Transplacental transfer mechanism of organochlorine pesticides: An in vitro transcellular transport study

Transplacental transport of per- and polyfluoroalkyl substances (PFAS): Mechanism exploration via BeWo cell monolayer model

Per- and polyfluoroalkyl substances (PFAS) have received global concern on adverse effects on pregnancy outcomes. Although human studies have reported fetal exposure to PFAS, the underlying mechanisms driving transplacental transfer of PFAS have not been sufficiently understood. The present study aimed to investigate chemical-specific transplacental transfer of PFAS and potential mechanisms based on a BeWo cell monolayer model. The findings of concentration- and time-dependent transport, asymmetry in bidirectional transport, molecular docking and transporter inhibition experiments indicate that passive diffusion and membrane transporter-involved active transport could collectively determine transplacental transport of PFAS. Membrane transporters could play important roles in chemical-specific transport. The inhibition of OAT transporter resulted in promotion of trans-monolayer transport for most PFAS, while an opposite trend was observed when P-gp, BCRP and MRP transporters were prohibited. By contrast, inhibition of OCT resulted in inhibitory effects on the transport of some PFAS (i.e., PFHxA, PFHpA, PFOA, and PFNA), and promotive effects on the other substances (i.e., PFUdA, PFHpS, PFOS, 6:2 Cl-PFESA and PFOSA). Therefore, simultaneous involvement of diverse membrane transporters in utero could result in complicated influence on transplacental transport. Our work constitutes a solid ground for further exploration of the effects of gestational PFAS exposure on birth outcomes.

Machine learning models based on residue interaction network for ABCG2 transportable compounds recognition

As the one of the most important protein of placental transport of environmental substances, the identification of ABCG2 transport molecules is the key step for assessing the risk of placental exposure to environmental chemicals. Here, residue interaction network (RIN) was used to explore the difference of ABCG2 binding conformations between transportable and non-transportable compounds. The RIN were treated as a kind of special quantitative data of protein conformation, which not only reflected the changes of single amino acid conformation in protein, but also indicated the changes of distance and action type between amino acids. Based on the quantitative RIN, four machine learning algorithms were applied to establish the classification and recognition model for 1100 compounds with transported by ABCG2 potential. The random forest (RF) models constructed with RIN presented the best and satisfied predictive ability with an accuracy of training set of 0.97 and the test set of 0.96 respectively. In conclusion, the construction of residue interaction network provided a new perspective for the quantitative characterization of protein conformation and the establishment of prediction models for transporter molecular recognition. The ABCG2 transport molecular recognition model based on residue interaction network provides a possible way for screening environmental chemistry transported through placenta.

Exposure to pesticide components causes recurrent pregnancy loss by increasing placental oxidative stress and apoptosis: a case-control study

We investigated the plasma levels of pesticides components namely polychlorinated biphenyls (PCBs), dieldrin, dichlorodiphenyldichloroethylene (DDE), ethion, malathion, and chlorpyrifos in recurrent pregnancy loss (RPL) cases, and tested their associations with placental oxidative stress (OS) biomarkers [nitric oxide (NO.), thiobarbituric acid reactive substances (TBARS), reduced glutathione (GSH), and superoxide dismutase (SOD)] and with placental apoptotic/antiapoptotic indices (Bcl-2 and caspase-3), and evaluated their possible cut-off points to distinguish RPL cases. The study recruited 101 pregnant women divided into; G1 [n = 49, control, normal 1st-trimester pregnancy, normal obstetric history with at least one previous normal live birth], G2 [n = 26, cases with missed abortion (< 3 abortions) before 24 weeks of gestation], and G3 [n = 26, cases with missed abortion (≥ 3 abortions) before 24 weeks of gestation]. The plasma pesticide levels were analyzed by gas chromatography-mass spectrometry. Plasma human chorionic gonadotrophin (HCG), placental OS, Bcl-2, and caspase-3, were analyzed by their corresponding methods and kits. Plasma PCBs, DDE, dieldrin, and ethion levels were significantly higher in RPL cases than in normal pregnancies (p ≤ 0.001). These levels correlated positively with placental OS and apoptosis and negatively with plasma HCG levels. Also, these levels were reliable markers of risk to RPL. Malathion and chlorpyrifos were not detected in any of the study's participants. Pesticides may be risk factors in cases of spontaneous RPL cases. They are associated with an increasing placental OS and placental apoptosis. Specific measures should be taken to decrease maternal exposure to these pollutants' sources, especially in underdeveloped and developing countries.

