L-Theanine Mitigates Chronic Alcoholic Intestinal Injury by Regulating Intestinal Alcohol and Linoleic-Arachidonic Acid Metabolism in Rats

Background: Chronic alcohol intake impairs intestinal function, while L-theanine (LTA) may support intestinal health. However, the protective effects of LTA to chronic alcoholic intestinal injuries remain unclear. Methods: SD rats were administered LTA for 8 weeks and then co-administered Lieber–DeCarli liquid alcohol feed and LTA for 4 weeks to establish a chronic alcoholic intestinal injury model and investigate the mitigating influence of LTA on chronic alcoholic intestinal injury. Results: LTA alleviated duodenal pathology and intestinal permeability injury and reduced intestinal oxidative stress and inflammatory response, thereby mitigating chronic alcoholic intestinal injury. Additionally, LTA ameliorated disturbances in the gut microbiota induced by chronic alcohol intake by increasing the beneficial bacteria abundance (Ruminococcus and Odoribacter) and decreasing the harmful bacteria abundance (Enterococcus). Moreover, LTA altered the metabolic profiles associated with ethanol and linoleic (LA) and arachidonic acid (AA) metabolism. ADH6, ALDH2, and ACSS1 mRNA and protein levels were upregulated by LTA, whereas those for CYP2E1, FADS2, ALOX-5, and COX-1 were downregulated. Concurrently, LTA increased the levels of metabolites, such as acetyl-CoA, and decreased the levels of ethanol, acetaldehyde, acetic acid, LA, AA, PGE2, 13-HPODE, and LTB4. Conclusions: L-theanine mitigates chronic alcoholic intestinal injury by regulating intestinal alcohol and LA-AA metabolism. Our findings support the functional potential of the dietary supplement LTA and highlight its potential for addressing chronic intestinal injury caused by chronic alcohol intake.