Neuroprotective effect of whey protein hydrolysate containing leucine-aspartate-isoleucine-glutamine-lysine on HT22 cells in hydrogen peroxide-induced oxidative stress

This study aimed to investigate the neuroprotective effects of whey protein hydrolysate (WPH) containing the pentapeptide leucine-aspartate-isoleucineglutamine-lysine (LDIQK). Whey protein hydrolysate (50, 100, and 200 mu g/mL) demonstrated the ability to restore the viability of HT22 cells subjected to 300 mu M hydrogen peroxide (H 2 O 2 )-induced oxidative stress. Furthermore, at a concentration of 200 mu g/mL, it significantly reduced the increase in reactive oxygen species production and calcium ion (Ca 2+ ) influx induced by H 2 O 2 by 46.1% and 46.2%, respectively. Similarly, the hydrolysate significantly decreased the levels of ptau, a hallmark of tauopathy, and BCL2 associated X (BAX), a proapoptosis factor, while increasing the protein levels of choline acetyltransferase (ChAT), an enzyme involved in acetylcholine synthesis, brain -derived neurotrophic factor (BDNF), a nerve growth factor, and B -cell lymphoma 2 (BCL2, an antiapoptotic factor. Furthermore, it increased nuclear factor erythroid 2 -related factor 2 (Nrf2)-hemoxygenase-1(HO-1) signaling, which is associated with the antioxidant response, while reducing the activation of mitogen-activated protein kinase (MAPK) signaling pathway components, namely phosphor-extracellular signal -regulated kinases (p-ERK), phosphor -c -Jun N -terminal kinases (p-JNK), and p -p38. Column chromatography and tandem mass spectrometry analysis identified LDIQK as a compound with neuroprotective effects in WPH; it inhibited Ca 2+ influx and regulated the BAX/BCL2 ratio. Collectively, WPH containing LDIQK demonstrated neuroprotective effects against H 2 O 2 -induced neuronal cell damage, suggesting that WPH or its active peptide, LDIQK, may serve as a potential edible agent for improving cognitive dysfunction.