Hepatic bilirubin-conjugating enzymes of man in the normal state and in liver disease

"Gilbert's-like" syndrome as part of a spectrum of persistent unconjugated hyperbilirubinemia in post-chronic hepatitis patients

Gilbert’s syndrome (GS) patients present with remittent unconjugated hyperbilirubinemia. In this study, we investigated the correlation between polymorphisms in the gene encoding UDP-glucuronosyltransferase, UGT1A1, and the development of unconjugated hyperbilirubinemia in clinical GS and post-hepatitis hyperbilirubinemia. Blood samples were collected from 285 patients, including 85 patients who were clinically diagnosed with GS, 70 patients who had indirect hyperbilirubinemia during the recovery period of chronic liver diseases, 109 patients with normal hepatic function and 21 chronic active hepatitis patients. All samples were tested for the presence of the *28/*6 UGT1A1 genotype by pyrosequencing. Compared with the GS-control group, a significant difference in variations of the UGT1A1*28/*6 allele gene was found in GS patients. The post-hepatitis group showed a significant difference in the UGT1A1*28/*6 allele gene frequency distribution relative to that in the hepatitis control group. There were no significant differences between the GS group and post-hepatitis group in the distribution of the UGT1A1*28/*6 allele gene frequency and UGT1A1 diplotypes. UGT1A1*28/*6 gene polymorphisms in patients who had indirect hyperbilirubinemia while recovering from chronic liver diseases presented similar patterns as those seen for GS patients. These findings suggest that a “Gilbert’s-like” syndrome might be part of the spectrum of persistent unconjugated hyperbilirubinemia in post-chronic hepatitis patients.

Reduction in hepatic secondary bile acids caused by short-term antibiotic-induced dysbiosis decreases mouse serum glucose and triglyceride levels

Antibiotic-caused changes in intestinal flora (dysbiosis) can have various effects on the host. Secondary bile acids produced by intestinal bacteria are ligands for specific nuclear receptors, which regulate glucose, lipid, and drug metabolism in the liver. The present study aimed to clarify the effect of changes in secondary bile acids caused by antibiotic-induced dysbiosis on the host physiology, especially glucose, lipid, and drug metabolism. After oral administration of non-absorbable antibiotics for 5 days, decreased amounts of secondary bile acid-producing bacteria in faeces and a reduction in secondary bile acid [lithocholic acid (LCA) and deoxycholic acid (DCA)] levels in the liver were observed. Serum glucose and triglyceride levels were also decreased, and these decreases were reversed by LCA and DCA supplementation. Quantitative proteomics demonstrated that the expression levels of proteins involved in glycogen metabolism, cholesterol, bile acid biosynthesis, and drug metabolism (Cyp2b10, Cyp3a25, and Cyp51a1) were altered in the liver in dysbiosis, and these changes were reversed by LCA and DCA supplementation. These results suggested that secondary bile acid-producing bacteria contribute to the homeostasis of glucose and triglyceride levels and drug metabolism in the host, and have potential as therapeutic targets for treating metabolic disease.

Hereditary spherocytosis coexisting with UDP-glucuronosyltransferase deficiency highly suggestive of Crigler-Najjar syndrome type II

Patients with co-existing hereditary spherocytosis (HS) and UDP-glucuronosyltransferase 1A1 (UGT1A1) deficiency as Gilbert's syndrome (GS) have been reported, and previous studies have demonstrated an increased risk for developing gallstones in patients with co-inheritance of GS and HS. We experienced an interesting case of HS showing persistent jaundice after splenectomy, and upon further evaluation, the 25-year-old female patient was found to have HS combined with UGT1A1 deficiency. Sequence analysis of the UGT1A1 gene revealed that she was a compound heterozygote with p.[G71R; Y486D] + [Y486D] mutations, which suggests Crigler-Najjar syndrome type II rather than GS. Careful evaluation of inappropriately elevated bilirubin level compared with the degree of hemolysis is important, reflecting the therapeutic implication of splenectomy and cholecystectomy.

