Effect of Dietary L-Theanine on Protein Expression in the Hippocampus of Senescence-Accelerated Mice (SAMP8).

L-Theanine is contained in green tea at 1-3% per dry matter as an amino acid with an umami taste, and the antidepressant effect and protective effect against stress-induced brain atrophy in mice, as well as the related mechanism have been reported. However, effects of theanine on the hippocampus from the proteome analysis and the action mechanism have not been examined. In this study, we mainly investigated the possibility of theanine's cognitive impairment-preventing function and the action mechanism by proteomics in the hippocampus of SAMP8 administered with theanine. In addition to improvement in the aging score with theanine administration, in proteomics, significant suppressions in the expressions of synapsin 2, α-synuclein, β-synuclein, and protein tau were observed by theanine administration, and the expression of CAM kinase II beta and alpha exhibited a significant increase and increasing tendency with theanine administration, respectively. The expression of tyrosine 3-monooxygenase/tryptophan 5-monooxygenase activation protein tended to increase by theanine administration. On the other hand, serotonin/tryptophan, GABA/glutamic acid and glutamine/glutamic acid ratios in the hippocampus showed an increasing tendency, a significant increase, and an increasing tendency with theanine administration, respectively. These results suggested that theanine might have been involved in the improvement of neurodegeneration or cognitive impairment by suppressing the productions of synapsin, synuclein and protein tau which are considered to be produced along with aging and oxidation, and by enhancing the production of serotonin by increasing the expression of CAM kinase II, and further by affecting the metabolism of glutamate.