INHIBITORS OF FREE-RADICAL FORMATION FAIL TO ATTENUATE DIRECT BETA-AMYLOID(23-35) PEPTIDE-MEDIATED NEUROTOXICITY IN RAT HIPPOCAMPAL CULTURES

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 Ca2+-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 Ca2+- 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-amyloid(25-35) peptide (5-50 mu M) induced a slow, concentration-dependent apoptotic neurotoxicity (25-85%) during a 6 day exposure. Co-incubation of cultures with beta-amyloid(25-35) peptide (25 mu M) and inhibitors of nitric oxide synthase and/or xanthine oxidase (N-G-monomethyl-L-arginine [1 mM], N omega-nitro-L-arginine [1 mM], oxypurinol [100 mu M], allopurinol [100 mu M]), 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-A(2) cyclooxygenase, and lipoxygenase activities with quinacrine (0.5 mu M), indomethacin (50 mu M), and nor-dihydroguaiaretic acid (0.5 mu M), 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 mu M), vitamin C (100 mu M), glutathione (100 mu M),