1
|
Martínez-García J, Molina M, Odriozola L, Molina A, González-Aseguinolaza G, Weber ND, Smerdou C. A minimal bile salt excretory pump promoter allows bile acid-driven physiological regulation of transgene expression from a gene therapy vector. Cell Biosci 2022; 12:79. [PMID: 35641984 PMCID: PMC9158313 DOI: 10.1186/s13578-022-00803-9] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2021] [Accepted: 04/26/2022] [Indexed: 01/23/2023] Open
Abstract
Background Bile acid (BA) homeostasis is mainly regulated by bile salt excretory pump (BSEP), a hepatocyte transporter that transfers BAs to the bile. BSEP expression is regulated by BA levels through activation of farnesoid X receptor transcription factor, which binds to the inverted repeat (IR-1) element in the BSEP promoter. Gene therapy of cholestatic diseases could benefit from using vectors carrying endogenous promoters physiologically regulated by BAs, however their large size limits this approach, especially when using adeno-associated viral vector (AAV) vectors. Results We evaluated the functionality and BA-mediated regulation of minimal versions of human and mouse BSEP promoters containing IR-1 using AAV vectors expressing luciferase. Unexpectedly, a minimal mouse BSEP promoter (imPr) showed higher BA-mediated expression and inducibility than a minimal human promoter (ihPr) or than full-length BSEP promoters in human hepatic cells. In addition, in mice receiving an AAV8 vector carrying imPr promoter-driven luciferase expression was efficiently regulated by administration of a BA-enriched diet. Interestingly, this vector also expressed significantly higher luciferase levels in Abcb4−/− mice, which have high levels of BAs, compared to wild type mice, or to mice receiving a vector containing the luciferase gene downstream of the constitutive alpha-1 antitrypsin promoter. In contrast, the AAV vector containing ihPr showed very low luciferase expression with no inducibility. Finally, we optimized imPr by adding three IR-1 repeats at its 5′ end. This new promoter provided higher levels of luciferase than imPr both in vitro and in vivo. Conclusions The imPr could represent a useful tool for gene therapy approaches in which physiological BA regulation is desired.
Supplementary Information The online version contains supplementary material available at 10.1186/s13578-022-00803-9.
Collapse
Affiliation(s)
- Javier Martínez-García
- Division of Gene Therapy and Regulation of Gene Expression, Cima Universidad de Navarra, Av. Pio XII 55, 31008, Pamplona, Spain
| | - Manuela Molina
- Division of Gene Therapy and Regulation of Gene Expression, Cima Universidad de Navarra, Av. Pio XII 55, 31008, Pamplona, Spain
| | - Leticia Odriozola
- Division of Gene Therapy and Regulation of Gene Expression, Cima Universidad de Navarra, Av. Pio XII 55, 31008, Pamplona, Spain
| | - Angie Molina
- Division of Gene Therapy and Regulation of Gene Expression, Cima Universidad de Navarra, Av. Pio XII 55, 31008, Pamplona, Spain
| | - Gloria González-Aseguinolaza
- Division of Gene Therapy and Regulation of Gene Expression, Cima Universidad de Navarra, Av. Pio XII 55, 31008, Pamplona, Spain.,Instituto de Investigación Sanitaria de Navarra (IdISNA), Pamplona, Spain.,Vivet Therapeutics S.L., Calle Arcadio María Larraona, 1 - 2ª planta, 31008, Pamplona, Spain
| | - Nicholas D Weber
- Vivet Therapeutics S.L., Calle Arcadio María Larraona, 1 - 2ª planta, 31008, Pamplona, Spain.
| | - Cristian Smerdou
- Division of Gene Therapy and Regulation of Gene Expression, Cima Universidad de Navarra, Av. Pio XII 55, 31008, Pamplona, Spain. .,Instituto de Investigación Sanitaria de Navarra (IdISNA), Pamplona, Spain.
| |
Collapse
|
2
|
Gillard BK, Rodriguez PJ, Fields DW, Raya JL, Lagor WR, Rosales C, Courtney HS, Gotto AM, Pownall HJ. Streptococcal serum opacity factor promotes cholesterol ester metabolism and bile acid secretion in vitro and in vivo. Biochim Biophys Acta Mol Cell Biol Lipids 2015; 1861:196-204. [PMID: 26709142 DOI: 10.1016/j.bbalip.2015.12.006] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2015] [Revised: 11/16/2015] [Accepted: 12/11/2015] [Indexed: 11/15/2022]
Abstract
Plasma high density lipoprotein-cholesterol (HDL-C) concentrations negatively correlate with atherosclerotic cardiovascular disease. HDL is thought to have several atheroprotective functions, which are likely distinct from the epidemiological inverse relationship between HDL-C levels and risk. Specifically, strategies that reduce HDL-C while promoting reverse cholesterol transport (RCT) may have therapeutic value. The major product of the serum opacity factor (SOF) reaction versus HDL is a cholesteryl ester (CE)-rich microemulsion (CERM), which contains apo E and the CE of ~400,000 HDL particles. Huh7 hepatocytes take up CE faster when delivered as CERM than as HDL, in part via the LDL-receptor (LDLR). Here we compared the final RCT step, hepatic uptake and subsequent intracellular processing to cholesterol and bile salts for radiolabeled HDL-, CERM- and LDL-CE by Huh7 cells and in vivo in C57BL/6J mice. In Huh7 cells, uptake from LDL was greater than from CERM (2-4X) and HDL (5-10X). Halftimes for [(14)C]CE hydrolysis were 3.0±0.2, 4.4±0.6 and 5.4±0.7h respectively for HDL, CERM and LDL-CE. The fraction of sterols secreted as bile acids was ~50% by 8h for all three particles. HDL, CERM and LDL-CE metabolism in mice showed efficient plasma clearance of CERM-CE, liver uptake and metabolism, and secretion as bile acids into the gall bladder. This work supports the therapeutic potential of the SOF reaction, which diverts HDL-CE to the LDLR, thereby increasing hepatic CE uptake, and sterol disposal as bile acids.
