[Highlights in gastroenterology 2006].
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Adult↗
Biomedical subjects
G A Kullak-Ublick
Publications and source records attributed to G A Kullak-Ublick.
Cholestasis protects the liver from ischaemic injury and post-ischaemic inflammation in the mouse.
BACKGROUND AND HYPOTHESIS: Cholestasis is associated with high morbidity and mortality in patients undergoing major liver surgery, but the mechanisms responsible remain elusive. Increased ischaemic liver injury and inflammation may contribute to the poor outcome. METHODS: Common bile duct ligation (biliary obstruction with hyperbilirubinaemia) or selective ligation of the left hepatic duct (biliary obstruction without hyperbilirubinaemia) was performed in C57BL/6 mice before 1 h of hepatic ischaemia and 1, 4 or 24 h of reperfusion. Infection with the intracellular hepatic pathogen Listeria monocytogenes for 12 and 48 h was used to study ischaemia-independent hepatic inflammation. RESULTS: Cholestatic mice showed considerable protection from ischaemic liver injury as determined by transaminase release, histological liver injury and neutrophil infiltration. In cholestatic mice, reduced injury correlated with a failure to activate nuclear factor kappaB (NFkappaB) and tumour necrosis factor alpha (TNFalpha) mRNA synthesis, two key mediators of post-ischaemic liver inflammation. After selective bile duct ligation, both the ligated and the non-ligated lobes showed blocked activation of NFkappaB as well as reduced induction of TNFalpha mRNA synthesis and neutrophil infiltration. By contrast, infection with L monocytogenes showed comparable activation of NFkappaB and hepatic recruitment of neutrophils 12 h after infection. CONCLUSION: Cholestasis does not increase but rather dramatically protects the liver from ischaemic injury and inflammation. This effect is mediated by a systemic factor, but not bilirubin, and is associated with a preserved capacity to trigger an inflammatory response to other stimuli such as a bacterial pathogen.
Animals↗
[Highlights in gastroenterology 2004].
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Colonoscopy↗
Thiopurine S-methyltransferase polymorphisms: efficient screening method for patients considering taking thiopurine drugs.
OBJECTIVE: More than 11% of the Caucasian population are heterozygous or homozygous carriers of thiopurine S-methyltransferase (TPMT) mutants and are at risk for toxic side effects when treated with thiopurine drugs. Therefore, screening for TPMT polymorphisms in a patient prior to prescribing these agents is recommended. The goal of this study was to determine a cut-off concentration of the TPMT activity assay beyond which genotyping of the TPMT gene should be performed. METHODS: The TPMT activity of 240 unrelated Caucasian subjects was measured using high-performance liquid chromatography. Genotyping for the most frequent allelic variants, TPMT*2, *3A, *3B, *3C and *7 was performed by LightCycler technology and sequencing. RESULTS: The inter-individual TPMT activity showed a range from 23 nmol MTG/g*Hb*h(-1) to 97 nmol MTG/g*Hb*h(-1) with a median of 56 nmol MTG/g*Hb*h(-1). Using a cut-off concentration of 45.5 nmol MTG/g*Hb*h(-1), a test sensitivity of 100% and a specificity of 89% were reached for heterozygous carriers of a TPMT mutation. We identified 1 carrier of TPMT*2, 14 carriers of TPMT*3A and 3 carriers of TPMT*3C, resulting in a TPMT heterozygosity prevalence of 7.5%. CONCLUSIONS: This study defines the cut-off value for the TPMT phenotyping assay at 45.5 nmol/g*Hb*h(-1), beyond which additional genotyping elucidates the individual risk for drug therapy. Using this cut-off concentration, the number of genotyping assays could be reduced by about 60%.
Female↗
Human ileal bile acid transporter gene ASBT (SLC10A2) is transactivated by the glucocorticoid receptor.
