Morphologic findings in progressive familial intrahepatic cholestasis 2 (PFIC2): correlation with genetic and immunohistochemical studies

What's new in pediatric genetic cholestatic liver disease: advances in etiology, diagnostics and therapeutic approaches

PURPOSE OF REVIEW

To highlight recent advances in pediatric cholestatic liver disease, including promising novel prognostic markers and new therapies.

FINDINGS

Additional genetic variants associated with the progressive familial intrahepatic cholestasis (PFIC) phenotype and new genetic cholangiopathies, with an emerging role of ciliopathy genes, are increasingly being identified. Genotype severity predicts outcomes in bile salt export pump (BSEP) deficiency, and post-biliary diversion serum bile acid levels significantly affect native liver survival in BSEP and progressive familial intrahepatic cholestasis type 1 (FIC1 deficiency) patients. Heterozygous variants in the MDR3 gene have been associated with various cholestatic liver disease phenotypes in adults. Ileal bile acid transporter (IBAT) inhibitors, approved for pruritus in PFIC and Alagille Syndrome (ALGS), have been associated with improved long-term quality of life and event-free survival.

SUMMARY

Next-generation sequencing (NGS) technologies have revolutionized diagnostic approaches, while discovery of new intracellular signaling pathways show promise in identifying therapeutic targets and personalized strategies. Bile acids may play a significant role in hepatic damage progression, suggesting their monitoring could guide cholestatic liver disease management. IBAT inhibitors should be incorporated early into routine management algorithms for pruritus. Data are emerging as to whether IBAT inhibitors are impacting disease biology and modifying the natural history of the cholestasis.

Emerging drugs for the treatment of progressive familial intrahepatic cholestasis: a focus on phase II and III trials

INTRODUCTION

Progressive familial intrahepatic cholestasis (PFIC) is a group of disorders characterized by inappropriate bile formation, causing hepatic accumulation of bile acids and, subsequently, liver injury. Until recently, no approved treatments were available for these patients.

AREAS COVERED

Recent clinical trials for PFIC treatment have focused on intestine-restricted ileal bile acid transporter (IBAT) inhibitors. These compounds aim to reduce the pool size of bile acids by interrupting their enterohepatic circulation. Other emerging treatments in the pipeline include systemic IBAT inhibitors, synthetic bile acid derivatives, compounds targeting bile acid synthesis via the FXR/FGF axis, and chaperones/potentiators that aim to enhance the residual activity of the mutated transporters.

EXPERT OPINION

Substantial progress has been made in drug development for PFIC patients during the last couple of years. Although data concerning long-term efficacy are as yet only scarcely available, new therapies have demonstrated robust efficacy in a considerable fraction of patients at least on the shorter term. However, a substantial fraction of PFIC patients do not respond to these novel therapies and thus still requires surgical treatment, including liver transplantation before adulthood. Hence, there is still an unmet medical need for long-term effective medical, preferably non-surgical, treatment for all PFIC patients.

The spectrum of novel ABCB11 gene variations in children with progressive familial intrahepatic cholestasis type 2 in Pakistani cohorts

Progressive familial intrahepatic cholestasis (PFIC) is a rare childhood manifested disease associated with impaired bile secretion with severe pruritus yellow stool, and sometimes hepatosplenomegaly. PFIC is caused by mutations in ATP8B1, ABCB11, ABCB4, TJP2, NR1H4, SLC51A, USP53, KIF12, ZFYVE19, and MYO5B genes depending on its type. ABCB11 mutations lead to PFIC2 that encodes the bile salt export pump (BSEP). Different mutations of ABCB11 have been reported in different population groups but no data available in Pakistani population being a consanguineous one. We sequenced coding exons of the ABCB11 gene along with its flanking regions in 66 unrelated Pakistani children along with parents with PFIC2 phenotype. We identified 20 variations of ABCB11: 12 in homozygous form, one compound heterozygous, and seven heterozygous. These variants include 11 missenses, two frameshifts, two nonsense mutations, and five splicing variants. Seven variants are novel candidate variants and are not detected in any of the 120 chromosomes from normal ethnically matched individuals. Insilico analysis revealed that four homozygous missense variations have high pathogenic scores. Minigene analysis of splicing variants showed exon skipping and the addition of exon. This data is a useful addition to the disease variants genomic database and would be used in the future to build a diagnostic algorithm.

Intrahepatic Cholestasis, Refractory Epilepsy, Skeletal Dysplasia, Endocrine Failure, and Dysmorphic Features in a Child With a Monoallelic 2q24-32.2 Deletion Encompassing ABCB11

We report a newborn who presented with multiple limb and facial anomalies, endocrine disorders, and progressively worsening low-GGT cholestasis. A liver biopsy revealed hepatocellular cholestasis with giant cell transformation. Immunohistochemical staining revealed complete absence of BSEP protein compared to control liver. A large 2q24-32.2 deletion leading to loss of 78 OMIM genes. Multiple structural anomalies, epilepsy and endocrine anomalies have been described with hemizygous loss of these genes. This deletion also resulted in complete heterozygous deletion of ABCB11, which encodes the bile salt export pump (BSEP). Genetic analysis did not reveal any pathogenic variants, deletions, or duplications in the other ABCB11 allele. A heterozygous variant in NR1H4, which causes the autosomal recessive progressive familial intrahepatic cholestasis type 5, was also detected. The possible explanations for the PFIC type 2 phenotype in heterozygous loss of ABCB11 include genetic modifiers or di-genic disease with a compound ABCB11 deletion and an NR1H4 missense variant; or undetected pathogenic variants in the other ABCB11 or NR1H4 alleles.

