Bile acid-induced apoptosis in hepatocytes is caspase-6-dependent

Assessing the efficacy of farnesoid X receptor agonists in the management of metabolic dysfunction-associated steatotic liver disease: A systematic review and meta-analysis: Efficacy of Farnesoid X Receptor Agonists in Metabolic Dysfunction-associated Steatotic Liver Disease: Systematic Review and Meta-analysis

BACKGROUND AND AIMS

Several randomized clinical trials have been conducted assessing the potential efficacy of Farnesoid X receptor (FXR) agonists in patients with metabolic dysfunction-associated steatotic liver disease (MASLD). A comprehensive review and analysis were needed to evaluate the findings of these trials. Hence, this systematic review and meta-analysis aim to study the association between FXR agonists and hepatic outcomes in patients with MASLD.

METHODS

Systematic review and meta-analysis evaluating the efficacy of FXR agonists in 1,227 patients assigned to the FXR intervention group compared to 650 patients in the placebo group. Changes in liver enzymes and hepatic steatosis assessed by MRI-PDFF were evaluated.

RESULTS

FXR agonist use was associated with a significant reduction in levels of AST, (WMD= -4.51, 95% CI=[-8.39,-0.63], P=0.02); ALT (WMD= -13.02, 95% CI=[-17.85,-8.19], P<0.00001); GGT (WMD= -32.20, 95% CI=[-38.63,-25.98], P<0.00001); MRI-PDFF, (SMD= -1.14, 95% CI=[-1.92,-0.35], P=0.005). FXR agonists did not significantly affect ALP levels, (WMD= 25.04, 95% CI=[19.22,30.87], P<0.00001] CONCLUSION: Results show promising evidence supporting the efficacy of FXR agonists in reducing hepatic steatosis and biomarkers of hepatic injury such as ALT, AST, and GGT.

Impairment of bile acid metabolism and altered composition by lead and copper in Bufo gargarizans tadpoles

Lead (Pb) and copper (Cu) are two common heavy metal contaminants in environments, and liver is recognized as one of the main target organs for toxicity of Pb and Cu in animal organisms. Bile acids play a critical role in regulating hepatic metabolic homeostasis by activating farnesoid X receptor (Fxr). However, there were few studies on the interactions between bile acids and liver pathology caused by heavy metals. In this work, the histopathological changes, targeted metabolome and transcriptome responses in the liver of Bufo gargarizans tadpoles to Pb and/or Cu were examined. We found that exposure to Pb and/or Cu altered the hepatic bile acid profile, resulting in increased hydrophobicity and toxicity of the bile acid pool. And the expression of genes involved in bile acid metabolism and their downstream signaling pathways in the liver were significantly altered by Pb and/or Cu exposure. The alteration of bile acid profiles and the expression of genes related to bile acid metabolism might induce oxidative stress and inflammation, ultimately inducing hepatocyte injury observed in the histological sections. To our knowledge, this is the first study to provide histological, biochemical, and molecular evidence for establishing the link between Pb and Cu exposure, disturbances in hepatic bile acid metabolism, and liver injury.

Lactobacillus johnsonii Attenuates Liver Steatosis and Bile Acid Dysregulation in Parenteral Nutrition-Fed Rats

Parenteral nutrition (PN), a vital therapy for patients with intestinal failure, can lead to the development of parenteral nutrition-associated liver disease (PNALD). In this study, we aimed to investigate the role of Lactobacillus johnsonii (L. johnsonii) in a rat model of PNALD. Total parenteral nutrition (TPN)-fed rats were used to assess the role of L. johnsonii in liver steatosis, bile acid metabolism, gut microbiota, and hepatocyte apoptosis. We observed a depletion of L. johnsonii that was negatively correlated with the accumulation of glycochenodeoxycholic acid (GCDCA), a known apoptosis inducer, in rats subjected to TPN. L. johnsonii attenuated TPN-induced liver steatosis by inhibiting fatty acid synthesis and promoting fatty acid oxidation. TPN resulted in a decrease in bile acid synthesis and biliary bile secretion, which were partially restored by L. johnsonii treatment. The gut microbial profile revealed depletion of pathogenic bacteria in L. johnsonii-treated rats. L. johnsonii treatment reduced both hepatic GCDCA levels and hepatocyte apoptosis compared with the TPN group. In vitro, L. johnsonii treatment inhibited GCDCA-induced hepatocyte apoptosis via its bile salt hydrolase (BSH) activity. Our findings suggest that L. johnsonii protects against liver steatosis, bile acid dysregulation, and hepatocyte apoptosis in TPN-fed rats.

In Vitro Cytotoxic Effect of Aqueous Extracts from Leaves and Rhizomes of the Seagrass Posidonia oceanica (L.) Delile on HepG2 Liver Cancer Cells: Focus on Autophagy and Apoptosis

Aqueous extracts from Posidonia oceanica's green and brown (beached) leaves and rhizomes were prepared, submitted to phenolic compound and proteomic analysis, and examined for their potential cytotoxic effect on HepG2 liver cancer cells in culture. The chosen endpoints related to survival and death were cell viability and locomotory behavior, cell-cycle analysis, apoptosis and autophagy, mitochondrial membrane polarization, and cell redox state. Here, we show that 24 h exposure to both green-leaf- and rhizome-derived extracts decreased tumor cell number in a dose-response manner, with a mean half maximal inhibitory concentration (IC₅₀) estimated at 83 and 11.5 μg of dry extract/mL, respectively. Exposure to the IC₅₀ of the extracts appeared to inhibit cell motility and long-term cell replicating capacity, with a more pronounced effect exerted by the rhizome-derived preparation. The underlying death-promoting mechanisms identified involved the down-regulation of autophagy, the onset of apoptosis, the decrease in the generation of reactive oxygen species, and the dissipation of mitochondrial transmembrane potential, although, at the molecular level, the two extracts appeared to elicit partially differentiating effects, conceivably due to their diverse composition. In conclusion, P. oceanica extracts merit further investigation to develop novel promising prevention and/or treatment agents, as well as beneficial supplements for the formulation of functional foods and food-packaging material with antioxidant and anticancer properties.

Gut microbiota alters host bile acid metabolism to contribute to intrahepatic cholestasis of pregnancy

Intrahepatic cholestasis of pregnancy (ICP) is a female pregnancy-specific disorder that is characterized by increased serum bile acid and adverse fetal outcomes. The aetiology and mechanism of ICP are poorly understood; thus, existing therapies have been largely empiric. Here we show that the gut microbiome differed significantly between individuals with ICP and healthy pregnant women, and that colonization with gut microbiome from ICP patients was sufficient to induce cholestasis in mice. The gut microbiomes of ICP patients were primarily characterized by Bacteroides fragilis (B. fragilis), and B. fragilis was able to promote ICP by inhibiting FXR signaling via its BSH activity to modulate bile acid metabolism. B. fragilis-mediated FXR signaling inhibition was responsible for excessive bile acid synthesis and interrupted hepatic bile excretion to ultimately promote the initiation of ICP. We propose that modulation of the gut microbiota-bile acid-FXR axis may be of value for ICP treatment.

Review article: insights into the bile acid-gut microbiota axis in intestinal failure-associated liver disease-redefining the treatment approach

BACKGROUND

Intestinal failure-associated liver disease (IFALD) increases mortality of patients with intestinal failure (IF), but lacks effective prevention or treatment approaches. Bile acids, gut microbiota and the host have close and complex interactions, which play a central role in modulating host immune and metabolic homeostasis. Increasing evidence suggests that derangement of the bile acid-gut microbiota (BA-GM) axis contributes to the development of IFALD.

AIMS

To review the BA-GM axis in the pathogenesis and clinical applications of IFALD, and to explore future directions for effective disease management.

METHODS

We conducted a literature search on bile acid and gut microbiota in IF and liver diseases.

RESULTS

The BA-GM axis demonstrates a unique IF signature manifesting as an increase in primary-to-secondary bile acids ratio, disturbed enterohepatic circulation, blunted bile acid signalling pathways, gut microbial dysbiosis, and altered microbial metabolic outputs. Bile acids and gut microbiota shape the compositional and functional alterations of each other in IF; collaboratively, they promote immune dysfunction and metabolic aberration in the liver. Diagnostic markers and treatments targeting the BA-GM axis showed promising potential in the management of IFALD.

CONCLUSIONS

Bile acids and gut microbiota play a central role in the development of IFALD and make attractive biomarkers as well as therapeutic targets. A multitarget, individualised therapy aiming at different parts of the BA-GM axis may provide optimal clinical benefits and requires future investigation.

Cumulative damage effect of jaundice may be an effective predictor of complications in patients undergoing radical resection of Bismuth type II or above hilar cholangiocarcinoma

Background

There is currently no preoperative risk assessment system for predicting complications after radical resection of hilar cholangiocarcinoma. This study examined the association between the cumulative damage effect of jaundice (CDEJ) and the complications of radical resection of Bismuth II or above hilar cholangiocarcinoma.

Methods

Patients who underwent radical resection of hilar cholangiocarcinoma at the Department of Hepatobiliary Surgery, West China Hospital of Sichuan University, from April 2010 to January 2018 were retrospectively included.

