Analysis of bilirubins in biological fluids by extraction and thin-layer chromatography of the intact tetrapyrroles: application to bile of patients with Gilbert's syndrome, hemolysis, or cholelithiasis

The relationship between UGT1A1 gene & various diseases and prevention strategies

UDP-glucuronyltransferase 1A1 (UGT1A1) is a member of the Phase II metabolic enzyme family and the only enzyme that can metabolize detoxified bilirubin. Inactivation and very low activity of UGT1A1 in the liver can be fatal or lead to lifelong Gilbert's syndrome (GS) and Crigler-Najjar syndrome (CN). To date, more than one hundred UGT1A1 polymorphisms have been discovered. Although most UGT1A1 polymorphisms are not fatal, which diseases might be associated with low activity UGT1A1 or UGT1A1 polymorphisms? This scientific topic has been studied for more than a hundred years, there are still many uncertainties. Herein, this article will summarize all the possibilities of UGT1A1 gene-related diseases, including GS and CN, neurological disease, hepatobiliary disease, metabolic difficulties, gallstone, cardiovascular disease, Crohn's disease (CD) obesity, diabetes, myelosuppression, leukemia, tumorigenesis, etc., and provide guidance for researchers to conduct in-depth study on UGT1A1 gene-related diseases. In addition, this article not only summarizes the prevention strategies of UGT1A1 gene-related diseases, but also puts forward some insights for sharing.

Mechanism of bilirubin elimination in urine: insights and prospects for neonatal jaundice

Despite a century of research, bilirubin metabolism and the transport mechanisms responsible for homeostasis of bilirubin in serum remain controversial. Emerging evidence on the hepatic membrane transporters and inherited disorders of bilirubin metabolism have contributed to a greater understanding of the various steps involved in bilirubin homeostasis and its associated excretory pathways. We discuss these recent research findings on hepatic membrane transporters and evaluate their significance on the newborn bilirubin metabolism and excretion. New insights gained speculate that a proportion of conjugated bilirubin is excreted via the renal system, as an alternative to the intestinal excretion, even in normal physiological jaundice with no associated pathological concerns. Finally, this paper discusses the clinical relevance of targeting the altered renal excretory pathway, as bilirubin in urine may hold diagnostic importance in screening for neonatal jaundice.

Glucuronides in the gut: Sugar-driven symbioses between microbe and host

The intestinal milieu is astonishingly complex and home to a constantly changing mixture of small and large molecules, along with an abundance of bacteria, viral particles, and eukaryotic cells. Such complexity makes it difficult to develop testable molecular hypotheses regarding host-microbe interactions. Fortunately, mammals and their associated gastrointestinal (GI) microbes contain complementary systems that are ideally suited for mechanistic studies. Mammalian systems inactivate endobiotic and xenobiotic compounds by linking them to a glucuronic acid sugar for GI excretion. In the GI tract, the microbiota express β-glucuronidase enzymes that remove the glucuronic acid as a carbon source, effectively reversing the actions of mammalian inactivation. Thus, by probing the actions of microbial β-glucuronidases, and by understanding which substrate glucuronides they process, molecular insights into mammalian-microbial symbioses may be revealed amid the complexity of the intestinal tract. Here, we focus on glucuronides in the gut and the microbial proteins that process them.

Lithogenesis and bile metabolism

Gallstone disease exacts a considerable financial and social burden worldwide leading to frequent physician visits and hospitalizations. Based on their composition, gallstones are categorized as cholesterol, black pigment, and brown pigment, with each category having a unique structural, epidemiologic, and risk factor profile. Cholesterol crystal formation requires the presence of one or more of the following: (a) cholesterol supersaturation, (b) accelerated nucleation, or (c) gallbladder hypomotility/bile stasis. Some risk factors for cholesterol stones include age, gender, genetics, obesity, rapid weight loss, and ileal disease. Generally, pigment stones are formed by the precipitation of bilirubin in bile, with black stones associated with chronic hemolytic states, cirrhosis, Gilbert syndrome, or cystic fibrosis, and brown stones associated with chronic bacterial or parasitic infections.

Coinheritance of Gilbert syndrome-associated UGT1A1 mutation increases gallstone risk in cystic fibrosis

The prevalence of "black" pigment gallstones is increased in patients with cystic fibrosis (CF). Bile acid malabsorption with augmented bilirubin uptake from the intestine and the development of "hyperbilirubinbilia" have been proposed as key factors in gallstone formation in CF patients. We have now tested the hypothesis that the coinheritance of the common UGT1A1 promoter mutation associated with Gilbert syndrome is an additional lithogenic risk factor for gallstone formation in CF. Our results show that patients with CF and gallstones are significantly more likely to carry at least one Gilbert UGT1A1 allele compared with stone-free patients (OR 7.3; P = .042) and that these carriers display significantly higher serum levels of unconjugated bilirubin (P = .002). In conclusion, the Gilbert UGT1A1 allele increases the risk of gallstone formation in CF. This genetic association supports the current concept for gallstone formation in CF and suggests that genetic and exogenous sources contributing to hyperbilirubinbilia might be lithogenic in CF patients.

Unconjugated bilirubin in human bile: the nucleating factor in cholesterol cholelithiasis?

AIMS

To investigate the concentrations of bilirubin, bilirubin conjugates, phospholipid, and cholesterol in the gall bladder bile obtained at surgery from patients with and without cholesterol gallstones.

METHODS

Gall bladder bile was collected during surgery, by puncture, from 20 patients with gallstones undergoing routine cholecystectomy and from eight patients with normal liver blood tests. Concentrations of bilirubin, bilirubin conjugates, phospholipid, and cholesterol were measured using standard procedures.

