Fibrates induce mdr2 gene expression and biliary phospholipid secretion in the mouse

Novel preclinical developments of the primary sclerosing cholangitis treatment landscape

INTRODUCTION

Primary sclerosing cholangitis (PSC) is a chronic cholestatic liver disease associated with inflammation, fibrosis, and destruction of intra- and extrahepatic bile ducts. Despite substantial recent advances in our understanding of PSC, the only proven treatment of PSC is liver transplantation. There is an urgent unmet need to find medical therapies for this disorder.

AREAS COVERED

Multiple drugs are currently under evaluation as therapeutic options for this disease. This article summarizes the literature on the various novel therapeutic options that have been investigated and are currently under development for the treatment of PSC.

EXPERT OPINION

In the next decade, more than one drug will likely be approved for the treatment of the disease, and we will be looking at combination therapies for the optimal management of the disease.

Obeticholic acid as a second-line treatment for low phospholipid-associated cholelithiasis syndrome

BACKGROUND

Low phospholipid-associated cholelithiasis (LPAC) syndrome is a rare genetic cause of hepatolithiasis. A pathogenic variant of the ABCB4 gene is reported in half of all patients. Ursodeoxycholic acid (UDCA) is the only drug approved. However, in some patients, UDCA fails to prevent recurrence of symptoms and complications. Experimental evidence suggests that agonists of the farnesoid-X receptor (FXR), the main transcription factor regulating ABCB4, may be beneficial in this context.

AIM

To study the efficacy of obeticholic acid (OCA) in patients with LPAC syndrome with an inadequate response or intolerance to UDCA.

METHODS

This was a retrospective study of patients with LPAC syndrome treated with OCA, a selective FXR agonist.

RESULTS

We reviewed the records of five OCA-treated patients (4 women; median age 29; ABCB4 variant in 4; no hepatic fibrosis). All patients received OCA at an initial dose of 5 mg daily and then 10 mg daily for a median period of 36 months in combination with UDCA (4 patients) or as a monotherapy (one patient). There were no adverse effects reported. Four patients had improvement in their symptoms - three completely and one partially. One patient had no clinical benefit. Abnormalities of blood liver tests persisted in one patient despite resolution of symptoms. Radiological signs of hepatolithiasis persisted in three of the four patients who responded clinically to OCA.

CONCLUSIONS

These preliminary observations suggest that OCA may have the potential to effectively treat LPAC syndrome in patients with inadequate response or intolerance to UDCA. Larger studies are needed to confirm these data.

PPAR agonists for the treatment of primary biliary cholangitis: Old and new tales

Introduction

Primary biliary cholangitis (PBC) is an autoimmune liver disease involving the small intrahepatic bile ducts; when untreated or undertreated, it may evolve to liver fibrosis and cirrhosis. Ursodeoxycholic Acid (UDCA) is the standard of care treatment, Obeticholic Acid (OCA) has been approved as second-line therapy for those non responder or intolerant to UDCA. However, due to moderate rate of UDCA-non responders and to warnings recently issued against OCA use in patients with cirrhosis, further therapies are needed.Areas covered. Deep investigations into the pathogenesis of PBC is leading to proposal of new therapeutic agents, among which peroxisome proliferator-activated receptor (PPAR) ligands seem to be highly promising given the preliminary, positive results in Phase 2 and 3 trials. Bezafibrate, the most evaluated, is currently used in clinical practice in combination with UDCA in referral centers. We herein describe completed and ongoing trials involving PPAR agonists use in PBC, analyzing pits and falls.

Expert opinion

Testing new therapeutic opportunities in PBC is challenging due to its low prevalence and slow progression. However, new drugs including PPAR agonists, are currently under investigation and should be considered for at-risk PBC patients.

Effects of pemafibrate on primary biliary cholangitis with dyslipidemia

AIM

The purpose of this study was to examine the effect of pemafibrate (PEM) in primary biliary cholangitis (PBC) patients with dyslipidemia.

METHODS

Patients who were diagnosed with PBC between June 2018 and December 31, 2020 were included in the study if they also had dyslipidemia and their alkaline phosphatase (ALP) or gamma-glutamyl transferase (GGT) levels remained above the normal range despite taking 600 mg/day ursodeoxycholic acid (UDCA) for at least 6 months. Patients who were treated with UDCA alone were administered PEM as an add-on (PEM-add group), and patients who were treated with UDCA and bezafibrate (BEZ) for at least 6 months were given PEM instead of BEZ (PEM-switch group). Clinical parameters were compared in all patients, and the levels of ALP, GGT, the estimated glomerular filtration rate (eGFR), and creatinine (Cr) were compared between the PEM-add and PEM-switch groups. Improvement in cholangitis was also evaluated.

RESULTS

In the PEM-add group, both ALP and GGT improved in 40 of 46 patients (87.0%). In the PEM-switch group, both ALP and GGT improved in 15 of 29 patients (51.7%). In the PEM-switch group, however, significant improvement was seen in eGFR and Cr.

CONCLUSIONS

Administration of PEM is effective in PBC patients with dyslipidemia who are refractory to UDCA monotherapy. In patients using both UDCA and BEZ, there was an advantage in switching to PEM if they had renal damage; however, improvement of ALP and GGT occurred in about 50%.

Definition and Management of Patients With Primary Biliary Cholangitis and an Incomplete Response to Therapy

Primary biliary cholangitis (PBC) is an immune-mediated chronic liver disease characterized by biliary epithelial injury, cholestasis, and progressive fibrosis that can lead to cirrhosis and requirement for liver transplantation. All patients with PBC should receive initial treatment with ursodeoxycholic acid (UDCA), and odds for response are based on characteristics at baseline. It is important to have clear definitions of patients at risk for a poor response to therapy, of biochemical markers of an incomplete response, and standardized management. Patients typically are assessed after 12 months of treatment with UDCA for biochemical markers of response. However, evaluation at 6 months has been proposed for patients with more severe disease or symptoms (such as pruritus or fatigue). Markers of response to therapy include reduced serum levels of alkaline phosphatase and bilirubin (Paris-2, Toronto, GLOBE, and so forth); patients with high levels of total and conjugated bilirubin or levels of alkaline phosphatase more than 1.5-fold the upper limit of normal should be considered for second-line therapy. Patients with adequate biochemical responses can continue UDCA monotherapy. Incomplete responders should be considered for second-line therapies with obeticholic acid (licensed) or fibrates (unlicensed) in addition to continued treatment with UDCA. Patients with PBC should be followed up for life.

Effects of Switching from Fenofibrate to Pemafibrate for Asymptomatic Primary Biliary Cholangitis

Background/Aims

The addition of a fibrate to ursodeoxycholic acid (UDCA) is the standard treatment for asymptomatic primary biliary cholangitis (aPBC) with an incomplete response to UDCA. Among the fibrates, bezafibrate and fenofibrate increase the serum creatinine level and reduce the estimated glomerular filtration rate (eGFR). Pemafibrate is an selective peroxisome proliferator-activated receptor alpha modulator (SPPARM-α) mainly metabolized by the liver that was recently approved to treat dyslipidemia. This study confirmed the changes in the biochemical markers after switching from fenofibrate to pemafibrate in aPBC patients.

Methods

This study examined the effects of switching treatment from fenofibrate to pemafibrate in 16 aPBC patients. The biological parameters of these patients were examined at the initiation of fenofibrate and after switching to pemafibrate, then at 24 and 48 weeks later, respectively.

Results

Among patients with aPBC treated with UDCA and fenofibrate, the ALP, GGT, and serum IgM levels decreased significantly (p<0.0001) over 48 weeks. On the other hand, serum creatinine levels increased significantly, and eGFR decreased significantly (p<0.0001). After switching to pemafibrate plus UDCA, patients with aPBC exhibited significantly lower serum creatinine levels (p=0.007) and significantly higher eGFR levels (p=0.014).

Conclusions

Pemafibrate has therapeutic efficacy for aPBC patients with an inadequate response to UDCA. Pemafibrate might be another option for aPBC patients given its beneficial effects on renal function, but larger, multicenter studies with a longer follow-up are needed.

