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Preventing SARS-CoV-2 infection by modulating viral host receptors, such as angiotensin-converting enzyme 2 (ACE2)1, could represent a new chemoprophylactic approach for COVID-19 that complements vaccination2,3. However, the mechanisms that control the expression of ACE2 remain unclear. Here we show that the farnesoid X receptor (FXR) is a direct regulator of ACE2 transcription in several tissues affected by COVID-19, including the gastrointestinal and respiratory systems. We then use the over-the-counter compound z-guggulsterone and the off-patent drug ursodeoxycholic acid (UDCA) to reduce FXR signalling and downregulate ACE2 in human lung, cholangiocyte and intestinal organoids and in the corresponding tissues in mice and hamsters. We show that the UDCA-mediated downregulation of ACE2 reduces susceptibility to SARS-CoV-2 infection in vitro, in vivo and in human lungs and livers perfused ex situ. Furthermore, we reveal that UDCA reduces the expression of ACE2 in the nasal epithelium in humans. Finally, we identify a correlation between UDCA treatment and positive clinical outcomes after SARS-CoV-2 infection using retrospective registry data, and confirm these findings in an independent validation cohort of recipients of liver transplants. In conclusion, we show that FXR has a role in controlling ACE2 expression and provide evidence that modulation of this pathway could be beneficial for reducing SARS-CoV-2 infection, paving the way for future clinical trials.

The liver has been studied extensively due to the broad number of diseases affecting its vital functions. However, therapeutic advances have been hampered by the lack of knowledge concerning human hepatic development. Here, we addressed this limitation by describing the developmental trajectories of different cell types that make up the human liver at single-cell resolution. These transcriptomic analyses revealed that sequential cell-to-cell interactions direct functional maturation of hepatocytes, with non-parenchymal cells playing essential roles during organogenesis. We utilized this information to derive bipotential hepatoblast organoids and then exploited this model system to validate the importance of signalling pathways in hepatocyte and cholangiocyte specification. Further insights into hepatic maturation also enabled the identification of stage-specific transcription factors to improve the functionality of hepatocyte-like cells generated from human pluripotent stem cells. Thus, our study establishes a platform to investigate the basic mechanisms directing human liver development and to produce cell types for clinical applications.

The burden of liver diseases is increasing worldwide, with liver transplantation remaining the only treatment option for end-stage liver disease. Regenerative medicine holds great potential as a therapeutic alternative, aiming to repair or replace damaged liver tissue with healthy functional cells. The properties of the cells used are critical for the efficacy of this approach. The advent of liver organoids has not only offered new insights into human physiology and pathophysiology, but also provided an optimal source of cells for regenerative medicine and translational applications. Here, we discuss various historical aspects of 3D organoid culture, how it has been applied to the hepatobiliary system, and how organoid technology intersects with the emerging global field of liver regenerative medicine. We outline the hepatocyte, cholangiocyte, and nonparenchymal organoids systems available and discuss their advantages and limitations for regenerative medicine as well as future directions.

The liver has been studied extensively due to the broad number of diseases affecting its vital functions. However, therapeutic advances, especially in regenerative medicine, are currently hampered by the lack of knowledge concerning human hepatic cell development. Here, we addressed this limitation by describing the developmental trajectories of different cell types comprising the human fetal liver at single-cell resolution. These transcriptomic analyses revealed that sequential cell-to-cell interactions direct functional maturation of hepatocytes, with non-parenchymal cells playing critical, supportive roles during organogenesis. We utilised this information to derive bipotential hepatoblast organoids and then exploited this novel model system to validate the importance of key signalling pathways and developmental cues. Furthermore, these insights into hepatic maturation enabled the identification of stage-specific transcription factors to improve the functionality of hepatocyte-like cells generated from human pluripotent stem cells. Thus, our study establishes a new platform to investigate the basic mechanisms of human liver development and to produce cell types for clinical applications.

Summary Our insight into the pathogenesis of cholestatic liver disease remains limited, partly owing to challenges in capturing the multitude of factors that contribute to disease pathogenesis in vitro. Tissue engineering could address this challenge by combining cells, materials and fabrication strategies into dynamic modelling platforms, recapitulating the multifaceted aetiology of cholangiopathies. Herein, we review the advantages and limitations of platforms for bioengineering the biliary tree, looking at how these can be applied to model biliary disorders, as well as exploring future directions for the field.

