Purpose: To characterize the transport mechanism of monocarboxylic acids across intestinal epithelial cells by examining the stereoselectivity of the transcellular transport of several chiral monocarboxylic acids.
Methods: The transport of monocarboxylic acids was examined using monolayers of human adenocarcinoma cell line, Caco-2 cells.
Results: The permeability of L-[14C]lactic acid at a tracer concentration (1 microM) exhibited pH- and concentration-dependencies and was significantly greater than that of the D-isomer. The permeabilities of both L-/D-[14C]lactic acids involve saturable and nonsaturable processes; the saturable process showed a higher affinity and a lower capacity for L-lactic acid compared with the D-isomer, while no difference between the isomers was seen for the nonsaturable process. The transport of L-lactic acid was inhibited by chiral monocarboxylic acids such as (R)/ (S)-mandelic acids and (R)/(S)-ibuprofen in a stereoselective manner. Mutually competitive inhibition was observed between L-lactic acid and (S)-mandelic acid.
Conclusions: Some chiral monocarboxylic acids are transported across the intestinal epithelial cells in a stereoselective manner by the specific carrier-mediated transport mechanism.