Effect of oxygen on multidrug resistance in the first trimester human placenta

Hypoxia modulates P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) drug transporters in brain endothelial cells of the developing human blood-brain barrier

P-glycoprotein (P-gp) and Breast Cancer Resistance Protein (BCRP) multidrug resistance (MDR) transporters are localized at the luminal surface of the blood-brain barrier (BBB). They confer fetal brain protection against harmful compounds that may be circulating in the peripheral blood. The fetus develops in low oxygen levels; however, some obstetric pathologies such as pre-eclampsia, placenta accreta/previa may result in even greater fetal hypoxic states. We investigated how hypoxia impacts MDR transporters in human fetal brain endothelial cells (hfBECs) derived from early and mid-stages of pregnancy. Hypoxia decreased BCRP protein and activity in hfBECs derived in early pregnancy. In contrast, in hfBECs derived in mid-pregnancy there was an increase in P-gp and BCRP activity following hypoxia. Results suggest a hypoxia-induced reduction in fetal brain protection in early pregnancy, but a potential increase in transporter-mediated protection at the BBB during mid-gestation. This would modify accumulation of various key physiological and pharmacological substrates of P-gp and BCRP in the developing fetal brain and potentially contribute to the pathogenesis of neurodevelopmental disorders commonly associated with in utero hypoxia.

Regulation of ABC transporters by sex steroids may explain differences in drug resistance between sexes

Drug efficacy is dependent on the pharmacokinetics and pharmacodynamics of therapeutic agents. Tight junctions, detoxification enzymes, and drug transporters, due to their localization on epithelial barriers, modulate the absorption, distribution, and the elimination of a drug. The epithelial barriers which control the pharmacokinetic processes are sex steroid hormone targets, and in this way, sex hormones may also control the drug transport across these barriers. Thus, sex steroids contribute to sex differences in drug resistance and have a relevant impact on the sex-related efficacy of many therapeutic drugs. As a consequence, for the further development and optimization of therapeutic strategies, the sex of the individuals must be taken into consideration. Here, we gather and discuss the evidence about the regulation of ATP-binding cassette transporters by sex steroids, and we also describe the signaling pathways by which sex steroids modulate ATP-binding cassette transporters expression, with a focus in the most important ATP-binding cassette transporters involved in multidrug resistance.

Effects of bacterial and viral pathogen-associated molecular patterns (PAMPs) on multidrug resistance (MDR) transporters in brain endothelial cells of the developing human blood-brain barrier

BACKGROUND

The multidrug resistance (MDR) transporters, P-glycoprotein (P-gp, encoded by ABCB1) and breast cancer resistance protein (BCRP/ABCG2) contribute to the blood-brain barrier (BBB), protecting the brain from drug exposure. The impact of infection on MDR in the developing human BBB remains to be determined. We hypothesized that exposure to bacterial and viral pathogen-associated molecular patterns (PAMPs) modify MDR expression and activity in human fetal brain endothelial cells (hfBECs) isolated from early and mid-gestation brain microvessels.

METHODS

We modelled infection (4 h and 24 h) using the bacterial PAMP, lipopolysaccharide (LPS; a toll-like receptor [TLR]-4 ligand) or the viral PAMPs, polyinosinic polycytidylic acid (Poly I:C; TLR-3 ligand) and single-stranded RNA (ssRNA; TLR-7/8 ligand). mRNA expression was assessed by qPCR, whereas protein expression was assessed by Western blot or immunofluorescence. P-gp and BCRP activity was evaluated by Calcein-AM and Chlorin-6 assays.

RESULTS

TLRs-3,4 and 8 were expressed by the isolated hfBECs. Infection mimics induced specific pro-inflammatory responses as well as changes in P-gp/ABCB1 or BCRP/ABCG2 expression (P < 0.05). LPS and ssRNA significantly decreased P-gp activity at 4 and 24 h in early and mid-gestation (P < 0.03-P < 0.001), but significantly increased BCRP activity in hfBECs in a dose-dependent pattern (P < 0.05-P < 0.002). In contrast, Poly-IC significantly decreased P-gp activity after 4 h in early (P < 0.01) and mid gestation (P < 0.04), but not 24 h, and had no overall effect on BCRP activity, though BCRP activity was increased with the highest dose at 24 h in mid-gestation (P < 0.05).

CONCLUSIONS

Infectious PAMPs significantly modify the expression and function of MDR transporters in hfBECs, though effects are PAMP-, time- and dose-specific. In conclusion, bacterial and viral infections during pregnancy likely have profound effects on exposure of the fetal brain to physiological and pharmacological substrates of P-gp and BCRP, potentially leading to altered trajectories of fetal brain development.

Infection and disruption of placental multidrug resistance (MDR) transporters: Implications for fetal drug exposure

P-glycoprotein (P-gp, encoded by the ABCB1 gene) and breast cancer resistance protein (BCRP/ABCG2) are efflux multidrug resistance (MDR) transporters localized at the syncytiotrophoblast barrier of the placenta and protect the conceptus from drug and toxin exposure throughout pregnancy. Infection is an important modulator of MDR expression and function. This review comprehensively examines the effect of infection on the MDR transporters, P-gp and BCRP in the placenta. Infection PAMPs such as bacterial lipopolysaccharide (LPS) and viral polyinosinic-polycytidylic acid (poly I:C) and single-stranded (ss)RNA, as well as infection with Zika virus (ZIKV), Plasmodium berghei ANKA (modeling malaria in pregnancy - MiP) and polymicrobial infection of intrauterine tissues (chorioamnionitis) all modulate placental P-gp and BCRP at the levels of mRNA, protein and or function; with specific responses varying according to gestational age, trophoblast type and species (human vs. mice). Furthermore, we describe the expression and localization profile of Toll-like receptor (TLR) proteins of the innate immune system at the maternal-fetal interface, aiming to better understand how infective agents modulate placental MDR. We also highlight important gaps in the field and propose future research directions. We conclude that alterations in placental MDR expression and function induced by infective agents may not only alter the intrauterine biodistribution of important MDR substrates such as drugs, toxins, hormones, cytokines, chemokines and waste metabolites, but also impact normal placentation and adversely affect pregnancy outcome and maternal/neonatal health.

Increasing maternal age predicts placental protein expression critical for fetal serotonin metabolism: Potential implications for neurodevelopmental research

High fetal exposure to serotonin and increasing maternal age both contribute to the risk for neurodevelopmental disorders. While identifying covariates for a study of placental protein expression, we found a significant negative correlation between maternal age and the expression of monoamine oxidase A (MAOA), and a significant positive correlation between maternal age and the expression of the serotonin transporter SERT. MAOA and SERT play key roles in placental serotonin metabolism relevant to fetal neurodevelopment. These preliminary findings suggest that the effect of increasing maternal age on neurodevelopmental risk may be mediated in part by changes in placental protein expression relevant to fetal serotonin metabolism.

Predicting Human Fetal Drug Exposure Through Maternal-Fetal PBPK Modeling and In Vitro or Ex Vivo Studies

Medication (drug) use in human pregnancy is prevalent. Determining fetal safety and efficacy of drugs is logistically challenging. However, predicting (not measuring) fetal drug exposure (systemic and tissue) throughout pregnancy is possible through maternal-fetal physiologically based pharmacokinetic (PBPK) modeling and simulation. Such prediction can inform fetal drug safety and efficacy. Fetal drug exposure can be quantified in 2 complementary ways. First, the ratio of the steady-state unbound plasma concentration in the fetal plasma (or area under the plasma concentration-time curve) to the corresponding maternal plasma concentration (ie, Kp,uu ). Second, the maximum unbound peak (Cu,max,ss,f ) and trough (Cu,min,ss,f ) fetal steady-state plasma concentrations. We (and others) have developed a maternal-fetal PBPK model that can successfully predict maternal drug exposure. To predict fetal drug exposure, the model needs to be populated with drug specific parameters, of which transplacental clearances (active and/or passive) and placental/fetal metabolism of the drug are critical. Herein, we describe in vitro studies in cells/tissue fractions or the perfused human placenta that can be used to determine these drug-specific parameters. In addition, we provide examples whereby this approach has successfully predicted systemic fetal exposure to drugs that passively or actively cross the placenta. Apart from maternal-fetal PBPK models, animal studies also have the potential to estimate fetal drug exposure by allometric scaling. Whether such scaling will be successful is yet to be determined. Here, we review the above approaches to predict fetal drug exposure, outline gaps in our knowledge to make such predictions and map out future research directions that could fill these gaps.

