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Li T, Apte U. Bile Acid Metabolism and Signaling in Cholestasis, Inflammation, and Cancer. ADVANCES IN PHARMACOLOGY (SAN DIEGO, CALIF.) 2015; 74:263-302. [PMID: 26233910 DOI: 10.1016/bs.apha.2015.04.003] [Citation(s) in RCA: 184] [Impact Index Per Article: 20.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Bile acids are synthesized from cholesterol in the liver. Some cytochrome P450 (CYP) enzymes play key roles in bile acid synthesis. Bile acids are physiological detergent molecules, so are highly cytotoxic. They undergo enterohepatic circulation and play important roles in generating bile flow and facilitating biliary secretion of endogenous metabolites and xenobiotics and intestinal absorption of dietary fats and lipid-soluble vitamins. Bile acid synthesis, transport, and pool size are therefore tightly regulated under physiological conditions. In cholestasis, impaired bile flow leads to accumulation of bile acids in the liver, causing hepatocyte and biliary injury and inflammation. Chronic cholestasis is associated with fibrosis, cirrhosis, and eventually liver failure. Chronic cholestasis also increases the risk of developing hepatocellular or cholangiocellular carcinomas. Extensive research in the last two decades has shown that bile acids act as signaling molecules that regulate various cellular processes. The bile acid-activated nuclear receptors are ligand-activated transcriptional factors that play critical roles in the regulation of bile acid, drug, and xenobiotic metabolism. In cholestasis, these bile acid-activated receptors regulate a network of genes involved in bile acid synthesis, conjugation, transport, and metabolism to alleviate bile acid-induced inflammation and injury. Additionally, bile acids are known to regulate cell growth and proliferation, and altered bile acid levels in diseased conditions have been implicated in liver injury/regeneration and tumorigenesis. We will cover the mechanisms that regulate bile acid homeostasis and detoxification during cholestasis, and the roles of bile acids in the initiation and regulation of hepatic inflammation, regeneration, and carcinogenesis.
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Affiliation(s)
- Tiangang Li
- Department of Pharmacology, Toxicology and Therapeutics, The University of Kansas Medical Center, Kansas City, Kansas, USA.
| | - Udayan Apte
- Department of Pharmacology, Toxicology and Therapeutics, The University of Kansas Medical Center, Kansas City, Kansas, USA
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Delgado-Coello B, Briones-Orta MA, Macías-Silva M, Mas-Oliva J. Cholesterol: recapitulation of its active role during liver regeneration. Liver Int 2011; 31:1271-84. [PMID: 21745289 DOI: 10.1111/j.1478-3231.2011.02542.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Liver regeneration is a compensatory hyperplasia produced by several stimuli that promotes proliferation in order to provide recovery of the liver mass and architecture. This process involves complex signalling cascades that receive feedback from autocrine and paracrine pathways, recognized by parenchymal as well as non-parenchymal cells. Nowadays the dynamic role of lipids in biological processes is widely recognized; however, a systematic analysis of their importance during liver regeneration is still missing. Therefore, in this review we address the role of lipids including the bioactive ones such as sphingolipids, but with special emphasis on cholesterol. Cholesterol is not only considered as a structural component but also as a relevant lipid involved in the control of the intermediate metabolism of different liver cell types such as hepatocytes, hepatic stellate cells and Kupffer cells. Cholesterol plays a significant role at the level of specific membrane domains, as well as modulating the expression of sterol-dependent proteins. Moreover, several enzymes related to the catabolism of cholesterol and whose activity is down regulated are related to the protection of liver tissue from toxicity during the process of regeneration. This review puts in perspective the necessity to study and understand the basic mechanisms involving lipids during the process of liver regeneration. On the other hand, the knowledge acquired in this area in the past years, can be considered invaluable in order to provide further insights into processes such as general organogenesis and several liver-related pathologies, including steatosis and fibrosis.
