Catalase protection of neuronal survival in vitro is not directed to the accumulation of peroxides in the culture medium.
Walicke et al. (1986, J. Neurosci. 6, 1114-1121) have shown that catalase can replace the pyruvate requirement for survival of CNS neurons cultured in vitro. Since presently the only known function of catalase is the enzymatic degradation of hydrogen peroxide to water and oxygen, the simplest interpretation of the ability of catalase to support neuronal survival would be that catalase removes from the culture medium hydrogen peroxide. To test this hypothesis 8-day embryonic chick forebrain cells were cultured for 24 hr in a modified Eagle's Basal Medium with the serum-free supplement N1 (HEBM/N1) in the presence or absence of Phenol Red, 20 micrograms/ml catalase, 1 mM pyruvate, and/or 25 mM N-2-hydroxyethylpiperazine-N'-2-ethane-sulfonic acid (HEPES) on a polyornithine-laminin substratum. The various media were then assayed for peroxide content using the potassium iodide method described by Wang and Nixon (1978, In Vitro 14, 714-722). The present data reveal that (1) HEBM/N1 normally contains approximately 50 microM peroxides, little of which is hydrogen peroxide, (2) the organic peroxide levels accumulating in this medium are not reduced by either catalase or pyruvate, and (3) medium modifications can reduce to no longer detectable levels the peroxides accumulating in the medium, but catalase or pyruvate is still required for neuronal survival. We conclude that catalase must exert its survival-promoting action at levels other than peroxides accumulating in the culture medium.