Increase In Biliary Excretion Research Articles

Effects of tetrathiomolybdate on copper metabolism in healthy volunteers and in patients with Wilson disease

In Wilson disease (WD), copper accumulates in the liver and brain causing disease. Bis-choline tetrathiomolybdate (TTM) is a potent copper chelator that may be associated with a lower risk of inducing paradoxical neurological worsening than conventional therapy for neurologic WD. To better understand the mode of action of TTM, we investigated its effects on copper absorption and biliary excretion. In a double-blind randomized setting, hepatic 64Cu activity was examined after orally administered 64Cu by PET/CT in 16 healthy volunteers before and after seven days of TTM treatment (15mg/d) or placebo. Oral 64Cu was administered one hour after the final TTM dose. Changes in hepatic 64Cu activity reflected changes in intestinal 64Cu uptake. Additionally, in four patients with WD, the distribution of 64Cu in venous blood, liver, gallbladder, kidney, and brain was followed after i.v. 64Cu dosing for up to 68 hours before and after seven days of TTM (15mg/day), using PET/MRI. Increased gallbladder 64Cu activity was taken as evidence of increased biliary 64Cu excretion. In healthy volunteers, TTM reduced intestinal 64Cu uptake by 82% 15 hours after the oral 64Cu dose. In patients with WD, gallbladder 64Cu activity was negligible before and after TTM, while TTM effectively retained 64Cu in the blood, significantly reduced hepatic 64Cu activity at all time-points and significantly reduced cerebral 64Cu activity two hours after the intravenous 64Cu dose. While we did not show an increase in biliary excretion of 64Cu following TTM administration, we demonstrated that TTM effectively inhibited most intestinal 64Cu uptake and retained 64Cu in the blood stream, limiting the exposure of organs like the liver and brain to 64Cu. Bis-choline tetrathiomolybdate (TTM) is an investigational copper chelator being developed for the treatment of Wilson disease. In animal models of Wilson disease, TTM has been shown to facilitate biliary copper excretion. In the present human study, TTM surprisingly did not facilitate biliary copper excretion but instead reduced intestinal copper uptake to a clinically significant degree. Our study builds on our understanding of human copper metabolism and the mechanism of action of TTM.

Updating physiologically based pharmacokinetic models for manganese by incorporating rapid association/dissociation processes in tissues

Previously, we developed a series of physiologically based pharmacokinetic (PBPK) models for manganese (Mn) in which saturable tissue binding and dose-dependent increases in biliary excretion captured key aspects of Mn homeostasis biology. These models reproduced the non-linear behavior of Mn kinetics in different tissues, accounting for dose-dependent changes in Mn kinetics. The original model construct had relatively slow association and dissociation rate constants for Mn binding in tissues. In this updated model, both rates of entry into tissue and the interaction of Mn with binding sites are rapid, and the step limiting Mn accumulation is the saturation of tissue binding sites. This binding reflects general cellular requirements for Mn with high affinity but rapid exchange between bound and free forms, which we captured using a dissociation constant (KD) of ~ 0.5 μM across tissues while maintaining different maximum binding capacities in each tissue. Variability in the binding capacities accounted for different background levels of Mn in particular tissues. This alternative structure successfully described Mn kinetics in tissues in adult rats exposed to Mn either in their diet or by inhalation, indicating that both the original and the present models capture the dose-dependent and tissue-specific kinetic behavior of Mn in adult rats. Although the published models that emphasize the role of smaller tissue binding rate constants in non-linear behaviors capture all relevant dose-dependent kinetic behaviors of this metal, increasing biological relevance of the model structure and parameters should provide greater confidence in applying the Mn PBPK models to risk assessment.

