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M Vore

Publications and source records attributed to M Vore.

At least 37 records · Page 2Linked to original sources
PubMed1997

Regulation of the rat liver sodium-dependent bile acid cotransporter gene by prolactin. Mediation of transcriptional activation by Stat5.

The intracellular mechanism(s) underlying the upregulation of the hepatic Na+/taurocholate cotransporting polypeptide (ntcp) by prolactin (PRL) are unknown. In this report, we demonstrate a time-dependent increase in nuclear translocation of phosphorylated liver Stat5 (a member of the ignal ransducers and ctivators of ranscription family) that correlated with suckling-induced increases in serum PRL levels. In electrophoretic mobility gel shift assays, nuclear Stat5 exhibited specific DNA-binding ability towards IFN-gamma-activated sequence (GAS)-like elements (GLEs; 5'TTC/A-PyNPu-G/TAA-3') located in the -937 to -904 bp region of the ntcp promoter. Transient cotransfections in HepG2 cells revealed that PRL inducibility (2.5-3-fold) required coexpression of the long form of the PRL receptor (PRLRL) and Stat5. Deletion analysis mapped the PRLinducible region to -1237 to -758 bp of the ntcp promoter. Linking this 0.5-kb region to a heterologous thymidine kinase (tk) promoter, or linking multimerized ntcp GLEs either upstream of the ntcp minimal promoter (-158 to +47 bp) or the heterologous promoter conferred dose-dependent PRL responsiveness. The short form of the PRL receptor failed to transactivate ntcp GLEs. These results indicate that PRL acts via the PRLRL to facilitate Stat5 binding to ntcp-GLEs and to transcriptionally regulate ntcp.

Animals↗
PubMed1997

Prolactin increases ATP-dependent taurocholate transport in canalicular plasma membrane from rat liver.

The taurocholate (TC) maximal secretory rate (SRm) in the isolated perfused liver is increased in postpartum rats and ovariectomized rats treated with ovine prolactin (oPRL). The present studies were designed to characterize the mechanism(s) by which oPRL increases TC transport in the liver. oPRL (300 micrograms/day i.v. for 7 days) increased the SRm 1.6-fold from 185 to 364 nmol.min-1.mg protein-1 in the perfused rat liver and the maximal rate of transport for ATP-dependent transport 1.7-fold from 66 to 109 nmol.min-1.mg protein-1 in canalicular liver plasma membrane (cLPM) vesicles without changing the Michaelis constant (5-6 microM). The oPRL-mediated increases in biliary excretion in the perfused liver and ATP-dependent TC transport in cLPM vesicles were significantly inhibited by cycloheximide treatment (2 mg/kg). oPRL (300 micrograms/day iv for 7 days) increased expression of Ca(2+)-Mg(2+)-ecto-adenosinetriphosphatase mRNA sixfold and increased protein expression two- to threefold, but had no effect on the expression of P-glycoprotein (mdr1b and mdr2) mRNA. Thus the increase in ATP-dependent transport in cLPM vesicles due to oPRL treatment accounts for the increased TC SRm in the perfused liver. The oPRL-mediated increased TC transport may be associated with increased expression of proteins related to bile acid transport.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1996

MDR1 substrates/modulators protect against beta-estradiol-17beta-D-glucuronide cholestasis in rat liver.