Functional Expression of Multidrug-Resistance (MDR) Transporters in Developing Human Fetal Brain Endothelial Cells

There is little information about the functional expression of the multidrug resistance (MDR) transporters P-glycoprotein (P-gp, encoded by ABCB1) and breast cancer resistance protein (BCRP/ABCG2) in the developing blood−brain barrier (BBB). We isolated and cultured primary human fetal brain endothelial cells (hfBECs) from early and mid-gestation brains and assessed P-gp/ABCB1 and BCRP/ABCG2 expression and function, as well as tube formation capability. Immunolocalization of the von Willebrand factor (marker of endothelial cells), zonula occludens-1 and claudin-5 (tight junctions) was detected in early and mid-gestation-derived hfBECs, which also formed capillary-like tube structures, confirming their BEC phenotype. P-gp and BCRP immunostaining was detected in capillary-like tubes and in the cytoplasm and nucleus of hfBECs. P-gp protein levels in the plasma membrane and nuclear protein fractions, as well as P-gp protein/ABCB1 mRNA and BCRP protein levels decreased (p < 0.05) in hfBECs, from early to mid-gestation. No differences in P-gp or BCRP activity in hfBECs were observed between the two age groups. The hfBECs from early and mid-gestation express functionally competent P-gp and BCRP drug transporters and may thus contribute to the BBB protective phenotype in the conceptus from early stages of pregnancy.

ATP-binding cassette (ABC) drug transporters in the developing blood-brain barrier: role in fetal brain protection

The blood-brain barrier (BBB) provides essential neuroprotection from environmental toxins and xenobiotics, through high expression of drug efflux transporters in endothelial cells of the cerebral capillaries. However, xenobiotic exposure, stress, and inflammatory stimuli have the potential to disrupt BBB permeability in fetal and post-natal life. Understanding the role and ability of the BBB in protecting the developing brain, particularly with respect to drug/toxin transport, is key to promoting long-term brain health. Drug transporters, particularly P-gp and BCRP are expressed in early gestation at the developing BBB and have a crucial role in developmental homeostasis and fetal brain protection. We have highlighted several factors that modulate drug transporters at the developing BBB, including synthetic glucocorticoid (sGC), cytokines, maternal infection, and growth factors. Some factors have the potential to increase expression and function of drug transporters and increase brain protection (e.g., sGC, transforming growth factor [TGF]-β). However, others inhibit drug transporters expression and function at the BBB, increasing brain exposure to xenobiotics (e.g., tumor necrosis factor [TNF], interleukin [IL]-6), negatively impacting brain development. This has implications for pregnant women and neonates, who represent a vulnerable population and may be exposed to drugs and environmental toxins, many of which are P-gp and BCRP substrates. Thus, alterations in regulated transport across the developing BBB may induce long-term changes in brain health and compromise pregnancy outcome. Furthermore, a large portion of neonatal adverse drug reactions are attributed to agents that target or access the nervous system, such as stimulants (e.g., caffeine), anesthetics (e.g., midazolam), analgesics (e.g., morphine) and antiretrovirals (e.g., Zidovudine); thus, understanding brain protection is key for the development of strategies to protect the fetal and neonatal brain.

Preterm Birth Associates With Increased Placental Expression of MDR Transporters Irrespective of Prepregnancy BMI

CONTEXT

Preterm birth (PTB) and suboptimal prepregnancy body mass index (BMI) operate through inflammatory pathways to impair fetoplacental development. Placental efflux transporters mediate fetal protection and nutrition; however, few studies consider the effect of both PTB and BMI on fetal protection. We hypothesized that PTB would alter the expression of placental multidrug resistance (MDR) transporters and selected proinflammatory cytokines, and that maternal underweight and obesity would further impair placental phenotype.

OBJECTIVE

To determine whether placental MDR transporters P-glycoprotein (P-gp, encoded by ABCB1) and breast cancer resistance protein (BCRP/ABCG2), and proinflammatory cytokine levels are altered by PTB and maternal BMI.

METHODS

A cross-sectional study was conducted to assess the effect of PTB (with/without chorioamnionitis), or the effect of maternal prepregnancy BMI on placental MDR transporter and interleukin (IL)-6 and -8 expression in 60 preterm and 36 term pregnancies.

RESULTS

ABCB1 expression was increased in preterm compared to term placentae (P = .04). P-gp (P = .008) and BCRP (P = .01) immunolabeling was increased among all preterm compared to term placentae, with P-gp expression further increased in preterm pregnancies with chorioamnionitis (PTC, P = .007). Placental IL-6 mRNA expression was decreased in PTC compared to term placentae (P = .0005) and PTC associated with the greatest proportion of anti-inflammatory medications administered during pregnancy. Maternal BMI group did not influence placental outcomes.

CONCLUSION

PTB and infection, but not prepregnancy BMI, alter placental expression of MDR transporters and IL-6. This may have implications for fetal exposure to xenobiotics that may be present in the maternal circulation in pregnancies complicated by PTB.

The effect of ethanol and nicotine on ER stress in human placental villous explants

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Nicotine increased the GRP78/BiP protein in first trimester and term placental villous explants.

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Nicotine can cause endoplasmic reticulum stress in human placenta.

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Placental villous explants can be isolated from first trimester and term placenta to compare responses to toxic compounds.

Pregnant mothers continue smoking and drinking during pregnancy. To clarify the mechanisms of nicotine and ethanol toxicity during development, we have examined their effects on endoplasmic reticulum (ER) stress in human first trimester and term placental explants. First trimester and term human placental explants were treated with ethanol (2 ‰) or nicotine (15 µM), or their combination. The ER stress markers glucose regulated protein 78 (GRP78/BiP) and inositol requiring enzyme 1 α (IRE1α) were analyzed by immunoblotting. A statistically significant increase (p < 0.05) of GRP78/BiP by nicotine was noted in first trimester placental explants at 48 h, and in term placental explants at 24 h. Ethanol did not change protein expression of GRP78/BiP in either first trimester or term placental explants. IRE1α increased, although not statistically significantly, by all treatments in both first trimester and term placental explants. Thus, regardless of the known structural and functional differences in early and late placenta, both responded very similarly to the toxic compounds studied. These data support our earlier results in BeWo cells (Repo et al., 2014) implicating that nicotine induces ER stress in human placenta and may interfere with placental functions potentially disrupting fetal growth and development.

Overview of Drug Transporters in Human Placenta

The transport of drugs across the placenta is a point of great importance in pharmacotherapy during pregnancy. However, the knowledge of drug transport in pregnancy is mostly based on experimental clinical data, and the underlying biological mechanisms are not fully understood. In this review, we summarize the current knowledge of drug transporters in the human placenta. We only refer to human data since the placenta demonstrates great diversity among species. In addition, we describe the experimental models that have been used in human placental transport studies and discuss their availability. A better understanding of placental drug transporters will be beneficial for the health of pregnant women who need drug treatment and their fetuses.

A review of pregnancy-induced changes in opioid pharmacokinetics, placental transfer, and fetal exposure: Towards fetomaternal physiologically-based pharmacokinetic modeling to improve the treatment of neonatal opioid withdrawal syndrome

Physiologically-based pharmacokinetic (PBPK) modeling has emerged as a useful tool to study pharmacokinetics (PK) in special populations, such as pregnant women, fetuses, and newborns, where practical hurdles severely limit the study of drug behavior. PK in pregnant women is variable and everchanging, differing greatly from that in their nonpregnant female and male counterparts typically enrolled in clinical trials. PBPK models can accommodate pregnancy-induced physiological and metabolic changes, thereby providing mechanistic insights into maternal drug disposition and fetal exposure. Fueled by the soaring opioid epidemic in the United States, opioid use during pregnancy continues to rise, leading to an increased incidence of neonatal opioid withdrawal syndrome (NOWS). The severity of NOWS is influenced by a complex interplay of extrinsic and intrinsic factors, and varies substantially between newborns, but the extent of prenatal opioid exposure is likely the primary driver. Fetomaternal PBPK modeling is an attractive approach to predict in utero opioid exposure. To facilitate the development of fetomaternal PBPK models of opioids, this review provides a detailed overview of pregnancy-induced changes affecting the PK of commonly used opioids during gestation. Moreover, the placental transfer of these opioids is described, along with their disposition in the fetus. Lastly, the implementation of these factors into PBPK models is discussed. Fetomaternal PBPK modeling of opioids is expected to provide improved insights in fetal opioid exposure, which allows for prediction of postnatal NOWS severity, thereby opening the way for precision postnatal treatment of these vulnerable infants.

