Triketocholanoic (dehydrocholic) acid. Hepatic metabolism and effect on bile flow and biliary lipid secretion in man

Sustainable Photoinduced Decarboxylative Chlorination Mediated by Halogen Atom Transfer

Chlorinated organic backbones constitute important components in existing biologically active chemicals, and they are extraordinary useful intermediates in organic synthesis. Herein, an operationally simple and sustainable halodecarboxylation protocol via halogen-atom transfer (XAT) as a key step is presented. The method merges a metal-free photoredox system with (diacetoxyiodo)benzene (PIDA) as a hypervalent iodine reagent using 1,2-dihaloethanes as halogen sources to afford haloalkanes in an efficient manner. The sustainability of this protocol is highlighted by an important waste recovery protocol as well as by atom economy and carbon efficiency parameters.

Clinical evaluation of ezetimibe on bile lithogenicity in humans: Use of transnasal endoscopy for bile sampling

AIM

Ezetimibe inhibits cholesterol absorption by blocking Niemann-Pick C1-like 1 proteins (NPC1L1) expressed in the small intestine. Because NPC1L1 is also expressed in human liver, ezetimibe conceivably alters biliary lipid compositions. Here, we performed a clinical trial investigating the effect of ezetimibe on biliary lipids using transnasal endoscopy for bile collection.

METHODS

Eight patients with dyslipidemia enrolled in this study completed blood and bile sampling before and at 3 months after ezetimibe treatment (10 mg/day), and the samples are analyzed.

RESULTS

Endoscopic bile sampling was performed safely and painlessly. Serum sterol-based biomarkers declared decreased cholesterol absorption and increased synthesis. On analysis of biliary lipids, four of the eight patients showed relative decrease of cholesterol and increase of bile acids with improved lithogenicity while the remainder exhibited the symmetrical changes.

CONCLUSION

Our data suggests that biliary lithogenicity is not worsened by ezetimibe. The regulation of biliary cholesterol is presumably multifactorial such as body cholesterol pool size and biliary cholesterol reabsorption by NPC1L1 in the liver.

History of hepatic bile formation: old problems, new approaches

Studies of hepatic bile formation reported in 1958 established that it was an osmotically generated water flow. Intravenous infusion of sodium taurocholate established a high correlation between hepatic bile flow and bile acid excretion. Secretin, a hormone that stimulates bicarbonate secretion, was also found to increase hepatic bile flow. The sources of the water entering the biliary system with these two stimuli were differentiated by the use of mannitol. An increase in its excretion parallels the increase in bile flow in response to bile acids but not secretin, which led to a quantitative distinction between canalicular and ductular water flow. The finding of aquaglyceroporin-9 in the basolateral surface of the hepatocyte accounted for the rapid entry of mannitol into hepatocytes and its exclusion from water movement in the ductules where aquaporin-1 is present. Electron microscopy demonstrated that bile acids generate the formation of vesicles that contain lecithin and cholesterol after their receptor-mediated canalicular transport. Biophysical studies established that the osmotic effect of bile acids varies with their concentration and also with the proportion of mono-, di-, and trihydroxy bile acids and provides a basis for understanding their physiological effects. Because of the varying osmotic effect of bile acids, it is difficult to quantify bile acid independent flow generated by other solutes, such as glutathione, which enters the biliary system. Monohydroxy bile acids, by markedly increasing aggregation number, severely reduce water flow. Developing biomarkers for the noninvasive assessment of normal hepatic bile flow remains an elusive goal that merits further study.

Ursodeoxycholic acid is conjugated with taurine to promote secretin-stimulated biliary hydrocholeresis in the normal rat

Background & Aims

Secretin induces bicarbonate-rich hydrocholeresis in healthy individuals, but not in untreated patients with primary biliary cirrhosis (PBC). Ursodeoxycholic acid (UDCA) – the first choice treatment for PBC – restores the secretin response. Compared with humans, secretin has poor effect in experimental normal-rat models with biliary drainage, although it may elicit hydrocholeresis when the bile-acid pool is maintained. In view of the benefits of UDCA in PBC, we used normal-rat models to unravel the acute contribution of UDCA (and/or taurine-conjugated TUDCA) for eliciting the biliary secretin response.

Methods

Intravascular and/or intrabiliary administration of agonists and inhibitors was performed in normal rats with biliary monitoring. Secretin/bile-acid interplay was analyzed in 3D cultured rat cholangiocytes that formed expansive cystic structures with intralumenal hydroionic secretion.

Results

In vivo, secretin stimulates hydrocholeresis upon UDCA/TUDCA infusion, but does not modify the intrinsic hypercholeretic effect of dehydrocholic acid (DHCA). The former effect is dependent on microtubule polymerization, and involves PKCα, PI3K and MEK pathways, as shown by colchicine (i.p.) and retrograde biliary inhibitors. In vitro, while secretin alone accelerates the spontaneous expansion of 3D-cystic structures, this effect is enhanced in the presence of TUDCA, but not UDCA or DHCA. Experiments with inhibitors and Ca²⁺-chelator confirmed that the synergistic effect of secretin plus TUDCA involves microtubules, intracellular Ca²⁺, PKCα, PI3K, PKA and MEK pathways. Gene silencing also demonstrated the involvement of the bicarbonate extruder Ae2.

Conclusions

UDCA is conjugated in order to promote secretin-stimulated hydrocholeresis in rats through Ae2, microtubules, intracellular Ca²⁺, PKCα, PI3K, PKA, and MEK.

A controlled trial of choleretic and hepatoprotective actions of Livzon and dehydrocholic acid in a model of obstructive jaundice in albino rats

The authors have tried to examine the hepatoprotective and cholerectic action of a new indigenised drug, Livzon (Hind Chemicals Ltd., Kanpur, India) and compared its action to Decholin (casella-Riedel Pharma GmbH, Frankfurt, Germany), a known hepatoprotective and choleretic agent. Albino rats were chosen as the experimental animals. Obstructive jaundice was created by ligating the common bile ducts after taking liver biopsies. The animals were divided into three groups: (i) Control group-no drug was given, (ii) Livzon trial group, (iii) Decholin group. The animals were reoperated, liver biopsies were taken and histologically examined. The study confirmed the hepatoprotective and choleretic actions of Livzon and Decholin. However, Decholin was more of a choleretic, the Livzon was more hepatoprotective.

