Effects of bile salts on the plasma membranes of isolated rat hepatocytes

Tolvaptan safety in autosomal-dominant polycystic kidney disease; a focus on idiosyncratic drug-induced liver injury liabilities

Tolvaptan is a vasopressin V2 receptor antagonist which has proven to be an effective and mostly well-tolerated agent for the treatment of autosomal-dominant polycystic kidney disease. However, its administration is associated with rare but serious idiosyncratic liver injury, which has warranted a black box warning on the drug labels and frequent monitoring of liver blood tests in the clinic. This review outlines mechanistic investigations that have been conducted to date and constructs a working narrative as an explanation for the idiosyncratic drug-induced liver injury (IDILI) events that have occurred thus far. Potential risk factors which may contribute to individual susceptibility to DILI reactions are addressed, and key areas for future investigative/clinical development are highlighted.

Characterization of individual bile acids in vivo utilizing a novel low bile acid mouse model

Bile acids (BAs) are signaling molecules synthesized in the liver initially by CYP7A1 and CYP27A1 in the classical and alternative pathways, respectively. BAs are essential for cholesterol clearance, intestinal absorption of lipids, and endogenous modulators of farnesoid x receptor (FXR). FXR is critical in maintaining BA homeostasis and gut-liver crosstalk. Complex reactions in vivo and the lack of suitable animal models impede our understanding of the functions of individual BAs. In this study, we characterized the in vivo effects of three-day feeding of cholic acid (CA), deoxycholic acid (DCA), or ursodeoxycholic acid (UDCA) at physiological/non-hepatotoxic concentrations in a novel low-BA mouse model (Cyp7a1-/-/Cyp27a1-/-, DKO). Liver injury, BA levels and composition and BA signaling by the FXR-fibroblast growth factor 15 (FGF15) axis were determined. Overall, higher basal inflammation and altered lipid metabolism in DKO mice might be associated with low BAs. CA, DCA, and UDCA feeding activated FXR signals with tissue specificity. Dietary CA and DCA similarly altered tissue BA profiles to be less hydrophobic, while UDCA promoted a more hydrophobic tissue BA pool with the profiles shifted toward non-12α-OH BAs and secondary BAs. However, UDCA did not offer any overt protective effects as expected. These findings allow us to determine the precise effects of individual BAs in vivo on BA-FXR signaling and overall BA homeostasis in liver physiology and pathologies.

Bile acids regulation of cellular stress responses in liver physiology and diseases

Bile acids are physiological detergents and signalling molecules that are critically implicated in liver health and diseases. Dysregulation of bile acid homeostasis alters cell function and causes cell injury in chronic liver diseases. Therapeutic agents targeting bile acid synthesis, transport and signalling hold great potential for treatment of chronic liver diseases. The broad cellular and physiological impacts of pharmacological manipulations of bile acid metabolism are still incompletely understood. Recent research has discovered new links of bile acid signalling to the regulation of autophagy and lysosome biology, redox homeostasis and endoplasmic reticulum stress. These are well-conserved mechanisms that allow cells to adapt to nutrient and organelle stresses and play critical roles in maintaining cellular integrity and promoting survival. However, dysregulation of these cellular pathways is often observed in chronic liver diseases, which exacerbates cellular dysfunction to contribute to disease pathogenesis. Therefore, identification of these novel links has significantly advanced our knowledge of bile acid biology and physiology, which is needed to understand the contributions of bile acid dysregulation in disease pathogenesis, establish bile acids as diagnostic markers and develop bile acid-based pharmacological interventions. In this review, we will first discuss the roles of bile acid dysregulation in the pathogenesis of chronic liver diseases, and then discuss the recent findings on the crosstalk of bile acid signalling and cellular stress responses. Future investigations are needed to better define the roles of these crosstalks in regulating cellular function and disease processes.

Study on the acute toxicity of sodium taurocholate via zebrafish mortality, behavioral response, and NMR-metabolomics analysis

Sodium taurocholate (NaT) is a hydrophobic bile salt that exhibits varying toxicity and antimicrobial activity. The accumulation of BSs during their entero-hepatic cycle causes cytotoxicity in the liver and intestine and could also alter the intestinal microbiome leading to various diseases. In this research, the acute toxicity of sodium taurocholate in different concentrations (3000 mg/L, 1500 mg/L, 750 mg/L, 375 mg/L, and 0 mg/L) was investigated on four months old zebrafish by immersion in water for 96 h. The results were determined based on the fish mortality, behavioral response, and NMR metabolomics analysis which revealed LC50 of 1760.32 mg/L and 1050.42 mg/L after 72 and 96 h treatment, respectively. However, the non-lethal NaT concentrations of 750 mg/L and 375 mg/L at 96 h exposure significantly (p ≤ 0.05) decreased the total distance traveled and the activity duration, also caused surface respiration on the zebrafish. Orthogonal Projections to Latent Structures Discriminant Analysis (OPLS-DA) revealed that the metabolome of the fish treated with 750 mg/L was discriminated from that of the control by PC1. Major significantly downregulated metabolites by NaT-induction include valine, isoleucine, 2-hydroxyvalerate, glycine, glycerol, choline, glucose, pyruvate, anserine, threonine, carnitine and homoserine. On the contrary, taurine, creatine, lactate, acetate and 3-hydroxybutyrate were upregulated suggesting cellular consumption of lipids, glucose and amino acids for adenosine triphosphate (ATP) generation during immune and inflammatory response. whereby these metabolites were released in the process. In conclusion, the research revealed the toxic effect of NaT and its potential to trigger changes in zebrafish metabolism.

Serum metabolic profiling of targeted bile acids reveals potentially novel biomarkers for primary biliary cholangitis and autoimmune hepatitis

BACKGROUND

Primary biliary cholangitis (PBC) and autoimmune hepatitis (AIH) are two unexplained immune diseases. The golden standard for diagnosis of these diseases requires a liver biopsy. Liver biopsy is not widely accepted by patients because of its invasive nature, and atypical liver histology can confuse diagnosis. In view of the lack of effective diagnostic markers for PBC and AIH, combined with the increasingly mature metabolomics technologies, including full-contour metabolomics and target.

AIM

To determine non-invasive, reliable, and sensitive biochemical markers for the differential diagnosis of PBC and AIH.

METHODS

Serum samples from 54 patients with PBC, 26 patients with AIH and 30 healthy controls were analyzed by Ultra-high performance liquid chromatography-tandem mass spectrometry serum metabolomics. The metabolites and metabolic pathways were identified, and the metabolic changes, metabolic pathways and inter-group differences between PBC and AIH were analyzed. Fifteen kinds of target metabolites of bile acids (BAs) were quantitatively analyzed by SRM, and the differential metabolites related to the diagnosis of PBC were screened by receiver operating characteristic curve analysis.

RESULTS

We found the changes in the levels of amino acids, BAs, organic acids, phospholipids, choline, sugar, and sugar alcohols in patients with PBC and AIH. Furthermore, the SRM assay of BAs revealed the increased levels of chenodeoxycholic acid, lithocholic acid (LCA), taurolithocholic acid (TLCA), and LCA + TLCA in the PBC group compared with those in the AIH group. The levels of BAs may be used as biomarkers to differentiate PBC from AIH diseases. The levels of glycochenodeoxycholic acid, glycochenodeoxycholic sulfate, and taurodeoxycholic acid were gradually elevated with the increase of Child-Pugh class, which was correlated with the severity of disease.

