Establishment of metabolism and transport pathways in the rodent and human fetal liver

UPLC-Q-Exactive/MS based analysis explore the correlation between components variations and anti-influenza virus effect of four quantified extracts of Chaihu Guizhi decoction

ETHNOPHARMACOLOGICAL RELEVANCE

Chaihu Guizhi decoction (CGD) is a classic Traditional Chinese Medicine (TCM) prescription for the treatment of influenza and fever, composes of Bupleuri Radix (Chaihu), Cinnamomi Ramulus (Guizhi), Scutellariae Radix (Huangqin), Codonopsis Radix (Dangshen), Glycyrrhizae Radix Et Rhizoma Praeparata Cum Melle (Zhigancao), Pinelliae Rhizoma Praeparatum (Fabanxia), Zingiberis Rhizoma Recens (Shengjiang), Paeoniae Radix Alba (Baishao) and Jujubae Fructus (Dazao) in the ratio of 12:4.5:4.5:4.5:3:6:4.5:4.5:4. The efficacy of TCM, if there are differences, depends on the different extraction methods and extracted components.

AIM OF THE STUDY

This study was to evaluate the anti-influenza virus effect of CGD extracts with different extraction methods, analyze the components and explore their correlation.

MATERIALS AND METHODS

CGD were prepared with four extraction methods respectively, the traditional decoction (TD), two steps alcohol-water extraction (AWE), alcohol reflux extraction (AE) and water reflux extraction (WE). Based on the influenza mouse model, the efficacy of anti-influenza virus in vivo of the four CGD extracts were evaluated with the therapeutic index of body weight, rectal temperature, lung index, thymus index and lung viral load of mice. The chemical components in four CGD extracts, and compounds absorbed in rats blood with prototypes or metabolites were identified by UPLC-Q-Exactive/MS. The partial least squares (PLS) method was used to explore the correlation between the components variation in CGD extracts and the comprehensive efficacy index. The potential effective components were further accessed by molecular docking.

RESULTS

Comparing with the other three extracts, AWE has the best anti-influenza effect. It could ameliorate the symptoms caused by influenza virus infection in mice, increase body weight and rectal temperature, reduce the lung index and virus load in lung tissue. 129, 144, 140 and 129 components were identified from TD, AWE, AE, and WE respectively. The identified components were mainly including flavonoids, terpenoids, organic acids, phenylpropanoids, amino acids, nucleosides, phenols, alkaloids, etc. 43 prototypes and 49 metabolites of CGD were detected in rat plasma after oral administration. Seven components, cinnamaldehyde, wogonoside, baicalin, baicalein, gallic acid, oroxylinA-7-O-glucuronide and coumarin, showed significant correlation with anti-influenza effects, all of which had good binding activity with NA, IL-6, STAT3, AKT1, EGFR and TNF.

CONCLUSION

Two steps alcohol-water extraction was optimal for CGD preparation. Cinnamaldehyde, wogonoside, oroxylinA-7-O-glucuronide, coumarin, gallic acid, baicalein and baicalin play a certain essential role in anti-influenza effects and may be taken as a potential maker compounds for quality evaluation of CGD.

Qualitative and quantitative studies on chemical constituents of Ling-gui-zhu-gan decoction: In vitro and in vivo

Ling-gui-zhu-gan decoction has significant therapeutic effects in the treatment of diseases related to phlegm and fluid retention. In this study, we aimed to qualitatively characterize the chemical constituents of Ling-gui-zhu-gan decoction in vitro and in vivo by HPLC coupled to Fourier transform ion cyclotron resonance MS, and quantitively determine the contents of typical chemical constituents by HPLC method. As a result, a total of 75 chemical constituents were discovered including 37 flavonoids and their glycosides, 20 saponins, 9 sterols, 3 organic acids and their derivatives, 3 lactones, 2 coumarins, and 1 alcohol. Among them, 17 chemical constituents were specifically identified. Subsequently, an HPLC method was established for simultaneous determination of seven chemical constituents. Finally, a total of 40 prototype components were initially detected by HPLC-MS method in the biological samples of rats after their water extract was orally administrated. Among them, 29, 27, 12, and 32 prototype components were detected in plasma, bile, urine, and feces, respectively. Moreover, 34 metabolites, including 16 phase II metabolites, were detected for the first time. In conclusion, this study lays the foundation for the identification of chemical components in vitro and in vivo and the elucidation of the potential pharmacodynamic components of Ling-gui-zhu-gan decoction.

