The relationship between the aggregational state of the amyloid‐β peptides and free radical generation by the peptides

In the present study, we investigated whether or not the amyloid‐β protein (Aβ) peptide itself spontaneously generates free radicals using electron spin resonance (ESR) spectroscopy while also monitoring the aggregational state of Aβ and Aβ‐induced cytotoxicity. The present results demonstrated a four‐line spectrum in the presence of both Aβ40 and Aβ42 with Ntert‐butyl‐α‐phenylnitrone (PBN), but not in the presence of PBN alone in phosphate‐buffered saline (PBS). The fact that the four‐line spectrum obtained for the Aβ/PBN in PBS was completely abolished in the presence of the iron‐chelating agent Desferal demonstrated the observed four‐line spectrum to be iron‐dependent. The present study also revealed that either Aβ40 or Aβ42 with PBN in phosphate buffer (PB) did not produce any definite four‐line spectrum. Both a thioflavine‐T (Th‐T) fluorometric assay and circular dichroism (CD) spectroscopy showed the amyloid fibril formation of Aβ in PBS to be much higher than that of Aβ in PB. Moreover, Aβ‐induced cytotoxicity assays showed Aβ incubated in PBS to be more cytotoxic than that incubated in PB. These results thus suggest that Aβ‐associated free radical generation is strongly influenced by the aggregational state of the peptides.