A novel enzyme system for the reduction of 3-oxo bile acids in human red blood cells

7 alpha,12 alpha-Dihydroxy-3-oxo- and 3,7,12-trioxo-5 beta-cholanoic acids labeled with 18O atoms were incubated with human red blood cells, and the biotransformation products were separated and characterized by gas chromatography-mass spectrometry as the pentafluorobenzyl ester-trimethylsilyl and -dimethylethylsilyl ether derivatives with the negative ion chemical ionization mode. The reduced products, 3 beta,7 alpha,12 alpha-trihydroxy-5 beta-cholanoic acid for the former, and 3 alpha-hydroxylated dioxo bile acid together with 3 beta-hydroxylated 7,12-dioxo-5 beta-cholanoic acid for the latter, were identified as metabolites. When 3-oxo bile acid was incubated with human blood denatured at 70 degrees C for 2 min, no metabolites were formed. The enzymic reduction activity has been localized in the red blood cell fraction.

Bile acids in the diagnosis, pathology, and therapy of hepatobiliary diseases

Bile acids are normally confined in the enterohepatic circulation in which they play an important role in bile formation, biliary lipid excretion, and intestinal lipid absorption. In hepatobiliary diseases, bile acids escape the confinement of the enterohepatic circulation, allowing the measurement of the serum total bile acid concentration as a diagnostic indicator. Accumulation of certain bile acids within the hepatocyte, amplified as a consequence of cholestatic hepatobiliary disease, probably enhances cytotoxicity and leads to secondary pathology. Ursodeoxycholate, a bile acid with atypical physiological effects, may be useful in the treatment of various long-term cholestatic hepatobiliary diseases. Presently, most of the information on the toxicity and therapeutic usefulness of bile acids are based on studies in humans and experimental animals. Further studies, both basic and clinical, are needed to determine the pathologic as well as the therapeutic effects of bile acids in domestic animals.

Bile salt secretion by hepatocytes incubated with bile salts and liposomes or low density lipoproteins

The purpose of this work was to determine the effect of exogenous unesterified cholesterol provided in either artificial liposomes or LDL on bile salt synthesis by isolated rat hepatocytes. Rates of de novo synthesis were determined in the presence of 300 or 600 microM taurocholate, 600 microM taurodehydrocholate, cholate, deoxycholate or chenodeoxycholate. There was no significant difference between the cholesterol uptake by hepatocytes when the degree of hydrophobicity of the bile salts changed (cholate vs deoxycholate or chenodeoxycholate). Compared to taurocholate, taurodehydrocholate lowered the hepatic incorporation of unesterified cholesterol for the first 60 minutes; compared to control, taurocholate stimulated the cholesterol incorporation for the first 20 minutes. A possible explanation for this finding would be an interaction between bile salts and exogenous cholesterol, depending on the kind of conjugated bile salt. Taurocholate increased the exchange of cholesterol between liposomes or LDL and hepatocyte membranes. It resulted in a significant increase of bile salt synthesis and secretion. This phenomenon was not observed with taurodehydrocholate.

Identification and characterization of dehydrocholic acid reductase system in the cytosol of human red blood cells

We conducted in vivo and in vitro studies of the reductive metabolism of the cholagogue, dehydrocholic acid (DHCA). Immediately after the intravenous administration of 1 g of DHCA in normal subjects (n = 6), the concentration of the reductive metabolite, 3 alpha-hydroxy-7,12-dioxo-cholanoic acid (unconjugated form), increased sharply in the systemic circulation, rising to 95.8 microM 10 min after administration. The results of in vitro experiments with DHCA and whole blood showed that 3 alpha-hydroxy-7,12-dioxocholanoic acid were produced from DHCA. In vitro experiments using DHCA and the red blood cell fraction, and DHCA and the red blood cell cytoplasmic fraction gave similar results to those described above with whole blood. However, a reductive metabolite was not formed by the incubation of DHCA and the red blood cell membrane fraction. These findings indicated that, contrary to the conventional theory that intravenously administered DHCA is subjected to reductive metabolism only in the liver, reduction also occurs in the systemic circulation, and the mechanism for this reductive metabolism is present in the cytoplasmic fraction of red blood cells. Further investigation to characterize this reductive metabolic system revealed an optimum temperature of 37 degrees C, an optimum pH of 7.4, a Km value of 2.0 x 10(-3) M, and inactivation by heat treatment (70 degrees C for 2 min).

Influence of dehydrocholic and cholic acids on the biliary secretion of anionic polypeptide fraction, the major apoprotein of the biliary lipoprotein complex

This work was undertaken to study the effect of intravenously infused dehydrocholate (DHCA) and cholate (CA) on lipid and anionic polypeptide fraction (APF) secretion in bile. APF is a small acidic amphipathic apoprotein closely associated with biliary lipids and bilirubin and involved in the control of bile-destined cholesterol. Rats were infused with increasing doses of DHCA (2 and 3 mumols/min/100 g b.w.) and then CA (1, 2, and 3 mumols/min/100 g b.w.). Each dose was infused for 30 min. As expected, intravenous DHCA inhibited biliary phospholipid (PL) and cholesterol secretion, and CA restored it. When DHCA was infused, the level of APF increased fourfold compared with controls. The APF/PL ratio also increased, but biliary albumin remained stable. When bile secretion was stimulated by infusion of CA, biliary APF returned to normal. These data indicate that biliary secretion of APF depends on the nature and the amount of bile salts returning to the liver, and consequently, APF can be considered a marker of bile secretion disorders.

