Pharmacotherapy of cholestatic liver diseases

New insights into the molecular mechanisms of bile formation and cholestasis have provided new concepts for pharmacotherapy of cholestatic liver diseases. The major aim in all forms of cholestasis is the reduction of hepatocellular retention of bile acids and other potentially toxic constituents of bile. Reduction of hepatocellular retention may be achieved by drugs that stimulate hepatocellular secretion via the canalicular route into the bile or via the alternative route across the basolateral membrane into the blood, and by drugs that stimulate the hepatocellular metabolism of hydrophobic bile acids to hydrophilic, less toxic metabolites. In cholestatic liver diseases that start with an injury of the biliary epithelium (e.g., primary biliary cirrhosis; PBC), protection of the cholangiocytes against the toxic effects of hydrophobic bile acids is most important. When hepatocellular retention of bile acids has occurred, the inhibition of bile acid-induced apoptosis becomes another target of therapy. Ursodeoxycholic acid protects the biliary epithelium by reducing the toxicity of bile, stimulates hepatobiliary secretion by upregulating transporters and inhibits apoptosis. It is the mainstay of therapy in PBC but of benefit also in a number of other cholestatic liver diseases. New drugs such as 6-ethyl-chenodeoxycholic acid and 24-nor-ursodeoxycholic acid are being evaluated for the treatment of cholestatic liver diseases.     

Genetic cholestasis: lessons from the molecular physiology of bile formation.

Progressive familial intrahepatic cholestasis (PFIC) is a group of severe genetic cholestatic liver diseases of early life. PFIC types 1 and 2 are characterized by cholestasis and a low to normal serum gamma-glutamyltransferase (GGT) activity, whereas in PFIC type 3, the serum GGT activity is elevated. PFIC types 1 and 2 occur due to mutations in loci at chromosome 18 and chromosome 2, respectively. The pathophysiology of PFIC type 1 is not well understood. PFIC types 2 and 3 are caused by transport defects in the liver affecting the hepatobiliary secretion of bile acids and phospholipids, respectively. Benign recurrent intrahepatic cholestasis (BRIC) is linked to a mutation in the same familial intrahepatic cholestasis 1 locus at chromosome 18. Defects of bile acid synthesis may be difficult to differentiate from these transport defects. Intrahepatic cholestasis of pregnancy (ICP) appears to be related to these cholestatic diseases. For example, heterozygosity in families with PFIC type 3 is associated with ICP, but ICP has also been reported in families with BRIC. In Dubin-Johnson syndrome there is no cholestasis; only the hepatobiliary transport of conjugated bilirubin is affected. This, therefore, is a mild disease, and patients have a normal lifespan.     

Cholestatic liver diseases: slow progress in understanding and treating slowly progressive disorders

BACKGROUND: Cholestatic liver diseases are characterized by failure of normal amounts of physiological bile to reach the gastrointestinal tract. Any interference with normal bile flow from the canalicular membrane of the hepatocyte to the distal common bile duct may result in cholestasis. METHODS: Literature review. RESULTS: In primary biliary cirrhosis (PBC), the small intrahepatic bile ducts are destructed, resulting in obstruction of intrahepatic bile flow, whereas extrahepatic and/or intrahepatic biliary strictures block the passage of bile towards the intestine in primary sclerosing cholangitis (PSC). In contrast, the biliary tree is morphologically unaffected in less common cholestatic liver diseases as benign recurrent intrahepatic cholestasis (BRIC) and progressive familiar intrahepatic cholestasis (PFIC1-4). Genetic defects in hepatic canalicular transport mechanisms and bile salt synthesis deficiencies seem to underlie these types of cholestatic disorders. CONCLUSION: Recent advances in understanding and treatment of cholestatic liver diseases may help in better diagnosing and treating the various conditions characterized by cholestasis.     

