Protective effects of L-theanine against bisphenol A-induced oxidative stress and gut microbiota disruption in Wistar rats

Gut microbiota homeostasis plays a central role in maintaining intestinal redox balance and immune regulation. Bisphenol A (BPA), a widely distributed environmental contaminant, has been associated with oxidative stress, inflammatory responses, and disturbances in intestinal microbial communities. L-theanine (LTN), a bioactive amino acid naturally present in green tea, possesses well-documented antioxidant and anti-inflammatory properties; however, its potential protective role against BPA-induced intestinal injury has not been fully clarified.

In the present study, female Wistar albino rats were randomly allocated into three groups: control, BPA (50 mg/kg/day), and BPA + LTN (100 mg/kg/day) and treated for 30 days. Oxidative stress and inflammatory responses in intestinal and colonic tissues were assessed by measuring malondialdehyde (MDA), reduced glutathione (GSH) levels and myeloperoxidase (MPO), catalase (CAT) activities. BPA exposure significantly increased MDA (p < 0.001) level and MPO (p < 0.001) activity while reducing GSH content (p < 0.001) and CAT activity (p < 0.001) compared with the control group. Compared to the BPA group, LTN treatment led to significant changes in MDA, MPO, and GSH levels in both tissues. MDA and MPO levels were significantly reduced in the intestine and colon tissues of the BPA + LTN group (p < 0.001). GSH and CAT levels were significantly increased in both the intestine and colon compared to the BPA group (p < 0.001). In addition, fecal microbiota composition was analyzed using 16 S rRNA gene sequencing, with taxonomic profiling performed at the phylum, genus and species levels. BPA exposure was associated with reduced microbial stability and compositional shifts within the gut microbiota, whereas LTN treatment partially restored microbial richness and community structure.

Collectively, these findings indicate that LTN alleviates BPA-induced intestinal oxidative stress and microbiota dysbiosis, suggesting its potential as a protective dietary compound against environmental toxicant-related intestinal injury.