CONCLUSION

The results demonstrated that the levels of BAs could serve as potential biomarkers for the early diagnosis and assessment of the severity of PBC and AIH.

Versatile Triad Alliance: Bile Acid, Taurine and Microbiota

Taurine is the most abundant free amino acid in the body, and is mainly derived from the diet, but can also be produced endogenously from cysteine. It plays multiple essential roles in the body, including development, energy production, osmoregulation, prevention of oxidative stress, and inflammation. Taurine is also crucial as a molecule used to conjugate bile acids (BAs). In the gastrointestinal tract, BAs deconjugation by enteric bacteria results in high levels of unconjugated BAs and free taurine. Depending on conjugation status and other bacterial modifications, BAs constitute a pool of related but highly diverse molecules, each with different properties concerning solubility and toxicity, capacity to activate or inhibit receptors of BAs, and direct and indirect impact on microbiota and the host, whereas free taurine has a largely protective impact on the host, serves as a source of energy for microbiota, regulates bacterial colonization and defends from pathogens. Several remarkable examples of the interaction between taurine and gut microbiota have recently been described. This review will introduce the necessary background information and lay out the latest discoveries in the interaction of the co-reliant triad of BAs, taurine, and microbiota.

A Recent Ten-Year Perspective: Bile Acid Metabolism and Signaling

Bile acids are important physiological agents required for the absorption, distribution, metabolism, and excretion of nutrients. In addition, bile acids act as sensors of intestinal contents, which are determined by the change in the spectrum of bile acids during microbial transformation, as well as by gradual intestinal absorption. Entering the liver through the portal vein, bile acids regulate the activity of nuclear receptors, modify metabolic processes and the rate of formation of new bile acids from cholesterol, and also, in all likelihood, can significantly affect the detoxification of xenobiotics. Bile acids not absorbed by the liver can interact with a variety of cellular recipes in extrahepatic tissues. This provides review information on the synthesis of bile acids in various parts of the digestive tract, its regulation, and the physiological role of bile acids. Moreover, the present study describes the involvement of bile acids in micelle formation, the mechanism of intestinal absorption, and the influence of the intestinal microbiota on this process.

Bile Acids Activate NLRP3 Inflammasome, Promoting Murine Liver Inflammation or Fibrosis in a Cell Type-Specific Manner

Bile acids (BA) as important signaling molecules are considered crucial in development of cholestatic liver injury, but there is limited understanding on the involved cell types and signaling pathways. The aim of this study was to evaluate the inflammatory and fibrotic potential of key BA and the role of distinct liver cell subsets focusing on the NLRP3 inflammasome. C57BL/6 wild-type (WT) and Nlrp3^−/− mice were fed with a diet supplemented with cholic (CA), deoxycholic (DCA) or lithocholic acid (LCA) for 7 days. Additionally, primary hepatocytes, Kupffer cells (KC) and hepatic stellate cells (HSC) from WT and Nlrp3^−/− mice were stimulated with aforementioned BA ex vivo. LCA feeding led to strong liver damage and activation of NLRP3 inflammasome. Ex vivo KC were the most affected cells by LCA, resulting in a pro-inflammatory phenotype. Liver damage and primary KC activation was both ameliorated in Nlrp3-deficient mice or cells. DCA feeding induced fibrotic alterations. Primary HSC upregulated the NLRP3 inflammasome and early fibrotic markers when stimulated with DCA, but not LCA. Pro-fibrogenic signals in liver and primary HSC were attenuated in Nlrp3^−/− mice or cells. The data shows that distinct BA induce NLRP3 inflammasome activation in HSC or KC, promoting fibrosis or inflammation.

The protective role of hydrophilic tetrahydroxylated bile acids (THBA)

Bile acids are key components of bile required for human health. In humans and mice, conditions of reduced bile flow, cholestasis, induce bile acid detoxification by producing tetrahydroxylated bile acids (THBA), more hydrophilic and less cytotoxic than the usual bile acids, which are typically di- or tri-hydroxylated. Mice deficient in the Bile Salt Export Pump (Bsep, or Abcb11), the primary bile acid transporter in liver cells, produce high levels of THBA, and avoid the severe liver damage typically seen in humans with BSEP deficiencies. THBA can suppress bile acid-induced liver damage in Mdr2-deficient mice, caused by their lack of phospholipids in bile exposing their biliary tracts to unbound bile acids. Here we review THBA-related works in both animals and humans, and discuss their potential relevance and applications as a class of functional bile acids.

Plasma membrane integrity: implications for health and disease

Plasma membrane integrity is essential for cellular homeostasis. In vivo, cells experience plasma membrane damage from a multitude of stressors in the extra- and intra-cellular environment. To avoid lethal consequences, cells are equipped with repair pathways to restore membrane integrity. Here, we assess plasma membrane damage and repair from a whole-body perspective. We highlight the role of tissue-specific stressors in health and disease and examine membrane repair pathways across diverse cell types. Furthermore, we outline the impact of genetic and environmental factors on plasma membrane integrity and how these contribute to disease pathogenesis in different tissues.

Changed Profile of Serum Transferrin Isoforms in Primary Biliary Cholangitis

Liver damage affects the synthesis of proteins and glycoproteins, and alters their posttranslational modification, such as glycosylation changing the serum profile of glycoprotein isoforms. The retention of hydrophobic bile acids in the course of cholestatic liver diseases is a major cause of liver damage in primary biliary cholangitis (PBC). The study objective was to determine the serum profile of transferrin isoforms in primary biliary cholangitis and compare it to transferrin isoforms profile in extrahepatic cholestasis. The study was carried out in 76 patients with PBC and 40 healthy blood donors. Transferrin isoforms were analyzed by the capillary electrophoresis method. The mean relative concentrations of disialotransferrin and trisialotransferrin in PBC were significantly lower than those in the healthy subjects (p < 0.001, p = 0.011; respectively). None of the transferrin isoforms changed according to the disease severity evaluated by the Ludwig scoring system. However, the disease stage affected the activity of alkaline phosphatase (ALP) and γ-glutamyl transferase (GGT), and albumin level (p = 0.002; p = 0.013 and p = 0.005, respectively). Our results indicate that serum profile of transferrin isoforms alters primary biliary cholangitis and differs in comparison to transferrin isoforms profile in extrahepatic cholestasis. The decreased concentrations of lower sialylated isoforms of transferrin (low percentage share in total transferrin level) are not associated with the histological stage of disease.

IL-13 as Target to Reduce Cholestasis and Dysbiosis in Abcb4 Knockout Mice

The Th2 cytokine IL-13 is involved in biliary epithelial injury and liver fibrosis in patients as well as in animal models. The aim of this study was to investigate IL-13 as a therapeutic target during short term and chronic intrahepatic cholestasis in an Abcb4-knockout mouse model (Abcb4^-/-). Lack of IL-13 protected Abcb4^-/- mice transiently from cholestasis. This decrease in serum bile acids was accompanied by an enhanced excretion of bile acids and a normalization of fecal bile acid composition. In Abcb4^-/-/IL-13^-/- double knockout mice, bacterial translocation to the liver was significantly reduced and the intestinal microbiome resembled the commensal composition in wild type animals. In addition, 52-week-old Abcb4^-/-IL-13^-/- mice showed significantly reduced hepatic fibrosis. Abcb4^-/- mice devoid of IL-13 transiently improved cholestasis and converted the composition of the gut microbiota towards healthy conditions. This highlights IL-13 as a potential therapeutic target in biliary diseases.

