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Export Pump (export + pump)
Kinds of Export Pump Selected AbstractsFunctional analysis of the rat bile salt export pump gene promoterFEBS JOURNAL, Issue 14 2002Regulation by bile acids, drugs, endogenous compounds The 5, flanking region of the bile salt export pump (Bsep) gene was systematically analysed to provide the basis for understanding the mechanisms which regulate Bsep transcription. In addition substrates and drugs were investigated for their ability to alter Bsep promoter activity. Bsep promoter function was restricted to hepatocyte derived HepG2 cells. The 5, deletional analysis revealed a biphasic shape of reporter gene activities, indicating a suppressive element between nucleotides ,800 and ,512. Two consensus sites for the farnesoid X receptor (FXR) were located at nucleotides ,473 and ,64. The latter was characterized as functionally active in bile acid-mediated feed-back regulation of Bsep transcription. Bsep promoter activity was reduced by rifampin and ,-estradiol. The anti-estrogen tamoxifen stimulated promoter activity. Dexamethasone, hydrocortisone and phenobarbital had no effect on Bsep promoter activity. In conclusion, the data suggest that transcriptional regulation of the Bsep gene can be modulated by a number of endogenous compounds and xenobiotics. FXR was a major regulatory factor, mediating bile acid feed-back stimulation of Bsep transcription. [source] Multidrug resistance,associated proteins are crucial for the viability of activated rat hepatic stellate cells,,HEPATOLOGY, Issue 2 2008Rebekka A. Hannivoort Hepatic stellate cells (HSCs) survive and proliferate in the chronically injured liver. ATP-binding cassette (ABC) transporters play a crucial role in cell viability by transporting toxic metabolites or xenobiotics out of the cell. ABC transporter expression in HSCs and its relevance to cell viability and/or activation have not been reported so far. The aim of this study was to investigate the expression, regulation, and function of multidrug resistance,associated protein (Mrp)-type and multidrug resistance protein (Mdr),type ABC transporters in activated rat HSCs. Rat HSCs were exposed to cytokines or oxidative stress. ABC transporter expression was determined by quantitative polymerase chain reaction and immunohistochemistry. HSCs were exposed to the Mdr inhibitors verapamil and PSC-833 and the Mrp inhibitor MK571. Mdr and Mrp transporter function was evaluated with flow cytometry. Apoptosis was determined by activated caspase-3 and acridine orange staining, and necrosis was determined by Sytox green nuclear staining. An in vivo model of carbon tetrachloride (CCl4),induced liver fibrosis was used. With respect to hepatocytes, activated HSCs expressed high levels of Mrp1 and comparable levels of Mrp3, Mrp4, Mdr1a, and Mdr1b but not the hepatocyte-specific transporters bile salt export pump, Mrp2, and Mrp6. Mrp1 protein staining correlated with desmin staining in livers from CCl4 -treated rats. Mrp1 expression increased upon activation of HSCs. Cytokines induced Mdr1b expression only. Oxidative stress was not a major regulator of Mdr and Mrp transporter expression. Activated HSCs became necrotic when exposed to the Mrp inhibitors. Conclusion: Activated HSCs contain relatively high levels of Mrp1. Mrp-type transporters are required for the viability of activated HSCs. Mrp-dependent export of endogenous metabolites is important for the survival of activated HSCs in chronic liver diseases. (HEPATOLOGY 2008.) [source] Linkage between a new splicing site mutation in the MDR3 alias ABCB4 gene and intrahepatic cholestasis of pregnancy,HEPATOLOGY, Issue 1 2007Gudrun Schneider Intrahepatic cholestasis of pregnancy (ICP) is defined as pruritus and elevated bile acid serum concentrations in late pregnancy. Splicing mutations have been described in the multidrug resistance p-glycoprotein 3 (MDR3, ABCB4) gene in up to 20% of ICP women. Pedigrees studied were not large enough for linkage analysis. Ninety-seven family members of a woman with proven ICP were asked about pruritus in earlier pregnancies, birth complications and symptomatic gallstone disease. The familial cholestasis type 1 (FIC1, ATP8B1) gene, bile salt export pump (BSEP, ABCB11) and MDR3 gene were analyzed in 55 relatives. We identified a dominant mode of inheritance with female restricted expression and a new intronic MDR3 mutation c.3486+5G>A resulting in a 54 bp (3465,3518) inframe deletion via cryptic splicing site activation. Linkage analysis of the ICP trait versus this intragenic MDR3 variant yielded a LOD score of 2.48. A Bayesian analysis involving