In Vitro Evaluation of a Novel Synthetic Bilirubin Analog as an Antioxidant and Cytoprotective Agent for Pancreatic Islet Transplantation

Bilirubin is a natural cytoprotective agent and physiologic doses have proven to be beneficial in various models of organ and cellular transplantation. Recently, we showed that bilirubin has protective effects in models of pancreatic islet transplantation, preventing cell death associated with islet stress and suppressing the release of damage-associated molecular patterns. Despite these promising therapeutic attributes, the natural bilirubin used in these research studies is animal-derived (porcine), making it unsuitable for clinical application. In the current study, we synthesized two bilirubin analogs that can be produced without the use of animal-derived products. Antioxidant activity for the analogs was measured using the ferric-reducing-ability-of-plasma (FRAP) and 2,2V-azinobis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) assays. Dose-dependent cytotoxicity and cytoprotective effects were then demonstrated in isolated rat islets. Compound 1 showed similar antioxidant activity to natural bilirubin. Dose-dependent cytotoxicity was seen following treatment with Compound 1 and natural bilirubin at doses >40 μM, resulting in significantly increased cell death when compared to control islets (P < 0.05) or islets treated with doses ≤20 μM (P < 0.05). Following hypoxic challenge, islet cell death was reduced in islets treated with Compound 1 at 10 μM (17.27% ± 0.26%) compared to natural bilirubin at 10 μM (51.36% ± 0.71%; P < 0.0001) or 20 μM (59.02% ± 0.83%; P < 0.0001) and control islets (36.51% ± 0.44%; P < 0.0001). Compound 1 was found to have promising antioxidant and cytoprotective effects, limiting islet cell death in a model of islet transplantation hypoxic stress. Compound 1 may serve as a synthetic drug lead for clinical islet transplantation and further evaluation of this molecule and its analogs is warranted.

Inhibition of Human UGT1A1-Mediated Bilirubin Glucuronidation by Polyphenolic Acids Impact Safety of Popular Salvianolic Acid A/B-Containing Drugs and Herbal Products

Bilirubin-related adverse reactions (ADR, e.g., jaundice and hyperbilirubinemia) induced by herbs rich in certain polyphenolic acids are widely reported. However, the causes and the mechanisms underlying these ADR are not well understood. The purpose of this article is to determine the mechanism by which certain polyphenolic acids inhibit UGT1A1-mediated bilirubin glucuronidation, leading to jaundice or hyperbilirubinemia. We investigated in vitro inhibitory effects on bilirubin glucuronidation of salvianolic acid A (SAA), salvianolic acid B (SAB), danshensu (DSS), protocatechuic aldehyde (PA), and rosmarinic acid (RA), as well as two Salvia miltiorrhiza injections (DSI and CDI) rich in polyphenolic acids. The results showed that average formation rates of three bilirubin glucuronides displayed a significant difference (p < 0.05) and the formation of monoglucuronide was favored regardless if an inhibitor was present or not. SAA, SAB, DSI, and CDI, but not DSS, PA, and RA, significantly inhibited human UGT1A1-mediated bilirubin glucuronidation via a mixed-type inhibitory mechanism. Average IC50 values of SAA, SAB, DSI, and CDI-mediated inhibition of bilirubin glucuronidation were bilirubin concentration-dependent, and their values (against total bilirubin glucuronidation) were in the range 0.44 ± 0.02 to 0.86 ± 0.04 μg/mL (for SAA), 4.22 ± 0.30 to 12.50 ± 0.93 μg/mL (for SAB), 9.29 ± 0.76 to 18.82 ± 0.63 μg/mL (for DSI), and 9.18 ± 2.00 to 22.36 ± 1.39 μg/mL (for CDI), respectively. In conclusion, SAA and its analog SAB are the main ingredients responsible for inhibition of bilirubin glucuronidation by DSI and CDI, whose use is associated with many high bilirubin-related ADR.

A Novel Liquid Chromatography Tandem Mass Spectrometry Method for the Estimation of Bilirubin Glucuronides and its Application to In Vitro Enzyme Assays

BACKGROUND

Bilirubin is a toxic waste product of metabolism, eliminated mainly through UGT1A1 mediated conjugation to mono- and di-glucuronides. Due to the potentially low Km value of bilirubin glucuronidation, the quantitative sensitivity obtained with most UV/visible light detection methods are not sufficient to accurately calculate UGT1A1 enzyme kinetics at low bilirubin concentrations. In addition, bilirubin, as well as its metabolites, are unstable during sample preparation and bioanalysis. This necessitates the need for a rapid, sensitive and robust assay to measure bilirubin glucuronides.

METHODS

A robust LC-MS/MS method was developed to measure low levels of bilirubin glucuronides accurately from in vitro incubations, as well as stabilizing the analytes during sample preparation and analysis. The metabolites were quantified using a qualitative/quantitative approach utilizing UV to MS correction, thereby eliminating the need for synthetic standards.

RESULTS

The method was sensitive enough to quantify mono- and di-glucuronides as low as 3 nM from in vitro incubations, and kinetic data was determined for total glucuronide formation. The Km and Vmax values for total bilirubin glucuronide formations were determined to be 0.05 ± 0.01 μM and 181.9 ± 5.3 pmol/min/mg-protein, respectively, in human recombinant UGT1A1, and 0.23 ± 0.05 μM and 875 ± 45 pmol/min/mg protein in human liver microsomes (HLM).

CONCLUSION

We have developed a sensitive LC-MS/MS based method for the quantitation of bilirubin and its glucuronides from in vitro incubations. This method was successfully utilized to determine bilirubin glucuronidation kinetics in HLM and human rUGT1A1.

Gunn Rats as a Surrogate Model for Evaluation of Hepatocyte Transplantation-Based Therapies of Crigler-Najjar Syndrome Type 1

Liver transplantation has been established as a curative therapy for acute and chronic liver failure, as well as liver-based inherited metabolic diseases. Because of the complexity of organ transplantation and the worldwide shortage of donor organs, hepatocyte transplantation is being developed as a bridging therapy until donor organs become available, or for amelioration of inherited liver-based diseases. The Gunn rat is a molecular and metabolic model of Crigler-Najjar syndrome type 1, which is characterized by lifelong unconjugated hyperbilirubinemia due to the lack of uridinediphosphoglucuronate glucuronosyltransferase-1 (UGT1A1)-mediated bilirubin glucuronidation. Gunn rats are convenient for evaluating the effect of hepatocyte transplantation or gene therapy, because the extent of UGT1A1 replacement can be assessed by serial determination of serum bilirubin levels, and excretion of bilirubin glucuronides in bile provide definitive evidence of the function of the transplanted hepatocytes or the effect of gene therapy. The core techniques involved in hepatocyte transplantation in Gunn rats are discussed in this chapter.

Analysis of binding ability of two tetramethylpyridylporphyrins to albumin and its complex with bilirubin

An interaction between 5,10,15,20-tetrakis-(N-methyl-x-pyridyl)porphyrins, x=2; 4 (TMPyPs) with bovine serum albumin (BSA) and its bilirubin (BR) complex was investigated by UV-Viz and fluorescence spectroscopy under imitated physiological conditions involving molecular docking studies. The parameters of forming intermolecular complexes (binding constants, quenching rate constants, quenching sphere radius etc.) were determined. It was showed that the interaction between proteins and TMPyPs occurs via static quenching of protein fluorescence and has predominantly hydrophobic and electrostatic character. It was revealed that obtained complexes are relatively stable, but in the case of TMPyP4 binding with proteins occurs better than TMPyP2. Nevertheless, both TMPyPs have better binding ability with free protein compared to BRBSA at the same time. The influence of TMPyPs on the conformational changes in protein molecules was studied using synchronous fluorescence spectroscopy. It was found that there is no competition of BR with TMPyPs for binging sites on protein molecule and BR displacement does not occur. Molecular docking calculations have showed that TMPyPs can bind with albumin via tryptophan residue in the hydrophilic binding site of protein molecule but it is not one possible interaction way.