Reduced hepatic global hydroxymethylation in mice treated with non-genotoxic carcinogens is transiently reversible with a methyl supplemented diet

Non-genotoxic carcinogens (NGCs) are known to cause perturbations in DNA methylation, which can be an early event leading to changes in gene expression and the onset of carcinogenicity. Phenobarbital (PB) has been shown to alter liver DNA methylation and hydroxymethylation patterns in mice in a time dependent manner. The goals of this study were to assess if clofibrate (CFB), a well-studied rodent NGC, would produce epigenetic changes in mice similar to PB, and if a methyl donor supplementation (MDS) would modulate epigenetic and gene expression changes induced by phenobarbital. CByB6F1 mice were treated with 0.5% clofibrate or 0.14% phenobarbital for 7 and 28 days. A subgroup of PB treated and control mice were also fed MDS diet. Liquid Chromatography-Ionization Mass Spectrometry (LC-MS) was used to quantify global liver 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC) levels. Gene expression analysis was conducted using Affymetrix microarrays. A decrease in liver 5hmC but not 5mC levels was observed upon treatment with both CFB and PB with varying time of onset. We observed moderate increases in 5hmC levels in PB-treated mice when exposed to MDS diet and lower expression levels of several phenobarbital induced genes involved in cell proliferation, growth, and invasion, suggesting an early modulating effect of methyl donor supplementation. Overall, epigenetic profiling can aid in identifying early mechanism-based biomarkers of non-genotoxic carcinogenicity and increases the quality of cancer risk assessment for candidate drugs. Global DNA methylation assessment by LC-MS is an informative first step toward understanding the risk of carcinogenicity.

Structure and Function of Hepatobiliary ATP Binding Cassette Transporters

The liver is beyond any doubt the most important metabolic organ of the human body. This function requires an intensive crosstalk within liver cellular structures, but also with other organs. Membrane transport proteins are therefore of upmost importance as they represent the sensors and mediators that shuttle signals from outside to the inside of liver cells and/or vice versa. In this review, we summarize the known literature of liver transport proteins with a clear emphasis on functional and structural information on ATP binding cassette (ABC) transporters, which are expressed in the human liver. These primary active membrane transporters form one of the largest families of membrane proteins. In the liver, they play an essential role in for example bile formation or xenobiotic export. Our review provides a state of the art and comprehensive summary of the current knowledge of hepatobiliary ABC transporters. Clearly, our knowledge has improved with a breath-taking speed over the last few years and will expand further. Thus, this review will provide the status quo and will lay the foundation for new and exciting avenues in liver membrane transporter research.

New treatments/targets for primary biliary cholangitis

Primary biliary cholangitis (PBC) is an autoimmune, cholestatic, chronic liver disease that ultimately progresses towards cirrhosis and liver failure if untreated. While ursodeoxycholic acid has been established as standard of care for PBC in the last few decades, significant advances in second-line treatment options have recently been made and new therapeutic developments are currently under evaluation. The purpose of this article is to provide the clinician with an overview of the current treatment options and future opportunities for patients with PBC.

Effects of Bezafibrate on Outcome and Pruritus in Primary Biliary Cholangitis With Suboptimal Ursodeoxycholic Acid Response

OBJECTIVES

Adding fibrates improves liver biochemistries in patients with primary biliary cholangitis (PBC) and suboptimal response to ursodeoxycholic acid (UDCA). As there are no consistent data regarding the course and outcome, we have assessed the effects of the combined treatment with UDCA and bezafibrate on a long-term basis.

METHODS

A total of 48 patients (45 female) with PBC treated with UDCA and alkaline phosphatase (ALP) above 1.5 times upper normal levels (× UNL) were treated with bezafibrate (400 mg/day) plus UDCA (13-16 mg/kg/day). Changes in clinical features, liver biochemistries, and prognosis after therapy were assessed, as well as pruritus, using a visual analog scale (43 patients) and the 5-D descriptive pruritus scale.

RESULTS

After a median of 38 months, 26 patients (54%) had normalized ALP. In these patients, jaundice, pruritus, and liver stiffness was lower, and age was higher than in patients who remained with elevated ALP. Biochemical improvement was less prominent in patients without ALP normalization. Five of these patients (23%) developed events of disease progression: 1 died, 3 were transplanted, and 1 developed hepatocellular carcinoma. Partial or complete itching relief was reported in all but one case with pruritus. Itching recurrence or worsening was observed after bezafibrate discontinuation.

CONCLUSIONS

The long-term treatment with UDCA and bezafibrate results in excellent response, and is associated with a complete or partial itching relief. Incomplete ALP normalization was observed in patients with advanced disease who remained at risk for developing severe events. The combined treatment is mainly effective in patients with lower fibrosis and severity of cholestasis.

Hepatic MDR3 expression impacts lipid homeostasis and susceptibility to inflammatory bile duct obstruction in neonates

BackgroundHeterozygous mutations in the gene ABCB4, encoding the phospholipid floppase MDR3 (Mdr2 in mice), are associated with various chronic liver diseases. Here we hypothesize that reduced ABCB4 expression predisposes to extrahepatic biliary atresia (EHBA).MethodsLivers from neonatal wild-type (wt) and heterozygous Mdr2-deficient mice were subjected to mass spectrometry-based lipidomics and RNA sequencing studies. Following postnatal infection with rhesus rotavirus (RRV), liver immune responses and EHBA phenotype were assessed. Hepatic microarray data from 40 infants with EHBA were mined for expression levels of ABCB4.ResultsPhosphatidylcholine (PC) and phosphatidylethanolamine (PE) were increased, whereas the PC/PE ratio was decreased in neonatal Mdr2+/- mice compared with wt mice. Following RRV challenge, hepatic expression of IFNγ and infiltration with CD8+ and NK+ lymphocytes were increased in Mdr2+/- mice. Plasma total bilirubin levels and prevalence of complete ductal obstruction were higher in these mice. In infants with EHBA, hepatic gene expression of ABCB4 was downregulated in those with an inflammatory compared with a fibrosing molecular phenotype.ConclusionDecreased expression of ABCB4 causes dysregulation in (phospho)lipid homeostasis, and predisposes to aberrant pro-inflammatory lymphocyte responses and an aggravated phenotype of EHBA in neonatal mice. Downregulated ABCB4 is associated with an inflammatory transcriptome signature in infants with EHBA.

A functional classification of ABCB4 variations causing progressive familial intrahepatic cholestasis type 3

Progressive familial intrahepatic cholestasis type 3 is caused by biallelic variations of ABCB4, most often (≥70%) missense. In this study, we examined the effects of 12 missense variations identified in progressive familial intrahepatic cholestasis type 3 patients. We classified these variations on the basis of the defects thus identified and explored potential rescue of trafficking-defective mutants by pharmacological means. Variations were reproduced in the ABCB4 complementary DNA and the mutants, thus obtained, expressed in HepG2 and HEK293 cells. Three mutants were either fully (I541F and L556R) or largely (Q855L) retained in the endoplasmic reticulum, in an immature form. Rescue of the defect, i.e., increase in the mature form at the bile canaliculi, was obtained by cell treatments with cyclosporin A or C and, to a lesser extent, B, D, or H. Five mutations with little or no effect on ABCB4 expression at the bile canaliculi caused a decrease (F357L, T775M, and G954S) or almost absence (S346I and P726L) of phosphatidylcholine secretion. Two mutants (T424A and N510S) were normally processed and expressed at the bile canaliculi, but their stability was reduced. We found no defect of the T175A mutant or of R652G, previously described as a polymorphism. In patients, the most severe phenotypes appreciated by the duration of transplant-free survival were caused by ABCB4 variants that were markedly retained in the endoplasmic reticulum and expressed in a homozygous status.

CONCLUSION

ABCB4 variations can be classified as follows: nonsense variations (I) and, on the basis of current findings, missense variations that primarily affect the maturation (II), activity (III), or stability (IV) of the protein or have no detectable effect (V); this classification provides a strong basis for the development of genotype-based therapies.

Combined ursodeoxycholic acid (UDCA) and fenofibrate in primary biliary cholangitis patients with incomplete UDCA response may improve outcomes

BACKGROUND

Fibrates appear to improve biochemistry in patients with primary biliary cholangitis (PBC), but it is unclear which factors predict response and whether treatment improves transplant-free survival.

AIM

To evaluate biochemical profiles, liver-related outcomes and adverse events following fenofibrate therapy in PBC patients with incomplete response to ursodeoxycholic acid (UDCA).

METHODS

A retrospective cohort study was performed at a tertiary centre. Cox regression was used to compare outcomes between patients treated with fibrates and UDCA (FF) or UDCA alone, adjusted for a propensity score to account for treatment selection bias.

RESULTS

A total of 120 patients were included (FF group n = 46, UDCA group n = 74, median fenofibrate treatment 11 months); 41% vs. 7% met the Toronto criteria for biochemical response [alkaline phosphatase ≤1.67 times the upper limit of normal] in the FF and UDCA groups, respectively (P = 0.0001). Fenofibrate was also associated with improved decompensation-free and transplant-free survival [hazard ratio (HR) 0.09, 95% CI 0.03-0.32, P = 0.0002]. However, only fenofibrate use, not biochemical response, was independently associated with improved outcomes on multivariable analysis (HR 0.40, 95% CI 0.17-0.93, P = 0.03). Twenty-two percent discontinued fenofibrate due to adverse events (most common: abdominal pain and myalgias). In cirrhotic patients, bilirubin increased more rapidly in the FF group (P = 0.005).

