Blocking Sodium-Taurocholate Cotransporting Polypeptide Stimulates Biliary Cholesterol and Phospholipid Secretion in Mice

Active secretion of bile salts into the canalicular lumen drives bile formation and promotes biliary cholesterol and phospholipid output. Disrupting hepatic bile salt uptake, by inhibition of sodium-taurocholate cotransporting polypetide (NTCP; Slc10a1) with Myrcludex B, is expected to limit bile salt flux through the liver and thereby to decrease biliary lipid excretion. Here, we show that Myrcludex B–mediated NTCP inhibition actually causes an increase in biliary cholesterol and phospholipid excretion whereas biliary bile salt output and bile salt composition remains unchanged. Increased lysosomal discharge into bile was excluded as a potential contributor to increased biliary lipid secretion. Induction of cholesterol secretion was not a consequence of increased ATP-binding cassette subfamily G member 5/8 activity given that NTCP inhibition still promoted cholesterol excretion in Abcg8−/− mice. Stimulatory effects of NTCP inhibition were maintained in Sr-b1−/− mice, eliminating the possibility that the increase in biliary lipids was derived from enhanced uptake of high-density lipoprotein–derived lipids. NTCP inhibition shifts bile salt uptake, which is generally more periportally restricted, toward pericentral hepatocytes, as was visualized using a fluorescently labeled conjugated bile salt. As a consequence, exposure of the canalicular membrane to bile salts was increased, allowing for more cholesterol and phospholipid molecules to be excreted per bile salt. Conclusion: NTCP inhibition increases biliary lipid secretion, which is independent of alterations in bile salt output, biliary bile salt hydrophobicity, or increased activity of dedicated cholesterol and phospholipid transporters. Instead, NTCP inhibition shifts hepatic bile salt uptake from mainly periportal hepatocytes toward pericentral hepatocytes, thereby increasing exposure of the canalicular membrane to bile salts linking to increased biliary cholesterol secretion. This process provides an additional level of control to biliary cholesterol and phospholipid secretion

Altered myocardial substrate metabolism is associated with myocardial dysfunction in early diabetic cardiomyopathy in rats: studies using positron emission tomography

0.05). CONCLUSION: Using PET and echocardiography, we found increases in myocardial FA oxidation with a concomitant decrease of insulin-mediated myocardial glucose utilisation in early DCM. In addition, the latter was associated with impaired myocardial function. These in vivo data expand previous in vitro findings showing that early alterations in myocardial substrate metabolism contribute to myocardial dysfunctio

Low efficacy of recombinant SV40 in Ugt1a1-/- mice with severe inherited hyperbilirubinemia

In contrast to AAV, Simian Virus 40 (rSV40) not inducing neutralizing antibodies (NAbs) allowing re-treatment seems a promising vector for neonatal treatment of inherited liver disorders. Several studies have reported efficacy of rSV40 in animal models for inherited liver diseases. In all studies the ubiquitous endogenous early promoter controlled transgene expression establishing expression in all transduced tissues. Restricting this expression to the target tissues reduces the risk of immune response to the therapeutic gene. In this study a liver specific rSV40 vector was generated by inserting a hepatocyte specific promoter. This increased the specificity of the expression of hUGT1A1 in vitro. However, in vivo the efficacy of rSV40 appeared too low to demonstrate tissue specificity while increasing the vector dose was not possible because of toxicity. In contrast to earlier studies, neutralizing antibodies were induced. Overall, the lack of a platform to produce high titered and pure rSV40 particles and the induction of NAbs, renders it a poor candidate for in vivo gene therapy

Human fetal liver cells for regulated ex vivo erythropoietin gene therapy

Possible risks and lack of donor livers limit application of liver transplantation. Liver cell transplantation is, at this moment, not a feasible alternative because engraftment in the liver is poor. Furthermore, there is also shortage of cells suitable for transplantation. Fetal liver cells are able to proliferate in cell culture and could therefore present an alternative source of cells for transplantation. In this study, we investigated the utility of human fetal liver cells for therapeutic protein delivery. We transplanted human fetal liver cells in immunodeficient mice but were not able to detect engraftment of human hepatocytes. In contrast, transplantation of human adult hepatocytes led to detectable engraftment of hepatocytes in murine liver. Transplantation of fetal liver cells did lead to abundant reconstitution of murine liver with human endothelium, indicating that endothelial cells are the most promising cell type for ex vivo liver cell gene therapy. Human liver endothelial cells were subsequently transduced with a lentiviral autoregulatory erythropoietin expression vector. After transplantation in immunodeficient mice, these cells mediated long-term regulation of murine hematocrits. Our study shows the potential of human liver endothelial cells for long-term regulated gene therapy