MDR3, BSEP, FIC1 and an unknown locus gave a posterior probability of >0.9966 in favor of MDR3 as causative ICP locus. During the episode of ICP the median ,-glutamyl transpeptidase (,-GT) activity was 10 U/l (95% CI, 6.9 to 14.7 U/l) in the index woman. Four stillbirths were reported in seven heterozygous women (22 pregnancies) and none in five women (14 pregnancies) without MDR3 mutation. Symptomatic gallstone disease was more prevalent in heterozygous relatives (7/21) than in relatives without the mutation (1/34), (P = 0.00341). Conclusion: This study demonstrates that splicing mutations in the MDR3 gene can cause ICP with normal ,-GT and may be associated with stillbirths and gallstone disease. (HEPATOLOGY 2007;45:150,158.) [source] Hepatocellular carcinoma in ten children under five years of age with bile salt export pump deficiency,HEPATOLOGY, Issue 2 2006A. S. Knisely Hepatocellular carcinoma (HCC) is rare in young children. We attempted to see if immunohistochemical and mutational-analysis studies could demonstrate that deficiency of the canalicular bile acid transporter bile salt export pump (BSEP) and mutation in ABCB11, encoding BSEP, underlay progressive familial intrahepatic cholestasis (PFIC),or "neonatal hepatitis" suggesting PFIC,that was associated with HCC in young children. We studied 11 cases of pediatric HCC in the setting of PFIC or "neonatal hepatitis" suggesting PFIC. Archival liver were retrieved and immunostained for BSEP. Mutational analysis of ABCB11 was performed in leukocyte DNA from available patients and parents. Among the 11 nonrelated children studied aged 13-52 months at diagnosis of HCC, 9 (and a full sibling, with neonatal hepatitis suggesting PFIC, of a tenth from whom liver was not available) had immunohistochemical evidence of BSEP deficiency; the eleventh child did not. Mutations in ABCB11 were demonstrated in all patients with BSEP deficiency in whom leukocyte DNA could be studied (n = 7). These mutations were confirmed in the parents (n = 14). With respect to the other 3 children with BSEP deficiency, mutations in ABCB11 were demonstrated in all 5 parents in whom leukocyte DNA could be studied. Thirteen different mutations were found. In conclusion, PFIC associated with BSEP deficiency represents a previously unrecognized risk for HCC in young children. Immunohistochemical evidence of BSEP deficiency correlates well with demonstrable mutation in ABCB11. (HEPATOLOGY 2006;44:478,486.) [source] BSEP and MDR3 haplotype structure in healthy Caucasians, primary biliary cirrhosis and primary sclerosing cholangitisHEPATOLOGY, Issue 3 2004Christiane Pauli-Magnus Primary biliary cirrhosis (PBC) and primary sclerosing cholangitis (PSC) are characterized by a cholestatic pattern of liver damage, also observed in hereditary or acquired dysfunction of the canalicular membrane transporters bile salt export pump (BSEP, ABCB11) and multidrug resistance protein type 3 (MDR3, ABCB4). Controversy exists whether a genetically determined dysfunction of BSEP and MDR3 plays a pathogenic role in PBC and PSC. Therefore, 149 healthy Caucasian control individuals (control group) were compared to 76 PBC and 46 PSC patients with respect to genetic variations in BSEP and MDR3. Sequencing spanned ,10,000 bp including promoter and coding regions as well as 50,350 bp of flanking intronic regions. In all, 46 and 45 variants were identified in BSEP and MDR3, respectively. No differences between the groups were detected either in the total number of variants (BSEP: control group: 37, PBC: 37, PSC: 31; and MDR3: control group: 35; PBC: 32, PSC: 30), or in the allele frequency of the common variable sites. Furthermore, there were no significant differences in haplotype distribution and linkage disequilibrium. In conclusion, this study provides an analysis of BSEP and MDR3 variant segregation and haplotype structure in a Caucasian population. Although an impact of rare variants on BSEP and MDR3 function cannot be ruled out, our data do not support a strong role of BSEP and MDR3 genetic variations in the pathogenesis of PBC and PSC. (HEPATOLOGY 2004;39:779,791.) [source] Matrine improves 17,-ethinyl estradiol-induced acute cholestasis in ratsHEPATOLOGY RESEARCH, Issue 11 2009Ying Zhao Aim:, To explore the effects of matrine (MT) on acute intrahepatic cholestasis induced by 17,-ethinyl estradiol (EE) in rats. Methods:, Acute intrahepatic cholestasis in rats were induced by EE, and the effects of MT on acute intrahepatic cholestasis were explored and compared with ursodeoxycholic acid (UDCA) by serum biochemical determination and bile excretion experiments. Results:, The serum biochemical and