Identification of a plant isoflavonoid that causes biliary atresia

A Bile Duct-on-a-Chip With Organ-Level Functions

BACKGROUND AND AIMS

Chronic cholestatic liver diseases, such as primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC), are frequently associated with damage to the barrier function of the biliary epithelium. Here, we report on a bile duct-on-a-chip that phenocopies not only the tubular architecture of the bile duct in three dimensions, but also its barrier functions.

APPROACH AND RESULTS

We showed that mouse cholangiocytes in the channel of the device became polarized and formed mature tight junctions, that the permeability of the cholangiocyte monolayer was comparable to ex vivo measurements, and that cholangiocytes in the device were mechanosensitive (as demonstrated by changes in calcium flux under applied luminal flow). Permeability decreased significantly when cells formed a compact monolayer with cell densities comparable to those observed in vivo. This device enabled independent access to the apical and basolateral surfaces of the cholangiocyte channel, allowing proof-of-concept toxicity studies with the biliary toxin, biliatresone, and the bile acid, glycochenodeoxycholic acid. The cholangiocyte basolateral side was more vulnerable than the apical side to treatment with either agent, suggesting a protective adaptation of the apical surface that is normally exposed to bile. Further studies revealed a protective role of the cholangiocyte apical glycocalyx, wherein disruption of the glycocalyx with neuraminidase increased the permeability of the cholangiocyte monolayer after treatment with glycochenodeoxycholic acid.

CONCLUSIONS

This bile duct-on-a-chip captured essential features of a simplified bile duct in structure and organ-level functions and represents an in vitro platform to study the pathophysiology of the bile duct using cholangiocytes from a variety of sources.

Biliary atresia: pathology, etiology and pathogenesis

Biliary atresia is a progressive fibrosing obstructive cholangiopathy of the intrahepatic and extrahepatic biliary system, resulting in obstruction of bile flow and neonatal jaundice. Histopathological findings in liver biopsies include the expansion of the portal tracts, with edematous fibroplasia and bile ductular proliferation, with bile plugs in duct lumen. Lobular morphological features may include variable multinucleate giant cells, bilirubinostasis and hemopoiesis. The etiopathogenesis of biliary atresia is multifactorial and multiple pathomechanisms have been proposed. Experimental and clinical studies have suggested that viral infection initiates biliary epithelium destruction and release of antigens that trigger a Th1 immune response, which leads to further injury of the bile duct, resulting in inflammation and obstructive scarring of the biliary tree. It has also been postulated that biliary atresia is caused by a defect in the normal remodelling process. Genetic predisposition has also been proposed as a factor for the development of biliary atresia.

Innate Immunity and Pathogenesis of Biliary Atresia

Biliary atresia (BA) is a devastating fibro-inflammatory disease characterized by the obstruction of extrahepatic and intrahepatic bile ducts in infants that can have fatal consequences, when not treated in a timely manner. It is the most common indication of pediatric liver transplantation worldwide and the development of new therapies, to alleviate the need of surgical intervention, has been hindered due to its complexity and lack of understanding of the disease pathogenesis. For that reason, significant efforts have been made toward the development of experimental models and strategies to understand the etiology and disease mechanisms and to identify novel therapeutic targets. The only characterized model of BA, using a Rhesus Rotavirus Type A infection of newborn BALB/c mice, has enabled the identification of key cellular and molecular targets involved in epithelial injury and duct obstruction. However, the establishment of an unleashed chronic inflammation followed by a progressive pathological wound healing process remains poorly understood. Like T cells, macrophages can adopt different functional programs [pro-inflammatory (M1) and resolutive (M2) macrophages] and influence the surrounding cytokine environment and the cell response to injury. In this review, we provide an overview of the immunopathogenesis of BA, discuss the implication of innate immunity in the disease pathogenesis and highlight their suitability as therapeutic targets.

Exome Sequencing in Individuals with Isolated Biliary Atresia

Biliary atresia (BA) is a severe pediatric liver disease resulting in necroinflammatory obliteration of the extrahepatic biliary tree. BA presents within the first few months of life as either an isolated finding or with additional syndromic features. The etiology of isolated BA is unknown, with evidence for infectious, environmental, and genetic risk factors described. However, to date, there are no definitive causal genes identified for isolated BA in humans, and the question of whether single gene defects play a major role remains open. We performed exome-sequencing in 101 North American patients of European descent with isolated BA (including 30 parent-child trios) and considered several experimental designs to identify potentially deleterious protein-altering variants that may be involved in the disease. In a case-only analysis, we did not identify genes with variants shared among more than two probands, and burden tests of rare variants using a case-case control design did not yield significant results. In the trio analysis of 30 simplex families (patient and parent trios), we identified 66 de novo variants in 66 genes including potentially deleterious variants in STIP1 and REV1. STIP1 is a co-chaperone for the heat-shock protein, HSP90, and has been shown to have diverse functions in yeast, flies and mammals, including stress-responses. REV1 is known to be a key player in DNA repair pathway and to interact with HSP90. In conclusion, our results do not support the hypothesis that a simple genetic model is responsible for the majority of cases of isolated BA. Our finding of de novo variants in genes linked to evolutionarily conserved stress responses (STIP1 and REV1) suggests that exploration of how genetic susceptibility and environmental exposure may interact to cause BA is warranted.

Coordinated development of the mouse extrahepatic bile duct: Implications for neonatal susceptibility to biliary injury

BACKGROUND & AIMS

The extrahepatic bile duct is the primary tissue initially affected by biliary atresia. Biliary atresia is a cholangiopathy which exclusively affects neonates. Current animal models suggest that the developing bile duct is uniquely susceptible to damage. In this study, we aimed to define the anatomical and functional differences between the neonatal and adult mouse extrahepatic bile ducts.

METHODS

We studied mouse passaged cholangiocytes, mouse BALB/c neonatal and adult primary cholangiocytes, as well as isolated extrahepatic bile ducts, and a collagen reporter mouse. The methods used included transmission electron microscopy, lectin staining, immunostaining, rhodamine uptake assays, bile acid toxicity assays, and in vitro modeling of the matrix.

