When bile ducts say NO: the good, the bad, and the ugly

Metabolomic Profiling of Portal Blood and Bile Reveals Metabolic Signatures of Primary Sclerosing Cholangitis

Primary sclerosing cholangitis (PSC) is a pathogenically complex, chronic, fibroinflammatory disorder of the bile ducts without known etiology or effective pharmacotherapy. Emerging in vitro and in vivo evidence support fundamental pathophysiologic mechanisms in PSC centered on enterohepatic circulation. To date, no studies have specifically interrogated the chemical footprint of enterohepatic circulation in PSC. Herein, we evaluated the metabolome and lipidome of portal venous blood and bile obtained at the time of liver transplantation in patients with PSC (n = 7) as compared to individuals with noncholestatic, end-stage liver disease (viral, metabolic, etc. (disease control, DC, n = 19)) and to nondisease controls (NC, living donors, n = 12). Global metabolomic and lipidomic profiling was performed on serum derived from portal venous blood (portal serum) and bile using ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) and differential mobility spectroscopy-mass spectroscopy (DMS-MS; complex lipid platform). The Mann–Whitney U test was used to identify metabolites that significantly differed between groups. Principal-component analysis (PCA) showed significant separation of both PSC and DC from NC for both portal serum and bile. Metabolite set enrichment analysis of portal serum and bile demonstrated that the liver-disease cohorts (PSC and DC) exhibited similar enrichment in several metabolite categories compared to NC. Interestingly, the bile in PSC was uniquely enriched for dipeptide and polyamine metabolites. Finally, analysis of patient-matched portal serum and biliary metabolome revealed that these biological fluids were more homogeneous in PSC than in DC or NC, suggesting aberrant bile formation and enterohepatic circulation. In summary, PSC and DC patients exhibited alterations in several metabolites in portal serum and bile, while PSC patients exhibited a unique bile metabolome. These specific alterations in PSC are amenable to hypothesis testing and, potentially, therapeutic pharmacologic manipulation.

Inhibitory effects of bile acids and synthetic farnesoid X receptor agonists on rotavirus replication

Rotaviruses (group A rotaviruses) are the most important cause of severe gastroenteritis in infants and children worldwide. Currently, an antiviral drug is not available and information on therapeutic targets for antiviral development is limited for rotavirus infection. Previously, it was shown that lipid homeostasis is important in rotavirus replication. Since farnesoid X receptor (FXR) and its natural ligands bile acids (such as chenodeoxycholic acid [CDCA]) play major roles in cholesterol and lipid homeostasis, we examined the effects of bile acids and synthetic FXR agonists on rotavirus replication in association with cellular lipid levels. In a mouse model of rotavirus infection, effects of oral administration of CDCA on fecal rotavirus shedding were investigated. The results demonstrate the following. First, the intracellular contents of triglycerides were significantly increased by rotavirus infection. Second, CDCA, deoxycholic acid (DCA), and other synthetic FXR agonists, such as GW4064, significantly reduced rotavirus replication in cell culture in a dose-dependent manner. The reduction of virus replication correlated positively with activation of the FXR pathway and reduction of cellular triglyceride contents (r(2) = 0.95). Third, oral administration of CDCA significantly reduced fecal virus shedding in mice (P < 0.05). We conclude that bile acids and FXR agonists play important roles in the suppression of rotavirus replication. The inhibition mechanism is proposed to be the downregulation of lipid synthesis induced by rotavirus infection.

Biliary secretion of S-nitrosoglutathione is involved in the hypercholeresis induced by ursodeoxycholic acid in the normal rat

Ursodeoxycholic acid (UDCA) induces bicarbonate-rich hypercholeresis by incompletely defined mechanisms that involve the stimulation of adenosine triphosphate (ATP) release from cholangiocytes. As nitric oxide (NO) at a low concentration can stimulate a variety of secretory processes, we investigated whether this mediator could be implicated in the choleretic response to UDCA. Our in vivo experiments with the in situ perfused rat liver model in anesthetized rats, showed that UDCA infusion increased the biliary secretion of NO derivatives, hepatic inducible NO synthase expression, and NO synthase activity in liver tissue. UDCA also stimulated NO release by isolated rat hepatocytes. In contrast to UDCA, cholic acid was a poor inducer of NO secretion, and tauroursodeoxycholic acid showed no effect on NO secretion. Upon UDCA administration, NO was found in bile as low-molecular-weight nitrosothiols, of which S-nitrosoglutathione (GSNO) was the predominant species. UDCA-stimulated biliary NO secretion was abolished by the inhibition of inducible NO synthase with N(omega)-nitro-L-arginine methyl ester in isolated perfused livers and also in rats whose livers were depleted of glutathione with buthionine sulfoximine. Moreover, the biliary secretion of NO species was significantly diminished in UDCA-infused transport mutant [ATP-binding cassette C2 (ABCC2)/multidrug resistance-associated protein 2 (Mrp2)-deficient] rats, and this finding was consistent with the involvement of the glutathione carrier ABCC2/Mrp2 in the canalicular transport of GSNO. It was particularly noteworthy that in cultured normal rat cholangiocytes, GSNO activated protein kinase B, protected against apoptosis, and enhanced UDCA-induced ATP release to the medium; this effect was blocked by phosphoinositide 3-kinase inhibition. Finally, retrograde GSNO infusion into the common bile duct increased bile flow and biliary bicarbonate secretion.

