Heterogeneity of bile pigment conjugates as revealed by chromatography of their ethyl anthranilate azopigments

Drug- and Drug Abuse-Associated Hyperbilirubinemia: Experience With Atazanavir

Hyperbilirubinemia is a common finding in individuals with a history of substance abuse. Although this may indicate a serious disorder of liver function, this is not always the case. An understanding of bilirubin formation, metabolism, and transport can provide a helpful approach to dealing with these patients. This is typified by studies of patients treated with the antiretroviral drug atazanavir. Atazanavir has been associated with hyperbilirubinemia in as many as one-third of individuals for whom it has been prescribed, evoking concerns of hepatotoxicity. The studies in this report were designed to determine mechanisms by which this occurs. The data show that this drug inhibits the enzyme UDP-glucuronosyl transferase-1A1, responsible for conjugating bilirubin with glucuronic acid. This conjugation step is required for bilirubin excretion into bile, and when it is inhibited, bilirubin refluxes from the liver into the circulation, causing unconjugated hyperbilirubinemia. Other parameters of bilirubin formation, binding to albumin in the circulation, uptake into hepatocytes, and intracellular protein binding in hepatocytes were unaffected by atazanavir. The effect of atazanavir on serum bilirubin levels is reversible, consistent with lack of structural damage to the liver.

Conformational study of 2-arylazo-1-vinylpyrroles

Conformational study of 2-phenylazo-1-vinylpyrrole and 2-(4-bromophenyl)azo-5-methyl-1-vinylpyrrole was performed on the basis of the experimental measurements and high-level ab initio calculations of their 13C--13C and 13C--1H spin-spin coupling constants, showing marked stereochemical behaviour upon the internal rotation of the vinyl group and the pyrrolyl moiety. In liquid phase, both compounds were found to adopt predominant s-trans-s-trans conformation with the noticeable population (ca. 30%) of the higher-energy s-cis-s-trans conformation in the latter compound. As follows from the X-ray data, 2-phenylazo-1-vinylpyrrole crystallizes in s-trans-s-trans conformation while the crystalline molecular structure of 2-(4-bromophenyl)azo-5-methyl-1-vinylpyrrole is s-cis-s-trans.

On how the conformation of biliverdins influences their reduction to bilirubins: a biological and molecular modeling study

The cyclic 2,18-bridged biliverdin (2) is excreted in rat bile without reduction to the corresponding bilirubin. Conformational analysis, employing an optimized Monte Carlo method and a mixed Monte Carlo/stochastic dynamics, reveals that biliverdin IXalpha (1) and the cyclic analogue 2 adopt 'lock washer' conformations, stabilized by the presence of intramolecular hydrogen bonds between N23...H22N and, to a lesser extent, between N23...H24N. Although 2 is very similar in overall shape to 1, the former adopts a 'locked lock washer' conformation unable to undergo fluctuations, thus possibly hampering a proper recognition by biliverdin reductase.

Exploring the conformation of bilirubins with natural and unnatural analogues: use of positional and bridged isomers of bilirubin IXalpha

Unlike bilirubin IXalpha (1), the isomers bilirubin IXdelta (2) and neobilirubin IXbeta (3) do not require conjugation with glucuronic acid in order to be excreted. A conformational analysis employing an optimized Monte Carlo method and a mixed Monte Carlo stochastic dynamics reveals that isomer 2 exhibits a structure more closed than the well known 'ridge-tile' conformation of 1. The change in the position of both propionic acid chains causes the loss of at least four hydrogen bonds. On the other hand, the change in the configuration of the distal dipyrrinone and the blockage of the lactamic nitrogen by the presence of a bridge in isomer 3 results in an open and more elongated structure, where the chance of hydrogen bond formation in this region is obliterated. The resulting molecular models for these compounds are consistent with 1H NM R, UV-vis, and TLC data.

Intestinal excretion of unconjugated bilirubin in man and rats with inherited unconjugated hyperbilirubinemia

Patients with Crigler-Najjar syndrome and Gunn rats cannot form bilirubin glucuronides owing to a lack of bilirubin UDP-glucuronosyltransferase activity. Because increased serum and tissue bilirubin levels remain constant, an alternative excretory route has to substitute for this deficiency. Gunn rats excrete in bile only 2-13% of the bilirubins eliminated in Wistar rats. In contrast, the biliary excretion rate of urobilinogen in Gunn and Wistar rats is comparable. The sum of bilirubins and urobilinogen excreted in the bile of Gunn rats amounts to 10-30% of pigments excreted in Wistar rats. Despite this low biliary excretion, the intestinal content and fecal excretion of bile pigments in Gunn and Wistar rats were similar. These data support an extrabiliary entrance of unconjugated bilirubin into the intestine. Additional proof for this was found in that the intestinal lumen of Gunn rats still contains a high amount of bilirubins and urobilinogen after 3 d of external biliary drainage. A similar procedure in Wistar rats resulted in the complete disappearance of bile pigments from the intestine. The direct transmural transport of bilirubin from blood to all parts of the intestinal lumen was demonstrated by injecting 14C-bilirubin i.v. into Gunn rats with isolated parts of small and large intestine. In Crigler-Najjar and Gilbert's syndrome patients, the biliary excretion of bile pigments has previously been shown to be strongly reduced. Their stools, however, contained approximately the same amount of bile pigments as in normal subjects. Although only traces of unconjugated bilirubin were detected in the stool of normal persons (4 +/- 3% of total bile pigments), higher amounts were found in patients with Crigler-Najjar disease (20 +/- 12&). These results suggest a direct intestinal permeation of unconjugated bilirubin in severe unconjugated hyperbilirubinemia both in man and rats.

