From folk medicine to functional biology: the dual roles of phenolics in enterocyte health

Introduction: Medicinal plants native to Northern Portugal — such as Tanacetum balsamita, Cymbopogon citratus, Aloysia citrodora, Thymus vulgaris, and Rosmarinus officinalis — are well recognised for their traditional use and their abundance in phenolic compounds. These bioactive molecules, including flavonoids and phenolic acids, are associated with multiple biological activities, such as antioxidant, anti-inflammatory, and antimicrobial effects. In the context of gut health, dietary phenolics can modulate intestinal homeostasis by influencing redox balance, inflammatory responses, and epithelial integrity. Enterocytes play a central role in maintaining intestinal barrier function and mediating metabolic and immune signalling, making them an appropriate in vitro model for assessing the biological impact of plant-derived extracts. This study aimed to investigate the cytotoxicity and antioxidant potential of phenolic-rich extracts obtained from the selected Portuguese medicinal plants using intestinal epithelial cell models. The goal was to identify safe and biologically active candidates for further exploration as functional food ingredients or nutraceutical agents supporting intestinal health. Conclusions: The evaluated extracts were no cytotoxic towards Caco-2 cells at 310 μg/mL (CC), 160 μg/mL (TB and Th) and 20 μg/mL (RO). Extracts were capable of modulating cellular antioxidant activity in the presence of a pro-inflammatory stimuli with statistically significant (p < 0.01 (*), p < 0.001 (**) and p < 0.0001 (***)) reductions observed, and TB showing the highest activity. Pearson correlation showed that distinct chemical classes show opposing correlations with cytotoxicity and CAA, indicating that different metabolites contribute variably to antioxidant and cytotoxic effects under stimulated and non-stimulated conditions. Pairwise correlation showed that distinct chemical classes show specific associations with cellular antioxidant activity, with terpenoids correlating positively and flavonoids negatively with CAA responses. PCA clearly separates extracts according to their CAA response, highlighting differential antioxidant behaviour under stimulated and non-stimulated conditions.