Hemolysis in Early Infancy: Still a Cause of Cholestatic Neonatal Giant Cell Hepatitis

Before the prophylactic use of anti-D antibodies in pregnancy, hemolytic anemia of the newborn was the most common cause of hyperbilirubinemia. Nowadays, given the rarity of hemolytic anemia of the newborn, hepatobiliary abnormalities, perinatal infections, and metabolic disorders have become the most common conditions in the differential diagnosis of neonatal cholestasis. Here, we report 3 instances of cholestatic giant cell hepatitis in 3 infants who had Coombs' positive hemolysis due to ABO incompatibility in 1, Rh incompatibility in another, and combined ABO and Rh incompatibility in the third. Although rare, cholestatic neonatal giant cell hepatitis associated with hemolysis still needs to be considered in patients with neonatal cholestasis. A marked elevation of aspartate aminotransferase over alanine aminotransferase can be a helpful clue to an early diagnosis.

The many facets of bile acids in the physiology and pathophysiology of the human liver

Bile acids perform vital functions in the human liver and are the essential component of bile. It is therefore not surprising that the biology of bile acids is extremely complex, regulated on different levels, and involves soluble and membrane receptors as well as transporters. Hereditary disorders of these proteins manifest in different pathophysiological processes that result in liver diseases of varying severity. In this review, we summarize our current knowledge of the physiology and pathophysiology of bile acids with an emphasis on recently established analytical approaches as well as the molecular mechanisms that underlie signaling and transport of bile acids. In this review, we will focus on ABC transporters of the canalicular membrane and their associated diseases. As the G protein-coupled receptor, TGR5, receives increasing attention, we have included aspects of this receptor and its interaction with bile acids.

Dialogs in the assessment of neonatal cholestatic liver disease

Neonatal cholestatic liver disease is rarely encountered by pathologists outside of specialized pediatric centers and navigating the long list of potential diseases can be daunting. However, the differential diagnosis can be rapidly narrowed through open conversations between the pathologist and pediatric gastroenterologist. The dialog should ideally begin before obtaining the liver biopsy and continue through the rendering of the final pathologic diagnosis. Such dialogs are necessary to first ensure the proper handling of the precious sample and then to allow for synthesis of the clinical, laboratory, imaging, and genetic data in the context of the histologic features seen in the liver biopsy. In this review, we aim to provide a broad template on which such dialogs may be based and pitfalls that may be encountered on both the clinical and pathologic sides. This review will focus on non-biliary atresia etiologies of neonatal cholestasis, including select infectious, genetic, and metabolic entities.

Structure and Function of Hepatobiliary ATP Binding Cassette Transporters

The liver is beyond any doubt the most important metabolic organ of the human body. This function requires an intensive crosstalk within liver cellular structures, but also with other organs. Membrane transport proteins are therefore of upmost importance as they represent the sensors and mediators that shuttle signals from outside to the inside of liver cells and/or vice versa. In this review, we summarize the known literature of liver transport proteins with a clear emphasis on functional and structural information on ATP binding cassette (ABC) transporters, which are expressed in the human liver. These primary active membrane transporters form one of the largest families of membrane proteins. In the liver, they play an essential role in for example bile formation or xenobiotic export. Our review provides a state of the art and comprehensive summary of the current knowledge of hepatobiliary ABC transporters. Clearly, our knowledge has improved with a breath-taking speed over the last few years and will expand further. Thus, this review will provide the status quo and will lay the foundation for new and exciting avenues in liver membrane transporter research.

Histological demonstration of BSEP/ABCB11 inhibition in transient neonatal cholestasis: a case report

BACKGROUND

Idiopathic or transient neonatal cholestasis (TNC) represents a group of cholestatic disorders with unidentified origin and remains a diagnosis of exclusion. Dysfunction of hepatobiliary transporters mediating excretion of biliary constituents from hepatocytes may play a central role in the pathogenesis of cholestasis. Despite variants of bile salt (BS) export pump (BSEP/ABCB11) have already been described in TNC, the pathogenic role of BSEP dysfunction in TNC remained so far elusive.

CASE PRESENTATION

We report on a newly-identified heterozygous ABCB11 missense variant (c.1345G > A, p.Glu449Lys) which was associated with prolonged cholestasis in a term infant after a complicated neonatal period. Moreover, we show for the first time almost completely abolished BSEP expression on the hepatocellular membrane in TNC.

CONCLUSION

This report demonstrates for the first time a close association between the prolonged cholestasis in infancy and impaired BSEP expression on the hepatocyte canalicular membrane in a heterozygous carrier of newly-identified ABCB11 variant.

Proposal of a liver histology-based scoring system for bile salt export pump deficiency

AIM

Bile salt export pump (BSEP) deficiency manifests a form of progressive intrahepatic cholestasis. This study aimed to establish a scoring system of liver histology for the uncommon genetic condition.

METHODS

After a roundtable discussion and histology review, a scoring system for BSEP deficiency was established. Eleven tissue samples were independently evaluated by three pathologists based on the proposed standard for an interobserver agreement analysis. In four cases with serial tissue samples available, correlation between changes in histology scores and clinical outcome was examined.

