Oral absorption mechanisms of Astragalus polysaccharides and potential as an excipient to increase the absorption of flavonoids.

Understanding the absorption of natural polysaccharides is crucial for advancing their development and application. However, their oral absorption mechanisms and potential applications remain unclear. In this study, Astragalus homogeneous polysaccharide (APS3a) was isolated and characterized. Based on the structural analysis, in vitro and in vivo tracking of APS3a was conducted using FITC- and Cy7 amine labeling to investigate its transport and absorption mechanisms. The results indicated that APS3a can traverse the intestinal mucus layer and is mainly absorbed in the jejunum, subsequently distributing gradually to the liver and kidneys. Further investigation of its transport mechanism revealed that APS3a undergoes energy-dependent active transport, utilizing transcellular transport pathways such as caveolin-mediated endocytosis, macropinocytosis, and sodium-glucose cotransporter 1 (SGLT1)-mediated endocytosis. Additionally, APS3a has the capacity to reversibly open tight junction proteins, facilitating transport through the paracellular transport pathway. Moreover, APS3a can function as an excipient, self-assembling with flavonoids from Astragalus Radix to form complexes, thereby enhancing the permeability and absorption of these flavonoids. These findings provide valuable insights into the oral absorption of APS3a and its potential applications, which are significant for the development and application of polysaccharides.