RESULTS

The proportion of total bilirubin that was unconjugated was significantly higher in the bile from patients with stones than in bile from control patients, whether or not the bile from either group was saturated with cholesterol or not. Indeed, the mean concentration of cholesterol was significantly higher in control bile samples.

CONCLUSION

The presence of stones was more closely related to the proportion of unconjugated bilirubin than to the degree of saturation of bile with cholesterol. Bilirubin and its metabolites probably play an important part in the formation of cholesterol gallstones.

[Micelle-mediated extraction for concentrating conjugated bilirubin in urine]

An extraction method based on the phase separation of aqueous micellar solutions of n-octyl-beta-D-thioglucoside (OTG) was applied to the concentrating conjugated bilirubin in urine. The analyte in sample solutions could be efficiently concentrated into a small volume of surfactant-rich phase, while hydrophilic matrix components including urinary protein, ascorbic acid, and saccharide remained in the aqueous phase. The concentrated OTG negligibly affected the diazo reaction and the subsequent spectrophotometric detection. Conjugated bilirubin was successfully determined in the concentration range from 0.05 microgram/ml to 5 micrograms/ml with a 96-well microplate reader absorption spectrophotometer.

Inhibitory effect of bilirubin on complement-mediated hemolysis

We investigated the in vitro action of the bile pigments, unconjugated bilirubin (UB) and bilirubin monoglucuronide (BMG) on complement (C) cascade reaction. Both UB and BMG inhibited hemolysis in the classical pathway (CP) in a dose-dependent manner at low micromolar concentrations, UB showing a stronger effect than BMG. The analysis of the action of UB on the hemolytic activity of the C1, C4, C2 and C-EDTA components of the C cascade revealed that the C1 step was the most inhibited. An enzyme immunoassay was developed to evaluate the effect of UB on the binding of C1q, one of the subcomponents of C1, to human IgM and IgG. The study demonstrated that the unconjugated pigment interferes both the C1q-IgM and -IgG interactions, thus tentatively explaining the inhibitory action of UB on hemolytic activity of C1. We conclude that the anti-complement effect of UB is mainly exerted on the C1 component, the recognition unit of CP. The potential clinical implication of the reported effects in hyperbilirubinemia is discussed.

Coinheritance of Gilbert Syndrome Increases the Risk for Developing Gallstones in Patients With Hereditary Spherocytosis

The precocious formation of bilirubinate gallstones is the most common complication of hereditary spherocytosis (HS), and the prevention of this problem represents a major impetus for splenectomy in many patients with compensated hemolysis. Because Gilbert syndrome has been considered a risk factor for gallstone formation, there are reasons for postulating that the association of this common inherited disorder of hepatic bilirubin metabolism with HS could increase cholelithiasis. To test this hypothesis, 103 children with mild to moderate HS who, from age 1, have undergone a liver and biliary tree ultrasonography every year, were retrospectively examined. The 2-bp (TA) insertion within the promoter of the uridine diphosphate-glucuronosyltransferase gene (UGT1A1), associated with Gilbert syndrome, was screened. The risk of developing gallstones was statistically different among the 3 groups of patients: homozygotes for the normal UGT1A1 allele, heterozygotes, and homozygotes for the allele with the TA insertion. Fitting a Cox regression model, in fact, a statistically significant hazard ratio of 2.19 (95% confidence interval: 1.31 to 3.66) was estimated from one to the next of these genetic classes. The individual proneness to form gallstones from TA insertion in the TATA-box of the UGT1A1 promoter should be considered during the follow-up of patients with HS. Although patients with HS were the only ones studied, extrapolating these data to patients who have different forms of inherited (eg, thalassemia, intraerythrocytic enzymatic deficiency) or acquired (eg, autoimmune hemolytic anemia, hemolysis from mechanical heart valve replacement) chronic hemolysis can be warranted.

Probing the conformation of bilirubins with monopropionic analogs: a biological, spectroscopic, and molecular modeling study

The in vivo metabolism of a bilirubin analog substituted with a propionic acid chain in C8 (5) showed that it is excreted in bile conjugated with glucuronic acid, while a positional isomer substituted with a propionate in C7 (6) is excreted in bile without conjugation. A conformational analysis employing an optimized Monte Carlo method and a mixed Monte Carlo/stochastic dynamics reveals that isomer 5 adopts a 'ridge tile' conformation, stabilized by the presence of three intramolecular hydrogen bonds. On the contrary, isomer 6 exhibits a more closed structure, where impairment in the formation of at least one of the hydrogen bonds occurs. These theoretical predictions agree well with 1H NMR, 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.

Bilirubin glucuronidation by intact Gunn rat fibroblasts expressing bilirubin UDP-glucuronosyltransferase

Crigler-Najjar (CN) disease is an inherited disorder of bilirubin metabolism. The disease is caused by a deficiency of the hepatic enzyme bilirubin UDP-glucuronosyltransferase (B-UGT). Patients with CN disease have high serum levels of the toxic compound, unconjugated bilirubin. The only defect in bilirubin metabolism of CN patients is the absence of B-UGT activity. The transplantation of cells able to glucuronidate bilirubin should therefore lower serum bilirubin levels. The Gunn rat is the animal model of CN disease. Primary Gunn rat fibroblasts (GURF) were transduced with a recombinant retrovirus, capable of transferring B-UGT cDNA. A cell line was obtained expressing B-UGT at a level comparable to hepatocytes. Bilirubin added to the culture medium of these cells was glucuronidated and excreted. The B-UGT activities of transduced GURF and freshly isolated Wistar hepatocytes were compared at different bilirubin concentrations. The specific B-UGT activities of these two cell types were comparable when physiological bilirubin concentrations (5-10 microM) were present in the culture media. At higher bilirubin concentrations (20-80 microM) the hepatocytes were more active than the transduced GURF. We conclude that with the addition of only one enzyme (B-UGT) fibroblasts can perform the complete set of reactions necessary for bilirubin glucuronidation. The difference in B-UGT activity between transduced GURF and hepatocytes at 20-80 microM bilirubin can be explained by lower UDP-glucuronic acid and glutathione S-transferase levels in GURF. Our findings also indicate that these cells could be used to develop extrahepatic gene therapy for CN disease.

