4-HYDROXYNONENAL, AN ALDEHYDIC PRODUCT OF MEMBRANE LIPID-PEROXIDATION, IMPAIRS GLUTAMATE TRANSPORT AND MITOCHONDRIAL-FUNCTION IN SYNAPTOSOMES

Removal of extracellular glutamate at synapses, by specific high-affin ity glutamate transporters. is critical to prevent excitotoxic injury to neurons. Oxidative stress has been implicated in the pathogenesis o f an array of prominent neurodegenerative conditions that involve dege neration of synapses and neurons in glutamatergic pathways including s troke, and Alzheimer's, Parkinson's and Huntington's diseases. Althoug h cell culture data indicate that oxidative insults can impair key mem brane regulatory systems including. ion-motive ATPases and amino acid transport systems, the effects of oxidative stress on synapses, and th e mechanisms that mediate such effects, are largely unknown. This stud y provides evidence that 4-hydroxynonenal, an aldehydic product of lip id peroxidation, mediates oxidation-induced impairment of glutamate tr ansport and mitochondrial function in synapses. Exposure of rat cortic al synaptosomes to 4-hydroxynonenal resulted in concentration-and time -dependent decreases in [H-3]glutamate uptake, and mitochondrial funct ion [assessed with the dye (4,5-dimethylthiazol-2-yl)-2,5-diphenyltetr azolium bromide (MTT)]. Other related aldehydes including malondialdeh yde and hexanal had little or no effect on glutamate uptake or mitocho ndrial function. Exposure of synaptosomes to insults known to induce l ipid peroxidation (FeSO4 and amyloid beta-peptide) also impaired gluta mate uptake and mitochondrial Function. The antioxidants propyl gallat e and glutathione prevented impairment of glutamate uptake and MTT red uction induced by FeSO4 and amyloid beta-peptide, but not that induced by 4-hydroxynonenal. Western blot analyses using an antibody to 4-hyd roxynonenal-conjugated proteins showed that 4-hydroxynonenal bound to multiple cell proteins including GLT-1, a glial glutamate transporter present al high levels in synaptosomes. 4-Hydroxynonenal itself induce d lipid peroxidation suggesting that, in addition to binding directly to membrane regulatory proteins, 4-hydroxynonenal potentiates oxidativ e cascades. Collectively, these findings suggest that 4-hydroxynonenal plays important roles in oxidative impairment of synaptic functions t hat would be expected to promote excitotoxic cascades. (C) 1997 IBRO. Published by Elsevier Science Ltd.