Mitochondrial membrane perturbations in cholestasis

Experimental Conditions That Influence the Utility of 2′7′-Dichlorodihydrofluorescein Diacetate (DCFH2-DA) as a Fluorogenic Biosensor for Mitochondrial Redox Status

Oxidative stress has been causally linked to various diseases. Electron transport chain (ETC) inhibitors such as rotenone and antimycin A are frequently used in model systems to study oxidative stress. Oxidative stress that is provoked by ETC inhibitors can be visualized using the fluorogenic probe 2′,7′-dichlorodihydrofluorescein-diacetate (DCFH₂-DA). Non-fluorescent DCFH₂-DA crosses the plasma membrane, is deacetylated to 2′,7′-dichlorodihydrofluorescein (DCFH₂) by esterases, and is oxidized to its fluorescent form 2′,7′-dichlorofluorescein (DCF) by intracellular ROS. DCF fluorescence can, therefore, be used as a semi-quantitative measure of general oxidative stress. However, the use of DCFH₂-DA is complicated by various protocol-related factors that mediate DCFH₂-to-DCF conversion independently of the degree of oxidative stress. This study therefore analyzed the influence of ancillary factors on DCF formation in the context of ETC inhibitors. It was found that ETC inhibitors trigger DCF formation in cell-free experiments when they are co-dissolved with DCFH₂-DA. Moreover, the extent of DCF formation depended on the type of culture medium that was used, the pH of the assay system, the presence of fetal calf serum, and the final DCFH₂-DA solvent concentration. Conclusively, experiments with DCFH₂-DA should not discount the influence of protocol-related factors such as medium and mitochondrial inhibitors (and possibly other compounds) on the DCFH₂-DA-DCF reaction and proper controls should always be built into the assay protocol.

Augmented Liver Uptake of the Membrane Voltage Sensor Tetraphenylphosphonium Distinguishes Early Fibrosis in a Mouse Model

Mitochondrial (mito-) oxidative phosphorylation (OxPhos) is a critical determinant of cellular membrane potential/voltage. Dysregulation of OxPhos is a biochemical signature of advanced liver fibrosis. However, less is known about the net voltage of the liver in fibrosis. In this study, using the radiolabeled [³H] voltage sensor, tetraphenylphosphonium (TPP), which depends on membrane potential for cellular uptake/accumulation, we determined the net voltage of the liver in a mouse model of carbon tetrachloride (CCl₄)-induced hepatic fibrosis. We demonstrated that the liver uptake of ³H-TPP significantly increased at 4 weeks of CCl₄-administration (6.07 ± 0.69% ID/g, p < 0.05) compared with 6 weeks (4.85 ± 1.47% ID/g) and the control (3.50 ± 0.22% ID/g). Analysis of the fibrosis, collagen synthesis, and deposition showed that the increased ³H-TPP uptake at 4 weeks corresponds to early fibrosis (F1), according to the METAVIR scoring system. Biodistribution data revealed that the ³H-TPP accumulation is significant in the fibrogenic liver but not in other tissues. Mechanistically, the augmentation of the liver uptake of ³H-TPP in early fibrosis concurred with the upregulation of mito-electron transport chain enzymes, a concomitant increase in mito-oxygen consumption, and the activation of the AMPK-signaling pathway. Collectively, our results indicate that mito-metabolic response to hepatic insult may underlie the net increase in the voltage of the liver in early fibrosis.

Acute and subacute toxicity tests of goat bile in BALB/c mice

Aim:

The aim of this study was to investigate the toxicity of goat bile in BALB/c mice since some Indonesian people consume raw goat gallbladder to treat malaria and increase stamina.

Materials and Methods:

Acute toxicity test was done in six groups of BALB/c mice using 100%, 50%, 25%, 12.5%, and 6.75% of goat bile and negative control. The death of mice was observed within 14 days. In the subacute toxicity test, the body weight and hematology parameters on day 0 and day 4 post-treatment were evaluated. The mice were closely observed for 28 days before plasma collection for the blood biochemistry evaluation.

Results:

Mild diarrhea was observed in acute and subacute toxicity tests. No death of mice was observed in acute test. Goat bile did not inhibit the increase of the body weight of mice. A slight reduction in hemoglobin and hematocrit levels in mice treated with 25% and 50% goat bile, however, remained normal in mice treated with 100% goat bile. The red and white blood cell count were not affected. Liver and kidney functions were not affected by goat bile treatment as revealed by the plasma level of aspartate aminotransferase and alanine aminotransferase, blood urea nitrogen, and creatinine, which remained in the normal range.

Conclusion:

Goat bile treatment in BALB/c mice caused mild toxicity in mice. Hydrophobic bile acids may cause the toxicity of goat bile in mice; therefore, it is recommended that goat bile consumption not to be taken oftenly to avoid its harmful effect.

