Regulation of human placental drug transporters in HCV infection and their influence on direct acting antiviral medications

Direct-Acting Antiviral Agents in Prevention of Maternal-Fetal Transmission of Hepatitis C Virus in Pregnancy

Prior to the Food and Drug Administration approval of ledipaspavir/sofosbuvir (Harvoni®) in 2014, the treatment of hepatitis C was interferon plus or minus ribavirin. This treatment had low cure rates for hepatitis C virus and was teratogenic and therefore avoided in pregnant patients. Vertical transmission is the most common transmission of hepatitis C in pediatric patients, whereas medical equipment that was not properly cleaned and sterilized, blood products which were not checked (historically), sharing and reusing syringes and needles, and dialysis are the most common forms of hepatitis C transmission in adults. The treatment of pregnant women with direct-acting antivirals is important because the treatment of pediatric patients cannot begin until three years of age and does not always occur prior to the symptom development of hepatitis C. This review article will include glecaprevir/pibrentasvir (Mayvret®), sofosbuvir/velpatasvir (Epclusa®), and sofosbuvir/velpatasvir plus voxilaprevir (Vosevi®). We aim to review the teratogenic risk of direct-acting antivirals as well as currently published clinical trials and ongoing research on direct-acting antiviral hepatitis C treatment in pregnancy in this publication.

Assessment of the role of nucleoside transporters, P-glycoprotein, breast cancer resistance protein, and multidrug resistance-associated protein 2 in the placental transport of entecavir using in vitro, ex vivo, and in situ methods

The nucleoside analog entecavir (ETV) is a first-line pharmacotherapy for chronic hepatitis B in adult and pediatric patients. However, due to insufficient data on placental transfer and its effects on pregnancy, ETV administration is not recommended for women after conception. To expand knowledge of safety, we focused on evaluating the contribution of nucleoside transporters (NBMPR sensitive ENTs and Na⁺ dependent CNTs) and efflux transporters, P-glycoprotein (ABCB1), breast cancer resistance protein (ABCG2), and multidrug resistance-associated transporter 2 (ABCC2), to the placental kinetics of ETV. We observed that NBMPR and nucleosides (adenosine and/or uridine) inhibited [³H]ETV uptake into BeWo cells, microvillous membrane vesicles, and fresh villous fragments prepared from the human term placenta, while Na⁺ depletion had no effect. Using a dual perfusion study in an open-circuit setup, we showed that maternal-to-fetal and fetal-to-maternal clearances of [³H]ETV in the rat term placenta were decreased by NBMPR and uridine. Net efflux ratios calculated for bidirectional transport studies performed in MDCKII cells expressing human ABCB1, ABCG2, or ABCC2 were close to the value of one. Consistently, no significant decrease in fetal perfusate was observed in the closed-circuit setup of dual perfusion studies, suggesting that active efflux does not significantly reduce maternal-to-fetal transport. In conclusion, ENTs (most likely ENT1), but not CNTs, ABCB1, ABCG2, and ABCC2, contribute significantly to the placental kinetics of ETV. Future studies should investigate the placental/fetal toxicity of ETV, the impact of drug-drug interactions on ENT1, and interindividual variability in ENT1 expression on the placental uptake and fetal exposure to ETV.

Genome-Wide Association Analysis Identified Variants Associated with Body Measurement and Reproduction Traits in Shaziling Pigs

With the increasing popularity of genomic sequencing, breeders pay more attention to identifying the crucial molecular markers and quantitative trait loci for improving the body size and reproduction traits that could affect the production efficiency of pig-breeding enterprises. Nevertheless, for the Shaziling pig, a well-known indigenous breed in China, the relationship between phenotypes and their corresponding genetic architecture remains largely unknown. Herein, in the Shaziling population, a total of 190 samples were genotyped using the Geneseek Porcine 50K SNP Chip, obtaining 41857 SNPs for further analysis. For phenotypes, two body measurement traits and four reproduction traits in the first parity from the 190 Shaziling sows were measured and recorded, respectively. Subsequently, a genome-wide association study (GWAS) between the SNPs and the six phenotypes was performed. The correlation between body size and reproduction phenotypes was not statistically significant. A total of 31 SNPs were found to be associated with body length (BL), chest circumference (CC), number of healthy births (NHB), and number of stillborns (NSB). Gene annotation for those candidate SNPs identified 18 functional genes, such as GLP1R, NFYA, NANOG, COX7A2, BMPR1B, FOXP1, SLC29A1, CNTNAP4, and KIT, which exert important roles in skeletal morphogenesis, chondrogenesis, obesity, and embryonic and fetal development. These findings are helpful to better understand the genetic mechanism for body size and reproduction phenotypes, while the phenotype-associated SNPs could be used as the molecular markers for the pig breeding programs.