RESULTS

The cholangiocyte monolayer of the neonatal extrahepatic bile duct was immature, lacking the uniform apical glycocalyx and mature cell-cell junctions typical of adult cholangiocytes. Functional studies showed that the glycocalyx protected against bile acid injury and that neonatal cholangiocyte monolayers were more permeable than adult monolayers. In adult ducts, the submucosal space was filled with collagen I, elastin, hyaluronic acid, and proteoglycans. In contrast, the neonatal submucosa had little collagen I and elastin, although both increased rapidly after birth. In vitro modeling of the matrix suggested that the composition of the neonatal submucosa relative to the adult submucosa led to increased diffusion of bile. A Col-GFP reporter mouse showed that cells in the neonatal but not adult submucosa were actively producing collagen.

CONCLUSION

We identified 4 key differences between the neonatal and adult extrahepatic bile duct. We showed that these features may have functional implications, suggesting the neonatal extrahepatic bile ducts are particularly susceptible to injury and fibrosis.

LAY SUMMARY

Biliary atresia is a disease that affects newborns and is characterized by extrahepatic bile duct injury and obstruction, resulting in liver injury. We identify 4 key differences between the epithelial and submucosal layers of the neonatal and adult extrahepatic bile duct and show that these may render the neonatal duct particularly susceptible to injury.

Biliary Atresia as a Disease Starting In Utero: Implications for Treatment, Diagnosis, and Pathogenesis

Biliary atresia (BA) is the most common reason for pediatric liver transplant. BA's varied presentation, natural history, and treatment with the Kasai portoenterostomy have been well described; however, when BA starts relative to birth has not been clearly defined. In this review, we discuss laboratory, imaging, and clinical data which suggest that most if not all forms of BA may start before birth. This early onset has implications in terms of delivering treatments earlier and identifying possible factors underlying BA's etiology.

Development of the Intrahepatic and Extrahepatic Biliary Tract: A Framework for Understanding Congenital Diseases

The involvement of the biliary tract in the pathophysiology of liver diseases and the increased attention paid to bile ducts in the bioconstruction of liver tissue for regenerative therapy have fueled intense research into the fundamental mechanisms of biliary development. Here, I review the molecular, cellular and tissular mechanisms driving differentiation and morphogenesis of the intrahepatic and extrahepatic bile ducts. This review focuses on the dynamics of the transcriptional and signaling modules that promote biliary development in human and mouse liver and discusses studies in which the use of zebrafish uncovered unexplored processes in mammalian biliary development. The review concludes by providing a framework for interpreting the mechanisms that may help us understand the origin of congenital biliary diseases.

What gastroenterologists and hepatologists should know about organoids in 2019

Most of the research behind new medical advances is carried out using either animal models or cancer cells, which both have their disadvantage in particular with regard to medical applications such as personalized medicine and novel therapeutic approaches. However, recent advances in stem cell biology have enabled long-term culturing of organotypic intestinal or hepatic tissues derived from tissue resident or pluripotent stem cells. These 3D structures, denoted as organoids, represent a substantial advance in structural and functional complexity over traditional in vitro cell culture models that are often non-physiological and transformed. They can recapitulate the in vivo architecture, functionality and genetic signature of the corresponding tissue. The opportunity to model epithelial cell biology, epithelial turnover, barrier dynamics, immune-epithelial communication and host-microbe interaction more efficiently than previous culture systems, greatly enhance the translational potential of organotypic hepato-gastrointestinal culture systems. Thus there is increasing interest in using such cultured cells as a source for tissue engineering, regenerative medicine and personalized medicine. This review will highlight some of the established and also some exciting novel perspectives on organoids in the fields of gastroenterology and hepatology.

Biliary atresia: a scientometric analysis of the global research architecture and scientific developments

Biliary atresia (BA) is a rare cholangiopathy of largely unknown etiology and unpredictable outcome. There has been an increasing number of BA-related publications, which may challenge researchers to determine their actual scientific value. This study aimed to evaluate the global research activity and developments relating to BA using a combination of scientometric methodologies and visualization tools. A comprehensive search strategy for the Web of Science™ database was designed to obtain bibliographic data on scientific BA publications for the timespan 1900-2018. Research output of countries, institutions, individual authors and collaborative networks was analyzed. Semi-qualitative research measures including citation rate and h-index were assessed. Choropleth mapping and network diagrams were used to visualize results. In total, 4,459 publications on BA were identified (88.5% in English), originating from 63 countries. The largest number was published by the USA (n = 991; 22.2%), Japan (n = 667; 15.0%) and the UK (n = 294; 6.6%). The USA combined the highest number of cooperation articles (n = 140). The most productive collaborative network was established between the USA and Canada (n = 17). Scientific papers from the UK received the highest average citation rate (16.7), whereas the USA had the highest country-specific h-index (59). Eighty-eight (2.0%) items were published under the auspices of multicenter consortiums and registries. The most productive institutions and authors were based in the USA, the UK, Japan, France, Canada and Taiwan. BA-related research has constantly been progressing, becoming more multidisciplinary but with main research endeavors concentrated in a few high-income countries. Studies into pathogenesis of BA remain uncommon, but are sorely needed to foster true scientific progress with this rare disease. Hence, international collaborative and translational research should be strengthened to allow further evolution in this field.

Developing zebrafish disease models for in vivo small molecule screens

The zebrafish is a model organism that allows in vivo studies to be performed at a scale usually restricted to in vitro studies. As such, the zebrafish is well suited to in vivo screens, in which thousands of small molecules are tested for their ability to modify disease phenotypes in zebrafish disease models. Numerous approaches have been developed for modeling human diseases in zebrafish, including mutagenesis, transgenesis, pharmacological approaches, wounding, and exposure to infectious or cancerous agents. We review the various strategies for modeling human diseases in zebrafish and discuss important considerations when developing zebrafish models for use in in vivo small molecule screens.

