Free radical reactions and the inhibitory and lethal actions of high-pressure gases.

This study was designed to test whether free radicals are involved in the deleterious effects of compressed gases on cells. The actions of xenon, nitrous oxide, argon, nitrogen, helium, and oxygen and their effects on the toxicity of paraquat (methyl viologen) were studied using Escherichia coli. Growth of E. coli in trypticase-soy broth in an atmosphere of 1.36 MPa (13.6 atm) N2O resulted in an induction of superoxide dismutase (SOD). In addition, when SOD was induced by oxygen, the resulting cells had increased resistance to the killing action of N2O. The toxicity of paraquat was increased in the presence of N2O but not He, N2, or Ar. However, addition of any of the latter three gases to N2O resulted in increased toxicity of paraquat beyond that due to N2O alone. Oxygen is known to increase the reaction of paraquat radicals within cells and to reduce leakage of the radicals out through the cell membrane. N2O and Xe seem to have this same action, and He, N2, or Ar could enhance the actions of N2O, Xe, or O2. The data indicate that the inhibitory and lethal actions of these gases may be due to enhanced reactivity of radicals with cell components and reduced leakage of the radicals to the environment.