Phlorotannins from Padina tetrastromatica: structural characterisation and functional studies

In this study, LC–MS/MS-based structural characterisation of phlorotannins from Padina tetrastromatica, a marine brown macroalga collected from South-West coastal region of Kerala, and its bioactivities are presented. The tandem mass spectrometric data revealed a series of phlorotannins with degree of polymerisation ranging from 2 to 18. The characteristic neutral loss of tandem mass spectra further confirmed that these molecules belong to fucophlorethol class of phlorotannins. DPPH assay of the HPLC-purified, phlorotannin-enriched fraction possesses significant free radical-scavenging activity. Cell viability assay indicated that phlorotannin concentration ranging from 1.5 to 50.0 μg mL−1 is non-toxic to THP-1 cell lines. Anti-inflammatory assay performed through gelatin zymography confirmed that phlorotannins ameliorated high-glucose-induced pro-MMP-9 expression in a dose-dependent manner whereas the level of pro-MMP-2 remains unaltered. The antimicrobial assays carried out using both the crude and HPLC-purified phlorotannin fraction showed its anti-MRSA potential.