Direct antiviral agents (DAAs) and their use in pregnant women with hepatitis C (HCV)

INTRODUCTION

Direct-Acting Antiviral Agents (DAAs) provide safer, efficacious, tolerable, and curative therapy for women with hepatitis C. Their preferred safety and efficacy profile make them potential therapies for the elimination of perinatal transmission of hepatitis C virus (HCV). However, DAAs are not currently recommended for use during pregnancy due to limited pharmacokinetic and safety data.

AREAS COVERED

This review covers the different DAA drug combinations, the available data on their pharmacodynamic and pharmacokinetic properties, how the physiology in pregnancy can potentially affect DAA drug disposition, known drug-drug interactions with DAAs, and available and planned epidemiological and pharmacokinetic studies on DAA use during pregnancy. Although no large randomized clinical trials or prospective cohort studies involving DAAs have been completed in pregnancy, the currently available studies demonstrate no significant changes in pharmacokinetics, and no major safety concerns in women with hepatitis C.

EXPERT OPINION

Initial pharmacokinetic and safety data suggest that DAAs have high efficacy and a low risk of adverse events during pregnancy. As more pharmacokinetic and epidemiologic data become available, DAAs could become a preferred option for treating HCV during pregnancy and elimination of perinatal transmission of hepatitis C virus.

Regulation of Placental Efflux Transporters during Pregnancy Complications

The placenta is essential for regulating the exchange of solutes between the maternal and fetal circulations. As a result, the placenta offers support and protection to the developing fetus by delivering crucial nutrients and removing waste and xenobiotics. ATP-binding cassette transporters, including multidrug resistance protein 1, multidrug resistance-associated proteins, and breast cancer resistance protein, remove chemicals through active efflux and are considered the primary transporters within the placental barrier. Altered transporter expression at the barrier could result in fetal exposure to chemicals and/or accumulation of xenobiotics within trophoblasts. Emerging data demonstrate that expression of these transporters is changed in women with pregnancy complications, suggesting potentially compromised integrity of placental barrier function. The purpose of this review is to summarize the regulation of placental efflux transporters during medical complications of pregnancy, including 1) placental inflammation/infection and chorioamnionitis, 2) hypertensive disorders of pregnancy, 3) metabolic disorders including gestational diabetes and obesity, and 4) fetal growth restriction/altered fetal size for gestational age. For each disorder, we review the basic pathophysiology and consider impacts on the expression and function of placental efflux transporters. Mechanisms of transporter dysregulation and implications for fetal drug and toxicant exposure are discussed. Understanding how transporters are up- or downregulated during pathology is important in assessing possible exposures of the fetus to potentially harmful chemicals in the environment as well as the disposition of novel therapeutics intended to treat placental and fetal diseases. SIGNIFICANCE STATEMENT: Diseases of pregnancy are associated with reduced expression of placental barrier transporters that may impact fetal pharmacotherapy and exposure to dietary and environmental toxicants.

Transporter Regulation in Critical Protective Barriers: Focus on Brain and Placenta

Drug transporters play an important role in the maintenance of chemical balance and homeostasis in different tissues. In addition to their physiological functions, they are crucial for the absorption, distribution, and elimination of many clinically important drugs, thereby impacting therapeutic efficacy and toxicity. Increasing evidence has demonstrated that infectious, metabolic, inflammatory, and neurodegenerative diseases alter the expression and function of drug transporters. However, the current knowledge on transporter regulation in critical protective barriers, such as the brain and placenta, is still limited and requires more research. For instance, while many studies have examined P-glycoprotein, it is evident that research on the regulation of highly expressed transporters in the blood–brain barrier and blood–placental barrier are lacking. The aim of this review is to summarize the currently available literature in order to better understand transporter regulation in these critical barriers.

Adverse Events During Pregnancy Associated With Entecavir and Adefovir: New Insights From a Real-World Analysis of Cases Reported to FDA Adverse Event Reporting System

Background: Due to the embryotoxicity found in animal studies and scarce clinical data in pregnant women, it is still controversial whether entecavir (ETV) and adefovir dipivoxil (ADV) are safe during human pregnancy. This is of paramount importance when counseling pregnant women with hepatitis B virus (HBV) on risks and benefits to their offspring.

Objective: To quantify the association between administration of ETV and ADV in pregnant women and occurrence of adverse events (AEs) during pregnancy (AEDP).

Methods: Pregnancy reports from the FDA Adverse Event Reporting System (FAERS) were used to perform a retrospective analysis of AEDP associated with ETV or ADV. Disproportionality analysis estimating the reporting odds ratio (ROR) was conducted to identify the risk signals. A signal was defined as ROR value >2, and lower limit of 95% confidence interval (CI)> 1.

Results: A total of 1,286,367 reports involving AEDP were submitted to FAERS by healthcare professionals. Of these, there were 547 cases reporting ETV and 242 cases reporting ADV as primary suspected drugs. We found a moderate or strong signal for increased risk of spontaneous abortion when comparing ETV with tenofovir disoproxil fumarate (TDF) and telbivudine (LdT), with RORs equal to 1.58 (95% CI, 1.09–2.30) and 2.13 (95% CI, 1.04–4.36), respectively. However, when the included reports were limited to indication containing HBV infection, no signals for increased AEDP were detected. Futhermore, a strong signal for increased risk of spontaneous abortion was identified in patients with HBV infection when comparing ETV or ADV with lamivudine (LAM), with RORs of 3.55 (95% CI, 1.54–8.18) and 2.85 (95% CI, 1.15–7.08), respectively.

