The synthetic toxin biliatresone causes biliary atresia in mice

Single-cell transcription reveals hepatocyte-to-cholangiocyte reprogramming and biliary gene profile in biliary atresia

BACKGROUND

Ductular reaction (DR), characterized by the expansion of biliary epithelial cells in the portal area, is a typical hepatic pathology for biliary atresia (BA). The cellular source and function of DR remain poorly understood. Herein, we performed single-cell RNA sequencing (scRNA-seq) in BA to resolve the complexity of DR in BA.

METHODS

A total of 4 BA and 3 normal control livers underwent scRNA-seq. The epithelial cells were extracted from all cells for further analysis. The cell types, functions, and differentiational trajectory of epithelial cells were determined. The biliary markers and transcription factors (TFs) were identified by combing public bulk and scRNA-seq data and validated by immunohistochemistry.

RESULTS

ScRNA-seq identified the existence of biliary reprogramming in BA, and the reprogrammed cells expressed both hepatocyte and cholangiocyte markers. When compared with hepatocytes, genes of epithelial-mesenchymal transition, fibrosis, inflammation, and RNA metabolism were enriched in cholangiocytes and upregulated in BA. Pseudotime analysis depicted a differentiation trajectory from hepatocytes across reprogrammed cells to cholangiocytes in BA. Matrix metalloproteinase 7 (MMP7), VTCN1, and LAMC2 were identified as the biliary markers, and KLF5 and HNF1B were determined as the biliary TFs in BA. All the biliary markers and TFs were upregulated in BA when compared with controls.

CONCLUSIONS

Dissecting the cellular source and function of cholangiocytes is essential to understand the pathological role of DR in BA. The identified specific biliary markers and TFs provide important insights into its potential diagnosis and mechanism exploration for BA in the future.

Biliary atresia susceptibility gene EFEMP1 regulates extrahepatic bile duct elastic fiber formation and mechanics

Background & Aims

EGF-containing fibulin extracellular matrix protein 1 (EFEMP1, also called fibulin-3) is an extracellular matrix protein linked in a genome-wide association study to biliary atresia, a fibrotic disease of the neonatal extrahepatic bile duct. Fibulin-3 is deposited in most tissues and Efemp1 null mice have decreased elastic fibers in visceral fascia; however, fibulin-3 does not have a role in the development of large elastic fibers and its overall function in the extrahepatic bile ducts remains unclear.

Methods

We used staining and histology to define the amount and organization of key extracellular matrix components in the extrahepatic bile ducts. We also repurposed pressure myography, a technique heretofore applied to the vasculature, to determine the contribution of elastin and fibulin-3 to extrahepatic bile duct mechanics. We examined extrahepatic bile duct structure and mechanics in three models: neonatal vs. adult rat ducts (n = 6 each), elastase-treated adult rat ducts (n = 6-7 each), and Efemp1 +/- vs. wild-type mouse ducts (n = 6 each).

Results

We demonstrated that fibulin-3 is expressed in the submucosa of both neonatal and adult mouse, rat and human extrahepatic bile ducts and that, in adult Efemp1 +/- mouse ducts, elastin organization into fibers is decreased by approximately half. Pressure myography showed that Efemp1 +/- ducts have altered mechanics compared to control ducts, with Efemp1 +/- ducts displaying significant stretch compared to controls (p = 0.0376); these changes in stretch are similar to those observed in elastase-treated vs. normal ducts (p <0.0001) and in neonatal ducts vs. adult ducts (p <0.0001).

Conclusion

Fibulin-3 has an important role in the formation of elastic fibers and the mechanical properties of the extrahepatic bile duct. This provides functional relevance for the biliary atresia susceptibility gene EFEMP1.

Impact and implications

The gene EFEMP1 was found via a genome-wide association study to be a susceptibility gene for the neonatal disease biliary atresia. EFEMP1 encodes the protein fibulin-3, which regulates elastic fiber organization in the extrahepatic bile duct (EHBD), the major site of disease in biliary atresia. We showed that neonatal EHBDs as well as mice heterozygous for Efemp1 have decreased numbers of elastic fibers, and that this alters EHBD mechanics. This work is important for understanding the mechanism of biliary atresia, in particular susceptibility to obstruction.

