Recent advances in the separation and analysis of diazo-positive bile pigments

The impact of intestinal microflora on serum bilirubin levels

BACKGROUND/AIMS

Intestinal microflora plays an important role in the pathogenesis of neonatal jaundice by inhibiting enterosystemic circulation of bilirubin. The present study aimed to investigate the influence of intestinal microflora on serum bilirubin levels in hyperbilirubinemic Gunn rats.

METHODS

After a baseline phase Gunn rats received oral antibiotics (either clindamycin/neomycine or co-trimethoxazole for four days, phase II). Intestinal colonization was carried out either with a bilirubin-reducing strain of C. perfringens or C. pasteurianum incapable of reducing bilirubin (phase III). Serum bilirubin and fecal bile pigments were determined at the end of each phase.

RESULTS

Oral administration of clindamycin/neomycine resulted in the disappearance of fecal urobilinoids. Simultaneously, serum bilirubin increased dramatically (186+/-31 vs. 289+/-35 micromol/l, P=0.004). Intestinal colonization with C. perfringens led to reappearance of fecal urobilinoid production accompanied with a partial decrease of serum bilirubin (289+/-35 vs. 239+/-17 micromol/l, P=0.013), whereas the effect of C. pasteurianum on bile pigment metabolism was negligible. Co-trimethoxazole therapy had no effect on serum and intestinal metabolism of bilirubin.

CONCLUSIONS

Intestinal microflora greatly affects intravascular metabolism of bilirubin. Prolonged use of certain antibiotics in man may lead to an increase in serum bilirubin levels, while the enhancement of intestinal catabolism may have an opposite effect.

Guideline for the evaluation of cholestatic jaundice in infants: recommendations of the North American Society for Pediatric Gastroenterology, Hepatology and Nutrition

For the primary care provider, cholestatic jaundice in infancy, defined as jaundice caused by an elevated conjugated bilirubin, is an uncommon but potentially serious problem that indicates hepatobiliary dysfunction. Early detection of cholestatic jaundice by the primary care physician and timely, accurate diagnosis by the pediatric gastroenterologist are important for successful treatment and a favorable prognosis. The Cholestasis Guideline Committee of the North American Society for Pediatric Gastroenterology, Hepatology and Nutrition has formulated a clinical practice guideline for the diagnostic evaluation of cholestatic jaundice in the infant. The Cholestasis Guideline Committee, consisting of a primary care pediatrician, a clinical epidemiologist (who also practices primary care pediatrics), and five pediatric gastroenterologists, based its recommendations on a comprehensive and systematic review of the medical literature integrated with expert opinion. Consensus was achieved through the Nominal Group Technique, a structured quantitative method. The Committee examined the value of diagnostic tests commonly used for the evaluation of cholestatic jaundice and how those interventions can be applied to clinical situations in the infant. The guideline provides recommendations for management by the primary care provider, indications for consultation by a pediatric gastroenterologist, and recommendations for management by the pediatric gastroenterologist. The Cholestasis Guideline Committee recommends that any infant noted to be jaundiced at 2 weeks of age be evaluated for cholestasis with measurement of total and direct serum bilirubin. However, breast-fed infants who can be reliably monitored and who have an otherwise normal history (no dark urine or light stools) and physical examination may be asked to return at 3 weeks of age and, if jaundice persists, have measurement of total and direct serum bilirubin at that time. This document represents the official recommendations of the North American Society for Pediatric Gastroenterology, Hepatology and Nutrition on the evaluation of cholestatic jaundice in infants. The American Academy of Pediatrics has also endorsed these recommendations. These recommendations are a general guideline and are not intended as a substitute for clinical judgment or as a protocol for the care of all patients with this problem.

Bilirubin-IXbeta is a marker of meconium, like zinc coproporphyrin

BACKGROUND

Because meconium accumulates continuously in the fetal intestine, analysis of the postnatally excreted material could yield important information of intrauterine metabolism and maturation. Therefore, a study of the bilirubin pigments in meconium and in the first neonatal stools was carried out.

METHODS

Meconium and stools from 37 neonates of various gestational ages were collected carefully, and stored at -20 degrees C, protected by aluminium foil. Samples were defrosted, vortex mixed with an equal amount of dimethyl sulfoxide, centrifuged, and submitted to analysis by high-pressure liquid chromatography using newly developed methods to identify and to quantitate the bilirubin-IXalpha, -IXbeta, -IXgamma, and -IXdelta isomers. In addition, samples were also submitted to diazo coupling with ethyl anthranilate. Total coproporphyrins and zinc coproporphyrin were assayed for comparison.