RESULTS

Of 14 initially listed histopathological findings, 12 were selected for scoring and grouped into the following four categories: cholestasis, parenchymal changes, portal tract changes and fibrosis. Each category consisted of two to four microscopic findings that were further divided into three to six scores; therefore, each category had a maximum score of 8-11. Interobserver agreement was highest for pericellular fibrosis (κ = 0.849) and lowest for hepatocellular cholestasis (κ = 0.241) with the mean and median κ values of the 12 parameters being 0.561 and 0.602, respectively. For two patients whose clinical features worsened, score changes between two time points were interpreted as deteriorated. In two patients, who showed a good clinical response to preprandial treatment with sodium 4-phenylbutyrate, histological changes were evaluated as improved or unchanged.

CONCLUSIONS

The proposed histology-based scoring system for BSEP deficiency with moderate interobserver agreement may be useful not only for monitoring microscopic changes in clinical practice but also for a surrogate endpoint in clinical trials.

Phenotype-Genotype Correlation of North Indian Progressive Familial Intrahepatic Cholestasis type2 Children Shows p.Val444Ala and p.Asn591Ser Variants and Retained BSEP Expression

Backgrounds and Aims: Progressive familial intrahepatic cholestasis type 2 (PFIC2) is caused by a defect or deficiency of bile salt export protein (BSEP) due to mutation in the ABCB11 gene. We intend to evaluate the phenotype-genotype correlation in 10 diagnosed cases of PFIC2 in a single tertiary care center in North India. Methods: The clinical, biochemical, histopathological, immunohistochemical, ultrastructural and genetic data of the 10 diagnosed cases of PFIC2 were recorded. Results: Icterus, pruritus and bleeding manifestations were the commonest clinical symptoms. Giant cell transformation was seen in 50% of the patients. Two predominant genetic variants were ABCB11 missense p.Val444Ala (c. 1331 T > C) and ABCB11 missense p.Asn591Ser (c. 1772 A > G) in their homozygous or compound heterozygous states and were associated with retained BSEP immunopositivity and reduced but retained BSEP immunopositivity respectively. Conclusion: Retention of BSEP is common in North Indian children of PFIC2 with no phenotype-genotype correlation.

Combination of Novel c.3484G> T/p.Glu162Ter Variant in ABCB11 and c.208G> A/p.Asp70Asn Variant in ATP8B1 Are Associated with Severe Symptoms in Progressive Family Intrahepatic Cholestasis

Progressive family intrahepatic cholestasis (PFIC) is an autosomal recessive disease that causes chronic cholestasis. It is associated with pathogenic variants in genes that encode proteins involved in bile secretion to canaliculus from hepatocytes. In this study, we present a 16-year-old boy who presented with severe pruritus and cholestatic jaundice. All possible infectious etiologies were negative. A liver biopsy was consistent with intrahepatic cholestasis and portal fibrosis. DNA was isolated from a peripheral blood sample, and whole exome sequencing was performed. A novel c.3484G > T/p.Glu162Ter variant in the ABCB11 gene and a c.208G> A/p.Asp70Asn variant in the ATP8B1 gene were detected. Despite traditional treatment, the patient's recurrent severe symptoms did not improve. The patient was referred for a liver transplantation. This novel c.3484G > T/p.Glu162Ter variant is associated with a severe and recurrent presentation, and the two compound variants could explain the severity of PFIC.

TJP2 hepatobiliary disorders: Novel variants and clinical diversity

To assess the spectrum of pediatric clinical phenotypes in TJP2 disease, we reviewed records of our seven patients in whom intrahepatic cholestasis was associated with biallelic TJP2 variants (13; 12 novel) and correlated clinical manifestations with mutation type. The effect of a splicing variant was analyzed with a minigene assay. The effects of three missense variants were analyzed with protein expression in vitro. Our patients had both remitting and persistent cholestasis. Three exhibited growth retardation. Six responded to treatment with cholestyramine, ursodeoxycholic acid, or both. Two had cholecystolithiasis. None required liver transplantation or developed hepatocellular or cholangiocellular malignancy. None manifested extrahepatic disease not attributable to effects of cholestasis. The variant c.2180-5T>G resulted in exon 15 skipping with in-frame deletion of 32 amino acid residues in TJP2. The three missense variants decreased but did not abolish TJP2 expression. Patients with truncating or canonical splice-site variants had clinically more severe disease. TJP2 disease in children includes a full clinical spectrum of severity, with mild or intermittent forms as well as the severe and minimal forms hitherto described. Biallelic TJP2 variants must be considered in children with clinically intermittent or resolved intrahepatic cholestasis.

Cholestasis in the Baby and Infant

Cholestasis in children is a serious condition due to various aetiologic factors. If children with jaundice present with acholic stool, dark urine colour, or direct hyperbilirubinaemia, the patient should be evaluated urgently. Early and timely diagnosis and initiation of appropriate treatment are extremely important determinants of morbidity and mortality. In the neonatal period, idiopathic neonatal cholestasis, alpha-1 antitrypsin deficiency, cholestasis from infections, and biliary atresia are the most common causes of cholestasis. Nowadays, with the development of genetic and molecular biological studies, the diagnosis of many diseases that have previously been evaluated as ‘idiopathic‘ can be made. It is the aetiological factor that determines the prognosis. The treatment plan is created in accordance with aetiological causes and in response to symptoms such as pruritus and malabsorption: this can be surgical treatment across a diverse spectrum, from biliary diversion to liver transplantation. In this study, the aetiology, diagnosis, and treatment of cholestasis in babies and infants are reviewed in the light of current literature.

