THE INTRACELLULAR COMPONENT OF CELLULAR (4,5-DIMETHYLTHIAZOL-2-YL)-2,5-DIPHENYLTETRAZOLIUM BROMIDE (MTT) REDUCTION IS SPECIFICALLY INHIBITED BY BETA-AMYLOID PEPTIDES

In vitro cell culture model systems for investigating the biochemical mechanisms involved in the neurodegenerative actions of beta-amyloid p eptide (beta-AP) have been established. Using rat pheochromocytoma PC1 2 or human epitheloid HeLa cell lines, submicromolar concentrations of the beta-AP fragments beta 1-40, beta 1-39, and beta 25-35, but not b eta 1-28, were found to inhibit the reduction of the redox dye 3-(4,5- dimethylthiazol-2-yl)-2,5-dipheny tetrazolium bromide (MTT). In both c ell lines, the beta-AP-sensitive component represented similar to 70% of total cellular MTT reduction. When the reduction of a series of str ucturally related dyes was compared with that of MTT, the reduction of 3 naphthyl-2-pheny1-5-(4-nitrophenyl)-2H-tetrazolium chloride (NTV) w as also found to be sensitive to beta 25-35, but that of seven other r edox dyes was not. A property common to MTT and NTV is that they are b oth readily taken up into PC12 and HeLa cells and do not require an ar tificial electron coupling agent to be reduced. Microscopic analysis o f MTT-formazan product formation in PC12 and HeLa cells following beta 25-35 treatment revealed that it was the intracellular component of t he reduction of this dye that was abolished. These results support the hypothesis that the cellular reduction of MTT represents a specific i ndicator of the initial events underlying the mechanism of beta-AP tox icity.