Results

Of the 171 included patients, 115 (67.3%) patients experienced complications. Multivariate analysis found that CDEJ [odds ratio (OR) =1.0001, 95% confidence interval (95% CI) =1.000027–1.000239, P=0.014], cholangitis (OR =9.638, 95% CI =2.683–34.622, P=0.001), and preoperative bilirubin (OR =1.006, 95% CI =1.002–1.01, P=0.004) were independently associated with the incidence of complications. CDEJ (OR =1.0001, 95% CI =1.00001–1.00019, P=0.024), age (OR =1.083, 95% CI =1.029–1.14, P=0.002), preoperative bilirubin (OR =1.083, 95% CI =1.029–1.14, P=0.002), and future liver remnant (FLR) (OR =0.963, 95% CI =0.941–0.986, P=0.002) were independently associated with hepatic failure. To predict the incidence of complications, the following criteria were used. For the CDEJ cutoff of 2,151, the area under the receiver operating characteristic curve (AUC) was 0.69 (95% CI =0.615–0.759), the sensitivity was 66.09%, and the specificity was 69.64%. For the preoperative bilirubin cutoff of 111.7 µmol/L, the AUC was 0.65 (95% CI =0.573–0.721), the sensitivity was 84.35%, and the specificity was 42.86%. To predict hepatic failure, the following criteria were used. For the CDEJ cutoff of 3,931.95, the AUC was 0.605 (95% CI =0.582–0.679), the sensitivity was 51.28%, and the specificity was 70.45%. For the preoperative bilirubin cutoff of 115.9 µmol/L, the AUC was 0.638 (95% CI =0.561–0.71), the sensitivity was 92.31%, and the specificity was 32.58%. For the FLR cutoff of 50, the AUC was 0.638 (95% CI =0.515–0.667), the sensitivity was 48.72%, and the specificity was 78.79%.

Conclusions

CDEJ was independently associated with complications and can moderately predict complications after surgical resection of hilar cholangiocarcinoma.

Bile Acid Toxicity and Protein Kinases

If the bile acids reach to pathological concentrations due to cholestasis, accumulation of hydrophobic bile acids within the hepatocyte may result in cell death. Thus, hydrophobic bile acids induce apoptosis in hepatocytes, while hydrophilic bile acids increase intracellular adenosine 3',5'-monophosphate (cAMP) levels and activate mitogen-activated protein kinase (MAPK) and phosphoinositide 3-kinase (PI3K) pathways to protect hepatocytes from apoptosis.Two apoptotic pathways have been described in bile acids-induced death. Both are controlled by multiple protein kinase signaling pathways. In mitochondria-controlled pathway, caspase-8 is activated with death domain-independent manner, whereas, Fas-dependent classical pathway involves ligand-independent oligomerization of Fas.Hydrophobic bile acids dose-dependently upregulate the inflammatory response by further stimulating production of inflammatory cytokines. Death receptor-mediated apoptosis is regulated at the cell surface by the receptor expression, at the death-inducing signaling complex (DISC) by expression of procaspase-8, the death receptors Fas-associated death domain (FADD), and cellular FADD-like interleukin 1-beta (IL-1β)-converting enzyme (FLICE) inhibitory protein (cFLIP). Bile acids prevent cFLIP recruitment to the DISC and thereby enhance initiator caspase activation and lead to cholestatic apoptosis. At mitochondria, the expression of B-cell leukemia/lymphoma-2 (Bcl-2) family proteins contribute to apoptosis by regulating mitochondrial cytochrome c release via Bcl-2, Bcl-2 homology 3 (BH3) interacting domain death agonist (Bid), or Bcl-2 associated protein x (Bax). Fas receptor CD95 activation by hydrophobic bile acids is initiated by reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase-dependent reactive oxygen species (ROS) signaling. However, activation of necroptosis by ligands of death receptors requires the kinase activity of receptor interacting protein1 (RIP1), which mediates the activation of RIP3 and mixed lineage kinase domain-like protein (MLKL). In this chapter, mainly the effect of protein kinases signal transduction on the mechanisms of hydrophobic bile acids-induced inflammation, apoptosis, necroptosis and necrosis are discussed.

Bile accelerates carcinogenic processes in pancreatic ductal adenocarcinoma cells through the overexpression of MUC4

Pancreatic cancer (PC) is one of the leading causes of mortality rate globally and is usually associated with obstructive jaundice (OJ). Up to date, there is no clear consensus on whether biliary decompression should be performed prior to surgery and how high levels of serum bile affects the outcome of PC. Therefore, our study aims were to characterise the effect of bile acids (BAs) on carcinogenic processes using pancreatic ductal adenocarcinoma (PDAC) cell lines and to investigate the underlying mechanisms. Liquid chromatography-mass spectrometry was used to determine the serum concentrations of BAs. The effects of BAs on tumour progression were investigated using different assays. Mucin expressions were studied in normal and PDAC cell lines and in human samples at gene and protein levels and results were validated with gene silencing. The levels of BAs were significantly higher in the PDAC + OJ group compared to the healthy control. Treating PDAC cells with different BAs or with human serum obtained from PDAC + OJ patients enhanced the rate of proliferation, migration, adhesion, colony forming, and the expression of MUC4. In PDAC + OJ patients, MUC4 expression was higher and the 4-year survival rate was lower compare to PDAC patients. Silencing of MUC4 decreased BAs-induced carcinogenic processes in PDAC cells. Our results show that BAs promote carcinogenic process in PDAC cells, in which the increased expression of MUC4 plays an important role. Based on these results, we assume that in PC patients, where the disease is associated with OJ, the early treatment of biliary obstruction improves life expectancy.

Augmenter of Liver Regeneration (ALR) regulates bile acid synthesis and attenuates bile acid-induced apoptosis via glycogen synthase kinase-3β (GSK-3β) inhibition

Bile acid synthesis is restricted to hepatocytes and is rate-limited by CYP7A1 (cholesterol 7α hydroxylase). CYP7A1 expression undergoes tight regulation and is repressed after partial hepatectomy to prevent the accumulation of toxic bile acids. Augmenter of Liver Regeneration (ALR) is a hepatotrophic factor shown to support liver regeneration by augmenting cell proliferation and reducing apoptosis. Nevertheless, less is known about ALR's role in protecting hepatocytes from bile acid accumulation and bile acid-induced apoptosis. Therefore, HepG2 and Huh-7 cells were incubated with recombinant human ALR (rALR) and the expression of CYP7A1, bile acid-induced apoptosis as well as potential molecular mechanisms were analyzed. We found that rALR reduces CYP7A1 expression by increasing nuclear NFκB levels. Moreover, rALR reduced glycochenodeoxycholate (GCDC)-induced-apoptosis by decreased expression of pro-apoptotic Bax and enhanced expression of anti-apoptotic Mcl-1, which is regulated by phosphatidylinositol-3-kinase (PI3K)/Akt activation and glycogen synthase kinase-3β (GSK3β) phosphorylation. Inhibitors for PI3K/Akt (GSK690693) and GSK3β (SB415286) confirmed the specificity of rALR treatment for this pathway. In addition, rALR reduces pro-death signaling by decreasing GCDC-induced JNK phosphorylation. Taken all together, rALR might contribute to protecting hepatocytes from toxic concentrations of bile acids by down-regulating their denovo synthesis, attenuating apoptosis by activation of PI3K/Akt - GSK3β pathway and inhibition of JNK signaling. Thereby this suggests a new role of ALR in augmenting the process of liver regeneration.

Dysregulation of Circulating FGF19 and Bile Acids in Primary Biliary Cholangitis-Autoimmune Hepatitis Overlap Syndrome

Background

Primary biliary cholangitis-autoimmune hepatitis overlap syndrome (PBC-AIH OS), which exhibits features between autoimmune hepatitis and cholestasis, is a common condition and usually shows a progressive course toward cirrhosis and liver failure without adequate treatment. Synthesis of bile acids (BAs) plays an important role in liver injury in cholestasis, and the process is regulated by fibroblast growth factor 19 (FGF19). The overall role of circulating FGF19 in BA synthesis and PBC-AIH OS requires further investigation.

Methods

We analyzed BA synthesis and correlated clinical parameters with serum BAs and FGF19 in 35 patients with PBC-AIH OS. Serum concentrations of 7alpha-hydroxycholest-4-en-3-one (C4) were used to quantify the synthesis of BA directly.

Results

Serum FGF19 levels were higher, while C4 levels were substantially lower in PBC-AIH OS patients than those in healthy controls. Circulating FGF19 levels strongly correlated with C4 (r = −0.695, p < 0.0001), direct bilirubin (r = 0.598, p = 0.0001), and total bile acids (r = 0.595, p = 0.002). Moreover, circulating FGF19 levels strongly correlated with the model for end-stage liver disease score (r = 0.574, p = 0.0005) and Mayo risk score (r = 0.578, p = 0.001).

Conclusions

Serum FGF19 is significantly increased in patients with PBC-AIH OS, while BA synthesis is suppressed. Circulating FGF19 primarily controls the regulation of BA synthesis in response to cholestasis and under cholestatic conditions. Therefore, modulation of circulating FGF19 could provide a promising targeted therapy for patients with PBC-AIH OS.

