Effects of ursodeoxycholic acid and chenodeoxycholic acid on human hepatocytes in primary culture

A Case Report: Idiopathic or Drug-Induced Autoimmune Hepatitis-Can We Draw a Line?

Idiosyncratic drug-induced liver injury (DILI) is an unpredictable reaction of individuals exposed to a certain drug, and drug-induced autoimmune hepatitis (DIAIH) presents a DILI phenotype that mimics idiopathic autoimmune hepatitis (AIH) when considering the clinical, biochemical, serological and histological parameters. We present a case report of a 48-year-old male who was hospitalized due to severe hepatocellular liver injury two months after self-treatment with a muscle-building dietary supplement based on arginine-alpha-ketoglutarate, L-citrulline, L tyrosine, creatine malate and beet extract. His immunology panel was positive with increased IgG levels, and radiologic methods showed no signs of chronic liver disease. He underwent corticosteroid treatment with adequate response. After therapy withdrawal, a clinical relapse occurred. Seven months after the initial presentation, liver MR suggested initial cirrhotic changes in the right liver lobe. A liver biopsy revealed abundant lymphoplasmacytic infiltrate with piecemeal necrosis and grade 2 fibrosis. He responded well to the corticosteroid treatment again, and was further treated with low-dose prednisone without additional relapses. Several years later, further management confirmed the presence of liver cirrhosis with no histological or biochemical signs of disease activity. DIAIH is a DILI phenotype that is difficult to distinguish from idiopathic AIH despite a wide armamentarium of diagnostic methods. It should always be considered among the differential diagnoses in patients presenting with hepatocellular liver injury.

Bile acid-based dual-functional prodrug nanoparticles for bone regeneration through hydrogen peroxide scavenging and osteogenic differentiation of mesenchymal stem cells

A high level of reactive oxygen species (ROS) such as hydrogen peroxide (H₂O₂) upregulates pro-inflammatory cytokines and inhibits the osteogenic differentiation of mesenchymal stem cells (MSCs), which are key factors in bone regeneration. Ursodeoxycholic acid (UDCA), a hydrophilic bile acid, has antioxidant and anti-inflammatory activities and also plays beneficial roles in bone regeneration by stimulating the osteogenic differentiation of MSCs while suppressing their adipogenic differentiation. Despite its remarkable capacity for bone regeneration, multiple injections of UDCA induce adverse side effects such as mechanical stress and contamination in bone defects. To fully exploit the beneficial roles of UDCA, a concept polymeric prodrug was developed based on the hypothesis that removal of overproduced H₂O₂ will potentiate the osteogenic functions of UDCA. In this work, we report bone regenerative nanoparticles (NPs) formulated from a polymeric prodrug of UDCA (PUDCA) with UDCA incorporated in its backbone through H₂O₂-responsive peroxalate linkages. The PUDCA NPs displayed potent antioxidant and anti-inflammatory activities in MSCs and induced osteogenic rather than adipogenic differentiation of the MSCs. In rat models of bone defect, the PUDCA NPs exhibited significantly better bone regeneration capacity and anti-inflammatory effects than equivalent amounts of UDCA. We anticipate that PUDCA NPs have tremendous translational potential as bone regenerative agents.

Imaging Mass Spectrometry Reveals the Changes in the Taurine Conjugates of Dihydroxycholanoic Acid During Hepatic Warm Ischemia and Reperfusion in a Rat Model

Warm ischemia and reperfusion injury (IRI) is a prognostic factor in donation after cardiac death donor transplantation. However, a reliable method to predict IRI before transplantation has not been established. The aim of this study was to identify predictive markers of hepatic IRI by simultaneous measurement of endogenous molecules using matrix-assisted laser desorption/ionization-imaging mass spectrometry (MALDI-IMS). Rats were subjected to hepatic warm ischemia (70%) for 30 or 90 minutes and subsequent reperfusion. The livers were collected at the end of ischemia and 1 hour, 6 hours, and 24 hours after reperfusion. The liver tissue sections were applied to IMS (m/z 200-2000). Candidate molecules were identified by tandem mass spectrometry. Imaging mass spectrometry (IMS) revealed a significant increase in the taurine conjugates of dihydroxycholanoic acid (TDHCA) during ischemia and a tendency to return to the basal level after reperfusion. Notably, high-resolution measurements revealed focal accumulation of TDHCA in the intrahepatic bile duct with ischemic time. In conclusion, IMS is a useful method to detect minute changes provoked by ischemia, which are barely detectable in assays involving homogenization. Accordingly, focal accumulation of TDHCA during ischemia may be a candidate marker for predicting later IRI.