Effects of Absence of Constitutive Androstane Receptor (CAR) on Bile Acid Homeostasis in Male and Female Mice

Accumulation of BAs in hepatocytes has a role in liver disease and also in drug-induced liver injury. The Constitutive Androstane Receptor (CAR) has been shown to protect against BA-induced liver injury. The polymorphism of CAR has recently been shown to modify the pharmacokinetics and pharmacodynamics of various drugs. Thus it was hypothesized that polymorphism of CAR may also influence BA homeostasis. Using CAR-null and WT mice, this study modeled the potential consequences of CAR polymorphism on BA homeostasis. Our previous study showed that chemical activation of CAR decreases the total BA concentrations in livers of mice. Surprisingly the absence of CAR also decreased the BA concentrations in livers of mice, but to a lesser extent than in CAR-activated mice. Neither CAR activation nor elimination of CAR altered the biliary excretion of total BAs, but CAR activation increased the proportion of 6-OH BAs (TMCA), whereas the lack of CAR increased the excretion of TCA, TCDCA and TDCA. Serum BA concentrations did not parallel the decrease in BA concentrations in the liver in either the mice after CAR activation or mice lacking CAR. Gene expression of BA synthesis, transporter and regulator genes were mainly similar in livers of CAR-null and WT mice. In summary, CAR activation decreases primarily the 12-OH BA concentrations in liver, whereas lack of CAR decreases the concentrations of 6-OH BAs in liver. In bile, CAR activation increases the biliary excretion of 6-OH BAs, whereas absence of CAR increases the biliary excretion of 12-OH BAs and TCDCA.

High Dose and Delayed Treatment with Bile Acids Ineffective in RML Prion-Infected Mice

Prion diseases are a group of neurodegenerative diseases associated with the misfolding of the cellular prion protein (PrP^C) into the infectious form (PrP^Sc). There are currently no treatments for prion disease. Bile acids have the ability to protect hepatocytes from apoptosis and are neuroprotective in animal models of other protein-folding neurodegenerative diseases, including Huntington's, Parkinson's, and Alzheimer's disease. Importantly, bile acids are approved for clinical use in patients with cirrhosis and have recently been shown to be safe and possibly effective in pilot trials of patients with amyotrophic lateral sclerosis (ALS). We previously reported that the bile acid ursodeoxycholic acid (UDCA), given early in disease, prolonged incubation periods in male RML-infected mice. Here, we expand on this result to include tauro-ursodeoxycholic acid (TUDCA) treatment trials and delayed UDCA treatment. We demonstrate that despite a high dose of TUDCA given early in disease, there was no significant difference in incubation periods between treated and untreated cohorts, regardless of sex. In addition, delayed treatment with a high dose of UDCA resulted in a significant shortening of the average survival time for both male and female mice compared to their sex-matched controls, with evidence of increased BiP, a marker of apoptosis, in treated female mice. Our findings suggest that treatment with high-dose TUDCA provides no therapeutic benefit and that delayed treatment with high-dose UDCA is ineffective and could worsen outcomes.

The importance of membrane microdomains for bile salt-dependent biliary lipid secretion

Alternative models explaining the biliary lipid secretion at the canalicular membrane of hepatocytes exist: successive lipid extraction by preformed bile salt micelles, or budding of membrane fragments with formation of mixed micelles. To test the feasibility of the latter mechanism, we developed a mathematical model that describes the formation of lipid microdomains in the canalicular membrane. Bile salt monomers intercalate into the external hemileaflet of the canalicular membrane, to form a rim to liquid disordered domain patches that then pinch off to form nanometer-scale mixed micelles. Model simulations perfectly recapitulate the measured dependence of bile salt-dependent biliary lipid extraction rates upon modulation of the membrane cholesterol (lack or overexpression of the cholesterol transporter Abcg5-Abcg8) and phosphatidylcholine (lack of Mdr2, also known as Abcb4) content. The model reveals a strong dependence of the biliary secretion rate on the protein density of the membrane. Taken together, the proposed model is consistent with crucial experimental findings in the field and provides a consistent explanation of the central molecular processes involved in bile formation.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD)-elicited effects on bile acid homeostasis: Alterations in biosynthesis, enterohepatic circulation, and microbial metabolism

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is a persistent environmental contaminant which elicits hepatotoxicity through activation of the aryl hydrocarbon receptor (AhR). Male C57BL/6 mice orally gavaged with TCDD (0.01–30 µg/kg) every 4 days for 28 days exhibited bile duct proliferation and pericholangitis. Mass spectrometry analysis detected a 4.6-fold increase in total hepatic bile acid levels, despite the coordinated repression of genes involved in cholesterol and primary bile acid biosynthesis including Cyp7a1. Specifically, TCDD elicited a >200-fold increase in taurolithocholic acid (TLCA), a potent G protein-coupled bile acid receptor 1 (GPBAR1) agonist associated with bile duct proliferation. Increased levels of microbial bile acid metabolism loci (bsh, baiCD) are consistent with accumulation of TLCA and other secondary bile acids. Fecal bile acids decreased 2.8-fold, suggesting enhanced intestinal reabsorption due to induction of ileal transporters (Slc10a2, Slc51a) and increases in whole gut transit time and intestinal permeability. Moreover, serum bile acids were increased 45.4-fold, consistent with blood-to-hepatocyte transporter repression (Slco1a1, Slc10a1, Slco2b1, Slco1b2, Slco1a4) and hepatocyte-to-blood transporter induction (Abcc4, Abcc3). These results suggest that systemic alterations in enterohepatic circulation, as well as host and microbiota bile acid metabolism, favor bile acid accumulation that contributes to AhR-mediated hepatotoxicity.

Protective effects of Balanites aegyptiaca extract, Melatonin and Ursodeoxycholic acid against hepatotoxicity induced by Methotrexate in male rats

OBJECTIVE

To compare the degree of ameliorative effects of Melatonin (MEL), Ursodeoxycholic acid (UDCA) and Balanites aegyptiaca (BA) against hepatotoxicity induced by MTX for one month.

METHODS

Eighty adult male rats (Sprague Dawely) weighing (190 ± 10 g), were randomly divided into eight equal groups: Control, MTX, MEL, BA, UDCA, MTX + MEL, MTX + BA, MTX + UDCA. Liver function biomarker enzymes, liver tissue oxidative stress parameters, together with total antioxidant capacity and tumor necrosis factor (TNF-α) were determined. Histopathological and immunohistochemistry examinations for TNF-α were also done.

RESULTS

MTX showed significant increase in alanine transaminase (ALT), aspartate transaminase (AST), alkaline phosphatase (ALP), gamma glutamyl transferase (GGT), total and direct bilirubin, as well as TNF-α levels, oxidized glutathione (GSSG), malodialdehyde (MDA) and nitric oxide (NO). Whereas total protein, albumin, total antioxidant capacity, reduced glutathione (GSH), glutathione peroxidase (GPx), glutathione reductase (GR), glutathione S-transferase (GST), superoxide dismutase (SOD) and catalase (CAT) levels were significantly decreased in MTX treated group. These alterations were improved by MEL and BA treatment, whereas no improvement was noticed in UDCA treatment.

CONCLUSIONS

BA may be as promising as MEL in the hepatoprotection against MTX toxicity through their antioxidant and radical scavenging activities. In addition, it is not recommended to co-administer UDCA with MTX as it enhanced inflammation and damage to the liver.

