Research Articles
Do Multidrug Resistance‐Associated Protein‐1 and ‐2 Play Any Role in the Elimination of Estradiol‐17β‐Glucuronide and 2,4‐Dinitrophenyl‐S‐Glutathione Across the Blood–Cerebrospinal Fluid Barrier?

https://doi.org/10.1002/jps.10521Get rights and content

Abstract

The purpose of this study was to examine the role of multidrug resistance‐associated protein‐1 and ‐2 (Mrp1 and Mrp2) in the efflux transport of organic anions across the blood–cerebrospinal fluid (CSF) barrier. The CSF concentration of estradiol‐17β‐glucuronide (E217βG) and 2,4‐dinitrophenyl‐S‐glutathione (DNP‐SG) in the CSF after intracerebroventricular and intravenous injection were compared between wild‐type and Mrp1 gene knockout mice. There was no significant difference in the apparent CSF elimination rate constants of E217βG (0.158 and 0.145 min.−1) and DNP‐SG (0.116 and 0.0779 min.−1) between wild‐type and Mrp1 knockout mice, respectively. After intravenous administration of E217βG, its brain‐to‐serum and CSF‐to‐serum concentration ratios in Mrp1 knockout mice were not significantly different from those in the wild‐type. Results from in vivo and in vitro studies using Eisai hyperbilirubinemic rats, in which Mrp2 is hereditarily deficient, were similar to those using normal rats. Quantitative polymerase chain reaction (PCR) showed that the expression level of Mrp4 and Mrp5 was several times higher than that of Mrp1, whereas the expression levels of Mrp2, Mrp3, and Mrp6 were negligible or low. Therefore, Mrp4 and Mrp5 may contribute to the efflux transport of E217βG and DNP‐ SG from the CSF. © 2004 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 93:99–107, 2004

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INTRODUCTION

The choroid plexus (CP), which forms the blood–cerebrospinal fluid barrier (BCSFB), secretes cerebrospinal fluid (CSF) and regulates its composition by active and selective transport processes.1 Within the CP, the complex vascular bed is composed of some fenestrated but permeable capillaries that permit all molecules smaller than proteins to gain easy access to the basolateral membrane of the choroid epithelial cells. For this reason, the anatomical entity of the BCSFB consists of choroid

Chemicals

[3H]Estradiol‐17β‐glucuronide (E217βG; 40.5 Ci/mmol), [14C]mannitol (51 mCi/mmol), and [14C]urea (40 mCi/mmol) were purchased from PerkinElmer Life Sciences (Boston, MA). [3H]2,4‐Dinitrophenyl‐S‐glutathione (DNP‐SG) was synthesized enzymatically using [3H]glutathione (PerkinElmer Life Science), 1‐chloro‐2,4‐dinitrobenzene, and glutathione S‐transferase (Sigma Chemical, St. Louis, MO) as described previously, and the purity (>90%) was checked by high‐performance liquid chromatography (HPLC).19

Elimination of E217βG and DNP‐SG from the CSF after Intracerebroventricular Administration in Mice

CSF concentrations of E217βG and DNP‐SG after intracerebroventricular administration in wild‐type and Mrp1 knockout mice are shown in Figure 1 as remaining concentration ratios of E217βG and DNP‐S, normalized by the simultaneously administered mannitol. The elimination of E217βG and DNP‐SG from CSF after intracerebroventricular administration was much faster than that of mannitol, the elimination of which is mediated entirely by simple diffusion and CSF turnover,21 both in wild‐type and Mrp1

DISCUSSION

E217βG is rapidly removed from the CSF by an efficient efflux transport system at the CP. Although Oatp3 accounts for the uptake of E217βG by isolated rat CP, the transporter responsible for the basolateral excretion remains to be identified. The present study highlighted Mrp1 and Mrp2 as candidate transporters responsible for the basolateral excretion of amphiphatic organic anions.

E217βG, a typical Mrp1 substrate, was eliminated from the CSF in both Mrp1 knockout and wild type mice after

Acknowledgements

This work was supported by the research grant from the Japan Foundation For Aging and Health.

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