Further increase in biliary excretion of asymmetric dimethylarginine during hepatic ischemia/reperfusion injury by obeticholic acid, a farnesoid-X-receptor agonist

Further increase in biliary excretion of asymmetric dimethylarginine during hepatic ischemia/reperfusion injury by obeticholic acid, a farnesoid-X-receptor agonist

Influence of Ion-pair Formation on the Pharmacokinetic Properties of Drugs. Pharmacokinetic Interactions of Bretylium and Hexylsalicylic Acid in Rabbits

The simultaneous i.v. administration of equimolar doses of bretylium and hexylsalicylic acid results in an increase in plasma area under the curve value of both substances in comparison with their separate administration. The higher plasma levels of both compounds were associated with a reduced renal excretion and an increased biliary elimination. However, the increase in biliary excretion did not compensate for the reduced elimination of bretylium and hexylsalicylic acid via the kidney. The results presented in this paper give further evidence that ion-pairing in-vivo may result in altered pharmacokinetics of drugs particularly due to changes in biliary or renal excretion.

Immediate and dose-response related increase of biliary excretion of reverse triiodothyronine after propylthiouracil administration.

In a group of rats infused with L-thyroxine (0.13 micrograms T4 in 0.6 ml alkaline saline per hour) for 6 h to which an infusion of propylthiouracil (PTU) was added beginning from the 3rd hour (2 mg PTU in 0.6 ml saline per hour) a significant increase of biliary excretion of reverse triiodothyronine (rT3) was found. In another experiment a dose-response related rT3 excretion by bile was observed in groups of rats infused with 0.05, 0.10, 0.20 or 0.40 mg PTU in 1.2 ml alkaline saline per 2 h, all animals receiving a pulse dose of 1 micrograms rT3 at the beginning of PTU infusion. It was concluded that the increase of rT3 excretion results from the inhibition of 5'-deiodinase type I activity in the liver caused by PTU. It thus appears that such phenomenon may be used as in vivo marker of that enzyme activity.

Carbon monoxide stimulates mrp2-dependent excretion of bilirubin-IXalpha into bile in the perfused rat liver.

Although carbon monoxide (CO) has been reported to protect against hepatobiliary dysfunction, mechanisms for its actions remain unknown. This study aimed to examine actions of physiologically relevant concentrations of CO on biliary excretion. The effects of transportal administration of CO on bile output and constituents were examined in perfused rat livers. In livers of fed rats, CO regulated bile output biphasically in a dose-dependent manner; transportal administration of CO at 4 micro mol/L stimulated bile output by 10%. Under these circumstances, CO increased paracellular junctional permeability and consequently decreased biliary excretion of bile salts. Choleresis elicited by 4 micro mol/L CO coincided with significant increases in biliary excretion of bilirubin-IXalpha and glutathione. The CO-induced choleresis occurred independently of cyclic GMP, coincided with elevated excretion of K(+) and HCO(3)(-), and was abolished by tetraethylammonium, suggesting stimulatory effects of the gas on potassium channels. CO-mediated choleresis and increased excretion of organic anions appeared to be mediated by mrp2, because Eisai hyperbilirubinemia rats, which genetically lack the transporter, did not exhibit choleresis upon the CO administration. These results suggest that CO stimulates mrp2-dependent excretion of bilirubin-IXalpha through mechanisms involving potassium channels, serving as a cooperator standing behind the heme oxygenase reaction to facilitate hepatic heme detoxification.

Interactions between selenium and group Va-metalloids (arsenic, antimony and bismuth) in the biliary excretion

