The blood-gas partition coefficient of xenon may be lower than generally accepted

A metabolic profile of xenon and metabolite associations with 6-month mortality after out-of-hospital cardiac arrest: A post-hoc study of the randomised Xe-Hypotheca trial

PURPOSE

Out-of-hospital cardiac arrest (OHCA) carries a relatively poor prognosis and requires multimodal prognostication to guide clinical decisions. Identification of previously unrecognized metabolic routes associated with patient outcome may contribute to future biomarker discovery. In OHCA, inhaled xenon elicits neuro- and cardioprotection. However, the metabolic effects remain unknown.

MATERIALS AND METHODS

In this post-hoc study of the randomised, 2-group, single-blind, phase 2 Xe-Hypotheca trial, 110 OHCA survivors were randomised 1:1 to receive targeted temperature management (TTM) at 33°C with or without inhaled xenon during 24 h. Blood samples for nuclear magnetic resonance spectroscopy metabolic profiling were drawn upon admission, at 24 and 72 h.

RESULTS

At 24 h, increased lactate, adjusted hazard-ratio 2.25, 95% CI [1.53; 3.30], p<0.001, and decreased branched-chain amino acids (BCAA) leucine 0.64 [0.5; 0.82], p = 0.007, and valine 0.37 [0.22; 0.63], p = 0.003, associated with 6-month mortality. At 72 h, increased lactate 2.77 [1.76; 4.36], p<0.001, and alanine 2.43 [1.56; 3.78], p = 0.001, and decreased small HDL cholesterol ester content (S-HDL-CE) 0.36 [0.19; 0.68], p = 0.021, associated with mortality. No difference was observed between xenon and control groups.

CONCLUSIONS

In OHCA patients receiving TTM with or without xenon, high lactate and alanine and decreased BCAAs and S-HDL-CE associated with increased mortality. It remains to be established whether current observations on BCAAs, and possibly alanine and lactate, could reflect neural damage via their roles in the metabolism of the neurotransmitter glutamate. Xenon did not significantly alter the measured metabolic profile, a potentially beneficial attribute in the context of compromised ICU patients.

TRIAL REGISTRATION

Trial Registry number: ClinicalTrials.gov Identifier: NCT00879892.

Combining a noble gas with radiotherapy: glutamate receptor antagonist xenon may act as a radiosensitizer in glioblastoma

BACKGROUND

Ionotropic glutamate receptors α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor (AMPAR) and N-methyl-D-aspartate receptor (NMDAR) modulate proliferation, invasion and radioresistance in glioblastoma (GB). Pharmacological targeting is difficult as many in vitro-effective agents are not suitable for in patient applications. We aimed to develop a method to test the well tolerated AMPAR- and NMDAR-antagonist xenon gas as a radiosensitizer in GB.

METHODS

We designed a diffusion-based system to perform the colony formation assay (CFA), the radiobiological gold standard, under xenon exposure. Stable and reproducible gas atmosphere was validated with oxygen and carbon dioxide as tracer gases. After checking for AMPAR and NMDAR expression via immunofluorescence staining we performed the CFA with the glioblastoma cell lines U87 and U251 as well as the non-glioblastoma derived cell line HeLa. Xenon was applied after irradiation and additionally tested in combination with NMDAR antagonist memantine.

RESULTS

The gas exposure system proved compatible with the CFA and resulted in a stable atmosphere of 50% xenon. Indications for the presence of glutamate receptor subunits were present in glioblastoma-derived and HeLa cells. Significantly reduced clonogenic survival by xenon was shown in U87 and U251 at irradiation doses of 4-8 Gy and 2, 6 and 8 Gy, respectively (p < 0.05). Clonogenic survival was further reduced by the addition of memantine, showing a significant effect at 2-8 Gy for both glioblastoma cell lines (p < 0.05). Xenon did not significantly reduce the surviving fraction of HeLa cells until a radiation dose of 8 Gy.

CONCLUSION

The developed system allows for testing of gaseous agents with CFA. As a proof of concept, we have, for the first time, unveiled indications of radiosensitizing properties of xenon gas in glioblastoma.

Effects of xenon anesthesia on postoperative neurocognitive disorders: a systematic review and meta-analysis

The latest clinical trials have reported conflicting outcomes regarding the effectiveness of xenon anesthesia in preventing postoperative neurocognitive dysfunction; thus, this study assessed the existing evidence. We searched the PubMed, Embase, Cochrane Library, and Web of Science databases from inception to April 9, 2023, for randomized controlled trials of xenon anesthesia in postoperative patients. We included English-language randomized controlled studies of adult patients undergoing surgery with xenon anesthesia that compared its effects to those of other anesthetics. Duplicate studies, pediatric studies, and ongoing clinical trials were excluded. Nine studies with 754 participants were identified. A forest plot revealed that the incidence of postoperative neurocognitive dysfunction did not differ between the xenon anesthesia and control groups (P = 0.43). Additionally, xenon anesthesia significantly shortened the emergence time for time to opening eyes (P < 0.001), time to extubation (P < 0.001), time to react on demand (P = 0.01), and time to time and spatial orientation (P = 0.04). However, the Aldrete score significantly increased with xenon anesthesia (P = 0.005). Postoperative complications did not differ between the anesthesia groups. Egger's test for bias showed no small-study effect, and a trim-and-fill analysis showed no apparent publication bias. In conclusion, xenon anesthesia probably did not affect the occurrence of postoperative neurocognitive dysfunction. However, xenon anesthesia may effectively shorten the emergence time of certain parameters without adverse effects.

Protein Kinase A Is Responsible for the Presynaptic Inhibition of Glycinergic and Glutamatergic Transmissions by Xenon in Rat Spinal Cord and Hippocampal CA3 Neurons

