Beneficial In Vitro Effects of Polysaccharide and Non-Polysaccharide Components of Dendrobium huoshanense on Gut Microbiota of Rats with Type 1 Diabetes as Opposed to Metformin

The extract ofDendrobium huoshanense, a traditional Chinese medicinal and food homologous plant belonging to the family Orchidaceae, was previously reported to have hypoglycemic and antioxidant effects. In this study, the direct effects of polysaccharide (DHP) and non-polysaccharide (NDHP) components ofD. huoshanense, as well as its water extract (DHWE) were compared with that of metformin (an antidiabetic drug) on the gut microbiota (collected from fecal flora) of rats with streptozotocin-induced type 1 diabetes (T1D) using an in vitro fermentation method. The results showed that DHWE, DHP, and NDHP reduced pH and increased bacterial proliferation and short-chain fatty acid (SCFA) content in fermentation broth. DHWE, DHP, NDHP and metformin promoted the production of acetic and propionic acid, acetic acid, propionic acid and butyric acid, and propionic acid, respectively. DHWE, DHP, and NDHP reduced the abundance ofProteobacteria(subdominant pathogenic bacteria) and increased the abundance ofFirmicutes(dominant beneficial gut bacteria). NDHP also reduced the abundance ofBacteroidetes(beneficial and conditional pathogenic). Metformin increased the abundance ofProteobacteriaand reduced the abundance ofFirmicutesandBacteroidetes. At the genus level, NDHP promoted the proliferation ofMegamonasandMegasphaeraand decreased harmful bacteria (e.g.,Klebsiella), and DHP increased the abundance ofPrevotellaceae(opportunistic and usually harmless). By contrast, metformin increased the abundance of harmful bacteria (e.g.,Citrobacter) and reduced the abundance of beneficial bacteria (e.g.,Oscillospira). Our study indicates that DHWE, DHP, and NDHP are potentially more beneficial than metformin on the gut microbiota of T1D rats in vitro.