Prevention of SARS-CoV-2 entry in cells through the modulation of viral host receptors, such as ACE2, could represent a new therapeutic approach complementing vaccination. However, the mechanisms controlling ACE2 expression remain elusive. Here, we identify the farnesoid X receptor (FXR) as a direct regulator of ACE2 transcription in multiple COVID19-affected tissues, including the gastrointestinal and respiratory systems. We demonstrate that FXR antagonists, including the over-the-counter compound z-guggulsterone (ZGG) and the off-patent drug ursodeoxycholic acid (UDCA), downregulate ACE2 levels, and reduce susceptibility to SARS-CoV-2 infection in lung, cholangiocyte and gut organoids. We then show that therapeutic levels of UDCA downregulate ACE2 in human organs perfused ex situ and reduce SARS-CoV-2 infection ex vivo. Finally, we perform a retrospective study using registry data and identify a correlation between UDCA treatment and positive clinical outcomes following SARS-CoV-2 infection, including hospitalisation, ICU admission and death. In conclusion, we identify a novel function of FXR in controlling ACE2 expression and provide evidence that this approach could be beneficial for reducing SARS-CoV-2 infection, thereby paving the road for future clinical trials.

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.

Background and aims Organoids provide a powerful system to study epithelia in vitro. Recently, this approach was applied successfully to the biliary tree, a series of ductular tissues responsible for the drainage of bile and pancreatic secretions. More precisely, organoids have been derived from ductal tissue located outside (extrahepatic bile ducts; EHBDs) or inside the liver (intrahepatic bile ducts; IHBDs). These organoids share many characteristics, including expression of cholangiocyte markers such as keratin (KRT) 19. However, the relationship between these organoids and their tissues of origin, and to each other, is largely unknown. Approach and results Organoids were derived from human gallbladder, common bile duct, pancreatic duct, and IHBDs using culture conditions promoting WNT signaling. The resulting IHBD and EHBD organoids expressed stem/progenitor markers leucine-rich repeat-containing G-protein-coupled receptor 5/prominin 1 and ductal markers KRT19/KRT7. However, RNA sequencing revealed that organoids conserve only a limited number of regional-specific markers corresponding to their location of origin. Of particular interest, down-regulation of biliary markers and up-regulation of cell-cycle genes were observed in organoids. IHBD and EHBD organoids diverged in their response to WNT signaling, and only IHBDs were able to express a low level of hepatocyte markers under differentiation conditions. Conclusions Taken together, our results demonstrate that differences exist not only between extrahepatic biliary organoids and their tissue of origin, but also between IHBD and EHBD organoids. This information may help to understand the tissue specificity of cholangiopathies and also to identify targets for therapeutic development.

The generation of bioengineered biliary tissue could contribute to the management of some of the most impactful cholangiopathies associated with liver transplantation, such as biliary atresia or ischemic cholangiopathy. Recent advances in tissue engineering and in vitro cholangiocyte culture have made the achievement of this goal possible. Here we provide an overview of these developments and review the progress towards the generation and transplantation of bioengineered bile ducts. This article is part of a Special Issue entitled: Cholangiocytes in Health and Diseaseedited by Jesus Banales, Marco Marzioni and Peter Jansen.

The difficulty in isolating and propagating functional primary cholangiocytes is a major limitation in the study of biliary disorders and the testing of novel therapeutic agents. To overcome this problem, we have developed a platform for the differentiation of human pluripotent stem cells (hPSCs) into functional cholangiocyte-like cells (CLCs). We have previously reported that our 26-d protocol closely recapitulates key stages of biliary development, starting with the differentiation of hPSCs into endoderm and subsequently into foregut progenitor (FP) cells, followed by the generation of hepatoblasts (HBs), cholangiocyte progenitors (CPs) expressing early biliary markers and mature CLCs displaying cholangiocyte functionality. Compared with alternative protocols for biliary differentiation of hPSCs, our system does not require coculture with other cell types and relies on chemically defined conditions up to and including the generation of CPs. A complex extracellular matrix is used for the maturation of CLCs; therefore, experience in hPSC culture and 3D organoid systems may be necessary for optimal results. Finally, the capacity of our platform for generating large amounts of disease-specific functional cholangiocytes will have broad applications for cholangiopathies, in disease modeling and for screening of therapeutic compounds.

