LC-HRMS/MS phytochemical profiling of Vernonia kotschyana Sch. Bip. ex Walp.: Potential involvement of highly-oxygenated stigmastane-type saponins in cancer cell viability, apoptosis and intracellular ROS production

Vernonia kotschyana Sch. Bip. ex Walp. (Asteraceae) is a traditional African medicinal plant used to treat gastritis, gastroduodenal ulcers, tuberculosis, arthritis, headaches and wounds. The aim of this study was to evaluate the effect of different V. kotschyana root extracts on cell viability, intracellular reactive oxygen species (ROS) levels, cell cycle and apoptosis in human breast adenocarcinoma MCF-7, prostate adenocarcinoma PC3 and alveolar adenocarcinoma A549 cell lines and correlate the observed biological outcomes with the liquid chromatography hyphenated with tandem high-resolution mass spectrometry (LC-HRMS/MS)-based phytochemical profile. The non-polar chloroform (VC) and ethyl acetate (VEA) extracts significantly decreased the viability of the three cancer cell lines at 100 μg/mL (cell viabilities between 30.92 ± 4.12% and 67.93 ± 2.98%), whereas the polar ethanol (VE) and aqueous (VA) extracts were generally less effective. In addition, VC increased the intracellular ROS levels by 2.1–3.8-fold, leading to a clear accumulation of apoptotic cancer cells at the sub-G1 phase. The LC-HRMS/MS profiling of the four extracts revealed two categories of phytochemicals. Caffeoylquinic acids were majorly observed in VEA, VE and VA, whereas highly-oxygenated stigmastane-type saponin glycosides were predominantly present in VC and VEA. Therefore, it can be assumed that the latter class of phytochemicals could play a central role in the observed cancer cell toxicity.