The effects of a general anesthetic xenon (Xe) on spontaneous, miniature, electrically evoked synaptic transmissions were examined using the "synapse bouton preparation," with which we can clearly evaluate pure synaptic responses and accurately quantify pre- and postsynaptic transmissions. Glycinergic and glutamatergic transmissions were investigated in rat spinal sacral dorsal commissural nucleus and hippocampal CA3 neurons, respectively. Xe presynaptically inhibited spontaneous glycinergic transmission, the effect of which was resistant to tetrodotoxin, Cd2+, extracellular Ca2+, thapsigargin (a selective sarcoplasmic/endoplasmic reticulum Ca2+-ATPase inhibitor), SQ22536 (an adenylate cyclase inhibitor), 8-Br-cAMP (membrane-permeable cAMP analog), ZD7288 (an hyperpolarization-activated cyclic nucleotide-gated channel blocker), chelerythrine (a PKC inhibitor), and KN-93 (a CaMKII inhibitor) while being sensitive to PKA inhibitors (H-89, KT5720, and Rp-cAMPS). Moreover, Xe inhibited evoked glycinergic transmission, which was canceled by KT5720. Like glycinergic transmission, spontaneous and evoked glutamatergic transmissions were also inhibited by Xe in a KT5720-sensitive manner. Our results suggest that Xe decreases glycinergic and glutamatergic spontaneous and evoked transmissions at the presynaptic level in a PKA-dependent manner. These presynaptic responses are independent of Ca2+ dynamics. We conclude that PKA can be the main molecular target of Xe in the inhibitory effects on both inhibitory and excitatory neurotransmitter release. SIGNIFICANCE STATEMENT: Spontaneous and evoked glycinergic and glutamatergic transmissions were investigated using the whole-cell patch clamp technique in rat spinal sacral dorsal commissural nucleus and hippocampal CA3 neurons, respectively. Xenon (Xe) significantly inhibited glycinergic and glutamatergic transmission presynaptically. As a signaling mechanism, protein kinase A was responsible for the inhibitory effects of Xe on both glycine and glutamate release. These results may help understand how Xe modulates neurotransmitter release and exerts its excellent anesthetic properties.

Effect of xenon on brain injury, neurological outcome, and survival in patients after aneurysmal subarachnoid hemorrhage-study protocol for a randomized clinical trial

BACKGROUND

Aneurysmal subarachnoid hemorrhage (aSAH) is a neurological emergency, affecting a younger population than individuals experiencing an ischemic stroke; aSAH is associated with a high risk of mortality and permanent disability. The noble gas xenon has been shown to possess neuroprotective properties as demonstrated in numerous preclinical animal studies. In addition, a recent study demonstrated that xenon could attenuate a white matter injury after out-of-hospital cardiac arrest.

METHODS

The study is a prospective, multicenter phase II clinical drug trial. The study design is a single-blind, prospective superiority randomized two-armed parallel follow-up study. The primary objective of the study is to explore the potential neuroprotective effects of inhaled xenon, when administered within 6 h after the onset of symptoms of aSAH. The primary endpoint is the extent of the global white matter injury assessed with magnetic resonance diffusion tensor imaging of the brain.

DISCUSSION

Despite improvements in medical technology and advancements in medical science, aSAH mortality and disability rates have remained nearly unchanged for the past 10 years. Therefore, new neuroprotective strategies to attenuate the early and delayed brain injuries after aSAH are needed to reduce morbidity and mortality.

TRIAL REGISTRATION

ClinicalTrials.gov NCT04696523. Registered on 6 January 2021. EudraCT, EudraCT Number: 2019-001542-17. Registered on 8 July 2020.

The Anaesthetics Isoflurane and Xenon Reverse the Synaptotoxic Effects of Aβ1-42 on Megf10-Dependent Astrocytic Synapse Elimination and Spine Density in Ex Vivo Hippocampal Brain Slices

It has been hypothesised that inhalational anaesthetics such as isoflurane (Iso) may trigger the pathogenesis of Alzheimer's disease (AD), while the gaseous anaesthetic xenon (Xe) exhibits many features of a putative neuroprotective agent. Loss of synapses is regarded as one key cause of dementia in AD. Multiple EGF-like domains 10 (MEGF10) is one of the phagocytic receptors which assists the elimination of synapses by astrocytes. Here, we investigated how β-amyloid peptide 1-42 (Aβ_1-42), Iso and Xe interact with MEGF10-dependent synapse elimination. Murine cultured astrocytes as well as cortical and hippocampal ex vivo brain slices were treated with either Aβ_1-42, Iso or Xe and the combination of Aβ_1-42 with either Iso or Xe. We quantified MEGF10 expression in astrocytes and dendritic spine density (DSD) in slices. In brain slices of wild type and AAV-induced MEGF10 knock-down mice, antibodies against astrocytes (GFAP), pre- (synaptophysin) and postsynaptic (PSD95) components were used for co-localization analyses by means of immunofluorescence-imaging and 3D rendering techniques. Aβ_1-42 elevated pre- and postsynaptic components inside astrocytes and decreased DSD. The combined application with either Iso or Xe reversed these effects. In the presence of Aβ_1-42 both anaesthetics decreased MEGF10 expression. AAV-induced knock-down of MEGF10 reduced the pre- and postsynaptic marker inside astrocytes. The presented data suggest Iso and Xe are able to reverse the Aβ_1-42-induced enhancement of synaptic elimination in ex vivo hippocampal brain slices, presumably through MEGF10 downregulation.

Quantitative assessment of regional lung ventilation in emphysematous mice using hyperpolarized 129Xe MRI with a continuous flow hyperpolarizing system

BACKGROUND

Lung ventilation function in small animals can be assessed by using hyperpolarized gas MRI. For these experiments a free breathing protocol is generally preferred to mechanical ventilation as mechanical ventilation can often lead to ventilation lung injury, while the need to maintain a gas reservoir may lead to a partial reduction of the polarization.

PURPOSE

To evaluate regional lung ventilation of mice by a simple but fast method under free breathing and give evidence for effectiveness with an elastase instilled emphysematous mice.

ANIMAL MODEL

Emphysematous mice.

MATERIALS AND METHODS

A Look-Locker based saturation recovery sequence was developed for continuous flow hyperpolarized (CF-HP) ¹²⁹Xe gas experiments, and the apparent gas-exchange rate, k', was measured by the analysis of the saturation recovery curve.

RESULTS

In mice with elastase-induced mild emphysema, reductions of 15-30% in k' values were observed as the results of lesion-induced changes in the lung.

DATA CONCLUSION

The proposed method was applied to an emphysematous model mice and ventilation dysfunctions have been approved as a definite decrease in k' values, supporting the usefulness for a non-invasive assessment of the lung functions in preclinical study by the CF-HP ¹²⁹Xe experiments.