Prenatal Exposure to Emerging Plasticizers and Synthetic Antioxidants and Their Potency to Cross Human Placenta

Gestational exposure to environmental chemicals and subsequent permeation through the placental barrier represents potential health risks to both pregnant women and their fetuses. In the present study, we explored prenatal exposure to a suite of 46 emerging plasticizers and synthetic antioxidants (including five transformation products of 2,6-di-tert-butyl-4-hydroxytoluene, BHT) and their potency to cross human placenta based on a total of 109 maternal and cord serum pairs. Most of these chemicals have rarely or never been investigated for prenatal exposure and associated health risks. Eleven of them exhibited detection frequency greater than 50% in maternal blood, including dibutyl fumarate (DBF), 2,6-di-tert-butylphenol (2,4-DtBP), 1,3-diphenylguanidine (DPG), methyl-2-(benzoyl)benzoate (MBB), triethyl citrate (TEC), BHT, and its five metabolites, with a median concentration from 0.05 to 3.1 ng/mL. The transplacental transfer efficiency (TTE) was determined for selected chemicals with valid measurements in more than 10 maternal/cord blood pairs, and the mean TTEs exhibited a large variation (i.e., 0.29-2.14) between chemicals. The determined TTEs for some of the target chemicals were comparable to the predicted values by our previously proposed models developed from molecular descriptors, indicating that their transplacental transfer potency could be largely affected by physicochemical properties and molecular structures. However, additional biological and physiological factors may influence the potency of environmental chemicals to cross human placenta. Overall, our study findings raise concern on human exposure to an increasing list of plastic additives during critical life stages (e.g., pregnancy) and potential health risks.

Dichlorodiphenyltrichloroethane and the Adrenal Gland: From Toxicity to Endocrine Disruption

Endocrine disruptors are exogenous compounds that pollute the environment and have effects similar to hormones when inside the body. One of the most widespread endocrine disruptors in the wild is the pesticide dichlorodiphenyltrichloroethane (DDT). Toxic doses of DDT are known to cause cell atrophy and degeneration in the adrenal zona fasciculata and zona reticularis. Daily exposure in a developing organism to supposedly non-toxic doses of DDT have been found to impair the morphogenesis of both the cortex and the medulla of the adrenal glands, as well as disturbing the secretion of hormones in cortical and chromaffin cells. Comparison of high and very low levels of DDT exposure revealed drastic differences in the morphological and functional changes in the adrenal cortex. Moreover, the three adrenocortical zones have different levels of sensitivity to the disruptive actions of DDT. The zona glomerulosa and zona reticularis demonstrate sensitivity to both high and very low levels of DDT in prenatal and postnatal periods. In contrast, the zona fasciculata is less damaged by low (supposedly non-toxic) exposure to DDT and its metabolites but is affected by toxic levels of exposure; thus, DDT exerts both toxic and disruptive effects on the adrenal glands, and sensitivity to these two types of action varies in adrenocortical zones. Disruptive low-dose exposure leads to more severe affection of the adrenal function.

