Bile Metabolism Research Articles

Bile acids as regulatory molecules

In the past, bile acids were considered to be just detergent molecules derived from cholesterol in the liver. They were known to be important for the solubilization of cholesterol in the gallbladder and for stimulating the absorption of cholesterol, fat-soluble vitamins, and lipids from the intestines. However, during the last two decades, it has been discovered that bile acids are regulatory molecules. Bile acids have been discovered to activate specific nuclear receptors (farnesoid X receptor, preganane X receptor, and vitamin D receptor), G protein coupled receptor TGR5 (TGR5), and cell signaling pathways (c-jun N-terminal kinase 1/2, AKT, and ERK 1/2) in cells in the liver and gastrointestinal tract. Activation of nuclear receptors and cell signaling pathways alter the expression of numerous genes encoding enzyme/proteins involved in the regulation of bile acid, glucose, fatty acid, lipoprotein synthesis, metabolism, transport, and energy metabolism. They also play a role in the regulation of serum triglyceride levels in humans and rodents. Bile acids appear to function as nutrient signaling molecules primarily during the feed/fast cycle as there is a flux of these molecules returning from the intestines to the liver following a meal. In this review, we will summarize the current knowledge of how bile acids regulate hepatic lipid and glucose metabolism through the activation of specific nuclear receptors and cell signaling pathways.

Beneficial Role of Dietary Folic Acid on Cholesterol and Bile Acid Metabolism in Ethanol-Fed Rats

Cholesterol metabolism is altered by chronic ethanol consumption. In previous articles, we demonstrated the anti-oxidant capacity of folic acid, which may be useful in the prevention of damage provoked by ethanol. We want to determine the effects of ethanol on cholesterol and bile metabolism and whether a folic acid-supplemented diet could change alterations provoked by a chronic ethanol intake in rats. We used four experimental groups: (1) control, (2) alcohol, (3) alcohol supplemented with folic acid, and (4) control supplemented with folic acid. In all the experimental groups, we measured hepatic 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase, and cholesterol and bile acids in serum, liver, bile, and feces. We have found that the alcohol-fed groups showed high hepatic HMG-CoA reductase activity, total hepatic and serum cholesterol concentration, bile cholesterol secretion concentration, and cholesterol enterohepatic circulation. Total serum and hepatic cholesterol levels decreased when alcohol-fed rats were supplemented with folic acid. The hepatic bile acid concentration increased in both chronic ethanol groups. Folic acid supplementation significantly increased bile cholesterol secretion, the bile acids in bile, and fecal bile acid excretion in ethanol-exposed rats. The independent bile acid fraction showed no significant differences between both ethanol groups with respect to Na+, K+, and Cl- concentrations. Folic acid increases bile flow, bile acid synthesis from cholesterol, and bile acid excretion via feces, thus provoking a decrease in serum and hepatic cholesterol. However none of these actions were observed in supplemented control rats. This, therefore, could be yet another beneficial effect of folic acid on alcoholic patients.

The molecular genetics of intrahepatic cholestasis of pregnancy.

Intrahepatic cholestasis of pregnancy (ICP), also known as obstetric cholestasis, causes maternal pruritus and liver impairment, and may be complicated by spontaneous preterm labour, fetal asphyxial events and intrauterine death. Our understanding of the aetiology of this disease has expanded significantly in the last decade due to a better understanding of the role played by genetic factors. In particular, advances in our knowledge of bile homeostasis has led to the identification of genes that play a considerable role in susceptibility to ICP. In this review we consider these advances and discuss the disease in the context of bile synthesis and metabolism, focusing on the genetic discoveries that have shed light on the molecular aetiology and pathophysiology of the condition.

