Estradiol-17 beta-glucuronide-induced cholestasis. Effects of ursodeoxycholate-3-O-glucuronide and 3,7-disulfate

Tauroursodeoxycholate prevents estradiol 17β-d-glucuronide-induced cholestasis and endocytosis of canalicular transporters by switching off pro-cholestatic signaling pathways

AIMS

Estradiol 17β-d-glucuronide (E217G) induces cholestasis by triggering endocytosis and further intracellular retention of the canalicular transporters Bsep and Mrp2, in a cPKC- and PI3K-dependent manner, respectively. Pregnancy-induced cholestasis has been associated with E217G cholestatic effect, and is routinely treated with ursodeoxycholic acid (UDCA). Since protective mechanisms of UDCA in E217G-induced cholestasis are still unknown, we ascertained here whether its main metabolite, tauroursodeoxycholate (TUDC), can prevent endocytosis of canalicular transporters by counteracting cPKC and PI3K/Akt activation.

MAIN METHODS

Activation of cPKC and PI3K/Akt was evaluated in isolated rat hepatocytes by immunoblotting (assessment of membrane-bound and phosphorylated forms, respectively). Bsep/Mrp2 function was quantified in isolated rat hepatocyte couplets (IRHCs) by assessing the apical accumulation of their fluorescent substrates, CLF and GS-MF, respectively. We also studied, in isolated, perfused rat livers (IPRLs), the status of Bsep and Mrp2 transport function, assessed by the biliary excretion of TC and DNP-SG, respectively, and Bsep/Mrp2 localization by immunofluorescence.

KEY FINDINGS

E217G activated both cPKC- and PI3K/Akt-dependent signaling, and pretreatment with TUDC significantly attenuated these activations. In IRHCs, TUDC prevented the E217G-induced decrease in apical accumulation of CLF and GS-MF, and inhibitors of protein phosphatases failed to counteract this protection. In IPRLs, E217G induced an acute decrease in bile flow and in the biliary excretion of TC and DNP-SG, and this was prevented by TUDC. Immunofluorescence studies revealed that TUDC prevented E217G-induced Bsep/Mrp2 endocytosis.

SIGNIFICANCE

TUDC restores function and localization of Bsep/Mrp2 impaired by E217G, by preventing both cPKC and PI3K/Akt activation in a protein-phosphatase-independent manner.

Mitigation of intrahepatic cholestasis induced by 17α-ethinylestradiol via nanoformulation of Silybum marianum L

BACKGROUND

Cholestasis is an important predisposing factor for hepatocyte damage, liver fibrosis, primary biliary cirrhosis, and even liver failure. Silybum marianum L. (SM) plant is used in teas or eaten in some countries due to its antioxidant and hepatoprotective properties. Because of its low and poor oral bioavailability, so we improve the therapeutic activity of Silybum marianum L. extract (SM) by studying the potential effects of nanoformulation of Silybum marianium L. extract (nano-SM) on 17α-ethinylestradiol (EE)-induced intrahepatic cholestasis.

METHODS

Thirty female Sprague-Dawley rats were divided into 5 groups (6 rats/group). Group I: Rats were received the treatment vehicle and served as normal group. Group II:Rats were injected daily with EE (10 mg/kg) for five successive days. Group III-V: Rats were injected daily with EE (10 mg/kg) and treated with either Ursodeoxycholic acid (UDCA) (40 mg/kg), SM (100 mg/kg) and nano-SM (100 mg/kg) orally once/day throughout the trialfor five successive days, respectively.

RESULTS

Nano-SM greatly dampened the increase in serum levels of total and direct bilirubin, alanine aminotransaminase, aspartate aminotransaminase, and alkaline phosphatase caused by EE. Furthermore, nano-SM increased the hepatic contents of reduced glutathione (GSH) and catalase (CAT) and also upregulated the relative hepatic gene expressions of Rho-kinase (ROCK-1), myosin light chain kinase (MLCK), and myosin phosphatase target subunit (MYPT1) compared to the EE-induced group. Administration of nano-SM reduced hepatic lipid peroxidation and downregulated the relative hepatic expressions of the nuclear factor-kappa B (NF-ҡB) and interleukin-1β (IL-1β). In addition, nano-SM improved the histopathological changes induced by EE.

