title: Inhibitors of free radical formation fail to attenuate direct beta-amyloid25-35 peptide-mediated neurotoxicity in rat hippocampal cultures.
abstract: The direct neurotoxic action of the beta-amyloid protein, the major constituent of senile plaques, may represent the underlying cause of neuronal degeneration observed in Alzheimer's disease. The apoptotic-mediated neuronal death induced by beta-amyloid appears to reside in its ability to form Ca(2+)-permeable pores in neuronal membranes resulting in an excessive influx of Ca2+ and the induction of neurotoxic cascades. It is possible that during beta-amyloid exposure a Ca(2+)-mediated increase in free radical generation may exceed the defensive capacity of cells and thus lead to cell death. Consequently, in the present study we have investigated the effect of a panoply of antioxidants and inhibitors of free radical formation on the development of beta-amyloid neurotoxicity. Acute exposure of rat hippocampal neurons to "aged" beta-amyloid25-35 peptide (5-50 microM) induced a slow, concentration-dependent apoptotic neurotoxicity (25-85%) during a 6 day exposure. Co-incubation of cultures with beta-amyloid25-35 peptide (25 microM) and inhibitors of nitric oxide synthase and/or xanthine oxidase (NG-monomethyl-L-arginine [1 mM), N omega-nitro-L-arginine [1 mM], oxypurinol [100 microM], allopurinol [100 microM]), important mediators of nitric oxide, superoxide, and hydroxyl radical formation, did not attenuate beta-amyloid neurotoxicity. Similarly, a reduction in free radical generation by selective inhibition of phospholipase-A2 cyclooxygenase, and lipoxygenase activities with quinacrine (0.5 microM), indomethacin (50 microM), and nor-dihydroguaiaretic acid (0.5 microM), respectively, did not reduce the proclivity of beta-amyloid to induce cell death. Exposure of cultures to catalase (25 U/ml) and/or superoxide dismutase (10 U/ml) as well as the free radical scavengers vitamin E (100 microM), vitamin C (100 microM), glutathione (100 microM), L-cysteine (100 microM), N-acetyl-cysteine (100 microM), deferoxamine (5 microM), or haemoglobin (35 micrograms/ml) failed to attenuate the neurotoxic action of beta-amyloid. On the other hand, pre-treatment of cultures with subtoxic concentrations of beta-amyloid peptide significantly increased the vulnerability of neurons to H2O2 exposure and suggest that beta-amyloid peptide renders neurons more sensitive to free radical attack. However, a potential beta-amyloid-mediated increase in free radical formation is not a proximate cause of the neurotoxic mechanism of beta-amyloid in vitro.
authors.affiliation: INSERM U-336, Développement, Plasticité et Vieillessement du Système Nerveux, Ecole Nationale Supérieure de Chimie, Montpellier, France.
authors.forename: B P
authors.initials: BP
authors.lastname: Lockhart
authors.forename: C
authors.initials: C
authors.lastname: Benicourt
authors.forename: J L
authors.initials: JL
authors.lastname: Junien
authors.forename: A
authors.initials: A
authors.lastname: Privat
mesh_terms: D000493:Allopurinol / Q000494:pharmacology; D000544:Alzheimer Disease / Q000378:metabolism / Q000473:pathology; D000594:Amino Acid Oxidoreductases / Q000037:antagonists & inhibitors; D016229:Amyloid beta-Peptides / Q000494:pharmacology*; D000818:Animals; D001120:Arginine / Q000031:analogs & derivatives / Q000494:pharmacology; D002374:Catalase / Q000494:pharmacology; D016923:Cell Death / Q000187:drug effects; D002478:Cells, Cultured; D004622:Embryo, Mammalian; D016166:Free Radical Scavengers / Q000494:pharmacology*; D005609:Free Radicals / Q000037:antagonists & inhibitors / Q000378:metabolism; D006624:Hippocampus / Q000378:metabolism*; D006801:Humans; D007213:Indomethacin / Q000494:pharmacology; D009637:Masoprocol / Q000494:pharmacology; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D009498:Neurotoxins / Q000494:pharmacology*; D019001:Nitric Oxide Synthase; D019335:Nitroarginine; D010117:Oxypurinol / Q000494:pharmacology; D010446:Peptide Fragments / Q000494:pharmacology*; D011796:Quinacrine / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013482:Superoxide Dismutase / Q000494:pharmacology; D014969:Xanthine Oxidase / Q000037:antagonists & inhibitors; D019323:omega-N-Methylarginine
chemical_list: D016229:Amyloid beta-Peptides; D016166:Free Radical Scavengers; D005609:Free Radicals; D009498:Neurotoxins; D010446:Peptide Fragments; C074636:amyloid beta-protein (25-35); D019335:Nitroarginine; D019323:omega-N-Methylarginine; D000493:Allopurinol; D009637:Masoprocol; D001120:Arginine; D002374:Catalase; D019001:Nitric Oxide Synthase; D013482:Superoxide Dismutase; D014969:Xanthine Oxidase; D000594:Amino Acid Oxidoreductases; D010117:Oxypurinol; D011796:Quinacrine; D007213:Indomethacin