bile biochemical results indicated that MT and UDCA had notable hepatoprotective effects by counteracting cholestasis induced by EE. The bile flow and the bile excretion of glycocholic acid (GC, a substrate of bile salt export pump [Bsep]), ketoprofen glucuronide (KPG) and rhodamine 123 (Rh123, a substrate of multidrug resistance protein 1 [MDR1]) decreased by EE, were significantly improved after administration of MT. Conclusion:, MT exhibited potential protection against EE-induced acute intrahepatic cholestasis. [source] Effect of genipin on the biliary excretion of cholephilic compounds in ratsHEPATOLOGY RESEARCH, Issue 6 2008Masaki Mikami Aim:, Genipin, a metabolite of geniposide, is reported to stimulate the insertion of multidrug resistance protein 2 (Mrp2) in the bile canalicular membrane, and to cause choleresis by increasing the biliary excretion of glutathione, which has been considered to be a substrate of Mrp2. In the present study, the effect of colchicine on the choleretic effect of genipin was investigated. The effect of genipin on the biliary excretion of the substrates of bile salt export pump and Mrp2 was also studied. Methods:, After bile duct cannulation into rats, genipin was administered at the rate of 0.2 ,mol/min/100 g, and the effect of colchicine pretreatment (0.2 mg/100 g) was examined. Metabolites of genipin in the bile were examined by a thin layer chromatography. Taurocholate (TC), sulfobromophthalein (BSP), and pravastatin were infused at the rate of 1.0, 0.2 and 0.3 ,mol/min/100 g, respectively, and the effect of genipin co-administration was examined. Results:, Genipin increased bile flow and the biliary glutathione excretion, and those increases were not inhibited by colchicine. The biliary excretion of genipin glucuronide was less than 10% of the genipin excreted into bile. The biliary excretion of TC, BSP, and pravastatin was unchanged by genipin co-administration. Conclusion:, It was indicated that colchicine-sensitive vesicular transport has no role on the genipin-induced insertion of Mrp2 to the canalicular membrane. Choleresis of genipin is considered to be mainly due to the increased biliary glutathione excretion by genipin, not by the biliary excretion of glucuronide. TC had no effect on the biliary glutathione excretion. [source] PFIC2 and ethnicity-specific bile salt export pump (BSEP, ABCB11) mutations: where do we go from here?LIVER INTERNATIONAL, Issue 6 2010Meenakshisundaram Ananthanarayanan No abstract is available for this article. [source] Analysis of bile acid-induced regulation of FXR target genes in human liver slicesLIVER INTERNATIONAL, Issue 1 2007Diana Jung Abstract Information about the role of nuclear receptors has rapidly increased over the last decade. However, details about their role in human are lacking. Owing to species differences, a powerful human in vitro system is needed. This study uses for the first time precision-cut human liver slices in the nuclear receptor field. The farnesoid X receptor (FXR) was chosen as a model. We were able to demonstrate that human liver slices efficiently take up bile acids and show a stable expression of a wide variety of genes relevant for bile acid metabolism, including bile acid transporters, cytochrome P450 enzymes and transcription factors. Treatment with chenodeoxycholate induced small heterodimer partner, bile salt export pump and p-glycoprotein, ABCB4 and repressed cholesterol 7, hydroxylase, hepatocyte nuclear factor (HNF)1, HNF4 and organic anion transporting peptide (OATP)1B1. OATP1B3, FXR, HNF3, and cytochrome P450 enzyme remained relatively constant. In contrast to what has been observed in mice and rat studies, SHP induction did not result in repression of sodium-dependent bile acid cotransporter expression. Further, regulation of genes seemed to be dependent on concentration and time. Taken together, the study shows that the use of liver slices is a powerful technique that enables to study nuclear receptors in the human liver. [source] Genetic cholestasis, causes and consequences for hepatobiliary transportLIVER INTERNATIONAL, Issue 5 2003Peter L. M. Jansen Abstract: Bile salts take part in an efficient enterohepatic circulation in which most of the secreted bile salts are reclaimed by absorption in the terminal ileum. In the liver, the sodium-dependent taurocholate transporter at the basolateral (sinusoidal) membrane and the bile salt export pump at the canalicular membrane mediate hepatic uptake and hepatobiliary secretion of bile salts. Canalicular secretion is the driving force for the enterohepatic cycling of bile salts and most genetic diseases are caused by defects of canalicular