Discrimination between Crigler-Najjar type I and II by expression of mutant bilirubin uridine diphosphate-glucuronosyltransferase

Crigler-Najjar (CN) disease is classified into two subtypes, type I and II. The molecular basis for the difference between these types is not well understood. Several mutations in the bilirubin UDP-glucuronosyl-transferase (B-UGT) gene of six CN type I and two CN type II patients were identified. Recombinant cDNAs containing these mutations were expressed in COS cells. B-UGT activity was measured using HPLC and the amount of expressed protein was quantitated using a sandwich ELISA. This enabled us to determine the specific activities of the expressed enzymes. All type I patients examined had mutations in the B-UGT1 gene that lead to completely inactive enzymes. The mutations in the B-UGT1 gene of patients with CN type II only partially inactivated the enzyme. At saturating concentrations of bilirubin (75 microM) CN type II patient A had 4.4 +/- 2% residual activity and CN type II patient B had 38 +/- 2% residual activity. Kinetic constants for the glucuronidation of bilirubin were determined. The affinities for bilirubin of B-UGT1 expressed in COS cells and B-UGT from human liver microsomes were similar with Km of 5.1 +/- 0.9 microM and 7.9 +/- 5.3 microM, respectively. B-UGT1 from patient B had a tenfold decreased affinity for bilirubin, Km = 56 +/- 23 microM. At physiological concentrations of bilirubin both type II patients will have a strongly reduced conjugation capacity, whereas type I patients have no B-UGT activity. We conclude that CN type I is caused by a complete absence of functional B-UGT and that in CN type II B-UGT activity is reduced.

Pathogenesis of gallstones

Gallstones form as a result of many disorders. Unphysiologic supersaturation, generally from hypersecretion of cholesterol, is essential for the formation of cholesterol gallstones. The other common abnormalities of the hepatobiliary system in gallstone patients are accelerated nucleation, gallbladder hypomotility, and the accumulation of mucin gel. An attempt is made here to relate hypersecretion of cholesterol and biliary supersaturation to the molecular basis of the associated phenomena. Supersaturation of bile with calcium hydrogen bilirubinate, the acid calcium salt of unconjugated bilirubin, is essential for pigment gallstone formation, but its magnitude remains undefined in model systems. Nucleation and the precipitation of calcium hydrogen bilirubinate with the polymerization of the pigment in the gallbladder, together with the deposition of the inorganic salts, calcium carbonate and phosphate, result in black pigment gallstone formation. On the basis of ex vivo muscle studies, gallbladder hypomotility is unlikely in patients with black pigment stones but is invariably present in patients with cholesterol stones. Pigment supersaturation in the gallbladder is the result of hepatic hypersecretion of bilirubin conjugates in hemolytic disorders and possibly enterohepatic cycling of unconjugated bilirubin in nonhemolytic states. Less common is bile salt hyposecretion from impaired synthesis in constitutional disorders and cirrhosis, and uncompensated interruption of the enterohepatic circulation in ileal dysfunction syndromes. Bile salt deficiency causes incomplete solubilization of unconjugated bilirubin and impaired binding of calcium ions. Stasis and anaerobic bacterial infection are responsible for brown pigment stones, which usually form in the bile ducts. In addition to the precipitation of calcium hydrogen bilirubinate that remains unpolymerized, there is also the deposition of the calcium salts of saturated fatty acids and free bile acids, both of which are the result of bacterial enzymatic hydrolysis of biliary lipids.

Therapeutic approaches to the problem of biliary sludge and gallstone formation during total parenteral nutrition

Prolonged total parenteral nutrition is associated with the development of biliary sludge, which consists of super-saturated bile containing cholesterol crystals, bilirubin granules and a very high concentration of mucin glycoprotein. Reduced gallbladder contractility in TPN patients appears to be essential for the pathogenesis of sludge, which represents an important stage in the formation of gallstones, a common and well recognised complication of TPN. Possible approaches to the prevention of these biliary complications of TPN include: 1) inhibition of prostaglandin mediated mucin hypersecretion with aspirin, NSAIDs or possibly by n-3 essential fatty acids; 2) stimulation of gallbladder contractility by early oral feeding or the use of CCK; and 3) reduction of cholesterol saturation and mucin secretion by ursodeoxycholic acid.

Non-mucin proteins in the matrix of human cholesterol gallstones

Human cholesterol gallstones contain a pigmented organic matrix that may originate from biliary sludge. The cholesterol gallstone matrix contains mucin, bile pigments, and calcium salts. The goal of this study was to examine whether non-mucin proteins are present in the matrix of cholesterol gallstones. Matrix was prepared from cholesterol gallstones from 18 patients. Proteins were identified by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and by molecular sieve high-performance liquid chromatography (HPLC). Two proteins were present in each gallstone and migrated with or just adjacent to standards of bovine serum albumin on SDS-PAGE. Several additional lower molecular weight proteins were identified, but not in every gallstone. Protein fractions contained visible pigment after chloroform extraction, and pigment co-eluted with proteins on HPLC, suggesting binding of pigments to proteins in the matrix. We conclude that low molecular weight proteins are present in the cholesterol gallstone matrix. The major protein appears to be serum albumin, although definitive identification has not been established. The origin of these matrix proteins and their possible significance in the pathogenesis of cholesterol cholelithiasis is unknown.