A practical approach to the pathology of neonatal cholestatic liver disease

Navigating the complexities of interpreting a liver biopsy performed on a neonate with conjugated/direct hyperbilirubinemia can be an arduous task given these biopsies are infrequently encountered. The list of entities is long and yet there are only a few histologic patterns of liver injury. The first step for the pathologist is to determine the histologic pattern, which will guide further inquiry into the useful clinical information to have while evaluating the biopsy. Ultimately, the goal is to identify those conditions that will benefit from early intervention. We begin with a review of biliary development to help understand what findings may be physiologic versus pathologic, particularly in premature infants. Then we review eight cases that cover the three most common histologic patterns of injury in patients with neonatal cholestasis: biliary obstructive, neonatal hepatitis, and paucity of intrahepatic bile ducts. The entities that serve as prototypes for these histologic patterns are covered, including biliary atresia, idiopathic neonatal hepatitis, and Alagille syndrome, along with rarer entities that have histologic overlap. The cases with accompanying tables and algorithms are intended to help place the histologic findings in the context of the overall clinical work-up, including genetic testing.

Progressive Familial Intrahepatic Cholestasis in Korea: A Clinicopathological Study of Five Patients

BACKGROUND

Progressive familial intrahepatic cholestasis (PFIC) is a heterogeneous group of autosomal recessive liver diseases that present as neonatal cholestasis. Little is known of this disease in Korea.

METHODS

The records of five patients histologically diagnosed with PFIC, one with PFIC1 and four with PFIC2, by liver biopsy or transplant were reviewed, and ATP8B1 and ABCB11 mutation status was analyzed by direct DNA sequencing. Clinicopathological characteristics were correlated with genetic mutations.

RESULTS

The first symptom in all patients was jaundice. Histologically, lobular cholestasis with bile plugs was the main finding in all patients, whereas diffuse or periportal cholestasis was identified only in patients with PFIC2. Giant cells and ballooning of hepatocytes were observed in three and three patients with PFIC2, respectively, but not in the patient with PFIC1. Immunostaining showed total loss of bile salt export pump in two patients with PFIC2 and focal loss in two. Lobular and portal based fibrosis were more advanced in PFIC2 than in PFIC1. ATP8B1 and ABCB11 mutations were identified in one PFIC1 and two PFIC2 patients, respectively. One PFIC1 and three PFIC2 patients underwent liver transplantation (LT). At age 7 months, one PFIC2 patient was diagnosed with concurrent hepatocellular carcinoma and infantile hemangioma in an explanted liver. The patient with PFIC1 developed steatohepatitis after LT. One patient showed recurrence of PFIC2 after 10 years and underwent LT.

CONCLUSIONS

PFIC is not rare in patients with neonatal cholestasis of unknown origin. Proper clinicopathologic correlation and genetic testing can enable early detection and management.

Progressive familial intrahepatic cholestasis: diagnosis, management, and treatment

Progressive familial intrahepatic cholestasis (PFIC) is a group of autosomal recessive cholestatic liver diseases which are subgrouped according to the genetic defect, clinical presentation, laboratory findings and liver histology. Progressive liver fibrosis, cirrhosis, and end stage liver disease (ESLD) may eventually develop. PFIC was first described in Amish descendants of Jacob Byler, therefore it was originally called Byler disease. But it can be seen anywhere on the globe. This review summarizes the main features of the subtypes of the disease and discusses the current available diagnosis, conservative and surgical therapeutic options.

New Insights in Genetic Cholestasis: From Molecular Mechanisms to Clinical Implications

Cholestasis is characterised by impaired bile secretion and accumulation of bile salts in the organism. Hereditary cholestasis is a heterogeneous group of rare autosomal recessive liver disorders, which are characterised by intrahepatic cholestasis, pruritus, and jaundice and caused by defects in genes related to the secretion and transport of bile salts and lipids. Phenotypic manifestation is highly variable, ranging from progressive familial intrahepatic cholestasis (PFIC)-with onset in early infancy and progression to end-stage liver disease-to a milder intermittent mostly nonprogressive form known as benign recurrent intrahepatic cholestasis (BRIC). Cases have been reported of initially benign episodic cholestasis that subsequently transitions to a persistent progressive form of the disease. Therefore, BRIC and PFIC seem to represent two extremes of a continuous spectrum of phenotypes that comprise one disease. Thus far, five representatives of PFIC (named PFIC1-5) caused by pathogenic mutations present in both alleles of ATP8B1, ABCB11, ABCB4, TJP2, and NR1H4 have been described. In addition to familial intrahepatic cholestasis, partial defects in ATP8B1, ABCB11, and ABCB4 predispose patients to drug-induced cholestasis and intrahepatic cholestasis in pregnancy. This review summarises the current knowledge of the clinical manifestations, genetics, and molecular mechanisms of these diseases and briefly outlines the therapeutic options, both conservative and invasive, with an outlook for future personalised therapeutic strategies.

Pathologic Features of Hereditary Cholestatic Diseases

The inherited diseases causing conjugated hyperbilirubinemia are diverse, with variability in clinical severity, histologic appearance, and time of onset. The liver biopsy appearances can also vary depending on whether the initial presentation is in the neonatal period or later. Although many of the disorders have specific histologic features in fully developed and classic cases, biopsies taken early in the disease course may be nonspecific, showing either cholestatic hepatitis or an obstructive pattern of injury requiring close correlation with the laboratory and clinical findings to reach the correct diagnosis. Additionally, increased understanding of the range of hepatic changes occurring in mild deficiencies of bile canalicular transporter proteins suggest that these disorders, particularly ABCB4 deficiency, may be more common than previously recognized; improved awareness should prompt 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).