BACKGROUND: Patients with Crohn's disease suffer from intestinal bile acid malabsorption. Intestinal bile acid absorption is mediated by the apical sodium dependent bile acid transporter ASBT/IBAT (SLC10A2). In rats, ASBT is induced by glucocorticoids. AIMS: To study whether human ASBT is activated by glucocorticoids and to elucidate the mechanism of regulation. PATIENTS AND METHODS: ASBT expression in ileal biopsies from patients with Crohn's disease and from healthy subjects was quantified by western blot. ASBT promoter function was studied in luciferase assays and by electrophoretic mobility shift assay. RESULTS: In 16 patients with Crohn's disease, ASBT expression was reduced to 69 (7.5)% compared with healthy controls (mean (SEM); p = 0.01). In 10 healthy male volunteers, ASBT protein expression was increased 1.34 (0.11)-fold (mean (SEM); p<0.05) after 21 days' intake of budesonide (9 mg/day) whereas expression of the peptide transporter 1 was unaffected. Reporter constructs of the human ASBT promoter were activated 15-20-fold by coexpression of the glucocorticoid receptor (GR) and exposure to the GR ligands dexamethasone or budesonide. Two glucocorticoid response elements in the ASBT promoter, arranged as inverted hexanucleotide repeats (IR3 elements), conferred inducibility by GR and dexamethasone in a heterologous promoter context and were shown to bind GR in mobility shift assays. CONCLUSIONS: Human ASBT is induced by glucocorticoids in vitro and in vivo. Induction of ASBT by glucocorticoids could be beneficial in patients with Crohn's disease who exhibit reduced ASBT expression. This study identifies ASBT as a novel target of glucocorticoid controlled gene regulation in the human intestine.
Adult↗
Constitutive rat multidrug-resistance protein 2 gene transcription is down-regulated by Y-box protein 1.
BACKGROUND/AIMS: Molecular mechanisms underlying transcriptional rat multidrug-resistance protein 2 (Mrp2, Abcc2) gene regulation are mostly unclear. Given the presence of putative binding sites for the Y-box binding protein YB-1 in the regulatory sequence, its trans-regulatory influence was analyzed. METHODS: Reporter assays in HepG2 cells with various Mrp2 deletion constructs in the absence and presence of co-transfected YB-1 were performed. DNA binding studies with recombinant YB-1 protein and nuclear extracts obtained from HepG2 cells and rat liver tissue were carried out. RESULTS: The minimal promoter sequence was confined to the proximal 186 bp. A YB-1 responsive element, Mrp2 YRE-1, was mapped at -186/-157, which exhibits specific YB-1 binding. YB-1 acts as a potent repressor of Mrp2 promoter activity in vitro. CONCLUSIONS: Constitutive Mrp2 gene expression is conferred through the proximal -186 bp. YB-1 acts as a repressor in vitro by specific binding to a defined element in the proximal promoter sequence.
ATP-Binding Cassette Transporters↗
[Role of nuclear receptors in hepatic and intestinal drug transport].
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Biological Availability↗
[Management of ulcerative colitis].
Ulcerative colitis is a chronic inflammatory bowel disease. The disease is diagnosed on the basis of clinical parameters and endoscopic-histologic evaluation. 5-aminosalicylic acid (5-ASA, mesalamine) represents the first-line treatment of choice. For patients with distal and left-sided disease the use of rectal preparations is effective. Most patients respond to 5-ASA suppositories or to topic steroids such as budesonide suppositories or hydrocortisone foam. For patients with extended disease, oral medications are mandatory. In case of low- to moderate-grade inflammation, 5-ASA preparations should be implemented. In the case of severe disease treatment with steroids is required. Following induction of remission, prophylactic treatment with 5-ASA (1.5 g/d) should be maintained. For patients with frequent or severe relapses, immunosuppressive therapy with azathioprine or 6-mercaptopurine is indicated. In case of a fulminant course of disease, treatment with intravenous cyclosporine is required in patients who have not responded to high-dose intravenous steroids. When all conservative treatment options fail, proctocolectomy with construction of an ileoanal pouch should be performed. New therapeutic strategies such as infliximab and interferons are being evaluated in clinical trials. The long-term complications of ulcerative colitis include steroid-induced osteoporosis and anemia and should be treated adequately. Finally, the risk for development of colorectal cancer increases steadily with disease duration and dysplasia should be screened for by endoscopic surveillance programs.