Hypoxia alters the expression of ACE2 and TMPRSS2 SARS-CoV-2 cell entry mediators in hCMEC/D3 brain endothelial cells

The mechanisms by which the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) induces neurological complications remain to be elucidated. We aimed to identify possible effects of hypoxia on the expression of SARS-CoV-2 cell entry mediators, angiotensin-converting enzyme 2 (ACE2) receptor and transmembrane protease serine 2 (TMPRSS2) protein, in human brain endothelial cells, in vitro. hCMEC/D3 cells were exposed to different oxygen tensions: 20% (Control group), 8% or 2% O₂ (Hypoxia groups). Cells were harvested 6-, 24- and 48 h following hypoxic challenge for assessment of mRNA and protein, using qPCR and Western Blot. The response of the brain endothelial cells to hypoxia was replicated using modular incubator chambers. We observed an acute increase (6 h, p < 0.05), followed by a longer-term decrease (48 h, p < 0.05) in ACE2 mRNA and protein expression, accompanied by reduced expression of TMPRSS2 protein levels (48 h, p < 0.05) under the more severe hypoxic condition (2% O₂). No changes in levels of von Willebrand Factor (vWF - an endothelial cell damage marker) or interleukin 6 (IL-6 - a pro-inflammatory cytokine) mRNA were observed. We conclude that hypoxia regulates brain endothelial cell ACE2 and TMPRSS2 expression in vitro, which may indicate human brain endothelial susceptibility to SARS-CoV-2 infection and subsequent brain sequelae.

Effect of Sublethal Prenatal Endotoxaemia on Murine Placental Transport Systems and Lipid Homeostasis

Infection alters the expression of transporters that mediate the placental exchange of xenobiotics, lipids and cytokines. We hypothesized that lipopolysaccharide (LPS) modifies the expression of placental transport systems and lipid homeostasis. LPS (150 μg/kg; i.p.) treatments were administered for 4 h or 24 h, animals were euthanized at gestational days (GD) 15.5 or 18.5, and maternal blood, fetuses and placentae were collected. Increased rates of fetal demise were observed at GD15.5 following LPS treatment, whereas at GD18.5, high rates of early labour occurred and were associated with distinct proinflammatory responses. Lipopolysaccharide did not alter ATP-binding cassette (ABC) transporter mRNA expression but decreased fatty acid binding protein associated with plasma membrane (Fabppm) at GD15.5 (LPS-4 h) and increased fatty acid translocase (Fat/Cd36) mRNA at GD18.5 (LPS-4 h). At the protein level, breast cancer-related protein (Bcrp) and ABC sub-family G member 1 (Abcg1) levels were decreased in the placental labyrinth zone (Lz) at GD15.5, whereas P-glycoprotein (P-gp) and Bcrp Lz-immunostaining was decreased at GD18.5. In the placental junctional zone (Jz), P-gp, Bcrp and Abcg1 levels were higher at GD18.5. Specific maternal plasma and placental changes in triacylglycerol, free fatty acid, cholesterol, cholesterol ester and monoacylglycerol levels were detected in a gestational age-dependent manner. In conclusion, LPS-increased risk of fetal death and early labour were associated with altered placental ABC and lipid transporter expression and deranged maternal plasma and placental lipid homeostasis. These changes may potentially modify fetal xenobiotic exposure and placental lipid exchange in cases of bacterial infection.

Effects of Maternal Obesity and Gestational Diabetes Mellitus on the Placenta: Current Knowledge and Targets for Therapeutic Interventions

Obesity and gestational diabetes mellitus (GDM) are becoming more common among pregnant women worldwide and are individually associated with a number of placenta-mediated obstetric complications, including preeclampsia, macrosomia, intrauterine growth restriction and stillbirth. The placenta serves several functions throughout pregnancy and is the main exchange site for the transfer of nutrients and gas from mother to fetus. In pregnancies complicated by maternal obesity or GDM, the placenta is exposed to environmental changes, such as increased inflammation and oxidative stress, dyslipidemia, and altered hormone levels. These changes can affect placental development and function and lead to abnormal fetal growth and development as well as metabolic and cardiovascular abnormalities in the offspring. This review aims to summarize current knowledge on the effects of obesity and GDM on placental development and function. Understanding these processes is key in developing therapeutic interventions with the goal of mitigating these effects and preventing future cardiovascular and metabolic pathology in subsequent generations.

Expression of severe acute respiratory syndrome coronavirus 2 cell entry genes, angiotensin-converting enzyme 2 and transmembrane protease serine 2, in the placenta across gestation and at the maternal-fetal interface in pregnancies complicated by preterm birth or preeclampsia

BACKGROUND

Although there is some evidence that severe acute respiratory syndrome coronavirus 2 can invade the human placenta, limited data exist on the gestational age-dependent expression profile of the severe acute respiratory syndrome coronavirus 2 cell entry mediators, angiotensin-converting enzyme 2 and transmembrane protease serine 2, at the human maternal-fetal interface. There is also no information as to whether the expression of these mediators is altered in pregnancies complicated by preeclampsia or preterm birth. This is important because the expression of decidual and placental angiotensin-converting enzyme 2 and transmembrane protease serine 2 across gestation may affect the susceptibility of pregnancies to vertical transmission of severe acute respiratory syndrome coronavirus 2.

OBJECTIVE

This study aimed to investigate the expression pattern of specific severe acute respiratory syndrome coronavirus 2 cell entry genes, angiotensin-converting enzyme 2 and transmembrane protease serine 2, in the placenta across human pregnancy and in paired samples of decidua and placenta in pregnancies complicated by preterm birth or preeclampsia compared with those in term uncomplicated pregnancies.

STUDY DESIGN

In this study, 2 separate cohorts of patients, totaling 87 pregnancies, were included. The first cohort was composed of placentae from first- (7-9 weeks), second- (16-18 weeks), and third-trimester preterm (26-31 weeks) and third-trimester term (38-41 weeks) pregnancies (n=5/group), whereas the second independent cohort included matched decidua and placentae from pregnancies from term uncomplicated pregnancies (37-41 weeks' gestation; n=14) and pregnancies complicated by preterm birth (26-37 weeks' gestation; n=11) or preeclampsia (25-37 weeks' gestation; n=42). Samples were subjected to quantitative polymerase chain reaction and next-generation sequencing or RNA sequencing for next-generation RNA sequencing for angiotensin-converting enzyme 2 and transmembrane protease serine 2 mRNA expression quantification, respectively.

RESULTS

In the first cohort, angiotensin-converting enzyme 2 and transmembrane protease serine 2, exhibited a gestational age-dependent expression profile, that is, angiotensin-converting enzyme 2 and transmembrane protease serine 2 mRNA was higher (P<.05) in the first-trimester placenta than in second-trimester, preterm birth, and term placentae (P<.05) and exhibited a negative correlation with gestational age (P<.05). In the second cohort, RNA sequencing demonstrated very low or undetectable expression levels of angiotensin-converting enzyme 2 in preterm birth, preeclampsia, and term decidua and in placentae from late gestation. In contrast, transmembrane protease serine 2 was expressed in both decidual and placental samples but did not change in pregnancies complicated by either preterm birth or preeclampsia.