Dose- and time-dependent effects of phenobarbital on gene expression profiling in human hepatoma HepaRG cells

Phenobarbital (PB) induces or represses a wide spectrum of genes in rodent liver. Much less is known about its effects in human liver. We used pangenomic cDNA microarrays to analyze concentration- and time-dependent gene expression profile changes induced by PB in the well-differentiated human HepaRG cell line. Changes in gene expression profiles clustered at specific concentration ranges and treatment times. The number of correctly annotated genes significantly modulated by at least three different PB concentration ranges (spanning 0.5 to 3.2 mM) at 20 h exposure amounted to 77 and 128 genes ( p ≤ 0.01) at 2- and 1.8-fold filter changes, respectively. At low concentrations (0.5 and 1 mM), PB-responsive genes included the well-recognized CAR- and PXR-dependent responsive cytochromes P450 (CYP2B6, CYP3A4), sulfotransferase 2A1 and plasma transporters (ABCB1, ABCC2), as well as a number of genes critically involved in various metabolic pathways, including lipid (CYP4A11, CYP4F3), vitamin D (CYP24A1) and bile (CYP7A1 and CYP8B1) metabolism. At concentrations of 3.2 mM or higher after 20 h, and especially 48 h, increased cytotoxic effects were associated with disregulation of numerous genes related to oxidative stress, DNA repair and apoptosis. Primary human hepatocyte cultures were also exposed to 1 and 3.2 mM PB for 20 h and the changes were comparable to those found in HepaRG cells treated under the same conditions. Taken altogether, our data provide further evidence that HepaRG cells closely resemble primary human hepatocytes and provide new information on the effects of PB in human liver. These data also emphasize the importance of investigating dose- and time-dependent effects of chemicals when using toxicogenomic approaches.

Bile Acids and Derivatives, Their Nuclear Receptors FXR, PXR and Ligands: Role in Health and Disease and Their Therapeutic Potential

Bile acids, their physiology and metabolism, their role in carcinogenesis and other major human diseases are recently undergoing significant progress. Starting in 1999 when the orphan nuclear receptor FXR was shown to be specifically activated by bile acids, these compounds became part of the arsenal of ligands of the steroid hormone superfamily of nuclear receptors, including receptors of Vitamin D3, retinoids (RAR, RXR), and thyroid hormone. Another decisive discovery pointed later that the pregnane X-receptor (PXR) is activated by the endogenous toxic lithocholic acid, as well as several xenobiotics and drugs. Bile acids have recently emerged as key regulators of their own metabolism, and of lipid and carbohydrate metabolism. They have important role as promoters of esophageal and colon cancers, cholangiocarcinoma, as well as new implications in breast cancer development and metastasis. This Review will emphasize novel aspects of bile acids, FXR and PXR as regulators of interfaces at cell proliferation and differentiation, cell death, survival, invasion, and metastasis during normal development and cancer progression. Signaling pathways controlled by bile acids will be presented and discussed in relation to their impact on gene expression. The biological and pharmacological significance of bile acids and their recently developed synthetic derivatives and conjugates, as well as new development in the design of FXR agonists and antagonists for clinical applications in cancer prevention and therapy, will be evaluated. This part includes advances in the utilization of bile acid transporters in drug resistance, therapeutic targeting and delivery of anticancer drugs, as well as therapeutic combinations using new bile acid derivatives, sequestrating agents and reabsorption inhibitors, and their limitations.

Hepatobiliary effects of cholic and lithocholic acids: experimental study in hamsters

Etiopathogenesis of biliary atresia remains unknown. Among several theories, one proposes that the disorder may be caused by the toxic effect of monohydroxy bile acids on fetal and neonatal hepatobiliary system. In this paper we evaluated toxic effects produced by ingestion of cholic acid, a trihydroxy bile acid, and lithocholic acid, a monohydroxy bile acid in the hepatobiliary system of a hamster during gestational and perinatal periods. A diet composed by 0.5% cholic acid and 0.25% lithocholic acid was administrated to pregnant hamsters. Liver and bile ducts of the adult and newborn animals were analyzed to point out the changes induced by these acids after birth. Because hamsters and humans have a similar bile metabolism, these animals were eligible for the study. The ingestion of 0.5% lithocholic acid, during hamster's gestation, caused maternal intense ductal/ductular proliferation, inflammatory signs, hepatic cells degeneration and regeneration, hyperplasia of extra hepatic ducts epithelium, and abortion. Both 0.5% cholic acid and 0.25% lithocholic acid ingested by pregnant hamsters, caused ductal/ductular proliferation and hepatobiliary inflammatory damage in a different degree of intensity in adult animals and mild intensity in the young; and also the number of the young was reduced in the litter. We found that the ingestion of these bile acids by hamsters, during gestational period caused different degrees of toxicity on maternal and neonatal hepatobiliary systems. The histopathologic findings observed in biliary atresia patients could not be found in newborn hamsters. New experimental models are needed in the attempt to establish a correlation of these acids with neonatal cholestatic diseases.