Suppressing microRNA-29c promotes biliary atresia-related fibrosis by targeting DNMT3A and DNMT3B

This study was designed to investigate the potential role of microRNA-29c (miR-29c) in biliary atresia-related fibrosis. The expression of miR-29c was determined in 15 pairs of peripheral blood samples from infants with biliary atresia (BA) and infants with non-BA neonatal cholestasis using quantitative real-time PCR. EMT was established by induction with TGF-β1 in HIBEpiC cells. MiR-29c was inhibited by lipofectamine transfection. The expressions of proteins related to epithelial-mesenchymal transition (EMT), i.e., E-cadherin, N-cadherin and vimentin, were determined using quantitative real-time PCR and western blotting. Direct interaction between miR-29c and DNMT3A and DNMT3B was identified using a luciferase reporter assay. The expressions of DNMT3A and DNMT3B were suppressed by treatment with SGI-1027. Patients with BA showed significantly lower miR-29c levels in peripheral blood samples than the control subjects. In vitro, TGF-β1-induced EMT significantly decreased the expression of miR-29c. Downregulation of miR-29c had a promotional effect on BA-related fibrosis in HIBEpiC cells, as confirmed by the decrease in E-cadherin and increase in N-cadherin and vimentin levels. MiR-29c was found to target the 3'UTR of DNMT3A and DNMT3B and inhibit their expression. Suppression of DNMT3A and DNMT3B reversed the effects of miR-29c downregulation on BA-related fibrosis in HIBEpiC cells. These data suggest that BA-related fibrosis is closely associated with the occurrence of EMT in HIBEpiC cells. MiR-29c might be a candidate for alleviating BA-related fibrosis by targeting DNMT3A and DNMT3B.

Genetics in biliary atresia

PURPOSE OF REVIEW

Biliary atresia is a poorly understood deadly disease. Genetic predisposition factors are suspected albeit not firmly established. This review summarizes recent evidence of genetic alterations in biliary atresia.

RECENT FINDINGS

Whole-genome association studies in biliary atresia patients identified four distinct predisposition loci with four different genes potentially involved in the disease occurrence. Variations in these genes were searched for, but none were found in patients with biliary atresia suggesting complex mechanisms.

SUMMARY

Despite decades since its description and decades of intensive researches, cause of biliary atresia disease remains enigmatic. The inheritance of biliary atresia is not Mendelian. Genetic predisposition factor is one of the explored fields to explain biliary atresia pathogenicity. Biliary atresia has been associated with several inborn syndromes, chromosome anomalies, and gene polymorphisms in specific populations. Four predisposition loci encompassing genes relevant to the disease have been identified, but no pathogenic variations were found in biliary atresia patients. Few reported cases of isolated biliary atresia manifestation in the context of known genetic diseases suggest coincidental findings. Alternatives to classic genetic alterations are proposed to explain genetic predisposition in biliary atresia including noncoding and epigenetic factors. Biliary atresia is most likely related to complex traits making its genetic exploration challenging.

Recent advances in understanding biliary atresia

Biliary atresia (BA) is a neonatal liver disease characterized by progressive obstruction and fibrosis of the extrahepatic biliary tree as well as fibrosis and inflammation of the liver parenchyma. Recent studies found that infants who will go on to develop BA have elevated direct bilirubin levels in the first few days of life, suggesting that the disease starts in utero. The etiology and pathogenesis of BA, however, remain unknown. Here, we discuss recent studies examining potential pathogenetic mechanisms of BA, including genetic susceptibility, involvement of the immune system, and environmental insults such as viruses and toxins, although it is possible that there is not a single etiological agent but rather a large group of injurious insults that result in a final common pathway of extrahepatic bile duct obstruction and liver fibrosis. The management and diagnosis of BA have not advanced significantly in the past decade, but given recent advances in understanding the timing and potential pathogenesis of BA, we are hopeful that the next decade will bring early diagnostics and novel therapeutics.

An improved and easy protocol for primary epithelial cell culture from atretic tissue in biliary atresia

Biliary atresia (BA) is a lethal disease of infancy with obscure etiology. Insight into the pathogenesis of this disorder is limited by lack of availability of adequate epithelial tissue. Primary culture of human biliary epithelium may help to provide material for diagnostic and research purposes. However, culture of these cells from atretic tissue is a challenging task. We aimed to develop a reliable and easier protocol for culture of human biliary epithelial cells from excised atretic extrahepatic bile duct. An explant culture was performed using tissue obtained from 30 children with diseases of biliary tract. The culture showed florid cell growth in less than 3 weeks. Epithelial nature and biliary origin of cultured cells was confirmed using pancytokeratin and cytokeratin -7 antibodies. The protocol showed 100% success rate as cells could be cultured in all 30 patients. Moreover, the cells remained viable for a duration of over 3 months in most of the cases. This easier culture technique is likely to have an impact on the study of biliary cell pathophysiology, particularly in BA.

Zebrafish as a Model to Study Cholestatic Liver Diseases

Cholestasis is a condition that impairs bile flow, resulting in retention of bile fluid in the liver. It may cause significant morbidity and mortality due to pruritus, malnutrition, and complications from portal hypertension secondary to biliary cirrhosis. The zebrafish (Danio rerio) has emerged as a valuable model organism for studying cholestasis that complements with the in vitro systems and rodent models. Its main advantages include conserved mechanisms of liver development and bile formation, rapid external development, ease of monitoring hepatobiliary morphology and function in live larvae, and accessibility to genetic and chemical manipulations. In this chapter, we provide an overview of the existing zebrafish models of cholestatic liver diseases. We discuss the strengths and limitations of using zebrafish to study cholestasis. We also provide step-by-step descriptions of the methodologies for analyzing cholestatic phenotypes in zebrafish.

Genetic investigation into an increased susceptibility to biliary atresia in an extended New Zealand Māori family

Background

Biliary atresia (BA), a fibrosing disorder of the developing biliary tract leading to liver failure in infancy, has an elevated incidence in indigenous New Zealand (NZ) Māori. We investigated a high rate of BA in a group of children (n = 12) belonging to a single Māori iwi (or ‘tribe’, related through a remote ancestor).

Methods

Population and geographical data was used to estimate the rate of BA in Māori sub-groups, and a pedigree linking most of the affected children was constructed from oral and documented history. Array genotyping was used to examine hypotheses about the inheritance of a possible genetic risk factor, and the history of the affected population, and Exome Sequencing to search for candidate genes.

Results

Most of these affected children (n = 7) link to a self-reported pedigree and carry a 50-fold increase in BA risk over unrelated Māori (χ² = 296P < 0.001, 95% CI 23–111). Genetic analysis using FEstim and SNP array genotypes revealed no evidence for elevated consanguinity between parents of affected children (FEstim: F (2,21) = 0.469, P > 0.63). Genome-wide quantitation of intervals of contiguous, homozygous-by-state markers reached a similar conclusion (F (2,399) = 1.99, P = 0.138). Principal component analysis and investigation with STRUCTURE found no evidence of increased allele frequency of either a recessive variant, or additive, low-risk variants due to reproductive isolation. To identify candidate causal factors, Exome Sequencing datasets were scrutinised for shared rare coding variants across 8 affected individuals. No rare, non-synonymous, phylogenetically conserved variants were common to 6 or more affected children.