Collapse
Affiliation(s)
- Baiba K Gillard
- The Laboratory of Atherosclerosis and Lipoprotein Research, Houston Methodist Research Institute, 6670 Bertner St., Houston, TX 77030, USA.
| | - Perla J Rodriguez
- The Laboratory of Atherosclerosis and Lipoprotein Research, Houston Methodist Research Institute, 6670 Bertner St., Houston, TX 77030, USA.
| | - David W Fields
- The Laboratory of Atherosclerosis and Lipoprotein Research, Houston Methodist Research Institute, 6670 Bertner St., Houston, TX 77030, USA.
| | - Joe L Raya
- Department of Medicine, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA.
| | - William R Lagor
- Department of Molecular Physiology and Biophysics, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA.
| | - Corina Rosales
- The Laboratory of Atherosclerosis and Lipoprotein Research, Houston Methodist Research Institute, 6670 Bertner St., Houston, TX 77030, USA.
| | - Harry S Courtney
- University of Tennessee Health Science Center, 956 Court Avenue Room H300A, Memphis, TN 38163 USA.
| | - Antonio M Gotto
- The Laboratory of Atherosclerosis and Lipoprotein Research, Houston Methodist Research Institute, 6670 Bertner St., Houston, TX 77030, USA; Department of Medicine, Weill Cornell Medical College, 1305 York Ave., New York, NY 10021, USA.
| | - Henry J Pownall
- The Laboratory of Atherosclerosis and Lipoprotein Research, Houston Methodist Research Institute, 6670 Bertner St., Houston, TX 77030, USA; Department of Medicine, Weill Cornell Medical College, 1305 York Ave., New York, NY 10021, USA.
| |
Collapse
|
3
|
Zollner G, Marschall HU, Wagner M, Trauner M. Role of nuclear receptors in the adaptive response to bile acids and cholestasis: pathogenetic and therapeutic considerations. Mol Pharm 2006; 3:231-51. [PMID: 16749856 DOI: 10.1021/mp060010s] [Citation(s) in RCA: 249] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Cholestasis results in intrahepatic accumulation of cytotoxic bile acids which cause liver injury ultimately leading to biliary fibrosis and cirrhosis. Cholestatic liver damage is counteracted by a variety of intrinsic hepatoprotective mechanisms. Such defense mechanisms include repression of hepatic bile acid uptake and de novo bile acid synthesis. Furthermore, phase I and II bile acid detoxification is induced rendering bile acids more hydrophilic. In addition to "orthograde" export via canalicular export systems, these compounds are also excreted via basolateral "alternative" export systems into the systemic circulation followed by renal elimination. Passive glomerular filtration of hydrophilic bile acids, active renal tubular secretion, and repression of tubular bile acid reabsorption facilitate renal bile acid elimination during cholestasis. The underlying molecular mechanisms are mediated mainly at a transcriptional level via a complex network involving nuclear receptors and other transcription factors. So far, the farnesoid X receptor FXR, pregnane X receptor PXR, and vitamin D receptor VDR have been identified as nuclear receptors for bile acids. However, the intrinsic adaptive response to bile acids cannot fully prevent liver injury in cholestasis. Therefore, additional therapeutic strategies such as targeted activation of nuclear receptors are needed to enhance the hepatic defense against toxic bile acids.
Collapse
Affiliation(s)
- Gernot Zollner
- Laboratory of Experimental and Molecular Hepatology, Division of Gastroenterology and Hepatology, Department of Internal Medicine, Medical University Graz, Austria, and Karolinska University Hospital Huddinge, Stockholm, Sweden
| | | | | | | |
Collapse
|
4
|
Cater MA, La Fontaine S, Shield K, Deal Y, Mercer JFB. ATP7B mediates vesicular sequestration of copper: insight into biliary copper excretion. Gastroenterology 2006; 130:493-506. [PMID: 16472602 DOI: 10.1053/j.gastro.2005.10.054] [Citation(s) in RCA: 105] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/22/2005] [Accepted: 10/19/2005] [Indexed: 01/11/2023]
Abstract
BACKGROUND & AIMS The Wilson protein (ATP7B) regulates levels of systemic copper by excreting excess copper into bile. It is not clear whether ATP7B translocates excess intrahepatic copper directly across the canalicular membrane or sequesters this copper into exocytic vesicles, which subsequently fuse with canalicular membrane to expel their contents into bile. The aim of this study was to clarify the mechanism underlying ATP7B-mediated copper detoxification by investigating endogenous ATP7B localization in the HepG2 hepatoma cell line and its ability to mediate vesicular sequestration of excess intracellular copper. METHODS Immunofluorescence microscopy was used to investigate the effect of copper concentration on the localization of endogenous ATP7B in HepG2 cells. Copper accumulation studies to determine whether ATP7B can mediate vesicular sequestration of excess intracellular copper were performed using Chinese hamster ovary cells that exogenously expressed wild-type and mutant ATP7B proteins. RESULTS In HepG2 cells, elevated copper levels stimulated trafficking of ATP7B to pericanalicular vesicles and not to the canalicular membrane as previously reported. Mutation of an endocytic retrieval signal in ATP7B caused the protein to constitutively localize to vesicles and not to the plasma membrane, suggesting that a vesicular compartment(s) is the final trafficking destination for ATP7B. Expression of wild-type and mutant ATP7B caused Chinese hamster ovary cells to accumulate copper in vesicles, which subsequently undergo exocytosis, releasing copper across the plasma membrane. CONCLUSIONS This report provides compelling evidence that the primary mechanism of biliary copper excretion involves ATP7B-mediated vesicular sequestration of copper rather than direct copper translocation across the canalicular membrane.