The interrelationship between the biliary excretion of exogenous group Va-metalloids (arsenic, antimony and bismuth) and selenium, as well as endogenous glutathione has been studied in rats injected intravenously with sodium selenite and one of the group Va-metalloids. Arsenic, antimony and bismuth appeared in the bile of rats together with large amounts of non-protein thiols (NPSH, representing glutathione and its SH-containing degradation products) and, with the exception of bismuth, they caused choleresis. Significant interactions were observed in the hepatobiliary disposition between selenium and each of the group Va-metalloids, however, their outcomes were not uniform. When coadministered with sodium arsenite or arsenate, selenite enhanced the initial biliary excretion of arsenic 2- and 8-fold, respectively, without further increasing the concomitant excretion of NPSH or the choleretic effect of arsenicals. However, selenite augmented neither the excretion of antimony or bismuth, nor the simultaneous biliary release of NPSH. In turn, arsenite, arsenate and antimony potassium tartrate increased the initial biliary excretion of selenium more than 10-fold and enhanced the accumulation of selenium in blood (exclusively in the erythrocytes). In contrast, administration of bismuth ammonium citrate diminished both the biliary excretion and the erythrocytic accumulation of selenium, while causing retention of selenium in the blood plasma. In rats receiving arsenic or antimony with selenite, the time courses of the biliary excretion of these group Va-metalloids, selenium and NPSH were similar. It is hypothesised that incorporation of selenol metabolites of selenite into the glutathione complexes of arsenic and antimony, resulting in cholephilic ternary complexes, accounts for the arsenic- and antimony-induced augmentation of the hepatobiliary transport of selenium. However, additional chemical and/or dispositional mechanisms are thought to be responsible for the selenite-induced increase in biliary excretion of arsenic.

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.

Protection by Clofibrate against Acetaminophen Hepatotoxicity in Male CD-1 Mice Is Associated with an Early Increase in Biliary Concentration of Acetaminophen–Glutathione Adducts

Repeated treatment with clofibrate (CFB) significantly increased hepatic glutathione (GSH) content and also diminished acetaminophen's (APAP) selective protein arylation, GSH depletion, and severity of hepatocellular necrosis. The present work was conducted to evaluate the role of elevated GSH and APAP detoxifying pathways in the amelioration of APAP's toxicity by CFB. Male CD-1 mice received 500 mg CFB/kg, ip, daily for 10 days. Controls were given corn oil vehicle. They were challenged with 700 mg APAP/kg in 50% propylene glycol/water after an overnight fast. Results indicate that CFB pretreatment had no effect on 24-hr urinary excretion of APAP–glucuronide, sulfate, or GSH-derived conjugates; however, there was 50% less unchanged APAP excreted in urine of CFB-pretreated mice. CFB also did not alter microsomal UDP–glucuronyl transferase activity toward APAPin vitro.However, elimination of APAP from plasma and liver was much greater in CFB-pretreated mice. This was accompanied by elevated biliary APAP–GSH content in CFB-pretreated mice at 2 hr after APAP dosing with diminished levels in bile at 12 hr. The CFB-induced increase in biliary excretion of APAP–GSH may mediate the protection against APAP-induced hepatotoxicity.

Taurocholate-stimulated leukotriene C 4 biosynthesis and leukotriene C 4-stimulated choleresis in isolated rat liver

Background/Aims: Cysteinyl-containing leukotrienes seem to exert a cholestatic effect. However, leukotriene inhibitors were found to reduce bile salt efflux in isolated rat hepatocytes, suggesting a role for leukotrienes in bile flow formation. Methods: In the isolated rat liver, the effects of two different concentrations of leukotriene C 4 on bile flow and bile salt excretion are analyzed, as well as the possible effect of taurocholate on the hepatic production of cysteinyl-containing leukotrienes. Results: Leukotriene C 4 (0.25 fmol) increased bile salt excretion (+22.2%; P < 0.05), whereas a much higher dose (0.25 × 10 6 fmol) showed the known cholestatic effect, reducing bile salt excretion (−25.9%; P < 0.01). These dose-dependent biphasic effects were specific because they could be prevented by the simultaneous administration of cysteinyl-containing leukotriene antagonists. On the other hand, taurocholate administration induced a dose-dependent increase in biliary excretion of cysteinyl-containing leukotrienes. Furthermore, taurocholate increased messenger RNA levels of 5-lipoxygenase, a key enzyme in leukotriene biosynthesis. Taurocholate increase of hepatocyte intracellular calcium was not significant, suggesting that taurocholate effects are not mediated by stimulation of calcium metabolism. Conclusions: These results constitute evidence for the existence of a positive feedback mechanism by which bile salts stimulate the synthesis of leukotrienes that, in turn, stimulate bile salt excretion.

Biliary excretion of plasma non-transferrin-bound iron in rats: pathogenetic importance in iron-overload disorders.