FXR-dependent reduction of hepatic steatosis in a bile salt deficient mouse model

It has been established that bile salts play a role in the regulation of hepatic lipid metabolism. Accordingly, overt signs of steatosis have been observed in mice with reduced bile salt synthesis. The aim of this study was to identify the mechanism of hepatic steatosis in mice with bile salt deficiency due to a liver specific disruption of cytochrome P450 reductase. In this study mice lacking hepatic cytochrome P450 reductase (Hrn) or wild type (WT) mice were fed a diet supplemented with or without either 0.1% cholic acid (CA) or 0.025% obeticholic acid, a specific FXR-agonist Feeding a CA-supplemented diet resulted in a significant decrease of plasma ALT in Hrn mice. Histologically, hepatic steatosis ameliorated after CA feeding and this was confirmed by reduced hepatic triglyceride content (115.5 +/- 7.3 mg/g liver and 47.9 +/- 4.6 mg/g liver in control- and CA-fed Hrn mice, respectively). The target genes of FXR-signaling were restored to normal levels in Hrn mice when fed cholic acid. VLDL secretion in both control and CA-fed Hrn mice was reduced by 25% compared to that in WT mice. In order to gain insight in the mechanism behind these bile salt effects, the FXR agonist also was administered for 3 weeks. This resulted in a similar decrease in liver triglycerides, indicating that the effect seen in bile salt fed Hrn animals is FXR dependent In conclusion, steatosis in Hrn mice is ameliorated when mice are fed bile salts. This effect is FXR dependent. Triglyceride accumulation in Hrn liver may partly involve impaired VLDL secretion. (c) 2014 Elsevier B.V. All rights reserve

Oral Availability of Cefadroxil Depends on ABCC3 and ABCC4

Some cephalosporins, such as cefadroxil, are orally available. H+-coupled peptide transporter 1 mediates the transport of cephalosporins across the apical membrane of enterocytes. It is not known which mechanism(s) is responsible for the subsequent transport of cephalosporins across the basolateral membrane toward the circulation. We have tested whether ATPbinding cassette (ABC) transporters ABCC3 and/or ABCC4 are involved in the latter process. Transport experiments with plasma membrane vesicles expressing these transporters were used to determine whether ABCC3 and ABCC4 can transport cephalosporins in vitro. The involvement of Abcc3 and Abcc4 in the transport of cefadroxil from enterocytes was subsequently studied using intestinal explants from wild-type, Abcc3(-/-), Abcc4(-/-), and Abcc3(-/-)/Abcc4(-/-) mice in an Ussing chamber setup. Finally, appearance of cefadroxil in portal blood was investigated in vivo after intrajejunal administration of ce-fadroxil in wild-type, Abcc3(-/-), Abcc4(-/-), and Abcc3(-/-)/ Abcc4(-/-)mice. ABCC3- and ABCC4-mediated transport of estradiol-17 beta-glucuronide was dose-dependently inhibited by cephalosporins in vesicular transport experiments. Furthermore, transport of cefadroxil by ABCC3 and ABCC4 was saturable with K-m values of 2.5 +/- 0.7 and 0.25 +/- 0.07 mM, respectively. Transport of cefadroxil from the apical to the basolateral side of jejunal tissue explants was unchanged in Abcc3(-/-) but significantly reduced (approximately 2-fold) in Abcc4(-/-) and Abcc3(-/-)/Abcc4(-/-) when compared with wild-type tissue. Upon instillation of cefadroxil in the jejunum, portal and peripheral blood concentrations were similar in Abcc3(-/-) and Abcc4(-/-) but approximately 2-fold reduced in Abcc3(-/-)/Abcc4(-/-) compared with wild-type mice. Our data demonstrate that intestinal absorption of cefadroxil depends partly on ABCC3 and ABCC

ATP8B1 and ATP11C: Two Lipid Flippases Important for Hepatocyte Function

P4 ATPases are lipid flippases and transport phospholipids from the exoplasmic to the cytosolic leaflet of biological membranes. Lipid flipping is important for the biogenesis of transport vesicles. Recently it was shown that loss of the P4 ATPases ATP8B1 and ATP11C are associated with severe Cholestatic liver disease. Mutation of ATP8B1 cause progressive familial Intrahepatic Cholestasis type 1 (PFIC1)and benign recurrent intrahepatic cholestasis type 1 (BRIC 1). From our observations we hypothesized that ATP8B1 deficiency causes a phospholipids randomization at the canalicular membrane, which results in extraction of cholesterol due to increase sensitivity of the canalicular membrane. Deficiency of ATP11C causes conjugated hyperbilirubinemia. In our preliminary result we observed accumulation of unconjugated bile salts in Atp11c deficient mice probably because of regulation in the expression or function of OATP1B2. Similar to ATP8B1, ATP11C have regulation on membrane transporter

