Theanine, an antitumor promoter, induces apoptosis of tumor cells via the mitochondrial pathway

Abstract

Theanine, an active component of green tea (Camellia sinensis), is considered a modulator of chemotherapy. To further investigate the anticancer activity of theanine, the present study investigated the cytotoxic effect of theanine at the concentration of 600 µg/ml, in the human HepG2 hepatoblastoma and HeLa adenocarcinoma cell lines, in comparison with the normal L02, H9c2 and HEK293 cell lines using a MTT assay. It was found that theanine induced cell death in the tumor cells, but not in the normal cells. Notably, when glutamine was restricted or reduced in the cell culture medium, the cell death induced by theanine was significantly enhanced. A terminal deoxynucleotidyl‑transferase‑mediated dUTP nick end labeling assay indicated that DNA damage was induced in theanine‑treated HepG2 cells. Further experiments demonstrated that theanine caused HepG2 cell apoptosis through the mitochondrial pathway, with a loss of membrane potential and the release of apoptosis‑inducing factor, endonuclease G and cytochrome c. Western blot analysis and caspase activity detection also revealed that caspase‑9 and caspase‑3 were activated, whereas caspase‑8 remained inactive. These observations suggested that theanine exerted potent cytotoxicity on tumor cells when glutamine was restricted.

Theanine and cancer: A systematic review of the literature

“…Four in vitro studies confirmed apoptotic effects of theanine on the liver cancer HepG2 (Xin et al, 2018), hepatocellular carcinoma SMMC7721 (G. Zhang et al, 2016), Lewis lung cancer (LLC) (Ji et al, 2014), and cervical HeLa (J. Liu et al, 2016) cells.…”

“…The main characteristics and results of the included studies are summarized in Tables 2 and 3. Of the 14 included articles, three were in vitro (Ayoub & Melzig, 2006; Friedman et al, 2007; Xin et al, 2018), four were in vivo (Fujii & Inai, 2008; Shojaei‐Zarghani, Khosroushahi, & Rafraf, 2020a; Sugiyama & Sadzuka, 1998; W.‐J. Zeng et al, 2018; G. Zhang et al, 2002), and seven were designed by a different combination of in vitro, ex vivo, and in vivo methods (Fan et al, 2020; Ji et al, 2014; J. Liu et al, 2016; Q. Liu et al, 2009; G. Zhang et al, 2016; G. Zhang et al, 2001; Zhao et al, 2019).…”

“…In the mitochondrial pathway, loss of membrane potential happens after cell stimulation, which induces cytochrome c efflux (Ly, Grubb, & Lawen, 2003; Zhang, B.‐b., Wang, D.‐g., Guo, F.‐f., & Xuan, C., 2015). Based on the reviewed studies, theanine may stimulate the intrinsic apoptosis pathway and caspase‐independent programmed cell death (through apoptosis‐inducing factor and endonuclease G) (Ji et al, 2014; J. Liu et al, 2016; Xin et al, 2018; G. Zhang et al, 2016), and so exhibits anticancer activity.…”

“…The main characteristics and results of the included studies are summarized in Tables 2 and 3. Of the 14 included articles, three were in vitro (Ayoub & Melzig, 2006;Friedman et al, 2007;Xin et al, 2018), four were in vivo (Fujii & Inai, 2008 The median STAIR score across the animal studies was 5 out of 10 (range: 4-5) (Table S4). Besides, according to the ARRIVE guidelines, the median quality score was 19 out of 36 (range: 18-21) (Table S5).…”

L-Theanine: A Unique Functional Amino Acid in Tea (Camellia sinensis L.) With Multiple Health Benefits and Food Applications

“…Secondly, L-theanine could induce or inhibit the digestive system cancers. It was shown that L-theanine (600 μg/mL) could induce apoptosis of tumor cells through the mitochondrial pathway in human HepG2 hepatoblastoma cells and HeLa adenocarcinoma cells ( 71 ). Furthermore, L-theanine and its semi-synthesized derivative (R)-2-(6,8-dibromo-2-oxo-2H-chromene-3-carboxamido)-5-(ethylamino)-5-oxopentanoic ethyl ester (DTBrC) also restrained the growth and migration of human hepatocellular carcinoma (HHC) cells in in vitro , ex vivo , and in vivo HHC models, and the mechanism of this effect was that L-theanine and DTBrC blocked the Met/EGFR/vascular endothelial growth factor receptor (VEGFR)-Akt/NF-κB pathways ( 72 ).…”