Identification of common genetic variants associated with serum concentrations of p, p'-DDE in non-occupational populations in eastern China

Dichlorodiphenyldichloroethylene (DDE) is the major and most stable toxic metabolite of dichlorodiphenyltrichloroethane (DDT), a well-known organochlorine pesticide banned worldwide in the 1980s. However, it remains easy to detect in humans, and internal levels vary widely among individuals. In the present study, a genome-wide association study (GWAS) (511 subjects) and two replications (812 and 1030 subjects) were performed in non-occupational populations in eastern China. An estimated dietary intake (EDI) of p, p'-DDT and p, p'-DDE was calculated by a food frequency questionnaire (FFQ) and the determination of 195 food and 85 drinking water samples. In addition, functional verifications of susceptible loci were performed by dual-luciferase reporter, immunoblotting and metabolic activity assays in vitro. p, p'-DDT and p, p'-DDE were measured using gas chromatography-tandem mass spectrometry (GC-MS/MS). A common loci rs3181842 (high linkage equilibrium with rs2279345) in CYP2B6 at 19p13.2 were found to be strongly associated with low serum levels of p, p'-DDE in this population in GWAS and were verified by two replications and combined analysis of 2353 subjects (P = 1.00 × 10^-22). In addition, p, p'-DDE levels were significantly lower in subjects with the rs3181842 C allele than in those carrying the normal genotype, even in individuals with similar EDIs of p, p'-DDT. Furthermore, the rs3181842 C allele functionally led to low CYP2B6 expression and activity, resulting in a low metabolic capacity for the formation of p, p'-DDE from p, p'-DDT. The study highlighted that CYP2B6 variants were more relevant than environmental exposure to internal p, p'-DDE exposure, which is important information for DDT risk assessments.

Reproductive Health Risks Associated with Occupational and Environmental Exposure to Pesticides

A marked reduction in fertility and an increase in adverse reproductive outcomes during the last few decades have been associated with occupational and environmental chemical exposures. Exposure to different types of pesticides may increase the risks of chronic diseases, such as diabetes, cancer, and neurodegenerative disease, but also of reduced fertility and birth defects. Both occupational and environmental exposures to pesticides are important, as many are endocrine disruptors, which means that even very low-dose exposure levels may have measurable biological effects. The aim of this review was to summarize the knowledge collected between 2000 and 2020, to highlight new findings, and to further interpret the mechanisms that may associate pesticides with infertility, abnormal sexual maturation, and pregnancy complications associated with occupational, environmental and transplacental exposures. A summary of current pesticide production and usage legislation is also included in order to elucidate the potential impact on exposure profile differences between countries, which may inform prevention measures. Recommendations for the medical surveillance of occupationally exposed populations, which should be facilitated by the biomonitoring of reduced fertility, is also discussed.

Differential study of the Parabramis pekinensis intestinal microbiota according to different habitats and different parts of the intestine

Purpose

To identify the differences in gut bacterial community of Parabramis pekinensis under different growth conditions, and the effect of the diet in a controlled habitat on the community structure, aiming to provide a comprehensive survey of how the gut microbiota in P. pekinensis varies depending on habitat.

Methods

A total of 73 P. pekinensis from Yangtze River (W), rivers in the outskirts of Jingjiang (Jiangsu province, China, R), and farms (C) were collected to analyze the intestinal microbiota using high-throughput sequencing of the V3-V4 16S ribosomal RNA gene. We also subdivided the gut into the foregut (F), midgut (M), and hindgut (B) to analyze the differences between them.

Results

The dominant bacterial phyla in P. pekinensis were Fusobacteria, Firmicutes, Proteobacteria, and Actinobacteria; meanwhile, Cyanobacteria, Bacteroidetes, Chloroflexi, and Verrucomicrobia were also highly abundant. It is worth noting that the abundance of Fusobacteria Cetobacterium was also very high. The abundance and diversity of the intestinal microbiota structure of fish taken from breeding farm were significantly lower than those taken from Yangtze river and Suburban river, and the abundance of Aeromonas in the gut of fish taken from Yangtze river was much higher than that of fish taken from Suburban river. Compared to midgut, foregut and hindgut have similar microbiota structures, but did not differ significantly in them.

Conclusions

The core intestinal microbiota of P. pekinensis is the same to other herbivorous and partially omnivorous fish. There were significant differences in the intestinal microbiota structure of P. pekinensis from different habitats, but no significant differences in the microbiota abundance and diversity between the different parts of the intestine.

