, these data suggest that helium 1) should not be administered before or together with tissue plasminogen activator therapy due to the risk of inhibiting the benefit of tissue plasminogen activator-induced thrombolysis; and 2) could be an efficient neuroprotective agent if given after tissue plasminogen activator-induced reperfusion.

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

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

[Neuroprotection by noble gases: New developments and insights]

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

Xenon-mediated neuroprotection in response to sustained, low-level excitotoxic stress

Noble gases such as xenon and argon have been reported to provide neuroprotection against acute brain ischemic/anoxic injuries. Herein, we wished to evaluate the protective potential of these two gases under conditions relevant to the pathogenesis of chronic neurodegenerative disorders. For that, we established cultures of neurons typically affected in Alzheimer's disease (AD) pathology, that is, cortical neurons and basal forebrain cholinergic neurons and exposed them to L-trans-pyrrolidine-2,4-dicarboxylic acid (PDC) to generate sustained, low-level excitotoxic stress. Over a period of 4 days, PDC caused a progressive loss of cortical neurons which was prevented substantially when xenon replaced nitrogen in the cell culture atmosphere. Unlike xenon, argon remained inactive. Xenon acted downstream of the inhibitory and stimulatory effects elicited by PDC on glutamate uptake and efflux, respectively. Neuroprotection by xenon was mimicked by two noncompetitive antagonists of NMDA glutamate receptors, memantine and ketamine. Each of them potentiated xenon-mediated neuroprotection when used at concentrations providing suboptimal rescue to cortical neurons but most surprisingly, no rescue at all. The survival-promoting effects of xenon persisted when NMDA was used instead of PDC to trigger neuronal death, indicating that NMDA receptor antagonism was probably accountable for xenon’s effects. An excess of glycine failed to reverse xenon neuroprotection, thus excluding a competitive interaction of xenon with the glycine-binding site of NMDA receptors. Noticeably, antioxidants such as Trolox and N-acetylcysteine reduced PDC-induced neuronal death but xenon itself lacked free radical-scavenging activity. Cholinergic neurons were also rescued efficaciously by xenon in basal forebrain cultures. Unexpectedly, however, xenon stimulated cholinergic traits and promoted the morphological differentiation of cholinergic neurons in these cultures. Memantine reproduced some of these neurotrophic effects, albeit with less efficacy than xenon. In conclusion, we demonstrate for the first time that xenon may have a therapeutic potential in AD.

Adding 5 h delayed xenon to delayed hypothermia treatment improves long-term function in neonatal rats surviving to adulthood

BACKGROUND

We previously reported that combining immediate hypothermia with immediate or 2 h delayed inhalation of an inert gas, xenon, gave additive neuroprotection in rats after a hypoxic-ischemic insult, compared to hypothermia alone. Defining the therapeutic time window for this new combined intervention is crucial in clinical practice when immediate treatment is not always feasible. The aim of this study is to investigate whether combined hypothermia and xenon still provide neuroprotection in rats after a 5 h delay for both hypothermia and xenon.

METHODS

Seven-day-old Wistar rat pups underwent a unilateral hypoxic-ischemic insult. Pups received 5 h of treatment starting 5 h after the insult randomized between normothermia, hypothermia, or hypothermia with 50% xenon. Surviving pups were tested for fine motor function through weeks 8-10 before being euthanized at week 11. Their hemispheric and hippocampal areas were assessed.

RESULTS

Both delayed hypothermia-xenon and hypothermia-only treated groups had significantly less brain tissue loss than those which underwent normothermia. The functional performance after 1 wk and adulthood was significantly better after hypothermia-xenon treatment as compared to the hypothermia-only or normothermia groups.

CONCLUSION

Adding 50% xenon to 5 h delayed hypothermia significantly improved functional outcome as compared to delayed hypothermia alone despite similar reductions in brain area.

Combination of therapeutic hypothermia and other neuroprotective strategies after an ischemic cerebral insult

Abrupt deprivation of substrates to neuronal tissue triggers a number of pathological events (the “ischemic cascade”) that lead to cell death. As this is a process of delayed neuronal cell death and not an instantaneous event, several pharmacological and non-pharmacological strategies have been developed to attenuate or block this cascade. The most promising neuroprotectant so far is therapeutic hypothermia and its beneficial effects have inspired researchers to further improve its protective benefit by combining it with other neuroprotective agents. This review provides an overview of all neuroprotective strategies that have been combined with therapeutic hypothermia in rodent models of focal cerebral ischemia. A distinction is made between drugs interrupting only one event of the ischemic cascade from those mitigating different pathways and having multimodal effects. Also the combination of therapeutic hypothermia with hemicraniectomy, gene therapy and protein therapy is briefly discussed. Furthermore, those combinations that have been studied in a clinical setting are also reviewed.