Administration, Oral↗
First clinical experience with Molecular Adsorbent Recirculating System (MARS) in six patients with severe acute on chronic liver failure.
UNLABELLED: Despite recent advances in general supportive care, the mortality rate of patients with severe liver insufficiency remains high. Recently a new artificial liver support system MARS has been used for selective removal of albumin-bound toxins. AIM: To assess the safety and efficacy of MARS treatment in patients with acute on chronic liver disease (n = 5) or liver failure after extended hepatic resection (n = 1). DESIGN/PATIENTS: Six patients, aged 34-58 years, with severe liver insufficiency (mean MELD-score 31 (range 24-35)) were treated one to 16 times with the MARS system. At baseline three patients were intubated, three were encephalopathic (HE) and three had multifactorial kidney failure requiring kidney replacement therapy. RESULTS AND CONCLUSION: In all the patients MARS treatment significantly reduced the serum bilirubin levels. In three patients encephalopathy improved. In two patients the extracorporeal treatment precipitated a disseminated intravascular coagulation with clinically significant bleeding. Bridging to liver transplantation was possible in one patient, the other five patients died 30 days (2-74 days) after starting MARS therapy. Our case series shows that MARS treatment in general can be safely performed in patients with severe liver disease. However, in patients with an activated clotting system severe bleeding complication can be triggered and MARS treatment should be used very cautiously in these situations. MARS seems to be a promising new treatment option for patients with acute on chronic liver failure. However, carefully conducted randomized controlled trials are necessary to define its potential place in the treatment of patients with severe liver disease.
Acute Disease↗
Characterization of the human OATP-C (SLC21A6) gene promoter and regulation of liver-specific OATP genes by hepatocyte nuclear factor 1 alpha.
OATP-C (SLC21A6) is the predominant Na(+)-independent uptake system for bile salts and bilirubin of human liver and is expressed exclusively at the basolateral (sinusoidal) hepatocyte membrane. To investigate the basis of liver-specific expression of OATP-C, we studied promoter function in the two hepatocyte-derived cell lines HepG2 and Huh7 and in nonhepatic HeLa cells. OATP-C promoter constructs containing from 66 to 950 nucleotides of 5'-regulatory sequence were active in HepG2 and Huh7 but not HeLa cells, indicating that determinants of hepatocyte-specific expression reside within the minimal promoter. Deoxyribonuclease I footprint analysis revealed a single region that was protected by HepG2 and Huh7 but not HeLa cell nuclear extracts. The liver-enriched transcription factor hepatocyte nuclear factor 1 alpha (HNF1 alpha) was shown by mobility shift assays to bind within this footprint. Coexpression of HNF1 alpha stimulated OATP-C promoter activity 30-fold in HepG2 and 49-fold in HeLa cells. Mutation of the HNF1 site abolished promoter function, indicating that HNF1 alpha is critical for hepatocyte-specific OATP-C gene expression. The human OATP8 (SLC21A8) and mouse Oatp4 (Slc21a6) promoters were also responsive to HNF1 alpha coexpression in HepG2 cells. These data support a role for HNF1 alpha as a global regulator of liver-specific bile salt and organic anion transporter genes.
Animals↗
Fatal hepatoxicity secondary to nimesulide.
This report describes a 57-year-old female patient with chronic lumbago, who died from the sequelae of acute liver failure induced by nimesulide medication. Nimesulide is a non-steroidal anti-inflammatory drug (NSAID) which preferentially inhibits cyclo-oxygenase 2 and has been associated with a total of 13 reported cases of severe liver injury including our case. On the basis of the literature reports, the following features of nimesulide-associated hepatotoxicity were identified: female sex (84% of cases), age (mean age 62 years), jaundice as a primary manifestation (90%) and the absence of peripheral blood eosinophilia. The average duration of therapy of the published cases was 62 days (range 7-180 days). Based on spontaneous reports to the World Health Organization, nimesulide induces a high proportion of severe adverse hepatic reactions compared with other NSAIDs registered in Switzerland. Hepatotoxicity thus represents an important risk factor of nimesulide usage.
