COMPARISON OF THE TRANSPORT CHARACTERISTICS OF D-METHIONINE AND L-METHIONINE IN A HUMAN INTESTINAL EPITHELIAL MODEL (CACO-2) AND IN A PERFUSED RAT INTESTINAL MODEL

Absorption mechanisms of L- and D-methionine (MET) in an in vitro cult ured human intestinal epithelial cell model (Caco-2) and an in situ pe rfused rat intestinal model were investigated to determine if the kine tic characteristics of absorption are comparable in these two popular absorption models. The results indicate that the transport of L- and D -MET were concentration-dependent in both model systems, and displayed comparable K-m values. The K-m value for L-MET is 1.34 mM in the Caco -2 model and 3.6 mM in the perfused rat intestinal model, while the K- m value for D-MET is 1.79 mM in the Caco-2 model and 2.87 mM in the pe rfused rat intestinal model. Although the J(max) values were not compa rable because of significant methodology differences, the J(max) value s for L-MET were always higher than that for D-MET. In addition, trans port of L- and D-MET across the Caco-2 cell monolayers were also inhib ited by 10 mM Phe and Lys while MeAIB, Pro and Glu were generally inef fective. Similar results were also observed with these inhibitors in t he perfused rat intestinal model with the exception that a combination of Pro and Glu stimulated the uptake of L-MET. In conclusion, the tra nsport characteristics of L- and D-MET are comparable in both model sy stems.