Modulating effects of Astragalus polysaccharide on immune disorders via gut microbiota and the TLR4/NF-κB pathway in rats with syndrome of dampness stagnancy due to spleen deficiency

Abstract

The syndrome of dampness stagnancy due to spleen deficiency (DSSD) is relatively common globally. Although the pathogenesis of DSSD remains unclear, evidence has suggested that the gut microbiota might play a significant role. Radix Astragali, used as both medicine and food, exerts the effects of tonifying spleen and qi. Astragalus polysaccharide (APS) comprises a macromolecule substance extracted from the dried root of Radix Astragali, which has many pharmacological functions. However, whether APS mitigates the immune disorders underlying the DSSD syndrome via regulating gut microbiota and the relevant mechanism remains unknown. Here, we used DSSD rats induced by high-fat and low-protein (HFLP) diet plus exhaustive swimming, and found that APS of moderate molecular weight increased the body weight gain and immune organ indexes, decreased the levels of interleukin-1β (IL-1β), IL-6, and endotoxin, and suppressed the Toll-like receptor 4/nuclear factor-κB (TLR4/NF-κB) pathway. Moreover, a total of 27 critical genera were significantly enriched according to the linear discriminant analysis effect size (LEfSe). APS increased the diversity of the gut microbiota and changed its composition, such as reducing the relative abundance of Pseudoflavonifractor and Paraprevotella, and increasing that of Parasutterella, Parabacteroides, Clostridium XIVb, Oscillibacter, Butyricicoccus, and Dorea. APS also elevated the contents of short-chain fatty acids (SCFAs). Furthermore, the correlation analysis indicated that 12 critical bacteria were related to the body weight gain and immune organ indexes. In general, our study demonstrated that APS ameliorated the immune disorders in DSSD rats via modulating their gut microbiota, especially for some bacteria involving immune and inflammatory response and SCFA production, as well as the TLR4/NF-κB pathway. This study provides an insight into the function of APS as a unique potential prebiotic through exerting systemic activities in treating DSSD.

摘要

脾虚水湿不化证亦称为脾虚湿困证, 可单独或伴随疾病存在, 是一种较为常见的中医证型, 尽管其发病机制尚不明确, 但有证据表明肠道菌群起着重要作用. 黄芪健脾益气, 既可药用, 又可食用. 黄芪多糖(APS)是从黄芪中提取的一种大分子物质, 具有多种药理作用. 然而, APS能否通过调节肠道菌群改善脾虚水湿不化证机体免疫功能紊乱及相关机制尚未可知. 本研究中, 我们使用高脂低蛋白饮食结合力竭游泳方法诱导脾虚水湿不化模型大鼠. 结果发现, 中等分子量的APS增加了模型大鼠的体重和免疫器官指数, 降低了IL-1β、IL-6和内毒素水平, 并抑制了TLR4/NF-κB通路. 此外, LEfSe分析结果显示, 共有27个关键菌属被显著富集. APS增加了肠道菌群的多样性, 改变了其组成. 例如, 减少了Pseudoflavonifractor和Paraprevotella的相对丰度, 并增加了Parasutterella、 Parabacteroides、 Clostridium XIVb、 Oscillibacter、 Butyricicoccus和Dorea的相对丰度. 同时, APS还提高了肠道短链脂肪酸含量. 相关分析也表明, 12种关键菌属相对丰度与体重增加和免疫器官指数有关. 综上所述, APS通过调节脾虚水湿不化大鼠的肠道菌群[特别是涉及免疫和炎症应答、短链脂肪酸(SCFA)产生的菌群]以及TLR4/NF-κB通路, 改善了大鼠免疫功能紊乱, 为我们深入了解APS治疗脾虚水湿不化证的机制及其作为益生元的潜力提供了实验依据.