Bile acid homeostasis and intestinal dysbiosis in alcoholic hepatitis

BACKGROUND

Intestinal microbiota plays an important role in bile acid homeostasis.

AIM

To study the structure of the intestinal microbiota and its function in bile acid homeostasis in alcoholic patients based on the severity of alcoholic liver disease.

METHODS

In this prospective study, we included four groups of active alcoholic patients (N = 108): two noncirrhotic, with (noCir_AH, n = 13) or without alcoholic hepatitis (noCir_noAH, n = 61), and two cirrhotic, with (Cir_sAH, n = 17) or without severe alcoholic hepatitis (Cir_noAH, n = 17). Plasma and faecal bile acid profiles and intestinal microbiota composition were assessed.

RESULTS

Plasma levels of total bile acids (84.6 vs 6.8 μmol/L, P < 0.001) and total ursodeoxycholic acid (1.3 vs 0.3 μmol/L, P = 0.03) were higher in cirrhosis with severe alcoholic hepatitis (Cir_sAH) than Cir_noAH, whereas total faecal (2.4 vs 11.3, P = 0.01) and secondary bile acids (0.7 vs 10.7, P < 0.01) levels were lower. Cir_sAH patients had a different microbiota than Cir_noAH patients: at the phyla level, the abundance of Actinobacteria (9 vs 1%, P = 0.01) was higher and that of Bacteroidetes was lower (25 vs 40%, P = 0.04). Moreover, the microbiota of Cir_sAH patients showed changes in the abundance of genes involved in 15 metabolic pathways, including upregulation of glutathione metabolism, and downregulation of biotin metabolism.

CONCLUSIONS

Patients with Cir_sAH show specific changes of the bile acid pool with a shift towards more hydrophobic and toxic species that may be responsible for the specific microbiota changes. Conversely, the microbiota may also alter the bile acid pool by transforming primary to secondary bile acids, leading to a vicious cycle.

LC-MS/MS analysis and pharmacokinetic study on five bioactive constituents of Tanreqing injection in rats

Tanreqing injection (TRQ), a well-known traditional Chinese medicine formula, is commonly used to treat respiratory diseases. In the present study, a rapid, selective, and sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed and validated to simultaneously determinate the plasma contents of 5 major constituents of TRQ, including chlorogenic acid (CHA), caffeic acid (CFA), baicalin (BA), ursodeoxycholic acid (UDCA) and chenodeoxycholic acid (CDCA) in rats after intravenous administration of TRQ. Chromatographic separation was performed on an Agilent Zorbax SB-C₁₈ column (3.5 μm, 100 mm × 2.1 mm), with acetonitrile and 0.1% aqueous formic acid as mobile phase at a flow rate of 0.3 mL·min^-1. The calibration curves were linear over the ranges of 27.0-13 333.0 ng·mL^-1 for CFA, 30.0-14 933.0 ng·mL^-1 for CHA, 50.0-50 333.0 ng·mL^-1 for BA, 550.0-55 000.0 ng·mL^-1 for UDCA, and 480.0-48 000.0 ng·mL^-1 for CDCA, respectively. Intra- and inter-day precisions (relative standard deviations, RSDs) were from 3.11% to 14.08%. The extraction recoveries were greater than 71% and accuracy (relative recovery) was from 89% to 137% for all analytes, except endogenous bile acids. This validated method was successfully applied to the first pharmacokinetic study of CFA, CHA, BA, UDCA and CDCA in rat plasma after intravenous administration of TRQ.

