Persistent biliary hypoxia and lack of regeneration are key mechanisms in the pathogenesis of posttransplant nonanastomotic strictures

Mechanism and endoscopic-treatment-induced evolution of biliary non-anastomotic stricture after liver transplantation revealed by single-cell RNA sequencing

BACKGROUND

Biliary complications, especially non-anastomotic stricture (NAS), are the main complications after liver transplantation. Insufficient sampling and no recognized animal models obstruct the investigation. Thus, the mechanisms and alterations that occur during endoscopic treatment (ET) of NAS remain unclear.

METHODS

Samples were obtained with endoscopic forceps from the hilar bile ducts of NAS patients receiving continuous biliary stent implantation after diagnosis. Retrospective analysis of multiple studies indicated that the duration of ET for NAS was approximately 1-2 years. Thus, we divided the patients into short-term treatment (STT) and long-term treatment (LTT) groups based on durations of less or more than 1 year. Samples were subjected to single-cell RNA sequencing. Transcriptomic differences between STT and normal groups were defined as the NAS mechanism. Similarly, alterations from STT to LTT groups were regarded as endoscopic-treatment-induced evolution.

RESULTS

In NAS, inflammation and immune-related pathways were upregulated in different cell types, with nonimmune cells showing hypoxia pathway upregulation and immune cells showing ATP metabolism pathway upregulation, indicating heterogeneity. We confirmed a reduction in bile acid metabolism-related SPP1+ epithelial cells in NAS. Increases in proinflammatory and profibrotic fibroblast subclusters indicated fibrotic progression in NAS. Furthermore, immune disorders in NAS were exacerbated by an increase in plasma cells and dysfunction of NK and NKT cells. ET downregulated multicellular immune and inflammatory responses and restored epithelial and endothelial cell proportions.

CONCLUSIONS

This study reveals the pathophysiological and genetic mechanisms and evolution of NAS induced by ET, thereby providing preventive and therapeutic insights into NAS.

HIGHLIGHTS

For the first time, single-cell transcriptome sequencing was performed on the bile ducts of patients with biliary complications. scRNA-seq analysis revealed distinct changes in the proportion and phenotype of multiple cell types during Nonanastomotic stricture (NAS) and endoscopic treatment. A reduction in bile acid metabolism-related SPP1+ epithelial cells and VEGFA+ endothelial cells, along with explosive infiltration of plasma cells and dysfunction of T and NK cells in NAS patients. SPP1+ macrophages and BST2+ T cells might serve as a surrogate marker for predicting endoscopic treatment.

Biliary stem cells in health and cholangiopathies and cholangiocarcinoma

PURPOSE OF REVIEW

This review discusses evidence regarding progenitor populations of the biliary tree in the tissue regeneration and homeostasis, and the pathobiology of cholangiopathies and malignancies.

RECENT FINDINGS

In embryogenesis biliary multipotent progenitor subpopulation contributes cells not only to the pancreas and gall bladder but also to the liver. Cells equipped with a constellation of markers suggestive of the primitive endodermal phenotype exist in the peribiliary glands, the bile duct glands, of the intra- and extrahepatic bile ducts. These cells are able to be isolated and cultured easily, which demonstrates the persistence of a stable phenotype during in vitro expansion, the ability to self-renew in vitro, and the ability to differentiate between hepatocyte and biliary and pancreatic islet fates.

SUMMARY

In normal human livers, stem/progenitors cells are mostly restricted in two distinct niches, which are the bile ductules/canals of Hering and the peribiliary glands (PBGs) present inside the wall of large intrahepatic bile ducts. The existence of a network of stem/progenitor cell niches within the liver and along the entire biliary tree inform a patho-biological-based translational approach to biliary diseases and cholangiocarcinoma since it poses the basis to understand biliary regeneration after extensive or chronic injuries and progression to fibrosis and cancer.

The management of a duodenal fistula involving the right hepatic duct: a rare case report

The formation of an internal fistula between the biliary system and the gastrointestinal tract is a rare condition with various etiologies, predominantly associated with recurrent chronic inflammation of the biliary system and tumors. Patients with this condition may lack specific clinical manifestations, presenting with symptoms such as abdominal pain, fever, jaundice, or may show no clinical signs at all. Common types of internal fistulas include cholecystoduodenal fistula, cholecystocolonic fistula, and choledochoduodenal fistula. Among these, the right hepaticoduodenal fistula is extremely rare and seldom reported in clinical literature. We herein report a case of right hepaticoduodenal fistula and analyze its mechanism, treatment principles, and preventive measures through a literature review.