The differential diagnosis of Crigler-Najjar disease, types 1 and 2, by bile pigment analysis

Phenobarbital response, bile pigment composition, and the fractional biliary excretion ratio of bilirubin were studied in nine children with Crigler-Najjar disease. In five children, serum bilirubin levels decreased during phenobarbital treatment by 26% or more and the pigment composition in bile changed with a decrease in the proportion of unconjugated bilirubin from 33% +/- 12% to 13% +/- 1% and an increase in monoconjugates and diconjugates from 57% +/- 14% and 10% +/- 2%, respectively, to 72% +/- 4% and 16% +/- 3%. In four children, serum bilirubin levels did not change significantly during phenobarbital treatment. In these patients, bile pigments comprised 91% +/- 10% unconjugated bilirubin, 9% +/- 11% monoconjugates, and 1% +/- 1% diconjugates. On the basis of these differences, the former group can be classified as having type 2 Crigler-Najjar disease and the latter, type 1. Bile pigment analysis in parents of patients with Crigler-Najjar disease showed an increased proportion of monoconjugates in at least one of the partners in three of four couples tested, despite normal serum bilirubin levels. Serum bilirubin levels were about the same in type 1 and 2 patients and amounted to 236 +/- 62 mumol/L and 214 +/- 82 mumol/L, respectively. In addition the fractional bilirubin excretion ratio, calculated as the ratio ([bilirubin in bile]/[bilirubin in serum])/([bile acid in bile]/[bile acid in serum]) could not differentiate between these two groups. However, there was a 10-fold and 100-fold difference of this ratio between patients with Crigler-Najjar disease and those with Gilbert's syndrome and between patients with Crigler-Najjar disease and controls. The fractional bilirubin excretion ratio proved an excellent tool to differentiate between Gilbert's syndrome and Crigler-Najjar disease, whereas Crigler-Najjar disease types 1 and 2 could be differentiated on the basis of bile pigment analysis.

Subfractionation of serum bilirubins by alkaline methanolysis and thin-layer chromatography. An aid in the differential diagnosis of icteric diseases

The determination of direct and indirect-reacting bilirubin fractions by diazo procedures does not allow a definite diagnosis of icteric diseases. Therefore, the clinical relevance of serum bilirubin subfractionation by alkaline methanolysis and subsequent thin-layer chromatography (AM-TLC) was evaluated. Esterified bilirubins could be detected and quantitated in all serum samples investigated. The ratio of serum esterified to total bilirubin was 10-28% in 60 healthy adults (mean 17 +/- 5% S.D.), 1-11% in 77 patients with Gilbert's syndrome (mean 6 +/- 2%), and 2 and 3%, respectively, in two patients with Crigler-Najjar disease type II. The difference was highly significant (p less than 0.001) and the overlap was restricted to three of 139 individuals. The ratio of esterified to total bilirubin was similar to that obtained with HPLC when corrected for with a blank run. The absolute concentration of bilirubin esters in serum from Gilbert's syndrome patients was similar to that from healthy controls, but the unconjugated pigment was increased. In patients with chronic haemolysis (n = 9) and chronic persistent hepatitis (n = 12), the hyperbilirubinaemia consisted of a proportional increase of both unconjugated and esterified bilirubin. As such, the ratio of conjugated to total bilirubin was not significantly different from control values. Patients with acute hepatitis during the first (n = 18) and third ('remission') week of the disease (n = 15), liver cirrhosis (n = 34), and extrahepatic cholestasis (n = 20) predominantly showed an increase in bilirubin conjugates.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of uridine diphosphate glucuronosyltransferase activity on the maximal secretion rate of bilirubin conjugates in the rat

It is generally accepted that biliary secretion is rate-limiting for the plasma-to-bile transport of a saturating load of bilirubin. Previous studies from this laboratory have suggested a relationship between the hepatic bilirubin uridine diphosphate glucuronosyltransferase activity and the apparent maximal rate of bilirubin secretion (excretory transport maximum). The present study was undertaken to further investigate this relationship in rats with a wide range of transferase levels and to analyze the effects of transferase activity on the formation of bilirubin monoglucuronides and diglucuronides in vivo and in vitro. Animals with moderately decreased enzyme activity still showed a near-normal excretory transport maximum but decreased fractional amounts of conjugated bilirubins in plasma and liver and a decreased ratio of bilirubins diconjugates to monoconjugates in bile, liver, and plasma. A more pronounced decrease in the level of transferase activity yielded lower excretory transport maximum values as well. Enhanced transferase activities were obtained by pretreatment with a series of enzyme-inducing agents, usually at dosages not influencing bile flow. An enhanced transferase activity produced significant increases in bilirubin excretory transport maximum, decreased concentrations of both unconjugated and conjugated bilirubins in plasma, and an increased ratio of diconjugates to monoconjugates in bile and in liver. In all animals, the ratio of disconjugates to monoconjugates observed in bile was correlated with the ratio found after incubation of liver homogenates in vitro at low concentrations of bilirubin substrate. Overall, the relationship between bilirubin excretory transport maximum and uridine diphosphate glucuronosyltransferase activity can best be described by a hyperbolic curve. At "saturation" of the excretory transport maximum values, no increase of conjugates in liver or in plasma could be observed, suggesting that not the biliary secretion, per se, but rather the conjugation rate in vivo is rate-limiting. The latter seems lower than the in vitro assayed enzyme activity. The present investigations point to an equilibration of bilirubin pigments between plasma, liver, and bile. The in vivo conjugation rate can be estimated from the in vitro assay (but not at high enzyme activities) and determines the maximal biliary secretion rate, the ratio of diconjugates to monoconjugates in the three compartments studied, and the relative amount of conjugates in plasma. Our studies suggest that the conjugation rate in vivo rather than the biliary secretion step is the major determinant of the maximal bilirubin secretion rate.