Collapse
Affiliation(s)
- Michael A Cater
- Centre for Cellular and Molecular Biology, School of Biological and Chemical Sciences, Deakin University, Burwood, Australia
| | | | | | | | | |
Collapse
|
5
|
vanBerge-Henegouwen GP, Venneman NG, Portincasa P, Kosters A, van Erpecum KJ, Groen AK. Relevance of hereditary defects in lipid transport proteins for the pathogenesis of cholesterol gallstone disease. SCANDINAVIAN JOURNAL OF GASTROENTEROLOGY. SUPPLEMENT 2004:60-9. [PMID: 15696852 DOI: 10.1080/00855920410011022] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
In the formation of cholesterol gallstones, cholesterol hypersecretion into bile causing cholesterol supersaturation and crystallization appears to be the primary factor, with disturbed gallbladder and intestinal motility as secondary factors. Although intestinal uptake mechanisms have not yet been fully elucidated, the HDL receptor scavenger receptor B1 (SRB1) may be involved. Since HDL-cholesterol, both from the intestine and peripheral sources, is the preferred type of cholesterol for biliary secretion, increased HDL transport to the liver can also cause cholesterol hypersecretion in bile. In the hepatocyte, bile formation is regulated by several transmembrane proteins, all belonging to the ABC family. A change in the activity in one of these proteins can have a profound impact on biliary lipid secretion. The bile salt export pump (BSEP or ABCB11) regulates the excretion of bile salts into bile and mutations cause severe cholestasis. The second ABC transporter, ABCB4 (MDR3) regulates the secretion in bile of phosphatidylcholine (PC), while ABCG5/G8 is active in the excretion of cholesterol and sterols into bile. These transporters also facilitate transport of sterols back into the intestinal lumen. Mutations in either of these genes cause sitosterolaemia with increased absorption of plant sterols and cholesterol. Until now, evidence for a genetic background of human gallstone disease is mostly indirect and based on ethnic differences. Only two single gene defects are associated with gallstones. One is an ABCB4 mutation which causes a deficiency in biliary PC secretion and the other is a CYP7A1 mutation, the rate-limiting enzyme in the synthesis of bile salts from cholesterol in the liver. Recently, several common DNA polymorphisms in the ABCG8 gene were discovered that are associated with variations in plasma sterols, which could also influence biliary cholesterol secretion, but there is still a paucity of human studies.
Collapse
|
6
|
Abstract
Bile acids derived from cholesterol and oxysterols derived from cholesterol and bile acid synthesis pathways are signaling molecules that regulate cholesterol homeostasis in mammals. Many nuclear receptors play pivotal roles in the regulation of bile acid and cholesterol metabolism. Bile acids activate the farnesoid X receptor (FXR) to inhibit transcription of the gene for cholesterol 7alpha-hydroxylase, and stimulate excretion and transport of bile acids. Therefore, FXR is a bile acid sensor that protects liver from accumulation of toxic bile acids and xenobiotics. Oxysterols activate the liver orphan receptors (LXR) to induce cholesterol 7alpha-hydroxylase and ATP-binding cassette family of transporters and thus promote reverse cholesterol transport from the peripheral tissues to the liver for degradation to bile acids. LXR also induces the sterol response element binding protein-1c that regulates lipogenesis. Therefore, FXR and LXR play critical roles in coordinate control of bile acid, cholesterol, and triglyceride metabolism to maintain lipid homeostasis. Nuclear receptors and bile acid/oxysterol-regulated genes are potential targets for developing drug therapies for lowering serum cholesterol and triglycerides and treating cardiovascular and liver diseases.
Collapse
Affiliation(s)
- John Y L Chiang
- Department of Biochemistry and Molecular Pathology, Northeastern Ohio Universities College of Medicine, Rootstown, Ohio 44272, USA.
| |
Collapse
|
7
|
Jung D, Podvinec M, Meyer UA, Mangelsdorf DJ, Fried M, Meier PJ, Kullak-Ublick GA. Human organic anion transporting polypeptide 8 promoter is transactivated by the farnesoid X receptor/bile acid receptor. Gastroenterology 2002; 122:1954-66. [PMID: 12055601 DOI: 10.1053/gast.2002.33583] [Citation(s) in RCA: 108] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
BACKGROUND & AIMS OATP8 (gene symbol: SLC21A8) is a multispecific uptake system for organic anions, xenobiotics, and peptides expressed at the basolateral (sinusoidal) membrane of human hepatocytes. We investigated whether OATP8 gene expression is regulated by the nuclear receptors farnesoid X receptor/bile acid receptor (FXR/BAR; NR1H4), pregnane X receptor (PXR), or liver X receptor (LXR). METHODS OATP8 promoter function was studied in reporter assays. OATP8 expression in cells was quantitated by real-time polymerase chain reaction. RESULTS The bile acid chenodeoxycholic acid (CDCA), a ligand of FXR/BAR, but not clotrimazole or 25-hydroxycholesterol, ligands of PXR or LXR, respectively, induced OATP8 promoter activity. An inverted hexanucleotide repeat motif (IR-1 element) in the promoter sequence was shown by electrophoretic mobility shift assays to bind the FXR (9-cis-retinoic acid receptor [RXRalpha]) heterodimer. Targeted mutagenesis of the IR-1 element abolished inducibility of the OATP8 promoter by CDCA, confirming its role as a bile acid response element. CDCA treatment increased OATP8 messenger RNA levels in human hepatoma cells, suggesting a physiologic role for FXR-mediated OATP8 gene regulation. CONCLUSIONS OATP8 gene expression is regulated by bile acids via FXR/BAR. Induction of OATP8 could serve to maintain hepatic extraction of xenobiotics and peptides in conditions of increased intracellular bile acids.
