Ingestion of theanine, an amino acid in tea, suppresses psychosocial stress in mice.

The antistress effect of theanine (γ-glutamylethylamide), an amino acid in tea, was investigated using mice that were psychosocially stressed from a conflict among male mice in conditions of confrontational housing. Two male mice were housed in the same cage separated by a partition to establish a territorial imperative. When the partition was removed, the mice were co-housed confrontationally. As a marker for the stress response, changes in the adrenal gland were studied in comparison to group-housed control mice (six mice in a cage). Significant adrenal hypertrophy was observed in mice during confrontational housing, which was developed within 24 h and persisted for at least 1 week. The size of cells in the zona fasciculata of the adrenal gland, from which glucocorticoid is mainly secreted, increased (∼1.11-fold) in mice during confrontational housing, which was accompanied by a flattened diurnal rhythm of corticosterone and ACTH in blood. The ingestion of theanine (>5 µg ml(-1)) prior to confrontational housing significantly suppressed adrenal hypertrophy. An antidepressant, paroxetin, suppressed adrenal hypertrophy in a similar manner in mice during confrontational housing. In mice that ingested theanine, behavioural depression was also suppressed, and a diurnal rhythm of corticosterone and ACTH was observed, even in mice that were undergoing confrontational housing. Furthermore, the daily dose of theanine (40 µg ml(-1)) blocked the counteracting effects of caffeine (30 µg ml(-1)) and catechin (200 µg ml(-1)). The present study demonstrated that theanine prevents and relieves psychosocial stress through the modulation of hypothalamic-pituitary-adrenal axis activity.

Theanine intake improves the shortened lifespan, cognitive dysfunction and behavioural depression that are induced by chronic psychosocial stress in mice.

To evaluate the psychosocial effect on lifespan and cognitive function, this study investigated the effect of confrontational housing on mice because conflict among male mice is a psychosocial stress. In addition, it investigated the anti-stress effect of theanine (γ-glutamylethylamide), an amino acid in tea. Mice were housed under confrontation. That is, two male mice were separately housed in the same cage with a partition for establishing the territorial imperative in each mouse. Then, the partition was removed and mice were co-housed confrontationally (confront-housing) using a model mouse of accelerated-senescence (SAMP10) that exhibited cerebral atrophy and cognitive dysfunction with ageing. It was found that mice began to die earlier under confront-housing than group-housed control mice. Additionally, it was found that cerebral atrophy, learning impairment and behavioural depression were higher in mice under the stressed condition of confront-housing than age-matched mice under group-housing. Furthermore, the level of oxidative damage in cerebral DNA was higher in mice housed confrontationally than group-housed control mice. On the other hand, the consumption of purified theanine (20 µg/ml, 5-6 mg/kg) suppressed the shortened lifespan, cerebral atrophy, learning impairment, behavioural depression and oxidative damage in cerebral DNA. These results suggest that psychosocial stress accelerates age-related alterations such as oxidative damage, lifespan, cognitive dysfunction and behavioural depression. The intake of theanine might be a potential candidate for suppression of disadvantage under psychosocial stress.

Protection of brain and pancreas from high-fat diet: effects of catechin and caffeine.

To investigate the effect of a high-fat diet on brain and pancreas functions, we used SAMP10 mice that have characteristics of brain atrophy and cognitive dysfunction with aging. Simultaneously, we investigated the effect of green tea catechin consumption on high-fat diet feeding, because green tea catechin has been reported to improve brain atrophy, brain dysfunction and obesity. The body weight of mice fed a high-fat diet from 2 to 12 months was higher than that of the control, although the calorie intake was not. The high-fat diet also increased insulin secretion; however, the hypersecretion of insulin and obesity were suppressed when mice were fed a high-fat diet with green tea catechin and caffeine. Furthermore, brain atrophy was suppressed and the working memory, tested using Y-maze, improved in mice fed a high-fat diet containing green tea catechin and caffeine. The secretion of insulin might affect both obesity and brain function. A strong correlation was found between working memory and insulin release in mice fed a high-fat diet with green tea catechin and/or caffeine. The results indicate the protective effect of green tea catechin and caffeine on the functions of brain and pancreas in mice fed a high-fat diet.

Daily ingestion of green tea catechins from adulthood suppressed brain dysfunction in aged mice.

Oxidative damage is believed to be an important cause of senescence. We have previously found that green tea catechins (GT-catechin), potent antioxidants, decrease oxidative damage to DNA and suppress brain dysfunction in aged senescence-accelerated mice (SAMP10) when ingested from the age of 1 month to the age of 12 months. To clarify the effect of GT-catechin on suppression of brain senescence, we investigated the effect of starting period to ingest GT-catechin. Six- or 9-month-old SAMP10 mice were allowed free access to water containing 0.02% GT-catechin. SAMP10 mice exhibit senescence characteristics such as shortened life span, atrophied forebrain and lowered learning and memory abilities. Learning ability was significantly higher in mice that ingested GT-catechin from the age of 6 months to 12 months when compared with same-aged control mice drank water without GT-catechin. Starting GT-catechin intake from the age of 9 months tended to improve learning ability. The ages of 6 and 9 months are thought to be adult and middle ages, respectively in SAMP10 mice. This result suggested that GT-catechin was helpful in suppressing brain dysfunction with aging even when ingestion started at the adult age.