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Abstracts

LE Magazine August 2005
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Theanine

Anti-obesity effects of three major components of green tea, catechins, caffeine and theanine, in mice.

To elucidate the anti-obesity effects of three major components of green tea, catechins, caffeine and theanine, female ICR mice were fed on diets containing 2% green tea powder and diets containing 0.3% catechins, 0.05% caffeine and 0.03% theanine, which correspond, respectively, to their concentrations in a 2% green tea powder diet, singly and in combination for 16 weeks. Body weight and food intake were determined monthly during this period, kidneys, adrenals, liver, spleen, brain, pituitary and intraperitoneal adipose tissues (IPAT) were weighed and lipid levels in the serum and liver were measured at the end of this period. The body weight increase and weight of IPAT were significantly reduced by the diets containing green tea, caffeine, theanine, caffeine + catechins, caffeine + theanine and caffeine + catechins + theanine. Noticeably, the IPAT weight decreased by 76.8% in the caffeine + catechins compared to the control group. Serum concentrations of triglycerides (TG) and non-esterified fatty acids (NEFA) were decreased by green tea, catechins and theanine. Moreover, caffeine + catechins, caffeine + theanine and caffeine + catechins + theanine also decreased NEFA in the serum. The TG level in the liver was significantly reduced by catechins and catechins + theanine in comparison with the control. These results indicated that at least caffeine and theanine were responsible for the suppressive effect of green tea powder (GTP) on body weight increase and fat accumulation. Moreover, it was shown that catechins and caffeine were synergistic in anti-obesity activities.

In Vivo. 2004 Jan-Feb;18(1):55-62

Possible involvement of group I mGluRs in neuroprotective effect of theanine.

We investigated the molecular mechanism underlying the neuroprotective effect of theanine, a green tea component, using primary cultured rat cortical neurons, focusing on group I metabotropic glutamate receptors (mGluRs). Theanine and a group I mGluR agonist, DHPG, inhibited the delayed death of neurons caused by brief exposure to glutamate, and this effect of theanine was abolished by group I mGluR antagonists. Although the administration of glutamate alone decreased the neuronal expression of phospholipase C (PLC)-beta1 and -gamma1, which are linked to group I mGluRs, their expression was equal to the control levels on cotreatment with theanine. Treatment with theanine or DHPG alone for 5-7 days resulted in increased expression of PLC-beta1 and -gamma1, and the action of theanine was completely abolished by group I mGluR antagonists. These findings indicate that group I mGluRs might be involved in neuroprotective effect of theanine by increasing the expression levels of PLC-beta1 and -gamma1.

Biochem Biophys Res Commun. 2004 Jul 16;320(1):116-22

Enhancement of the activity of doxorubicin by inhibition of glutamate transporter.

Theanine enhanced doxorubicin (DOX) induced antitumor activity by increasing the concentration of DOX in the tumor through the inhibition of efflux of DOX from tumor cells. As theanine reduced the level of glutamate via suppression of the glutamate transporter in tumor cells, we studied the change in the intracellular concentration of glutathione (GSH) and the correlation with the GSH S-conjugate export (GS-X) pump. The reduction in the concentration of glutamate in tumor cells caused by theanine, induced decreases in the intracellular GSH and GS-DOX levels. The expression of MRP5 in M5076 cells, was confirmed. We concluded that the GS-DOX conjugate was transported extracellularly via the MRP5/GS-X pump in M5076 cells and that theanine affected this route. Namely, theanine increases the concentration of DOX in a tumor in vivo through inhibition of the glutamate transporter via the GS-X pump.

Toxicol Lett. 2001 Sep 15;123(2-3):159-67

Theanine, a specific glutamate derivative in green tea, reduces the adverse reactions of doxorubicin by changing the glutathione level.

We previously showed that theanine, a specific glutamate derivative in green tea, decreased doxorubicin (DOX)-induced adverse reactions such as the induction of the lipid peroxide level and the reduction of glutathione peroxidase activity in normal tissues. In order to clarify how theanine attenuates the adverse reactions of DOX, we have focused on the effects of theanine on glutamate and glutathione (GSH) levels in normal tissues. The administration of theanine to mice increased the glutamate concentration in the liver and heart, and not in tumors. In vitro examinations indicated that theanine was metabolized to glutamate mainly in the liver. Moreover, theanine inhibited GSH reduction induced by DOX in the liver and heart. Therefore, these results suggested that theanine attenuated the DOX-induced adverse reactions involved in oxidative damage, due to increase in glutamate and the recovery of GSH levels in normal tissues.

Cancer Lett. 2004 Aug 30;212(2):177-84