Neuroprotection by nitrous oxide: facts and evidence.
OBJECTIVE
Preliminary studies have shown that nitrous oxide, like xenon, may possess potentially neuroprotective properties. However, because of its possible neurotoxic and proneurotoxic effects (obtained under particular conditions) and its bad reputation at anesthetic concentrations, no thorough investigations have been performed on the potentially neuroprotective properties of nitrous oxide. The aim of this study was to investigate the possible neuroprotective effects of nitrous oxide at nonanesthetic concentrations on different models of excitotoxic insult and brain ischemia.


RESULTS
Here, we show using multiple models of ex vivo and in vivo excitotoxic insults and brain ischemia that nitrous oxide, administered alone at nonanesthetic doses, offers global neuroprotection from reduction of neurotransmitter release induced by ischemia to reduction of subsequent cell injury. In vivo, in rats subjected to transient cerebral ischemia, nitrous oxide at 50 vol% offers full neuroprotection at both the histologic and neurologic outcome levels when administered up to 2 hrs, but not 3 hrs, after ischemia onset.


CONCLUSIONS
These data provide experimental evidence that nitrous oxide, which is a cost-efficient and easily available gas, has potentially neuroprotective properties in rodents when given alone at nonanesthetic concentrations. Therefore, because there is a lot at stake for the affected patients and society--in terms of easy access to treatment, profound impact of brain damage, cost of treatment, and subsequent financial cost on society--we believe that further studies should investigate thoroughly the possible potential clinical interest of nitrous oxide for the treatment of ischemic stroke in terms of optimal indications, type of ischemic injury, duration and time points for treatment, and the optimal concentration of gas to be used in clinical circumstances.
Haelewyn
Benoit
B
NNOXe Pharmaceuticals, Avenue des Hôtels, Québec, QC, Canada.
David
Hélène N
HN
Rouillon
Christophe
C
Chazalviel
Laurent
L
Lecocq
Myriam
M
Risso
Jean-Jacques
JJ
Lemaire
Marc
M
Abraini
Jacques H
JH
D000818:Animals; D001831:Body Temperature; D001921:Brain / Q000187:drug effects* / Q000378:metabolism; D002545:Brain Ischemia / Q000209:etiology / Q000503:physiopathology / Q000517:prevention & control*; D004298:Dopamine / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005947:Glucose / Q000378:metabolism; D066298:In Vitro Techniques; D020244:Infarction, Middle Cerebral Artery / Q000150:complications; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D008297:Male; D009043:Motor Activity; D016202:N-Methylaspartate; D018696:Neuroprotective Agents / Q000494:pharmacology* / Q000627:therapeutic use; D009609:Nitrous Oxide / Q000494:pharmacology* / Q000627:therapeutic use; D010100:Oxygen / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley
D018696:Neuroprotective Agents; D016202:N-Methylaspartate; D007770:L-Lactate Dehydrogenase; D005947:Glucose; D009609:Nitrous Oxide; D010100:Oxygen; D004298:Dopamine