UPTAKE AND PASSAGE OF BETA-LACTOGLOBULIN, PALMITIC ACID AND RETINOL ACROSS THE CACO-2 MONOLAYER

Caco-2 cell line grown on collagen coated polycarbonate membranes in b icameral chambers has been used to study the effect of the binding of palmitic acid or retinol on the uptake and passage of iodinated beta-l actoglobulin and albumin across cell monolayers. The percentage of bet a-lactoglobulin transported through the monolayer was higher than that of albumin, about 50% and 30% of the total protein after 24 h of incu bation, respectively. In all cases, less than 1% of protein was retain ed intracellularly. No differences were found in the uptake and transp ort of beta-lactoglobulin or albumin in the presence or absence of lig ands. Furthermore, uptake and passage across Caco-2 monolayer of retin ol or palmitic acid added either bound to beta-lactoglobulin or to alb umin have been compared. The percentage of retinol found in the lower chamber was about 35% of the total retinol after 24 h of incubation fo r both proteins. However, the amount of retinol associated to cells wa s higher when it was added bound to beta-lactoglobulin than to albumin , about 26% and 10%, respectively. This fact suggests that the metabol ic processing of retinol by Caco-2 cells is the rate-limiting step for retinol transport. The percentage of palmitic acid that crossed the m onolayer was about 7%, remaining approx. 90% in the cells for beta-lac toglobulin and albumin. These data support the hypothesis that palmiti c acid internalized by Caco-2 cells is mainly destined to serve the st ructural and energy needs. These results show evidence of retinol and palmitic uptake by Caco-2 cells when beta-lactoglobulin or albumin are the donors, and indicate that the type of binding protein does not af fect the transport of both ligands through Caco-2 monolayer.