Organoids regenerate human bile ducts Bile ducts carry bile from the liver and gall bladder to the small intestine, where it aids digestion. Cholangiocytes are epithelial cells that line bile ducts and modify bile as its transported through the biliary tree. Chronic liver diseases involving cholangiocytes account for a large fraction of liver failure and the need for liver transplantation. Because liver donors are in short supply, Sampaziotis et al. used organoid technology to develop a cell-based therapy using human tissue (see the Perspective by Kurial and Willenbring). Cholangiocyte organoids were transplanted into the intrahepatic ducts of deceased human donor livers undergoing ex vivo normothermic perfusion. The livers could be maintained for up to 100 hours, and the transplanted organoids engrafted, exhibited function, and could repair bile ducts. Science , this issue p. 839 ; see also p. 786

The epicardium and its derivatives provide trophic and structural support for the developing and adult heart. Here we tested the ability of human embryonic stem cell (hESC)-derived epicardium to augment the structure and function of engineered heart tissue in vitro and to improve efficacy of hESC-cardiomyocyte grafts in infarcted athymic rat hearts. Epicardial cells markedly enhanced the contractility, myofibril structure and calcium handling of human engineered heart tissues, while reducing passive stiffness compared with mesenchymal stromal cells. Transplanted epicardial cells formed persistent fibroblast grafts in infarcted hearts. Cotransplantation of hESC-derived epicardial cells and cardiomyocytes doubled graft cardiomyocyte proliferation rates in vivo, resulting in 2.6-fold greater cardiac graft size and simultaneously augmenting graft and host vascularization. Notably, cotransplantation improved systolic function compared with hearts receiving either cardiomyocytes alone, epicardial cells alone or vehicle. The ability of epicardial cells to enhance cardiac graft size and function makes them a promising adjuvant therapeutic for cardiac repair. Cell therapy in a rat model of heart attack is enhanced by stem-cell-derived epicardium.

Pediatric liver transplantation is often required as a consequence of biliary disorders because of the lack of alternative treatments for repairing or replacing damaged bile ducts. To address the lack of availability of pediatric livers suitable for transplantation, we developed a protocol for generating bioengineered biliary tissue suitable for biliary reconstruction. Our platform allows the derivation of cholangiocyte organoids (COs) expressing key biliary markers and retaining functions of primary extra- or intrahepatic duct cholangiocytes within 2 weeks of isolation. COs are subsequently seeded on polyglycolic acid (PGA) scaffolds or densified collagen constructs for 4 weeks to generate bioengineered tissue retaining biliary characteristics. Expertise in organoid culture and tissue engineering is desirable for optimal results. COs correspond to mature functional cholangiocytes, differentiating our method from alternative organoid systems currently available that propagate adult stem cells. Consequently, COs provide a unique platform for studies in biliary physiology and pathophysiology, and the resulting bioengineered tissue has broad applications for regenerative medicine and cholangiopathies.

Cholangiocytes play a crucial role in the pathophysiology of cholestasis. However, research on human cholangiocytes has been restricted by challenges in long-term propagation and large-scale expansion of primary biliary epithelium. The advent of organoid technology has overcome this limitation allowing long-term culture of a variety of epithelia from multiple organs. Here, we describe two methods for growing human cholangiocytes in organoid format. The first applies to the generation of intrahepatic bile ducts using human induced pluripotent stem cells using a protocol of differentiation that recapitulates physiological bile duct development. The second method allows the propagation of primary biliary epithelium from the extrahepatic ducts or gallbladder. Both protocols result in large numbers of cholangiocyte organoids expressing biliary markers and maintaining key cholangiocyte functions.

Cholangiocytes play a crucial role in the pathophysiology of cholestasis. However, research on human cholangiocytes has been restricted by challenges in long-term propagation and large-scale expansion of primary biliary epithelium. The advent of organoid technology has overcome this limitation allowing long-term culture of a variety of epithelia from multiple organs. Here, we describe two methods for growing human cholangiocytes in organoid format. The first applies to the generation of intrahepatic bile ducts using human induced pluripotent stem cells using a protocol of differentiation that recapitulates physiological bile duct development. The second method allows the propagation of primary biliary epithelium from the extrahepatic ducts or gallbladder. Both protocols result in large numbers of cholangiocyte organoids expressing biliary markers and maintaining key cholangiocyte functions.

Pediatric liver transplantation is often required as a consequence of biliary disorders because of the lack of alternative treatments for repairing or replacing damaged bile ducts. To address the lack of availability of pediatric livers suitable for transplantation, we developed a protocol for generating bioengineered biliary tissue suitable for biliary reconstruction. Our platform allows the derivation of cholangiocyte organoids (COs) expressing key biliary markers and retaining functions of primary extra- or intrahepatic duct cholangiocytes within 2 weeks of isolation. COs are subsequently seeded on polyglycolic acid (PGA) scaffolds or densified collagen constructs for 4 weeks to generate bioengineered tissue retaining biliary characteristics. Expertise in organoid culture and tissue engineering is desirable for optimal results. COs correspond to mature functional cholangiocytes, differentiating our method from alternative organoid systems currently available that propagate adult stem cells. Consequently, COs provide a unique platform for studies in biliary physiology and pathophysiology, and the resulting bioengineered tissue has broad applications for regenerative medicine and cholangiopathies.