beta-Estradiol 17beta-D-glucuronide (E(2)17G), an endogenous cholestatic metabolite of estradiol, has been identified as a substrate for both hepatic P-glycoprotein (P-gp) and the multispecific organic anion transporter (MOAT), the liver-specific homologue of the multidrug resistance protein. The aim of the present studies was to determine the role of hepatic P-gp and MOAT in E(2)17G-mediated cholestasis and its biliary excretion using the isolated perfused rat liver. A bolus dose of E(2)17G (2 micromol) alone decreased the bile flow maximally from 1.5 to 0.3 microl/min/g liver. In the presence of an infusion of 1.5 microM daunorubicin or 1.0 microM Taxol, P-gp substrates, E(2)17G cholestasis was blocked such that 2 micromol E(2)17G decreased the bile flow from 1.48 to 1.31 or from 1.70 to 1.31 microl/min/g liver, respectively. In the presence of 1 and 3 microM Taxol, the log dose-response curves for E(2)17G cholestasis were shifted to the right 2-fold and 5-fold, respectively, in a parallel manner. Taxol (10 and 50 microM) inhibited the ATP-dependent transport of 10 microM E(2)17G in canalicular plasma membrane vesicles by 46 and 81%, respectively. Daunorubicin (1.5 microM) also shifted the log dose-response curve for E(2)17G cholestasis to the right about 4-fold. Neither Taxol nor daunorubicin decreased the biliary excretion of E(2)17G. Infusion of cyclosporine (6 microM), an inhibitor of both P-gp and MOAT, significantly blocked both E(2)17G cholestasis and biliary excretion, such that 16 micromol E(2)17G decreased the bile flow only 15-20%. In contrast, bromosulfophthalein, a MOAT substrate, had no effect on either E(2)17G-mediated cholestasis or its biliary excretion. These data indicate that P-gp plays an essential role in E(2)17G-mediated cholestasis and suggest that MOAT functions to deliver high concentrations of E(2)17G to P-gp.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1996

ATP-dependent transport of beta-estradiol 17-(beta-D-glucuronide) in rat canalicular membrane vesicles.

The ATP-dependent transport of beta-estradiol 17-(beta-D-glucuronide) (E217G), a cholestatic metabolite of estradiol, was investigated in rat liver canalicular membrane vesicles. ATP-dependent transport was dependent on time and temperature and occurred into an osmotically sensitive space; kinetic analysis indicated a saturable transport system (Michaelis-Menten constant value, 75 microM; maximum transport rate, 598 pmol.min-1.mg protein-1). The steroid conjugates estradiol glucuronide, estriol 3-glucuronide, estriol 16 alpha-glucuronide, testosterone glucuronide, and the three-sulfate conjugate of 17G were effective inhibitors of transport. Bromosulfophthalein, S-(2,4-dinitrophenyl)glutathione, and glutathione disulfide, all substrates of the canalicular ATP-dependent non-bile acid organic anion transport system, were also effective inhibitors, whereas taurocholate had no effect on transport. Conversely, E217G inhibited the ATP-dependent transport of S-(2,4-dinitrophenyl)glutathione. Daunorubicin, vinblastine, etoposide, cyclosporin, and PSC-833, substrates/modulators of P-glycoprotein, were also potent inhibitors of E217G transport, and E217G competitively inhibited the ATP-dependent transport of daunorubicin. C219, a monoclonal antibody against P-glycoprotein, inhibited ATP-dependent transport of E217G and daunorubicin but not of taurocholate or S-(2,4-dinitrophenyl)glutathione. These data indicate that E217G is substrate of both the non-bile acid organic anion transport system and P-glycoprotein but not of the ATP-dependent bile acid transport system in canalicular membranes.

Adenosine Triphosphate↗
PubMed1996

Estradiol 17 beta-D-glucuronide is a high-affinity substrate for oatp organic anion transporter.

Although substantial evidence indicates that estradiol-17 beta (E2) is conjugated to the glucuronide in the kidney and then excreted by a direct tubular secretory route and that the liver transports E2 glucuronides via carrier-mediated mechanisms, the transporters involved in these processes have not been identified. The so-called "organic anion-transporting polypeptide" (i.e., oatp) has a number of known substrates, including bromosulfophthalein (BSP) and taurocholic acid (TCA) (E. Jacquemin, B. Hagenbuch, B. Stieger, A. W. Wolkoff, and P. J. Meier. Proc. Natl. Acad. Sci. USA 91: 133-137, 1994). In a companion study, we determined that steroid hormones represent a class of hormones that interact strongly with oatp when the latter is transiently expressed in vitro. Here, we studied more extensively steroids and steroid anion conjugates as candidate oatp substrates. In HeLa cell monolayers transfected with a full-length oatp cDNA, [3H]estradiol 17 beta-D-glucuronide ([3H]E2-17G) was transported with a signal-to-noise ratio of 15:1 over that of monolayers transfected with a control plasmid. The affinity of oatp for [3H]E2-17G was significantly higher than that for TCA (K(m) of 3 microM vs. 27 microM, respectively). In contrast to E2-17G, unconjugated estradiol (E2) was not significantly transported by oatp. Several unconjugated steroids and anionic steroid conjugates were tested for their ability to compete with tracer E2-17G for oatp-mediated transport. Conjugation at the 17 or 3 position with the anion of a strong acid (sulfate) resulted in a greater degree of inhibition of tracer E2-17G transport than did conjugation at the 17 or 3 position with an uncharged group (acetate), suggesting that the strength of the negative charge at these positions is an important determinant of the affinity of a given steroid conjugate for oatp. We conclude that the preferred substrates for oatp are steroids with a strong 17- or 3-position anionic group. Since steroid sulfotransferases and glucuronosyltransferases are expressed in the proximal tubule, as is oatp, the transporter may serve as an apical exit pathway for steroids following their conjugation within the tubule cell.

