Two polysaccharides from Rehmannia glutinosa: isolation, structural characterization, and hypoglycemic activities

Area of Science:

• Pharmacology and Natural Product Chemistry
• Biochemistry and Molecular Biology

Background:

• Rehmannia glutinosa (RG) is a traditional Chinese herb with medicinal and food applications.
• RG polysaccharides are known for their hypoglycemic effects, but the activity of RG homopolysaccharides is not well understood.

Purpose of the Study:

• To isolate and characterize RG homopolysaccharides.
• To investigate the hypoglycemic activity and mechanism of action of these isolated polysaccharides.

Main Methods:

• Isolation and purification of two RG homopolysaccharides (RGP70-1-1 and RGP70-1-2) using chromatographic techniques.
• Structural analysis including monosaccharide composition, linkage analysis (FT-IR, HPLC, GC-MS, NMR), Congo red test, and SEM.
• In vitro enzyme inhibition assays (α-glucosidase and α-amylase).
• In vitro cell studies on STC-1 cells to assess GLP-1 secretion and related protein expression (PI3K, p-AKT).

Main Results:

• Two homopolysaccharides, RGP70-1-1 (4.9 kDa) and RGP70-1-2 (2.8 kDa), were successfully isolated and characterized.
• Both polysaccharides consist of glucose, mannose, arabinose, and galactose with complex linkage patterns.
• RGP70-1-1 and RGP70-1-2 exhibited inhibitory effects against α-glucosidase and α-amylase.
• RGP70-1-1 significantly stimulated glucagon-like peptide-1 (GLP-1) secretion in STC-1 cells, associated with PI3K/p-AKT pathway activation.

Conclusions:

• The study elucidates the structure and hypoglycemic potential of two novel RG homopolysaccharides.
• These compounds show promise as inhibitors of carbohydrate digestion and as GLP-1 secretagogues.
• RGP70-1-1 and RGP70-1-2 represent potential functional food ingredients for managing type 2 diabetes.