Regulation of Placental Efflux Transporters during Pregnancy Complications

Human trophoblast organoids for improved prediction of placental ABC transporter-mediated drug transport

ATP-binding cassette (ABC) transporters, the important transmembrane efflux transporters, play an irreplaceable role in the placenta barrier. The disposition and drug-drug interaction of clinical drugs are also closely related to the functions of ABC transporters. The trophoblast is a unique feature of the placenta, which is crucial for normal placentation and maintenance during pregnancy. ABC transporters are abundantly expressed in placental syncytiotrophoblast, especially P-gp, BCRP, and MRPs. However, due to the lack of appropriate modeling systems, the molecular mechanisms of regulation between ABC transporters and trophoblast remains unclear. In this report, trophoblast organoids were cultured from human placental villi and developed into three-dimension structures with cavities. Trophoblast organoids exhibited transporter expression and localization comparable to that in villous tissue, indicating their physiological relevance for modeling drug transport. Moreover, fluorescent substrates can accumulate in organoids and be selectively inhibited by inhibitors, indicating the efflux function of ABC transporters (P-gp, BCRP, MRP1, and MRP2) in organoids. Two commonly used hypertension drugs and three antipsychotics were chosen to further validate this drug transport model and demonstrate varying degrees of inhibitory effects on ABC transporters. Overall, a new drug transport model mediated by ABC transporter has been successfully established based on human trophoblast organoids, which can be used to study drug transport in the placenta.

Placenta: an old organ with new functions

The transition from oviparity to viviparity and the establishment of feto-maternal communications introduced the placenta as the major anatomical site to provide nutrients, gases, and hormones to the developing fetus. The placenta has endocrine functions, orchestrates maternal adaptations to pregnancy at different periods of pregnancy, and acts as a selective barrier to minimize exposure of developing fetus to xenobiotics, pathogens, and parasites. Despite the fact that this ancient organ is central for establishment of a normal pregnancy in eutherians, the placenta remains one of the least studied organs. The first step of pregnancy, embryo implantation, is finely regulated by the trophoectoderm, the precursor of all trophoblast cells. There is a bidirectional communication between placenta and endometrium leading to decidualization, a critical step for maintenance of pregnancy. There are three-direction interactions between the placenta, maternal immune cells, and the endometrium for adaptation of endometrial immune system to the allogeneic fetus. While 65% of all systemically expressed human proteins have been found in the placenta tissues, it expresses numerous placenta-specific proteins, whose expression are dramatically changed in gestational diseases and could serve as biomarkers for early detection of gestational diseases. Surprisingly, placentation and carcinogenesis exhibit numerous shared features in metabolism and cell behavior, proteins and molecular signatures, signaling pathways, and tissue microenvironment, which proposes the concept of "cancer as ectopic trophoblastic cells". By extensive researches in this novel field, a handful of cancer biomarkers has been discovered. This review paper, which has been inspired in part by our extensive experiences during the past couple of years, highlights new aspects of placental functions with emphasis on its immunomodulatory role in establishment of a successful pregnancy and on a potential link between placentation and carcinogenesis.

A Literature Review of Changes in Phase II Drug-Metabolizing Enzyme and Drug Transporter Expression during Pregnancy

The purpose of this literature review is to comprehensively summarize changes in the expression of phase II drug-metabolizing enzymes and drug transporters in both the pregnant woman and the placenta. Using PubMed®, a systematic search was conducted to identify literature relevant to drug metabolism and transport in pregnancy. PubMed was searched with pre-specified terms during the period of 26 May 2023 to 10 July 2023. The final dataset of 142 manuscripts was evaluated for evidence regarding the effect of gestational age and hormonal regulation on the expression of phase II enzymes (n = 16) and drug transporters (n = 38) in the pregnant woman and in the placenta. This comprehensive review exposes gaps in current knowledge of phase II enzyme and drug transporter localization, expression, and regulation during pregnancy, which emphasizes the need for further research. Moreover, the information collected in this review regarding phase II drug-metabolizing enzyme and drug transporter changes will aid in optimizing pregnancy physiologically based pharmacokinetic (PBPK) models to inform dose selection in the pregnant population.

Changes in Expression and Function of Placental and Intestinal P-gp and BCRP Transporters during Pregnancy

ABC transporters are ubiquitous in the human body and are responsible for the efflux of drugs. They are present in the placenta, intestine, liver and kidney, which are the major organs that can affect the pharmacokinetic and pharmacologic properties of drugs. P-gp and BCRP transporters are the best-characterized transporters in the ABC superfamily, and they have a pivotal role in the barrier tissues due to their efflux mechanism. Moreover, during pregnancy, drug efflux is even more important because of the developing fetus. Recent studies have shown that placental and intestinal ABC transporters have great importance in drug absorption and distribution. Placental and intestinal P-gp and BCRP show gestational-age-dependent expression changes, which determine the drug concentration both in the mother and the fetus during pregnancy. They may have an impact on the efficacy of antibiotic, antiviral, antihistamine, antiemetic and oral antidiabetic therapies. In this review, we would like to provide an overview of the pharmacokinetically relevant expression alterations of placental and intestinal ABC transporters during pregnancy.

