Characterization, antioxidativity, and anti-carcinoma activity of exopolysaccharide extract from Rhodotorula mucilaginosa CICC 33013

The water-soluble exopolysaccharide REPS2-A was isolated and characterized from R. mucilaginosa CICC 33013. REPS2-A was composed of galactose, arabinose, glucose, and mannose at a molar ratio of 63.1:0.2:18.3:18.3, respectively, with a molecular weight of 7.125 × 106 Da. Based on FT-IR, NMR, and methylation analysis, REPS2-A was identified to be a highly branched polysaccharide with a backbone of (1 → 3)-linked Gal with Man, Gal, and Ara terminals. The branches were identified as (1 → 2)-linked Glc, (1 → 4)-linked Man, (1 → 3)-linked Glc, (1 → 4,6)-linked Man, and (1 → 2,3,4)-linked Ara. In addition, REPS2-A exhibited excellent free radical scavenging (DPPH, ABTS, and reducing power) and antitumor activities. These results indicate its activity against growth of the human hepatocarcinoma cell HepG2 with IC50 values of 1.0 mg/mL, compared to lower cytotoxic effects on normal human hepatocyte cell L02. Studying the underlying mechanisms indicated that REPS2-A induced both dose- and time-dependent cell cycle arrest at the G1/S phase.