Effects of polysaccharide from mycelia of Ganoderma lucidum on intestinal barrier functions of rats
Introduction
Recent studies have demonstrated that the intestinal mucosa plays an essential role not only in the digestion and absorption of nutrients, but also the innate defense against most intestinal pathogens [1]. Intestinal mucosa acts as a selective barrier, allowing the transcelluar transport of essential dietary nutrients from the lumen into the circulation, and preventing the passage of harmful or unwanted substances (such as food antigens, bile, endotoxin and microorganisms) from entering the internal environment, thus maintaining the intracellular homeostasis [2]. The intestinal mucosal barriers are mainly composed of mechanical barrier, chemical barrier, biological barrier, and immunological barrier. Among them, the mechanical barrier, biological barrier and immunological barrier are the chief components of intestinal mucosal immunity [3], [4]. Intestinal barrier dysfunction has been reported to be associated with pathogenesis of many intestinal diseases, such as diarrhea, inflammatory bowel disease, Crohn's disease, ulcerative colitis, and food allergy [5]. Therefore, the research on the regulation of intestinal mucosal barrier function will provide practical implications for the treatment and prevention of intestinal diseases.
Ganoderma lucidum, also called Lingzhi in Chinese and Reishi in Japanese, is a species of Basidiomycetes that belongs to Ganodermataceae of Aphyllophorales [6]. As one of the most well-known health-promoting folk medicines in China and other eastern countries, it has been historically used as an immunomodulating agent for the prevention and treatment of various diseases, such as gastric ulcer, arthritis, chronic hepatitis, nephritis, hypertension, hyperlipemia, arteriosclerosis, asthma, diabetes, cancer, and immunological disorders [6], [7], [8], [9], [10], [11]. However, the amount of wild G. lucidum is not sufficient for commercial exploitation as it is very scarce in nature [12]. With the development of fermentation techniques, the submerged cultivation provided an advantageous and promising alternative for the industrialized production of G. lucidum to meet its increasing demands [13]. A large and diverse spectrum of chemical compounds with pharmacological activities have been isolated from fermented G. lucidum mycelia, such as polysaccharides, triterpenoids, steroids, amino acids, nucleotides, alkaloids, lactones, fatty acids and enzymes [14]. In the last few years, the polysaccharide, as one of the major ingredients of G. lucidum mycelia, has attracted much attention of researchers. Recent studies on pharmacology have demonstrated that the polysaccharides from the mycelia of G. lucidum (GLP) had various bioactivities, such as immunomodulation [15], [16], anti-tumor [17], [18], antioxidant [14], anti-diabetes [19], anti-inflammation [20], and neuroprotection [21].
The biological activities of polysaccharide mainly depend on its physiochemical and molecular structural features [22]. It was reported that GLP, the polysaccharide isolated and purified from the mycelia of G. lucidum, was composed of d-glucose, d-galcatose, d-mannose, d-xylose, l-fucose and l-rhamnose in the molar ratio of 5.35:2.67:1.00:1.19:0.38:0.37 with the mean molecular weight of approximately 3.7 × 104 Da. Furthmore, GLP had a backbone composed of β(1 → 3)-linked glucose residues with branches comprised of terminal L-fucose, 1,6-linked d-galactopyranosyl and 1,4-linked d-xylopyranosyl residues linked to O-3 and O-4 of mannosyl residues [23]. Due to the high molecular weight, the polysaccharide administrated orally cannot be easily absorbed by gastrointestinal tract into the blood stream directly for functional activities [24]. As the intestine is one of the most important immune organs consisting of a complex cellular network [25], therefore, we assume that intestinal mucosal immune response might trigger the immune regulation of GLP. To the best of our knowledge, there is limited information available so far about the effect of GLP on intestinal mucosal barrier functions in vivo.
In the present study, the effects of GLP on intestinal barrier functions in rats, including the mechanical barrier, immunological barrier and biological barrier function, were investigated. The purpose of this research is to explore the naturally occurring agent that could be used for the regulation of intestinal barrier functions, and further treatment and prevention of intestinal diseases.
Section snippets
Materials and reagents
Rat interferon-γ (IFN-γ), interleukin-2 (IL-2), IL-4, IL-6, diamine oxidase (DAO), and secretory immunoglobulin A (SIgA) enzyme linked immunosorbent assay (ELISA) kits were obtained from R&D Systems (Minneapolis, MN, USA). The antibody used in this study were the following: inhibitor of κB (IκB) rabbit monoclonal antibody (Epitomics, China), phosphorylated IκB (p-IκB) mouse monoclonal antibody (CST, USA), occludin rabbit polyclonal antibody (Abcam, USA), nuclear factor-κB (NF-κB) p65 and
Body weight and growth performance
As shown in Fig. 1, administration of GLP (100 mg/kg BW) for 21 day did not significantly affect the body weight of rats (P > 0.05), which was in accordance with the previous study [7].
IFN-γ, IL-2, IL-4, IL-6, and DAO in serum and SIgA in ileum
As shown in Fig. 2, in the GLP group, serum levels of IFN-γ, IL-2, and IL-4 were significantly higher (P < 0.05), while serum level of DAO was significantly lower (P < 0.05) compared with those in the control group. There was no significant difference in serum level of IL-6 between the control and GLP groups (mean ± SEM,
Discussion
Previous studies have shown that polysaccharides from the submerged culture of G lucidum improved the level of necrosis factor alpha (TNF-α) and IFN-γ in primary cultures of human peripheral blood mononuclear cells in vitro [12], and increased the mass of spleen tissue, enhanced the T and B lymphocyte proliferation and antibody production in mice [41]. However, the effects of GLP on intestinal barrier functions in vivo, especially the mechanical barrier, immunological barrier and biological
Conclusions
In summary, this study demonstrated that GLP could improve the intestinal mechanical barrier function through the up-regulation of the expression of occludin and decrease of intestinal permeability. GLP could regulate the intestinal immunological barrier functions by increase of the expression of NF-κB and SIgA in ileum, and the levels of serum cytokines such as IFN-γ, IL-2, and IL-4. Furthermore, GLP could also modulate the intestinal biological barrier functions via the increase of microbiota
Acknowledgements
This study was supported by Fundamental Research Funds for the Central Universities (Nos. 3102014JCQ15001 and 3102015BJ(II)MYZ29), China Postdoctoral Science Foundation (Nos. 2011M501481 and 2012T50821), and Shaanxi Provincial Natural Science Foundation (No. 2015JQ3083).
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