On the Mechanisms of Biliary Flux

Primary sclerosing cholangitis

Primary sclerosing cholangitis (PSC) is a chronic biliary inflammation associated with periductular fibrosis of the intrahepatic and extrahepatic bile ducts leading to strictures, bacterial cholangitis, decompensated liver disease and need for liver transplantation. This rare focal liver disease affects all races and ages, with a predominance of young males. There is an up to 88% association with inflammatory bowel disease. Although the aetiology is unknown and the pathophysiology is poorly understood, PSC is regarded as an autoimmune liver disease based on a strong immunogenetic background. Further, the associated risk for various malignancies, particularly cholangiocellular carcinoma, is also poorly understood. No medical therapy has been approved so far nor has been shown to improve transplant-free survival. However, ursodeoxycholic acid is widely used since it improves the biochemical parameters of cholestasis and is safe at low doses. MRI of the biliary tract is the primary imaging technology for diagnosis. Endoscopic interventions of the bile ducts should be limited to clinically relevant strictures for balloon dilatation, biopsy and brush cytology. End-stage liver disease with decompensation is an indication for liver transplantation with recurrent PSC in up to 38% of patients. Several novel therapeutic strategies are in various stages of development, including apical sodium-dependent bile acid transporter and ileal bile acid transporter inhibitors, integrin inhibitors, peroxisome proliferator-activated receptor agonists, CCL24 blockers, recombinant FGF19, CCR2/CCR5 inhibitors, farnesoid X receptor bile acid receptor agonists, and nor-ursodeoxycholic acid. Manipulation of the gut microbiome includes faecal microbiota transplantation. This article summarizes present knowledge and defines unmet medical needs to improve quality of life and survival.

Hepatocyte aquaporin 8-mediated water transport facilitates bile dilution and prevents gallstone formation in mice

BACKGROUND & AIMS

Although water channel aquaporin-8 (AQP8) has been implicated in hepatic bile formation and liver diseases associated with abnormal bile flow in human and animal studies, direct evidence of its involvement in bile secretion is still lacking. This study aimed to determine the role of AQP8 in bile secretion and gallstone formation.

METHODS

We generated various transgenic knock-in and knockout mouse models and assessed liver AQP8 expression by immunostaining and immunoblotting, hepatic bile secretion by cannulation of the common bile duct, cholesterol gallstone formation by feeding a high-fat lithogenic diet, and identified regulatory small molecules by screening the organic fractions of cholagogic Chinese herbs and performing biochemical characterization.

RESULTS

We identified a novel expression pattern of AQP8 protein in the canalicular membrane of approximately 50% of the liver lobules. AQP8-deficient mice exhibited impaired hepatic bile formation, characterized by the secretion of concentrated bile with a lower flow rate and higher levels of bile lipids than that of wild-type littermates. Aqp8-/- mice showed accelerated gallstone formation, which was rescued by AAV-mediated hepatic expression of AQP8 or AQP1. Moreover, we identified a small molecule, scutellarin, that upregulates hepatocyte AQP8 expression in vitro and in vivo. In Aqp8+/+ mice, scutellarin significantly increased bile flow, decreased bile lipid concentrations, and prevented gallstone formation compared to Aqp8-/- mice. Molecular studies revealed that scutellarin promoted the ubiquitination and degradation of HIF-1α, a negative transcriptional regulator of AQP8, by disrupting its interactions with HSP90.

CONCLUSIONS

AQP8 plays a crucial role in facilitating water transport and bile dilution during hepatic bile formation, thereby mitigating gallstone formation in mice. Small-molecule intervention validated hepatocyte AQP8 as a promising drug target for gallstone therapy.

IMPACT AND IMPLICATIONS

The incidence of gallstone disease is high, and current drug treatments for gallstones are very limited, necessitating the identification of novel drug targets for therapeutic development with universal applicability. To our knowledge, this is the first study to provide direct evidence that the hepatic water channel AQP8 plays a key role in bile dilution and gallstone formation. Modulation of hepatic water transport may provide a universal therapeutic strategy for all types of gallstone diseases.

Exploration of the Combined Mechanism of Direct and Indirect Effects of Paeoniflorin in the Treatment of Cholestasis