Non-pharmaceutical therapies for stroke: mechanisms and clinical implications

Stroke is deemed a worldwide leading cause of neurological disability and death, however, there is currently no promising pharmacotherapy for acute ischemic stroke aside from intravenous or intra-arterial thrombolysis. Yet because of the narrow therapeutic time window involved, thrombolytic application is very restricted in clinical settings. Accumulating data suggest that non-pharmaceutical therapies for stroke might provide new opportunities for stroke treatment. Here we review recent research progress in the mechanisms and clinical implications of non-pharmaceutical therapies, mainly including neuroprotective approaches such as hypothermia, ischemic/hypoxic conditioning, acupuncture, medical gases and transcranial laser therapy. In addition, we briefly summarize mechanical endovascular recanalization devices and recovery devices for the treatment of the chronic phase of stroke and discuss the relative merits of these devices.

XENON in medical area: emphasis on neuroprotection in hypoxia and anesthesia

Xenon is a medical gas capable of establishing neuroprotection, inducing anesthesia as well as serving in modern laser technology and nuclear medicine as a contrast agent. In spite of its high cost, its lack of side effects, safe cardiovascular and organoprotective profile and effective neuroprotective role after hypoxic-ischemic injury (HI) favor its applications in clinics. Xenon performs its anesthetic and neuroprotective functions through binding to glycine site of glutamatergic N-methyl-D-aspartate (NMDA) receptor competitively and blocking it. This blockage inhibits the overstimulation of NMDA receptors, thus preventing their following downstream calcium accumulating cascades. Xenon is also used in combination therapies together with hypothermia or sevoflurane. The neuroprotective effects of xenon and hypothermia cooperate synergistically whether they are applied synchronously or asynchronously. Distinguishing properties of Xenon promise for innovations in medical gas field once further studies are fulfilled and Xenon’s high cost is overcome.

Modulation by the noble gas argon of the catalytic and thrombolytic efficiency of tissue plasminogen activator

Argon has been shown to provide cortical as well as, under certain conditions, subcortical neuroprotection in all models so far (middle cerebral artery occlusion, trauma, neonatal asphyxia, etc.). This has led to the suggestion that argon could be a cost-efficient alternative to xenon, a metabolically inert gas thought to be gold standard in gas pharmacology but whose clinical development suffers its little availability and excessive cost of production. However, whether argon interacts with the thrombolytic agent tissue plasminogen activator, which is the only approved therapy of acute ischemic stroke to date, still remains unknown. This latter point is not trivial since previous data have clearly demonstrated the inhibiting effect of xenon on tPA enzymatic and thrombolytic efficiency and the critical importance of the time at which xenon is administered, during or after ischemia, in order not to block thrombolysis and to obtain neuroprotection. Here, we investigated the effect of argon on tPA enzymatic and thrombolytic efficiency using in vitro methods shown to provide reliable prediction of the in vivo effects of both oxygen and the noble inert gases on tPA-induced thrombolysis. We found that argon has a concentration-dependent dual effect on tPA enzymatic and thrombolytic efficiency. Low and high concentrations of argon of 25 and 75 vol% respectively block and increase tPA enzymatic and thrombolytic efficiency. The possible use of argon at low and high concentrations in the treatment of acute ischemic stroke if given during ischemia or after tPA-induced reperfusion is discussed as regards to its neuroprotectant action and its inhibiting and facilitating effects on tPA-induced thrombolysis. The mechanisms of argon-tPA interactions are also discussed.

Ex vivo and in vivo neuroprotection induced by argon when given after an excitotoxic or ischemic insult

In vitro studies have well established the neuroprotective action of the noble gas argon. However, only limited data from in vivo models are available, and particularly whether postexcitotoxic or postischemic argon can provide neuroprotection in vivo still remains to be demonstrated. Here, we investigated the possible neuroprotective effect of postexcitotoxic-postischemic argon both ex vivo in acute brain slices subjected to ischemia in the form of oxygen and glucose deprivation (OGD), and in vivo in rats subjected to an intrastriatal injection of N-methyl-D-aspartate (NMDA) or to the occlusion of middle-cerebral artery (MCAO). We show that postexcitotoxic-postischemic argon reduces OGD-induced cell injury in brain slices, and further reduces NMDA-induced brain damage and MCAO-induced cortical brain damage in rats. Contrasting with its beneficial effect at the cortical level, we show that postischemic argon increases MCAO-induced subcortical brain damage and provides no improvement of neurologic outcome as compared to control animals. These results extend previous data on the neuroprotective action of argon. Particularly, taken together with previous in vivo data that have shown that intraischemic argon has neuroprotective action at both the cortical and subcortical level, our findings on postischemic argon suggest that this noble gas could be administered during but not after ischemia, i.e. before but not after reperfusion has occurred, in order to provide cortical neuroprotection and to avoid increasing subcortical brain damage. Also, the effects of argon are discussed as regards to the oxygen-like chemical, pharmacological, and physical properties of argon.