Acute infusions of bile salts increase biliary excretion of iron in iron-loaded rats

The mechanisms of biliary excretion of iron are not well known. The aim of this study was to examine the effect of choleresis induced by several agents on biliary iron excretion in iron-loaded rats. Iron overload was obtained with a diet supplemented by 3% iron carbonyl during a 6-week period. Bile was collected with an external bile fistula. Biliary iron concentration was measured by atomic absorption spectrophotometry, and hepatic iron concentration was measured by a chemical method. Compared with controls, iron overload resulted in a 14-fold increase in hepatic iron concentration but only a 3.9-fold increase in biliary iron output. In iron-loaded rats, taurocholate infusion caused a 1.8-fold significant increase in biliary iron output. Dehydrocholate, given at the same dose, induced a significant but less pronounced (1.3-fold) increase in biliary iron output in spite of a higher bile flow. Taurochenodeoxycholate, tauroursodeoxycholate, and tauro-7-ketolithocholate induced an increase in biliary iron output similar to that observed with taurocholate. The canalicular bile salt-independent choleretic dihydroxydibutyl ether caused a significant but less pronounced increase in biliary iron output (1.4-fold). These results confirm that in iron-loaded rats biliary iron excretion is increased much less than hepatic iron concentration. They show that in iron loaded rats (a) bile salts can increase biliary iron secretion, and (b) this increase is related in part to choleresis and in part to bile salts themselves. This increase may be related to an interaction of iron with bile salt monomers and/or micelles.

Purification and properties of 3 alpha-hydroxysteroid dehydrogenase as a 3-keto bile acid reductase from human liver cytosol

The NADPH-dependent 3 alpha-hydroxysteroid dehydrogenases (peaks 1, 2 and 3) acting on 3-keto-5 beta-cholanoic acid separated by carboxymethyl-cellulose chromatography from human liver cytosol were purified to homogeneous protein on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, using Affi-Gel blue, phenyl-Sepharose CL-4B, TSKgel G3000 SW chromatography and chromatofocusing. The overall purifications of the enzymes from cytosol were 316-fold (peak 1), 232-fold (peak 2) and 345-fold (peak 3) and the recoveries of the enzymes were 0.4% (peak 1), 7.1% (peak 2) and 3.7% (peak 3). The isoelectric points of the enzymes were found to be 7.34, 7.46 and 7.88 by chromatofocusing. The molecular weights of the enzymes were similar and estimated to be about 32,000 by size exclusion chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The enzymological properties were nearly identical among the three forms. The reaction was reversible and the optimum pH of the enzymes for oxidation was about 8.4 and that for reduction was about 7.4. The enzymes could not reduce 7 alpha,12 alpha-dihydroxy-3-keto-5 beta-cholanoic acid, 7 alpha-hydroxy-5 beta-cholestan-3-one and 7 alpha, 12 alpha-dihydroxy-5 beta-cholestan-3-one to the corresponding 3 alpha-hydroxysteroids, whereas the enzymes could reduce 3,7-disubstituted 3-keto bile acids. Thus, the enzymes purified in this study were found to have a stereospecific character for some 3-ketosteroids. The enzyme activity was inhibited by p-chloromercuribenzoate; however, the inhibition was prevented by addition of dithiothreitol to the reaction mixture, indicating that the enzyme required a sulfhydryl group for activity.

Estradiol-17 beta-D-glucuronide (E-17G) cholestasis in perfused rat liver: fate of E-17G and choleretic responses to bile salts

This study was designed to test the hypothesis that increasing the infusion rate of bile salts could overcome drug-induced cholestasis. Cholestasis was induced by administration of 17.5 mumol/L estradiol-17 beta-D-glucuronide during the infusion of taurocholate, tauroursodeoxycholate or dehydrocholate at 20 nmol/min/gm liver. After 30 min, a bolus of 10 mumol of the bile salts was added to the perfusate, and the infusion rate of each bile salt was increased. Taurocholate at a rate of 62 or 125 nmol/min/gm liver, caused a prompt dose-dependent increase of the depressed bile flow and bile salt excretion. A higher rate of taurocholate infusion (180 nmol/min/gm liver) was less effective than either the 62 or 125 rate in increasing bile flow. Infusion of tauroursodeoxycholate at 250 or 390 nmol/min/gm liver also led to a dose-dependent recovery. Further increase of tauroursodeoxycholate infusion rate of 580 nmol/min/gm liver did not provide any additional recovery in bile flow. Dehydrocholate, at rates of 62 or 125 nmol/min/gm liver, gave only a slight enhancement of bile flow. Both taurocholate and tauroursodeoxycholate caused a marked removal of the estradiol-17 beta-D-glucuronide, which had accumulated in the liver. At lower taurocholate infusion rates, the estradiol-17 beta-D-glucuronide was excreted mainly in the bile. At the highest rate, however, biliary excretion of estradiol-17 beta-D-glucuronide declined significantly, and a marked back-efflux of the estrogen into the perfusate was noted. In contrast, tauroursodeoxycholate led to enhanced biliary estradiol-17 beta-D-glucuronide excretion at all increased tauroursodeoxycholate infusion rates and to only a small increase in back-efflux of estradiol-17 beta-D-glucuronide at the two highest tauroursodeoxycholate infusion rates.(ABSTRACT TRUNCATED AT 250 WORDS)

Simultaneous determination of keto and non-keto bile acids in human serum by gas chromatography with selected ion monitoring

A reliable method for the simultaneous determination of keto and non-keto bile acids in human serum was developed. Carbonyl substituents of bile acid ethyl esters were converted into methyloxime and hydroxyl substituents into dimethylethylsilyl ethers and the products were analysed directly by capillary gas chromatography with selected ion monitoring using [2H4]chenodeoxycholic and [2H4]3 alpha-hydroxy-7-oxo-5 beta-cholanoic acids as internal standards. The bile acid peaks on the selected ion chromatogram were separated without interference from endogenous substances present in serum. Recoveries of individual keto bile acids added to serum range from 74.4 to 94.7% with a mean of 87.1%. Eight kinds of keto bile acids not previously found in sera of normal subjects, namely 3-oxo-, 3-oxo-7 alpha-hydroxy-, 3-oxo-12 alpha-hydroxy-, 3 alpha-hydroxy-7-oxo, 3 alpha-hydroxy-12-oxo-, 3-oxo-7 alpha,12 alpha-dihydroxy-, 3 alpha,7 alpha-dihydroxy-12-oxo- and 3 alpha,12 alpha-dihydroxy-7-oxo-5 beta-cholanoic acids were identified and quantified. The total concentration of keto bile acids was found to be 0.16 +/- 0.08 nmol/ml and constituted 2.9 +/- 1.5% of that of the usual non-keto bile acids in peripheral venous serum.