RESULTS

Unconjugated bilirubin-IXalpha and -IXbeta were detected in meconium but not the -IXgamma or the -IXbeta isomer. Bilirubin-IXbeta was the predominant pigment and comprised 63% to 96% of the unconjugated bilirubins in the first sample of meconium excreted. Its amount decreased rapidly during the first 5 days in full-term newborns, but this occurred more slowly in preterm neonates, especially in those with a gestational age less than 30 weeks. The decrease of bilirubin-IXbeta over time correlated with that of coproporphyrin.

CONCLUSIONS

Bilirubin-IXbeta is the prevailing bile pigment in the first excreted sample of meconium. It gradually decreases after birth and can be considered a biochemical marker of meconium, like zinc coproporphyrin.

The association between rifamycin-SV (R-SV) related hyperbilirubinaemia and antipyrine clearance as a new test of liver function in cirrhosis

Several clearance tests have been used to assess the residual hepatic efficiency in liver cirrhosis. However, the altered clearance values found in cirrhotic patients may reflect not only the impairment in liver function but also a derangement in the hepatic blood-flow. Therefore, this study was designed to explore the possibility that the competition between Rifamycin-SV and bilirubin at the hepatic uptake site might be used as an index for quantitative assessment of residual hepatic efficiency in 48 patients with chronic liver disease. In this test, the interference of hepatic blood flow would be negligible. Antipyrine clearance was also evaluated in the same subjects in order to explore the cytoplasmic microsomal efficiency. Rifamycin-SV intravenous load was followed by a sustained increase in bilirubinaemia which significantly related with the degree of liver function as assessed by the Child-Pugh criteria. Also, antipyrine clearance was significantly altered in cirrhotic patients compared to controls. Moreover, a positive correlation was found between the Rifamycin-SV test and Antipyrine clearance. We suggest that a combination of these tests might be of use in the quantitative assessment of liver function.

The origins and kinetics of bilirubin in healthy dogs, in comparison with man

The origins and the kinetics of unconjugated bilirubin were assessed in 25 healthy dogs. Bilirubin kinetics were measured by the analysis of the plasma disappearance of [3H]bilirubin in a two-compartment model. The relative bilirubin productions from erythrocyte haem degradation and early labeled bilirubin were determined by measuring the incorporation of [14C]glycine in erythrocyte haem and in fecal stercobilin. The incorporation of this relation into the model permitted the quantitation of the bilirubin production from erythrocyte destruction, ineffective erythropoiesis and the catabolism of hepatic haemoproteins. The contribution of the three bilirubin sources to the plasma concentration was derived from the calculated fraction reflux into the plasma of bilirubin produced in the liver from hepatic haemoproteins. Other calculated model-dependent and -independent parameters were plasma bilirubin clearance, hepatic bilirubin extraction efficiency, pool sizes, and the fractional transfer rates which reflect the hepatic uptake process, reflux from liver to the plasma, and the conjugating enzyme activity. In plasma of healthy dogs only unconjugated bilirubin was detected. It averaged 0.68 mumol/l, which is far below levels in man. This is probably due to the 20-fold higher hepatic clearance rate in dogs (median 32.2; range 21.6-43.9 ml/kg per min). In addition, fasting hyperbilirubinaemia could not be documented in the dog. The total bilirubin turnover was 14.9 (12.6-17.1) mumol/kg (median and 95% range), with 67 (60-70)% derived from erythrocyte degradation, 5.3 (4.7-5.5)% from ineffective erythropoiesis and 27.7 (24.5-35.3)% from hepatic haemoproteins. The figures for the plasma bilirubin turnover were 12.3 (10.3-14.2) mumol/kg per day, 79 (75-84)%, 6.3 (6.0-6.6)% and 14.8 (9.2-18.9)%, respectively. The presented model permits the simultaneous quantitation of both the origins and the kinetics of bilirubin. The application of this approach in pathological conditions is expected to provide better insight in the pathophysiology of acquired hyperbilirubinaemia.

