Characterization of a heteropolysaccharide isolated from diploid Gynostemma pentaphyllum Makino
Highlights
► A new polysaccharide was isolated from Gynostemma pentaphyllum Makino. ► Its chemical structure was determined. ► The polysaccharide showed antioxidant and bile acid binding capacities.
Introduction
Gynostemma pentaphyllum Makino (Cucurbitaceae), a perennial liana herb, has been used in beverage, food and traditional herb medicine. The botanical is widely distributed in China, Korea, Japan and Southeast Asia. G. pentaphyllum Makino has been used to prevent and treat cardiovascular disease, hyperlipidaemia, hypertension, hepatitis, diabetes and cancer (Lu et al., 2008). The known chemical constituents of G. pentaphyllum Makino include but are not limited to saponins (Zhang et al., 2010b), carotenoids (Liu, Kao, & Chen, 2004), flavonoids (Xie et al., 2011), chlorophylls (Huang, Hung, Wu, & Chen, 2008), lignin (Wang, Zhang, Chen, Wang, & Wen, 2009), polysaccharides (Yang, Zhao, Yang, & Ruan, 2008). Among them, saponins, well known as gynosaponins or gypenosides, are believed to be the functional components responsible for its diverse biological properties (Bai et al., 2010). However, recent studies suggested that the polysaccharide components exhibited significant bioactivities, such as antioxidant (Wang & Luo, 2007), anti-exercise fatigue (Chi, Chen, Wang, Xiong, & Li, 2008), antitumor (Chen et al., 2011) and immunostimulatory activities (Yang et al., 2008). Polysaccharides may have greater bioavailability because they may be water soluble and could be soaked out easily into tea infusion compared with saponins and essential oil (Yang et al., 2008). To date, very few studies investigated the chemical structure and bioactivities of G. pentaphyllum polysaccharides.
Oxidation is essential to many living organisms for energy production through biological processes. However, the uncontrolled production of oxygen-derived free radicals may cause lipid peroxidation, DNA damage and protein oxidation, which may lead to impaired living cells. There are growing evidences showed that lipid peroxidation and toxicity associated with free radicals may induce cancer, atherosclerosis and aging process. Potent natural antioxidants with low cytotoxicity are in high demand for reducing the risk of chronic human diseases because of the potential toxicity of synthetic antioxidants such as BHA (Yuan, Zhang, Fan, & Yang, 2008). Many polysaccharides have showed antioxidant capacities (He et al., 2012, Wang et al., 2012, Wu et al., 2012, Ye and Huang, 2012). Polysaccharides may also bind bile acids and fats in the intestine and enhance their excretion, which stimulates the conversion of cholesterol to bile acids in liver, and consequently reduce plasma and LDL cholesterols (Liu et al., 2010a, Liu et al., 2010b, Niu et al., 2012).
In this study, a novel polysaccharide, named GPP, was purified from G. pentaphyllum Makino. Its monosaccharide composition and chemical structure were characterized by chemical and instrumental analyses. The in vitro antioxidant activity and bile acid binding property of the GPP were also determined. The results are important for developing G. pentaphyllum polysaccharides derived nutraceutical and functional food products.
Section snippets
Materials
Diploid whole-plant G. pentaphyllum Makino, grown in the Dabashan area of Shaanxi province of China in 2009, was gifted by the Asian Citrus Holdings Limited (Hong Kong, China). After being washed using tap water, the sample was dried at 70–76 °C, then pulverized and kept in zip lock bags. The ploidy was identified by root tip chromosome checking.
Diethylaminoethyl Cellulose (DE-32) was purchased from Whatman International Ltd. (Kent, UK). Ambelite IRA-93 was purchased from Polysciences, Inc.
Isolation and purification
The crude polysaccharide with a yield of 2.57 g/100 g was isolated by hot water extraction from dry G. pentaphyllum Makino powder. After purification through DEAE-cellulose-32 column, GPP was obtained as the one major peak eluted with distilled water. The total carbohydrate content of GPP was 98.7%.
HPLC analysis (Data not shown) showed a single, symmetric and sharp peak, which indicated that GPP was homogeneous, with a purity of 97.3%. No significant absorbance was observed at 260 nm or near 280 nm
Conclusion
A novel bioactive polysaccharide, GPP, was obtained from the whole-plant of diploid G. pentaphyllum Makino. Its molecular weight was 7.1 × 103 Da with a 1,4)-linkage-α-glucose backbone, branch chain of -1)-α-glucose-(4,6-linkage and mainly terminal residue of -1)-α-glucose. GPP is an effective HO, O2− and DPPH scavenging agents and has significant bile acid-binding capacity, suggesting its possible application as nutraceuticals in reducing the risk of heart diseases. Additional research shall
Acknowledgments
This research was partially supported by a grant from the China Postdoctoral Science Foundation (2012M511098), a grant from the Joint Institute for Food Safety and Applied Nutrition (JIFSAN), grants from SJTU 985-III disciplines platform and talent fund (Grant Nos. TS0414115001; TS0320215001), a grant from Major National Science and Technology Project of China for Significant New Drugs Creation (2012ZX09502001-004), a research gift from the Asian Citrus Holdings Limited (Hong Kong), and a
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Authors contributed to the manuscript equally.