Ikterus – Differentialdiagnose am Krankenbett

Der klinische Begriff Ikterus (= Gelbsucht) bezeichnet eine Gelbverfarbung von Geweben infolge einer Ablagerung von Bilirubin. Letzteres ist das physiologische Abbauprodukt des Hamstoffwechsels. Der Ikterus gilt als Leitsymptom einer ganzen Reihe von Erkrankungen des hepatobiliaren Systems. Neben Leber und Gallenwegen konnen aber auch Erkrankungen von anderen Organen wie Herz, blutbildendem System und Pankreas seiner Entstehung zugrunde liegen. Das Spektrum der Manifestation reicht von akut mit schwerem Krankheitsgefuhl bis chronisch und von den Patienten kaum bemerkt. Im folgenden Artikel wird zunachst die Ikterusentstehung auf wissenschaftlicher Grundlage anhand der Physiologie des Hamstoffwechsels erlautert. Die Kenntnis der Grundprinzipien von Hamabbau, Gallesekretion und enterohepatischem Kreislauf erleichtert das Verstandnis, weshalb klinisch zwischen prahepatischem, hepatischem und cholestatischem Ikterus unterschieden wird. Die entsprechende Zuordnung ist haufig bereits aufgrund einer grundlichen Anamnese und korperlichen Untersuchung in Zusammenschau mit den routinemasig erhobenen Laborwerten moglich. Auf die Vielzahl der klinischen Differentialdiagnosen wird praxisrelevant anhand einiger Fallbeispiele, erganzt durch eine tabellarische Auflistung, eingegangen.

Proteomic Analysis of Ischemia-Reperfusion Injury upon Human Liver Transplantation Reveals the Protective Role of IQGAP1

Ischemia-reperfusion injury (IRI) represents a major determinant of liver transplantation. IRI-induced graft dysfunction is related to biliary damage, partly due to a loss of bile canaliculi (BC) integrity associated with a dramatic remodeling of actin cytoskeleton. However, the molecular mechanisms associated with these events remain poorly characterized. Using liver biopsies collected during the early phases of organ procurement (ischemia) and transplantation (reperfusion), we characterized the global patterns of expression and phosphorylation of cytoskeleton-related proteins during hepatic IRI. This targeted functional proteomic approach, which combined protein expression pattern profiling and phosphoprotein enrichment followed by mass spectrometry analysis, allowed us to identify IQGAP1, a Cdc42/Rac1 effector, as a potential regulator of actin cytoskeleton remodeling and maintenance of BC integrity. Cell fractionation and immunohistochemistry revealed that IQGAP1 expression and localization were affected upon IRI and related to actin reorganization. Furthermore using an IRI model in human hepatoma cells, we demonstrated that IQGAP1 silencing decreased the basal level of actin polymerization at BC periphery, reflecting a defect in BC structure coincident with reduced cellular resistance to IRI. In summary, this study uncovered new mechanistic insights into the global regulation of IRI-induced cytoskeleton remodeling and led to the identification of IQGAP1 as a regulator of BC structure. IQGAP1 therefore represents a potential target for the design of new organ preservation strategies to improve transplantation outcome.

Targeted Deletion of FATP5 Reveals Multiple Functions in Liver Metabolism: Alterations in Hepatic Lipid Homeostasis

Fatty acid transport protein 5 (FATP5/Slc27a5) has been shown to be a multifunctional protein that in vitro increases both uptake of fluorescently labeled long-chain fatty acid (LCFA) analogues and bile acid/coenzyme A ligase activity on overexpression. The aim of this study was to further investigate the diverse roles of FATP5 in vivo. We studied FATP5 expression and localization in liver of C57BL/6 mice in detail. Furthermore, we created a FATP5 knockout mouse model and characterized changes in hepatic lipid metabolism (this report) and bile metabolism (the accompanying report by Hubbard et al). FATP5 is exclusively expressed by the liver and localized to the basal plasma membrane of hepatocytes, congruent with a role in LCFA uptake from the circulation. Overexpression of FATP5 in mammalian cells increased the uptake of 14C-oleate. Conversely, FATP5 deletion significantly reduced LCFA uptake by hepatocytes isolated from FATP5 knockout animals. Moreover, FATP5 deletion resulted in lower hepatic triglyceride and free fatty acid content despite increased expression of fatty acid synthetase and also caused a redistribution of lipids from liver to other LCFA-metabolizing tissues. Detailed analysis of the hepatic lipom of FATP5 knockout livers showed quantitative and qualitative alterations in line with a decreased uptake of dietary LCFAs and increased de novo synthesis. Our findings support the hypothesis that efficient hepatocellular uptake of LCFAs, and thus liver lipid homeostasis in general, is largely a protein-mediated process requiring FATP5. These new insights into the physiological role of FATP5 should lead to an improved understanding of liver function and disease.

