Xenon, the "inert" gaseous anesthetic, is an antagonist at the N-methyl-D-aspartate (NMDA)-type glutamate receptor. Because of the pivotal role that NMDA receptors play in neuronal injury, the authors investigated the efficacy of xenon as a neuroprotectant in both in vitro and in vivo paradigms.
In a mouse neuronal-glial cell coculture, injury was provoked either by NMDA, glutamate, or oxygen deprivation and assessed by the release of lactate dehydrogenase into the culture medium. Increasing concentrations of either xenon or nitrogen (10-75% of an atmosphere) were coadministered and maintained until injury was assessed. In separate in vivo experiments, rats were administered N-methyl-dl-aspartate and killed 3 h later. Injury was quantified by histologic assessment of neuronal degeneration in the arcuate nucleus of the hypothalamus.
Xenon exerted a concentration-dependent protection against neuronal injury provoked by NMDA (IC(50) = 19 +/- 6% atm), glutamate (IC(50) = 28 +/- 8% atm), and oxygen deprivation (IC(50) = 10 +/- 4% atm). Xenon (60% atm) reduced lactate dehydrogenase release to baseline concentrations with oxygen deprivation, whereas xenon (75% atm) reduced lactate dehydrogenase release by 80% with either NMDA- or glutamate-induced injury. In an in vivo brain injury model in rats, xenon exerted a concentration-dependent protective effect (IC(50) = 78 +/- 8% atm) and reduced the injury by 45% at the highest xenon concentration tested (75% atm).
Xenon, when coadministered with the injurious agent, exerts a concentration-dependent neuroprotective effect at concentrations below which anesthesia is produced in rodents. Unlike either nitrous oxide or ketamine (other anesthetics with NMDA antagonist properties), xenon is devoid of both neurotoxicity and clinically significant adverse hemodynamic properties. Studies are proposed to determine whether xenon can be used as a neuroprotectant in certain clinical settings.
"This deprivation activates excitoxicity in which NMDA glutamate receptors are over stimulated, leading to neuronal death through apoptosis and necrosis . It has been shown that Xenon reduces neuronal injury by its administration before and during the insult [20,44,54]. Bantel et al. demonstrated neuronal preconditioning property of Xenon by exposing neuronal-glial co-cultures to 75% Xenon for 2 hours  as illustrated in Table 1. "
[Show abstract][Hide abstract] ABSTRACT: 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.
"The neuroprotective properties of xenon and sevoflurane has been evaluated in both in vivo and in vitro studies , , , , , , , , , but the underlying mechanisms have not been clearly identified. Xenon is a competitive N-methyl-D-aspartate (NMDA) receptor antagonist at the glycine site , , which may contribute to xenon-induced neuroprotective effects . "
[Show abstract][Hide abstract] ABSTRACT: It is not possible to identify all pregnancies at risk of neonatal hypoxic-ischemic encephalopathy (HIE). Many women use some form of analgesia during childbirth and some anesthetic agents have been shown to be neuroprotective when used as analgesics at subanesthetic concentrations. In this study we sought to understand the effects of two anesthetic agents with presumptive analgesic activity and known preconditioning-neuroprotective properties (sevoflurane or xenon), in reducing hypoxia-induced brain damage in a model of intrauterine perinatal asphyxia. The analgesic and neuroprotective effects at subanesthetic levels of sevoflurane (0.35%) or xenon (35%) were tested in a rat model of intrauterine perinatal asphyxia. Analgesic effects were measured by assessing maternal behavior and spinal cord dorsal horn neuronal activation using c-Fos. In separate experiments, intrauterine fetal asphyxia was induced four hours after gas exposure; on post-insult day 3 apoptotic cell death was measured by caspase-3 immunostaining in hippocampal neurons and correlated with the number of viable neurons on postnatal day (PND) 7. A separate cohort of pups was nurtured by a surrogate mother for 50 days when cognitive testing with Morris water maze was performed. Both anesthetic agents provided analgesia as reflected by a reduction in the number of stretching movements and decreased c-Fos expression in the dorsal horn of the spinal cord. Both agents also reduced the number of caspase-3 positive (apoptotic) neurons and increased cell viability in the hippocampus at PND7. These acute histological changes were mirrored by improved cognitive function measured remotely after birth on PND 50 compared to control group. Subanesthetic doses of sevoflurane or xenon provided both analgesia and neuroprotection in this model of intrauterine perinatal asphyxia. These data suggest that anesthetic agents with neuroprotective properties may be effective in preventing HIE and should be tested in clinical trials in the future.
PLoS ONE 05/2012; 7(5):e37020. DOI:10.1371/journal.pone.0037020 · 3.23 Impact Factor
"Xenon has been approved in Europe as a medical gas, and its utility has been demonstrated through clinical and basic research studies. Although major interest focuses on xenon's hemodynamic and analgesic properties, increasing interest has recently focused on its potential long-lasting neuroprotective properties, which have been demonstrated both in in vivo and in vitro models of neuronal injury     . Similar properties have been observed in the setting of anesthetic preconditioning   , suggesting that xenon may play a useful clinical role in therapeutically unmet disease states such as stroke or neonatal asphyxia. "
[Show abstract][Hide abstract] ABSTRACT: Xenon can induce cell and organ protection through different molecular mechanisms related to oxygen level. We explored the effect of xenon on oxygen-related signalling in the central nervous system via hypoxia inducible factor 1 alpha (HIF-1α) and mammalian target of rapamycin (mTOR). Methods. Postnatal day 7 (P7) Sprague Dawley rats were exposed to 25% oxygen/75% nitrogen (air group) or 25% oxygen/75% xenon (treatment group) for 120 min. Brains were collected immediately (transcript analysis—relative real-time polymerase chain reaction) or 24 hours (protein analysis—immunohistochemistry) after the 120-minute exposure period; peak anesthetic preconditioning has been previously identified at 24 hours post-exposure. Results. HIF-1α transcript and protein levels were found to be increased in xenon-exposed compared to air-exposed brains. Sustained nuclear translocation of the protein, accounting for an increased activity of HIF-1α, was also noted. mTOR transcript analysis revealed no significant difference between xenon-exposed and air-exposed brains immediately after the 120-minute exposure. Conclusion. Our data suggest that xenon induces the upregulation of HIF-1α transcription and translation, which may contribute to xenon's neuroprotective preconditioning effect. However, given that xenon exposure did not affect mTOR transcription, further investigation into other signalling cascades mediating xenon’s effects on HIF-1α in developing brain is warranted.
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