Epitope of 24G7 anti-bilirubin monoclonal antibody

We examined an antigenic epitope recognized by an anti-bilirubin monoclonal antibody designated 24G7 (Shimizu, S., Izumi, Y., Yamazaki, M., Shimizu, K., Yamaguchi, T., and Nakajima, H. (1988) Biochim. Biophys. Acta 967, 255-260). The reactivity of bilirubin-IX alpha, its analogues (III alpha, XIII alpha, and mesobilirubin-IX alpha) and related azo compounds, with 24G7 was compared by means of an enzyme-linked immunosorbent assay (ELISA). The order of reactivity was as follows: (a) aniline azopigment > ethyl anthranilate azopigment > sulfanilic acid azopigment, (b) bilirubin-XIII alpha > bilirubin-IX alpha > bilirubin-III alpha, (c) bilirubin-IX alpha = mesobilirubin-IX alpha. These findings indicated that the epitope is present in (a) the dipyrrolic moiety of the endovinyl (correspond to N-21 and N-22 of bilirubin), or exovinyl types (N-23 and N-24); (b) the dipyrrolic moiety of the endovinyl type, which contains (c) a methyl group (C-2) but not a vinyl group (C-3) in the dipyrrolic moiety of endovinyl type. Therefore, we concluded that the epitope was the region containing the oxo group at C-1, the methyl group at C-2, C-(4,5,6,9), and the N-21 and -22 of bilirubin-IX alpha.

Changes in the composition of bilirubin-IX isomers during human prenatal development

We analyzed the isomeric composition of bilirubin-IX in human fetal bile using HPLC. The approximate ratio of the bilirubin-IX isomers obtained from the fetal bile at 20 weeks of gestation was IX alpha, 6%; IX beta, 87%; IX gamma, 0.5%; and IX delta, 6%. From 15 to 22 weeks, bilirubin-IX beta was predominant and bilirubin-IX delta and bilirubin-IX alpha were also present in the bile as minor components. By 28 weeks, bilirubin-IX alpha constituted about 50% of the total bilirubin. There was a general correlation between fetal age and the proportion of bilirubin-IX alpha to bilirubin-IX beta in the bile and the small intestinal contents of fetuses. As development proceeded from mid-gestation to near term, the isomeric composition dramatically changed, with a decrease in the IX beta isomer and a subsequent increment of the IX alpha isomer. In contrast, the IX delta isomer changes little. Recently, we identified four forms of biliverdin reductase including two biliverdin-IX alpha reductases and two biliverdin-IX beta reductases in human liver cytosolic fractions [Yamaguchi, T., Komoda, Y. & Nakajima. H. (1994) J. Biol. Chem. 269, 24,343-24,348]. The proportion of the total activity of biliverdin-IX beta reductases to that of biliverdin-IX alpha reductases was considerably higher in the fetal, than in the adult liver.

Fetal cocaine exposure and neonatal bilirubinemia

To assess the effect of fetal exposure to cocaine on neonatal serum bilirubin values, we compared 17 infants whose cocaine exposure was confirmed by urine toxicology studies, with no evidence of other drug exposure by history or urinalysis, with 31 sequentially born healthy term infants without evidence of maternal drug use. The mean (+/- SD) bilirubin concentration in control infants was 110 +/- 32 mumol/L (6.5 +/- 1.9 mg/dl) at 30.5 +/- 5.4 hours of age, compared with 55 +/- 26 mumol/L (3.2 +/- 1.5 mg/dl) at 30.8 +/- 5.3 hours in cocaine-exposed infants (p < 0.001). We also compared the abilities of cocaine and clofibrate, a known inducer of bilirubin uridine diphosphate-glucuronosyl transferase (BGT), to induce drug and bilirubin metabolizing pathways in young male Sprague-Dawley rats. Animals received drugs or saline solution for 7 days, and livers were assayed for cytochrome P-450, peroxisomal beta-oxidase, delta 5-3-ketosteroid isomerase (KSI), glutathione-S-transferase (GST), and BGT. Cocaine was a weak inducer of GST but a strong inducer of KSI, a member of the GST family of enzymes that is closely associated with bilirubin transport (ligandin) in liver, and a moderately strong inducer of BGT. Neither drug increased cytochrome P-450 levels, and only clofibrate induced peroxisomal beta-oxidase. We conclude that cocaine appears to induce bilirubin metabolizing pathways, resulting in a lower risk of neonatal hyperbilirubinemia.

Effect of adjuvant-induced arthritis on hepatic drug metabolism in rats

1. Hepatic drug metabolism was investigated in normal, adjuvant-induced arthritic (AA), indomethacin-treated AA and prednisolone-treated AA rats. The contents of P450 and b5 and the activities of NADH-b5 reductase (fp2), NADPH-ferrihaemoprotein reductase, P450 mixed function oxidase, FAD-monooxygenase and several enzymes involved in conjugation were remarkably lower in AA than in normal rats. 2. Many of the decreased enzyme activities were restored to normal levels by the continuous administration (3 weeks) of indomethacin or prednisolone, which improved the arthritic states of the animals. However, the restoration of FAD-monooxygenase activity by the administration of indomethacin or prednisolone was incomplete. The P450 and b5 contents and the fp2 activity in prednisolone-treated AA rats were also significantly lower than those in normal rats. 3. These findings indicate that the ability of the liver to metabolize drugs (both oxidation and conjugation) in AA rats is greatly decreased and that a long series of the treatment of AA rats with anti-inflammatory drugs is required to restore several enzyme activities.

Occurrence of bilirubin-IX beta in the gallbladder bile of eel, Anguilla japonica

Bilirubin-IX beta isomer was detected in the bile of eel, Anguilla japonica, as evidenced by high-performance liquid chromatography (HPLC) analysis of free acid and its ethyl anthranilate diazo derivatives. Bilirubin-IX beta accounted for 16.7 +/- 6.0 (mean +/- S.D.) percent of the total bilirubins in the bile of 40 eels analysed, and the percentage was much higher than that reported in the biles of mammals.

Stimulating effects of bovine small intestine mucosal factors on rat hepatocyte development

A mass of pure adult rat parenchymal hepatocytes, obtained by a newly devised isolation technique, developed into organized micro-liverlike layered multicellular colonies in long-term primary cultures grown in the presence of bovine small intestine mucosal factors (SIMFs). These factors stimulated proliferation, aggregation, and orderly arrangement of the hepatocytes, and differentiation into partially functional micro-livers in vitro. SIMFs derived from other mammalian species affected rat hepatocytes in the same manner. Studies of the effects of mammalian SIMFs on hepatocytes may provide new insights into the kinetics and mechanisms of liver regeneration.

