Structural elucidation, anti-inflammatory activity and intestinal barrier protection of longan pulp polysaccharide LPIIa
Introduction
Inflammatory bowel disease (IBD) is a chromic intestinal inflammatory disease, which severely compromises the quality of the patients’ daily life and is affecting massive population around the world (Staudacher, Irving, Lomer, & Whelan, 2014). The intestinal barrier destruction is the fundamental in IBD process (Gao et al., 2018; Gong, Li, & Li, 2016; Khan & Ghia, 2010). The intact intestinal epithelium is an important physical intestinal barrier by separating intestinal luminal antigens and immune cells to maintain intestinal homeostasis. Destruction of intestinal epithelial barrier increased the risk of luminal antigens flowing into the immune system, leading to inappropriate sustained immune responses (Arijs et al., 2011), which in turn results in continuous inflammatory responses (Gao et al., 2018; Gong et al., 2016; Khan & Ghia, 2010; Nagao-Kitamoto et al., 2016). In active IBD process, pro-inflammatory cytokines increased, including tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, IL-6, and IL-8, which play an important role in activating and facilitating the intestinal mucosal inflammation (Bergmann et al., 2013; Putt, Pei, White, & Bolling, 2017). Meanwhile, inflammatory mediators oxide synthase (NO) and prostaglandin E2 (PGE2), which are produced by inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2), respectively, were enhanced at the apical side of epithelial cells, indicating that they are involved in mediating the inflammatory process of intestinal tissue injury (Wang, Li, Yang, & Yao, 2013; Sun, Shi, Zheng, Nie, & Xu, 2019). Therefore, inhibiting inflammatory response is one of the effective ways in IBD therapy.
Natural products with low side effects and possible therapeutic effects on IBD attracted wide attentions. Studies have revealed that supplementation with natural polysaccharides is considered as an alternative or complementary treatment for IBD (Canani et al., 2011; Sun et al., 2019; Wang et al., 2013; Zuo et al., 2015). Longan (Dimocarpus longan Lour.) is an important edible-medicinal fruit with pleasant taste and high nutritional value. Polysaccharide is one of the main bioactive ingredients of longan pulp. It has potent anti-inflammatory (Kunworarath, Rangkadilok, Suriyo, Thiantanawat, & Satayavivad, 2016), immunomodulatory (Rong et al., 2019; Yi et al., 2012), and intestinal-flora-regulatory effects (Zhang et al., 2017). Previously, we found that crude longan pulp polysaccharide (LP) protected intestinal barrier by increasing the expression of tight junction proteins in intestinal epithelia in chemotherapy mice (Bai et al., 2019). The structure of polysaccharides is correlated with their activities (Shen, Jiang, Li, Zheng, & Zhu, 2017). However, the detailed structure of LP is still unclear. Therefore, this study elucidated the detailed structure of LPIIa, a purified active polysaccharide from LP. The anti-inflammatory activity and intestinal barrier protection of LPIIa was evaluated by the LPS-treated co-culture model of Caco-2 enterocyte-like cells with RAW 264.7 macrophages, which simulates the intestinal inflammatory process and mimics the acute phase of IBD (Olejnik et al., 2016).
Section snippets
Materials and reagents
Longan (cv. Chu-liang) fruit was provided by the Pomology Research Institute of Guangdong Academy of Agricultural Sciences (Guangzhou, China). The human colon cancer cell line Caco-2 and murine macrophage cell line RAW 264.7 were obtained from the Type Culture Collection of the Chinese Academy of Sciences (Shanghai, China). DEAE-Sepharose Fast Flow column and HiPrep Sephacryl S-300 HR column were purchased from GE Healthcare (Uppsala, Sweden). Monosaccharide standards (rhamnose, arabinose,
Basic chemical composition of LP-IIa
The carbohydrate and uronic acid contents of LP-IIa were 69.11 ± 1.79 % and 10.32 ± 0.67 %, respectively. Its protein content was 0.48 ± 0.20 %. It is indicated that LP-IIa was mainly comprised of neutral sugar and sort of acid sugar. The neutral monosaccharide compositions of LP-IIa were rhamnose, ribose, arabinose, xylose, glucose and galactose in a molar ratio of 1.05:1:22.88:1.01:2.59:34.58 (Fig. 1B). It represents that arabinose and galactose were the main monosaccharide compositions of
Conclusion
In this study, a bioactive longan pulp polysaccharide named LPIIa was isolated and its detailed structure was elucidated. Its average molecular weight was 159.3 kDa. The backbone of LPIIa was composed of (1→3,4)-linked-α-Rhap, (1→4)-linked-β-Galp, (1→6)-linked-β-Galp, and (1→3,6)-linked-β-Galp, with branches at the O-4 of Rha and O-3 of Gal, consisting of side chains of α-Araf, β-Galp, and α-Glcp. Meanwhile, LPIIa exhibited the anti-inflammation via decreasing the pro-inflammatory mediators and
Declaration of Competing Interest
There are no conflicts to declare.
Acknowledgements
This work was supported by the National Key Research Project of China (2017YFC1601002), Guangdong Provincial Science and Technology Project (2018A050506050), Guangdong special support program (2019BT02N112), Guangzhou Science and Technology Plan Project (202002030315), and the Special fund for scientific innovation strategy-construction of high level Academy of Agriculture Science (201602TD).
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