The in vitro toxicity of synthetic beta-amyloid (beta A4) is variable
and unpredictable, limiting its use as a research tool. This study des
cribes a method using Congo red (CR) to predict the in vitro toxicity
of beta A4 solutions. Histopathologically, CR is used to stain the neu
ritic, beta A4-containing plaques, one of the hallmarks of Alzheimer's
disease. In this study, synthetic beta A4 solutions were incubated wi
th CR at a molar ratio of 1.0:2.5. The solutions were centrifuged and
the absorbance of the supernatants were measured. Predictions of nonto
xicity correlated with absorbance readings near zero. Toxicity was eva
luated relative to control cells (vehicle only), using a hemocytometer
to count PC-12 cells that excluded trypan blue. The positive predicti
ve value of the test was 78% and the negative predictive value was 100
%. To use this test, the toxic concentration(s) of beta A4 must first
be established empirically. Then, the CR test can be used to evaluate
the potential toxicity of beta A4 solutions ar similar concentrations.
Thus, this test can be used under a variety of laboratory circumstanc
es. (C) 1997 Elsevier Science Inc.