Effect of bile duct ligation on bile acid metabolism in rats

Coronary Microvascular Dysfunction in Acute Cholestasis-Induced Liver Injury

BACKGROUND

Previous studies have shown cardiac abnormalities in acute liver injury, suggesting a potential role in the associated high mortality.

METHODS

We designed an experimental study exploring the short-term effects of acute cholestasis-induced liver injury on cardiac function and structure in a rodent bile duct ligation (BDL) model to elucidate the potential interplay. Thirty-seven male Sprague-Dawley rats were subjected to BDL surgery (n = 28) or served as sham-operated (n = 9) controls. Transthoracic echocardiography, Doppler evaluation of the left anterior descending coronary artery, and myocardial contrast echocardiography were performed at rest and during adenosine and dobutamine stress 5 days after BDL. Immunohistochemical staining of myocardial tissue samples for hypoxia and inflammation as well as serum analysis were performed.

RESULTS

BDL animals exhibited acute liver injury with elevated transaminases, bilirubin, and total circulating bile acids (TBA) 5 days after BDL (TBA control: 0.81 ± 2.54 µmol/L vs. BDL: 127.52 ± 57.03 µmol/L; p < 0.001). Concurrently, cardiac function was significantly impaired, characterized by reduced cardiac output (CO) and global longitudinal strain (GLS) in the echocardiography at rest and under pharmacological stress (CO rest control: 120.6 ± 24.3 mL/min vs. BDL 102.5 ± 16.6 mL/min, p = 0.041; GLS rest control: -24.05 ± 3.8% vs. BDL: -18.5 ± 5.1%, p = 0.01). Myocardial perfusion analysis revealed a reduced myocardial blood flow at rest and a decreased coronary flow velocity reserve (CFVR) under dobutamine stress in the BDL animals (CFVR control: 2.1 ± 0.6 vs. BDL: 1.7 ± 0.5 p = 0.047). Immunofluorescence staining indicated myocardial hypoxia and increased neutrophil infiltration.

CONCLUSIONS

In summary, acute cholestasis-induced liver injury can lead to impaired cardiac function mediated by coronary microvascular dysfunction, suggesting that major adverse cardiac events may contribute to the mortality of acute liver failure. This may be due to endothelial dysfunction and direct bile acid signaling.

Mechanisms of bile acid mediated inflammation in the liver

Bile acids are synthesized in the liver and are the major component in bile. Impaired bile flow leads to cholestasis that is characterized by elevated levels of bile acid in the liver and serum, followed by hepatocyte and biliary injury. Although the causes of cholestasis have been extensively studied, the molecular mechanisms as to how bile acids initiate liver injury remain controversial. In this chapter, we summarize recent advances in the pathogenesis of bile acid induced liver injury. These include bile acid signaling pathways in hepatocytes as well as the response of cholangiocytes and innate immune cells in the liver in both patients with cholestasis and cholestatic animal models. We focus on how bile acids trigger the production of molecular mediators of neutrophil recruitment and the role of the inflammatory response in this pathological process. These advances point to a number of novel targets where drugs might be judged to be effective therapies for cholestatic liver injury.

Plasma lipid profiling of different types of hepatic fibrosis induced by carbon tetrachloride and lomustine in rats

Background

Plasma lipid profiling has emerged as a useful tool for understanding the pathophysiology of hepatic injury and disease. Hepatic fibrosis results from chronic, progressive damage to the liver and can lead, in turn, to more serious conditions such as hepatic cirrhosis and hepatocellular carcinoma. Thus, the present study aimed to investigate the plasma lipid profiles of two types of hepatic fibrosis in order to aid the understanding of the pathophysiology of hepatic fibrosis.

Methods

A liquid chromatography and mass spectrometry platform was used to reveal and compare the plasma lipid profiles of two types of chemical-induced hepatic fibrosis. Rat models of centrilobular fibrosis and bile duct fibrosis were established via chronic exposure to the known fibrogenic hepatotoxins, carbon tetrachloride (CCl₄) or lomustine (LS), respectively, over a 28-day period. To delineate the specific alterations in the lipid profiles as a result of the hepatic fibrosis, we also employed non-fibrogenic hepatotoxicants (2-acetamidofluorene, N-nitrosodiethylamine, and ethambutol) as well as 3-day treatment of CCl₄ and LS, which did not induce fibrosis.

Results

Our assay platform identified 228 lipids in the rat plasma, and the global lipid profile clearly distinguished these models from the control via principal component analysis. In addition, the alteration of the plasma lipid profile caused by CCl₄ and LS were clearly different. Furthermore, a number of lipids were identified as specific alterations caused by fibrosis induced only by CCl₄ and LS, respectively. Three lysophosphatidylcholines (LPC[18:3], LPC[20:4], and LPC[22:6]), and three phosphatidylcholines (PC[18:2/20:4], PC[40:8], and PC[20:4/22:6]) are specific circulating lipids, the levels of which were altered by both CCl₄ and LS treatment; however, their levels were decreased by chronic exposure to CCl₄ and increased by chronic exposure to LS.

Conclusions

These results suggest that different types of chemical-induced hepatic fibrosis demonstrate clear differences in their plasma lipid profiles. Our study provides insights into the alteration of plasma lipidomic profiles as a result of the fibrosis of different parts of the hepatic lobule, and may help to understand the pathophysiology of different types of hepatic fibrosis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12944-016-0244-1) contains supplementary material, which is available to authorized users.

Ethyl acetate fraction of Amomum xanthioides improves bile duct ligation-induced liver fibrosis of rat model via modulation of pro-fibrogenic cytokines

We investigated anti-hepatofibrotic effects of ethyl acetate fraction of Ammomum xanthoides (EFAX) using bile duct ligation (BDL)-induced hepatic fibrosis in a rat model. Male SD rats (6 weeks old) underwent BDL followed by 15 days of orall administration of EFAX (12.5, 25 or 50 mg/kg) or ursodeoxycholic acid (25 mg/kg). BDL caused animal death, ascites formation, alterations in serum biochemistries, and severe hepatic injury with excessive collagen deposition, whereas EFAX treatment significantly attenuated these effects. BDL markedly increased the pro-fibrogenic cytokines (TGF-β, PDGF-β, and CTGF) and the extracellular matrix indicators α-SMA, TIMP-1 and collagen type 1 in hepatic proteins and gene expression levels, which were notably normalized by EFAX treatment. EFAX also markedly normalized pro-fibrogenic signaling molecules including Smad2/3, Smad7, Akt, p44/42, and p38. We further explored EFAX mechanisms of actions using LX-2 cells (human derived hepatic stellate cell line). Pre-treatment with EFAX drastically attenuated the activation of α-SMA and Smad2/3, which are downstream molecules of TGF-β. These findings suggest that EFAX may be a potent anti-hepatofibrotic agent, and its corresponding mechanisms primarily involve the modulation of pro-fibrogenic cytokines.

Effect of bile duct ligation on bile acid composition in mouse serum and liver

BACKGROUND

Cholestatic liver diseases can be caused by genetic defects, drug toxicities, hepatobiliary malignancies or obstruction of the biliary tract. Cholestasis leads to accumulation of bile acids (BAs) in hepatocytes. Direct toxicity of BAs is currently the most accepted hypothesis for cholestatic liver injury. However, information on which bile acids are actually accumulating during cholestasis is limited.

AIM

To assess the BA composition in liver and serum after bile duct ligation (BDL) in male C57Bl/6 mice between 6 h and 14 days and evaluate toxicity of the most abundant BAs.