Glycochenodeoxycholate Promotes Liver Fibrosis in Mice with Hepatocellular Cholestasis

Hydrophobic bile salts are considered to promote liver fibrosis in cholestasis. However, evidence for this widely accepted hypothesis remains scarce. In established animal models of cholestasis, e.g., by Mdr2 knockout, cholestasis and fibrosis are both secondary to biliary damage. Therefore, to test the specific contribution of accumulating bile salts to liver fibrosis in cholestatic disease, we applied the unique model of inducible hepatocellular cholestasis in cholate-fed Atp8b1^G308V/G308V mice. Glycochenodeoxycholate (GCDCA) was supplemented to humanize the murine bile salt pool, as confirmed by HPLC. Biomarkers of cholestasis and liver fibrosis were quantified. Hepatic stellate cells (HSC) isolated from wild-type mice were stimulated with bile salts. Proliferation, cell accumulation, and collagen deposition of HSC were determined. In cholestatic Atp8b1^G308V/G308V mice, increased hepatic expression of αSMA and collagen1a mRNA and excess hepatic collagen deposition indicated development of liver fibrosis only upon GCDCA supplementation. In vitro, numbers of myofibroblasts and deposition of collagen were increased after incubation with hydrophobic but not hydrophilic bile salts, and associated with EGFR and MEK1/2 activation. We concluded that chronic hepatocellular cholestasis alone, independently of biliary damage, induces liver fibrosis in mice in presence of the human bile salt GCDCA. Bile salts may have direct pro-fibrotic effects on HSC, putatively involving EGFR and MEK1/2 signaling.

Farnesoid X receptor alpha (FXRα) is a critical actor of the development and pathologies of the male reproductive system

The farnesoid-X-receptorα (FXRα; NR1H4) is one of the main bile acid (BA) receptors. During the last decades, through the use of pharmalogical approaches and transgenic mouse models, it has been demonstrated that the nuclear receptor FXRα controls numerous physiological functions such as glucose or energy metabolisms. It is also involved in the etiology or the development of several pathologies. Here, we will review the unexpected roles of FXRα on the male reproductive tract. FXRα has been demonstrated to play functions in the regulation of testicular and prostate homeostasis. Even though additional studies are needed to confirm these findings in humans, the reviewed reports open new field of research to better define the effects of bile acid-FXRα signaling pathways on fertility disorders and cancers.

Exogenous exosomes from mice with acetaminophen-induced liver injury promote toxicity in the recipient hepatocytes and mice

Exosomes are small extracellular membrane vesicles released from endosomes of various cells and could be found in most body fluids. The main functions of exosomes have been recognized as important mediators of intercellular communication and as potential biomarkers of various disease states. This study investigated whether exogenous exosomes from mice with acetaminophen (APAP)-induced liver injury can damage the recipient hepatic cells or promote hepatotoxicity in mice. We observed that exogenous exosomes derived from APAP-exposed mice were internalized into the primary mouse hepatocytes or HepG2 hepatoma cells and significantly decreased the viability of these recipient cells. They also elevated mRNA transcripts and proteins associated with the cell death signaling pathways in primary hepatocytes or HepG2 cells via exosomes-to-cell communications. In addition, confocal microscopy of ex vivo liver section showed that exogenously added exosomes were accumulated in recipient hepatocytes. Furthermore, plasma reactive oxygen species and hepatic TNF-α/IL-1β production were elevated in APAP-exosomes recipient mice compared to control-exosomes recipient mice. The levels of apoptosis-related proteins such as phospho-JNK/JNK, Bax, and cleaved caspase-3 were increased in mouse liver received APAP-exosomes. These results demonstrate that exogenous exosomes from APAP-exposed mice with acute liver injury are functional and stimulate cell death or toxicity of the recipient hepatocytes and mice.

Farnesoid X receptor signaling activates the hepatic X-box binding protein 1 pathway in vitro and in mice

Bile acids are endogenous ligands of the nuclear receptor, farnesoid X receptor (FXR), and pharmacological FXR modulators are under development for the treatment of several liver disorders. The inositol-requiring enzyme 1α/X-box binding protein 1 (IRE1α/XBP1) pathway of the unfolded protein response (UPR) is a protective cellular signaling pathway activated in response to endoplasmic reticulum (ER) stress. We investigated the role of FXR signaling in activation of the hepatic XBP1 pathway. Mice were treated with deoxycholic acid (DCA), cholestyramine, GW4064, or underwent bile duct ligation (BDL), and hepatic UPR activation was measured. Huh7-Ntcp and HepG2 cells were treated with FXR agonists, inhibitor, small interfering RNA (siRNA), or small heterodimer partner (SHP) siRNA to determine the mechanisms of IRE1α/XBP1 pathway activation. DCA feeding and BDL increased and cholestyramine decreased expression of hepatic XBP1 spliced (XBP1s). XBP1 pathway activation increased in Huh7-Ntcp and HepG2 cells treated with bile acids, 6α-ethyl-chenodeoxycholic acid (6-ECDCA) or GW4064. This effect decreased with FXR knockdown and treatment with the FXR inhibitor guggulsterone. FXR agonists increased XBP1 splicing and phosphorylated IRE1α (p-IRE1α) expression. Overexpression of SHP similarly increased XBP1 splicing, XBP1s, and p-IRE1α protein expression. SHP knockdown attenuated FXR agonist-induced XBP1s and p-IRE1α protein expression. Co-immunoprecipitation (Co-IP) assays demonstrate a physical interaction between overexpressed green fluorescent protein (GFP)-SHP and FLAG-IRE1α in HEK293T cells. Mice treated with GW4064 had increased, and FXR and SHP null mice had decreased, basal Xbp1s gene expression.

CONCLUSION

FXR signaling activates the IRE1α/XBP1 pathway in vivo and in vitro. FXR pathway activation increases XBP1 splicing and enhances p-IRE1α expression. These effects are mediated, at least in part, by SHP. IRE1α/XBP1 pathway activation by bile acids and pharmacological FXR agonists may be protective during liver injury and may have therapeutic implications for liver diseases. (Hepatology 2018;68:304-316).

Stepwise Aggregation of Cholate and Deoxycholate Dictates the Formation and Loss of Surface-Available Chirally Selective Binding Sites

Bile salts are facially amphiphilic, naturally occurring chemicals that aggregate to perform numerous biochemical processes. Because of their unique intermolecular properties, bile salts have also been employed as functional materials in medicine and separation science (e.g., drug delivery, chiral solubilization, purification of single-walled carbon nanotubes). Bile micelle formation is structurally complex, and it remains a topic of considerable study. Here, the exposed functionalities on the surface of cholate and deoxycholate micelles are shown to vary from one another and with the micelle aggregation state. Collectively, data from NMR and capillary electrophoresis reveal preliminary, primary, and secondary stepwise aggregation of the salts of cholic (CA) and deoxycholic (DC) acid in basic conditions (pH 12, 298 K), and address how the surface availability of chirally selective binding sites is dependent on these sequential stages of aggregation. Prior work has demonstrated sequential CA aggregation (pH 12, 298 K) including a preliminary CMC at ca. 7 mM (no chiral selection), followed by a primary CMC at ca. 14 mM that allows chiral selection of binaphthyl enantiomers. In this work, DC is also shown to form stepwise preliminary and primary aggregates (ca. 3 mM DC and 9 mM DC, respectively, pH 12, 298 K) but the preliminary 3 mM DC aggregate is capable of chirally selective solubilization of the binaphthyl enantiomers. Higher-order, secondary bile aggregates of each of CA and DC show significantly degraded chiral selectivity. Diffusion NMR reveals that secondary micelles of CA exclude the BNDHP guests, while secondary micelles of DC accommodate guests, but with a loss of chiral selectivity. These data lead to the hypothesis that secondary aggregates of DC have an exposed binding site, possibly the 7α-edge of a bile dimeric unit, while secondary CA micelles do not present binding edges to the solution, potentially instead exposing the three alcohol groups on the hydrophilic α-face to the solution.

Biliary bile acids in hepatobiliary injury - What is the link?

The main trigger for liver injury in acquired cholestatic liver disease remains unclear. However, the accumulation of bile acids (BAs) undoubtedly plays a role. Recent progress in deciphering the pathomechanisms of inborn cholestatic liver diseases, decoding mechanisms of BA-induced cell death, and generating modern BA-derived drugs has improved the understanding of the regulation of BA synthesis and transport. Now is the appropriate time to reassess current knowledge about the specific role of BAs in hepatobiliary injury.

The Bile Acid Nuclear Receptor FXRα Is a Critical Regulator of Mouse Germ Cell Fate

Spermatogenesis is the process by which spermatozoa are generated from spermatogonia. This cell population is heterogeneous, with self-renewing spermatogonial stem cells (SSCs) and progenitor spermatogonia that will continue on a path of differentiation. Only SSCs have the ability to regenerate and sustain spermatogenesis. This makes the testis a good model to investigate stem cell biology. The Farnesoid X Receptor alpha (FXRα) was recently shown to be expressed in the testis. However, its global impact on germ cell homeostasis has not yet been studied. Here, using a phenotyping approach in Fxrα^−/− mice, we describe unexpected roles of FXRα on germ cell physiology independent of its effects on somatic cells. FXRα helps establish and maintain an undifferentiated germ cell pool and in turn influences male fertility. FXRα regulates the expression of several pluripotency factors. Among these, in vitro approaches show that FXRα controls the expression of the pluripotency marker Lin28 in the germ cells.

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FXRα regulated germ cell apoptotis independently of androgen homeostasis

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FXRα controls germ cell differentiation

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FXRα regulates the establishment and maintenance of undifferentiated germ cells

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In germ cells, FXRα controls the expression of pluripotency markers such as Lin28

Circulating FGF19 closely correlates with bile acid synthesis and cholestasis in patients with primary biliary cirrhosis

BACKGROUND AND AIM

Bile acid (BA) synthesis in the liver is regulated by Fibroblast Growth Factor 19 (FGF19) secreted from the ileum as an enterohepatic feedback mechanism. Although FGF19 mRNA is absent in normal liver, FGF19 gene expression was reported to increase in response to both extrahepatic and intrahepatic cholestasis. The impact of upregulated FGF19 expression on BA synthesis is unclear and the overall role of circulating FGF19 and BA synthesis under cholestatic conditions needs to be further investigated.