Preventive effect of artemisinin extract against cholestasis induced via lithocholic acid exposure

Obstructive cholestasis characterized by biliary pressure increase leading to leakage of bile back that causes liver injury. The present study aims to evaluate the effects of artemisinin in obstructive cholestasis in mice. The present study was carried out on 40 adult healthy mice that were divided into 4 groups, 10 mice each; the negative control group didn’t receive any medication. The normal group was fed normally with 100 mg/kg of artemisinin extract orally. The cholestatic group fed on 1% lithocholic acid (LCA) mixed into control diet and cholestatic group co-treated with 100 mg/kg of artemisinin extract orally. Mice were treated for 1 month then killed at end of the experiment. A significant increase in alanine aminotransferase, aspartate aminotransferase, and total and direct bilirubin was detected in mice exposed to LCA toxicity. That increase was significantly reduced to normal values in mice co-treated with artemisinin. LCA toxicity causes multiple areas of necrosis of irregular distribution. However, artemisinin co-treatment showed normal hepatic architecture. Moreover, LCA causes down-regulation of hepatic mRNA expressions of a set of genes that are responsible for ATP binding cassette and anions permeability as ATP-binding cassette sub-family G member 8, organic anion-transporting polypeptide, and multidrug resistance-associated protein 2 genes that were ameliorated by artemisinin administration. Similarly, LCA toxicity significantly down-regulated hepatic mRNA expression of constitutive androstane receptor, OATP4, and farnesoid x receptor genes. However, artemisinin treatment showed a reasonable prevention. In conclusion, the current study strikingly revealed that artemisinin treatment can prevent severe hepatotoxicity and cholestasis that led via LCA exposure.

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.

Free fatty acids repress small heterodimer partner (SHP) activation and adiponectin counteracts bile acid-induced liver injury in superobese patients with nonalcoholic steatohepatitis

Nonalcoholic fatty liver disease (NAFLD) is the most common liver disease in industrialized countries and may proceed to steatohepatitis (NASH). Apoptosis and free fatty acid (FFA)-induced lipotoxicity are important features of NASH pathogenesis. We have shown a hepatoprotective effect of adiponectin in steatotic livers of hepatitis C virus (HCV) patients and recent data links bile acid (BA) metabolism to the pathogenesis of NAFLD. The aim of this study was to identify potential interactions between BA and FFA metabolism in NAFLD. Liver biopsies and serum samples from 113 morbidly obese patients receiving bariatric surgery, healthy individuals, and moderately obese NAFLD patients were studied. Serum FFA, BA, and M30 were increased in NASH versus simple steatosis, while adiponectin was significantly decreased. The NAFLD activity score (NAS) score correlated with BA levels and reversely with adiponectin. Adiponectin reversely correlated with CD95/Fas messenger RNA (mRNA) and hepatocellular apoptosis. The BA transporter high-affinity Na+ /taurocholate cotransporter (NTCP) and the BA synthesizing enzyme cholesterol 7 alpha-hydroxylase (CYP7A1) were significantly up-regulated in obese patients and hepatoma cells exposed to FFA. Up-regulation of NTCP and CYP7A1 indicate failure to activate small heterodimer partner (SHP) upon farnesoid X receptor (FXR) stimulation by increasing BA concentrations. In line with the NAS score, adiponectin levels were reversely correlated with BA levels. Adiponectin correlated with NTCP and affects Cyp7A1 expression both in vivo and in vitro.

CONCLUSION

BA synthesis and serum BA levels correlated with disease severity in NAFLD, while adiponectin is reversely correlated. FFA exposure prevented SHP-mediated repression of NTCP and Cyp7A1 expression, which lead to increased BA synthesis and uptake. In NASH, BA accumulation induced hepatocyte cell death and late FXR activation failed to prevent hepatocyte injury due to decreased adiponectin levels. Early treatment with FXR ligands and/or adiponectin-receptor agonists might prevent NASH.

Lithocholic acid disrupts phospholipid and sphingolipid homeostasis leading to cholestasis in mice

Lithocholic acid (LCA) is an endogenous compound associated with hepatic toxicity during cholestasis. LCA exposure in mice resulted in decreased serum lysophosphatidylcholine (LPC) and sphingomyelin levels due to elevated lysophosphatidylcholine acyltransferase (LPCAT) and sphingomyelin phosphodiesterase (SMPD) expression. Global metabolome analysis indicated significant decreases in serum palmitoyl-, stearoyl-, oleoyl-, and linoleoyl-LPC levels after LCA exposure. LCA treatment also resulted in decreased serum sphingomyelin levels and increased hepatic ceramide levels, and induction of LPCAT and SMPD messenger RNAs (mRNAs). Transforming growth factor-β (TGF-β) induced Lpcat2/4 and Smpd3 gene expression in primary hepatocytes and the induction was diminished by pretreatment with the SMAD3 inhibitor SIS3. Furthermore, alteration of the LPCs and Lpcat1/2/4 and Smpd3 expression was attenuated in LCA-treated farnesoid X receptor-null mice that are resistant to LCA-induced intrahepatic cholestasis.

CONCLUSION

This study revealed that LCA induced disruption of phospholipid/sphingolipid homeostasis through TGF-β signaling and that serum LPC is a biomarker for biliary injury.

Liver fibrosis in biliary atresia

Biliary atresia (BA) is the most common cholestatic liver disorder requiring liver transplantation in children. Hepatic fibrosis is not only a universal and prominent feature of BA, it is also the most important predictor of outcome following portoenterostomy (PE). Without PE, the progression of hepatic fibrosis is quite dramatic, such that liver cirrhosis is established within a few weeks after birth. Etiologies and molecular networks underpinning such an expeditious fibrogenic process have not been well established. However, immune and nonimmune factors implicated in the pathogenesis of BA, and the resultant cholestasis and oxidative stress, appear to be the main triggers of hepatic fibrosis in BA. Owing to a lack of validated noninvasive tools to monitor liver fibrosis, current prognostic models of BA entail clinical and biochemical variables reflecting liver dysfunction rather than hepatic fibrogenesis. Further work is necessary to validate the results of preliminary studies indicating a good relationship between liver fibrosis determined by transient elastography and other clinical and routinely performed biochemical parameters in pediatric patients. Although a prime candidate for a number of antifibrotic therapies on the horizon, owing to poor understanding of molecular mechanisms, a clear framework of antifibrotic targets has not been outlined in BA. Similarly, specific antifibrotic therapies have not yet been incorporated in clinical practice, limiting these measures to prompt diagnosis and PE operation, prevention and treatment of cholangitis and optimal nutritional support including the administration of fat-soluble vitamins.

