Unveiling the anti-proliferative and pro-thermogenic activity of Staurosirella pinnata (Bacillariophyta) bioproducts

Biorefinery co-products obtained from biomass of the field isolated diatom Staurosirella pinnata have been investigated for their bioactivity on selected human and murine cell lines. Biomass grown in indoor photobioreactor, collected at the stationary phase, was subjected to methanolic extraction to produce a crude extract, sequentially fractionated (hydrophilic-hydrophobic gradient) to obtain six fractions (A4, A5, A7; B4, B5, B6). Fractions' bioactivity was tested on BRAFwt and BRAFV600E human melanoma cell lines, compared to normal keratinocytes. All fractions showed cytotoxic activity, but only fraction A4 showed a remarkable cell-type selectivity, with cell death induction up to 70 % on melanoma cells. Further characterization allowed to identify and purify four apocarotenoids from fraction A4, representing the first report of such class of compound s in mass cultivated diatoms. In addition, fraction A5 resulted to be a mixture of oxylipins and fraction B4 of purine nucleosides, with adenosine as main component. Residual biomass was further processed to obtain an enriched lipidic extract, characterized by a high content of poly-unsaturated fatty acids. Anti-diabetic and anti-obesity activities were assessed by evaluating the expression levels of key proteins involved into thermogenesis (UCP1), lipolysis (Perilipin, HSL660), and mitochondrial dynamics (pDRP1, VDAC), on murine white adipocyte cell line. Overall, the data here reported confirmed S. pinnata as a platform for the discovery and purification of bioactive compounds with biomedical potential, and the biorefinery pipeline allow their combined isolation, thus advancing the sustainability of diatom exploitation for the discovery and production of bioactive molecules.