Reduction of bilirubin ditaurate by the intestinal bacterium Clostridium perfringens

Bilirubin is degraded in the human gut by microflora into urobilinoids. In our study we investigated whether the bilirubin-reducing strain of Clostridium perfringens can reduce bilirubin ditaurate (BDT), a bile pigment of some lower vertebrates, without hydrolysis of the taurine moiety. C. perfringes was incubated under anaerobic conditions with BDT; reduction products were quantified by spectrophotometry and separated by TLC. Based on Rf values of BDT reduction products and synthetic urobilinogen ditaurate, three novel taurine-conjugated urobilinoids were identified. It is likely that bilirubin-reducing enzyme(s) serve for the effective disposal of electrons produced by fermentolytic processes in these anaerobic bacteria.

Plasma bilirubin correlations in non-obstructive cholestasis after partial hepatectomy

BACKGROUND

The aim of this study was to provide an improved outline of the patterns and correlates of changes in plasma bilirubin after partial hepatectomy.

METHODS

A large series of blood measurements and complementary variables were prospectively collected from 85 patients undergoing liver resection, and bilirubin correlations were assessed by regression analysis.

RESULTS

Early postoperatively, the best simultaneous correlates of increasing bilirubin were the preoperative value, the duration of surgery, and the number of blood transfusions (r2 = 0.74, p < 0.001). Subsequently, increasing bilirubin became related to the number of resected liver segments, the duration of intraoperative liver ischemia, the use of continuous vs. intermittent ischemia, and the presence of sepsis (r2 = 0.82, p < 0.001); these were also the best simultaneous correlates of peak bilirubin. This pattern was characterized by prominently conjugated hyperbilirubinemia, hypocholesterolemia, and moderately increased alkaline phosphatase, and occurred in the absence of obstructive cholestasis.

CONCLUSIONS

Major hepatectomy, parenchymal ischemia, and sepsis have similar and synergistic impacts as determinants of prominently conjugated hyperbilirubinemia after liver resection. This is likely related to impaired hepatocellular bilirubin transport and occurs in the absence of obstructive components.

Bilirubin as an antioxidant in micelles and lipid bilayers: its contribution to the total antioxidant capacity of human blood plasma

The antioxidant capacities, antioxidant activities, k(inh), and stoichiometric factors, n, of water-soluble derivatives of bilirubin (BR), BR-human serum albumin (BR-HSA), and BR-ditaurate disodium conjugate (BRC) were determined in aqueous/lipid dispersions of sodium dodecyl sulfate (SDS) micelles/methyl linoleate and in bilayers of dilinoleoylphosphatidylcholine (DLPC) during initiation by water-soluble azo-bis-amidinopropane dihydrochloride (ABAP). The inhibition rate constants for BRC and BR-HSA were similar in micelles (k(inh) approximately 1.3 x 10(4) M(-1) s(-1)), where n approximately 2, whereas the k(inh) for BR-HSA dropped by (1/2) in bilayers. The dimethyl ester of bilirubin (BRDE) gave a k(inh) only one-tenth that of the vitamin E analog, pentamethylhydroxychroman (PMHC) in SDS micelles/methyl linoleate when initiated by lipid-soluble azo-bis-2,4-dimethylvaleronitrile (DMVN). Biliverdin hydrochloride (BVHCl) was NOT an effective peroxyl radical-trapping agent in the micellar phase during initiation by ABAP or DMVN containing methyl linoleate but it inhibited oxygen uptake in the aqueous phase. Both BRC and BR-HSA extended the total radical antioxidant parameter (TRAP) of human blood plasma and their contribution to TRAP was in the range of 5-10% of the natural TRAP of blood plasma, depending on the BR content determined in the blood plasma.

Structure and function of the MRP2 (ABCC2) protein and its role in drug disposition

The multi-drug resistance protein 2 (MRP2; ABCC2) is an ATP-binding cassette transporter playing an important role in detoxification and chemoprotection by transporting a wide range of compounds, especially conjugates of lipophilic substances with glutathione, glucuronate and sulfate, which are collectively known as phase II products of biotransformation. In addition, MRP2 can also transport uncharged compounds in cotransport with glutathione, and thus can modulate the pharmacokinetics of many drugs. The other way around, its expression and activity are also altered by certain drugs and disease states. Unlike other members of the MRP/ABCC family, MRP2 is specifically expressed on the apical membrane domain of polarised cells as hepatocytes, renal proximal tubular cells, enterocytes and syncytiotrophoblasts of the placenta. Several naturally occurring mutations leading to the absence of functional MRP2 protein from the apical membrane have been described causing the human Dubin-Johnson syndrome associated with conjugated hyperbilirubinaemia. Experimental mutation studies have revealed critical amino acids for substrate binding in the MRP2 molecule. This review is, therefore, focused on the structure and function of MRP2, the substrates transported and the clinical relevance of MRP2.

In vitro production of bilirubin photoisomers by light irradiation using neoBLUE

BACKGROUND

The light-emitting diode is used as one of the new light sources for phototherapy. NeoBLUE (Atom Medical, Tokyo, Japan) incorporates blue light-emitting diodes for the treatment of neonatal hyperbilirubinemia. The authors compared the in vitro efficacy of neoBLUE with conventional phototherapy devices.

METHODS

The three light devices used included neoBLUE and two conventional phototherapy devices with six blue-white (BW) or six green (GR) fluorescent tubes. A bilirubin/human serum albumin solution (15 mg/dL) in 200 x 300 mm elliptical bag was irradiated with each three light device. The average light intensity of neoBLUE, BW and GR was 22.5, 10.2 and 2.6 microW/cm(2) per nm, respectively, for the irradiated area. Bilirubin photoisomers and native bilirubin were measured by high-performance liquid chromatography.

RESULTS

In neoBLUE, BW and GR, the respective production rate of cyclobilirubin was 6.0, 3.7 and 3.9 x 10(-2) mg/dL/min, and the respective (4Z, 15E)-bilirubin/(4Z, 15Z)-bilirubin ratio after irradiation was 0.44, 0.33 and 0.12; the (4Z, 15Z)-bilirubin reduction rate at 20 min after irradiation was 60, 68 and 82%, respectively. The reduction rate of (4Z, 15Z)-bilirubin correlated with the (4Z, 15E)-bilirubin/(4Z, 15Z)-bilirubin ratio.

CONCLUSION

Phototherapy using the neoBLUE under high level may be clinically more effective than therapy using the conventional light source from the results of the production rate of cyclobilirubin.

Energy change in the formation of conjugated bilirubin: a possible responsive mechanism for liver cell pathology

Bilirubin is formed when red blood cells die and their hemoglobin is broken down within the macrophages into heme and globins. In the liver, bilirubin is conjugated with UDP-glucuronate, making it water-soluble diglucuronide. Concerning this conjugation, a molecule of bilirubin reacts with two molecules of glucoronic acid. However, the nature of this energy-consuming reaction in the formation of conjugated bilirubin has never been reported, and this can be important for its potential implication in hyperbilirubinemia. In this work, the author calculated the energy required by conjugated-bilirubin formation per molecule. The energy required for complex formation is -22 kCal/mol. The nature of this energy-producing reaction can be a good explanation. Increased energy delivery in conjugated hyperbilirubinemia in liver disease might be a responsive mechanism to hepatic damage.

Influence of Conformation and Intramolecular Hydrogen Bonding on the Acyl Glucuronidation and Biliary Excretion of Acetylenic Bis-Dipyrrinones Related to Bilirubin

Glucuronidation and transporter-mediated efflux into bile are important in the elimination of xeno- and endobiotics, including the natural biladienone pigment bilirubin. The mechanisms of these processes and the structural factors that dictate whether cholephilic compounds are excreted directly in bile or require prior glucuronidation are poorly understood. To investigate effects of molecular shape and intramolecular hydrogen bonding on the interplay between direct excretion and glucuronidation in the liver, we studied a series of novel synthetic exploded and homologated bilirubin analogues. These include dicarboxylic mono- and diacetylenic tetrapyrroles with linear shapes that are unable to adopt the folded ridge-tile conformations that are crucially important in bilirubin metabolism. Intramolecular hydrogen bonding was varied by adjusting the alkyl chain lengths of the pendent carboxyl groups, and preferred conformations were predicted by molecular dynamics calculations. Metabolism studies were done in rats, including Gunn rats, congenitally deficient in UGT1 glucuronosyl tranferases, and TR- rats, deficient in the canalicular transporter Mrp2 (Abcc2). The results show strikingly that minor, seemingly inconsequential, changes in constitution, amplified by their influence on hydrogen bonding and molecular conformation, can profoundly influence competing clearance pathways in the liver, an effect that is unlikely to be restricted to bis-dipyrrinone carboxylic acids. Exposed carboxyl groups seem to favor the direct route of elimination, whereas the potential for carboxyl infolding by hydrogen bonding seems to favor glucuronidation. The results also show that molecular shape is less important in the hepatic glucuronidation and biliary excretion of bilirubin and of this series of acids than the capacity for intramolecular hydrogen bonding.