Gene expression profiling after exposure to a chemical carcinogen, Pentabrominated Diphenyl Ether, at different life stages

Exposure to environmental hazards occurs at different stages of our lifetime-infant, child, adult. This study integrates recently published toxicogenomics data to examine how exposure to a known rat chemical carcinogen (pentabrominated diphenyl ether (PBDE)) upregulated liver transcriptomic changes at different life cycle stages (PND 4, PND 22, adult). We found that at all three life cycle stages PBDE exposure induced hepatocellular transcriptomic changes in disease pathways including cancer, metabolic, membrane function, and Nrf2 antioxidant pathways, pathways all characteristics of chemical carcinogens. In addition, in the adult rat after a 5-day exposure to the chemical carcinogen, there was upregulation of members of the Ras oncogenic pathway, a specific pathway found to be activated in the PBDE-induced tumors in rats in a previous hazard identification cancer study. The findings of liver transcript changes characteristic of carcinogenic activity after early life exposures and after short-term adult exposures provides data to support the use of transcriptomic data to predict the apical cancer endpoints in model studies. Using data from gene expression profiling studies after neonatal, young, or adult short-term chemical exposure helps to meet the 21st century toxicology goal of developing study designs to reduce, refine, and replace the use of traditional 2-year rodent cancer studies to provide hazard identification information. The studies reported here find that key transcripts associated with carcinogenesis were elevated in neonate (PND 4), young (PND 22) and adult animals after short-term exposure to PBDE, a known experimental chemical carcinogen in model systems.

DNA damage, DNA repair gene expression, and topoisomerase IIα activity in CD-1 mice following in utero benzene exposure

Benzene is an environmental toxicant and known human carcinogen. Recent epidemiological studies show a relationship between exposure to benzene in pregnant women and increased incidence of childhood leukemias. Studies in murine models demonstrate a relationship between carcinogenicity and in utero benzene exposure which was sex dependent, thus the cellular mechanisms of benzene toxicity by sex require further studies. A hypothesized mechanism of benzene-induced in utero carcinogenicity is through increased DNA damage and reduced fetal DNA repair capacity. This includes the potential inhibition of topoisomerase IIα (topo IIα), in part, to generate double stranded DNA (dsDNA) breaks and induction of error-prone DNA repair. Using a mouse model of transplacental benzene carcinogenicity, gestational day (GD) 14 fetal livers were harvested 2, 6, and 24 h following maternal exposure to 200 mg/kg benzene and used to assess DNA damage, DNA repair gene expression and topo IIα activity. DNA damage, measured by levels of modified histone H2AX (γH2AX), is significantly increased in benzene exposed pups, with sex-dependent significance seen only in female pups. Comet assay results confirmed that benzene exposure in utero induces dsDNA damage in the GD14 fetal liver. Genes involved in DNA repair were assessed, and DNA repair gene expression changes were observed after 24 h in genes related to nucleotide excision repair, homologous recombination, and non-homologous end-joining. There were no significant differences in topo IIα activity in GD14 fetal livers at any timepoint, or between sexes. Overall, this study shows that 200 mg/kg benzene exposure induces dsDNA damage and alters fetal DNA repair gene expression in utero, without perturbing fetal topo IIα in CD-1 mice.

