Methotrexate is excreted into the bile by canalicular multispecific organic anion transporter in rats.
Methotrexate [(+) amethopterin, L-MTX] has two carboxyl groups in its structure and is eliminated mainly by excretion into urine and bile. To investigate the biliary excretion mechanism of L-MTX, we performed in vivo and in vitro studies using mutant rats, Eisai hyperbilirubinemic rats (EHBRs), whose canalicular multispecific organic anion transporter (cMOAT) is defective as a consequence of heredity. After i.v. administration of L-MTX to EHBRs, its plasma disappearance and biliary excretion was slower than in normal Sprague Dawley rat (SDR). ATP-dependence and overshoot phenomena were observed in the uptake of [3H]L-MTX by canalicular membrane vesicles (CMV) prepared from SDR, whereas no ATP-dependence was observed in CMV from EHBRs. The ATP-dependent uptake of L-MTX by SDR CMV exhibited saturable kinetics with a Km of 295 microM. L-MTX competitively inhibited the ATP-dependent uptake of [3H]2,4-dinitrophenyl-S-glutathione, a typical substrate for cMOAT, and the inhibition constant (Ki) of L-MTX was comparable with its own Km. These results suggest that L-MTX is excreted into bile by cMOAT. The inhibitory effects of L-MTX and its optical isomer, (-) amethopterin (D-MTX), on the uptake of [3H]L-MTX differed with Kis of 326 and 93 microM, respectively, indicating that the biologically inactive D form has a higher affinity for cMOAT than L-MTX.
Masuda
M
M
Toho University School of Pharmaceutical Sciences, Chiba, Japan.
I'izuka
Y
Y
Yamazaki
M
M
Nishigaki
R
R
Kato
Y
Y
Ni'inuma
K
K
Suzuki
H
H
Sugiyama
Y
Y
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D027321:Anion Transport Proteins; D000964:Antimetabolites, Antineoplastic / Q000097:blood / Q000378:metabolism* / Q000493:pharmacokinetics; D001646:Bile / Q000378:metabolism*; D001648:Bile Canaliculi / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D008297:Male; D008727:Methotrexate / Q000097:blood / Q000378:metabolism* / Q000493:pharmacokinetics; D051381:Rats
D027321:Anion Transport Proteins; D000964:Antimetabolites, Antineoplastic; D002352:Carrier Proteins; D000255:Adenosine Triphosphate; D008727:Methotrexate