In vivo antioxidative effects of l-theanine in the presence or absence of Escherichia coli-induced oxidative stress

l-Theanine (LTA), a non-protein-derived amino acid, is isolated from tea and is used as dietary supplement or beverage ingredient. This study established an enterotoxigenic Escherichia coli (ETEC)-infected mouse model of oxidative stress to examine the antioxidative mechanisms of LTA in vivo. LTA regulated non-enzymatic antioxidative activity and increased catalase (CAT) mRNA expression in non-ETEC-infected mice. In addition, LTA decreased oxidative parameters and the activity and mRNA levels of CAT in ETEC-infected mice. LTA increased superoxide dismutase (SOD) activity and mRNA expression of CuZn-SOD, ECSOD and glutathione peroxidase 1 (Gpx1); it restored MnSOD mRNA levels as well. Our results demonstrate that LTA has antioxidative properties via regulation of non-enzymatic pathways. In addition, LTA protects against superoxide and hydrogen peroxide via SOD or Gpx1 as the first and second defence line. Thus, LTA differentially regulates antioxidative enzymes depending on the dose and pathophysiological conditions through transcription, post-transcriptional and post-translational mechanisms in mice.