Estradiol protects against injury-induced cell death in cortical explant cultures: a role for estrogen receptors

Estradiol has been shown to exert trophic and protective actions in the bra in. Our laboratory has shown that in vivo, low physiological levels of estr adiol protect the female rat brain against ischemic injury. In the present study, we used organotypic cortical explant cultures to begin to decipher t he mechanisms of estradiol's actions. Injury was induced by exposure to kai nic acid or potassium cyanide/2-deoxyglucose (KCN/2-DG) for varying lengths of time, and cell death was monitored by LDH release at 2, 6, 12, 24, 48, 72 and 96 h after injury. We found that exposure to 1 mM KCN/2 mM 2-DG for 2 h produced consistent delayed cell death that was detectable by 24 h. The presence of 17 beta-estradiol (E2) during the 7 days prior to injury signi ficantly reduced the extent of cell death; whereas, administration of E2 at the time of injury did not protect. The protective effects of estradiol we re dose dependent. Low doses of E2 (1, 10, and 30 nM) significantly reduced cell death; however, higher concentrations of E2 (>60 nM) had no protectiv e effect. The observations that low levels of E2 protect against cell death , and that pretreatment is required suggest that the protective actions of estradiol may involve estrogen receptors. Therefore, we examined the abilit y of 17 alpha-estradiol, which does not efficiently activate the estrogen r eceptor, and the addition of the estrogen receptor antagonist, ICI 182,780, to influence the extent of cell death induced by KCN/2-DG. 17 alpha-Estrad iol failed to protect, and ICI 182,780 prevented E2 from protecting against cell death. Furthermore, E2 pretreatment is required for more than 24 h to be neuroprotective. Our results clearly show that in cortical explant cult ures, estradiol protects cells against ischemic injury, and suggest that th ese protective actions involve estrogen receptors. (C) 2000 Elsevier Scienc e B.V. All rights reserved.