Microcystin-RR is a biliary toxin selective for neonatal extrahepatic cholangiocytes

Background & Aims

Biliary atresia is a fibrosing cholangiopathy affecting neonates that is thought to result from a prenatal environmental insult to the bile duct. Biliatresone, a plant toxin with an α-methylene ketone group, was previously implicated in biliary atresia in Australian livestock, but is found in a limited location and is unlikely to be a significant human toxin. We hypothesized that other unsaturated carbonyl compounds, some with the potential for significant human exposure, might also be biliary toxins.

Methods

We focused on the family of microcystins, cyclic peptide toxins from blue-green algae that are found worldwide, particularly during harmful algal blooms. We used primary extrahepatic cholangiocyte spheroids and extrahepatic bile duct explants from both neonatal [a total of 86 postnatal day (P) 2 mouse pups and 18 P2 rat pups (n = 8-10 per condition for both species)] and adult rodents [a total of 31 P15-18 mice (n = 10 or 11 per condition)] to study the biliary toxicity of microcystins and potential mechanisms involved.

Results

Results showed that 400 nM microcystin (MC)-RR, but not six other microcystins or the related algal toxin nodularin, caused >80% lumen closure in cell spheroids made from extrahepatic cholangiocytes isolated from 2-3-day-old mice (p <0.0001). By contrast, 400 nM MC-RR resulted in less than an average 5% lumen closure in spheroids derived from neonatal intrahepatic cholangiocytes or cells from adult mice (p = 0.4366). In addition, MC-RR caused occlusion of extrahepatic bile duct explants from 2-day-old mice (p <0.0001), but not 18-day-old mice. MC-RR also caused a 2.3-times increase in reactive oxygen species in neonatal cholangiocytes (p <0.0001), and treatment with N-acetyl cysteine partially prevented microcystin-RR-induced lumen closure (p = 0.0004), suggesting a role for redox homeostasis in its mechanism of action.

Conclusions

We identified MC-RR as a selective neonatal extrahepatic cholangiocyte toxin and suggest that it acts by increasing redox stress.

Impact and implications

The plant toxin biliatresone causes a biliary atresia-like disease in livestock and vertebrate animal model systems. We tested the widespread blue-green algal toxin, microcystin-RR, another highly electrophilic unsaturated carbonyl compound that is released during harmful algal blooms, and found that it was also a biliary toxin with specificity for neonatal extrahepatic cholangiocytes. This work should drive further animal studies and, ultimately, studies to determine whether human exposure to microcystin-RR causes biliary atresia.

Generation of human induced pluripotent stem cell lines derived from patients of cystic biliary atresia

Biliary atresia (BA), resulting from abnormal development of the liver's internal or external bile ducts, can lead to liver damage and potentially fatal cirrhosis. Type I cystic biliary atresia is a relatively uncommon, but clinically significant variant of BA. It is critical to develop experimental models of BA to examine the etiology and pathogenesis, which remain elusive, and to develop future therapeutics. Here, we have successfully generated a panel of human induced pluripotent stem cells (hiPSCs) from five Japanese patients carrying type I cystic BA. These hiPSC lines exhibited characteristics of self-renewal and pluripotency. These cells held normal karyotypes mostly, but one of them carried hemizygous deletions, the clinical significance of which is unknown yet. Whole genome sequence analysis indicated that some of the mutations or single nucleotide polymorphisms (SNPs) commonly found in these patients are related to hepatobiliary abnormality. Given the limited understanding of the molecular pathogenesis of cystic BA, attributed to unknown factors of genetic and environmental causes, these cellular resources will be instrumental in replicating disease phenotypes and in advancing novel therapies for this disease.