Altered bile acid profiles in duodenal bile and urine in diabetic subjects

The bile acid composition in duodenal bile was analysed in 22 diet-treated and 11 insulin-treated middle-aged patients with diabetes mellitus and in 20 normoglycaemic controls. In 10 subjects with diabetes mellitus the bile acid profile in urine was also investigated. In the non-insulin-dependent diabetic patients the percentage of cholic acid was reduced and that of deoxycholic acid increased. As a highly significant finding there was a three-fold increase of the percentage of 12-ketolithocholic acid in duodenal bile in non-insulin-dependent diabetics, whereas the bile acid composition in insulin-dependent diabetics was similar to that in a control group. The percentage of 12-ketolithocholic acid in duodenal bile was positively correlated to the percentage in urine. In nine of the subjects studied, 12-ketolithocholic acid was the major individual bile acid in urine. It constituted 36.3 +/- 4.4% of the bile acids analysed and the excretion was 6.1 +/- 2.3 mumol 24 h-1. Together with 3 alpha, 12 beta-dihydroxy-5 beta-cholanoic acid it was predominantly present in the glycine conjugate fraction, whereas in bile its conjugation was similar to that of the other bile acids. The results may reflect an increased formation of secondary bile acids from cholic acid combined with a metabolic disturbance in non-insulin-dependent diabetics affecting the oxidoreduction of bile acids at C-12.

Output of lysosomal contents and cholesterol into bile can be stimulated by taurodehydrocholate

Although biliary secretion of phospholipids and cholesterol is principally dependent on bile-salt secretion, at low bile-salt output secretion of some lipids continues; also the amount of cholesterol secretion is more than that of phospholipid under these conditions, but the origin of this cholesterol is not known. Taurodehydrocholate was continuously infused in isolated perfused rat livers under recycling perfusion conditions and the biliary lysosomal output and lipid output measured. The rate of acid phosphatase and beta-glucuronidase output increased 30-60 and 60-90 min respectively after liver isolation under these conditions. The rate of output of cholesterol and phospholipid increased in all the samples collected from taurodehydrocholate-infused livers. The increase in cholesterol output was approximately twice that of phospholipid output, leading to an increase in the cholesterol/phospholipid ratio in the bile.

Bile acid structure and bile formation in the guinea pig

The effects of intravenous infusions (1-4 mumol/min/kg) of 14 bile acids, cholic, deoxycholic, ursodeoxycholic, chenodeoxycholic, dehydrocholic, and their glycine and taurine conjugates, on bile flow and composition and on the biliary permeation of inert carbohydrates have been studied in the guinea pig bile fistula. Hydroxy bile acids were eliminated in bile without major transformation, except for conjugation (over 90%) when unconjugated bile acids were infused. During infusion of dehydrocholate and taurodehydrocholate, 77-100% of the administered dose was recovered in bile as 3-hydroxy bile acids, thus indicating that reduction of the keto group in position 3 was virtually complete. All bile acids produced choleresis at the doses employed: the strongest choleretic was deoxycholate (81.78 microliters/mumol), the weakest was taurodehydrocholate (10.2 microliters/mumol). Choleretic activity was directly and linearly related to bile acid hydrophobicity, as inferred by HPLC, both for similarly conjugated bile acids, and for bile acids having the same number, position, or configuration of the hydroxyl groups. In all instances, the rank ordering was: deoxycholate greater than chenodeoxycholate greater than cholate greater than ursodeoxycholate. During choleresis produced by any of the bile acids tested, bicarbonate concentration in bile slightly declined, but the calculated concentration in bile-acid-stimulated bile (45-57 mmol/l) was always higher than that measured in plasma (23-26 mmol/l). Biliary concentrations of cholesterol (20-68 mumol/l) and phospholipid (14-63 mumol/l) were very low during spontaneous secretion, and declined even further following bile acid choleresis. None of the infused bile acids consistently modified biliary excretion of cholesterol and phospholipid. Consistent with a previous observation from this laboratory, all hydroxy bile acids reversibly diminished [14C]erythritol and [14C]mannitol biliary entry during choleresis, while they increased or failed to modify that of [3H]sucrose and [3H]inulin. The rank ordering for the inhibitory effect on [14C]erythritol and [14C]mannitol permeation was: 3 alpha,7 alpha,12 alpha-trihydroxy greater than 3 alpha,7 alpha-dihydroxy greater than 3 alpha,7 beta-dihydroxy greater than 3 alpha,12 alpha-dihydroxy bile acids.(ABSTRACT TRUNCATED AT 400 WORDS)

The effect of drugs on bile flow and composition. An overview

Many drugs are eliminated via the hepatobiliary route, after biotransformation in the liver. Some of them may affect bile flow and/or the hepatic secretion of biliary lipids such as bile acids, cholesterol and phospholipids. Bile acids are the most potent agents which increase bile flow, especially unconjugated bile acids. Other drugs which increase bile flow include phenobarbitone (phenobarbital), theophylline, glucagon and insulin. In contrast, ethacrynic acid, amiloride, ouabain, oestrogens and chlorpromazine are among those agents which decrease bile flow. Biliary bile acid secretion is altered by a variety of drugs, including cheno- and ursodeoxycholic acids (CDCA and UCDA), the bile acid sequestrants cholestyramine and colestipol, and ethinyloestradiol. The composition of bile can also be altered by drug therapy. Thus, clofibrate increases biliary cholesterol secretion, and reduces bile acid concentrations, without altering biliary phospholipid concentrations. However, other clofibrate derivatives may produce changes of a different pattern, suggesting that the risk of developing gallstones may differ for each derivative. Nicotinic acid and d-thyroxine also increase biliary cholesterol saturation, while CDCA and UDCA reduce biliary cholesterol concentration. The potential consequences of drug-induced changes in bile flow and composition extend to the liver, the gallbladder and the intestine. If adverse effects are to be avoided, further study in this often overlooked area is required.