CONCLUSION

The increased expression of these severe acute respiratory syndrome coronavirus 2 cell entry-associated genes in the placenta in the first trimester of pregnancy compared with those in later stages of pregnancy suggests the possibility of differential susceptibility to placental entry to severe acute respiratory syndrome coronavirus 2 across pregnancy. Even though there is some evidence of increased rates of preterm birth associated with severe acute respiratory syndrome coronavirus 2 infection, we found no increase in mRNA expression of angiotensin-converting enzyme 2 or transmembrane protease serine 2 at the maternal-fetal interface.

Function of Multidrug Resistance Transporters is Disrupted by Infection Mimics in Human Brain Endothelial Cells

P-glycoprotein (P-gp/ABCB1) and breast cancer resistance protein (BCRP/ABCG2) modulate the distribution of drugs and toxins across the blood-brain barrier (BBB). Animal studies reported that infection-induced disruption of these transporters in the developing BBB impairs fetal brain protection. However, the impact of infection mimics on P-gp/BCRP function in human brain endothelium is less well understood. We hypothesized that Toll-like receptor ligands mimicking bacterial and viral infection would modify the expression and function of P-gp and BCRP in human brain endothelial cells (BECs). Human cerebral microvascular endothelial cells (hCMEC/D3) were challenged with bacterial [Lipopolysaccharide (LPS)] and viral-mimics [polyinosinic:polycytidylic acid (PolyI:C) or single-stranded RNA (ssRNA)], or pro-inflammatory cytokines interleukin (IL)-6, tumor necrosis factor (TNF)-α and interferon gamma (IFN)-ɣ. P-gp and BCRP function was assessed after 4 or 24 h, using Calcein-AM and Chlorin-6 assays, respectively. Western blot and qPCR quantified P-gp/ABCB1 and BCRP/ABCG2 expression following treatments. Infection mimics are potent modulators of drug transporters in human BECs in vitro. LPS and PolyI:C increased, while ssRNA exposure reduced P-gp activity. In contrast, LPS and PolyI:C decreased, while ssRNA increased BCRP activity (P < .05). There was little correlation between drug transporter function, gene expression and total protein level. Altered plasma membrane BCRP may suggest modified intracellular trafficking induced by infection in human BECs. Bacterial and viral infection mimics modify P-gp and BCRP transport function in human BECs, in vitro. This knowledge may contribute and have important implications for human brain protection and possible altered biodistribution of drugs and xenobiotics in the brain following exposure to TLR agonists.

Low oxygen tension differentially regulates the expression of placental solute carriers and ABC transporters

Low oxygen concentration, or hypoxia, is an important physiological regulator of placental function including chemical disposition. Here, we compared the ability of low oxygen tension to alter the expression of solute carriers (SLC) and ABC transporters in two human placental models, namely BeWo cells and term placental explants. We found that exposure to low oxygen concentration differentially regulates transporter expression in BeWo cells, including downregulation of ENT1, OATP4A1, OCTN2, BCRP, and MRP2/3/5, and upregulation of CNT1, OAT4, OATP2B1, SERT, SOAT, and MRP1. Similar upregulation of MRP1 and downregulation of MRP5 and BCRP were observed in explants, whereas uptake transporters were decreased or unchanged. Furthermore, a screening of transcriptional regulators of transporters revealed that hypoxia leads to a decrease in the mRNA levels of aryl hydrocarbon receptor, nuclear factor erythroid 2-related factor 2, and retinoid x receptor alpha in both human placental models. These data suggest that transporter expression is differentially regulated by oxygen concentration across experimental human placental models.

The impact of intrauterine growth restriction on cytochrome P450 enzyme expression and activity

With the increased prevalence of non-communicable disease and availability of medications to treat these and other conditions, a pregnancy free from prescribed medication exposure is rare. Up to 99% of women take at least one medication during pregnancy. These medications can be divided into those used to improve maternal health and wellbeing (e.g., analgesics, antidepressants, antidiabetics, antiasthmatics), and those used to promote the baby's wellbeing in either fetal (e.g., anti-arrhythmics) or postnatal life (e.g., antenatal glucocorticoids). These medications are needed for pre-existing or coincidental illnesses in the mother, maternal conditions induced by the pregnancy itself through to conditions that arise in the fetus or that will be encountered by the newborn. Thus, medications administered to the mother may be used to treat the mother, the fetus or both. Metabolism of medications is regulated by a range of physiological processes that change during pregnancy. Other pathological processes such as placental insufficiency can in turn have both immediate and lifelong adverse health consequences for babies. Individuals born growth restricted are more likely to require medications but may also have an altered ability to metabolise these medications in fetal and postnatal life. This review aims to determine the effect of suboptimal fetal growth on the fetal expression of the drug metabolising enzymes (DMEs) that convert medications into active or inactive metabolites, and the transporters that remove both these medications and their metabolites from the fetal compartment.

Inter-individual variations and modulators of MDR1 transport activity in human placenta

INTRODUCTION

ATP binding cassette (ABC) membrane transporter multidrug resistance 1 (MDR1) is one of the most important efflux transporters in the human placenta protecting the fetus from exposure to xenobiotic toxicity. Recent studies have focused on placental MDR1 expression, but few studies have analyzed placental MDR1 transport activity. The purpose of this study was to investigate placental MDR1 transport activity using a relatively large sample size of human placentas. Furthermore, the effect of ABCB1 gene polymorphisms were investigated along with physiological factors including maternal age, times of pregnancy, BMI, delivery mode or pregnancy complications on placental MDR1 transport activity.

METHODS

A total of 252 human placentas were obtained after delivery. MDR1 transport activity was detected by N-methyl quinidine uptake in placental microvillus membrane vesicles (MVMVs). Nine common single nucleotide polymorphisms (SNPs) in ABCB1 genes were determined by Snapshot. The association between ABCB1 gene polymorphisms, maternal age, times of pregnancy, BMI, delivery mode or pregnancy complications, and transporter activity was investigated.

RESULTS

Inter-individual variations of MDR1 transport activity were observed among 252 subjects. The per unit protein activity was ranged from 0.05 to 0.15/mg. Nine SNPs in ABCB1 gene didn't exhibit significant association with transporter activity of MDR1. Likewise, neither age, times of pregnancy, delivery mode nor pregnancy complications showed any significant effect of placental MDR1 transport activity. But placental MDR1 transport activity in obese pregnant women was lower than those in non-obese pregnant women.

CONCLUSION

Inter-individual variations of MDR1 transport activity existed in human placentas. This may contribute to variations in drug exposure to the fetus affecting clinical outcomes. Maternal age, times of pregnancy, delivery mode nor pregnancy complications included in this study maybe not significantly impact placental MDR1 transport activity, but maternal obese could inhibit placental MDR1 activity.

Role of Elevated SFLT-1 on the Regulation of Placental Transporters in Women With Pre-Eclampsia

Pre-eclampsia (PE) is an obstetric complication associated with elevated levels of fms-like tyrosine kinase 1 (sFlt-1) and dysregulated trophoblast differentiation. However, limited information exists on the expression and regulation of placental drug transporters in PE. Transporter mRNA and protein expression were analyzed in human placentas diagnosed with PE (n = 34) and gestational age-matched controls (n = 24), whereas placental BeWo cells were treated with angiogenic factors in vitro. Significant downregulation of breast cancer resistance protein (BCRP) and several other transporters were seen in placentas complicated by PE compared with controls, whereas mRNA levels of sFlt-1 were induced by 2.5-fold in PE placentas (P < 0.01). Treatment of BeWo cells with sFlt-1 resulted in an 85-90% downregulation of BCRP, which was attenuated by vascular endothelial growth factor. Our findings suggest that placental function is compromised during PE due to altered expression of clinically important transporters. Furthermore, our in vitro results show that sFlt-1 is involved in the regulation of BCRP.

Placental transporter-mediated drug interactions and offspring congenital anomalies

Aims

P‐glycoprotein (P‐gp) and breast cancer resistance protein (BCRP) are efflux transporters expressed in the placenta, limiting their substrates from reaching the foetus. Our aim was to investigate if concomitant prenatal exposure to several substrates or inhibitors of these transporters increases the risk of congenital anomalies.