Comprehensive bile acid pool analysis during ex-vivo liver perfusion in a porcine model of ischemia-reperfusion injury

Bile acids (BA) are key for liver regeneration and injury. This study aims at analyzing the changes in the BA pool induced by ischemia-reperfusion (IRI) and investigates the impact of hypothermic oxygenated perfusion (HOPE) on the BA pool compared to static cold storage (SCS). In a porcine model of IRI, liver grafts underwent 30 min of asystolic warm ischemia followed by 6 h of SCS (n = 6) ± 2 h of HOPE (n = 6) and 2 h of ex-situ warm reperfusion. The BA pool in bile samples was analyzed with liquid chromatography coupled with tandem mass spectrometry. We identified 16 BA and observed significant changes in response to ischemia-reperfusion, which were associated with both protective and injury mechanisms. Second, HOPE-treated liver grafts exhibited a more protective BA phenotype, characterized by a more hydrophilic BA pool compared to SCS. Key BA, such as GlycoCholic Acid, were identified and were associated with a decreased transaminase release and improved lactate clearance during reperfusion. Partial Least Square-Discriminant Analysis revealed a distinct injury profile for the HOPE group. In conclusion, the BA pool changes with liver graft IRI, and preservation with HOPE results in a protective BA phenotype compared to SCS.

Extended criteria liver donation after circulatory death with prolonged warm ischemia: a pilot experience of normothermic regional perfusion and no subsequent ex-situ machine perfusion

BACKGROUND

Livers from controlled donation after circulatory death (cDCD) with very prolonged warm ischemic time (WIT) are regularly transplanted after abdominal normothermic regional perfusion (aNRP) plus ex-situ machine perfusion (MP). Considering aNRP as in-situ MP, we investigated whether the results of a pilot experience of extended criteria cDCD liver transplantation (LT) with prolonged WIT, with aNRP alone, were comparable to the best possible outcomes in low-risk cDCD LT.

METHODS

Prospectively collected data on 24 cDCD LT, with aNRP alone, were analyzed.

RESULTS

The median total and asystolic WIT were 51 and 25 min. Measures within benchmark cut-offs were: median duration of surgery (5.9 h); median intraoperative transfusions (3 units of red blood cells); need for renal replacement therapy (2/24 patients); median intensive care stay (3 days); key complications; overall morbidity, graft loss, and retransplantation up to 12 months; 12-month mortality (2/21 patients). The median hospital stay (33 days, due to logistics) and mortality up to 6 months (2/24 patients, due to graft-unrelated causes) exceeded benchmark thresholds.

CONCLUSIONS

This pilot experience suggests that livers from cDCD with very prolonged WIT that appear viable during adequate quality aNRP may be safely transplanted, with no need for ex-situ MP, with considerable resource savings.

Bile proteome reveals biliary regeneration during normothermic preservation of human donor livers

Normothermic machine perfusion (NMP) after static cold storage is increasingly used for preservation and assessment of human donor livers prior to transplantation. Biliary viability assessment during NMP reduces the risk of post-transplant biliary complications. However, understanding of molecular changes in the biliary system during NMP remains incomplete. We performed an in-depth, unbiased proteomics analysis of bile collected during sequential hypothermic machine perfusion, rewarming and NMP of 55 human donor livers. Longitudinal analysis during NMP reveals proteins reflective of cellular damage at early stages, followed by upregulation of secretory and immune response processes. Livers with bile chemistry acceptable for transplantation reveal protein patterns implicated in regenerative processes, including cellular proliferation, compared to livers with inadequate bile chemistry. These findings are reinforced by detection of regenerative gene transcripts in liver tissue before machine perfusion. Our comprehensive bile proteomics and liver transcriptomics data sets provide the potential to further evaluate molecular mechanisms during NMP and refine viability assessment criteria.

Endothelin Receptor-A Inhibition Decreases Ductular Reaction, Liver Fibrosis, and Angiogenesis in a Model of Cholangitis

BACKGROUND & AIMS

Primary sclerosing cholangitis (PSC) leads to ductular reaction and fibrosis and is complicated by vascular dysfunction. Cholangiocyte and endothelial cell crosstalk modulates their proliferation in cholestatic models. Endothelin (ET)-1 and ET-2 bind to their receptor, ET-A, and cholangiocytes are a key source of ET-1 after bile duct ligation. We aimed to evaluate the therapeutic potential of ET-A inhibition in PSC and biliary-endothelial crosstalk mediated by this pathway.

METHODS

Wild-type and multidrug resistance 2 knockout (Mdr2-/-) mice at 12 weeks of age were treated with vehicle or Ambrisentan (ET-A antagonist) for 1 week by daily intraperitoneal injections. Human control and PSC samples were used.