Bile salt independent flow during bile salt‐induced choleresis and cholestasis in the rat: role of biliary thiol secretion

Abstract: Aims/Background: Previous studies have shown that the generation of the so‐called “bile salt‐independent flow” (BSIF) may be partly dependent on the hepatic availability and rate of canalicular secretion of osmotically active substances such as glutathione (GSH) and derived thiols. This study examined the role of common bile salts (BS) on the BSIF formation under both choleretic and cholestatic conditions, and on the relationship of the BSIF to the biliary thiol secretion. Methods: Experiments were carried out in adult male Sprague‐Dawley rats both in situ in the isolated perfused rat liver and in vivo. The effect of choleretic and cholestatic doses of BS on the biliary BS secretion rate (BSSR), BS‐dependent flow (BSDF), and BSIF was evaluated. Results: In the perfused rat liver, the infusion of low and physiological doses of taurocholic acid stimulated the biliary BSSR, BSDF, and BSIF. This was associated with increased biliary thiol secretion and thiol‐dependent bile flow. In vivo administration of taurocholic acid, taurochenodeoxycholic acid or taurolithocholic acid in step‐wise increasing doses leading to cholestasis showed that the onset of cholestasis was not accompanied by a significant decline in the BSSR or BSDF but rather by a marked inhibition of the apparent BSIF. During cholestasis, the three BS produced a significant reduction of biliary thiol secretion, with a marked decrease in thiol‐dependent bile flow sufficient to account for a major proportion of BSIF inhibition. This decline in thiol secretion occurred before the drop in biliary BS secretion and was more pronounced than the reduction in BS output. No change in hepatic thiol content was observed. Administration of free or glyco‐conjugated BS also resulted in a significant decrease of BSIF during the cholestatic period, suggesting a common role for BSIF inhibition in BS‐induced cholestasis. Conclusion: The changes in bile flow during BS‐induced choleresis and cholestasis are mediated by changes in the portion of the BSIF regulated by the thiol secretion.     

Partial Internal Biliary Diversion: A Solution for Intractable Pruritus in Progressive Familial Intrahepatic Cholestasis Type 1

Biliary diversion offers a potential option for intractable pruritus in children with chronic cholestatic disorders. Progressive familial intrahepatic cholestasis (PFIC) is an inherited disorder of impaired bile acid transport and excretion, which presents with jaundice and pruritus in the first few months of life and progresses to cirrhosis by infancy or adolescence. We report a child with PFIC type 1 who underwent internal biliary diversion for intractable pruritus and was relieved of his symptoms.     

Medical treatment of cholestatic liver diseases： From pathobiology to pharmacological targets

Bile secretion is dependent on the coordinated functions of a number of hepatobiliary transport systems. Cholestasis may be caused by an impairment of bile secretion, an obstruction of bile flow or a combination of the two. The common consequence of all forms of cholestasis is retention of bile acids and other potentially toxic compounds in the hepatocytes leading to apoptosis or necrosis of hepatocytes and eventually to chronic cholestatic liver disease. In certain cholestatic disorders there is also leakage of bile acids into the peribiliary space causing portal inflammation and fibrosis. The following pharmacological targets for treatment of intrahepatic cholestasis can be identified: stimulation of orthograde biliary secretion and retrograde secretion of bile acids and other toxic cholephils into the systemic circulation for excretion via the kidneys to reduce their retention in the hepatocytes; stimulation of the metabolism of hydrophobic bile acids and other toxic compounds to more hydrophilic, less toxic metabolites; protection of injured cholangiocytes against toxic effects of bile; inhibition of apoptosis caused by elevated levels of cytotoxic bile acids; inhibition of fibrosis caused by leakage of bile acids into the peribiliary space. The clinical results of ursodeoxcholic acid therapy of primary biliary cirrhosis may be regarded as the first success of this strategy.     

Targeted inactivation of sister of P-glycoprotein gene (spgp) in mice results in nonprogressive but persistent intrahepatic cholestasis

Mutations in the sister of P-glycoprotein (Spgp) or bile salt export pump (BSEP) are associated with Progressive Familial Intrahepatic Cholestasis (PFIC2). Spgp is predominantly expressed in the canalicular membranes of liver. Consistent with in vitro evidence demonstrating the involvement of Spgp in bile salt transport, PFIC2 patients secrete less than 1% of biliary bile salts compared with normal infants. The disease rapidly progresses to hepatic failure requiring liver transplantation before adolescence. In this study, we show that the knockout of spgp gene in mice results in intrahepatic cholestasis, but with significantly less severity than PFIC2 in humans. Some unexpected characteristics are observed. Notably, although the secretion of cholic acid in mutant mice is greatly reduced (6% of wild-type), total bile salt output in mutant mice is about 30% of wild-type. Also, secretion of an unexpectedly large amount of tetra-hydroxylated bile acids (not detected in wild-type) is observed. These results suggest that hydroxylation and an alternative canalicular transport mechanism for bile acids compensate for the absence of Spgp function and protect the mutant mice from severe cholestatic damage. In addition, the spgp(-/-) mice display a significant increase in the secretion of cholesterol and phospholipids into the bile. This latter observation in spgp(-/-) mice suggests that intrahepatic, rather than intracanalicular, bile salts are the major driving force for the biliary lipid secretion. The spgp(-/-) mice thus provide a unique model for gaining new insights into therapeutic intervention for intrahepatic cholestasis and understanding mechanisms associated with lipid homeostasis.     