Potency of individual bile acids to regulate bile acid synthesis and transport genes in primary human hepatocyte cultures

Bile acids (BAs) are known to regulate their own homeostasis, but the potency of individual bile acids is not known. This study examined the effects of cholic acid (CA), chenodeoxycholic acid (CDCA), deoxycholic acid (DCA), lithocholic acid (LCA) and ursodeoxycholic acid (UDCA) on expression of BA synthesis and transport genes in human primary hepatocyte cultures. Hepatocytes were treated with the individual BAs at 10, 30, and 100μM for 48 h, and RNA was extracted for real-time PCR analysis. For the classic pathway of BA synthesis, BAs except for UDCA markedly suppressed CYP7A1 (70-95%), the rate-limiting enzyme of bile acid synthesis, but only moderately (35%) down-regulated CYP8B1 at a high concentration of 100μM. BAs had minimal effects on mRNA of two enzymes of the alternative pathway of BA synthesis, namely CYP27A1 and CYP7B1. BAs increased the two major target genes of the farnesoid X receptor (FXR), namely the small heterodimer partner (SHP) by fourfold, and markedly induced fibroblast growth factor 19 (FGF19) over 100-fold. The BA uptake transporter Na(+)-taurocholate co-transporting polypeptide was unaffected, whereas the efflux transporter bile salt export pump was increased 15-fold and OSTα/β were increased 10-100-fold by BAs. The expression of the organic anion transporting polypeptide 1B3 (OATP1B3; sixfold), ATP-binding cassette (ABC) transporter G5 (ABCG5; sixfold), multidrug associated protein-2 (MRP2; twofold), and MRP3 (threefold) were also increased, albeit to lesser degrees. In general, CDCA was the most potent and effective BA in regulating these genes important for BA homeostasis, whereas DCA and CA were intermediate, LCA the least, and UDCA ineffective.

Effects of bile acids on expression of the human apical sodium dependent bile acid transporter gene

Using a luciferase reporter assay in both LMH cells and Caco2 cells we found that certain bile acids including unconjugated deoxycholic and others transactivated the ileal apical sodium-dependent bile acid transporter (ASBT) at concentrations ranging from 20 to 300 microM. Confirming this effect, addition of deoxycholic acid to fresh human ileal biopsies caused an approximate 40% increase in endogenous ASBT mRNA production. Promoter deletion analysis indicated the effect of bile acids was mediated by a response element located in the downstream half of the 5'-UTR, a region known to contain a retinoic acid (RXR/RAR) response element and an activated protein-1 (AP-1) response element. Site-directed mutagenesis of the RAR/RXR response element actually enhanced response to deoxycholic acid. Site-directed mutagenesis of the downstream AP-1 response element reduced activation by deoxycholic acid while deletion of this response element completely eliminated this response. The epidermal growth factor (EGF) receptor inhibitor, AG1478, completely eliminated the response to bile acid while the mitogen-activated protein extracellular signal-regulated kinase cascade (MEK) inhibitor, U0126, partially inhibited the response to bile acid. These studies demonstrate that certain bile acids stimulate ASBT gene expression acting on the down-stream AP-1 response element via the EGF receptor and MEK cascade.

Mitochondrially mediated synergistic cell killing by bile acids

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

Ursodeoxycholate and tauroursodeoxycholate inhibit cholangiocyte growth and secretion of BDL rats through activation of PKC alpha

Accumulating bile acids (BA) trigger cholangiocyte proliferation in chronic cholestasis. The aim of this study was to determine if ursodeoxycholate (UDCA) or tauroursodeoxycholate (TUDCA) chronic feeding prevents the increased cholangiocyte growth and secretion in bile duct-ligated (BDL) rats, if UDCA and TUDCA effects are associated with increased cholangiocyte apoptosis, and to determine if this inhibition is dependent on increased intracellular Ca(2+) ([Ca(2+)](i)) and activation of protein kinase C (PKC) alpha. Immediately after BDL, rats were fed UDCA or TUDCA (both 275 micromol/d) for 1 week. We determined the number of bile ducts in liver sections, cholangiocyte proliferation (by measurement of H(3) histone and proliferating cellular nuclear antigen in isolated cholangiocytes), and ductal secretion. In purified cholangiocytes from 1-week BDL rats, we evaluated if UDCA and TUDCA directly inhibit cholangiocyte proliferation and secretin-stimulated adenosine 3', 5'-monophosphate levels. We determined if UDCA and TUDCA activate PKC, increase [Ca(2+)](i), and alter the apical BA transporter (ABAT) expression in cholangiocytes. UDCA and TUDCA inhibited in vivo the cholangiocyte proliferation, secretion, and ABAT expression. In vitro UDCA and TUDCA inhibition of cholangiocyte growth and secretion required increased [Ca(2+)](i) and PKC alpha. In conclusion, activation of Ca(2+)-dependent PKC alpha is required for UDCA and TUDCA inhibition of cholangiocyte growth and secretion. Reduced cholangiocyte ABAT may decrease endogenous BA stimulation of cholangiocyte growth and secretion.

