Protective Effect and Mechanism of L‐Theanine on Acute Alcoholic Liver Injury in Mice

SCOPE: Acute alcoholic liver injury (AALI), a global health concern, is exacerbated by excessive episodic drinking. L-theanine (LTA), a compound found in tea leaves, mitigates the AALI-induced liver oxidative stress and inflammation. However, its relationship with alcohol metabolism and its liver-protective mechanism remains unexplored. METHODS AND RESULTS: This study investigates the protective mechanisms of LTA against AALI in mice. The results demonstrate that LTA mitigates liver tissue damage and reduces the serum levels of aspartate aminotransferase and alanine aminotransferase, and liver levels of triglycerides, malondialdehyde, reactive oxygen species (ROS), tumor necrosis factor-α, interleukin-6, and interleukin-1β. However, LTA enhances the activity of ethanol-metabolizing enzymes and decreases ethanol and acetaldehyde serum levels. Mechanistically, LTA accelerates alcohol metabolism by upregulating the hepatic expression of ADH6, ALDH1B1, ALDH2, CAT, and ACSS1 mRNA and protein in AALI mice, LTA downregulates the expression of CYP2E1 mRNA and protein and promoting antioxidative activities thus reducing the accumulation of ROS. This attenuated inflammation by inhibiting the phosphorylation of nuclear factor-kappa B inhibitor alpha (IκBα) and downregulating the hepatic expression of NF-κB p65, TNF-α, IL-1β, IL-6 mRNA, and protein. CONCLUSION: LTA is a beneficial dietary supplement that protects against AALI by modulating alcohol metabolism and the TNF-α/NF-κB pathway.