Anion Transport Proteins↗
PubMed1995

Expression of an epidermal keratin protein in liver of transgenic mice causes structural and functional abnormalities.

To examine the role of keratin intermediate filament proteins in cell structure and function, transgenic mice were isolated that express a modified form of the human K14 keratin protein in liver hepatocytes. A modified K14 cDNA (K14.P) sequence was linked downstream of the mouse transthyretin (TTR) gene promoter and enhancer elements to achieve targeted expression in hepatocytes. Hepatocytes expressing high levels of the transgene were found to have abnormal keratin filament networks as detected by indirect immunofluorescence using an antibody specific for the transgene product. Light and electron microscopic level histological analysis of isolated liver tissue showed in many cases degenerative changes that included inflammatory infiltration, ballooning degeneration, an increase in fat containing vacuoles, and glycogen accumulation. These changes were most evident in older mice over four months of age. No indication of typical Mallory body structures were identified at either the light or electron microscopic level. To evaluate secretory function in transgenic livers, bile acid secretion rates were measured in isolated perfused liver and found to be approximately twofold lower than aged-matched controls. These findings indicate that expression of an abnormal keratin in liver epithelial cells in the in vivo setting can alter the structure and function of a tissue and suggest a role of the keratin network in cellular secretion.

Animals↗
PubMed1995

Prolactin increases mRNA encoding Na(+)-TC cotransport polypeptide and hepatic Na(+)-TC cotransport.

We have shown that prolactin (Prl) increases the transhepatic transport of taurocholate (TC) in postpartum rats and following treatment of ovariectomized (Ovx) rats with ovine Prl (oPrl). The present studies were designed to determine if treatment of Ovx rats with oPrl (100, 300, or 600 micrograms/day, 7 days iv) 1) increases Na(+)-TC cotransport in basolateral plasma membrane vesicles (bLPM), 2) induces a corresponding increase in the steady-state levels of Na(+)-TC cotransport polypeptide (Ntcp mRNA), and 3) if the oPrl-mediated increase in Na(+)-TC cotransport activity is blocked by cycloheximide, an inhibitor of protein synthesis. oPrl (300 micrograms/day) induced a twofold increase in the maximal velocity for Na(+)-TC cotransport in both hepatocytes and bLPM vesicles with little change in the Michaelis constant. Infusion of oPrl at a dose of 100, 300, or 600 micrograms/day increased steady-state Ntcp mRNA four-, ten-, and twofold, respectively. Finally, cycloheximide blocked the oPrl-mediated increase in Na(+)-TC cotransport but did not affect basal activity. These data support the hypothesis that an increase in Ntcp mRNA followed by increased synthesis and incorporation of Ntcp in the plasma membrane is responsible for the oPrl-mediated increase in Na(+)-TC cotransport in the basolateral plasma membrane domain of the hepatocyte.

Animals↗
PubMed1994

Prolactin increases hepatic Na+/taurocholate co-transport activity and messenger RNA post partum.