Repetitive xenon treatment improves post-stroke sensorimotor and neuropsychiatric dysfunction

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

Xenon Nanobubbles for the Image-Guided Preemptive Treatment of Acute Ischemic Stroke via Neuroprotection and Microcirculatory Restoration

Early lesion site diagnosis and neuroprotection are crucial to the theranostics of acute ischemic stroke. Xenon (Xe), as a nontoxic gaseous neuroprotectant, holds great promise for ischemic stroke therapy. In this study, Xe-encapsulated lipid nanobubbles (Xe-NBs) have been prepared for the real-time ultrasound image-guided preemptive treatment of the early stroke. The lipids are self-assembled at the interface of free Xe bubbles, and the mean diameter of Xe-NBs is 225 ± 11 nm with a Xe content of 73 ± 2 μL/mL. The in vitro results show that Xe-NBs can protect oxygen/glucose-deprived PC12 cells against apoptosis and oxidative stress. Based on the ischemic stroke mice model, the biodistribution, timely ultrasound imaging, and the therapeutic effects of Xe-NBs for stroke lesions were investigated in vivo. The accumulation of Xe-NBs to the ischemic lesion endows ultrasound contrast imaging with the lesion area. The cerebral blood flow measurement indicates that the administration of Xe-NBs can improve microcirculatory restoration, resulting in reduced acute microvascular injury in the lesion area. Furthermore, local delivery of therapeutic Xe can significantly reduce the volume of cerebral infarction and restore the neurological function with reduced neuron injury against apoptosis. Therefore, Xe-NBs provide a novel nanosystem for the safe and rapid theranostics of acute ischemic stroke, which is promising to translate into the clinical management of stroke.

Radiobiological shot noise explains Three Mile Island biodosimetry indicating nearly 1,000 mSv exposures

The 1979 accident at the Three Mile Island nuclear power station in Pennsylvania released about 22 million Curies of xenon-133 into the environment. Because physical dosimetry indicated exposures to the nearby population of less than about 2 mSv, discernible impacts to the health of the exposed population are not generally believed to have resulted. However, there is contrary evidence, including especially the results of biodosimetry via cytogenetic analysis using the FISH method. This report examines the discrepancy between the results of physical dosimetry and biodosimetry, which among the small number of persons examined indicated exposures between 600 and 900 mSv. The paradox reveals a fundamental error in the health physics body of knowledge: the definition of the energy imparted to tissue, ε, fails to properly account for the temporal distribution of ionization products resulting from dilute contamination with an internally incorporated beta-emitting radionuclide. Application of a century-old result describing "shot noise" in an electronic system repairs the deficiency. The Xe-133 concentration in the tissue of those individuals exposed to the most intense portion of the radioactive plume released from the TMI facility is shown to have been on the order of 0.1 μCi/l, persisting for multiple hours. Shot noise reference doses in the range from 820 to 1,700 mSv follow, a result which is consistent with biodosimetric analysis. The finding should motivate a comprehensive re-evaluation of the conventional understanding of the 1979 accident at the Three Mile Island nuclear power station, especially regarding its impact upon the population of the surrounding area.

Xenon blunts NF-κB/NLRP3 inflammasome activation and improves acute onset of accelerated and severe lupus nephritis in mice

Xenon, an inert anesthetic gas, is increasingly recognized to possess desirable properties including cytoprotective and anti-inflammatory effects. Here we evaluated the effects of xenon on the progression of lupus nephritis (LN) in a mouse model. A two hour exposure of either 70% xenon or 70% nitrogen balanced with oxygen was administered daily for five weeks to female NZB/W F1 mice that had been induced to develop accelerated and severe LN. Xenon treatment improved kidney function and renal histology, and decreased the renal expression of neutrophil chemoattractants, thereby attenuating glomerular neutrophil infiltration. The effects of xenon were mediated primarily by deceasing serum levels of anti-double stranded DNA autoantibody, inhibiting reactive oxygen species production, NF-κB/NLRP3 inflammasome activation, ICAM-1 expression, glomerular deposition of IgG and C3 and apoptosis, in the kidney; and enhancing renal hypoxia inducible factor 1-α expression. Proteomic analysis revealed that the treatment with xenon downregulated renal NLRP3 inflammasome-mediated cellular signaling. Similarly, xenon was effective in improving renal pathology and function in a spontaneous LN model in female NZB/W F1 mice. Thus, xenon may have a therapeutic role in treating LN but further studies are warranted to determine applicability to patients.

Closed circuit xenon delivery for 72h in neonatal piglets following hypoxic insult using an ambient pressure automated control system: Development, technical evaluation and pulmonary effects

BACKGROUND

Therapeutic hypothermia (TH) for 72h is the standard treatment following neonatal encephalopathy (NE). However, one-third do not benefit and adjunctive therapies are urgently needed. Xenon enhances neuroprotection with TH when administered at 50% concentration within 5hours of hypoxia in experimental studies. Delayed initiation (~10 hours of age) of 30% xenon for 24 hours during TH did not improve early adverse biomarkers in a clinical trial of Xenon+TH vs TH. After hypoxia-ischemia, excitotoxic injury via N-methyl-D-aspartate receptor overactivation lasts days. Since xenon partially inhibits this receptor, we hypothesised that giving 50% xenon throughout the entire 72h TH and rewarming periods would enhance neuroprotection. Xenon costs $30/litre, so a closed-circuit breathing system is desirable with automated fresh gas delivery.

METHODS

Seven mechanically ventilated newborn pigs were randomized to receive 50% inhaled xenon for 72h during hypothermia (rectal-temperature 35°C) and subsequent rewarming following a global hypoxic-ischemic insult (XeHT, N = 4) or under normothermia for 72h (rectal-temperature 38.5°C) following sham insult (XeNT, N = 3). An automated fresh gas delivery system injected oxygen/air/xenon boluses into a closed-circuit based on measured gas concentrations.

RESULTS AND DISCUSSION

Median (IQR) xenon consumption was 0.31 L/h (0.18, 0.50) and 0.34L/h (0.32, 0.49) for hypothermic and normothermic groups respectively, 0.34L/h (0.25, 0.53) overall. 92% of 9626 xenon and 69% of 9635 oxygen measurements were within 20% variation from targets. For xenon concentration, the median absolute performance errors for the XeHT and XeNT groups were 6.14% and 3.84% respectively and 4.31% overall. For oxygen these values were 13.42%, 15.05% and 12.4% respectively. There were no adverse pulmonary pathophysiology findings. Clinical problems over the total period included three related to sensors, seven breathing system leaks, ten partial and one complete tracheal tube occlusion episodes.

CONCLUSION

The automated controller functioned as intended maintaining an inhaled xenon concentration close to the 50% target for 72-78h at a xenon cost of $11.1/h.

The Effect of Xenon-Based Anesthesia on Somatosensory-Evoked Potentials in Patients Undergoing Carotid Endarterectomy

OBJECTIVES

The aim of this study was to investigate the influence of xenon-based anesthesia on somatosensory-evoked potentials.

DESIGN

Observational cohort study.

SETTING

University hospital.

PARTICIPANTS

Twenty subsequent adult patients undergoing elective carotid endarterectomy.

INTERVENTIONS

Xenon-based anesthesia.