Combined effect of regulatory polymorphisms on transcription of UGT1A1 as a cause of Gilbert syndrome

Background

Gilbert syndrome is caused by defects in bilirubin UDP-glucuronosyltransferase (UGT1A1). The most common variation believed to be involved is A(TA)7TAA. Although several polymorphisms have been found to link with A(TA)7TAA, the combined effect of regulatory polymorphisms in the development of Gilbert syndrome remains unclear.

Methods

In an analysis of 15 patients and 60 normal subjects, we detected 14 polymorphisms and nine haplotypes in the regulatory region. We classified the 4-kbp regulatory region of the patients into: the TATA box including A(TA)7TAA; a phenobarbital responsive enhancer module including c.-3275T>G; and a region including other ten linked polymorphisms. The effect on transcription of these polymorphisms was studied.

Results

All haplotypes with A(TA)7TAA had c.-3275T>G and additional polymorphisms. In an in-vitro expression study of the 4-kbp regulatory region, A(TA)7TAA alone did not significantly reduce transcription. In contrast, c.-3275T>G reduced transcription to 69% of that of wild type, and the linked polymorphisms reduced transcription to 88% of wild type. Transcription of the typical regulatory region of the patients was 56% of wild type. Co-expression of constitutive androstane receptor (CAR) increased the transcription of wild type by a factor of 4.3. Each polymorphism by itself did not reduce transcription to the level of the patients, however, even in the presence of CAR.

Conclusions

These results imply that co-operation of A(TA)7TAA, c.-3275T>G and the linked polymorphisms is necessary in causing Gilbert syndrome.

Yondelis (trabectedin, ET-743): the development of an anticancer agent of marine origin

Yondelis (trabectedin, ET-743) is a novel antitumor agent derived from a marine source, the Caribbean tunicate Ecteinascidia turbinata. Preclinical studies demonstrated activity at low concentrations against a variety of tumors. The mechanism by which ET-743 exerts its antitumor activity has not been completely elucidated yet. Binding to the minor groove of DNA which causes a bend towards the major groove has been demonstrated. Furthermore, ET-743 interferes with DNA binding proteins and transcription factors. Clinical studies have been initiated as phase I dose-finding studies at four different treatment regimens. Dose-limiting toxicities were hematological, including neutropenia and thrombocytopenia. Furthermore, significant liver toxicity was observed, especially as a rise in transaminase levels. Antitumor activity in phase I and phase II trials was studied in multiple tumor types, including soft tissue sarcomas, melanomas and breast cancer. ET-743 is currently being extensively investigated in advanced soft tissue sarcomas. The present review describes the development of ET-743, highlighting chemical properties, mode of action, metabolism and preclinical and clinical studies.

Identification of a defect in the UGT1A1 gene promoter and its association with hyperbilirubinemia

The UDP-glucuronosyltransferase UGT1A1 plays a critical role in the detoxification of potentially neurotoxic bilirubin by conjugating it with glucuronic acid. We identified a polymorphism that results in a T to G substitution at nucleotide number -3263 of the phenobarbital-responsive enhancer module of the UGT1A1 gene, thereby significantly decreasing transcriptional activity as indicated by the luciferase-reporter assay. At least one T-3263G allele was found in 21 of 25 subjects with mild hyperbilirubinemia (Gilbert's syndrome); this frequency (0.58) was significantly higher than that in normobilirubinemic controls (0.17; n = 8 of 27). Homozygous mutations in the TATA element (A[TA](7)TAA) or at nucleotide 211 of exon 1 (G to A substitution) were found in 5 and 2 of the hyperbilirubinemic group, respectively, while 12 of these subjects were double heterozygotes for the T-3263G and G211A mutations. Plasma total bilirubin levels in these double heterozygotes were significantly higher than those in control subjects carrying one or other of these mutations singly, indicating that compound heterozygous mutations may result in more strongly reduced UGT1A1 activity. Our results indicate that homozygosity and compound heterozygosity for mutations in the UGT1A1 gene promoter (T-3263G and A[TA](7)TAA) and/or exon 1 of the gene (G211A) could explain the hyperbilirubinemia seen in the majority of individuals with Gilbert's syndrome.