METHODS

BA synthesis was directly quantified by measuring serum concentrations of 7alpha-hydroxycholest-4-en-3-one (C4), along with serum FGF19 and other parameters, in 44 patients with primary biliary cirrhosis (PBC) and 10 healthy subjects.

RESULTS

Serum C4 were substantially lower, while those of FGF19 were higher, in cirrhotic PBC patients, as compared to those of either healthy or non-cirrhotic PBC patients. Analyses of the relationships between circulating FGF19, BA synthesis and cholestasis revealed that circulating FGF19 was strongly correlated with BA synthesis (r = -0.735, p<0.0001) and the severity of cholestasis (r = 0.590, p<0.001). Moreover, BA synthesis was found to be strongly correlated with the degree of cholestasis (r = 0.522, p = 0.0005).

CONCLUSION

These findings demonstrate that the regulation of BA synthesis in response to cholestasis is primarily controlled by circulating FGF19 and that under cholestatic conditions, the FGF19-BA synthesis feedback mechanism remains intact. Administering FGF19, or suitable mimetic, as a pharmacological intervention to increase circulating levels of FGF19 and suppress BA synthesis by inhibiting CYP7A1 gene expression is likely to provide therapeutic benefits for many PBC patients.

Possible Involvement of Nitric Oxide in Enhanced Liver Injury and Fibrogenesis during Cholestasis in Cytoglobin-deficient Mice

This study clarified the role of Cygb, the fourth globin in mammals originally discovered in rat hepatic stellate cells (HSCs), in cholestatic liver disease. Bile duct ligation (BDL) augmented inflammatory reactions as revealed by increased infiltrating neutrophils, CD68⁺-macrophages, and chemokine expression in Cygb^-/- mice. In these mice, impairment of bile canalicular indicated by the loss of CD10 expression, down-regulation of bile salt transporters, increased total bile acid, and massive apoptotic and necrotic hepatocytes occurred with the release of cytochrome c, activation of caspase 3, resulting in reduced animal survival compared to wild-type mice. In Cygb^-/- mouse liver, all of NO metabolites and oxidative stress were increased. Treatment with NO inhibitor restrained all above phenotypes and restored CD10 expression in BDL Cygb^-/- mice, while administration of NO donor aggravated liver damage in BDL-wild type mice to the same extent of BDL-Cygb^-/- mice. N-acetylcysteine administration had a negligible effect in all groups. In mice of BDL for 1-3 weeks, expression of all fibrosis-related markers was significantly increased in Cygb^-/- mice compared with wild-type mice. Thus, Cygb deficiency in HSCs enhances hepatocyte damage and inflammation in early phase and fibrosis development in late phase in mice subjected to BDL, presumably via altered NO metabolism.

Integrative microRNA profiling in alcoholic hepatitis reveals a role for microRNA-182 in liver injury and inflammation

OBJECTIVE

MicroRNAs (miRNAs) are well-known regulators of disease pathogenesis and have great potential as biomarkers and therapeutic targets. We aimed at profiling miRNAs in alcoholic hepatitis (AH) and identifying miRNAs potentially involved in liver injury.

DESIGN

MiRNA profiling was performed in liver samples from patients with AH, alcohol liver disease, non-alcoholic steatohepatitis, HCV disease and normal liver tissue. Expression of miRNAs was assessed in liver and serum from patients with AH and animal models. Mimic and decoy miR-182 were used in vitro and in vivo to evaluate miR-182's biological functions.

RESULTS

MiRNA expression profile in liver was highly altered in AH and distinctive from alcohol-induced cirrhotic livers. Moreover, we identified a set of 18 miRNAs predominantly expressed in AH as compared with other chronic liver conditions. Integrative miRNA-mRNA functional analysis revealed the association of AH-altered miRNAs with nuclear receptors, IGF-1 signalling and cholestasis. Interestingly, miR-182 was the most highly expressed miRNA in AH, which correlated with degree of ductular reaction, disease severity and short-term mortality. MiR-182 mimic induced an upregulation of inflammatory mediators in biliary cells. At experimental level, miR-182 was increased in biliary cells in mice fed with 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) diet but not upregulated by alcohol intake or fibrosis. Inhibition of miR-182 in DDC-fed mice reduced liver damage, bile acid accumulation and inflammatory response.

CONCLUSIONS

AH is characterised by a deregulated miRNA profile, including miR-182, which is associated with disease severity and liver injury. These results highlight the potential of miRNAs as therapeutic targets and biomarkers in AH.

Identification of Caspase-6 as a New Regulator of Alternatively Activated Macrophages

Alternatively activated macrophages (AAMs) play essential roles in the promotion of tissue remodeling, vasculogenesis, and tumor progression; however, the detailed mechanisms underlying the activation of AAMs remain largely unknown. Here, by using quantitative proteomic analysis, we identified 62 proteins that were up-regulated in IL-4-induced macrophages. Among these, Caspase-6 was increased significantly. Caspase-6 is important in the apoptotic signaling pathway; however, its role in non-apoptosis is also reported. Here, we first examined the non-apoptotic role of Caspase-6 in the alternative activation of macrophages after administration of IL-4, 4T1 tumor conditional medium, or co-culture with 4T1 cells. Both treatments promoted alternative activation of RAW264.7 cells and primary macrophages, whereas disruption of caspase-6 expression and activity could markedly suppress the biomarker levels of AAMs. Overexpression of Caspase-6 could significantly promote the activation of AAMs. Importantly, we further present evidence that caspase-6 could regulate breast cancer cell invasion by modulating MMP-2 and MMP-9 expression in 4T1 tumor-associated macrophages, as ablation of protein levels or activity of caspase-6 suppressed tumor cell invasion in vitro In conclusion, the observed results markedly expanded our views of the dynamic changes in protein composition during alternative activation of macrophages, and they revealed a critical new role of caspase-6 in regulating this cellular biological process, which suggested that caspase-6 might be a key nod molecule to regulate immunological steady-state and be a therapeutic candidate for tumor immunotherapy.

ATP11C targets basolateral bile salt transporter proteins in mouse central hepatocytes

ATP11C is a homolog of ATP8B1, both of which catalyze the transport of phospholipids in biological membranes. Mutations in ATP8B1 cause progressive familial intrahepatic cholestasis type1 in humans, which is characterized by a canalicular cholestasis. Mice deficient in ATP11C are characterized by a conjugated hyperbilirubinemia and an unconjugated hypercholanemia. Here, we have studied the hypothesis that ATP11C deficiency interferes with basolateral uptake of unconjugated bile salts, a process mediated by organic anion-transporting polypeptide (OATP) 1B2. ATP11C localized to the basolateral membrane of central hepatocytes in the liver lobule of control mice. In ATP11C-deficient mice, plasma total bilirubin levels were 6-fold increased, compared to control, of which ∼65% was conjugated and ∼35% unconjugated. Plasma total bile salts were 10-fold increased and were mostly present as unconjugated species. Functional studies in ATP11C-deficient mice indicated that hepatic uptake of unconjugated bile salts was strongly impaired whereas uptake of conjugated bile salts was unaffected. Western blotting and immunofluorescence analysis demonstrated near absence of basolateral bile salt uptake transporters OATP1B2, OATP1A1, OATP1A4, and Na(+) -taurocholate-cotransporting polypeptide only in central hepatocytes of ATP11C-deficient liver. In vivo application of the proteasome inhibitor, bortezomib, partially restored expression of these proteins, but not their localization. Furthermore, we observed post-translational down-regulation of ATP11C protein in livers from cholestatic mice, which coincided with reduced OATP1B2 levels.

CONCLUSIONS

ATP11C is essential for basolateral membrane localization of multiple bile salt transport proteins in central hepatocytes and may act as a gatekeeper to prevent hepatic bile salt overload. Conjugated hyperbilirubinemia and unconjugated hypercholanemia and loss of OATP expression in ATP11C-deficient liver strongly resemble the characteristics of Rotor syndrome, suggesting that mutations in ATP11C can predispose to Rotor syndrome. (Hepatology 2016;64:161-174).

Hydrophobic bile acid apoptosis is regulated by sphingosine-1-phosphate receptor 2 in rat hepatocytes and human hepatocellular carcinoma cells

The hepatotoxic bile acid glycochenodeoxycholate (GCDC) modulates hepatocyte cell death through activation of JNK, Akt, and Erk. The nonhepatotoxic bile acid taurocholate activates Akt and Erk through the sphingosine-1-phosphate receptor 2 (S1PR2). The role of the S1PR2 in GCDC-mediated apoptosis and kinase activation is unknown. Studies were done in rat hepatocytes, HUH7 cells, and HUH7 cells stably transfected with rat Ntcp (HUH7-Ntcp). Cells were treated with GCDC and apoptosis was monitored morphologically by Hoechst staining and biochemically by immunoblotting for the active cleaved fragment of caspase 3. Kinase activation was determined by immunoblotting with phospho-specific antibodies. JTE-013, an inhibitor of S1PR2, significantly attenuated morphological evidence of GCDC-induced apoptosis and prevented caspase 3 cleavage in rat hepatocytes and HUH7-Ntcp cells. In hepatocytes, JTE-013 mildly suppressed, augmented, and had no effect on GCDC-induced JNK, Akt, and Erk phosphorylation, respectively. Similar results were seen in HUH7-Ntcp cells except for mild suppression of JNK and Erk phosphorylation. Knockdown of S1PR2 in HUH7-Ntcp augmented Akt, inhibited JNK, and had no effect on Erk phosphorylation. GCDC failed to induce apoptosis or kinase activation in HUH7 cells. In conclusion, SIPR2 inhibition attenuates GCDC-induced apoptosis and inhibits and augments GCDC-induced JNK and Akt phosphorylation, respectively. In addition, GCDC must enter hepatocytes to mediate cell death or activate kinases. These results suggest that SIPR2 activation is proapoptotic in GCDC-induced cell death but that this effect is not due to direct ligation of the S1PR2 by the bile acid.