Bile salts and cholestasis

Bile salts have a crucial role in hepatobiliary and intestinal homeostasis and digestion. Primary bile salts are synthesized by the liver from cholesterol, and may be modified by the intestinal flora to form secondary and tertiary bile salts. Bile salts are efficiently reabsorbed from the intestinal lumen to undergo enterohepatic circulation. In addition to their function as a surfactant involved in the absorption of dietary lipids and fat-soluble vitamins bile salts are potent signaling molecules in both the liver and intestine.Under physiological conditions the bile salt pool is tightly regulated, but the adaptive capacity may fall short under cholestatic conditions. Elevated serum and tissue levels of potentially toxic hydrophobic bile salts during cholestasis may cause mitochondrial damage, apoptosis or necrosis in susceptible cell types.Therapeutic nontoxic bile salts may restore impaired hepatobiliary secretion in cholestatic disorders. The hydrophilic bile salt ursodeoxycholate is today regarded as the effective standard treatment of primary biliary cirrhosis and intrahepatic cholestasis of pregnancy, and is implicated for use in various other cholestatic conditions. Novel therapeutic bile salts that are currently under evaluation may also prove valuable in the treatment of these diseases.     

Biliary diversion for progressive familial intrahepatic cholestasis: improved liver morphology and bile acid profile

BACKGROUND AND AIMS: Progressive familial intrahepatic cholestasis (PFIC) is characterized by pruritus, intrahepatic cholestasis, low serum gamma-glutamyltransferase levels, and characteristic "Byler bile" on electron microscopy. Many patients require liver transplantation, but partial external biliary diversion (PEBD) has shown therapeutic promise. However, the effect of PEBD on liver morphology and bile composition has not been evaluated. METHODS: We reviewed liver biopsy specimens from 3 children with low gamma-glutamyltransferase PFIC before and after PEBD. Follow-up liver biopsies were performed 9-60 months after PEBD. Light and electron microscopic features were scored blindly. Biliary bile acid composition was analyzed by gas chromatography-mass spectrometry before and after PEBD in 1 patient and after PEBD in 2 patients. RESULTS: Following PEBD, all patients improved clinically. Preoperative biopsy specimens showed characteristic features of PFIC, including portal fibrosis, chronic inflammation, cholestasis, giant cell transformation, and central venous mural sclerosis. Ultrastructural findings included coarse, granular canalicular Byler bile, effaced canalicular microvilli, and proliferative pericanalicular microfilaments. Following diversion, histology showed almost complete resolution of cholestasis, portal fibrosis, and inflammation with resolution of ultrastructural abnormalities. Biliary bile acids before PEBD consisted predominantly of cholic acid. After PEBD, the proportion of chenodeoxycholic acid increased significantly in 1 patient and was above the PFIC range in a second patient. CONCLUSIONS: The resolution of hepatic morphologic abnormalities following PEBD supports PEBD as an effective therapy for PFIC. The improved biliary bile acid composition suggests enhanced bile acid secretion after PEBD, perhaps by induction of alternative canalicular transport proteins.     