Identification of components and metabolites in plasma of type 2 diabetic rat after oral administration of Jiao-Tai-Wan using ultra-performance liquid chromatography/quadrupole time-of-flight mass spectrometry

Jiao-Tai-Wan, which is composed of Coptis Rhizoma and Cinnamon Cortex, has been recently used to treat type 2 diabetes. Owing to lack of data on its prototypes and metabolites, elucidation of the pharmacological and clinically safe levels of this formula has been significantly hindered. To screen more potential bioactive components of Jiao-Tai-Wan, we identified its multiple prototypes and metabolites in the plasma of type 2 diabetic rats by ultra high performance liquid chromatography/quadrupole-time-of-flight mass spectrometry. A total of 47 compounds were identified in the plasma of type 2 diabetic rats, including 22 prototypes and 25 metabolites, with alkaloids constituting the majority of the absorbed prototype components. In addition, this is the first study to detect vanillic acid, gallic acid, chlorogenic acid, protocatechuic acid, 2-hydroxycinnamic acid, 3-hydroxycinnamic acid, 4-hydroxycinnamic acid, and 2-methoxy cinnamic acid after oral administration of Jiao-Tai-Wan. The prototypes from Jiao-Tai-Wan were extensively metabolized by demethylation, hydroxylation, and reduction in phase Ⅰ metabolic reactions and by methylation or conjugation of glucuronide or sulfate in phase Ⅱ reactions. This is the first systematic study on the components and metabolic profiles of Jiao-Tai-Wan in vivo. This study provides a useful chemical basis for further pharmacological research and clinical application of Jiao-Tai-Wan.

Transplacental transport of paracetamol and its phase II metabolites using the ex vivo placenta perfusion model

In Europe, 50-60% of pregnant women uses paracetamol (PCM), also known as acetaminophen. While it was considered to be safe, recent studies have shown an association between prenatal exposure to PCM and increased incidences of autism, cryptorchidism, asthma and ADHD. In this study the transplacental transfer of PCM and its metabolites was investigated using an ex vivo human placenta perfusion model (closed circuit; n = 38). Maternal-to-foetal (M-F) and foetal-to-maternal (F-M) transplacental transfer was determined at a concentration correlating with the maximum and steady state concentration in normal clinical use. Antipyrine (AP) was added as reference compound. Samples of the foetal and maternal perfusion medium were taken until 210 (PCM) or 360 min (paracetamol sulphate (PCM-S) and paracetamol glucuronide (PCM-G). PCM and AP concentrations reached an equilibrium between foetal and maternal compartments within the duration of the perfusion experiment and irrespective of the transfer direction. The percentage placental transfer of PCM was 45% (M-F and F-M). For PCM-S, transfer was 39% (M-F) and 28% (F-M), while the PCM-G transfer was 34% (M-F) and 25% (F-M). During placenta perfusions with the metabolites slight conversion (3.5-4.1%) to PCM was observed. In conclusion, PCM crosses the placental barrier rapidly via passive diffusion. Differences in flow rate and villous placental structure explain the significantly faster M-F transfer than F-M transfer of PCM. The larger and more hydrophilic molecules PCM-S and PCM-G cross the placenta at a significantly lower rate. Moreover, their F-M transport is about 40% slower than M-F transport, suggesting involvement of a transporter.