Collapse
Affiliation(s)
- Diana Jung
- Division of Clinical Pharmacology and Toxicology, University Hospital, Zurich, Switzerland
| | | | | | | | | | | | | |
Collapse
|
8
|
Monte MJ, Badia MD, Serrano MA, Sacristan MP, Cassio D, Marin JJ. Predominance of human versus rat phenotype in the metabolic pathways for bile acid synthesis by hybrid WIF-B9 cells. BIOCHIMICA ET BIOPHYSICA ACTA 2001; 1534:45-55. [PMID: 11750886 DOI: 10.1016/s1388-1981(01)00175-5] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The rat hepatoma-human fibroblast hybrid cell line WIF-B9 stably exhibits the structural and functional characteristics of normal differentiated hepatocytes. The abilities of these cells to synthesize bile acids and amidate them with glycine and taurine were investigated. The release of bile acids into the culture media over 72 h was assessed by gas chromatography-mass spectrometry. WIF-B9 cells were able to synthesize bile acids (1.10+/-0.17 nmol/mg protein) but less efficiently than rat hepatocytes in primary culture (2.19+/-0.19 nmol/mg protein; P<0.01). The patterns of major bile acid species produced by both types of cells were also different. Cholic acid (CA; 72%) and beta-muricholic acid (19%) were the major bile acids produced by rat hepatocytes, while chenodeoxycholic acid (CDCA) accounted for only 4.5% of total bile acids. In contrast, muricholic acids were absent, while CA (62%) and CDCA (34%) were the most abundant bile acids synthesized by WIF-B9 cells. Using reverse transcription-polymerase chain reaction and gene- and species-specific primers for key enzymes involved in bile acid synthesis, the expression of human, but not rat, orthologues of CYP7A1, CYP27, CYP8B and CYP7B1 was found in WIF-B9 cells. Induction of cell stress by serum deprivation did not change the amount of total bile acids synthesized by these cells, but an inversion of the CA-to-CDCA ratio from 1.8 to 0.3 together with a marked increase in the proportion of intermediate metabolites related to the acidic pathway was found. Using 500 microM radiolabeled CA and 2 mM of taurine or glycine, the ability to amidate CA over 48 h was determined by high performance liquid chromatography. Rat hepatocytes conjugated more than 90% CA with either amino acid, whereas this ability was very poor (< 2%) in WIF-B9 cells. Regarding the expression of enzymes and the products of bile acid synthesis, it may be concluded that the human phenotype predominates over that of the rat in WIF-B9 cells. Moreover, these cells are almost completely unable to further conjugate primary bile acids, which facilitates the manipulation of these steroids in analytical procedures. These characteristics make WIF-B9 cells a suitable in vitro model to carry out studies on bile acid synthesis by 'human-like' metabolic pathways.
Collapse
|
9
|
Ananthanarayanan M, Balasubramanian N, Makishima M, Mangelsdorf DJ, Suchy FJ. Human bile salt export pump promoter is transactivated by the farnesoid X receptor/bile acid receptor. J Biol Chem 2001; 276:28857-65. [PMID: 11387316 DOI: 10.1074/jbc.m011610200] [Citation(s) in RCA: 555] [Impact Index Per Article: 24.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
The bile salt excretory pump (BSEP, ABCb11) is critical for ATP-dependent transport of bile acids across the hepatocyte canalicular membrane and for generation of bile acid-dependent bile secretion. Recent studies have demonstrated that the expression of this transporter is sensitive to the flux of bile acids through the hepatocyte, possibly at the level of transcription of the BSEP gene. To determine the mechanisms underlying the regulation of BSEP by bile acids, the promoter of the BSEP gene was cloned. The sequence of the promoter contained an inverted repeat (IR)-1 element (5'-GGGACA T TGATCCT-3') at base pairs -63/-50 consisting of two nuclear receptor half-sites organized as an inverted repeat and separated by a single nucleotide. This IR-1 element has been shown in several recent studies to serve as a binding site for the farnesoid X receptor (FXR), a nuclear receptor for bile acids. FXR activity requires heterodimerization with RXR alpha, and when bound by bile acids, the complex effectively regulates the transcription of several genes involved in bile acid homeostasis. Gel mobility shift assays demonstrated specific binding of FXR/RXR alpha heterodimers to the IR-1 element in the BSEP promoter. In HepG2 cells, co-transfection of FXR and RXR alpha is required to attain full transactivation of the BSEP promoter by bile acids. Two FXR transactivation-deficient mutants (an AF-2 deletion and a W469A point mutant) failed to transactivate, indicating that the effect of bile acids is FXR-dependent. Further, mutational analysis confirms that the FXR/RXR alpha heterodimer activates transcription through the IR-1 site in the human BSEP promoter. These results demonstrate a mechanism by which bile acids transcriptionally regulate the activity of the bile salt excretory pump, a critical component involved in the enterohepatic circulation of bile acids.
Collapse
MESH Headings
- ATP Binding Cassette Transporter, Subfamily B, Member 11
- ATP-Binding Cassette Transporters/genetics
- ATP-Binding Cassette Transporters/metabolism
- Alitretinoin
- Amino Acid Substitution
- Base Sequence
- Bile Acids and Salts/metabolism
- Binding Sites
- Carcinoma, Hepatocellular
- DNA Primers
- DNA-Binding Proteins/genetics
- DNA-Binding Proteins/metabolism
- Gene Expression Regulation/drug effects
- Genes, Reporter
- Hepatocytes/metabolism
- Humans
- Liver Neoplasms
- Molecular Sequence Data
- Mutagenesis
- Mutagenesis, Site-Directed
- Point Mutation
- Promoter Regions, Genetic
- Receptors, Cytoplasmic and Nuclear/metabolism
- Receptors, Retinoic Acid/genetics
- Receptors, Retinoic Acid/metabolism
- Recombinant Proteins/metabolism
- Retinoid X Receptors
- Sequence Deletion
- TATA Box
- Transcription Factors/genetics
- Transcription Factors/metabolism
- Transcription, Genetic
- Transcriptional Activation/drug effects
- Transfection
- Tretinoin/pharmacology
- Tumor Cells, Cultured
Collapse
Affiliation(s)
- M Ananthanarayanan
- Laboratory of Developmental and Molecular Hepatology, Department of Pediatrics, The Mount Sinai Medical Center, New York, New York 10029, USA.
