Modulation of human placental P-glycoprotein expression and activity by MDR1 gene polymorphisms

Influence of hepatic and intestinal efflux transporters and their genetic variants on the pharmacokinetics and pharmacodynamics of raloxifene in osteoporosis treatment

Raloxifene exhibits a large and unexplained interindividual variability in its pharmacokinetics and pharmacodynamics. The aim of our study was to identify transporters involved in the efflux of raloxifene and its glucuronide metabolites by various in vitro models and by an in vivo study to explore the possible involvement of P-glycoprotein (Pgp), multidrug resistance-associated protein (MRP)1, MRP2, MRP3, and breast cancer resistance protein in the observed high interindividual variability. Experiments with the parallel artificial membrane permeability assay showed the highest passive permeability for raloxifene, followed by raloxifene-6-β-glucuronide (M1), raloxifene-4'-β-glucuronide (M2), and raloxifene-6,4'-diglucuronide (M3). Caco-2 cell monolayer experiments indicated an interaction of raloxifene with Pgp. The ATPase assay confirmed the raloxifene interaction with Pgp and indicated interactions of all raloxifene species with MRP1, MRP2, MRP3, and breast cancer resistance protein, except for M1, which did not show any interactions with MRP2. Furthermore, the vesicular experiments confirmed the interaction of M2 and M3 with MRP2. Although the in vivo study on osteoporotic postmenopausal women on raloxifene could not confirm a significant influence of ABCB1 and ABCC2 genetic polymorphisms on its pharmacokinetics, a clear trend toward higher total raloxifene concentrations was observed in carriers of at least 1 ABCB1 c.3435T allele. Moreover, the same polymorphism effect was also observed as a significant increase in total hip bone mineral density after 1 year of treatment. The results of our study support the involvement of efflux transporters in disposition of raloxifene and its metabolites and may partially explain the observed raloxifene variability by the influence of the ABCB1 c.3435C>T polymorphism.

ATP-binding cassette efflux transporters in human placenta

Pregnant women are often complicated with diseases including viral or bacterial infections, epilepsy, hypertension, or pregnancy-induced conditions such as depression and gestational diabetes that require treatment with medication. In addition, substance abuse during pregnancy remains a major public health problem. Many drugs used by pregnant women are off label without the necessary dose, efficacy, and safety data required for rational dosing regimens of these drugs. Thus, a major concern arising from the widespread use of drugs by pregnant women is the transfer of drugs across the placental barrier, leading to potential toxicity to the developing fetus. Knowledge regarding the ATP-binding cassette (ABC) efflux transporters, which play an important role in drug transfer across the placental barrier, is absolutely critical for optimizing the therapeutic strategy to treat the mother while protecting the fetus during pregnancy. Such transporters include P-glycoprotein (P-gp, gene symbol ABCB1), the breast cancer resistance protein (BCRP, gene symbol ABCG2), and the multidrug resistance proteins (MRPs, gene symbol ABCCs). In this review, we summarize the current knowledge with respect to developmental expression and regulation, membrane localization, functional significance, and genetic polymorphisms of these ABC transporters in the placenta and their relevance to fetal drug exposure and toxicity.

ABCB1 and ABCG2 expression in the placenta and fetus: an interspecies comparison

IMPORTANCE OF THE FIELD

ABCB1 and ABCG2 are efflux transporters which have a major impact on the pharmacological behavior of numerous drugs. They are expressed, for example, in the intestine, liver, kidney, BBB and placenta. It has become evident that ABCB1 and ABCG2 modify the pharmaco/toxicokinetics in the placenta and fetus and may consequently affect the outcome of pregnancy.

AREAS COVERED IN THIS REVIEW

Comprehensive literature searches were done using PubMed (until June 2010) to identify publications on ABCB1 and ABCG2 expression in placenta and fetal tissues in human, mouse, rat, guinea-pig and rabbit.

WHAT THE READER WILL GAIN

In this review, we aim to provide an overview of the current knowledge on the ABCB1 and ABCG2 transporter expression profiles in the placenta and fetal tissues in humans relative to other species.