Function of multidrug resistance-associated protein 2 in acute hepatic failure rats

The function of multidrug resistance-associated protein 2 (Mrp2) in the intestine and liver, as well as intestinal Mrp2 expression, was analyzed in CCl(4)-induced acute hepatic failure rats with hyperbilirubinemia. The plasma level of bilirubin glucuronides, endogenous Mrp2-substrates, was 26 microM at 24 h after CCl(4) treatment. Mrp2 protein levels in jejunum decreased to 41% of control level. Mrp2-mediated efflux of 2,4-dinitrophenyl-S-glutathione (DNP-GSH), an Mrp2-substrate, in jejunum decreased to 31% of control in vitro, and was almost completely suppressed in vivo to the same level as that in the presence of probenecid, an Mrp2-inhibitor. Biliary excretion of DNP-GSH was suppressed to the same level as that inhibited by intravenous probenecid. The suppression of Mrp2 and the increased plasma bilirubin glucuronides recovered within 24 h thereafter. These results suggest that hyperbilirubinemia in disease states may be related to the systemic suppression of Mrp2 function.

Synthesis and hepatic transport of strongly fluorescent cholephilic dipyrrinones

A new class of highly fluorescent (phi(F) 0.3-0.8) low molecular weight water-soluble cholephilic compounds has been synthesized in two steps from dipyrrinones. The dipyrrinone nitrogens are first bridged by reaction with 1,1'-carbonyldiimidazole to form an N,N'-carbonyldipyrrinone (3H,5H-dipyrrolo[1,2-c:2',1'-f]pyrimidine-3,5-dione) nucleus, and a sulfonic acid group is then introduced at C(8) by reaction with concd H(2)SO(4). The resulting sulfonated N,N'-carbonyl-bridged dipyrrinones ("sulfoglows") are isolated as their sodium salts. When the alkyl substituents of the lactam ring are lengthened from ethyl to decyl, sulfoglows become increasingly lipophilic while maintaining water solubility. Low molecular weight sulfoglows were rapidly excreted intact in both bile and urine after intravenous infusion into rats, but higher molecular weight sulfoglows were excreted more selectively in bile. Hepatobiliary excretion of sulfoglows was partially, but not completely, blocked in mutant rats deficient in the multidrug-resistance associated transport protein Mrp2 (ABCC2). These observations point to the feasibility of developing simple sulfoglows with clinical diagnostic potential that are normally excreted in bile but appear in urine when hepatic elimination is impaired by cholestatic liver disease.

Mice lacking Mrp3 (Abcc3) have normal bile salt transport, but altered hepatic transport of endogenous glucuronides

BACKGROUND/AIM

Multidrug Resistance Protein 3 (MRP3) transports bile salts and glucuronide conjugates in vitro and is postulated to protect the liver in cholestasis. Whether the absence of Mrp3 affects these processes in vivo is tested.

METHODS

Mrp3-deficient mice were generated and the contribution of Mrp3 to bile salt and glucuronide conjugate transport was tested in (1): an Ussing-chamber set-up with ileal explants (2), the liver during bile-duct ligation (3), liver perfusion experiments, and (4) in vitro vesicular uptake experiments.

RESULTS

The Mrp3((-/-)) mice show no overt phenotype. No differences between WT and Mrp3-deficient mice were found in the trans-ileal transport of taurocholate. After bile-duct ligation, there were no differences in histological liver damage and serum bile salt levels between Mrp3((-/-)) and WT mice, but Mrp3-deficient mice had lower serum bilirubin glucuronide concentrations. Glucuronide conjugates of hyocholate and hyodeoxycholate are substrates of MRP3 in vitro and in livers that lack Mrp3, there is reduced sinusoidal secretion of hyodeoxycholate-glucuronide after perfusion with hyodeoxycholate.

CONCLUSIONS

Mrp3 does not have a major role in bile salt physiology, but is involved in the transport of glucuronidated compounds, which could include glucuronidated bile salts in humans.

Characterization of mice lacking the multidrug resistance protein MRP2 (ABCC2)

The multidrug resistance protein Mrp2 is an ATP-binding cassette (ABC) transporter mainly expressed in liver, kidney, and intestine. One of the physiological roles of Mrp2 is to transport bilirubin glucuronides from the liver into the bile. Current in vivo models to study Mrp2 are the transporter-deficient and Eisai hyperbilirubinemic rat strains. Previous reports showed hyperbilirubinemia and induction of Mrp3 in the hepatocyte sinusoidal membrane in the mutant rats. In addition, differences in liver cytochrome P450 and UGT1a levels between wild-type and mutant rats were detected. To study whether these compensatory mechanisms were specific to rats, we characterized Mrp2(-/-) mice. Functional absence of Mrp2 in the knockout mice was demonstrated by showing increased levels of bilirubin and bilirubin glucuronides in serum and urine, a reduction in biliary excretion of bilirubin glucuronides and total glutathione, and a reduction in the biliary excretion of the Mrp2 substrate dibromosulfophthalein. To identify possible compensatory mechanisms in Mrp2(-/-) mice, the expression levels of 98 phase I, phase II, and transporter genes were compared in liver, kidney, and intestine of male and female Mrp2(-/-) and control mice. Unlike in Mrp2 mutant rats, no induction of Mrp3 in Mrp2(-/-) mice was detected. However, Mrp4 mRNA and protein in liver and kidney were increased approximately 6- and 2-fold, respectively. Phenotypic analysis of major cytochrome P450-mediated activities in liver microsomes did not show differences between wild-type and Mrp2(-/-) mice. In conclusion, Mrp2(-/-) mice are a new valuable tool to study the role of Mrp2 in drug disposition.

Polypyrroles as Antioxidants: Kinetic Studies on Reactions of Bilirubin and Biliverdin Dimethyl Esters and Synthetic Model Compounds with Peroxyl Radicals in Solution. Chemical Calculations on Selected Typical Structures

[reaction: see text] Rate constants for hydrogen-atom transfer (HAT) from bilirubin dimethyl ester (BRDE) and biliverdin dimethyl ester (BVDE) to peroxyl radicals during inhibited autoxidation of styrene initiated by azo-bisisobutyronitrile (AIBN) were k(inh)(BRDE) = 22.5 x 10(4) and k(inh)(BVDE) = 10.2 x 10(4) M(-1) s(-1), and the stoichiometric factors (n) were 2.0 and 2.7, respectively. A synthetic tetrapyrrole (bis(dipyrromethene)) containing the alpha-central (2,2') CH2 linkage gave k(inh) = 39.9 x 10(4) M(-1) s(-1) and n = 2.3, whereas the beta-linked (3,3') isomer was not an active antioxidant. Several dipyrrinones were synthesized as mimics of the two outer heterocyclic rings of bilirubin and biliverdin. The dipyrrinones containing N-H groups in each ring were active antioxidants, whereas those lacking two such "free" N-H groups, such as N-CH3 dipyrrinones and dipyrromethenes, did not exhibit antioxidant activity. Overall, the relative k(inh) values compared to those of phenolic antioxidants, 2,6-di-tert-butyl-4-methoxyphenol (DBHA) and 2,6-di-tert-butyl-4-methylphenol (BHT), were 2,2'-bis(dipyrromethene) > BRDE > DBHA > dipyrrinones > BVDE > BHT. This general trend in antioxidant activities was also observed for the inhibited autoxidation of cumene initiated by AIBN. Chemical calculations of the N-H bond dissociation enthalpies (BDEs) of the typical structures support a HAT mechanism from N-H groups to trap peroxyl radicals. Intramolecular hydrogen bonding of intermediate nitrogen radicals has a major influence on the antioxidant activities of all compounds studied. Indeed, chemical calculations showed that the initial nitrogen radical from a dipyrrinone is stabilized by 9.0 kcal/mol because of H-bonding between the N-H remaining on one ring and the ground-state pyrrolyl radical of the adjacent ring in the natural zusammen structure. The calculated minimum structure of bilirubin shows strong intramolecular H-bonding of the N-H groups with carbonyl groups resulting in the known "ridge-tile" structure which is not an active HAT antioxidant. The calculated minimum structure of biliverdin is planar. BRDE is readily converted into BVDE by reaction with the electron-deficient DPPH* radical under argon in chlorobenzene. An electron-transfer mechanism is proposed for the initiating step in this reaction, and this is supported by the relatively low ionizing potential of a model dipyrrole representing the two central rings of bilirubin.