Transplacental Transfer of Environmental Chemicals: Roles of Molecular Descriptors and Placental Transporters

Transplacental transfer of environmental chemicals results in direct risks to fetal development. Although numerous studies have investigated transplacental transfer efficiencies (TTEs) of environmental chemicals, the underlying mechanisms and influencing factors remain poorly understood. The present study aims to synthesize a current state of knowledge on the TTEs of major environmental chemicals and explore the roles of chemicals' molecular descriptors and placental transporters in the transplacental transfer. The results indicate great variations in TTEs (median: 0.29-2.86) across 51 chemicals. Chemical-dependent TTEs may partially be attributed to the influences of chemicals' molecular descriptors. Predictive models based on experimental TTEs and 1790 computed molecular descriptors indicate that a very limited number of molecular descriptors, such as the topological polar surface area, may substantially influence and efficiently predict chemicals' TTEs. In addition, molecular docking analyses were conducted to determine the binding affinities between 51 chemicals and six selected transporters, including BCRP, MDR1, hENT1, FRα, SERT, and MRP1. The results reveal transporter- and chemical-dependent binding affinities. Therefore, our study demonstrates that molecular descriptors and placental transporters, among a variety of other factors, can play important roles in the transplacental transfer of environmental chemicals. However, the underlying mechanisms and several important knowledge gaps identified herein require further investigations.

Factors associated with partitioning behavior of persistent organic pollutants in a feto-maternal system: A multiple linear regression approach

Prenatal exposure to persistent organic pollutants (POPs) has been a matter of particular concern because such exposure can severely affect the health of the fetus. The mechanistic understanding of the partitioning behavior of POPs in the feto-maternal system and the associated factors, however, have rarely been studied. Here, we employed a new approach based on multiple linear regression (MLR) analysis to predict the feto-maternal ratio (FM-ratio) of POPs and to assess the factors associated with feto-maternal partitioning behavior. Two preliminary exploratory MLR models were built using physiological conditions of the participants, and molecular descriptors were calculated with a computational model. The FM-ratio was calculated from the concentrations of polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs), and polybrominated diphenyl ethers (PBDEs) in 20 pairs of maternal and cord blood. The models showed that the lipids and cholesterols in the maternal and cord blood and the placenta significantly influence the partitioning of POPs. The body mass index (BMI) change during pregnancy was also related to the FM-ratio. The physicochemical properties associated with lipophilicity and molecular size were also related to the FM-ratio. Even though the results should be interpreted with caution, the preliminary MLR models illustrate that feto-maternal partitioning is governed by transplacental transporting mechanisms, toxicokinetics, and the molecular physicochemical properties of POPs. Overall, the new approach used in this study can improve our understanding of the partitioning behavior in the feto-maternal system.

A review of the transplacental transfer of persistent halogenated organic pollutants: Transfer characteristics, influential factors, and mechanisms