Synthesis, chromatographic purification, and analysis of isomers of biliverdin IX and bilirubin IX

Neutral solvent systems were developed to isolate the alpha, beta, gamma, and delta isomers of biliverdin IX dimethyl ester by TLC. The individual free acids of biliverdin IX were obtained by saponification of the corresponding dimethyl esters. The bilirubin IX isomers were prepared by reducing the corresponding biliverdin IX isomers with NaBH3CN. Starting from a pure biliverdin IX dimethyl ester, the corresponding free acid of biliverdin IX or bilirubin IX was available within 3-4 h. Preparation of spectrally pure bile pigment required final TLC on acid-cleaned neutral TLC plates. The absorption spectra of the free acids and dimethyl esters of biliverdin IX in methanol showed a broad band at about 650 nm and a sharp band at about 375 nm. The long-wave-length band was extremely sensitive to the presence of strong acid. A 10-fold molar excess of HCl caused a 35- to 50-nm shift of the absorption maximum to longer wavelengths and near doubling of the maximum absorption. The molar absorption coefficients of biliverdins were identical for each free acid and dimethyl ester pair. In each case, Beer's law was followed in both methanol and acidified methanol. Methanol also proved to be a suitable solvent for spectroscopic determination of the non-alpha isomers of bilirubin IX. The wavelength of maximum absorption and molar absorption coefficient of each dipyrrolic ethyl anthranilate azo pigment derived from the various bilirubin IX isomers are also reported.

The influence of gestational age on bilirubin conjugation in newborns

Unconjugated, mono- and diconjugated bilirubin levels were determined in serum soon after birth, and followed up for several days. Fourteen preterm neonates were studied with a gestational age below 33 weeks (n = 7) or between 34 and 37 weeks (n = 7), respectively, as well as 19 full-term newborns either untreated (n = 9) or treated by phototherapy (n = 10). Bilirubin and its derivatives were analysed by alkaline methanolysis and spectrometry after separation by thin-layer chromatography. In normal full-term neonates total and unconjugated bilirubin reached peak levels at days 2-4. Thereafter, a decline of 11% per day was detectable. Monoconjugates in serum amounted to 3.1 +/- 1.1% of total pigment and remained at that level. The relative amount of diconjugates increased from 0.55 +/- 0.25% (2-4th postnatal day) to 1.62 +/- 0.99% (9-13th day of life). The rapid decline of unconjugated bilirubin paralleled by an increase of diconjugates are an expression of the maturation process for bilirubin conjugation. The premature neonates with less than 33 weeks gestation exhibited an increase of unconjugated serum bilirubin up to the 4-5th postnatal day, the decline thereafter amounted 2% per day. The fraction of 2.3 +/- 1.1% monoconjugates was small and exhibited only a moderate increase in the follow up. In contrast diconjugates were undetectable or very low and remained at this level. These results suggest the presence of a more severe immaturity as well as a slower maturation process of bilirubin conjugation in preterm newborns.(ABSTRACT TRUNCATED AT 250 WORDS)

HPLC separation and quantification of bilirubin and its glucuronide conjugates in faeces and intestinal contents of germ-free rats

We describe an accurate reverse-phase high-performance liquid chromatography (HPLC) method for the separation and quantification of unconjugated bilirubin (UCB) and its monoglucuronide (BMG) and diglucuronide (BDG) conjugates in faeces and intestinal contents from germ-free (GF) rats. We demonstrated that female GF rats excreted predominantly BMG and that the percentage of this conjugate was at most 71.7% of the total bilirubin excreted with the faeces. The highest percentages for BDG and the UCB were 27.9% and 6.0%, respectively. The bile pigment composition in duodenal contents was 59.8% BDG and 40.2% BMG (median percentage) and was 47.7% BDG, 50.1% BMG and 2.2% UCB in ileal contents. Deconjugation of BDG to BMG was profound in caecal contents with 26.0% BDG, 67.4% BMG and 6.6% UCB. Endogenous (mammalian) beta-glucuronidase activity was present in intestinal contents throughout the entire length of the intestine and in faeces of the GF rats. The results indicated that it is very likely that endogenous beta-glucuronidase plays a role in the deconjugation of bilirubin glucuronides as well as of other glucuronides in the intestine of the GF rat.

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.

