Hindakia tetrachotoma ME03 (Chlorophyta) has high phenolic content, antioxidant capacity, and attenuates H₂O₂-induced oxidative stress and apoptosis in human cells

Oxidative stress damages cellular components and may lead to cell death when it is not effectively counterbalanced by the endogenous antioxidant mechanisms. Exogenous sources of antioxidants are also necessary to cope with high levels of free radicals. Microalgae are rich sources of diverse metabolites with high antioxidant potential. In this study, metabolites of Hindakia tetrachotoma ME03, a green microalga previously isolated from thermal springs in Turkiye, were chemically fractionated using four solvents (ethanol-water, ethyl acetate, hexane and water). The extracts were evaluated for their antioxidant capacities, total phenolics, flavonoids and carotenoids. The highest antioxidant capacity, phenolic and carotenoid contents were obtained in the ethanol-water extracts. The antioxidant capacity in the ethanol-water extracts was measured as 12.42 +/- 1.21 mu mol Trolox g(-1) DW and 67.98 +/- 3.45 mu mol Trolox g(-1) DW by DPPH and FRAP assays, respectively. Twelve different phenolic compounds in the ethanol-water and ethyl acetate extracts were quantified by reverse phase high pressure liquid chromatography. Quercetin and rutin were the most abundant phenolics in the ethanol-water extracts, whereas the ethyl acetate extract was rich in phenolic precursor, benzoic acid. Finally, the cytoprotective effect of ethanol-water extracts of H. tetrachotoma ME03 against H2O2-induced oxidative damage was investigated using an in vitro cell line model of human breast adenocarcinoma (MCF7). Hindakia tetrachotoma ME03 extracts significantly decreased the intracellular reactive oxygen species levels and the percentage of apoptotic and necrotic cells in MCF7 cells. These findings suggest the strong cytoprotective activity of H. tetrachotoma ME03 extracts, which may be conferred by its antioxidative properties.