Methods

The national Drugs and Pregnancy database, years 1996–2014, was utilized in this population‐based birth cohort study. In the database, the Medical Birth Register, the Register on Induced Abortions, the Malformation register and the Register on Reimbursed Drug Purchases have been linked. The University of Washington Metabolism and Transport Drug Interaction Database was used to identify substrates and inhibitors of P‐gp and BCRP. We included singleton pregnancies ending in birth or elective termination of pregnancy due to foetal anomaly. Known teratogens were excluded. We identified women exposed 1 month before pregnancy or during the first trimester to P‐gp/BCRP polytherapy (n = 21 186); P‐gp/breast cancer resistance protein monotherapy (n = 97 906); non‐P‐gp/BCRP polytherapy (n = 78 636); and unexposed (n = 728 870). We investigated the association between the exposure groups and major congenital anomalies using logistic regression adjusting for several confounders.

Results

The prevalence of congenital anomalies was higher in the P‐gp/BCRP polytherapy group (5.5%) compared to the P‐gp/BCRP monotherapy (4.7%, OR 1.13; 95% CI 1.05–1.21), the non‐P‐gp/BCRP polytherapy (4.9%, OR 1.14; 95% CI 1.06–1.22), and to the unexposed groups (4.2%, OR 1.23; 95% CI 1.15–1.31).

Conclusion

The results suggest a role of placental transporter‐mediated drug interactions in teratogenesis.

Maternal malnutrition impacts placental morphology and transporter expression: an origin for poor offspring growth

The placenta promotes fetal growth through nutrient transfer and selective barrier systems. An optimally developed placenta can adapt to changes in the pregnancy environment, buffering the fetus from adverse exposures. We hypothesized that the placenta adapts differently to suboptimal maternal diets, evidenced by changes in placental morphology, developmental markers and key transport systems. Mice were fed a control diet (CON) during pregnancy, undernourished (UN) by 30% of control intake from gestational day (GD) 5.5-18.5 or fed 60% high-fat diet (HF) 8 weeks before and during pregnancy. At GD18.5, placental morphometry, development and transport were assessed. Junctional and labyrinthine areas of UN and HF placentae were smaller than CON by >10%. Fetal blood space area and fetal blood space:fetal weight ratios were reduced in HF vs. CON and UN. Trophoblast giant cell marker Ctsq mRNA expression was lower in UN vs. HF, and expression of glycogen cell markers Cx31.1 and Pcdh12 was lower in HF vs. UN. Efflux transporter Abcb1a mRNA expression was lower in HF vs. UN, and Abcg2 expression was lower in UN vs. HF. mRNA expression of fatty acid binding protein Fabp_pm was higher in UN vs. CON and HF. mRNA and protein levels of the lipid transporter FAT/CD36 were lower in UN, and FATP4 protein levels were lower in HF vs. UN. UN placentae appear less mature with aberrant transport, whereas HF placentae adapt to excessive nutrient supply. Understanding placental adaptations to common nutritional adversities may reveal mechanisms underlying the developmental origins of later disease.

Contributions of Drug Transporters to Blood-Placental Barrier

The placenta is the only organ linking two different individuals, mother and fetus, termed as blood-placental barrier. The functions of the blood-placental barrier are to regulate material transfer between the maternal and fetal circulation. The main functional units are the chorionic villi within which fetal blood is separated by only three or four cell layers (placental membrane) from maternal blood in the surrounding intervillous space. A series of drug transporters such as P-glycoprotein (P-GP), breast cancer resistance protein (BCRP), multidrug resistance-associated proteins (MRP1, MRP2, MRP3, MRP4, and MRP5), organic anion-transporting polypeptides (OATP4A1, OATP1A2, OATP1B3, and OATP3A1), organic anion transporter 4 (OAT4), organic cation transporter 3 (OCT3), organic cation/carnitine transporters (OCTN1 and OCTN2), multidrug and toxin extrusion 1 (MATE1), and equilibrative nucleoside transporters (ENT1 and ENT2) have been demonstrated on the apical membrane of syncytiotrophoblast, some of which also expressed on the basolateral membrane of syncytiotrophoblast or fetal capillary endothelium. These transporters are involved in transport of most drugs in the placenta, in turn, affecting drug distribution in fetus. Moreover, expressions of these transporters in the placenta often vary along with the gestational ages and are also affected by pathophysiological factor. This chapter will mainly illustrate function and expression of these transporters in placentas, their contribution to drug distribution in fetus, and their clinical significance.

Loss of Placental P-Glycoprotein May Be a Common Pathophysiologic Pathway for First Trimester Spontaneous Miscarriages

INTRODUCTION

P-glycoprotein the highly conserved mammalian adenosine triphosphate-binding cassette transmembrane multidrug protein transporter is involved in peri-implantation events and fetal placental development. Greater expression in early versus late pregnancy and localization in both syncytio- and cytotrophoblast indicate that P-glycoprotein transports substances across the uterine epithelium during early pregnancy and protects the conceptus from toxic substances during implantation and early embryogenesis. We hypothesized that P-glycoprotein is involved in the physiologic maintenance of early pregnancy and that P-glycoprotein dysregulation may be involved in early pregnancy pathologies.

METHODS

First trimester dilation and curettage specimens were selected retrospectively from the archives of the Department of Pathology from spontaneous miscarriages (n = 36) and elective termination of pregnancy (n = 20). Two P-glycoprotein specific monoclonal antibodies JSB1and C219 were used on formalin-fixed, paraffin-embedded 5µ tissue sections. The location, intensity, and percentage of P-glycoprotein chorionic villous immunostaining were semiquantitated.

RESULTS

Spontaneous miscarriages demonstrated absence or significant reduction in P-glycoprotein compared to elective terminations; 75% (27/36) showed total absence of P-glycoprotein, 19% (7/36) showed only rare villi with discontinuous immunostaining, and 6% (2/36) showed weak immunostaining. In contrast, 90% of elective terminations (18/20) showed positive immunostaining for P-glycoprotein and only 10% (2/20) showed loss of P-glycoprotein expression (P < .0001).

DISCUSSION

We report a dramatic loss/decrease of P-glycoprotein in first trimester spontaneous miscarriages. This finding in conjunction with the known high expression of P-glycoprotein in normal first trimester placental tissues suggests an important role of P-glycoprotein in the maintenance of early pregnancy.

Breast Cancer Resistance Protein (BCRP/ABCG2) Inhibits Extra Villous Trophoblast Migration: The Impact of Bacterial and Viral Infection

Extravillous trophoblasts (EVT) migration into the decidua is critical for establishing placental perfusion and when dysregulated, may lead to pre-eclampsia (PE) and intrauterine growth restriction (IUGR). The breast cancer resistance protein (BCRP; encoded by ABCG2) regulates the fusion of cytotrophoblasts into syncytiotrophoblasts and protects the fetus from maternally derived xenobiotics. Information about BCRP function in EVTs is limited, however placental exposure to bacterial/viral infection leads to BCRP downregulation in syncitiotrophoblasts. We hypothesized that BCRP is involved in the regulation of EVT function and is modulated by infection/inflammation. We report that besides syncitiotrophoblasts and cytotrophoblasts, BCRP is also expressed in EVTs. BCRP inhibits EVT cell migration in HTR8/SVneo (human EVT-like) cells and in human EVT explant cultures, while not affecting cell proliferation. We have also shown that bacterial-lipopolysaccharide (LPS)-and viral antigens-single stranded RNA (ssRNA)-have a profound effect in downregulating ABCG2 and BCRP levels, whilst simultaneously increasing the migration potential of EVT-like cells. Our study reports a novel function of BCRP in early placentation and suggests that exposure of EVTs to maternal infection/inflammation could disrupt their migration potential via the downregulation of BCRP. This could negatively influence placental development/function, contribute to existing obstetric pathologies, and negatively impact pregnancy outcomes and maternal/neonatal health.