Persistent halogenated organic pollutants (HOPs) are a class of toxic chemicals, which may have adverse effects on fetuses via transplacental transfer from their mothers. Here, we review reported internal exposure levels of various HOPs (organochlorinated pesticides, polychlorinated biphenyls, polybrominated diphenyl ethers, short- and medium-chain chlorinated paraffins, and per- and poly-fluoroalkyl substances) in placenta, and both maternal and umbilical cord sera. We also present analyses of the transplacental transfer and placental distribution characteristics of each class of compounds, and discuss effects of several factors on the transfer and accumulation efficiencies of HOPs, as well as the main mechanisms of HOPs' transfer across the placental barrier. Reported compound-specific transplacental transfer efficiencies and distribution efficiencies, expressed as umbilical cord:maternal serum and placental:maternal serum concentration ratios (R_CM and R_PM, respectively), are summarized. Average published R_CM values of the HOPs range from 0.24 to 3.08 (lipid-adjusted) and from 0.04 to 3.1 (based on wet weights), and are highest for perfluoroalkylcarboxylates (PFCAs) and tetrabromobisphenol A. Average published R_PM values range from 0.14 to 1.02 (lipid-adjusted) and from 0.30 to 1.4 (based on wet weights). The broad R_CM and R_PM ranges may reflect effects of various factors, inter alia physicochemical properties of HOPs, metabolic capacities of mothers and fetuses, placental maturity, and differential expression of influx/efflux transporters in the placenta. Generally, HOPs' R_CM values decline linearly with molecular size, and are curvilinearly related to solubility. Plasma protein binding affinity and the difference between maternal and fetal metabolic capacities may also affect some HOPs' transfer efficiencies. HOPs' molecular size may be influential. Transplacental transport of HOPs likely occurs mostly through passive diffusion, although influx/efflux transporters expressed on maternal and/or fetal sides of the placenta may also facilitate or hinder their transport. Overall, the review highlights clear gaps in our understanding of mechanisms involved in HOPs' transplacental transport.

Insight into the transplacental transport mechanism of methoxylated polybrominated diphenyl ethers using a BeWo cell monolayer model

Methoxylated polybrominated diphenyl ethers (MeO-PBDEs), a type of emerging environmental contaminants, can accumulate through the food chain and eventually enter the human body. For pregnant women, these chemicals may be transplacentally transported to their fetuses, causing early intrauterine exposure. This study was designed to explore the transport process and characteristics of MeO-PBDEs using a BeWo cell monolayer model to simulate the placental barrier effect. Concentration-dependent transplacental transport indicates that the transport of MeO-PBDEs may be dominated by passive diffusion within the studied concentration range. According to the apparent permeability coefficients, MeO-BDE congeners investigated can be classified as poorly transported compounds, with the exception of MeO-BDE28. Time-dependent transplacental transport was observed (R² = 0.97-0.99), which showed that the intracellular accumulation of MeO-PBDEs followed pseudo-first-order kinetics process. The transport process of MeO-PBDEs in the BeWo cell assay was not found to be sensitive to the pH of 6.5-7.4. An efflux transporter, breast cancer resistance protein, may be involved in the transport process of some MeO-PBDE congeners, and influx transporters, including organic anion transporters and organic cation transporters, may also be involved in the transport process. Although the present results indicated the possible transplacental transport mechanism, more molecular biological studies should be conducted to advance the understanding of the transport mechanisms.

Transplacental Transfer of Per- and Polyfluoroalkyl Substances (PFASs): Differences between Preterm and Full-Term Deliveries and Associations with Placental Transporter mRNA Expression

Previous studies demonstrated that per- and polyfluoroalkyl substances (PFASs) can cross the human placental barrier. However, their transplacental transfer efficiencies (TTEs) have not been investigated in preterm delivery, and the role of placental transport proteins has rarely been explored. Our study hypothesized that the TTEs of PFASs could differ between preterm and full-term deliveries, and some placental transporters could be involved in active maternofetal PFAS transfer. In the present study, the median TTEs of 16 individual PFAS chemicals or isomers were determined to be 0.23 to 1.72 in matched maternal-cord serum pairs with preterm delivery (N = 86), which were significantly lower than those (0.35 to 2.26) determined in full-term delivery (N = 187). Significant associations were determined between the TTEs of several PFASs and the mRNA expression levels of selected transporters located on the brush border membrane. The association patterns also significantly differed between preterm and full-term deliveries and exhibited a chemical-specific manner. For example, the expression of MRP2 exhibited significantly positive associations with the TTEs of linear and branched perfluorooctanesulfonic acid (PFOS) isomers in full-term delivery, but negative, nonsignificant associations were observed in preterm delivery. This is the first study to compare the transplacental transfer of PFASs between preterm and full-term deliveries and indicate that some placental transport proteins could be involved in active transmission. The mechanisms underlying the cross-placental transfer of PFASs require further investigations to better elucidate their risks to fetal health and birth outcomes.