Metabolism of two hydroxy-7-oxocholanic acids in isolated perfused rat liver

The metabolism of 7-oxolithocholic acid and 7-oxodeoxycholic acid in isolated perfused rat livers was compared. The metabolites extracted from the bile of perfused livers were analysed by gas chromatography. The amount of bile acids excreted in bile was greater after infusion with 7-oxolithocholic acid than with 7-oxodeoxycholic acid. When 7-oxolithocholic acid was infused almost all of the bile acids excreted in bile were taurine conjugates; with 7-oxodeoxycholic acid about 10 percent remained unconjugated. 7-Oxolithocholic acid was more susceptible to reduction than 7-oxodeoxycholic acid. 7-Oxolithocholic acid was preferably reduced to 7 beta-hydroxy rather than to 7 alpha-hydroxy metabolites. In contrast, 7-oxodeoxycholic acid was reduced predominantly to the 7 alpha-hydroxy rather than to the 7 beta-hydroxy metabolite.

Cholestasis induced by estradiol-17 beta-D-glucuronide: mechanisms and prevention by sodium taurocholate

Estradiol-17 beta-D-glucuronide (E-17G), a metabolite of natural estrogen, is a potent cholestatic agent in vivo. We, therefore, studied the mechanisms of E-17G cholestasis using in vitro perfused rat liver system. Furthermore, since it has been postulated that sodium taurocholate (TC) may interfere with either uptake or biliary excretion of other steroid agents, we tested whether E-17G cholestasis could be modified by TC administration. During a constant infusion of TC at a physiological rate (0.50 mumole per min), a dose-dependent decrease of bile flow was observed after E-17G addition from 1.5 to 5 X 10(-5) M. E-17G decreased bile acid excretory rate but not bile acid concentration in bile. In separate experiments, TC was infused at different rates (0, 0.25, 0.50, and 0.75 mumole per min) into the perfusate over the entire experimental period, and E-17G was added at 1.75 X 10(-5) M. In this setting, E-17G cholestasis was diminished by increasing TC infusion rate and was prevented by TC at 0.75 mumole per min. Infusion of sodium dehydrocholate (0.75 mumole per min), a nonmicelle-forming bile acid, did not prevent E-17G cholestasis. During E-17G cholestasis, an increased biliary permeability to 14C-sucrose was observed. This effect was also prevented by TC, but not by sodium dehydrocholate which was infused at 0.75 mumole per min. The perfusate disappearance curves of 3H-E-17G at the different TC infusion rates showed no changes in the initial uptake phase, but a profound dose-dependent difference in the excretory phase.(ABSTRACT TRUNCATED AT 250 WORDS)

The bile flow and biliary excretion of ursocholate in the rat

Several studies reported that ursodeoxycholate (but not its conjugates), when administered intravenously, increased the biliary bicarbonate concentration in the rat (1-3). At the same time, a complete dissociation between bile flow and the bile salt excretion rate was produced in the second hr of infusion (2). In order to examine whether this property was due to the 7 beta-hydroxy group in its molecular structure, the choleretic property of ursocholate (3 alpha, 7 beta, 12 alpha-trihydroxy-5 beta-cholanoic acid) was investigated in male Wistar rats. Immediately after the start of iv infusion of ursocholate at a rate of 1.2 mumole/min/100 g b. wt., both the bile flow and bile salt excretion rate began to increase. However, unlike with ursodeoxycholate, the bile salt excretion rate continued to be high in the second and third hr of infusion, while the bile flow rate gradually increased. Furthermore, the bicarbonate concentration in the bile fell slightly 10 min after the start of ursocholate infusion. Although the concentration tended to return to the baseline value before the bile salt infusion in the later period of observation, no significant increase in bicarbonate concentration was observed during the whole observation period. These properties were quite similar to those of cholate rather than those of ursodeoxycholate. However, a cholate infusion at the same rate of 1.2 mumole/min/100 g b.wt. caused a cholestasis as early as 20 to 30 min after the start of an infusion. These results suggest that the previously reported properties of ursodeoxycholate (that it causes a complete dissociation between the bile flow and bile salt excretion rate in the second hr and that it increases the biliary bicarbonate concentration) were not due to the 7 beta-hydroxy group in its steroidal structure, and that the choleretic property of ursocholate is similar to its 7 alpha-hydroxy epimer, cholate. However, the much lower cytotoxicity of ursocholate compared to cholate appears to be due to the 7 beta-hydroxy group that ursocholate has.

Stereospecific reduction of 3- and 7-oxo groups of oxocholanic acids in isolated perfused rat liver

The metabolism of 3- and 7-oxo groups of oxocholanic acids was studied in isolated perfused rat liver. The metabolites in bile were determined enzymatically using 3 alpha- and 7 alpha-hydroxysteroid dehydrogenases. The 3-oxo group of all the oxocholanic acids tested (dehydrocholate, glycodehydrocholate, taurodehydrocholate, 3,7-dioxocholanate, 3,12-dioxocholanate and tauro-7,12-dihydroxy-3-oxocholanate) was reduced stereospecifically to 3 alpha-hydroxy metabolites. On the other hand the 7-oxo group was excreted partially unchanged (30% of the dose) and partially as 7 alpha-hydroxy metabolites (6-10% of the dose). The remainder of the 7-oxo group was concluded to have been reduced to 7 beta-hydroxy metabolites. These results indicate that the 7-oxo group of oxocholanic acids is reduced predominantly to 7 beta-hydroxy metabolites in rats rather than to 7 alpha-hydroxy metabolites as found in man.