TAKE HOME MESSAGE

The available information on ABCB1 and ABCG2 temporal expression profiles in placenta and fetus indicates rather good correlation among human, mouse and rat although some specific differences have been reported. However, at this point no detailed comparisons or comparative functional data are available. Detailed knowledge on the expression patterns and functional activity of ABCB1 and ABCG2 transporters placenta and developing embryo/fetus in different species could possibly help the interspecies extrapolation.

Drug transporter pharmacogenetics in nucleoside-based therapies

This article focuses on the different types of transporter proteins that have been implicated in the influx and efflux of nucleoside-derived drugs currently used in the treatment of cancer, viral infections (i.e., AIDS) and other conditions, including autoimmune and inflammatory diseases. Genetic variations in nucleoside-derived drug transporter proteins encoded by the gene families SLC15, SLC22, SLC28, SLC29, ABCB, ABCC and ABCG will be specifically considered. Variants known to affect biological function are summarized, with a particular emphasis on those for which clinical correlations have already been established. Given that relatively little is known regarding the genetic variability of the players involved in determining nucleoside-derived drug bioavailability, it is anticipated that major challenges will be faced in this area of research.

Role of human placental apical membrane transporters in the efflux of glyburide, rosiglitazone, and metformin

OBJECTIVE

Substrates of placental efflux transporters could compete for a single transporter, which could result in an increase in the transfer of each substrate to the fetal circulation. Our aim was to determine the role of placental transporters in the biodisposition of oral hypoglycemic drugs that could be used as monotherapy or in combination therapy for gestational diabetes.

STUDY DESIGN

Inside-out brush border membrane vesicles from term placentas were used to determine the efflux of glyburide, rosiglitazone, and metformin by P-glycoprotein, breast cancer resistance protein, and multidrug resistance protein.

RESULTS

Glyburide was transported by multidrug resistance protein (43 +/- 4%); breast cancer resistance protein (25 +/- 5%); and P-glycoprotein (9 +/- 5%). Rosiglitazone was transported predominantly by P-glycoprotein (71 +/- 26%). Metformin was transported by P-glycoprotein (58 +/- 20%) and breast cancer resistance protein (25 +/- 14%).

CONCLUSION

Multiple placental transporters contribute to efflux of glyburide, rosiglitazone, and metformin. Administration of drug combinations could lead to their competition for efflux transporters.

Concentration-dependent effects and intracellular accumulation of HIV protease inhibitors in cultured CD4 T cells and primary human lymphocytes

BACKGROUND

The intracellular and plasma concentrations of HIV protease inhibitors (HPIs) vary widely in vivo. It is unclear whether there is a concentration-dependent effect of HPIs such that at increasing concentration they may either block their own efflux (leading to 'autoboosting') or influx (leading to saturability/decreased intracellular accumulation).

METHOD

The effects of various concentrations (0-30 microM) of lopinavir, saquinavir, ritonavir and atazanavir on the accumulation of [(14)C]lopinavir, [(3)H]saquinavir, [(3)H]ritonavir and [(3)H]atazanavir, respectively, were investigated in CEM(parental), CEM(VBL) [P-glycoprotein (ABCB1) overexpressing], CEM(E1000) (MRP1 overexpressing) and in peripheral blood mononuclear cells (PBMCs). We also investigated the effects of inhibitors of ABCB1/ABCG2 (tariquidar), ABCC (MK571) and ABCC1/2 (frusemide), singly and in combination with HPIs, on cellular accumulation.

RESULTS

In all the cell lines, with increasing concentration of lopinavir, saquinavir and ritonavir, there was a significant increase in the cellular accumulation of [(14)C]lopinavir, [(3)H]saquinavir and [(3)H]ritonavir. Tariquidar, MK571 and frusemide (alone and in combination with lopinavir, saquinavir and ritonavir) significantly increased the accumulation of [(14)C]lopinavir, [(3)H]saquinavir and [(3)H]ritonavir. Ritonavir (alone or in combination with tariquidar) decreased the intracellular accumulation of [(3)H]ritonavir in PBMCs. Atazanavir decreased the accumulation of [(3)H]atazanavir in a concentration-dependent manner in all of the cells tested.

CONCLUSIONS

There are complex and variable drug-specific rather than class-specific effects of the HPIs on their own accumulation.