Identification of two novel peptides with antioxidant activity and their potential in inhibiting amyloid-β aggregation in vitro.

Two novel peptides WW4 and WW7 were evaluated for their antioxidant activity, membrane penetrance and inhibiting activity of amyloid- protein (A) aggregation. The results showed that both WW7 (10.38 +/- 0.22 mol TE per mol) and WW4 (6.32 +/- 0.77 mol TE per mol) possessed a significant oxygen radical absorption capacity (ORAC) and strong 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging capacity (WW7, IC50 0.05 +/- 0.002; WW4, 1.06 +/- 0.07). Interestingly, WW7 exhibited relatively higher antioxidant activity than WW4. In addition, both WW4 and WW7 showed high cell membrane penetrance characteristics in HEK293 cells. To measure the metabolic stability of WW4 and WW7 in cells, we labelled the peptides with FITC and then analyze the co-localization with lysosomes by imaging Flow-cytometry. We found that WW7 had a lower co-localization rate (1.39%) than WW4 (8.44%), indicating that WW7 was more stable than WW4. In vivo imaging assay demonstrated that WW7 presented higher metabolic stability with a much longer stability time (2687.33 +/- 54.01 min) in BALB-c nude mice than WW4 (148 +/- 26.85 min), which was consistent with the in vitro result. To illustrate the potential function of antioxidant capacity, an A aggregation cell model was applied to examine anti-A aggregation ability of WW4 and WW7. Surprisingly, WW7 (23.04 +/- 13.64%) had stronger anti-A aggregation ability but WW4 did not show obvious potential, which was due to their structure difference. The present work would offer novel insight into the activity of antioxidants and anti-A aggregation, and uncover the under-appreciated function of peptides in effective application in AD therapy.