CONCLUSION

Nano-SM possessed a superior effect over SM, which can be considered an effective protective modality against EE-induced cholestatic liver injury through its antioxidant, anti-inflammatory activities, and enhancing bile acid (BA) efflux.

Rodent models of cholestatic liver disease: A practical guide for translational research

Cholestatic liver disease denotes any situation associated with impaired bile flow concomitant with a noxious bile acid accumulation in the liver and/or systemic circulation. Cholestatic liver disease can be subdivided into different types according to its clinical phenotype, such as biliary atresia, drug-induced cholestasis, gallstone liver disease, intrahepatic cholestasis of pregnancy, primary biliary cholangitis and primary sclerosing cholangitis. Considerable effort has been devoted to elucidating underlying mechanisms of cholestatic liver injuries and explore novel therapeutic and diagnostic strategies using animal models. Animal models employed according to their appropriate applicability domain herein play a crucial role. This review provides an overview of currently available in vivo animal models, fit-for-purpose in modelling different types of cholestatic liver diseases. Moreover, a practical guide and workflow is provided which can be used for translational research purposes, including all advantages and disadvantages of currently available in vivo animal models.

The Interaction of PPARα and CYP7B1 with ERα, β Impacted the Occurrence and Development of Intrahepatic Cholestasis in Pregnant Rats

Intrahepatic cholestasis of pregnancy (ICP) is a disorder of bile acid (BA) synthesis, excretion, and metabolism, with systemic accumulation of BAs, which can lead to prematurity, fetal distress, and intrauterine death. Here, we investigate the expression of peroxisome proliferator-activated receptor alpha and cytochrome P450 oxysterol 7alpha-hydroxylase by exposing to 17α-ethynylestradiol with or without the estrogen receptor signaling pathway in pregnant rats with intrahepatic cholestasis. In vivo and in vitro evidences showed that estrogen receptor alpha (ERα) may be the key point of occurrence and development of intrahepatic cholestasis in pregnant rats. Besides, the abnormalities in genes could be reversed by ERα small interfering RNA. Our findings provide the ERα-centered hypothesis on the mechanisms of ICP. New perspectives are emerging for the treatment of estrogen-induced hepatic complication.

Effect of genipin on cholestasis induced by estradiol-17beta-glucuronide and lithocholate-3-O-glucuornide in rats

AIM

Genipin is reported to stimulate the insertion of multidrug resistance protein 2 (Mrp2) in the bile canalicular membrane, thereby causing choleresis by the increased the biliary excretion of glutathione, which has been considered to be a substrate of Mrp2. In the present study, we examined the effect of genipin on cholestasis induced by estradiol-17beta-glucuronide and lithocholate-3-O-glucuronide, Mrp2 substrates, in rats. Further, the effect of genipin on the biliary excretion of substrates of P-glycoprotein (P-gp), vinblastine and erythromycin, was also studied.

METHODS

The effect of genipin infusion at the rate of 0.5 micromol/min/100 g on cholestasis induced by estradiol-17beta-glucuronide (0.075 micromol/min/100 g for 20 min) and lithocholate-3-O-glucuronide (0.15 micromol/min/100 g for 40 min) was studied. The effect of genipin infusion on the biliary excretion of a tracer dose of vinblastine and erythromycin infused at the rate of 0.1 micromol/min/100 g was also studied.

RESULTS

Genipin relieved estradiol-17beta-glucuronide-induced cholestasis, and cumulative biliary estradiol-17beta-glucuronide excretion for 120 min was increased from 50 +/- 20%-81 +/- 20% dose. In contrast, genipin had no effect on lithocholate-3-O-glucuronide-induced cholestasis. Biliary excretion of a tracer dose of vinblastine and the maximum biliary excretion of erythromycin were significantly decreased by genipin.

CONCLUSIONS

Genipin protected estradiol-17beta-glucuronide-induced cholestasis. The mechanism of the protection of cholestasis by genipin is unknown, but it is speculated to be due to a conformational change of P-gp by genipin, in addition to the stimulation of Mrp2 insertion into the bile canaliculi.