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Affiliation(s)
- Blanca Delgado-Coello
- Departamento de Bioquímica y Biología Estructural, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, México, DF Mexico
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Song KH, Ellis E, Strom S, Chiang JYL. Hepatocyte growth factor signaling pathway inhibits cholesterol 7alpha-hydroxylase and bile acid synthesis in human hepatocytes. Hepatology 2007; 46:1993-2002. [PMID: 17924446 DOI: 10.1002/hep.21878] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
UNLABELLED Bile acid synthesis in the liver is regulated by the rate-limiting enzyme cholesterol 7alpha-hydroxylase (CYP7A1). Transcription of the CYP7A1 gene is inhibited by bile acids and cytokines. The rate of bile acid synthesis is reduced immediately after partial hepatectomy and during the early stage of liver regeneration. Hepatocyte growth factor (HGF) released from stellate cells activates a receptor tyrosine kinase c-Met, in hepatocytes and stimulates signaling pathways that regulate cell growth, proliferation, and apoptosis. This study demonstrated that HGF strongly and rapidly repressed CYP7A1 mRNA expression and the rate of bile acid synthesis in primary human hepatocytes. HGF rapidly induced c-Jun and small heterodimer partner mRNA and protein expression and increased phosphorylation of ERK1/2, JNK, and c-Jun. Specific inhibitors of protein kinase C, extracellular signal-regulated kinase 1/2 (ERK1/2), and c-Jun N-terminal kinase (JNK) blocked HGF inhibition of CYP7A1 expression. Knockdown of c-Met by small interfering RNA resulted in a significant increase in CYP7A1 and blocked HGF inhibition of CYP7A1 mRNA expression. Chromatin immunoprecipitation assays showed that HGF induced recruitment of c-Jun and small heterodimer partner (SHP) but reduced recruitment of the coactivators peroxisome proliferators activated receptor rho coactivator 1alpha (PGC-1alpha) and cAMP response element binding protein (CREB)-binding protein (CBP) to chromatin. CONCLUSION This study demonstrated that HGF is a novel regulator of CYP7A1 and bile acid synthesis in human hepatocytes and may protect hepatocytes from accumulating toxic bile acids and developing intrahepatic cholestasis during the early stage of liver regeneration.
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Affiliation(s)
- Kwang-Hoon Song
- Department of Microbiology, Immunology and Biochemistry, Northeastern Ohio Universities College of Medicine, Rootstown, OH 44272, USA
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Tanaka SI, Chijiiwa K, Maeda Y. Biliary lipid output in the early stage of acute liver failure induced by 90% hepatectomy in the rat. J Surg Res 2006; 134:81-6. [PMID: 16464471 DOI: 10.1016/j.jss.2005.12.023] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2005] [Revised: 11/25/2005] [Accepted: 12/27/2005] [Indexed: 11/23/2022]
Abstract
BACKGROUND Differences in biliary lipid output were compared in rats after 70% or 90% hepatectomy (Hx) to evaluate a possible index of the early stage of acute liver failure. METHODS Male Sprague-Dawley (SD) rats weighing 300 to 350 g were randomly divided into two groups for 70% Hx or 90% Hx, and animals were sacrificed at 0, 6, 24, and 48 h after Hx. Before sacrifice, a polyethylene tube was cannulated into the bile duct and bile was collected for 1 h. Outputs of total bile acids, phospholipid, and total cholesterol in serum and bile were determined. Biliary total cholesterol, bile acid concentrations, and bile acid component levels were determined using gas liquid chromatography. Hepatic microsomal cholesterol 7alpha-hydroxylase and sterol 12alpha-hydroxylase activities were also determined using high performance liquid chromatography. RESULTS The 3-day survival rate after 90% Hx was 50%. In the 90% Hx group, the serum total bile acid concentration at each point was significantly higher than it was in the 70% Hx group. The bile flow rate and biliary outputs of cholesterol, phospholipid, and bile acids were significantly lower at 6 h after 90% Hx than after 70% Hx. Among bile acid species, cholic and chenodeoxycholic acid outputs into bile were significantly less at 6 h after 90% Hx. The activities of cholesterol 7alpha-hydroxylase and sterol 12alpha-hydroxylase were decreased after 90% Hx. CONCLUSIONS Our results suggest that determinations of the bile flow rate and biliary lipid outputs are supposed to be useful for early detection of hepatic failure after extensive hepatectomy.
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Affiliation(s)
- Shun-ichi Tanaka
- Department of Surgery I, Miyazaki University School of Medicine, Miyazaki, Japan
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Holterman AXL, Tan Y, Kim W, Yoo KW, Costa RH. Diminished hepatic expression of the HNF-6 transcription factor during bile duct obstruction. Hepatology 2002; 35:1392-9. [PMID: 12029624 DOI: 10.1053/jhep.2002.33680] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/07/2022]
Abstract
Hepatocyte nuclear factor 6 (HNF-6) is a member of the one cut family of transcription factors and potentially regulates expression of numerous target genes important for hepatocyte function. In the liver, HNF-6 is expressed not only in hepatocytes, but also in biliary epithelial cells (BEC). To evaluate the in vivo function of HNF-6, we examined the hepatic expression pattern of HNF-6 messenger RNA (mRNA) and protein after bile duct ligation (BDL)-mediated liver injury. We found that HNF-6 protein levels in BEC and hepatocytes were diminished within 15 hours of BDL injury and remained suppressed through the fifth day of injury. The onset of BEC proliferation in response to bile duct obstruction was associated with diminished HNF-6 protein levels. To maintain hepatic HNF-6 protein levels during BDL liver injury, we used mouse tail vein injections with recombinant adenovirus expressing HNF-6 complementary DNA (cDNA) (AdH6). We found that maintaining hepatic HNF-6 levels with AdH6 infection resulted in significant decreases in BEC proliferation at 15 and 24 hours after biliary obstruction compared with adenovirus control. Our results showed that HNF-6 expression is diminished in BEC and hepatocytes and that maintaining hepatic HNF-6 expression hinders the normal biliary proliferative response to bile duct injury. This suggests that diminished hepatic HNF-6 levels are required for repair in response to biliary injury and that it regulates expression of genes that possess differentiation-specific function that are inhibitory to proliferation. In conclusion, we propose a biologic role for diminished HNF-6 protein levels in bile duct disease.
