Identification of the core active structure of a Dendrobium officinale polysaccharide and its protective effect against dextran sulfate sodium-induced colitis via alleviating gut microbiota dysbiosis
Graphical abstract
Introduction
Ulcerative colitis (UC) is one of the typical inflammatory bowel diseases caused by chronic inflammation and ulceration of the rectum and colonic lining (Jairath, McDonald, & Feagan, 2019). Increasing reports have suggested that UC is an intricate pathological process induced by numerous factors, including genes diversity, pro-inflammatory cytokines over-release, gut barrier dysfunction, gut microbiome disorders and environmental factors (Sandborn et al., 2020, Ungaro et al., 2017). Currently, the mainstay medication for the treatment of UC, such as anti-inflammatory drugs corticosteroids, amino salicylates, immunosuppressive agents, biological agents, and antibiotics, can only alleviate the disease with some serious side effects (Ming-yu et al., 2018, Tripathi and Feuerstein, 2019). What way to further optimize the treatment strategy of UC has become an urgent problem to be solved.
Recent investigations have demonstrated that dysregulation of gut microbiota might be the potential pathogenesis of UC (Nishida et al., 2018, Zuo et al., 2018). The gut microbiota dysbiosis and the diversification of bacterial metabolites, especially SCFAs were frequently considered to be the two most critical factors (Parada Venegas et al., 2019). The dysbiosis in UC has been further found to involve the elevation of pathogenic bacteria such as Proteobacteria and the decrease of some probiotics, such as Lactobacillus (J. Liang et al., 2015, Matijašić et al., 2016). Furthermore, the bacterial metabolites have been proved to be essential in the host metabolism of substances such as SCFAs (Y. Zhao et al., 2018) which could affect the development of UC. Studies have shown that by activating the GPR41/43 receptors, SCFAs (especially acetic acid and butyric acid) could exert their anti-inflammatory activity (Kobayashi et al., 2017, Li et al., 2018). Hence, it provides a new strategy in the UC treatment with high efficiency and low toxicity to develop anti-inflammatory medicines via restoring intestinal microflora homeostasis.
Dendrobium species have been used as a functional food in China for centuries (Ng et al., 2012). Polysaccharides focused the most attention as the major components among the active ingredients of Dendrobium officinale, which have been suggested to be capable of exerting various pharmacological properties, including anti-inflammatory, immunomodulatory activities and the therapeutic effects on diabetes and liver fibrosis (Liu et al., 2020, Tao et al., 2019, Wang et al., 2020, Zhang et al., 2018a). Recent studies showed that the polysaccharide extracted from Dendrobium Officinaleon exhibited the ability to prevent UC via suppressing the activation of NLRP3 inflammasome and β-arrestin1 in vivo and in vitro and regulating the expressions of TLR-2, TLR-4, TLR-6, and TLR-9 (Liang et al., 2018, Zhang et al., 2019). However, there was still little report on the mechanisms of polysaccharides from Dendrobium officinale with anti-colitis activity accomplished by restoring the levels of SCFAs, activating the GPRs and modulating gut microbiota. Furthermore, it was well accepted that polysaccharides are generally large in molecular weight and complex in structure. However, recent research indicated specific oligosaccharide fragments (active core domains) might be required for the display of the similar biological activity (Li et al., 2019, Zha et al., 2017). Therefore, locating the particular oligosaccharide fragment facilitates revealing the structural basis of the polysaccharide required for biological activity.
In this study, we provided a specific enzymatic method to obtain the oligosaccharide fragment (EDOP) based on the linear structural features of Dendrobium officinale polysaccharide (DOP) and its structure was characterized. Meanwhile, the potential to alleviate UC symptoms in DSS-induced colitis mice and the relative mechanisms (restoring the levels of SCFAs, activating the GPRs and modulating gut microbiota) of DOP and EDOP were investigated. Combined with the structural information and pharmacological mechanisms, we aimed to explore whether EDOP was the active specific oligosaccharide fragment of DOP.
Section snippets
Materials and reagents
The dried stems of the Dendrobium officinale Kimura et Migo were purchased from “Zhong Fangrun Shihu” Co. (Zhejiang, China), and authenticated by Prof. Jinlan Ruan in the Department of Pharmacy at Tongji Medical College of Huazhong University of Science and Technology, China. D-Glucose (Glc), D-galactose (Gal), D-mannose (Man), D-arabinose (Ara), D-xylose (Xyl), L-rhamnose (Rha), D-Galacturonic acid (GalA), D-Glucuronic acid (GlcA) were obtained from Sigma (St. Louis, USA). T-series dextran
Structural analysis of DOP and EDOP
It has been proved that DOP had a backbone composed of (1 → 4)-β-D-Manp, (1 → 4)-β-D-Glcp and 2-OAc-(1 → 4)-β-D-Manp, the specific contents related to structural characterization including periodate oxidation and smith degradation, methylation analysis and nuclear magnetic resonance (NMR) spectroscopy (1D 1H, 13C, COSY, HSQC and HMBC spectra) was shown in Supplementary materials (Fig. S1, Table S1, Table S2, Table S3). The possible repeating unit for DOP was proposed in Fig. 1A. Since the
Discussions
Structure characterization revealed that DOP was a linear polysaccharide with a major glycosidic linkage of (1 → 4)-β-D-Manp. However, the high viscosity of the DOP D2O solution resulted in the difficulty of obtaining high resolution 2D NMR spectra (Zha, Luo, Luo, & Jiang, 2007), therefore we selected a weak acid hydrolysis method to obtain samples for NMR analysis and examined the effects of hydrolysis conditions on the samples (Goldberg et al., 1991, Price et al., 2011, Shi et al., 2018). The
Conclusions
In conclusion, the results of our present work indicated that the protective effects of DOP and EDOP against DSS-induced colitis were associated with the inhibition of the overproduction of pro-inflammatory cytokines in the colonic mucosa, modulation of gut microbiota, and stimulation of the production and utilization of SCFAs in the colon. The enzymatic fragments (EDOP) remained the similar structure which was determined to consist of (1 → 4)-β-D-Glcp and (1 → 4)-β-D-Manp with some attached 2-O
CRediT authorship contribution statement
Yu Zhang: Conceptualization, Methodology, Writing - original draft. Zhijing Wu: Writing - review & editing, Data curation. Junxi Liu: Data curation. Ziming Zheng: Formal analysis. Qiang Li: Data curation. HongJing Wang: Investigation. Zehong Chen: Validation. Kaiping Wang: Methodology, Supervision, Funding acquisition, Project administration, Resources.
Declaration of Competing Interest
The authors declared that there is no conflict of interest.
Acknowledgments
This research was financially supported by National Key R&D Program of China (2017YFC0909900). The authors are grateful to the staff from the Analysis and Testing Center of Huazhong University of Science and Technology for their technical assistance.
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