Isolation, structure and activity of a novel water-soluble polysaccharide from Dioscorea opposita Thunb

https://doi.org/10.1016/j.ijbiomac.2019.04.087Get rights and content

Abstract

A previously unknown, water-soluble polysaccharide, named DOTP-B, was isolated from the roots of the plant Dioscorea opposita Thunb, a well-known edible and medicinal plant in China. DOTP-B was found to be neutral in charge, with an average molecular weight of 5623 Da. Monosaccharide composition analysis by GC–MS revealed that DOTP-B was a hetero-polysaccharide consisting of glucose and galactose at a molar ratio of 14.6:1.0. Structural features of DOTP-B were investigated with a combination of chemical and instrumental methods, including complete acid hydrolysis, periodate oxidation, methylation, GC–MS, FTIR and several NMR spectra. Highly correlated results demonstrated that the main chain of DOTP-B consisted of →4)-α-d-glc(1 → residues, with about 6% internal →6)-β-d-gal(1 → residues. The antioxidant activity of DOTP-B was also evaluated as the EC50 values against DPPH and PTIO radicals were 2.1 ± 0.1 mg/mL and 1.6 ± 0.1 mg/mL, respectively. Therefore, the polysaccharide DOTP-B could be possibly developed as a promising natural antioxidant for application in medical and food industries.

Introduction

Dioscorea opposita Thunb (D. opposita), a perennial twining vine plant (family: Dioscoreaceae, Dioscorea), is an edible and traditional Chinese medicinal (TCM) plant [1]. Its tubers are often used to treat poor appetite, chronic diarrhea, asthma, dry coughs, frequent or uncontrollable urination and diabetes [2]. The polysaccharides of D. opposita are considered to be the main active components. Accordingly, D. opposita has become a research topic of interest in recent years [3]. Existing research shows that the polysaccharides of D. opposita have many other therapeutic effects, such as anti-aging [4,5], immunoregulation [6,7], antioxidation [8,9], anti-fatigue [10], hypoglycemic activity [11,12], blood pressure suppressor [13,14], anti-tumor [15] and intestinal microecology modulation [16].

To date, most studies on D. opposita have examined the activities of crude extracts, and low molecular weight substances, such as diosgenin, trace elements, alkaloids, allantoin and dopamine [3,17,18]. However, due to the complexity of structural and compositional analysis of polysaccharides, little progress has been made on the isolation, purification and activity analysis of the water-soluble polysaccharides from D. opposita [[18], [19], [20], [21]]. Since the structure and functions of polysaccharides are closely related, in-depth study of such structures are needed. Therefore, the aim of this work was to isolate and characterize the structure as well as activity of a novel water-soluble polysaccharide, DOTP-B, from the roots of D. opposita.

Section snippets

Materials and chemicals

The roots of Dioscorea opposita Thunb, was collected from Wenxian, Henan province, China. It was identified and authenticated by Dr. Huzhigang, College of Pharmacy, Hubei University of Chinese Medicine. The voucher specimen was deposited in the Department Museum. The roots were air dried and ground into a fine powder in a mill.

DEAE-cellulose DE-52 was purchased from BOMEI BIOTECHNOLOGY.CO (Hefei, China). Dextrans of different molecular weights and pure monosaccharide standards were obtained

Isolation and purification of the polysaccharide

In summary, 108.0 g of water-soluble crude polysaccharide, named DOTPs, was isolated from 1.8 kg of dried roots powder of D. opposite, with a yield of 6.0%. DOTPs were purified after employing DEAE-cellulose 52 and Amicon Ultra-15 ml Centrifugal Filter Units (10 kDa and 3 kDa). The DOTP-B fraction was collected and lyophilized with a yield of 0.76 ± 0.09% for further analysis of structure and antioxidant activity. Remarkably, DOTP-B showed a single and symmetrical peak on HPGPC (Fig. 1),

Conclusion

In this study, a purified polysaccharide from the roots of D. opposite Thunb (DOTP-B) was isolated using DEAE cellulose and Amicon Ultra-15 ml Centrifugal Filter Units. HPGPC analysis and GC–MS analysis demonstrated that DOTP-B was characterized as a homopolysaccharide with an average molecular weight of 5623 Da and consisted of glucose and galactose at a molar ratio of 14.6:1.0. Structural analysis demonstrated that DOTP-B has a backbone made of →4)-α-d-Glcp(1 → and →6)-β-d-Galp(1 → (14:1)

Acknowledgements

This study is financially supported by the Research Fund of the Major Projects of Technology Innovation of Department of Science and Technology, Hubei Province (Grant No. 2016ACA145), which is gratefully acknowledged.

Author contributions

Fei Zhi performed the chemical experiments, analyzed the structure characteristics and preparation of the manuscript; Tian-Le Yang and Qiang Wang extracted the crude polysaccharide and purified the polysaccharide; Bin Jiang developed the NMR experiment and conducted the data analysis; Zhong-Ping Wang and Jing Zhang performed the antioxidant activity experiments and conducted the data analysis; Yun-Zhong Chen designed the whole experiments and revised the paper.

Declaration of conflicts of interest

The authors declare no conflicts of interest.

Availability of data statement

All data included in this study are available upon request by contact with the corresponding author.

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