Walnut-derived peptides cross the blood-brain barrier and ameliorate Aβ-induced hypersynchronous neural network activity.

Walnut peptides exhibit promising neuroprotective effects; however, they must be absorbed in their intact form through the gastrointestinal tract into the bloodstream and brain. In this study, the effects of the walnut peptide TWLPLPR (TW-7) were evaluated in mice, including its absorption and distribution ability to cross the blood-brain barrier, and inhibitory effects on hyperactivity of primary hippocampal neurons. TW-7 was stable in plasma, and the peptide retention rate was 88.19 ± 0.70 % after 48 h. In vitro imaging indicated that TW-7 was distributed in the brain, liver, lungs, and kidneys of mice after gavage, and an immunofluorescence analysis indicated that TW-7 could accumulate in mouse brain parenchyma; in addition, TW-7 reached its maximum concentration (5.36 ± 1.59 µg/mL) in plasma 2 h after gavage, and reached its peak concentration (0.95 ± 0.19 µg/g) in brain tissue 4 h after gavage. Microelectrode array and immunofluorescence analyses confirmed that TW-7 ameliorates the overexcitation of primary hippocampal neurons induced by Aβ25-35 through inhibiting the excessive release of glutamate and protecting synaptic structure and function. These results suggest that TW-7 can penetrate the blood-brain barrier in mice and positively affect the electrophysiological activity of neurons. More broadly, these findings provide a theoretical basis for the development and application of walnut peptide-based functional food for Alzheimer's disease intervention.