Systemic ASBT inactivation protects against liver damage in obstructive cholestasis in mice

Background & Aims

Non-absorbable inhibitors of the apical sodium-dependent bile acid transporter (ASBT; also called ileal bile acid transporter [IBAT]) are recently approved or in clinical development for multiple cholestatic liver disorders and lead to a reduction in pruritus and (markers for) liver injury. Unfortunately, non-absorbable ASBT inhibitors (ASBTi) can induce diarrhoea or may be ineffective if cholestasis is extensive and largely precludes intestinal excretion of bile acids. Systemically acting ASBTi that divert bile salts towards renal excretion may alleviate these issues.

Methods

Bile duct ligation (BDL) was performed in ASBT-deficient (ASBT knockout [KO]) mice as a model for chronic systemic ASBT inhibition in obstructive cholestasis. Co-infusion of radiolabelled taurocholate and inulin was used to quantify renal bile salt excretion after BDL. In a second (wild-type) mouse model, a combination of obeticholic acid (OCA) and intestine-restricted ASBT inhibition was used to lower the bile salt pool size before BDL.

Results

After BDL, ASBT KO mice had reduced plasma bilirubin and alkaline phosphatase compared with wild-type mice with BDL and showed a marked reduction in liver necrotic areas at histopathological analysis, suggesting decreased BDL-induced liver damage. Furthermore, ASBT KO mice had reduced bile salt pool size, lower plasma taurine-conjugated polyhydroxylated bile salt, and increased urinary bile salt excretion. Pretreatment with OCA + ASBTi in wild-type mice reduced the pool size and greatly improved liver injury markers and liver histology.

Conclusions

A reduced bile salt pool at the onset of cholestasis effectively lowers cholestatic liver injury in mice. Systemic ASBT inhibition may be valuable as treatment for cholestatic liver disease by lowering the pool size and increasing renal bile salt output even under conditions of minimal faecal bile salt secretion.

Lay summary

Novel treatment approaches against cholestatic liver disease (resulting in reduced or blocked flow of bile) involve non-absorbable inhibitors of the bile acid transport protein ASBT, but these are not always effective and/or can cause unwanted side effects. In this study, we demonstrate that systemic inhibition/inactivation of ASBT protects mice against developing severe cholestatic liver injury after bile duct ligation, by reducing bile salt pool size and increasing renal bile salt excretion.

Human iPSC-derived hepatocyte system models cholestasis with tight junction protein 2 deficiency

Background & Aims

The truncating mutations in tight junction protein 2 (TJP2) cause progressive cholestasis, liver failure, and hepatocyte carcinogenesis. Due to the lack of effective model systems, there are no targeted medications for the liver pathology with TJP2 deficiency. We leveraged the technologies of patient-specific induced pluripotent stem cells (iPSC) and CRISPR genome-editing, and we aim to establish a disease model which recapitulates phenotypes of patients with TJP2 deficiency.

Methods

We differentiated iPSC to hepatocyte-like cells (iHep) on the Transwell membrane in a polarized monolayer. Immunofluorescent staining of polarity markers was detected by a confocal microscope. The epithelial barrier function and bile acid transport of bile canaliculi were quantified between the two chambers of Transwell. The morphology of bile canaliculi was measured in iHep cultured in the Matrigel sandwich system using a fluorescent probe and live-confocal imaging.

Results

The iHep differentiated from iPSC with TJP2 mutations exhibited intracellular inclusions of disrupted apical membrane structures, distorted canalicular networks, altered distribution of apical and basolateral markers/transporters. The directional bile acid transport of bile canaliculi was compromised in the mutant hepatocytes, resembling the disease phenotypes observed in the liver of patients.

Conclusions

Our iPSC-derived in vitro hepatocyte system revealed canalicular membrane disruption in TJP2 deficient hepatocytes and demonstrated the ability to model cholestatic disease with TJP2 deficiency to serve as a platform for further pathophysiologic study and drug discovery.

Lay summary

We investigated a genetic liver disease, progressive familial intrahepatic cholestasis (PFIC), which causes severe liver disease in newborns and infants due to a lack of gene called TJP2. By using cutting-edge stem cell technology and genome editing methods, we established a novel disease modeling system in cell culture experiments. Our experiments demonstrated that the lack of TJP2 induced abnormal cell polarity and disrupted bile acid transport. These findings will lead to the subsequent investigation to further understand disease mechanisms and develop an effective treatment.

Potent suppression of hydrophobic bile acids by aldafermin, an FGF19 analogue, across metabolic and cholestatic liver diseases

Background & Aims

Higher serum bile acid levels are associated with an increased risk of cirrhosis and liver-related morbidity and mortality. Herein, we report secondary analyses of aldafermin, an engineered analogue of the gut hormone fibroblast growth factor 19, on the circulating bile acid profile in prospective, phase II studies in patients with metabolic or cholestatic liver disease.