Cellular Localization and Biochemical Analysis of Mammalian CDC50A, a Glycosylated beta-subunit for P4 ATPases

CDC50 proteins are beta-subunits for P4 ATPases, which upon heterodimerization form a functional phospholipid translocation complex. Emerging evidence in mouse models and men links mutations in P4 ATPase genes with human disease. This study analyzed the tissue distribution and cellular localization of CDC50A, the most abundant and ubiquitously expressed CDC50 homologue in the mouse. The authors have raised antibodies that detect mouse and human CDC50A and studied CDC50A localization and glycosylation status in mouse liver cells. CDC50A is a terminal-glycosylated glycoprotein and is expressed in hepatocytes and liver sinusoidal endothelial cells, where it resides in detergent-resistant membranes. In pancreas and stomach, CDC50A localized to secretory vesicles, whereas in the kidney, CDC50A localized to the apical region of proximal convoluted tubules of the cortex. In WIF-B9 cells, CDC50A partially costains with the trans-Golgi network. Data suggest that CDC50A is present as a fully glycosylated protein in vivo, which presumes interaction with distinct P4 ATPases. (J Histochem Cytochem 60: 205-218, 2012

Biliverdin Reductase inhibitors did not improve severe unconjugated hyperbilirubinemia in vivo

We aimed to identify potent biliverdin reductase (BVRA) inhibitors as a novel concept for the treatment of severe unconjugated hyperbilirubinemia. 1280 FDA-approved compounds were screened in vitro for their ability to inhibit human and rat BVRA activity and 26 compounds were identified as BVRA inhibitors. Montelukast and Disulfiram were selected as potentially clinically applicable drugs and tested to reduce serum unconjugated bilirubin (UCB) levels in the Ugt1a1-deficient rat, a model for chronic unconjugated hyperbilirubinemia. Oral administration of Disulfiram was toxic in the Ugt1a1-deficient rat (weight loss, transaminase elevation). Oral Montelukast administration led to low serum concentrations and did not alter serum UCB levels. Intraperitoneal injections of Montelukast resulted in concentrations up to 110 mu mol/L in serum and 400 mu mol/L in the liver. Still, serum UCB levels remained unaltered. This first study on biliverdin reductase inhibition as a novel concept for treatment of unconjugated hyperbilirubinemia identified putative in vitro BVRA inhibitors. Montelukast, the clinically most suitable inhibitor, did not result in reduction of serum UCB in the Ugt1a1-deficient rat. The proposed treatment strategy will not result in amelioration of severe unconjugated hyperbilirubinemia in humans without the identification or development of more potent BVRA inhibitor

Biliverdin Reductase inhibitors did not improve severe unconjugated hyperbilirubinemia in vivo

We aimed to identify potent biliverdin reductase (BVRA) inhibitors as a novel concept for the treatment of severe unconjugated hyperbilirubinemia. 1280 FDA-approved compounds were screened in vitro for their ability to inhibit human and rat BVRA activity and 26 compounds were identified as BVRA inhibitors. Montelukast and Disulfiram were selected as potentially clinically applicable drugs and tested to reduce serum unconjugated bilirubin (UCB) levels in the Ugt1a1-deficient rat, a model for chronic unconjugated hyperbilirubinemia. Oral administration of Disulfiram was toxic in the Ugt1a1-deficient rat (weight loss, transaminase elevation). Oral Montelukast administration led to low serum concentrations and did not alter serum UCB levels. Intraperitoneal injections of Montelukast resulted in concentrations up to 110 mu mol/L in serum and 400 mu mol/L in the liver. Still, serum UCB levels remained unaltered. This first study on biliverdin reductase inhibition as a novel concept for treatment of unconjugated hyperbilirubinemia identified putative in vitro BVRA inhibitors. Montelukast, the clinically most suitable inhibitor, did not result in reduction of serum UCB in the Ugt1a1-deficient rat. The proposed treatment strategy will not result in amelioration of severe unconjugated hyperbilirubinemia in humans without the identification or development of more potent BVRA inhibitor