CONCLUSIONS

Fenofibrate therapy is associated with significant improvement in alkaline phosphatase, decompensation-free and transplant-free survival in PBC patients with incomplete UDCA response. However, fenofibrate should be used cautiously in cirrhosis, with close monitoring for clinical/biochemical decompensation. Additional studies are required to assess the validity of alkaline phosphatase as an appropriate response criteria for fibrate therapy.

Fibrates and cholestasis

Cholestasis, including primary biliary cirrhosis (PBC) and primary sclerosing cholangitis (PSC), results from an impairment or disruption of bile production and causes intracellular retention of toxic bile constituents, including bile salts. If left untreated, cholestasis leads to liver fibrosis and cirrhosis, which eventually results in liver failure and the need for liver transplantation. Currently, the only therapeutic option available for these patients is ursodeoxycholic acid (UDCA), which slows the progression of PBC, particularly in stage I and II of the disease. However, some patients have an incomplete response to UDCA therapy, whereas other, more advanced cases often remain unresponsive. For PSC, UDCA therapy does not improve survival, and recommendations for its use remain controversial. These considerations emphasize the need for alternative therapies. Hepatic transporters, located along basolateral (sinusoidal) and apical (canalicular) membranes of hepatocytes, are integral determinants of bile formation and secretion. Nuclear receptors (NRs) are critically involved in the regulation of these hepatic transporters and are natural targets for therapy of cholestatic liver diseases. One of these NRs is peroxisome proliferator-activated receptor alpha (PPARα), which plays a central role in maintaining cholesterol, lipid, and bile acid homeostasis by regulating genes responsible for bile acid synthesis and transport in humans, including cytochrome P450 (CYP) isoform 7A1 (CYP7A1), CYP27A1, CYP8B1, uridine 5'-diphospho-glucuronosyltransferase 1A1, 1A3, 1A4, 1A6, hydroxysteroid sulfotransferase enzyme 2A1, multidrug resistance protein 3, and apical sodium-dependent bile salt transporter. Expression of many of these genes is altered in cholestatic liver diseases, but few have been extensively studied or had the mechanism of PPARα effect identified. In this review, we examine what is known about these mechanisms and consider the rationale for the use of PPARα ligand therapy, such as fenofibrate, in various cholestatic liver disorders.

Pathophysiological analysis of primary biliary cirrhosis focusing on choline/phospholipid metabolism

BACKGROUND & AIMS

Injury to biliary epithelial cells caused by disorders in bile composition may be the initial step in the pathogenesis of primary biliary cirrhosis (PBC). We therefore examined choline/phospholipid metabolism in livers of patients with PBC.

METHODS

Hepatic levels of mRNA encoded by choline metabolism-related genes in early stage PBC patients were quantified by real-time RT-PCR. Serum cholesterol and triglyceride concentrations in each lipoprotein compartment and serum/tissue choline levels were also measured. OCT1 expression was quantified by genotype (rs683369 and rs622342).

RESULTS

Serum choline concentrations were significantly higher in PBC patients than in normal individuals, with the concentrations in the former lowered by treatment with fibrates. Hepatic choline levels were markedly lower in PBC patients than in controls. The levels of expression of genes associated with choline uptake (OCT1 and CTL1), phosphatidylcholine synthesis (PEMT and BHMT), and phosphatidylcholine transport (MDR3) were significantly upregulated in PBC compared with control livers. Serum cholesterol concentrations and the cholesterol/triglyceride ratio in serum very low density lipoprotein were markedly higher in PBC patients than in controls. In PBC liver, OCT1 protein levels were lower in patients with minor (CG/GG at rs683369 and/or CC at rs622342) than major (CC at rs683369 and AA at rs622342) genotypes of the OCT1 gene.

CONCLUSION

During early stage PBC, hepatocellular choline uptake and PC synthesis become dysregulated. OCT1 genotypes may influence the pathogenesis of PBC.

ABCB4: Insights from pathobiology into therapy

Adenosine triphosphate (ATP)-binding cassette, sub-family B, member 4 (ABCB4), also called multidrug resistance 3 (MDR3), is a member of the ATP-binding cassette transporter superfamily, which is localized at the canalicular membrane of hepatocytes, and mediates the translocation of phosphatidylcholine into bile. Phosphatidylcholine secretion is crucial to ensure solubilization of cholesterol into mixed micelles and to prevent bile acid toxicity towards hepatobiliary epithelia. Genetic defects of ABCB4 may cause progressive familial intrahepatic cholestasis type 3 (PFIC3), a rare autosomic recessive disease occurring early in childhood that may be lethal in the absence of liver transplantation, and other cholestatic or cholelithiasic diseases in heterozygous adults. Development of therapies for these conditions requires understanding of the biology of this transporter and how gene variations may cause disease. This review focuses on our current knowledge on the regulation of ABCB4 expression, trafficking and function, and presents recent advances in fundamental research with promising therapeutic perspectives.

Primary biliary cirrhosis in adults

Primary biliary cirrhosis (PBC) is a chronic, autoimmune, cholestatic liver disease. It is characterized by slow destruction of small intrahepatic bile ducts, impaired biliary secretion and stasis of toxic endogenous bile acids within the liver with progression to liver fibrosis and cirrhosis. It has an increasing prevalence worldwide. It occurs more commonly in women than men at a ratio of 10:1. In most cases, diagnosis relies on a positive antimitochondrial antibody in the context of chronic cholestasis, without the need for a liver biopsy. Ursodeoxycholic acid improves survival even in patients with advanced liver disease. Certain findings such as fatigue, anti-nuclear antibodies, anti-centromere antibodies and the GP210 antinuclear antibody predict a poor outcome. Up to 40% of patients do not respond satisfactorily to ursodeoxycholic acid therapy and should be considered for adjunctive therapies. Several adjunctive and newer therapies are being tested and some appear promising. We provide a review of PBC with a focus on advances in therapies that may impact the management of PBC in the near future.

Peroxisome proliferator-activated receptor α activates human multidrug resistance transporter 3/ATP-binding cassette protein subfamily B4 transcription and increases rat biliary phosphatidylcholine secretion

Multidrug resistance transporter 3/ATP-binding cassette protein subfamily B4 (MDR3/ABCB4) is a critical determinant of biliary phosphatidylcholine (PC) secretion. Clinically, mutations and partial deficiencies in MDR3 result in cholestatic liver injury. Thus, MDR3 is a potential therapeutic target for cholestatic liver disease. Fenofibrate is a peroxisome proliferator-activated receptor (PPAR) α ligand that has antiinflammatory actions and regulates bile acid detoxification. Here we examined the mechanism by which fenofibrate regulates MDR3 gene expression. Fenofibrate significantly up-regulated MDR3 messenger RNA (mRNA) and protein expression in primary cultured human hepatocytes, and stimulated MDR3 promoter activity in HepG2 cells. In silico analysis of 5'-upstream region of human MDR3 gene revealed a number of PPARα response elements (PPRE). Electrophoretic mobility shift (EMSA) and chromatin immunoprecipitation (ChIP) assays demonstrated specific binding of PPARα to the human MDR3 promoter. Targeted mutagenesis of three novel PPREs reduced inducibility of the MDR3 promoter by fenofibrate. In collagen sandwich cultured rat hepatocytes, treatment with fenofibrate increased secretion of fluorescent PC into bile canaliculi.

CONCLUSION

Fenofibrate transactivates MDR3 gene transcription by way of the binding of PPARα to three novel and functionally critical PPREs in the MDR3 promoter. Fenofibrate treatment further stimulates biliary phosphatidylcholine secretion in rat hepatocytes, thereby providing a functional correlate. We have established a molecular mechanism that may contribute to the beneficial use of fenofibrate therapy in human cholestatic liver disease.

Bezafibrate normalizes alkaline phosphatase in primary biliary cirrhosis patients with incomplete response to ursodeoxycholic acid

BACKGROUND & AIMS

Ursodeoxycholic acid (UDCA) is the standard treatment for primary biliary cirrhosis (PBC) but excellent response is not observed in all cases. Since potential favourable effects of fibrates have been reported in short series with inconclusive results, we have carried out a pilot study to analyse the effects of bezafibrate in patients with suboptimal response to UDCA.

METHODS

Thirty women (age 52.3 ± 2.3 years) treated with UDCA and abnormal alkaline phosphatase (AP) levels received bezafibrate (400 mg/d) for 1 year. Changes were measured every 3 months during the study period of 12 months, 3 months after discontinuation and 3 months after resuming bezafibrate.