Conclusion

The substantially elevated risk for development of BA in this subgroup could be mediated by genetic factors, but the iwi exhibits no properties indicative of recent or remote reproductive isolation. Resolution of any risk loci may rely on extensive genomic sequencing studies in this iwi or investigation of other mechnaisms such as copy number variation.

Electronic supplementary material

The online version of this article (10.1186/s12920-018-0440-0) contains supplementary material, which is available to authorized users.

Cholangiopathies - Towards a molecular understanding

Liver diseases constitute an important medical problem, and a number of these diseases, termed cholangiopathies, affect the biliary system of the liver. In this review, we describe the current understanding of the causes of cholangiopathies, which can be genetic, viral or environmental, and the few treatment options that are currently available beyond liver transplantation. We then discuss recent rapid progress in a number of areas relevant for decoding the disease mechanisms for cholangiopathies. This includes novel data from analysis of transgenic mouse models and organoid systems, and we outline how this information can be used for disease modeling and potential development of novel therapy concepts. We also describe recent advances in genomic and transcriptomic analyses and the importance of such studies for improving diagnosis and determining whether certain cholangiopathies should be viewed as distinct or overlapping disease entities.

Biliary Atresia: Clinical and Research Challenges for the Twenty-First Century

Biliary atresia (BA) is a fibroinflammatory disease of the intrahepatic and extrahepatic biliary tree. Surgical hepatic portoenterostomy (HPE) may restore bile drainage, but progression of the intrahepatic disease results in complications of portal hypertension and advanced cirrhosis in most children. Recognizing that further progress in the field is unlikely without a better understanding of the underlying cause(s) and pathogenesis of the disease, the National Institutes of Diabetes and Digestive and Kidney Diseases (NIDDK) sponsored a research workshop focused on innovative and promising approaches and on identifying future areas of research. Investigators discussed recent advances using gestational ultrasound and results of newborn BA screening with serum direct (conjugated) bilirubin that support a prenatal onset of biliary injury. Experimental and human studies implicate the toxic properties of environmental toxins (e.g., biliatresone) and of viruses (e.g., cytomegalovirus) to the biliary system. Among host factors, sequence variants in genes related to biliary development and ciliopathies, a notable lack of a cholangiocyte glycocalyx and of submucosal collagen bundles in the neonatal extrahepatic bile ducts, and an innate proinflammatory bias of the neonatal immune system contribute to an increased susceptibility to damage and obstruction following epithelial injury. These advances form the foundation for a future research agenda focused on identifying the environmental and host factor(s) that cause BA, the potential use of population screening, studies of the mechanisms of prominent fibrosis in young infants, determinations of clinical surrogates of disease progression, and the design of clinical trials that target subgroups of patients with initial drainage following HPE. (Hepatology 2018; 00:000-000).

A detailed guide to lipid therapy in intestinal failure

Intravenous lipid emulsions are an integral part of nutrition therapy in the intestinal failure patient. In addition to being a concentrated source of non-protein calories, they provide the essential fatty acids necessary for growth and development. Depending upon the oil source used in these products, complications such as intestinal failure associated liver disease (IFALD) can occur. This review will discuss the risks and benefits associated with these products, especially as they relate to the pediatric intestinal failure patient.

Intrahepatic bile duct primary cilia in biliary atresia

AIM

The etiopathogenesis of non-syndromic biliary atresia (BA) is obscure. The primary aim was to investigate intrahepatic bile duct cilia (IHBC) in BA at diagnosis and its correlation with clinical outcome. The secondary aim was to analyze IHBC in routine paraffin-embedded liver biopsies using conventional scanning electron microscopy (SEM).

METHODS

Surgical liver biopsies taken at diagnosis from 22 BA infants (age range, 39-116 days) and from eight children with non-BA chronic cholestasis (age range, 162 days -16.8 years) were evaluated for IHBC by immunofluorescence (IF) and SEM. A minimum 18-month follow-up after surgery was available for all patients.

RESULTS

By IF, cilia were present in 6/8 (75%) non-BA but only in 3/22 (14%) BA cases, and cilia were reduced or absent in 19/22 (86%) BA and 2/8 (25%) non-BA livers (P < 0.01). In BA, cilia presence was found to be associated with clearance of jaundice at 6-month follow-up (P < 0.05). However, high overall survival rates with native liver, >90% at 12 months, and >70% at 24 months post-surgery, were recorded regardless of cilia presence/absence at diagnosis. Electron microscopy was able to detect bile ducts and cilia in routine liver biopsies, revealing significant abnormalities in 100% BA livers.

CONCLUSIONS

The presence of IHBC in BA livers at the diagnosis was associated with resolution of cholestasis, although was not predictive of short-term survival with native liver. Scanning electron microscopy represents a powerful new tool to study routine liver biopsies in biliary disorders. Cilia dysfunction in BA pathogenesis and/or disease progression warrants further investigation.

Zebrafish abcb11b mutant reveals strategies to restore bile excretion impaired by bile salt export pump deficiency

Bile salt export pump (BSEP) adenosine triphosphate-binding cassette B11 (ABCB11) is a liver-specific ABC transporter that mediates canalicular bile salt excretion from hepatocytes. Human mutations in ABCB11 cause progressive familial intrahepatic cholestasis type 2. Although over 150 ABCB11 variants have been reported, our understanding of their biological consequences is limited by the lack of an experimental model that recapitulates the patient phenotypes. We applied CRISPR/Cas9-based genome editing technology to knock out abcb11b, the ortholog of human ABCB11, in zebrafish and found that these mutants died prematurely. Histological and ultrastructural analyses showed that abcb11b mutant zebrafish exhibited hepatocyte injury similar to that seen in patients with progressive familial intrahepatic cholestasis type 2. Hepatocytes of mutant zebrafish failed to excrete the fluorescently tagged bile acid that is a substrate of human BSEP. Multidrug resistance protein 1, which is thought to play a compensatory role in Abcb11 knockout mice, was mislocalized to the hepatocyte cytoplasm in abcb11b mutant zebrafish and in a patient lacking BSEP protein due to nonsense mutations in ABCB11. We discovered that BSEP deficiency induced autophagy in both human and zebrafish hepatocytes. Treatment with rapamycin restored bile acid excretion, attenuated hepatocyte damage, and extended the life span of abcb11b mutant zebrafish, correlating with the recovery of canalicular multidrug resistance protein 1 localization.