Activation of Constitutive Androstane Receptor (CAR) in Mice Results in Maintained Biliary Excretion of Bile Acids Despite a Marked Decrease of Bile Acids in Liver

Activation of Constitutive Androstane Receptor (CAR) protects against bile acid (BA)-induced liver injury. This study was performed to determine the effect of CAR activation on bile flow, BA profile, as well as expression of BA synthesis and transport genes. Synthetic CAR ligand 1,4-bis-[2-(3,5-dichloropyridyloxy)]benzene (TCPOBOP) was administered to mice for 4 days. BAs were quantified by UPLC-MS/MS (ultraperformance liquid chromatography-tandem mass spectrometry). CAR activation decreases total BAs in livers of male (49%) and female mice (26%), largely attributable to decreases of the 12α-hydroxylated BA taurocholic acid (T-CA) (males (M) 65%, females (F) 45%). Bile flow in both sexes was increased by CAR activation, and the increases were BA-independent. CAR activation did not alter biliary excretion of total BAs, but overall BA composition changed. Excretion of muricholic (6-hydroxylated) BAs was increased in males (101%), and the 12α-OH proportion of biliary BAs was decreased in both males (37%) and females (28%). The decrease of T-CA in livers of males and females correlates with the decreased mRNA of the sterol 12α-hydroxylase Cyp8b1 in males (71%) and females (54%). As a response to restore BAs to physiologic concentrations in liver, mRNA of Cyp7a1 is upregulated following TCPOBOP (males 185%, females 132%). In ilea, mRNA of the negative feedback regulator Fgf15 was unaltered by CAR activation, indicating biliary BA excretion was sufficient to maintain concentrations of total BAs in the small intestine. In summary, the effects of CAR activation on BAs in male and female mice are quite similar, with a marked decrease in the major BA T-CA in the liver.

Hormesis in Cholestatic Liver Disease; Preconditioning with Low Bile Acid Concentrations Protects against Bile Acid-Induced Toxicity

Introduction

Cholestasis is characterized by accumulation of bile acids and inflammation, causing hepatocellular damage. Still, liver damage markers are highest in acute cholestasis and drop when this condition becomes chronic, indicating that hepatocytes adapt towards the hostile environment. This may be explained by a hormetic response in hepatocytes that limits cell death during cholestasis.

Aim

To investigate the mechanisms that underlie the hormetic response that protect hepatocytes against experimental cholestatic conditions.

Methods

HepG2.rNtcp cells were preconditioned (24 h) with sub-apoptotic concentrations (0.1–50 μM) of various bile acids, the superoxide donor menadione, TNF-α or the Farsenoid X Receptor agonist GW4064, followed by a challenge with the apoptosis-inducing bile acid glycochenodeoxycholic acid (GCDCA; 200 μM for 4 h), menadione (50 μM, 6 h) or cytokine mixture (CM; 6 h). Levels of apoptotic and necrotic cell death, mRNA expression of the bile salt export pump (ABCB11) and bile acid sensors, as well as intracellular GCDCA levels were analyzed.

Results

Preconditioning with the pro-apoptotic bile acids GCDCA, taurocholic acid, or the protective bile acids (tauro)ursodeoxycholic acid reduced GCDCA-induced caspase-3/7 activity in HepG2.rNtcp cells. Bile acid preconditioning did not induce significant levels of necrosis in GCDCA-challenged HepG2.rNtcp cells. In contrast, preconditioning with cholic acid, menadione or TNF-α potentiated GCDCA-induced apoptosis. GCDCA preconditioning specifically reduced GCDCA-induced cell death and not CM- or menadione-induced apoptosis. The hormetic effect of GCDCA preconditioning was concentration- and time-dependent. GCDCA-, CDCA- and GW4064- preconditioning enhanced ABCB11 mRNA levels, but in contrast to the bile acids, GW4064 did not significantly reduce GCDCA-induced caspase-3/7 activity. The GCDCA challenge strongly increased intracellular levels of this bile acid, which was not lowered by GCDCA-preconditioning.

Conclusions

Sub-toxic concentrations of bile acids in the range that occur under normal physiological conditions protect HepG2.rNtcp cells against GCDCA-induced apoptosis, which is independent of FXR-controlled changes in bile acid transport.

Pharmacological inhibition of apical sodium-dependent bile acid transporter changes bile composition and blocks progression of sclerosing cholangitis in multidrug resistance 2 knockout mice

Deficiency of multidrug resistance 2 (mdr2), a canalicular phospholipid floppase, leads to excretion of low-phospholipid "toxic" bile causing progressive cholestasis. We hypothesize that pharmacological inhibition of the ileal, apical sodium-dependent bile acid transporter (ASBT), blocks progression of sclerosing cholangitis in mdr2(-/-) mice. Thirty-day-old, female mdr2(-/-) mice were fed high-fat chow containing 0.006% SC-435, a minimally absorbed, potent inhibitor of ASBT, providing, on average, 11 mg/kg/day of compound. Bile acids (BAs) and phospholipids were measured by mass spectrometry. Compared with untreated mdr2(-/-) mice, SC-435 treatment for 14 days increased fecal BA excretion by 8-fold, lowered total BA concentration in liver by 65%, reduced total BA and individual hydrophobic BA concentrations in serum by >98%, and decreased plasma alanine aminotransferase, total bilirubin, and serum alkaline phosphatase levels by 86%, 93%, and 55%, respectively. Liver histology of sclerosing cholangitis improved, and extent of fibrosis decreased concomitant with reduction of hepatic profibrogenic gene expression. Biliary BA concentrations significantly decreased and phospholipids remained low and unchanged with treatment. The phosphatidylcholine (PC)/BA ratio in treated mice corrected toward a ratio of 0.28 found in wild-type mice, indicating decreased bile toxicity. Hepatic RNA sequencing studies revealed up-regulation of putative anti-inflammatory and antifibrogenic genes, including Ppara and Igf1, and down-regulation of several proinflammatory genes, including Ccl2 and Lcn2, implicated in leukocyte recruitment. Flow cytometric analysis revealed significant reduction of frequencies of hepatic CD11b(+) F4/80(+) Kupffer cells and CD11b(+) Gr1(+) neutrophils, accompanied by expansion of anti-inflammatory Ly6C(-) monocytes in treated mdr2(-/-) mice.

CONCLUSION

Inhibition of ASBT reduces BA pool size and retention of hydrophobic BA, favorably alters the biliary PC/BA ratio, profoundly changes the hepatic transcriptome, attenuates recruitment of leukocytes, and abrogates progression of murine sclerosing cholangitis.

Changes in Liver Ganglioside Metabolism in Obstructive Cholestasis - the Role of Oxidative Stress

Bile acids have been implicated in cholestatic liver damage, primarily due to their detergent effect on membranes and induction of oxidative stress. Gangliosides can counteract these harmful effects by increasing the rigidity of the cytoplasmic membrane. Induction of haem oxygenase (HMOX) has been shown to protect the liver from increased oxidative stress. The aim of this study was to determine the changes in the synthesis and distribution of liver gangliosides following bile duct ligation (BDL), and to assess the effects of HMOX both on cholestatic liver injury and ganglioside metabolism. Compared to controls, BDL resulted in a significant increase in total as well as complex gangliosides and mRNA expression of corresponding glycosyltransferases ST3GalV, ST8SiaI and B3GalTIV. A marked shift of GM1 ganglioside from the intracellular compartment to the cytoplasmic membrane was observed following BDL. Induction of oxidative stress by HMOX inhibition resulted in a further increase of these changes, while HMOX induction prevented this effect. Compared to BDL alone, HMOX inhibition in combination with BDL significantly increased the amount of bile infarcts, while HMOX activation decreased ductular proliferation. We have demonstrated that cholestasis is accompanied by significant changes in the distribution and synthesis of liver gangliosides. HMOX induction results in attenuation of the cholestatic pattern of liver gangliosides, while HMOX inhibition leads to the opposite effect.

