Oral absorption, cellular uptake and transport mechanisms of a novel glucuronogalactomannan from Tetrastigma hemsleyanum Diels et Gilg in the intestinal epithelium.

Understanding the oral absorption mechanisms of natural polysaccharides is critical for their further study and application. This study focused on a novel glucuronogalactomannan (STHP5) isolated from Tetrastigma hemsleyanum Diels et Gilg and systematically investigated its intestinal absorption and transcellular transport. STHP5 was fluorescently labeled with Cyanine5.5 amine (CSTHP5) and 5-(4,6-dichlorotriazinyl) aminofluorescein (FSTHP5) for in vivo and in vitro tracking. Fluorescence spectroscopy, fourier-transform infrared spectroscopy, and nuclear magnetic resonance analyses confirm successful fluorescent labeling of STHP5. Near-infrared imaging demonstrated that CSTHP5 was absorbed in the small intestine and predominantly accumulated in the liver and kidney. Single-pass intestinal perfusion confirmed preferential absorption of FSTHP5 in the ileum. In vitro, FSTHP5 uptake occurred through macropinocytosis, clathrin-mediated, and caveolae-mediated endocytosis; its intracellular trafficking was governed by the endoplasmic reticulum (ER)-Golgi and endosome-lysosome pathways with microtubule participation; and its exocytosis was predominantly mediated by the ER-Golgi pathway and microtubules. In Caco-2 cell monolayers, transcellular transport was dose- and time-dependent and likely receptor-mediated. Together, STHP5 achieves efficient oral absorption across the intestinal epithelium via an integrated transport mode involving multi-pathway endocytosis, directed intracellular trafficking, and exocytosis, providing new insights into the absorption mechanisms of hydrophilic, high-molecular-weight polysaccharides and informing delivery system design.