Potential Mechanisms of Casein Hexapeptide YPVEPF on Stress-Induced Anxiety and Insomnia Mice and Its Molecular Effects and Key Active Structure

The hexapeptide YPVEPF with strong sleep-enhancing effects could be detected in rat brain after a single oral administration as we previously proved. In this study, the mechanism and molecular effects of YPVEPF in the targeted stress-induced anxiety mice were first investigated, and its key active structure was further explored. The results showed that YPVEPF could significantly prolong sleep duration and improve the anxiety indexes, including prolonging the time spent in the open arms and in the center. Meanwhile, YPVEPF showed strong sleep-enhancing effects by significantly increasing the level of the GABA/Glu ratio, 5-HT, and dopamine in brain and serum and regulating the anabolism of multiple targets, but the effects could be blocked by bicuculline and WAY100135. Moreover, the molecular simulation results showed that YPVEPF could stably bind to the vital GABAA and 5-HT1A receptors due to the vital structure of Tyr-Pro-Xaa-Xaa-Pro-, and the electrostatic and van der Waals energy played dominant roles in stabilizing the conformation. Therefore, YPVEPF displayed sleep-enhancing and anxiolytic effects by regulating the GABA-Glu metabolic pathway and serotoninergic system depending on distinctive self-folding structures with Tyr and two Pro repeats.