Cholestatic syndromes

Further insights into the molecular regulation of bile acid transport and metabolism have provided the basis for a better understanding of the pathogenesis of cholestatic liver diseases. Novel insights into the mechanisms of action of ursodeoxycholic acid should advance our understanding of the treatment of cholestatic liver diseases. Mutations of transporter genes can cause hereditary cholestatic syndromes in both infants and adults as well as cholesterol gallstone disease. Important studies have been published on the pathogenesis, clinical features, and treatment of primary biliary cirrhosis, drug-induced cholestasis, and cholestasis of pregnancy.

Dietary phospholipid alters biliary lipid composition in formula‐fed piglets

Plasma cholesterol, arachidonic acid (AA, 20:4n-6), and docosahexaenoic acid (DHA, 22:6n-3) are higher in breast-fed infants than in infants fed formula without cholesterol, AA, or DHA. This study investigated differences in plasma, hepatic, and bile lipids and phospholipid fatty acids, and expression of hepatic proteins involved in sterol metabolism that result from feeding formula with cholesterol with egg phospholipid to provide AA and DHA. For this study, three groups of piglets were evaluated: piglets fed formula with 0.65 mmol/L cholesterol, the same formula with 0.8% AA and 0.2% DHA from egg phospholipid, and piglets fed sow milk. Piglets fed the formula with phospholipid AA and DHA had higher plasma high density lipoprotein, but not apoprotein (apo) B cholesterol or triglyceride; higher bile acid and phospholipid concentrations in bile; and higher liver and bile phospholipid AA and DHA than piglets fed formula without AA and DHA (P < 0.05). Hydroxy methylglutaryl (HMG)-CoA reductase and 7-alpha-hydroxylase, the rate-limiting enzymes of cholesterol and bile acid synthesis, respectively, and low density lipoprotein receptor mRNA levels were not different between piglets fed formula without and with phospholipid AA and DHA, but HMG-CoA reductase and 7alpha-hydroxylase mRNA were higher, and plasma apo B containing lipoprotein cholesterol was lower in all piglets fed formula than in piglets fed milk. These studies show that supplementing formula with AA and DHA from egg phospholipid alters bile metabolism by increasing the bile AA and DHA, and bile acid and phospholipid.

Bile ductular proliferation and altered leukotriene elimination in thioacetamide-induced fibrosis of rat liver

Background/Aims: Liver fibrosis is accompanied by both bile ductular proliferation and inflammation under various conditions. The functional consequences and the interrelationships between these changes are unknown. Altered biliary elimination and retention of cholephilic mediators may be a factor in fibrogenesis. Therefore, the relationship between fibrosis, ductular proliferation and functional changes in biliary elimination was studied. Methods: Micronodular liver fibrosis was induced by thioacetamide in rats. The relative amount of bile ductular epithelial cells was determined by microscopic morphometry. The functional changes in bile secretion and metabolism of leukotriene C4 were assessed in isolated perfused livers of treated rats. Results: Pretreatment with thioacetamide in vivo resulted in enhanced bile fluid formation in subsequently isolated and perfused livers. Infusion of isoproterenol into the portal vein stimulated bile flow. Both unstimulated and isoproterenol-stimulated bile flows were increased in fibrotic livers and were correlated with liver content of bile ductular epithelia. In contrast, biliary secretion of infused leukotriene C4 was lowered in correlation with that of taurocholate. Enhanced metabolism resulted in a shift of major fraction in bile from leukotriene C4 to leukotriene D4. Conclusions: Thioacetamide-induced liver fibrosis is associated with an increased number of functionally intact bile ductules that are responsive to isoproterenol stimulating bile fluid formation. In contrast, biliary secretion of cysteinyl-leukotrienes and taurocholate is inhibited and the relative amount of leukotriene D4 is increased. Bile ductular proliferation as well as retention and altered metabolism of leukotrienes are factors associated with the development of liver fibrosis.

