Ethyl pyruvate does not require microglia for mediating neuroprotection after excitotoxic injury

Aims: Ethyl pyruvate (EP) mediates protective effects after neuronal injury. Besides a direct conservation of damaged neurons, the modulation of indigenous glial cells has been suggested as one important mechanism for EP-related neuroprotection. However, the specific contribution of glial cells is still unknown. Methods: Organotypic hippocampal slice cultures (OHSC) were excitotoxically lesioned by 50 mmol/L N-methyl-D-aspartate (NMDA, for 4 hours) or left untreated. In an additional OHSC subset, microglia was depleted using the bisphosphonate clodronate (100 mg/mL) before lesion. After removal of NMDA, EP containing culture medium (0.84 mmol/L, 8.4 mmol/L, 42 mmol/L, 84 mmol/L, 168 mmol/L) was added and incubated for 72 hours. OHSC were stained with propidium iodide to visualize degenerating neurons and isolectin IB4-FITC to identify microglia. Effects of EP at concentrations of 0.84, 8.4, and 84 mmol/L (0-48 hours) were analyzed in the astrocytic scratch wound assay. Results: EP significantly reduced neurodegeneration following induced excitotoxicity except for 168 mmol/L. For 84 mmol/L, a reduction in the microglia cells was observed. Microglia depletion did not affect neuronal survival after EP treatment. EP decelerated astrocytic wound closure at 48 hours after injury. Conclusion: EP-mediated neuroprotection seems to be mediated by astrocytes and/or neurons.