HEMOGLOBIN POTENTIATES EXCITOTOXIC INJURY IN CORTICAL CELL-CULTURE

Excessive activation of glutamate receptors may contribute to neuronal loss after a traumatic or ischemic central nervous system insult, Suc h injuries are often associated with hemorrhage and extravasation of h emoglobin, a prooxidant and putative neurotoxin. In this study, we inv estigated the effect of nontoxic concentrations of hemoglobin on the n eurotoxicity of the synthetic glutamate receptor agonists NMDA, AMPA, and kainate in primary murine cortical cultures, Continuous exposure t o each excitotoxin alone for 24-28 h produced concentration-dependent neuronal death (EC(50) about 12 mu M for AMPA, 50 mu M for kainate, an d 12 mu M for NMDA), Hemoglobin 0.25-1.0 mu M consistently potentiated the neurotoxicity of low concentrations of AMPA and kainate, increasi ng neuronal loss by about 150% at 6 mu M AMPA and by about 90% at 30 m u M kainate, This effect was attenuated by the iron chelator deferoxam ine and the alpha-tocopherol analogue trolox, Hemoglobin coexposure ha d less impact on slowly triggered NMDA neurotoxicity, significantly in creasing neuronal death only at agonist concentrations that alone prod uced little or no injury, Hemoglobin pretreatment had no effect on the rapidly triggered excitotoxicity induced by brief exposure to high co ncentrations of NMDA, These results suggest that hemoglobin may contri bute to neuronal loss after CNS hemorrhage by exacerbating excitotoxic ity, At moderate levels of agonist exposure, this effect may be somewh at selective for the AMPA/kainate component of injury.