Anti-bilirubin monoclonal antibody. I. Preparation and properties of monoclonal antibodies to covalently coupled bilirubin-albumin

We have prepared 16 anti-bilirubin monoclonal antibodies and described their unique reactivity to bilirubin and related compounds. Using the modified mixed anhydride method, bilirubin was covalently coupled to bovine serum albumin. We performed somatic cell fusion between murine spleen cells immunized with this bilirubin-albumin complex and murine myeloma P3-X63-Ag8-U1 cells. After screening assays, 16 clones were identified which were producing antibodies not to albumin but to haptenic bilirubin. In inhibition analysis, the antibodies in the culture supernatants cross-reacted with bilirubin glucuronides to varying degrees, but rarely reacted with structurally related biliverdin, hemin, and azodipyrroles of bilirubin. Albumin, when present in the solution, much reduced the reactivity of several monoclonal antibodies to unconjugated bilirubin, and this effect was partly reversed by addition of salicylate which dissociates the binding between bilirubin and albumin.

Monoconjugated bilirubin is a major component of hemolysis-induced gallstones in mice

The role of bilirubin conjugates in the formation of pigment gallstones is not known. In this study, we completely solubilized and then analyzed by high-performance liquid chromatography specimens of black pigment gallstones from eight nb/nb mice with hereditary hemolytic anemia. Each dried gallstone specimen of about 200 micrograms was dissolved in 5 ml of dimethyl sulfoxide/0.15 M HCI/50 mM disodium-EDTA (8:1:1 by volume) at room temperature. Stone dissolution was complete by 30 min as monitored by the A456 and direct observation, and no oxidative products of bilirubin were observed in the visible spectrum, 350 to 750 nm. By high-performance liquid chromatography, the intact tetrapyrroles were separated as diconjugated and monoconjugated bilirubins; unconjugated bilirubin was resolved as XIII, IX and III alpha-isomers. The isocratic solvent system used was 0.1 M di-n-dodecylamine acetate/0.1 M di-n-octylamine acetate (4:1, v/v) in methanol, pH 7.4, at a flow of 1 ml per min. Diconjugated bilirubin accounted for 6.0 +/- 2.4 molar % (mean +/- S.E.), monoconjugated bilirubin for 37.4 +/- 8.4% and unconjugated bilirubin for 56.3 +/- 8.9% of the solubilized pigments. The IX alpha-isomer represented 96 +/- 1.9% of the unconjugated bilirubin. The presence of bilirubin conjugates in gallstones was confirmed by ethylanthranilate diazotization: the conjugated azodipyrrole in stone had the same retention time as that of conjugated azodipyrrole from rat and mouse bile. A majority of the bilirubin conjugates was sensitive to beta-glucuronidase of liver origin, indicating that the C-1 glucuronide ester was present.(ABSTRACT TRUNCATED AT 250 WORDS)

Novel method for high-performance liquid chromatography of azo derivatives of conjugated and unconjugated bilirubin

A method for the separation and quantitation of ethyl anthranilate or p-iodoaniline azo derivatives of bile pigments was developed using reversed-phase high-performance liquid chromatography. A convenient separation was achieved in 15 min, permitting the quantitation of the unconjugated azo-dipyrrole (alpha o) and its glucuronide (delta), xyloside (alpha 2) and glucoside (alpha 3) conjugates. The pathological beta- and gamma-azo pigments, derived from bilirubin glucuronide isomers that occur in cholestatic bile or plasma, are also detected in this system. The results of this method as applied to bile from 25 healthy dogs were in excellent agreement with the values obtained by reversed-phase chromatography of bilirubin and its mono- and dimethyl esters produced from the corresponding conjugates by alkaline methanolysis. This system permits the sensitive and convenient determination of bilirubin and its conjugation pattern in biological fluids.

Influence of antibiotics on the faecal excretion of bile pigments in healthy subjects

We have evaluated the effects of 10 antibiotics, given orally for 6 days to healthy subjects, on faecal excretion of urobilinogen. Intake of bacitracin, vancomycin, clindamycin, erythromycin, and ampicillin resulted in a pronounced suppression of the faecal excretion of urobilinogen (p less than 0.05). Intake of doxycycline, metronidazole, nalidixic acid, ofloxacin, and trimethoprim/sulphamethoxazole had no significant effect. The effects of three antibiotics-ampicillin, clindamycin, and metronidazole--on faecal excretion of conjugated bilirubin were similarly evaluated. Intake of clindamycin led to a marked increase of conjugated bilirubin (p less than 0.05) in the faeces, and the pattern of separated azopigment derivatives of the bilirubin conjugates became altered. Intake of ampicillin and metronidazole resulted in far less alterations in faecal conjugated bilirubin, although a significant change was observed in the subjects receiving metronidazole (p less than 0.05). The differences between the antibiotics with regard to altered intestinal bile pigment metabolism may be due to differences in antimicrobial spectra and/or intestinal concentrations of the drugs. Our findings indicate that orally taken antibiotics may cause a suppression of the microbial deconjugation of conjugated bilirubin and urobilinogen formation, respectively. This may reflect a pronounced disturbance of the intestinal microflora.

Survival, organization, and function of microcarrier-attached hepatocytes transplanted in rats

Hepatocytes harvested by collagenase perfusion of rat liver were attached to collagen-coated microcarriers and injected intraperitoneally into congeneic or allogeneic bilirubin-UDP-glucuronosyltransferase (EC 2.4.1.17)-deficient (Gunn) rats or allogeneic analbuminemic (NAR) rats. Five days later, the microcarriers were observed to have formed conglomerates chiefly on the anterior surface of the pancreas. Scanning electron microscopy showed hepatocytes attached to the granular collagen-coated surface of the microcarriers and newly formed connective tissue. Light microscopy revealed that the microcarriers formed a lattice with the collagen tissue; hepatocytes were seen within this lattice or on the surface of the microcarriers. Hepatocyte plasma membranes were nucleoside-diphosphatase (NDPase)-positive. Newly formed blood islands, blood vessels containing erythrocytes and leukocytes and NDPase-positive endothelium were observed in close proximity to the hepatocytes and fibroblasts. Transmission electron microscopic examination showed hepatocytes with microvilli and nucleoid-containing peroxisomes with catalase activity. Hepatocytes were present for up to 2 months in congeneic recipients, the longest period of observation after transplantation. After normal microcarrier-attached hepatocytes were transplanted into allogeneic Gunn rats, bilirubin glucuronides were present in bile for 6 days. When congeneic Gunn rat recipients were used, bilirubin glucuronides were present in bile throughout the study (28 days); this was accompanied by reduction of serum bilirubin concentrations to nearly normal levels. After injection of normal hepatocytes into allogeneic NAR rats, plasma albumin concentration progressively increased for 6 days and then declined. In NAR recipients which were immunosuppressed with cyclosporin A, peak plasma albumin levels were reached in 14 days and persisted nearly at that level throughout the study (28 days).

