Cellular antioxidant activities and cytotoxic properties of ethanolic extracts of four tropical green leafy vegetables

The present investigation sought to evaluate cellular antioxidant activities of some green leafy vegetables: Vernonia amygdalina, Asteraceae (Va,); Manihot utilissima Pohl., Euphoriaceae (Mu);Corchorous olitorius L., Malvaceae (Co) and Occimum gratissimum L., Lamiaceae (Og) against peroxyl radical-induced oxidation in HepG2 cells and also evaluate their cytotoxic properties against drug sensitive and drug resistant Lovo and Lovo/Adr cancer cell lines respectively. HPLC/DAD/MS investigation of the ethanolic extract of the vegetal matter revealed the presence of 4, 5, 6, and 7 phenolic compounds in Mu, Co, Og and Va respectively. The cellular antioxidant activity was tested with different concentrations (0.1, 0.25, 0.5 and 1.00 mg/ml dried weight) of the extracts. At a concentration of 1.00 mg/ml, the quenching of peroxyl radical in HepG2 cells as shown by the fluorescence units revealed that Og has the best inhibition capacity, followed by Co, Va respectively and with the least inhibition capacity recorded for Mu. However, pro-oxidant activities were observed at lower concentrations of Va (0.1 mg/ml) and Mu (0.1, 0.25 and 0.5 mg/ml). Cytotoxic investigation revealed that the extracts were active against both cell lines with EC50 (µg/ml) ranging from 1.3 to 2.6 for Lovo and 1.5 to 2.7 for Lovo/Adr respectively, and that Va was the most active, while the least activity was recorded for Mu and Co for Lovo and Lovo Adr respectively. The observed cytotoxic properties and the elicited antioxidant activities would be due to the phytochemical constituents among which could be the rich content of flavonoids and cynammoyl derivatives as revealed by the chromatographic investigations.