In vitro inhibition of UDP glucuronosyltransferases by atazanavir and other HIV protease inhibitors and the relationship of this property to in vivo bilirubin glucuronidation

Several human immunodeficiency virus (HIV) protease inhibitors, including atazanavir, indinavir, lopinavir, nelfinavir, ritonavir, and saquinavir, were tested for their potential to inhibit uridine 5'-diphospho-glucuronosyltransferase (UGT) activity. Experiments were performed with human cDNA-expressed enzymes (UGT1A1, 1A3, 1A4, 1A6, 1A9, and 2B7) as well as human liver microsomes. All of the protease inhibitors tested were inhibitors of UGT1A1, UGT1A3, and UGT1A4 with IC(50) values that ranged from 2 to 87 microM. The IC50 values found for all compounds for UGT1A6, 1A9, and 2B7 were >100 microM. The inhibition (IC50) of UGT1A1 was similar when tested against the human cDNA-expressed enzyme or human liver microsomes for atazanavir, indinavir, and saquinavir (2.4, 87, and 7.3 microM versus 2.5, 68, and 5.0 microM, respectively). By analysis of the double-reciprocal plots of bilirubin glucuronidation activities at different bilirubin concentrations in the presence of fixed concentrations of inhibitors, the UGT1A1 inhibition by atazanavir and indinavir was demonstrated to follow a linear mixed-type inhibition mechanism (Ki = 1.9 and 47.9 microM, respectively). These results suggest that a direct inhibition of UGT1A1-mediated bilirubin glucuronidation may provide a mechanism for the reversible hyperbilirubinemia associated with administration of atazanavir as well as indinavir. In vitro-in vivo scaling with [I]/Ki predicts that atazanavir and indinavir are more likely to induce hyperbilirubinemia than other HIV protease inhibitors studied when a free Cmax drug concentration was used. Our current study provides a unique example of in vitro-in vivo correlation for an endogenous UGT-mediated metabolic pathway.

Developmental changes in serum half-life of (EZ)-cyclobilirubin

BACKGROUND

Phototherapy has been a standard treatment for neonatal hyperbilirubinemia for more than 40 years, but it has remained sub-optimal.

AIMS

To clarify the developmental changes in parameters of (4E, 15Z)-cyclobilirubin ((EZ)-C) elimination in order to obtain basic data for establishing optimal phototherapy.

STUDY DESIGN

Blood samples were taken at regular intervals after stopping phototherapy, and bilirubin fractions were analyzed by high-performance liquid chromatography.

SUBJECTS AND METHODS

The subjects were 46 infants with hyperbilirubinemia who underwent phototherapy. The gestational age and birth weight of the subjects ranged from 25.0 to 41.0 weeks and from 656 to 3810 g, respectively, and the age at cessation of phototherapy was a median of 5 days. A kinetic model of (EZ)-C elimination was established, and the serum half-life of (EZ)-C was calculated on the basis of the determined model. Relationships of the half-life of (EZ)-C with birth weight and gestational age were investigated.

RESULTS

Serum (EZ)-C elimination followed a first-order kinetic model in 43 infants and a zero-order kinetic model in three extremely low birth weight infants. The half-life of (EZ)-C calculated on the basis of a first-order elimination model in serum ranged from 68 to 274 min and showed weak negative correlations with birth weight and gestational age.

CONCLUSIONS

Serum (EZ)-C excretion followed a first-order kinetic model in most of the neonates. The half-life of (EZ)-C becomes more prolonged in the very low birth weight infant and early gestational age.

CANALICULAR AND SINUSOIDAL DISPOSITION OF BILIRUBIN MONO- AND DIGLUCURONIDES IN SANDWICH-CULTURED HUMAN AND RAT PRIMARY HEPATOCYTES

Due to cholestasis or adverse drug effects, the excretion of bilirubin conjugates can decrease; therefore, the level of bilirubin (B) and bilirubin glucuronides (BGs) increases in the serum with the concomitant shift of bilirubin diversus monoglucuronide (BDG/BMG) equilibrium. The aim of this study was to utilize the collagen-sandwich culture of hepatocytes as an in vitro model for studying B conjugation and canalicular versus sinusoidal disposition of BGs. Canalicular and sinusoidal efflux of BMG and BDG obtained in sandwich-cultured rat primary hepatocytes was compared with that measured in human hepatocyte cultures. The BMG and BDG were separated by high-performance liquid chromatography and identified by mass spectrometry. The biliary excretion index (BEI) was estimated by measuring disposition of BGs into standard and Ca(2+), Mg(2+)-free medium. Significantly more BGs were excreted into the canalicular networks than into the medium in 96-h sandwich culture of both human and rat hepatocytes (BEI, 62.5 and 80.6, respectively). The BDG/BMG ratio in the medium versus that in the canalicular networks was 0.55/1.48, which is similar to the serum/bile values (0.6/1.5) observed in vivo by Mesa et al. [Mesa VA, De Vos R, and Fevery J (1997) J Hepatol 27:912-916]. In contrast, the BEI for p-nitrophenol glucuronide was 5.2. The low BEI value is in agreement with empirical observations, which suggest that molecules with low molecular weight are preferably excreted by the kidney. In conclusion, sandwich-cultured primary hepatocytes provide a useful in vitro method to differentiate between sinusoidal and canalicular disposition of BGs. Since the normal BDG/BMG ratio changes in hyperbilirubinemia, this model could be used to predict drug effects leading to hyperbilirubinemia.

Conjugated bilirubin measurements in Gilbert's syndrome: method dependence

BACKGROUND

Introducing new methodology often requires alteration to reference ranges and may cause inconvenience. Reagent suppliers may not have validated reference ranges quoted in their method sheets. When ratios of analytes are important, as for conjugated and unconjugated bilirubin, the combined changes can cause confusion.

METHODS

The effect on bilirubin result interpretation following a change from Vitros (E950) dry slide technology to the Bayer ADVIA 1650 wet chemistry system was studied.

RESULTS AND CONCLUSION

Over-estimation of conjugated bilirubin without an appropriate reference range can cause interpretative confusion. It is important to identify key patient groups likely to be affected by method changes well in advance. These need to be worked up in addition to reference range checks. It is unwise to rely on manufacturers for advice in this area. This report gives conjugated or direct bilirubin and total bilirubin values obtained using the above methods in nine patients with Gilbert's syndrome.

[Oxidative stress related diseases and biopyrrins]

Reactive oxygen species (ROS) cause damage to the structure and function of tissues. Therefore tissues have systems that eliminate ROS. Bilirubin is one antioxidant that reacts with ROS to produce oxidative metabolites. Biopyrrins are one of the metabolites, the level of which in urine reflects oxidative stress. They are measured by non-competitive inhibition ELISA that employs anti-bilirubin antibody (24G7) and the results are corrected for the urinary concentration of cereatinine. Some reports suggested that psychological stress increased oxidative stress markers. Urinary biopyrrins were also elevated by speech stress, and the subjective stress score recorded by the speakers correlated with the level. The result suggests that bilirubin might eliminate ROS generated by psychological stress. From the beginning of the study of biopyrrins, their urinary level has been known to be increased by surgical stress. Furthermore, it was significantly higher in a major operation patient group than in a minor one, and correlated with operation duration. Sepsis increased the level in surgical patients. Ischemia-reperfusion elevates ROS and, as a result, biopyrrin production. An increase in urinary biopyrrins was observed in a coronary spastic angina group after a spasm provocation test, and the level in myocardial infarction patients with NYHA (New York Heart Association) classification became higher. Correlation between urinary biopyrrins and plasma B-type natriuretic peptide (BNP) was also reported. Research that determines the structures of biopyrrins and their clinical application are in progress.