Super-resolution imaging lysosome vesicles and establishing a gallbladder-visualizable zebrafish model via a fluorescence probe

Advanced probes for imaging viscous lipids microenvironment in vitro and in vivo are desirable for the study of membranous organelles and lipids traffic. Herein, a reaction-based dihydroquinoline probe (DCQ) was prepared via linking a diethylamino coumarin fluorophore with a N-methylquinoline moiety. DCQ is stable in low viscous aqueous mediums and exhibits green fluorescence, which undergoes fast autoxidation in high viscous mediums to form a fluorescent product with deep-red to near-infrared (NIR) emission, rendering the ability for dual-color imaging. Living cell imaging indicated that DCQ can effectively stain lysosomal membranes with deep-red fluorescence. Super-resolution imaging of lysosome vesicles has been achieved by DCQ and stimulated emission depletion (STED) microscopy. In addition, DCQ realizes multiple organs imaging in zebrafish, whose dual-color emission can perfectly discriminate zebrafish's yolk sac, digestive tract and gallbladder. Most importantly, DCQ has been successfully used to establish a gallbladder-visualizable zebrafish model for the evaluation of drug stress.

Mechanism of biliary atresia caused by T follicular helper cells-induced immune injury

BACKGROUND

Biliary atresia (BA) has diverse and unclear pathogenesis, which may be related to immune response in response to a foreign stimulus. T follicular helper (Tfh) cells have been found to play an important role in various immune diseases.

AIMS

To investigate the expression of Tfh cells in BA and non-BA cholestatic diseases in children.

METHODS

Transcriptome sequencing and Gene Ontology (GO) enrichment analysis were performed to investigate the differences in gene expression between the BA group and the non-BA cholestasis group. Study the distribution of Tfh cells in liver tissues of the BA and non-BA cholestatic groups through single sample gene set enrichment analysis (ssGSEA). Tfh cells (CD3+Bcl6+) in liver tissues from BA patients were labeled by double immunofluorescent staining to verify their distribution in the liver.

RESULTS

Transcriptome sequencing showed differences in gene expression between the BA group and the non-BA cholestasis group. A total of 808 genes were up-regulated and 405 genes were down-regulated in BA, suggesting that there might be a specific immune response in BA. GO enrichment analysis showed that BA group had augmented response to foreign stimulus and increased metabolic process compared to the non-BA cholestatic group. The relative proportion of immune cells was analyzed by ssGSEA method. The proportions of Tfh cells, activated B cells, CD4+ T cells, memory B cells and Th2 cells were higher in the BA group than in the non-BA cholestatic group. Fluorescence immunostaining showed that Tfh cells were significantly increased in liver tissue samples of the BA group compared to the non-BA cholestasis group, which was consistent with the transcriptome sequencing results.

CONCLUSION

Tfh cells share in immune cascade involvement in BA. Our work support immune pathogenesis of the in response to a stimulus that might be foreign in BA.

Biliary atresia: the role of gut microbiome, and microbial metabolites

Biliary atresia (BA) is a progressive fibroinflammatory disease affecting both the extrahepatic and intrahepatic bile ducts, potentially leading to chronic cholestasis and biliary cirrhosis. Despite its prevalence, the exact mechanisms behind BA development remain incompletely understood. Recent research suggests that the gut microbiota and its metabolites may play significant roles in BA development. This paper offers a comprehensive review of the changing characteristics of gut microbiota and their metabolites at different stages of BA in children. It discusses their influence on the host's inflammatory response, immune system, and bile acid metabolism. The review also explores the potential of gut microbiota and metabolites as a therapeutic target for BA, with interventions like butyrate and gut microbiota preparations showing promise in alleviating BA symptoms. While progress has been made, further research is necessary to untangle the complex interactions between gut microbiota and BA, paving the way for more effective prevention and treatment strategies for this challenging condition.

Biliary atresia

Biliary atresia (BA) is a progressive inflammatory fibrosclerosing disease of the biliary system and a major cause of neonatal cholestasis. It affects 1:5,000-20,000 live births, with the highest incidence in Asia. The pathogenesis is still unknown, but emerging research suggests a role for ciliary dysfunction, redox stress and hypoxia. The study of the underlying mechanisms can be conceptualized along the likely prenatal timing of an initial insult and the distinction between the injury and prenatal and postnatal responses to injury. Although still speculative, these emerging concepts, new diagnostic tools and early diagnosis might enable neoadjuvant therapy (possibly aimed at oxidative stress) before a Kasai portoenterostomy (KPE). This is particularly important, as timely KPE restores bile flow in only 50-75% of patients of whom many subsequently develop cholangitis, portal hypertension and progressive fibrosis; 60-75% of patients require liver transplantation by the age of 18 years. Early diagnosis, multidisciplinary management, centralization of surgery and optimized interventions for complications after KPE lead to better survival. Postoperative corticosteroid use has shown benefits, whereas the role of other adjuvant therapies remains to be evaluated. Continued research to better understand disease mechanisms is necessary to develop innovative treatments, including adjuvant therapies targeting the immune response, regenerative medicine approaches and new clinical tests to improve patient outcomes.

