Effects of Moringa oleifera leaf extracts and its bioactive compound gallic acid on reducing toxicities of heavy metals and metalloid in Saccharomyces cerevisiae.

Moringa oleifera leaf extract is rich in antioxidants and has high potential for use to alleviate metal toxicity. Previously, we have reported the roles of aqueous M. oleifera leaf extract in mitigating intracellular cadmium (Cd) accumulation and Cd-induced oxidative stress. In this study, we investigated the protective role of aqueous and/or ethanolic M. oleifera leaf extracts (AMOLE and/or EMOLE) against other metal(loid)s in the eukaryotic model Saccharomyces cerevisiae. Our results show that only the AMOLE remarkably promoted the growth of yeast cells grown in the presence of arsenite (As(III)), Cd, nickel (Ni), and lead (Pb). Although the AMOLE contained lower amount of total phenolic and flavonoid contents and displayed lower DPPH scavenging capacity than the EMOLE, both AMOLE and EMOLE had the same capacity for reducing intracellular ROS levels in yeast cells exposed to As(III), Cd, Ni, and Pb. Moreover, the AMOLE was more effective than the EMOLE in inhibiting intracellular accumulation of these toxic metal(loid)s. In addition, we found that gallic acid, one of important phenolic constituents present in both extracts, could protect yeast cells against As(III) toxicity, likely through its role in decreasing As(III) accumulation and As(III)-induced ROS production. Furthermore, the hydroxyl and carboxyl groups of gallic acid appear to play a critical role in chelating As(III). The present study suggests the promising applications of the AMOLE (and also gallic acid) as protective agents against hazardous metal(loid)s.