Urinary and fecal keto bile acids in liver cirrhosis

The urinary and fecal bile acids of thirteen male patients with liver cirrhosis were analyzed by gas chromatography and gas chromatography-mass spectrometry to obtain information on their keto bile acid excretion. 3 alpha-Hydroxy-12-keto-5 beta-cholanoic, 3 alpha,12 alpha-dihydroxy-7-keto-5 beta-cholanoic, 3 alpha,7 alpha-dihydroxy-12-keto-5 beta-cholanoic and 3 alpha-hydroxy-7,12-diketo-5 beta-cholanoic acids were found in the urine of ten patients. In four of these patients, keto bile acids were the main bile acids excreted in the urine. However, the ratios of fecal keto bile acids to the total fecal bile acids in these four patients were similar to those in the other six patients whose urinary excretion of keto bile acids was low. Three of the four patients had clinical abnormalities, such as ascites, esophageal varices or a history of hepatic encephalopathy, that may indicate advanced liver dysfunction and/or presence of collateral circulation. These findings suggest that the occurrence of keto bile acids in the urine might be ascribed to the escape of these acids from reduction to hydroxy-forms in the liver, not to bacterial over-production in the intestine. However, the mechanism and significance of the presence of keto bile acids in the urine are still unknown.

The influence of micelle formation on bile salt secretion

1. The influence of micelle formation on bile salt secretion was assessed by analysing the secretory characteristics of, and interaction between, the natural micelle-forming bile salts, taurocholate and cholate, and the artificial non-micelle-forming bile salts, taurodehydrocholate and dehydrocholate (both of which are subjected to reductive metabolism), in anaesthetized dogs. 2. Competitive secretory interaction between these two classes of bile salt was demonstrated thereby indicating that they share the same biliary transport system. Taurodehydrocholate had a lower affinity for the transport system than that of taurocholate and the metabolic derivatives of dehydrocholate. 3. The (initially determined) biliary secretory maxima for taurodehydrocholate (4 . 9 +/- 1 . 9 (S.D.) mumole/min. kg, n = 6) and total 'dehydrocholate' in taurine replete dogs (4 . 2 +/- 1 . 0 mumole/min. kg, n = 16) were both significantly less than those for taurocholate (8 . 0 +/- 1 . 8 mumole/min. kg, n = 16) and total cholate in taurine replete dogs (6 . 9 +/- 1 . 2 mumole/min. kg, n = 12). 4. The initially determined secretory maxima of taurodehydrocholate and 'dehydrocholate' were elevated by about 30 and 36%, respectively, by an earlier period of taurocholate administration; the most likely explanation (which is supported by independent morphological studies) for this effect is that taurocholate increases the number of functional 'carriers' in the canalicular membrane. When calculated for optimal conditions, the secretory maxima of the non-micelle-forming bile salts closely approached those of the micelle formers. 5. The above results would seem to indicate that micelle formation (in the hepatocyte, canalicular membrane or bile) is not essential for the effective translocation of bile salt by the specific canalicular membrane receptors. The results also suggest that the effective concentration of bile salt in bile (possibly 60--70 times greater in the case of the non-micelle-formers) is not an important determinant of the net secretory performance of conjugated bile salt. 6. At the same bile salt secretion rate (3 . 06 mumole/min. kg), the bile flow rate associated with taurodehydrocholate (44 . 3 +/- 2 . 7 (S.D. along regression line) microliter/min. kg, n = 38) was significantly greater than that associated with taurocholate (29 . 5 +/- 7 . 7 microliter/min. kg, n = 80) but significantly less than that associated with 'dehydrocholate' in taurine replete dogs (51 . 7 +/- 4 . 8 microliter./min. kg, n = 33), 'dehydrocholate' after acute taurine depletion (61 . 2 microliter./min. kg, n = 1) and free cholate after taurine depletion (49 . 8 +/- 9 . 8 microliter/min. kg, n = 92). The extra flow associated with the free bile salts is derived by means that are largely or entirely independent of their osmotic activity in bile.

Influence of taurocholate, taurochenodeoxycholate, and taurodehydrocholate on sulfobromophthalein transport into bile

To test the hypothesis that incorporation of sulfobromophthalein (BSP) into mixed micelles could account for the increase in its biliary transport maximum (Tmax) by bile salts, we have compared in hamsters the influence on BSP Tmax of taurocholate and taurochenodeoxycholate (two micelle-forming physiological bile salts) to that of taurodehydrocholate, a bile salt which, in vitro, does not form micelles. In a first series of experiments, it was observed that taurocholate and taurochenodeoxycholate increased the secretion of phospholipid (40 and 53%, respectively), and cholesterol (50 and 110%, respectively), whereas taurodehydrocholate decreased the secretion of phospholipid (-31%) and cholesterol (-43%). This result suggests that, in vivo, taurodehydrocholate or its metabolites do not form mixed micelles. In a second series of experiments, it was seen that the three bile salts induced a similar increase in BSP Tmax (63% with taurocholate, 52% with taurochenodeoxycholate, and 51% with taurodehydrocholate). These results provide circumstantial evidence for the hypothesis that mixed micelle formation is not an important determinant of maximal BSP secretion into bile.

Biliary excretion of diethylstilbestrol in the rhesus monkey

The biliary excretion of diethylstilbestrol in the bile fistula rhesus monkey was investigated during exogenous taurocholate- and taurodehydrocholate-induced choleresis. Following intravenous administration, 36% of the dose was excreted into the bile (as diethylstilbestrol monoglucuronide) and 53% in the urine (as diethylstilbestrol monoglucuronide plus more polar unidentified metabolites). During the steady-state infusion of diethylstilbestrol, with taurocholate-induced choleresis, a bile flow dependent transport for the biliary excretion of diethylstilbestrol monoglucuronide was observed. Evidence for carrier-mediated transport of this metabolite was a bile-to-blood concentration ratio which ranged from 228 to 279 during steady-state experiments. In vitro experiments indicated that diethylstilbestrol monoglucuronide forms an association with taurocholate, as well as the micellar structures of bile, resulting in a severalfold enhancement of solubility above that in aqueous buffer alone. Taurodehydrocholate, a non-micelle-forming bile salt, did not interact with this metabolite and had no effect on its solubility. Substitution of taurodehydrocholate for taurocholate during the steady-state infusion of diethylstilbestrol produced no significant changes in the transport of diethylstilbestrol monoglucuronide from blood to bile.