Role of interleukin-1 and its antagonism of hepatic stellate cell proliferation and liver fibrosis in the Abcb4-/- mouse model

AIM: To study the interleukin-1 (IL-1) pathway as a therapeutic target for liver fibrosis in vitro and in vivo using the ATP-binding cassette transporter b4^-/- (Abcb4^-/-) mouse model.

METHODS: Female and male Abcb4^-/- mice from 6 to 13 mo of age were analysed for the degree of cholestasis (liver serum tests), extent of liver fibrosis (hydroxyproline content and Sirius red staining) and tissue-specific activation of signalling pathways such as the IL-1 pathway [quantitative polymerase chain reaction (qPCR)]. For in vivo experiments, murine hepatic stellate cells (HSCs) were isolated via pronase-collagenase perfusion followed by density gradient centrifugation using female mice. Murine HSCs were stimulated with up to 1 ng/mL IL-1β with or without 2.5 μg/mL Anakinra, an IL-1 receptor antagonist, respectively. The proliferation of murine HSCs was assessed via the BrdU assay. The toxicity of Anakinra was evaluated via the fluorescein diacetate hydrolysis (FDH) assay. In vivo 8-wk-old Abcb4^-/- mice with an already fully established hepatic phenotype were treated with Anakinra (1 mg/kg body-weight daily intraperitoneally) or vehicle and liver injury and liver fibrosis were evaluated via serum tests, qPCR, hydroxyproline content and Sirius red staining.

RESULTS: Liver fibrosis was less pronounced in males than in female Abcb4^-/- animals as defined by a lower hydroxyproline content (274 ± 64 μg/g vs 436 ± 80 μg/g liver, respectively; n = 13-15; P < 0.001; Mann-Whitney U-test) and lower mRNA expression of the profibrogenic tissue inhibitor of metalloproteinase-1 (TIMP) (1 ± 0.41 vs 0.66 ± 0.33 fold, respectively; n = 13-15; P < 0.05; Mann-Whitney U-test). Reduced liver fibrosis was associated with significantly lower levels of F4/80 mRNA expression (1 ± 0.28 vs 0.71 ± 0.41 fold, respectively; n = 12-15; P < 0.05; Mann-Whitney U-test) and significantly lower IL-1β mRNA expression levels (1 ± 0.38 vs 0.44 ± 0.26 fold, respectively; n = 13-15; P < 0.001; Mann-Whitney U-test). No gender differences in the serum liver parameters [bilirubin; alanine aminotransferase (ALT); aspartate aminotransferase and alkaline phosphatase (AP)] were found. In vitro, the administration of IL-1β resulted in a significant increase in HSC proliferation [0.94 ± 0.72 arbitrary units (A.U.) in untreated controls, 1.12 ± 0.80 A.U. at an IL-1β concentration of 0.1 ng/mL and 1.18 ± 0.73 A.U. at an IL-1β concentration of 1 ng/mL in samples from n = 6 donor animals; P < 0.001; analyses of variance (ANOVA)]. Proliferation was reduced significantly by the addition of 2.5 μg/mL Anakinra (0.81 ± 0.60 A.U. in untreated controls, 0.92 ± 0.68 A.U. at an IL-1β concentration of 0.1 ng/mL, and 0.91 ± 0.69 A.U. at an IL-1β concentration of 1 ng/mL; in samples from n = 6 donor animals; P < 0.001; ANOVA) suggesting an anti-proliferative effect of this clinically approved IL-1 receptor antagonist. The FDH assay showed this dose to be non-toxic in HSCs. In vivo, Anakinra had no effect on the hepatic hydroxyproline content, liver serum tests (ALT and AP) and pro-fibrotic (collagen 1α1, collagen 1α2, transforming growth factor-β, and TIMP-1) and anti-fibrotic [matrix metalloproteinase 2 (MMP2), MMP9 and MMP13] gene expression after 4 wk of treatment. Furthermore, the hepatic IL-1β and F4/80 mRNA expression levels were unaffected by Anakinra treatment.

CONCLUSION: IL-1β expression is associated with the degree of liver fibrosis in Abcb4^-/- mice and promotes HSC proliferation. IL-1 antagonism shows antifibrotic effects in vitro but not in Abcb4^-/- mice.

Ursodeoxycholyl lysophosphatidylethanolamide protects against hepatic ischemia and reperfusion injury in mice

The ischemia and reperfusion (I/R) injury that occurs during liver transplantation causes severe complications leading to transplantation failure. We have designed a cytoprotective agent, ursodeoxycholyl lysophosphatidylethanolamide (UDCA-LPE), which promotes the survival of cultured hepatocellular cell lines and inhibits apoptosis and inflammation in the in vivo models of liver injury. Here, we show that UDCA-LPE increased the viability of mouse hepatocytes by activating the Akt/glycogen synthase kinase 3β survival signaling pathways. We further tested whether UDCA-LPE could protect hepatic I/R injury in mice by clamping liver lobes of C57/BL6 mice for 90 min of ischemia followed by unclamping and reperfusion for 2 h. Two regimens for UDCA-LPE treatment were carried out; with a single dose of 100 mg/kg UDCA-LPE intraperitoneally injected 30 min prior to ischemia and a double dose of 50 mg/kg UDCA-LPE given 30 min prior to ischemia and just prior to reperfusion. Using histology and liver enzyme determination, we observed that hepatic I/R caused significant hepatic necrosis, which was decreased in UDCA-LPE-treated mice undergoing I/R. Ursodeoxycholyl LPE concomitantly protected against I/R-induced apoptosis (cleaved caspase 3, cleaved poly[ADP-ribose] polymerase 1), inflammation (IL-1β, CD11b, chemokine ligands 2 and 3, chemokine receptor 2), and portal fibrogenesis (α-smooth muscle actin, plasminogen activator inhibitor 1), as determined by Western blot, quantitative real-time polymerase chain reaction, and immunohistochemical analyses. The protection by UDCA-LPE was found to be better in the double-dose than in the single-dose regimen. Thus, UDCA-LPE promoted the survival of mouse hepatocytes and protected against hepatic I/R injury and thus may be of therapeutic use in liver transplantation settings.

Bile Acid-Induced Toxicity in HepaRG Cells Recapitulates the Response in Primary Human Hepatocytes

Cholestatic liver injury is a pathological component of numerous disease states. Much of the current literature on cholestatic liver injury is derived from in vitro studies using rodent hepatocytes or cell lines transfected with bile acid (BA) uptake transporters. While these studies demonstrate BA-driven apoptosis, it is debatable whether these models reflect the human pathophysiology, as primary human hepatocytes undergo primarily necrosis. HepaRG cells are a bipotential, human hepatoma line that express apical and basolateral BA transporters. Thus, we sought to determine whether HepaRG cells could replicate the response of primary human hepatocytes to BA exposure in vitro. HepG2 cells, primary murine hepatocytes (PMH) or HepaRG cells, were exposed to taurocholic acid (TCA), or glycochenodeoxycholate (GCDC) and lactate dehydrogenase release were measured to determine cell death. Cell death occurred dose-responsively in HepaRG cells when exposed to GCDC; however, HepG2 cells died acutely only at very high concentrations of GCDC. In HepaRG cells, pre-treatment with the caspase inhibitor z-VD-FMK had no effect on cell death, indicating a lack of apoptotic cell death, and while c-jun N-terminal kinase (JNK) protein was activated by GCDC treatment in HepaRG cells, the inhibition of JNK did not protect. Although previous data indicate that TCA stimulates pro-inflammatory gene induction in PMH, there was no change in gene expression after TCA stimulation in HepaRG cells, which mimicked previous data found in primary human hepatocytes. These data provide evidence for HepaRG cells as a new model for the study of the effect of BA on human hepatocytes.

The Cholangiocyte Glycocalyx Stabilizes the 'Biliary HCO3 Umbrella': An Integrated Line of Defense against Toxic Bile Acids

BACKGROUND

Destruction of cholangiocytes is the hallmark of chronic cholangiopathies such as primary biliary cirrhosis. Under physiologic conditions, cholangiocytes display a striking resistance to the high, millimolar concentrations of toxic bile salts present in bile. We recently showed that a 'biliary HCO3(-) umbrella', i.e. apical cholangiocellular HCO3(-) secretion, prevents cholangiotoxicity of bile acids, and speculated on a role for extracellular membrane-bound glycans in the stabilization of this protective layer. This paper summarizes published and thus far unpublished evidence supporting the role of the glycocalyx in stabilizing the 'biliary HCO3(-) umbrella' and thus preventing cholangiotoxicity of bile acids.

KEY MESSAGES

The apical glycocalyx of a human cholangiocyte cell line and mouse liver sections were visualized by electron microscopy. FACS analysis was used to characterize the surface glycan profile of cultured human cholangiocytes. Using enzymatic digestion with neuraminidase the cholangiocyte glycocalyx was desialylated to test its protective function. Using lectin assays, we demonstrated that the main N-glycans in human and mouse cholangiocytes were sialylated biantennary structures, accompanied by high expression of the H-antigen (α1-2 fucose). Apical neuraminidase treatment induced desialylation without affecting cell viability, but lowered cholangiocellular resistance to bile acid-induced toxicity: both glycochenodeoxycholate and chenodeoxycholate (pKa ≥4), but not taurochenodeoxycholate (pKa <2), displayed cholangiotoxic effects after desialylation. A 24-hour reconstitution period allowed cholangiocytes to recover to a pretreatment bile salt susceptibility pattern.

