Cytoprotective Effect of Trachystemon orientalis against cigarette smoke extract- Induced toxicity on human bronchial epithelial cells

Trachystemon orientalis D.Don is a perennial species belonging to the family Boraginaceae. It is predominantly distributed in the northern parts of Türkiye. The stems, roots, and aerial parts of the species are consumed as food and traditionally used in the treatment of various types of cancer. The aim of this study was to evaluate the cytoprotective effects of its extracts and metabolites against cigarette smoke extract (CSE)-induced toxicity on BEAS-2B cells. For the study, T. orientalis roots (A) and aerial parts (B) were extracted separately using 80 % methanol. B exhibited a higher cytoprotective effect than A on the BEAS-2B cell line for 24 h. Therefore, B was partitioned against n-hexane (B1) and n-butanol (B2) to yield sub-extracts. B2 exhibited the lowest cytotoxicity profile among the tested concentrations (0.1–1 mg/mL). Chromatographic separation on B2 led to the isolation of rosmarinic acid (1), kaempferol 3-O-glucoside (astragalin) (2), and kaempferol 7-O-glucoside (3). Notably, compound 2 was isolated for the first time from the genus Trachystemon, while compound 3 was obtained for the first time from the family Boraginaceae. The extract B2 (0.1 mg/mL), and isolated compounds 1 (50 μM), 2 (12.5 μM), and 3 (25 μM) exhibited statistically significant cytoprotective activity against CSE-induced cytotoxicity on human bronchial epithelia in the MTT assay. It is anticipated that these findings will provide valuable insights into the development of plant-based adjuvant therapies for respiratory diseases, with a particular focus on secondary metabolites that are responsible for cytoprotective activity.