Dependence of excitotoxic neurodegeneration on mitochondrial aconitase inactivation

Using the inactivation of mitochondrial and cytosolic aconitases as markers of compartment-specific superoxide (O-2(-)) production, we show that oxyge n-glucose deprivation (OGD) or excitotoxin exposure produce a time-dependen t inactivation of mitochondrial, but not cytosolic, aconitase in cortical c ultures. To determine if mitochondrial O-2(-) production was an important d eterminant in neuronal death resulting from OGD, metalloporphyrins with var ying superoxide dismutase (SOD) activity were tested for their ability to p rotect against mitochondrial aconitase inactivation and cell death. OGD-ind uced mitochondrial aconitase inactivation and cell death was inhibited by m anganese tetrakis (4-benzoic acid) porphyrin (MnTBAP), manganese tetrakis ( N-ethylpyridinium-2yl) porphyrin (MnTE-2-PyP) and NMDA receptor antagonists . By contrast, NMDA- or kainate (KA)-induced mitochondrial aconitase inacti vation and cell death was inhibited by MnTBAP, but not MnTE-2-PyP. Moreover , both MnTBAP and MnTE-2-PyP penetrated mitochondrial fractions of cortical cells. These data suggest that mitochondrial aconitase inactivation closel y correlates with subsequent neuronal death following excitotoxicity produc ed by OGD or NMDA/KA exposure. Assessment of biological rather biochemical antioxidant activities better predicted neuroprotection by metalloporphyrin s. Moreover, antioxidants that protect oxidant-sensitive mitochondrial targ ets such as aconitase may be useful as therapies for disease states involvi ng excitotoxicity.