CONCLUSION

Experimental evidence indicates that an apical cholangiocyte glycocalyx with glycosylated mucins and other glycan-bearing membrane glycoproteins stabilizes the 'biliary HCO3(-) umbrella', thus aiding in the protection of human cholangiocytes against bile acid toxicity.

Bile acid-induced necrosis in primary human hepatocytes and in patients with obstructive cholestasis

Accumulation of bile acids is a major mediator of cholestatic liver injury. Recent studies indicate bile acid composition between humans and rodents is dramatically different, as humans have a higher percent of glycine conjugated bile acids and increased chenodeoxycholate content, which increases the hydrophobicity index of bile acids. This increase may lead to direct toxicity that kills hepatocytes, and promotes inflammation. To address this issue, this study assessed how pathophysiological concentrations of bile acids measured in cholestatic patients affected primary human hepatocytes. Individual bile acid levels were determined in serum and bile by UPLC/QTOFMS in patients with extrahepatic cholestasis with, or without, concurrent increases in serum transaminases. Bile acid levels increased in serum of patients with liver injury, while biliary levels decreased, implicating infarction of the biliary tracts. To assess bile acid-induced toxicity in man, primary human hepatocytes were treated with relevant concentrations, derived from patient data, of the model bile acid glycochenodeoxycholic acid (GCDC). Treatment with GCDC resulted in necrosis with no increase in apoptotic parameters. This was recapitulated by treatment with biliary bile acid concentrations, but not serum concentrations. Marked elevations in serum full-length cytokeratin-18, high mobility group box 1 protein (HMGB1), and acetylated HMGB1 confirmed inflammatory necrosis in injured patients; only modest elevations in caspase-cleaved cytokeratin-18 were observed. These data suggest human hepatocytes are more resistant to human-relevant bile acids than rodent hepatocytes, and die through necrosis when exposed to bile acids. These mechanisms of cholestasis in humans are fundamentally different to mechanisms observed in rodent models.

Protein kinase Cδ protects against bile acid apoptosis by suppressing proapoptotic JNK and BIM pathways in human and rat hepatocytes

Retained bile acids, which are capable of inducing cell death, activate protein kinase Cδ (PKC-δ) in hepatocytes. In nonhepatic cells, both pro- and antiapoptotic effects of PKC-δ are described. The aim of this study was to determine the role of PKC-δ in glycochenodeoxycholate (GCDC)-induced apoptosis in rat hepatocytes and human HUH7-Na-taurocholate-cotransporting polypeptide (Ntcp) cells. Apoptosis was monitored morphologically by Hoechst staining and biochemically by immunoblotting for caspase 3 cleavage. The role of PKC-δ was evaluated with a PKC activator (phorbol myristate acetate, PMA) and PKC inhibitors (chelerythrine, H-7, or calphostin), PKC-δ knockdown, and wild-type (WT) or constitutively active (CA) PKC-δ. PKC-δ activation was monitored by immunoblotting for PKC-δ Thr505 and Tyr311 phosphorylation or by membrane translocation. JNK and Akt phosphorylation and the amount of total bisindolylmaleimide (BIM) were determined by immunoblotting. GCDC induced the translocation of PKC-δ to the mitochondria and/or plasma membrane in rat hepatocytes and HUH7-Ntcp cells and increased PKC-δ phosphorylation on Thr505, but not on Tyr311, in HUH7-Ntcp cells. GCDC-induced apoptosis was attenuated by PMA and augmented by PKC inhibition in rat hepatocytes. In HUH-Ntcp cells, transfection with CA or WT PKC-δ attenuated GCDC-induced apoptosis, whereas knockdown of PKC-δ increased GCDC-induced apoptosis. PKC-δ silencing increased GCDC-induced JNK phosphorylation, decreased GCDC-induced Akt phosphorylation, and increased expression of BIM. GCDC translocated BIM to the mitochondria in rat hepatocytes, and knockdown of BIM in HUH7-Ntcp cells decreased GCDC-induced apoptosis. Collectively, these results suggest that PKC-δ does not mediate GCDC-induced apoptosis in hepatocytes. Instead PKC-δ activation by GCDC stimulates a cytoprotective pathway that involves JNK inhibition, Akt activation, and downregulation of BIM.

Alveolar type II epithelial cell dysfunction in rat experimental hepatopulmonary syndrome (HPS)

The hepatopulmonary syndrome (HPS) develops when pulmonary vasodilatation leads to abnormal gas exchange. However, in human HPS, restrictive ventilatory defects are also observed supporting that the alveolar epithelial compartment may also be affected. Alveolar type II epithelial cells (AT2) play a critical role in maintaining the alveolar compartment by producing four surfactant proteins (SPs, SP-A, SP-B, SP-C and SP-D) which also facilitate alveolar repair following injury. However, no studies have evaluated the alveolar epithelial compartment in experimental HPS. In this study, we evaluated the alveolar epithelial compartment and particularly AT2 cells in experimental HPS induced by common bile duct ligation (CBDL). We found a significant reduction in pulmonary SP production associated with increased apoptosis in AT2 cells after CBDL relative to controls. Lung morphology showed decreased mean alveolar chord length and lung volumes in CBDL animals that were not seen in control models supporting a selective reduction of alveolar airspace. Furthermore, we found that administration of TNF-α, the bile acid, chenodeoxycholic acid, and FXR nuclear receptor activation (GW4064) induced apoptosis and impaired SP-B and SP-C production in alveolar epithelial cells in vitro. These results imply that AT2 cell dysfunction occurs in experimental HPS and is associated with alterations in the alveolar epithelial compartment. Our findings support a novel contributing mechanism in experimental HPS that may be relevant to humans and a potential therapeutic target.

Altered FXR signalling is associated with bile acid dysmetabolism in short bowel syndrome-associated liver disease

BACKGROUND & AIMS

Despite the mortality associated with liver disease observed in patients with short bowel syndrome (SBS), mechanisms underlying the development of SBS-associated liver disease (SBS-ALD) are poorly understood. This study examines the impact of bacterially-mediated bile acid (BA) dysmetabolism on farnesoid X receptor (FXR) signalling pathways and clinical outcome in a piglet model of SBS-ALD.

METHODS

4-week old piglets underwent 75% small bowel resection (SBR) or sham operation. Liver histology and hepatic inflammatory gene expression were examined. Abundance of BA biotransforming bacteria was determined and metabolomic studies detailed the alterations in BA composition of stool, portal serum and bile samples. Gene expression of intestinal and hepatic FXR target genes and small heterodimer partner (SHP) transrepression targets were assessed.

RESULTS

Histological evidence of SBS-ALD included liver bile duct proliferation, hepatocyte ballooning and fibrosis. Inflammatory gene expression was increased. Microbiota changes included a 10-fold decrease in Clostridium and a two-fold decrease in Bacteroides in SBS-ALD piglets. BA composition was altered and reflected a primary BA dominant composition. Intestinal and hepatic regulation of BA synthesis was characterised by a blunted intestinal FXR activation response and a failure of SHP to repress key hepatic targets.

CONCLUSIONS

We propose a pathological scenario in which microbial dysbiosis following SBR results in significant BA dysmetabolism and consequent outcomes including steatorrhoea, persistent diarrhoea and liver damage. Furthermore alterations in BA composition may have contributed to the observed disturbance in FXR-mediated signalling pathways. These findings provide an insight into the complex mechanisms mediating the development of liver disease in patients with SBS.

A morphological and immunohistochemical study of the effects of prednisolone or ursodeoxycholic acid on liver histology in feline lymphocytic cholangitis

Feline lymphocytic cholangitis (LC) has been commonly treated with prednisolone, and more recently with ursodeoxycholic acid (UDCA). Previously, we found that prednisolone treatment resulted in a statistically longer survival time than treatment with UDCA. In order to explain this difference, we compared the effects of prednisolone and UDCA treatment on hepatic tissue by evaluating consecutive liver biopsies. Archival serial biopsy materials from cats with LC treated with prednisolone (n = 5) or UDCA (n = 4) were evaluated. We employed haematoxylin and eosin staining to evaluate inflammation, and reticulin staining for fibrosis. Immunohistochemical stainings for Ki-67, K19 (Cytokeratin 19) and α-smooth muscle actin were used to evaluate cell type-specific proliferation and activation of hepatic stellate cells. Inflammation decreased more in the group treated with prednisolone, while the number of cholangiocytes, progenitor cells and fibroblasts did not differ between the treatment groups. Additionally, no difference was found for the amount of fibrosis in both treatment groups.

Physiological hypoxia prevents bile salt-induced apoptosis in human and rat hepatocytes

BACKGROUND & AIMS

Hydrophobic bile salts such as glycochenodeoxycholate (GCDC) accumulate in cholestatic liver disease and induce hepatocellular apoptosis, promoting profibrotic signalling. The tissue microenvironment is an integral player in cellular pathophysiology, but it is not routinely incorporated into laboratory studies. Tissue oxygen partial pressure (pO₂) may be an underestimated component of the microenvironment: in the liver, a pO₂ of 30-45 mmHg (approximately 6% O₂) is physiological, because of predominant portal blood supply. It was the aim of this project to investigate the impact of physiological hypoxia (i.e. 6% O₂) on hepatocellular function, namely, bile salt-induced apoptosis.

