Cytotoxic amyloid peptides inhibit cellular 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction by enhancing MTT formazan exocytosis.
Amyloid beta peptide (A beta) neurotoxicity is believed to play a central role in the pathogenesis of Alzheimer's disease. An early indicator of A beta toxicity is the inhibition of cellular 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction to MTT formazan, a widely used assay for measuring cell viability. In this report we show that A beta and other cytotoxic amyloid peptides such as human amylin dramatically enhance MTT formazan exocytosis, resulting in the inhibition of cellular MTT reduction. Only the amyloid peptides that are known to be cytotoxic enhanced MTT formazan exocytosis. Basal MTT formazan exocytosis and amyloid peptide-enhanced MTT formazan exocytosis are blocked by several drugs with diverse known effects. These and other data suggest that MTT formazan exocytosis is a multistep process and that cytotoxic amyloid peptides enhance MTT formazan exocytosis through an intracellular signal transduction pathway.
Liu
Y
Y
Cellular Neurobiology Laboratory, Salk Institute for Biological Studies, La Jolla, California 92037-1099, U.S.A.
Schubert
D
D
D000682:Amyloid / Q000494:pharmacology*; D016229:Amyloid beta-Peptides / Q000494:pharmacology; D000818:Animals; D002462:Cell Membrane / Q000187:drug effects; D003603:Cytotoxins / Q000494:pharmacology*; D005089:Exocytosis / Q000187:drug effects*; D005562:Formazans / Q000378:metabolism*; D006801:Humans; D058228:Islet Amyloid Polypeptide; D010084:Oxidation-Reduction / Q000187:drug effects; D016716:PC12 Cells; D010446:Peptide Fragments / Q000494:pharmacology*; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects; D013778:Tetrazolium Salts / Q000378:metabolism*; D013844:Thiazoles / Q000378:metabolism*; D013997:Time Factors; D014407:Tumor Cells, Cultured
D000682:Amyloid; D016229:Amyloid beta-Peptides; D003603:Cytotoxins; D005562:Formazans; D058228:Islet Amyloid Polypeptide; D010446:Peptide Fragments; D013778:Tetrazolium Salts; D013844:Thiazoles; C079782:MTT formazan; C022616:thiazolyl blue