New method of hepatocyte transplantation and extracorporeal liver support

A technique has been developed by the authors that allows hepatocyte attachment on collagen-coated microcarriers resulting in prolonged hepatocyte viability and function both in vivo and in vitro. Rat hepatocytes were obtained by portal vein collagenase perfusion. Intraperitoneally transplanted microcarrier-attached normal hepatocytes into congeneic Gunn rats were functioning 3-4 weeks later, as shown by the presence and persistence of conjugated bilirubin in recipient bile, sustained decrease in serum bilirubin, uptake of Tc99m-DESIDA, and morphologic criteria. Intraperitoneal transplantation of normal microcarrier-attached hepatocytes into genetically albumin deficient rats (NAR) resulted in marked increase in plasma albumin levels (6 days without and 21 days with Cyclosporin A immunosuppression). Microcarrier-attached hepatocytes transplanted after 2 weeks of storage at -80 C into congeneic Gunn rats were viable and functional as assessed by criteria outlined above. An extracorporeal liver perfusion system was developed using the microcarrier-attached hepatocytes that was capable of synthesizing and conjugating bilirubin and synthesizing liver-specific proteins.

Liver microsomal bilirubin UDP-glucuronyltransferase disturbances in bile duct ligated rats

The activity of bilirubin UDP-Glucuronyltransferase was determined in microsomes from normal and bile duct ligated rats. It was measured after 2 and 8 days following bile duct ligation and compared with normal rats. A decrease of 33% in the total enzyme activity was observed on day 2; a fall of 70% was founded on day 8. Bilirubin diglucuronide represented approximately 20% of total conjugates in both groups of cholestatic rats, as compared with 65% found in normals. It was concluded that bilirubin microsomal conjugating capacity is markedly altered during cholestasis. This can be attributed to microsomal membrane damage produced by stagnant bile.

Deconjugation of bilirubin conjugates and urobilin formation by conventionalized germ-free rats

The amounts of conjugated bilirubin and urobilins/urobilinogen were determined semiquantitatively in faeces of germ-free (GF) rats during GF condition and after conventionalization by oral administration of faeces suspension from conventional (CONV) rats. The amount of bilirubin conjugates, detected as their ethyl anthranilate azopigments, decreased rapidly 1 day after conventionalization. Thin-layer chromatography analysis of the corresponding faecal azopigment preparations showed that some azopigments started to disappear a few days after the conventionalization, indicating that their corresponding bilirubin conjugates were deconjugated by the bacteria in the intestine. On day 21 after conventionalization, only two azopigments were detected, namely the unconjugated and glucuronic acid conjugated dipyrroles of bilirubin, respectively, thus indicating the presence of only one bilirubin conjugate, the monoglucuronide. After 69 days no azopigments could be detected, indicating the total absence of conjugated bilirubin in these faeces samples. No urobilins were detected in faeces of the rats during their GF state, but these metabolites appeared in faeces one day after conventionalization and increased during a few days to a CONV level.

Methods for determination of conjugated bilirubin in rat faeces

Conjugated bilirubin was prepared from the faeces of germ-free (GF) rats by three different preparative methods. The bilirubin conjugate preparations were coupled with diazotized ethyl anthranilate and the formed ethyl anthranilate azopigments were quantified spectrophotometrically and separated by thin-layer chromatography (tlc). The most polar azopigment was purified by tlc and subjected to ammonolysis followed by tlc of the released saccaride. As a result of this procedure, only glucuronic acid was detected as the conjugating saccaride thus indicating that the most polar azopigment prepared from GF rat faeces was the delta ethyl anthranilate azopigment. Reference azopigments were prepared from GF rat small intestinal contents and subjected to separation by tlc. The azopigment pattern was very similar to the pattern obtained with the faecal azopigment preparations and a maximum of ten separated azopigment spots were detected. The findings indicated that, in addition to bilirubin glucuronides, other bilirubin conjugates with unknown structure are excreted with the faeces of GF rats. One of the preparative methods used for the preparation of conjugated bilirubin from GF rat faeces was tested on faeces from conventional (CONV) rats. From these preparations, no ethyl anthranilate azopigments were formed, thus indicating that faeces from CONV rats is devoid of conjugated bilirubin.

Glucuronide formation of various drugs in liver microsomes and in isolated hepatocytes from phenobarbital- and 3-methylcholanthrene-treated rats

Various substrates of rat liver microsomal UDP-glucuronosyltransferase were classified in vitro as preferred substrates of either 3-methylcholanthrene- or phenobarbital-inducible enzyme forms. Microsomal UDP-glucuronosyltransferase activities towards a third group of substrates (including oestrone, phenolphthalein, paracetamol and oxazepam) are not markedly altered by treatment with either 3-methylcholanthrene or phenobarbital. Some substrates of the 3-methylcholanthrene- and phenobarbital-inducible enzyme activities were selected to evaluate the importance of multiple enzyme forms for glucuronide formation in the intact cell. The metabolism of these compounds was compared in isolated hepatocytes from untreated controls and from rats treated with 3-methylcholanthrene (MC-hepatocytes) or phenobarbital (PB-hepatocytes). Glucuronidation of 1-naphthol and 3-hydroxybenzo[a]pyrene was chiefly enhanced in MC-hepatocytes (greater than 2-fold), whereas glucuronidation of chloramphenicol and bilirubin was chiefly enhanced in PB-hepatocytes. These observations are in agreement with differential induction of UDP-glucuronosyltransferase activities in vitro suggesting that, besides other factors such as cofactor supply, physiological activators, etc., the levels of the multiple enzyme forms are critically determining glucuronide formation in the intact cell.