Inhibition of Human Hepatic Bile Acid Transporters by Tolvaptan and Metabolites: Contributing Factors to Drug-Induced Liver Injury?

Tolvaptan is a vasopressin V(2)-receptor antagonist that has shown promise in treating Autosomal Dominant Polycystic Kidney Disease (ADPKD). Tolvaptan was, however, associated with liver injury in some ADPKD patients. Inhibition of bile acid transporters may be contributing factors to drug-induced liver injury. In this study, the ability of tolvaptan and two metabolites, DM-4103 and DM-4107, to inhibit human hepatic transporters (NTCP, BSEP, MRP2, MRP3, and MRP4) and bile acid transport in sandwich-cultured human hepatocytes (SCHH) was explored. IC(50) values were determined for tolvaptan, DM-4103 and DM-4107 inhibition of NTCP (∼41.5, 16.3, and 95.6 μM, respectively), BSEP (31.6, 4.15, and 119 μM, respectively), MRP2 (>50, ∼51.0, and >200 μM, respectively), MRP3 (>50, ∼44.6, and 61.2 μM, respectively), and MRP4 (>50, 4.26, and 37.9 μM, respectively). At the therapeutic dose of tolvaptan (90 mg), DM-4103 exhibited a C(max)/IC(50) value >0.1 for NTCP, BSEP, MRP2, MRP3, and MRP4. Tolvaptan accumulation in SCHH was extensive and not sodium-dependent; intracellular concentrations were ∼500 μM after a 10-min incubation duration with tolvaptan (15 μM). The biliary clearance of taurocholic acid (TCA) decreased by 43% when SCHH were co-incubated with tolvaptan (15 μM) and TCA (2.5 μM). When tolvaptan (15 μM) was co-incubated with 2.5 μM of chenodeoxycholic acid, taurochenodeoxycholic acid, or glycochenodeoxycholic acid in separate studies, the cellular accumulation of these bile acids increased by 1.30-, 1.68-, and 2.16-fold, respectively. Based on these data, inhibition of hepatic bile acid transport may be one of the biological mechanisms underlying tolvaptan-associated liver injury in patients with ADPKD.

Coenzyme Q in pregnant women and rats with intrahepatic cholestasis

BACKGROUND & AIMS

Intrahepatic cholestasis of pregnancy is a high-risk liver disease given the eventual deleterious consequences that may occur in the foetus. It is accepted that the abnormal accumulation of hydrophobic bile acids in maternal serum are responsible for the disease development. Hydrophobic bile acids induce oxidative stress and apoptosis leading to the damage of the hepatic parenchyma and eventually extrahepatic tissues. As coenzyme Q (CoQ) is considered an early marker of oxidative stress in this study, we sought to assess CoQ levels, bile acid profile and oxidative stress status in intrahepatic cholestasis.

METHODS

CoQ, vitamin E and malondialdehyde were measured in plasma and/or tissues by HPLC-UV method whereas serum bile acids by capillary electrophoresis in rats with ethinyl estradiol-induced cholestasis and women with pregnancy cholestasis.

RESULTS

CoQ and vitamin E plasma levels were diminished in both rats and women with intrahepatic cholestasis. Furthermore, reduced CoQ was also found in muscle and brain of cholestatic rats but no changes were observed in heart or liver. In addition, a positive correlation between CoQ and ursodeoxycholic/lithocholic acid ratio was found in intrahepatic cholestasis suggesting that increased plasma lithocholic acid may be intimately related to CoQ depletion in blood and tissues.

CONCLUSION

Significant CoQ and vitamin E depletion occur in both animals and humans with intrahepatic cholestasis likely as the result of increased hydrophobic bile acids known to produce significant oxidative stress. Present findings further suggest that antioxidant supplementation complementary to traditional treatment may improve cholestasis outcome.

Lithocholic acid-induced placental tumor necrosis factor-α upregulation and syncytiotrophoblast cell apoptosis in intrahepatic cholestasis of pregnancy

AIM

To investigate tumor necrosis factor (TNF)-α expression and its relationship with serum bile acids in placental trophoblasts from patients with intrahepatic cholestasis of pregnancy (ICP).

METHODS

Human placenta, including normal pregnancies (n = 10) and patients with ICP (n = 10), were collected at term and subject to TNF-α measurements. Bile acid-induced TNF-α expression and cell apoptosis were evaluated in cultured syncytiotrophoblasts in vitro.

RESULTS

ICP placental trophoblasts displayed apoptotic histological abnormalities. TNF-α levels in ICP tissue were significantly greater than those of controls as measured by quantitative polymerase chain reaction and western blot. Levels of placental TNF-α mRNA were positively correlated with serum bile acid concentration in ICP patients. In vitro, lithocholic acid (LCA) significantly enhanced TNF-α mRNA at both doses, by 2.07-fold at 15 μm and by 3.41-fold at 30 μm, whereas deoxycholic acid mildly increased TNF-α mRNA by 1.41-fold at 100 μm only. LCA treatment produced significantly higher percentage of caspase-3 positive cells than vehicle treatment, rescuable by the addition of a TNF-α inhibitor, indicative of apoptosis induced by LCA-TNF-α pathway.

CONCLUSION

This study shows that the increase of TNF-α expression in placental trophoblasts is strongly associated with ICP pathology and is inducible by LCA in vitro, suggesting its potential value in the clinical prevention, diagnosis and treatment of ICP.

Choline supplementation protects against liver damage by normalizing cholesterol metabolism in Pemt/Ldlr knockout mice fed a high-fat diet

Dietary choline is required for proper structure and dynamics of cell membranes, lipoprotein synthesis, and methyl-group metabolism. In mammals, choline is synthesized via phosphatidylethanolamine N-methyltransferase (Pemt), which converts phosphatidylethanolamine to phosphatidylcholine. Pemt(-/-) mice have impaired VLDL secretion and developed fatty liver when fed a high-fat (HF) diet. Because of the reduction in plasma lipids, Pemt(-/-)/low-density lipoprotein receptor knockout (Ldlr(-/-)) mice are protected from atherosclerosis. The goal of this study was to investigate the importance of dietary choline in the metabolic phenotype of Pemt(-/-)/Ldlr(-/-) male mice. At 10-12 wk of age, Pemt(+/+)/Ldlr(-/-) (HF(+/+)) and half of the Pemt(-/-)/Ldlr(-/-) (HF(-/-)) mice were fed an HF diet with normal (1.3 g/kg) choline. The remaining Pemt(-/-)/Ldlr(-/-) mice were fed an HF diet supplemented (5 g/kg) with choline (HFCS(-/-) mice). The HF diet contained 60% of calories from fat and 1% cholesterol, and the mice were fed for 16 d. HF(-/-) mice lost weight and developed hepatomegaly, steatohepatitis, and liver damage. Hepatic concentrations of free cholesterol, cholesterol-esters, and triglyceride (TG) were elevated by 30%, 1.1-fold and 3.1-fold, respectively, in HF(-/-) compared with HF(+/+) mice. Choline supplementation normalized hepatic cholesterol, but not TG, and dramatically improved liver function. The expression of genes involved in cholesterol transport and esterification increased by 50% to 5.6-fold in HF(-/-) mice when compared with HF(+/+) mice. Markers of macrophages, oxidative stress, and fibrosis were elevated in the HF(-/-) mice. Choline supplementation normalized the expression of these genes. In conclusion, HF(-/-) mice develop liver failure associated with altered cholesterol metabolism when fed an HF/normal choline diet. Choline supplementation normalized cholesterol metabolism, which was sufficient to prevent nonalcoholic steatohepatitis development and improve liver function. Our data suggest that choline can promote liver health by maintaining cholesterol homeostasis.

