TNF alpha potentiates glutamate neurotoxicity by inhibiting glutamate uptake in organotypic brain slice cultures: neuroprotection by NF kappa B inhibition

Glutamate and the proinflammatory cytokine, tumor necrosis factor alpha (TNF alpha), have been suggested to contribute to neurodegenerative diseases. We investigated the interaction of TNF alpha and glutamate on neuronal cell death using fluorescence propidium iodide uptake in rat organotypic hippocampal-entorhinal cortex (HEC) brain slice culture that maintains the cytoarchitecture of the intact brain. Time course and concentration studies indicate that glutamate produced significant neuronal cell death in all four brain areas examined, for example, entorhinal cortex, hippocampal CA1 and CA3 fields, and dentate gyrus. TNF alpha alone at concentration of 20 ng/ml caused little or no detectable neuronal cell death, however, when combined with submaximal glutamate (3.3 mM), TNF alpha significantly increased and accelerated glutamate neurotoxicity. TNF alpha potentiation of glutamate neurotoxicity is blocked by NMDA receptor antagonists but not by AMPA antagonists CNQX and NBQX. Studies directly measuring [14C]-glutamate uptake in HEC slices indicate that TNF alpha dose-dependently inhibited glutamate uptake. Further, inhibitors of glial glutamate transporters potentiated glutamate neurotoxicity similar to TNF alpha. The antioxidant butylated hydroxytoluene (BHT) and the NF kappa B inhibitor PTD-p65 peptide inhibit NF kappa B activation and TNF alpha potentiation of glutamate neurotoxicity. BHT prevented the inhibition of TNFalpha on glutamate transport in HEC slices and also blocked nuclear translocation of NF kappa B subunit p65. These data indicate that TNF alpha and glutamate can act synergistically to induce neuronal cell death. TNF alpha potentiation of glutamate neurotoxicity through the blockade of glutamate transporter activity may represent an important mechanism of neurodegeneration associated with neuroinflammation.