Urobilinogen-i is a major derivative of bilirubin in bile of homozygous Gunn rats

Gunn rats lack bilirubin UDP-glycosyltransferases, but diazo-negative derivatives of bilirubin have been described in their bile. In order to investigate this alternative disposal of bilirubin, crude bile samples from Gunn and Wistar rats were directly analysed by h.p.l.c. Besides bilirubin (in Gunn rats) or its glycosides (in Wistar rats), two major compounds were detected. A yellow one corresponded to the previously documented vitamin B-2 and was equally prominent in Gunn rats or Wistar-rat bile. The other compound was colourless, but on standing in contact with air it was spontaneously oxidized to a pinkish-yellow pigment. It was far more prominent in Gunn-rat bile. Analysis of bile obtained after intravenous injection of [14C]bilirubin to Gunn rats demonstrated that this compound was highly labelled. Freezing and thawing of the bile resulted in the formation of a series of diazo-negative derivatives, demonstrating that the original compound was quite labile. Spectral (adsorption and fluorescent) and chromatographic (h.p.l.c., t.l.c. and paper chromatography) analysis of the oxidized form of the labelled compound allowed its identification as urobilin-i. The colourless compound secreted in bile was urobilinogen-i. Administration of neomycin and bacitracin to Gunn rats or gut resection suppressed the biliary excretion of urobilinogen and thus confirmed its intestinal origin. Urobilinogen seems thus to represent the major bilirubin derivative present in Gunn-rat bile. Its breakdown products might represent the so-far-unidentified diazo-negative polar bilirubin derivatives. Since only a small amount of bilirubin is present in Gunn-rat bile, the urobilinogen formed in the intestinal lumen seems to be derived from bilirubin reaching the gut via routes other than the biliary one.

Proportion of conjugated bilirubin in bile in relation to hepatic bilirubin UDP-glucuronyltransferase activity

To elucidate the diagnostic relevance of biliary conjugated bilirubin, biliary bilirubin from normal volunteers (NV), patients with Gilbert's syndrome (GS) and Crigler-Najjar syndrome type II (C-N II), and from various rat strains was fractionated. Biliary bilirubin diglucuronide (BDG) was present at lower levels, and bilirubin monoglucuronide (BMG) and unconjugated bilirubin were present at higher levels in GS and C-N II compared with NV, which is consistent with decreased hepatic bilirubin UDP-glucuronyltransferase activity (BGTA). The level of biliary BDG was higher in Wistar-Kyoto rats and lower in heterozygous (Jj) Gunn rats than in SD and Wistar rats. The hepatic BGTA level in heterozygous (Jj) Gunn rats was decreased to 60% of that in Wistar rats, in accordance with decreased biliary BDG. On the other hand, BGTA in Wistar-Kyoto rats whose biliary BDG level was high, was not different from that of Wistar and SD rats. Thus, a correlation between BGTA and biliary bilirubin fractions may not exist on some occasions.

Spontaneous formation of pigmentary precipitates in bile salt-depleted rat bile and its prevention by micelle-forming bile salts

During studies on the effect of bile salt-pool depletion in the bile-fistula rat (adult male Sprague-Dawley), the spontaneous formation of an orange-brown precipitate was noted. The nature of this phenomenon and its relationship to BS and calcium concentration was investigated in depth. Bile from 18 animals was collected in the dark into transparent tubes containing sodium azide, ascorbic acid, and glucaro-1,4-lactone. The tubes were flushed with nitrogen, sealed, and incubated at 37 degrees C. The pigmentary precipitate formed in all the bile salt-depleted (less than 3-5 mM) bile samples (i.e., those collected after 5-7 h of external biliary drainage), but not in bile salt-rich biles. It appeared within 30-240 min after collection, both in bile samples collected at room temperature and at 37 degrees C, initially as a pale flocculation and then slowly sedimenting to form, after centrifugation, a solid, dark-orange pellet. There were no pH changes during incubation, and bile cultures were negative. Under polarizing microscopy, the precipitate appeared amorphous, and there was no evidence of birefringence. High-performance liquid chromatography showed that unconjugated bilirubin was the prevalent pigmentary component, but significant amounts of monoconjugated bilirubin also coprecipitated. Lipid chemistry showed the presence of lecithin (80.1% of total lipids), which was rich in palmitoyl and linoleoyl fatty acids, and of fatty acids (predominantly palmitic and oleic). Infrared spectroscopy and x-ray diffraction showed the presence of calcium bilirubinate and palmitate. In-vivo replenishment of the bile salt pool by intravenous infusion of either taurocholate or taurochenodeoxycholate (1 mumol/min) completely prevented the pigmentary precipitation. In vitro experiments showed inhibition of the precipitate formation by the addition of individual bile salt in concentrations approximating their critical micellar concentration. Precipitate formation was hastened by the addition of calcium chloride (4-12 mM), but only in bile salt-depleted biles. As the composition of the precipitate closely resembles that of human brown-pigment stones and sludge, these findings may provide new insights into an understanding of the pathogenesis of pigment gallstone disease.

Cellular uptake of conjugated bilirubin and sulfobromophthalein (BSP) by the human hepatoma cell line Hep G2 is mediated by a membrane BSP/bilirubin binding protein

Cellular influx kinetics of 4-50 microM bilirubin diglucuronide and sulfobromophthalein (BSP) by the human hepatoma cell line Hep G2 was examined at 37 degrees C. In confluent monolayer cultures, cellular influx of increasing concentrations of conjugated bilirubin and BSP revealed similar saturation kinetics with Km values of 9.9 and 12.1 microM, and Vmax values of 0.512 and 0.473 nmol.mg cell protein-1.min-1, respectively. Uptake of [3H]bilirubin diglucuronide was competitively inhibited by unlabeled BSP, and was temperature dependent with maximal cellular influx rates at 37 degrees C. When the confluent monolayer cultures were pretreated with a monospecific antibody to the rat liver BSP/bilirubin binding membrane protein, initial uptake rates of conjugated and unconjugated bilirubin as well as of BSP were significantly inhibited, whereas uptake of oleate was not affected. Furthermore, immunoblot analysis of the homogenate of Hep G2 cells with the same antibody revealed predominant reactivity with a 55 kDa protein. These data suggest that cellular uptake of bilirubin and related cholephilic organic anions by the human hepatoma cell line Hep G2 is mediated by a specific 55 kDa membrane BSP/bilirubin binding protein.