| | | | | | | | | |
Collapse
|
10
|
Lyons MA, Brown AJ. Metabolism of an oxysterol, 7-ketocholesterol, by sterol 27-hydroxylase in HepG2 cells. Lipids 2001; 36:701-11. [PMID: 11521968 DOI: 10.1007/s11745-001-0775-8] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
7-Ketocholesterol (7K) is a quantitatively important oxysterol in both atherosclerotic lesions and macrophage foam cells. We reported recently that radiolabeled 7K delivered to rodents in a modified lipoprotein or chylomicron remnant-like emulsion, both cleared predominantly by the liver, was rapidly excreted into the intestine as water-soluble products, presumably bile acids. Herein, we aimed to elucidate the early or initial reactions in 7K metabolism. The hypothesis was tested that sterol 27-hydroxylase, a mitochondrial cytochrome P450 and the first enzyme of the acidic bile acid pathway, is responsible for the initial metabolism of 7K by HepG2 cells, a human hepatoblastoma cell-line. The 27-hydroxylated product of 7K (27OH-7K) was shown to be the initial, lipid-soluble product of 7K metabolism. It was produced in mitochondrial incubations and whole cells and was readily released into the media from cells. Intact cells generated metabolites of 7K that had undergone conversion from lipid-soluble precursors to water-soluble products rapidly and extensively. Their production was ablated with cyclosporin A, a sterol 27-hydroxylase inhibitor. Furthermore, we demonstrated the effectiveness of two novel selective inhibitors of this enzyme, GW273297X and GI268267X. These inhibitors also ablated the production of water-soluble products by cells; and the inhibitor of choice, GW273297X, decreased the production of 27OH-7K in mitochondrial preparations. This is the first study to demonstrate that sterol 27-hydroxylase plays an important role in the metabolism of oxysterols such as 7K in liver cells.
Collapse
Affiliation(s)
- M A Lyons
- Cell Biology Group, Heart Research Institute, Sydney, New South Wales, Australia
| | | |
Collapse
|
11
|
Ellis E, Roeb E, Marschall H. Primary cultures of human hepatocytes but not HepG2 hepatoblastoma cells are suitable for the study of glycosidic conjugation of bile acids. BIOCHIMICA ET BIOPHYSICA ACTA 2001; 1530:155-61. [PMID: 11239818 DOI: 10.1016/s1388-1981(00)00179-7] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
To define the role of glycosidic conjugation of bile acids in humans, an in vitro model system is desirable. We studied the formation of glycosidic conjugates of bile acids in primary cultures of human hepatocytes, isolated from organ donor liver, and the human hepatoblastoma cell line, HepG2. Cells were incubated with 100 microM bile acids (chenodeoxycholic, CDCA; hyodeoxycholic, HDCA; and isoursodeoxycholic acids, isoUDCA) and 1-2 mM uridine diphosphoglycosides (UDP-glucose, UDP-Glc; UDP-glucuronic acid, UDP-GlcA, and UDP-N-acetylglucosamine, UDP-GlcNAc), and octyl glucoside. Media were analysed by electrospray-/gas chromatography-mass spectrometry and electrospray with collision induced dissociation. Primary cultures of human hepatocytes formed glycosidic bile acid conjugates with UDP-sugars (6alpha-Glc-HDCA, 6alpha-GlcA-HDCA, and 7beta-GlcNAc-isoUDCA) and octyl glucoside as sugar donors (3alpha-Glc-CDCA). HDCA was completely metabolised to either Glc-HDCA, a compound yet not found in vivo, or GlcA-HDCA. No glycosidic bile acid conjugate was found in media from experiments with HepG2. Thus, primary cultures of human hepatocytes, but not HepG2, are suitable in vitro systems for the study of glycosidic bile acid conjugation reactions.
Collapse
Affiliation(s)
- E Ellis
- Karolinska Institutet, Department of Medicine, Huddinge University Hospital, Stockholm, Sweden
| | | | | |
Collapse
|
12
|
Whitfield PD, Clayton PT, Muller DP. Effect of intravenous lipid emulsions on hepatic cholesterol metabolism. J Pediatr Gastroenterol Nutr 2000; 30:538-46. [PMID: 10817285 DOI: 10.1097/00005176-200005000-00014] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/10/2022]
Abstract
BACKGROUND Total parenteral nutrition offers the chance of survival to children who have had extensive gut resections or gut failure. However, in infants it is often associated with serious complications including cholestatic liver disease. The causes of these complications remain unclear, although it has been suggested that the lipid emulsions used in total parenteral nutrition may be responsible. METHODS An in vitro system was developed to study the effect of lipid emulsions on hepatic cholesterol metabolism using cultured hepatocytes. RESULTS Incubations of Hep G2 cells with medium containing Intralipid (Pharmacia and Upjohn, Milton Keynes, UK) demonstrated that the fat emulsion mediated a powerful dose-dependent but reversible inhibition of cholesterol uptake. In addition Intralipid was shown to stimulate the efflux of cholesterol from Hep G2 cells. The component or components of the Intralipid responsible for these effects and the mechanism by which they act remain to be established. CONCLUSIONS Intravenous lipid emulsions may interfere with hepatic cholesterol metabolism in vivo. This may have implications for the development of total parenteral nutrition-associated cholestasis in neonates.
Collapse
Affiliation(s)
- P D Whitfield
- Biochemistry, Endocrinology, and Metabolism Unit, Institute of Child Health, University College London, United Kingdom
| | | | | |
Collapse
|
13
|
Zoltowska M, Delvin EE, Paradis K, Seidman E, Levy E. Bile duct cells: a novel in vitro model for the study of lipid metabolism and bile acid production. THE AMERICAN JOURNAL OF PHYSIOLOGY 1999; 276:G407-14. [PMID: 9950814 DOI: 10.1152/ajpgi.1999.276.2.g407] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/10/2023]
Abstract
Immortalized bile duct cells (BDC), derived from transgenic mice harboring the SV40 thermosensitive immortalizing mutant gene ts458, were utilized to investigate the role of the biliary epithelium in lipid and sterol metabolism. This cell model closely resembles the in vivo situation because it expresses the specific phenotypic marker cytokeratin 19 (CK-19), exhibits the formation of bile duct-like structures, and displays well-formed microvilli projected from the apical side to central lumen. The BDC were found to incorporate [14C]oleic acid (in nmol/mg protein) into triglycerides (121 +/- 6), phospholipids (PL; 59 +/- 3), and cholesteryl ester (16 +/- 1). The medium lipid content represented 5.90 +/- 0.16% (P < 0. 005) of the total intracellular production, indicating a limited lipid export capacity. Analysis of PL composition demonstrated the synthesis of all classes of polar lipids, with phosphatidylcholine and phosphatidylethanolamine accounting for 60 +/- 1 and 24 +/- 1%, respectively, of the total. Differences in PL distribution were apparent between cells and media. Substantial cholesterol synthesis was observed in BDC, as determined by the incorporation of [14C]acetate suggesting the presence of hydroxymethylglutaryl-CoA (HMG-CoA) reductase, the rate-limiting enzyme in the cholesterol biosynthetic pathway. With the use of [14C]acetate and [14C]cholesterol as precursors, both tauro- and glycoconjugates of bile acids were synthesized, indicating the presence of cholesterol 7alpha- and 26R-hydroxylases, the key enzymes involved in bile acid formation. The transport of bile acids was not limited, as shown by their marked accumulation in the medium (>6-fold of cell content). HMG-CoA reductase (53.0 +/- 6.7), cholesterol 7alpha-hydroxylase (15. 5 +/- 0.5), and acyl-CoA:cholesterol acyltransferase (ACAT; 201.7 +/- 10.2) activities (in pmol. min-1. mg protein-1) were present in the microsomal fractions. Our data show that biliary epithelial cells actively synthesize lipids and may directly contribute bile acids to the biliary fluid in vivo. This BDC line thus represents an efficient experimental tool to evaluate biliary epithelium sterol metabolism and to study biliary physiology.
