Biliary permeability during ethinyl estradiol-induced cholestasis studied by segmented retrograde intrabiliary injections in rats

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.

Visualization of the transport of primary and secondary bile acids across liver tissue in rats: in vivo study with fluorescent bile acids

BACKGROUND/AIMS

Lysyl fluorescein conjugated bile acid analogues (LFCBAA) closely parallel their natural counterparts. To assess LFCBAA as a tool for the visualization of bile acid transport within liver tissue.

METHODS

Wistar rats were administered physiological concentrations of the primary bile acid analogue cholyllysyl fluoroscein (CLF) and of the secondary bile acid analogue lithocholyllysyl fluorescein (LLF) and serial liver biopsies were taken at fixed intervals. Both compounds were also injected retrogradely into the biliary tree. Frozen sections were examined by fluorescence microscopy.

RESULTS

Both CLF and LLF were rapidly taken up from sinusoidal blood but differed significantly in their hepatic handling. CLF was rapidly transported into bile, whereas LLF transport was slower and produced significantly more bile duct fluorescence. LLF clearance showed a lobular gradient with last remaining bile acid being confined largely to zone 3. Both compounds were avidly taken up by cholangiocytes after injection intravenously or retrogradely into the biliary tree.

CONCLUSIONS

Visualization of LFCBAA by fluorescence microscopy may yield further information regarding hepatobiliary bile acid localization during studies of physiological and pathological mechanisms involved in transport of bile acids. The presence of both compounds within cholangiocytes strongly suggests that they may undergo a degree of chole-hepatic recirculation.

Impaired activity of the bile canalicular organic anion transporter (Mrp2/cmoat) is not the main cause of ethinylestradiol-induced cholestasis in the rat

To test the hypothesis that impaired activity of the bile canalicular organic anion transporting system mrp2 (cmoat) is a key event in the etiology of 17alpha-ethinylestradiol (EE)-induced intrahepatic cholestasis in rats, EE (5 mg/kg subcutaneously daily) was administered to male normal Wistar (NW) and mrp2-deficient Groningen Yellow/Transport-deficient Wistar (GY/TR-) rats. Elevated plasma bilirubin levels in GY/TR- rats increased upon EE-treatment from 65 +/- 8.4 micromol/L to 183 +/- 22.7 micromol/L within 3 days, whereas bilirubin levels remained unaffected in NW rats. Biliary bilirubin secretion was 1.5-fold increased in NW rats but remained unaltered in GY/TR- rats. Plasma bile salt concentrations remained unchanged in both strains, although hepatic levels of the sinusoidal Na+-taurocholate cotransporting protein (ntcp) were markedly reduced. Biliary secretion of endogenous bile salt was not affected in either strain. A clear reduction of mrp2 levels in liver plasma membranes of NW rats was found after 3 days of treatment. The bile salt-independent fraction of bile flow (BSIF) was reduced from 2.6 to 2.0 microL/min/100 g body weight in NW rats with a concomitant 62% reduction of biliary glutathione secretion. The absence of mrp2 and biliary glutathione in GY/TR- rats did not prevent induction of EE-cholestasis; a similar absolute reduction of BSIF, i.e., from 1.1 to 0.6 microL/min/100 g bodyweight, was found in these animals. EE treatment caused a reduction of the maximal biliary secretory rate (S(RM)) of the mrp2 substrate, dibromosulphthalein (DBSP), from 1,040 to 695 nmol/min/100 g body weight (-38%) in NW rats and from 615 to 327 nmol/min/100 g body weight (-46%) in GY/TR- rats. These results demonstrate that inhibition of mrp2 activity and/or biliary glutathione secretion is not the main cause of EE-induced cholestasis in rats. The data indicate that alternative pathways exist for the biliary secretion of bilirubin and related organic anions that are also affected by EE.

Ethinylestradiol increases volume and decreases sinusoidal membrane surface in the rat liver: a stereological analysis

Structural alterations of liver parenchyma caused by ethinylestradiol, a synthetic estrogen known to induce cholestasis and to act as a tumor promoter factor, were investigated. Male rats treated with 17 alpha-ethinylestradiol (5 mg/kg body weight for 5 days) were compared with controls (n = 5 each). After perfusion fixation and systematic random sampling, paraffin sections, semithin sections and thin sections were examined observing standard stereological techniques. Ethinylestradiol treatment induced an increase in liver volume by 65% (p less than 0.001), which was caused more by hypertrophy (volume of singular hepatocyte +35%, p less than 0.001) than by hyperplasia (number of hepatocytes +23%, p less than 0.001). A decrease in sinusoidal membrane surface density (-43%, p less than 0.005) associated with a decrease in sinusoidal microvillar volume density (-50%, p less than 0.005) were both compensated for by the increase in liver volume. No canalicular alterations were observed. Thus changes in hepatocytes detectable with stereological techniques affect the sinusoidal pole where decreased sinusoidal membrane surface is associated with or reflects a substantial loss of membrane phospholipids. The increased liver volume may constitute an adaptive response compensating for the relative decrease in sinusoidal membrane surface and displays characteristics comparable to those of preneoplastic hepatocytes.