RESULTS

Bile acid concentrations increased in liver (27-fold) and serum (1400-fold) within 6 h after surgery and remained elevated up to 14 days. BAs in livers of BDL mice became more hydrophilic than sham controls, mainly because of increased 6β-hydroxylation and taurine conjugation. Among the eight unconjugated and 16 conjugated BAs identified in serum and liver, only taurocholic acid (TCA), β-muricholic acid (βMCA) and TβMCA were substantially elevated representing >95% of these BAs over the entire time course. Although glycochenodeoxycholic acid and other conjugated BAs increased in BDL animals, the changes were several orders of magnitude lower compared with TCA, βMCA and TβMCA. A mixture of these BAs did not cause apoptosis or necrosis, but induced inflammatory gene expression in cultured murine hepatocytes.

CONCLUSION

The concentrations of cytotoxic BAs are insufficient to cause hepatocellular injury. In contrast, TCA, βMCA and TβMCA are able to induce pro-inflammatory mediators in hepatocytes. Thus, BAs act as inflammagens and not as cytotoxic mediators after BDL in mice.

Fibrinogen deficiency increases liver injury and early growth response-1 (Egr-1) expression in a model of chronic xenobiotic-induced cholestasis

Chronic cholestatic liver injury induced by cholestasis in rodents is associated with hepatic fibrin deposition, and we found evidence of fibrin deposition in livers of patients with cholestasis. Key components of the fibrinolytic pathway modulate cholestatic liver injury by regulating activation of hepatocyte growth factor. However, the exact role of hepatic fibrin deposition in chronic cholestasis is not known. We tested the hypothesis that fibrinogen (Fbg) deficiency worsens liver injury induced by cholestasis. Fbg-deficient mice (Fbgα(-/-) mice) and heterozygous control mice (Fbgα(+/-) mice) were fed either the control diet or a diet containing 0.025% α-naphthylisothiocyanate (ANIT), which selectively injures bile duct epithelial cells in the liver, for 2 weeks. Hepatic fibrin and collagen deposits were evident in livers of heterozygous control mice fed the ANIT diet. Complete Fbg deficiency was associated with elevated serum bile acids, periportal necrosis, and increased serum alanine aminotransferase activity in mice fed the ANIT diet. Fbg deficiency was associated with enhanced hepatic expression of the transcription factor early growth response-1 (Egr-1) and enhanced induction of genes encoding the Egr-1-regulated proinflammatory chemokines monocyte chemotactic protein-1, KC growth-regulated protein, and macrophage inflammatory protein-2. Interestingly, peribiliary collagen deposition was not evident near necrotic areas in Fbg-deficient mice. The results suggest that in this model of chronic cholestasis, fibrin constrains the release of bile constituents from injured intrahepatic bile ducts, thereby limiting the progression of hepatic inflammation and hepatocellular injury.

The role of lipophilic bile acids in the development of cirrhotic cardiomyopathy

Marked hemodynamic changes occur in humans and experimental animals with cirrhotic liver disease. In the heart, basal contractility, responsiveness to beta-adrenoceptor activation, and excitation-contraction coupling (ECC) are negatively affected in models of cirrhosis and portal hypertension with portosystemic shunting (PVS), and comprise what has been called cirrhotic cardiomyopathy. These effects are accompanied by elevated circulating levels of bile acids. We investigated whether elevated bile acids act as a myocardial toxicant by exposing cardiac muscle in vitro to bile acids and compared these results with two models of cirrhotic cardiomyopathy with elevated bile acids: CCl4-induced cirrhosis and PVS. Cholic acid, a lipophilic bile acid, produced a decrease in basal cardiac contractility and responsiveness to beta-adrenoceptor activation, both of which appeared to result from altered ECC. beta-Adrenoceptor density and signaling were unaffected. Acutely, ursodeoxycholic acid, a more hydrophilic bile acid, had no effect. Cirrhosis produced a decrease in basal force, depressed beta-adrenoceptor responsiveness, and altered ECC similar to cholic acid. However, cirrhosis also altered beta-adrenoceptor signaling including decreases in cyclic AMP formation, expression of the stimulatory G protein, GS, and beta-adrenoceptor density. Displacement of lipophilic bile acids by chronic administration of ursodeoxycholic acid to rats during the development of cirrhotic cardiomyopathy produced by PVS produced attenuation of the effect on ECC. These results suggest a possible role for lipophilic bile acids in some, but not all of the myocardial consequences of chronic portal vein stenosis and CCl4-induced cirrhosis.

ADP-degrading enzymes inhibit platelet activation in bile duct-ligated rats

BACKGROUND

The effect of cholestatic liver disease on primary hemostasis function remains ill-defined.

OBJECTIVES

To determine platelet function and identify the mechanisms involved in the observed platelet function in cholestatic rats.

METHODS

Platelet function was studied in a model of 2-week bile duct ligation and compared to that in sham-operated rats with and without a storage pool defect.

RESULTS

ADP-induced and collagen-induced platelet aggregation were clearly impaired following bile duct ligation (P<0.01 for areas under the curve). Crossover experiments, with sham platelets in bile duct-ligated plasma and vice versa, demonstrated that this is due to inhibition by a plasmatic factor, as sham platelets aggregated less in cholestatic plasma (P<0.03) and to an equal extent as platelets from bile duct-ligated rats when they were in the same sham or cholestatic plasma. Moreover, in bile duct-ligated rats, platelet ultrastructure was unaffected and platelet aggregation was similar to that of sham platelets when resuspended in the same plasma (P-value not significant). Additionally, studies in storage pool-deficient rats showed no role of platelet exhaustion. The plasmatic factor causing impaired aggregation was shown to be increased total activity of ADP-degrading enzymes upon bile duct ligation (P<0.01), as there was no decreased aggregation with a stable ADP analog in bile duct-ligated rats (P-value not significant vs. sham-operated rats). Furthermore, preincubation of plasma from bile duct-ligated rats with ADP decreased aggregation more than was seen with sham plasma (P<0.01).

CONCLUSIONS

Bile duct ligation does not affect intrinsic platelet function, but impairs platelet activation via release of ADP-degrading enzymes in the circulation.

In vivo dynamic metabolic imaging of obstructive cholestasis in mice

We tried to image obstructive cholestasis by using a newly developed imaging system to measure the alterations of hepatobiliary function in living mice with their bile ducts ligated. A hepatic imaging window was installed on the upper abdomen soon after the mice underwent ligation of the common bile duct. On the next day, the mice received intravenous injection of rhodamine B isothiocyanate-dextran and carboxyfluorescein diacetate. The later would be transformed into fluorogenic carboxyfluorescein (detected at approximately 500-550 nm) by hepatocytes and then excreted into bile canaliculi. The images were acquired by multiphoton microscopy. The fluorescence intensities at approximately 500-550 nm within hepatocytes or sinusoids were measured in time series. In mice with bile duct ligation, bile canaliculi failed to appear during the whole observation period over 100 min following carboxyfluorescein diacetate injection, whereas the fluorescence was retained much longer within sinusoids. Furthermore, the fluorescence intensities in sinusoids were persistently higher than in hepatocytes during the course. Bile duct ligation impedes hepatocytes to excrete carboxyfluorescein into bile canaliculi. The kinetics of fluorescence intensities in hepatocytes and sinusoids indicated there is an active machinery operating backflow of this fluorogenic bile solute from hepatocytes into sinusoids in the liver with obstructive cholestasis.