Human insulin resistance is associated with increased plasma levels of 12α-hydroxylated bile acids

Bile acids (BAs) exert pleiotropic metabolic effects, and physicochemical properties of different BAs affect their function. In rodents, insulin regulates BA composition, in part by regulating the BA 12α-hydroxylase CYP8B1. However, it is unclear whether a similar effect occurs in humans. To address this question, we examined the relationship between clamp-measured insulin sensitivity and plasma BA composition in a cohort of 200 healthy subjects and 35 type 2 diabetic (T2D) patients. In healthy subjects, insulin resistance (IR) was associated with increased 12α-hydroxylated BAs (cholic acid, deoxycholic acid, and their conjugated forms). Furthermore, ratios of 12α-hydroxylated/non-12α-hydroxylated BAs were associated with key features of IR, including higher insulin, proinsulin, glucose, glucagon, and triglyceride (TG) levels and lower HDL cholesterol. In T2D patients, BAs were nearly twofold elevated, and more hydrophobic, compared with healthy subjects, although we did not observe disproportionate increases in 12α-hydroxylated BAs. In multivariate analysis of the whole dataset, controlling for sex, age, BMI, and glucose tolerance status, higher 12α-hydroxy/non-12α-hydroxy BA ratios were associated with lower insulin sensitivity and higher plasma TGs. These findings suggest a role for 12α-hydroxylated BAs in metabolic abnormalities in the natural history of T2D and raise the possibility of developing insulin-sensitizing therapeutics based on manipulations of BA composition.

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.

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.

Elucidation of the mechanism of ribose conjugation in a pyrazole-containing compound in rodent liver

1. Here we report on the mechanism of ribose conjugation, through NADH as a cofactor, of a pyrazole-containing compound (PT). Incubation of PT in rat liver microsomes supplemented with NADP⁺/H, NAD⁺/H, and β-nicotinamide mononucleotide (NMN) resulted in complete conjugation to the adenine dinucleotide phosphate conjugate (ADP-C), adenine dinucleotide conjugate (AD-C), and 5-phosphoribose conjugate (Rib-C1), respectively. In hepatocytes, PT predominantly formed three ribose conjugates: Rib-C1, the ribose conjugate (Rib-C2), and the carboxylic acid of Rib-C2 (Rib-C3). 2. Phosphatase inhibitors were added to hepatocyte incubations. AD-C was detected in this reaction, which suggests that one of the major pathways for the formation of the ribose conjugates is through NAD⁺/H. When AD-C was incubated with phosphatase, Rib-C1 and Rib-C2 formed. 3. To understand the in vivo relevance of this metabolic pathway, rats were dosed with PT and Rib-C2 was found in the urine. 4. Structure-activity relationship shows that replacement of the distal thiazole group in the PT to a phenyl group abolishes this conjugation. Three amino acid residues in the active site preferentially interact with the sulfur atom in the thiazole of PT. 5. In summary, PT forms direct AD-C in hepatocytes, which is further hydrolyzed by phosphatase to give ribose conjugates.

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.

A placental phenotype for intrahepatic cholestasis of pregnancy

Intrahepatic cholestasis of pregnancy (ICP) is a pregnancy specific liver disease associated with significant risk of fetal complications. It is hypothesised that the risk of adverse fetal outcomes relates to the toxic effects of bile acids, the levels of which are increased in both maternal and fetal serum. Human and rodent studies have shown that transplacental transfer of bile acids is impaired in ICP. Furthermore, the morphology of placentas from the rodent model of ICP is markedly abnormal, and is associated with increased expression of apoptotic markers and oxidative stress. Using placental tissue from ICP cases and normal pregnancies and cultured placental explant fragments we investigated the histological and molecular effects of cholestasis. We also examined the influence of ursodeoxycholic acid (UDCA) administration on these parameters. Here we report that ICP is associated with several morphological abnormalities of the placenta, including an increase in the number of syncytial knots, and that these can be reproduced in an in vitro (explant) model exposed to the bile acids taurocholic acid and taurochenodoexycholic acid. Furthermore, we demonstrate that ursodeoxycholic acid, a drug commonly used in the management of ICP, has a protective effect on placental tissue both in vivo and in vitro.

Ursodeoxycholic acid in cholestasis: linking action mechanisms to therapeutic applications

UDCA (ursodeoxycholic acid) is the therapeutic agent most widely used for the treatment of cholestatic hepatopathies. Its use has expanded to other kinds of hepatic diseases, and even to extrahepatic ones. Such versatility is the result of its multiple mechanisms of action. UDCA stabilizes plasma membranes against cytolysis by tensioactive bile acids accumulated in cholestasis. UDCA also halts apoptosis by preventing the formation of mitochondrial pores, membrane recruitment of death receptors and endoplasmic-reticulum stress. In addition, UDCA induces changes in the expression of metabolizing enzymes and transporters that reduce bile acid cytotoxicity and improve renal excretion. Its capability to positively modulate ductular bile flow helps to preserve the integrity of bile ducts. UDCA also prevents the endocytic internalization of canalicular transporters, a common feature in cholestasis. Finally, UDCA has immunomodulatory properties that limit the exacerbated immunological response occurring in autoimmune cholestatic diseases by counteracting the overexpression of MHC antigens and perhaps by limiting the production of cytokines by immunocompetent cells. Owing to this multi-functionality, it is difficult to envisage a substitute for UDCA that combines as many hepatoprotective effects with such efficacy. We predict a long-lasting use of UDCA as the therapeutic agent of choice in cholestasis.

Dose-response of five bile acids on serum and liver bile Acid concentrations and hepatotoxicty in mice

Feeding bile acids (BAs) to rodents has been used to study BA signaling and toxicity in vivo. However, little is known about the effect of feeding BAs on the concentrations of BAs in serum and liver as well as the dose of the fed BAs that causes liver toxicity. The present study was designed to investigate the relative hepatotoxicity of individual BAs by feeding mice cholic acid (CA), chenodeoxycholic acid (CDCA), deoxycholic acid (DCA), lithocholic acid (LCA), or ursodeoxycholic acid (UDCA) at concentrations of 0.01, 0.03, 0.1, 0.3, 1.0, or 3% in their diet for 7 days. The data demonstrate that (1) the ability of the fed BAs to produce hepatotoxicity is UDCA<CA<CDCA<DCA<LCA; (2) the lowest concentration of each BA in the feed that causes hepatotoxicity in mice is CA and CDCA at 0.3%, DCA at 0.1%, and LCA at 0.03%; (3) BA feeding results in a dose-dependent increase in the total serum BA concentrations but had little effect on liver total BA concentrations; (4) hepatotoxicity of the fed BAs does not simply depend on the concentration or hydrophobicity of total BAs in the liver; and (5) liver BA-conjugation enzymes are saturated by feeding UDCA at concentrations higher than 0.3%. In conclusion, the findings of the present study provide guidance for choosing the feeding concentrations of BAs in mice and will aid in interpreting BA hepatotoxicity as well as BA-mediated gene regulation.