RESULTS

Two patients discontinued the treatment after few days, three at 6 and one at 9 months. Bezafibrate treatment resulted in a significant decrease in AP as early as 3 months. Normalization or decrease of AP below 1.5 times normal levels was observed in 13 and 4 patients respectively. There was also a significant decrease in γ-glutamyl transferase and alanine aminotransferase, cholesterol and triglyceride levels. Bezafibrate treatment resulted in significant improvement of pruritus. A rebound in liver biochemistries and pruritus occurred upon drug discontinuation, changes which improved again after resuming bezafibrate. Response to bezafibrate was associated with lower liver stiffness and severity of cholestasis. No severe adverse effects were observed.

CONCLUSIONS

Combination treatment of bezafibrate and UDCA is associated with marked decrease or normalization of alkaline phosphatase as early as 3 months in patients with PBC. Better biochemical response was observed in patients with early disease and lower cholestasis.

Gemfibrozil disrupts lysophosphatidylcholine and bile acid homeostasis via PPARα and its relevance to hepatotoxicity

Gemfibrozil, a ligand of peroxisome proliferator-activated receptor α (PPARα), is one of the most widely prescribed anti-dyslipidemia fibrate drugs. Among the adverse reactions observed with gemfibrozil are alterations in liver function, cholestatic jaundice, and cholelithiasis. However, the mechanisms underlying these toxicities are poorly understood. In this study, wild-type and Ppara-null mice were dosed with a gemfibrozil-containing diet for 14 days. Ultra-performance chromatography electrospray ionization quadrupole time-of-flight mass spectrometry-based metabolomics and traditional approaches were used to assess the mechanism of gemfibrozil-induced hepatotoxicity. Unsupervised multivariate data analysis revealed four lysophosphatidylcholine components in wild-type mice that varied more dramatically than those in Ppara-null mice. Targeted metabolomics revealed taurocholic acid and tauro-α-muricholic acid/tauro-β-muricholic acid were significantly increased in wild-type mice, but not in Ppara-null mice. In addition to the above perturbations in metabolite homeostasis, phenotypic alterations in the liver were identified. Hepatic genes involved in metabolism and transportation of lysophosphatidylcholine and bile acid compounds were differentially regulated between wild-type and Ppara-null mice, in agreement with the observed downstream metabolic alterations. These data suggest that PPARα mediates gemfibrozil-induced hepatotoxicity in part by disrupting phospholipid and bile acid homeostasis.

Effects of three different fibrates on intrahepatic cholestasis experimentally induced in rats

Background. Activation of PPAR α modulates cholesterol metabolism and suppresses bile acid synthesis. This study aims to evaluate the effect of PPAR α agonists, fenofibrate, bezafibrate, and gemfibrozil, on acute cholestasis induced by ethinylestradiol (EE) plus chlorpromazine (CPZ) in rats. Method. 100 male albino rats (150-200 gm) were divided randomly into 10 equal groups. Control group received 1% methylcellulose vehicle; disease group received CPZ plus EE for 5 consecutive days; four groups received either ursodeoxycholic acid, fenofibrate, bezafibrate, or gemfibrozil for 7 days; 2 days before EE + CPZ, three other groups received one of the three fibrates after GW6471, a selective PPAR α antagonist in addition to EE + CPZ. The final group received GW6471 alone. Results. The three fibrates showed marked reduction (P < 0.05) in serum levels of ALP, GGT, ALT, AST, total bile acids, bilirubin, TNF α , and IL-1 β and in hepatic malondialdehyde level as well as a significant increase in bile flow rate (P < 0.05) in addition to improvements in histopathological parameters compared to diseased group. In groups which received GW6471, these effects were completely abolished with fenofibrate and partially blocked with bezafibrate and gemfibrozil. Conclusion. Short-term administration of fibrates to EE/CPZ-induced intrahepatic cholestatic rats exerted beneficial effects on hepatocellular damage and apoptosis. Fenofibrate anticholestatic effect was solely PPAR α dependent while other mechanisms played part in bezafibrate and gemfibrozil actions.

PPAR Medicines and Human Disease: The ABCs of It All

ATP-dependent binding cassette (ABC) transporters are a family of transmembrane proteins that pump a variety of hydrophobic compounds across cellular and subcellular barriers and are implicated in human diseases such as cancer and atherosclerosis. Inhibition of ABC transporter activity showed promise in early preclinical studies; however, the outcomes in clinical trials with these agents have not been as encouraging. Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors that regulate genes involved in fat and glucose metabolism, and inflammation. Activation of PPAR signaling is also reported to regulate ABC gene expression. This suggests the potential of PPAR medicines as a novel means of controlling ABC transporter activity at the transcriptional level. This paper summarizes the advances made in understanding how PPAR medicines affect ABC transporters, and the potential implications for impacting on human diseases, in particular with respect to cancer and atherosclerosis.

Efficacy of fenofibrate in Chinese patients with primary biliary cirrhosis partially responding to ursodeoxycholic acid therapy

OBJECTIVE

To investigate the efficacy of fenofibrate combination therapy in Chinese patients with primary biliary cirrhosis (PBC) who had a partial response to standard dose of ursodeoxycholic acid (UDCA) for at least one year.

METHODS

PBC patients were treated with UDCA (13-15 mg/kg/day) for more than one year. The biochemical response to UDCA treatment was evaluated after treatment. Fenofibrate (200 mg/day) was added to 22 patients with partial response to UDCA.

RESULTS

In patients with partial response to UDCA, serum alkaline phosphatase (ALP) and γ-glutamyl transpeptidase levels significantly decreased after 3-month combination therapy of UDCA and fenofibrate, 68% of these patients even reached normal ALP level. Serum triglyceride (TG) and cholesterol levels were improved, and alanine transaminase (ALT) and aspartate transaminase (AST) were also decreased during the combination therapy. However, fenofibrate had no significant effect on serum bilirubin levels. The improvement of liver biochemical tests was maintained in some patients with long-term therapy (at least 6 months). No obvious adverse effects were observed in patients taking fenofibrate.

CONCLUSIONS

Fenofibrate is effective for improving liver biochemical tests in patients who have partial response to UDCA monotherapy. It is worth exploring the efficacy of fenofibrate on histological changes in PBC patients.

Bezafibrate for primary biliary cirrhosis

BACKGROUND

Treatment of primary biliary cirrhosis is complicated. There are studies suggesting that bezafibrate, alone or in combination with ursodeoxycholic acid (UDCA), is effective in the treatment of primary biliary cirrhosis, but no systematic review has summarised the evidence yet.

OBJECTIVES

To assess the beneficial and harmful effects of bezafibrate in patients with primary biliary cirrhosis.

SEARCH METHODS

The Cochrane Hepato-Biliary Group Controlled Trials Register, The Cochrane Central Register of Controlled Trials (CENTRAL) in The Cochrane Library, MEDLINE, EMBASE, Science Citation Index Expanded, LILACS, Clinicaltrials.gov, the WHO International Clinical Trials Registry Platform, and full text searches were conducted until November 2011. The searches in Chinese Bio-medical Literature Database, China Network Knowledge Information, Chinese Science Journal Database, Chinese Medical Citation Index, Wanfang Database, and full text searches were conducted until January 2011. Manufacturers and authors were contacted.

SELECTION CRITERIA

All randomised clinical trials comparing bezafibrate at any dose or regimen in patients with primary biliary cirrhosis with placebo or no intervention, or with another drug. Any concomitant interventions were allowed if received equally by all treatment groups in a trial.

DATA COLLECTION AND ANALYSIS

Two authors extracted data. RevMan Analysis was used for statistical analysis of dichotomous data with risk ratio (RR) or risk difference (RD), and of continuous data with mean difference (MD), both with 95% confidence intervals (CI). Methodological domains were used to assess risk of systematic errors (bias). Trial sequential analysis was used to control for random errors (play of chance).

