Early and late cytotoxic effects of external application of the Alzheimer's Abeta result from the initial formation and function of Abeta ion channels.

Extracellular application of the Alzheimer's beta-amyloid (Abeta) peptide evokes a series of cellular responses that leads to the death of cells by apoptosis. Some responses to freshly prepared Abeta occur immediately, including changes in intracellular calcium concentration and changes in membrane permeability and phosphatidylserine asymmetry. We show here that the cytotoxic action of externally applied Abeta, such as caspase activation and apoptotic loss of cell viability, occurs and persists even several days after Abeta is removed from the medium. We find that the mechanism for this persistent cytotoxic action of extracellular Abeta is based on the sustained activity of active Abeta ion channels that remain incorporated in the cell membrane. To confirm this assessment, we blocked the late cytotoxic action of Abeta with the classically known Abeta channel blockers zinc and tromethamine. To further validate this conclusion, we developed a specific peptide segment from the sequence forming the mouth of the Abeta channel to block Abeta Ca2+ channels acutely and to block late Abeta effects on caspase activation and apoptosis. This is the first report of a specific Abeta channel blocker compound, NA4, which efficaciously and potently blocks the most known cellular responses to Abeta.