Plasma non-transferrin-bound iron (NTB-iron) is a potentially toxic form of iron, which is efficiently taken up by the normal, as well as the chronically iron-overloaded liver. In fact, NTB-iron may represent the major source of iron gaining access to hepatocytes in the iron-loaded state. We postulated that efficient biliary excretion of this form of iron could protect against iron-related hepatocellular injury. To characterize the biliary excretion of NTB-iron in intact normal and iron-loaded rats, the plasma disappearance and biliary excretion kinetics of plasma 55Fe-labeled NTB-iron were determined. In normal rats, prompt biliary excretion of plasma NTB-iron was evident, with peak radioactivity approximately 10 min after 55Fe injection (4.1% mean recovery at 3 h). In contrast, biliary iron excretion in iron-loaded rats was minimal (0.1%). In normal rats, a marked increase in biliary excretion of plasma NTB-iron was observed after intravenous desferrioxamine (mean recovery 20.9%) and the new oral iron chelator 1,2-dimethyl-3-hydroxypyrid-4-one administered intravenously (mean recovery 16.1%) or orally (11.4%). In iron-loaded rats, the cumulative recoveries of 55Fe in bile achieved by chelators were lower than in controls (7.6, 3.9, and 3.7%, respectively). Collectively, these findings demonstrate that 1) the normal liver rapidly excretes significant amounts of plasma NTB-iron in bile; 2) the iron-loaded liver exhibits a marked decrease in the capacity to excrete plasma NTB-iron into bile; and 3) chelating agents greatly enhance the biliary excretion of plasma NTB-iron, although the response in terms of cumulative recoveries is less pronounced in the iron-loaded state.(ABSTRACT TRUNCATED AT 250 WORDS)

Biliary Excretion of Lysosomal Enzymes, Iron, and Oxidized Protein in Fischer-344 and Sprague-Dawley Rats and the Effects of Diquat and Acetaminophen

Administration of hepatotoxic doses of diquat to male Fischer-344 rats increases biliary excretion of nonheme iron, whereas comparably hepatotoxic doses of acetaminophen decrease biliary export of iron. The effects of acetaminophen and diquat on the activities in bile of representative lysosomal enzymes, β-N-acetylglucosaminidase (β-NAG) and β-glucuronidase (β-GLUC) were examined as a means of assessing the possible role of lysosomal exocytosis in the effects of these hepatotoxins on biliary excretion of iron. In pentobarbital-anesthetized male Fischer-344 rats, diquat at 0.1 mmol/kg increased the biliary export of biliary β-NAG and β-GLUC, in conjunction with similar increases in iron. Sprague-Dawley rats, which are resistant to diquat-induced hepatic necrosis despite showing marked oxidant stress responses, showed no increases in biliary efflux of iron, β-NAG, or β-GLUC in response to diquat. Conversely, acetaminophen at doses of 400 or 1500 mg/kg markedly decreased biliary concentrations and efflux rates of β-NAG and β-GLUC in Fischer-344 rats in parallel with decreases in biliary iron, suggesting that the hepatotoxin-induced effects on biliary iron excretion may be mediated through effects on lysosomal exocytosis. Both acetaminophen and diquat increased total protein content of bile in both strains of rats; however, the proteins excreted after administration of diquat to Fischer-344 rats showed marked increases in contents of protein carbonyls, as assayed with 2,4-dinitrophenylhydrazine, whereas biliary proteins in acetaminophen-treated animals were not more oxidized than in controls. Sprague-Dawley rats given diquat showed no increase in the biliary excretion of protein carbonyls, despite the increased excretion of glutathione disulfide observed in these animals. The significant increases in biliary excretion of protein carbonyls by the diquat-treated Fischer-344 rats suggest oxidation of cellular proteins catalyzed by chemically reactive iron chelates and the excretion of at least some of the oxidized proteins to the bile, possibly through lysosomal exocytosis. The effects of acetaminophen on biliary protein excretion do not appear to involve oxidation.

