Non-involvement of the human monocarboxylic acid transporter I (MCT1) in the transport of phenolic acid

Phenolic acids such as p-coumaric acid and microbial metabolites of poorly absorbed polyphenols are absorbed by the monocarboxylic acid transporter (MCT)-mediated transport system which is identical to the fluorescein/H+ cotransport system. We focus here on the physiological impact of MCT-mediated absorption and distribution. We examined whether MCTI, the best-characterized isoform found in almost all tissues, is involved in this MCT-mediated transport system. The induction of MCT1 expression in Caco-2 cells by a treatment with sodium butyrate (NaBut) did not increase the fluorescein permeability. Moreover, the transfection of Caco-2 cells with an expression vector encoding MCT1 caused no increase in either the permeability or uptake of fluorescein. Furthermore, in the MCT1-expressing oocytes, no increase of p-coumaric acid uptake was apparent, whereas the uptake of salicylic acid, a substrate of MCTI, nearly doubled. Our data therefore establish that MCT1 was not involved in the MCT-mediated transport of phenolic acids.