Cellular influx of sulfobromophthalein by the biliary epithelium carcinoma cell line Sk-Cha-1 reveals kinetic criteria of a carrier-mediated uptake mechanism

Cellular uptake of the cholephilic organic anion sulphobromophthalein (BSP) by the human biliary epithelium carcinoma cell line Sk-Cha-1 was examined at 37 degrees C. In confluent monolayer cultures the cellular influx rate of increasing concentrations of [35S]BSP followed saturation kinetics with a Km value of 18 microM and a Vmax value of 243 pmol.min-1.mg protein-1. Uptake of [35S]BSP was competitively inhibited by the presence of bilirubin diglucuronide, but not by taurocholate or cholate. Furthermore, uptake was temperature dependent with maximal cellular influx rates at 37 degrees C.

Chromatographic analysis and structure determination of biliverdins and bilirubins

Recent applications of thin-layer chromatographic (TLC) and high-performance liquid chromatographic (HPLC) procedures has revealed an unexpected wide variety of naturally occurring unconjugated and conjugated bilirubins. Biliverdins seems to occur only in unconjugated forms, mainly as the IX alpha isomer. Several synthetic biliverdins and bilirubins present interesting models for biochemical and metabolic studies. Owing to recent recognition of the astounding heterogeneity of natural bilirubins and to the various artifactual changes that bile pigments can undergo, considerable confusion has existed, and still exists, with regard to the nomenclature of the bile pigments and their derivatives. To set a background for further discussion, the present review starts with a brief discussion of nomenclature and of the various characteristic forms of lability of the bile pigments. TLC and HPLC procedures for preparation and analysis of unconjugated biliverdins and bilirubins and their methyl ester and sugar ester conjugates, as well as procedures for analysis of bilirubin-protein conjugates, are then discussed. Since, in view of the lability and pronounced heterogeneity of bile pigments, it is important to assess the composition and nature of chromatographically isolated pigments, the review is concluded by a brief evaluation of various structural tests.

Similarities in maximal biliary bilirubin output in the normal rat after administration of unconjugated bilirubin or bilirubin diglucuronide

The rate-limiting step in the overall plasma-to-bile transport of a saturating load of bilirubin is still a matter of controversy. We reassessed the apparent maximal biliary bilirubin excretion following i.v. infusion of unconjugated bilirubin and--for the first time--of highly purified bilirubin diglucuronide in the rat. The bilirubin diglucuronide preparation could be kept in a stable form at -20 degrees C for at least 2 months after addition of 3 mM sodium ascorbate. The biliary bilirubin excretion rates in animals with and without bile depletion in order to induce different flow rates were comparable after infusion of unconjugated bilirubin and of bilirubin diglucuronide. No significant hydrolysis of bilirubin diglucuronide seemed to occur during the hepatic transport of the pigment. Injection of bilirubin diglucuronide into rats which were already being infused with saturating doses of unconjugated bilirubin did not result in increased biliary bilirubin excretion. In contrast, a reversible inhibition of bilirubin output and bile acid-dependent bile flow was observed. If unconjugated and diglucuronidated bilirubin follow the same intracellular routes, the present results would suggest that conjugation did not restrict maximal biliary excretion. However, if exogenously administered diglucuronide utilizes a separate pathway, as was recently proposed, the biliary secretion of this exogenous conjugate might be restricted, presumably due to a toxic effect of the high local concentration of diglucuronide. The pathways utilized by the unconjugated pigment, on the other hand, could be primarily determined by the conjugating capacity.

Gilbert's syndrome

While Gilbert's syndrome is extremely common and benign, its pathogenesis may not be as straightforward as once believed. It has been used as a model to examine aberrations of virtually every step in bilirubin metabolism. The clinical hallmarks are of a hereditary, chronic, mild unconjugated hyperbilirubinaemia. Not infrequently subclinical haemolysis may coexist. Liver histology is normal although some minor ultrastructural abnormalities may be evident. The universal defect appears to be a reduction in hepatic bilirubin-GT activity. However, other associated abnormalities in bilirubin metabolism, which occur less consistently, suggest that this may not be the sole defect in all patients. The syndrome is almost certainly part of a spectrum which includes the Crigler-Najjar syndromes; molecular biology data suggests that there is an absence of one (or even more) GT isoenzymes in these disorders. Whether one or more genes is consistently culpable remains open to speculation. Despite the complicated pathogenesis of Gilbert's syndrome, management remains simply reassurance alone.

