Background: 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.
Methods: 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.
Results: 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).
Conclusions: 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.