MEASUREMENTS AND MAIN RESULTS

Cortical-evoked responses to median nerve stimulation were quantified by measurement of the amplitude and latency of the N20 wave, which are typically assessed during carotid surgery to detect intraoperative cerebral hypoperfusion and ischemia. Primary (N20 amplitude and latency) and secondary (mean arterial pressure, norepinephrine requirements and depth of anesthesia) were assessed during (1) propofol/remifentanil and (2) subsequent xenon/remifentanil anesthesia. Xenon at an inspiratory fraction of 62.5 ± 7% decreased norepinephrine requirement (0.067 ± 0.04 v 0.028 ± 0.02 µg/kg/min, p < 0.001), and mean arterial pressure was unchanged (90.6 ± 15.0 v 93.1 ± 9.6 mmHg, p = 0.40). Somatosensory-evoked potentials were available in all patients during xenon/remifentanil. Despite similar depth of anesthesia (Narcotrend index 38.4 ± 6.2 v 38.5 ± 5.8) during propofol and xenon, N20 amplitude was reduced after xenon wash-in from 3.7 ± 1.7 to 1.4 ± 2.8 µV, p < 0.001 on the surgical and 3.6 ± 1.6 to 1.4 ± 0.6 µV, p < 0.001 on the contralateral side. N20 latency remained unchanged during xenon (22.9 ± 2.1 v 22.5 ± 2.8 ms, p = 0.34 and 22.9 ± 2.0 v 22.9 ± 3.0, p = 0.97).

CONCLUSIONS

Xenon influences somatosensory-evoked potentials measurement by reducing N20 wave amplitude but not latency. When xenon is considered as an anesthetic for carotid endarterectomy, wash-in needs to be completed before carotid surgery is commenced to provide stable baseline somatosensory-evoked potential measurement.

Characterization and Imaging of Lipid-Shelled Microbubbles for Ultrasound-Triggered Release of Xenon

Xenon (Xe) is a bioactive gas capable of reducing and stabilizing neurologic injury in stroke. The goal of this work was to develop lipid-shelled microbubbles for xenon loading and ultrasound-triggered release. Microbubbles loaded with either xenon (Xe-MB) or xenon and octafluoropropane (Xe-OFP-MB) (9:1 v/v) were synthesized by high-shear mixing. The size distribution and the frequency-dependent attenuation coefficient of Xe-MB and Xe-OFP-MB were measured using a Coulter counter and a broadband acoustic attenuation spectroscopy system, respectively. The Xe dose was evaluated using gas chromatography/mass spectrometry. The total Xe doses in Xe-MB and Xe-OFP-MB were 113.1 ± 13.5 and 145.6 ± 25.5 μl per mg of lipid, respectively. Co-encapsulation of OFP increased the total xenon dose, attenuation coefficient, microbubble stability (in an undersaturated solution), and shelf life of the agent. Triggered release of gas payload was demonstrated with 6-MHz duplex Doppler and 220-kHz pulsed ultrasound. These results constitute the first step toward the use of lipid-shelled microbubbles for applications such as neuroprotection in stroke.

Development of a hybrid CFD-PBPK model to predict the transport of xenon gas around a human respiratory system to systemic regions

Administering incorrect doses of conventional anesthetic agents through the pulmonary route can cause potential health risks such as blood coagulation, platelet dysfunction, and deteriorating organ function. As an alternative, xenon can minimize the impact on the cardiovascular system and provide the neuroprotective effect, hemodynamic stability, and fast recovery. However, the inhalation pattern still needs to be carefully monitored and controlled to avoid health risks caused by over administering xenon to patients during unconsciousness. Thus, high-resolution lung absorption and whole-body translocation data are critically needed to fully understand how to administer the gas and coordinate with the patient to accurately control the dose. Clinical studies are not able to provide accurate dosimetry data due to their limited operational flexibility and imaging resolution. Therefore, a computational fluid dynamics (CFD) model was employed in this study to simulate the transport and absorption of the inhaled xenon which is connected with a physiologically based pharmacokinetic (PBPK) model to predict the translocation into the systemic regions. To study the effects of different breathing patterns on xenon transport dynamics in the human body, a realistic breathing waveform and two steady-state flow rates with inhalation durations of 2 and 1.5 seconds were selected. For the realistic breathing cycle, the inhalation-exhalation periods are defined for a human at rest and the other two cases have a fixed volumetric flow rate of 15 L/min. As the two latter cases only simulate the inspiratory phase, a 1-second holding time was applied to represent the missing periods of the full breathing time. Simulations were performed in a subject-specific human upper airway configuration from mouth to G6. Numerical results show that with the accurate lung uptake predictions obtained from the CFD model, the hybrid CFD-PBPK model with TRANSIT compartments generates more precise and breath-specific trends compared to simple PBPK models. Numerical results demonstrate that breathing pattern can significantly influence the xenon uptake in the human body, which can be utilized as a critical factor to be coordinated by clinicians to achieve the optimized xenon dose. Furthermore, parametric analyses were performed for the influence of breathing patterns on local airflow distributions, gas species translocations, and lung elimination mechanisms followed by species diffusion into the systemic regions.

Lasting effects of general anesthetics on the brain in the young and elderly: "mixed picture" of neurotoxicity, neuroprotection and cognitive impairment

General anesthetics are commonly used in major surgery. To achieve the depth of anesthesia for surgery, patients are being subjected to a variety of general anesthetics, alone or in combination. It has been long held an illusory concept that the general anesthesia is entirely reversible and that the central nervous system is returned to its pristine state once the anesthetic agent is eliminated from the active site. However, studies indicate that perturbation of the normal functioning of these targets may result in long-lasting desirable or undesirable effects. This review focuses on the impact of general anesthetic exposure to the brain and summarizes the molecular and cellular mechanisms by which general anesthetics may induce long-lasting undesirable effects when exposed at the developing stage of the brain. The vulnerability of aging brain to general anesthetics, specifically in the context of cognitive disorders and Alzheimer’s disease pathogeneses are also discussed. Moreover, we will review emerging evidence regarding the neuroprotective property of xenon and anesthetic adjuvant dexmedetomidine in the immature and mature brains. In conclusion, “mixed picture” effects of general anesthetics should be well acknowledged and should be implemented into daily clinical practice for better patient outcome.

Multibreath Hyperpolarized 3He Imaging Scheme to Measure Alveolar Oxygen Tension and Apparent Diffusion Coefficient

RATIONALE AND OBJECTIVES

In this study, we compared a newly developed multibreath simultaneous alveolar oxygen tension and apparent diffusion coefficient (P_AO₂-ADC) imaging sequence to a single-breath acquisition, with the aim of mitigating the compromising effects of intervoxel flow and slow-filling regions on single-breath measurements, especially in chronic obstructive pulmonary disease (COPD) subjects.

