COMPETITION OF CONGO-RED AND THIOFLAVIN-S BINDING TO AMYLOID SITES INALZHEIMERS DISEASED TISSUE

Though the strong affinity of Congo red and thioflavin S for amyloid d eposits has been known for a long time, the binding mechanism of these biological dyes to amyloid sites is still not understood. In the pres ent work, the competition of these two dyes for binding in Alzheimer a myloid is investigated. Analyses by optical microscopy and microspectr ofluorimetry were performed on several series of stained diseased brai n sections. Microspectrofluorimetric analyses showed that bound Congo red and bound thioflavin S have characteristic spectra in which the fl uorescence maxima are distinct of those for the free dyes. Both, optic al microscopic analyses and fluorescence measurements of stained brain sections indicated that Congo red and thioflavin S compete with each other at the same interacting site on diseased cerebral tissue. The st aining efficiency of the replacing dye seems to be a maximum for a con centration of about 1%. (C) 1995 John Wiley & Sons, Inc.