Downregulation of ileal bile acid absorption in bile-duct-ligated rats

BACKGROUND/AIMS: Accumulation of toxic bile acids in cholestasis contributes to liver injury and depends on their synthesis, secretion and intestinal absorption. In the present study, we investigated the effect of cholestasis on the active ileal absorption of bile acids in vivo and the adaptation of transporters involved in ileal bile acid absorption. METHODS: Male Wistar rats underwent ligation of the common bile duct or biliary diversion. Sham-operated rats served as controls. Active ileal bile acid absorption of taurocholate was measured by an intestinal perfusion technique. Transporter mRNA levels of the Na+/bile acid cotransporting protein (IBAT), ileal lipid binding protein (ILBP) and organic anion transporter subtype 3 (Oatp3) and protein expression of IBAT and ILBP were determined in the distal ileum. RESULTS: After bile duct ligation the intestinal absorption rates of taurocholate were lower (p<0.05) and after biliary diversion absorption rates were higher compared to sham-operated animals (p<0.05). The absorption rates were inversely correlated to serum bile acid concentrations. Levels of IBAT-, ILBP- and Oatp3- mRNA were not different between the groups. However, in cholestatic rats, the expression of the 99-kDa dimer of IBAT was decreased compared to controls (p<0.05), whereas the 46-kDa monomeric protein of IBAT and the expression of ILBP was unchanged. After biliary diversion a similar pattern of protein expression was observed, despite an increased absorption rate. CONCLUSIONS: Cholestasis leads to a decreased active ileal absorption of taurocholate. The changes in protein expression may not account for the different absorption rates. The intestinal absorption of bile acids seems to be regulated by their systemic concentration.     

Progressive familial intrahepatic cholestasis and inborn errors of bile acid synthesis

Progressive familial intrahepatic cholestasis (PFIC), types 1, 2 and 3, are due to defects in genes involved in bile secretion (FIC1, BSEP, MDR3). PFIC and inborn errors of bile acid synthesis (IEBAS) often present in infancy with cholestasis. The distinctive feature of PFIC 1 and 2 and IEBAS is a normal level of GGT, while IEBAS are suspected in patients with low plasma bile acids concentration. Molecular testing, urinary bile acid analysis (IEBAS), liver biopsy and immuno-staining are used for the diagnosis. Some patients with PFIC can be successfully treated with ursodeoxycholic acid or partial external biliary diversion. IEBAS is treated with cholic acid. Liver transplantation is required for cirrhosis with liver failure. Hepatocarcinoma has been reported in PFIC2.     

Treatment of cholestatic hepatic diseases: more than the substitution of fat soluble vitamins?

The clinical-biochemical syndrome of cholestasis is characterized by an alteration in bile constituents. As a consequence, the concentrations of bilirubin, bile acids, phospholipids and cholesterol are elevated. The main clinical symptoms of cholestasis are icterus and pruritus, and in severe cases xanthelasma and xanthoma. Primary intrahepatic cholestasis, caused by impaired bile secretion in the liver, should be separated from the extrahepatic secondary cholestasis which is a consequence of a biliary obstruction. This paper evaluates the therapy of liver diseases which developed as consequence of a primary disturbance in bile secretion.     

Therapie cholestatischer Lebererkrankungen

The clinical-biochemical syndrome of cholestasis is characterized by an alteration in bile constituents. As a consequence, the concentrations of bilirubin, bile acids, phospholipids and cholesterol are elevated. The main clinical symptoms of cholestasis are icterus and pruritus, and in severe cases xanthelasma and xanthoma. Primary intrahepatic cholestasis, caused by impaired bile secretion in the liver, should be separated from the extrahepatic secondary cholestasis which is a consequence of a biliary obstruction. This paper evaluates the therapy of liver diseases which developed as consequence of a primary disturbance in bile secretion.     

Ursodeoxycholic acid treatment of vanishing bile duct syndromes

Vanishing bile duct syndromes (VBDS) are characterized by progressive loss of small intrahepatic ducts caused by a variety of different diseases leading to chronic cholestasis, cirrhosis, and premature death from liver failure. The majority of adult patients with VBDS suffer from primary biliary cirrhosis (PBC) and primary sclerosing cholangitis (PSC). Ursodeoxycholic acid (UDCA), a hydrophilic dihydroxy bile acid, is the only drug currently approved for the treatment of patients with PBC, and anticholestatic effects have been reported for several other cholestatic syndromes. Several potential mechanisms of action of UDCA have been proposed including stimulation of hepatobiliary secretion, inhibition of apoptosis and protection of cholangiocytes against toxic effects of hydrophobic bile acids.     

Bile acid transport

Bile acids undergo a unique enterohepatic circulation, which allows them to be efficiently reused with minimal loss. With the cloning of key bile acid transporter genes in the liver and intestine, clinicians now have a detailed understanding of how the different components in the enterohepatic circulation operate. These advances in basic knowledge of this process have directly led to a rapid and highly detailed understanding of rare genetic disorders of bile acid transport, which usually present as pediatric cholestatic disorders. Mutations in specific bile acid or lipid transporters have been identified within specific cholestatic disorders, which allows for genetic tests to be established for specific diseases and provides a unique opportunity to understand how these genes operate together. These same transporters may also prove useful for development of novel drug delivery systems, which can either enhance intestinal absorption of drugs or be used to target delivery to the liver or biliary system. Knowledge gained from these transporters will provide new therapeutic modalities to treat cholestatic disorders caused by common diseases.     