CONCLUSIONS

Collectively, these data suggest a model that rapamycin rescues BSEP-deficient phenotypes by prompting alternative transporters to excrete bile salts; multidrug resistance protein 1 is a candidate for such an alternative transporter. (Hepatology 2018;67:1531-1545).

Pediatric Intestinal Failure-Associated Liver Disease: Challenges in Identifying Clinically Relevant Biomarkers

BACKGROUND

Intestinal failure-associated liver disease (IFALD) is complex and diagnosed by concurrent use of parenteral nutrition, clinical presentation, and alterations in hepatic biomarkers exclusive of other causes of liver disease. In comparison with individual measures, composite biomarkers may provide a more effective means for assessing disease progression and response to treatment than single parameters. Since IFALD is considered by some to be a type of drug-induced liver injury (DILI), those diagnostic criteria could potentially be used in this population. Using a preexisting database of children treated for IFALD, our aim was to determine if a similar composite biomarker could be applied to this population.

STUDY DESIGN

Adult DILI criteria were applied at baseline, when treatment for IFALD (ie, direct bilirubin ≥2.0 mg/dL) was initiated.

RESULTS

A total of 214 patients with IFALD treated at Boston Children's Hospital were identified; 168 patients were eligible for analysis. Most patients analyzed were male (61%) and preterm (87%). Alkaline phosphatase (ALP) ≥2× upper limit of normal (ULN) captured the least amount of DILI (11%), while γ-glutamyltransferase (GGT) ≥1× ULN accounted for the most (62%). Using adult DILI criteria, 60 (39%) patients with IFALD were found to have DILI. Substituting GGT ≥1× ULN for ALP ≥2× ULN improved the sensitivity, with 105 (69%) of patients meeting at least 1 criterion for DILI.

CONCLUSION

Numerous challenges made it difficult to apply the DILI criteria to children with IFALD. Direct bilirubin, fractionated ALP, and perhaps GGT may be more suitable. Given its complex etiology and the age-based differences due to hepatic immaturity and growth, a more suitable composite marker needs to be developed to assess IFALD in this population.

Synthesis and Structure-Activity Relationship Study of Biliatresone, a Plant Isoflavonoid That Causes Biliary Atresia

We report the first synthesis of the plant isoflavonoid biliatresone. The convergent synthesis has been applied to the synthesis of several analogs, which have facilitated the first structure-activity relationship study for this environmental toxin that, on ingestion, recapitulates the phenotype of biliary atresia.

Update on investigations pertaining to the pathogenesis of biliary atresia

Biliary atresia is a devastating biliary disease of neonates that results in liver transplantation for the vast majority. The etiology of biliary atresia is unknown and is likely multifactorial, with components of genetic predisposition, environmental trigger and autoimmunity contributing to disease pathogenesis. This review highlights recent work related to investigations of disease pathogenesis in biliary atresia.

Newborn screening for biliary atresia in the United States

Despite advances in our understanding of the pathogenesis of biliary atresia (BA), BA remains the most common cause of end-stage liver disease in children and the leading indication for pediatric liver transplantation. Age at time of Kasai portoenterostomy (KPE), performed to provide bile drainage, strongly correlates with transplant-free survival, mostly due to progression of intrahepatic fibrosis to cirrhosis. Unfortunately, challenges remain in recognizing that a jaundiced infant may have BA. To better diagnose infants with BA at an earlier age, population-based screening programs in countries such as Taiwan, Japan, and China have utilized stool color cards. Early results have been promising demonstrating earlier diagnosis, earlier KPE, and, hence, improved outcomes. Cost-effectiveness studies focused on stool color card screening in North America where the incidence of BA is much lower also project improved transplant-free survival rate with a savings in terms of healthcare expenditure. There is also evidence that postnatal serum bilirubin levels may also be effective as a screening tool given that all infants with BA exhibit hyperbilirubinemia at birth. The American Academy of Pediatrics (AAP) recently advocated studying the implementation of newborn screening for BA in the United States. Further efforts and analyses within the United States are ongoing, but current evidence is supportive of screening for BA even in low incidence countries.

Three-dimensional structural analysis reveals a Cdk5-mediated kinase cascade regulating hepatic biliary network branching in zebrafish

The intrahepatic biliary network is a highly branched three-dimensional network lined by biliary epithelial cells, but how its branching patterns are precisely established is not clear. We designed a new computer-based algorithm that quantitatively computes the structural differences of the three-dimensional networks. Utilizing the algorithm, we showed that inhibition of Cyclin-dependent kinase 5 (Cdk5) led to reduced branching in the intrahepatic biliary network in zebrafish. Further, we identified a previously unappreciated downstream kinase cascade regulated by Cdk5. Pharmacological manipulations of this downstream kinase cascade produced a crowded branching defect in the intrahepatic biliary network and influenced actin dynamics in biliary epithelial cells. We generated larvae carrying a mutation in cdk5 regulatory subunit 1a (cdk5r1a), an essential activator of Cdk5. cdk5r1a mutant larvae show similar branching defects as those observed in Cdk5 inhibitor-treated larvae. A small-molecule compound that interferes with the downstream kinase cascade rescued the mutant phenotype. These results provide new insights into branching morphogenesis of the intrahepatic biliary network.

tomm22 Knockdown-Mediated Hepatocyte Damages Elicit Both the Formation of Hybrid Hepatocytes and Biliary Conversion to Hepatocytes in Zebrafish Larvae

The liver has a highly regenerative capacity. In the normal liver, hepatocytes proliferate to restore lost liver mass. However, when hepatocyte proliferation is impaired, biliary epithelial cells (BECs) activate and contribute to hepatocytes. We previously reported in zebrafish that upon severe hepatocyte ablation, BECs extensively contribute to regenerated hepatocytes. It was also speculated that BEC-driven liver regeneration might occur in another zebrafish liver injury model in which temporary knockdown of the mitochondrial import gene tomm22 by morpholino antisense oligonucleotides (MO) induces hepatocyte death. Given the importance of multiple BEC-driven liver regeneration models for better elucidating the mechanisms underlying innate liver regeneration in the diseased liver, we hypothesized that BECs would contribute to hepatocytes in tomm22 MO-injected larvae. In this MO-based liver injury model, by tracing the lineage of BECs, we found that BECs significantly contributed to hepatocytes. Moreover, we found that surviving, preexisting hepatocytes become BEC-hepatocyte hybrid cells in tomm22 MO-injected larvae. Intriguingly, both the inhibition of Wnt/β-catenin signaling and macrophage ablation suppressed the formation of the hybrid hepatocytes. This new liver injury model in which both hepatocytes and BECs contribute to regenerated hepatocytes will aid in better understanding the mechanisms of innate liver regeneration in the diseased liver.

