Ultrasonic extraction and structural identification of polysaccharides from Prunella vulgaris and its antioxidant and antiproliferative activities

Response surface methodology was used to optimize the ultrasonic extraction of Prunella vulgaris polysaccharides (PVP). When the quality of P. vulgaris was 4.0 g, the optimal extraction conditions were ultrasonic power 210 W, time 50 min, and temperature 70 °C. Using this condition, the experimental yield was agreed closely with the predicted value. Compared with conventional extraction, ultrasonic extraction showed a higher polysaccharide yield. The molecular weights were determined by high-performance gel permeation chromatography. Gas chromatography analysis suggested that PVP comprised of rhamnose, arabinose, xylose, mannose, glucose, and galactose with molar percentages of 2.8, 28.2, 38.5, 11.0, 3.0, and 16.5 %, respectively. The glycosidic linkage analysis showed that PVP contained 1→ and 1→6 glycosidic linkages (48.0 %), 1→2 and 1→4 glycosidic linkages (8.1 %), and 1→3 glycosidic linkages (43.9 %). PVP showed good antioxidant activities by the methods of DPPH radical scavenging assay, oxygen radical absorbance capacity assay, and cellular antioxidant activity assay. The antiproliferative activities of PVP (2.0 mg/mL) on the growth of human hepatoma HepG2, gastric carcinoma SGC 901, and human breast cancer MCF-7 cells were 51.2, 35.2, and 31.8 %, respectively. PVP did not exhibit cytotoxicity against normal liver L02 cells within the tested concentrations. These results demonstrated that polysaccharides isolated from P. vulgaris may be helpful to develop potential antioxidant and antitumor agents for food and pharmaceutical industries.