Effect of chronic administration of tauro-hyodeoxycholic acid on biliary bile acid composition and on biliary lipid secretion in humans

BACKGROUND: Tauro-hyodeoxycholic acid is a hydrophilic bile acid of potential interest for treating cholestatic liver diseases. Bile acid pool is enriched with this bile acid during acute administration in patients with interrupted enterohepatic circulation. The aim of our study was to check the effect of chronic administration of tauro-hyodeoxycholic acid on biliary lipid composition and secretion in man with intact enterohepatic circulation. METHODS: We studied 7 dyspeptic patients before and during taurohyodeoxycholic acid 750 mg/day given for 6-8 weeks. We measured bile acid composition in duodenal aspirate, and biliary lipid secretion was also measured in 5 of these patients using a duodenal perfusion technique. RESULT: Tauro-hyodeoxycholic was undetectable in duodenal aspirate in all patients before treatment, and was 2%, 4%, 5%, 7%, 7%, 8% and 13% of biliary bile acid during treatment in individual patients. The proportion of cholic, deoxycholic, chenodeoxycholic ursodeoxycholic and lithocholic acid was similar before and during treatment. Bile acid duodenal output remained unchanged during taurohyodeoxycholic by comparison with pretreatment with median difference -0.3 mmol (95% confidence interval 1.6 mmol). The corresponding difference for duodenal cholesterol and phospholipid output was 0.1 mmol (0.2 mmol) and 0.2 mmol (0.6 mmol). CONCLUSIONS: By contrast with acute administration in patients with interrupted enterohepatic circulation, chronic administration of tauro-hyodeoxycholic to man with intact enterohepatic circulation has little effect on biliary lipid composition and secretion.     

An update on genetic analysis of cholestatic liver diseases: digging deeper

Investigations into the molecular mechanisms of cholestasis have revealed intricate and intriguing details of bile salt metabolism as well as its regulatory mechanisms in health and disease. Extensive studies on genotype-phenotype correlations in monogenic diseases, such as progressive familial and benign recurrent intrahepatic cholestasis, facilitate diagnostics and improve the risk assessment of hepatobiliary transporter gene variants in bile transport pathophysiology. While the comparatively easy targets in monogenic cholestasis have been identified for some time now, progress in complex liver disease is rather laborious but steady. Genome-wide association scans are the next step in gathering information about common contributors towards polygenic (multifactorial) cholestatic diseases. New determinants of bile salt metabolism affecting feedback loops within the liver or the enterohepatic circulation are presently under investigation for their contribution towards complex cholestatic syndromes.     

Biliary secretion and excretion in health and disease: current concepts

Biliary secretion in health and disease is reviewed. The powerful techniques of molecular biology have enabled cloning of the transporters involved in biliary secretion and the enterohepatic circulation of bile acids. This, in turn has permitted elucidation of their function as well as their regulation by nuclear receptors. Bile acid secretion is required for efficient lipid absorption, and bile acids also possess powerful direct and indirect antimicrobial functions in the small intestine. The enterohepatic circulation results from efficient ileal absorption, and is highly regulated at two sites. In the hepatocyte, biosynthesis of bile acids is regulated in negative feedback manner by the nuclear receptor FXR as well as by cytokines and by a peptide (FGF-19) liberated by bile acids from the ileal enterocyte. In the ileal enterocyte, bile acid reclamation is regulated in negative feedback manner by FXR and other nuclear receptors. The bile salt export pump (BSEP) mediates uphill canalicular bile acid secretion. Inborn defects in its function cause intrahepatic cholestasis in infants; inhibition of its function by drugs causes hepatotoxicity. Bile acid therapy is based on correction of bile acid deficiency by supplemental bile acids or displacement in which a noncytotoxic bile acid (ursodeoxycholic acid, ursodiol, UDCA) is administered and dilutes out the endogenous cytotoxic bile acids. Administration of primary bile acids may be lifesaving in inborn defects of bile acid biosynthesis. A synthetic bile acid, norUDCA is absorbed by the biliary ductules after secretion and cures the peribiliary fibrosis occurring in the MDR2-/- mouse which lacks biliary phospholipid.