Inhibitory effects of theanine and sera from theanine-fed rats on receptor-mediated cancer cell invasion beneath mesothelial-cell monolayers.

To investigate the bioavailability and mode of action of theanine against cancer, we examined in vitro and ex vivo effects of theanine on invasion of a rat ascites hepatoma cell line of AH109A. Theanine dose-dependently inhibited the invasion of AH109A cells across rat mesentery-derived mesothelial-cell (M-cell) monolayers without restraining AH109A cell proliferation in vitro. Rat sera obtained after oral intubation of theanine also inhibited the invasion. A competitive N-methyl-D-aspartate (NMDA) type glutamate receptor antagonist, (+/-) 2-amino-5-phosphonopentanoic acid (AP-5), dose-dependently counteracted the theanine-mediated in vitro and ex vivo inhibition of AH109A invasion. A competitive non-NMDA type glutamate receptor antagonist, 6,7-dinitroquinoxaline 2,3-dione (DNQX), did not affect this inhibition by theanine in vitro. These results suggest that the inhibition of AH109A invasion by theanine may be mediated by the NMDA receptor of AH109A.