Antioxidant enzymes in human tears

Minimally stimulated tear samples collected from human subjects were assayed for the major antioxidant enzymes: superoxide dismutase, catalase and glutathione peroxidase. No catalase or glutathione peroxidase activity was detected. However, human tear film does contain the CuZn superoxide dismutase (103 +/- 32 ng/mg soluble protein), which is inactivated by hydrogen peroxide (0.2 mM). These data indicate that the tear film has the enzyme generally required for control of inflammatory conditions but is lacking the usual physiological defense systems against the toxicity of hydrogen peroxide. Concern has been raised as to the safety of contact lens disinfectant solutions containing hydrogen peroxide. These results indicate that the tear film is lacking the enzyme systems to provide significant protection to the cornea, to the tear film itself, or to the SOD of the tear film from the oxidant action of hydrogen peroxide.