The bile ducts form a network of tubes within the liver and transfer bile produced in the liver to the bowel. In biliary disorders, this transport system fails, leading to the accumulation of toxic bile in the liver, damage, and permanent scarring (cirrhosis), which can ultimately be treated only through liver transplantation. Indeed, bile duct diseases (cholangiopathies) are the leading disorder treated (70%) by pediatric liver transplantation and account for a third of adult transplanted livers.

Background: Treatment guidelines recommend a stepwise approach to primary biliary cholangitis: all patients begin treatment with ursodeoxycholic acid (UDCA) monotherapy and those with an inadequate biochemical response after 12 months are subsequently considered for second-line therapies. However, as a result, patients at the highest risk can wait the longest for effective treatment. We determined whether UDCA response can be accurately predicted using pretreatment clinical parameters. Methods: We did logistic regression analysis of pretreatment variables in a discovery cohort of patients in the UK with primary biliary cholangitis to derive the best-fitting model of UDCA response, defined as alkaline phosphatase less than 1·67 times the upper limit of normal (ULN), measured after 12 months of treatment with UDCA. We validated the model in an external cohort of patients with primary biliary cholangitis and treated with UDCA in Italy. Additionally, we assessed correlations between model predictions and key histological features, such as biliary injury and fibrosis, on liver biopsy samples. Findings: 2703 participants diagnosed with primary biliary cholangitis between Jan 1, 1998, and May 31, 2015, were included in the UK-PBC cohort for derivation of the model. The following pretreatment parameters were associated with lower probability of UDCA response: higher alkaline phosphatase concentration (p

OBJECTIVES Fully covered self-expanding metal stents (FCSEMS) constitute the first type of metal stent that can easily be removed endoscopically and/or intraoperatively, which may be advantageous in the management of distal malignant biliary strictures (DMBS). To assess the efficacy of FCSEMS as first-line treatment for DMBS, we compared patency, survival and complication rates between FCSEMS, uncovered self-expanding metal stents (USEMS) and plastic stents (PS). METHODS This was a multicentre retrospective study of 315 consecutive patients with DMBS, who underwent endoscopic retrograde cholangiopancreatography and stenting (FCSEMS, USEMS or PS) at two hospitals between 1 January 2007 and 31 December 2013. Stent patency and patient survival were compared using the Kaplan-Meier method; complication rates were compared using Fisher's exact test; and Cox regression analysis was used to screen for confounding factors. RESULTS FCSEMS were associated with prolonged stent patency (median=145 days) compared with USEMS (median=110 days, P

The study of biliary disease has been constrained by a lack of primary human cholangiocytes. Here we present an efficient, serum-free protocol for directed differentiation of human induced pluripotent stem cells into cholangiocyte-like cells (CLCs). CLCs show functional characteristics of cholangiocytes, including bile acids transfer, alkaline phosphatase activity, γ-glutamyl-transpeptidase activity and physiological responses to secretin, somatostatin and vascular endothelial growth factor. We use CLCs to model in vitro key features of Alagille syndrome, polycystic liver disease and cystic fibrosis (CF)-associated cholangiopathy. Furthermore, we use CLCs generated from healthy individuals and patients with polycystic liver disease to reproduce the effects of the drugs verapamil and octreotide, and we show that the experimental CF drug VX809 rescues the disease phenotype of CF cholangiopathy in vitro. Our differentiation protocol will facilitate the study of biological mechanisms controlling biliary development, as well as disease modeling and drug screening.

Liver disease is a leading cause of death in the Western world. However, our insight into the underlying disease mechanisms and the development of novel therapeutic agents has been hindered by limited availability of primary tissue, intraspecies variability associated with the use of animal models, and reduced long-term viability of isolated and diseased liver cells. The emergence of human induced pluripotent stem cells and differentiation protocols to generate hepatocyte-like cells has opened the possibility of addressing these issues. Here, we discuss the recent progress and potential in the production of various cell types constituting the liver and their applications to model liver diseases and test drug toxicity in vitro.

