Superoxide, hydrogen peroxide, and oxygen toxicity in two free-living nematode species

Two species of free-living nematodes, Turbatrix aceti and Caenorhabditis elegans, exhibited a marked sensitivity to 3 atm of 100% O2. Environmental changes in pH and temperature, which altered nematode respiration, resulted in alterations in the survival of these organisms under high pO2. Levels of defensive enzymes such as superoxide dismutase, catalase, glutathione peroxidase, and dianisidine peroxidase were measured in the two species. No changes in the level of superoxide dismutase or catalase activity were induced by exposure of the nematodes to high pO2. Manipulation of these two enzymes was however achieved using the inhibitors 3-amino-1,2,4-triazole and diethyldithiocarbamate. 3-Amino-1,2,4-triazole (20 mM) eliminated greater than or equal to 80% of the catalase activity in vivo and diethyldithiocarbamate (5 mM) decreased the level of CuZn superoxide dismutase by greater than or equal to 70%. Both of these compounds increased the sensitivity of C. elegans to high pO2 toxicity. Compounds capable of intracellular redox-cycling with O2- -production, such as plumbagin, increased CN- -resistant respiration in the nematodes and imposed an O2-dependent toxicity. These experiments demonstrate the toxicity of intracellular O2- and H2O2 in nematodes and the importance of superoxide dismutase and catalase in providing a defense against these toxic molecules in vivo.