High-performance liquid chromatography of bilirubin conjugates in bile: effect of beta-glucuronidase on the bile pigments

A simple, specific, and technically easy high-performance liquid chromatography (HPLC) method for the separation and quantification of unconjugated bilirubin, bilirubin monoglucoside-monoglucuronide, bilirubin diglucuronide, and bilirubin monoglucuronide has been developed. The method was used to determine the bilirubin compounds of bile obtained endoscopically from the common bile duct in 43 patients with gallstone disease and in 6 subjects without gallstones or liver disease. The bile samples were also assessed for the presence of beta-glucuronidase-producing bacteria. The amount of unconjugated bilirubin was significantly higher (p less than 0.01) in bile containing bacteria producing beta-glucuronidase than in bile without such bacterial strains. In six 'normal' bile samples the following quantities of bilirubin conjugates and unconjugated bilirubin were found (median and range): bilirubin monoglucoside-monoglucuronide (mixed conjugate), 61 (27-80) mumol/l; bilirubin diglucuronide, 632 (512-861) mumol/l; bilirubin monoglucuronide, 113 (70-175) mumol/l; and unconjugated bilirubin, 3 (1-7) mumol/l. These results are in good agreement with those obtained with other HPLC methods. The concentrations of unconjugated bilirubin were lower than those found when using conventional diazo methods and thin-layer chromatography. HPLC proved to be a useful tool in gallstone pathogenesis studies. Our results support bacterial glucuronidase as a possible pathogenic factor in pigment gallstone disease.

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.

Tissue levels of bilirubin and biliverdin in the sea lamprey, Petromyzon marinus L., before and after biliary atresia

1. Liver, intestine, kidney, muscle and epidermis from larvae, juvenile adults and upstream migrants of the sea lamprey, Petromyzon marinus L., were assayed for the presence of biliverdin and bilirubin. Urine was also examined for these bile pigments in juveniles and upstream migrants. 2. Bilirubin concentration increased dramatically in the liver and caudal intestine following loss of larval bile ducts while biliverdin levels were highest in the liver of upstream migrants and rose sharply in the caudal intestine immediately following the atresia. 3. Small amounts of bile pigment were present in larval kidneys but high concentrations were found in this organ in upstream migrants. The urine of the latter possessed biliverdin. 4. Mucus of the epidermis may be a vehicle for transport and release of bilirubin in upstream migrants. 5. These data indicate that lampreys utilize different avenues for bile pigment storage and elimination over the course of their life cycle.

Increased production, hepatic conjugation, and biliary secretion of bilirubin in the rat after chronic ethanol consumption

Disturbances of bilirubin metabolism such as jaundice or pigment gallstone formation, or both, occur in alcoholic cirrhosis of the liver. We have studied the influence of chronic ethanol consumption on bilirubin metabolism as well as on biliary calcium and bile acids in 16 pair-fed male rats. The animals received nutritionally adequate liquid diets containing 36% of total calories either as ethanol or isocaloric carbohydrates for 4 wk. Bile flow was significantly enhanced after chronic ethanol feeding (p less than 0.05 after 90-min bile collection) and was found to be mainly bile acid-independent. The biliary output and concentration of bilirubin monoconjugates, bilirubin diconjugates, and total calcium was significantly increased (p less than 0.01) in alcohol-fed rats compared with controls. This was not the case for unconjugated bilirubin and for the calcium/bile acid ratio. Hepatic bilirubin uridine-5'-diphosphate-glucuronosyltransferase activity (p less than 0.01), serum total bilirubin (p less than 0.01), and serum free hemoglobin (p less than 0.001) were significantly increased after ethanol consumption. These data provide evidence for enhanced bilirubin production, probably due to hemolysis, after alcohol ingestion. The enhanced bile production is associated with an increased hepatic conjugation and subsequent biliary secretion of bilirubin conjugates. In advanced alcoholic liver disease, these compensatory mechanisms may fail and contribute to the development of jaundice.

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.

Intestinal deconjugation of bilirubin in germfree and conventional rats

The content of conjugated bilirubin (CB) was about the same in small intestinal contents from germfree (GF) and conventional (CONV) rats. Caecal contents from GF rats contained considerably more CB than from CONV rats. The results indicated that the caecum is the major site of microbial deconjugation of CB in the CONV rat. Separation of azopigments prepared from small intestinal contents of GF and CONV rats revealed similar patterns. Similar separation patterns were also observed with azopigments prepared from caecal contents and faeces of GF rats. Some chemical properties of CB prepared from GF rat faeces were studied.