We have shown that Na+/taurocholate co-transport activity is decreased in pregnancy, but rebounds post partum relative to non-pregnant controls, and that activity can be increased by treatment with ovine prolactin [Ganguly, Hyde and Vore (1993) J. Pharmacol. Exp. Ther. 267, 82-87]. To determine the basis for these effects, Na+/taurocholate co-transport was determined in purified basolateral liver plasma-membrane (bLPM) vesicles and compared with steady-state mRNA levels encoding the Na+/taurocholate-co-transporting polypeptide (Ntcp) in non-pregnant controls, pregnant rats (19-20 days pregnant), rats post partum (48 h post partum) and rats post partum treated with bromocriptine to inhibit prolactin secretion. Na+/taurocholate co-transport activity (nmol/5 s per mg of protein) in bLPM was decreased from 10.4 +/- 1.8 in non-pregnant controls to 7.9 +/- 0.6 in bLPM in pregnant rats, but rebounded to 17.5 +/- 1.3 post partum; treatment of rats post partum with bromocriptine to inhibit prolactin secretion decreased activity to 14.1 +/- 0.9. Northern and slot-blot analyses revealed similar changes in mRNA for Ntcp, so that a positive correlation was observed between Na+/taurocholate co-transport activity and Ntcp mRNA. Furthermore, treatment of ovariectomized rats with ovine prolactin increased Ntcp mRNA 10-fold compared with solvent-treated controls, consistent with the 2-fold increase in Vmax, for Na+/taurocholate co-transport in isolated hepatocytes. These data are the first to demonstrate endogenous physiological regulation by prolactin of Ntcp mRNA in parallel with Na+/taurocholate co-transport activity.

Animals↗
PubMed1994

Carrier-mediated electrogenic transport of estradiol-17 beta-glucuronide in rat liver BMV.

Estradiol-17 beta-glucuronide (E(2)17G) is one of a series of naturally occurring glucuronide conjugates of the steroid D-ring that induce cholestasis in the rat and nonhuman primate. The present studies characterized the transport of [3H]E(2)17G in basolateral membrane vesicles (BMVs) from male rat liver. The uptake of E(2)17G was temperature dependent, occurred into an osmotically sensitive space, and was saturable, with an apparent Michaelis constant and maximal velocity of 13 microM and 29 pmol.mg protein-1.5 s-1, respectively. Uptake was not coupled to the uptake of Na+ nor to Cl-or OH- exchange but was markedly stimulated by an inside-positive membrane potential. Bromosulfophthalein inhibited the uptake of E217G noncompetitively; estriol-16 alpha-glucuronide, but not estradiol-3-glucuronide or estradiol-3-SO4-17 beta-glucuronide, inhibited the uptake of E(2)17G. Thus E(2)17G is transported as an anion by facilitated diffusion by a system that differs from the multispecific Na(+)-taurocholate cotransport system and the bromosulfophthalein transport system.

Animals↗
PubMed1993

17 beta-estradiol glucuronide: an inducer of cholestasis and a physiological substrate for the multidrug resistance transporter.

The multidrug resistance (MDR) gene family has been shown to be highly expressed in several normal tissues including the canalicular membrane of the hepatocyte. We report that a cholestatic estrogen metabolite, 17 beta-estradiol glucuronide (E217G), is a substrate for the MDR transporter, P-glycoprotein. In cytotoxicity studies, the MDR sarcoma cell line Dx5 was 4.7-fold resistant to E217G, and the K562/R7 leukemia MDR cell line was 5.0-fold resistant to E217G relative to their parental cell lines. There was also a 2- to 3-fold accumulation defect of [3H]E217G in the MDR cells relative to their parental cell lines. E217G (100 microM) modulated resistance ot doxorubicin, taxol, vinblastine, and etoposide in the Dx5 cells, completely reversing the 30- to 60-fold resistance observed with these agents. E217G had no effect on the toxicity of these compounds in the parental cell line (MES-SA). In contrast, MDR cells were not resistant to the noncholestatic estrogen metabolite, estriol 3-glucuronide, and this metabolite did not modulate resistance to MDR substrates. ATP-dependent transport of [3H]E217G in rat canalicular membranes was inhibited by several MDR substrates including vinblastine, etoposide, verapamil, cyclosporine, and PSC-833.

Cholestasis↗
PubMed1993

Endothelins 1 and 3: potent cholestatic agents secreted and excreted by the liver that interact with cyclosporine.