METHODS

Human hepatoma cells (HepG2-Ntcp) and primary rat hepatocytes were cultured at standard laboratory (hyperoxic) conditions (21% O₂) and at physiological hypoxia (6% O₂) in parallel for 1-8 days to study hepatocellular apoptosis and activation of signalling pathways. Standard laboratory analyses were applied for bile salt uptake, caspase-3/-7 activity, western blotting and gene-array analysis.

RESULTS

Culturing at physiological hypoxia protected both human and rat hepatocytes against GCDC-induced apoptosis: caspase-3/-7 activation was diminished by 3.1 ± 0.5-fold in human HepG2-Ntcp and completely abolished in primary rat hepatocytes. Bile salt uptake was unaffected. Induction of hypoxia-inducible factor-1α indicated adaption to physiological hypoxia. The MEK/ERK cascade was activated and anti-apoptotic mediators were induced: N-Myc down-regulated gene, gelsolin and carbonic anhydrase IX were upregulated 12.4-, 6.5- and 5.2-fold respectively.

CONCLUSIONS

We conclude from these data that (i) physiological hypoxia protects hepatocytes from bile salt-induced apoptosis, (ii) tissue pO₂ is a crucial, underestimated component of the microenvironment and should (iii) be considered when studying hepatocellular physiology in vitro.

Cystic fibrosis related liver disease--another black box in hepatology

Due to improved medical care, life expectancy in patients with cystic fibrosis (CF) has veritably improved over the last decades. Importantly, cystic fibrosis related liver disease (CFLD) has become one of the leading causes of morbidity and mortality in CF patients. However, CFLD might be largely underdiagnosed and diagnostic criteria need to be refined. The underlying pathomechanisms are largely unknown, and treatment strategies with proven efficacy are lacking. This review focuses on current invasive and non-invasive diagnostic standards, the current knowledge on the pathophysiology of CFLD, treatment strategies, and possible future developments.

Lithocholic acid feeding results in direct hepato-toxicity independent of neutrophil function in mice

Lithocholic acid (LCA) supplementation in the diet results in intrahepatic cholestasis and bile infarcts. Previously we showed that an innate immune response is critical for cholestatic liver injury in the bile duct ligated mice. Thus, the purpose of this study was to investigate the role of neutrophils in the mechanism of liver injury caused by feeding mice a diet containing LCA. C57BL/6 mice were given control or 1% LCA containing diet for 24-96 h and then examined for parameters of hepatotoxicity. Plasma ALT levels were significantly increased by 48 h after LCA feeding, which correlated with both neutrophil recruitment to the liver and upregulation of numerous pro-inflammatory genes. The injury was confirmed by histology. Deficiency in intercellular adhesion molecule-1 (ICAM-1) expression or inhibition of neutrophil function failed to protect against the injury. Bile acid levels were quantified in plasma and bile of LCA-fed mice after 48 and 96 h. Only the observed biliary levels of taurochenodeoxycholic acid and potentially tauro-LCA caused direct cytotoxicity in mouse hepatocytes. These data support the conclusion that neutrophil recruitment occurs after the onset of bile acid-induced necrosis in LCA-fed animals, and is not a primary mechanism of cell death when cholestasis occurs through accumulation of hydrophobic bile acids.

Caspase-6 activity in the CA1 region of the hippocampus induces age-dependent memory impairment

Active Caspase-6 is abundant in the neuropil threads, neuritic plaques and neurofibrillary tangles of Alzheimer disease brains. However, its contribution to the pathophysiology of Alzheimer disease is unclear. Here, we show that higher levels of Caspase-6 activity in the CA1 region of aged human hippocampi correlate with lower cognitive performance. To determine whether Caspase-6 activity, in the absence of plaques and tangles, is sufficient to cause memory deficits, we generated a transgenic knock-in mouse that expresses a self-activated form of human Caspase-6 in the CA1. This Caspase-6 mouse develops age-dependent spatial and episodic memory impairment. Caspase-6 induces neuronal degeneration and inflammation. We conclude that Caspase-6 activation in mouse CA1 neurons is sufficient to induce neuronal degeneration and age-dependent memory impairment. These results indicate that Caspase-6 activity in CA1 could be responsible for the lower cognitive performance of aged humans. Consequently, preventing or inhibiting Caspase-6 activity in the aged may provide an efficient novel therapeutic approach against Alzheimer disease.

Apoptosis and necrosis in the liver

Because of its unique function and anatomical location, the liver is exposed to a multitude of toxins and xenobiotics, including medications and alcohol, as well as to infection by hepatotropic viruses, and therefore, is highly susceptible to tissue injury. Cell death in the liver occurs mainly by apoptosis or necrosis, with apoptosis also being the physiologic route to eliminate damaged or infected cells and to maintain tissue homeostasis. Liver cells, especially hepatocytes and cholangiocytes, are particularly susceptible to death receptor-mediated apoptosis, given the ubiquitous expression of the death receptors in the organ. In a quite unique way, death receptor-induced apoptosis in these cells is mediated by both mitochondrial and lysosomal permeabilization. Signaling between the endoplasmic reticulum and the mitochondria promotes hepatocyte apoptosis in response to excessive free fatty acid generation during the metabolic syndrome. These cell death pathways are partially regulated by microRNAs. Necrosis in the liver is generally associated with acute injury (i.e., ischemia/reperfusion injury) and has been long considered an unregulated process. Recently, a new form of "programmed" necrosis (named necroptosis) has been described: the role of necroptosis in the liver has yet to be explored. However, the minimal expression of a key player in this process in the liver suggests this form of cell death may be uncommon in liver diseases. Because apoptosis is a key feature of so many diseases of the liver, therapeutic modulation of liver cell death holds promise. An updated overview of these concepts is given in this article.

Plasma biomarkers of liver injury and inflammation demonstrate a lack of apoptosis during obstructive cholestasis in mice

Cholestasis is a pathological common component of numerous liver diseases that results in hepatotoxicity, inflammation, and cirrhosis when untreated. While the predominant hypothesis in cholestatic liver injury remains hepatocyte apoptosis due to direct toxicity of hydrophobic bile acid exposure, recent work suggests that the injury occurs through inflammatory necrosis. In order to resolve this controversy, we used novel plasma biomarkers to assess the mechanisms of cell death during early cholestatic liver injury. C57Bl/6 mice underwent bile duct ligation (BDL) for 6-72 h, or sham operation. Another group of mice were given d-galactosamine and endotoxin as a positive control for apoptosis and inflammatory necrosis. Plasma levels of full length cytokeratin-18 (FL-K18), microRNA-122 (miR-122) and high mobility group box-1 protein (HMGB1) increased progressively after BDL with peak levels observed after 48 h. These results indicate extensive cell necrosis after BDL, which is supported by the time course of plasma alanine aminotransferase activities and histology. In contrast, plasma caspase-3 activity, cleaved caspase-3 protein and caspase-cleaved cytokeratin-18 fragments (cK18) were not elevated at any time during BDL suggesting the absence of apoptosis. In contrast, all plasma biomarkers of necrosis and apoptosis were elevated 6 h after Gal/End treatment. In addition, acetylated HMGB1, a marker for macrophage and monocyte activation, was increased as early as 12 h but mainly at 48-72 h. However, progressive neutrophil accumulation in the area of necrosis started at 6h after BDL. In conclusion, these data indicate that early cholestatic liver injury in mice is an inflammatory event, and occurs through necrosis with little evidence for apoptosis.

Effect of quercetin 7-rhamnoside on glycochenodeoxycholic acid-induced L-02 human normal liver cell apoptosis

Quercetin 7-rhamnoside (Q7R) is one of the main flavonoid components of Hypericum japonicum. However, whether Q7R is one of the active ingredients responsible for the hepatopreventive effects of Hypericum japonicum has not yet been ascertained. Thus, the aim of the present study was to elucidate whether Q7R attenuates apoptosis induced by glycochenodeoxycholic acid (GCDC) in vitro, and to elucidate the mechanisms involved. L-02 human normal liver cells were pre-incubated with 0, 50, 100 and 200 µM Q7R for 30 min and then exposed to 100 µM GCDC for the indicated periods of time. Methylthiazolyldiphenyl-tetrazolium bromide (MTT) was performed to examine cell viability. Apoptosis was evaluated by Hoechst 33258 staining and Annexin V-FITC/PI double staining. Intracellular reactive oxygen species (ROS) were detected by flow cytometry using the oxidation-sensitive fluorescent probe, DCFH-DA. The assay for glutathione (GSH) was performed using a GSH detection kit. Intracellular Ca2+ concentration was evaluated using a confocal laser scanning microscope with Fluo-3 as the Ca2+ probe and mitochondrial membrane potential (Δψm) was measured by rhodamine 123 (Rh123) fluorescence. Q7R attenuated the GCDC-induced reduction in cell viability and the high apoptotic rate. Moreover, Q7R protected the L-02 cells from ROS overproduction, GSH depletion, intracellular Ca2+ accumulation and Δψm decrease induced by GCDC. These results suggest that Q7R attenuates L-02 cell injury induced by GCDC, possibly by inhibiting the overproduction of ROS, GSH depletion, intracellular Ca2+ accumulation and Δψm decrease, thereby minimizing L-02 cell apoptosis.