Cholestasis is a multifactorial hepatobiliary disorder, characterized by obstruction of bile flow and accumulation of bile, which in turn causes damage to liver cells and other tissues. In severe cases, it can result in the development of life-threatening conditions, including cirrhosis and liver cancer. Paeoniflorin (PF) has been demonstrated to possess favourable therapeutic potential for the treatment of cholestasis. The objective of this research was to examine the molecular mechanism of PF in the treatment of ANIT-induced cholestasis and to propose novel avenues for further research on the pharmacological effects of PF. In vivo and in vitro models of cholestasis were developed. The histopathological changes in the bile ducts and liver were evaluated through the use of hematoxylin and eosin (HE) staining. The extent of apoptosis was evaluated through the use of immunofluorescence (IF), immunoblotting (WB), and electron microscopy. The JNK signalling pathway was identified as the direct mechanism of action of PF through the utilisation of HuProt™ 20 K chips and other technologies. The present study demonstrated that PF markedly alleviated liver injury in an ANIT-induced cholestasis model. Specifically, PF was observed to attenuate cholestasis-induced liver injury by reducing the abnormal elevation of liver function indices and suppressing the expression of inflammatory mediators. Furthermore, PF exhibited anti-apoptotic properties in both in vivo and in vitro experiments, thereby mitigating cholestasis-induced hepatocyte apoptosis. These protective effects are attributable to the fact that PF exerts its action through direct interaction with the JNK pathway. It has been demonstrated that PF is capable of binding directly to MAPK8 (JNK1) and MAPK9 (JNK2), thereby inhibiting JNK activation and reducing apoptosis. With regard to the protection of bile ducts, PF may indirectly inhibit hepatocyte apoptosis by maintaining the structural integrity and tight junctions of bile duct cells. PF improved cholestasis by inhibiting hepatocyte apoptosis directly by targeting the JNK signaling pathway and indirectly inhibited hepatocyte apoptosis by improving the tight junctions of bile duct cells to regulate the bile duct microenvironment.

Presence of cholestasis and its impact on survival in SARS-CoV-2 associated acute respiratory distress syndrome

Data on cholestasis and biliary injury in patients with COVID-19 are scarce. The primary aim of this study was to evaluate the prevalence of cholestasis and factors associated with its development and outcome in critically ill patients with COVID-19 associated acute respiratory distress syndrome (ARDS). In this retrospective exploratory study, COVID-19 patients with ARDS admitted to an intensive care unit (ICU) at the Medical University of Vienna were evaluated for the development of cholestasis defined as an alkaline phosphatase level of 1.67x upper limit of normal for at least three consecutive days. Simple and multiple logistic regression analysis was used to evaluate parameters associated with development of cholestasis and survival. Of 225 included patients 119 (53%) developed cholestasis during ICU stay. Patients with cholestasis had higher peak levels of alkaline phosphatase, gamma-glutamyl transferase, bilirubin and inflammation parameters. Factors independently associated with cholestasis were extracorporeal membrane oxygenation support, ketamine use, high levels of inflammation parameters and disease severity. Presence of cholestasis and peak ALP levels were independently associated with worse ICU and 6-month survival. Development of cholestasis is a common complication in critically ill COVID-19 patients and represents a negative prognostic marker for survival. It is associated with disease severity and specific treatment modalities of intensive care.

Pediatric Cholestatic Diseases: Common and Unique Pathogenic Mechanisms

Cholestasis is the predominate feature of many pediatric hepatobiliary diseases. The physiologic flow of bile requires multiple complex processes working in concert. Bile acid (BA) synthesis and excretion, the formation and flow of bile, and the enterohepatic reuptake of BAs all function to maintain the circulation of BAs, a key molecule in lipid digestion, metabolic and cellular signaling, and, as discussed in the review, a crucial mediator in the pathogenesis of cholestasis. Disruption of one or several of these steps can result in the accumulation of toxic BAs in bile ducts and hepatocytes leading to inflammation, fibrosis, and, over time, biliary and hepatic cirrhosis. Biliary atresia, progressive familial intrahepatic cholestasis, primary sclerosing cholangitis, and Alagille syndrome are four of the most common pediatric cholestatic conditions. Through understanding the commonalities and differences in these diseases, the important cellular mechanistic underpinnings of cholestasis can be greater appreciated.

Understanding bacterial infiltration of the pancreas through a deformable pancreatic duct

Tiny amount of bacteria are found in the pancreas in pancreatitis and cancer, which seemed involved in inflammation and carcinogenesis. However, bacterial infiltration from the duodenum is inhibited by the physical defense mechanisms such as bile flow and the sphincter of Oddi. To understand how the bacteria possibly infiltrate the pancreas through a deformable pancreatic duct, influenced by the periodic contractions of the sphincter of Oddi, a mathematical model of bacterial infiltration is developed that considered large deformation, fluid flow, and bacterial transport in a deformable pancreatic duct. In addition, the sphincter's contraction wave is modeled by including its propagation from the pancreas toward the duodenum. Simulated structure of the deformed duct with the relaxed sphincter and simulated bile distribution agreed reasonably well with the literature, validating the model. Bacterial infiltration from the duodenum in a deformable pancreatic duct, following the sphincter's contraction, is counteracted by a gradual peristalsis-like deformation of the pancreatic duct, due to an antegrade contraction wave propagation from the pancreas to the duodenum, Parametric sensitivity analysis demonstrated that bacterial infiltration is increased with lower bile and pancreatic juice flow rate, greater contraction amplitude and frequency, thinner wall thickness, and retrograde contraction wave propagation. Since contraction waves following retrograde propagation are increased in patients with common bile duct stones and pancreatitis, they may possibly be factors for continuum inflammation of pancreas. (224 words).

