Bile Acid Transport in Sister of P-Glycoprotein (ABCB11) Knockout Mice (original) (raw)
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Regulation of protein secretion into bile: Studies in mice with a disrupted mdr2 p-glycoprotein gene
Gastroenterology, 1995
Background & Aims: Protein is secreted into bile via several independent pathways. The aim of this study was to investigate whether these pathways are influenced by secretion of biliary lipid. Methods: Protein secretion and biliary lipid output were studied in wildtype mice (+/+), heterozygotes (+/-), and homozygotes (-/-) for mdr2gene disruption. Biliary lipid and protein output were varied by infusion with taurocholate (TC) and tauroursodeoxycholate (TUDC). Results: Exocytosis and transcytosis were unaltered in (-/-) mice. Infusion with TC strongly induced secretion of alkaline phosphatase in (-/-) mice but had little effect in (+/-) and (+/+) mice. Infusion with TUDC had little effect on alkaline phosphatase output. In contrast, both TUDC and TC strongly stimulated secretion of aminopeptidase N and lysosomal enzymes in (+/+) mice but had no effect in (-/-) animals. Aminopeptidase N secretion correlated with phospholipid output, but only at high flux. At low flux, aminopeptidase N was secreted independently from both phospholipid and bile salts. Conclusions: The canalicular membrane enzymes alkaline phosphatase and aminopeptidase N are secreted via separate pathways. Part of alkaline phosphatase output is controlled by bile salt hydrophobicity, whereas at high lipid flux, aminopeptidase N secretion seems to be coupled to phospholipid output. Lysosomal enzymes follow the latter pathway.
Regulation of MDR2 P-glycoprotein expression by bile salts
Hepatology, 1995
The phosphatidyl translocating activity of the mdr2 P-glycoprotein (Pgp) in the canalicular membrane of the mouse hepatocyte is a rate-controlling step in the biliary secretion of phospholipid. Since bile salts also regulate the secretion of biliary lipids, we investigated the influence of the type of bile salt in the circulation on mdr2 Pgp expression and activity. Male mice were fed a purified diet to which either 0.1 % (w\w) cholate or 0.5 % (w\w) ursodeoxycholate was added. This led to a near-complete replacement of the endogenous bile salt pool (mainly tauromuricholate) by taurocholate or tauroursodeoxycholate respectively. The phospholipid secretion capacity was then determined by infusion of increasing amounts of tauroursodeoxycholate.
The Sister of P-glycoprotein Represents the Canalicular Bile Salt Export Pump of Mammalian Liver
Journal of Biological Chemistry, 1998
Canalicular secretion of bile salts is a vital function of the vertebrate liver, yet the molecular identity of the involved ATP-dependent carrier protein has not been elucidated. We cloned the full-length cDNA of the sister of P-glycoprotein (spgp; M r ϳ160,000) of rat liver and demonstrated that it functions as an ATP-dependent bile salt transporter in cRNA injected Xenopus laevis oocytes and in vesicles isolated from transfected Sf9 cells. The latter demonstrated a 5-fold stimulation of ATP-dependent taurocholate transport as compared with controls. This spgp-mediated taurocholate transport was stimulated solely by ATP, was inhibited by vanadate, and exhibited saturability with increasing concentrations of taurocholate (K m Ӎ 5 M). Furthermore, spgp-mediated transport rates of various bile salts followed the same order of magnitude as ATP-dependent transport in canalicular rat liver plasma membrane vesicles, i.e. taurochenodeoxycholate > tauroursodeoxycholate ؍ taurocholate > glycocholate ؍ cholate. Tissue distribution assessed by Northern blotting revealed predominant, if not exclusive, expression of spgp in the liver, where it was further localized to the canalicular microvilli and to subcanalicular vesicles of the hepatocytes by in situ immunofluorescence and immunogold labeling studies. These results indicate that the sister of P-glycoprotein is the major canalicular bile salt export pump of mammalian liver.