Does prolonged biliary obstructive jaundice sensitize the liver to endotoxemia?

Biliary obstructive jaundice (OJ) is an important clinical consideration concerning high bacteremic risk. Hepatocyte apoptosis is one of the causes of cholestatic liver injury. The aim of the current study was to examine the precise pathway and time course of hepatocyte apoptosis during OJ with LPS administration and to determine if OJ sensitizes the liver to endotoxemia. Male C57BL/6 mice were subjected to bile duct ligation and division and were administered with LPS at 3 (OJ3) or 14 (OJ14) days after surgery. Fas ligand expression, poly (adenosine diphosphate-ribose) polymerase p85 fragment immunohistochemistry, activation of caspases 3, 8, and 9, serum alanine aminotransferase levels, and hepatic adenosine triphosphate (ATP) contents were examined. Survival after LPS administration in male C57BL/6 or gld/gld (Fas ligand-deficient) mice was determined. The expression of Fas ligand increased during OJ. After LPS administration, the expression of cleaved caspases 3 and 8 increased in Sham3, Sham14, OJ3, and OJ14 mice, and it significantly increased in OJ14 compared with other mice. Poly (adenosine diphosphate-ribose) polymerase p85 immunohistochemistry showed significant hepatocyte apoptosis after LPS administration in OJ14 mice relative to OJ3. In OJ14 with LPS administration, ATP contents significantly decreased and alanine aminotransferase levels increased. Hepatocyte apoptosis was decreased in gld/gld OJ14 mice compared with C57BL/6 OJ14. All C57BL/6 OJ14 mice with LPS died, but survival in gld/gld OJ14 significantly ameliorated. In prolonged OJ with LPS administration, hepatocyte apoptosis depending on Fas ligand expression significantly increased in association with a decrease in ATP contents, thus resulting in liver necrapoptosis.

Relationship between parameters of lipid peroxidation during obstructive jaundice and after bile flow restoration

Restoration of bile flow after 9-day cholestasis in rat liver normalized the content of lipid peroxidation products. The removal of the cholestatic factor after 12-day cholestasis was not followed by recovery of these parameters. We showed that measurement of serum concentration of lipid peroxidation products in patients with cholelithiasis during the preoperative period holds promise for selection of the optimum time for surgical treatment and prediction of the risk of postoperative complications.

Bile acid levels are increased in the liver of patients with steatohepatitis

BACKGROUND/AIMS

The pathogenesis of steatohepatitis remains largely unknown; however, bile acids may play a role as potential mediators of liver damage. The aim of this study was to characterize bile acid profiles in liver tissue of patients with steatohepatitis.

METHODS

Bile acid composition was determined by gas-liquid chromatography in liver tissue from patients with nonalcoholic steatohepatitis (NASH; n=15), patients with alcoholic steatohepatitis (ASH; n=14), and controls (n=8). Liver biopsies were graded for steatosis, inflammation, and fibrosis.

RESULTS

Bile acids were moderately increased in liver tissue of steatohepatitis patients compared with controls (P<0.05). Deoxycholic, chenodeoxycholic, and cholic acids were elevated by 92, 64, and 43%, respectively, in patients with steatohepatitis (P<0.05). Cholic acid was the prevailing bile acid in NASH patients and in controls. More hydrophobic bile acid species were elevated in ASH patients compared with controls (P<0.05). Significant correlations were found in NASH patients between hepatic chenodeoxycholic acid and fibrosis, and between cholic acid and trihydroxy/dihydroxy bile acids and inflammation (P<0.05). In patients with ASH, cholic acid and trihydroxy/dihydroxy bile acids were correlated with steatosis (P<0.01).

CONCLUSION

This study shows a distinct pattern of bile acids in the liver of patients with steatohepatitis. Further, the association between bile acids and histological liver injury suggests an association of specific bile acids and disease progression, possibly through bile acid-induced liver injury.

Role of mitochondria in drug-induced cholestatic injury

Mitochondria have multiple functions in eukaryotic cells and are organized into dynamic tubular networks that continuously undergo changes through coordinated fusion and fission and migration through the cytosol. Mitochondria integrate cell-signaling networks, especially those involving the intracellular messenger Ca(2+), into the regulation of metabolic pathways. Recently, it has become clear that mitochondria are central to the three main cell death pathways, namely necrosis, apoptosis, and autophagic cell death. This article discusses the role of mitochondria in drug-induced cholestatic injury to the liver. The role of mitochondria in the cellular adaptation against the toxic effects of bile acids is discussed also.