RESULTS

Mdr2-/- mice at 4, 8, and 12 weeks displayed angiogenesis that peaked at 12 weeks. Mdr2-/- mice at 12 weeks had enhanced biliary ET-1/ET-2/ET-A expression and secretion, whereas human PSC had enhanced ET-1/ET-A expression and secretion. Ambrisentan reduced biliary damage, immune cell infiltration, and fibrosis in Mdr2-/- mice. Mdr2-/- mice had squamous cholangiocytes with blunted microvilli and dilated arterioles lacking cilia; however, Ambrisentan reversed these alterations. Ambrisentan decreased cholangiocyte expression of pro-angiogenic factors, specifically midkine, through the regulation of cFOS. In vitro, ET-1/ET-A caused cholangiocyte senescence, endothelial cell angiogenesis, and macrophage inflammation. In vitro, human PSC cholangiocyte supernatants increased endothelial cell migration, which was blocked with Ambrisentan treatment.

CONCLUSIONS

ET-A inhibition reduced biliary and liver damage in Mdr2-/- mice. ET-A promotes biliary angiocrine signaling that may, in turn, enhance angiogenesis. Targeting ET-A may prove therapeutic for PSC, specifically patients displaying vascular dysfunction.

Restoration of Bile Duct Injury of Donor Livers During Ex Situ Normothermic Machine Perfusion

BACKGROUND

End-ischemic ex situ normothermic machine perfusion (NMP) enables assessment of donor livers prior to transplantation. The objective of this study was to provide support for bile composition as a marker of biliary viability and to investigate whether bile ducts of high-risk human donor livers already undergo repair during NMP.

METHODS

Forty-two livers that were initially declined for transplantation were included in our NMP clinical trial. After NMP, livers were either secondary declined (n = 17) or accepted for transplantation (n = 25) based on the chemical composition of bile and perfusate samples. Bile duct biopsies were taken before and after NMP and assessed using an established histological injury severity scoring system and a comprehensive immunohistochemical assessment focusing on peribiliary glands (PBGs), vascular damage, and regeneration.

RESULTS

Bile ducts of livers that were transplanted after viability testing during NMP showed better preservation of PBGs, (micro)vasculature, and increased cholangiocyte proliferation, compared with declined livers. Biliary bicarbonate, glucose, and pH were confirmed as accurate biomarkers of bile duct vitality. In addition, we found evidence of PBG-based progenitor cell differentiation toward mature cholangiocytes during NMP.

CONCLUSIONS

Favorable bile chemistry during NMP correlates well with better-preserved biliary microvasculature and PBGs, with a preserved capacity for biliary regeneration. During NMP, biliary tree progenitor cells start to differentiate toward mature cholangiocytes, facilitating restoration of the ischemically damaged surface epithelium.

Modeling bile duct ischemia and reoxygenation injury in human cholangiocyte organoids for screening of novel cholangio-protective agents

BACKGROUND

Ischemia of the bile duct is a common feature in liver disease and transplantation, which represents a major cause of morbidity and mortality, especially after liver transplantation. Detailed knowledge of its pathogenesis remains incomplete due to the lack of appropriate in vitro models.

METHODS

To recapitulate biliary damage induced by ischemia and reperfusion in vitro, human intrahepatic cholangiocyte organoids (ICOs) were grown at low oxygen levels of 1% up to 72 h, followed by re-oxygenation at normal levels.

FINDINGS

ICOs stressed by ischemia and subsequent re-oxygenation represented the dynamic change in biliary cell proliferation, upregulation of epithelial-mesenchymal transition (EMT)-associated markers, and the evocation of phase-dependent cell death programs similar to what is described in patients. Clinical-grade alpha-1 antitrypsin was identified as a potent inhibitor of both ischemia-induced apoptosis and necroptosis.

INTERPRETATION

These findings demonstrate that ICOs recapitulate ischemic cholangiopathy in vitro and enable drug assessment studies for the discovery of new therapeutics for ischemic cholangiopathies.

FUNDING

Dutch Digestive FoundationMLDS D16-26; TKI-LSH (Topconsortium Kennis en Innovatie-Life Sciences & Health) grant RELOAD, EMC-LSH19002; Medical Delta program "Regenerative Medicine 4D"; China Scholarship Council No. 201706230252.