Drug Transporters Expressed in the Human Placenta and Models for Studying Maternal-Fetal Drug Transfer

Tremendous efforts have been directed to investigate the ontogeny of drug transporters in fetuses, neonates, infants, and children based on their importance for understanding drug pharmacokinetics. During development (ie, in the fetus and newborn infant), there is special interest in transporters expressed in the placenta that modulate placental drug transfer. Many of these transporters can decrease or increase drug concentrations in the fetus and at birth, stressing the relevance of elucidating expression in the placenta and potential gestational age-dependent changes therein. Hence, the main objective of this review was to summarize the current knowledge about expression and ontogeny of transporters in the human placenta in healthy pregnant women. In addition, various in vitro, ex vivo, and in silico models that can be used to investigate placental drug transfer, namely, placental cancer cell lines, ex vivo cotyledon perfusion experiments, and physiologically based pharmacokinetic (PBPK) models, are discussed together with their advantages and shortcomings. A particular focus was placed on PBPK models because these models can integrate different types of information, such as expression data, ontogeny information, and observations obtained from the ex vivo cotyledon perfusion experiment. Such a mechanistic modeling framework may leverage the available information and ultimately help to improve knowledge about the adequacy and safety of pharmacotherapy in pregnant women and their fetuses.

Gestational age-dependent gene expression profiling of ATP-binding cassette transporters in the healthy human placenta

The ATP‐binding cassette (ABC) transporters control placental transfer of several nutrients, steroids, immunological factors, chemicals, and drugs at the maternal‐fetal interface. We and others have demonstrated a gestational age‐dependent expression pattern of two ABC transporters, P‐glycoprotein and breast cancer resistance protein throughout pregnancy. However, no reports have comprehensively elucidated the expression pattern of all 50 ABC proteins, comparing first trimester and term human placentae. We hypothesized that placental ABC transporters are expressed in a gestational‐age dependent manner in normal human pregnancy. Using the TaqMan^® Human ABC Transporter Array, we assessed the mRNA expression of all 50 ABC transporters in first (first trimester, n = 8) and third trimester (term, n = 12) human placentae and validated the resulting expression of selected ABC transporters using qPCR, Western blot and immunohistochemistry. A distinct gene expression profile of 30 ABC transporters was observed comparing first trimester vs. term placentae. Using individual qPCR in selected genes, we validated the increased expression of ABCA1 (P < 0.01), ABCA6 (P < 0.001), ABCA9 (P < 0.001) and ABCC3 (P < 0.001), as well as the decreased expression of ABCB11 (P < 0.001) and ABCG4 (P < 0.01) with advancing gestation. One important lipid transporter, ABCA6, was selected to correlate protein abundance and characterize tissue localization. ABCA6 exhibited increased protein expression towards term and was predominantly localized to syncytiotrophoblast cells. In conclusion, expression patterns of placental ABC transporters change as a function of gestational age. These changes are likely fundamental to a healthy pregnancy given the critical role that these transporters play in the regulation of steroidogenesis, immunological responses, and placental barrier function and integrity.

Role of the efflux transporters BCRP and MRP1 in human placental bio-disposition of pravastatin

The expression and activity of human placental transporters during pregnancy could be altered by several factors including pathological changes associated with preeclampsia. The aims of this study were to identify the placental efflux transporters involved in the bio-disposition of pravastatin, determine the protein expression of these transporters and their encoding genes as well as the activity of pravastatin uptake in placentas obtained from patients with preeclampsia. ATP-dependent uptake of [3H]-pravastatin by trophoblast tissue apical and basal membrane vesicles exhibited sigmoidal kinetics. The curved shapes of Eadie-Hofstee plots indicate that more than one placental transporter are involved in the uptake of pravastatin. ATP-dependent uptake of [3H]-pravastatin into vesicles expressing MRP1-5, BCRP, and P-gp, as well as the results of inhibition studies suggest that BCRP and MRP1 are the major placental efflux transporters responsible for the in vitro uptake of pravastatin. Compared to placentas from healthy pregnancies, preeclamptic placentas had increased number of syncytial knots with increased expression of BCRP in their apical membrane and increased expression of MRP1 in the cytoplasm of the syncytiotrophoblast and in cytoplasm of syncytial knots. There was a concomitant increase in ABCC1 but not in ABCG2 gene expressions in preeclamptic placentas. ATP-dependent uptake of [3H]-pravastatin by vesicles prepared from apical membranes of preeclamptic placentas was similar to the uptake by vesicles prepared from placentas obtained after uncomplicated pregnancies (13.9 ± 6.5 vs 14.1 ± 5.8 pmol·mg protein^-1 min^-1). The transporter-specific changes in the expression of BCRP and MRP1 in preeclamptic placentas did not affect the efflux activity of transporters localized on the apical membrane of the syncytiotrophoblast.

P-Glycoprotein (P-gp)/ABCB1 plays a functional role in extravillous trophoblast (EVT) invasion and is decreased in the pre-eclamptic placenta

Dysregulation of trophoblast differentiation is implicated in the placental pathologies of intrauterine growth restriction and pre‐eclampsia. P‐glycoprotein (P‐gp encoded by ABCB1) is an ATP‐binding cassette transporter present in the syncytiotrophoblast layer of the placenta where it acts as a molecular sieve. In this study, we show that P‐gp is also expressed in the proliferating cytotrophoblast (CT), the syncytiotrophoblast (ST) and the extravillous trophoblast (EVT), suggesting our hypothesis of a functional role for P‐gp in placental development. Silencing of ABCB1, via siRNA duplex, results in dramatically reduced invasion and migration, and increased tube formation and fusion in the EVT‐like HTR8/SV_neo cell line. In both EVT and CT explant differentiation experiments, silencing of ABCB1 leads to induction of the fusion markers human hCG, ERVW‐1 and GJA1 and terminal differentiation of both trophoblast subtypes. Moreover, P‐gp protein levels are decreased in both the villous and the EVT of severe early‐onset pre‐eclamptic placentas. We conclude that, in addition to its role as a syncytial transporter, P‐gp is a key factor in the maintenance of both CT and EVT lineages and that its decrease in severe pre‐eclampsia may contribute to the syncytial and EVT placental pathologies associated with this disease.

An update on expression and function of P-gp/ABCB1 and BCRP/ABCG2 in the placenta and fetus

INTRODUCTION

P-glycoprotein (P-gp)/ABCB1 and breast cancer resistance protein (BCRP)/ABCG2 are highly expressed in the placenta and fetus throughout gestation and can modulate exposure and toxicity of drugs and xenobiotics to the vulnerable fetus during the sensitive times of growth and development. We aim to provide an update on current knowledge on placental and fetal expressions of the two transporters in different species, and to provide insight on interpreting transporter expression and fetal exposure relative to the concept of fraction of drug transported. Areas covered: Comprehensive literature review through PubMed (primarily from July 2010 to February 2018) on P-gp and BCRP expression and function in the placenta and fetus of primarily human, mouse, rat, and guinea pig. Expert opinion: While there are many commonalities in the expression and function of P-gp and BCRP in the placenta and fetal tissues across species, there are distinct differences in expression levels and temporal changes. Further studies are needed to quantify protein abundance of these transporters and functionally assess their activities at various gestational stages. Combining the knowledge of interspecies differences and the concept of fraction of drug transported, we may better predict the magnitude of impact these transporters have on fetal drug exposure.

Glucocorticoids modulate multidrug resistance transporters in the first trimester human placenta

The placental multidrug transporters, P‐glycoprotein (P‐gp, encoded by ABCB1) and breast cancer resistance protein (BCRP,ABCG2) protect the foetus from exposure to maternally derived glucocorticoids, toxins and xenobiotics. During pregnancy, maternal glucocorticoid levels can be elevated by stress or exogenous administration. We hypothesized that glucocorticoids modulate the expression of ABCB1/P‐gp and ABCG2/BCRP in the first trimester human placenta. Our objective was to examine whether dexamethasone (DEX) or cortisol modulate first trimester placental expression of multidrug transporters and determine whether cytotrophoblasts or the syncytiotrophoblast are/is responsible for mediating these effects. Three models were examined: (i) an ex‐vivo model of placental villous explants (7‐10 weeks), (ii) a model of isolated first trimester syncytiotrophoblast and cytotrophoblast cells and (iii) the BeWo immortalized trophoblast cell line model. These cells/tissues were treated with DEX or cortisol for 24 hour to 72 hour. In first trimester placental explants, DEX (48 hour) increased ABCB1 (P < .001) and ABCG2 (P < .05) mRNA levels, whereas cortisol (48 hour) only increased ABCB1 mRNA levels (P < .01). Dexamethasone (P < .05) and cortisol (P < .01) increased BCRP but did not affect P‐gp protein levels. Breast cancer resistance protein expression was primarily confined to syncytiotrophoblasts. BeWo cells, when syncytialized with forskolin, increased expression of BCRP protein, and this was further augmented by DEX (P < .05). Our data suggest that the protective barrier provided by BCRP increases as cytotrophoblasts fuse to form the syncytiotrophoblast. Increase in glucocorticoid levels during the first trimester may reduce embryo/foetal exposure to clinically relevant BCRP substrates, because of an increase in placental BCRP.

