Isolation of an antioxidant peptide from krill protein hydrolysates as a novel agent with potential hepatoprotective effects

Krill accounts for the highest abundant animal biomass on earth though it remains underexplored. During the present study, krill protein hydrolysates (KPH) were prepared using several proteases, optimizing reaction time for dose-response analysis of antioxidant activity. Bioassay-guided fractionation of selected KPH of pepsin, first by ultrafiltration ( < 1 kDa, 1-3 kDa, and > 3 kDa), revealed the active fraction, 1-3 kDa, which was consecutively separated by ion-exchange chromatography and stepwise RP-HPLC. Three peptides were identified, sequenced and synthesized. The peptide P2 was effective in reducing H2O2-induced oxidative stress and lipid peroxidation by increasing antioxidant enzyme activities, including superoxide dismutase, catalase, and glutathione peroxidase. P2 reduced apoptosis in H2O2 -stimulated hepatocytes by regulating the expression levels of Bcl-2/Bax and caspase-3. P2 pre-treatment increased nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase 1 (HO-1) expression in cultured hepatocytes. Furthermore, P2 induced the activation of Nrf2/HO-1 by activating the ERK pathway.