MATERIALS AND METHODS

Both single-breath and multibreath simultaneous P_AO₂-ADC imaging schemes were performed on a total of 10 human subjects (five asymptomatic smokers and five COPD subjects). Estimated P_AO₂ and ADC values derived from the different sequences were compared both globally and regionally. The distribution of voxels with nonphysiological values was also compared between the two schemes.

RESULTS

The multibreath protocol decreased the ventilation defect volumes by an average of 12.9 ± 6.6%. The multibreath sequence generated nonphysiological P_AO₂ values in 11.0 ± 8.5% fewer voxels than the single-breath sequence. Single-breath P_AO₂ maps also showed more regions with gas-flow artifacts and general signal heterogeneity. On average, the standard deviation of the P_AO₂ distribution was 16.5 ± 7.0% lower using multibreath P_AO₂-ADC imaging, suggesting a more homogeneous gas distribution. Both mean and standard deviation of the ADC increased significantly from single- to multibreath imaging (p = 0.048 and p = 0.070, respectively), suggesting more emphysematous regions in the slow-filling lung.

CONCLUSION

Multibreath P_AO₂-ADC imaging provides superior accuracy and efficiency compared to previous imaging protocols. P_AO₂ and ADC maps generated by multibreath imaging allowed for the qualification of various regions as emphysematous or obstructed, which single-breath P_AO₂ maps can only identify as defects. The simultaneous P_AO₂ and ADC measurements generated by the presented multibreath method were also more physiologically realistic, and allowed for more detailed analysis of the slow-filling regions characteristic of COPD subjects.

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.

Xenon anesthesia and beyond: pros and cons

Xenon is a colorless and odorless noble gas, licensed for human use as an anesthetic gas as well as a radiological marker. The MAC of this gas is about 63% but xenon anesthesia is associated with fast recovery of cognitive function and cardiovascular stability. Nevertheless, postoperative nausea and vomiting (PONV) incidence for xenon anesthesia is very high. It has been reported that Xenon has cytoprotective effects that may have therapeutic values in both CNS protection, and in organ graft preservation. Currently, there are few studies about the effect of xenon on ischemia reperfusion injury of transplantable organs and insufficient clinical data upon its effect on intracranial and cerebral perfusion pressure. We shortly review the pros and cons of xenon as an anesthetic agent.

Clinical efficacy of xenon versus propofol: A systematic review and meta-analysis

BACKGROUND

Interest in the anesthetic use of xenon, a noble gas, has waxed and waned for decades, and the clinical effects of xenon are still debated. We performed a meta-analysis to compare the clinical efficacy of xenon with that of propofol.

METHODS

Electronic searches were performed through December 2017 using various databases, including PubMed, Embase, and the Cochrane Library. We identified thirteen trials that included a total of 817 patients.

RESULTS

Patients treated with xenon had a lower bispectral index (BIS) (weighted mean difference (WMD): -6.26, 95% confidence interval (CI): -11.33 to -1.18, P = .02), a higher mean arterial blood pressure (MAP) (WMD: 7.00, 95% CI: 2.32-11.68, P = .003) and a lower heart rate (HR) (WMD: -9.45, 95% CI: -12.28 to -6.63, P < 0.00001) than propofol-treated patients. However, there were no significant differences between the 2 treatment groups in the effects of nondepolarizing muscular relaxants, the duration spent in the postanesthesia care unit (PACU) (WMD: -0.94, 95% CI: -8.79-6.91, P = .81), or the incidence of perioperative complications [assessed using the outcomes of postoperative nausea and vomiting (PONV) (relative risk (RR): 2.01, 95% CI: 0.79-5.11, P = .14), hypotension (RR: 0.62, 95% CI: 0.27 to 1.40, P = .25), hypertension (RR: 1.27, 95% CI: 0.73-2.21, P = .39) and bradycardia (RR: 1.00, 95% CI: 0.36-2.74, P = 1.00)].

CONCLUSION

In this meta-analysis of randomized controlled trials, we found that xenon treatment resulted in a higher MAP, a lower HR, and a smaller BIS index than treatment with propofol.

Brain Imaging Using Hyperpolarized 129Xe Magnetic Resonance Imaging

Hyperpolarized (HP) ¹²⁹Xe magnetic resonance imaging (MRI) is a novel iteration of traditional MRI that relies on detecting the spins of ¹H. Since ¹²⁹Xe is a gaseous signal source, it can be used for lung imaging. Additionally, ¹²⁹Xe dissolves in the blood stream and can therefore be detectable in the brain parenchyma and vasculature. In this work, we provide detailed information on the protocols that we have developed to image ¹²⁹Xe within the brains of both rodents and human subjects.

Waste anesthetic gas exposure and strategies for solution

As inhaled anesthetics are widely used, medical staff have inevitably suffered from exposure to anesthetic waste gases (WAGs). Whether chronic exposure to WAGs has an impact on the health of medical staff has long been a common concern, but conclusions are not consistent. Many measures and equipment have been proposed to reduce the concentration of WAGs as far as possible. This review aims to dissect the current exposure to WAGs and its influence on medical staff in the workplace and the environment, and summarize strategies to reduce WAGs.

The Modification and Performance of a Large Animal Anesthesia Machine (Tafonius®) in Order to Deliver Xenon to a Horse

Introduction

Xenon, due to its interesting anesthetic properties, could improve the quality of anesthesia protocols in horses despite its high price. This study aimed to modify and test an anesthesia machine capable of delivering xenon to a horse.

Materials and methods

An equine anesthesia machine (Tafonius, Vetronic Services Ltd., UK) was modified by including a T-connector in the valve block to introduce xenon, so that the xenon was pushed into the machine cylinder by the expired gases. A xenon analyzer was connected to the expiratory limb of the patient circuit. The operation of the machine was modeled and experimentally tested for denitrogenation, wash-in, and maintenance phases. The system was considered to consist of two compartments, one being the horse’s lungs, the other being the machine cylinder and circuit. A 15-year-old, 514-kg, healthy gelding horse was anesthetized for 70 min using acepromazine, romifidine, morphine, diazepam, and ketamine. Anesthesia was maintained with xenon and oxygen, co-administered with lidocaine. Ventilation was controlled. Cardiorespiratory variables, expired fraction of xenon (FeXe), blood gases were measured and xenon was detected in plasma. Recovery was unassisted and recorded.

Results

FeXe remained around 65%, using a xenon total volume of 250 L. Five additional boli of ketamine were required to maintain anesthesia. PaO₂ was 45 ± 1 mmHg. The recovery was calm. Xenon was detected in blood during the entire administration time.