LITTLE FISH, BIG DATA: ZEBRAFISH AS A MODEL FOR CARDIOVASCULAR AND METABOLIC DISEASE

The burden of cardiovascular and metabolic diseases worldwide is staggering. The emergence of systems approaches in biology promises new therapies, faster and cheaper diagnostics, and personalized medicine. However, a profound understanding of pathogenic mechanisms at the cellular and molecular levels remains a fundamental requirement for discovery and therapeutics. Animal models of human disease are cornerstones of drug discovery as they allow identification of novel pharmacological targets by linking gene function with pathogenesis. The zebrafish model has been used for decades to study development and pathophysiology. More than ever, the specific strengths of the zebrafish model make it a prime partner in an age of discovery transformed by big-data approaches to genomics and disease. Zebrafish share a largely conserved physiology and anatomy with mammals. They allow a wide range of genetic manipulations, including the latest genome engineering approaches. They can be bred and studied with remarkable speed, enabling a range of large-scale phenotypic screens. Finally, zebrafish demonstrate an impressive regenerative capacity scientists hope to unlock in humans. Here, we provide a comprehensive guide on applications of zebrafish to investigate cardiovascular and metabolic diseases. We delineate advantages and limitations of zebrafish models of human disease and summarize their most significant contributions to understanding disease progression to date.

Using zebrafish to model liver diseases-Where do we stand?

Purpose of Review

The liver is the largest internal organ and performs both exocrine and endocrine function that is necessary for survival. Liver failure is among the leading causes of death and represents a major global health burden. Liver transplantation is the only effective treatment for end-stage liver diseases. Animal models advance our understanding of liver disease etiology and hold promise for the development of alternative therapies. Zebrafish has become an increasingly popular system for modeling liver diseases and complements the rodent models.

Recent Findings

The zebrafish liver contains main cell types that are found in mammalian liver and exhibits similar pathogenic responses to environmental insults and genetic mutations. Zebrafish have been used to model neonatal cholestasis, cholangiopathies, such as polycystic liver disease, alcoholic liver disease, and non-alcoholic fatty liver disease. It also provides a unique opportunity to study the plasticity of liver parenchymal cells during regeneration.

Summary

In this review, we summarize the recent work of building zebrafish models of liver diseases. We highlight how these studies have brought new knowledge of disease mechanisms. We also discuss the advantages and challenges of using zebrafish to model liver diseases.

Embryonic cholecystitis and defective gallbladder contraction in the Sox17-haploinsufficient mouse model of biliary atresia

The gallbladder excretes cytotoxic bile acids into the duodenum through the cystic duct and common bile duct system. Sox17 haploinsufficiency causes biliary atresia-like phenotypes and hepatitis in late organogenesis mouse embryos, but the molecular and cellular mechanisms underlying this remain unclear. In this study, transcriptomic analyses revealed the early onset of cholecystitis in Sox17^+/- embryos, together with the appearance of ectopic cystic duct-like epithelia in their gallbladders. The embryonic hepatitis showed positive correlations with the severity of cholecystitis in individual Sox17^+/- embryos. Embryonic hepatitis could be induced by conditional deletion of Sox17 in the primordial gallbladder epithelia but not in fetal liver hepatoblasts. The Sox17^+/- gallbladder also showed a drastic reduction in sonic hedgehog expression, leading to aberrant smooth muscle formation and defective contraction of the fetal gallbladder. The defective gallbladder contraction positively correlated with the severity of embryonic hepatitis in Sox17^+/- embryos, suggesting a potential contribution of embryonic cholecystitis and fetal gallbladder contraction in the early pathogenesis of congenital biliary atresia.

Making It New Again: Insight Into Liver Development, Regeneration, and Disease From Zebrafish Research

The adult liver of most vertebrates is predominantly comprised of hepatocytes. However, these cells must work in concert with biliary, stellate, vascular, and immune cells to accomplish the vast array of hepatic functions required for physiological homeostasis. Our understanding of liver development was accelerated as zebrafish emerged as an ideal vertebrate system to study embryogenesis. Through work in zebrafish and other models, it is now clear that the cells in the liver develop in a coordinated fashion during embryogenesis through a complex yet incompletely understood set of molecular guidelines. Zebrafish research has uncovered many key players that govern the acquisition of hepatic potential, cell fate, and plasticity. Although rare, some hepatobiliary diseases-especially biliary atresia-are caused by developmental defects; we discuss how research using zebrafish to study liver development has informed our understanding of and approaches to liver disease. The liver can be injured in response to an array of stressors including viral, mechanical/surgical, toxin-induced, immune-mediated, or inborn defects in metabolism. The liver has thus evolved the capacity to efficiently repair and regenerate. We discuss the emerging field of using zebrafish to study liver regeneration and highlight recent advances where zebrafish genetics and imaging approaches have provided novel insights into how cell plasticity contributes to liver regeneration.

Loss of a Candidate Biliary Atresia Susceptibility Gene, add3a, Causes Biliary Developmental Defects in Zebrafish

OBJECTIVES

Biliary atresia (BA) is a progressive fibroinflammatory cholangiopathy affecting the bile ducts of neonates. Although BA is the leading indication for pediatric liver transplantation, the etiology remains elusive. Adducin 3 (ADD3) and X-prolyl aminopeptidase 1 (XPNPEP1) are 2 genes previously identified in genome-wide association studies as potential BA susceptibility genes. Using zebrafish, we investigated the importance of ADD3 and XPNPEP1 in functional studies.

METHODS

To determine whether loss of either gene leads to biliary defects, we performed morpholino antisense oligonucleotide (MO) knockdown studies targeting add3a and xpnpep1 in zebrafish. Individuals were assessed for decreases in biliary function and the presence of biliary defects. Quantitative polymerase chain reaction was performed on pooled 5 days postfertilization larvae to assess variations in transcriptional expression of genes of interest.