Thyroid hormones and the hepatic handling of bilirubin. I. Effects of hypothyroidism and hyperthyroidism on the hepatic transport of bilirubin mono- and diconjugates in the Wistar rat

The effects of thyroidectomy and of thyroid hormone administration on the hepatic transport of endogenous bilirubin were investigated in the Wistar R/APfd rat. Hypothyroidism resulted in an enhanced hepatic bilirubin UDP-glucuronosyltransferase activity and in a decreased p-nitrophenol transferase activity. It caused a cholestatic condition with a 50% decrease in bile flow and bile salt excretion, and an increased proportion of conjugated bilirubin in serum. The biliary output of unconjugated and monoconjugated bilirubins decreased in parallel by about 65%, whereas the excretion rate of the diconjugate dropped by only 47%, resulting in an increased di- to monoconjugate ratio in bile. Hyperthyroidism was characterized by a decreased bilirubin and an increased p-nitrophenol transferase activity, and by an augmented bilirubin output in bile. The output of unconjugated and monoconjugated bilirubins increased in parallel by about 50 or 100%, whereas the excretion of the diconjugate increased by only 20 to 50%, depending on the dose of thyroxine administered; this resulted in a decreased di- to monoconjugate ratio in bile. A linear positive relationship was found between bilirubin UDP-glucuronosyltransferase activity and the ratio of bilirubin di- to monoconjugates present in bile or formed by in vitro incubation of liver homogenates at low concentration of bilirubin (10 to 15 microM), indicating that bile pigment composition is mainly determined by the conjugation activity in the liver. The inverse relationship observed between hepatic beta-glucuronidase activity and the ratio of di- to monoconjugates in bile warrants further investigation to analyze whether this enzyme activity also plays a possible role in the changes in bile pigment composition in hypo- and hyperthyroid rats.

Molecular differences between rat-liver and rat-kidney biliverdin reductase. Implications for their in vivo regulation

Rat-liver biliverdin reductase exists in two molecular forms. The major form 1 has a molecular mass of 34 kDa, while the minor form 2 has a molecular mass of 56 kDa. Form 1 was converted into a second major form (form 3) with a molecular mass of 68 kDa by a NAD+-dependent peroxisomal dehydrogenase which was induced under conditions of oxidative stress [Frydman, R. B., Tomaro, M. L., Awruch, J. & Frydman, B. (1984) Biochem. Biophys. Res. Commun. 121, 249]. Molecular form 1 from rat kidney was not affected by the dehydrogenase, and a structural explanation for this difference was therefore sought. Both form 1 biliverdin reductases, isolated from rat liver and kidney, were purified to homogeneity using affinity chromatography, FPLC and HPLC techniques. The homogeneous enzymes were found to be identical when compared by their HPLC retention times, amino acid compositions and electrophoretic behaviour on polyacrylamide gels under non-denaturing conditions and on SDS/polyacrylamide gels. On HPLC analysis the peptides resulting from the CNBr cleavage were found to be the same for both enzymes, when either the native enzymes or their thioethylpyridine derivatives were compared. When the HPLC fingerprints of the tryptic digests were compared, they were found to be very similar, except for a peptide eluting at 31.60 min in the liver digest and at 23.60 min in the kidney digest. When the enzyme from both origins was alkylated with 4-dimethylaminoazobenzene-4'-iodoacetamide and then digested with trypsin, the HPLC fingerprints of the alkylated cysteine-carrying peptides were almost identical, except for a peptide with a retention time of 19.03 min in the liver digest and of 18.19 min in the kidney digest. The liver reductase was not amenable to Edman degradation suggesting a block at the NH2-terminus; in the kidney enzyme, however, it was free and an NH2-terminal sequence of 12 amino acids could be determined. The liver enzyme was found to be more sensitive toward p-hydroxymercuriphenyl sulfonate than the kidney enzyme.

Bilirubin excretion and bile flow in fed and fasted Brazilian squirrel monkeys (Saimiri sciureus)

Fasted Brazilian squirrel monkeys (BrSMs) exhibited slightly higher serum bilirubin levels (0.30 +/- 0.05 mg/dl) than others in the fed state (0.13 +/- 0.01). The mean liver weight was 50% lower following a 22 h fast. The rate of bile flow was unaffected by fasting and averaged 13.8 microliters/min/kg and 47.5 microliters/min/100g liver in six BrSMs. No significant difference in mean bilirubin excretion/min was observed on a body weight basis following fasting. When the mean rate of bilirubin excretion was calculated as a function of liver weight, a two-fold higher rate was present in fasted monkeys, but only at the p = 0.06 level of statistical significance. From data collected in this and earlier studies, it would appear that BrSMs represent the best animals studied to date to serve as experimental controls in comparative studies with Bolivian squirrel monkeys which exhibit a Gilbert-like syndrome.

Thyroid hormones and the hepatic handling of bilirubin. II. Effects of hypothyroidism and hyperthyroidism on the apparent maximal biliary secretion of bilirubin in the Wistar rat

This study was undertaken in the Wistar R/A Pfd rat to investigate the effects of hypothyroidism and of hyperthyroidism on the maximal biliary excretion (Tm) of bilirubin and on the concentration and composition of bilirubin in liver and plasma at the end of a bilirubin load. Hypothyroidism caused a cholestatic condition with a 50% decrease in bile flow and in bilirubin Tm, and with an increased proportion of conjugated bilirubin in liver and plasma. This was associated with an increased ratio of bilirubin diconjugates to monoconjugates in bile, liver, and plasma, which can be ascribed to the increased hepatic conjugation activity towards bilirubin and/or to the prolonged retention of bile pigments in the hepatocytes with increased conversion of monoconjugates to diconjugates. Cholestasis induced by hypothyroidism was further characterized by a decreased biliary output of unconjugated bilirubin. The latter phenomenon might represent an indirect effect related to a decreased output of bilirubin monoconjugates with impaired hydrolysis to unconjugated bilirubin; it might also reflect the cholestatic condition with decreased excretion of the unesterified bile pigment as such. Hyperthyroidism resulted in a 1.3-1.4-fold increase in bile flow. The maximal bilirubin concentration in bile decreased 1.3-1.4-fold, so that the apparent maximal bilirubin excretion rate remained unchanged at 115 nmol.min-1.100 g-1, as observed in untreated rats. Hyperthyroidism lowered the bilirubin UDP-glucuronosyltransferase activity, produced a decreased ratio of bilirubin di- to monoconjugates in bile and plasma, and a decreased ratio of conjugated to total bile pigment concentration in liver and in plasma. Similar findings are present in the heterozygous Gunn rat strain and in patients with hepatic bilirubin UDP-glucuronosyltransferase deficiency. We therefore propose the hyperthyroid rat as an experimental animal model of Gilbert's syndrome.