MAIN RESULTS

Six trials with 151 Japanese patients were included. All trials had high risk of bias. Four trials compared bezafibrate plus UDCA with no intervention plus UDCA (referenced as bezafibrate versus no intervention in the remaining text), and two trials compared bezafibrate with UDCA. No patient died and no patient developed liver-related complications in any of the included trials. Bezafibrate was without significant effects on the occurrence of adverse events compared with no intervention (5/32 (16%) versus 0/28 (0%)) (RR 5.40, 95% CI 0.69 to 42.32; 3 trials with 60 patients; I² = 0%) or with UDCA (2/32 (6%) versus 0/37 (0%)) (RR 6.19, 95% CI 0.31 to 122.05; 2 trials with 69 patients; I² = 0%). Bezafibrate significantly decreased the activity of serum alkaline phosphatases compared with no intervention (MD -186.04 U/L, 95% CI -249.03 to -123.04; 4 trials with 79 patients; I² = 34%) and when compared with UDCA (MD -162.90 U/L, 95% CI -199.68 to -126.12; 2 trials with 48 patients; I² = 0%). These results were supported by trial sequential analyses. Bezafibrate compared with no intervention significantly decreased plasma immunoglobulin M (MD -164.00 mg/dl, 95% CI -259.47 to -68.53; 3 trials with 50 patients; I² = 46%) and serum bilirubin concentration (MD -0.19 mg/dl, 95% CI -0.38 to -0.00; 2 trials with 34 patients; I² = 0%). However, the latter two results were not supported by trial sequential analyses. Bezafibrate compared with no intervention had no significant effect on the activity of serum gamma-glutamyltransferase (MD -1.22 U/L, 95% CI -11.97 to 9.52; 4 trials with 79 patients; I² = 42%) and serum alanine aminotransferase (MD -5.61 U/L, 95% CI -24.50 to 13.27; 2 trials with 35 patients; I² = 34%). Bezafibrate compared with UDCA had no significant effect on the activity of serum gamma-glutamyltransferase (MD 38.44 U/L, 95% CI -180.67 to 257.55; 2 trials with 49 patients; I² = 89%), serum alanine aminotransferase (MD -2.34 U/L, 95% CI -34.73 to 30.06; 2 trials with 49 patients; I² = 95%), and plasma immunoglobulin M concentration (MD -20.23 mg/dl, 95% CI -218.71 to 178.25; 2 trials with 41 patients; I² = 90%) in random-effects model meta-analyses, but bezafibrate significantly decreased the activity of serum gamma-glutamyltransferase (MD -58.18, 95% CI -76.49 to -39.88; 2 trials with 49 patients; I² = 89%), serum alanine aminotransferase (MD -13.94, 95% CI -18.78 to -9.09; 2 trials with 49 patients; I² = 95%), and plasma immunoglobulin M concentration (MD -99.90, 95% CI -130.72 to -69.07; 2 trials with 41 patients; I² = 90%) in fixed-effect model meta-analyses. One patient had bezafibrate withdrawn due to an adverse event compared to no intervention (RD 0.03, 95% CI -0.09 to 0.16; 2 trials with 60 patients; I² = 0%).

AUTHORS' CONCLUSIONS

This systematic review did not demonstrate any effect of bezafibrate versus no intervention on mortality, liver-related morbidity, adverse events, and pruritus in patients with primary biliary cirrhosis. Furthermore, we found no significant effects of bezafibrate on mortality, liver-related morbidity, or adverse events when compared with ursodeoxycholic acid, None of the trials assessed quality of life or fatigue. The data seem to indicate a possible positive intervention effect of bezafibrate on some liver biochemistry measures compared with the control group, but the observed effects could be due to systematic errors or random errors. We need more randomised clinical trials on the effects of bezafibrate on primary biliary cirrhosis with low risks of systematic errors and random errors.

Targeting the ABCB4 gene to control cholesterol homeostasis

INTRODUCTION

Multidrug resistance 3 (MDR3) P-glycoprotein is a lipid floppase that is encoded by the ATP-binding cassette sub-family B member 4 (ABCB4) gene and plays a crucial role in proper bile formation by transporting phosphatidylcholine across the canalicular plasma membrane of the hepatocyte into bile. The relevance of this function is underscored by the severe pathology that develops in patients with ABCB4 deficiency. This deficiency leads to the destruction of hepatocytes and cholangiocytes by bile salts, because their cytolytic action is not reduced by formation of mixed micelles with phospholipid.

AREAS COVERED

Evidence that phospholipid secretion into bile is also essential for biliary cholesterol secretion as cholesterol dissolves much better in mixed micelles of bile salts and phospholipid than in pure bile salt micelles. As a consequence, net biliary cholesterol secretion depends on the amount of phospholipid secreted and hence, the expression of ABCB4 indirectly determines biliary cholesterol output.

EXPERT OPINION

It can be argued that upregulation of the ABCB4 gene expression may not only be beneficial for liver pathology in patients with partial ABCB4 deficiency, but also for the prevention of gallstone formation and optimal cholesterol disposition in a much larger population.

The Multiple Facets of ABCB4 (MDR3) Deficiency

ABCB4 (MDR3), a lipid translocator, moves phosphatidylcholine from the inner to the outer leaflet of the canalicular membrane. Genetic mutations of ABCB4 lead to three distinct but related hepatobiliary diseases. Progressive familial intrahepatic cholestasis (PFIC) type 3 is a chronic cholestatic syndrome characterized by a markedly elevated gamma-glutamyltranspeptidase. Patients present with jaundice, pruritus, and hepatosplenomegaly. Periportal inflammation progresses to biliary cirrhosis and causes portal hypertension. Ursodeoxycholic acid (UDCA) normalizes liver function tests in approximately one half of treated PFIC type 3 patients. Partial responders or nonresponders eventually will require liver transplantation. Gallstone patients with ABCB4 mutations may have low phospholipid-associated cholelithiasis syndrome, characterized by cholesterol gallstones and intrahepatic microlithiasis, along with recurrent biliary symptoms, despite cholecystectomy. Patients with ABCB4 mutations also may develop intrahepatic brown pigment stones. UDCA may improve biliary symptoms even before the dissolution of stones occurs. Additional therapies such as farnesoid X receptor ligands/agonists and benzfibrates show future therapeutic promise. Intrahepatic cholestasis of pregnancy affects pregnant women with abnormal ABCB4. These women suffer from disabling pruritus and also may experience steatorrhea. Fetuses are at high risk for prematurity and stillbirths. The definitive treatment is delivery of the baby. In the interim, limited fat intake, fat-soluble vitamin supplementation, and UDCA with or without S-adenosylmethionine can provide symptomatic relief. Additional hepatobiliary diseases related to ABCB4 mutations are likely to be identified. This may result in the discovery of additional therapies for PFIC type 3, gallstones, and intrahepatic cholestasis of pregnancy.

Bezafibrate treatment of primary biliary cirrhosis following incomplete response to ursodeoxycholic acid

BACKGROUND AND GOALS

Ursodeoxycholic acid (UDCA) is the only current pharmacologic treatment for primary biliary cirrhosis (PBC). However, some patients show persistent liver biochemical abnormalities even after 6 to 12 months treatment. Bezafibrate retard is a commonly used medication for hyperlipidemia. In Japanese studies, it was found to lower liver enzyme levels, apparently through its action on multiple drug resistance gene 3, a transport element of the ATP-dependent bile secretion system, and on peroxisome proliferator-activated receptor-alpha. The aim of this study was to evaluate the effect of adding bezafibrate to the treatment regimen in patients with PBC and a partial response to UDCA.

STUDY

The study group included 8 White patients, 7 women and 1 man, aged 52 to 76 years with PBC who had been treated at our Liver Institute with UDCA (900 mg/d to 1500 mg/d) for 2 to 11 years (mean, 5.7 y) with only a partial response (19% to 56% reduction in alkaline phosphatase level). Bezafibrate (400 mg/d) was added to UDCA and the patients were followed for 4 to 12 months.

RESULTS

Alkaline phosphatase levels (normal range, 35 to 104 U/L) decreased in all patients, from 140 to 360 U/L (mean, 201.2) to 68 to 158 U/L (mean, 98.4), and normalized in 6 patients. In addition, levels of gamma-glutamyl transferase (normal range, 6 to 42 U/L) decreased from 70 to 192 U/L (mean, 130) to 41 to 122 U/L (mean, 71.8). These findings were maintained throughout follow-up.

CONCLUSIONS

Combination therapy with bezafibrate and UDCA improves the biochemical profile of patients with PBC who respond only partially to UDCA. A larger controlled study is needed to evaluate the clinical implications of these findings.

Fenofibrate in primary biliary cirrhosis: a pilot study

Background:

Most patients with primary biliary cirrhosis (PBC) are treated with ursodeoxycholic acid (UDCA); however, some do not respond fully. PBC is also associated with dyslipidemia, but a link with vascular risk has not been confirmed.

Methods and Results:

In this study we compared UDCA monotherapy with fenofibrate plus UDCA in PBC patients with incomplete biochemical response to UDCA monotherapy for ≥ 8 months. Ten patients (57.2±13.3 years old) with PBC and persistent elevations of liver enzymes after treatment with UDCA (600 mg/day) were randomized to continue UDCA (4 patients) or to receive micronized fenofibrate (200 mg/day) plus UDCA (6 patients) for 8 weeks. Significant reductions in total cholesterol, triglycerides and non-high density lipoprotein cholesterol were observed in the combination treatment group. The serum activities of alkaline phosphatase, gamma-glutamyl transpeptidase and alanine aminotranferase also decreased in this group compared with baseline (-32.6%; p=0.012, -44%; p=0.031 and -16.9%; p=0.029, respectively). In contrast, no significant alterations in liver enzymes or lipid profile were observed in patients who continued UDCA monotherapy. The changes in the lipid and enzyme variables differed significantly (p<0.03) between the 2 groups. Fenofibrate was well tolerated.