Identification of urinary biomarkers useful for distinguishing a difference in mechanism of toxicity in rat model of cholestasis

This (1)H nuclear magnetic resonance metabonomics study was aimed to determine urinary biomarkers of cholestasis resulting from inhibition of biliary secretion of bile or obstruction of bile flow. To inhibit biliary secretion of bile, cyclosporine A was administered to male Sprague-Dawley rats. Obstruction of bile flow was induced by administration of 4,4'-methylene dianiline, alpha-naphthylisothiocyanate or bile duct ligation. Clinical pathological and histopathological examinations were performed to confirm cholestatic injury and (1)H nuclear magnetic resonance spectral data for urine samples were analysed to determine similarities and differences in profiles of metabolites using the Spotfire. In cyclosporine A-treated groups, serum total bilirubin and bile acid were significantly increased but no remarkable hepatic histopathological-changes were observed. In 4,4'-methylene dianiline-, alpha-naphthylisothiocyanate- and bile duct ligation-treated groups, serum alkaline phosphatase, gamma-glutamyltranspeptidase and total bilirubin levels increased significantly, and hepatic histopathological-changes were observed. On urinary (1)H nuclear magnetic resonance spectral analysis, area intensities derived from 0.66 to 1.90 ppm were decreased by cyclosporine A, whereas they were increased by other treatments. These metabolites were identified using the NMR suite as bile acids, branched-chain amino acids, n-butyrate, propionate, methyl malonate and valerate. These metabolites were further investigated by K-means clustering analysis. The cluster of these metabolites is considered to be altered by cholestasis. We conclude that bile acids, valine and methyl malonate have a possibility to be urinary cholestatic biomarkers, which distinguish a difference in mechanism of toxicity. (1)H nuclear magnetic resonance metabonomics thus appears to be useful for determining the mechanisms of toxicity and can be front-loaded in drug safety evaluation and biomarker discovery.

Bile Acid sulfation: a pathway of bile acid elimination and detoxification

Sulfotransferase-2A1 catalyzes the formation of bile acid-sulfates (BA-sulfates). Sulfation of BAs increases their solubility, decreases their intestinal absorption, and enhances their fecal and urinary excretion. BA-sulfates are also less toxic than their unsulfated counterparts. Therefore, sulfation is an important detoxification pathway of BAs. Major species differences in BA sulfation exist. In humans, only a small proportion of BAs in bile and serum are sulfated, whereas more than 70% of BAs in urine are sulfated, indicating their efficient elimination in urine. The formation of BA-sulfates increases during cholestatic diseases. Therefore, sulfation may play an important role in maintaining BA homeostasis under pathologic conditions. Farnesoid X receptor, pregnane X receptor, constitutive androstane receptor, and vitamin D receptor are potential nuclear receptors that may be involved in the regulation of BA sulfation. This review highlights current knowledge about the enzymes and transporters involved in the formation and elimination of BA-sulfates, the effect of sulfation on the pharmacologic and toxicologic properties of BAs, the role of BA sulfation in cholestatic diseases, and the regulation of BA sulfation.

Reduced susceptibility to epinephrine-induced arrhythmias in cirrhotic rats: the roles of nitric oxide and endogenous opioid peptides

BACKGROUND/AIMS

The clinical relevance of QT prolongation, the most widely recognized cardiac electrophysiological abnormality of cirrhosis, is still undefined. The aim of this study is to examine the susceptibility of chronic (4-week) bile duct-ligated rats to epinephrine-induced arrhythmias. The roles of nitric oxide and endogenous opioids were also evaluated.

METHODS

Sham-operated and cirrhotic rats were treated with daily subcutaneous administrations of normal saline (1 ml/kg/day), L-NAME (a non-selective nitric oxide synthase inhibitor, 3mg/kg/day), and naltrexone (20mg/kg/day) during the fourth week after operation. In order to evaluate the effects of acute nitric oxide synthesis inhibition, additional groups of animals were treated by acute intraperitoneal L-NAME injections (3mg/kg). Arrhythmias were induced by intravenous injections of 10 microg/kg epinephrine.

RESULTS

Despite QT prolongation (P<0.001), epinephrine induced fewer arrhythmias in cirrhotic rats compared to sham-operated animals (P<0.05). Chronic, but not acute, L-NAME administration corrected the QT prolongation in cirrhotic rats (P<0.001), and restored the susceptibility of cirrhotic rats to arrhythmias (P<0.05). Naltrexone injection without a significant effect on epinephrine-induced arrhythmias corrected QT interval in cirrhotic rats (P<0.001).

CONCLUSIONS

This study shows that despite QT prolongation, cirrhotic animals are resistant against epinephrine-induced arrhythmias. This resistance is mediated by chronic nitric oxide overproduction.

Involvement of endogenous opioid peptides and nitric oxide in the blunted chronotropic and inotropic responses to beta-adrenergic stimulation in cirrhotic rats

It is well known that chronotropic and inotropic responses to beta-adrenergic stimulation are impaired in cirrhosis, but the exact reason is not clear. Considering the inhibitory effect of endogenous opioid peptides and nitric oxide (NO) on beta-adrenergic pathway, we examined their roles in hyporesponsiveness of isolated atria and papillary muscles to isoproterenol stimulation in cirrhotic rats. Cirrhosis was induced by chronic bile duct ligation. Four weeks after ligation or sham operation, the responses of the isolated atria and papillary muscles to isoproterenol stimulation were evaluated in the absence and presence of naltrexone HCl (10(-6) m), N(omega)-nitro-L-arginine methyl ester (L-NAME, 10(-4) m), and naltrexone plus L-NAME in the organ bath. Considering the role of inducible NOS (iNOS) in hemodynamic abnormalities of cirrhotic rats, the chronotropic and inotropic responses of cirrhotic rats to isoproterenol stimulation were also assessed in the presence of aminoguanidine (a selective inhibitor of iNOS, 3 x 10(-4) m). Sham operation had no significant effect on basal atrial beating rate, contractile force, and maximal time derivatives for the development and the dissipation of papillary muscle tension. The basal atrial beating rate of cirrhotic rats did not show any significant difference compared with the sham-operated ones; however, the basal contractile parameters were significantly decreased in cirrhosis. Although the maximum effects of isoproterenol on chronotropic and inotropic responses were significantly reduced in cirrhotic rats, there was no difference in half-maximal effective concentrations of isoproterenol in these concentration-response curves. The basal abnormalities and the attenuated chronotropic and inotropic responses to isoproterenol were completely corrected by the administration of naltrexone, L-NAME and aminoguanidine. Concurrent administration of naltrexone and L-NAME also restored to normal the basal abnormalities and the blunted responses to isoproterenol in cirrhotic rats, and did not show any antagonistic effect. Based on these findings, both the endogenous opioid peptides and NO may be involved in the attenuated chronotropic and inotropic responses to beta-adrenergic stimulation in cirrhosis. It seems that the iNOS activity results in NO-induced hyporesponsiveness to beta-adrenergic stimulation in cirrhosis.