Conjugated bilirubin induces multidrug resistance-associated protein 2 mRNA expression and in vivo cisplatin resistance in rat hepatoma AH66 cells

In vivo cisplatin resistance of rat ascites hepatoma AH66 cells is suggested to result from the induction of multidrug resistance-associated protein 2 (MRP2) expression by ascites fluid (ASF) in the peritoneal cavity. The in vitro cisplatin sensitivity of AH66 cells grown in assay medium containing 5% fetal bovine serum in Dulbecco's modified Eagle's medium (5% FBS DMEM) did not change when the cells were treated with probenecid, an inhibitor of anion transporters, while the decreased cisplatin sensitivity of AH66 cells cultured in an assay medium containing 5% ASF (5% ASF DMEM) was restored by probenecid. Furthermore, in an in vivo study, the survival span (%ILS) of AH66-bearing rats was markedly extended by combination therapy with cisplatin and probenecid, compared with either agent alone. The expression of MRP2 mRNA was increased when AH66 cells were cultured in medium containing 5% ASF or 5% bile for 24 h. The induction of MRP2 mRNA expression in AH66 cells was also observed in the presence of heat-denatured ASF. The bilirubin content in ASF was characteristically higher than that in FBS, normal rat serum or AH66-bearing rat serum. Unconjugated bilirubin did not change the expression of MRP2 mRNA, whereas conjugated bilirubin markedly increased it. The cisplatin uptake in AH66 cells after culture in 5% FBS DMEM containing conjugated bilirubin was about half that of the cells cultured in 5% FBS DMEM alone (p < 0.01). In addition, the cisplatin sensitivity of the cells was significantly lowered by the addition of conjugated bilirubin. The expression of MRP2 mRNA in rat normal hepatocytes was also increased after culture in medium containing 5% ASF or 5% bile. These results indicated that conjugated bilirubin, a component of ASF, induces the mRNA expression of MRP2, which is a determinant of the in vivo cisplatin resistance of AH66 cells.

A New Class of Linear Tetrapyrroles: Acetylenic 10,10a-Didehydro-10a-homobilirubins

Novel bilirubin analogues with dipyrrinones conjoined to an acetylene rather than a methylene group were synthesized and examined spectroscopically. Despite the increased separation of the dipyrrinones forced by replacing a -CH(2)- by a -C(triple bond)C- unit, molecular dynamics calculations show that, like bilirubin, they may still engage in intramolecular hydrogen bonding to carboxylic acid groups when the propionic acid chains are slightly lengthened, e.g., butanoic acids. Unlike bilirubin, however, which is bent in the middle and has a ridge-tile shape, the acetylene orients the attached dipyrrinones along a linear path, and intramolecular hydrogen bonding preserves a twisted linear molecular shape. The extended planes of the dipyrrinones intersect along the -C(triple bond)C- axis at an angle of 136 degrees for the conformation stabilized by intramolecular hydrogen bonding in the bis-butyric acid rubin (1b). With shorter acid chains (propionic), only one CO(2)H can engage an opposing dipyrrinone in intramolecular hydrogen bonding, and in this energy-minimum conformation of the linear pigment 1a, the intersection of the extended planes of the dipyrrinones has an angle of 171 degrees. Spectroscopic evidence for such linearized and twisted structures was found in the pigments' NMR spectral data and their exciton UV-vis and induced circular dichroism spectra.

Novel Benzoic Acid Congeners of Bilirubin

Three regioisomeric bilirubins and biliverdins with propionic acids replaced by benzoic acids were synthesized from the corresponding xanthobilirubic acids by oxidative coupling. The rubins were found to exhibit widely varying polarity, spectroscopic properties, and stereochemistry. The isomer with ortho benzoic acids (1o) was much less polar than either the meta (1m) or para (1p) because 1o (but not 1m and 1p) can adopt a folded conformation with both carboxylic acids intramolecularly hydrogen bonded to the opposing dipyrrinones. The consequences of such conformational differentiation are found in the varying 1H NMR, UV-vis, and circular dichroism spectral properties.

Influence of glucuronosyl bilirubin and (EZ)-cyclobilirubin on determination of serum unbound bilirubin by UB-analyser

BACKGROUND

In the enzyme reaction for the determination of the unbound (free) bilirubin concentration by glucose oxidase and peroxidase, materials with low affinity for serum protein are reactive. The influence of these materials on the determination of serum unbound bilirubin was investigated. METHODS Serum samples from patients with neonatal hyperbilirubinaemia were analysed by high-performance liquid chromatography for total glucuronosyl bilirubin concentration (TGC) and (EZ)-cyclobilirubin concentration [(EZ)-C]. Based on these measurements, the samples were classified into three groups: group I [13 samples, TGC <2 micromol/L and (EZ)-C < 2.5 micromol/L]; group II [four samples, TGC < 2 micromol/L and (EZ)-C > or = 2.5 micromol/L]; and group III (five samples, TGC > or = 2 micromol/L). The concentrations of total bilirubin and unbound bilirubin were measured in these same samples with a UB-analyser. When the absorbance at 460nm was monitored, the decrease in absorbance was non-linear (concave curve). The degree of concavity was estimated (D15 value) as the deviation from linearity at 15s.

RESULTS

The D15 value was significantly higher in groups II and III than in group I. D15 value correlated significantly with TGC, (EZ)-C and unbound bilirubin concentration, and the unbound bilirubin concentration correlated significantly with TGC and (EZ)-C.

CONCLUSION

These results indicated that determination of serum unbound bilirubin concentration using the UB-analyser could be positively skewed by high concentrations of TGC and (EZ)-C.

Bilirubin dehydrogenase, an enzyme in Aspergillus ochraceus IB-3 useful for diagnostic measurement of bilirubin

Bilirubin dehydrogenase, a membrane-bound enzyme that catalyzes the one-step oxidation of ditaurobilirubin and bilirubin to ditaurobiliverdin and biliverdin, respectively, in the presence of an electron acceptor, was found in Aspergillus ochraceus IB-3, and purified from the membrane fraction through solubilization by Triton X-100. Phenazine and quinone derivatives acted as electron acceptors. Accumulation of ditaurobiliverdin and biliverdin by enzyme catalysis increased the absorbance at 660 nm, which is far from the range of wavelengths affected by serum ingredients. The enzyme selectively oxidized ditaurobilirubin at low pH, so changes in the reaction pH enable the enzyme to discriminate between the bilirubin fractions ditaurobilirubin (an example of conjugated bilirubin) and bilirubin (an example of unconjugated bilirubin). Using the enzyme, 2 to 80 microM of ditaurobilirubin were measured accurately by monitoring the changes in absorbance at 660 nm.

Comparison of urinary biopyrrin levels in acute myocardial infarction (after reperfusion therapy) versus stable angina pectoris and their usefulness in predicting subsequent cardiac events

We examined the relation between oxidative stress and cardiac events in patients with acute myocardial infarction (AMI). There is now increasing evidence that reactive oxygen species cause reperfusion injury to the previously ischemic myocardium after reperfusion. We measured urinary biopyrrin/creatinine levels, an oxidative stress marker, in 41 patients with AMI, 34 patients with stable angina pectoris (SAP), and 29 control subjects. In the patients with AMI, urine samples were taken before, at 4 and 24 hours, and at 1 and 2 weeks after reperfusion therapy. Of these 41 patients with AMI, 38 received reperfusion therapy, and the urinary biopyrrin/creatinine levels (micromol/g.creatinine) before reperfusion were significantly higher than those of the other 2 groups (AMI 4.24 +/- 0.49, SAP 2.45 +/- 0.15, control subjects 2.31 +/- 0.16; p = 0.0003 vs AMI). The onset of reperfusion significantly increased the levels of urinary biopyrrins/creatinine, and this time course was mapped out, peaking at 4 hours (8.21 +/- 0.96 vs 4.24 +/- 0.49 before, p = 0.0001), and decreasing to control levels between 24 hours and 7 days. The peak levels of urinary biopyrrins/creatinine were higher in the positive cardiac event group than in the negative cardiac event group (11.89 +/- 1.77 vs 7.57 +/- 1.00 micromol/g.creatinine, p = 0.029). These findings add further evidence that oxidative stress contributes to the complications of reperfusion injury, and suggest that urinary assessment of biopyrrins may be useful in predicting subsequent cardiac events after reperfusion in AMI.