Conclusions:

The administration of fenofibrate plus UDCA seems to be safe and may improve lipid and liver indices in patients with PBC who do not respond fully to UDCA monotherapy. Whether the improved lipid profile translates into a decreased risk of vascular events remains to be established.

Nuclear receptors as drug targets in cholestasis and drug-induced hepatotoxicity

Nuclear receptors are key regulators of various processes including reproduction, development, and metabolism of xeno- and endobiotics such as bile acids and drugs. Research in the last two decades provided researchers and clinicians with a detailed understanding of the regulation of these processes and, most importantly, also prompted the development of novel drugs specifically targeting nuclear receptors for the treatment of a variety of diseases. Some nuclear receptor agonists are already used in daily clinical practice but many more are currently designed or tested for the treatment of diabetes, dyslipidemia, fatty liver disease, cancer, drug hepatotoxicity and cholestasis. The hydrophilic bile acid ursodeoxycholic acid is currently the only available drug to treat cholestasis but its efficacy is limited. Therefore, development of novel treatments represents a major goal for both pharmaceutical industry and academic researchers. Targeting nuclear receptors in cholestasis is an intriguing approach since these receptors are critically involved in regulation of bile acid homeostasis. This review will discuss the general role of nuclear receptors in regulation of transporters and other enzymes maintaining bile acid homeostasis and will review the role of individual receptors as therapeutic targets. In addition, the central role of nuclear receptors and other transcription factors such as the aryl hydrocarbon receptor (AhR) and the nuclear factor-E2-related factor (Nrf2) in mediating drug disposition and their potential therapeutic role in drug-induced liver disease will be covered.

Liver disease associated with canalicular transport defects: current and future therapies

Bile formation at the canalicular membrane is a delicate process. This is illustrated by inherited liver diseases due to mutations in ATP8B1, ABCB11, ABCB4, ABCC2 and ABCG5/8, all encoding hepatocanalicular transporters. Effective treatment of these canalicular transport defects is a clinical and scientific challenge that is still ongoing. Current evidence indicates that ursodeoxycholic acid (UDCA) can be effective in selected patients with PFIC3 (ABCB4 deficiency), while rifampicin reduces pruritus in patients with PFIC1 (ATP8B1 deficiency) and PFIC2 (ABCB11 deficiency), and might abort cholestatic episodes in BRIC (mild ATP8B1 or ABCB11 deficiency). Cholestyramine is essential in the treatment of sitosterolemia (ABCG5/8 deficiency). Most patients with PFIC1 and PFIC2 will benefit from partial biliary drainage. Nevertheless liver transplantation is needed in a substantial proportion of these patients, as it is in PFIC3 patients. New developments in the treatment of canalicular transport defects by using nuclear receptors as a target, enhancing the expression of the mutated transporter protein by employing chaperones, or by mutation specific therapy show substantial promise. This review will focus on the therapy that is currently available as well as on those developments that are likely to influence clinical practice in the near future.

Receptor for activated C-kinase 1 regulates the cellular localization and function of ABCB4

AIM

Multidrug resistance protein 3 (MDR3/ABCB4), located on the bile canalicular membrane of hepatocytes, is responsible for the translocation of phosphatidylcholine across the plasma membrane, and its hereditary defect causes liver disorders, such as progressive familial intrahepatic cholestasis type 3. We aimed to identify the proteins responsible for the surface expression of human ABCB4.

METHODS

We performed yeast two-hybrid screening with the cytoplasmic linker region of ABCB4 against a human liver cDNA library. This screening allowed us to identify the receptor for activated C-kinase 1 (RACK1) as a novel binding partner of ABCB4. The association of RACK1 with the linker region of ABCB4 was further confirmed by GST-pulldown assay, although we could not find out the interaction of full length of ABCB4 and RACK1 in co-immunoprecipitation assay in HeLa cells.

RESULTS

Down-regulation of endogenous RACK1 expression by siRNA in HeLa cells resulted in the localization of ABCB4 in the cytosolic compartment as well as reduced protein expression of ABCB4, although mRNA expression and the protein stability of ABCB4 were not affected by the suppression of endogenous RACK1. Similar alterations in cellular localization of ABCB4 were also found by suppressing endogenous RACK1 expression in HepG2 cells. Consequently, ABCB4-mediated phosphatidylcholine translocation activity was significantly reduced when endogenous RACK1 expression was suppressed in HeLa cells. In contrast, the membrane surface localization and the protein expression of ABCB1 were not affected by the suppression of endogenous RACK1 expression.

CONCLUSION

These results suggest that RACK1 may have a functional significance as a regulatory cofactor of ABCB4 and is indispensable for the plasma membrane localization and translocation function of ABCB4.

A human hepatocyte-bearing mouse: an animal model to predict drug metabolism and effectiveness in humans

Preclinical studies to predict the efficacy and safety of drugs have conventionally been conducted almost exclusively in mice and rats as rodents, despite the differences in drug metabolism between humans and rodents. Furthermore, human (h) viruses such as hepatitis viruses do not infect the rodent liver. A mouse bearing a liver in which the hepatocytes have been largely repopulated with h-hepatocytes would overcome some of these disadvantages. We have established a practical, efficient, and large-scale production system for such mice. Accumulated evidence has demonstrated that these hepatocyte-humanized mice are a useful and reliable animal model, exhibiting h-type responses in a series of in vivo drug processing (adsorption, distribution, metabolism, excretion) experiments and in the infection and propagation of hepatic viruses. In this review, we present the current status of studies on chimeric mice and describe their usefulness in the study of peroxisome proliferator-activated receptors.

The state of cholesterol metabolism in the liver of patients with primary biliary cirrhosis: the role of MDR3 expression

AIM

Because dyslipidemia, such as hypercholesterolemia, is a characteristic of primary biliary cirrhosis (PBC), hepatic lipid metabolism may be disturbed in PBC patients. We examined the expression of lipid metabolism-associated genes in PBC liver.

METHODS

All of the patients examined were in stage I or II PBC and without medication. RNA was isolated from liver specimens by needle biopsies of PBC patients and controls. The expression levels of various genes were measured by real-time RT-PCR. Multidrug resistance 3 (MDR3) expression was examined immunohistochemically. Statistical correlations between the gene expression levels and indices of blood testing were calculated.

RESULTS

The expression levels of sterol regulatory element-binding protein (SREBP) 2 and LDL receptor were significantly lower, and those of apolipoprotein B, microsomal triglyceride transfer protein, ATP-binding cassette G5, and liver X receptor α (LXRα) were significantly higher in the PBC liver than in the normal control liver. The expression levels of bile acid synthesis- and excretion-associated genes did not change, and those of farnesoid X receptor, peroxisome proliferator-activated receptor α, and SREBP-1c were similar between the PBC and normal liver. MDR3 gene expression levels in the PBC liver were more than 4-fold higher than those in the control liver. Immunohistochemically, strong canalicular staining for MDR3 was observed in the PBC liver. LXRα expression was positively correlated with MDR3 levels. Serum levels of γ-glutamyl transpeptidase (GGT) and IgM were negatively correlated with MDR3 levels.

CONCLUSIONS

Hepatocellular cholesterol metabolism was at least partially disturbed, even in the early stage of PBC. The most characteristic finding was a distinct elevation of MDR3 expression, and the MDR3 levels were negatively correlated with GGT and IgM levels.

Nuclear receptors as therapeutic targets in cholestatic liver diseases

Cholestasis results in intrahepatic accumulation of cytotoxic bile acids, which cause liver damage ultimately leading to biliary fibrosis and cirrhosis. Cholestatic liver injury is counteracted by a variety of adaptive hepatoprotective mechanisms including alterations in bile acid transport, synthesis and detoxification. The underlying molecular mechanisms are mediated mainly at a transcriptional level via a complex network involving nuclear receptors including the farnesoid X receptor, pregnane X receptor, vitamin D receptor and constitutive androstane receptor, which target overlapping, although not identical, sets of genes. Because the intrinsic adaptive response to bile acids cannot fully prevent liver injury in cholestasis, therapeutic targeting of these receptors via specific and potent agonists may further enhance the hepatic defence against toxic bile acids. Activation of these receptors results in repression of bile acid synthesis, induction of phases I and II bile acid hydroxylation and conjugation and stimulation of alternative bile acid export while limiting hepatocellular bile acid import. Furthermore, the use of nuclear receptor ligands may not only influence bile acid transport and metabolism but may also directly target hepatic fibrogenesis and inflammation. Many drugs already used to treat cholestasis and its complications such as pruritus (e.g. ursodeoxycholic acid, rifampicin, fibrates) may act via activation of nuclear receptors. More specific and potent nuclear receptor ligands are currently being developed. This article will review the current knowledge on nuclear receptors and their potential role in the treatment of cholestatic liver diseases.