Bile acid analysis in biliary tract cancer

The etiology of biliary tract cancer is obscure, but there are evidences that bile acid plays a role in carcinogenesis. To find the association between biliary tract cancer and bile acid, this study compared the bile acid concentration and composition among patients with biliary cancer, biliary tract stones, and no biliary disease. Bile was compared among patients with biliary tract cancer (n = 26), biliary tract stones (n = 29), and disease free controls (n = 9). Samples were obtained by percutaneous transhepatic biliary drainage, endoscopic nasobiliary drainage, or gallbladder puncture, and analyzed for cholic, deoxycholic, chenodeoxycholic, lithocholic, and ursodeoxycholic acid composition. Total bile acid concentration was lower in the cancer group than the biliary stone and control groups; the proportions of deoxycholic (2.2% vs. 10.2% and 23.6%, p < 0.001 and p < 0.001, respectively) and lithocholic acid (0.3% vs. 0.6% and 1.0%, p = 0.065 and p < 0.001, respectively) were also lower. This result was similar when disease site was limited to bile duct or gallbladder. Analysis of cases with bilirubin <or= 2.0 mg/dL also showed lower total bile acid concentration and deoxycholic acid composition in the cancer group compared to controls (5.7% vs. 23.6%, p = 0.003). Although the presence of bile duct obstruction explains some of the difference in total concentration and composition of bile acid, there are other contributing mechanisms. We suspect the alteration of bile acid transport might decrease bile acid excretion and cause the accumulation of carcinogenic bile acid in bile duct epithelium.

Species difference in cholesterol 7alpha-hydroxylase expression of rabbit and rat liver microsomes after bile duct ligation

BACKGROUND

Bile duct ligation (BDL) produces a good animal model for investigation of the metabolic changes in obstructive jaundice. The aim of this study was to investigate the species difference in expression of cholesterol 7alpha-hydroxylase (7alpha-hydroxylase) in rabbits and rats after BDL.

MATERIALS AND METHODS

Ten male New Zealand white rabbits weighing 2.5-3 kg and 12 male Wistar strain rats weighing 250-300 g were used. Half the animals underwent BDL, and half were sham operated (Sham). The animals were sacrificed on day 5 after operation. The livers were harvested, and levels of mRNA and 7alpha-hydroxylase activity were determined. Concentrations of serum bilirubin and bile acids were also measured.

RESULTS

In BDL rats, the levels of mRNA were increased 30%, and 7alpha-hydroxylase activity was three times that of the Sham group. In BDL rabbits, however, these values were approximately 60 and 50% lower than the Sham group, respectively. Serum bile acid concentrations increased up to 13 times in BDL rabbits and 70 times in BDL rats over that of the Sham groups. Serum cholesterol and serum total bilirubin concentration also increased after BDL in both animals.

CONCLUSION

These results suggest that there is a species difference in the expression of 7alpha-hydroxylase after BDL in rabbits and rats and the reason for this difference is most likely pretranslational regulation.

Feed-forward regulation of bile acid detoxification by CYP3A4: studies in humanized transgenic mice

Bile acids are potentially toxic end products of cholesterol metabolism and their concentrations must be tightly regulated. Homeostasis is maintained by both feed-forward regulation and feedback regulation. We used humanized transgenic mice incorporating 13 kb of the 5' regulatory flanking sequence of CYP3A4 linked to a lacZ reporter gene to explore the in vivo relationship between bile acids and physiological adaptive CYP3A gene regulation in acute cholestasis after bile duct ligation (BDL). Male transgenic mice were subjected to BDL or sham surgery prior to sacrifice on days 3, 6, and 10, and others were injected with intraperitoneal lithocholic acid (LCA) or vehicle alone. BDL resulted in marked hepatic activation of the CYP3A4/lacZ transgene in pericentral hepatocytes, with an 80-fold increase in transgene activation by day 10. Individual bile acids were quantified by liquid chromatography/mass spectrometry. Serum 6beta-hydroxylated bile acids were increased following BDL, confirming the physiological relevance of endogenous Cyp3a induction to bile acid detoxification. Although concentrations of conjugated primary bile acids increased after BDL, there was no increase in LCA, a putative PXR ligand, indicating that this cannot be the only endogenous bile acid mediating this protective response. Moreover, in LCA-treated animals, 5-bromo-4-chloro-3-indolyl-beta-d-galactopyranoside staining showed hepatic activation of the CYP3A4 transgene only on the liver capsular surface, and minimal parenchymal induction, despite significant liver injury. This study demonstrates that CYP3A up-regulation is a significant in vivo adaptive response to cholestasis. However, this up-regulation is not dependent on increases in circulating LCA and the role of other bile acids as regulatory molecules requires further exploration.

Growth hormone modulation of the rat hepatic bile transporter system in endotoxin-induced cholestasis

Treatment with high dose human GH, although an effective anabolic agent, has been associated with increased incidence of sepsis, inflammation, multiple organ failure, and death in critically ill patients. We hypothesized that GH might increase mortality by exacerbating cholestasis through modulation of bile acid transporter expression. High dose GH was continuously infused over 4 d into rats, and on the final day lipopolysaccharides were injected. Hepatic bile acid transporter expression was measured by Northern analysis and immunoblotting and compared with serum markers of cholestasis and endotoxinemia. Compared with non-GH-treated controls, GH increased endotoxin-induced markers of cholestasis and liver damage as well as augmented IL-6 induction. In endotoxinemia, GH treatment significantly induced multidrug resistance-associated protein 1 mRNA and protein and suppressed organic anion transporting polypeptides, Oatp1 and Oatp4, mRNA, suggesting impaired uptake of bilirubin and bile acids at the basolateral surface of the hepatocyte, which could contribute to the observed worsening of cholestasis by GH. This study of endotoxinemia may thus provide a mechanistic link between GH treatment and exacerbation of cholestasis through modulation of basolateral bile acid transporter expression in the rat hepatocyte.

Repetitive short-term bile duct obstruction and relief causes reproducible and reversible bile acid regurgitation

BACKGROUND

Long-term bile duct obstruction causes sinusoidal regurgitation of bile acids, a shift in bile acid metabolism, and alterations of liver histology. In this study we investigated the regurgitation of bile acids during short-term bile duct obstruction and its reversibility and reproducibility. In addition, the biotransformation of taurodeoxycholate and its appearance in bile and perfusate effluent were studied as well as liver histology.

METHODS

Rat livers (n = 5) were perfused in vitro with 32 nmol/min/g liver taurodeoxycholate over 85 min with the bile duct being intermittently closed for 30 and 20 min, respectively.

RESULTS

Within the first 5 min after bile duct obstruction bile acids started to regurgitate to the perfusate effluent amounting to approximately 15% of hepatic uptake until the end of the perfusion period. After relief of obstruction, bile flow and biliary bile acid excretion showed an overshoot phenomenon and were almost doubled compared to preobstruction. In contrast, sinusoidal bile acid regurgitation declined. The same phenomenon was observed during the second closure/opening cycle of the bile duct. Regurgitated bile acids consisted of significantly more taurodeoxycholate metabolites (approximately 70%) than did biliary bile acids (approximately 30%). Histology of liver parenchyma was preserved.

CONCLUSIONS

During repetitive short-term bile duct obstruction bile acid regurgitation is reversible and reproducible. The absence of altered mechanical barriers suggests that specific pathways are involved in the regurgitation process of bile acids.

Selective inhibition of CYP27A1 and of chenodeoxycholic acid synthesis in cholestatic hamster liver

The aim of this study was to explore the regulation of serum cholic acid (CA)/chenodeoxycholic acid (CDCA) ratio in cholestatic hamster induced by ligation of the common bile duct for 48 h. The serum concentration of total bile acids and CA/CDCA ratio were significantly elevated, and the serum proportion of unconjugated bile acids to total bile acids was reduced in the cholestatic hamster similar to that in patients with obstructive jaundice. The hepatic CA/CDCA ratio increased from 3.6 to 11.0 (P<0.05) along with a 2.9-fold elevation in CA concentration (P<0.05) while the CDCA level remained unchanged. The hepatic mRNA and protein level as well as microsomal activity of the cholesterol 7alpha-hydroxylase, 7alpha-hydroxy-4-cholesten-3-one 12alpha-hydroxylase and 5beta-cholestane-3alpha,7alpha,12alpha-triol 25-hydroxylase were not significantly affected in cholestatic hamsters. In contrast, the mitochondrial activity and enzyme mass of the sterol 27-hydroxylase were significantly reduced, while its mRNA levels remained normal in bile duct-ligated hamster. In conclusion, bile acid biosynthetic pathway via mitochondrial sterol 27-hydroxylase was preferentially inhibited in bile duct-ligated hamsters. The suppression of CYP27A1 is, at least in part, responsible for the relative decreased production of CDCA and increased CA/CDCA ratio in the liver, bile and serum of cholestatic hamsters.