Autoradiographic studies have shown that the liver accumulates endothelin. High-affinity binding sites for endothelin have been identified on rat liver plasma membranes. We investigated the role of endothelin isopeptides as mediators of cholestasis with isolated rat liver perfused by a recirculating solution of buffer and blood. These studies demonstrated that endothelin-1, as measured by means of radioimmunoassay, was cleared from the perfusate by the liver and that the liver concentrated both endothelin-1 and endothelin-3 in bile. Addition of endothelin-1 to the liver perfusate solution increased the concentration of endothelin-3 measured in the perfusate, suggesting that endothelin-1 caused release or secretion of endothelin-3. Both endothelin-1 and endothelin-3 at 5 nmol/L caused almost complete cessation of bile flow, but this effect was more prolonged after endothelin-1 than after endothelin-3 administration. Because it has been reported that cyclosporine increases endothelin levels, we studied the interaction of these two compounds. Cyclosporine (100 mumol/L) also produced cholestasis. Endothelin-3 secretion in bile, however, was decreased in livers perfused with cyclosporine compared with secretion in controls. Simultaneous addition of endothelin-1 and cyclosporine that on their own were not significantly cholestatic produced cholestasis. In conclusion, endothelin is a potent cholestatic agent secreted and excreted by the liver. It may potentiate the cholestatic action of cyclosporine.

Animals↗
PubMed1993

Canalicular transport: discovery of ATP-dependent mechanisms.

Biliary excretion is well recognized as a major pathway for the elimination of xenobiotics which are amphipathic and of high molecular weight. Excretion in bile thus complements the renal elimination of hydrophilic compounds of low molecular weight. The liver metabolizes many endogenous and exogenous compounds, frequently by oxidation reactions followed by conjugation pathways that yield substrates, particularly glucuronide and glutathione conjugates, suitable for secretion into bile. The features of a compound which make it a substrate for biliary secretion, other than that it must be an amphipathic molecule with a high molecular weight, are still not clearly defined. However, the recent discovery of ATP-dependent transport of glucuronide and glutathione conjugates in canalicular membranes has provided the opportunity to understand the mechanism of transport and the substrate specificity and regulation of the transporter(s). It is the purpose of this article to review these discoveries and their implications for toxicology.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1993

Prolactin increases Na+/taurocholate cotransport in isolated hepatocytes from postpartum rats and ovariectomized rats.

The role of prolactin (PRL) in regulating the transport of the bile acid taurocholate (TC) was assessed using isolated rat hepatocytes. Na(+)-dependent TC cotransport was determined in hepatocytes from female nonpregnant, pregnant (19-20 days pregnant), postpartum (48 hr postpartum) and postpartum rats treated with bromocriptine to block PRL secretion. In separate experiments ovariectomized rats were infused i.v. with solvent alone (OVX) or with ovine PRL (100, 300 and 600 micrograms/day) for 7 days (OVX+oPRL). The least squares estimates of Km (microM) and Vmax (nmol/min/mg protein) for Na(+)-dependent TC uptake were, respectively: 15 and 1 in nonpregnant, 9 and 0.4 in pregnant, 9 and 1.1 in postpartum and 15 and 1 in bromocriptine-treated postpartum rats, and were 15 and 1 in OVX, 15 and 1 in OVX+oPRL (100 micrograms/day), 30 and 2 in OVX+oPRL (300 micrograms/day) and 18 and 2 in OVX+oPRL (600 micrograms/day) rats, respectively. Calculation of the 95% joint confidence limits for Km and Vmax showed that Na(+)-dependent TC uptake was significantly decreased in pregnant rats, and significantly increased in postpartum rats relative to nonpregnant controls. Bromocriptine-treated postpartum rats were not different from controls. Infusion of 300 and 600 micrograms/day oPRL significantly increased Na(+)-dependent TC transport relative to OVX rats. Na(+)-K(+)-ATPase activity did not differ among the groups. These data indicate that PRL is responsible for the increased Na(+)-dependent transport of TC in the maternal liver postpartum, and that administration of oPRL to ovariectomized rats increases this transport in a dose-dependent manner.

Animals↗
PubMed1992

Identification of an anion-transport ATPase that catalyzes glutathione conjugate-dependent ATP hydrolysis in canalicular plasma membranes from normal rats and rats with conjugated hyperbilirubinemia (GY mutant).