Conclusion

This pilot study describes how to deliver xenon to a horse. Although many technical problems were encountered, their correction could guide future endeavors to study the use of xenon in horses.

Gas chromatography/mass spectrometry measurement of xenon in gas-loaded liposomes for neuroprotective applications

RATIONALE

We have produced a liposomal formulation of xenon (Xe-ELIP) as a neuroprotectant for inhibition of brain damage in stroke patients. This mandates development of a reliable assay to measure the amount of dissolved xenon released from Xe-ELIP in water and blood samples.

METHODS

Gas chromatography/mass spectrometry (GC/MS) was used to quantify xenon gas released into the headspace of vials containing Xe-ELIP samples in water or blood. In order to determine blood concentration of xenon in vivo after Xe-ELIP administration, 6 mg of Xe-ELIP lipid was infused intravenously into rats. Blood samples were drawn directly from a catheterized right carotid artery. After introduction of the samples, each vial was allowed to equilibrate to 37°C in a water bath, followed by 20 minutes of sonication prior to headspace sampling. Xenon concentrations were calculated from a gas dose-response curve and normalized using the published xenon water-gas solubility coefficient.

RESULTS

The mean corrected percent of xenon from Xe-ELIP released into water was 3.87 ± 0.56% (SD, n = 8), corresponding to 19.3 ± 2.8 μL/mg lipid, which is consistent with previous independent Xe-ELIP measurements. The corresponding xenon content of Xe-ELIP in rat blood was 23.38 ± 7.36 μL/mg lipid (n = 8). Mean rat blood xenon concentration after intravenous administration of Xe-ELIP was 14 ± 10 μM, which is approximately 15% of the estimated neuroprotective level.

CONCLUSIONS

Using this approach, we have established a reproducible method for measuring dissolved xenon in fluids. These measurements have established that neuroprotective effects can be elicited by less than 20% of the calculated neuroprotective xenon blood concentration. More work will have to be done to establish the protective xenon pharmacokinetic range. Copyright © 2016 John Wiley & Sons, Ltd.

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.

Xenon elimination kinetics following brief exposure

Xenon is a modern inhalative anaesthetic with a very low solubility in tissues providing rapid elimination and weaning from anaesthesia. Besides its anaesthetic properties, Xenon promotes the endogenous erythropoietin biosynthesis and thus has been enlisted as prohibited substance by the World Anti-Doping Agency (WADA). For effective doping controls, knowledge about the elimination kinetics of Xenon and the duration of traceability are of particular importance. Seventy-seven full blood samples were obtained from 7 normal weight patients undergoing routine Xenon-based general anaesthesia with a targeted inspiratory concentration of 60% Xenon in oxygen. Samples were taken before and during Xenon inhalation as well as one, two, 4, 8, 16, 24, 32, 40, and 48 h after exposure. Xenon concentrations were assessed in full blood by gas chromatography and triple quadrupole tandem mass spectrometry with a detection limit of 0.25 µmol/L. The elimination of Xenon was characterized by linear regression of log-transformed Xenon blood concentrations, as well as non-linear regression. Xenon exposure yielded maximum concentrations in arterial blood of 1.3 [1.1; 1.6] mmol/L. Xenon was traceable for 24 to 48 h. The elimination profile was characterized by a biphasic pattern with a rapid alpha phase, followed by a slower beta phase showing a first order kinetics (c[Xe] = 69.1e^-0.26x , R²  = 0.83, t_1/2  = 2.7 h). Time in hours after exposure could be estimated by 50*ln(1.39/c[Xe]^0.077 ). Xenon's elimination kinetics is biphasic with a delayed beta phase following a first order kinetics. Xenon can reliably be detected for at least 24 h after brief exposure. Copyright © 2016 John Wiley & Sons, Ltd.

High resolution spectroscopy and chemical shift imaging of hyperpolarized (129) Xe dissolved in the human brain in vivo at 1.5 tesla

Purpose

Upon inhalation, xenon diffuses into the bloodstream and is transported to the brain, where it dissolves in various compartments of the brain. Although up to five chemically distinct peaks have been previously observed in ¹²⁹Xe rat head spectra, to date only three peaks have been reported in the human head. This study demonstrates high resolution spectroscopy and chemical shift imaging (CSI) of ¹²⁹Xe dissolved in the human head at 1.5 Tesla.

Methods

A ¹²⁹Xe radiofrequency coil was built in‐house and ¹²⁹Xe gas was polarized using spin‐exchange optical pumping. Following the inhalation of ¹²⁹Xe gas, NMR spectroscopy was performed with spectral resolution of 0.033 ppm. Two‐dimensional CSI in all three anatomical planes was performed with spectral resolution of 2.1 ppm and voxel size 20 mm × 20 mm.

Results

Spectra of hyperpolarized ¹²⁹Xe dissolved in the human head showed five distinct peaks at 188 ppm, 192 ppm, 196 ppm, 200 ppm, and 217 ppm. Assignment of these peaks was consistent with earlier studies.

Conclusion

High resolution spectroscopy and CSI of hyperpolarized ¹²⁹Xe dissolved in the human head has been demonstrated. For the first time, five distinct NMR peaks have been observed in ¹²⁹Xe spectra from the human head in vivo. Magn Reson Med 75:2227–2234, 2016. © 2016 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Comparison of recovery parameters for xenon versus other inhalation anesthetics: systematic review and meta-analysis

STUDY OBJECTIVE

To summarize and evaluate the available data describing the recovery parameters of xenon anesthesia.

DESIGN

Systematic review and meta-analysis.

SETTING

Anesthesia for elective surgeries.

PATIENTS

Systematic review of randomized controlled trials (RCTs) from databases including Medline (1964-2013), the Cochrane Central Register of Controlled Trials (CENTRAL, 1990-2012), and Google Scholar (1966-2013).

INTERVENTIONS

Inhalation of xenon or other anesthetics was administered in elective surgery.

MEASUREMENTS

Recovery parameters (time to recovery, alertness/sedation scale scores at "eye opening," bispectral index at "reaction on demand," time to extubation, and time to orientation).

MAIN RESULTS

Eleven RCTs (N = 661 patients) met the inclusion criteria. Recovery from xenon anesthesia was significantly faster in terms of the time to eye opening (mean difference [MD], -4.18 minutes; 95% confidence interval [CI], -5.03 to -3.32 minutes; P < .00001), the time to reaction on demand (MD, -5.35 minutes; 95% CI, -6.59 to -4.11 minutes; P < .00001), the time to extubation (MD, -4.49 minutes; 95% CI, -5.40 to -3.58 minutes; P < .00001), and the time to orientation (MD, -4.99 minutes; 95% CI, -6.45 to -3.52 minutes; P < .00001).

