Oral Administration of the Food-Derived Hydrophilic Antioxidant Ergothioneine Enhances Object Recognition Memory in Mice.

BACKGROUND: The enhancement of learning and memory through food-derived ingredients is of great interest to healthy individuals as well as those with diseases. Ergothioneine (ERGO) is a hydrophilic antioxidant highly contained in edible golden oyster mushrooms (Pleurotus cornucopiae var. citrinopileatus), and systemically absorbed by its specific transporter, carnitine/organic cation transporter OCTN1/SLC22A4. OBJECTIVE: This study aims to examine the possible enhancement of object recognition memory by oral administration of ERGO in normal mice. METHODS: Novel object recognition test, spatial recognition test, LC-MS/MS, Golgi staining, neuronal culture, western blotting, immunocytochemistry, and quantitative RT-PCR were utilized. RESULT: After oral administration of ERGO (at a dose of 1-50 mg/kg) three times per week for two weeks in ICR mice, the novel object recognition test revealed a longer exploration time for the novel object than for the familiar object. After oral administration of ERGO, the spatial recognition test also revealed a longer exploration time for the spatially moved object than the unmoved one in mice fed ERGO-free diet. The discrimination index was significantly higher in the ERGO-treated group than the control in both behavioral tests. ERGO administration led to an increase in its concentration in the plasma and hippocampus. The systemic concentration reached was relevant to those found in humans after oral ERGO administration. Golgi staining revealed that ERGO administration increased the number of matured spines in the hippocampus. Exposure of cultured hippocampal neurons to ERGO elevated the expression of the synapse formation marker, synapsin I. This elevation of synapsin I was inhibited by the tropomyosin receptor kinase inhibitor, K252a. Treatment with ERGO also increased the expression of neurotrophin-3 and -5, and phosphorylated mammalian target of rapamycin in hippocampal neurons. CONCLUSION: Oral intake of ERGO may enhance object recognition memory at its plasma concentration achievable in humans, and this enhancement effect could occur, at least in part, through the promotion of neuronal maturation in the hippocampus.

Homostachydrine is a Xenobiotic Substrate of OCTN1/SLC22A4 and Potentially Sensitizes Pentylenetetrazole-Induced Seizures in Mice.

Understanding of the underlying mechanism of epilepsy is desired since some patients fail to control their seizures. The carnitine/organic cation transporter OCTN1/SLC22A4 is expressed in brain neurons and transports food-derived antioxidant ergothioneine (ERGO), L-carnitine, and spermine, all of which may be associated with epilepsy. This study aimed to clarify the possible association of this transporter with epileptic seizures. In both pentylenetetrazole (PTZ)-induced acute seizure and kindling models, ocnt1 gene knockout mice (octn1-/-) showed lower seizure scores compared with wild-type mice. Up-regulation of the epilepsy-related genes, c-fos and Arc, and the neurotrophic factor BDNF following PTZ administration was observed in the hippocampus of wild-type, but not octn1-/- mice. To find the OCTN1 substrate associated with the seizure, untargeted metabolomics analysis using liquid chromatography-quadrupole time-of-flight mass spectrometry was conducted on extracts from the hippocampus, frontal cortex, and plasma of both strains, leading to the identification of a plant alkaloid homostachydrine as a compound present in a lower concentration in octn1-/- mice. OCTN1-mediated uptake of deuterium-labeled homostachydrine was confirmed in OCTN1-transfected HEK293 cells, suggesting that this compound is a substrate of OCTN1. Homostachydrine administration increased PTZ-induced acute seizure scores and the expression of Arc in the hippocampus and that of Arc, Egr1, and BDNF in the frontal cortex. Conversely, administration of the OCTN1 substrate/inhibitor ERGO inhibited PTZ-induced kindling and reduced the plasma homostachydrine concentration. Thus, these results suggest that OCTN1 is at least partially associated with PTZ-induced seizures, which is potentially deteriorated by treatment with homostachydrine, a newly identified food-derived OCTN1 substrate.

Hydrolyzed Salmon Milt Extract Enhances Object Recognition and Location Memory Through an Increase in Hippocampal Cytidine Nucleoside Levels in Normal Mice.

Salmon milt extract contains high levels of nucleic acids and has antioxidant potential. Although salmon milt extract is known to improve impaired brain function in animal models with brain disease, its effects on learning and memory ability in healthy subjects is unknown. The purpose of the present study was to clarify the effect of hydrolyzed salmon milt extract (HSME) on object recognition and object location memory under normal conditions. A diet containing 2.5% HSME induced normal mice to devote more time to exploring novel and moved objects than in exploring familiar and unmoved objects, as observed during novel object recognition and spatial recognition tests, respectively. A diet containing 2.5% nucleic acid fraction purified from HSME also induced similar effects, as measured by the same behavioral tests. This suggests that the nucleic acids may be a functional component contributing to the effects of HSME on brain function. Quantitative polymerase chain reaction analysis revealed that gene expression of the markers for brain parenchymal cells, including neural stem cells, astrocytes, oligodendrocytes, and microglia, in the hippocampi of mice on an HSME diet was higher than that in mice on a control diet. Oral administration of HSME increased concentrations of cytosine, cytidine, and deoxycytidine in the hippocampus. Overall, ingestion of HSME may enhance object recognition and object location memory under normal conditions in mice, at least, in part, via the activation of brain parenchymal cells. Our results thus indicate that dietary intake of this easily ingestible food might enhance brain function in healthy individuals.