secretion. Impairment of bile flow leads to adaptive changes in the expression of transporter proteins and enzymes of the cytochrome P-450 system involved in the metabolism of cholesterol and bile acids. Bile salts act as ligands for transcription factors. As such, they stimulate or inhibit the transcription of genes encoding transporters and enzymes involved in their own metabolism. Together these changes appear to serve mainly a hepatoprotective function. Progressive familial intrahepatic cholestasis (PFIC) results from mutations in various genes encoding hepatobiliary transport proteins. Mutations in the FIC1 gene cause relapsing or permanent cholestasis. The relapsing type of cholestasis is called benign recurrent intrahepatic cholestasis, the permanent type of cholestasis PFIC type 1. PFIC type 2 results from mutations in the bile salt export pump (BSEP) gene. This is associated with permanent cholestasis since birth. Serum gamma-glutamyltransferase (gamma-GT) activity is low to normal in PFIC types 1 and 2. Bile diversion procedures, causing a decreased bile salt pool, have a beneficial effect in a number of patients with these diseases. However, liver transplantation is often necessary. PFIC type 3 is caused by mutations in the MDR3 gene. MDR3 is a phospholipid translocator in the canalicular membrane. Because of the inability to secrete phospholipids, patients with PFIC type 3 produce bile acid-rich toxic bile that damages the intrahepatic bile ducts. Serum gamma-GT activity is elevated in these patients. Ursodeoxycholic acid therapy is useful for patients with a partial defect. Liver transplantation is a more definitive therapy for these patients. [source] Cloning of the dog bile salt export pump (BSEP; ABCB11) and functional comparison with the human and rat proteinsBIOPHARMACEUTICS AND DRUG DISPOSITION, Issue 8 2008Hikaru Yabuuchi Abstract The dog bile salt export pump (BSEP; ABCB11) was cloned and expressed in a Sf9 insect cell system. The deduced amino acid sequence encodes a 1325-amino-acid protein, which shows 89.4% and 80.2% homology with human BSEP and rat Bsep, respectively. The transcript of the dog Bsep gene was detected at a high level in liver, but not other tissues, by quantitative RT-PCR. The BSEP-expressing membrane vesicles isolated from Sf9 cells exhibited saturable uptake of [3H]taurocholic acid with Michaelis constants (Km) of 33.7, 22.2 and 19.9,µM for the dog, rat and human transporters, respectively. The uptake of [3H]taurocholic acid by all three transporters was significantly inhibited by troglitazone, glibenclamide, and other several inhibitors, while pravastatin inhibited dog Bsep and human BSEP, but not rat Bsep at 100,µM. The IC50 of troglitazone for dog Bsep, human BSEP, and rat Bsep were 32, 20, and 60,µM, and those of pravastatin were 441, 240 and >1,000,µM, respectively. In conclusion, while dog Bsep shows similar ATP-dependent bile acid transport characteristics to human BSEP and rat Bsep, there is a species difference in affinity for drugs such as pravastatin and troglitazone. Copyright © 2008 John Wiley & Sons, Ltd. [source] Effects of bosentan, an endothelin receptor antagonist, on bile salt export pump and multidrug resistance,associated protein 2BIOPHARMACEUTICS AND DRUG DISPOSITION, Issue 1 2007Yuji Mano Abstract The bile salt export pump (BSEP/Bsep/ABCB11) and multidrug resistance-associated protein 2 (MRP2/Mrp2/ABCC2) are involved in bile acid-dependent and -independent bile secretion, respectively. It has been reported that bosentan, an endothelin receptor antagonist, inhibits Bsep, which may lead to cholestatic liver injury due to the intracellular accumulation of bile salts, while increasing bile salt-independent bile flow. Thus, in this study, the effects of bosentan on BSEP/Bsep and MRP2/Mrp2 were evaluated using membrane vesicles derived from Spodoptera frugiperda (Sf) 9 cells, which express these transporters. The adenosine 5,-triphosphate (ATP)-dependent uptake of 3H-taurocholic acid into membrane vesicles for BSEP/Bsep was inhibited by bosentan, and its IC50 values were 76.8 and 101 µM for BSEP and Bsep, respectively. In contrast, bosentan stimulated the MRP2/Mrp2-mediated ATP-dependent vesicular transport of 3H-estradiol 17,-glucuronide by shifting the sigmoidal dependence of transport rate on substrate concentration to a more hyperbolic one. Collectively, these results suggest that bosentan inhibits BSEP in humans with a similar potency to rats, and that increased bile salt-independent flow in rats by bosentan is at least partly attributable to the activation of Mrp2. Copyright © 2006 John Wiley & Sons, Ltd. [source] | ||||||||||