Loss of apical sodium bile acid transporter alters bile acid circulation and reduces biliary damage in cholangitis

Primary sclerosing cholangitis (PSC) is characterized by increased ductular reaction (DR), liver fibrosis, hepatic total bile acid (TBA) levels, and mast cell (MC) infiltration. Apical sodium BA transporter (ASBT) expression increases in cholestasis, and ileal inhibition reduces PSC phenotypes. FVB/NJ and multidrug-resistant 2 knockout (Mdr2-/-) mice were treated with control or ASBT Vivo-Morpholino (VM). We measured 1) ASBT expression and MC presence in liver/ileum; 2) liver damage/DR; 3) hepatic fibrosis/inflammation; 4) biliary inflammation/histamine serum content; and 5) gut barrier integrity/hepatic bacterial translocation. TBA/BA composition was measured in cholangiocyte/hepatocyte supernatants, intestine, liver, serum, and feces. Shotgun analysis was performed to ascertain microbiome changes. In vitro, cholangiocytes were treated with BAs ± ASBT VM, and histamine content and farnesoid X receptor (FXR) signaling were determined. Treated cholangiocytes were cocultured with MCs, and FXR signaling, inflammation, and MC activation were measured. Human patients were evaluated for ASBT/MC expression and histamine/TBA content in bile. Control patient- and PSC patient-derived three-dimensional (3-D) organoids were generated; ASBT, chymase, histamine, and fibroblast growth factor-19 (FGF19) were evaluated. ASBT VM in Mdr2-/- mice decreased 1) biliary ASBT expression, 2) PSC phenotypes, 3) hepatic TBA, and 4) gut barrier integrity compared with control. We found alterations between wild-type (WT) and Mdr2-/- mouse microbiome, and ASBT/MC and bile histamine content increased in cholestatic patients. BA-stimulated cholangiocytes increased MC activation/FXR signaling via ASBT, and human PSC-derived 3-D organoids secrete histamine/FGF19. Inhibition of hepatic ASBT ameliorates cholestatic phenotypes by reducing cholehepatic BA signaling, biliary inflammation, and histamine levels. ASBT regulation of hepatic BA signaling offers a therapeutic avenue for PSC.NEW & NOTEWORTHY We evaluated knockdown of the apical sodium bile acid transporter (ASBT) using Vivo-Morpholino in Mdr2KO mice. ASBT inhibition decreases primary sclerosing cholangitis (PSC) pathogenesis by reducing hepatic mast cell infiltration, altering bile acid species/cholehepatic shunt, and regulating gut inflammation/dysbiosis. Since a large cohort of PSC patients present with IBD, this study is clinically important. We validated findings in human PSC and PSC-IBD along with studies in novel human 3-D organoids formed from human PSC livers.

Prolonged preservation by hypothermic machine perfusion facilitates logistics in liver transplantation: A European observational cohort study

A short period (1-2 h) of hypothermic oxygenated machine perfusion (HOPE) after static cold storage is safe and reduces ischemia-reperfusion injury-related complications after liver transplantation. Machine perfusion time is occasionally prolonged for logistical reasons, but it is unknown if prolonged HOPE is safe and compromises outcomes. We conducted a multicenter, observational cohort study of patients transplanted with a liver preserved by prolonged (≥4 h) HOPE. Postoperative biochemistry, complications, and survival were evaluated. The cohort included 93 recipients from 12 European transplant centers between 2014-2021. The most common reason to prolong HOPE was the lack of an available operating room to start the transplant procedure. Grafts underwent HOPE for a median (range) of 4:42 h (4:00-8:35 h) with a total preservation time of 10:50 h (5:50-20:50 h). Postoperative peak ALT was 675 IU/L (interquartile range 419-1378 IU/L). The incidence of postoperative complications was low, and 1-year graft and patient survival were 94% and 88%, respectively. To conclude, good outcomes are achieved after transplantation of donor livers preserved with prolonged (median 4:42 h) HOPE, leading to a total preservation time of almost 21 h. These results suggest that simple, end-ischemic HOPE may be utilized for safe extension of the preservation time to ease transplantation logistics.

Utilization of dielectric properties for assessment of liver ischemia-reperfusion injury in vivo and during machine perfusion

There is a shortage of donor livers and patients consequently die on waiting lists worldwide. Livers are discarded if they are clinically judged to have a high risk of non-function following transplantation. With the aim of extending the pool of available donor livers, we assessed the condition of porcine livers by monitoring the microwave dielectric properties. A total of 21 livers were divided into three groups: control with no injury (CON), biliary injury by hepatic artery occlusion (AHEP), and overall hepatic injury by static cold storage (SCS). All were monitored for four hours in vivo, followed by ex vivo plurithermic machine perfusion (PMP). Permittivity data was modeled with a two-pole Cole–Cole equation, and dielectric properties from one-hour intervals were analyzed during in vivo and normothermic machine perfusion (NMP). A clear increasing trend in the conductivity was observed in vivo in the AHEP livers compared to the control livers. After four hours of NMP, separations in the conductivity were observed between the three groups. Our results indicate that dielectric relaxation spectroscopy (DRS) can be used to detect and differentiate liver injuries, opening for a standardized and reliable point of evaluation for livers prior to transplantation.