Effect of spironolactone on bilirubin metabolism in rat liver and small intestinal mucosa

In vitro and in vivo experimental models were designed for the study of the effect of spironolactone (SP) on bilirubin metabolism in rat liver and small intestinal mucosa. In vitro studies included uptake of bilirubin by liver slices and intestinal sheets, determination of glucuronyltransferase activity in mucosal homogenates, and the handling of bilirubin by the isolated perfused liver after bilirubin overload. In vitro studies were carried out to measure the plasma disappearance rate of bilirubin and to determine the extent of bilirubin conjugation and biliary excretion of the pigment infused intravenously. The results obtained suggested that the mechanisms involved in the uptake of bilirubin by tissues were not influenced by SP pretreatment. Glucuronyltransferase activity in the small intestinal mucosa was significantly induced by SP, as previously observed in rat liver. Isolated perfused livers from SP-treated rats, as well as treated living rats, exhibited a greater than normal capacity for bilirubin excretion into bile at the expense of bilirubin diglucuronide. Conjugated bilirubin in the small intestinal mucosa of rats infused with unconjugated pigment was also increased after SP pretreatment. The results favoured the conclusion that SP is an inducer of bilirubin conjugation in the livers as well as in extrahepatic tissues, such as the small intestinal mucosa.

Bilirubin diglucuronide formation in intact rats and in isolated Gunn rat liver

Bilirubin diglucuronide (BDG) may be formed in vitro by microsomal UDP glucuronosyl transferase (EC 2.4.1.17)-mediated transfer of a second mole of glucuronic acid from UDP-glucuronic acid, or by dismutation of bilirubin monoglucuronide (BMG) to BDG and unconjugated bilirubin, catalyzed by an enzyme (EC 2.4.1.95) that is concentrated in plasma membrane-enriched fractions of rat liver. To evaluate the role of these two enzymatic mechanisms in vivo, [(3)H]bilirubin mono-[(14)C]glucuronide was biosynthesized, purified by thin-layer chromatography, and tracer doses were infused intravenously in homozygous Gunn (UDP glucuronyl transferase-deficient) rats or Wistar rats. Bilirubin conjugates in bile were separated by high-pressure liquid chromatography and (3)H and (14)C were quantitated. In Gunn rats, the (14)C:(3)H ratio in BDG excreted in bile was twice the ratio in injected BMG. In Wistar rats the (14)C:(3)H ratio in biliary BDG was 1.25 +/- 0.06 (mean +/- SEM) times the ratio in injected BMG. When double labeled BMG was injected in Wistar rats after injection of excess unlabeled unconjugated bilirubin (1.7 mumol), the (14)C:(3)H ratio in BDG excreted in bile was identical to the ratio in injected BMG. Analysis of isomeric composition of bilirubin conjugates after alkaline hydrolysis or alkaline methanolysis indicated that the bile pigments retained the IX(alpha) configuration during these experiments. The results indicate that both enzymatic dismutation and UDP glucuronyl transferase function in vivo in BDG formation, and that dismutation is inhibited by a high intrahepatic concentration of unconjugated bilirubin. This hypothesis was supported by infusion of [(3)H]bilirubin-monoglucuronide in isolated perfused homozygous Gunn rat liver after depletion of intrahepatic bilirubin by perfusion with bovine serum albumin (2.5%), and after bilirubin repletion following perfusion with 0.34 mM bilirubin. From 20 to 25% of injected radioactivity was recovered in BDG in bile in the bilirubin-depleted state; only 8-10% of radioactivity was in BDG in bile after bilirubin repletion. After infusion of [(3)H]bilirubin di-[(14)C]glucuronide in homozygous Gunn rats, 5-7% of the injected pigment was excreted in bile as BMG. The (14)C:(3)H ratio in the injected BDG was 10% greater than the (14)C:(3)H ratio in BMG excreted in bile. These results indicate that in vivo, dismutation rather than partial hydrolysis, is responsible for BMG formation. Incubation of [(3)H]bilirubin, BDG and a rat liver plasma membrane preparation resulted in formation of BMG (3.3 nmol/min per mg protein) indicating that dismutation is also reversible in vitro.

Separation of bilirubin species in serum and bile by high-performance reversed-phase liquid chromatography

A high-performance, reversed-phase liquid chromatographic (HPLC) procedure has been developed for the separation of at least three major bilirubin fractions in bile and four fractions in human serum. This procedure was unlike most others, in that serum was not totally deproteinized prior to injection onto the HPLC column; instead, serum was treated with an excess of sodium sulfate solution to precipitate primarily proteins larger than albumin. Injection of the filtered and diluted supernatant onto a reversed-phase column then resulted in the separation of the bilirubin species in a 24-min gradient elution run. Both the initial aqueous acidic mobile phase and the final isopropyl alcohol-based mobile phase contained 5% methoxyethanol (v/v) to facilitate elution of albumin still present in the treated sample. Bilirubin species eluting from the column were detected by absorbance at 450 nm. Results of a number of chromatographic separations of pathological sera indicated a wide variation in the relative proportions of the four bilirubin fractions observed. A correlation of the sum of the areas of the bilirubin peaks observed by HPLC was found with the total bilirubin value obtained by a standard reference procedure.

A low molecular weight binding protein for organic anions (Z protein) from human hepatic cytosol: purification and quantitation

Human Z protein from liver was purified to homogeneity. The protein has a molecular weight of 11,000 an an isoelectric point of pH 5.8. Circular dichroism spectra of Z protein-bilirubin (unconjugated and diglucuronide) complexes revealed two ellipticity extrema, a negative peak at 460 nm, and a positive peak at 410 nm. Human serum albumin had a higher affinity for bilirubin than did Z protein. Fluorescence studies showed the approximate association constants of this protein and bilirubin, bromosulfophthalein, and indocyanine green were 10(6) M-1, 10(5) M-1, and 10(6) M-1, respectively. Immunofluorescence studies revealed that Z protein was localized in the cytoplasm of hepatocytes, proximal tubular epithelium, and epithelial cells of the small intestine. Radioimmunoassay studies were done to assess the amount of Z protein in controls and in various liver diseases. The highest concentrations of Z protein were found in the liver, kidney, heart muscle, and small intestine, in that order. In cases of acute and chronic hepatitis, hepatic Z protein concentrations were generally decreased, whereas serum Z protein concentrations were increased. In contrast, both serum and hepatic Z protein concentrations were decreased in cases of constitutional hyperbilirubinemia.