Significance of altered bilirubin subfractions in bile following hepatectomy

BACKGROUND

Hyperbilirubinemia occurs as a sign of hepatic failure after hepatectomy. The pathogenesis of this event has not been elucidated. In cases complicated with postoperative infection, hyperbilirubinemia is prolonged and the composition of bilirubin subfractions in bile changes markedly. A reduction in the proportion of bilirubin diglucuronide (BDG) is especially notable. This study was aimed at clarifying the relationship between infection and biliary bilirubin subfractions, with a view to shedding light on the mechanisms of change.

MATERIALS AND METHODS

Rats underwent either laparotomy or partial hepatectomy (Hx). Daily intraperitoneal injections of lipopolysaccharide (LPS) or natural saline were administered for 3 days following surgery. Total serum bilirubin levels and proportions of BDG and bilirubin in bile were measured until Day 5 after the operation. Hepatic levels of UDP-glucuronic acid (UDP-GA), UDP-glucose, NAD(+), and total adenine nucleotides (TAN) and activities of UDP-glucuronyltransferase (UDP-GT) and UDP-glucose dehydrogenase were measured on Day 4.

RESULTS

In hepatectomized rats treated with LPS (Hx-LPS), total serum bilirubin levels were elevated, biliary bilirubin levels were decreased, and the proportion of biliary BDG was decreased on Day 4. Hepatic levels of UDP-GA, NAD(+), and TAN and activities of UDP-GT in Hx-LPS were reduced. In all groups tested, a significant linear correlation between BDG and UDP-GA and between UDP-GA and NAD(+) was found.

CONCLUSIONS

The reduction of UDP-GA might be effected by reduced hepatic levels of NAD(+) in endotoxemia following hepatectomy. It is therefore suggested that alterations in biliary bilirubin subfractions might accurately reflect the energy state of the remnant liver following hepatectomy.

Synthesis and spectroscopic properties of a new class of strongly fluorescent dipyrrinones

A new, highly fluorescent (Phi(F) > or = 0.8) chromophore has been synthesized in one step from dipyrrinones by reaction with N,N-carbonyldiimidazole to form the 3H,5H-dipyrrolo[1,2-c:2',1'-f]pyrimidine-3,5-dione nucleus.

Increased renal expression of bilirubin glucuronide transporters in a rat model of obstructive jaundice

Regulation of bilirubin glucuronide transporters during hyperbilirubinemia in hepatic and extrahepatic tissues is not completely clear. In the present study, we evaluated the regulation of the bilirubin glucuronide transporters, multidrug resistance-associated proteins (MRP)2 and 3, in rats with obstructive jaundice. Bile duct ligation (BDL) or sham operation was performed in Wistar rats. Liver and kidneys were removed 1, 3, and 5 days after BDL (n = 4, in each group). Serum and urine were collected to measure bilirubin levels just before animal killing. MRP2 And MRP3 mRNA expressions were determined by real-time RT-PCR. Protein expression of MRP2 and MRP3 was determined by Western blotting. Renal MRP2 function was evaluated by para-aminohippurate (PAH) clearance. The effect of conjugated bilirubin, unconjugated bilirubin, human bile, and sulfate-conjugated bile acid on MRP2 gene expression was also evaluated in renal and hepatocyte cell lines. Serum bilirubin and urinary bilirubin excretion increased significantly after BDL. In the liver, the mRNA expression of MRP2 decreased 59, 86, and 82%, and its protein expression decreased 25, 74, and 93% compared with sham-operated animals after 24, 72, and 120 h of BDL, respectively. In contrast, the liver expression of MRP3 mRNA increased 138, 2,137, and 3,295%, and its protein expression increased 560, 634, and 612% compared with sham-operated animals after 24, 72, and 120 h of BDL, respectively. On the other hand, in the kidneys, the mRNA expression of MRP2 increased 162, 73, and 21%, and its protein expression increased 387, 558, and 472% compared with sham-operated animals after 24, 72, and 120 h of BDL, respectively. PAH clearance was significantly increased after BDL. The mRNA expression of MRP2 increased in renal proximal tubular epithelial cells after treatment with conjugated bilirubin, sulfate-conjugated bile acid or human bile. Upregulation of MRP2 in the kidneys and MRP3 in the liver may be a compensatory mechanism to improve bilirubin clearance during obstructive jaundice.

D-glucaric acid in common duct bile and relation to choledocholithiasis

BACKGROUND

The aim was to investigate a possible association between D-glucaric acid (DGA), biliary bilirubin glucuronidation and brown pigment stones in the common bile duct.

METHODS

A high performance liquid chromatography method with a strong cation resin (HPX-87H) was developed for measuring biliary DGA. Bile was obtained during ERCP by deep cannulation of the common bile duct in 100 patients with suspected biliary disease.

RESULTS

The concentration of DGA in common bile duct bile was 60 (1.1-633) micromol l(-1) (median, range). The values were lower than previously reported. There were no differences in DGA concentrations in patients with common bile duct stones compared to patients without common bile duct stones, irrespective of stone type, cholesterol or brown pigment stones. Bilirubin conjugates in common duct bile did not vary with DGA concentrations.

CONCLUSION

DGA is probably insignificant in the pathogenesis of common bile duct stones.

[Effect of bilirubin derivative on HIV-1 in vitro]

BACKGROUND

To study the effect of DTB against HIV-1, for developing anti-HIV drugs.

METHODS

Different concentration of DTB was added to cell culture system after viral inoculation, MTT staining method for viable cells (MTT assay) and p24 (ELISA) were used as markers to monitor the viral replication.

RESULTS

The inhibition rates of DTB at concentrations 160, 80, and 40mg/ml were 93.0%, 56.2% and 18.1%, respectively.

CONCLUSIONS

DTB could effectively inhibit HIV-1 in vitro.

[Using purified conjugated bilirubin as a calibrator for bilirubin measurement]

OBJECTIVES

To improve the accuracy and precision of the determination of bilirubin, especially direct bilirubin (DB), and the standardization of that as well.

METHODS

Purified conjugated bilirubin (Bc) and ditaurobilirubin(DTB) and their diazo products were subjected to absorption spectrum analysis. The diazo reaction characters of their calibration solutions were compared by the method of Doumas J-G(TB & DB).

RESULTS

Bc, DTB and their azopigments were found to have the similar absorption spectra with the same lambda max. Their TB standard curves almost superposed together all over. Although the slopes of their DB standard curves were not markedly different ((YBc = 0.00366X + 0.00933, rBc2 = 0.9977, P < 0.01; YDTB = 0.00391X + 0.00023, rDTB2 = 0.9987, P < 0.01; Pb1-b2 > 0.05, n1 = n2 = 5), the DB value measured for Bc differed from that for DTB(n = 5, P < 0.05). In addition, the calibrators made from Bc based different matrices, such as HSA, BSA and human serum, were significantly different in DB/Bc, but no difference was seen among the concentrations. Furthermore, the DB values determined for DTB or Bc increased linearly with the corresponding concentrations, respectively, with no difference between the slopes (YBc = 0.8300XBc + 1.9463, rBc2 = 0.9977, P < 0.01; YDTB = 0.8853XDTB-0.0251, rDTB2 = 0.9986, P < 0.01; n1 = n2 = 5, Pb1-b2 > 0.05).

CONCLUSIONS

The results demonstrate that the diazo reaction characters of Bc are identified with those of DTB. However, under the condition of DB, Bc reacts differently from DTB. This study also indicates that as a calibrator of DB based human serum, Bc has the similar constant effect of HCl as serum samples do, so it is a more reliable calibrator to eliminate the matrix effects.

Fourier-transform Raman and infrared spectroscopic analysis of dipyrrinones and mesobilirubins

The Fourier-transform Raman (FT-Raman), infrared (FT-IR), and UV-visible absorption spectra of four dipyrrinones and two mesobilirubins have been investigated in the solid state and in CH2Cl2 solutions. A detailed spectral analysis, assignment and discussion of these spectra are presented. The bands at 1735-1738, 1691-1707 and 1359-1377 cm(-1) which were assigned to the stretching vibrations of the C-O-C and C-O-H and symmetric deformation of C-H bonds, respectively, can act as a marker to distinguish the compounds of this class. The striking differences between the spectra of the compounds suggest that mesobilirubin XIIIalpha is tending to adopt as ridge-tile conformation, rather than linear conformation.