Hepatology, 1994
To study the effect of bile acids on P-glycoproteinmediated drug transport, we performed experiments using multidrug resistant cells and rat canalicular membrane vesicles. Cellular accumulation and efflux of rhodamine 123 were measured in drug-resistant cells by means of computerized quantitative image analysis and fluorescence microscopy. ATP-dependent [3H]daunomycin transport was studied by means of rapid filtration in canalicular membrane vesicles prepared from normal rats. Doxorubicin-sensitive (PSI-2) and-resistant (PNlA) 3T3 cells and human-derived hepatocellular carcinoma doxorubicin-sensitive and-resistant cells were used. Taurochenodeoxycholate and glycochenodeoxycholate, taurolithocholate and ursodeoxycholate (50 to 200 Fmol/L) inhibited rhodamine 123 and [SH]daunomycin transport in multidrug-resistant cells and canalicular membrane vesicles, respectively, whereas taurocholate, taurodeoxycholate and tauroursodeoxycholate did not. Primary and secondary unconjugated bile acids had no effect. These results reveal that taurolithocholate, taurochenodeoxycholate and glycochenodeoxycholate and ursodeoxycholate inhibit P-glycoprotein-mediated drug transport function in multidrug resistant cell lines and in canalicular membrane vesicles. These results suggest possible interaction between P-glycoprotein function and bile acids in cholestasis and after treatment of patients with ursodeoxycholic or chenodeoxycholic acid. (HEPATOLOGY 1994;20:170-176.) Multidrug resistance (MDR) frequently occurs during cancer chemotherapy and can be produced in cell lines in
Journal of basic and clinical physiology and pharmacology, 2013
Bile acids are synthesized in the liver from cholesterol. This study investigated the impact and expression of different carriers of bile acid in the liver and kidneys. Eight-week-old male mice were used, which were fed for 15 days and divided into two groups: 15 mice fed with standard diet (control group) and another 15 mice fed with a rich diet of 5% cholesterol (second group). Bile acid dosage was based on their oxidation by 7α hydroxyl-steroid dehydrogenize. The mRNA expression was quantitatively analyzed by the real time of polymerase chain reaction (RT-PCR), and the expression of the renal carrier bile acid protein was analyzed by Western blot. The expression of bile salt export pump involved in the uptake of bile acids in the basolateral membrane of hepatocytes revealed no differences between the two groups of mice. However, the expression of multidrug resistance-associated protein 2 was reduced in mice of the second group. Moreover, the expressions of organic anion transport...
Liver International, 2005
Background/Aims: Bile fl ow consists of bile salt-dependent bile fl ow (BSDF), generated by canalicular secretion of bile salts, and bile salt-independent fl ow (BSIF), probably of combined canalicular and ductular origin. Bile salt transport proteins have been identifi ed in cholangiocytes, suggesting a role in control of BSDF and/or in control of bile salt synthesis through cholehepatic shunting. Methods: We studied effects of bile duct proliferation under non-cholestatic conditions in Mdr2 P-glycoprotein (Abcb4)-defi cient (Mdr2 (-/-) ) mice. BSDF and BSIF were determined in wild-type and Mdr2 (-/-) mice during infusion of step-wise increasing dosages of tauroursodeoxycholate (TUDC). Cholate synthesis rate was determined by [ 2 H 4 ]-cholate dilution. Results were related to expression of transport proteins in liver and intestine. Results: During TUDC infusion, BSDF was increased by ~50% and BSIF by ~100% in Mdr2 (-/-) mice compared to controls. Cholate synthesis rate was unaffected in Mdr2 (-/-) mice. Hepatic expression of the apical sodium-dependent bile salt transporter (Asbt), its truncated form (tAbst) and the multidrug resistancerelated protein (Mrp3) were up-regulated in Mdr2 (-/-) mice. Conclusions: Bile duct proliferation in Mdr2 (-/-) mice enhances cholehepatic shunting of bile salts, which is associated with a disproportionally high bile fl ow but does not affect bile salt synthesis.
Expression and regulation of hepatic drug and bile acid transporters
Toxicology, 2000
Transport across hepatocyte plasma membranes is a key parameter in hepatic clearance and usually occurs through different carrier-mediated systems. Sinusoidal uptake of compounds is thus mediated by distinct transporters, such as Na + -dependent or Na + -independent anionic transporters and by some cationic transporters. Similarly, several membrane proteins located at the apical pole of hepatocytes have been incriminated in the excretion of compounds into the bile. Indeed, biliary elimination of anionic compounds, including glutathione S-conjugates, is mediated by MRP2, whereas bile salts are excreted by a bile salt export pump (BSEP) and Class I-P-glycoprotein (P-gp) is involved in the secretion of amphiphilic cationic drugs, whereas class II-P-gp is a phospholipid transporter. The expression of hepatic transporters and their activity are regulated in various situations, such as ontogenesis, carcinogenesis, cholestasis, cellular stress and after treatment by hormones and xenobiotics. Moreover, a direct correlation between a defect and the absence of transporter with hepatic disease has been demonstrated for BSEP, MDR3-P-gp and MRP2.