Role of mitochondria in cell death induced by Photofrin-PDT and ursodeoxycholic acid by means of SLIM

The present study was undertaken to find new ways to improve efficacy of photodynamic therapy (PDT). We investigated the combinatory effect of the photosensitizer Photofrin and ursodeoxycholic acid (UDCA). UDCA is a relatively non-toxic bile acid which is used inter alia as a treatment for cholestatic disorders and was reported to enhance PDT efficiency of two other photosensitizers. Since besides necrosis and autophagic processes apoptosis has been found to be a prominent form of cell death in response to PDT for many cells in culture, several appropriate tests, such as cytochrome c release, caspase activation and DNA fragmentation were performed. Furthermore spectral resolved fluorescence lifetime imaging (SLIM) was used to analyse the cellular composition of Photofrin and the status of the enzymes of the respiratory chain. Our experiments with two human hepatoblastoma cell lines revealed that the combination of Photofrin with UDCA significantly enhanced efficacy of PDT for both cell lines even though the underlying molecular mechanism for the mode of action of Photofrin seems to be different to some extent. In HepG2 cells cell death was clearly the consequence of mitochondrial disturbance as shown by cytochrome c release and DNA fragmentation, whereas in Huh7 cells these features were not observed. Other mechanisms seem to be more important in this case. One reason for the enhanced PDT effect when UDCA is also applied could be that UDCA destabilizes the mitochondrial membrane. This could be concluded from the fluorescence lifetime of the respiratory chain enzymes which turned out to be longer in the presence of UDCA in HepG2 cells, suggesting a perturbation of the mitochondrial membrane. The threshold at which PDT damages the mitochondrial membrane was therefore lower and correlated with the enhanced cytochrome c release observed post PDT. Thus enforced photodamage leads to a higher loss of cell viability.

Ursodeoxycholic acid in primary biliary cirrhosis improves glutathione status but fails to reduce lipid peroxidation

BACKGROUND

Ursodeoxycholic acid (UDCA) may slow progression in primary biliary cirrhosis (PBC), but its effect on survival is controversial. We have previously demonstrated that oxidant stress, with severely depressed plasma glutathione, is a feature of untreated PBC; this study examines the effect of UDCA on lipid peroxidation, antioxidant status and associated processes.

PATIENTS AND METHODS

Markers of lipid peroxidation, antioxidant status, hepatic fibrogenesis, inflammation, cholestasis and synthetic function were measured at 0, 3, 6, 9 and 12 months in blood and urine from 35 PBC patients receiving UDCA.

RESULTS

Plasma glutathione, reflecting intrahepatic levels, climbed steadily on UDCA; although still subnormal, the median value at 12 months was 2.4-fold higher than the untreated level. Liver enzyme markers and C-reactive protein also improved, whilst PIIINP improved steadily, but the change did not attain statistical significance. Serum bilirubin remained unchanged and total antioxidant capacity, albumin and vitamin E decreased after 12 months' UDCA treatment. 8-Isoprostane increased and malondialdehyde was unchanged.

CONCLUSIONS

UDCA treatment partially corrected plasma glutathione status and some other biomarkers greatly improved, but lipid peroxidation was not reduced. UDCA may, therefore, require supplementation with glutathione precursors and/or antioxidant cocktails to reduce oxidant stress and thus delay disease progression to cirrhosis.

"Let there be bile"--understanding hepatic injury in cholestasis

Cholestatic liver disorders account for a large proportion of chronic liver ailments in adults, children and infants, and are among the leading indications for liver transplantation in all age groups. Recent studies have begun to characterize the cellular and molecular mechanisms of hepatocyte injury caused by the retention of hydrophobic bile acids in cholestasis. Steatocholestasis is the combined presence of hepatic steatosis and cholestasis, common in genetic causes of metabolic liver disease in childhood. Retention of hydrophobic bile acids promotes hepatocellular injury and subsequent portal fibrosis in these conditions. Investigations at the mechanistic level have revealed that activation of hepatocyte death receptors, induction of oxidative stress, mitochondrial perturbations and activation of caspases are intracellular pathways that mediate hepatocyte injury. Several compounds in licorice root have been shown to modulate bile acid-induced apoptosis and necrosis of hepatocytes. Further investigations will be needed to identify novel molecular and cellular targets for which pharmaceuticals might be developed, to reduce liver injury and fibrosis in cholestasis and steatocholestasis.

Medical treatment of primary biliary cirrhosis and primary sclerosing cholangitis

Chronic cholestasis is the main feature of primary biliary cirrhosis (PBC) and primary sclerosing cholangitis (PSC), the most common chronic cholestatic liver diseases in adults. Although the etiology of both diseases remains poorly understood, auto-immune processes appear to be important, particularly in PBC. PBC and PSC usually slowly progress to cirrhosis,liver failure, and death, unless liver transplantation is performed. Ursodeoxycholic acid(UDCA), a hydrophilic dihydroxy bile acid, is the only drug currently approved for the treatment of patients with PBC and is also used in patients with PSC. In addition to UDCA, patients with PSC should be referred to endoscopic dilatation of major bile duct stenoses. Several potential mechanisms of action of UDCA have been proposed, including intracellular modulation of signaling events and secretion. Various immunosuppressive drugs have been evaluated alone or in combination with UDCA-especially for the treatment of PBC. Of these drugs,the topical corticosteroid budesonide, together with UDCA, appears promising in the treatment of early stage PBC, but data remain insufficient to warrant use of budesonide outside of controlled studies.

