Basolateral efflux mediated by multidrug resistance-associated protein 3 (Mrp3/Abcc3) facilitates intestinal absorption of folates in mouse.

Purpose: This study investigated the role of an ABC transporter, Mrp3/Abcc3 in intestinal folate absorption.
Methods: Plasma concentrations of folic acid and leucovorin, given orally, were determined in wild-type and Mrp3 ( -/- ) mice. Mucosal-to-serosal transport was determined in the everted intestinal sacs. The plasma concentrations of endogenous 5-methyltetrahydrofolic acid, homocysteine and vitamin B(12), and mRNA levels of hepatic and intestinal folate metabolizing enzymes were compared between wild-type and Mrp3 ( -/- ) mice.
Results: C ( max ) and area-under plasma concentration-time curve of folic acid were 3.0- and 2.3-fold lower in Mrp3 ( -/- ) mice compared with wild-type mice, whereas the total body clearance was unchanged. Absorption of leucovorin was significantly delayed in Mrp3 ( -/- ) mice. Mucosal-to-serosal transport of folic acid and leucovorin was significantly decreased in the duodenum of Mrp3 ( -/- ) mice, where their PS ( serosal ) was decreased to 6.3 and 22% of that in wild-type mice, respectively. PS ( serosal ) of 5-methyltetrahydrofolic acid was moderately decreased in Mrp3 ( -/- ) mice. There was no obvious abnormality in folate homeostasis in Mrp3 ( -/- ) mice.
Conclusions: Mrp3 accounts for the serosal efflux of folic acid and leucovorin, while it makes a moderate contribution to the serosal efflux of 5-methyltetrahydrofolic acid in mice. Mrp3 dysfunction does not disrupt folate homeostasis in mouse.