Progressive stages of mitochondrial destruction caused by cell toxic bile salts

The cell-toxic bile salt glycochenodeoxycholic acid (GCDCA) and taurochenodeoxycholic acid (TCDCA) are responsible for hepatocyte demise in cholestatic liver diseases, while tauroursodeoxycholic acid (TUDCA) is regarded hepatoprotective. We demonstrate the direct mitochondrio-toxicity of bile salts which deplete the mitochondrial membrane potential and induce the mitochondrial permeability transition (MPT). The bile salt mediated mechanistic mode of destruction significantly differs from that of calcium, the prototype MPT inducer. Cell-toxic bile salts initially bind to the mitochondrial outer membrane. Subsequently, the structure of the inner boundary membrane disintegrates. And it is only thereafter that the MPT is induced. This progressive destruction occurs in a dose- and time-dependent way. We demonstrate that GCDCA and TCDCA, but not TUDCA, preferentially permeabilize liposomes containing the mitochondrial membrane protein ANT, a process resembling the MPT induction in whole mitochondria. This suggests that ANT is one decisive target for toxic bile salts. To our knowledge this is the first report unraveling the consecutive steps leading to mitochondrial destruction by cell-toxic bile salts.

Angiotensin II protects primary rat hepatocytes against bile salt-induced apoptosis

Angiotensin II (AT-II) is a pro-fibrotic compound that acts via membrane-bound receptors (AT-1R/AT-2R) and thereby activates hepatic stellate cells (HSCs). AT-II receptor blockers (ARBs) are thus important candidates in the treatment of liver fibrosis. However, multiple case reports suggest that AT-1R blockers may induce hepatocyte injury. Therefore, we investigated the effect of AT-II and its receptor blockers on cytokine-, oxidative stress- and bile salt-induced cell death in hepatocytes. Primary rat hepatocytes were exposed to TNF-α/Actinomycin D, the ROS-generating agent menadione or the bile salts: glycochenodeoxycholic acid (GCDCA) and tauro-lithocholic acid-3 sulfate (TLCS), to induce apoptosis. AT-II (100 nmol/L) was added 10 minutes prior to the cell death-inducing agent. AT-1R antagonists (Sartans) and the AT-2R antagonist PD123319 were used at 1 µmol/L. Apoptosis (caspase-3 activity, acridine orange staining) and necrosis (Sytox green staining) were quantified. Expression of CHOP (marker for ER stress) and AT-II receptor mRNAs were quantified by Q-PCR. AT-II dose-dependently reduced GCDCA-induced apoptosis of hepatocytes (−50%, p<0.05) without inducing necrosis. In addition, AT-II reduced TLCS-induced apoptosis of hepatocytes (−50%, p<0.05). However, AT-II did not suppress TNF/Act-D and menadione-induced apoptosis. Only the AT-1R antagonists abolished the protective effect of AT-II against GCDCA-induced apoptosis. AT-II increased phosphorylation of ERK and a significant reversal of the protective effect of AT-II was observed when signaling kinases, including ERK, were inhibited. Moreover, AT-II prevented the GCDCA-induced expression of CHOP (the marker of the ER-mediated apoptosis).

Novel insight into mechanisms of cholestatic liver injury

Cholestasis results in a buildup of bile acids in serum and in hepatocytes. Early studies into the mechanisms of cholestatic liver injury strongly implicated bile acid-induced apoptosis as the major cause of hepatocellular injury. Recent work has focused both on the role of bile acids in cell signaling as well as the role of sterile inflammation in the pathophysiology. Advances in modern analytical methodology have allowed for more accurate measuring of bile acid concentrations in serum, liver, and bile to very low levels of detection. Interestingly, toxic bile acid levels are seemingly far lower than previously hypothesized. The initial hypothesis has been based largely upon the exposure of μmol/L concentrations of toxic bile acids and bile salts to primary hepatocytes in cell culture, the possibility that in vivo bile acid concentrations may be far lower than the observed in vitro toxicity has far reaching implications in the mechanism of injury. This review will focus on both how different bile acids and different bile acid concentrations can affect hepatocytes during cholestasis, and additionally provide insight into how these data support recent hypotheses that cholestatic liver injury may not occur through direct bile acid-induced apoptosis, but may involve largely inflammatory cell-mediated liver cell necrosis.

Glycochenodeoxycholate induces rat alveolar epithelial type II cell death and inhibits surfactant secretion in vitro

Bile acid-induced lung injury has become an important topic for neonatologists after the discovery of a high incidence of infant respiratory distress syndrome complicated from maternal intrahepatic cholestasis. To explore the molecular pathway of bile acid-induced lung injury, we investigated the cytotoxicity of the glycochenodeoxycholate (GCDC) to alveolar epithelial type II cells (AECII), as the main component of bile acid. The results demonstrated that glycochenodeoxycholate induced oxidative stress, mitochondrial damage, and increased caspase activity in the primary cultured AECII. Moreover, ROS scavengers and caspase inhibitors could rescue cell death induced by GCDC in rat AECII. Our results also indicated that GCDC inhibited AECII surfactant secretion. In conclusion, this study suggested that cell death prevention and cell therapy should be considered as therapeutic strategies for infant respiratory distress syndrome complicated from maternal intrahepatic cholestasis.

Effect of ursodeoxycholic acid on bile acid profiles and intestinal detoxification machinery in primary biliary cirrhosis and health

BACKGROUND & AIMS

Ursodeoxycholic acid (UDCA) exerts anticholestatic, antifibrotic and antiproliferative effects in primary biliary cirrhosis (PBC) via mechanisms not yet fully understood. Its adequate biliary enrichment is considered mandatory for therapeutic efficacy. However, precise determination of biliary enrichment of UDCA is not possible in clinical practice. Therefore, we investigated (i) the relationship between biliary enrichment and plasma pharmacokinetics of UDCA, (ii) the effect of UDCA on plasma and biliary bile acid composition and conjugation patterns, and (iii) on the intestinal detoxification machinery in patients with PBC and healthy controls.

METHODS

In 11 PBC patients and 11 matched healthy subjects, cystic bile and duodenal tissue were collected before and after 3 weeks of administration of UDCA (15 mg/kg/day). Extensive pharmacokinetic profiling of bile acids was performed. The effect of UDCA on the intestinal detoxification machinery was studied by quantitative PCR and Western blotting.

RESULTS

The relative fraction of UDCA and its conjugates in plasma at trough level[x] correlated with their biliary enrichment[y] (r=0.73, p=0.0001, y=3.65+0.49x). Taurine conjugates of the major hydrophobic bile acid, chenodeoxycholic acid, were more prominent in bile of PBC patients than in that of healthy controls. Biliary bile acid conjugation patterns normalized after treatment with UDCA. UDCA induced duodenal expression of key export pumps, BCRP and P-glycoprotein.

CONCLUSIONS

Biliary and trough plasma enrichment of UDCA are closely correlated in PBC and health. Taurine conjugation may represent an adaptive mechanism in PBC against chenodeoxycholic acid-mediated bile duct damage. UDCA may stabilize small intestinal detoxification by upregulation of efflux pumps.

The biliary HCO(3)(-) umbrella: experimental evidence revisited

PURPOSE OF REVIEW

To critically review most recent experimental evidence for the protective action of biliary HCO(3)(-) secretion against bile acid-induced bile duct damage and development of fibrosing cholangiopathy in humans and experimental animals.

RECENT FINDINGS

Studies in human cholangiocytes in vitro indicate that a biliary HCO(3)(-) umbrella protects against bile acid-induced cholangiocyte damage and apoptosis in humans. The Cl(-)/HCO(3)(-) exchanger, AE2, and an intact biliary glycocalyx appear crucial for its stability. Related studies with experimental animal models in vivo have to be interpreted with caution as humans and mice differ not only with regard to bile salt pool, but also their expression patterns of transport proteins and signalling molecules.

SUMMARY

Adequate biliary HCO(3)(-) secretion may protect against bile salt-induced cholangiopathies. Future therapeutic strategies in biliary diseases will aim at stabilizing the biliary HCO(3)(-) umbrella.

A biliary HCO3- umbrella constitutes a protective mechanism against bile acid-induced injury in human cholangiocytes

Human cholangiocytes are continuously exposed to millimolar levels of hydrophobic bile salt monomers. We recently hypothesized that an apical biliary HCO3- umbrella might prevent the protonation of biliary glycine-conjugated bile salts and uncontrolled cell entry of the corresponding bile acids, and that defects in this biliary HCO3- umbrella might predispose to chronic cholangiopathies. Here, we tested in vitro whether human cholangiocyte integrity in the presence of millimolar bile salt monomers is dependent on (1) pH, (2) adequate expression of the key HCO3- exporter, anion exchanger 2 (AE2), and (3) an intact cholangiocyte glycocalyx. To address these questions, human immortalized cholangiocytes and cholangiocarcinoma cells were exposed to chenodeoxycholate and its glycine/taurine conjugates at different pH levels. Bile acid uptake was determined radiochemically. Cell viability and apoptosis were measured enzymatically. AE2 was knocked down by lentiviral short hairpin RNA. A cholangiocyte glycocalyx was identified by electron microscopy, was enzymatically desialylated, and sialylation was quantified by flow cytometry. We found that bile acid uptake and toxicity in human immortalized cholangiocytes and cholangiocarcinoma cell lines in vitro were pH and AE2 dependent, with the highest rates at low pH and when AE2 expression was defective. An apical glycocalyx was identified on cholangiocytes in vitro by electron microscopic techniques. Desialylation of this protective layer increased cholangiocellular vulnerability in a pH-dependent manner.

CONCLUSION

A biliary HCO3- umbrella protects human cholangiocytes against damage by bile acid monomers. An intact glycocalyx and adequate AE2 expression are crucial in this process. Defects of the biliary HCO3- umbrella may lead to the development of chronic cholangiopathies.