The mechanisms of neuronal death produced by mitochondrial toxin 3-nitropropionic acid: the roles of N-methyl-D-aspartate glutamate receptors and mitochondrial calcium overload.

Previous studies showed that 3-nitropropionic acid, an irreversible inhibitor of succinate dehydrogenase, produced neuronal death secondary to perturbed intracellular calcium homeostasis. However, the response of intramitochondrial calcium ([Ca(2+)](m)) to 3-nitropropionic acid remains unknown. In this study, we investigated the roles of and relationships among [Ca(2+)](m) overload, mitochondrial reactive oxygen species, and mitochondrial membrane depolarization in 3-nitropropionic acid-induced neuronal death. Following 1 mM 3-nitropropionic acid treatment on primary rat neuronal cultures, there was a gradual increase of [Ca(2+)](m) beginning at 2-4 h post 3-nitropropionic acid application, and a twofold increase of mitochondrial reactive oxygen species at 4 h. These were followed by mitochondrial membrane depolarization at 6-8 h post-treatment. By inhibiting [Ca(2+)](m) uptake, Ruthenium Red attenuated the production of reactive oxygen species, and prevented the 3-nitropropionic acid-induced mitochondrial membrane depolarization and 70% of apoptotic neuronal death (P<0.001). Inhibition of caspase activation attenuated the elevation of [Ca(2+)](m) (P<0.001), indicating that caspase activation plays a role in the elevation of [Ca(2+)](m). MK-801, an antagonist of N-methyl-D-aspartate (NMDA) glutamate receptors, prevented 3-nitropropionic acid-induced [Ca(2+)](m) elevation, caspase-3 activation, mitochondrial depolarization, and neuronal death. We conclude that the activation of NMDA glutamate receptor contributes to mitochondrial alterations induced by 3-nitropropionic acid. Inhibition of its activation and [Ca(2+)](m) overload with subsequent mitochondrial membrane depolarization can therefore attenuate the neuronal death induced by 3-nitropropionic acid.