Clinical phenotype and molecular analysis of a homozygous ABCB11 mutation responsible for progressive infantile cholestasis

The bile salt export pump (BSEP) plays an important role in biliary secretion. Mutations in ABCB11, the gene encoding BSEP, induce progressive familial intrahepatic cholestasis type 2 (PFIC2), which presents with severe jaundice and liver dysfunction. A less severe phenotype, called benign recurrent intrahepatic cholestasis type 2, is also known. About 200 missense mutations in ABCB11 have been reported. However, the phenotype-genotype correlation has not been clarified. Furthermore, the frequencies of ABCB11 mutations differ between Asian and European populations. We report a patient with PFIC2 carrying a homozygous ABCB11 mutation c.386G>A (p.C129Y) that is most frequently reported in Japan. The pathogenicity of BSEP^C129Y has not been investigated. In this study, we performed the molecular analysis of this ABCB11 mutation using cells expressing BSEP^C129Y. We found that trafficking of BSEP^C129Y to the plasma membrane was impaired and that the expression of BSEP^C129Y on the cell surface was significantly lower than that in the control. The amount of bile acids transported via BSEP^C129Y was also significantly lower than that via BSEP^WT. The transport activity of BSEP^C129Y may be conserved because the amount of membrane BSEP^C129Y corresponded to the uptake of taurocholate into membrane vesicles. In conclusion, we demonstrated that c.386G>A (p.C129Y) in ABCB11 was a causative mutation correlating with the phenotype of patients with PFIC2, impairment of biliary excretion from hepatocytes, and the absence of canalicular BSEP expression in liver histological assessments. Mutational analysis in ABCB11 could facilitate the elucidation of the molecular mechanisms underlying the development of intrahepatic cholestasis.

Post-transplant Recurrent Bile Salt Export Pump Disease: A Form of Antibody-mediated Graft Dysfunction and Utilization of C4d

Recurrent bile salt export pump (rBSEP) disease has been reported in progressive familial intrahepatic cholestasis type 2 (PFIC2) patients following liver transplantation (LT) and is often refractory to standard anti-cellular rejection immunosuppressants. The mechanism of rBSEP disease is proposed to be a form of type II hypersensitivity reaction with de novo anti-BSEP antibodies blocking the function of allograft BSEP. Utilization of C4d has not been evaluated in rBSEP. We describe a girl with 3 episodes of rBSEP with severe pruritus at 8.9, 10.3, and 11.0 years post-LT, respectively. Patient's serum reacted with normal liver canaliculi by indirect immunofluorescence (IF), whereas patient's liver showed canalicular immunoglobulin G deposition. The histologic features of all 3 liver biopsies recapitulate PFIC2 with cholestatic giant cell hepatitis. Canalicular BSEP expression was not detected in areas of feathery degeneration by immunohistochemistry, but was retained in morphologically normal liver. By direct IF, C4d showed diffuse sinusoidal staining in the third biopsy. Patient responded well to rituximab with or without intravenous immunoglobulin with subsiding symptoms and normalization of serum bile acid levels. In conclusion, rBSEP disease should be considered in the differential diagnosis when evaluating for rejection in a PFIC2 patient post-LT presenting with pruritus. A portion of liver core may be snap frozen in OCT medium for possible direct IF for C4d, that can serve as a surrogate marker for complement activation and antibody-mediated graft dysfunction.

Vps33b is crucial for structural and functional hepatocyte polarity

BACKGROUND & AIMS

In the normal liver, hepatocytes form a uniquely polarised cell layer that enables movement of solutes from sinusoidal blood to canalicular bile. Whilst several cholestatic liver diseases with defects of hepatocyte polarity have been identified, the molecular mechanisms of pathogenesis are not well defined. One example is arthrogryposis, renal dysfunction and cholestasis syndrome, which in most patients is caused by VPS33B mutations. VPS33B is a protein involved in membrane trafficking that interacts with RAB11A at recycling endosomes. To understand the pathways that regulate hepatocyte polarity better, we investigated VPS33B deficiency using a novel mouse model with a liver-specific Vps33b deletion.

METHODS

To assess functional polarity, plasma and bile samples were collected from Vps33b liver knockout (Vps33bfl/fl-AlfpCre) and control (Vps33bfl/fl) mice; bile components or injected substrates were quantitated by mass spectrometry or fluorometry. For structural analysis, livers underwent light and transmission electron microscopy. Apical membrane and tight junction protein localisation was assessed by immunostaining. Adeno-associated virus vectors were used for in vivo gene rescue experiments.

RESULTS

Like patients, Vps33bfl/fl-AlfpCre mice showed mislocalisation of ATP-binding cassette proteins that are specifically trafficked to the apical membrane via Rab11a-positive recycling endosomes. This was associated with retention of bile components in blood. Loss of functional tight junction integrity and depletion of apical microvilli were seen in knockout animals. Gene transfer partially rescued these defects.

CONCLUSIONS

Vps33b has a key role in establishing structural and functional aspects of hepatocyte polarity and may be a target for gene replacement therapy.