Induction of multidrug resistance gene expression during cholestasis in rats and nonhuman primates

P-glycoprotein, an energy-dependent plasma membrane drug-efflux pump capable of reducing the intracellular concentration of a variety of hydrophobic xenobiotics, is encoded by mdr1, a member of the multidrug-resistant ( mdr) gene family. The physiological function of this protein is unknown. Because of its location on the bile canalicular domain of the hepatocyte, we and others have hypothesized that P-glycoprotein may have a physiological role as a biliary transporter of xenobiotics and endobiotics and that its expression may therefore be altered in cholestasis. Both obstructive and α-naphthylisothiocyanate-induced cholestasis increased mdr1a and 1b gene expression in rat liver. Hepatic P-glycoprotein levels were also increased, and the protein remained localized at the biliary hepatocyte domain. Induction of mdr1a and mdr1b gene expression in rat liver was accomplished by means of increased transcription. α-Naphthylisothiocyanate-induced cholestasis in cynomolgus monkeys increased hepatic expression of both the mdr1 and 2 genes. To investigate the possible role of P-glycoprotein as a biliary efflux transporter, biliary excretion of vinblastine, a representative substrate of P-glycoprotein, was studied in rats. Increased hepatic mdr messenger RNA and P-glycoprotein levels, mediated by the xenobiotic inducer 2-acetylaminofluorene, resulted in a significant increase in biliary excretion of vinblastine, which was antagonized by the P-glycoprotein inhibitor verapamil. These findings suggest that P-glycoprotein functions as a biliary efflux pump for xenobiotics and, possibly, for unidentified physiological inducers that may mediate increased transcription of the mdr gene observed during cholestasis.

Induction of multidrug resistance gene expression during cholestasis in rats and nonhuman primates

P-glycoprotein, an energy-dependent plasma membrane drug-efflux pump capable of reducing the intracellular concentration of a variety of hydrophobic xenobiotics, is encoded by mdr1, a member of the multidrug-resistant (mdr) gene family. The physiological function of this protein is unknown. Because of its location on the bile canalicular domain of the hepatocyte, we and others have hypothesized that P-glycoprotein may have a physiological role as a biliary transporter of xenobiotics and endobiotics and that its expression may therefore be altered in cholestasis. Both obstructive and alpha-naphthylisothiocyanate-induced cholestasis increased mdr1a and 1b gene expression in rat liver. Hepatic P-glycoprotein levels were also increased, and the protein remained localized at the biliary hepatocyte domain. Induction of mdr1a and mdr1b gene expression in rat liver was accomplished by means of increased transcription. alpha-Naphthylisothiocyanate-induced cholestasis in cynomolgus monkeys increased hepatic expression of both the mdr1 and 2 genes. To investigate the possible role of P-glycoprotein as a biliary efflux transporter, biliary excretion of vinblastine, a representative substrate of P-glycoprotein, was studied in rats. Increased hepatic mdr messenger RNA and P-glycoprotein levels, mediated by the xenobiotic inducer 2-acetylaminofluorene, resulted in a significant increase in biliary excretion of vinblastine, which was antagonized by the P-glycoprotein inhibitor verapamil. These findings suggest that P-glycoprotein functions as a biliary efflux pump for xenobiotics and, possibly, for unidentified physiological inducers that may mediate increased transcription of the mdr gene observed during cholestasis.

Relationship between biliary excretion of bilirubin and glutathione disulfide

The effects of two glutathione-oxidizing agents, t-butyl hydroperoxide and diamide, on biliary excretion of bilirubin and glutathione disulfide were investigated in anesthetized male Sprague-Dawley rats. Bilirubin (unconjugated) was infused at a constant rate of 100 nmol/kg/min through the jugular vein. When biliary excretion of bilirubin was stabilized, either of the glutathione-oxidizing agents was administered via the mesenteric vein. Biliary excretion of glutathione disulfide increased temporarily after the administration and returned to its basal levels within 20 min. The biliary excretion of bilirubin decreased during the same period and returned to the former levels thereafter. Changes in bile flow rates remained within 20% of the basal levels. A linear correlation was found between the increments in the bile concentration of glutathione disulfide and the decrements in that of bilirubin. Furthermore, separate experiments revealed that reduction of hepatocellular glutathione per se had little effect on biliary excretion of bilirubin. The results thus indicate that the reduction of biliary excretion of bilirubin by glutathione-oxidizing agents was due to the increase in biliary excretion of glutathione disulfide, and suggest that a common biliary excretory mechanism is shared, at least partially, by bilirubin and glutathione disulfide in Sprague-Dawley rats.