Human hepatic mitochondria generate reactive oxygen species and undergo the permeability transition in response to hydrophobic bile acids

OBJECTIVES

Hydrophobic bile acids accumulate in the liver during cholestasis and are believed to cause hepatocellular necrosis and apoptosis in part through induction of the mitochondrial permeability transition (MPT) and the mitochondrial generation of oxidative stress. The purpose of this study was to determine if human hepatic mitochondria respond to bile acids in this manner.

METHODS

The MPT was measured spectrophotometrically and morphologically in normal human liver mitochondria exposed to glycochenodeoxycholic acid (GCDC) with and without cyclosporin A, an inhibitor of the MPT, antioxidants, and tauroursodeoxycholic acid (TUDC). Hydroperoxide generation was measured by dichlorofluorescein fluorescence. Cytochrome c and apoptosis-inducing factor were assessed by immunoblotting.

RESULTS

GCDC induced the MPT in a dose-dependent manner, which was inhibited by cyclosporin A, alpha-tocopherol, beta-carotene, idebenone, and TUDC. GCDC stimulated reactive oxygen species generation and release of cytochrome c and apoptosis-inducing factor, which were significantly inhibited by the antioxidants, cyclosporin A, and TUDC.

CONCLUSIONS

Mitochondrial pathways of cell death are stimulated in human hepatic mitochondria exposed to GCDC consistent with the role of mitochondrial dysfunction in the pathogenesis of cholestatic liver injury. These results parallel those reported in rodents, supporting the extrapolation of mechanistic studies of bile acid toxicity from rodent to humans.

Increased susceptibility of fat-laden Zucker-rat hepatocytes to bile acid-induced oncotic necrosis: an in vitro model of steatocholestasis

Metabolic liver disorders cause chronic liver disease and liver failure in childhood. Many of these disorders share the histologic features of steatosis and cholestasis, or steatocholestasis. In this study we sought to (1) develop an in vitro model of steatocholestasis, (2) determine the mechanisms of cell death in this model, and (3) determine the role of mitochondrial disturbances in this model.

METHODS

Hepatocytes were isolated from 8-week-old obese (fa/fa) and lean Zucker rats. Cell suspensions were treated with glycochenodeoxycholic acid (GCDC), after which reactive oxygen species (ROS) generation, oncotic necrosis, apoptosis, and ATP content were assessed. Isolated liver mitochondria were exposed to GCDC and analyzed for ROS generation, mitochondrial membrane-permeability transition (MPT), and cytochrome c release. Oncotic necrosis was significantly increased and apoptosis reduced in fa/fa hepatocytes exposed to GCDC compared with that in lean hepatocytes. Necrosis occurred by way of an ROS- and MPT-dependent pathway. Basal and dynamic ATP content did not differ between fa/fa and lean hepatocytes. GCDC stimulated ROS generation, MPT, and cytochrome c release to a similar extent in purified mitochondria from both fa/fa and lean rats. These findings suggest that fat-laden hepatocytes favor a necrotic rather than an apoptotic cell death when exposed to low concentrations of bile acids. The protective effects of antioxidants and MPT blockers suggest novel therapeutic strategies for the treatment of steatocholestatic metabolic liver diseases.

Melatonin prevents oxidative stress and hepatocyte cell death induced by experimental cholestasis

The induction of oxidative stress precedes liver injury during experimental obstructive jaundice (OJ). In this sense, different evidences suggest that melatonin (MEL), as antioxidant, may be useful in the protection against apoptosis and necrosis during experimental cholestasis. In addition, we will also assess if MEL-dependent protection is related to a recovery of antioxidant status disturbances induced by OJ. Cholestasis was achieved by double ligature and sectioning of the principal bile duct. MEL was injected intraperitoneally (500 microg/kg/day). Lipid peroxidation was evaluated by the measurement of malondialdehyde (MDA) content in liver. Different parameters related to antioxidant status, such as reduced glutathione (GSH), glutathione peroxidase (GPx), catalase and superoxide dismutase (SOD) were determined in liver. Liver injury was assessed by alanine amino-transferase (ALT) in serum, histological examination, DNA fragmentation and TUNEL assay. The activation of perisinusoidal stellate cells was evaluated by immunohistochemical measurement of alpha-smooth muscle actin in liver sections. The induction of OJ increased all the parameters related to apoptosis and necrosis in liver. The induction of liver injury was associated with stellate cell activation, as well as an increase in MDA (p < 0.0001) and a reduction in GSH, GPx, catalase and SOD content (p < 0.0001) in liver. MEL reduced hepatic apoptosis and necrosis (p < 0.004) with a significant improvement in all oxidative stress markers. In conclusion, our results showed that MEL recovered the antioxidant status and reduced apoptosis and necrosis induced by experimental cholestasis.

Bile acid-induced negative feedback regulation of the human ileal bile acid transporter

Ileal expression of the apical sodium-dependent bile acid transporter (ASBT) in the rat is unaffected by bile salts, yet in the mouse it is under negative-feedback regulation. The bile acid responsiveness of human ASBT is unknown. The human ASBT promoter linked to a luciferase reporter was studied in Caco-2 cells treated with chenodeoxycholic acid (CDCA) and transfected with expression plasmids for farnesoid X-receptor (FXR), short heterodimer partner (SHP), and retinoic acid receptor/retinoid X receptor (RAR/RXR). CDCA treatment of Caco-2 cells led to a 75% reduction in steady-state ASBT messenger RNA levels and a 78% reduction in human ASBT promoter activity. A dominant negative FXR abrogated the response to CDCA. Site-directed mutagenesis of an RAR/RXR cis element in the human ASBT promoter reduced its activity by 50% and eliminated the bile acid response. Retinoic acid activated the human ASBT promoter fourfold. SHP repressed the activity of the ASBT promoter and reduced activation by retinoic acid. Antisense mediated knock-down of SHP in Caco-2 cells partially offset the bile acid mediated repression of ASBT promoter activity. In conclusion, the human ASBT is positively regulated by retinoic acid. Bile acids induce a negative feedback regulation of human ASBT via an FXR-mediated, SHP-dependent effect upon RAR/RXR activation of ASBT.

