Gamma-aminobutyric acid (GABA) is present in the mammalian brain as the main inhibitory neurotransmitter and in foods. It is widely used as a supplement that regulates brain function through stress-reducing and sleep-enhancing effects. However, its underlying mechanisms remain poorly understood, as it is reportedly unable to cross the blood–brain barrier. Here, we explored whether a single peroral administration of GABA affects feeding behavior as an evaluation of brain function and the involvement of vagal afferent nerves. Peroral GABA at 20 and 200 mg/kg immediately before refeeding suppressed short-term food intake without aversive behaviors in mice. However, GABA administration 30 min before refeeding demonstrated no effects. A rise in circulating GABA concentrations by the peroral administration of 200 mg/kg GABA was similar to that by the intraperitoneal injection of 20 mg/kg GABA, which did not alter feeding. The feeding suppression by peroral GABA was blunted by the denervation of vagal afferents. Unexpectedly, peroral GABA alone did not alter vagal afferent activities histologically. The coadministration of a liquid diet and GABA potentiated the postprandial activation of vagal afferents, thereby enhancing postprandial satiation. In conclusion, dietary GABA activates vagal afferents in collaboration with meals or meal-evoked factors and regulates brain function including feeding behavior.

Osteoarthritis (OA) is a major public health issue in Japan and other countries, and foods that prevent or treat OA are in strong demand. Proteins and peptides in chicken meat and bones are known for being rich in functional and nutritional ingredients for the improvement of osteoporosis. We speculated that chicken legs, a food consumed in many regions of the world, may also contain such ingredients. In this study, we aim to (i) evaluate the effect of chicken leg extract (CLE) on the promotion of cartilage matrix production and (ii) identify the active ingredient in CLE that contributes to this function. Artificial CLE digest was prepared, and the acid mucopolysaccharide production-promoting activity of the CLE digest was evaluated by alcian blue staining of ATDC5 cells. CLE was orally administered to rabbits with burr holes in the knee joint of the femur, and the degree of regeneration of cartilage matrix was evaluated. Furthermore, we investigated orally administered CLE-derived peptides in human plasma using LC-MS. From measuring the acid mucopolysaccharide production-promotion activity of these peptides, a molecule considered to be an active ingredient in the CLE digest was identified. CLE digest promoted acid mucopolysaccharide production and facilitated regeneration of cartilage matrix in in vitro and in vivo experiments. Four peptides including phenylalanyl-hydroxyproline (Phe-Hyp) were detected as CLE-derived peptides in human plasma. The effect of CLE was inferred to be due to Phe-Hyp, which was confirmed to be present in the CLE digest. It was shown that CLE stimulated the production of articular cartilage matrix both in vitro and in vivo, and that CLE could be an effective food for preventing or treating OA. Furthermore, only Phe-Hyp was confirmed as the active compound in the CLE digest, suggesting that the activity of CLE was due to Phe-Hyp.

Glutathione (GSH) is present in almost all human cells and has a beneficial effect on human skin brightness. Cysteinylglycine (Cys-Gly) and γ-glutamylcysteine (γ-Glu-Cys) are GSH synthesis components. In this study, we defined glutathione (GSH), cysteinylglycine (Cys-Gly), and γ-glutamylcysteine (γ-Glu-Cys) as cysteine peptide and performed a randomized, double-blind, placebo-controlled study to investigate the effects of orally administered cysteine peptide on human skin brightness using a CM-26d portable spectrophotometer in healthy males and females aged between 20 and 65 years old. Eligible participants were randomly allocated into three groups (cysteine peptide 45 mg: n = 16, 90 mg: n = 15, and placebo: n = 16). Each subject ingested six tablets every day for 12 weeks, and skin brightness was measured at 0, 4, 8, and 12 weeks. As a result, the 45 mg group exhibited arm brightening in a time-dependent manner, and a significant difference was observed compared to the placebo at week 12 (p = 0.028). Moreover, no serious adverse events and changes related to 270 mg study food were observed in the safety trial. Here, we suggest that cysteine peptide is a promising and safe compound for human skin brightness.

Objective: This study focused on the effect of γ-aminobutyric acid (GABA) intake on psychological state and game performance during esports gameplay. Methods: A randomized, double-blind, placebo-controlled crossover study was conducted with eight healthy male university students aged 20–24 years who regularly play esports. The participants ingested either 200 mg of GABA or a placebo prior to gameplay and then completed a standardized esports task using the Mobalytics Proving Ground™ (MPG), a perceptual-cognitive task within “League of Legends” designed to train and evaluate player performance. Subjective psychological states were assessed pre- and post-gameplay using the Profile of Mood States 2 (POMS2^®) short version. Esports task performance was evaluated based on MPG scores. Results: GABA intake significantly reduced psychological confusion–bewilderment and fatigue in the POMS 2^® short version during esports gameplay. Furthermore, the game scores were significantly higher in the GABA group compared to the placebo group. Conclusions: These findings suggest that GABA intake may serve as a potential strategy to enhance both the mental state and performance of esports players.

Gamma-aminobutyric acid (GABA) has been implicated in gut–brain interactions and neuronal activation. We hypothesized that GABA could ameliorate memory decline. We investigated whether oral GABA administration ameliorated age-related cognitive decline in aged mice (C57BL/6J, male) and explored the role of circulating exosomes in mediating these effects. Aged mice that drank water containing 0.5% GABA exhibited significantly improved discrimination index scores compared with that of controls, indicating enhanced memory function. Their plasma-derived exosomes induced neurite outgrowth and mitochondrial activation and restored neuronal activity in SH-SY5Y cells. GABA enhanced the exosomal expression of several miRNAs linked to neuronal activation, longevity, and anti-senescence pathways. Plasma-derived exosomes also restored object recognition memory, reduced hippocampal neuroinflammation, and decreased senescent cell markers (p21 and γH2AX) in aged mice. Additionally, mitochondria- and neurite-related genes were upregulated, and pathways associated with oxidative phosphorylation and Alzheimer’s disease were enriched. Collectively, long-term GABA administration was found to improve cognitive function of aged mice through the secretion of functional exosomes.