Increased biliary excretion of glutathione is generated by the glutathione-dependent hepatobiliary transport of antimony and bismuth

We have recently demonstrated that the hepatobiliary transport of arsenic is glutathione-dependent and is associated with a profound increase in biliary excretion of glutathione (GSH), hepatic GSH depletion and diminished GSH conjugation (Gyurasics Á, Varga F and Gregus Z, Biochem Pharmacol 41: 937–944 and Gyurasics Á, Varga F and Gregus Z, Biochem Pharmacol 42: 465–468, 1991). The present studies in rats aimed to determine whether antimony and bismuth, other metalloids in group Va of the periodic table, also possess similar properties. Antimony potassium tartrate (25–100 μmol/kg, i.v.) and bismuth ammonium citrate (50–200 μmol/kg, i.v.) increased up to 50- and 4-fold, respectively, the biliary excretion of non-protein thiols (NPSH). This resulted mainly from increased hepatobiliary transport of GSH as suggested by a close parallelism in the biliary excretion of NPSH and GSH after antimony or bismuth administration. Within 2 hr, rats excreted into bile 55 and 3% of the dose of antimony (50 μmol/kg, i.v.) and bismuth (150 μmol/kg, i.v.), respectively. The time courses of the biliary excretion of these metalloids and NPSH or GSH were strikingly similar suggesting co-ordinate hepatobiliary transport of the metalloids and GSH. However, at the peak of their excretion, each molecule of antimony or bismuth resulted in a co-transport of approximately three molecules of GSH. Diethyl maleate, indocyanine green and sulfobromophthalein (BSP), which decreased biliary excretion of GSH, significantly diminished excretion of antimony and bismuth into bile indicating that hepatobiliary transport of these metalloids is GSH-dependent. Administration of antimony, but not bismuth, decreased hepatic GSH level by 30% and reduced the GSH conjugation and biliary excretion of BSP. These studies demonstrate that the hepatobiliary transport of trivalent antimony and bismuth is GSH-dependent similarly to the hepatobiliary transport of trivalent arsenic. Proportionally to their biliary excretion rates, these metalloids generate increased biliary excretion of GSH probably because they are transported from liver to bile as unstable GSH complexes. The significant loss of hepatic GSH into bile as induced by arsenic or antimony may compromise conjugation of xenobiotics with GSH.

Effect of lipoic acid on biliary excretion of glutathione and metals

Several metals are excreted in bile as glutathione complexes, and their biliary excretion is facilitated by increased hepatobiliary transport of glutathione. The present study analyzed the effect of lipoic acid (LA; thioctic acid; 37.5–300 μmol/kg, iv), an endogenous disulfide which can be reduced in vivo to a dithiol, on the hepatobiliary disposition of glutathione-related thiols and the biliary excretion of metals (10 μmol/kg, iv) in rats. Administration of LA enhanced the biliary excretion of reduced glutathione in a dose-dependent fashion. Despite increasing glutathione output, LA (150 μmol/kg, iv) did not increase, but rather decreased, the biliary excretion of methylmercury, cadmium, zinc, and copper, which are transported into bile in a glutathione-dependent manner, as indicated by a marked reduction in their biliary excretion after diethyl maleate-induced glutathione depletion. In contrast, biliary excretion of inorganic mercury, which is minimally affected by glutathione depletion, was dramatically enhanced (12- to 37-fold) by LA administration. Following injection of LA, the concentrations of endogenous disulfides in arterial blood plasma (e.g., cystine, glutathione disulfide, cysteine-glutathione, protein-cysteine, and protein-glutathione mixed disulfides) were considerably diminished, while the levels of endogenous thiols (e.g., glutathione and cysteine) were increased. This finding indicates that LA, probably after enzymatic conversion to dihydrolipoic acid, can reduce endogenous disulfides to thiols. It appears that LA induces the transport of glutathione into bile by the temporary formation of dihydrolipoic acid-glutathione mixed disulfide, which after being translocated into bile is cleaved to LA and reduced glutathione. Because the glutathione molecule thus transported into bile cannot complex metals at the thiol group, this might be the mechanism for the observed failure of the LA-induced increase in biliary excretion of glutathione to enhance the hepatobiliary transport of metals that are transported into bile as glutathione complexes (i.e., methylmercury, cadmium, zinc, and copper). The observations also raise the possibility that endogenous dihydrolipoic acid, by forming a stable complex with mercuric ion, may play the role of a carrier molecule in the hepatobiliary transport of inorganic mercury.

