A bioactive polysaccharide from fermented Dark brick tea: Structural characterization and in vitro antitumor activity

Dark brick tea is a traditionally fermented tea originating from China, valued for its unique sensory properties and health-promoting properties. In this study, a polysaccharide fraction (DTP-2) was extracted and purified from Dark brick tea, and its structural features and antitumor activity were investigated. DTP-2 (20,898 Da) comprises glucose, galactose, arabinose, rhamnose, and galacturonic acid in a molar ratio of 40.3:40.3:15.0:2.5:2.0. Methylation analysis and 2 D NMR spectroscopy revealed that the main backbone of DTP-2 consists of →4)-β-D- Galp -(1→, →4,6)-β-D- Galp -(1→, →5)-α-L- Araf -(1→, and →3)-β-D- Galp -(1→ residues, with →4)-α-D- Glcp -(1→ and terminal α-L- Araf -(1→ serving as branch substituents. Congo red analysis suggested that DTP-2 adopts a random coil conformation in aqueous solution. In vitro assays revealed that DTP-2 inhibited the proliferation, induced apoptosis, and suppressed cell migration in human liver cancer SMMC-7721 and lung cancer A549 cells in a dose-dependent manner. Notably, DTP-2 exhibited no obvious cytotoxic effects on normal human liver L02 cells or bronchial epithelial 16HBE cells, indicating that DTP-2 is a natural bioactive polysaccharide that possesses selective antitumor potential in vitro and warrants further investigation.