High-performance liquid chromatography of bile pigments: application to the determination of unconjugated bilirubin in serum

A rapid, sensitive and specific method for the determination of unconjugated bilirubin in serum is described. Reversed-phase chromatography on short-chain alkylsilica (C2) or octadecylsilica (C18) with acetonitrile--dimethylsulphoxide--water as eluent is used for the separation of bilirubin. The method is applied to the analysis of bilirubin in patients with disorders associated with jaundice.

Analysis of bilirubin and bilirubin mono- and di-conjugates. Determination of their relative amounts in biological samples

1. A novel method for determination of the relative amounts of unconjugated bilirubin and sugar mono- and di-conjugates of bilirubin in biological samples, including serum, is described and illustrated by its application to the analysis of bilinoids in rat bile. 2. The method is based on specific conversion of the carbohydrate conjugates of bilirubin into the corresponding mono- or di-methyl esters by base-catalysed transesterification in methanol. Under the selected reaction conditions, unconjugated biliru-in remains intact and no dipyrrole exchange in the bilinoids is detectable; transesterification of bilirubin mono- or di-glucuronide is virtually complete (approx. 99%), and sponification is negligible (less than 1%); recovery of the pigments is approx. 95%. 3. The reaction products bilirubin and its methyl esters are separated by t.l.c. and determined spectrophotometrically; the two isomeric bilirubin-IX alpha monomethyl esters are separated and therefore can be determined individually. 4. Reference bilirubin mono- and di-methyl esters have been synthesized and characterized, and the two isomers of bilirubin-IX alpha monomethyl ester and bilirubin dimethyl ester were obtained individually, in crystalline form. 5. With this new method, virtually all bilinoids (over 99%) in normal rat bile have been found to be conjugated, with diconjugates (71%) predominating. A significantly increased proportion of monoconjugates is present in bile collected from heterozygous Gunn rats or from normal rats that were refused with large amounts of bilirubin.

Plasma bile pigment conjugation modalities in icterus syndromes of various origin

Plasma azopigments derived from conjugated bilirubin were analyzed by thin-layer chromatography according to HEIRWEGH et al. in 14 cases of obstructive jaundice and in 11 of acute hepatitis. The chromatographic patterns were compared with those obtained from azopigments derived from 8 normal bile samples. The plasma pigment patterns did not differ from those of the bile in number and chromatographic mobility of the spots. However, the quantitative percentages of the plasma azopigments were significantly modified: the alpha 0 fraction (free azodipyrrolic pigment) increased in both icteric syndromes, while the delta fraction (mainly glucuronide azopigment) decreased. Moreover, the behavior of two closed components of the delta group showed significant differences in both icteric syndromes. It can be postulated that the synthesis of bilirubin diconjugates decreases both in hepatocellular and cholestatic jaundice, while monoglucuronidated as well as saccharide and glucoside conjugates increase. In cholestatic jaundice the conjugation with glucuronic acid mainly takes place in the normal way, whereas compounds with different features are formed in hepatitis.

A new animal model with hyperbilirubinemia: the indigo snake

An unconjugated hyperbilirubinemia has been observed in all species of normal indigo snakes. The plasma clearance of large organic anions such as sulfobromophthalein and unconjugated bilirubin was markedly delayed when compared to other snake species. Endogenous bile flow and biliverdin and bilirubin excretory rates and the excretion of bile pigments after a bilirubin load were measured in various snakes. The indigo snake represents a new animal model in which to study mechanisms important to hepatic anion uptake and biliary transport.

Inaccuracies in measurement of conjugated and unconjugated bilirubin in bile with ethyl anthranilate diazo and solvent-partition methods

A criticial evaluation was made of the ethyl anthranilate diazo and two solvent-partition methods for the determination of conjugated and unconjugated bilirubin in human and rat bile. The ethyl anthranilate diazo reagent, which reacts only with conjugated bilirubin in serum, also diazotized a variable proportion of unconjugated bilirubin in bile and thus overestimated the concentration of monoconjugates. With the Weber-Schalm and modified Folsch solvent-partition methods applied to human or rat bile, 4--9% of added 14C-labelled unconjugated bilirubin partitioned with the conjugated bilirubin in the upper phase, and 4--9% of added 14C-labelled conjugated bilirubin partitioned into the lower phase. With dog bile, the spill-over of 14C-labelled bilirubin into the lower phase was 9--11%. Analysis of azopigments from the Weber-Schalm partition confirmed that over two-thirds of the bilirubin in the lower phase represents monoconjugates, principally the less-polar monoxylosides and monoglucosides. These solvent-partition methods thus overestimate the concentration of unconjugated bilirubin in bile.

Hepatic conversion of bilirubin monoglucuronide to diglucuronide in uridine diphosphate-glucuronyl transferase-deficient man and rat by bilirubin glucuronoside glucuronosyltransferase

The microsomal enzyme uridine diphosphate (UDP) glucuronate glucuronyltransferase (E.C. 2.4.1.17) catalyzes formation of bilirubin mono-glucuronide from bilirubin and UDPglucuronic acid. Bilirubin glucuronoside glucuronosyltransferase (E.C. 2.4.1.95), an enzyme concentrated in plasma membrane-enriched fractions of rat liver, converts bilirubin monoglucuronide to bilirubin diglucuronide. Bilirubin glucuronoside glucuronosyltransferase activity was studied in homogenates of liver biopsy specimens obtained from patients with the Crigler-Najjar syndrome (Type I) and in subcellular liver fractions of rats homozygous for UDP glucuronate glucuronyltransferase deficiency (Gunn strain). In patients with the Crigler-Najjar syndrome (Type I) and in Gunn rats, hepatic UDPglucuronate glucuronyltransferase activity was not measurable; however, bilirubin glucuronoside glucuronosyltransferase activity was similar to that in normal controls. The subcellular distribution of bilirubin glucuronoside glucuronosyltransferase activity in Gunn rat liver was similar to the distribution observed in normal Wistar rat liver.When bilirubin monoglucuronide was infused intravenously into Gunn rats, 29+/-5% of the conjugated bilirubin excreted in bile was bilirubin diglucuronide. After transplantation of normal Wistar rat kidney, which contained UDPglucuronate glucuronyltransferase activity, in Gunn rats, the serum bilirubin concentration decreased by 80% in 4 days. The major route of bilirubin removal was biliary excretion of conjugated bilirubin, approximately 70% of which was bilirubin diglucuronide. Although patients with the Crigler-Najjar syndrome (Type I) and Gunn rats lack UDP glucuronate glucuronyltransferase, their livers enzymatically convert bilirubin monoglucuronide to diglucuronide in vitro. Conversion in bilirubin monoglucuronide to diglucuronide was demonstrated in Gunn rats in vivo.