Methods

One hundred and seventy-six patients with biopsy-confirmed non-alcoholic steatohepatitis (NASH) and fibrosis and elevated liver fat content (≥8% by magnetic resonance imaging-proton density fat fraction) received 0.3 mg (n = 23), 1 mg (n = 49), 3 mg (n = 49), 6 mg (n = 28) aldafermin or placebo (n = 27) for 12 weeks. Sixty-two patients with primary sclerosing cholangitis (PSC) and elevated alkaline phosphatase (>1.5× upper limit of normal) received 1 mg (n = 21), 3 mg (n = 21) aldafermin or placebo (n = 20) for 12 weeks. Serum samples were collected on day 1 and week 12 for determination of bile acid profile and neoepitope-specific N-terminal pro-peptide of type III collagen (Pro-C3), a direct measure of fibrogenesis.

Results

Treatment with aldafermin resulted in significant dose-dependent reductions in serum bile acids. In particular, bile acids with higher hydrophobicity indices, such as deoxycholic acid, lithocholic acid, glycodeoxycholic acid, glycochenodeoxycholic acid, and glycocholic acid, were markedly lowered by aldafermin in both NASH and PSC populations. Moreover, aldafermin predominantly suppressed the glycine-conjugated bile acids, rather than the taurine-conjugated bile acids. Changes in levels of bile acids correlated with changes in the novel fibrogenesis marker Pro-C3, which detects a neo-epitope of the type III collagen during its formation, in the pooled NASH and PSC populations.

Conclusions

Aldafermin markedly reduced major hydrophobic bile acids that have greater detergent activity and cytotoxicity. Our data provide evidence that bile acids may contribute to sustaining a pro-fibrogenic microenvironment in the liver across metabolic and cholestatic liver diseases.

Lay summary

Aldafermin is an analogue of a gut hormone, which is in development as a treatment for patients with chronic liver disease. Herein, we show that aldafermin can potently and robustly suppress the toxic, hydrophobic bile acids irrespective of disease aetiology. The therapeutic strategy utilising aldafermin may be broadly applicable to other chronic gastrointestinal and liver disorders.

Clinical Trials Registration

The study is registered at Clinicaltrials.govNCT02443116 and NCT02704364.

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Higher serum bile acid levels are associated with an increased risk of liver-related morbidity and mortality.

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Aldafermin produces significant dose-dependent reductions in toxic hydrophobic bile acids in NASH and PSC.

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Changes in bile acids correlate with changes in the novel fibrogenesis marker Pro-C3.

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Bile acids may contribute to a pro-fibrogenic microenvironment in the liver.

NASH-related increases in plasma bile acid levels depend on insulin resistance

Background & Aims

Plasma bile acids (BAs) have been extensively studied as pathophysiological actors in non-alcoholic steatohepatitis (NASH). However, results from clinical studies are often complicated by the association of NASH with type 2 diabetes (T2D), obesity, and insulin resistance (IR). Here, we sought to dissect the relationship between NASH, T2D, and plasma BA levels in a large patient cohort.

Methods

Four groups of patients from the Biological Atlas of Severe Obesity (ABOS) cohort (Clinical Trials number NCT01129297) were included based on the presence or absence of histologically evaluated NASH with or without coincident T2D. Patients were matched for BMI, homeostatic model assessment 2 (HOMA2)-assessed IR, glycated haemoglobin, age, and gender. To study the effect of IR and BMI on the association of plasma BA and NASH, patients from the HEPADIP study were included. In both cohorts, fasting plasma BA concentrations were measured.

Results

Plasma BA concentrations were higher in NASH compared with No-NASH patients both in T2D and NoT2D patients from the ABOS cohort. As we previously reported that plasma BA levels were unaltered in NASH patients of the HEPADIP cohort, we assessed the impact of BMI and IR on the association of NASH and BA on the combined BA datasets. Our results revealed that NASH-associated increases in plasma total cholic acid (CA) concentrations depend on the degree of HOMA2-assessed systemic IR, but not on β-cell function nor on BMI.

Conclusions

Plasma BA concentrations are elevated only in those NASH patients exhibiting pronounced IR.

Lay summary

Non-alcoholic steatohepatitis (NASH) is a progressive liver disease that frequently occurs in patients with obesity and type 2 diabetes. Reliable markers for the diagnosis of NASH are needed. Plasma bile acids have been proposed as NASH biomarkers. Herein, we found that plasma bile acids are only elevated in patients with NASH when significant insulin resistance is present, limiting their utility as NASH markers.

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Bile acids have been studied as pathophysiological actors and biomarkers in NASH.

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Plasma BAs have been reported to be higher in NASH vs. No-NASH patients.

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Plasma BAs are altered in patients with T2D, IR, and obesity, risk factors for NASH.

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Thus, the independent association between plasma BA increases and NASH is unclear.

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NASH-associated increases in plasma BA depend on the degree of insulin sensitivity.

