Antioxidant, Antidiabetic, Antiproliferative Activities, and Verbascoside Content of Four Endemic Verbascum Species: V. leiocarpum, V. ozturkii, V. alyssifolium, and V. tuna-ekimii

This study, for the first time, investigated the antioxidant, antidiabetic, and antiproliferative properties of methanolic extracts from the aerial and root parts of four endemic Verbascum species—Verbascum leiocarpum Murb., Verbascum ozturkii Karavel., Uzunh. & S.Çelik, Verbascum alyssifolium Boiss., and Verbascum tuna-ekimii Karavel., A.Duran & Hamzaoğlu—and quantitatively determined their verbascoside content using HPLC-DAD. Antioxidant capacity was evaluated by DPPH and FRAP assays, and total phenolic content (TPC) and total flavonoid content (TFC) were also determined. Antidiabetic activity was assessed through α-glucosidase inhibition, and antiproliferative effects were determined in A549, MDA-MB-453, and HT-29 human cancer cell lines. Among the tested samples, the root of V. leiocarpum exhibited the highest TPC (50.89 mg GAE/g extract), FRAP value (124.16 mg TE/g extract), DPPH scavenging ability (IC50: 58.82 μg/mL), and verbascoside content (129.06 mg verbascoside/g extract). This extract also exhibited significant antiproliferative effects against A549 and MDA-MB-453 cells, with inhibition rates of 85% and 69%, respectively. In contrast, both aerial and root extracts of V. tuna-ekimii exhibited low biological activity and a lower concentration of verbascoside. Pearson correlation analysis demonstrated strong positive associations between verbascoside content and both antioxidant and antiproliferative parameters. However, no significant correlation was found between verbascoside content and α-glucosidase inhibition, suggesting that other phytochemicals may be responsible for the antidiabetic activity. These findings indicate that V. leiocarpum, especially its root extract, may be considered a valuable source of natural antioxidants and antiproliferative agents. The study highlights the pharmacological potential of endemic Verbascum species that have not been comprehensively investigated phytochemically or pharmacologically and supports their further evaluation in the context of phytopharmaceutical research. © 2026 Royal Society of New Zealand Te Apārangi.