Hepatic Gene Expression During the Perinatal Transition in the Rat

During the immediate postnatal (PN) period, the liver, with its role in energy metabolism and macromolecule synthesis, plays a central role in the perinatal transition. Using RNA microarrays and several complementary computational analyses, we characterized changes in hepatic gene expression in the rat across a developmental period starting with the late gestation fetus (embryonic day 21), and including 30 min PN, 4 h PN, 12 h PN, 1 day PN, and 1 week after birth. Following subtle changes in gene expression at the earliest PN time point, there were marked changes that occurred between 4 and 12 h after birth. These reflected changes in multiple metabolic pathways, with expression of enzymes involved in glycolysis and cholesterol synthesis showing the greatest change. Over 50% of nuclear-encoded mitochondrial genes changed in the first 7 days of PN life, with 25% changing within the first 24 h. We also observed changes coinciding with a transient period of synchronous hepatocyte proliferation that we had observed previously, which occurs during the first PN week. Analysis for upstream regulators of gene expression indicated multiple initiating factors, including cell stress, hormones, and cytokines. Also implicated were multiple canonical transcription factor networks. We conclude that changes in gene expression during the early phases of the perinatal transition involve a complex, choreographed network of signaling pathways that respond to a variety of environmental stimuli. This transcriptomic response during the immediate PN period reflects a complex metabolic adaptive response that incorporates a panoply of signaling pathways and transcriptional regulators.

Developmental Exposure to 2,2',4,4'-Tetrabromodiphenyl Ether Permanently Alters Blood-Liver Balance of Lipids in Male Mice

Polybrominated diphenyl ethers (PBDEs) were used as flame-retardant additives starting 1965 and were recently withdrawn from commerce in North America and Europe. Approximately 1/5 of the total U.S. population were born when environmental concentrations of PBDE plateaued at their maximum. Accumulating evidence suggests that developmental exposures to PBDE may result in long-lasting programming of liver metabolism. In this study, CD-1 mice were exposed prenatally or neonatally to 1 mg/kg body weight of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47), and changes in liver histology, transcriptome, and liver-blood balance of triglycerides were analyzed in 10 months old male offspring. In both exposure groups, long-term reprogramming of lipid metabolism was observed, including increased liver triglycerides and decreased blood triglycerides, and altered expression of metabolic genes in the liver. Significant upregulation of lipid influx transporter Cd36 2.3- and 5.7-fold in pre- and neonatal exposure groups, respectively was identified as a potential mechanism of blood/liver imbalance of triglycerides. Analysis of our and previously published all-genome gene expression data identified changes in expression of ribosomal protein genes as a transcriptomic signature of PBDE exposure. Further comparison of our new data and published data demonstrate that low doses (0.2 mg/kg body weight) of PBDE induce long-lasting up-regulation of ribosomal genes, suppression of Cd36 in liver and increase circulating triglycerides in blood, while moderated doses (≥1 mg/kg body weight) produce opposite long-lasting effects. To conclude, this study shows that an environmentally relevant developmental exposures to BDE-47 permanently alter lipid uptake and accumulation in the liver, with low and moderate doses having opposite effect on liver transcriptomics and triglyceride balance. Similar effects of pre- and neonatal exposures point at hepatocyte maturation as a sensitive window of the liver metabolism programming. These results suggest that PBDE exposure may be an important factor increasing risks of cardio-vascular disease and non-alcoholic fatty liver disease via modulation of liver/blood balance of lipids. The translational relevance of these findings for human remain to be studied.

Engraftment and Repopulation Potential of Late Gestation Fetal Rat Hepatocytes

BACKGROUND

The limited availability of donor organs has led to a search for alternatives to liver transplantation to restore liver function and bridge patients to transplantation. We have shown that the proliferation of late gestation (embryonic day 19) fetal rat hepatocytes is mitogen-independent and that mechanisms regulating mRNA translation, cell cycle progression, and gene expression differ from those of adult rat hepatocytes. In the present study, we investigated whether E19 fetal hepatocytes can engraft and repopulate an injured adult liver.

METHODS

Fetal hepatocytes were isolated using a monoclonal antibody against a hepatic surface protein, leucine amino peptidase (LAP). LAP+ and LAP- fractions were analyzed by immunofluorescence and microarray. Immunopurified E19 liver cells from DPPIV+ rats were transplanted via splenic injection into partial hepatectomized DPPIV- rats that had been pretreated with mitomycin C.

