Structural features of an immunoactive acidic arabinogalactan from Centella asiatica

doi:10.1016/j.carbpol.2004.07.005

Carbohydrate Polymers

Volume 59, Issue 3, 18 February 2005, Pages 281-288

https://doi.org/10.1016/j.carbpol.2004.07.005 Get rights and content

Abstract

A water-soluble acidic arabinogalactan, named HBN with a molecular mass of 5.4×10⁵ Da determined by HPGPC, was obtained from Centella asiatica. HBN contained Ara, Gal, Rha, GalA and Xyl in molar ratios of 1.0:1.9:0.26:0.30:0.15. The acetyl content was estimated to be 2.5%. Using methylation analysis, partial acid hydrolysis, NaIO₄ oxidation–Smith degradation, RI, NMR, ESI-MS, HPGPC, pectolyase-treatment methods, the structure of HBN was elucidated. HBN had a core composed of Rha and GalA, with arabinogalactosyl and xylosyl chains were attached to this core. Seventy-six percent Ara residues were located at termini and linked to O-6 of Gal residues. HBN had remarkable immunoenhancing activities on T- and B-lymphocytes in vitro and vivo tests. It increased spleen index and inhibited the level of IgG. With the stimulation of SAC, it enhanced the secretion of IFN-γ, IL-12 and IL-6, and inhibited IL-10. Its derivatives by NaIO₄ oxidation–Smith degradation and enzyme-treatment possessed immunological activities in vitro.

Introduction

Arabinogalactans are widely distributed in the plant kingdom (Clarke, Anderson, & Stone, 1979). Usually, arabinogalactan contain a high proportion of β-d-Galp and α-l-Araf residues, and smaller and variable levels of a range of other neutral and acidic monosaccharides, including α-l-Arap, α-l-Rhap, β-d-Glcp and β-d-GlcpA (Fincher, Stone, & Clarke, 1983). Arabinogalactans can be grouped into three main structural types. Arabino-1,4/6-β-galactans (type I) have backbone of 1,4-linked Galp. Arabino-1,3/6-β-galactan (type II) have β-1,3-linked galactosyl backbone. Type III is formed by the cell wall glycoproteins containing Ara and Gal (Clarke et al., 1979, Aspinall, 1980, Timell, 1969). Centella asiatica, predominantly growing in the Southern hemisphere, has been used as a remedy for sedation and against leprosy, ulcers (Chopra et al., 1956, Yoshinori et al., 1982, Maquart et al., 1990) in oriental countries. An arabinogalactan (HBN) isolated and purified from C. asiatica was tested in immunological assays and it was found to exhibit significant immunoenhancing activity in comparison with that of other polysaccharides from this plant (Wang, Dong, Zuo, & Fang, 2003). In the present paper, we elucidate the structural features and pharmacological activity of HBN, as well as its structure–activity relationship.

Section snippets

Materials

The dried plant of C. asiatica was purchased from the Shanghai Medicinal Materials Cooperation, P.R. China (code: 000201), and stored as a voucher specimen in the Shanghai Institute of Materia Medica, Shanghai, P.R. China. Pectolyase was obtained from Aspergillus japonicus (P-3026, Sigma). MTT, ConA and LPS (from E. coli., Serotype 055: B5) were products of Sigma. ³H-TdR was obtained from Shanghai Institute of Nuclear Research. Medium RPMI 1640 was purchased from Gibco Laboratories. IFN-γ,

Structural features

HBN, extracted from C. asiatica with hot-water, had specific rotation ${[α]}_{D}^{20} : - 10.4 °$ (ca. 0.70, H₂O). It was repeatedly subjected to Sephacryl S-300 chromatography and Sephadex G-200 gel-permeation chromatography, and assayed using a refractive-index detector and also the phenol–H₂SO₄ method. The results showing HBN was homogeneous. In HPGPC, it showed only one symmetrical peak, and its molecular mass was estimated to be 5.4×10⁵ Da (Fig. 1). No absorption at 280 nm and a negative response to the

Conclusion

HBN, firstly obtained from C. asiatica, is an acidic arabinogalactan. Rha and GalA residues constitute the core, and, arabinogalactosyl chains and Xylosyl chains are attached to O-4 of Rha. Ara residues are linked to O-6 of Gal mostly. Galactosyl chains are very complex and contain the following moieties:

Among the three moieties, the proportion of I is more than the other two (II and III). According to the analysis of the arabinogalactosyl region, which is the main component in HBN, it

Acknowledgements

We are grateful to Mr Yu Zhou and YongXin Ren for their help with the immunological assays and for valuable suggestions.

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Structural features of an immunoactive acidic arabinogalactan from Centella asiatica

Abstract

Introduction

Section snippets

Materials

Structural features

Conclusion

Acknowledgements

Phytochemistry

Carbohydrate Research

Phytochemistry

Carbohydrate Polymer

Carbohydrate Research

Carbohydrate Research

Journal of Immunological Methods

Carbohydrate Research

Journal of Biological Chemistry

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Carbohydrate Research

Carbohydrate Research

Carbohydrate Research

Carbohydrate Research

Structural features of an immunostimulating and antioxidant acidic polysaccharide from the seeds of Cuscuta chinesis

Planta Medica