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. 2022 Feb 25:13:839635.
doi: 10.3389/fphar.2022.839635. eCollection 2022.

Relationship Between the Structure and Immune Activity of Components From the Active Polysaccharides APS-II of Astragali Radix by Enzymolysis of Endo α-1,4-Glucanase

Ke Li  1   2   3   4 , Xue-Qin Li  1   3   4 , Guang-Xin Li  5 , Lian-Jie Cui  1   3   4 , Xue-Mei Qin  1   3   4 , Zhen-Yu Li  1   3   4 , Yu-Guang Du  2 , Yue-Tao Liu  1   3   4 , Ai-Ping Li  1   3   4 , Xing-Yun Zhao  1   3   4 , Xin-Hui Fan  1   3   4
Affiliations

Relationship Between the Structure and Immune Activity of Components From the Active Polysaccharides APS-II of Astragali Radix by Enzymolysis of Endo α-1,4-Glucanase

Ke Li et al. Front Pharmacol. .

Abstract

Astragali Radix polysaccharides (APSs) have a wide range of biological activities. Our preliminary experiment showed that APS-Ⅱ (10 kDa) was the main immunologically active component of APSs. However, the characteristic structure related to activity of APS-Ⅱ needs further verification and clarification. In this study, APS-II was degraded by endo α-1,4-glucosidase. The degraded products with different degrees of polymerization [1-3 (P1), 3-6 (P2), 7-14 (P3), and 10-18 (P4)] were obtained using a polyacrylamide gel chromatography column. The structural features of the different products were characterized by HPGPC, monosaccharide composition, Fourier transform infrared spectrum, GC-MS, nuclear magnetic resonance, and UPLC-ESI-QTOF-MS analysis. Specific immune and non-specific immune cell tests were used to identify the most immunogenic fractions of the products. The backbone of P4 was speculated to be α-D-1,4-linked glucans and rich in C2 (25.34%) and C6 (34.54%) branches. Immune screening experiments indicated that the activity of P4 was better than that of APS-II and the other three components. In this research, the relationship between the structure of APS-Ⅱ and the immune activity from the degradation level of polysaccharides was studied, laying a foundation for the quality control and product development of APSs.

Keywords: APS-Ⅱ; enzymolysis; immune activity; structure analysis; structure-activity relationship.

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Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

FIGURE 1
FIGURE 1
HPLC chromatogram of standard oligosaccharide samples (A), APOS (B), P1 (C), P2 (D), P3 (E), and P4 (F). 1–17: chromatographic peak of dextran with degree of polymerization of 2–18.
FIGURE 2
FIGURE 2
Mixture monosaccharide standard of HPLC–UV chromatogram (A); (B–G) indicate the HPLC–UV chromatogram of APS-II, APOS, P1, P2, P3, and P4.1: PMP, 2: glucuronic acid, 3: rhamnose, 4: galacturonic acid, 5: glucose, 6: galactose, 7: arabinose.
FIGURE 3
FIGURE 3
FT-IR spectra of APS-II (A), APOS (B), P1 (C), P2 (D), P3 (E) and P4 (F).
FIGURE 4
FIGURE 4
1H–NMR (A), 13C–NMR (B), HMBC (C), and HSQC (D) spectra of APOS.
FIGURE 5
FIGURE 5
Mass spectra of two to nine sugars from APOS (A–H).
FIGURE 6
FIGURE 6
Possible repeating unit of APOS.
FIGURE 7
FIGURE 7
Effects of different saccharide components on phagocytic activity (A), killing activity of mouse spleen NK cells (B), proliferation of B lymphocytes (C), proliferation of T lymphocytes (D), and IgG secretion of splenic lymphocytes (E) (n = 6, *p < 0.05, **p < 0.01, ***p < 0.001 versus APS-II; # p < 0.05, ## p < 0.01, ### p < 0.001 versus blank control group).
See this image and copyright information in PMC

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