Unconjugated bilirubin in hepatic bile with brown pigment gallstones and cholangitis

To investigate the role of cholangitis in hydrolysis of bilirubin in bile with brown pigment gallstones, bilirubin composition and bacterial growth in hepatic bile with and without cholangitis were studied. The study included 38 brown pigment gallstone cases (28 without cholangitis and 10 with cholangitis). The proportion of unconjugated bilirubin in hepatic bile with cholangitis (16.9 +/- 8.5%, mean +/- SD) was significantly higher than that without cholangitis (3.7 +/- 1.8%, P less than 0.001). A positive correlation was found between bacterial population with beta-glucuronidase activity and the proportion of unconjugated bilirubin in bile in cases of brown pigment stones with cholangitis (P less than 0.05) but not in those without cholangitis despite the fact that bacterial species and population are similar regardless of the presence of cholangitis. In cholangitis, pH of bile becomes lower toward the optimal pH of bacterial beta-glucuronidase. Together the lower concentration of bile acid and the lower pH in bile result in lower solubility of unconjugated bilirubin, promoting its precipitation. Thus occasional bouts of cholangitis may result in periodic deposition of bilirubinate on brown pigment stones with layered structures by inducing cyclic changes of bile composition in situ.

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)

Isoextraction studies of partition of UCB between chloroform and aqueous solution

Bilirubin is a major component of gallstones and the solubility of unconjugated bilirubin (UCB) has been shown to play an Important role in gallstone formation. The mechanism of gallstone formation and solubilization of UCB is, however, still unknown. Several investigators have attempted to determine the chemical nature of bilirubin which are thought to be closely related to its solubility. However, there is some controversy over the ionization constants and pK values of carboxyl groups of UCB. In the present study, the effect of pH, the type and concentration of bile salt on UCB solubility were studied and the pK values of bilirubin were calculated. The first ionization censtants of the carboxyl group of UCB (pk₁) were 7.2 in saline, 6.7 in TC (Taurocholic acid), and 6.6 in TDHC (Taurodehydrocholic acid). The pK₂ was 9.2 in 50 m M TC. Thus, UCB monoanion (BH⁻) accounted for over 90% of the ionized UCB at physiologic pH values. Our results suggest that: 1. With the isoextraction method of UCB from chloroform, crystal surface effects are avoided and the partition equilibrium could also be attained rapidly. 2. There are more solubilities with higher bile salt concentrations and with increasing pH, and bile salt plays an important role in solubilizing UCB in bile. 3. Bile salt monomers, dimers and micelles are equally effective in solubilizing bilirubin. 4. The bilirubin in bile is almost entirely in the monoanion (BH⁻) form at physiological pH values.

Non-enzymic hydrolysis of bilirubin mono- and diglucuronide to unconjugated bilirubin in model and native bile systems. Potential role in the formation of gallstones

Pigment gallstones contain considerable amounts of unconjugated bilirubin (UCB) in the form of calcium bilirubinate and/or bilirubin polymers. Since more than 98% of bile pigments are excreted as conjugates of bilirubin, the source of this UCB needs to be identified. By using a rapid h.p.l.c. method, we compared the non-enzymic hydrolysis of bilirubin monoglucuronide (BMG) and bilirubin diglucuronide (BDG) to UCB in model bile and in native guinea-pig bile. Model biles containing 50 microM solutions of pure BMG and BDG were individually incubated in 25 mM-sodium taurocholate (NaTC) and 0.4 M-imidazole/5 mM-ascorbate buffer (TC-BUF) at 37 degrees C. Over an 8 h period, BMG hydrolysis produced 4-6 times more UCB than BDG hydrolysis. At pH 7.4, 25% of the BMG was converted into UCB, whereas only 4.5% of BDG was converted into UCB. Hydrolysis rates for both BMG and BDG followed the pH order 7.8 greater than 7.6 approximately equal to 7.4 greater than 7.1 Incubation with Ca2+ (6.2 mM) at pH 7.4 in TC-BUF resulted in precipitated bile pigment which, at 100 X magnification, appeared similar to precipitates seen in the bile of patients with pigment gallstones. At pH 7.4, lecithin (crude phosphatidylcholine) (4.2 mM) was a potent inhibitor of hydrolysis of BMG and BDG. The addition of a concentration of cholesterol equimolar with that of lecithin eliminated this inhibitory effect. Guinea-pig gallbladder bile incubated with glucaro-1,4-lactone (an inhibitor of beta-glucuronidase) underwent hydrolysis similar to the model bile systems. The non-enzymic hydrolysis of bile pigments, especially BMG, may be an important mechanism of bile-pigment precipitation and, ultimately, of gallstone formation.

Orthotopic liver transplantation for type I Crigler-Najjar syndrome

A neurologically normal 3-year-old girl with Type I Crigler-Najjar syndrome was successfully treated with orthotopic liver transplantation. Preoperative serum bilirubin concentrations as high as 31 mg per dl were not diminished with phenobarbital or phototherapy. Bilirubin fractionation of duodenal bile prior to transplantation revealed 87.1% unconjugated bilirubin and 12.9% monoconjugates as determined by alkaline methanolysis-high-performance liquid chromatography. Postoperatively, the serum bilirubin concentration quickly fell to normal. Uridine diphosphate glucuronyl transferase activity in the recipient liver was not detectable. The gallbladder bile bilirubin concentration of 23.9 mg per dl was less than 15% of previously reported normal values. Since devastating kernicteric brain injury is the invariable outcome of Type I Crigler-Najjar syndrome, liver transplantation should be performed when phototherapy cannot maintain the serum bilirubin concentration at an unequivocally safe level.