Increasing evidence indicates that gut microbiota is an important factor in mediating the development of metabolic disorders, especially type 2 diabetes. Herein, we investigated the protective effects of polysaccharides from mulberry fruit on diabetic db/db mice. We observed an inhibition in the body weight increase, a decrease in the blood glucose levels, and an improvement in glucose tolerance. Furthermore, our data showed increased enzymatic activities as evidenced by parameters such as superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and catalase (CAT). In addition, high density lipoprotein cholesterol (HDL-C) increased, while total cholesterol (TC), triacylglycerol (TG), low density lipoprotein cholesterol (LDL-C), lipid peroxide content malonaldehyde (MDA), and free fatty acid (FFA) levels decreased, accompanied by the recovery from damage to the liver, kidneys and pancreas. Meanwhile, metformin and polysaccharide similarly shifted the abundance of the main gut microbiota, Bacteroidetes and Firmicutes, in diabetic mice toward levels observed in healthy mice. Especially at the genus level, the enrichment of some key bacteria like Bacteroidales, Lactobacillus, Allobaculum, Bacteroides, and Akkermansia was observed. Taken together, our findings suggest that polysaccharides from the mulberry fruit modulate gut microbiota, including enriching functional bacteria and reducing microbial diversity, which may contribute to their antidiabetic effects.

Astragalus membranaceuspolysaccharides (APP), the main active constituent, possess numerous bioactivities.

A novel acidic polysaccharide (RTFP-3) was isolated and purified from Rosa roxburghii Tratt fruits. Structural analyses revealed that RTFP-3 is a homogeneous polysaccharide with a molecular weight of 67.2 kDa and mainly consists of arabinose (37.20%), galactose (34.40%), glucose (10.02%) and fucose (18.30%). The structural chain of RTFP-3 was proven to be composed of →6)-α-D-Galp-(1→, →4)-α-D-GalpA-(1→, →5)-α-L-Araf-(1→, →4)-β-D-Glcp-(1→, β-D-Glcp-(1→ and →3,4)-β-L-Fucp-(1→ residues by periodate oxidation–Smith degradation, methylation, and 1D- and 2D-NMR analyses. Bioassay results showed that RTFP-3 exerted favorable mixed type inhibitory activities against α-glucosidase, and its half inhibitory concentration (IC₅₀) value was determined as 4.15 mg mL⁻¹. RTFP-3 showed static type quenching of the intrinsic fluorescence of α-glucosidase, during which the binding process induced the conformational change of α-glucosidase. These results suggest that RTFP-3 has the potential to be a novel α-glucosidase inhibitory agent for use in functional foods.