Twenty-five years of progress in bilirubin metabolism (1952-77)

This review deals with the development of our understanding of the chemistry of bilirubin and its glucuronide derivatives during the years 1952-1977. It examines the relation between haem metabolism and bilirubin formation and our present knowledge of hepatic transport of bilirubin. The heterogeneity of familial hyperbilirubinaemia is discussed.

Glucuronic acid conjugates of bilirubin-IXalpha in normal bile compared with post-obstructive bile. Transformation of the 1-O-acylglucuronide into 2-, 3-, and 4-O-acylglucuronides

Structures have been determined for bilirubin-IXalpha conjugates in freshly collected bile of normal rats, dogs and man and in post-obstructive bile of man and rats. The originally secreted conjugate has been characterized as azopigment (I), i.e. a 1-O-acyl-beta-d-glucopyranuronic acid glycoside. Conversion of the acetylated methyl ester of azopigment (I) into methyl 2,3,4-tri-O-acetyl-1-bromo-1-deoxy-beta-d-glucopyranuronate (V) indicates the pyranose ring structure for the carbohydrate and a C-1 attachment for the bilirubin-IXalpha acyl group. Alternative procedures for deconjugation of azopigment (I) and its derivatives are also described. In post-obstructive bile, the 1-O-acylglucuronide is converted into 2-, 3- and 4-O-acylglucuronides via sequential intramolecular migrations of the bilirubin acyl group. The following approach was utilized. (1) The tetrapyrrole conjugates were cleaved to dipyrrolic aniline and ethyl anthranilate azopigments, and the azopigments were separated as the acids or methyl esters. (2) The isomeric methyl esters were characterized by mass spectral analysis of the acetates and silyl ethers. (3) The free glycosidic function was demonstrated by 1-oxime and 1-methoxime derivative formation. (4) The position of the dipyrrolic O-acyl group was determined for the methyl esters by protecting the free hydroxyl groups of the glucuronic acid moieties as the acetals formed with ethyl vinyl ether and by further conversion of the carbohydrates into partially methylated alditol acetates. These were analysed by using g.l.c.-mass spectrometry. The relevance of the present results with regard to previous reports on disaccharidic conjugates is discussed. Details of procedures for the formation of chemical derivatives for g.l.c. and mass spectrometry have been deposited as Supplementary Publication SUP 50081 (15 pages) at the British Library Lending Division, Boston Spa, West Yorkshire LS23 7BQ, U.K., from whom copies can be obtained on the terms indicated in Biochem. J. (1978), 169, 5.

The fate of bilirubin-IXalpha glucuronide in cholestasis and during storage in vitro. Intramolecular rearrangement to positional isomers of glucuronic acid

1. In aqueous solution above pH7 bilirubin-IXalpha 1-O-acylglucuronide rapidly isomerizes to the non-C-1 glucuronides by sequential migration of the bilirubin acyl group from position 1 to positions 2, 3 and 4 of the sugar moiety. The transformations are enhanced by increasing the pH. Compared with the rates at 37 degrees C the transformations are rather slow at 0 degrees C. Virtually complete inhibition is observed at values below pH6. The isomerization at 25 degrees C and pH 7.4 is not affected by the presence in the solutions of a molar excess of human serum albumin. 2. Isomerization in bile kept at 37 degrees C at pH7.7-7.8 is probably non-enzymic, as the rates of change are similar to those observed under comparable conditions for aqueous solutions of glucuronides of bilirubin-1Xalpha and of azodipyrrole. 3. Analysis without delay of normal biles of man and rats collected at 0 degrees C over a maximum period of 10 min shows that the bilirubin-IXalpha mono- and di-glucuronides consist exclusively of the 1-O-acyl isomers. 4. The mixtures of the four positional isomers of bilirubin-IXalpha glucuronide found in freshly collected biles of man and rats with cholestasis probably originate from initially synthesized 1-O-acylglucuronide by the same mechanism of sequential migration as has been observed in aqueous solutions of conjugated bilirubin-IXalpha.

Hepatic accumulation and intracellular binding of conjugated bilirubin

After the intravenous injection of unconjugated [(3)H]bilirubin into normal Sprague-Dawley and Wistar R rats, radiolabeled bile pigments rapidly accumulated in the liver. By 1.5 min after injection, an average of 36% of the injected isotope was present in liver homogenates. Between 3 and 15 min, 37-64% of the total intrahepatic radiolabeled bilirubin was conjugated, as demonstrated by extraction of label into the polar phase of a solvent partition system. This indicates both rapid conjugation, and accumulation of conjugated bilirubin within the liver cell. Fluorometric determination of the dissociation constants of purified bilirubin and its mono- and diglucuronides for homogeneous preparations of two human and four rat glutathione S-transferases, including ligandin, revealed avid binding of all three bile pigments to this class of proteins. Hence, the observation that the intrahepatic bile pigment pool contains substantial amounts of conjugated bilirubin can be attributed to the high binding affinities observed. Thin-layer chromatographic analysis of the (3)H-pigments produced by p-iodoaniline diazotization of homogenates and cytosol demonstrated that the intrahepatic pool of conjugated bilirubin was almost exclusively monoglucuronide. Examination of radiolabeled bilirubin conjugates excreted in bile during the first 20 min after injection of [(3)H]bilirubin showed no preferential excretion of diglucuronide. These studies indicate that (a) both bilirubin and its monoglucuronide accumulate within the liver cell as ligands with the glutathione S-transferase; and (b) bilirubin diglucuronide does not significantly accumulate within the general intrahepatocellular pool of protein-bound bile pigments. The latter observation is compatible with the formation and excretion of bilirubin diglucuronide directly from the canalicular pool of the liver cell.