Management of Biliary Tract Stones in Heart Transplant Patients

The authors report their experience with biliary tract stones in adult and pediatric heart transplant patients, and review the current literature relative to this problem. Prior studies in adults have noted that heart transplant patients frequently have cholelithiasis, but offer no consensus about treatment strategy. Few studies exist for pediatric heart transplant patients. A higher rate of hemolysis and cyclosporine-induced changes in bile metabolism may contribute to lithogenesis in this population. A chart review was conducted for 211 patients who had heart transplants between January 1988 and September 1994 to determine prevalence of biliary tract stones, management strategies used, and outcome. Of 175 long-term heart transplant survivors, 52 (29.7%) had stones detected: 32.8% of adults (47/143) and 15.6% of children (5/32). The majority of patients (31) were diagnosed 4 months (mean) after transplantation; cholelithiasis developed in 10 of these patients (32%) within 11 months (median) after a negative ultrasound. Symptoms developed in 45% of patients. All patients underwent either elective (36) or urgent (6) cholecystectomy via an open (32) or laparoscopic (10) approach, or endoscopy for common bile duct stones (2). There were no deaths or complications during a follow-up period of up to 7 years. Heart transplant patients have a high prevalence of symptomatic biliary tract stone disease. They can be treated safely via an open or laparoscopic approach after transplantation. The authors recommend routine gallbladder ultrasound screening and elective cholecystectomy in the post-transplant period if stones are detected.

Intrahepatic Cholestasis of Pregnancy

Cholestasis of pregnancy may be relatively benign causing little more than maternal pruritus, or it may cause significant fetal mortality. It is likely under-diagnosed as it is not always considered, and the most appropriate testing is often unavailable. Subsequent pregnancies may or may not be affected. There appear to be both genetic and environmental factors at play.The biochemistry of bile metabolism is altered during pregnancy. This may be due to an inherited hypersensitivity to estrogens at a genetic level. This increase in bile may affect the fetus by decreasing placental blood flow through a number of mechanisms, with the most severe outcome being fetal demise. Non-stress testing does not appear to be predictive of fetal demise. No studies have assessed the role of the biophysical profile in managing this disease.Treatment of the disease only alters maternal morbidity. There is little information on future long-term effects on the mothers. While it is known that they do not tolerate oral contraceptive agents, there have been no studies regarding susceptible women’s responses to post-menopausal hormone replacement.

Amino acid interaction with taurine metabolism in cats.

Taurine deficiency represents an important nutritional problem in cats because they cannot synthesize appreciable quantities of taurine, even though substantial taurine is required for biological functions, e.g. bile metabolism and vision1,2.Although some taurine is synthesized from methionine and cysteine, the main pathway of taurine biosynthesis appears to be limited by low activity of cysteine sulfinic acid decarboxylase. Thus, a dietary source of taurine is considered essential for maintaining normal health in cats, rendering taurine an essential amino acid for this species3,4.a Feeding cats purified, taurine-free diets depletes plasma taurine to barely detectable levels5–8. Supplementation with sulfur amino acids failed to improve plasma taurine status substantially (i.e. clinically)8,9. By contrast, a large intake of dietary cystine (5%) restored plasma and platelet taurine concentrations to approximately 50% of normal, and taurine concentrations in white and red blood cells approximated those in taurine-supplemented cats6. However, this high level of dietary cystine caused debilitating neurological symptoms which resulted in death of some cats6.

Cholecystectomy and right colon cancer in Puerto Rico

A case-control study was undertaken to evaluate the possible relationship between cholecystectomy and right colon cancer. Two hundred patients with adenocarcinoma of the cecum or ascending colon (diagnosed between 1984 and 1989) were compared with 200 matched neighborhood controls. Cholecystectomy history was obtained through interviews using structured questionnaires and subsequently validated from hospital records. A statistically significant association (odds ratio = 2.14) was found between right colon cancer and a history of prior cholecystectomy. The altered bile metabolism which occurs after removal of the gallbladder may have a carcinogenic effect on the right colon. Dietary habits of the colon cancer patients in our study were consistent with prior reports in the literature, showing that this group has a lower intake of vegetables and cereal fiber than the control population.