Primary biliary cirrhosis: incidence and predictive factors of cirrhosis development in ursodiol-treated patients

BACKGROUND & AIMS

Ursodeoxycholic acid (UDCA) slows the progression of primary biliary cirrhosis (PBC). However, some UDCA-treated patients escape and progress toward cirrhosis and end-stage disease. This study aimed to assess the incidence of cirrhosis in UDCA-treated patients with PBC and to determine the predictive factors of cirrhosis development under this treatment.

METHODS

A Markov model was used to describe the progression toward cirrhosis in 183 UDCA-treated patients with PBC. A total of 254 pairs of liver biopsy specimens collected during 655 patient-years were studied.

RESULTS

The incidence of cirrhosis after 5 years of UDCA treatment was 4%, 12%, and 59% among patients followed-up from stages I, II, and III, respectively. At 10 years, the incidence was 17%, 27%, and 76%, respectively. The median time for developing cirrhosis from stages I, II, and III was 25 years, 20 years, and 4 years, respectively. The independent predictive factors of cirrhosis development were serum bilirubin greater than 17 mumol/L, serum albumin less than 38 g/L, and moderate to severe lymphocytic piecemeal necrosis.

CONCLUSIONS

This study provides new data about the time course of PBC under UDCA and constitutes a rationale for the design and evaluation of clinical trials aimed to assess the efficacy of drugs associated with UDCA.

Interactions of combined bile acids on hepatocyte viability: cytoprotection or synergism

Cholestasis results from hepatocyte dysfunction due to the accumulation of bile acids in the cell, many of which are known to be cytotoxic. Recent evidence implicates competitive antagonism of key cytotoxic responses as the mechanism by which certain therapeutic bile acids might afford cytoprotection against cholestasis. In this work, we compare the relative cytotoxicity of bile acids in terms of dose- and time-dependence. To better elucidate the controversy related to the therapeutic use of ursodeoxycholate (UDCA) in cholestatic patients, we also evaluated the effects of bile acid combinations. Viability of Wistar rat hepatocytes in primary culture was measured by LDH leakage after 12 and 24 h exposure of cells to the various bile acids. All unconjugated bile acids caused a dose-dependent decrease in cell viability. The tauro- and glyco-conjugates of chenodeoxycholate (CDCA) and UDCA were all less toxic than the corresponding unconjugated form. Although relatively non-toxic, UDCA caused synergistic cell killing by lithocholate (LCA), CDCA, glyco-CDCA (GCDC) and tauro-CDCA (TCDC). Glycoursodeoxycholate decreased the toxicity of GCDC, but potentiated the toxicity of unconjugated CDCA and LCA. The tauro-conjugate of UDCA had no significant effect. These data suggest that at cholestatic concentrations, bile acid-induced cell death correlates with the degree of lipophilicity of individual bile acids. However, these results indicate that the reported improvement of biochemical parameters in cholestatic patients treated with UDCA is not due to a direct effect of UDCA on hepatocyte viability. Therefore, any therapeutic effect of UDCA must be secondary to some other process, such as altered membrane transport or nonparenchymal cell function.

