Bioactivity of autotrophic and mixotrophic Tetraselmis chuii (CCAP 66/21B) extracts against H₂O₂-mediated stress in A549 cells.

The trophic regime experienced by microalgae can influence their accumulation of antioxidant products such as phenolic compounds. This study investigated the antioxidant capacity and bioactivity of Dulbecco's phosphate-buffered saline (DPBS) extracts from the marine chlorophyte Tetraselmis chuii (CCAP 66/21B) cultivated under autotrophic and mixotrophic regimes. Compared to autotrophic conditions, mixotrophic cultivation significantly increased biomass yield (6.0-fold), soluble protein yield (5.7-fold) and Trolox-equivalent antioxidant capacity as measured by Folin-Ciocalteu (6.8-fold), DPPH (42.2-fold) and ABTS (15.3-fold) assays. For bioactivity, DPBS extracts (normalised by soluble protein content) were examined for their protective effects against hydrogen peroxide (H₂O₂)-mediated apoptosis in pulmonary carcinoma epithelial cells (A549). Both autotrophic and mixotrophic-derived extracts exhibited a dose-dependent response in H₂O₂-stressed A549 cells, with significant cytoprotection observed at higher concentrations (200 µg soluble protein mL⁻¹), while lower concentrations were insufficient to mitigate oxidative damage and were associated with reduced cell viability. These effects involved modulation of apoptosis-related mRNA expression (BCL2 and BAX). The bioactive content of both autotrophic and mixotrophic-derived extracts exhibited similar biological activity with properties that may be beneficial in pulmonary pharmacology. Importantly, mixotrophy significantly upregulated the bioactive content of T. chuii (CCAP 66/21B) compared to obligate autotrophy (34.2-fold accounting for soluble protein yield and biomass generation).