Conclusion: We found a strong signal for increased risk of spontaneous abortion in patients with HBV infection taking ETV or ADV, in comparison with those prescribed with LAM. Moreover, no obvious signal association of human teratogenicity with exposure to ETV or ADV was identified in fetuses during pregnancy. Nevertheless, owing to the limitations of a spontaneous reporting database, which inevitably contains potential biases, there is a pressing need for well-designed comparative safety studies to validate these results in clinical practice.

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.

Role of HIV and Antiretroviral Therapy on the Expression of Placental Transporters in Women with HIV

Treatment guidelines recommend continuation of combination antiretroviral therapy (cART) throughout pregnancy for all women living with human immunodeficiency virus (HIV). Many of these drugs are substrates of transporters expressed in the placenta and therefore play a role in fetal exposure. As placental transporters can be impacted by both HIV infection and drug therapy, our objective was to explore the impact of HIV infection and cART on transporter expression. Drug transporter expression was examined in human placental samples collected from women with HIV (n = 25) and from healthy HIV(-) controls (n = 23). The effect of exposure to drugs commonly used in cART during pregnancy was examined in vitro in placental villous explants obtained from healthy women. Gene expression was measured via qRT-PCR. Several ABC (ABCG2, ABCC1,2,4) and SLC (SLC21A9, SLC22A1,3,11) transporters were significantly downregulated in placentas isolated from HIV(+) women as compared with HIV(-) controls (p < 0.05-0.001), while ABCB1 and SLC21A12 were significantly upregulated (p < 0.001). Twenty-four to 48-h exposure of human placental explants to agents used in cART resulted in significant upregulation of ABCB1 and downregulation of SLC22A11. Our findings suggest that transplacental transport may be compromised during HIV infection due to altered expression of clinically important transporters. Furthermore, in vitro results indicate that cART imposes significant alterations in placental transporters but not all changes are consistent with findings in the placenta from HIV(+) women, indicating disease effects. As this may impact in utero-fetal exposure to clinically used medications, further studies are needed to determine the overall impact on maternal-fetal transfer.

Sofosbuvir shows a protective effect against vertical transmission of Zika virus and the associated congenital syndrome in rhesus monkeys

The outbreaks of Zika virus (ZIKV) infection in Brazil, 2015-2016, were associated with severe congenital malformations. Our translational study aimed to test the efficacy of the antiviral agent sofosbuvir (SOF) against vertical transmission of ZIKV and the associated congenital syndrome (CZS), using a rhesus monkey model. Eight pregnant macaques were successfully infected during the organogenesis phase with a Brazilian ZIKV strain; five of them received SOF from two to fifteen days post-infection. Both groups of dams showed ZIKV-associated clinical signals, detectable ZIKV RNA in several specimens, specific anti-ZIKV IgM and IgG antibodies, and maternal neutralizing antibodies. However, malformations occurred only among non-treated dam offspring. Compared to non-treated animals, all SOF-treated dams had a shorter ZIKV viremia and four of five neonates had undetectable ZIKV RNA in blood and tissue samples. These results support further clinical evaluations aiming for the prevention of CZS.

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.

Quantification of ENT1 and ENT2 Proteins at the Placental Barrier and Contribution of These Transporters to Ribavirin Uptake

The aims of this study are to quantify the protein levels of nucleoside transporters in placental microvillous membranes (MVMs) and to clarify the contributions of these transporters to ribavirin uptake at the placental barrier. Placental MVMs of human and rat expressed equilibrative nucleoside transporter (ENT) 1 protein, whereas the expression of ENT2 protein was obscure. Maternal-to-fetal transfer of [³H]ribavirin in rats was much higher than that of [¹⁴C]sucrose. The uptake of [³H]ribavirin by rat placental trophoblast TR-TBT 18 d-1 cells, which functionally express both ENT1 and ENT2 proteins, was saturable, and was significantly inhibited by 0.1 μM nitrobenzylthioinosine, which selectively abolishes ENT1-mediated uptake. Dipyridamole at 10 μM is capable of inhibiting ENT2 as well as ENT1, but a degree of inhibition by 10 μM dipyridamole on [³H]ribavirin uptake was not much different from that by 0.1 μM nitrobenzylthioinosine (ENT1-specific inhibitor). Therefore, ENT2 may contribute little to [³H]ribavirin uptake by these cells. Rat ENT1 cRNA-injected oocytes showed increased [³H]ribavirin uptake compared with water-injected oocytes, while rat ENT2 cRNA-injected oocytes did not. In conclusion, ENT1 protein expressed in placental MVMs appears to play a predominant role in the uptake of ribavirin.

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.