Reverse-phase h.p.l.c. separation, quantification and preparation of bilirubin and its conjugates from native bile. Quantitative analysis of the intact tetrapyrroles based on h.p.l.c. of their ethyl anthranilate azo derivatives

We describe a facile and sensitive reverse-phase h.p.l.c. method for analytical separation of biliary bile pigments and direct quantification of unconjugated bilirubin (UCB) and its monoglucuronide (BMG) and diglucuronide (BDG) conjugates in bile. The method can be 'scaled up' for preparative isolation of pure BDG and BMG from pigment-enriched biles. We employed an Altex ultrasphere ODS column in the preparative steps and a Waters mu-Bondapak C18 column in the separatory and analytical procedures. Bile pigments were eluted with ammonium acetate buffer, pH 4.5, and a 20 min linear gradient of 60-100% (v/v) methanol at a flow rate of 2.0 ml/min for the preparative separations and 1.0 ml/min for the analytical separations. Bile pigments were eluted in order of decreasing polarity (glucuronide greater than glucose greater than xylose conjugates greater than UCB) and were chemically identified by t.l.c. of their respective ethyl anthranilate azo derivatives. Quantification of UCB was carried out by using a standard curve relating a range of h.p.l.c. integrated peak areas to concentrations of pure crystalline UCB. A pure crystalline ethyl anthranilate azo derivative of UCB (AZO . UCB) was employed as a single h.p.l.c. reference standard for quantification of BMG and BDG. We demonstrate that: separation and quantification of biliary bile pigments are rapid (approximately 25 min); bile pigment concentrations ranging from 1-500 microM can be determined 'on line' by using 5 microliters of bile without sample pretreatment; bilirubin conjugates can be obtained preparatively in milligram quantities without degradation or contamination by other components of bile. H.p.l.c. analyses of a series of mammalian biles show that biliary UCB concentrations generally range from 1 to 17 microM. These values are considerably lower than those estimated previously by t.l.c. BMG is the predominant, if not exclusive, bilirubin conjugate in the biles of a number of rodents (guinea pig, hamster, mouse, prairie dog) that are experimental models of both pigment and cholesterol gallstone formation. Conjugated bilirubins in the biles of other animals (human, monkey, pony, cat, rat and dog) are chemically more diverse and include mono-, di- and mixed disconjugates of glucuronic acid, xylose and glucose in proportions that give distinct patterns for each species.

An unusual case of Crigler-Najjar disease in the adult. Classification into types I and II revisited

We present the case of a 25-year-old man with Crigler-Najjar disease who had since birth a marked unconjugated hyperbilirubinemia without bilirubin overproduction, without any neurological involvement and in whom phenobarbital administration failed to produce any effect. Analysis of his biliary bile pigments on two occasions showed (i) a decrease excretion of bilirubin, as indirectly suggested by a high ratio of biliary bile acids over total bilirubin; (ii) an increase in unconjugated bilirubin IX alpha quantitated by thin-layer chromatography (TLC) following alkaline methanolysis and by direct extraction and TLC of the tetrapyrroles; (iii) a high proportion of bilirubin monoconjugates whereas the excretion of diconjugates was very low. Classification of the present patient into Crigler-Najjar disease type I or II was not possible. The most striking and practical difference among the various cases of Crigler-Najjar disease remains the response to phenobarbital. Among cases of Crigler-Najjar disease which respond to enzyme induction and Gilbert's syndrome, the continuous spectrum suggests a common defect.

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.

Properties and determination of serum and bilirubin

The accurate determination of the types and amounts of bilirubin species in serum is important for diagnostic purposes as well as for therapeutic monitoring. However, of the determinations routinely performed in the clinical laboratory, those for bilirubins are not among the more accurate and exhibit significant method variability. In this review, the structural, stability, solubility, and albumin-binding properties of serum bilirubins are discussed with respect to their impact on analytical methods. Following a consideration of analytical standards, methods for the determination of unconjugated and conjugated bilirubins are reviewed and recent developments are evaluated. Finally, the present capabilities and future potential of the methods for producing information applicable to the development of new or improved methods of determination are summarized.

Bilirubin diglucuronide formation by rat liver microsomes: demonstration by affinity and thin layer chromatography of bile pigment tetrapyrroles

The conjugates formed in vitro by bilirubin UDP-glucuronyl transferase were studied by examining reaction products as intact tetrapyrroles, rather than as dipyrrolic azoderivatives. Bile pigments were extracted from conventional microsomal enzyme reaction mixtures by affinity chromatography over albumin-agarose, eluted with 50% ethanol, and separated by a silica gel thin layer chromatographic system. In the presence of UDPGA, native and activated microsomal preparations all formed both bilirubin mono- and diglucuronides from unconjugated bilirubin, and bilirubin diglucuronide from bilirubin monoglucuronide. No significant non-enzymatic conversion of mono- to diglucuronide occurred without UDPGA, or in the presence of denatured enzyme. Hence, bilirubin diglucuronide is a major product of bilirubin-UDP-glucuronyl transferase.

