Transepithelial transports of rare sugar D-psicose in human intestine.

D-Psicose (Psi), the C3-epimer of D-fructose (Fru), is a noncalorie sugar with a lower glycemic response. The trans-cellular pathway of Psi in human enterocytes was investigated using a Caco-2 cell monolayer. The permeation rate of Psi across the monolayer was not affected by the addition of phlorizin, an inhibitor of sugar transporter SGLT1, whereas it was accelerated by treatment with forskolin, a GLUT5-gene inducer, clearly showing that GLUT5 is involved in the transport of Psi. The permeability of Psi was suppressed in the presence of D-glucose (Glc) and Fru, suggesting that the three monosaccharides are transported via the same transporter. Since GLUT2, the predominant sugar transporter on the basolateral membrane of enterocytes, mediates the transport of Glc and Fru, Psi might be mediated by GLUT2. The present study shows that Psi is incorporated from the intestinal lumen into enterocytes via GLUT5 and is released to the lamina propria via GLUT2.