Congo red reverses amyloid beta protein-induced cellular stress in astrocytes

An amyloid-binding dye Congo red has been reported to prevent the neurotoxic effect of Alzheimer's amyloid beta protein (A beta). In the present study, we investigated the effect of Congo red in cultured rat cortical astrocytes. A beta (1 nM-10 mu M) did not cause cell death, but potently inhibited the cellular redox activity as determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction assay. Congo red (0.2-20 mu M), when added together with or prior to A beta, significantly blocked A beta-induced inhibition of redox activity. Furthermore, when Congo red was added after treatment with A beta, the inhibited redox activity was restored to normal, indicating that Congo red can reverse A beta-induced cellular stress. The reversing effect of Congo red cannot be explained by the inhibition of A beta fibril formation and suggests a novel aspect of the interaction of Congo red with A beta. (C) 1997 Elsevier Science Ireland Ltd.