LAY SUMMARY

Hepatocytes are liver cells with tops and bottoms; that is, they are polarised. At their bottoms they absorb substances from blood. They then, at their tops, secrete these substances and their metabolites into bile. When polarity is lost, this directional flow of substances from blood to bile is disrupted and liver disease follows. In this study, using a new mouse model with a liver-specific mutation of Vps33b, the mouse version of a gene that is mutated in most patients with arthrogryposis, renal dysfunction and cholestasis (ARC) syndrome, we investigated how the Vps33b gene product contributes to establishing hepatocyte polarity. We identified in these mice abnormalities similar to those in children with ARC syndrome. Gene transfer could partly reverse the mouse abnormalities. Our work contributes to the understanding of VPS33B disease and hepatocyte polarity in general, and may point towards gene transfer mediated treatment of ARC liver disease.

Immunohistochemistry and Special Stains in Medical Liver Pathology

Histochemical and immunostains are routinely used to evaluate medical liver biopsy specimens. The use of these special stains allows the identification of more clinically important information than is available on hematoxylin and eosin stains alone. These special stains are important for evaluating active and chronic injury and for establishing a specific diagnosis. The skillful use of these stains greatly improves patient care. Information on the use of special stains can be scattered in different sources, making the information hard to access. In this article, the use of special stains in medical liver biopsies is concisely reviewed.

MYO5B mutations cause cholestasis with normal serum gamma-glutamyl transferase activity in children without microvillous inclusion disease

Some patients with microvillus inclusion disease due to myosin 5B (MYO5B) mutations may develop cholestasis characterized by a progressive familial intrahepatic cholestasis-like phenotype with normal serum gamma-glutamyl transferase activity. So far MYO5B deficiency has not been reported in patients with such a cholestasis phenotype in the absence of intestinal disease. Using a new-generation sequencing approach, we identified MYO5B mutations in five patients with progressive familial intrahepatic cholestasis-like phenotype with normal serum gamma-glutamyl transferase activity without intestinal disease.

CONCLUSION

These data show that MYO5B deficiency may lead to isolated cholestasis and that MYO5B should be considered as an additional progressive familial intrahepatic cholestasis gene. (Hepatology 2017;65:164-173).

Liver transplantation and the management of progressive familial intrahepatic cholestasis in children

Progressive familial intrahepatic cholestasis (PFIC) is a constellation of inherited disorders that result in the impairment of bile flow through the liver that predominantly affects children. The accumulation of bile results in progressive liver damage, and if left untreated leads to end stage liver disease and death. Patients often present with worsening jaundice and pruritis within the first few years of life. Many of these patients will progress to end stage liver disease and require liver transplantation. The role and timing of liver transplantation still remains debated especially in the management of PFIC1. In those patients who are appropriately selected, liver transplantation offers an excellent survival benefit. Appropriate timing and selection of patients for liver transplantation will be discussed, and the short and long term management of patients post liver transplantation will also be described.

Retargeting of bile salt export pump and favorable outcome in children with progressive familial intrahepatic cholestasis type 2

We investigated predictors of clinical evolution in progressive familial intrahepatic cholestasis type 2 patients and how they relate to bile salt export pump (BSEP) expression and its (re)targeting. Our retrospective study included 22 children with progressive familial intrahepatic cholestasis type 2. Clinical, biochemical, and histological characteristics were reviewed on admittance and following treatment with either ursodeoxycholic acid alone (10 mg/kg thrice daily, n = 19) or partial biliary diversion (n = 3). Immunostaining of BSEP was performed in 20 patients. Response to treatment was defined as normalization of pruritus, disappearance of jaundice, and alanine aminotransferase (ALT) levels <1.5 times the upper limit of normal. Ten of 22 patients were responders, and paired biopsies were available in six. De novo or retargeted canalicular expression of BSEP occurred in four of these six, two of whom exhibited baseline intracellular expression. Twelve of 22 were nonresponders and exhibited earlier onset of jaundice (<9 months), neonatal cholestasis, and higher ALT levels. An ALT >165 IU/L produced 72% sensitivity and 55% specificity in predicting nonresponse. Seven patients were still responding at last follow-up (median = 20 months, range 5-67 months). Three responders relapsed after 56, 72, and 82 months, respectively. Of nine surviving responders, median relapse-free survival time was 72 months (95% confidence interval 48-96 months) and 5-year relapse-free survival was 75% (95% confidence interval 33-100%). Intracellular BSEP at baseline was seen in six, of whom five were responders. Genetic analysis was performed in 17 of 22, confirming diagnosis in 13 (76%) and in four (24%) in whom only heterozygous mutation was identified.

CONCLUSION

De novo or retargeted canalicular expression of BSEP occurs in treatment responders; children with late-onset presentation, lower ALT, and intracellular BSEP expression are likely to respond, at least transiently, to nontransplant treatment.