In Utero Extrahepatic Bile Duct Damage and Repair: Implications for Biliary Atresia

Biliary atresia (BA) is a cholangiopathy affecting the extrahepatic bile duct (EHBD) of newborns. The etiology and pathophysiology of BA are not fully understood; however, multiple causes of damage and obstruction of the neonatal EHBD have been identified. Initial damage to the EHBD likely occurs before birth. We discuss how different developmental stages in utero and birth itself could influence the susceptibility of the fetal EHBD to damage and a damaging wound-healing response. We propose that a damage-repair response of the fetal and neonatal EHBD involving redox stress and a program of fetal wound healing could-regardless of the cause of the initial damage-lead to either obstruction and BA or repair of the duct and recovery. This overarching concept should guide future research targeted toward identification of factors that contribute to recovery as opposed to progression of injury and fibrosis. Viewing BA through the lens of an in utero damage-repair response could open up new avenues for research and suggests exciting new therapeutic targets.

Low-dose biliatresone treatment of pregnant mice causes subclinical biliary disease in their offspring: Evidence for a spectrum of neonatal injury

Biliary atresia is a neonatal disease characterized by damage, inflammation, and fibrosis of the liver and bile ducts and by abnormal bile metabolism. It likely results from a prenatal environmental exposure that spares the mother and affects the fetus. Our aim was to develop a model of fetal injury by exposing pregnant mice to low-dose biliatresone, a plant toxin implicated in biliary atresia in livestock, and then to determine whether there was a hepatobiliary phenotype in their pups. Pregnant mice were treated orally with 15 mg/kg/d biliatresone for 2 days. Histology of the liver and bile ducts, serum bile acids, and liver immune cells of pups from treated mothers were analyzed at P5 and P21. Pups had no evidence of histological liver or bile duct injury or fibrosis at either timepoint. In addition, growth was normal. However, serum levels of glycocholic acid were elevated at P5, suggesting altered bile metabolism, and the serum bile acid profile became increasingly abnormal through P21, with enhanced glycine conjugation of bile acids. There was also immune cell activation observed in the liver at P21. These results suggest that prenatal exposure to low doses of an environmental toxin can cause subclinical disease including liver inflammation and aberrant bile metabolism even in the absence of histological changes. This finding suggests a wide potential spectrum of disease after fetal biliary injury.

Environmental Toxin Biliatresone-Induced Biliary Atresia-like Abnormal Cilia and Bile Duct Cell Development of Human Liver Organoids

Biliary atresia (BA) is a poorly understood and devastating obstructive bile duct disease of newborns. Biliatresone, a plant toxin, causes BA-like syndrome in some animals, but its relevance in humans is unknown. To validate the hypothesis that biliatresone exposure is a plausible BA disease mechanism in humans, we treated normal human liver organoids with biliatresone and addressed its adverse effects on organoid development, functions and cellular organization. The control organoids (without biliatresone) were well expanded and much bigger than biliatresone-treated organoids. Expression of the cholangiocyte marker CK19 was reduced, while the hepatocyte marker HFN4A was significantly elevated in biliatresone-treated organoids. ZO-1 (a tight junction marker) immunoreactivity was localized at the apical intercellular junctions in control organoids, while it was markedly reduced in biliatresone-treated organoids. Cytoskeleton F-actin was localized at the apical surface of the control organoids, but it was ectopically expressed at the apical and basal sides in biliatresone-treated organoids. Cholangiocytes of control organoids possess primary cilia and elicit cilia mechanosensory function. The number of ciliated cholangiocytes was reduced, and cilia mechanosensory function was hampered in biliatresone-treated organoids. In conclusion, biliatresone induces morphological and developmental changes in human liver organoids resembling those of our previously reported BA organoids, suggesting that environmental toxins could contribute to BA pathogenesis.