RESULTS

More than a third of LAP+ fetal hepatocytes expressed ductal markers. Transcriptomic analysis revealed that these dual-expressing cells represent a population of less well-differentiated hepatocytes. Upon transplantation, LAP+ late gestation fetal hepatocytes formed hepatic, endothelial, and ductal colonies within 1 month. By 10 months, colonies derived from LAP+ cells increased so that up to 35% of the liver was repopulated by donor-derived cells.

CONCLUSIONS

Late gestation fetal hepatocytes, despite being far along in the differentiation process, possess the capacity for extensive liver repopulation. This is likely related to the unexpected presence of a significant proportion of hepatocyte marker-positive cells maintaining a less well-differentiated phenotype.

A framework and case studies for evaluation of enzyme ontogeny in children's health risk evaluation

Knowledge of the ontogeny of Phase I and Phase II metabolizing enzymes may be used to inform children's vulnerability based upon likely differences in internal dose from xenobiotic exposure. This might provide a qualitative assessment of toxicokinetic (TK) variability and uncertainty pertinent to early lifestages and help scope a more quantitative physiologically based toxicokinetic (PBTK) assessment. Although much is known regarding the ontogeny of metabolizing systems, this is not commonly utilized in scoping and problem formulation stage of human health risk evaluation. A framework is proposed for introducing this information into problem formulation which combines data on enzyme ontogeny and chemical-specific TK to explore potential child/adult differences in internal dose and whether such metabolic differences may be important factors in risk evaluation. The framework is illustrated with five case study chemicals, including some which are data rich and provide proof of concept, while others are data poor. Case studies for toluene and chlorpyrifos indicate potentially important child/adult TK differences while scoping for acetaminophen suggests enzyme ontogeny is unlikely to increase early-life risks. Scoping for trichloroethylene and aromatic amines indicates numerous ways that enzyme ontogeny may affect internal dose which necessitates further evaluation. PBTK modeling is a critical and feasible next step to further evaluate child-adult differences in internal dose for a number of these chemicals.

Residential exposure to pesticides as risk factor for childhood and young adult brain tumors: A systematic review and meta-analysis

BACKGROUND

Accumulating evidence suggests a positive association between exposure to non-agricultural pesticides and childhood brain tumors (CBT).

OBJECTIVE

(1) To conduct a systematic review and meta-analysis of published studies on the association between residential/household/domestic exposure to pesticides and childhood brain tumors. (2) To clarify variables that could impact the results.

METHODS

Publications in English were identified from a MEDLINE search through 28 February 2017 and from the reference list of identified publications. Risk estimates were extracted from 18 case-control studies published between 1979 and 2016 and study quality assessments were performed. Summary odds ratios (mOR) were calculated according to fixed and random-effect meta-analysis models. Separate analyses were conducted after stratification for study quality, critical exposure period, exposure location, specific exposures, pesticide category, application methods, type of pest treated, type of CBT, child's age at diagnosis and geographic location.

RESULTS

Statistically significant associations were observed with CBT after combining all studies (mOR: 1.26; 95% CI: 1.13-1.40) without evidence of inconsistency between study results or publication bias. Specifically, increased risks were observed for several groupings and more particularly for gliomas and exposure involving insecticides. Statistical significance was also reached for high quality studies, for all exposure periods, for indoor exposure and, more particularly, during the prenatal period for all stratifications involving insecticides (except for outdoor use), for pet treatments, for flea/tick treatment, for studies from USA/Canada and studies from Europe (borderline) as well as for data from studies including children of up to 10years at diagnosis and of up to 15years.

CONCLUSIONS

Our findings support an association between residential exposure to pesticides and childhood brain tumors. Although causality cannot be established, these results add to the evidence leading to recommend limiting residential use of pesticides and to support public health policies serving this objective.

