HPLC-DAD-ESI-MS/MS characterization of bioactive secondary metabolites from Strelitzia nicolai leaf extracts and their antioxidant and anticancer activities In vitro

Background: Strelitzia nicolai Regel and Körn (Strelitziaceae) is native to Southern Africa whose phytochemistry and pharmacology were slightly investigated. Materials and Methods: In the current work, different solvent extracts of S. nicolai were screened for their chemical profiles through high-performance liquid chromatography coupled with diode array detection and electrospray ionization mass spectrometry (HPLC-DAD-ESI-MS/MS) analyses. Furthermore, their in vitro antioxidant, cytotoxic, and anticancer activities were evaluated using 2,2'-diphenyl-1-picrylhydrazyl radical (DPPH), 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) & ferric reducing antioxidant power (FRAP) and crystal violet staining (CVS) colorimetric assays, respectively. Results: HPLC-DAD-ESI-MS/MS analyses led to the identification of nineteen and eleven phenolic compounds from the ethyl acetate and n-butanol extracts, respectively including flavonoids (e.g., quercetin 3-(2 G-rhamnosylrutinoside, quercetin, quercetin-3-O-glucoside, kaempferol-3,7-O-dirhamnoside, isorhamnetin-3-O-rutinoside and kaempferol-3-O-glucoside), phenolic acids derivatives (e.g., chlorogenic acid glycoside, protocatechuic acid-O-glucoside and caftaric acid), chalcones (e.g., xanthoangelol), and phenylethanoids (e.g., ligstroside glucoside). Moreover, in the DPPH assay the IC50value of the most active ethyl acetate extract was 20.49 μg/mL, relative to 2.92 μg/mL of ascorbic acid. ABTS and FRAP results reinforced the results of DPPH assay. According to the National Cancer Institute criteria, the tested extracts showed weak to moderate cytotoxic activities with IC50values ranged from 65.23 to 451.29 μg/mL. Furthermore, the EtOAc and n-BuOH extracts showed a noticeable anticancer activity with CVS spectroscopic readings for liver hepatocellular carcinoma growth 0.806 and 0.684 at a concentration (125 μg/mL), as well as 0.730 and 0.618 at concentration (500 μg/mL), respectively against control at 1.022. Conclusion: The obtained results reveal the high efficacy of the phenolic-rich extracts from S. nicolai as naturally occurring antioxidant and anti-tumor agents. Abbreviations Used: HPLC-DAD-ESI-MS/MS: High-performance liquid chromatography-diode array detection-electrospray ionization-mass/mass; DPPH: 2,2'-Diphenyl-1-picrylhydrazyl radical; ABTS: 2,2'-Azino-bis (3-ethylbenzothiazoline-6-sulphonic acid); FRAP: Ferric reducing antioxidant power; TPTZ: Tripyridyl-s-triazine; FE: Ferrous equivalents; DMEM: