Ovomemolins: Egg-derived peptides that improved cognitive decline after oral administration in mice

Eggs not only contain all the molecules necessary to nurture new life but are also rich in nutrients such as high-quality protein. For example, epidemiologic studies have shown that egg intake is positively correlated with cognitive function. Thus, we specifically examined the effect of ovalbumin, a major protein present in egg whites, on cognitive function. First, we found that an orally administered enzymatic digest of ovalbumin improves cognitive function in mice fed a high-fat diet. Then, we narrowed down candidate peptides based on the prediction of peptide production according to enzyme-substrate specificity and comprehensive peptide analysis of the digest. We found that three peptides, namely ILPEY, LYRGGLEP, and ILELP, improve cognitive function after oral administration. We also showed that ILPEY, LYRGGLEP, and ILELP were present in the digest and named them ovomemolins A (OMA), B, and C, respectively. Notably, ovomemolins are the first peptides derived from egg whites that have been shown to improve cognitive function. The cognitive improvement induced by OMA, the most abundant of the peptides in the digest, was inhibited by methyllycaconitine, an antagonist of α7nAChR, which is known to be related to memory. These results suggest that OMA improves cognitive function through the acetylcholine system. After OMA administration, brain-derived neurotrophic factor (BDNF) mRNA expression and the number of 5-bromo-2'-deoxyuridine-positive cells suggested that OMA increases hippocampal BDNF expression and neurogenesis.

Fatty acid amides present in Camembert cheese improved cognitive decline after oral administration in mice

Herein, we investigated the effects of Camembert cheese (CC) and its fatty acid contents on cognitive function in mice by employing the object recognition test to evaluate hippocampus-dependent memory. Orally administered CC improved the cognitive decline induced by a high-fat diet. Next, we focused on myristamide (MA), oleamide, and stearamide, which are fatty acid amides produced during the fermentation process of CC. We found that oral administration of MA improved cognitive decline. Notably, an improvement was not observed using myristic acid, a free fatty acid that is not amidated. Thus, fatty acid amidation may contribute to the physiological activity. Moreover, we investigated changes in gene expression related to neurogenesis in the hippocampus. After MA administration, mRNA expression analysis indicated that MA increased hippocampal brain-derived neurotrophic factor expression.

Medium-chain triglycerides tricaprin TC10 and tricaprylin TC8 attenuated HFD-induced cognitive decline in a manner dependent on or independent of GLP-1

Population aging is the most important social and medical demographic issue worldwide; therefore, healthy aging is important. The increasing prevalence of dementia and cognitive decline are major health concerns. Medium-chain triglycerides (MCTs) have been shown to improve cognitive decline. The present study investigated the effects and mechanisms of action of orally administered MCTs, including tricaprylin (TC8), tricaprin (TC10), and trilaurin (TC12), on cognitive function in mice fed a high-fat diet (HFD). The administration of TC8 and TC10 attenuated cognitive decline. A relationship has been reported between cognitive dysfunction and impaired glucose metabolism. The administration of TC8 and TC10 also reduced blood glucose levels in the glucose tolerance test. Cognitive improvements by MCTs are widely attributed to the ketogenic effect. In the present study, TC8 significantly increased blood ketone concentrations, whereas TC10 did not. On the other hand, TC10 increased the plasma concentration of glucagon-like peptide-1 (GLP-1), the hormone that promotes insulin secretion. The administration of the GLP-1 receptor antagonist, exendin(9-39), blocked the cognitive-enhancing effects of TC10. These results suggest that TC10 improved cognitive function via the GLP-1 receptor. The in vitro experiment indicated that 2-monocaprin (2-MC10), not TC10, stimulated the secretion of GLP-1 and decreased intracellular cAMP concentrations. In conclusion, we herein demonstrated that TC8 and TC10 attenuated cognitive decline through different mechanisms. This is the first study to suggest that TC10 attenuates cognitive decline via GLP-1.

Characterization of rice endosperm-derived antidepressant-like peptide (REAP): An orally active novel tridecapeptide derived from rice protein

It is ideal to ingest bioactive substances from daily foods to stay healthy. Rice is the staple food for almost half of the human population. We found that an orally administered enzymatic digest of rice endosperm protein exhibits antidepressant-like effects in the tail suspension test (TST) using mice. A comprehensive peptide analysis of the digest using liquid chromatography-tandem mass spectrometry was performed, and a tridecapeptide QQFLPEGQSQSQK, detected in the digest, was chemosynthesized. Oral administration of the tridecapeptide exhibited antidepressant-like effects at a low dose comparable to classical antidepressant in the TST. This also exhibited anti-depressant-like effect in the forced swim test. We named it rice endosperm-derived antidepressant-like peptide (REAP). Intriguingly, intraperitoneal administration had no effect. Orally administered REAP(8-13) but not REAP(1-7) exhibited antidepressant-like activity, suggesting that the C-terminal structure is important for the antidepressant-like effect. We confirmed the presence of REAP, corresponding to rice glutelin type B4(130-142) and B5(130-142), in the digest. The effects of REAP were blocked by both dopamine D1 and D2 antagonists. These results suggest that it exerts its antidepressant-like activity through activation of the dopamine system. Taken together, oral administration of a novel tridecapeptide exhibited antidepressant-like effects via the dopamine system. This is the first report of a rice-derived peptide that exhibits antidepressant-like effects.