Physicochemical and immunohistological studies of a sulfobromophthalein- and bilirubin-binding protein from rat liver plasma membranes

Affinity chromatography over bilirubinagarose and sulfobromophthalein (BSP)-agarose was used to isolate two proteins, with high affinities for bilirubin and BSP, respectively, from Triton X-100-solubilized rat liver plasma membranes. The protein eluted from either affinity column migrated as a single band of approximately 55,000 D on sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis, and either protein cochromatographed with both [14C]bilirubin and [35S]BSP on Sephadex G-75. On gradient gels without reduction or SDS, or on Sephadex G-150, the native BSP-binding protein had an estimated molecular mass of approximately 100,000 D. After incubation with SDS, an additional Sephadex G-150 peak of molecular mass of 56,000 D was observed. Both, the 100,000- and 56,000-D G-150 peaks cochromatographed with [35S]BSP. The native protein had an isoelectric point of 3.5, stained with periodic acid-Schiff but not Sudan black, and contained 4 mol of sialic acid per mol of protein. A rabbit antibody to the BSP-binding protein gave a line of identity with both the BSP- and bilirubin-binding antigens, and inhibited the binding of [14C]bilirubin and [35S]BSP, but not [14C]oleate or [14C]taurocholate, to rat liver plasma membranes. Immunohistochemical studies revealed the presence of the antigen on all surface domains of rat hepatocytes, but not on other cell populations from normal rat liver. It was not found in other organs. These data are compatible with the hypothesis that a specific liver cell plasma membrane protein mediates the hepatocytic sequestration of bilirubin and BSP.

UDP-glucuronosyltransferase activity and bilirubin conjugation in the bullfrog

Bile pigments of bile and serum of Rana catesbeiana were investigated by means of high-pressure liquid chromatography. The major pigment in both bile and serum was bilirubin IX alpha. Bilirubin UDP-glucuronosyltransferase activity was found in the livers of all animals examined, but no conjugated bilirubin was detectable in the bile. Frog bile was found to contain large amounts of beta-glucuronidase. When the beta-glucuronidase inhibitor saccharo-1,4-lactone was introduced into the gall bladder followed by an exogenous bilirubin load, bilirubin glucuronide appeared in the bile.

Bile pigments and bilirubin UDP-glucuronyl transferase during the metamorphosis of Rana catesbeiana tadpoles

The major bile pigments in Rana catesbeiana tadpoles was bilirubin IX alpha. The concentration of bilirubin IX alpha increases in bile and plasma during metamorphosis. Bilirubin IX alpha and biliverdin IX alpha were also present in the bile of tadpoles. Bilirubin UDP-glucuronyl transferase activity was present in the livers of all tadpoles examined. Bilirubin UDP-glucuronyl transferase activity increases slightly during spontaneous metamorphosis and increases approximately 2-fold during T3-induced metamorphosis.

Pigment gallstone disease: Summary of the National Institutes of Health--international workshop

This report summarizes the proceedings of the first National Institutes of Health--International Workshop on Pigment Gallstone Disease. The meeting held at the University of Pennsylvania in May, 1981 consisted of eight sessions in which the following aspects of pigment gallstone disease were discussed: (a) classification; (b) epidemiology; (c) radiographic assessment; (d) gallstone composition; (e) composition of bile; (f) pathogenesis; (g) animal models, genetics, and computer analysis, and (h) medical treatment. The interaction of participants interested in various aspects of pigment stone disease was stimulating. This workshop should be a major stimulus for future studies in this relatively neglected, but important area of biliary tract lithiasis.

Uridine diphosphate-glucuronic acid-independent conversion of bilirubin monoglucuronides to diglucuronide in presence of plasma membranes from rat liver is nonenzymic