Immune-mediated cholangiopathies in children: the need to better understand the pathophysiology for finding the future possible treatment targets

Cholangiopathies are defined as focal or extensive damage of the bile ducts. According to the pathogenetic mechanism, it may be immune-mediated or due to genetic, infectious, toxic, vascular, and obstructive causes. Their chronic evolution is characterized by inflammation, obstruction of bile flow, cholangiocyte proliferation, and progression toward fibrosis and cirrhosis. Immune-mediated cholangiopathies comprise primary sclerosing cholangitis (PSC), autoimmune cholangitis and IgG4-associated cholangitis in adults and biliary atresia (BA), neonatal sclerosing cholangitis (NSC) in children. The main purpose of this narrative review was to highlight the similarities and differences among immune-mediated cholangiopathies, especially those frequent in children in which cholangiocyte senescence plays a key role (BA, NSC, and PSC). These three entities have many similarities in terms of clinical and histopathological manifestations, and the distinction between them can be hard to achieve. In BA, bile duct destruction occurs due to aggression of the biliary cells due to viral infections or toxins during the intrauterine period or immediately after birth. The consequence is the activation of the immune system leading to severe inflammation and fibrosis of the extrahepatic biliary tract, lumen stenosis, and impairment of the biliary flow. PSC is characterized by inflammation and fibrosis of intra- and extrahepatic bile ducts, leading to secondary biliary cirrhosis. It is a multifactorial disease that occurs because of genetic predisposition [human leukocyte antigen (HLA) and non-HLA haplotypes], autoimmunity (cellular immune response, autoantibodies, association with inflammatory bowel disease), environmental factors (infections or toxic bile), and host factors (intestinal microbiota). NSC seems to be a distinct subgroup of childhood PSC that appears due to the interaction between genetic predisposition (HLA B8 and DR3) and the disruption of the immune system, validated by elevated IgG levels or specific antibodies [antinuclear antibody (ANA), anti-smooth muscle antibody (ASMA)]. Currently, the exact mechanism of immune cholangiopathy is not fully understood, and further data are required to identify individuals at high risk of developing these conditions. A better understanding of the immune mechanisms and pathophysiology of BA, NSC, and PSC will open new perspectives for future treatments and better methods of preventing severe evolution.

Zebrafish as a Useful Model System for Human Liver Disease

Liver diseases represent a significant global health challenge, thereby necessitating extensive research to understand their intricate complexities and to develop effective treatments. In this context, zebrafish (Danio rerio) have emerged as a valuable model organism for studying various aspects of liver disease. The zebrafish liver has striking similarities to the human liver in terms of structure, function, and regenerative capacity. Researchers have successfully induced liver damage in zebrafish using chemical toxins, genetic manipulation, and other methods, thereby allowing the study of disease mechanisms and the progression of liver disease. Zebrafish embryos or larvae, with their transparency and rapid development, provide a unique opportunity for high-throughput drug screening and the identification of potential therapeutics. This review highlights how research on zebrafish has provided valuable insights into the pathological mechanisms of human liver disease.

Microcystin-RR is a biliary toxin selective for neonatal cholangiocytes

BACKGROUND AND AIMS

Biliary atresia is a fibrosing cholangiopathy affecting neonates that is thought to be caused by a prenatal environmental insult to the bile duct. Biliatresone, a plant toxin with an α-methylene ketone group, was previously implicated in toxin-induced biliary atresia in Australian livestock, but is found in a limited location and is highly unlikely to be a significant human toxin. We hypothesized that other molecules with α-methylene ketone groups, some with the potential for significant human exposure, might also be biliary toxins.

APPROACH AND RESULTS

We focused on the family of microcystins, cyclic peptide toxins from blue-green algae that have an α-methylene ketone group and are found worldwide, particularly during harmful algal blooms. We found that microcystin-RR, but not 6 other microcystins, caused damage to cell spheroids made using cholangiocytes isolated from 2-3-day-old mice, but not from adult mice. We also found that microcystin-RR caused occlusion of extrahepatic bile duct explants from 2-day-old mice, but not 18-day-old mice. Microcystin-RR caused elevated reactive oxygen species in neonatal cholangiocytes, and treatment with N-acetyl cysteine partially prevented microcystin-RRinduced lumen closure, suggesting a role for redox homeostasis in its mechanism of action.