RESULTS

Although both xpnpep1 and add3a are expressed in the developing zebrafish liver, only knockdown of add3a produced intrahepatic defects and decreased biliary function. Similar results were observed in homozygous add3a mutants. MO-mediated knockdown of add3a also showed higher mRNA expression of hedgehog (Hh) targets. Inhibition of Hh signaling rescued biliary defects caused by add3a knockdown. Combined knockdown of add3a and glypican-1 (gpc1), another mediator of Hh activity that is also a BA susceptibility gene, resulted in more severe biliary defects than knockdown of either alone.

CONCLUSIONS

Our results support previous studies identifying ADD3 as a putative genetic risk factor for BA susceptibility. Our results also provide evidence that add3a may be affecting the Hh pathway, an important factor in BA pathogenesis.

The toxin biliatresone causes mouse extrahepatic cholangiocyte damage and fibrosis through decreased glutathione and SOX17

Biliary atresia, the most common indication for pediatric liver transplantation, is a fibrotic disease of unknown etiology affecting the extrahepatic bile ducts of newborns. The recently described toxin biliatresone causes lumen obstruction in mouse cholangiocyte spheroids and represents a new model of biliary atresia. The goal of this study was to determine the cellular changes caused by biliatresone in mammalian cells that ultimately lead to biliary atresia and extrahepatic fibrosis. We treated mouse cholangiocytes in three-dimensional (3D) spheroid culture and neonatal extrahepatic duct explants with biliatresone and compounds that regulate glutathione (GSH). We examined the effects of biliatresone on SOX17 levels and determined the effects of Sox17 knockdown on cholangiocytes in 3D culture. We found that biliatresone caused disruption of cholangiocyte apical polarity and loss of monolayer integrity. Spheroids treated with biliatresone had increased permeability as shown by rhodamine efflux within 5 hours compared with untreated spheroids, which retained rhodamine for longer than 12 hours. Neonatal bile duct explants treated with the toxin showed lumen obstruction with increased subepithelial staining for α-smooth muscle actin and collagen, consistent with fibrosis. Biliatresone caused a rapid and transient decrease in GSH, which was both necessary and sufficient to mediate its effects in cholangiocyte spheroid and bile duct explant systems. It also caused a significant decrease in cholangiocyte levels of SOX17, and Sox17 knockdown in cholangiocyte spheroids mimicked the effects of biliatresone.

CONCLUSION

Biliatresone decreases GSH and SOX17 in mouse cholangiocytes. In 3D cell systems, this leads to cholangiocyte monolayer damage and increased permeability; in extrahepatic bile duct explants, it leads to disruption of the extrahepatic biliary tree and subepithelial fibrosis. This mechanism may be important in understanding human biliary atresia. (Hepatology 2016;64:880-893).

Glutathione antioxidant pathway activity and reserve determine toxicity and specificity of the biliary toxin biliatresone in zebrafish

Biliatresone is an electrophilic isoflavone isolated from Dysphania species plants that has been causatively linked to naturally occurring outbreaks of a biliary atresia (BA)-like disease in livestock. Biliatresone has selective toxicity for extrahepatic cholangiocytes (EHCs) in zebrafish larvae. To better understand its mechanism of toxicity, we performed transcriptional profiling of liver cells isolated from zebrafish larvae at the earliest stage of biliatresone-mediated biliary injury, with subsequent comparison of biliary and hepatocyte gene expression profiles. Transcripts encoded by genes involved in redox stress response, particularly those involved in glutathione (GSH) metabolism, were among the most prominently up-regulated in both cholangiocytes and hepatocytes of biliatresone-treated larvae. Consistent with these findings, hepatic GSH was depleted at the onset of biliary injury, and in situ mapping of the hepatic GSH redox potential using a redox-sensitive green fluorescent protein biosensor showed that it was significantly more oxidized in EHCs both before and after treatment with biliatresone. Pharmacological and genetic manipulation of GSH redox homeostasis confirmed the importance of GSH in modulating biliatresone-induced injury given that GSH depletion sensitized both EHCs and the otherwise resistant intrahepatic cholangiocytes to the toxin, whereas replenishing GSH level by N-acetylcysteine administration or activation of nuclear factor erythroid 2-like 2 (Nrf2), a transcriptional regulator of GSH synthesis, inhibited EHC injury.

CONCLUSION

These findings strongly support redox stress as a critical contributing factor in biliatresone-induced cholangiocyte injury, and suggest that variations in intrinsic stress responses underlie the susceptibility profile. Insufficient antioxidant capacity of EHCs may be critical to early pathogenesis of human BA. (Hepatology 2016;64:894-907).

Biliary atresia and other cholestatic childhood diseases: Advances and future challenges

Biliary Atresia and other cholestatic childhood diseases are rare conditions affecting the function and/or anatomy along the canalicular-bile duct continuum, characterised by onset of persistent cholestatic jaundice during the neonatal period. Biliary atresia (BA) is the most common among these, but still has an incidence of only 1 in 10-19,000 in Europe and North America. Other diseases such as the genetic conditions, Alagille syndrome (ALGS) and Progressive Familial Intrahepatic Cholestasis (PFIC), are less common. Choledochal malformations are amenable to surgical correction and require a high index of suspicion. The low incidence of such diseases hinder patient-based studies that include large cohorts, while the limited numbers of animal models of disease that recapitulate the spectrum of disease phenotypes hinders both basic research and the development of new treatments. Despite their individual rarity, collectively BA and other cholestatic childhood diseases are the commonest indications for liver transplantation during childhood. Here, we review the recent advances in basic research and clinical progress in these diseases, as well as the research needs. For the various diseases, we formulate current key questions and controversies and identify top priorities to guide future research.

Molecular mechanisms of Sox transcription factors during the development of liver, bile duct, and pancreas

The liver and pancreas are the prime digestive and metabolic organs in the body. After emerging from the neighboring domains of the foregut endoderm, they turn on distinct differentiation and morphogenesis programs that are regulated by hierarchies of transcription factors. Members of SOX family of transcription factors are expressed in the liver and pancreas throughout development and act upstream of other organ-specific transcription factors. They play key roles in maintaining stem cells and progenitors. They are also master regulators of cell fate determination and tissue morphogenesis. In this review, we summarize the current understanding of SOX transcription factors in mediating liver and pancreas development. We discuss their contribution to adult organ function, homeostasis and injury responses. We also speculate how the knowledge of SOX transcription factors can be applied to improve therapies for liver diseases and diabetes.

