Involvement of multidrug resistance associated protein 1 (Mrp1) in the efflux transport of 17beta estradiol-D-17beta-glucuronide (E217betaG) across the blood-brain barrier.
OBJECTIVE
The purpose of present study is to investigate the involve ment of multidrug resistance-associated protein 1 (Mrp1), Mrp2, an P-glycoprotein (Mdr1a) in the efflux transport of 17beta-estradiol-D-17beta-glucuronide (E217betaG) across the blood-brain barrier (BBB).


METHODS
The expression of Mrp1 and Mrp2 at the BBB was investigated by RT-PCR and Western blot analyses. The time profiles of the remaining radioactivity of [3H]E217pG in the brain were compared in wild-type, Mdr1a/Mdr1b and Mrp1 knockout mice and normal and Mrp2-deficient mutant rats [Sprague-Dawley and Eisai hyperbilirubinemic rats (EHBR), respectively] after intracerebral microinjection.


RESULTS
RT-PCR and Western blot analyses revealed the expression of Mrp1 in isolated rat brain capillary; however, RT-PCR was unable to detect any expression of Mrp2. Significant elimination of E217betaG was observed in wild-type mice at a rate constant of 0.007 min(-1) which was significantly decreased (0.004 min(-1)) in Mrp1 knockout mice. In contrast, there was no difference in the efflux of E217betaG from the brain in wild-type and Mdr1a/Mdr1b knockout mice and in normal and EHBR. No significant difference was observed in the accumulation of E217betaG by brain slices prepared from wild-type and Mrp1 knockout mice.


CONCLUSIONS
Mrp1, but not Mrp2, is involved in the excretion of E217betaG at the BBB and provides a barrier function by extruding conjugated metabolites into the blood.
Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
Daisuke
D
Sugiyama
Hiroyuki
H
Kusuhara
Yong-Joo
YJ
Lee
Yuichi
Y
Sugiyama
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism; D018528:ATP-Binding Cassette Transporters; D000818:Animals; D001812:Blood-Brain Barrier / Q000378:metabolism*; D015153:Blotting, Western; D001921:Brain / Q000098:blood supply / Q000378:metabolism; D002196:Capillaries / Q000378:metabolism; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D004958:Estradiol / Q000031:analogs & derivatives / Q000493:pharmacokinetics*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D008845:Microinjections; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013045:Species Specificity; D013997:Time Factors
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D018528:ATP-Binding Cassette Transporters; D002352:Carrier Proteins; D004958:Estradiol; D027425:ATP-Binding Cassette, Sub-Family C Proteins; C423013:Abcc2 protein, rat; C025483:estradiol-17 beta-glucuronide; C421109:multidrug resistance-associated protein 1