Collapse
Affiliation(s)
- M Zoltowska
- Departments of Nutrition, Biochemistry, and Pediatrics, Centre de Recherche, Hôpital Ste-Justine, Université de Montréal, Montreal, Quebec, Canada H3T 1C5
| | | | | | | | | |
Collapse
|
14
|
Martin KO, Reiss AB, Lathe R, Javitt NB. 7 alpha-hydroxylation of 27-hydroxycholesterol: biologic role in the regulation of cholesterol synthesis. J Lipid Res 1997. [DOI: 10.1016/s0022-2275(20)37229-1] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
|
15
|
Clerc T, Sbarra V, Domingo N, Rault JP, Diaconescu N, Moutardier V, Hasselot N, Lafont H, Jadot G, Laruelle C, Chanussot F. Differences in hypolipidaemic effects of two statins on Hep G2 cells or human hepatocytes in primary culture. Br J Pharmacol 1996; 118:1862-8. [PMID: 8842455 PMCID: PMC1909841 DOI: 10.1111/j.1476-5381.1996.tb15615.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
1. The objective of this study was to compare in cultured human hepatocytes or Hep G2 cells, changes in the fate of unesterified low density lipoprotein (LDL)-cholesterol induced by crilvastatin, a new cholesterol lowering drug and a reference statin, simvastatin. 2. The experiments were carried out for 20 h, each well contained 4.2 x 10(5)/cm2 Hep G2 cells or 0.5 x 10(5)/Cm2 human hepatocytes, 130 microM ursodeoxycholate, 0.68 microCi or 1.59 microCi unesterified human [14C]-LDL-cholesterol, crilvastatin or simvastatin at 0 or 50 microM (both cell types) or 300 microM (Hep-G2 cells). Incubation with the two drugs resulted in increased amounts of unesterified [14C]-LDL-cholesterol taken by the two cell types, compared to control. 3. Crilvastatin 50 microM led to significantly higher quantities of [14C]-glyco-tauro-conjugated bile salts, compared to simvastatin. Statins reduced the apo B100 level secreted by the two cell types (simvastatin) or human hepatocytes (crilvastatin). Crilvastatin enhanced both the level of apo A1 secreted by the Hep G2 cells and the level of APF, a high density lipoprotein (HDL) and biliary apoprotein. 4. Crilvastatin not only acts by stimulating LDL-cholesterol uptake by hepatocytes, but also by enhancing the catabolism of LDL-cholesterol in bile salts and probably by stimulating HDL and/or bile component secretion. Such a mechanism was not previously described for HMG CoA reductase inhibitors. Our results on APF show that this apoprotein could be considered also as an indicator of changes in bile and/or HDL compartments. 5. The human hepatocyte model appeared to be a suitable and relevant model in the pharmacological-metabolic experiments carried out in this study. It led to more consistent data than those obtained with Hep G2 cells.
Collapse
Affiliation(s)
- T Clerc
- INSERM, Unité 130, Marseille, France
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
16
|
Sauter G, Fischer S, Pahernik S, Koebe HG, Paumgartner G. Formation of cholic acid and chenodeoxycholic acid from 7 alpha-hydroxycholesterol and 27-hydroxycholesterol by primary cultures of human hepatocytes. BIOCHIMICA ET BIOPHYSICA ACTA 1996; 1300:25-9. [PMID: 8608157 DOI: 10.1016/0005-2760(95)00231-6] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
It has been suggested that chenodeoxycholic acid is preferentially formed by the alternative or 'acidic' pathway of bile acid biosynthesis starting with 27-hydroxylation of cholesterol, while cholic acid is derived from 7 alpha-hydroxycholesterol which initiates the 'neutral' pathway. We have studied bile acid formation from each of these precursors using human hepatocytes cultured in a novel sandwich collagen configuration. Culture supernatants were analyzed using capillary gas chromatography and gas chromatography-mass spectrometry. 27-Hydroxycholesterol and 7 alpha-hydroxycholesterol were both found to be efficiently converted to cholic acid as well as chenodeoxycholic acid. Analysis of acidic intermediates after addition of 7 alpha-hydroxycholesterol to the cultures revealed a significant increase of side-chain oxygenated C24- and C27-steroids with a 3-oxo-7 alpha-hydroxy-delta 4-ring structure. These data indicate that (i) the 'neutral' pathway is connected to the 'acidic' pathway by side-chain oxidation of C27-steroids with a 3-oxo-7 alpha-hydroxy-delta 4-ring structure and that (ii) the relative formation of cholic acid and chenodeoxycholic acid is regulated by metabolic events distal to the initial hydroxylation at either position 7 or position 27 of the cholesterol molecule.