Endogenous bile salts are associated with bile duct injury in the rat liver transplantation model

BACKGROUND

Nonanastomotic biliary strictures are a serious complication after orthotopic liver transplantation (OLT) and are difficult to cure. We examined the role of endogenous bile salt toxicity in the pathogenesis of bile duct injury after OLT.

MATERIALS AND METHODS

A total of 90 Sprague-Dawley rats were divided into three groups: Sham-operated group (Sham, n=30), OLT group with 1 hr donor liver preservation (OLT-1h, n=30), and OLT group with 12 hr donor liver preservation (OLT-12h, n=30). Bile was collected and analyzed biochemically. The histopathologic study was performed to determine the intrahepatic bile duct morphologic changes. Hepatic expressions of bile transporters Ntcp, Bsep, Mdr2, and Oatps were detected.

RESULTS

During the first 2 weeks after transplantation, bile salt secretion was not parallel with phospholipid secretion, resulting in high biliary bile salt-to-phospholipid (BS:PL) ratio. The expression of bile transporters was consistent with the change of bile composition. Bile duct injury correlated significantly with bile salt secretion and BS:PL ratio. Moreover, OLT group with longer donor liver preservation time (OLT-12h) had significantly lower Mdr2 messenger RNA/protein level, higher BS:PL ratio, and better correlation between BS:PL ratio and bile duct injury compared with those of OLT-1h.

CONCLUSIONS

The unparallel secretion of bile salts and phospholipids results in cytotoxic bile formation with high BS:PL ratio after liver transplantation. Longer donor liver preservation time will increase graft bile cytotoxicity. The results of this study suggest that endogenous bile salts play a role in the pathogenesis of bile duct injury after OLT.

Alteration of canalicular transporters in a mouse model of total parenteral nutrition

OBJECTIVES

Parenteral nutrition-associated liver disease (PNALD) is a major problem with prolonged total parenteral nutrition (TPN) administration. Our laboratory previously demonstrated significant changes in the expression of multidrug resistance genes (MDRs) 1 and 2, hepatocyte transporters, in a TPN mouse model. The present study hypothesized that these changes would lead to functional changes in the liver, and would contribute to the development of liver dysfunction.

MATERIALS AND METHODS

Mice received either intravenous saline and standard chow or TPN with or without intravenous lipids. Functional assays were performed after 7 days of infusion.

RESULTS

TPN with lipids led to a significant increase in serum bile acid levels, consistent with an early state of PNALD. Use of TPN without lipids prevented an elevation in bile acid levels. In both TPN groups, MDR2 expression was significantly (68%) lower than controls and bile phosphatidylcholine content, a functional measure of MDR2, was 40% less than controls. MDR1 expression in the TPN with lipid group was 31% higher than controls, whereas in the TPN without lipids mice there was no significant change. Hepatocyte extrusion of rhodamine dye, a measure of MDR1 function, declined only in the TPN with lipid group. Peroxisome proliferator-activated receptor-alpha expression decreased in both TPN groups. Fenofibrate given with TPN resulted in an increased expression of MDR1 and MDR2, and functionally increased hepatocyte rhodamine extrusion and presence of bile phosphatidylcholine in the TPN with lipid group.

CONCLUSIONS

The study shows that TPN led to alterations in the function of MDR1- and MDR2-expressed proteins. The changes help in the understanding of the mechanisms leading to PNALD, and suggest that fibrate administration may palliate these changes.

Therapeutic effects of fibrates in postprandial lipemia

Hypertriglyceridemia is observed in many metabolic diseases such as the metabolic syndrome, diabetes mellitus, or mixed dyslipidemia frequently leading to premature coronary heart disease (CHD). Additionally, several studies have shown that postprandial hypertriglyceridemia is pronounced in patients with CHD, metabolic syndrome, hypertension, and other pathologic conditions. The triglyceride-rich lipoprotein remnants accumulating in the postprandial state seem to be involved in atherogenesis and in events leading to thrombosis. Since abnormal postprandial lipemia is associated with pathologic conditions, its treatment is of clinical importance.Fibrates are of significant help in managing hypertriglyceridemia. This review summarizes the effect of fibric acid derivatives on postprandial lipemia. Fibrates decrease the production of and enhance the catabolism of triglyceride-rich lipoproteins through the activation of peroxisome proliferator-activated receptor-alpha. Results of clinical studies with fibrates have confirmed their action in decreasing postprandial triglyceride levels by increasing lipoprotein lipase activity, decreasing apolipoprotein CIII production, and by increasing fatty acid oxidation in the liver.It is concluded that fibrates are effective agents in lowering the postprandial increase in remnant lipoprotein particles and retinyl palmitate. Furthermore, fibrates can also affect the postprandial lipid profile by increasing hepatic lipase levels and in some cases, by reducing cholesterol ester transfer protein activity. The main target of fibrate therapy is to improve fasting hypertriglyceridemia, which is an essential component associated with improving postprandial lipemia. Fibrates are well tolerated by patients and adverse effects have been reported rarely after their administration.

Effects of bezafibrate on dyslipidemia with cholestasis in children with familial intrahepatic cholestasis-1 deficiency manifesting progressive familial intrahepatic cholestasis

No appropriate pharmaceutical therapy has been established for dyslipidemia with cholestasis in progressive familial intrahepatic cholestasis (PFIC)-1. We evaluated the efficacy of bezafibrate in PFIC-1. We monitored the clinical presentation and lipoprotein metabolism of 3 patients, aged 3, 4, and 8 years, with FIC1 deficiency, manifesting PFIC-1, over 12 months of bezafibrate therapy. Pruritus was substantially alleviated in the 3 patients after initiation of bezafibrate. Cholestasis was alleviated in 2 of them. Serum high-density lipoprotein cholesterol and low-density lipoprotein cholesterol increased 1.6- to 2.0-fold and 1.1- to 1.2-fold, respectively; but the values remained low and normal, respectively. Serum lipoprotein X, which was at normal levels before treatment, was elevated to levels above the upper limit of the reference range. High serum triglyceride levels decreased by 15% to 30%, to normal levels, after treatment initiation. The activities of lipoprotein lipase and hepatic triglyceride lipase were increased, but those of high-density lipoprotein regulators remained unchanged. Liver expression of multidrug resistance protein-3, which regulates lipoprotein X synthesis, was enhanced by bezafibrate therapy. Bezafibrate treatment favorably affected pruritus, dyslipidemia, and cholestasis in PFIC-1.

Tissue distribution, gender-divergent expression, ontogeny, and chemical induction of multidrug resistance transporter genes (Mdr1a, Mdr1b, Mdr2) in mice

Multidrug resistance (Mdr) transporters are ATP-binding cassette transporters that efflux amphipathic cations from cells and protect tissues from xenobiotics. Unfortunately, Mdr transporters also efflux anticancer drugs from some tumor cells, resulting in multidrug resistance. There are two groups of Mdrs in mice: group I includes Mdr1a and Mdr1b that transport xenobiotics, whereas group II is Mdr2, a flipase that facilitates phospholipid excretion into bile. Little is known about the regulation of Mdr genes in vivo. The purpose of this study was to determine tissue distribution, gender differences, ontogeny, and chemical induction of Mdrs in mice. The mRNA of Mdr1a is highest in gastrointestinal tract, Mdr1b in ovary and placenta, and Mdr2 in liver. Both Mdr1a and Mdr1b in kidney show female-predominant expression patterns due to repression by androgens. The ontogeny of mouse Mdr1a in duodenum and brain as well as Mdr1b in brain, kidney, and liver all share a similar developmental pattern: low expression at birth, followed by a gradual increase to mature levels at approximately 30 days of age. In contrast, Mdr2 mRNA in liver is markedly up-regulated at birth, which returns to low levels by 5 days of age and then gradually increases to mature levels. None of the Mdrs in liver are readily inducible by any class of microsomal enzyme inducers. In conclusion, the three Mdr transporters in mice are expressed in a tissue-specific and age-dependent pattern, there are gender differences in expression, and Mdr transporters are inducible by only a few microsomal enzyme inducers.