Anti-Inflammatory Agents, Non-Steroidal↗
Effect of phenobarbital on the expression of bile salt and organic anion transporters of rat liver.
BACKGROUND/AIMS: The hepatic clearance of drugs and cholephilic organic anions is stimulated by phenobarbital (PB). Our aim was to analyze the effects of PB on the expression of hepatocellular bile salt and organic anion transporters. METHODS: Male Sprague-Dawley rats were treated intraperitoneally with PB (80 mg/kg/d) or saline for 5 days. Transporter expression was quantified by northern and western blot analysis and initial uptake rates of bromosulphophthalein (BSP) and digoxin were measured in isolated hepatocytes. RESULTS: Compared to control rats, PB treatment increased expression of the organic anion transporting polypeptide 2 (Oatp2; Slc21aS) more than 2-fold on the RNA (P < 0.05) and protein (P < 0.001) levels. Expression of Oatpl (Slc21al), Oatp4 (Slc21a6) and the Na+-taurocholate cotransporting polypeptide (Ntcp; Slc10a1) was unaltered. At the canalicular pole, expression of the bile salt export pump (Bsep; ABCB11) and of the multidrug resistance proteins 2 (Mrp2; ABCC2) and 6 (Mrp6; ABCC6) was not significantly changed. Whereas hepatocellular BSP uptake was unaffected by PB, digoxin uptake was stimulated 4-fold. CONCLUSIONS: The induction of digoxin uptake by PB correlates with Oatp2 expression. In contrast, the lack of increase of Oatpl and Oatp4 expression is in accordance with unchanged BSP uptake. These data challenge the previously held view that PB induces hepatocellular BSP uptake systems.
ATP Binding Cassette Transporter, Subfamily B, Mem↗
Expression of hepatic transporters OATP-C and MRP2 in primary sclerosing cholangitis.
BACKGROUND/AIMS: In chronic cholestatic liver diseases, biliary excretion of organic anions from blood into bile is impaired. The aim of this study was to identify the underlying mechanism. METHODS: Expression of the basolateral organic anion transporting polypeptide OATP-C (SLC21A6) and the canalicular multidrug resistance protein 2 (MRP2) was studied in patients with primary sclerosing cholangitis (PSC) (n=4), a chronic cholestatic liver disease, and in non-cholestatic controls (n=4) (two with chronic hepatitis C, one with idiopathic liver cirrhosis and one with fatty liver). Total RNA was isolated from liver tissue, reverse transcribed and subjected to polymerase chain reaction (PCR) amplification using primers specific for OATP-C, MRP2 and beta-actin. PCR products were quantified densitometrically. RESULTS: When normalized for beta-actin expression, the level of OATP-C mRNA in liver tissue of patients with PSC was 49% of controls (OATP-C/beta-actin 1.60+/-0.25 vs. 3.24+/-0.69; p<0.05) and the level of MRP2 mRNA was 27% of controls (MRP2/beta-actin 0.70+/-0.36 vs. 2.54+/-0.56; p<0.01). CONCLUSIONS: Both OATP-C and MRP2 are decreased as measured by mRNA level in PSC. Downregulation of OATP-C might be the consequence of impaired canalicular secretion of organic anions and could serve to reduce the organic anion load of cholestatic hepatocytes.
ATP Binding Cassette Transporter, Subfamily B↗
Organic anion-transporting polypeptide B (OATP-B) and its functional comparison with three other OATPs of human liver.