Chorioamnionitis Induces a Specific Signature of Placental ABC Transporters Associated with an Increase of miR-331-5p in the Human Preterm Placenta

Background/Aims

The ATP-binding cassette (ABC) transporters mediate drug biodisposition and immunological responses in the placental barrier. In vitro infective challenges alter expression of specific placental ABC transporters. We hypothesized that chorioamnionitis induces a distinct pattern of ABC transporter expression.

Methods

Gene expression of 50 ABC transporters was assessed using TaqMan® Human ABC Transporter Array, in preterm human placentas without (PTD; n=6) or with histological chorioamnionitis (PTDC; n=6). Validation was performed using qPCR, immunohistochemistry and Western blot. MicroRNAs known to regulate P-glycoprotein (P-gp) were examined by qPCR.

Results

Up-regulation of ABCB9, ABCC2 and ABCF2 mRNA was detected in chorioamnionitis (p<0.05), whereas placental ABCB1 (P-gp; p=0.051) and ABCG2 (breast cancer resistance protein-BCRP) mRNA levels (p=0.055) approached near significant up-regulation. In most cases, the magnitude of the effect significantly correlated to the severity of inflammation. Upon validation, increased placental ABCB1 and ABCG2 mRNA levels (p<0.05) were observed. At the level of immunohistochemistry, while BCRP was increased (p<0.05), P-gp staining intensity was significantly decreased (p<0.05) in PTDC. miR-331-5p, involved in P-gp suppression, was upregulated in PTDC (p<0.01) and correlated to the grade of chorioamnionitis (p<0.01).

Conclusions

Alterations in the expression of ABC transporters will likely lead to modified transport of clinically relevant compounds at the inflamed placenta. A better understanding of the potential role of these transporters in the events surrounding PTD may also enable new strategies to be developed for prevention and treatment of PTD.

Placental transporter localization and expression in the Human: the importance of species, sex, and gestational age differences†

The placenta is a critical organ during pregnancy, essential for the provision of an optimal intrauterine environment, with fetal survival, growth, and development relying on correct placental function. It must allow nutritional compounds and relevant hormones to pass into the fetal bloodstream and metabolic waste products to be cleared. It also acts as a semipermeable barrier to potentially harmful chemicals, both endogenous and exogenous. Transporter proteins allow for bidirectional transport and are found in the syncytiotrophoblast of the placenta and endothelium of fetal capillaries. The major transporter families in the human placenta are ATP-binding cassette (ABC) and solute carrier (SLC), and insufficiency of these transporters may lead to deleterious effects on the fetus. Transporter expression levels are gestation-dependent and this is of considerable clinical interest as levels of drug resistance may be altered from one trimester to the next. This highlights the importance of these transporters in mediating correct and timely transplacental passage of essential compounds but also for efflux of potentially toxic drugs and xenobiotics. We review the current literature on placental molecular transporters with respect to their localization and ontogeny, the influence of fetal sex, and the relevance of animal models. We conclude that a paucity of information exists, and further studies are required to unlock the enigma of this dynamic organ.

Acute Effects of Viral Exposure on P-Glycoprotein Function in the Mouse Fetal Blood-Brain Barrier

BACKGROUND/AIMS

Viral infection during pregnancy is known to affect the fetal brain. The toll-like receptor (TLR)-3 is a pattern recognition receptor activated by viruses known to elicit adverse fetal neurological outcomes. The P-glycoprotein (P-gp) efflux transporter protects the developing fetus by limiting the transfer of substrates across both the placenta and the fetal blood-brain barrier (BBB). As such, inhibition of P-gp at these blood-barrier sites may result in increased exposure of the developing fetus to environmental toxins and xenobiotics present in the maternal circulation. We hypothesized that viral exposure during pregnancy would impair P-gp function in the placenta and in the developing BBB. Here we investigated whether the TLR-3 ligand, polyinosinic:polycytidylic acid (PolyI:C), increased accumulation of one P-gp substrate in the fetus and in the developing fetal brain.

METHODS

Pregnant C57BL/6 mice (GD15.5) were injected (i.p.) with PolyI:C (5 mg/kg or 10 mg/kg) or vehicle (saline). [3H]digoxin (P-gp substrate) was injected (i.v.) 3 or 23h post-treatment and animals were euthanized 1h later. Maternal plasma, 'fetal-units' (fetal membranes, amniotic fluid and whole fetus), and fetal brains were collected.

RESULTS

PolyI:C exposure (4h) significantly elevated maternal plasma IL-6 (P<0.001) and increased [3H]digoxin accumulation in the fetal brain (P<0.05). In contrast, 24h after PolyI:C exposure, no effect on IL-6 or fetal brain accumulation of P-gp substrate was observed.

CONCLUSION

Viral infection modeled by PolyI:C causes acute increases in fetal brain accumulation of P-gp substrates and by doing so, may increase fetal brain exposure to xenobiotics and environmental toxins present in the maternal circulation.

Down-regulation of the placental BCRP/ABCG2 transporter in response to hypoxia signaling

INTRODUCTION

The BCRP/ABCG2 efflux transporter protects the developing fetus by limiting the transplacental transfer of drugs and chemicals and prevents the apoptosis of trophoblasts. The purpose of this study was to determine whether hypoxia-related signaling alters placental BCRP expression and function in vitro and in human pregnancies.

METHODS

Human BeWo choriocarcinoma cells were treated with the hypoxia mimetic, cobalt chloride (CoCl₂), or 3% oxygen for 24-48 h. Activation of HIF-1α signaling and regulation of BCRP was assessed using qPCR, ELISA, western blotting and a fluorescent substrate transport assay. In addition, healthy term placentas from high altitude pregnancies with chronic hypoxia were assessed for BCRP expression.

RESULTS

CoCl₂ and 3% oxygen increased HIF-1α protein signaling and decreased the mRNA and protein expression of BCRP by 30-75% in BeWo cells. Reduced BCRP expression corresponded with impaired efflux activity during hypoxia as evidenced by accumulation of the substrate Hoechst 33342. A number of transcription factors known to regulate BCRP, including AHR, NRF2 and PPARγ, were also coordinately down-regulated by 3% oxygen in BeWo cells. Moreover, women who gave birth at a high altitude (3100 m) exhibited signs of chronic placental hypoxia, including enhanced protein expression of the HIF-1α target GLUT1, and had reduced BCRP levels in microvillous membranes compared to women at a moderate altitude (1600 m).

DISCUSSION

This study provides novel insight into the regulation of the placental BCRP transporter by hypoxia, which may be important for exposure of the fetus to chemicals during early development and in hypoxia-related pregnancy disorders.

Placental ABC Transporters: Biological Impact and Pharmaceutical Significance

The human placenta fulfills a variety of essential functions during prenatal life. Several ABC transporters are expressed in the human placenta, where they play a role in the transport of endogenous compounds and may protect the fetus from exogenous compounds such as therapeutic agents, drugs of abuse, and other xenobiotics. To date, considerable progress has been made toward understanding ABC transporters in the placenta. Recent studies on the expression and functional activities are discussed. This review discusses the placental expression and functional roles of several members of ABC transporter subfamilies B, C, and G including MDR1/P-glycoprotein, the MRPs, and BCRP, respectively. Since placental ABC transporters modulate fetal exposure to various compounds, an understanding of their functional and regulatory mechanisms will lead to more optimal medication use when necessary in pregnancy.

