Paracellular transport of avidin saturated or not with biotinylated cobalamin through Caco-2 cell epithelium monolayer

Background: The cationic charge of molecules may promote their uptake acros s epithelia, which are rich in brush border anionic sites. The transport of unsaturated avidin and avidin saturated with a biotinylated compound was i nvestigated across Caco-2 adenocarcinoma cell with fetal enterocyte phenoty pe. Methods: The unsaturated avidin and avidin saturated with either biotin or a biotinyl-cobalamin conjugate (biotinyl-Cbl) were iodinated to follow thei r transport through the cell monolayer. Their apparent permeability coeffic ient (Papp) and transepithelial pathway were determined and compared to tho se for control radiolabeled markers [H-3]-mannitol, [I-125]-beta -lactoglob ulin and [Co-57]-cobalamin/intrinsic factor (Cbl/IF). Results: The Papp of [I-125]-avidin estimated at 2.8 x 10(-7) +/- 0.08 cm/s was close to that for mannitol that uses paracellular pathway. The binding of biotin or biotin conjugate to avidin enhanced its tetrameric conformati on. The Papp for [I-125]-avidin/biotin and [I-125]-fold, compared to that f or [I-125]-avidin and 4-fold, compared to that for [I-125]-beta -lactoglobu lin and [Co-54]-Cbl/IF. The protein was not accumulated in the cell and was found in intact form in the basolateral side, after its transport across t he monolayer. Chloroquine (0.66 mu mol/ml) did not significantly decrease t he Papp for [I-125]-avidin/biotinyl-Cbl. Conversely it decreased by 80% the Papp for Cbl/IF, that uses transepithelial pathway. Conclusions: Avidin (either saturated or not with biotin and biotinyl-Cbl) was able to cross the monolayer of Caco-2 cell line through a paracellular pathway. This study pointed out the interest for using this protein as a sh uttle for increasing the transport rate of biotinylated compounds through f etal epithelial barriers. Copyright (C) 2001 S. Karger AG, Basel.