Integration of hepatic drug transporters and phase II metabolizing enzymes: Mechanisms of hepatic excretion of sulfate, glucuronide, and glutathione metabolites

The liver is the primary site of drug metabolism in the body. Typically, metabolic conversion of a drug results in inactivation, detoxification, and enhanced likelihood for excretion in urine or feces. Sulfation, glucuronidation, and glutathione conjugation represent the three most prevalent classes of phase II metabolism, which may occur directly on the parent compounds that contain appropriate structural motifs, or, as is usually the case, on functional groups added or exposed by phase I oxidation. These three conjugation reactions increase the molecular weight and water solubility of the compound, in addition to adding a negative charge to the molecule. As a result of these changes in the physicochemical properties, phase II conjugates tend to have very poor membrane permeability, and necessitate carrier-mediated transport for biliary or hepatic basolateral excretion into sinusoidal blood for eventual excretion into urine. This review summarizes sulfation, glucuronidation, and glutathione conjugation reactions, as well as recent progress in elucidating the hepatic transport mechanisms responsible for the excretion of these conjugates from the liver. The discussion focuses on alterations of metabolism and transport by chemical modulators, and disease states, as well as pharmacodynamic and toxicological implications of hepatic metabolism and/or transport modulation for certain active phase II conjugates. A brief discussion of issues that must be considered in the design and interpretation of phase II metabolite transport studies follows.

HEPATIC TRANSPORT OF PKI166, AN EPIDERMAL GROWTH FACTOR RECEPTOR KINASE INHIBITOR OF THE PYRROLO-PYRIMIDINE CLASS, AND ITS MAIN METABOLITE, ACU154

PKI166, a specific inhibitor of the tyrosine kinase activity of two epidermal growth factor receptors, was under development for the treatment of cancer. In preclinical studies PKI166 was mainly cleared by metabolism, and its metabolites were eliminated by biliary excretion, emphasizing the role of liver transport processes for its disposition. Here the transport properties of [14C]PKI166 and its main metabolite [14C]ACU154, an O-glucuronide, were analyzed using 1) Madin-Darby canine kidney II (MDCKII) cells stably transfected with human multidrug resistance-associated protein 2 (MRP2) and/or human organic anion-transporting peptide 2 (OATP2) and 2) liver canalicular membrane vesicles (CMVs) prepared from Wistar and mrp2-deficient TR- rats. Analysis of transport through MDCKII cells revealed that [14C]ACU154 was a substrate of MRP2 and OATP2. Rat mrp2 was shown to transport [14C]ACU154 with a Km of approximately 1 microM. [14C]PKI166 efficiently crossed MDCKII cells, particularly toward the apical side, but expression of MRP2 and/or OATP2 did not increase the flux. The effect of PKI166 and ACU154 on transport of [3H]estradiol-17beta-d-glucuronide (EG; via mrp2/MRP2 and OATP2) or [3H]taurocholic acid (TCA; via bile salt export pump (bsep) was analyzed. PKI166 inhibited the transport of [3H]EG by OATP2. ACU154 did strongly inhibit [3H]TCA uptake into CMVs from Wistar but not from TR- rats, demonstrating a dependence of bsep inhibition on mrp2 activity. ATP-dependent uptake of [3H]EG into CMVs from Wistar rats was inhibited by ACU154 but up to 4-fold increased by PKI166. In conclusion, OATP2 and MRP2/mrp2 were identified as transporters involved in ACU154 transport into bile. Both PKI166 and its O-glucuronide ACU154 affected mrp2/MRP2-, OATP2-, and/or bsep-mediated transport processes.

Effect of tauroursodeoxycholate and S-adenosyl-L-methionine on 17beta-estradiol glucuronide-induced cholestasis

BACKGROUND/AIMS

S-adenosyl-L-methionine (SAMe) and tauroursodeoxycholate (TUDC) exert an additive ameliorating effect on taurolithocholate (TLC)-induced cholestasis. The aims were to investigate the protective effect of SAMe on 17beta-estradiol-glucuronide (17betaEG) cholestasis and to find out whether SAMe and TUDC may exert an additive, ameliorating effect.