BACKGROUND & AIMS: Hepatic uptake of cholephilic organic compounds is mediated by members of the organic anion-transporting polypeptide (OATP) family. We aimed to characterize the novel OATP-B with respect to tissue distribution and hepatocellular localization and to compare its substrate specificity with those of OATP-A, OATP-C, and OATP8. METHODS: Tissue distribution and hepatocellular localization of OATP-B were analyzed by Northern blotting and immunofluorescence, respectively. Transport of 16 substrates was measured for each individual human OATP in complementary RNA-injected Xenopus laevis oocytes. RESULTS: Expression of OATP-B was most abundant in human liver, where it is localized at the basolateral membrane of hepatocytes. OATP-B, OATP-C, and OATP8 mediated high-affinity uptake of bromosulphophthalein (K(m), approximately 0.7, 0.3, and 0.4 micromol/L, respectively). OATP-B also transported estrone-3-sulfate but not bile salts. Although OATP-A, OATP-C, and OATP8 exhibit broad overlapping substrate specificities, OATP8 was unique in transporting digoxin and exhibited especially high transport activities for the anionic cyclic peptides [D-penicillamine(2,5)]enkephalin (DPDPE; opioid-receptor agonist) and BQ-123 (endothelin-receptor antagonist). CONCLUSIONS: OATP-B is the third bromosulphophthalein uptake system localized at the basolateral membrane of human hepatocytes. OATP-B, OATP-C, and OATP8 account for the major part of sodium-independent bile salt, organic anion, and drug clearance of human liver.
Animals↗
Hepatic uptake of cholecystokinin octapeptide by organic anion-transporting polypeptides OATP4 and OATP8 of rat and human liver.
BACKGROUND & AIMS: Cholecystokinin (CCK) is a major gastrointestinal peptide hormone that is released postprandially from the small intestine and exerts marked effects on gallbladder and gastrointestinal motility. The smaller isoforms CCK-8 and CCK-4 are rapidly taken up into hepatocytes, metabolized, and excreted into bile. Our aim was to identify and characterize the hepatocellular CCK-8 uptake system. METHODS: CCK-8 uptake was measured in Xenopus laevis oocytes expressing the organic anion-transporting polypeptides of rat liver (Oatp1, Oatp2, Oatp3, or Oatp4) and of human liver (OATP-A, OATP-B, OATP-C, or OATP8) and in primary cultured rat hepatocytes. RESULTS: Rat Oatp4 and human OATP8 efficiently mediated CCK-8 uptake in oocytes, with Michaelis constant (Km) values of 14.9 +/- 2.9 micromol/L and 11.1 +/- 2.9 micromol/L, respectively. CCK-8 uptake by hepatocytes was also saturable, with a Km of 6.7 +/- 2.1 micromol/L. The Km value in rat hepatocytes is consistent with Oatp4-mediated transport. CONCLUSIONS: CCK-8 is selectively transported by rat Oatp4 and human OATP8, both of which are exclusively expressed at the basolateral membrane of hepatocytes. These 2 transporters are the first and probably the predominant hepatic uptake systems for CCK-8 and may be critical for the rapid clearance of this hormone from the circulation.
Animals↗
Tauroursodeoxycholic acid inserts the apical conjugate export pump, Mrp2, into canalicular membranes and stimulates organic anion secretion by protein kinase C-dependent mechanisms in cholestatic rat liver.
Ursodeoxycholic acid (UDCA) exerts anticholestatic effects by undefined mechanisms. Previous work suggested that UDCA stimulates biliary exocytosis via Ca(++)- and protein kinase C (PKC)-dependent mechanisms. Therefore, the effect of taurine-conjugated UDCA (TUDCA) was studied in the experimental model of taurolithocholic acid (TLCA)-induced cholestasis on bile flow, hepatobiliary exocytosis, distribution of PKC isoforms, and density of the apical conjugate export pump, Mrp2, in canalicular membranes. Isolated perfused rat livers were preloaded with horseradish peroxidase (HRP), a marker of vesicular exocytosis, and were perfused with bile acids or dimethylsulfoxide (control) only. PKC isoform distribution and membrane density of Mrp2 were studied using immunoblotting and immunoelectron-microscopic techniques. Biliary secretion of the Mrp2 substrate, 2,4-dinitrophenyl-S-glutathione (GS-DNP), was studied in the presence or absence of the PKC inhibitor, bisindolylmaleimide I (BIM-I; 1 micromol/L). TLCA (10 micromol/L) impaired bile flow by 51%; biliary secretion of HRP and GS-DNP by 46% and 95%, respectively; membrane binding of the Ca(++)-sensitive alpha-isoform of PKC by 32%; and density of Mrp2 in the canalicular membrane by 79%. TUDCA (25 micromol/L) reversed the effects of TLCA on bile flow, secretion of HRP and GS-DNP, and distribution of alpha-PKC. TUDCA reduced membrane binding of epsilon-PKC and increased Mrp2 density 4-fold in canalicular membranes of cholestatic hepatocytes. BIM-I inhibited the effect of TUDCA on GS-DNP secretion in cholestatic livers by 49% without affecting secretion in controls. In conclusion, TUDCA may enhance the secretory capacity of cholestatic hepatocytes by stimulation of exocytosis and insertion of transport proteins into apical membranes via PKC-dependent mechanisms.