Basic concepts of mixture toxicity and relevance for risk evaluation and regulation

Exposure to multiple substances is a challenge for risk evaluation. Currently, there is an ongoing debate if generic "mixture assessment/allocation factors" (MAF) should be introduced to increase public health protection. Here, we explore concepts of mixture toxicity and the potential influence of mixture regulation concepts for human health protection. Based on this analysis, we provide recommendations for research and risk assessment. One of the concepts of mixture toxicity is additivity. Substances may act additively by affecting the same molecular mechanism within a common target cell, for example, dioxin-like substances. In a second concept, an "enhancer substance" may act by increasing the target site concentration and aggravating the adverse effect of a "driver substance". For both concepts, adequate risk management of individual substances can reliably prevent adverse effects to humans. Furthermore, we discuss the hypothesis that the large number of substances to which humans are exposed at very low and individually safe doses may interact to cause adverse effects. This commentary identifies knowledge gaps, such as the lack of a comprehensive overview of substances regulated under different silos, including food, environmentally and occupationally relevant substances, the absence of reliable human exposure data and the missing accessibility of ratios of current human exposure to threshold values, which are considered safe for individual substances. Moreover, a comprehensive overview of the molecular mechanisms and most susceptible target cells is required. We conclude that, currently, there is no scientific evidence supporting the need for a generic MAF. Rather, we recommend taking more specific measures, which focus on compounds with relatively small ratios between human exposure and doses, at which adverse effects can be expected.

Alcohol-dependent downregulation of apolipoprotein H exacerbates fatty liver and gut microbiota dysbiosis in mice

Background

Alcohol-related liver disease (ALD) is a major chronic liver ailment caused by alcohol overconsumption and abuse. Apolipoprotein H (APOH) participates in lipid metabolism and might have a potential regulatory role in ALD. Therefore, this study aimed to explore the effects of ApoH on alcohol-induced liver injury and gut microbiota dysbiosis.

Methods

ApoH^−/− mice were generated and the synergic alcoholic steatohepatitis mouse model was constructed, which were used to assess liver function and pathological changes.

Results

ApoH^−/− mice clearly exhibited spontaneous steatohepatitis. Severe hepatic steatosis was observed in alcohol-fed WT and ApoH^−/− mice, in which ApoH expression was reduced post alcohol consumption. Moreover, RNA-seq and KEGG pathway analyses indicated that differential expression genes enriched in lipid metabolism and oxidation–reduction process between in alcohol-fed ApoH^−/− mice and pair-fed control mice. Finally, gut microbiota diversity and composition were assessed by 16S rRNA Illumina next-generation sequencing. Alpha diversity of enterobacteria was lower in ApoH^−/− mice with ethanol feeding than in ethanol-fed WT mice and all control-fed mice (P < 0.05). Moreover, KEGG enrichment analysis, using PICRUSt software, revealed that metabolic functions were activated in the gut microorganisms of ApoH^−/− mice with ethanol feeding (P < 0.05).

Conclusions

Alcohol-downregulated ApoH expression, leading to the progress of fatty liver disease and gut microbiota dysbiosis.

Liver specific, systemic and genetic contributors to alcohol-related liver disease progression

Alcohol-related liver disease (ALD) impacts millions of patients worldwide each year and the numbers are increasing. Disease stages range from steatosis via steatohepatitis and fibrosis to cirrhosis, severe alcohol-associated hepatitis and liver cancer. ALD is usually diagnosed at an advanced stage of progression with no effective therapies. A major research goal is to improve diagnosis, prognosis and also treatments for early ALD. This however needs prioritization of this disease for financial investment in basic and clinical research to more deeply investigate mechanisms and identify biomarkers and therapeutic targets for early detection and intervention. Topics of interest are communication of the liver with other organs of the body, especially the gut microbiome, the individual genetic constitution, systemic and liver innate inflammation, including bacterial infections, as well as fate and number of hepatic stellate cells and the composition of the extracellular matrix in the liver. Additionally, mechanical forces and damaging stresses towards the sophisticated vessel system of the liver, including the especially equipped sinusoidal endothelium and the biliary tract, work together to mediate hepatocytic import and export of nutritional and toxic substances, adapting to chronic liver disease by morphological and functional changes. All the aforementioned parameters contribute to the outcome of alcohol use disorder and the risk to develop advanced disease stages including cirrhosis, severe alcoholic hepatitis and liver cancer. In the present collection, we summarize current knowledge on these alcohol-related liver disease parameters, excluding the aspect of inflammation, which is presented in the accompanying review article by Lotersztajn and colleagues.