Hepatocellular apoptosis after hepatectomy in obstructive jaundice in rats

AIM: To investigate the hepatocellular apoptosis after hepatectomy in obstructive jaundice and biliary decompression rats.

METHODS: After bile duct ligation for 7 days, rats were randomly divided into OB group in which the rats underwent 70% hepatectomy, OB-CD group in which the rats underwent hepatectomy accompanied by choledochoduodenostomy, CD-Hx group in which the rats underwent choledochoduodenostomy and then received 70% hepatectomy on the fifth day after biliary decompression. The control group (Hx group) only underwent hepatectomy.

RESULTS: The level of total serum bilirubin and serum enzymes was significantly lower in CD-Hx group than in OB-CD and OB groups on day 1, 3 and 5 after hepatectomy. The apoptotic index was significantly lower in CD-Hx group than in OB-CD and OB groups on day 3 and 5. The oligonucleosomal DNA fragments and Caspase-3 activity were also lower in CD-Hx group than in OB-CD and OB groups 3 days after hepatectomy, without differences between CD-Hx and Hx groups.

CONCLUSION: Hepatocellular apoptosis plays vital roles in jaundice rats, and biliary decompression is more effective in treatment of patients with severe jaundice before operation.

Resistance of rat hepatocytes against bile acid-induced apoptosis in cholestatic liver injury is due to nuclear factor-kappa B activation

BACKGROUND/AIMS

To examine the extent and mechanisms of apoptosis in cholestatic liver injury and to explore the role of the transcription factor nuclear factor-kappa B in protection against bile acid-induced apoptosis.

METHODS

Cholestatic liver injury was induced by bile duct ligation in Wistar rats. Furthermore, primary cultures of rat hepatocytes were exposed to glycochenodeoxycholic acid (GCDCA), tauroursodeoxycholic acid (TUDCA), taurochenodeoxycholic acid (TCDCA) and to cytokines. Apoptosis was determined by TUNEL-staining, active caspase-3 staining, activation of caspase-8, -9 and -3.

RESULTS

Limited hepatocyte apoptosis and an increased expression of NF-kappaB-regulated anti-apoptotic genes A1 and cIAP2 were detected in cholestatic rat livers. Bcl-2 expression was restricted to bile duct epithelium. In contrast to TCDCA and TUDCA, GCDCA induced apoptosis in a Fas-associated protein with death domain (FADD)-independent pathway in hepatocytes. Although bile acids do not activate NF-kappaB, NF-kappaB activation by cytokines (induced during cholestasis) protected against GCDCA-induced apoptosis in vitro by upregulating A1 and cIAP2.

CONCLUSIONS

GCDCA induces apoptosis in a mitochondria-controlled pathway in which caspase-8 is activated in a FADD-independent manner. However, bile acid-induced apoptosis in cholestasis is limited. This could be explained by cytokine-induced activation of NF-kappaB-regulated anti-apoptotic genes like A1 and cIAP2.

Primary biliary cirrhosis

Primary biliary cirrhosis is a chronic cholestatic liver disease of adults. This disorder is characterised histologically by chronic non-suppurative destruction of interlobular bile ducts leading to advanced fibrosis, cirrhosis, and liver failure. The precise aetiopathogenesis of primary biliary cirrhosis remains unknown, although dysregulation of the immune system and genetic susceptibility both seem to be important. Affected patients are typically middle-aged women with abnormal serum concentrations of alkaline phosphatase. Presence of antimitochondrial antibody in serum is almost diagnostic of the disorder. Identification of primary biliary cirrhosis is important, because effective treatment with ursodeoxycholic acid has been shown to halt disease progression and improve survival without need for liver transplantation. However, therapeutic options for disease-related complications-including fatigue and metabolic bone disease-remain unavailable. Mathematical models have been developed that accurately predict the natural history of primary biliary cirrhosis in individuals. Despite advances in understanding of the disease, it remains one of the major indications for liver transplantation worldwide.

Cardiac Mitochondrial Calcium Loading Capacity is Severely Affected after Chronic Cholestasis in Wistar Rats

Background

Cardiovascular changes correlated with some forms of hepatic disease are being reported in the literature. Objectives: The aim of this work was to characterize cardiac mitochondrial bioenergetics and calcium buffering capacity in Wistar rats injected with six weekly doses of α-naphthylisothio-cyanate (ANIT), a compound known to induce cholestasis in animal models.

Methods

Isolated heart mitochondria were obtained from both injected and control animals and bioenergetic parameters were measured, as well as the capacity to buffer externally added calcium and the mitochondrial content of reduced protein thiol groups. Blood biochemistry analyses were obtained at the initial and end points of treatment. The in vitro ANIT effect on isolated heart mitochondria was also studied.