Animals↗
Arterial and venous pharmacokinetics of intravenous heroin in subjects who are addicted to narcotics.
BACKGROUND: In Switzerland, medical prescription of heroin (diacetylmorphine) is currently being evaluated as a treatment option for heavily dependent addicts. Therefore the diacetylmorphine pharmacokinetics in opioid-addicted patients was studied. METHODS: Three different diacetylmorphine doses (up to 210 mg) and 20 mg deuterium-labeled morphine (morphine-d3) were administered intravenously to 8 heroin-addicted patients. Arterial and venous plasma samples were collected, and diacetylmorphine, monoacetylmorphine, morphine, morphine-3-glucuronide, morphine-6-glucuronide, and morphine-d3 plasma concentrations were measured by liquid chromatography-mass spectrometry. RESULTS: Maximal arterial concentrations of diacetylmorphine, monoacetylmorphine, and morphine were 2.4, 5.4, and 1.4 times higher and occurred 2 to 3 minutes earlier than maximal venous concentrations. Venous areas under the concentration-time curves (AUC) of diacetylmorphine and monoacetylmorphine were 35% and 26% lower than arterial AUC values, whereas for morphine the venous AUC was 15% higher. Morphine-3-glucuronide and morphine-6-glucuronide exhibited no arteriovenous differences. AUCs for diacetylmorphine, monoacetylmorphine, and morphine increased linearly with dose. Diacetylmorphine was completely metabolized to morphine. Substantial morphine input into the arterial circulation persisted for up to 90 minutes. The arterial clearances of diacetylmorphine, monoacetylmorphine, and morphine-d3 were 8.7 +/- 2.6, 6.7 +/- 1.6, and 2.3 +/- 0.3 L/min, respectively. The arterial half-lives of diacetylmorphine and morphine-d3 were 2. 4 +/- 0.8 and 88 +/- 21 minutes, respectively. CONCLUSIONS: These data indicate that substantial arteriovenous differences exist for diacetylmorphine and metabolite kinetics, that the pharmacokinetics of diacetylmorphine and metabolites is linear even in the high dose range used by opioid addicts, and that not only diacetylmorphine but also monoacetylmorphine is substantially metabolized peripherally to morphine.
Adult↗
Transport of bile acids in hepatic and non-hepatic tissues.
Bile acids are steroidal amphipathic molecules derived from the catabolism of cholesterol. They modulate bile flow and lipid secretion, are essential for the absorption of dietary fats and vitamins, and have been implicated in the regulation of all the key enzymes involved in cholesterol homeostasis. Bile acids recirculate through the liver, bile ducts, small intestine and portal vein to form an enterohepatic circuit. They exist as anions at physiological pH and, consequently, require a carrier for transport across the membranes of the enterohepatic tissues. Individual bile acid carriers have now been cloned from several species. Na+-dependent transporters that mediate uptake into hepatocytes and reabsorption from the intestine and biliary epithelium and an ATP-dependent transporter that pumps bile acids into bile comprise the classes of transporter that are specific for bile acids. In addition, at least four human and five rat genes that code for Na+-independent organic anion carriers with broad multi-substrate specificities that include bile acids have been discovered. Studies concerning the regulation of these carriers have permitted identification of molecular signals that dictate eventual changes in the uptake or excretion of bile acids, which in turn have profound physiological implications. This overview summarizes and compares all known bile acid transporters and highlights findings that have identified diseases linked to molecular defects in these carriers. Recent advances that have fostered a more complete appreciation for the elaborate disposition of bile acids in humans are emphasized.
Animals↗