Bile acid structure and biliary lipid secretion. II. A comparison of three hydroxy and two keto bile acids

The effect of five bile acids on biliary lipid secretion was studied in the pentobarbital-anesthetized cat. The dihydroxy acid, taurohyodeoxycholic acid, was indistinguishable from another dihydroxy acid, taurochenodeoxycholic acid, but secretion of both phospholipid and cholesterol was considerably reduced with two mono-keto dihydroxy acids, tauro-3alpha,12alpha-dihydroxy-7-keto-5beta-cholanoic acid and tauro-3alpha,7alpha-dihydroxy-12-keto-5beta-cholanoic acid. The effect of a trihydroxy bile acid, taurocholic acid was as previously described. The effect of the keto bile acids may be explained by the ability of these bile acids to solubilize lipid, but such an explanation is inadequate for the difference between di- and trihydroxy bile acids. An intracellular effect of bile acid is postulated.

Choleretic properties of ursodeoxycholic acid and chenodeoxycholic acid in dogs

Choleretic effects and properties of ursodeoxycholic and chenodeoxycholic acids given orally were investigated in comparison with dehydrocholic acid in conscious dogs with cholecystectomy. Ursodeoxycholic acid as well as chenodeoxycholic acid increased the bile flow and the concentrations of phospholipid, cholesterol and bile acids in the bile. After administration of either ursodeoxycholic acid or chenodeoxycholic acid, a great amount of each bile acid appeared in the bile. Ursodeoxycholic and chenodeoxycholic acids increased the outputs of phospholipid, cholesterol and bilirubin in the bile. On the other hand, dehydrocholic acid markedly decreased the concentrations and outputs of all the above materials in the bile, despite a considerable increase in the bile flow. After administration of dehydrocholic acid, 3alpha, 7alpha-dihydroxy-12-keto-cholanoic acid appeared in the bile instead of dehydrocholic acid. The results suggest that ursodeoxycholic and chenodeoxycholic acids are transported into the bile from the hepatic cells where they produce a choleresis due to the bile acid-dependent mechanism. Dehydrocholic acid is metabolized in the liver and the metabolites produced hydrocholeresis.

Bile salt metabolism. I. The physiology of bile salts

Bile salts are synthesized in the liver from cholesterol, conjugated with glycine or taurine and secreted in bile with cholesterol and lecithin. The molar concentrations of these three lipids determine solubility of cholesterol in bile. Within the gastrointestinal lumen bile salts play an essential role in lipid absorption and faty transport. An efficienct entero-hepatic circulation maintains hepatic bile salt secretion and provides a "feed-back" control of the bile salt and cholesterol metabolism. Potentially hepatotoxic lithocholic acid formed in the intestinal lumen by bacterial action on chenodeoxycholic acid is sulphated in the liver thus decreasing intestinal reabsorption. The total faecal excretion of bile salts balances hepatic synthesis and represents a major catabolic path in cholesterol metabolism.

The secretory characteristics of dehydrocholate in the dog: comparison with the natural bile salts

1. During dehydrocholate administration in the taurine replete dog, the maximum excretory rate of total bile salt (almost entirely dehydrocholate derivative, mostly conjugated) was 3-84 +/- 0-53 (S.D.) mumole/min. kg body wt. (eleven experiments). This was much less than the excretory maximum previously obtained for taurocholate (8-64 +/- 1-31 (S.D.) mumole/min. kg total cholate, mostly conjugated). 2. The superimposition of taurocholate infusion did not cause any significant change in the 'dehydrocholate' maximum but taurocholate itself was excreted into bile at no more than about half its normal maximum. When taurocholate maximum excretion was established first, it was reduced by dehydrocholate administration. In both types of experiment the joint bile salt excretory maximum was of the same order as that of taurocholate alone, provided taurocholate made up at least 40-50% of the total bile salt. 3. When taurocholate administration was stopped, the maximum excretory rate of 'dehydrocholate' rose to values up to 63% above the initially determined excretory maximum; the enhanced 'dehydrocholate' excretory maximum, when calculated for optimal conditions, approached that of actively conjugated vholate, even though the effective 'dehydrocholate' concentration in bile was ten to twenty times the critical micellar concentration of taurocholate. This suggests that the effective bile salt concentration in bile is not an important determinant of the secretory performance of a bile salt. 4. To explain findings (2) and (3) it is necessary to postulate that taurocholate has both a facilitatory and an inhibitory action on 'dehydrocholate' excretion. The facilitatory action, which persists after taurocholate has left the animal, may consist either of an increase in the maximum rate at which modification of dehydrocholate takes place within the liver cell, or an increase in the number of functioning 'carriers' for 'dehydrocholate' transfer. The data suggest that the inhibitory effect is due to the competitive interaction that also appears to exist between the two bile salts. 5. The increase in bile flow rate per unit increase in 'dehydrocholate' excretion (15 ml./m-mole) was about twice that obtained for taurocholate. There was no significant formation of micellar aggregates during 'dehydrocholate' excretion, as judged from the total electrolyte concentration of bile and its osmalality. 6. During the excretion of 'dehydrocholate'-taurocholate mixtures (approximately 1:1) at submaximal rates the associated bile flow rate was not less than the sum of the separate components, thus suggesting that 'dehydrocholate' was not being incorporated in taurocholate mixed micelles.