Results and Discussion

Our results showed that the respiratory control ratio was the only parameter affected in injected animals ( p < .05, n = 5). Nevertheless, heart mitochondria from injected animals showed an inability to accumulate added calcium owing to an increased susceptibility to the calcium-dependent mitochondrial permeability transition ( p < .0001, n = 5). The effects were still present 1 week after ending ANIT administration, when serum markers for liver injury and hyperbilirubinemia were already abated (although in the presence of bile duct proliferation). To our knowledge, this is the first time that cardiac mitochondrial calcium homeostasis and mitochondrial respiratory ratio are seen affected during ANIT-induced cholestasis, prevailing even in the absence of hepatic damage serum markers.

Reduction in cardiac mitochondrial calcium loading capacity is observable during alpha-naphthylisothiocyanate-induced acute cholestasis: a clue for hepatic-derived cardiomyopathies?

Cardiovascular changes of still obscure origin are sometimes correlated with co-existing liver diseases, as cholestasis. The aim of this work was to examine and compare cardiac mitochondrial bioenergetics and calcium loading capacity from rats injected with a single dose of alpha-naphthylisothiocyanate (ANIT), a cholestasis-inducing compound. Forty-eight hours after ANIT administration, blood samples were collected and markers for hepatic disease were determined. Heart mitochondria from both control and ANIT-injected rats were isolated and subjected to biochemical characterization, including the susceptibility to the calcium-dependent permeability transition. The results showed that cardiac mitochondria from cholestatic animals did not have significant changes in respiratory parameters or in the basal levels of adenine nucleotide. The most impressive result from this work was that cardiac mitochondria from ANIT-injected animals had a lower calcium loading capacity. The prevention of this property by cyclosporin-A, a specific inhibitor of the mitochondrial permeability transition, showed that this phenomenon was reason for the reduced calcium loading capacity in ANIT-injected animals. The results suggest that, during the development of ANIT-induced cholestasis, heart mitochondria loose their default ability to buffer calcium. Our results may contribute to explain the occurrence of cardiomyopathies sometimes associated with cholestatic disease.

Sinusoidal efflux of taurocholate correlates with the hepatic expression level of Mrp3

Multidrug resistance-associated protein 3 (Mrp3/ABCC3), which can mediate the cellular extrusion of bile acids, is induced on the hepatic sinusoidal membrane of Mrp2/ABCC2-deficient rats (Eisai hyperbilirubinemic rats; EHBRs) and phenobarbital-treated Sprague-Dawley rats. In the present study, the correlation between the sinusoidal efflux clearance (PS(eff)) of [3H]taurocholate (TC) and the hepatic expression of Mrp3 was investigated using perfused liver from these rats. A significant correlation was observed between the PS(eff) and the hepatic expression level of Mrp3, suggesting a contribution by Mrp3 to the sinusoidal efflux of TC. The results of the kinetic analysis also suggested that other transporter(s) on the sinusoidal plasma membrane may participate in the efflux of TC under physiological conditions. The contribution of Mrp3 to the sinusoidal efflux of TC in EHBRs and phenobarbital (80 and 40 mg/kg)-treated rats was revealed to be 58%, 48%, and 31%, respectively.

Cholestasis induces murine hepatocyte apoptosis and DNA synthesis with preservation of the immediate-early gene response

BACKGROUND

Major hepatic resection in patients with unrelieved obstructive jaundice carries an increased risk of postoperative liver failure. We hypothesized that cholestasis induces hepatocyte apoptosis and impairs hepatic regeneration by inhibiting up-regulation of the known immediate-early response genes, nuclear factor kappa B (NF-kappaB) and activating protein-1 (AP-1). The aim of this study was to determine whether the immediate-early gene response in hepatic regeneration remains intact in extrahepatic cholestasis.

METHODS

Eight-week-old BALB/c mice underwent either sham operation (SO) or common bile duct ligation (BDL). Two-thirds partial hepatectomy (PH) was performed at 4 and 7 days, with remnant liver harvested 0, 15, 30, or 60 minutes after PH. Serum analysis for markers of cholestasis and histopathology was obtained. Proliferating cell nuclear antigen and terminal deoxyuridine triphosphate nick end labeling (TUNEL) immunohistochemistry for detection of DNA synthesis and apoptosis, respectively, was performed 4, 7, or 10 days after SO or BDL. Liver samples from 0, 15, 30, or 60 minutes after PH were analyzed for NF-kappaB and AP-1 DNA binding activity by using electrophoretic mobility shift assays.

RESULTS

Increased serum bilirubin level and hematoxylin-eosin-stained liver sections confirmed cholestasis in BDL mice. BDL induced marked DNA synthesis and hepatocyte apoptosis in prehepatectomy liver at both 4 and 7 days. Substantially higher basal levels of both NF-kappaB and AP-1 binding activity were present in BDL compared with SO mice. Fold induction of NF-kappaB and AP-1, however, was similar between BDL and SO mice. Cholestasis induced hepatocyte DNA synthesis and apoptosis. Basal NF-kappaB and AP-1 DNA binding activity was increased in BDL mice, but fold induction of these immediate-early genes did not differ from controls.

CONCLUSIONS

Although basal NF-kappaB and AP-1 DNA binding is increased in cholestasis, the immediate-early gene response to PH remains intact in BDL mice.