Biliary fibrosis associated with altered bile composition in a mouse model of erythropoietic protoporphyria

BACKGROUND & AIMS

Reduced activity of ferrochelatase in erythropoietic protoporphyria (EPP) results in protoporphyrin (PP) accumulation in erythrocytes and liver. Liver disease may occur in patients with EPP, some of whom develop progressive liver failure that necessitates transplantation. We investigated the mechanisms underlying EPP-associated liver disease in a mouse model of EPP.

METHODS

Liver histology, indicators of lipid peroxidation, plasma parameters of liver function, and bile composition were studied in mice homozygous (fch/fch) for a point mutation in the ferrochelatase gene and in heterozygous (fch/+) and wild-type (+/+) mice.

RESULTS

Microscopic examination showed bile duct proliferation and biliary fibrosis with portoportal bridging in fch/fch mice. PP content was 130-fold increased, and thiobarbituric acid-reactive substances (+30%) and conjugated dienes (+75%) were slightly higher in fch/fch than in fch/+ and +/+ livers. Levels of hepatic thiols (-12%) and iron (-52%) were reduced in fch/fch livers. Liver enzymes and plasma bilirubin were markedly increased in the homozygotes. Plasma bile salt levels were 80 times higher in fch/fch than in fch/+ and +/+ mice, probably related to the absence of the Na(+)-taurocholate cotransporting protein (Ntcp) in fch/fch liver. Paradoxically, bile flow was not impaired and biliary bile salt secretion was 4 times higher in fch/fch mice than in controls. Up-regulation of the intestinal Na(+)-dependent bile salt transport system in fch/fch mice may enhance efficiency of bile salt reabsorption. The bile salt/lipid ratio and PP content of fch/fch bile were increased 2-fold and 85-fold, respectively, compared with +/+, whereas biliary glutathione was reduced by 90%. Similar effects on bile formation were caused by griseofulvin-induced inhibition of ferrochelatase activity in control mice.

CONCLUSIONS

Bile formation is strongly affected in mice with impaired ferrochelatase activity. Rather than peroxidative processes, formation of cytotoxic bile with high concentrations of bile salts and PP may cause biliary fibrosis in fch/fch mice by damaging bile duct epithelium.

Effect of sodium tauroursodeoxycholate (UR-906) on liver dysfunction in bile duct-ligated rats

We investigated the effect of sodium tauroursodeoxycholate (UR-906) on cholestasis in common bile duct-ligated rats in comparison with the effect of dehydrocholic acid. UR-906 (30-180 mumol/kg) and dehydrocholic acid (180 mumol/kg) were intravenously given once daily for consecutive 20 days in rats and the common bile duct was ligated for the last 10 days. On the next day after the last test drug administration, serum biochemical and plasma hemostatic variables were determined. UR-906 significantly ameliorated the elevation of serum cholesterol, phospholipid, bilirubin and bile acid concentrations in bile duct-ligated rats. UR-906 significantly suppressed the prolongation of plasma prothrombin time and activated partial thromboplastin time. Furthermore, UR-906 significantly suppressed the decreases in plasma coagulation factor II and X activities. However, dehydrocholic acid did not cause significant changes in any of the variables examined in this model. These results suggest that UR-906 has a beneficial effect against cholestasis induced by bile duct ligation in rats and that this drug may be useful in the treatment of clinical cholestatic disorders.

Feedback regulation of hepatic 7alpha-hydroxylase expression by bile salts in the hamster

Hepatic 7alpha-hydroxylase activity appears to be regulated at the transcriptional level by the quantity of bile salts fluxing through the enterohepatic circulation. Whether bile salts directly suppress 7alpha-hydroxylase expression at the level of the hepatocyte or do so indirectly by promoting the release or absorption of an intestinal factor has not been resolved. We have investigated the ability of primary bile salts to suppress hepatic 7alpha-hydroxylase expression in bile-diverted hamsters. Biliary diversion was accompanied by derepression of both hepatic 7alpha-hydroxylase activity (4-5-fold) and bile salt secretion (approximately 3-fold). Derepression of hepatic 7alpha-hydroxylase expression could be prevented by several interventions that increase the availability of bile salts within the hepatocyte including 1) overexpression of an exogenous 7alpha-hydroxylase gene by adenovirus-mediated gene transfer, 2) obstruction of the common bile duct, and 3) intravenous infusions of taurocholate. In contrast, none of these interventions prevented derepression of hepatic cholesterol synthesis or significantly down-regulated hepatic low density lipoprotein receptor expression over the relatively short time course (24 h) of these studies. Together, these data indicate that primary bile salts contribute to the regulation of bile salt synthesis through feedback repression of 7alpha-hydroxylase expression at the level of the hepatocyte.

Differential effects between tauroursodeoxycholic and taurochenodeoxycholic acids in hepatic fibrosis: an assessment by primary cultured Ito and Kupffer cells from the rat liver

The pathogenesis of hepatic fibrosis in cholestasis is still unknown, except for endotoxaemia. There is a possibility that the elevation of serum bile acids in cholestasis may play an important role in hepatic fibrogenesis due to a reaction to perisinusoidal cells, such as Ito or Kupffer cells. To assess the effects of bile acids, we investigated the cell proliferation and collagen formation of primary cultured Ito cells that were incubated with a Kupffer cell conditioned medium (KCCM) treated with either taurochenodeoxycholic acid (TCDCA) or tauroursodeoxycholic acid (TUDCA) in short-term (8 h) or long-term (48 h) cultures. KCCM treated with TCDCA (100 mumol/L) but not with TUDCA increased cell proliferation of Ito cells in short-term cultures and also partially elevated collagen formation by Ito cells in long-term cultures. The release of tumour necrosis factor-alpha (TNF alpha) from Kupffer cells was increased by TCDCA in short-term cultures, but not in long-term cultures. The release of transforming growth factor-beta 1 (TGF beta 1) from Kupffer cells was increased by TCDCA in long-term cultures, but not in the short-term cultures. TUDCA showed no significant effect on the release of TNF alpha and TGF beta 1 from Kupffer cells. TUDCA or TCDCA itself showed no direct effect on the cell proliferation and collagen formation of Ito cells. In conclusion, these findings are thus considered to show the potentially important role of TCDCA on the development of hepatic fibrosis in the early phase of cholestasis without endotoxaemia.