A preliminary trial of high-dose ursodeoxycholic acid in primary sclerosing cholangitis

BACKGROUND & AIMS

Ursodeoxycholic acid (UDCA) is used for the treatment of cholestatic liver diseases including primary biliary cirrhosis (PBC) for which it has a positive effect on laboratory values, may delay the development of liver failure and prolong the transplant-free disease period. Standard doses of UDCA (8-15 mg/kg daily) have been shown to be ineffective in the treatment of primary sclerosing cholangitis (PSC). We report on the findings (clinical, biochemical, histological, and cholangiographic) and side effects of a 2-year double-blind placebo-controlled preliminary study of high-dose UDCA in PSC patients.

METHODS

Twenty-six patients with PSC were randomized to high-dose (20 mg/kg daily) UDCA or placebo. Cholangiography and liver biopsy were performed at entry and after 2 years. Symptoms, clinical signs, and liver biochemical tests were recorded at 3 monthly intervals.

RESULTS

High-dose UDCA did not influence symptoms, but there was a significant improvement in liver biochemistry (serum alkaline phosphatase, P = 0.03; gamma-glutamyl transferase, P = 0.01) and a significant reduction in progression in cholangiographic appearances (P = 0.015) and liver fibrosis as assessed by disease staging (P = 0.05). In the treatment group, a significant increase in total bile acids and saturation with UDCA >70% confirmed patient compliance. No significant side effects were reported.

CONCLUSIONS

High-dose UDCA may be of clinical benefit in PSC, but trials with a larger number of participants and of longer duration are required to establish whether the effect of high-dose UDCA on liver biochemistry, histology, and cholangiography in patients with PSC is translated into improved long-term survival.

Role of hepatocytes and bile duct cells in preservation-reperfusion injury of liver grafts

In liver transplantation, it is currently hypothesized that nonparenchymal cell damage and/or activation is the major cause of preservation-related graft injury. Because parenchymal cells (hepatocytes) appear morphologically well preserved even after extended cold preservation, their injury after warm reperfusion is ascribed to the consequences of nonparenchymal cell damage and/or activation. However, accumulating evidence over the past decade indicated that the current hypothesis cannot fully explain preservation-related liver graft injury. We review data obtained in animal and human liver transplantation and isolated perfused animal livers, as well as isolated cell models to highlight growing evidence of the importance of hepatocyte disturbances in the pathogenesis of normal and fatty graft injury. Particular attention is given to preservation time-dependent decreases in high-energy adenine nucleotide levels in liver cells, a circumstance that (1) sensitizes hepatocytes to various stimuli and insults, (2) correlates well with graft function after liver transplantation, and (3) may also underlie the preservation time-dependent increase in endothelial cell damage. We also review damage to bile duct cells, which is increasingly being recognized as important in the long-lasting phase of reperfusion injury. The role of hydrophobic bile salts in that context is particularly assessed. Finally, a number of avenues aimed at preserving hepatocyte and bile duct cell integrity are discussed in the context of liver transplantation therapy as a complement to reducing nonparenchymal cell damage and/or activation.

Ursodeoxycholic acid prevents hepatic cytochrome P450 isozyme reduction in rats with deoxycholic acid-induced liver injury

BACKGROUND/AIMS

Hydrophobic bile acids, such as deoxycholic acid produce cholestatic liver injury. Ursodeoxycholic acid has been shown to be useful in the treatment of cholestatic liver disease.

METHODS

In this study, we investigated the effects of deoxycholic acid or ursodeoxycholic acid (1% of diet, for 14 days) and their combination (1% each) on expression of hepatic cytochrome P450 isozymes, their related enzyme activities and mRNA level in rats.

