Related Experiment Videos
Reduced folate derivatives are endogenous substrates for cMOAT in rats
H Kusuhara1, Y H Han, M Shimoda
1Graduate School of Pharmaceutical Sciences, University of Tokyo, Bunkyo-ku, Tokyo 113, Japan.
The American Journal of Physiology
|October 2, 1998
Summary
The canalicular multispecific organic anion transporter (cMOAT) facilitates the biliary excretion of reduced folate derivatives. This study identifies these folate compounds as the first endogenous cMOAT substrates not containing glutathione, glucuronide, or sulfate.
Area of Science:
- Hepatobiliary Transport
- Molecular Biology
- Biochemistry
Background:
- The canalicular multispecific organic anion transporter (cMOAT) plays a crucial role in the excretion of various organic anions into bile.
- The transport mechanisms of reduced folate derivatives, essential for cellular processes, are not fully understood, particularly their interaction with cMOAT.
Purpose of the Study:
- To investigate the involvement of cMOAT in the biliary excretion of reduced folate derivatives.
- To determine if reduced folate derivatives are substrates for cMOAT using in vivo and in vitro models.
Main Methods:
- Utilized normal Sprague-Dawley rats (SDR) and cMOAT-deficient Eisai hyperbilirubinemic rats (EHBR) for in vivo biliary excretion studies.
- Employed isolated canalicular membrane vesicles from SDR and EHBR for in vitro uptake experiments of radiolabeled folate derivatives and DNP-SG.
- Assessed ATP-dependent transport and performed inhibition studies with known cMOAT substrates and folate derivatives.
Main Results:
- Biliary excretion of tetrahydrofolate (H4PteGlu), 5-methyltetrahydrofolate (5-CH3-H4PteGlu), and 5,10-methylenetetrahydrofolate (5, 10-CH2-H4PteGlu) was significantly reduced in EHBR compared to SDR.
- ATP-dependent uptake of 5-CH3-H4PteGlu into canalicular vesicles was observed only in SDR and was saturable, with kinetic parameters comparable to those of DNP-SG, a known cMOAT substrate.
- Reduced folate derivatives inhibited the uptake of DNP-SG, indicating a shared transport mechanism via cMOAT.
Conclusions:
- Reduced folate derivatives, including 5-methyltetrahydrofolate, are transported by the canalicular multispecific organic anion transporter (cMOAT).
- These folate compounds represent the first identified endogenous substrates for cMOAT that lack glutathione, glucuronide, or sulfate moieties.
- The findings elucidate a novel role for cMOAT in folate homeostasis and biliary excretion.