Protective role of the placental efflux transporter BCRP/ABCG2 in the relationship between prenatal cadmium exposure, placenta weight, and size at birth

BACKGROUND AND AIM

Placental efflux transporter proteins, such as BCRP, reduce the placental and fetal toxicity of environmental contaminants but have received little attention in perinatal environmental epidemiology. Here, we evaluate the potential protective role of BCRP following prenatal exposure to cadmium, a metal that preferentially accumulates in the placenta and adversely impacts fetal growth. We hypothesized that individuals with a reduced function polymorphism in ABCG2, the gene encoding BCRP, would be most vulnerable to the adverse impacts of prenatal cadmium exposure, notably, smaller placental and fetal size.

METHODS

We measured cadmium in maternal urine samples at each trimester and in term placentas from UPSIDE-ECHO study participants (NY, USA; n = 269). We fit adjusted multivariable linear regression and generalized estimating equation models to examine log-transformed urinary and placental cadmium concentrations in relation to birthweight, birth length, placental weight, and fetoplacental weight ratio (FPR) and stratified models by ABCG2 Q141K (C421A) genotype.

RESULTS

Overall 17% of participants expressed the reduced-function ABCG2 C421A variant (AA or AC). Placental cadmium concentrations were inversely associated with placental weight (β = -19.55; 95%CI: -37.06, -2.04) and trended towards higher FPR (β = 0.25; 95%CI: -0.01, 0.52) with stronger associations in 421A variant infants. Notably, higher placental cadmium concentrations in 421A variant infants were associated with reduced placental weight (β = -49.42; 95%CI: 98.87, 0.03), and higher FPR (β = 0.85, 95%CI: 0.18, 1.52), while higher urinary cadmium concentration was associated with longer birth length (β = 0.98; 95%CI: 0.37, 1.59), lower ponderal index (β = -0.09; 95%CI: 0.15, -0.03), and higher FPR (β = 0.42; 95%CI: 0.14, 0.71).

CONCLUSIONS

Infants with reduced function ABCG2 polymorphisms may be particularly vulnerable to the developmental toxicity of cadmium as well as other xenobiotics that are BCRP substrates. Additional work examining the influence of placental transporters in environmental epidemiology cohorts is warranted.

The Effect of Tobacco Use on the Expression of Placental Transporters in Alaska Native Women

Prenatal tobacco use among Alaska Native (AN) women has decreased substantially over the past two decades. Previous research suggests that providing AN women with feedback regarding fetal exposure to tobacco may further promote cessation. Transporters in the placenta regulate fetal exposure to nutrients and xenobiotics, including compounds associated with tobacco use. We examined whether prenatal tobacco use impacts transporter expression in the placenta, and whether this is influenced by fetal sex, degree of tobacco exposure, or transporter genotype. At delivery, we obtained placental samples from AN research participants who smoked cigarettes, used commercial chew or iqmik (oral tobacco), or did not use tobacco during pregnancy. Transporter expression was evaluated using qRT-PCR and Western blotting and tested for correlations between transcript levels and urinary biomarkers of tobacco use. The impact of BCRP/ABCG2 and OATP2B1/SLCO2B1 genotypes on protein expression was also examined. Oral tobacco use was associated with decreased P-gp and increased MRP1, MRP3, LAT1, and PMAT mRNA expression. Transcript levels of multiple transporters significantly correlated with tobacco biomarkers in maternal and fetal urine. In women carrying male fetuses, both smoking and oral tobacco were associated with decreased P-gp. Oral tobacco was also associated with decreased LAT1 in women carrying female fetuses. BCRP and OATP2B1 genotypes did not appear to impact protein expression. In conclusion, prenatal tobacco use is associated with altered expression of multiple placental transporters which differs by fetal sex. As transcript levels of multiple transporters were significantly correlated with tobacco use biomarkers, eliminating prenatal tobacco use should alleviate these changes.

Clinical Implications of Altered Drug Transporter Abundance/Function and PBPK Modeling in Specific Populations: An ITC Perspective

The role of membrane transporters on pharmacokinetics (PKs), drug-drug interactions (DDIs), pharmacodynamics (PDs), and toxicity of drugs has been broadly recognized. However, our knowledge of modulation of transporter expression and/or function in the diseased patient population or specific populations, such as pediatrics or pregnancy, is still emerging. This white paper highlights recent advances in studying the changes in transporter expression and activity in various diseases (i.e., renal and hepatic impairment and cancer) and some specific populations (i.e., pediatrics and pregnancy) with the focus on clinical implications. Proposed alterations in transporter abundance and/or activity in diseased and specific populations are based on (i) quantitative transporter proteomic data and relative abundance in specific populations vs. healthy adults, (ii) clinical PKs, and emerging transporter biomarker and/or pharmacogenomic data, and (iii) physiologically-based pharmacokinetic modeling and simulation. The potential for altered PK, PD, and toxicity in these populations needs to be considered for drugs and their active metabolites in which transporter-mediated uptake/efflux is a major contributor to their absorption, distribution, and elimination pathways and/or associated DDI risk. In addition to best practices, this white paper discusses current challenges and knowledge gaps to study and quantitatively predict the effects of modulation in transporter activity in these populations, together with the perspectives from the International Transporter Consortium (ITC) on future directions.