Cyclooxygenase-2-dependent neuronal death proceeds via superoxide anion generation

Cyclooxygenase-2 (COX-2) expression is induced in the neurons of the pathologic brain and elevated COX-2 expressions can lead to neuronal death. Here, we report that COX-2 induction in cortical neurons induced by LPS pretreatment for more than 12 h increased the neurotoxic effects of low doses of Fe²⁺ by more than 2.5-fold. Moreover, the neurotoxicity induced by 30 μM Fe²⁺ in LPS-pretreated cells exceeded that induced by 100 μM Fe²⁺ in LPS-untreated cells. LPS pretreatment also similarly aggravated the neurotoxic effects of low doses of H₂O₂, Zn²⁺, and sodium nitroprusside. This LPS-induced Fe²⁺-toxicity enhancement was blocked by trolox, vitamin C, the SOD mimetic MnTBAP, and by the COX-2-specific inhibitor NS398, but not by inhibitors of xanthine oxidase, NADPH oxidase, NOS, and monoamine oxidase. Cortical neurons with enhanced COX-2 expression showed superoxide generation, GSH depletion, and lipid peroxidation in response to low doses of Fe²⁺, and all of these changes were repressed by MnTBAP or NS398. Consistent with this pharmacological data, cortical neurons prepared from COX-2 knockout mice showed marked reductions in LPS-induced Fe²⁺-toxicity enhancement and superoxide generation. These results suggest that COX-2 functions as a cellular factor which induces superoxide-mediated cell death in primary cortical neurons.