Comparative transcriptomics of hepatic differentiation of human pluripotent stem cells and adult human liver tissue

Hepatocytes derived from human pluripotent stem cells (hPSC-HEP) have the potential to replace presently used hepatocyte sources applied in liver disease treatment and models of drug discovery and development. Established hepatocyte differentiation protocols are effective and generate hepatocytes, which recapitulate some key features of their in vivo counterparts. However, generating mature hPSC-HEP remains a challenge. In this study, we applied transcriptomics to investigate the progress of in vitro hepatic differentiation of hPSCs at the developmental stages, definitive endoderm, hepatoblasts, early hPSC-HEP, and mature hPSC-HEP, to identify functional targets that enhance efficient hepatocyte differentiation. Using functional annotation, pathway and protein interaction network analyses, we observed the grouping of differentially expressed genes in specific clusters representing typical developmental stages of hepatic differentiation. In addition, we identified hub proteins and modules that were involved in the cell cycle process at early differentiation stages. We also identified hub proteins that differed in expression levels between hPSC-HEP and the liver tissue controls. Moreover, we identified a module of genes that were expressed at higher levels in the liver tissue samples than in the hPSC-HEP. Considering that hub proteins and modules generally are essential and have important roles in the protein-protein interactions, further investigation of these genes and their regulators may contribute to a better understanding of the differentiation process. This may suggest novel target pathways and molecules for improvement of hPSC-HEP functionality, having the potential to finally bring this technology to a wider use.

Prediction of hepatotoxicity for drugs using human pluripotent stem cell-derived hepatocytes

Drug-induced liver toxicity is a main reason for withdrawals of new drugs in late clinical phases and post-launch of the drugs. Thus, hepatotoxicity screening of drug candidates in pre-clinical stage is important for reducing drug attrition rates during the clinical development process. Here, we show commercially available hepatocytes that could be used for early toxicity evaluation of drug candidates. From our hepatic differentiation technology, we obtained highly pure (≥98%) hepatocytes from human embryonic stem cells (hESCs) having mature phenotypes and similar gene expression profiles with those of primary human tissues. Furthermore, we optimized 96-well culture condition of hESC-derived hepatocytes suitable for toxicity tests in vitro. To this end, we demonstrated the efficacy of our optimized hepatocyte model for predicting hepatotoxicity against the Chinese herbal medicines and showed that toxicity patterns from our hepatocyte model was similar to those of human primary cultured hepatocytes. We conclude that toxicity test using our hepatocyte model could be a good alternative cell source for pre-clinical study to predict potential hepatotoxicity in drug discovery industries.

The Profiling and Identification of the Absorbed Constituents and Metabolites of Guizhi Decoction in Rat Plasma and Urine by Rapid Resolution Liquid Chromatography Combined with Quadrupole-Time-of-Flight Mass Spectrometry

Guizhi decoction (GZD), a well-known traditional Chinese medicine (TCM) prescription consisting of Ramulus Cinnamomi, Radix Paeoniae Alba, Radix Glycyrrhizae, Fructus Jujubae and Rhizoma Zingiberis Recens, is usually used for the treatment of common colds, influenza, and other pyretic conditions in the clinic. However, the absorbed ingredients and metabolic compounds of GZD have not been reported. In this paper, a method incorporating rapid resolution liquid chromatography (RRLC) with quadrupole-time-of-flight mass spectrometry (Q-TOF-MS) was used to identify ingredients after oral administration of GZD. Identification of the primary components in GZD, drug-containing serum and urine samples was carried out in order to investigate the assimilation and metabolites of the decoction in vivo. By comparing the total ion chromatograms (TICs) of GZD, a total of 71 constituents were detected or characterized. By comparing TICs of blank and dosed rat plasma, a total of 15 constituents were detected and identified as prototypes according to their retention time (tR) and MS, MS/MS data. Based on this, neutral loss scans of 80 and 176 Da in samples of rat plasma and urine helped us to identify most of the metabolites. Results showed that the predominant metabolic pathways of (epi) catechin and gallic acid were sulfation, methylation, glucuronidation and dehydroxylation; the major metabolic pathways of flavone were hydrolysis, sulfation and glucuronidation. Furthermore, degradation, oxidation and ring fission were found to often occur in the metabolism process of GZD in vivo.