METHODS

Hepatocyte couplet function was assessed by canalicular vacuolar accumulation (cVA) of cholyllysylfluorescein (CLF). Cells were co-treated with 17betaEG and SAMe, TUDC, or both (protection study), or treated with 17betaEG and then with SAMe, TUDC or both (reversion study) before CLF uptake. Couplets were also co-treated with SAMe and dehydroepiandrosterone (DHEA), a competitive substrate for the sulfotransferase involved in 17betaEG detoxification. The effects of 17betaEG, SAMe and TUDC were also examined on intracellular distribution of F-actin.

RESULTS

Both SAMe and TUDC significantly protected against, and reversed, 17betaEG-induced cholestasis, but their effects were not additive. DHEA abolished the protective effect of SAMe. 17BetaEG did not affect the uptake of CLF into hepatocytes at the concentrations used, and also, it did not affect the intracellular distribution of F-actin.

CONCLUSIONS

17BetaEG does not affect the uptake of CLF into hepatocytes. SAMe and TUDC protect and reverse 17betaEG-induced cholestasis, but without an additive effect. Protection by SAMe may involve facilitating the sulfation of 17betaEG.

Mrp2 is essential for estradiol-17beta(beta-D-glucuronide)-induced cholestasis in rats

The present study evaluates the roles of the multidrug resistance-1 P-glycoprotein, Mdr1a/1b, the bile salt export pump (Bsep), and the multidrug resistance-associated protein-2 (Mrp2) in mediating cholestasis induced by estradiol-17beta(beta-D-glucuronide) (E(2)17G). Administration of ¿(3)HE(2)17G (18 nmol/g body weight) gave a similar degree of cholestasis and biliary excretion of E(2)17G-equivalents in wild-type and Mdr1a(-/-)/1b(-/-) mice. When expressed in Sf9 cells, Bsep-mediated adenosine triphosphate (ATP)-dependent transport of taurocholate (TC, 1 micromol/L) in membrane vesicles was 110% +/- 12.5% and 108% +/- 17.3% of control in the presence of 10 and 50 micromol/L E(2)17G, respectively, whereas in rat canalicular membrane, both E(2)17G and the choleretic estradiol-3-beta-D-glucuronide (E(2)3G) inhibited ATP-dependent transport of TC to the same extent. Infusion of ¿(3)HE(2)17G (24 micromol) did not induce cholestasis in Mrp2-deficient TR(-) rats whereas 2 micromol of ¿(3)HE(2)17G inhibited bile flow by 51% in control Wistar rats. The maximal biliary concentration of E(2)17G was 3.5 and 2.5 mmol/L in control and TR(-) rats, respectively. However, 2.2 mmol/L of E(2)17G in bile is associated with inhibition of bile flow in control rats. These data show that (1) Mdr1a/1b are not essential for E(2)17G-mediated cholestasis, (2) direct inhibition of Bsep-mediated bile acid transport is not the mechanism for E(2)17G cholestasis, and (3) accumulation of E(2)17G in bile alone is not sufficient to induce cholestasis. These data indicate that the process of Mrp2-mediated transport of high concentrations of E(2)17G is essential for its induction of cholestasis.

Mechanisms of cholestasis

From the multiple mechanisms of cholestasis presented in this article, a unifying hypothesis may be deduced by parsimony. The disturbance of the flow of bile must inevitably lead to the intracellular retention of biliary constituents. Alternatively, the lack of specific components of bile unmasks the toxic potential of other components, as in the case of experimental mdr2 deficiency. In the sequence of events that leads to liver injury, the cytotoxic action of bile salts is pivotal to all forms of cholestasis. The inhibition of the bsep by drugs, sex steroids, or monohydroxy bile salts is an example of direct toxicity to the key mediator in canalicular bile salt excretion. In other syndromes, the dysfunction of distinct hepatocellular transport systems is the primary pathogenetic defect leading to cholestasis. Such dysfunctions include the genetic defects in PFIC and the direct inhibition of gene transcription by cytokines. Perturbations in the short-term regulation of transport protein function are exemplified by the cholestasis of endotoxinemia. The effect of bile salts on signal transduction, gene transcription, and transport processes in hepatocytes and cholangiocytes has become the focus of intense research in recent years. The central role of bile salts in the pathogenesis of cholestasis has, ironically, become all the more evident from the improvement of many cholestatic syndromes with oral bile salt therapy.