CONCLUSION

UDCA induces biliary secretion of GSNO, which contributes to stimulating ductal secretion.

[Sepsis as a cause of intrahepatic cholestasis]

INTRODUCTION

The causes of intrahepatic cholestasis include cholestatic viral hepatitis, primary biliary cirrhosis, benign recurrent cholestasis, primary sclerosing cholangitis and sepsis. During sepsis, proinflammatory cytokines and nitric oxide cause cholestasis by impairing hepatocellular and ductal bile formation.

CASE OUTLINE

We report a 48-year-old woman who was admitted to hospital due to malaise, jaundice, fever and pain in the neck. Physical examination revealed jaundice, tachycardia (pulse rate was 120/min), hypotension 90/60 mm Hg. Laboratory findings showed normocytic normochromic anaemia, inflammatory syndrome and abnormal liver function tests indicating cholestasis and hepatocellular necrosis. Abdominal ultrasonography detected hepatosplenomegaly. Chest computed tomography showed bronchopneumonic infiltrates. Percutaneous liver biopsy was performed using a Menghini needle of 1.4 mm. Pathohystological analysis of the liver tissue confirmed reactive, intrahepatic cholestasis. Blood cultures isolated Staphylococcus aureus. After the diagnosis was established the treatment with broad-spectrum antibiotics was carried out, resulting in the improvement of general condition of the patient, regression of inflammatory syndrome, disappearance of cholestasis and regression of pulmonary infiltrates. Abdominal ultrasonography after antibiotic treatment did not show hepatosplenomegaly.

CONCLUSION

Concerning patients with cholestasis of uncertain origin, we should always think of sepsis as a possible cause in order to start antibiotic treatment in time.

Sepsis and cholestasis

Cholestasis is a common complication of bacterial infections and sepsis. This article gives a comprehensive overview of the underlying molecular mechanisms of sepsis-associated cholestasis and jaundice, their clinical presentation, and diagnostic and therapeutic management.

Mechanisms of Disease: mechanisms and clinical implications of cholestasis in sepsis

Cholestasis is a common complication in patients with extrahepatic bacterial infection and sepsis. This article gives a comprehensive overview of the molecular and cellular mechanisms of sepsis-associated cholestasis. Recent advances in the understanding of intrahepatic cholestasis have allowed us to delineate the molecular mechanisms that underlie sepsis-associated cholestasis and to describe their potential clinical and therapeutic applications. The mechanisms and clinical presentation of sepsis-associated liver injury vary according to the severity of the bacterial infection. Proinflammatory cytokines and nitric oxide cause cholestasis by impairing hepatocellular and ductal bile formation. Ischemic liver injury and, rarely, progressive sclerosing cholangitis can also be found in patients with septic shock, or major trauma with systemic inflammatory response syndrome. Treatment is mainly focused on eradication of the underlying infection and managing the sepsis. The use of ursodeoxycholic acid or extracorporeal liver support as treatments for sepsis-associated cholestasis is under investigation, but neither can be recommended in routine clinical practice at present. Patients with progressive sclerosing cholangitis should be considered for orthotopic liver transplantation.

Expression of inducible nitric oxide (NO) synthase but not prevention by its gene ablation of hepatocarcinogenesis with fibrosis caused by a choline-deficient, L-amino acid-defined diet in rats and mice

Expression of inducible nitric oxide synthase (iNOS) and effects of iNOS gene ablation on the hepatocarcinogenesis associated with fibrosis caused by a choline-deficient, L-amino acid-defined (CDAA) diet, were examined in male F344 rats and C57BL/6J wild-type and iNOS-/- mice. Western blot, RT-PCR and immunohistochemical analyses revealed increased expression of iNOS protein and mRNA in the livers of rats and wild-type mice fed a CDAA diet for 12-80 weeks, associated with elevated serum NO(x) and liver nitrotyrosine levels. iNOS-/- mice demonstrated greater liver injury and fibrosis in the early stage than their wild-type counterparts, but this did not significantly affect the incidence and multiplicity of altered foci, adenomas and hepatocellular carcinomas in spite of immunohistochemical iNOS expression in these lesions. Results suggested no major determinant roles of the expressed iNOS in the development of liver tumors caused by the CDAA diet.