Role of cholangiocyte bile Acid transporters in large bile duct injury after rat liver transplantation

BACKGROUND

The pathogenesis of nonanastomotic strictures with a patent hepatic artery remains to be investigated. This study focuses on the role of cholangiocyte bile acid transporters in bile duct injury after liver transplantation.

METHODS

Sprague-Dawley rats were divided into three groups (n=20 for each): the sham-operated group (Sham), the transplant group with 1-hr donor liver cold preservation (CP-1h), and the transplant group with 12-hr donor liver cold preservation (CP-12h). Bile was collected for biochemical analysis. The histopathologic evaluation of bile duct injury was performed and the cholangiocyte bile acid transporters apical sodium-dependent bile acid transporter (ASBT), ileal lipid binding protein (ILBP), and Ostalpha/Ostbeta were investigated. RESULTS.: The immunohistochemical assay suggested that ASBT and ILBP were expressed exclusively on large bile duct epithelial cells, whereas Ostalpha and Ostbeta were expressed on both small and large bile ducts. Western blot and quantitative polymerase chain reaction analysis showed that the expression levels of these transporters dramatically decreased after transplantation. It took seven to 14 days for ILBP, Ostalpha, and Ostbeta to recover, whereas ASBT recovered within 3 days and even reached a peak above the normal level seven days after operation. In the CP-12h group, the ratios of the ASBT/ILBP, ASBT/Ostalpha and ASBT/Ostbeta expression levels were correlated with the injury severity scores of large but not small bile ducts.

CONCLUSIONS

The results suggest that the unparallel alteration of cholangiocyte bile acid transporters may play a potential role in large bile duct injury after liver transplantation with prolonged donor liver preservation.

Bile-acid-induced cell injury and protection

Several studies have characterized the cellular and molecular mechanisms of hepatocyte injury caused by the retention of hydrophobic bile acids (BAs) in cholestatic diseases. BAs may disrupt cell membranes through their detergent action on lipid components and can promote the generation of reactive oxygen species that, in turn, oxidatively modify lipids, proteins, and nucleic acids, and eventually cause hepatocyte necrosis and apoptosis. Several pathways are involved in triggering hepatocyte apoptosis. Toxic BAs can activate hepatocyte death receptors directly and induce oxidative damage, thereby causing mitochondrial dysfunction, and induce endoplasmic reticulum stress. When these compounds are taken up and accumulate inside biliary cells, they can also cause apoptosis. Regarding extrahepatic tissues, the accumulation of BAs in the systemic circulation may contribute to endothelial injury in the kidney and lungs. In gastrointestinal cells, BAs may behave as cancer promoters through an indirect mechanism involving oxidative stress and DNA damage, as well as acting as selection agents for apoptosis-resistant cells. The accumulation of BAs may have also deleterious effects on placental and fetal cells. However, other BAs, such as ursodeoxycholic acid, have been shown to modulate BA-induced injury in hepatocytes. The major beneficial effects of treatment with ursodeoxycholic acid are protection against cytotoxicity due to more toxic BAs; the stimulation of hepatobiliary secretion; antioxidant activity, due in part to an enhancement in glutathione levels; and the inhibition of liver cell apoptosis. Other natural BAs or their derivatives, such as cholyl-N-methylglycine or cholylsarcosine, have also aroused pharmacological interest owing to their protective properties.

The role of membrane cholesterol in determining bile acid cytotoxicity and cytoprotection of ursodeoxycholic acid

In cholestatic liver diseases, the ability of hydrophobic bile acids to damage membranes of hepatocytes/ductal cells contributes to their cytotoxicity. However, ursodeoxycholic acid (UDC), a hydrophilic bile acid, is used to treat cholestasis because it protects membranes. It has been well established that bile acids associate with and solubilize free cholesterol (CHOL) contained within the lumen of the gallbladder because of their structural similarities. However, there is a lack of understanding of how membrane CHOL, which is a well-established membrane stabilizing agent, is involved in cytotoxicity of hydrophobic bile acids and the cytoprotective effect of UDC. We utilized phospholipid liposomes to examine the ability of membrane CHOL to influence toxicity of individual bile acids, such as UDC and the highly toxic sodium deoxycholate (SDC), as well as the cytoprotective mechanism of UDC against SDC-induced cytotoxicity by measuring membrane permeation and intramembrane dipole potential. The kinetics of bile acid solubilization of phosphatidylcholine liposomes containing various levels of CHOL was also characterized. It was found that the presence of CHOL in membranes significantly reduced the ability of bile acids to damage synthetic membranes. UDC effectively prevented damaging effects of SDC on synthetic membranes only in the presence of membrane CHOL, while UDC enhances the damaging effects of SDC in the absence of CHOL. This further demonstrates that the cytoprotective effects of UDC depend upon the level of CHOL in the lipid membrane. Thus, changes in cell membrane composition, such as CHOL content, potentially influence the efficacy of UDC as the primary drug used to treat cholestasis.

[Seropositivity for Chlamydia pneumoniae in patients with primary biliary cirrhosis]

INTRODUCTION

Primary biliary cirrhosis (PBC) is a chronic cholestatic liver disease characterized by inflammatory injury and bile duct destruction. Recent studies suggest that Chlamydia pneumoniae could be associated with the development of PBC. The aim of this study was to determine the seroprevalence of C. pneumoniae in a cohort of patients with PBC.

PATIENTS AND METHODS

The presence of IgG antibodies against C. pneumoniae was investigated in 46 patients with PBC and in 105 subjects without cirrhosis.

RESULTS

Twenty-one patients (46%) with PBC had antibodies against C. pneumoniae compared with 74 subjects (71%) in the control group (OR = 0.6; 95% CI, 0.3-1.2; p = NS). Subanalysis of the PBC group showed that patients with C. pneumoniae antibodies had a higher frequency of advanced Child-Pugh stages (24% A, 52% B and 24% C vs 64% A, 32% B and 4% C; p = 0.01), a higher score on the Mayo Clinic Prognostic Index (7.8 +/- 2.1 vs 5.6 +/- 1.2; p = 0.004), a higher frequency of ascites (29% vs 4%; OR = 9.6; 95% CI, 1-87; p = 0.02), higher total bilirubin levels (4.5 +/- 2.5 mg/dl vs 2.4 +/- 4.3 mg/dl, p = 0.001) and lower serum albumin levels (2.6 +/- 0.9 g/dl vs 3.3 +/- 0.6 g/dl, p = 0.02).

CONCLUSION

No association was found between C. pneumoniae infection and PBC in this study. An association was found between the severity of PBC and C. pneumoniae, which may suggest a deleterious effect of C. pneumoniae infection or a predisposition in advanced stages of PBC to acquire infection with this microorganism.

Cholesterol crystals enhance and phospholipids protect against pancreatitis induced by hydrophobic bile salts: a rat model study

OBJECTIVES

The role of bile composition in the pathogenesis of biliary pancreatitis is unknown. The objective of this experiment was to explore the potential role of bile salts, phospholipids, and cholesterol crystals in the pathogenesis of biliary pancreatitis in a rat model.

METHODS

Model systems composed of taurodeoxycholate (TDC), mixed bile salts (MBS), or tauroursodeoxycholate (TUDC) [in 10 mM phosphate-buffered saline (PBS), pH 7.4], with or without cholesterol crystals or phosphatidylcholine, were infused into bile ducts of male Sprague-Dawley rats. Twenty-four hours later, animals were killed for histopathologic scoring of (peri)pancreatic inflammation.