Hepatitis and Copper Accumulation in Skye Terriers

Livers of nine related Skye terriers with liver disease were evaluated for histological changes and copper content. Lesions ranged from hepatocellular degeneration and necrosis (zone 3) with intracanalicular cholestasis and mild inflammation, to chronic hepatitis with cholangioplasia and cirrhosis. Excess copper (801-2,257 micrograms/g) was related to the severity of cholestasis. Skye terrier hepatitis is a distinct disease entity and may be derived from a disorder of intracellular bile metabolism culminating in disturbed bile secretion and the accumulation of copper.

Identification of pp120, an endogenous substrate for the hepatocyte insulin receptor tyrosine kinase, as an integral membrane glycoprotein of the bile canalicular domain.

An endogenous membrane-bound substrate of the insulin receptor beta-subunit tyrosine kinase in liver, pp120, has been identified as HA4, a 110-kDa membrane glycoprotein localized primarily to the bile canalicular domain of the hepatocyte. HA4 has been implicated in bile salt transport and cell adhesion. Monoclonal antibodies to HA4 were used to identify it as a substrate of the insulin receptor kinase. Anti-pp120 and anti-HA4 were found to cross-react, and phosphopeptide maps for each of the corresponding antigens were identical. The identification of pp120 as HA4 serves to link insulin action through the receptor tyrosine kinase activity to bile metabolism and raises questions pertaining to the intracellular site(s) of action of the insulin receptor.

Effect of Cholecystokinin‐Octapeptide on Total Parenteral Nutrition‐Induced Changes in Hepatic Bile Secretion and Composition in the Rat

SummaryThese studies investigated the ability of twice‐daily administration of cholecystokinin‐octapep‐tide (CCK‐8) to prevent changes in hepatic bile secretory function and bile composition resulting from total parenteral nutrition (TPN) in young, growing rats. Bile was collected from the common duct before and during i.v. infusion of sodium taurocholate following 7 days of TPN. TPN resulted in a reduction of hepatic bile flow, reduced bile molar cholesterol and phospholipid content, and reduction of the taurocholate secretory rate maximum (SRm) and bile salt‐independent bile flow (BSIF). Rats treated with CCK‐8 throughout their TPN retained high bile flows, BSIF, and SRm. CCK‐8 at the dose used did not correct abnormalities in the hepatic bile composition or the magnitude of bile flow generated in response to i.v. taurocholate infusion. These findings suggest that the ability of CCK‐8 to maintain high bile flows during TPN may have prophylactic relevance for prevention of TPN‐induced gallbladder disease. However, these studies also suggest that a component of current TPN systems induces damage to hepatic bile metabolism and excretion that is additional to that due to the reduced stimulation of bile flow that accompanies elimination of oral food intake.

Effect of cholecystokinin-octapeptide on total parenteral nutrition-induced changes in hepatic bile secretion and composition in the rat.

These studies investigated the ability of twice-daily administration of cholecystokinin-octapeptide (CCK-8) to prevent changes in hepatic bile secretory function and bile composition resulting from total parenteral nutrition (TPN) in young, growing rats. Bile was collected from the common duct before and during i.v. infusion of sodium taurocholate following 7 days of TPN. TPN resulted in a reduction of hepatic bile flow, reduced bile molar cholesterol and phospholipid content, and reduction of the taurocholate secretory rate maximum (SRm) and bile salt-independent bile flow (BSIF). Rats treated with CCK-8 throughout their TPN retained high bile flows, BSIF, and SRm. CCK-8 at the dose used did not correct abnormalities in the hepatic bile composition or the magnitude of bile flow generated in response to i.v. taurocholate infusion. These findings suggest that the ability of CCK-8 to maintain high bile flows during TPN may have prophylactic relevance for prevention of TPN-induced gallbladder disease. However, these studies also suggest that a component of current TPN systems induces damage to hepatic bile metabolism and excretion that is additional to that due to the reduced stimulation of bile flow that accompanies elimination of oral food intake.