Hepatobiliary transport

The alterations of hepatobiliary transport that occur in cholestasis can be divided into primary defects, such as mutations of transporter genes or acquired dysfunctions of transport systems that cause defective canalicular or cholangiocellular secretion, and secondary defects, which result from biliary obstruction. The dysfunction of distinct biliary transport systems as a primary cause of cholestasis is exemplified by the genetic defects in progressive familial intrahepatic cholestasis or by the direct inhibition of transporter gene expression by cytokines. In both, the hepatocellular accumulation of toxic cholephilic compounds causes multiple alterations of hepatocellular transporter expression. In addition, lack of specific components of bile caused by a defective transporter, as in the case of mdr2/MDR3 deficiency, unmasks the toxic potential of other components. The production of bile is critically dependent upon the coordinated regulation and function of sinusoidal and canalicular transporters, for instance of Na+-taurocholate cotransporting polypeptide (NTCP) and bile salt export pump (BSEP). Whereas the downregulation of the unidirectional sinusoidal uptake system NTCP protects the hepatocyte from further intracellular accumulation of bile salts, the relative preservation of canalicular BSEP expression serves to uphold bile salt secretion, even in complete biliary obstruction. Conversely, the strong downregulation of canalicular MRP2 (MRP, multidrug resistance protein) in cholestasis forces the hepatocyte to upregulate basolateral efflux systems such as MRP3 and MRP1, indicating an inverse regulation of basolateral and apical transporters The regulation of hepatocellular transporters in cholestasis adheres to the law of parsimony, since many of the cellular mechanisms are pivotally governed by the effect of bile salts. The discovery that bile salts are the natural ligand of the farnesoid X receptor has shown us how the major bile component is able to regulate its own enterohepatic circulation by affecting transcription of the genes critically involved in transport and metabolism.

Drug- and estrogen-induced cholestasis through inhibition of the hepatocellular bile salt export pump (Bsep) of rat liver

BACKGROUND & AIMS

Drug-induced cholestasis is a frequent form of acquired liver disease. To elucidate the molecular pathogenesis of drug-induced cholestasis, we investigated the effects of prototypic cholestatic drugs on the canalicular bile salt export pump (Bsep) of rat liver.

METHODS

Vesicles were isolated from Bsep-, Mrp2-, and Bsep/Mrp2-expressing Sf9 cells. Canalicular plasma membrane (cLPM) vesicles from rat liver and Sf9 cell vesicles were used to study adenosine triphosphate (ATP)-dependent solute uptake by a rapid filtration technique.

RESULTS

Bsep-expressing Sf9 cell vesicles showed ATP-dependent transport of numerous monoanionic bile salts with similar Michaelis constant values as in cLPM vesicles, whereas several known substrates of the multispecific organic anion transporter Mrp2 were not transported by Bsep. Cyclosporin A, rifamycin SV, rifampicin, and glibenclamide cis-inhibited Bsep-mediated bile salt transport to similar extents as ATP-dependent taurocholate transport in cLPM vesicles. In contrast, the cholestatic estrogen metabolite estradiol-17beta-glucuronide inhibited ATP-dependent taurocholate transport only in normal cLPM and in Bsep/Mrp2-coexpressing Sf9 cell vesicles, but not in Mrp2-deficient cLPM or in selectively Bsep-expressing Sf9 cell vesicles, indicating that it trans-inhibits Bsep only after its secretion into bile canaliculi by Mrp2.

CONCLUSIONS

These results provide a molecular basis for previous in vivo observations and identify Bsep as an important target for induction of drug- and estrogen-induced cholestasis in mammalian liver.