MYO5B and bile salt export pump contribute to cholestatic liver disorder in microvillous inclusion disease

Microvillous inclusion disease (MVID) is a congenital disorder of the enterocyte related to mutations in the MYO5B gene, leading to intractable diarrhea often necessitating intestinal transplantation (ITx). Among our cohort of 28 MVID patients, 8 developed a cholestatic liver disease akin to progressive familial intrahepatic cholestasis (PFIC). Our aim was to investigate the mechanisms by which MYO5B mutations affect hepatic biliary function and lead to cholestasis in MVID patients. Clinical and biological features and outcome were reviewed. Pretransplant liver biopsies were analyzed by immunostaining and electron microscopy. Cholestasis occurred before (n = 5) or after (n = 3) ITx and was characterized by intermittent jaundice, intractable pruritus, increased serum bile acid (BA) levels, and normal gamma-glutamyl transpeptidase activity. Liver histology showed canalicular cholestasis, mild-to-moderate fibrosis, and ultrastructural abnormalities of bile canaliculi. Portal fibrosis progressed in 5 patients. No mutation in ABCB11/BSEP or ATP8B1/FIC1 genes were identified. Immunohistochemical studies demonstrated abnormal cytoplasmic distribution of MYO5B, RAB11A, and BSEP in hepatocytes. Interruption of enterohepatic BA cycling after partial external biliary diversion or graft removal proved the most effective to ensure long-term remission.

CONCLUSION

MVID patients are at risk of developing a PFIC-like liver disease that may hamper outcome after ITx. Our results suggest that cholestasis in MVID patients results from (1) impairment of the MYO5B/RAB11A apical recycling endosome pathway in hepatocytes, (2) altered targeting of BSEP to the canalicular membrane, and (3) increased ileal BA absorption. Because cholestasis worsens after ITx, indication of a combined liver ITx should be discussed in MVID patients with severe cholestasis. Future studies will need to address more specifically the effect of MYO5B dysfunction in BA homeostasis.

Diagnosis of ABCB11 gene mutations in children with intrahepatic cholestasis using high resolution melting analysis and direct sequencing

Intrahepatic cholestasis represents a heterogeneous group of disorders that begin during childhood, most commonly manifesting as neonatal cholestasis, and lead to ongoing liver dysfunction in children and adults. For children, inherited pathogenic factors of cholestasis have gained increasing attention owing to the rapid development of molecular biology technology. However, these methods have their advantages and disadvantages in terms of simplicity, sensitivity, specificity, time required and expense. In the present study, an effective, sensitive and economical method is recommended, termed high-resolution melting (HRM) analysis and direct sequencing, based on general polymerase chain reaction, to detect mutations in disease-causing genes. As one type of inherited intrahepatic cholestasis, progressive familial intrahepatic cholestasis type 2 (PFIC2) is caused by pathogenic mutations in the ABCB11 gene, HRM was used to detect mutations in the ABCB11 gene in the present study, and the diagnosis for PFIC2 was made by comprehensive analysis of genetic findings and clinical features. Furthermore, the characteristics of mutations and single nucleotide polymorphisms (SNPs) in the ABCB11 gene were elucidated. A total of 14 types of mutations/polymorphisms were identified in 20 patients from mainland China, including six missense mutations (p.Y337H, p.Y472C, p.R696W, p.Q931P, p.D1131V and p.H1198R), one nonsense mutation (p.R928X) and seven SNPs (p.D36D/rs3815675, p.F90F/rs4148777, p.Y269Y/rs2287616, p.I416I/rs183390670, p.V444A/rs2287622, p.A865V/rs118109635 and p.A1028A/rs497692). Five mutations were novel. The majority of the mutations were different from those detected in other population groups. A total of 4/20 patients (1/5) were diagnosed to be PFIC2 by combining genetic findings with the clinical features. Polymorphisms V444A and A1028A, with an allele frequency of 74.5 and 67.2%, respectively, were highly prevalent in the mainland Chinese subjects. No differences were found between the patients with cholestasis and the control subjects. Efficient genetic screening facilitates the clinical diagnosis of genetic disorders. The present study demonstrated that HRM analysis was efficient and effective in detecting mutations and expanded the known spectrum of ABCB11 gene mutations.

Progressive familial intrahepatic cholestasis

Progressive familial intrahepatic cholestasis (PFIC) is a group of rare disorders which are caused by defect in bile secretion and present with intrahepatic cholestasis, usually in infancy and childhood. These are autosomal recessive in inheritance. The estimated incidence is about 1 per 50,000 to 1 per 100,000 births, although exact prevalence is not known. These diseases affect both the genders equally and have been reported from all geographical areas. Based on clinical presentation, laboratory findings, liver histology and genetic defect, these are broadly divided into three types-PFIC type 1, PFIC type 2 and PFIC type 3. The defect is in ATP8B1 gene encoding the FIC1 protein, ABCB 11 gene encoding BSEP protein and ABCB4 gene encoding MDR3 protein in PFIC1, 2 and 3 respectively. The basic defect is impaired bile salt secretion in PFIC1/2 whereas in PFIC3, it is reduced biliary phospholipid secretion. The main clinical presentation is in the form of cholestatic jaundice and pruritus. Serum gamma glutamyl transpeptidase (GGT) is normal in patients with PFIC1/2 while it is raised in patients with PFIC3. Treatment includes nutritional support (adequate calories, supplementation of fat soluble vitamins and medium chain triglycerides) and use of medications to relieve pruritus as initial therapy followed by biliary diversion procedures in selected patients. Ultimately liver transplantation is needed in most patients as they develop progressive liver fibrosis, cirrhosis and end stage liver disease. Due to the high risk of developing liver tumors in PFIC2 patients, monitoring is recommended from infancy. Mutation targeted pharmacotherapy, gene therapy and hepatocyte transplantation are being explored as future therapeutic options.