Collapse
Affiliation(s)
- G Sauter
- Department of Medicine II, Klinikum Grosshadern, University of Munich, Germany
| | | | | | | | | |
Collapse
|
17
|
Abstract
Bile acids, which are synthesized in the liver from cholesterol, are important in the production of bile flow, excretion of cholesterol, and intestinal digestion and absorption of fats and fat-soluble vitamins. Increases and/or alterations in concentrations of bile acids in serum are specific and sensitive indicators of hepatobiliary disorders. Synthesis of bile acids in hepatocytes involves steps in endoplasmic reticulum, cytosol, mitochondria, and peroxisomes. Other important hepatocellular processes involving bile acids include active uptake by the basolateral membrane, intracellular transport, P-450-mediated conjugations and hydroxylations, and canalicular secretion. Hydrophobic bile acids produce hepatotoxicity in vivo and in vitro. In experimental and epidemiologic studies, some of these forms have been identified as causative agents in the development of colon and liver (experimental only) cancer. Conversely, several hydrophilic forms, primarily ursodeoxycholic acid, have demonstrated cytoprotective properties in a variety of clinical and experimental hepatobiliary diseases and disorders. Because bile acids can have dramatically different properties and effects, determination of mechanisms of action of these compounds has become an active area of research. Primary isolated hepatocytes provide an opportunity to investigate bile acid-related functions and effects in well-designed, carefully controlled studies. Short-term cultures have been used to study a variety of issues related to bile acids, including cytotoxicity, synthesis, and hepatocellular processing. With these systems, however, many functions of mature hepatocytes, including those pertaining to bile acids, can be lost when cultures are maintained for more than several days. Recent developments in culture techniques permit long-term maintenance of functionally stable, differentiated cells. Pertaining to bile acid research, these systems remain to be fully characterized but, in appropriate situations, they should provide important alternatives to in vivo studies and short-term in vitro assays.
Collapse
Affiliation(s)
- M B Thompson
- Laboratory of Experimental Pathology, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709, USA
| |
Collapse
|
18
|
Crestani M, Stroup D, Chiang JY. Hormonal regulation of the cholesterol 7 alpha-hydroxylase gene (CYP7). J Lipid Res 1995. [DOI: 10.1016/s0022-2275(20)39723-6] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
|
19
|
Cooper AD, Craig WY, Taniguchi T, Everson GT. Characteristics and regulation of bile salt synthesis and secretion by human hepatoma HepG2 cells. Hepatology 1994; 20:1522-31. [PMID: 7982652 DOI: 10.1002/hep.1840200623] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Bile salt uptake, synthesis and secretion by the human hepatoma-derived cell line HepG2 were studied. The cells transported and secreted bile salts largely by means of passive mechanisms. The cells synthesized and secreted the normal human primary bile salts. The ratio of cholate to chenodeoxycholate was 1.5:1. The degree of conjugation, about 35%, was lower than normal, and the glycine-to-taurine ratio was abnormal (4.5:1). This was not due to amino acid deficiency in the medium. Contrary to the report of others, little 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholestan-26-oic acid was secreted. This was confirmed by gas chromatography-mass spectrometry. The total rate of synthesis was about 33% that of normal liver. The specific activity of bile salts synthesized from [3H]mevalonate was about 20 times higher than that of the cellular cholesterol derived from the same precursor. The regulation of bile salt synthesis by two compounds that could alter the precursor pool of cholesterol was studied. After a 24-hr incubation in serum-free medium, the compound 25(OH)cholesterol inhibited the rate of bile salt synthesis compared with control values, possibly by depleting the intracellular free cholesterol pool. Surprisingly, however, progesterone, which inhibits cholesterol esterification and should have expanded this pool, also inhibited bile salt synthesis under those conditions. The effect of these compounds on the level of mRNA for cholesterol 7 alpha-hydroxylase was also determined by Northern-blot analysis. The cholesterol 7 alpha-hydroxylase mRNA was 3.7 kb, similar to that in the rat. The incubation of cells in 25(OH)cholesterol or progesterone, as above, resulted in a decreased level of mRNA. The reduction was proportional to the reduction in bile salt synthesis, suggesting that these compounds act at a pretranslational level. Taken together, these results suggest that our particular subclone of HepG2 cells will be useful for studies of the regulation of bile salt synthesis, but not of transport, by human liver-derived tissue.
Collapse
Affiliation(s)
- A D Cooper
- Department of Medicine, Stanford University School of Medicine, California 94305
| | | | | | | |
Collapse
|
20
|
|
21
|
Human hepatoblastoma cells (HepG2) and rat hepatoma cells are defective in important enzyme activities in the oxidation of the C27 steroid side chain in bile acid formation. J Lipid Res 1993. [DOI: 10.1016/s0022-2275(20)35346-3] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
|
22
|
Cholesterol and 27-hydroxycholesterol 7 alpha-hydroxylation: evidence for two different enzymes. J Lipid Res 1993. [DOI: 10.1016/s0022-2275(20)39981-8] [Citation(s) in RCA: 76] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
|
23
|
Cohen LH, Griffioen M, van Roermund CW, Wanders RJ. Subcellular localization of squalene synthase in human hepatoma cell line Hep G2. BIOCHIMICA ET BIOPHYSICA ACTA 1992; 1126:114-8. [PMID: 1318747 DOI: 10.1016/0005-2760(92)90224-j] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Using the Hep G2 cell line as a model for the human hepatocyte the question was studied whether Hep G2-peroxisomes could be able to synthesize cholesterol. Hep G2 cell homogenates were applied to density gradient centrifugation on Nycodenz, resulting in good separation between the organelles. The different organelle fractions were characterized by assaying the following marker enzymes: catalase for peroxisomes, glutamate dehydrogenase for mitochondria and esterase for endoplasmic reticulum. Squalene synthase activity was not detectable in the peroxisomal fraction. Incubation of Hep G2 cells with U18666A, an inhibitor of the cholesterol synthesis at the site of oxidosqualene cyclase, together with heavy high density lipoprotein, which stimulates the efflux of cholesterol, led to a marked increase in the activity of squalene synthase as well as HMG-CoA reductase, whereas no significant effect on the marker enzymes was observed. Neither enzyme activity was detectable in the peroxisomal density gradient fraction, suggesting that in Hep G2-peroxisomes cholesterol synthesis from the water-soluble early intermediates of the pathway cannot take place. Both stimulated and non-stimulated cells gave rise to preparations where squalene synthase activity was comigrating with the reductase activity at the lower density side of the microsomal fraction; however, it was also present at the high density side of the microsomal peak, where reductase activity was not detected.