Pattern of bile acid regurgitation and metabolism during perfusion of the bile duct obstructed rat liver

Bile acid processing in the long-term, bile duct obstructed rat liver was studied ex vivo. Twenty four and 72 h, respectively, after bile duct obstruction the isolated liver was perfused with taurodeoxycholate (16 nmol/min per g liver) the bile duct still being closed. Uptake, metabolism and regurgitation profile were traced by bolus injection of tritium-labeled bile acid; in addition, concurrent histological changes were examined by light- and electron microscopy. Ligation caused dilatation of the intrahepatic ductular branches and increased the serum bile acid concentration to 740 +/- 75 microM (controls: 16 +/- 2.12), reaching its maximum within 24 h. At 16 nmol/min per g liver uptake rate was > 96% in controls and in bile duct obstructed rats. Maximal uptake rates (assessed separately) differed between controls and bile duct obstructed rats (700 nmol/min per g liver vs. 460). Controls excreted more than 80% of labeled bile acid in bile within 10 min after bolus injection. Biliary recovery of label was virtually completed after 30 min. In bile duct obstructed rats excretion of label back to the perfusate effluent (regurgitation) started quantitatively 5 min after bolus application and peaked between 10 and 40 min; after 80 min, effluent recovery was incomplete (about 60% of bolus injected). Biliary bile acids of controls consisted of about 20% taurodeoxycholate-metabolites; bile acids in the perfusate effluent of bile duct obstructed rats of about 55%. The major metabolite in all animal groups was taurocholate; minor metabolites were tauroursocholate, tauro-3 alpha,7 = 0,12 alpha-cholanoic acid and 3-sulfo-taurodeoxycholate. Histologically, inflammation and periportal edema were present after 1 day of bile duct obstruction. After 3 days, marked proliferation of bile ductules was the dominant histological feature. It is concluded that during initial bile duct obstruction, bile acid processing is not altered, although ultrastructural alterations occur early.

Reversible bile acid changes in bile duct obstruction and its potential for hepatocellular injury

The etiology of hepatocellular dysfunction resulting from chronic biliary obstruction is not clearly understood. Alterations in bile acid metabolism due to changes in microsomal cytochrome P-450 enzyme activities may have a fundamental role in cholestatic liver injury. This study examines the very early changes in both biliary bile acids and hepatic microsomal cytochrome P-450 content after bile duct obstruction in the rat and the effects of the restoration of bile flow after 3 days of biliary obstruction. We found that early induction of cytochrome P-450 may be a fundamental step in the generation of cholestatic liver injury mediated by hepatotoxic bile acids. The rapid reversal of bile acid changes with reconstituted bile flow indicate that the liver is able to quickly recover when obstruction is relieved. Characterization of this fundamental process may ultimately provide a means of modulation of cholestatic hepatotoxicity.

Effects of bile duct obstruction and decompression on hepatic microsomal mixed function oxidase system in rats

The effects of biliary obstruction and drainage on the hepatic microsomal mixed function oxidase system were studied in rats. Bile duct obstruction produced a significant reduction in the hepatic cytochrome P-450 dependent mixed function oxidase system. After release of the bile duct obstruction, the reduction in microsomal enzymes was practically reversible; however, the process of recovery was slow and differed with the microsomal enzymes in question. Increases in cytochrome b5 content and NADH-cytochrome b5 reductase activity were slower than increases in cytochrome P-450 content and NADPH-cytochrome c reductase activity. Aniline hydroxylase activity increased more rapidly and corresponded to cytochrome P-450 contents more so than did the aminopyrine demethylase activity. After the release of bile duct obstruction, however, the bile acids which had accumulated in the liver during cholestasis were reduced rapidly, to a normal range. These results suggests that there is a discrepancy between reductions in hepatic bile acids and those in the hepatic microsomal mixed function oxidase system after biliary decompression.

Feedback regulation of bile acid synthesis in the rat by dietary vs. intravenous cholate or taurocholate

The regulation of bile acid synthesis was studied (i) in intact or colectomized rats receiving cholate or taurocholate as a dietary supplement and (ii) in experiments using chow-fed animals with a graded intravenous or intraduodenal taurocholate infusion. After the 2-week diet period a bile fistula was established and rates of taurocholate, tauromuricholate and taurochenodeoxycholate secretion were quantitated by high-performance liquid chromatography. During the infusion experiments taurocholate production was calculated from the difference in specific activity of [14C]taurocholate between infusate and bile, whereas tauromuricholate and taurochenodeoxycholate synthesis was derived directly from their secretion rates after pool depletion. Both the 0.5% cholate and taurocholate diet suppressed tauromuricholate and taurochenodeoxycholate secretion nearly totally, but only cholate led to a prolonged inhibition taurocholate synthesis. The diets stimulated total bile acid secretion and expanded the total bile acid pool size 2- to 3-fold, but they also prompted a dramatic increase in the biliary secretion of taurodeoxycholate. In contrast, colectomized animals did not secrete taurodeoxycholate following the cholate diet and, despite a comparable increase in bile acid pool size, tauromuricholate and taurochenodeoxycholate secretion was inhibited to a lesser extent. In addition, the rate of bile acid secretion and synthesis was significantly enhanced when compared to that of intact rats. To determine whether taurocholate affected bile acid synthesis directly, the bile acid was infused intravenously or intraduodenally at varying rates up to 300 mumoles per kg per hr for 54 hr, i.e. a rate exceeding normal total bile acid secretion in these acute bile fistula animals nearly 3-fold.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of cholesterol feeding to maternal rats on metabolism of cholesterol and bile acids in the dams and their offspring

The influence of feeding cholesterol to rats during pregnancy and postpartum (from the 11th day of gestation to the third day after delivery) on the serum and hepatic cholesterol levels and on the bile acid composition in the pool and in the liver in relationship to the dams and their pups was examined. The hepatic content of cholesterol in both dam and offspring increased during cholesterol feeding without any changes in serum cholesterol level. In the dams, mainly the esterified cholesterol was increased; in the pups, mainly the free cholesterol was increased. Cholesterol feeding led to a pronounced increase in the pool of beta-muricholic acid and a relative decrease in the lithocholic acid concentration in pregnant rats. In fetal rats, the chenodeoxycholic acid pool was increased by cholesterol intake. The lithocholic acid pool was larger in the postpartum rats fed cholesterol than in the controls, while the concentration of alpha- and beta-muricholic acids was decreased. The neonates of cholesterol-fed dams had a larger pool of chenodeoxycholic acid but a smaller pool of beta-muricholic acid. These results suggest that the metabolism of cholesterol and of bile acids in dams and their offspring respond differently to cholesterol intake.

Medroxyprogesterone acetate- and ethinylestradiol-induced changes in biliary bile acids of the rat studied by high-performance liquid chromatography

The effects of subcutaneous administration (5 mg/kg per day) for seven days of medroxyprogesterone acetate (MPA) or 17 alpha-ethinylestradiol (EE) on bile flow, total bile acid output and individual biliary acids have been studied in adult male Wistar rats. Biliary bile acid composition was quantitated by a simple isocratic high-performance liquid chromatographic technique using a C18 reversed-phase radial compression column and refractive index detection. This method revealed that muricholic acids, analysed as taurine and glycine conjugates, constituted a higher proportion of biliary bile acids in the rat than previously observed with gas chromatographic techniques. Marked cholestasis was produced by EE while MPA had little effect on bile flow or total bile acid output. Despite this, both steroids significantly increased the proportion of taurine-conjugated muricholic acids relative to taurocholic acid, although the estrogen had the more pronounced effect. Further study of the hepatobiliary consequences of high doses of MPA would seem warranted in view of the important use of this progestogen for cancer therapy.

