Phytochemical screening, antioxidant, and cytotoxic activities of sequentially extracted Euclea natalensis leaf extracts

Oxidative stress plays a major role in the pathogenesis of many diseases like diabetes, cancer, cardiovascular diseases, and neurodegenerative diseases. Oxidative stress has become a potential for therapeutic target in the prevention and management of such diseases. This has spiked the interest in the use of natural antioxidants for disease prevention. The present study was aimed at assessing the antioxidant and cytotoxic properties of sequentially extracted Euclea natalensis leaf extracts. The total phenolics and flavonoids were estimated, and antioxidant activity was determined using 2,2-diphenyl-1-picryl hydrazyl (DPPH), 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid (ABTS), total antioxidant capacity, and the ferric reducing/antioxidant power (FRAP) assays. The cytotoxic capacity against HeLa cells was evaluated using WST-1 (4-3-(4-Iodophenyl)-2-(4-nitro-phenyl)-2H-5-tetrazolio-1,3-benzene sulfonate) colorimetric assay. Qualitative phytochemical screening showed the presence of phytochemicals such as phenols, flavonoids, tannins, terpenoids and glycosides except in the hexane extract. The total phenolic and flavonoid content ranged from 0.58–118.7 mg GAE/g DW and 9.8–20.1 mg GAE/g DW respectively. All extracts displayed a concentration-dependent inhibition of DPPH and ABTS, with IC50 values in the range 0.04–0.122 mg/mL and 0.079–0.205 mg/mL respectively. The aqueous extract had the highest total antioxidant capacity and ferric reducing power of 40.4 mg AAE/g DW and 0.98 mg Vitamin C equivalence/g DW. The IC50 value for cytotoxicity was in the range 155.3–211.3 mg/mL with the dichloromethane-methanol extracts being the least cytotoxic. It was concluded that Euclea natalensis leaf extracts contain bioactive phytochemicals with antioxidant potential and less cytotoxic capacity.