Rat liver canalicular plasma membranes were found to contain a 37-kDa protein that is immunologically cross-reactive with the dinitrophenyl glutathione-stimulated ATPase previously identified in human tissues. The protein, which was partially purified by affinity chromatography, exhibited ATPase activity dependent on dinitrophenyl glutathione, bilirubin ditaurate, and other dianionic compounds. The localization of this protein in the canalicular membrane and its measured enzymatic activity indicate that it is involved in the transport of glutathione derivatives and other dianionic organic compounds. A rat mutant in which the above transport activities are impaired contained the protein in amounts similar to those in a normal control.

Adenosine Triphosphatases↗
PubMed1992

Prolactin regulates maternal bile secretory function post partum.

The single-pass isolated perfused rat liver was used to assess bile secretory function in pregnancy and the post partum period and to evaluate the regulatory role of prolactin. Nonpregnant controls, post partum rats (48 hr post partum), pregnant rats (19-20 days of pregnancy) and pregnant rats treated with bromocriptine (3 mg/kg/day, s.c.) from day 20 of pregnancy until 48 hr post partum to block prolactin secretion were examined. In a separate set of experiments, ovariectomized rats were implanted with osmotic minipumps containing solvent alone or solvent plus varying concentrations of ovine prolactin (oPRL). Livers were isolated, [3H]taurocholate (TC) was infused at increasing concentrations and bile flow, bile acid secretory rate and hepatic clearance of TC from the perfusate were determined. Maximal bile flow (microliters/min/g liver) in response to infusion of TC was significantly higher in post partum rats (3.4 +/- 0.3) than in pregnant rats (1.4 +/- 0.3) and bromocriptine-treated post partum rats (1.7 +/- 0.3). The maximal bile acid secretory rate (SRm, nmol/min/g liver) in post partum rats was 276 +/- 19 and was significantly greater than SRm in pregnant (103 +/- 26) and bromocriptine-treated post partum rats (142 +/- 25). Hepatic clearance (ml/min) was significantly greater in post partum rats than in pregnant, control and bromocriptine-treated post partum rats at the highest TC concentration. Infusion of oPRL at doses of 100, 250 and 500 micrograms/day significantly increased maximal bile flow and SRm in a dose-dependent manner; these measures were increased to 4.38 +/- 0.21 microliters/min/g liver and 338.2 +/- 16.3 nmol/min/g liver, respectively, in rats treated with 500 micrograms/day oPRL.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Mirex inhibits bile acid secretory function in vivo and in the isolated perfused rat liver.

The insecticides mirex and chlordecone suppress the biliary excretion of a wide variety of non-bile acid organic anions in vivo in the rat, and mirex inhibits the uptake of taurocholate (TC), a common bile acid, in isolated rat hepatocytes. We have therefore investigated the effects of mirex and chlordecone on bile acid secretory function (bile flow, bile acid concentration, bile acid secretory rate) in vivo and in the single-pass isolated perfused liver. Male Sprague-Dawley rats were orally dosed with corn oil, mirex (50 mg/kg), or chlordecone (18.75 mg/kg; in vivo studies only) for 3 consecutive days and experiments performed on Day 6. Mirex significantly increased liver weight from 12.2 +/- 0.8 to 20.8 +/- 1.3 g with no change in body weight whereas chlordecone had no significant effect on liver weight (11.9 +/- 0.7 g) or body weight. Mirex significantly decreased while chlordecone increased bile flow per gram liver in vivo; both compounds, however, increased bile flow when expressed per kilogram of body weight. Mirex and chlordecone significantly decreased the bile acid concentration in bile and the bile acid secretory rate (nmol/min/g liver and mumol/min/kg body weight). Studies in the isolated perfused liver were designed to determine the effect of mirex on the ability of the liver to extract increasing concentrations of [3H]TC from the perfusate and excrete it in the bile. Mirex treatment significantly decreased the TC extraction ratio by 40-89% and the hepatic intrinsic clearance by 85-95%. Mirex also significantly decreased the TC-induced choleresis, the concentration of TC in the bile, and the TC secretory rate. The data indicate that mirex treatment markedly inhibits the ability of the liver to extract TC from the blood/perfusate and concentrate it in the bile.

Animals↗