Regulation of liver development: implications for liver biology across the lifespan

The liver serves a spectrum of essential metabolic and synthetic functions that are required for the transition from fetal to postnatal life. Processes essential to the attainment of adequate liver mass and function during fetal life include cell lineage specification early in development, enzymic and other functional modes of differentiation throughout gestation, and ongoing cell proliferation to achieve adequate liver mass. Available data in laboratory rodents indicate that the signaling networks governing these processes in the fetus differ from those that can sustain liver function and mass in the adult. More specifically, fetal hepatocytes may develop independent of key mitogenic signaling pathways, including those involving the Erk mitogen-activated protein kinases MAPK1/3 and the mechanistic target of rapamycin (mTOR). In addition, the fetal liver is subject to environmental influences that, through epigenetic mechanisms, can have sustained effects on function and, by extension, contribute to the developmental origin of adult metabolic disease. Finally, the mitogen-independent phenotype of rat fetal hepatocytes in late gestation makes these cells suitable for cell-based therapy of liver injury. In the aggregate, studies on the mechanisms governing fetal liver development have implications not only for the perinatal metabolic transition but also for the prevention and treatment of liver disorders throughout the lifespan.

Altered Hepatic Transport by Fetal Arsenite Exposure in Diet-Induced Fatty Liver Disease

Non-alcoholic fatty liver disease can result in changes to drug metabolism and disposition potentiating adverse drug reactions. Furthermore, arsenite exposure during development compounds the severity of diet-induced fatty liver disease. This study examines the effects of arsenite potentiated diet-induced fatty liver disease on hepatic transport in male mice. Changes were detected for Mrp2/3/4 hepatic transporter gene expression as well as for Oatp1a4/2b1/1b2. Plasma concentrations of Mrp and Oatp substrates were increased in arsenic exposure groups compared with diet-only controls. In addition, murine embryonic hepatocytes and adult primary hepatocytes show significantly altered transporter expression after exposure to arsenite alone: a previously unreported phenomenon. These data indicate that developmental exposure to arsenite leads to changes in hepatic transport which could increase the risk for ADRs during fatty liver disease.

Correlation between Conjugated Bisphenol A Concentrations and Efflux Transporter Expression in Human Fetal Livers

Because of its widespread use in the manufacturing of consumer products over several decades, human exposure to bisphenol A (BPA) has been pervasive. Fetuses are particularly sensitive to BPA exposure, with a number of negative developmental and reproductive outcomes observed in rodent perinatal models. Xenobiotic transporters are one mechanism to extrude conjugated and unconjugated BPA from the liver. In this study, the mRNA expression of xenobiotic transporters and relationships with total, conjugated, and free BPA levels were explored utilizing human fetal liver samples. The mRNA expression of breast cancer resistance protein (BCRP) and multidrug resistance-associated transporter (MRP)4, as well as BCRP and multidrug resistance transporter 1 exhibited the highest degree of correlation, with r(2) values of 0.941 and 0.816 (P < 0.001 for both), respectively. Increasing concentrations of conjugated BPA significantly correlated with high expression of MRP1 (P < 0.001), MRP2 (P < 0.05), and MRP3 (P < 0.05) transporters, in addition to the NF-E2-related factor 2 transcription factor (P < 0.001) and its prototypical target gene, NAD(P)H quinone oxidoreductase 1 (P < 0.001). These data demonstrate that xenobiotic transporters may be coordinately expressed in the human fetal liver. This is also the first report of a relationship between environmentally relevant fetal BPA levels and differences in the expression of transporters that can excrete the parent compound and its metabolites.