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.

Xenon enhances hypothermic neuroprotection in asphyxiated newborn pigs

OBJECTIVE

To investigate whether inhaling 50% xenon during hypothermia (HT) offers better neuroprotection than xenon or HT alone.

METHODS

Ninety-eight newborn pigs underwent a 45-minute global hypoxic-ischemic insult severe enough to cause permanent brain injury, and 12 pigs underwent sham protocol. Pigs then received intravenous anesthesia and were randomized to 6 treatment groups: (1) normothermia (NT; rectal temperature 38.5 degrees C, n = 18); (2) 18 hours 50% xenon with NT (n = 12); (3) 12 hours HT (rectal temperature 33.5 degrees C, n = 18); (4) 24 hours HT (rectal temperature 33.5 degrees C, n = 17); (5) 18 hours 50% xenon with 12 hours HT (n = 18); and (6) 18 hours 50% xenon with 24 hours HT (n = 17). Fifty percent xenon was administered via a closed circle with 30% oxygen and 20% nitrogen. After 10 hours rewarming, cooled pigs remained normothermic until terminal perfusion fixation at 72 hours. Global and regional brain neuropathology and clinical neurological scores were performed.

RESULTS

Xenon (p = 0.011) and 12 or 24 hours HT (p = 0.003) treatments offered significant histological global, and regional neuroprotection. Combining xenon with HT yielded an additive neuroprotective effect, as there was no interaction effect (p = 0.54). Combining Xenon with 24 hours HT offered 75% global histological neuroprotection with similarly improved regional neuroprotection: thalamus (100%), brainstem (100%), white matter (86%), basal ganglia (76%), cortical gray matter (74%), cerebellum (73%), and hippocampus (72%). Neurology scores improved in the 24-hour HT and combined xenon HT groups at 72 hours.

INTERPRETATION

Combining xenon with HT is a promising therapy for severely encephalopathic infants, doubling the neuroprotection offered by HT alone.

Xenon anesthesia improves respiratory gas exchanges in morbidly obese patients

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

A closed-circuit neonatal xenon delivery system: a technical and practical neuroprotection feasibility study in newborn pigs

BACKGROUND

Asphyxia accounts for 23% of the 4 million annual global neonatal deaths. In developed countries, the incidence of death or severe disability after hypoxic-ischemic (HI) encephalopathy is 1-2/1000 infants born at term. Hypothermia (HT) benefits newborns post-HI and is rapidly entering clinical use. Xenon (Xe), a scarce and expensive anesthetic, combined with HT markedly increases neuroprotection in small animal HI models. The low-Xe uptake of the patient favors the use of closed-circuit breathing system for efficiency and economy. We developed a system for delivering Xe to mechanically ventilated neonates, then investigated its technical and practical feasibility in a previously described neonatal pig model approximating the clinical scenario of global HI injury, prolonged Xe delivery with and without HT as a potential therapy, subsequent neonatal intensive care unit management, and tracheal extubation.

METHODS

Sixteen newborn pigs underwent a global 45 min HI insult (4%-6% inspired oxygen reducing the electroencephalogram amplitude to <7 microV), then received 16 h 50% inspired Xe during normothermia (39.0 degrees C) or HT (33.5 degrees C). A conventional neonatal ventilator provided breaths of oxygen to a lower chamber compressing a hanging bag within. This bag communicated with the upper closed part of the breathing system containing soda lime, unidirectional valves, Xe/oxygen analyzers, and a tracheal tube connection. At each end-inspiration, this bag emptied fully and a bolus of oxygen, the driving gas, crossed from the lower to upper chamber via an additional valve. This mechanically substituted the gas uptake from the circle during the previous breath cycle (oxygen + small volume of Xe) with an equivalent volume of oxygen creating a slow-rising inspired oxygen concentration. This was offset by manual injection of Xe boluses, infrequently at steady state, due to the low-Xe uptake of the patient.

RESULTS

Total mean Xe usage was 0.18 (0.16-0.21) L/h with no differences between Xe-HT and Xe-NT groups, which had weights of 1767 (1657-1877) g and 1818 (1662-1974) g, respectively (95% CI). HT reduced heart rate in the cooled animals; 180 (165-195) vs 148 (142-155) bpm (P < 0.0001) with no differences in arterial blood pressure, oxygen saturation, arterial carbon dioxide tension, or weaning times between these groups.

CONCLUSION

We describe a closed-circuit Xe delivery system with automatic mechanical oxygen replenishment, which could be developed as a single use device. Gas exchange was maintained while Xe consumption was minimal (<$2/h at $10/L*). We have shown it is both feasible and cost-efficient to use this Xe delivery method in newborn pigs for up to 16 h with or without concurrent cooling after a severe HI insult.