TWO ROUTES HAVE BEEN PROPOSED FOR CONVERSION OF BILIRUBIN MONOGLUCURONIDE TO THE DIGLUCURONIDE: glucuronyl transfer (a) from UDP-glucuronic acid to bilirubin monoglucuronide, catalyzed by a microsomal UDP-glucuronyltransferase, and (b) from one molecule of bilirubin monoglucuronide to another (transglucuronidation), catalyzed by an enzyme present in liver plasma membranes. The evidence regarding the role of the latter enzyme for in vivo formation of bilirubin diglucuronide is conflicting. We therefore decided to reexamine the transglucuronidation reaction in plasma membranes and to study the conversion of bilirubin monoglucuronide to diglucuronide in vivo. Purified bilirubin monoglucuronide was incubated with homogenates and plasma membrane-enriched fractions from liver of Wistar and Gunn rats. Stoichiometric formation of bilirubin and bilirubin diglucuronide out of 2 mol of bilirubin monoglucuronide was paralleled by an increase of the IIIalpha- and XIIIalpha-isomers of the bilirubin aglycone, thus showing that dipyrrole exchange, not transglucuronidation, is the underlying mechanism. Complete inhibition by ascorbic acid probably reflects intermediate formation of free radicals of dipyrrolic moieties. The reaction was nonenzymic because it proceeded independently of the protein concentration and heat denaturation of the plasma membranes did not result in decreased conversion rates. Collectively, these findings show spontaneous, nonenzymic dipyrrole exchange when bilirubin monoglucuronide is incubated in the presence of rat liver plasma membranes. Because bilirubin glucuronides present in biological fluids contain exclusively the bilirubin-IXalpha aglycone, formation of the diglucuronide from the monoglucuronide by dipyrrole exchange does not occur in vivo. Rapid excretion of unchanged bilirubin monoglucuronide in Gunn rat bile after injection of the pigment provides confirmatory evidence for the absence of a UDP-glucuronic acid-independent process.

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.

beta-Glucuronidase-resistant bilirubin glucuronide isomers in cholestatic liver disease--determination of bilirubin metabolites in serum by means of high-pressure liquid chromatography

"Direct reacting bilirubin" in serum of patients with cholestatic liver disease and in serum of bile duct-ligated rats consists of a complex mixture of bilirubin metabolites. These metabolites were studied by means of high-pressure liquid chromatography. Bilirubin glucuronides in normal bile are beta-glycosidic 1-O-acyl conjugates which are completely hydrolyzed on incubation with beta-glucuronidase. Cholestatic serum contains glucuronide and non-glucuronide bilirubin metabolites. The glucuronides were only partially hydrolyzable with beta-glucuronidase. Compernolle et al. [11] showed that the 1-O-acyl bond of bilirubin glucuronides is labile and prone to migrate from the C1 position at the glucuronosyl residue to positions C2, C3 and C4. The isomerisation products are non-beta-glycosidic, beta-glucuronidase-resistant conjugates. The main beta-glucuronidase-resistant conjugates in cholestatic serum were characterized as: non-beta-glycosidic bilirubin monoglucuronide, non-beta-glycosidic diglucuronide and a diglucuronide isomer with beta-glycosidic and non-beta-glycosidic glucuronosyl groups. Moreover, a substantial amount of bilirubin monoglucoside monoglucuronide was detected in cholestatic human serum.

Glucuronidation of bilirubin and the occurrence of pigment gallstones in patients with chronic haemolytic diseases

A group of thirty-seven patients with increased haem catabolism has been studied to gain insight in their bilirubin conjugating capacity. Bilirubin UDP-glucuronyl transferase activity (GlcATa) in the liver and bilirubin monoconjugates in bile were measured and the hepatic bilirubin clearance was calculated from the radio-chromium-survival data. In the present group, 41% of the patients clearly had a deficiency in bilirubin conjugation similar to what is classically found in Gilbert's syndrome. The association may facilitate detection of these patients as serum bilirubin levels were higher (65.8 microM +/- 19) (m +/- 1 SD) in the fifteen patients with associated Gilbert's syndrome versus thirteen having only haemolysis (43.6 microM +/- 15). A fair correlation was found between the percentage of monoconjugates in bile and the GlcATa levels in the liver as well as with the calculated hepatic bilirubin clearance, although some discrepancies exist. Using these determinations, a clearcut separation from normal values was not obtained, suggesting at least in the present group of patients that Gilbert' syndrome represents only one end of a continuum of bilirubin conjugation rates and not a separate entity. Pigment stones in the gall-bladder were documented in 51% of the patients and usually at an early age. There was no relationship towards sex, serum bilirubin, GlcATa in liver, total bilirubin or monoconjugates in bile. Age played some role as well as the type of haemolysis as all patients with congenital dyserythropoiesis (n = 4) or acquired haemolysis (n = 3) had lithiasis. Moderate chronic cholecystitis was present, whereas an accumulation of iron and bile pigment was evident in the liver.