The therapeutic effects of ursodeoxycholic acid as an anti-apoptotic agent

The dihydroxy bile acid, ursodeoxycholic acid (UDCA), has been in widespread clinical use in the Western world since the mid 1980s, when it was initially used for gallstone dissolution [1,2] and subsequently for the treatment of chronic cholestatic liver diseases [3,4]. Many clinical trials of UDCA in a variety of cholestatic disorders established biochemical and clinical improvements, and most importantly showed a significant prolongation of transplant-free survival after four years of treatment with UDCA in patients with primary biliary cirrhosis [5]. Despite its clinical efficacy, the precise mechanism(s) by which UDCA improves liver function during cholestasis is still a matter of debate [6]. It was initially considered that the choleretic effect of UDCA, coupled with its ability to cause a marked shift in the composition of the bile acid pool towards hydrophilicity, accounted for its mechanism of action. In recent years, however, it has become evident that UDCA and its conjugated derivatives are capable of exerting direct effects at the cellular, subcellular, and molecular levels by stabilising cell membranes, affecting signal transduction pathways, and regulating immune responses. In addition, we have shown that UDCA plays a unique role in modulating the apoptotic threshold in both hepatic and non-hepatic cells [7-10]. The purpose of this article is to examine the mechanism(s) by which UDCA prevents apoptotic cell death associated with cholestasis. In addition, we will also review a potentially novel and, heretofore, unrecognised role of UDCA as a therapeutic agent in the treatment of non-liver diseases associated with increased levels of apoptosis as a pathogenesis of the disorder.

Cholestatic syndromes

New insights into the regulation of hepatobiliary transport proteins have provided the basis for a better understanding of the pathogenesis of cholestatic liver diseases. Mutations of transporter genes can cause hereditary cholestatic syndromes, the study of which has shed much light on the basic mechanisms of bile secretion and cholestasis. Important new studies have been published about the pathogenesis, clinical features, and treatment of primary biliary cirrhosis, primary sclerosing cholangitis, cholestasis of pregnancy, total parenteral nutrition-induced cholestasis, and drug-induced cholestasis.

Modulation of steady-state messenger RNA levels in the regenerating rat liver with bile acid feeding

Liver regeneration after two thirds partial hepatectomy (PH) is an orchestrated hyperplastic growth process requiring coordinated expression of many genes. The synchronous progression of 95% of the remnant hepatocytes through the cell cycle provides an in vivo model for examining the influence of bile acids on the molecular regulation of hepatocyte replication and growth. In this study, we examined the effects of endogenous deoxycholic acid (DCA) and ursodeoxycholic acid (UDCA) on messenger RNA (mRNA) expression and growth rate during liver regeneration. Rats were fed diets containing no addition, 0.4% DCA, UDCA, or both for 14 days; they then underwent 70% PH and were maintained on the diets for an additional 14 days. mRNA transcript levels for a variety of cell cycle-regulated genes were examined post-PH by Northern blot analysis. Bile acid concentrations were determined in liver, isolated nuclei, and plasma by gas chromatography and mass spectrometry. The results indicated that the addition of DCA and UDCA to the diet markedly shifted the bile-acid compositions of liver and plasma. In addition, DCA dramatically altered the abundance of many transcripts post-PH, whereas coadministration of UDCA suppressed the effect. DCA feeding significantly inhibited liver growth through day 3; however, by day 8, it induced an approximately 20% increase in mass compared with controls, UDCA-fed, or combination-fed animals. UDCA was concentrated greater than 20-fold in nuclei compared with whole liver in controls and DCA-fed animals and greater than 2-fold with UDCA feeding. These data suggest that bile acids may have a key role in liver regeneration, which is significantly altered by modulation of the bile-acid pool.

Apoptotic cell death does not parallel other indicators of liver damage in chronic hepatitis C patients

The mechanisms of hepatocyte damage and the events that lead to high rates of chronic liver disease in hepatitis C virus (HCV) infection remain unclear. Recent in vitro studies have suggested that the HCV core protein may disrupt specific signalling pathways of apoptosis. This prompted us to study patients with chronic HCV infection to: determine the extent of apoptosis in the liver; evaluate whether clinical and biochemical data are correlated with histological findings; and to investigate if apoptosis is related to the histological activity of the disease. Twelve patients with chronic hepatitis C were included in the study. Liver histology was scored by using the histological activity index (HAI) of Knodell et al. DNA fragmentation was assessed in liver tissue by the terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end-labelling (TUNEL) assay. Routine methods were used to determine serum markers of liver disease. Bile acids were measured in serum and liver by gas chromatography. Patients were placed, according to their HAI score, into group A (3.8 +/- 0.3) or group B (7.8 +/- 0.8) (P < 0.01). Liver enzymes tended to be higher in group B patients than in patients of group A. Levels of toxic bile acids in serum were greater in patients than in controls (P < 0.01). Chenodeoxycholic acid values were slightly higher in serum and liver of patients in group A. Liver biopsies with low HAI scores showed an increased rate of apoptosis (18.0 +/- 4.0 apoptotic cells per field) compared to those with higher HAI scores (6.6 +/- 2.1, P < 0.05) or to controls (3.5 +/- 0.4, P < 0.01). Hence, less severe liver disease, associated with lower histological grades and biochemistries, as well as increased levels of chenodeoxycholic acid, induces an expanded apoptotic response. The lower apoptotic rate in advanced liver disease may be associated with the high incidence of hepatocellular dysplasia/neoplasia.