Aminooxyacetic acid results in excitotoxin lesions by a novel indirect mechanism
Nervous System Diseases
Aminooxyacetic acid (AOAA) is an inhibitor of several pyridoxal phosphate-depedent enzymes in the brain. In the present experiments intrastriatal injections of AOAA produced dose-dependent excitotoxic lesions. The lesions were dependent on a pyridoxal phosphate mechanisms because pyridoxine blocked them. The lesions were blocked by the noncompetitive N-methyl-D-aspartate (NMDA) antagonist MK-801 and by coinjection of kynurenate, a result indicating an NMDA receptor-mediated excitotoxic process. Electrophysiologic studies showed that AOAA does not directly activate ligand-gated ion channels in cultured cortical or striatal neurons. Pentobarbital anesthesia attenuated the lesions. AOAA injections resulted in significant increases in lactate content and depletions of ATP levels. AOAA striatal lesions closely resemble Huntington's disease both neurochemically and histologically because they show striking sparing of NADPH-diaphorase and large neurons within the lesioned area. AOAA produces excitotoxic lesions by a novel indirect mechanism, which appears to be due to impairment of intracellular energy metabolism, secondary to its ability to block the mitochondrial malate-aspartate shunt. These results raise the possibility that a regional impairment of intracellular energy metabolism may secondarily result in excitotoxic neuronal death in chronic neurodegenerative illnesses, such as Huntington's disease.