Adenosine triphosphate-dependent transport of estradiol-17beta(beta-D-glucuronide) in membrane vesicles by MDR1 expressed in insect cells

MDR1, an ABC transporter that confers multidrug resistance in tumor cells, is constitutively expressed in normal liver canalicular membrane. Human MDR1-expressing multidrug-resistant cells display increased resistance to estradiol-17beta(beta-D-glucuronide) (E217G). MDR1 substrates/modulators inhibit adenosine triphosphate (ATP)-dependent transport of E217G in the rat canalicular membrane and protect against E217G-mediated cholestasis in isolated perfused rat liver. The present studies were designed to determine if E217G is a substrate for MDR1 using a baculovirus expression system and if other estrogen glucuronides interact with MDR1. ATP-dependent transport of E217G (10 micromol/L) was linear for up to 2 minutes and yielded a rate of 45.6 pmol/min/mg protein in membrane vesicles from Sf9 cells infected with MDR1-baculovirus. This transport was saturable (Km = 62 micromol/L) and occurred into an osmotically sensitive space. ATP-dependent transport of E217G (10 micromol/L) was inhibited 63% by 10 micromol/L daunomycin, but not by 100 micromol/L S-(2,4-dinitrophenyl)glutathione (GS-DNP) (a substrate for canalicular multispecific organic anion transporter [cMOAT]). Glucuronide conjugates of the estrogen D-ring (100 micromol/L), estriol-17beta(beta-D-glucuronide) (E317G) and estriol-16(beta-D-glucuronide) (E316G), inhibited MDR1-mediated E217G transport by 58% and 35%, respectively. In contrast, noncholestatic glucuronides, estradiol-3-(beta-D-glucuronide) (E23G) or estradiol-3-sulfate-17beta(beta-D-glucuronide) (E23SO417G), had no effect. E217G neither stimulated MDR1 ATPase activity nor inhibited verapamil-stimulated ATPase activity. Infusion of 1.5 micromol/L doxorubicin or 1 micromol/L taxol protected against cholestasis induced by E316G and E317G in isolated perfused rat liver. These studies identify E217G, and probably E316G and E317G, as endogenous substrates for MDR1.

Changes in biliary excretory mechanisms in rats with ethinyloestradiol-induced cholestasis

Several excretory pathways for cholephilic compounds have been known. To examine the changes in excretory pathways in cholestasis induced by ethinyloestradiol, various bile acids, organic anions and organic cations were intravenously administered to ethinyloestradiol-treated rats and their biliary excretion was studied. Biliary excretion of taurocholate was slightly delayed, but its excretory maximum was markedly decreased. Biliary excretion of lithocholate-3-O-glucuronide, leukotriene C4, sulphobromophthalein and pravastatin was markedly impaired to a similar extent. Biliary excretion of vinblastine, a P-glycoprotein substrate, was increased, suggesting increased expression of P-glycoprotein. In contrast, biliary excretion of erythromycin, a cationic antibiotic, was markedly impaired. In conclusion, ethinyloestradiol treatment altered the biliary excretion of organic compounds, which may partly be related to changes of the canalicular transporters.

Absorption of unconjugated bile acids and tauroursodeoxycholate in the rat intestine

The absorption of ursodeoxycholate and its tauro-conjugate by the jejunum and the terminal ileum of rat intestine was compared with that of other unconjugated bile acids and taurocholate. In the ligated jejunum, the efficacy of absorption of unconjugated bile acids was in the following order: ursodeoxycholate = deoxycholate > chenodeoxycholate = cholate > lithocholate. This order cannot be explained by the theory that the passive diffusion of bile acids is faster the less hydroxyl bonds in the molecule. These findings on the unconjugated bile acids in the ligated jejunum were further confirmed by perfusion experiments. In the ligated terminal ileum, ursodeoxycholate, cholate and deoxycholate were absorbed as fast as taurocholate or tauroursodeoxycholate, whereas absorption of chenodeoxycholate was significantly slower. The Na+-dependency of the absorption of ursodeoxycholate and cholate in the terminal ileum was confirmed by perfusion studies. In conclusion, intestinal absorption of ursodeoxycholate was efficient in both the jejunum and ileum and these results may contribute to the high availability of ursodeoxycholate in various hepatobiliary diseases.

