ABSTRACT
The fact that Alzheimer's beta amyloid (Aâ) peptides forms cation channels in lipid bilayers was discovered during the course of our experiments in the laboratory of "Guayo" Rojas at NIH in Bethesda, Maryland (USA). Recently, we found that the Aâ ion channel could be blocked selectively with small peptides that copy the amino acid sequence of the predicted mouth region of the Aâ channel pore. We now have searched for the essential amino acid residues required for this blocking effect by mutations. We found that the ability of peptides to block Aâ channel activity could be lost by replacement of histidines 13 and 14 by alanine or lysine. The amino acid substitution also resulted in the loss of the capacity of the peptides to protect cells from Aâ cytotoxicity. These data thus contribute to the definition of the region of the Aâ sequence that participates in the formation of the channel pore. Additionally, these data support the hypothesis that the ion channel activity of Ab contributes significantly to the cytotoxic properties of Aâ. These data also emphasize the potential value in using inhibition of Aâ ion channel activity as an end point for Alzheimer's disease drug discovery.
Subject(s)
Animals , Rats , Alzheimer Disease/metabolism , Amyloid beta-Peptides/metabolism , Histidine/toxicity , Ion Channels/antagonists & inhibitors , Amino Acid Sequence , Alzheimer Disease/genetics , Amyloid beta-Peptides/genetics , Cell Line, Tumor , Cell Membrane/chemistry , Cell Survival/drug effects , Electric Conductivity , Membrane Potentials , Models, Biological , Molecular Sequence DataABSTRACT
The role of hydroxyl radical (OH.) in H2O2-mediated stimulation of lipid peroxidation in microsomes of bovine pulmonary arterial smooth muscle tissue and the protective effects of DIDS, the anion channel blocker have been studied. Treatment of microsomes with H2O2 (1 mM) stimulate iron release, OH. production and lipid peroxidation. Pretreatment with DFO (an iron chelator) or DMTU (a hydroxyl radical scavenger) prevents OH. production and thereby reduces lipid peroxidation without any appreciable reduction of iron release. Simultaneous treatment of either DFO or DMTU with H2O2 significantly reduces lipid peroxidation and prevents OH. production without any significant reduction of iron release. However, addition of DFO or DMTU 2 min after treatment of the microsome with H2O2 does not produce any significant reduction of lipid peroxidation, OH production and iron release. Pretreatment of microsomes with DIDS markedly reduces the stimulation of lipid peroxidation without appreciably altering the increase in OH. production and iron release caused by H2O2.