Structure and metabolism of natural and synthetic bilirubins

The secondary structure of bilirubin, with a ridge-tile shape and six intramolecular hydrogen bonds, is more stable than any other conformation and perhaps the most important determinant of its solubility and properties in solution and its hepatic metabolism/excretion. Uncoupling the intramolecular hydrogen bonding, increasing the acidity of the propionic acid, or even increasing its length can decrease the pigment's hydrophobicity and permit its excretion intact across the liver into bile; less intuitively obvious, so can subtle modifications at C(10), the pivotal carbon in the ridge tile.

Expression of bacterial beta-glucuronidase in human bile: an in vitro study

BACKGROUND

Bacterial beta-glucuronidase causes deconjugation of bilirubin diglucuronide resulting in the precipitation of calcium bilirubinate, which contributes to biliary sludge and stone formation. This process is attributed to enzyme activity produced by the aerobic enterobacteriaceae such as Escherichia coli and Klebsiella sp. The presence of Clostridium sp. was detected in 48 of 56 intrahepatic stones by using polymerase chain reaction techniques and cultured Clostridium perfringens from 14 of 18 unblocked biliary stents. Such bacteria are reported to produce beta-glucuronidase activity. The aim of this study was to determine the proportion of biliary bacteria isolated from pigment stones and stents that produce beta-glucuronidase and to compare the enzyme activity expressed by the different bacteria in human bile.

METHODS

A total of 202 bacteria were isolated from blocked and unblocked biliary stents and pigment ductal stones recovered from patients. Of these, 61 bacteria expressed beta-glucuronidase activity in brain heart infusion broth. These 61 bacteria were subsequently grown in human bile under aerobic or anaerobic conditions to the early stationary phase and assayed for beta-glucuronidase activity by using rho-nitrophenyl beta-D glucuronide as substrate. Results were normalized and reported as units of enzyme activity per milligram protein of the bacteria.

RESULTS

C. perfringens produced beta-glucuronidase enzyme activity that was 34-fold higher than that for E coli, Staphylococcus, Corynebacterium sp., Bacillus sp., Enterococcus sp., Acinetobacter sp., Streptococcus sp., and Klebsiella sp.

CONCLUSION

C. perfringens with its higher enzyme activity is more important in the deconjugation of bilirubin diglucuronide than E coli and Klebsiella sp.

Relationships between serum (ZZ)-bilirubin, its subfractions and biliverdin concentrations in infants at 1-month check-ups

In 150 infants, including those with breast milk jaundice, who were brought to our hospital for their 1-month check-ups, the serum concentrations of (ZZ)-bilirubin, its subfractions and biliverdin were measured by high-performance liquid chromatography and the relationships among them investigated. (ZZ)-Bilirubin was found to have the highest serum concentration, followed by (ZE)-bilirubin, accounting for 14.0 (geometric mean) % of (ZZ)-bilirubin. Biliverdin had a serum concentration of 0.95% of (ZZ)-bilirubin. There was only a small amount of total (di- and mono-) glucuronosyl bilirubin, 0.42% of (ZZ)-bilirubin. (ZE)-Bilirubin, (EZ)-bilirubin, (EZ)-cyclobilirubin. biliverdin, diglucuronosyl bilirubin and monoglucuronosyl bilirubin (C-8 and C-12) showed positive logarithmic correlations with (ZZ)-bilirubin (R2=0.16 or above, P<0.05). (ZE)-Bilirubin showed a significant positive logarithmic correlation with (ZZ)-bilirubin (R2=0.863, P<0.0001). Furthermore, (EZ)-cyclobilirubin, the most important photoisomer in phototherapy for neonatal hyperbilirubinaemia, was detected in very small amounts in approximately half of the neonates (84 of 150) when they were in conditions of only weak ambient light. The relationship between total glucuronosyl bilirubin and (ZZ)-bilirubin concentrations fitted a model of saturation kinetics of bilirubin UDP-glucuronosyltransferase.

Cyclobilirubin formation by in vitro photoirradiation with neonatal phototherapy light

BACKGROUND

The main mechanism of phototherapy for neonatal hyperbilirubinemia is the production and excretion of (EZ)- and (EE)-cyclobilirubin (4E,15Z- and 4E,15E-cyclobilirubin). Thus, the clinical efficacy of the light source for phototherapy must be evaluated by cyclobilirubin formation from (ZZ)-bilirubin in in vitro photoirradiation.

METHODS

In the present study, we investigated the in vitro production pattern of bilirubin photoisomers by phototherapy light from the bilirubin-human serum albumin complex.

RESULTS

No clear difference was found in the curves relative to (ZZ)-bilirubin and its photoisomers under aerobic and anaerobic conditions. The ratio of (EZ)-cyclobilirubin to (ZZ)-bilirubin increased proportionately to the dose of irradiating light and no photoequilibrium state was observed analogous to that found in configurational photoisomerization. The concentration of (EZ)- and (EE)-cyclobilirubin increased proportionately with the grade of the percentage decrease in A(460 nm) from 0 to 23%. With a percentage decrease in A(460 nm) of 23% or more, the cyclobilirubin concentrations reached a steady state. The reason for this appears to be that the concentration of (ZZ)-bilirubin, a substrate for photoisomers, dropped below 1 mg/100 mL. Biliverdin was produced only in trace amounts. However, the absorption at 520--700 nm increased after a percentage decrease in A(460 nm) of more than 23%.

CONCLUSIONS

The results of the present study show that little bilirubin photooxidation occurred with in vitro aerobic photoirradiation. Before the concentration of cyclobilirubin reaches a steady state, it is theoretically valid to use the percentage decrease in A(460 nm) for the evaluation of the clinical efficacy of the light source.

Recent advances in bilirubin metabolism research: the molecular mechanism of hepatocyte bilirubin transport and its clinical relevance

Bilirubin is taken up from blood into hepatocytes by sinosuidal membrane transporters and then excreted into bile through the bile canalicular membrane mainly as bilirubin glucuronides. (1) Mechanism of bilirubin uptake into hepatocytes: many organic anions are incorporated into hepatocytes by organic anion transporting polypeptides (rat, oatp1, oatp2, oatp3; human, OATP), liver-specific transporter (rlst/HLST), and/or by organic anion transporters (OAT2, OAT3). Oatp1 and HLST transport bilirubin monoglucuronide. However, a transporter of unconjugated bilirubin in the sinusoidal membrane has not as yet been identified. Unconjugated bilirubin may also go across the hepatocyte sinusoidal membrane by a diffusion process. (2) Intrahepatic transport and conjugation of bilirubin: ligandin carries bilirubin to the endoplasmic reticulum (ER) of hepatocytes. In the ER, bilirubin is conjugated by bilirubin uridine diphosphate (UDP)-glycosyltransferase (bilirubin UGT; UGT1A1) to form mono- and diglucuronides of bilirubin. (3) Transport mechanism of bilirubin glucuronides across the hepatocyte canalicular membrane: at the canalicular membrane, bilirubin glucuronides are excreted into bile by multidrug resistance-associated protein 2 (MRP2), a member of the ATP-binding cassette transporter family. (4) Regurgitation of bilirubin glucuronides into blood: MRP3, which is located in the lateral membrane, transports bilirubin glucuronides into blood under conditions of impaired biliary bilirubin excretion.

Sodium etiobilirubin-IVgamma-C10-sulfonate: a highly solvated bile pigment structure containing two different non-ridge-tile conformers in the unit cell

The crystal structure of the title compound is the first example of a bilirubin existing in both extended and cyclic conformations and the first bile pigment structure showing two markedly different conformations in the unit cell. In contrast to previous rubin structures the dipyrrinone rings are twisted out of planarity in both conformers. Because of numerous hydrogen-bonding and ionic interactions a highly complex tetrameric structure is observed in which each extended conformer is held pincer-like by another.