Bezafibrate prevents hepatic stellate cell activation and fibrogenesis in a murine steatohepatitis model, and suppresses fibrogenic response induced by transforming growth factor-beta1 in a cultured stellate cell line

AIM

The aim of this study was to investigate the preventive actions of bezafibrate against non-alcoholic steatohepatitis (NASH), the activation of hepatic stellate cells (HSC), and fibrogenesis by using a model of NASH and an in vitro model.

METHODS

Male KK-A(y)/TaJcl (KK-A(y)) mice were fed a methionine and choline-deficient (MCD) diet or a MCD diet containing bezafibrate or pioglitazone for 7 weeks, after which biochemical parameters, pathological changes, and hepatic mRNA levels were assessed. An in vitro HSC model was designed by using a previously described RI-T cell line stimulated by transforming growth factor-beta1 (TGF-beta1).

RESULTS

MCD diet-fed KK-A(y) mice developed hepatic steatosis, oxidative stress, inflammation, and hepatic fibrosis. Bezafibrate markedly decreased the hepatic content of triglyceride accumulation of fatty droplets within hepatocytes, and increased the expression of hepatic fatty acid beta-oxidative genes in MCD diet-fed KK-A(y) mice. Bezafibrate markedly inhibited the increases in the plasma alanine aminotransferase level and hepatic content of thiobarbituric acid-reactive substances in this model. Moreover, it dramatically reduced hepatic inflammatory changes and fibrosis concomitantly with marked reductions in the mRNA levels for inflammatory cytokine, chemokine, and profibrogenic genes. Importantly, both bezafibrate and pioglitazone markedly reduced the mRNA levels of profibrogenic and fibrogenic genes in TGF-beta1-stimulated cells.

CONCLUSION

Bezafibrate improved hepatic steatosis and potently prevented inflammation, oxidative stress, HSC activation, and fibrogenesis in the liver. Moreover, this study was the first to demonstrate that bezafibrate directly inhibits hepatic fibrogenic response induced by TGF-beta1 in vitro. Hence bezafibrate may be a new therapeutic strategy against NASH and hepatic fibrosis.

The role of bile salt toxicity in the pathogenesis of bile duct injury after non-heart-beating porcine liver transplantation

BACKGROUND

Intrahepatic bile duct strictures are a serious complication after non-heart-beating (NHB) liver transplantation. Bile salt toxicity has been identified as an important factor in the pathogenesis of bile duct injury and cholangiopathies. The role of bile salt toxicity in the development of biliary strictures after NHB liver transplantation is unclear.

METHODS

In a porcine model of NHB liver transplantation, we studied the effect of different periods of warm ischemia in the donor on bile composition and subsequent bile duct injury after transplantation. After induction of cardiac arrest in the donor, liver procurement was delayed for 0 min (group A), 15 min (group B), or more or equal to 30 min (group C). Livers were subsequently transplanted after 4 hr of cold preservation. In the recipients, bile flow was measured, and bile samples were collected daily to determine the bile salt-to-phospholipid ratio. Severity of bile duct injury was semiquantified by using a histologic grading scale.

RESULTS

Posttransplantation survival was directly related to the duration of warm ischemia in the donor. The bile salt-to-phospholipid ratio in bile produced early after transplantation was significantly higher in group C, compared with group A and B. Histopathologic condition showed the highest degree of bile duct injury in group C.

CONCLUSION

Prolonged warm ischemia in NHB donors is associated with the formation of toxic bile after transplantation, with a high biliary bile salt-to-phospholipid ratio. These data suggest that bile salt toxicity contributes to the pathogenesis of bile duct injury after NHB liver transplantation.

The efficacy of ursodeoxycholic acid and bezafibrate combination therapy for primary biliary cirrhosis: A prospective, multicenter study

AIM

Treatment with ursodeoxycholic acid (UDCA) improves the survival of stage I and II primary biliary cirrhosis (PBC) patients. However, new therapeutic options are needed for patients who are refractory to UDCA and for those whose disease is at an advanced stage. Bezafibrate could be useful in PBC treatment, since it increases phospholipid output into the bile and reduces the cytotoxicity of hydrophobic bile acids, which are increased with cholestasis.

METHODS

We conducted two prospective, multicenter randomized open studies in non-cirrhotic patients with PBC to evaluate the efficacy of bezafibrate. One study compared UDCA and bezafibrate monotherapy (study 1: 45 patients [37 females], mean age 55.9 years), and the other evaluated the addition of bezafibrate to patients who were refractory to UDCA (study 2: 21 patients [18 females], mean age 54.1 years).

RESULTS

Study 1 demonstrated that bezafibrate monotherapy was as effective as UDCA and study 2 revealed that bezafibrate combined with UDCA was effective in improving and maintaining biliary enzymes where the ineffectiveness of long-term treatment with UDCA was confirmed.

CONCLUSION

This multicenter, randomized, open study revealed that combination therapy of bezafibrate and UDCA improved biliary enzymes in non-cirrhotic Japanese patients with PBC refractory to UDCA. Further studies are needed to evaluate whether combination therapy improves histological staging and prognosis.

Dearterialization of the liver causes intrahepatic cholestasis due to reduced bile transporter expression

BACKGROUND

Bile duct injury after hepatic artery thrombosis (HAT) in liver transplantation is believed to be caused by ischemia predominantly. We aimed to define the involvement of bile secretory dysfunction in the pathogenesis of liver injury after HAT.

METHODS

In a murine model, the main hepatic artery, the extrahepatic peribiliary plexus, or both arterial connections to the liver were interrupted (n=5 for each group). After 1, 14, or 28 days, hepatobiliary function was assessed by analysis of bile transporter expression, serum bile acids and bilirubin, and hepatic ATP content. In addition, cellular injury was assessed by light microscopy and biochemical markers.

RESULTS

There were no signs of hepatobiliary dysfunction or injury in sham-operated animals or in mice with interruption of the hepatic artery or the extrahepatic peribiliary plexus alone. However, as early as 24 hr after complete dearterialization, bile transporter expression was significantly reduced and intrahepatic cholestasis started to progress the following weeks. Histologic studies at 28 days after complete dearterialization showed severe hepatobiliary injury.

CONCLUSIONS

This study indicates that arterial blood supply is critical for normal bile secretion. Bile duct injury after complete arterial deprivation is preceded by a loss of bile secretory function and subsequent intrahepatic cholestasis.

Identification of negative transcriptional factor E4BP4-binding site in the mouse circadian-regulated gene Mdr2

The hepatic transporter Mdr2 is an ATP-binding cassette transporter which excretes phosphatidylcholine into the bile. We showed that the level of Mdr2 mRNA oscillated in circadian fashion in mouse liver whereas such oscillation was dampened in the liver of Clock mutants. To examine transcriptional regulation of the Mdr2 gene we performed luciferase reporter assays using plasmid constructs containing the 5'-flanking region of the Mdr2 gene. Reporter assays using deletion constructs demonstrated that E4BP4 represses the transcriptional activity of the promoter including the D1 and D2 sites within four putative E4BP4-binding sites. Chromatin immunoprecipitation and gel shift assays showed that E4BP4 binds to the D2 site, but not to the D1 site. These data suggested that E4BP4 is a negative transcription factor for circadian Mdr2 mRNA expression.

Fenofibrate reduces intestinal cholesterol absorption via PPARalpha-dependent modulation of NPC1L1 expression in mouse

Fibrates, including fenofibrate, exert their biological effects by binding peroxisome proliferator-activated receptor alpha (PPARalpha), a member of the nuclear receptor superfamily of ligand-activated transcription factors. Treatment with PPARalpha agonists enhances fatty acid oxidation, decreases plasma triglycerides, and may promote reverse cholesterol transport. In addition, fibrate administration can reduce intestinal cholesterol absorption in patients, although the molecular mechanism for this effect is unknown. Because Niemann-Pick C1-Like 1 (NPC1L1) is already known to be a critical protein for cholesterol absorption, we hypothesized that fenofibrate might modulate NPC1L1 expression to alter intestinal cholesterol transport. Here, we find that fenofibrate-treated wild-type mice have decreased fractional cholesterol absorption (35-47% decrease) and increased fecal neutral sterol excretion (51-83% increase), which correspond to decreased expression of NPC1L1 mRNA and protein (38-66% decrease) in the proximal small intestine. These effects of fenofibrate are dependent on PPARalpha, as Ppar alpha-knockout mice fail to respond like wild-type littermates. Fenofibrate affects the ezetimibe-sensitive pathway and retains the ability to decrease cholesterol absorption and NPC1L1 mRNA expression in chow-fed liver X receptor alpha/beta-double-knockout mice and high-cholesterol- or cholic acid-fed wild-type mice. These data demonstrate that fenofibrate specifically acts via PPARalpha to decrease cholesterol absorption at the level of intestinal NPC1L1 expression.