Peroxynitrite-Dependent Upregulation of Src Kinases in Red Blood Cells: Strategies to Study the Activation Mechanisms

Several studies have demonstrated that treatment of cells with oxidants, and in particular with peroxynitrite, may cause the upregulation of tyrosine phosphorylation signaling. In erythrocytes, peroxynitrite induces tyrosine phosphorylation of the major intrinsic membrane protein, band 3. A closer look at the enzymes involved revealed that the effect of peroxynitrite was due to the inhibition of phosphotyrosine phosphatases and/or to the activation of src kinases. The activity of src kinases is modulated not only by phosphatases and other kinases but also through redox modification of cysteine residues: Peroxynitrite can, thus, affect src kinase activity by means of direct and indirect mechanisms. In this chapter, we describe the different pathways leading to src kinase activation and the experimental procedures that can be performed to reveal the activation mechanism. The aim is to provide a more general strategy adaptable to different cell types and different oxidants.

Regurgitation of bile acids from leaky bile ducts causes sclerosing cholangitis in Mdr2 (Abcb4) knockout mice

BACKGROUND & AIMS

Because the mechanisms leading to bile duct damage in sclerosing cholangitis are unknown, we aimed to determine the pathogenesis of bile duct injury in multidrug resistance gene (Mdr2) (Abcb4) knockout mice (Mdr2(-/-)) as a novel model of the disease.

METHODS

Mdr2(-/-) and wild-type controls (Mdr2(+/+)) were studied at 2, 4, and 8 weeks of age. Liver histology, ultrastructure, immunofluorescence microscopy (to study inflammatory cells, tight junction protein ZO-1, basement membrane protein laminin, fluorescence-labeled ursodeoxycholic acid), immunohistochemistry (for alpha-smooth muscle actin, nitrotyrosine), sirius red staining, bacterial cultures of intra-abdominal organs, and polymerase chain reaction (PCR) for Helicobacter bilis DNA were compared between both genotypes. Hepatic cytokine expression was determined by reverse-transcription PCR.

RESULTS

Bile ducts of Mdr2(-/-) showed disrupted tight junctions and basement membranes, bile acid leakage into portal tracts, induction of a portal inflammatory (CD11b, CD4-positive) infiltrate, and activation of proinflammatory (tumor necrosis factor [TNF]-alpha, interleukin [IL]-1beta) and profibrogenic cytokines (transforming growth factor [TGF]-beta1). This resulted in activation of periductal myofibroblasts, leading to periductal fibrosis, separating the peribiliary plexus from bile duct epithelial cells and, finally, causing atrophy and death of the bile duct epithelium. Bacterial translocation was not increased and H. bilis was not detectable in Mdr2(-/-).

CONCLUSIONS

Sclerosing cholangitis in Mdr2(-/-) mice is a multistep process with regurgitation of bile from leaky ducts into the portal tracts, leading to induction of periductal inflammation, followed by activation of periductal fibrogenesis, finally causing obliterative cholangitis owing to atrophy and death of bile duct epithelial cells.

Nitric oxide synthase inhibitors modulate lipopolysaccharide-induced hepatocyte injury: dissociation between in vivo and in vitro effects

Effects of endotoxemia-induced NO production on rat liver and hepatocytes in culture were investigated. Rats were treated intraperitoneally with saline, lipopolysaccharide (LPS, 10 mg/kg), L-nitroarginine methyl ester (L-NAME)+LPS, aminoguanidine (AG)+LPS, FK 506+LPS, S-nitroso-N-acetyl penicillamine (SNAP)+L-NAME+LPS and SNAP+FK 506+LPS. Mortality, hepatocyte viability and liver function test were estimated. Liver morphology was observed by light and electron microscopy. Hepatocyte cultures were treated with LPS, cytokine mixture (CM) with or without FK 506, L-NAME or AG. Hepatocyte function and inducible form of NOS (iNOS) expression were evaluated. Twenty-four hours after treatments with saline, LPS, L-NAME+LPS, AG+LPS, FK 506+LPS, SNAP+L-NAME+LPS and SNAP+FK 506+LPS, rat mortalities were 0%, 10%, 48%, 8%, 20%, 38% and 0%, and hepatocyte viabilities were 93+/-3%, 80+/-3%, 52+/-8%, 88+/-1%, 70+/-3%, 80+/-4% and 82+/-3%, respectively. AG+LPS or L-NAME+LPS administration was followed by excessive vacuolization of hepatocytes with lesions in the intermediary lobule zone characterized by features of secondary necrosis as a continuation of apoptotic processes. SNAP+L-NAME+LPS resulted in a well-preserved structure of central vein lobules with sparse signs of apoptosis. Treatment with LPS or CM increased iNOS expression in hepatocyte culture, which was inhibited by L-NAME, FK 506 or AG. AG reduced LPS-induced rise in alanine aminotransferase leakage. LPS-induced NO exerts cytoprotective effects in vivo, while LPS-induced NO in vitro appears to be toxic. Based on the data of this report, one cannot use in vitro results to predict in vivo responses to LPS-induced NO production. The pharmacological modulation of iNOS expression or NO production in vivo or in vitro, therefore, by the development of specific NO donors or inhibitors is promising for improvement of hepatocyte functions under the two experimental conditions, respectively.