RESULTS

Adding 1% deoxycholic acid to chow caused a marked increase in serum total bilirubin (47-fold) and total bile acid (8-fold) concentrations and in alkaline phosphatase (2.5-fold, p<0.01) and alanine aminotransferase activities (23.5-fold, p<0.01). Adding the same dose of ursodeoxycholic acid along with the deoxycholic acid mitigated both the rise in serum total bilirubin and bile acid concentrations and that in alkaline phosphatase and alanine aminotransferase activities, although the use of ursodeoxycholic acid alone did not affect any of the above. Feeding 1% deoxycholic acid caused a decrease (48% of control) in total cytochrome P450 content in hepatic microsomes. Addition of 1% ursodeoxycholic acid along with the 1% deoxycholic acid completely prevented the decrease in total cytochrome P450 content. Feeding ursodeoxycholic acid alone did not affect the total cytochrome P450 content. The expression of cytochrome P450 2B1, 2E1, 3A2, 2C6, 2C11 and 4A1 proteins in hepatic microsomes was decreased by deoxycholic acid (44, 51, 23, 59, 30 and 74% of control, respectively). Likewise, the activities of cytochrome P450 2B1 (pentoxyresorufin O-depentylation), 2E1 (aniline p-hydroxylation) and 3A2 (testosterone 6beta-hydroxylation) isozymes and the 3A2 mRNA levels in liver were decreased by deoxycholic acid. Addition of 1% ursodeoxycholic acid to 1% deoxycholic acid also prevented the decrease in these cytochrome P450 proteins, related enzyme activities and mRNA levels in liver.

CONCLUSIONS

These results indicate that, in rats with deoxycholic acid-induced liver injury, ursodeoxycholic acid prevents the decrease in hepatic cytochrome P450 isozymes and suggest that ursodeoxycholic acid is useful for the treatment of liver injury in terms of aiding the normalization of the hepatic drug-metabolizing system.

Present status of hepatoprotectants

Perpetual exposure of liver to xenobiotics and therapeutic agents leads to toxic manifestations of a complex and diverse nature. Not a single curative therapeutic agent has been found so far which could provide lasting remedy to patients suffering from hepatic disorders. In fact, the remedies available in the modern system of medicine provide only symptomatic relief without any significant changes on the disease process. Moreover, their use is associated with severe side effects and chances of relapses. Except some natural products claimed to be effective, no safe synthetic product is yet available for the management of hepatic disorders. Lack of effective, least toxic and curative hepatoprotectants made the task difficult to discover newer drugs. This review is an attempt to provide an overall view of the development of synthetic and natural products as hepatoprotective agents.

Taurohyodeoxycholic acid protects against taurochenodeoxycholic acid-induced cholestasis in the rat

The prevention of the hepatotoxic effects produced by intravenous infusion of taurochenodeoxycholic acid (TCDCA) by coinfusion with taurohyodeoxycholic acid (THDCA) was evaluated in bile fistula rats; the hepatoprotective effects of the latter were also compared with those of tauroursodeoxycholic acid (TUDCA). Rats infused with TCDCA at a dose of 8 micromol/min/kg showed reduced bile flow and calcium secretion, as well as increased biliary release of alkaline phosphatase (AP) and lactate dehydrogenase (LDH). This was associated with a very low biliary secretion rate of TCDCA (approximately 1 micromol/min/kg). Simultaneous infusion of THDCA or TUDCA at the same dose preserved bile flow and almost totally abolished the pathological leakage of the two enzymes into bile. The effect was slightly more potent for THDCA. The maximum secretion rate of TCDCA increased to the highest value (8 micromol/min/kg) when coinfused with either of the two hepatoprotective bile acids (BA), which were efficiently and completely secreted in the bile, without metabolism. Calcium output was also restored and phospholipid (PL) secretion increased with respect to the control saline infusion. This increase was higher in the THDCA study. These data show that THDCA is highly effective in the prevention of hepatotoxicity induced by intravenous infusion of TCDCA by facilitating its biliary secretion and reducing its hepatic residence time; this was associated with selective stimulation of PL biliary secretion.

Use of ursodeoxycholic acids in a dog with chronic hepatitis: effects on serum hepatic tests and endogenous bile acid composition

A dog with severe cholestasis secondary to chronic hepatitis was treated with ursodeoxycholic acid (UDCA) PO. After 2 weeks of daily treatment, the dog was more active and had an improved appetite. Monthly serum biochemical determinations and analysis of individual bile acid profiles documented improvement in hepatobiliary tests and a marked reduction in the concentrations of potentially hepatotoxic endogenous bile acids. These effects were maintained for approximately 6 months. The findings in this dog are similar to those reported for human patients treated with UDCA and provide preliminary evidence in support of its continued evaluation in the treatment of cholestatic liver disease in the dog.