Bile acid metabolism in partially hepatectomized rats

The bile flow and the bile acid secretion, calculated on liver weight basis, increased 12 H and 24 H after 60-70% hepatectomy and returned to the initial levels thereafter. The biliary phospholipid secretion much more increased than bile acids, but the cholesterol secretion decreased. Bile acid composition changed with an increase of the cholic acid group and a decrease of the chenodeoxycholic acid group in both bile and feces. These changes almost disappeared on Day 14. The pool size of bile acid decreased maximally on Day 4 to about 40% of the initial, but the distribution of bile acids in the enterohepatic circulation was not changed. The fecal cholesterol and coprostanol markedly decreased on Day 2 but gradually returned to the initial levels according to the recovery of diet intake. The fecal bile acids decreased on Day 2, increased on Day 4, and returned to the normal range after Day 7. In conclusion, the regenerating liver secretes more bile, bile acids and phospholipids, and less cholesterol than the normal liver. Cholic acid predominates in the bile acids. These changes restored to the initial levels by about one week after the operation.

Mechanisms of liver adaptation to prolonged selective biliary obstruction (SBO) in the rat

To determine changes which occur in selective biliary obstruction (SBO), we studied male adult Fischer rats after one month of either SBO or selective biliary cannulation (SBC) of the median lobe duct (MLD). In rats with SBC the ML was obstructed with a sealed PE-10 catheter placed in the MLD. One month later at laparotomy the ML was either drained or not drained for 30 min before the injection of 200 microCi [99Tc]DIDA (2,6-diethylacetoanilido-imino-diacetic acid). Bile was collected and biopsies of the obstructed ML and non-obstructed right lobe (RL) were taken at 1, 3, 10 and 30 min. Serum bile acid concentrations were higher in SBC not drained rats than in control as were hepatic bile acid concentrations. The latter, however, did not achieve statistical significance. In SBC-drained rats biliary bile acid secretion from the obstructed lobe was lower than that from the non-obstructed lobe for 30 min after the release of obstruction but was thereafter the same. Hepatic DIDA levels in both the obstructed and non-obstructed portions of liver from SBO animals were higher than in liver from controls, despite normal DIDA biliary excretion. This is in part explained by increased cytosolic binding of DIDA. In rats with SBO the MLD was simply ligated and transected. After one month uptake kinetics of [14C]taurocholate in freshly isolated hepatocytes from obstructed and non-obstructed lobes were similar suggesting that no major impairment of BA uptake occurs. We conclude that cholestasis is still present after 30 days of SBO in spite of the presence of interlobular biliary connections. The observed increased hepatic storage capacity for DIDA is probably an adaptive mechanism in mild chronic cholestasis.

Bioluminescence assays for bile acids in the detection and follow-up of experimental liver injury

We evaluated the usefulness of recently developed bioluminescence assays for serum bile acids (BA) in the detection and follow-up of experimental liver injury. Liver damage was induced in rats by either D-galactosamine or CCl4, and BA were compared to SGPT and aminopyrine breath test (ABT). In severe liver injury, following D-galactosamine administration, all three methods revealed a significant difference from control values. The degree of abnormality was, however, far greater with SGPT and BA than with ABT. In moderate liver injury, induced by CCl4, the increase in BA was not significant. Values of SGPT and BA showed a very good correlation (3 alpha-OH: r = 0.88; 7 alpha-OH: r = 0.90; 12 alpha-OH: r = 0.83; p less than 0.001 for all correlations). Application of different assays for 3 alpha-OH, 7 alpha-OH and 12 alpha-OH BA allowed us to assess changes in individual BA. A 96-hr follow-up study in D-galactosamine-treated animals showed an increase in BA up to 48 hr and a decrease thereafter. The bioluminescence assays for BA are simple, rapid and require only 10 microliter of serum. Thus, these assays may be the method of choice in detecting and monitoring liver injury in small laboratory animals.

Hepatic transport of sulfated and nonsulfated bile acids in the rat following relief of bile duct obstruction

The effect of bile duct ligation for 5 days on the hepatic transport of sulfated and nonsulfated bile acids was studied. Tracer doses of radioactive bile acids [3H]taurochenodeoxycholate-3-sulfate [3H]chenodeoxycholate-3-sulfate, [3H]taurochenodeoxycholic acid and [14C]taurocholic acid were injected 90 min after relief of obstruction when the plasma total bile acid concentration had reverted to normal. Plasma clearance and biliary excretion of sulfated bile acids were lower than those of nonsulfated bile acids, particularly in the cholestatic rats (p less than 0.02). For each bile acid, hepatic transport in the cholestatic rats was significantly reduced compared with the control rats. [3H]Chenodeoxycholate-3-sulfate and [3H]taurochenodeoxycholic acid were partially metabolized to [3H]taurochenodeoxycholate-3-sulfate prior to biliary excretion. This data suggests that the hepatic transport system for sulfated bile acids is less efficient and more easily impaired by cholestasis than that for nonsulfated bile acids.

Methods in testing interrelationships between excretion of drugs via urine and bile

The liver and kidney are largely responsible for inactivating and eliminating drugs and other chemicals. As the excretory capabilities of the two organs overlap, a damage of one system might be compensated by the other. Because of the specificity of both renal and hepatic elimination mechanisms such an alternative excretion route is not possible generally. Several interferences are possible to characterize the relation between hepatic and renal excretion of drugs and xenobiotics. Firstly, the simultaneous assay of excreted drug amounts in urine and bile can give some information concerning the main transport routes of this drug. Thereafter the total interruption of liver or kidney function elucidates the general possibility of alternative excretion routes. But it is important for clinical practice to distinguish between different localizations of organ damages. Today some experimental possibilities exist to exclude partial functions of both kidney and liver separately. Thus it can be clarified why a compound might be excreted via liver or kidney. Moreover it can be characterized whether or not a compensation for the loss of one main excretion organ is possible or not. Such investigations are of some practical importance. Dosing guidelines for drug therapy must be completed for cases of renal or hepatic failure. Moreover the developmental pattern of both elimination routes has consequences for drug use in paediatrics as well as geriatrics. Beside this point of view such investigations are necessary for the prediction of changes in the toxicity of drugs after renal or hepatic insufficiency.

The effect of dibutyryladenosine 3',5'-monophosphate on the synthesis of bile salts in isolated hepatocytes from rat

The effect of dibutyryladenosine 3',5'-monophosphate (Bt2cAMP) on the synthesis of conjugated cholic, chenodeoxycholic and beta-muricholic acids has been investigated. Hepatocytes were incubated with 1 mM Bt2cAMP for 3 h at 37 degrees C. In cells from rats with a basal rate of bile salt synthesis (soft-diet-fed rats) production of conjugated cholic acid was increased about two fold, synthesis of conjugated chenodeoxycholic acid was increased 10-20-fold but formation of its metabolite, conjugated beta-muricholic acid, was decreased by 30-50% in the presence of the cyclic nucleotide. The sum of the amounts of the three bile salts produced (total bile salt synthesis) was increased 30-50% by Bt2cAMP. When hepatocytes were prepared from rats in which bile salt synthesis had been stimulated by feeding the bile salt sequestrant, cholestyramine, Bt2cAMP had no effect on conjugated cholic acid synthesis, increased conjugated chenodeoxycholic acid production 3-5-fold and decreased conjugated beta-muricholic acid synthesis by about 50%. Total bile salt synthesis was unchanged. The ratio of the amount of conjugated cholic acid to conjugated chenodeoxycholic acid + conjugated beta-muricholic acid produced, an indication of the activity of 7 alpha-hydroxycholest-4-en-3-one 12 alpha-hydroxylase, was raised by Bt2cAMP in hepatocytes from soft-diet-fed but not in those from cholestyramine-fed rats. The effects of the cyclic nucleotide on the synthesis of the three bile salts in hepatocytes from soft-diet-fed rats were found to be saturable at a concentration of about 2 mM. Responses were half-maximal at concentrations of Bt2cAMP varying between 0.5 and 1.5 mM. These results suggest that in hepatocytes from rats with a basal rate of bile salt synthesis Bt2cAMP has effects at three different stages in the pathway, at the level of cholesterol 7 alpha-hydroxylase, 7 alpha-hydroxycholest-4-en-3-one 12 alpha-hydroxylase and chenodeoxycholine acid 6 beta-hydroxylase. In cells from rats in which bile salt synthesis has been stimulated only the effect at the chenodeoxycholic acid 6 beta-hydroxylase level is apparent. Bt2cGMP and Bt2cCMP had no effect on the synthesis of any of the bile salts measure, showing that the effects are specific for Bt2cAMP. The ratio of the amounts of the three bile salts found inside the cells to those found in the medium was decreased by about 90% when Bt2cAMP was present in the hepatocyte incubations. This effect was mimicked by Bt2cGMP and to a lesser extent by Bt2cCMP.(ABSTRACT TRUNCATED AT 400 WORDS)

