The multidrug resistance 1 gene Abcb1 in brain and placenta: comparative analysis in human and guinea pig.

Jane J Pappas,Moshe Szyf,Matthew Suderman,Stephen G Matthews,Sophie Petropoulos,Vasilis Moisiadis,Majid Iqbal,Gustavo Turecki,Jyotshna Kanungo

doi:10.1371/journal.pone.0111135

Abstract

The Multidrug Resistance 1 (MDR1; alternatively ABCB1) gene product P-glycoprotein (P-gp), an ATP binding cassette transporter, extrudes multiple endogenous and exogenous substrates from the cell, playing an important role in normal physiology and xenobiotic distribution and bioavailability. To date, the predominant animal models used to investigate the role of P-gp have been the mouse and rat, which have two distinct genes, Abcb1a and Abcb1b. In contrast, the human has a single gene, ABCB1, for which only a single isoform has been validated. We and others have previously shown important differences between Abcb1a and Abcb1b, limiting the extrapolation from rodent findings to the human. Since the guinea pig has a relatively long gestation, hemomonochorial placentation and neuroanatomically mature offspring, it is more similar to the human, and may provide a more comparable model for investigating the regulation of P-gp in the brain and placenta, however, to date, the Abcb1 gene in the guinea pig remains to be characterized. The placenta and fetal brain are barrier sites that express P-gp and that play a critical role of protection of the fetus and the fetal brain from maternally administered drugs and other xenobiotics. Using RNA sequencing (RNA-seq), reverse transcription-polymerase chain reaction (RT-PCR) and quantitative PCR (QPCR) to sequence the expressed isoforms of guinea pig Abcb1, we demonstrate that like the human, the guinea pig genome contains one gene for Abcb1 but that it is expressed as at least three different isoforms via alternative splicing and alternate exon usage. Further, we demonstrate that these isoforms are more closely related to human than to rat or mouse isoforms. This striking, overall similarity and evolutionary relatedness between guinea pig Abcb1 and human ABCB1 indicate that the guinea pig represents a relevant animal model for investigating the function and regulation of P-gp in the placenta and brain.

Highlights

Up to 96% of pregnant women are administered at least one prescription drug during gestation
From RNA isolated from guinea pig placental and brain microvessel (MV)-derived tissues, five transcripts were identified as potential Abcb1 transcripts using Cufflinks software, but only three of these were found to bear significant homology to Abcb1 with multiple species including human, so only these were retained for further study (Fig. S1)
The two transcripts that were excluded from analysis (Fig. S2A) were built from scaffolds other than scaffold 11 and shared greater homology to other members of the ABC superfamily, Abcb11, Abcb4, and Abcb8

Summary

Introduction

Up to 96% of pregnant women are administered at least one prescription drug during gestation. Where the fetus is not the intended target of treatment, there is significant risk of drug exposure in the developing fetus [1,2]. Multidrug Resistance 1 (MDR1; alternatively ABCB1 or P-glycoprotein (P-gp)) has been shown to limit the transplacental passage of substrates (endogenous and exogenous) into the fetal compartment and as such protects the fetus from potentially harmful compounds present in the maternal circulation [3,4,5]. Another level of fetal protection is found at the BBB. Abcb in endothelial cells of the brain microvasculature limits the passage of substrates across the BBB and minimizes the entry of substrates into the fetal brain [6,7]

Objectives

Methods

Results

Discussion

Conclusion