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Affiliation(s)
- Ai-Xuan L Holterman
- Department of Surgery, Division of Pediatric Surgery, University of Illinois at Chicago, 60607-7170, USA.
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Monte MJ, Martinez-Diez MC, El-Mir MY, Mendoza ME, Bravo P, Bachs O, Marin JJG. Changes in the pool of bile acids in hepatocyte nuclei during rat liver regeneration. J Hepatol 2002; 36:534-42. [PMID: 11943426 DOI: 10.1016/s0168-8278(01)00296-3] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
BACKGROUND/AIMS To investigate changes in nuclear bile acids (BAs) during rat liver regeneration. METHODS Nuclei were isolated from control rat livers and after two-thirds partial hepatectomy (PH). BAs in bile, liver homogenate and nuclei were measured by gas chromatography-mass spectrometry. Nuclear translocation of radiolabeled BAs was determined using fresh isolated hepatocytes from control donors. RESULTS Liver BA concentrations were transiently reduced after PH. Relative increases in: -MCA at 1 day, deoxycholic acid at 7 days and cholic acid (CA) at 3 and 14 days were found. Nuclear BAs accounted for <0.5% of liver BAs. Contamination with cytosolic BAs during nuclei isolation was <4%. Unconjugated- and conjugated-CA were able to reach the nucleus with similar efficiency. The pattern of nuclear BAs--CA (80%) and ursodeoxycholic acid (UDCA) (8.5%) being the most abundant--did not match that found in liver or bile. A transient decrease in CA/UDCA ratio, in absence of significant change in total BA content, was observed in nuclei after PH. "Flat" BA species were only detected in homogenate, but not in nuclei, at 1 day after PH. CONCLUSIONS BA pool in nuclei of rat hepatocytes, whose composition is different to that of total liver BA pool, undergoes important changes during liver regeneration.
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Affiliation(s)
- Maria J Monte
- Department of Physiology and Pharmacology, University of Salamanca, Campus Miguel de Unamuno, E.I.D. S-09 37007, Salamanca, Spain
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Yu C, Wang F, Kan M, Jin C, Jones RB, Weinstein M, Deng CX, McKeehan WL. Elevated cholesterol metabolism and bile acid synthesis in mice lacking membrane tyrosine kinase receptor FGFR4. J Biol Chem 2000; 275:15482-9. [PMID: 10809780 DOI: 10.1074/jbc.275.20.15482] [Citation(s) in RCA: 274] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Heparan sulfate-regulated transmembrane tyrosine kinase receptor FGFR4 is the major FGFR isotype in mature hepatocytes. Fibroblast growth factor has been implicated in the definition of liver from foregut endoderm where FGFR4 is expressed and stimulation of hepatocyte DNA synthesis in vitro. Here we show that livers of mice lacking FGFR4 exhibited normal morphology and regenerated normally in response to partial hepatectomy. However, the FGFR4 (-/-) mice exhibited depleted gallbladders, an elevated bile acid pool and elevated excretion of bile acids. Cholesterol- and bile acid-controlled liver cholesterol 7alpha-hydroxylase, the limiting enzyme for bile acid synthesis, was elevated, unresponsive to dietary cholesterol, but repressed normally by dietary cholate. Expression pattern and cholate-dependent, cholesterol-induced hepatomegaly in the FGFR4 (-/-) mice suggested that activation of receptor interacting protein 140, a co-repressor of feed-forward activator liver X receptor alpha, may mediate the negative regulation of cholesterol- and bile acid-controlled liver cholesterol 7alpha-hydroxylase transcription by FGFR4 and cholate. The results demonstrate that transmembrane sensors interface with metabolite-controlled transcription networks and suggest that pericellular matrix-controlled liver FGFR4 in particular may ensure adequate cholesterol for cell structures and signal transduction.
