Naturally occurring p3 peptides, Aβ17-40 and Aβ17-42, inhibit the Aβ-fibrinogen interaction. (A) Biotinylated Aβ42 was incubated with fibrinogen in the presence of various concentrations (0.05-20 µM) of 16 nonbiotinylated Aβ fragments listed in supplemental Figure 1. The inhibitory efficacy of the Aβ fragments on the Aβ42-fibrinogen interaction was analyzed using AlphaLISA. Of the 16 Aβ fragments tested, only Aβ17-40 (IC₅₀ = 13.4 µM) and Aβ17-42 (IC₅₀ = 1.03 µM) showed inhibitory efficacy (n = 3). (B) Western blot analysis with anti-fibrinogen antibody shows that Aβ17-42 blocks the ability of biotinylated Aβ42 to pull down fragment D (FD) in a dose-dependent manner. (C) Various concentrations (0.01-20 µM) of 5 alanine-scanning Aβ peptides (L17A, V18A, F19A, F20A, and D23A) were incubated with biotinylated Aβ42 and fibrinogen, and their ability to inhibit the Aβ42-fibrinogen interaction was analyzed using AlphaLISA (n = 3-6). Aβ L17A and D23A had almost no inhibitory activity (IC₅₀ > 20 µM), whereas F19A (IC₅₀ = 3.7 µM) and F20A (IC₅₀ = 6.8 µM) showed a compatible inhibitory efficacy to original Aβ17-42. Interestingly, V18A (IC₅₀ = 0.26 µM) had fivefold greater inhibitory efficacy than Aβ17-42. Results presented in graphs are mean ± SEM.