CONCLUSIONS

This meta-analysis confirmed that recovery from xenon anesthesia is faster than other inhalation anesthesia.

Xenon Blocks Neuronal Injury Associated with Decompression

Despite state-of-the-art hyperbaric oxygen (HBO) treatment, about 30% of patients suffering neurologic decompression sickness (DCS) exhibit incomplete recovery. Since the mechanisms of neurologic DCS involve ischemic processes which result in excitotoxicity, it is likely that HBO in combination with an anti-excitotoxic treatment would improve the outcome in patients being treated for DCS. Therefore, in the present study, we investigated the effect of the noble gas xenon in an ex vivo model of neurologic DCS. Xenon has been shown to provide neuroprotection in multiple models of acute ischemic insults. Fast decompression compared to slow decompression induced an increase in lactate dehydrogenase (LDH), a well-known marker of sub-lethal cell injury. Post-decompression administration of xenon blocked the increase in LDH release induced by fast decompression. These data suggest that xenon could be an efficient additional treatment to HBO for the treatment of neurologic DCS.

A technique for administering xenon gas anesthesia during surgical procedures in mice

Carrying out invasive procedures in animals requires the administration of anesthesia. Xenon gas offers advantages as an anesthetic agent compared with other agents, such as its protection of the brain and heart from hypoxia-induced damage. The high cost of xenon gas has limited its use as an anesthetic in animal experiments, however. The authors designed and constructed simple boxes for the induction and maintenance of xenon gas and isoflurane anesthesia in small rodents in order to minimize the amount of xenon gas that is wasted. While using their anesthesia delivery system to anesthetize pregnant mice undergoing caesarean sections, they measured the respiratory rates of the anesthetized mice, the survival of the pups and the percentages of oxygen and carbon dioxide within the system to confirm the system's safety.

Urine analysis concerning xenon for doping control purposes

RATIONALE

On September 1(st) 2014, a modified Prohibited List as established by the World Anti-Doping Agency (WADA) became effective featuring xenon as a banned substance categorized as hypoxia-inducible factor (HIF) activator. Consequently, the analysis of xenon from commonly provided doping control specimens such as blood and urine is desirable, and first data on the determination of xenon from urine in the context of human sports drug testing, are presented.

METHODS

In accordance to earlier studies utilizing plasma as doping control matrix, urine was enriched to saturation with xenon, sequentially diluted, and the target analyte was detected as supported by the internal standard d6 -cyclohexanone by means of gas chromatography/triple quadrupole mass spectrometry (GC/MS/MS) using headspace injection. Three major xenon isotopes at m/z 128.9, 130.9 and 131.9 were targeted in (pseudo) selected reaction monitoring mode enabling the unambiguous identification of the prohibited substance. Assay characteristics including limit of detection (LOD), intraday/interday precision, and specificity as well as analyte recovery under different storage conditions were determined. Proof-of-concept data were generated by applying the established method to urine samples collected from five patients before, during and after (up to 48 h) xenon-based general anesthesia.

RESULTS

Xenon was traceable in enriched human urine samples down to the detection limit of approximately 0.5 nmol/mL. The intraday and interday imprecision values of the method were found below 25%, and specificity was demonstrated by analyzing 20 different blank urine samples that corroborated the fitness-for-purpose of the analytical approach to unequivocally detect xenon at non-physiological concentrations in human urine. The patients' urine specimens returned 'xenon-positive' test results up to 40 h post-anesthesia, indicating the limits of the expected doping control detection window.

CONCLUSIONS

Since xenon has been considered a prohibited substance according to WADA regulations in September 2014, its analysis from common specimens of routine sports drug testing is desirable. In previous studies, its traceability in whole blood and plasma was shown, and herein a complementary approach utilizing doping control urine samples for the GC/MS/MS analysis of xenon was reported.

Equipotent Subanesthetic Concentrations of Sevoflurane and Xenon Preventing Cold-stimulated Vocalization of Neonatal Rats

Background:

The effects of inhaled anesthetics on the developing brain are studied using neonatal rodents exposed to fractions of minimum alveolar concentration (to avoid cardiorespiratory compromise). However, these fractions cannot be assumed to be equipotent. Xenon’s anesthetic and neuroprotective properties warrant investigation in these models. Therefore, equipotent, subanesthetic concentrations of inhaled anesthetics are needed.

Methods:

Forty-eight Wistar rats (Charles River Laboratories, Kent, United Kingdom) on postnatal day 9 were randomized to eight concentrations of inhaled anesthetics: isoflurane, sevoflurane, or xenon. Exposure was closely monitored in individual metal-based chambers resting on a 35°C mat to maintain normothermia. A 25°C mat was used to stimulate vocalization and a sound recording made (1 min, 1 to 100 kHz). Rectal temperature or partial pressure of carbon dioxide and pH of mixed arteriovenous blood were measured immediately after the exposure. Concentration–response models were constructed using logistic regression (dependent variable: vocalization and explanatory variable: concentration). The effects of all other explanatory variables were assessed by inserting them individually into the model.

Results:

The effective inhaled concentrations preventing cold-stimulated vocalization in 50 and 95% of neonatal rats (EiC50 and EiC95) on postnatal day 9 were 0.46 and 0.89% sevoflurane and 20.15 and 34.81% xenon, respectively. The effect on the EiC50 of all other explanatory variables, including duration, was minimal. Stability of EiC50 isoflurane was not achieved over three durations (40, 80, and 120 min exposure). Partial pressure of carbon dioxide and pH in mixed arteriovenous blood appeared normal.

Conclusions:

The authors report equipotent subanesthetic concentrations of sevoflurane and xenon in neonatal rats with preserved cardiopulmonary function. This may be useful in designing neonatal rodent models of anesthesia.

Measuring xenon in human plasma and blood by gas chromatography/mass spectrometry

RATIONALE

Due to the favorable pharmacokinetic properties and minimal side effects of xenon, its use in modern anesthesia has been well accepted, and recent studies further demonstrated the intra- and postoperative neuro-, cardio-, and reno-protective action of the noble gas. Since the production of the hypoxia-inducible factor 1α (HIF-1α) and its downstream effector erythropoietin as well as noradrenalin reuptake inhibition have been found to play key roles in this context, the question arose as to whether the use of xenon is a matter for doping controls and preventive doping research. The aim of the present study was hence to evaluate whether the (ab)use of xenon can be detected from doping control samples with the instrumentation commonly available in sports drug testing laboratories.