Changes of the pattern of biliary bile acids during isolated rat liver perfusion

In spite of the extensive use of isolated perfused liver systems for bile acid related studies, the composition of biliary bile acids during liver perfusion is not well known. Using recently developed bioluminescence assays for 3 alpha-OH-, 7 alpha-OH-, and 12 alpha-OH- bile acids we studied the hydroxylation pattern of bile acids in bile during 90 minutes perfusion of isolated rat liver without added bile acid load. At the beginning 7 alpha-hydroxylated bile acids comprised more than 50% of total bile acids from male livers and more than 90% from female livers, this percentage declined rapidly during the first 40-50 minutes of perfusion to values between 10 and 20%. 12 alpha-hydroxylated bile acids comprised between 15 and 30% of the total at beginning of the perfusion and decreased to about 10% after 40 minutes. Sex differences as well as the influence of the duration of perfusion should be considered when the isolated perfused rat liver is used for bile acid related studies.

The metabolism of chenodeoxycholic acid to beta-muricholic acid in rat liver

1. The synthesis of conjugated chenodeoxycholic acid and tauro-beta-muricholic acid in isolated rat hepatocytes was measured by radioimmunoassay. Production of tauro-beta-muricholic acid was linear over 4 h of incubation at 37 degrees C. The net synthesis of conjugated chenodeoxycholic acid was very much lower than that of tauro-beta-muricholic acid. 2. When hepatocytes were prepared from rats in which the enterohepatic circulation had been broken, either by feeding the bile salt sequestrant, cholestyramine or by total biliary drainage for 48 h, synthesis of tauro-beta-muricholic acid was increased compared to that in cells from control rats. Conjugated chenodeoxycholic acid accumulation during incubation of the hepatocytes was increased by cholestyramine feeding but not by total biliary drainage. These results suggest that there is a metabolic difference between the two methods of breaking the enterohepatic circulation with regard to chenodeoxycholic acid synthesis. 3. Hepatocytes prepared from rats given 1% cholesterol in the diet for at least 2 weeks synthesised significantly more tauro-beta-muricholic acid than those from control rats. The total amount of conjugated cholic, chenodeoxycholic and tauro-beta-muricholic acids synthesised by cells from cholesterol fed animals, however was not significantly different from that produced by hepatocytes from normal rats. 4. Exogenous taurochenodeoxycholic acid was metabolised to tauromuricholic acid by isolated hepatocytes. Production of tauro-beta-muricholic acid reached a maximum at a concentration of 20 microM taurochenodeoxycholic acid. The total metabolism of taurochenodeoxycholic acid, however, increased linearly up to the highest concentration measured, 50 microM. 5. The biliary content of tauro-beta-muricholic acid during total biliary drainage fell rapidly in the first 10 h and thereafter continued to decline, reaching a minimum after about 24 h. No significant rise was observed during the remainder of the experimental period. 6. It is concluded that a large proportion of the conjugated chenodeoxycholic acid synthesised by isolated hepatocytes in vitro is metabolised to tauro-beta-muricholic acid, and therefore it is necessary to take this into account when using this system to study bile salt synthesis.

The effect of dietary fat on bile salt synthesis in rat liver

The effect of dietary fat on conjugated cholic, chenodeoxycholic and tauro-beta-muricholic acid synthesis was studied using hepatocytes isolated from rats given a low-fat diet, or a low-fat diet mixed with 10% olive oil or 10% corn oil. The rats were totally biliary drained for 48 h prior to preparation of the cells in order to raise bile salt synthesis to a level which was measurable by radioimmunoassay. Synthesis of both conjugated cholic and chenodeoxycholic acid was raised in hepatocytes from rats given a fat supplement (either corn oil or olive oil) in the diet as compared to that in cells from low-fat-fed animals. Tauro-beta-muricholic acid synthesis, however, was unaffected by corn oil feeding. Production of conjugated cholic acid was increased to a greater extent when rats were given olive oil as opposed to corn oil, but these differences were not statistically significant. The conjugated cholic, chenodeoxycholic, and tauro-beta-muricholic acid and cholesterol content of bile collected at 2-h intervals during the biliary drainage of the same groups of rats was also determined. The pool size of both conjugated cholic and chenodeoxycholic acid in the enterohepatic circulation was found to be significantly decreased in rats given olive oil as compared to those given corn oil or the low-fat diet only. The pool size of tauro-beta-muricholic acid was also decreased in the olive oil-fed rats compared to the other two groups, but this difference was not statistically significant. After the pool had been drained out, animals which had received fat in the diet secreted more conjugated cholic and chenodeoxycholic acid into the bile than rats which had received the low-fat diet only. This effect was more marked when the fat given was olive oil rather than corn oil. Secretion of tauro-beta-muricholic acid into bile at this stage of biliary drainage was not changed by dietary fat supplements. Biliary cholesterol excretion was also increased in rats on diets containing 10% fat, with olive oil again having a greater effect than corn oil. The results show that supplementing the diet with fat leads to increased synthesis of conjugated cholic and chenodeoxycholic acids and biliary cholesterol secretion in the rat. The relatively more saturated fat, olive oil (85% oleate), gave a consistently larger increase than the more unsaturated, corn oil (50% linoleate), but the type of fat appeared less important than the presence of fat in the diet.

Similarities and differences between models of extrahepatic biliary obstruction and complete biliary retention without obstruction in the rat

Biliary obstruction in the rat causes known biochemical and morphological abnormalities. These abnormalities might be caused simply by retention of biliary constituents or might require other factors such as high biliary pressure, interruption of the normal flux of fluid, ions, and other biliary constituents through the hepatocyte and/or changes in intracellular concentrations, binding, and distribution of biliary constituents. We studied a choledochocaval (CC) fistula rat model characterized by complete biliary retention without bile stasis. CC fistula animals were compared with biliary obstructed rats over a 46-hr period. Bile flow and bile acid excretion rate reached high levels by hour 5 and remained high in CC fistula rats. Urinary bile acid excretion, shrinkage of the rapidly exchangeable bile acid pool, and serum bile acid and bilirubin concentrations were equivalent in the two models. Serum cholesterol concentration was higher and serum alkaline phosphatase and 5'-nucleotidase activities lower in obstructed rats. The percentage of beta-muricholate rose and the percentage of cholate decreased in bile acid from obstructed rats. This was associated with increased microsomal 6 beta-hydroxylase activity. Bile acid composition and microsomal 6 beta-hydroxylase activity changed little in CC fistula rats. Morphological examination revealed greater damage in obstructed rat livers. These data indicate that factors other than simple retention of biliary constituents contribute to the abnormalities observed in extrahepatic biliary obstruction.