Ablation of gut microbiota alleviates obesity-induced hepatic steatosis and glucose intolerance by modulating bile acid metabolism in hamsters

Since metabolic process differs between humans and mice, studies were performed in hamsters, which are generally considered to be a more appropriate animal model for studies of obesity-related metabolic disorders. The modulation of gut microbiota, bile acids and the farnesoid X receptor (FXR) axis is correlated with obesity-induced insulin resistance and hepatic steatosis in mice. However, the interactions among the gut microbiota, bile acids and FXR in metabolic disorders remained largely unexplored in hamsters. In the current study, hamsters fed a 60% high-fat diet (HFD) were administered vehicle or an antibiotic cocktail by gavage twice a week for four weeks. Antibiotic treatment alleviated HFD-induced glucose intolerance, hepatic steatosis and inflammation accompanied with decreased hepatic lipogenesis and elevated thermogenesis in subcutaneous white adipose tissue (sWAT). In the livers of antibiotic-treated hamsters, cytochrome P450 family 7 subfamily B member 1 (CYP7B1) in the alternative bile acid synthesis pathway was upregulated, contributing to a more hydrophilic bile acid profile with increased tauro-β-muricholic acid (TβMCA). The intestinal FXR signaling was suppressed but remained unchanged in the liver. This study is of potential translational significance in determining the role of gut microbiota-mediated bile acid metabolism in modulating diet-induced glucose intolerance and hepatic steatosis in the hamster.

Dietary fat and gut microbiota interactions determine diet-induced obesity in mice

Objective

Gut microbiota may promote positive energy balance; however, germfree mice can be either resistant or susceptible to diet-induced obesity (DIO) depending on the type of dietary intervention. We here sought to identify the dietary constituents that determine the susceptibility to body fat accretion in germfree (GF) mice.

Methods

GF and specific pathogen free (SPF) male C57BL/6N mice were fed high-fat diets either based on lard or palm oil for 4 wks. Mice were metabolically characterized at the end of the feeding trial. FT-ICR-MS and UPLC-TOF-MS were used for cecal as well as hepatic metabolite profiling and cecal bile acids quantification, respectively. Hepatic gene expression was examined by qRT-PCR and cecal gut microbiota of SPF mice was analyzed by high-throughput 16S rRNA gene sequencing.

Results

GF mice, but not SPF mice, were completely DIO resistant when fed a cholesterol-rich lard-based high-fat diet, whereas on a cholesterol-free palm oil-based high-fat diet, DIO was independent of gut microbiota. In GF lard-fed mice, DIO resistance was conveyed by increased energy expenditure, preferential carbohydrate oxidation, and increased fecal fat and energy excretion. Cecal metabolite profiling revealed a shift in bile acid and steroid metabolites in these lean mice, with a significant rise in 17β-estradiol, which is known to stimulate energy expenditure and interfere with bile acid metabolism. Decreased cecal bile acid levels were associated with decreased hepatic expression of genes involved in bile acid synthesis. These metabolic adaptations were largely attenuated in GF mice fed the palm-oil based high-fat diet. We propose that an interaction of gut microbiota and cholesterol metabolism is essential for fat accretion in normal SPF mice fed cholesterol-rich lard as the main dietary fat source. This is supported by a positive correlation between bile acid levels and specific bacteria of the order Clostridiales (phylum Firmicutes) as a characteristic feature of normal SPF mice fed lard.

Conclusions

In conclusion, our study identified dietary cholesterol as a candidate ingredient affecting the crosstalk between gut microbiota and host metabolism.

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Cholesterol-based but not plant sterol-based high-fat diet protects germfree (GF) mice from diet-induced obesity (DIO).

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DIO resistant GF mice show preferential carbohydrate oxidation, higher energy expenditure and energy and fat excretion.

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DIO resistance in GF mice is accompanied by increased steroid hormone levels but decreased bile acid levels in the cecum.

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Substrate oxidation and fat excretion in DIO resistant GF mice is linked to decreased hepatic Cyp7a1 and Nr1h4 expression.

Role of farnesoid X receptor and bile acids in alcoholic liver disease

Alcoholic liver disease (ALD) is one of the major causes of liver morbidity and mortality worldwide. Chronic alcohol consumption leads to development of liver pathogenesis encompassing steatosis, inflammation, fibrosis, cirrhosis, and in extreme cases, hepatocellular carcinoma. Moreover, ALD may also associate with cholestasis. Emerging evidence now suggests that farnesoid X receptor (FXR) and bile acids also play important roles in ALD. In this review, we discuss the effects of alcohol consumption on FXR, bile acids and gut microbiome as well as their impacts on ALD. Moreover, we summarize the findings on FXR, FoxO3a (forkhead box-containing protein class O3a) and PPARα (peroxisome proliferator-activated receptor alpha) in regulation of autophagy-related gene transcription program and liver injury in response to alcohol exposure.

Bile acid signaling and biliary functions

This review focuses on various components of bile acid signaling in relation to cholangiocytes. Their roles as targets for potential therapies for cholangiopathies are also explored. While many factors are involved in these complex signaling pathways, this review emphasizes the roles of transmembrane G protein coupled receptor (TGR5), farnesoid X receptor (FXR), ursodeoxycholic acid (UDCA) and the bicarbonate umbrella. Following a general background on cholangiocytes and bile acids, we will expand the review and include sections that are most recently known (within 5-7 years) regarding the field of bile acid signaling and cholangiocyte function. These findings all demonstrate that bile acids influence biliary functions which can, in turn, regulate the cholangiocyte response during pathological events.