Cooling combined with immediate or delayed xenon inhalation provides equivalent long-term neuroprotection after neonatal hypoxia-ischemia

Hypothermia (HT) improves outcome after neonatal hypoxia-ischemia. Combination therapy may extend neuroprotection. The noble anesthetic gas xenon (Xe) has an excellent safety profile. We have shown earlier that 3 h of 50% Xe plus HT (32 degrees C) additively gives more protection (72%) than either alone (HT=31.1%, Xe=10.2%). Factors limiting clinical use include high-cost and specialist administration requirements. Thus, combinations of 1 h of 50% Xe were administered concurrently for either the first (1 h(Immediate)Xe) or last (1 h(Delayed)Xe) of 3 h of posthypoxic-ischemic HT as compared with 3 h of 50%Xe/HT to investigate how brief Xe exposure with a delay would affect efficacy. An established neonatal rat hypoxia-ischemia model was used. Serial functional neurologic testing into adulthood was performed, followed by neuropathological examination. Xenon with HT was more effective with longer Xe duration (3 h versus 1 h) (P=0.015). However, 1 h Xe/3 h HT resulted in better neuroprotection than 3 h HT alone (P=0.03), this significant effect was also present with 1 h Xe after a 2-h delay. One (immediate or with a delay) or 3 h Xe also significantly improved motor function (P=0.024). Females had significantly better motor scores than males, but no sex-dependent difference in pathology results. The neuroprotection of short, delayed Xe treatment would allow transport to specialist facilities to receive Xe.

Xenon and hypothermia combine additively, offering long-term functional and histopathologic neuroprotection after neonatal hypoxia/ischemia

BACKGROUND AND PURPOSE

Hypoxic/ischemic (HI) brain injury affects 1 to 6 per 1000 live human births, with a mortality of 15% to 20%. A quarter of survivors have permanent disabilities. Hypothermia is the only intervention that improves outcome; however, further improvements might be obtained by combining hypothermia with additional treatments. Xenon is a noble anesthetic gas with an excellent safety profile, showing great promise in vitro and in vivo as a neuroprotectant. We investigated combinations of 50% xenon (Xe(50%)) and hypothermia of 32 degrees C (HT(32 degrees C)) as a post-HI therapy.

METHODS

An established neonatal rat HI model was used. Serial functional neurologic testing into adulthood 10 weeks after injury was performed, followed by global and regional brain histopathology evaluation.

RESULTS

In the combination Xe(50%)HT(32 degrees C) group, complete restoration of long-term functional outcomes was seen. Hypothermia produced improvement on short- (P<0.001) and long- (P<0.001) term functional testing, whereas Xe(50%) alone predominantly improved long-term function (P<0.05), suggesting that short-term testing does not always predict eventual outcome. Similarly, the Xe(50%)HT(32 degrees C) combination produced the greatest (71%) improvement in global histopathology scores, a pattern mirrored in the regional scores, whereas Xe(50%) and HT(32 degrees C) individually produced smaller improvements (P<0.05 and P<0.001, respectively). The interaction between the 2 treatments was additive.

CONCLUSIONS

The xenon/hypothermia combination additively confers greater protection after HI than either treatment alone. The functional improvement is almost complete, is sustained long term, and is accompanied by greatly improved histopathology. The unique safety profile differentiates xenon as an attractive combination therapy with hypothermia to improve the otherwise bleak outcome from neonatal HI.

Neuroprotective effects of xenon: a therapeutic window of opportunity in rats subjected to transient cerebral ischemia

Brain insults are a major cause of acute mortality and chronic morbidity. Given the largely ineffective current therapeutic strategies, the development of new and efficient therapeutic interventions is clearly needed. A series of previous investigations has shown that the noble and anesthetic gas xenon, which has low-affinity antagonistic properties at the N-methyl-D-aspartate (NMDA) receptor, also exhibits potentially neuroprotective properties with no proven adverse side effects. Surprisingly and in contrast with most drugs that are being developed as therapeutic agents, the dose-response neuroprotective effect of xenon has been poorly studied, although this effect could be of major critical importance for its clinical development as a neuroprotectant. Here we show, using ex vivo and in vivo models of excitotoxic insults and transient brain ischemia, that xenon, administered at subanesthetic doses, offers global neuroprotection from reduction of neurotransmitter release induced by ischemia, a critical event known to be involved in excitotoxicity, to reduction of subsequent cell injury and neuronal death. Maximal neuroprotection was obtained with xenon at 50 vol%, a concentration at which xenon further exhibited significant neuroprotective effects in vivo even when administered up to 4 h after intrastriatal NMDA injection and up to at least 2 h after induction of transient brain ischemia.