Collapse
Affiliation(s)
- L H Cohen
- TNO Institute for Ageing and Vascular Research, Gaubius Laboratory, Leiden, Netherlands
| | | | | | | |
Collapse
|
24
|
Kraft HG, Demosky SJ, Schumacher K, Brewer HB, Hoeg JM. Regulation of LDL receptor, apoB, and apoE protein and mRNA in Hep G2 cells. DNA Cell Biol 1992; 11:291-300. [PMID: 1605852 DOI: 10.1089/dna.1992.11.291] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
The regulation of low-density lipoprotein (LDL) receptor activity, protein synthesis, and cellular mRNA content was evaluated in the human hepatoma cell line Hep G2. Incubation of the cells with LDL led to a complete downregulation of LDL receptor mRNA and LDL receptor protein synthesis. This LDL regulation of the LDL receptor and its mRNA was both time- and concentration-dependent. In contrast to protein synthesis and cellular mRNA concentrations of the LDL receptor, which were reduced to undetectable levels by prolonged incubation in the presence of LDL, LDL receptor activity was reduced to only 44% of preincubation levels. These findings support the presence of a second metabolic pathway for LDL uptake in human hepatocytic cells. The effect of LDL on cellular LDL receptor expression was specific for LDL because incubation in the presence of HDL did not affect any of these study end points. The potential coordinate regulation of the expression of the LDL receptor with its principal ligands, apolipoproteins (apo) B and E, was also investigated. In contrast to the LDL receptor mRNA downregulation with LDL incubation, cellular apoB and apoE mRNA concentrations were not affected by either LDL or HDL. Secretion of apoB, however, was significantly increased by incubating Hep G2 cells with LDL. These findings indicate that, in contrast to LDL receptor which is regulated at the mRNA level, the ligands for the LDL receptor are regulated either co- or post-translationally.
Collapse
Affiliation(s)
- H G Kraft
- Molecular Disease Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892
| | | | | | | | | |
Collapse
|
25
|
Marchegiano P, Carubbi F, Tiribelli C, Amarri S, Stebel M, Lunazzi GC, Levy D, Bellentani S. Transport of sulfobromophthalein and taurocholate in the HepG2 cell line in relation to the expression of membrane carrier proteins. Biochem Biophys Res Commun 1992; 183:1203-8. [PMID: 1567398 DOI: 10.1016/s0006-291x(05)80318-3] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The transport of two different classes of organic anions (cholephilic dyes; the sulfobromophthalein, BSP, and bile acids; taurocholate, TC) was investigated in the HepG2 cell line. At 37 degrees C, BSP uptake was found to be biphasic with an apparent saturative curve in the concentration range between 0-6 microM followed by a linear component up to 18 microM. Kinetic constant determination showed an apparent Km of 26.6 +/- 3.1 microM and a Vmax of 5.64 +/- 0.82 nmol BSP.min-1.mg prot-1. At 4 degrees C, uptake was linear. By subtracting this latter component from the total uptake, a saturable, carrier mediated uptake was found with an apparent Km of 3.6 +/- 1.0 microM BSP and a Vmax of 0.37 +/- 0.04 nmol BSP.min-1.mg prot-1 (m +/- SEM, n = 6). These values were fully comparable with those found in freshly isolated male hepatocyte. Immunoblot analysis of HepG2 cell plasma membrane revealed the presence of bilitranslocase when tested against a monospecific antibody against this carrier molecule. On the contrary, TC uptake was linear up to concentration of 100 microM TC. No difference was observed in the presence or absence of Na+. Immunoprecipitation analysis showed the absence of the putative carrier of TC. These data indicate that the HepG2 cell line expresses a functioning bilitranslocase-mediated system. Conversely, carrier mediated bile acid uptake is absent in line with the lack of expression of the carrier protein.
Collapse
Affiliation(s)
- P Marchegiano
- Cattedra Gastroenterologia, University of Modena, Italy
| | | | | | | | | | | | | | | |
Collapse
|
26
|
|
27
|
Schwarz KB, Moore TJ, Willoughby RE, Wee SB, Vonderfecht SL, Yolken RH. Growth of group A rotaviruses in a human liver cell line. Hepatology 1990; 12:638-43. [PMID: 2170264 DOI: 10.1002/hep.1840120403] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Recent observations in children with rotavirus gastroenteritis and in infant mice given rotavirus vaccine by oral administration suggest that this well-known gastrointestinal pathogen may infect the liver. To examine this possibility, the susceptibility of Hep G2 cells to infection with a variety of rotavirus strains was tested. These cells were used because they are considered to be well differentiated and exhibit many liver-specific functions. The Hep G2 cells supported the growth of the simian strain rhesus rotavirus (MMU 18006), a strain currently being used in vaccine trails, but did not support the growth of any human strain (D, DS1, Price or ST3). The rhesus rotavirus infection was cytopathic and resulted in release of lactate dehydrogenase. Rhesus rotavirus growth in Hep G2 cells displayed trypsin-enhanced infectivity and was inhibited by pretreatment of cells with Arthrobacter ureafaciens neuraminidase but not with neuraminidase from Clostridium perfringens. Hep G2 cells were also permissive for another simian strain (SA11), a bovine strain (UK) and single gene substitution reassortants containing VP7 (the major outer capsid neutralization protein) from a human rotavirus strain and the remaining 10 genes from either rhesus rotavirus or UK. In general, UK and its reassortants produced lower levels of antigen than did rhesus rotavirus and its reassortants. Hep G2 cells and other hepatic cell lines may prove to be useful tools to explore the hepatotropic potential of wild-type rotaviruses and candidate vaccine strains.
Collapse
Affiliation(s)
- K B Schwarz
- Division of Pediatric Gastroenterology and Nutrition, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | | | | | | | | | | |
Collapse
|
28
|
|