Astrocyte-mediated regulation of multidrug resistance p-glycoprotein in fetal and neonatal brain endothelial cells: age-dependent effects

Brain endothelial cells (BECs) form a major component of the blood-brain barrier (BBB). In late gestation, these cells express high levels of the multidrug transporter p-glycoprotein (P-gp; encoded by Abcb1), which prevents the passage of an array of endogenous factors and xenobiotics into the fetal brain. P-gp levels in the BECs increase dramatically in late gestation, coincident with astrocyte differentiation. However, the role of astrocytes in modulating P-gp in the developing BBB is unknown. We hypothesized that factors produced by astrocytes positively regulate P-gp in BECs. Astrocytes and BECs were isolated from fetal and postnatal guinea pigs. Levels of Abcb1 mRNA and P-gp were increased in BECs co-cultured with astrocytes compared to BECs in monoculture. Moreover, postnatal astrocytes enhanced P-gp function in fetal BECs but fetal astrocytes had no effect on postnatal BECs. These effects were dependent on secreted proteins with a molecular weight in the range of 3-100 kDa. LC/MS-MS revealed significant differences in proteins secreted by fetal and postnatal astrocytes. We propose that astrocytes are critical modulators of P-gp at the developing BBB. As such, aberrations in astrocyte maturation, observed in neurodevelopmental disorders, will likely decrease P-gp at the BBB. This would allow increased transfer of P-gp endogenous and exogenous substrates into the brain, many of which have neurodevelopmental consequences.

The xenoestrogens, bisphenol A and para-nonylphenol, decrease the expression of the ABCG2 transporter protein in human term placental explant cultures

Many endogenous and xenobiotic compounds are substrates and regulators of human placental ABC transporters. ABCG2 is protecting fetus against foreign chemicals. Environmental xenoestrogens, like bisphenol A (BPA) and p-nonylphenol (p-NP), mimic natural estrogens and can affect hormonal systems. Effects of BPA, p-NP, DES (diethylstilbestrol) and estradiol (E2), on ABCG2 expression were studied using human first trimester and term placental explants. Role of estrogen receptors (ER) in the effects of chemicals was studied by ER antagonist. Term placenta expressed less ABCG2 protein. In term placentas BPA (p < 0.05), p-NP (p < 0.01) and E2 (p < 0.05) decreased the ABCG2 protein expression after 48 h exposure while after 24 h exposure, only E2 decreased the expression (p < 0.05). The chemicals did not affect ABCG2 in first trimester placentas. The ER antagonist affected differently the responses of chemicals. In conclusion, environmental xenoestrogens downregulate placental ABCG2 protein expression depending on gestational age.

ATP-binding cassette transporters in reproduction: a new frontier

BACKGROUND

The transmembrane ATP-binding cassette (ABC) transporters actively efflux an array of clinically relevant compounds across biological barriers, and modulate biodistribution of many physiological and pharmacological factors. To date, over 48 ABC transporters have been identified and shown to be directly and indirectly involved in peri-implantation events and fetal/placental development. They efflux cholesterol, steroid hormones, vitamins, cytokines, chemokines, prostaglandins, diverse xenobiotics and environmental toxins, playing a critical role in regulating drug disposition, immunological responses and lipid trafficking, as well as preventing fetal accumulation of drugs and environmental toxins.

METHODS

This review examines ABC transporters as important mediators of placental barrier functions and key reproductive processes. Expression, localization and function of all identified ABC transporters were systematically reviewed using PubMed and Google Scholar websites to identify relevant studies examining ABC transporters in reproductive tissues in physiological and pathophysiological states. Only reports written in English were incorporated with no restriction on year of publication. While a major focus has been placed on the human, extensive evidence from animal studies is utilized to describe current understanding of the regulation and function of ABC transporters relevant to human reproduction.

RESULTS

ABC transporters are modulators of steroidogenesis, fertilization, implantation, nutrient transport and immunological responses, and function as 'gatekeepers' at various barrier sites (i.e. blood-testes barrier and placenta) against potentially harmful xenobiotic factors, including drugs and environmental toxins. These roles appear to be species dependent and change as a function of gestation and development. The best-described ABC transporters in reproductive tissues (primarily in the placenta) are the multidrug transporters p-glycoprotein and breast cancer-related protein, the multidrug resistance proteins 1 through 5 and the cholesterol transporters ABCA1 and ABCG1.

CONCLUSIONS

The ABC transporters have various roles across multiple reproductive tissues. Knowledge of efflux direction, tissue distribution, substrate specificity and regulation of the ABC transporters in the placenta and other reproductive tissues is rapidly expanding. This will allow better understanding of the disposition of specific substrates within reproductive tissues, and facilitate development of novel treatments for reproductive disorders as well as improved approaches to protecting the developing fetus.

Impact of bacterial and viral challenge on multidrug resistance in first- and third-trimester human placenta

The ABC transporters P-glycoprotein (P-gp, official gene symbol ABCB1) and breast cancer resistance protein (BCRP, official gene symbol ABCG2) protect the conceptus from exposure to toxins and xenobiotics present in the maternal circulation. Viral or bacterial challenges alter expression of placental multidrug transporters in rodents. We hypothesized that exposure to lipopolysaccharide (LPS, bacterial antigen) and polyinosinic-polycytidylic acid (poly(I:C), viral antigen) would decrease P-gp and BCRP in the human placenta. Placental explants from first and third trimesters were challenged with 0.1 to 10 μg/mL LPS or 1 to 50 μg/mL poly(I:C) for 4 or 24 hours; mRNA levels, protein expression, and localization were assessed by quantitative real-time PCR, Western blot analysis, and immunohistochemistry, respectively. Toll-like receptor (TLR)-3 and TLR-4 mRNA expression increased from the first to third trimester (P < 0.01), and the receptors localized to cytotrophoblasts in the first trimester and to syncytiotrophoblasts in the third trimester. LPS exposure in first-trimester explants decreased (P < 0.001) ABCB1 and ABCG2 mRNA and protein levels. In contrast, poly(I:C) decreased (P < 0.05) ABCB1, TLR-3, and TLR-4 mRNA levels in the third trimester but not first trimester. LPS and poly(I:C) treatments increased (P < 0.01) IL-8 and chemokine ligand 2. Results suggest that bacterial infections likely alter exposure of the conceptus to toxins and drugs during early pregnancy, whereas viral infections may disrupt fetal protection in later stages of pregnancy.

Effect of oxygen on multidrug resistance in term human placenta

INTRODUCTION

The placenta contains efflux transporters, including P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP), that limit the passage of xenobiotics, certain hormones and nutrients from the maternal to the fetal circulation. The expression of these transporters changes with gestational age, yet the mechanisms involved remain unknown. However, the changes in P-gp and BCRP transporter expression coincide with those of oxygen tension in the placenta, and oxygen tension has been shown to modulate P-gp and BCRP expression in other tissues. The objective of this study was to investigate the effects of oxygen tension on P-gp and BCRP expression in the term human placenta.

METHODS

Following equilibration in culture (96 h), term placental explants (n = 7) were cultured in 3% or 20% oxygen for 24 and 48 h. Culture medium was collected every 24 h to measure lactate dehydrogenase (LDH; explant viability) and human chorionic gonadotropin (hCG; syncytiotrophoblast function). P-gp (encoded by ABCB1) and BCRP (encoded by ABCG2) protein and mRNA, as well as VEGFA mRNA were measured using western blot and qRT-PCR. P-gp localization was determined using immunofluorescence.

RESULTS

Oxygen tension had a significant effect on P-gp expression, with ABCB1/P-gp mRNA and protein levels increased in the hypoxic condition (3% O2) after 48 h (p < 0.05). VEGFA mRNA was elevated by hypoxia at both 24 and 48 h (p < 0.05). In contrast, placental ABCG2/BCRP mRNA and protein expression were stable with changes in oxygen tension. We identified profound differences in the glycosylation of P-gp between cultured and non-cultured placental tissue, with cultured explants expressing deglycosylated P-gp.

CONCLUSIONS

These findings demonstrate that, at term, the expression of placental P-gp, is regulated by oxygen tension. This suggests that changes in oxygenation of the placenta in the third trimester may alter levels of placental P-gp, and in doing so alter fetal exposure to P-gp substrates, including xenobiotics and certain hormones.