Effects of taurodihydrofusidate, a bile salt analogue, on bile formation and biliary lipid secretion in the rhesus monkey

Bile salts play a major role in bile formation and biliary lipid secretion. Sodium taurodihydrofusidate (TDHF), a derivative of the antibiotic fusidic acid, closely resembles bile salts in terms of structure, micellar characteristics, and capacity ot solubilize otherwise insolbule lipids. We have therefore studied the biliary secretion of this bile salt analogue and its influence on bile formation and biliary lipid secretion in primates. Alert, unanesthetized female rhesus monkeys prepared with a total biliary fistula were allowed to reach a steady bile salt secretion rate before each study. In three animals (group I),[14C]TDHF was infused intravenously. Most of the compound was secreted rapidly in bile chemically unchanged. The biliary secretion of this drug produced a twofold increase in bile flow; however, the bile salt output was markedly reduced during the infusion. In spite of this reduction, the phospholipid output remained essentially unchanged whereas the cholesterol output increased almost twofold. In five other animals (group II), the effect of TDHF on the bile salt secretion was further investigated by an intravenous infusion of [14C]taurocholate followed by a combined infusion of [14C]taurocholate and TDHF. When TDHF was added to the infusate, a reduction in the [14C]taurocholate output and a progressive rise in the plasma [14C]taurocholate concentration were observed in each animal. An analysis of the data in both groups indicates that (a) the most likely explanation to account for the decreased bile salt output is that the bile salt analogue, TDHF, interfered with bile salt secretion into the biliary canaliculi; (b) TDHF induces a greater secretion of biliary water than was observed with bile salts, an effect consistent with a stimulation of the bile salt-independent canalicular flow; (c) at similar 3alpha-hydroxysteroid secretion rates TDHF caused a significant increase in cholesterol secretion compared to that induced by bile salt. This finding suggests that TDHF affects cholesterol metabolism or secretion in a way distinct from bile salts. Thus, the solubilization of biliary lipids in mixed micelles, although essential, is only one of the factors which determine their secretion into bile.

Effects of meals and interruption of enterohepatic circulation on flow, lipid composition, and cholesterol saturation of bile in man after cholecystectomy

In 4 patients studied after cholecystectomy and common-duct exploration for cholesterol gallstones, bile salt (BS) and phospholipid (PL) output and bile flow increased significantly in response to breakfast, but cholesterol (Ch) output was unaltered. Simultaneously, Ch concentration decreased while PL and BS concentrations did not change. The degree of Ch saturation of bile, [BS PLUS PL]/[ch], decreased in each study, whether or not the original ratio indicated Ch supersaturation; in 3 of 5 studies, an initially super-saturated bile became unsaturated with Ch in response to breakfast. No significant changes were noted after lunch. During interruption of enterohepatic circulation (EHC), studies with radiolabeled bile acids indicated that the increased bile acid output in response to meals was secondary to increased recirculation of intestinal bile acids rather than to de novo bile acid synthesis. This mechanism may account for the adequate delivery of BS and for the decreased degree of Ch saturation of bile postprandially in cholecystectomized patients.

Choleresis and hepatic transport mechanisms. II. Influence of bile salt choleresis and biliary micelle binding on biliary excretion of various organic anions

To investigate, whether binding to micelles has a function in hepatic transport, biliary excretion of three organic anions, phenolphthalein-beta-D-glucuronide (PG), dibromosulphthalein (DBSP) and indocyanine green (ICG) was studied in rats during saline, taurocholate or dehydrocholate administration. Taurocholate causes a weak choleresis with formation of biliary micelles, dehydrocholate a strong choleresis with little micelle formation. The two bile salts did not uniformly influence biliary excretion of the organic anions: biliary excretion of ICG (12.9 mumoles/kg) and DBSP (75.0 mumoles/kg) was stimulated by both bile salts: ICG excretion most pronounced by taurocholate and DBSP excretion most strongly by dehydrocholate. Biliary output of PG (25.8 and 200 mumoles/kg) was not stimulated by bile salt administration. Binding of PG, DBSP and ICG to biliary micelles was studied in sedimentation experiments by ultracentrifugation. PG, DBSP and ICG in bile showed a similar sedimentation pattern as 3H-taurocholate in bile, which indicates an association of all three anions with biliary micelles. Thus, the influence of bile salts on biliary transport of organic anions varies with the compound studied and the bile salt used, effects which cannot be explained by differences in binding to biliary micelles.

Canalicular bile secretion in man. Studies utilizing the biliary clearance of (14C)mannitol

[(14)C]Mannitol was administered i.v. as a bolus injection to five postcholecystectomy patients with indwelling T-tubes and re-established enterohepatic circulations to evaluate the biliary clearance of [(14)C]mannitol as a means of estimating canalicular bile flow in man. [(14)C]Mannitol appeared in collections of bile 9-22.5 min after intravenous injection, rose to a peak, and thereafter paralleled the plasma [(14)C]mannitol disappearance curve. Bile-plasma [(14)C]mannitol ratios and [(14)C]mannitol clearances were determined during control and choleretic periods after correction of the bile [(14)C]mannitol points for the transit time of a given sample. After i.v. injection of sodium dehydrocholate in five studies, bile flow and mannitol clearance increased proportionately. However, when ductular secretion was stimulated with an i.v. bolus of secretin in three other studies, [(14)C]mannitol clearance remained essentially unchanged, indicating that [(14)C]mannitol entered bile at the level of the hepatocyte and could be utilized as a marker of canalicular flow in man. During control studies, when bile drained spontaneously from biliary fistulae in fasting patients, bileplasma [(14)C]mannitol ratios averaged 0.62+/-0.18 and canalicular flow, as estimated by [(14)C]mannitol clearance. (0.27+/-0.16 ml/min) accounted for 44-95% of total bile production (0.43+/-0.12 ml/min). When the rate of bile flow was plotted as a function of bile salt excretion after correction for the effects of biliary dead space, linear regression analysis revealed that approximately 7 mul of bile were secreted with each mumol of bile salt. Estimates of bile salt-independent canalicular flow accounted for at least one-third of the estimated 24-h bile production (604 ml) in these patients, indicating that this fraction of canalicular flow is a significant source of bile secretion in man.