Mechanism of bilirubin diglucuronide formation in intact rats: bilirubin diglucuronide formation in vivo

Although it is well established that bilirubin monoglucuronide is formed in the liver from bilirubin by a microsomal bilirubin uridine diphosphate (UDP)-glucuronosyltransferase, the subcellular site of conversion of monoglucuronide to diglucuronide and the molecular mechanism involved in diglucuronide synthesis have not been identified. Based on in vitro studies, it has been proposed that two fundamentally different enzyme systems may be involved in diglucuronide synthesis in rat liver: (a) a microsomal UDP-glucuronosyltransferase system requiring UDP-glucuronic acid as sugar donor or (b) a transglucuronidation mechanism that involves transfer of a glucuronosyl residue from one monoglucuronide molecule to another, catalyzed by a liver plasma membrane enzyme. To clarify the mechanism by which bilirubin monoglucuronide is converted in vivo to diglucuronide, three different experimental approaches were used. First, normal rats were injected with either equal amounts of bilirubin-IIIalpha [(14)C]monoglucuronide and unlabeled bilirubin-XIIIalpha monoglucuronide, or bilirubin-XIIIalpha [(14)C]monoglucuronide and unlabeled bilirubin-IIIalpha monoglucuronide. Analysis of radiolabeled diglucuronide excreted in bile showed that [(14)C]glucuronosyl residues were not transferred between monoglucuronide molecules. Second, in normal rats infused intravenously with dual-labeled [(3)H]bilirubin [(14)C]monoglucuronide, no transfer or exchange of the [(14)C]glucuronosyl group between injected and endogenously produced bilirubin monoglucuronide could be detected in the excreted bilirubin diglucuronide. Third, in homozygous Gunn rats, injected (14)C-labeled or unlabeled bilirubin mono- or diglucuronides were excreted in bile unchanged (except that diglucuronide was hydrolyzed to a minor degree). This indicates that Gunn rats, which lack bilirubin UDP-glucuronosyltransferase activity, are unable to convert injected monoglucuronide to diglucuronide. Collectively, these findings establish that a transglucuronidation mechanism is not operational in vivo and support the concept that bilirubin diglucuronide is formed by a microsomal UDP-glucuronosyltransferase system.

Changes in bilirubins in human prenatal development

1. A densitometric method has been developed for the quantification of azodipyrroles derived from dog bile pigments treated with diazotized ethyl anthranilate. 2. This method was used to estimate the bilirubins in bile and meconium from foetuses of 14-36 weeks gestation. 3. The proportion of the bilirubins in foetal bile changed during gestation. (a) No bile pigments were found until 14 weeks. (b) Between 14 and 15 weeks bilirubin-IX beta was the only bile pigment detected. (c) At 16-17 weeks some unconjugated bilirubin-IX alpha was found in the bile, but up to 20 weeks bilirubin-IX beta was the predominant bilirubin in the bile. (d) At about 20 weeks glucose, xylose, and an unidentified bilirubin-IX alpha monoconjugate were found in the bile. (e) Between 20 and 23 weeks bilirubin-IX alpha glucuronide appeared in the bile. (f) At 30 weeks monoconjugates of bilirubin-IX alpha were the predominant bilirubins in the bile. (g) Only in full-term foetuses was bilirubin-IX alpha monoglucuronide the major bilirubin derivative.

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.

An accurate and sensitive analysis by high-pressure liquid chromatography of conjugated and unconjugated bilirubin IX-alpha in various biological fluids

An accurate and sensitive method was developed for the complete separation of the native tetrapyrroles, such as bilirubin and its mono- and di-conjugates of glucuronic acid, glucose and xylose, by ion-pair reversed-phase high-pressure liquid chromatography. The application of this method was demonstrated by the analysis of bile pigments in human bile and urine, and the method also makes it possible to estimate very low UDP-glucuronyltransferase activity, such as is found in the human foetal and neonatal liver.

Comparative aspects of bile pigment formation and excretion

Breakdown of haem which is of key importance in most organisms, involves oxidative CO-evolving cleavage of the macrocyclic ring with formation of biliverdin-IX. In two major pathways established so far formation of biliverdin-IX alpha is followed by (a) biliary secretion or (b) reduction to bilirubin-IX alpha, formation of more hydrophilic derivatives (usually glycosidic conjugates) and biliary secretion. The scattered comparative information available indicates marked species variation with regard to the methin-bridge carbon atom removed from haem and the metabolic site of cleavage, the nature of bilirubin conjugates and the developmental sequence of maturation of enzyme activities and transport proteins involved in the chain of events leading from breakdown of haem to the excretion of the final end products.

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.

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.

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.

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.