CONCLUSIONS

This study highlights the potential for environmental toxins to cause neonatal biliary disease and identifies microcystin-RR acting via increased redox stress as a possible neonatal bile duct toxin.

Biliatresone induces cholangiopathy in C57BL/6J neonates

Exposure to plant toxins or microbiota that are able to digest common food ingredients to toxic structures might be responsible for biliary atresia (BA). An isoflavonoid, biliatresone is known to effectively alter the extrahepatic bile duct (EHBD) development in BALB/c mice. Biliatresone causes a reduction of Glutathione (GSH) levels, SOX17 downregulation and is effectively countered with N-Acetyl-L-cysteine treatment in vitro. Therefore, reversing GSH-loss appears to be a promising treatment target for a translational approach. Since BALB/c mice have been described as sensitive in various models, we evaluated the toxic effect of biliatresone in robust C57BL/6J mice and confirmed its toxicity. Comparison between BALB/c and C57BL/6J mice revealed similarity in the toxic model. Affected neonates exhibited clinical symptoms of BA, such as jaundice, ascites, clay-colored stools, yellow urine and impaired weight gain. The gallbladders of jaundiced neonates were hydropic and EHBD were twisted and enlarged. Serum and histological analysis proved cholestasis. No anomalies were seen in the liver and EHBD of control animals. With our study we join a chain of evidence confirming that biliatresone is an effective agent for cross-lineage targeted alteration of the EHBD system.

Biliatresone: progress in biliary atresia study

BACKGROUND

Biliary atresia (BA) is one of the main causes of neonatal end-stage liver disease. Without timely diagnosis and treatment, most children with BA will develop irreversible liver fibrosis within the first two months. While current theorized causes of BA include viral infection, immune disorders, and genetic defects, the comprehensive etiology is still largely unknown. Recently, biliatresone attracted much interest for its ability to induce BA in both zebrafish and mice, so we summarized the latest progress of biliatresone research in BA and tried to answer the question of whether it could provide further clues to the etiology of human BA.

DATA SOURCES

We conducted a PubMed search for any published articles related to the topic using search terms including "biliary atresia", "biliatresone", "GSH", and "HSP90". Relevant data were extracted from the original text or supplementary materials of the corresponding articles.

RESULTS

Biliatresone had shown its unique toxicity in multiple species such as zebrafish and mice, and pathogenic factors involved included glutathione (GSH), heat shock protein 90 (HSP90) and the related pathways. In combination with epidemiological evidence and recent studies on the intestinal flora in biliary atresia, a new pathogenic hypothesis that the occurrence of biliary atresia is partly due to biliatresone or its structure-like compounds depositing in human body via vegetables or/and the altered intestinal flora structure can be tentatively established.

CONCLUSIONS

Based on the existing evidence, we emphasized that GSH and HSP90 are involved in the development of BA, and the maternal diet, especially higher vegetable intake of Asian women of childbearing age, accompanied by the altered intestinal flora structure, may contribute to the occurrence of biliary atresia and the higher incidence in the Asia group. However, the evidence from large sample epidemiological research is necessary.

Incidence of Isolated Biliary Atresia during the COVID Lockdown in Europe: Results from a Collaborative Project by RARE-Liver

BACKGROUND

Biliary atresia (BA) is a rare cholangiopathy where one of the proposed aetiological mechanisms is an infectious viral trigger. Coronavirus disease-19 (COVID) lockdown restrictions were implemented to reduce the transmission of infections. Strictness of lockdown varied across European countries. This study aimed to investigate if there was an association between strictness of lockdown and change in isolated BA (IBA) incidence in Europe.

METHODS

We approached European centres involved in the European Reference Network RARE-LIVER. We included IBA patients born between 2015 and June 2020. We calculated the number of IBA patients born per centre per month. The Stringency Index (SI) was used as lockdown strictness indicator. The association between percentage change of mean number of IBA patients born per month and the SI was assessed.