Genetic determinants of cholestasis

Cholestasis is an overarching term applied for conditions whereby biliary constituents are found in the circulation because of impairment to bile flow. A variety of processes can lead to cholestasis, be they acute or chronic injuries to hepatocytes, cholangiocytes, or the broader biliary tree itself. Such injuries may be driven by rare but highly informative primary genetic abnormalities, or may be seen in individuals with a prior genetic predisposition when confronted by specific environmental challenges such as drug exposure. This review provides a broad outline of some fundamental primary genetic cholestatic syndromes and an update on varying genetic predisposition underlying several acquired cholestatic processes.

The bile salt export pump (BSEP) in health and disease

The bile salt export pump (BSEP) is the major transporter for the secretion of bile acids from hepatocytes into bile in humans. Mutations of BSEP are associated with cholestatic liver diseases of varying severity including progressive familial intrahepatic cholestasis type 2 (PFIC-2), benign recurrent intrahepatic cholestasis type 2 (BRIC-2) and genetic polymorphisms are linked to intrahepatic cholestasis of pregnancy (ICP) and drug-induced liver injury (DILI). Detailed analysis of these diseases has considerably increased our knowledge about physiology and pathophysiology of bile secretion in humans. This review focuses on expression, localization, and function, short- and long-term regulation of BSEP as well as diseases association and treatment options for BSEP-associated diseases.

Abcb11 deficiency induces cholestasis coupled to impaired β-fatty acid oxidation in mice

The bile salt export pump (BSEP) is an ATP-binding cassette transporter that serves as the primary system for removing bile salts from the liver. In humans, deficiency of BSEP, which is encoded by the ABCB11 gene, causes severe progressive cholestatic liver disease from early infancy. In previous studies of Abcb11 deficiency in mice generated on a mixed genetic background, the animals did not recapitulate the human disease. We reasoned that ABCB11 deficiency may cause unique changes in hepatic metabolism that are predictive of liver injury. To test this possibility, we first determined that Abcb11 knock-out (KO) C57BL/6J mice recapitulate human deficiency. Before the onset of cholestasis, Abcb11 KO mice have altered hepatic lipid metabolism coupled with reduced expression of genes important in mitochondrial fatty acid oxidation. This was associated with increased serum free-fatty acids, reduced total white adipose, and marked impairment of long-chain fatty acid β-oxidation. Importantly, metabolomic analysis confirmed that Abcb11 KO mice have impaired mitochondrial fatty acid β-oxidation with the elevated fatty acid metabolites phenylpropionylglycine and phenylacetylglycine. These metabolic changes precede cholestasis but may be of relevance to cholestatic disease progression because altered fatty acid metabolism can enhance reactive oxygen species that might exacerbate cholestatic liver damage.

Bile acid-CoA ligase deficiency--a new inborn error of bile acid metabolism

Born at 27 weeks gestation, a child of consanguineous parents of Pakistani origin required prolonged parenteral nutrition. She developed jaundice, with extensive fibrosis and architectural distortion at liver biopsy; jaundice resolved with supportive care. Serum γ-glutamyl transpeptidase values were within normal ranges. The bile acids in her plasma and urine were >85% unconjugated (non-amidated). Two genes encoding bile-acid amidation enzymes were sequenced. No mutations were found in BAAT, encoding bile acid-CoA : aminoacid N-acyl transferase. The patient was homozygous for the missense mutation c.1012C > T in SLC27A5, predicted to alter a highly conserved amino-acid residue (p.H338Y) in bile acid-CoA ligase (BACL). She also was homozygous for the missense mutation c.1772A > G in ABCB11, predicted to alter a highly conserved amino-acid residue (p.N591S) in bile salt export pump (BSEP). BACL is essential for reconjugation of bile acids deconjugated by gut bacteria, and BSEP is essential for hepatocyte-canaliculus export of conjugated bile acids. A female sibling born at term had the same bile-acid phenotype and SLC27A5 genotype, without clinical liver disease. She was heterozygous for the c.1772A > G ABCB11 mutation. This is the first report of a mutation in SLC27A5. The amidation defect may have contributed to cholestatic liver disease in the setting of prematurity, parenteral nutrition, and homozygosity for an ABCB11 mutation.

Ursodeoxycholic acid in cholestasis: linking action mechanisms to therapeutic applications

UDCA (ursodeoxycholic acid) is the therapeutic agent most widely used for the treatment of cholestatic hepatopathies. Its use has expanded to other kinds of hepatic diseases, and even to extrahepatic ones. Such versatility is the result of its multiple mechanisms of action. UDCA stabilizes plasma membranes against cytolysis by tensioactive bile acids accumulated in cholestasis. UDCA also halts apoptosis by preventing the formation of mitochondrial pores, membrane recruitment of death receptors and endoplasmic-reticulum stress. In addition, UDCA induces changes in the expression of metabolizing enzymes and transporters that reduce bile acid cytotoxicity and improve renal excretion. Its capability to positively modulate ductular bile flow helps to preserve the integrity of bile ducts. UDCA also prevents the endocytic internalization of canalicular transporters, a common feature in cholestasis. Finally, UDCA has immunomodulatory properties that limit the exacerbated immunological response occurring in autoimmune cholestatic diseases by counteracting the overexpression of MHC antigens and perhaps by limiting the production of cytokines by immunocompetent cells. Owing to this multi-functionality, it is difficult to envisage a substitute for UDCA that combines as many hepatoprotective effects with such efficacy. We predict a long-lasting use of UDCA as the therapeutic agent of choice in cholestasis.