Apolipoprotein E protects against oxidative stress in mixed neuronal–glial cell cultures by reducing glutamate toxicity

Abstract

Apolipoprotein E (ApoE) deficiency has been shown to adversely affect outcome after transient cerebral ischemia and head trauma. Since oxidative stress contributes to these injuries, the ability of ApoE to reduce irreversible oxidative damage was studied in primary mixed neuronal–glial cell cultures. Cells (13–16 days in vitro) were exposed to 50 μM hydrogen peroxide (H 2O 2) for 30 min, and toxicity was determined by the release of lactate dehydrogenase (LDH) 24 h after exposure. The presence of recombinant human ApoE2 (100, 300, or 1000 nM) in the culture media partially protected against oxidative injury. This protection was not reversed by pre-treatment with receptor associated protein. The NMDA receptor antagonist, MK-801, also provided partial protection against H 2O 2 toxicity. The degree of protection was similar to that conferred by ApoE treatment. The protective effects of ApoE and MK-801 were not additive; no ApoE protection was observed in cultures treated with MK-801 prior to H 2O 2 exposure. ApoE treatment had no effect on H 2O 2 stimulated glutamate release, but did increase the rate of glutamate uptake via the high affinity glutamate transporter in H 2O 2 treated cultures. Pre-treatment with ApoE also conferred partial protection against glutamate-induced LDH release. Taken together, these findings suggest that ApoE protects mixed neuronal–glial cell cultures against irreversible oxidative injury from H 2O 2 by reducing secondary glutamate excitotoxicity.