METHODS

Plasma was saturated with xenon according to reported protocols, and the target analyte was measured by means of gas chromatography/time-of-flight and triple quadrupole mass spectrometry with headspace injection. Recording the accurate mass of three major xenon isotopes at m/z 128.9048, 130.9045 and 131.9042 allowed for the unequivocal identification of the analyte and the detection assay was characterized concerning limit of detection (LOD), intraday precision, and specificity as well as analyte recovery under different storage conditions.

RESULTS

Xenon was detected in fortified plasma samples with detection limits of approximately 0.5 nmol/mL to 50 nmol/mL, depending on the type of mass spectrometer used. The method characteristics of intraday precision (coefficient of variation <20%) and specificity demonstrated the fitness-for-purpose of the analytical approach to unambiguously detect xenon at non-physiological concentrations in human plasma and blood. Eventually, authentic plasma and blood samples collected pre-, intra-, and post-operative (4, 8, and 24 h) were positively analyzed after storage for up to 30 h, and provided proof-of-concept for the developed assay.

CONCLUSIONS

If relevant to doping controls, xenon can be determined from plasma and blood samples, i.e. common specimens of routine sports drug testing in the context of Athlete Biological Passport (ABP) analyses. Optimization of sampling and analytical procedures will allow the detection limit to be further improved and potentially enable accurate quantification of the anesthetic agent.

Determination of natural in vivo noble-gas concentrations in human blood

Although the naturally occurring atmospheric noble gases He, Ne, Ar, Kr, and Xe possess great potential as tracers for studying gas exchange in living beings, no direct analytical technique exists for simultaneously determining the absolute concentrations of these noble gases in body fluids in vivo. In this study, using human blood as an example, the absolute concentrations of all stable atmospheric noble gases were measured simultaneously by combining and adapting two analytical methods recently developed for geochemical research purposes. The partition coefficients determined between blood and air, and between blood plasma and red blood cells, agree with values from the literature. While the noble-gas concentrations in the plasma agree rather well with the expected solubility equilibrium concentrations for air-saturated water, the red blood cells are characterized by a distinct supersaturation pattern, in which the gas excess increases in proportion to the atomic mass of the noble-gas species, indicating adsorption on to the red blood cells. This study shows that the absolute concentrations of noble gases in body fluids can be easily measured using geochemical techniques that rely only on standard materials and equipment, and for which the underlying concepts are already well established in the field of noble-gas geochemistry.

Radiofrequency pulse design for the selective excitation of dissolved 129Xe

PURPOSE

To optimize radiofrequency (RF) pulses for the selective excitation of dissolved phase (129)Xe that take into account the very short T2*, while simultaneously, minimally exciting the much larger gas signal.

METHODS

Numerical simulations of Shinnar le-Roux pulses and binomial coefficient composite-element pulses were performed and experimentally implemented on a 1.5 Tesla (T) clinical scanner. These were compared with pulses commonly used for short T2* imaging from the literature. The pulses were then experimentally tested in vivo with healthy volunteers inhaling hyperpolarized (129)Xe using nuclear MR spectroscopy on a 1.5T clinical scanner.

RESULTS

Standard RF excitation pulses inadvertently excite the gas compartment, or are long enough that the T2* of the dissolved compartment deteriorates the received signal. Amplitude modulated binomial composite pulses perform well being short and having high selectivity, however, deteriorate at high amplifier gain setting. Composite pulses using pulse width modulation provide the desired frequency response even in these nonlinear, high gain regimes.

CONCLUSION

Composite pulses provide a means of very narrow band frequency selectivity in a short duration pulse that is well suited to dissolved (129)Xe imaging. Pulse width modulation maintains the desired frequency response even in the presence of amplitude distortion.

Inert gas transport in blood and tissues

This article establishes the basic mathematical models and the principles and assumptions used for inert gas transfer within body tissues-first, for a single compartment model and then for a multicompartment model. From these, and other more complex mathematical models, the transport of inert gases between lungs, blood, and other tissues is derived and compared to known experimental studies in both animals and humans. Some aspects of airway and lung transfer are particularly important to the uptake and elimination of inert gases, and these aspects of gas transport in tissues are briefly described. The most frequently used inert gases are those that are administered in anesthesia, and the specific issues relating to the uptake, transport, and elimination of these gases and vapors are dealt with in some detail showing how their transfer depends on various physical and chemical attributes, particularly their solubilities in blood and different tissues. Absorption characteristics of inert gases from within gas cavities or tissue bubbles are described, and the effects other inhaled gas mixtures have on the composition of these gas cavities are discussed. Very brief consideration is given to the effects of hyper- and hypobaric conditions on inert gas transport.

miR-21 contributes to xenon-conferred amelioration of renal ischemia-reperfusion injury in mice

BACKGROUND

MicroRNAs participate in the regulation of numerous physiological and disease processes. The in vivo role of microRNAs in anesthetics-conferred organoprotection is unknown.

METHODS

Mice were exposed for 2 h to either 70% xenon, or 70% nitrogen, 24 h before the induction of renal ischemia-reperfusion injury. The role of microRNA, miR-21, in renal protection conferred by the delayed xenon preconditioning was examined using in vivo knockdown of miR-21 and analysis of miR-21 target pathways.

RESULTS

Xenon preconditioning provided morphologic and functional protection against renal ischemia-reperfusion injury (n = 6), characterized by attenuation of renal tubular damage, apoptosis, and oxidative stress. Xenon preconditioning significantly increased the expression of miR-21 in the mouse kidney. A locked nucleic acid-modified anti-miR-21, given before xenon preconditioning, knocked down miR-21 effectively, and exacerbated subsequent renal ischemia-reperfusion injury. Mice treated with anti-miR-21 and ischemia-reperfusion injury showed significantly higher serum creatinine than antiscrambled oligonucleotides-treated mice, 24 h after ischemia-reperfusion (1.37 ± 0.28 vs. 0.81 ± 0.14 mg/dl; n = 5; P < 0.05). Knockdown of miR-21 induced significant up-regulation of programmed cell death protein 4 and phosphatase and tensin homolog deleted on chromosome 10, two proapoptotic target effectors of miR-21, and resulted in significant down-regulation of phosphorylated protein kinase B and increased tubular cell apoptosis. In addition, xenon preconditioning up-regulated hypoxia-inducible factor-1α and its downstream effector vascular endothelial growth factor in a time-dependent manner. Knockdown of miR-21 resulted in a significant decrease of hypoxia-inducible factor-1α.

CONCLUSIONS

These results indicate that miR-21 contributes to the renoprotective effect of xenon preconditioning.