RESULTS

We included 412 IBA patients from thirteen different centres. The median number of patients per month did not change: 6 (1-15) pre-lockdown and 7 (6-9) during lockdown (p = 0.34). There was an inverse association between SI and percentage change in IBA (B = -0.73, p = 0.03). Median age at Kasai portoenterostomy (days) did not differ between time periods (51 (9-179) vs. 53 (19-126), p = 0.73).

CONCLUSION

In this European study, a stricter COVID-lockdown was seemingly accompanied by a simultaneous larger decrease in the number of IBA patients born per month in the lockdown. Results should be interpreted with caution due to the assumptions and limitations of the analysis.

Biliary Atresia in Children: Update on Disease Mechanism, Therapies, and Patient Outcomes

Biliary atresia is a rare disease but remains the most common indication for pediatric liver transplantation as there are no effective medical therapies to slow progression after diagnosis. Variable contribution of genetic, immune, and environmental factors contributes to disease heterogeneity among patients with biliary atresia. Developing a deeper understanding of the disease mechanism will help to develop targeted medical therapies and improve patient outcomes.

Biliary Atresia Animal Models: Is the Needle in a Haystack?

Biliary atresia (BA) is a progressive fibro-obliterative process with a variable degree of inflammation involving the hepatobiliary system. Its consequences are incalculable for the patients, the affected families, relatives, and the healthcare system. Scientific communities have identified a rate of about 1 case per 10,000-20,000 live births, but the percentage may be higher, considering the late diagnoses. The etiology is heterogeneous. BA, which is considered in half of the causes leading to orthotopic liver transplantation, occurs in primates and non-primates. To consolidate any model, (1) more transport and cell membrane studies are needed to identify the exact mechanism of noxa-related hepatotoxicity; (2) an online platform may be key to share data from pilot projects and new techniques; and (3) the introduction of differentially expressed genes may be useful in investigating the liver metabolism to target the most intricate bilio-toxic effects of pharmaceutical drugs and toxins. As a challenge, such methodologies are still limited to very few centers, making the identification of highly functional animal models like finding a "needle in a haystack". This review compiles models from the haystack and hopes that a combinatorial search will eventually be the root for a successful pathway.

Biliary Atresia: A Complex Hepatobiliary Disease with Variable Gene Involvement, Diagnostic Procedures, and Prognosis

The diagnosis of biliary atresia is still terrifying at the 3rd decade of the 21st century. In a department of neonatal intensive care unit, parents and physicians face a challenge with a jaundiced baby, who may or may not have a surgically correctable hepatopathy. The approach has been systematically evaluated, but the etiology remains ambiguous. The study of families with recurrent biliary atresia has been undertaken at a molecular level. The primary interest with this disease is to identify the etiology and change the treatment from symptomatic to curative. The occurrence of this obstructive cholangio-hepatopathy in well-known genetic syndromes has suggested just coincidental finding, but the reality can be more intriguing because some of these diseases may have some interaction with the development of the intrahepatic biliary system. Several genes have been investigated thoroughly, including ADD3 and GPC1 shifting the interest from viruses to genetics. In this review, the intriguing complexities of this hepatobiliary disease are highlighted.

Biliary Atresia - emerging diagnostic and therapy opportunities

Biliary Atresia is a devastating pediatric cholangiopathy affecting the bile ducts of the liver. In this review, we describe recent progress in the understanding of liver development with a focus on cholangiocyte differentiation and how use of technical platforms, including rodent, zebrafish and organoid models, advances our understanding of Biliary Atresia. This is followed by a description of potential pathomechanisms, such as autoimmune responses, inflammation, disturbed apical-basal cell polarity, primary cilia dysfunction as well as beta-amyloid accumulation. Finally, we describe current and emerging diagnostic opportunities and recent translation breakthroughs for Biliary Atresia in the area of emerging therapy development, including immunomodulation and organoid-based systems for liver and bile duct repair.

