Amazake is a traditional Japanese fermented-rice beverage and this non-alcoholic drink is produced using rice koji by saccharification. The purpose of his study was to investigate the protective effects of amazake-derived peptides against scopolamine-induced cognitive impairment in mice and their potential mechanisms. Mice were intraperitoneally administered amazake peptides at dose of 25 and 100 mg/kg for 7 days, followed by intraperitoneal injection of scopolamine. The administration of amazake peptides suppressed scopolamine-induced cognitive impairment in passive-avoidance test and significantly upregulated levels of brain-derived neurotrophic factor (BDNF) in the hippocampus. Amazake peptides administration also induced significant increases in the phosphorylation of cAMP response element binding (CREB) protein and extracellular signal-regulated kinase (ERK) in the hippocampus of the mice. On the other hand, scopolamine-treated mice showed significantly decreased acetylcholine levels and increased acetylcholine-esterase activity in the hippocampus as compared with controls, whereas these changes were suppressed by the administration of amazake peptides. Among the fractions separated by size-exclusion chromatography, the non-glycosylated peptide fraction suppressed H2O2-induced neuronal damage in SK-N-SH cells by upregulating BDNF expression. The amino acid sequence of the major peptide in this subfraction was identified as a hexadeca peptide with a molecular weight of 1848.87 Da. These results demonstrated that amazake peptides prevented cognitive impairment and the underlying mechanism might involve the activation of ERK/CREB/BDNF signaling pathway. Our findings suggest amazake-derived peptides as a potential agent for the prevention of age-related cognitive decline and dementia.
