Amyloid ²-peptide spin trapping I: Peptide enzyme toxicity is related to free radical spin trap reactivity

Synthetic β-amyloid peptides (Aβs) demonstrate lot-to- lot variation in toxicity that has not been adequately explained. Studies from our laboratory have shown that Aβtoxicity may result from the ability of the peptide to promote oxidation reactions. Both Aβ(l-40) and Aβ(25- 35) inactivate the oxidation-sensitive enzyme glutamine synthetase (GS) and generate electron paramagnetic resonance (EPR)-detectable products upon reaction with the spin trap phenyl-tert-butylnitrone (PBN). We now report that samples of synthetic Aβ(l-40) and Aβ(25-35) with attenuated toxicity with respect to peptide-induced GS inactivation, produce qualitatively different EPR spectra when the peptides are incubated with PBN. The results suggest an interpretation of conflicting observations regarding the toxicity of synthetic Aβs, and that investigators must be careful to assess the reactivity state of Aβ being studied.