Pharmacokinetics of hypolipedemic agents. 9. The question of biliary excretion of the hypolipidemic agent ciprofibrate (1) (2-(4-(2,2-dichlorocyclopropyl)-phenoxy)-2-methylpropionic acid

After oral administration of 200 mg Ciprofibrate (1) to 10 patients, who were cholecystectomated with subsequent T-drainage, 1 could be determined in the collected bile only as its 1-O-beta-acylglucuronide to a very small amount. Approximative calculations have shown that two days after a single dose, less than 0.5% of the administered dose of 1 is excreted on the biliary route. It is an unsolved problem if there is an increase of biliary excretion after multiple dose.

Diquat hepatotoxicity in the Fischer-344 rat: The role of covalent binding to tissue proteins and lipids

Diquat produces hepatic necrosis in the Fischer-344 rat, and although reactive oxygen species generated by redox cycling are thought to mediate the damage, the possibility that covalent binding of diquat or diquat metabolites to tissue macromolecules contributes to the observed hepatotoxicity of diquat needed to be examined experimentally. Intraperitoneal administration of [ ethylene- 14C]diquat (0.1 mmol/kg) results in distribution of radioactivity to all organs examined. Measurable radioactivity remains associated with hepatic and renal protein even after extensive solvent extraction, but the amount (12–16 pmol/mg protein) is 100-fold less than the extent of covalent binding observed with comparably hepatotixic doses of other hepatotoxins such as acetaminophen and bromobenzene. Similarly, although small amounts of radioactivity remain in Folch lipid extracts of liver and kidney (56–179 pmol/mg lipid), this is virtually completely removed by transesterification of the lipid (<5 pmol/mg lipid), indicating that the radioactivity does not represent an alkylation of electroneutral alkyl residues of the lipid. The diquat-induced increase in biliary excretion of glutathione disulfide temporally parallels the biliary excretion of radioactivity. Although the present results do not prove the absence of a contribution by alkylation mechanisms to diquat hepatotoxicity, the extremely low upper limits placed on possible covalent interactions reinforce the confidence with which the diquat-treated Fischer-344 rat can be employed as an animal model for mechanisms of cell death mediated by reactive oxygen species.

Taurocholate increases the biliary output of bilirubin pigments in the rat, due to haemolysis

In order to investigate the effect of bile salts on the biliary transport of bilirubin, we infused rats with taurocholate at 1–3 μmol/min/kg body weight. When administered in saline, taurocholate induced haemolysis, and a dosedependent increase in biliary excretion and serum concentration of all bilirubin pigments. The addition of human or rat serum albumin to the infusate, at an albuminataurocholate molar ratio equal to or above 200, completely prevented haemolysis and the above-mentioned alterations in bilirubin transport, without any change in the bile acid output. In order to mimic a haemolytic condition, an erythrocyte haemolysate was further added to the taurocholate-alburnin solution. This again resulted in an increased bilirubin output. We suggest that taurocholate treatment increases bilirubin output due to the increased load of the pigment on the liver, as a result of the bile acid-induced haemolysis.