Nitrous oxide: a cause of cancer or chemotherapeutic adjuvant?

The administration of nitrous oxide rapidly inactivates the vitamin B12-dependent enzyme methionine synthase. This inactivation disrupts the normal interrelationships between vitamin B12 and folic acid, and results in altered levels of folic acid derivatives and certain amino acids and their metabolites. Attempts have been made to use the antifolate properties of nitrous oxide to treat patients with leukemia. Although transient improvements may be observed in patients with leukemia who are given nitrous oxide, prolonged administration of nitrous oxide is highly toxic and causes marked hematological and neurological abnormalities. Animal and in vitro studies suggest that the action of nitrous oxide may be tumor selective, and that nitrous oxide may interact with and enhance the therapeutic effect of other antitumor agents. However, there is a delicate balance between the possible beneficial and harmful effects of nitrous oxide, and the conditions for which nitrous oxide may prove useful as a chemotherapeutic adjuvant remain to be defined. Concern has also been raised that nitrous oxide may have carcinogenic potential, especially in operating room and dental personnel who are chronically exposed to trace concentrations of this gas. However, there is no convincing evidence to date that nitrous oxide causes cancer in either animals or humans.