RESULTS

: Severity of acute pancreatitis depended on bile salt hydrophobicity (TDC > MBS >> TUDC = PBS; histopathologic scores: 25.6 +/- 0.5, 23.0 +/- 1.5, 14.4 +/- 2.2, 14.8 +/- 1.0, respectively; P < 0.001), with corresponding differences in serum lipase concentration. Phosphatidylcholine protected against detrimental effects of TDC at physiological, but not at low, concentrations (scores: 19.5 +/- 2.3 vs 28.3 +/- 1.9 in case of Phosphatidycholine/(TDC + Phosphatidycholine) ratios 0.25 or 0.05, respectively). Cholesterol crystals increased severity of pancreatitis in model systems containing TDC or MBS, but not TUDC or PBS (33.2 +/- 0.4, 29.6 +/- 1.2, 18.6 +/- 1.5, 18.5 +/- 2.2, respectively; P < 0.001).

CONCLUSIONS

In the rat model, hydrophobic bile salts and cholesterol crystals aggravate biliary pancreatitis, whereas phospholipids have a protective effect.

Indomethacin enhances bile salt detergent activity: relevance for NSAIDs-induced gastrointestinal mucosal injury

Gastroduodenal toxicity of nonsteroidal anti-inflammatory drugs (NSAIDs) is partly independent from cyclooxygenase inhibition, possibly related to increased intermixed micellar-vesicular (nonphospholipid-associated) bile salt concentrations thought to be responsible for bile salt cytotoxicity. We evaluated the effects of indomethacin on bile salt cytotoxicity with complementary in vitro and ex vivo systems. In the erythrocyte model, indomethacin alone did not induce hemolysis. In contrast, indomethacin enhanced and phospholipids decreased hemolysis induced by hydrophobic taurodeoxycholate (TDC). Hydrophilic tauroursodeoxycholate (TUDC) enhanced rather than decreased TDC-induced hemolysis in the presence of indomethacin. Indomethacin did not affect intermixed micellar-vesicular bile salt concentrations or compositions. Indomethacin also increased TDC-induced lactate dehydrogenase release in CaCo-2 cells and bile salt-induced rat colonic mucosal injury, and prevented potential protective effects of TUDC in these systems. Our data show that indomethacin enhances bile salt-induced cytotoxicity without affecting intermixed micellar-vesicular bile salt concentrations or compositions. These findings may be relevant for gastroduodenal injury during NSAID therapy.

Oxidative stress and apoptosis in fetal rat liver induced by maternal cholestasis. Protective effect of ursodeoxycholic acid

BACKGROUND/AIMS

The sensitivity of fetal rat liver to maternal obstructive cholestasis during pregnancy (OCP), and the effect of ursodeoxycholic acid (UDCA) were investigated.

METHODS

UDCA was administered (i.g. 0.6 mg/kg b.wt./day) from day 14 to day 21 of pregnancy after maternal common bile duct ligation.

RESULTS

Impairment in the activity of antioxidant enzymes, levels of total glutathione and GSH/GSSG ratio and the degrees of lipid peroxidation and protein carbonylation were similar in livers of OCP mothers and fetuses at term, despite hypercholanemia was milder in fetuses. Treatment of OCP rats with UDCA reduced maternal and fetal liver oxidative stress. Although maternal hypercholanemia was not corrected, fetal serum concentrations of major bile acids (except UDCA and beta-muricholic acid) were reduced. Fetal liver expression of key enzyme in bile acid synthesis, Cyp7a1, Cyp27 and Cyp8b1 was not affected by OCP or UDCA treatment. In OCP fetal livers, the relative expression of Bax-alpha and Bcl-2 and the activity of caspase-3, but not caspase-8, were increased. These changes were markedly reduced in fetuses of OCP animals treated with UDCA.

CONCLUSIONS

OCP induced moderate fetal hypercholanemia but marked liver oxidative stress and apoptosis that were partly prevented by treatment of pregnant rats with UDCA.

Maternal cholestasis induces placental oxidative stress and apoptosis. Protective effect of ursodeoxycholic acid

We have investigated whether maternal obstructive cholestasis during pregnancy (OCP) causes oxidative stress and apoptosis in rat placenta and whether treatment with ursodeoxycholic acid (UDCA, i.g., 60 microg/100 g b.wt./day, following complete biliary obstruction on day 14 of pregnancy) has protective effects on this organ. In rats with OCP, increased (15-fold) serum bile acid concentrations (BAs) together with signs of placental oxidative stress (lipid peroxidation and protein carbonylation) were found. The latter were partly prevented by UDCA, even though hypercholanemia was not corrected. Some elements of the antioxidant system (total glutathione content, GSH/GSSG ratio and catalase, glutathione peroxidase, and glutathione-S-transferase--but not glutathione reductase--activities) were impaired in placentas from the OCP group. UDCA treatment partly prevented changes in the antioxidant system. OCP induced an increase in Bax-alpha/Bcl-2 mRNA ratio, as determined by real-time quantitative PCR, suggesting enhanced susceptibility to apoptosis activation through the mitochondria-mediated pathway. Accordingly, the activity of caspase-3, but not caspase-8, was increased in OCP placentas, in which DNA-ladder analysis and TUNEL confirmed the existence of apoptosis. UDCA prevented changes in the Bax-alpha/Bcl-2 mRNA ratio and caspase-3 activity. In conclusion, OCP causes oxidative stress and apoptosis in rat placenta, which can be prevented by treatment with UDCA.

Mitochondrially-mediated toxicity of bile acids

In the healthy hepatocyte, uptake of bile acids across the basolateral membrane and export via the canalicular export pump, are tightly coupled. Impairment of bile formation or excretion results in cholestasis, characterized by accumulation of bile acids in systemic blood and within the hepatocyte. When the concentration of bile acids exceeds the binding capacity of the binding protein located in the cytosol of the hepatocyte, bile acids induce apoptosis and necrosis, by damage to mitochondria. Mitochondria play a central role on the toxicity of bile acids. In this article, we review the published literature regarding bile acid effects on cell function, especially at the mitochondrial level. In patients with cholestatic liver disease, the extent of hepatocyte damage caused by intracellular accumulation of bile acids appears to be delayed by ingesting a hydrophilic bile acid. However, its effects on disease progression are not completely clarified. Therefore, identification of the mechanisms of cell injury will be of clinical utility, helping in the development of new therapeutic strategies. The goal of this review is to include a fresh consideration of all possible targets and integrating pathways that are involved in cholestasis, as well as in the benefits of bile acid therapy.

Mitochondrially mediated synergistic cell killing by bile acids

The accumulation of endogenous bile acids contributes to hepatocellular damage during cholestatic liver disease. To examine the controversy regarding the therapeutic use of ursodeoxycholate (UDCA) in cholestatic patients, we investigated the possible cytoprotection or synergistic effects of UDCA against chenodeoxycholate (CDCA)-induced injury to isolated rat hepatocytes. Our aim was to investigate the role of the mitochondrial permeability transition (MPT) in the mechanism of cytotoxicity caused by UDCA plus CDCA. Although not toxic by itself, UDCA potentiated the mitochondrial depolarization, ATP depletion and cell killing caused by CDCA. Fructose maintained ATP levels and prevented bile acid-induced cell killing. Cyclosporine A (CyA), a potent inhibitor of the MPT, substantially reduced mitochondrial depolarization, ATP depletion and cell killing caused by CDCA. Our results demonstrate that the synergistic cytotoxicity by UDCA plus CDCA is mediated by impairment of mitochondrial function, an event that is expressed via induction of the MPT.