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Affiliation(s)
- C Yu
- Department of Biochemistry and Biophysics, Texas A&M University, Institute of Biosciences and Technology, Texas A&M University System Health Science Center, Houston, Texas 77030-3303, USA
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Abstract
Oxygenated derivatives of cholesterol (oxysterols) present a remarkably diverse profile of biological activities, including effects on sphingolipid metabolism, platelet aggregation, apoptosis, and protein prenylation. The most notable oxysterol activities center around the regulation of cholesterol homeostasis, which appears to be controlled in part by a complex series of interactions of oxysterol ligands with various receptors, such as the oxysterol binding protein, the cellular nucleic acid binding protein, the sterol regulatory element binding protein, the LXR nuclear orphan receptors, and the low-density lipoprotein receptor. Identification of the endogenous oxysterol ligands and elucidation of their enzymatic origins are topics of active investigation. Except for 24, 25-epoxysterols, most oxysterols arise from cholesterol by autoxidation or by specific microsomal or mitochondrial oxidations, usually involving cytochrome P-450 species. Oxysterols are variously metabolized to esters, bile acids, steroid hormones, cholesterol, or other sterols through pathways that may differ according to the type of cell and mode of experimentation (in vitro, in vivo, cell culture). Reliable measurements of oxysterol levels and activities are hampered by low physiological concentrations (approximately 0.01-0.1 microM plasma) relative to cholesterol (approximately 5,000 microM) and by the susceptibility of cholesterol to autoxidation, which produces artifactual oxysterols that may also have potent activities. Reports describing the occurrence and levels of oxysterols in plasma, low-density lipoproteins, various tissues, and food products include many unrealistic data resulting from inattention to autoxidation and to limitations of the analytical methodology. Because of the widespread lack of appreciation for the technical difficulties involved in oxysterol research, a rigorous evaluation of the chromatographic and spectroscopic methods used in the isolation, characterization, and quantitation of oxysterols has been included. This review comprises a detailed and critical assessment of current knowledge regarding the formation, occurrence, metabolism, regulatory properties, and other activities of oxysterols in mammalian systems.
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Affiliation(s)
- G J Schroepfer
- Departments of Biochemistry, Rice University, Houston, Texas, USA.
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Kuroki S, Naito T, Chijiiwa K, Tanaka M. Effects of cholestyramine on hepatic cholesterol 7alpha-hydroxylase and serum 7alpha-hydroxycholesterol in the hamster. Lipids 1999; 34:817-23. [PMID: 10529092 DOI: 10.1007/s11745-999-0428-y] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
Cholestyramine increases activities of hepatic cholesterol 7alpha-hydroxylase and serum levels of 7alpha-hydroxycholesterol. To examine if serum 7alpha-hydroxycholesterol levels parallel with enzyme activity, 0, 0.5, 1, 2, 4, and 10% of cholestyramine was administered to female golden Syrian hamsters for 28 d in the dose-dependent study, and 2% cholestyramine for 0, 1, 3, 7, 14, 21, and 28 d in the time-dependent study. In the dose-dependent study, hepatic and serum cholesterol levels were significantly decreased dose-dependently when more than 0.5% of cholestyramine was fed for 28 d. Cholestyramine increased the cholesterol 7alpha-hydroxylase activity in a dose-dependent manner, while the serum 7alpha-hydroxycholesterol level was essentially unchanged. No correlation was found between the serum level and the hepatic enzyme activity. In the time-dependent study, hepatic and serum cholesterol levels markedly decreased when 2% cholestyramine was fed for longer than 3 d. The serum triglyceride level increased significantly for the first 7 d and then decreased. Cholesterol 7alpha-hydroxylase activity increased significantly as early as day 1, reached maximum activity level on day 7, and then kept the significantly high values until day 28. The serum 7alpha-hydroxycholesterol level significantly increased for the first 7 d and decreased to the pretreatment level thereafter. 7Alpha-hydroxycholesterol levels significantly correlated with serum cholesterol and triglyceride levels. We conclude that the serum 7alpha-hydroxycholesterol level does not always reflect the activity of hepatic cholesterol 7alpha-hydroxylase, when cholesterol metabolism is severely disturbed by cholestyramine.
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Affiliation(s)
- S Kuroki
- Department of Surgery I, Kyushu University Faculty of Medicine, Fukuoka, Japan.
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Abstract
This article provides a review of the pathways through which cholesterol is degraded to bile acids. Regulation of key enzymes in the bile acid biosynthestic pathways is discussed. The important role of these pathways in the maintenance of cholesterol homeostasis and the possible therapeutic implications for the treatment of hypercholesterolemia are emphasized.
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Affiliation(s)
- Z R Vlahcevic
- Division of Gastroenterology, Medical College of Virginia, Virginia Commonwealth University, Richmond, USA
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