The treatment of common bile duct (CBD) disorders, such as biliary atresia or ischemic strictures, is restricted by the lack of biliary tissue from healthy donors suitable for surgical reconstruction. Here we report a new method for the isolation and propagation of human cholangiocytes from the extrahepatic biliary tree in the form of extrahepatic cholangiocyte organoids (ECOs) for regenerative medicine applications. The resulting ECOs closely resemble primary cholangiocytes in terms of their transcriptomic profile and functional properties. We explore the regenerative potential of these organoids $\textit{in vivo}$ and demonstrate that ECOs self-organize into bile duct–like tubes expressing biliary markers following transplantation under the kidney capsule of immunocompromised mice. In addition, when seeded on biodegradable scaffolds, ECOs form tissue-like structures retaining biliary characteristics. The resulting bioengineered tissue can reconstruct the gallbladder wall and repair the biliary epithelium following transplantation into a mouse model of injury. Furthermore, bioengineered artificial ducts can replace the native CBD, with no evidence of cholestasis or occlusion of the lumen. In conclusion, ECOs can successfully reconstruct the biliary tree, providing proof of principle for organ regeneration using human primary cholangiocytes expanded $\textit{in vitro}$.

Inducible loss of gene function experiments are necessary to uncover mechanisms underlying development, physiology and disease. However, current methods are complex, lack robustness and do not work in multiple cell types. Here we address these limitations by developing single-step optimized inducible gene knockdown or knockout (sOPTiKD or sOPTiKO) platforms. These are based on genetic engineering of human genomic safe harbors combined with an improved tetracycline-inducible system and CRISPR/Cas9 technology. We exemplify the efficacy of these methods in human pluripotent stem cells (hPSCs), and show that generation of sOPTiKD/KO hPSCs is simple, rapid and allows tightly controlled individual or multiplexed gene knockdown or knockout in hPSCs and in a wide variety of differentiated cells. Finally, we illustrate the general applicability of this approach by investigating the function of transcription factors (OCT4 and T), cell cycle regulators (cyclin D family members) and epigenetic modifiers (DPY30). Overall, sOPTiKD and sOPTiKO provide a unique opportunity for functional analyses in multiple cell types relevant for the study of human development., Highlighted article: Novel optimized inducible knockdown and knockout platforms are developed and used to assess gene function in human pluripotent stem cells and their differentiated progeny.

Endoscopic Retrograde Cholangiopancreatography (ERCP) is a widely used diagnostic and therapeutic modality in the management of biliary and pancreatic disease. Some of the complications of the procedure, although rare, may carry significant morbidity and mortality risks. We describe the case of a 68-year-old female who underwent elective ERCP for ductal stone clearance. Immediately postprocedure, the patient developed subcutaneous emphysema and bilateral pneumothoraces. Further imaging revealed the presence of free intra-abdominal air. The patient made a very quick recovery after bilateral chest drain insertion and no further intervention was required. We propose that pneumothorax, pneumomediastinum, and subcutaneous emphysema during ERCP, in the absence of duodenal perforation may be explained by leakage of air from a site of low resistance such as the sphincterotomy site, or as a result of copious Valsalva manoeuvres performed by a patient tolerating the procedure poorly.

Etodolac is a cyclooxygenase 2 (COX-2)-specific non-steroidal anti-inflammatory agent, used predominantly in the management of musculoskeletal disease and arthritis. Dyspepsia, headache, dizziness, rash and pruritus are the commonest side effects. Hepatic impairment is extremely rare, occurring in less than 0.3% of patients [1, 2]. Liver failure has been reported only once, in a patient with underlying alcohol related chronic liver disease and cocaine abuse, contributing to the presentation [3]. We report the first case of etodolac induced acute liver failure in the absence of confounding factors such as chronic liver disease or concomitant use of other hepatotoxic agents.

Pruritus is one of the most disabling clinical manifestations of cholestatic liver disease. Antipruritic agents are effective only in a proportion of patients [1], [2]. Rifampicin is an antituberculous agent recommended for relieving pruritus refractory to bile acid sequestrants [3]–[6]. This is the first report of severe, reversible prolongation of prothrombin time in patients with primary sclerosing cholangitis (PSC), following the introduction of rifampicin.

A 66-year-old woman with a background of diverticular disease, hypertension, chronic kidney disease and amaurosis fugax was referred to our unit for colonoscopy as part of the bowel cancer screening programme following a positive faecal occult blood result. The colonoscopy was performed following bowel preparation with Moviprep and under sedation with Midazolam 1.5 mg and Pethidine 25 mg. The procedure was straightforward using carbon dioxide for insufflation. Upon examination of the ascending colon several bright red linear lesions with some extravasation of fresh blood were noted (figure 1). These lesions were visualised in …