Synthesis and metabolism of the first thia-bilirubin

A symmetrical C(10)-thiabilirubin analogue, 8,12-bis(2-carboxyethyl)-2,3,17,18-tetraethyl-7,13-dimethyl-10-thia-(21H,23H,24H)-bilin-1,19-dione (1), was synthesized from 8-(2-carboxyethyl)-2,3-diethyl-7-methyl-10H-dipyrrin-1-one in one step by reaction with sulfur dichloride. The thia-rubin exhibited the expected IR, UV-vis, and NMR spectroscopic properties, which are rather similar to those of mesobilirubin-XIIIalpha. Like bilirubin and mesobilirubin, 1 adopts an intramolecularly hydrogen-bonded conformation, shaped like a ridge-tile but with a steeper pitch. The longer C-S bond lengths and smaller bond angles at C-S-C, as compared to C-CH(2)-C, lead to an interplanar angle between the two dipyrrinones of only 74 degrees -or considerably less than that of bilirubin (approximately 100 degrees). On normal- and reversed-phase chromatography, 1 is substantially less polar than bilirubin. Despite this conformational distortion, 1 is metabolized in normal rats to acyl glucuronides, which are secreted into bile. In mutant (Gunn) rats lacking bilirubin glucuronosyl transferase, 1 (like bilirubin) was not excreted in bile.

An evaluation of the characteristics and performance of neonatal phototherapy equipment

This paper reviews the current state of knowledge and practice in neonatal phototherapy, and assesses methods of evaluating the characteristics and performance of different equipment. Artificial lighting (usually fluorescent) has been used for the past 30 years in the treatment of neonatal jaundice. Widely differing light outputs and spectra are used, making comparison and evaluation difficult for clinicians. Manufacturers of neonatal phototherapy equipment have no standard for assessing the performance of their equipment, and information that is supplied is at best confusing or deceptive to the users. Best practice is usually based on empirical data from equipment in use, but there is wide agreement that present phototherapy is sub-optimal, i.e. does not achieve maximum rate of bilirubin clearance for minimum therapeutic dose. Several studies in the last ten years have emphasized the importance of both the wavelength and intensity of light for optimal phototherapy. These are discussed and a technique is proposed for normalizing the output of different systems to make comparison easier and to enable optimal treatments to be designed.

Bilirubin overload modulates bile canalicular membrane fluidity in rats: association with disproportionate reduction of biliary lipid secretion

We recently demonstrated that several organic anions cause dissociation of biliary lipid secretion from that of bile acids; namely, the "uncoupling phenomenon," in association with changes in the phospholipid molecular species in the canalicular membrane lipid bilayer. Because of the uncoupling phenomenon, transcytotic vesicles are retained inside cells, resulting in the accumulation of substances normally excreted in the bile. In the present study, bilirubin ditaurate (BDT; synthetic bilirubin) was used to investigate the effect of bilirubin overload on biliary lipid secretion and the lipid composition of hepatic subcellular fractions, as well as canalicular membrane packing density and fluidity. Male Sprague-Dawley rats underwent cannulation of the bile duct and femoral vein. Sodium taurocholate was infused intravenously at 100 nmol/min per 100 g body weight. Then BDT (50 nmol/min per 100 g body weight) was infused concomitantly, followed by periodic bile collection for analysis of lipids. Bile acid secretion was not significantly affected by the infusion of BDT. In contrast, the secretion of cholesterol and phospholipids was decreased by 56.7% and 49.2%, respectively, compared with control. The phosphatidylcholine hydrophobicity of canalicular membrane vesicles, estimated by the molar ratio of saturated to unsaturated fatty acids (S/U ratio) was decreased, but not significantly by BDT infusion. With BDT infusions, the biliary cholesterol/phospholipid (C/P) ratio was increased by 19%; canalicular membrane vesicle fluidity was decreased by 5.8%, whereas P-glycoprotein expression was unchanged. As P-glycoprotein expression was not altered, our findings suggested that the reduced canalicular membrane vesicle fluidity was a crucial regulator of canalicular membrane transporter function.

Characterization of inducible nature of MRP3 in rat liver

We found previously that expression of multidrug resistance-associated protein (MRP) 3 is induced in a mutant rat strain (Eisai hyperbilirubinemic rats) whose canalicular multispecific organic anion transporter (cMOAT/MRP2) function is hereditarily defective and in normal Sprague-Dawley (SD) rats after ligation of the common bile duct. In the present study, the inducible nature of MRP3 was examined, using Northern and Western blot analyses, in comparison with that of other secondary active [Na(+)-taurocholic acid cotransporting polypeptide (Ntcp), organic anion transporting polypeptide 1 (oatp1), and organic cation transporter (OCT1)] and primary active [P-glycoprotein (P-gp), cMOAT/MRP2, and MRP6] transporters. alpha-Naphthylisothiocyanate treatment and common bile duct ligation induced expression of P-gp and MRP3, whereas expression of Ntcp, oatp1, and OCT1 was reduced by the same treatment. Although expression of MRP3 was also induced by administration of phenobarbital, that of cMOAT/MRP2, MRP1, and MRP6 was not affected by any of these treatments. Moreover, the mRNA level of MRP3, but not that of P-gp, was increased in SD rats after administration of bilirubin and in Gunn rats whose hepatic bilirubin concentration is elevated because of a defect in the expression of UDP-glucuronosyl transferase. However, the MRP3 protein level was not affected by bilirubin administration. Although the increased MRP3 mRNA level was associated with the increased concentration of bilirubin and/or its glucuronides in mutant rats and in SD rats that had undergone common bile duct ligation or alpha-naphthylisothiocyanate treatment, we must assume that factor(s) other than these physiological substances are also involved in the increased protein level of MRP3.

Intracellular supply of phospholipids for biliary secretion: evidence for a nonvesicular transport component

Phospholipids (PL) for biliary secretion could be supplied from the endoplasmic reticulum (ER) to the plasma membrane by cytosolic transfer proteins or transport vesicles. Therefore, we studied whether biliary secretions of PL and apolipoprotein A-I (apo A-I), as markers for the ER-to-Golgi vesicular transport pathway, are tightly coupled in isolated perfused rat livers with enhanced secretion (+60%) of PL after withdrawal of the cholesterol synthesis inhibitor pravastatin (0.1% of chow, fed for 7 days). Blocking agents dissociated the secretion of apo A-I and PL. Brefeldin A as well as cycloheximide inhibited biliary secretion of apo A-I (-52%; -68%), however, not of PL. Both bilirubin ditaurate and taurodehydrocholic acid reduced biliary secretion of PL (-27%; -79%), but not of apo A-I. The data support the concept that PL destined for biliary secretion bypass the vesicular transport pathway of apo A-I through the Golgi compartment, most likely via cytosolic transfer proteins.

Brown pigment stones in the common bile duct: reduced bilirubinate diconjugate in bile

BACKGROUND

Bilirubin is the main component of most common bile duct stones. Normally, almost all bilirubin in bile is conjugated to glucuronic acid or some other sugar moiety. These conjugates are unstable and liable to deconjugation. Unconjugated bilirubin is insoluble and may precipitate as the calcium salt found in brown pigment stones. The pattern of bilirubin conjugates in common duct bile of patients with choledocholithiasis has been unknown.

METHODS

In a clinical series of 55 patients with choledocholithiasis common-duct bile was aspirated, and the bilirubin conjugates analyzed with high-performance liquid chromatography. One stone from each patient was analyzed for cholesterol and bilirubin content to determine stone type.

RESULTS

Sixteen patients had cholesterol stones, 38 patients had brown pigment stones, and 1 patient had a black stone. Patients with pigment stones had a lower percentage of bilirubin diglucuronide (median, 60.3%; interquartile range, 49.7%-67.3%) than patients with cholesterol stones (64.0%; 60.2%-73.3%) (Mann-Whitney, P=0.015). No significant difference was found for the other bilirubin conjugates, total bilirubin, or biliary pH when pigment and cholesterol stone patients were compared. The time of bile sampling in relation to papillotomy and treatment of cholestasis was not associated with the low percentage of bilirubin diglucuronide. The observation of reduced values for bilirubin diglucuronide could not be ascribed to duodenal diverticula or Billroth-II gastric resection.

CONCLUSION

The percentage of the main bilirubinate conjugate, bilirubin diglucuronide, is decreased in the common duct bile of patients with pigmented compared with cholesterol stones.