Current Concepts of Biliary Atresia and Matrix Metalloproteinase-7: A Review of Literature

Biliary atresia (BA) is a rare cholangiopathy of infancy in which the bile ducts obliterate, leading to profound cholestasis and liver fibrosis. BA is hypothesized to be caused by a viral insult that leads to over-activation of the immune system. Patients with BA are surgically treated with a Kasai portoenterostomy (KPE), which aims to restore bile flow from the liver to the intestines. After KPE, progressive liver fibrosis is often observed in BA patients, even despite surgical success and clearance of their jaundice. The innate immune response is involved during the initial damage to the cholangiocytes and further differentiation of the adaptive immune response into a T-helper 1 cell (Th1) response. Multiple studies have shown that there is continuing elevation of involved cytokines that can lead to the progressive liver fibrosis. However, the mechanism by which the progressive injury occurs is not fully elucidated. Recently, matrix metalloproteinase-7 (MMP-7) has been investigated to be used as a biomarker to diagnose BA. MMPs are involved in extracellular matrix (ECM) turnover, but also have non-ECM related functions. The role of MMP-7 and other MMPs in liver fibrosis is just starting to be elucidated. Multiple studies have shown that serum MMP-7 measurements are able to accurately diagnose BA in a cohort of cholestatic patients while hepatic MMP-7 expression correlated with BA-related liver fibrosis. While the mechanism by which MMP-7 can be involved in the pathophysiology of BA is unclear, MMP-7 has been investigated in other fibrotic pathologies such as renal and idiopathic pulmonary fibrosis. MMP-7 is involved in Wnt/β-catenin signaling, reducing cell-to-cell contact by shedding of E-cadherin, amplifying inflammation and fibrosis via osteopontin (OPN) and TNF-α while it also appears to play a role in induction of angiogenesis This review aims to describe the current understandings of the pathophysiology of BA. Subsequently, we describe how MMP-7 is involved in other pathologies, such as renal and pulmonary fibrosis. Then, we propose how MMP-7 can potentially be involved in BA. By doing this, we aim to describe the putative role of MMP-7 as a prognostic biomarker in BA and to provide possible new therapeutic and research targets that can be investigated in the future.

A novel model of injured liver ductal organoids to investigate cholangiocyte apoptosis with relevance to biliary atresia

PURPOSE

The fibrogenic process in cholangiopathic diseases such as biliary atresia (BA) involves bile duct injury and apoptosis of cholangiocytes, which leads to the progression of liver fibrosis into liver cirrhosis and can result in end-staged liver disease. Recent advances in the development of organoids or mini-organ structures have allowed us to create an ex vivo injury model of the bile duct that mimics bile duct injury in BA. The aim of this experimental study was to develop a novel model of injured intrahepatic cholangiocytes as this can be relevant to BA. Our new model is important for studying the pathophysiological response of bile ducts to injury and the role of cholangiocytes in initiating the fibrogenic cascade. In addition, it has the potential to be used as a tool for developing new treatment strategies for BA.

METHODS

Liver ductal organoids were generated from the liver of healthy neonatal mouse pups. Intrahepatic bile duct fragments were isolated and cultured in Matrigel dome. Injury was induced in the organoids by administration of acetaminophen in culture medium. The organoids were then evaluated for fibrogenic cytokines expression, cell apoptosis marker and cell proliferation marker.

RESULTS

Organoids generated from intrahepatic bile duct fragments organized themselves into single-layer epithelial spheroids with lumen on the inside mimicking in vivo bile ducts. After 24-h exposure to acetaminophen, cholangiocytes in the organoids responded to the injury by increasing expression of fibrogenic cytokines, transforming growth factor beta-1 (TGF-β1) and platelet-derived growth factor-BB (PDGF-BB). This fibrogenic response of injured organoids was associated with increased cholangiocyte apoptosis and decreased cholangiocyte proliferation.

CONCLUSION

To our knowledge this is the first description of cholangiocyte injury in the organoids derived from intrahepatic bile ducts. Our injury model demonstrated that cholangiocyte apoptosis and its fibrogenic response may play a role in initiation of the fibrogenic process in cholangiopathic diseases such as BA. These findings are important for the development of novel therapy to reduce cholangiocyte apoptosis and to halt the early fibrogenic cascade in liver fibrogenesis. This novel injury model can prove very valuable for future research in biliary atresia.