Oestradiol 17 beta-glucuronide increases tight-junctional permeability in rat liver

By using rat liver perfusion under one-pass conditions with a single pulse of horseradish peroxidase (HRP), the biliary output of HRP was used as an indicator of paracellular permeability change caused by the cholestatic compound oestradiol 17 beta-glucuronide (E17G). Since E17G reduced bile flow, we have also used, during the assessment of junctional permeability after E17G treatment, the choleretic compound taurodehydrocholate to enhance bile flow back to control levels. At both low and restored bile flow rates, the acute administration of E17G (3.4 mumol) increased the HRP peak height, thereby indicating that one of the hepatotoxic actions of E17G is to increase the permeability of hepatic tight junctions. The action of E17G in affecting bile acid secretion and biliary volume are also explored.

Synthesis and biliary excretion of tyrosine-conjugated bile salts in Wistar rats

Tyrosine-labelled free and glycine-conjugated bile acids were synthesized and radiolabelled with 125I to high purity. The synthetic method utilized excess tyrosine methyl ester hydrochloride (1.4 equiv.) and bile acid (one equiv.) via dicyclohexylcarbodiimide (1.4 equiv.) with yields of 90-93% for tyrosine bile acid conjugates and glycyltyrosine conjugates and 56-60% yields for the glycylglycyltyrosine conjugates. All of the eight iodinated tyrosine bile acids tested were rapidly excreted into bile following intravenous injection. In bile duct-cannulated rats with ligated renal pedicles under pentobarbital anaesthesia the percentages of injected dose recovered from bile within 20 min were as follows: cholylglycine ([14C]cholylGly), 81.2 +/- 1.3%; taurocholate ([14C]taurocholate), 94.3 +/- 1.0%; cholyltyrosine (125I-cholylTyr), 85.5 +/- 3.3%; deoxycholyltyrosine (125I-deoxycholylTyr), 87.9 +/- 6.3%; chenodeoxycholyltyrosine (125I-chenodeoxycholylTyr), 93.4 +/- 2.9; cholylglycyltyrosine (125I-cholylGlyTyr), 95.7 +/- 6.7%; deoxycholylglycyltyrosine (125I-deoxylcholylGlyTyr), 92.5 +/- 3.2%; chenodeoxycholylglycyltyrosine (125I-chenodeoxycholylGlyTyr), 94.1 +/- 3.1%; cholyldiglycyltyrosine (125I-cholylGlyGlyTyr), 85.2 +/- 3.6%, and deoxycholyldiglycyltyrosine (125I-deoxycholylGlyGlyTyr), 85.5 +/- 2.7%. Values are means +/- SD. Thus the biliary excretion of 125I-chenodeoxycholylGlyTyr, 125I-chenodeoxycholylTyr, 125I-deoxycholylGlyTyr and 125I-cholylGlyTyr was similar to that of [14C]taurocholate, the major naturally occurring bile acid in the rat, and the biliary excretion of all the tyrosine conjugates was similar to or exceeded that of [14C]cholylglycine. Conjugation with tyrosine enhanced the efficiency of plasma-to-bile transport of most naturally occurring bile acids. Comparison of glycyltyrosine conjugates with glycylglycyltyrosine conjugates suggests that any additional benefit derived by elongation of the side-chain is probably negated by obscuring the 12 alpha-hydroxyl function on the steroid nucleus in the bile acid glycylglycyltyrosine conjugates.

Selectively reduced biliary excretion of cholyldiglycylhistamine but not of cholyltetraglycylhistamine in ethinyl estradiol-treated rats. A possible indicator of increased bile canalicular permeability

A series of bile acid derivatives were synthesized, purified and radiolabelled. These were [125I]cholylglycylhistamine [( 125I]CGH), [125I] cholyldiglycylhistamine [( 125I]CG2H), [125I]cholyltriglycylhistamine [( 125I]CG3H), and [125I]cholyltetraglycylhistamine [( 125I]CG4H). These derivatives were rapidly excreted unchanged into the bile of bile-fistula rats. In normal rats the 30-min cumulative excretion following intravenous administration was only 39.0 +/- 0.7% for [125I]CGH but greater than 80% for the three larger compounds. This marked difference in biliary recovery between CGH and the other larger compounds could be due to a threshold biliary permeability, and we postulated that the critical molecular weight threshold for effective biliary retention of such compounds falls between [125I]CGH (MW 683) and [125I]CG2H (MW 740). Increased permeability, involving a shift to a higher molecular weight threshold would then be anticipated to diminish biliary excretion of [125I]CG2H (MW 740) before exerting a major influence on the biliary excretion of [125I]CG4H (MW 854). We previously reported functional and morphological studies which suggest that ethinyl estradiol (EE) may alter the permeability of bile canalicular tight junctions. In this study we have looked for further evidence of a progressive permeability change in EE-induced cholestasis by observing the biliary excretion of CG2H and CG4H in rats. Treatment with EE (5 mg/kg/day) for 3 days (EE3) or with the injection vehicle propylene glycol for 7 days (C7) reduced biliary excretion to a significant extent when compared to 3-day controls (C3) but had no differential effect on the 30-min recoveries from bile of CG2H and CG4H, respectively: C3 (81.2 +/- 1.8% and 81.7 +/- 2.1%, P = CN): C7 (72.3 +/- 3.0% and 73.5 +/- 3.6%, P = NS): EE3 61.8 +/- 2.5% and 61.9 +/- 2.7%, P = NS). However, treatment with EE for 7 days significantly reduced the biliary recovery of CG2H (46.8 +/- 9%) compared to EE3 rats (P less than 0.0025) but there was no significant change of biliary CG4H recovery (61.0 +/- 2.5%, P = NS) compared with EE3 rats. These results are compatible with our hypothesis that EE-induced cholestasis is associated with a change of biliary permeability which, as it progresses, affects successively larger molecules.