Characterization of the neuroprotective effects of estrogens on hydrogen peroxide-induced cell death in hippocampal HT22 cells: time and dose-dependency.

Time and dose-dependency of the effects of estrogens (17-beta estradiol, estrone) and non-estrogenic steroids (progesterone, dexamethasone and methylprednisolone) on the toxicity of hydrogen peroxide were examined in mouse hippocampal HT22 cells. Hydrogen peroxide, an important intermediate of various disease-relevant oxidative stressors, induced cell death in HT22 cells in extracellular concentrations between 0.5 and 1.5 mM in a dose-dependent manner (EC50=0.95 mM). Regarding the underlying mechanisms of toxicity, incubation with hydrogen peroxide did not induce lipid peroxidation in living HT22 cells under these conditions. After preincubation with estrogens and non-estrogenic steroids for 22 hours, estrogen compounds protected the cells against hydrogen peroxide toxicity. Estrogens showed a maximal protective effect at 60-70% of hydrogen peroxide toxicity which diminished at higher and lower concentrations of the toxic challenge. Dose-dependency studies of estrogens revealed that concentrations of 1 microM already exerted a significant cytoprotective effect. Co- and postincubation with 17-beta estradiol and estrone also resulted in significant cell protection even if the estrogens were added 30 min after the initiation of the challenge with hydrogen peroxide. In contrast, preincubation with other steroids like progesterone, a physiological gonadal steroid, dexamethasone, a synthetic glucocorticoid and methylprednisolone, a glucocorticoid with radical scavenging properties, did not protect the cells against hydrogen peroxide toxicity but resulted in a dose-related decrease of HT22 cell survival in the course of the toxic challenge.