Effect of taurolithocholate-3-sulphate on biliary excretion of sulphobromophthalein and dibromosulphophthalein in the Eisai hyperbilirubinaemic rat

We previously reported that biliary lithocholate-3-sulphate excretion was inhibited by dibromosulphophthalein, not by sulphobromophthalein in Eisai hyperbilirubinaemic rats (EHBR); instead its excretion was inhibited by both organic anions in control rats. In the present study, the effect of taurolithocholate-3-sulphate on the excretion of sulphobromophthalein and dibromosulphophthalein was studied in EHBR and control Sprague-Dawley rats. Taurolithocholate-3-sulfate infusion inhibited biliary excretion of sulphobromophthalein and dibromosulphophthalein in both EHBR and control rats. These findings indicate that in control rats biliary excretion of taurolithocholate-3-sulphate is mediated by a carrier common for both organic anions, and that in EHBR, in which the canalicular multispecific organic anion transporter is impaired, the excretory pathway for taurolithocholate-3-sulphate is also partly identical to that for both organic anions.

Effect of tauro-alpha-muricholate and tauro-beta-muricholate on oestradiol-17 beta-glucuronide-induced cholestasis in rats

The effect of tauro-beta-muricholate (beta MC-tau) and tauro-alpha-muricholate (alpha MC-tau) on oestradiol-17 beta-glucuronide (E217G)-induced cholestasis was compared with that of tauroursodeoxycholate (UDC-tau) in rats. Like UDC-tau, alpha MC-tau and beta MC-tau infused at the rate of 0.2 mumol/min per 100 g bodyweight (BW) completely inhibited the cholestasis induced by E217G infused at the rate of 0.06 mumol/min per 100 g BW for 20 min. These findings indicate that beta MC-tau and alpha MC-tau are useful in protecting against various types of experimental cholestasis, as well as against bile acid-induced cholestasis.

Mechanisms of biliary excretion of lithocholate-3-sulfate in Eisai hyperbilirubinemic rats (EHBR)

Biliary excretion of lithocholate-3-sulfate is markedly impaired in EHBR. To examine the mechanism of biliary lithocholate-3-sulfate excretion in EHBR, the effects of colchicine treatment, a vesicular transport inhibitor, and infusion of taurocholate and organic anions were studied in EHBR and Sprague-Dawley rats. Colchicine treatment and taurocholate infusion had no effect of biliary lithocholate-3-sulfate excretion in EHBR, suggesting that biliary lithocholate-3-sulfate excretion is not mediated by the vesicular transport or by the bile acid excretory pathway. In control Sprague-Dawley rats, both sulfobromophthalein and dibromosulfophthalein infusion inhibited biliary lithocholate-3-sulfate excretion. In contrast, in EHBR dibromosulfophthalein infusion inhibited biliary lithocholate-3-sulfate excretion but BSP infusion did not. Indocyanine green and pravastatin infusion did not affect biliary lithocholate-3-sulfate excretion but pravastatin infusion had no effect in EHBR. These findings indicate that, whether physiologically important or not, two of more excretory pathways for organic anions exist at the canalicular membrane other than the ATP-dependent one.

Decreased biliary glutathione content is responsible for the decline in bile salt-independent flow induced by ethinyl estradiol in rats

Glutathione appears to be a major osmotic factor in the generation of bile salt-independent flow (BSIF). This study was designed to investigate its importance in the pathology of 17-alpha-ethinyl estradiol (EE)-induced cholestasis. Five-day EE treatment at the dose level of 5 mg/kg/day significantly decreased bile flow (57% of controls) and biliary glutathione secretion. Evaluation of the contribution of bile salt dependent flow (BSDF), glutathione dependent flow (GSDF) and the bile flow generated independently of both bile salts and glutathione (BS-GSIF) revealed that EE decreased all portions of the flow (63, 44 and 52% of control values, respectively). At 4 and 20 h after a single administration of the same EE dose, a significant diminution of bile flow was noted (decreases of 17 and 29%, respectively) in association with a significant fall in biliary glutathione content. Under these conditions, BSDF and BS-GSIF were not modified (98 and 112% of control BSDF values, respectively; 96 and 99% of control BS-GSIF values, respectively) while GSDF was decreased markedly, representing 65 and 50% of control values. Biliary glutathione secretion was diminished without modification of liver and blood glutathione concentration or redox status following single EE dose whereas, after 5 days of EE treatment, a significant increase in liver glutathione was observed, suggesting that EE may interfere with the glutathione secretory process. This study demonstrates that EE rapidly alters biliary glutathione content, leading to a marked decline in GSDF. This reduction may explain the decrease in BSIF produced by EE at the outset of cholestasis.