Histamine is correlated with liver fibrosis in biliary atresia

BACKGROUND AND AIMS

Biliary atresia (BA) is a severe neonatal cholestasis disease that is caused by obstruction of extra bile ducts. Liver fibrosis progresses dramatically in BA, and the underlying molecular mechanism is largely unknown.

METHODS

Amino acids and biogenic amines were quantified by targeted metabolomic methods in livers of 52 infants with BA and 16 infants with neonatal hepatitis syndrome (NHS). Normal adjacent nontumor liver tissues from 5 hepatoblastoma infants were used as controls. Orthogonal partial least-squares discriminant analysis was used to identify the differences between BA, NHS, and control tissues. Histamine metabolism enzymes and receptors were analyzed by immunohistochemistry and Western blot.

RESULTS

The orthogonal partial least-squares discriminant analysis clearly separated BA from NHS and the controls using amino acid and biogenic amine profiles. Histamine was significantly increased in the livers of BA infants and was positively correlated with the severity of fibrosis. This finding was supported by the elevated l-histidine decarboxylase and reduced monoamine oxidase type B expressions in the BA infants with severe fibrosis. Furthermore, histamine receptor H1 was observed in the cholangiocytes of BA livers.

CONCLUSIONS

Histamine was positively correlated with fibrosis and may be a potential target to prevent liver fibrosis in BA.

Biliary atresia: Clinical advances and perspectives

Biliary atresia (BA) is a rare and severe inflammatory and obliterative cholangiopathy that affects both extra- and intrahepatic bile ducts. BA symptoms occur shortly after birth with jaundice, pale stools and dark urines. The prognosis of BA has dramatically changed in the last decades: before the Kasai operation most BA patients died, while nowadays with the sequential treatment with Kasai operation±liver transplantation BA patient survival is close to 90%. Early diagnosis is very important since the chances of success of the Kasai procedure decrease with time. The causes of BA remain actually unknown but several mechanisms including genetic and immune dysregulation may probably lead to the obliterative cholangiopathy. Current research focuses on the identification of blood or liver factors linked to the pathogenesis of BA that could become therapeutic targets and avoid the need for liver transplantation. No similar disease leading to total obstruction of the biliary tree exists in older children or adults. But understanding the physiopathology of BA may highlight the mechanisms of other destructive cholangiopathies, such as sclerosing cholangitis.

Reactivity of Biliatresone, a Natural Biliary Toxin, with Glutathione, Histamine, and Amino Acids

In our previous work, we identified a natural toxin, biliatresone, from Dysphania glomulifera and D. littoralis, endemic plants associated with outbreaks of biliary atresia in Australian neonatal livestock. Biliatresone is a very rare isoflavonoid with an α-methylene ketone between two phenyls, 1,2-diaryl-2-propenone, along with methylenedioxy, dimethoxyl, and hydroxyl functional groups, that causes extrahepatic biliary toxicity in zebrafish. The toxic core of biliatresone is a methylene in the α-position relative to the ketone of 1,2-diaryl-2-propenone that serves as an electrophilic Michael acceptor. The α-methylene of biliatresone spontaneously conjugated with water and methanol (MeOH), respectively, via Michael addition in a reverse phase high-performance liquid chromatography (RP-HPLC) analysis. We here report the reactivity of biliatresone toward glutathione (GSH), several amino acids, and other thiol- or imidazole-containing biomolecules. LC-MS and HPLC analysis of the conjugation reaction showed the reactivity of biliatresone to be in the order histidine > N-acetyl-d-cysteine (D-NAC) = N-acetyl-l-cysteine (L-NAC) > histamine > glutathione ≥ cysteine ≫ glycine > glutamate > phenylalanine, while serine and adenine had no reactivity due to intramolecular hydrogen bonding in the protic solvents. The reactivity of ethyl vinyl ketone (EVK, 1-penten-3-one), an example of a highly reactive α,ß-unsaturated ketone, toward GSH gave a 6.7-fold lower reaction rate constant than that of biliatresone. The reaction rate constant of synthetic 1,2-diaryl-2-propen-1-one (DP), a core structure of the toxic molecule, was 10-fold and 1.5-fold weaker in potency compared to the reaction rate constants of biliatresone and EVK, respectively. These results demostrated that the methylenedioxy, dimethoxyl, and hydroxyl functional groups of biliatresone contribute to the stronger reactivity of the Michael acceptor α-methylene ketone toward nucleophiles compared to that of DP and EVK.

Zebrafish: an important tool for liver disease research

As the incidence of hepatobiliary diseases increases, we must improve our understanding of the molecular, cellular, and physiological factors that contribute to the pathogenesis of liver disease. Animal models help us identify disease mechanisms that might be targeted therapeutically. Zebrafish (Danio rerio) have traditionally been used to study embryonic development but are also important to the study of liver disease. Zebrafish embryos develop rapidly; all of their digestive organs are mature in larvae by 5 days of age. At this stage, they can develop hepatobiliary diseases caused by developmental defects or toxin- or ethanol-induced injury and manifest premalignant changes within weeks. Zebrafish are similar to humans in hepatic cellular composition, function, signaling, and response to injury as well as the cellular processes that mediate liver diseases. Genes are highly conserved between humans and zebrafish, making them a useful system to study the basic mechanisms of liver disease. We can perform genetic screens to identify novel genes involved in specific disease processes and chemical screens to identify pathways and compounds that act on specific processes. We review how studies of zebrafish have advanced our understanding of inherited and acquired liver diseases as well as liver cancer and regeneration.

Biliatresone, a Reactive Natural Toxin from Dysphania glomulifera and D. littoralis: Discovery of the Toxic Moiety 1,2-Diaryl-2-Propenone

We identified a reactive natural toxin, biliatresone, from Dysphania glomulifera and D. littoralis collected in Australia that produces extrahepatic biliary atresia in a zebrafish model. Three additional isoflavonoids, including the known isoflavone betavulgarin, were also isolated. Biliatresone is in the very rare 1,2-diaryl-2-propenone class of isoflavonoids. The α-methylene of the 1,2-diaryl-2-propenone of biliatresone spontaneously reacts via Michael addition in the formation of water and methanol adducts. The lethal dose of biliatresone in a zebrafish assay was 1 μg/mL, while the lethal dose of synthetic 1,2-diaryl-2-propen-1-one was 5 μg/mL, suggesting 1,2-diaryl-2-propenone as the toxic Michael acceptor.