Conjugated and unconjugated bilirubins in bile of humans and rhesus monkeys. Structure of adult human and rhesus-monkey bilirubins compared with dog bilirubins

1. Bilirubin-IXalpha, -IXalpha diglucuronide, -IXalpha monoglucuronide, -IXalpha monoglucoside -IXalpha monoxyloside, a bilirubin-IXalpha diconjugate containing glucose and another unknown compound, and bilirubin-IXbeta are present in gall-bladder bile of adult human, rhesus monkey and dog. Dog bile normally also contains other bilirubin-IXalpha diconjugates, i.e. compounds containing two conjugating sugars such as glucuronic acid and glucose, glucuronic acid and xylose and glucose xylose. 2. Azopigments alphaF, alphaO, alpha2, alpha3, betax and delta derived from human and rhesus-monkey bilirubins are identical in their chemical composition with those obtained from the dog. 3. Azopigments alphaF and betax found in diazotized biles of adult humans, rhesus monkeys and dogs are products of unconjugated bilirubin-IXbeta. 4. Technical modifications of previously published procedures [Heirwegh, Fevery, Michiels, Van Hees & Compernolle, (1975) Biochem. J. 145, 185-199] were introduced which make it possible to separate the bilirubins, diazotize the separated bilirubins, extract the azopigments and chromatograph them in one working day (6-8h).

Unconjugated bilirubin and an increased proportion of bilirubin monoconjugates in the bile of patients with Gilbert's syndrome and Crigler-Najjar disease

Bilirubin pigments were studied in the bile of 20 normal adults, 25 patients with Gilbert's syndrome, 9 children with Crigler-Najjar disease, and 6 patients with hemolysis, to determine how a deficiency of hepatic bilirubin UDP-glucuronosyltransferase would affect the end products of bilirubin biotransformation. In the bile from patients with Gilbert's syndrome, a striking increase was found in the proportion of bilirubin monoconjugates (48.6+/-9.8% of total conjugates) relative to that in normal bile (27.2+/-7.8%). This increase was even more pronounced in children with Crigler-Najjar disease, in whom, even in the most severe cases, glucuronide could always be demonstrated in the bile. Furthermore, unconjugated bilirubin-IXalpha was unquestionably present in the bile of these children and amounted to 30-57% of their total bilirubin pigments (<1% in the controls). It was not possible to predict from the biliary bilirubin composition whether a child would respond to phenobarbital therapy or not. Bile composition was normal in patients with hemolysis, except when there was associated deficiency of hepatic glucuronosyltransferase. Therefore, the observed alterations were not a simple consequence of unconjugated hyperbilirubinemia. The present findings suggest that Crigler-Najjar disease represents a more pronounced expression than Gilbert's syndrome of a common biochemical defect. Hepatic bilirubin UDP-glucuronosyltransferase deficiency leads to decreased formation of diconjugates with an ensuing increase in the proportion of bilirubin monoconjugates in bile; in the most severe cases, an elevated content of biliary unconjugated bilirubin is also found.

The isolation and further characterization of the bilirubin tetrapyrroles in bile-containing human duodenal juice and dog gall-bladder bile

Bilirubin and its conjugates were extracted from either dog gall-bladder bile or bile-containing human duodenal juice into chloroform containing 10mm-tetraheptylammonium chloride. The intact bilirubin tetrapyrroles were then separated by t.l.c. Structural elucidation was made after coupling of the individual pigments with diazonium salts. Four azopigments were detected: azopigment alpha(o) or dipyrrolic azobilirubin; azopigment delta or dipyrrolic azobilirubin monoglucuronide; azopigment alpha(3) or dipyrrolic azobilirubin monoglucoside; and, from dog gall-bladder bile, azopigment alpha(2). The last conjugate required further verification of its structure. After methanolysis, it was shown by combined g.l.c.-mass spectrometry to contain xylose in a 1:1 molar ratio with the azopigments of bilirubin. Human bile contained 86% bilirubin diglucuronide, 7% bilirubin monoglucuronide monoglucoside diester, 4% bilirubin monoglucuronide and 3% bilirubin. Dog gall-bladder bile had a considerably different composition; it contained 47% bilirubin diglucuronide, 40% bilirubin monoglucuronide monoglucoside diester, 8% bilirubin monoglucuronide, 4% bilirubin diglucoside, 1-2% bilirubin and traces of conjugates containing xylose. The total bilirubin content and proportions of the conjugates did not change in bile that was frozen and stored at -20 degrees C under N(2), whereas in the chloroform/tetraheptylammonium chloride extract, similarly stored, total pigment was slowly lost and the diglucuronide conjugate converted into the monoglucuronide.

Comparison in different species of biliary bilirubin-IX alpha conjugates with the activities of hepatic and renal bilirubin-IX alpha-uridine diphosphate glycosyltransferases

The bilrubin-IXalpha conjugates in bile and the activities of bilirubin-IX alpha--UDP-glycosyltransferases in liver and kidney were determined for ten species of mammals and for the chicken. 1. In the mammalian species, bilirubin-IX alpha glucuronide was the predominant bile pigment. Excretion of neutral glycosides was unimportant, except in the cat, the mouse, the rabbit and the dog, where glucose and xylose represented 12--41% of total conjugating groups bound to bilirubin-IX alpha. In chicken bile, glucoside and glucuronide conjugates were of equal importance. They probably represent only a small fraction of the total bile pigment. 2. The transferase activities in liver showed pronounced species variation. This was also apparent with regard to activation by digitonin, pH optimum and relative activities of transferases acting on either UDP-glucuronic acid or neutral UDP-sugars. 3. Man, the dog, the cat and the rat excrete bilirubin-IX alpha largely as diconjugated derivatives. In general, diconjugated bilirubin-IX alpha could also be synthesized in vitro with liver homogenate, bilirubin-IX alpha and UDP-sugar. In contrast, for the other species examined, bilirubin pigments consisted predominantly of monoconjugated bilirubin-IX alpha. Synthesis in vitro with UDP-glucuronic acid, UDP-glucose or UDP-xylose as the sugar donor led exclusively to the formation of monoconjugated bilirubin-IX alpha. 4. The transferase activities in the kidney were restricted to the cortex and were important only for the rat and the dog. No activity at all could be detected for several species, including man. 5. Comparison of the transferase activities in liver with reported values of the maximal rate of excretion in bile suggests a close linkage between conjugation and biliary secretion of bilirubin-IX alpha.