Bisphenol A glucuronide deconjugation is a determining factor of fetal exposure to bisphenol A

Previous studies in experimental animals have shown that maternal exposure to bisphenol A (BPA) during late pregnancy leads to high plasma concentrations of BPA glucuronide (BPAG) in fetus compared to mother due to the inability of BPAG to cross the placental barrier. A recent in vitro study has reported that BPAG can exert adipogenic effect underlining the need for characterization of the fetal disposition of BPAG. Experiments were conducted in chronically catheterized fetal sheep to determine the contribution of BPAG hydrolysis to BPA to the elimination of BPAG from the fetal compartment and its resulting effect on the overall fetal exposure to free BPA. Serial sampling of fetal arterial blood, amniotic fluid, maternal venous blood and urine was performed following separate single doses of BPA and BPAG administered intravenously to eight fetal/maternal pairs after cesarean section, and repeated BPAG doses given to two fetal sheep. On average 67% of the BPA entering the fetal circulation was rapidly eliminated through fetal to maternal clearance, with a very short half-life (20 min), while the remaining fraction (24%) was glucuronoconjugated. BPA conjugation-deconjugation cycling was responsible for a 43% increase of the overall fetal exposure to free BPA. A very specific pattern of fetal exposure to free BPA was observed due to its highly increased persistence with a hydrolysis-dependent plasma terminal free BPA half-life of several tens of hours. These findings suggest that although the high fetal to maternal clearance of free BPA protects the fetus from transient increases in free BPA plasma concentrations associated with maternal BPA intake, low but sustained basal free BPA concentrations are maintained in the fetus through BPA conjugation-deconjugation cycling. The potential health implications of these low but sustained basal concentrations of free BPA in fetal plasma should be addressed especially when considering time-dependent effects.

Orchestrating liver development

The liver is a central regulator of metabolism, and liver failure thus constitutes a major health burden. Understanding how this complex organ develops during embryogenesis will yield insights into how liver regeneration can be promoted and how functional liver replacement tissue can be engineered. Recent studies of animal models have identified key signaling pathways and complex tissue interactions that progressively generate liver progenitor cells, differentiated lineages and functional tissues. In addition, progress in understanding how these cells interact, and how transcriptional and signaling programs precisely coordinate liver development, has begun to elucidate the molecular mechanisms underlying this complexity. Here, we review the lineage relationships, signaling pathways and transcriptional programs that orchestrate hepatogenesis.

Genetic and epigenetic regulation of gene expression in fetal and adult human livers

Background

The liver plays a central role in the maintenance of homeostasis and health in general. However, there is substantial inter-individual variation in hepatic gene expression, and although numerous genetic factors have been identified, less is known about the epigenetic factors.

Results

By analyzing the methylomes and transcriptomes of 14 fetal and 181 adult livers, we identified 657 differentially methylated genes with adult-specific expression, these genes were enriched for transcription factor binding sites of HNF1A and HNF4A. We also identified 1,000 genes specific to fetal liver, which were enriched for GATA1, STAT5A, STAT5B and YY1 binding sites. We saw strong liver-specific effects of single nucleotide polymorphisms on both methylation levels (28,447 unique CpG sites (meQTL)) and gene expression levels (526 unique genes (eQTL)), at a false discovery rate (FDR) < 0.05. Of the 526 unique eQTL associated genes, 293 correlated significantly not only with genetic variation but also with methylation levels. The tissue-specificities of these associations were analyzed in muscle, subcutaneous adipose tissue and visceral adipose tissue. We observed that meQTL were more stable between tissues than eQTL and a very strong tissue-specificity for the identified associations between CpG methylation and gene expression.

Conclusions

Our analyses generated a comprehensive resource of factors involved in the regulation of hepatic gene expression, and allowed us to estimate the proportion of variation in gene expression that could be attributed to genetic and epigenetic variation, both crucial to understanding differences in drug response and the etiology of liver diseases.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-860) contains supplementary material, which is available to authorized users.