Search for metabolites of ecteinascidin 743, a novel, marine-derived, anti-cancer agent, in man

Ecteinascidin 743 (ET-743) is a potent anti-tumoral agent of a marine origin. It is currently being tested in phase II clinical trials using a 3-weekly 24-h i.v. infusion of 1500 microg/m(2) and 3-h infusions of 1650 microg/m(2). Knowledge of the metabolism of ET-743 is, however, still scarce. In the present study, a qualitative chromatographic discovery of metabolites of ET-743 in man is reported. ET-743 and its demethylated analog ET-729 were incubated at 37 degrees C in the presence of enzyme systems, pooled human microsomes, pooled human plasma and uridine 5'-diphosphoglucuronyltransferase, respectively, in appropriate media. Reaction products were investigated chromatographically using photodiode array and ion spray-mass spectrometric detection (LC-MS). The main reaction products in microsomal incubations of ET-743 resulted from a remarkable breakdown of the molecule. In plasma the drugs were deacetylated, and the transferase did actually yield a glucuronide of both ET-743 and ET-729. In contrast, screening of urine, plasma and bile, collected from patients treated with ET-743 at the highest dose levels, using a sensitive LC-MS assay, did not result in detection of ET-729 and metabolites which were generated in vitro. The urinary excretion of ET-743 in man was lower than 0.7% of the administered dose for a 24-h infusion.

Contribution of two missense mutations (G71R and Y486D) of the bilirubin UDP glycosyltransferase (UGT1A1) gene to phenotypes of Gilbert's syndrome and Crigler-Najjar syndrome type II

In our mutation analyses of bilirubin UDP glycosyltransferase (UGT1A1) gene, we encountered six patients with Crigler-Najjar syndrome type II who were double homozygotes for G71R and Y486D, a patient with Gilbert's syndrome who was a single homozygote for G71R and six patients with Gilbert's syndrome who were single heterozygote for G71R. To clarify the role of each mutation in the occurrence of the two syndromes, we made four mutant expression models. Relative UGT1A1 activity of a single homozygous model of G71R was 32.2+/-1.6% of normal, that of a single homozygous model of Y486D was 7.6+/-0.5%, that of a double homozygous model of G71R and Y486D was 6.2+/-1.6% and that of a heterozygous model of G71R was 60.2+/-3.5%. The decreased activities of the single homozygous model of G71R and the double homozygous model were at an appropriate level to be diagnosed as Gilbert's syndrome and CN-II, respectively. The activity of a single heterozygous model of G71R was somewhat high to develop to the phenotype of Gilbert's syndrome, suggesting the presence of additional factors for the etiology of Gilbert's syndrome.

Type II crigler-Najjar syndrome with intrahepatic cholestasis

A 58-year-old Japanese man was admitted to our hospital with appendicitis and marked unconjugated hyperbilirubinemia (11.6 mg/dl). The jaundice worsened following appendectomy, and the direct-reacting bilirubin increased, probably due to the ceftizoxime administered postoperatively. Bilirubin diglucuronide was the main component of the serum direct-reacting bilirubin (51%) in serum measured by liquid chromatography. Because the discontinuation of ceftizoxime did not markedly improve the jaundice, epomediol, 200 mg tid, was administered orally. There was a marked decrease of serum bilirubin with an increase in the delta bilirubin/(conjugated bilirubin + delta bilirubin) ratio. After improvement of jaundice to below the pre-surgical level (4.4 mg/dl), we analyzed the duodenal bile for bilirubin fractions; those showed a marked reduction in bilirubin diglucuronide and a marked increase in bilirubin monoglucuronide, which was consistent with type II Crigler-Najjar syndrome. A marked increase of bilirubin diglucuronide in serum of this patient during cholestasis suggests that bilirubin conjugation proceeds in this syndrome when excretion of conjugated bilirubin decreases.

Serum bilirubin fractions in healthy subjects and patients with unconjugated hyperbilirubinemia

Serum bilirubin fractions were determined by a newly developed, high performance liquid chromatography method in 23 healthy subjects, and in 15 patients with Gilbert's syndrome, five with type 2 Crigler-Najjar syndrome, seven with hemolytic disorders, and 26 with neonatal jaundice. In the healthy subjects, 92.6% of the bilirubin was unconjugated (UCB), 6.2% was bilirubin monoglucoronide (BMG), and 0.5% was bilirubin diglucuronide (BDG). Delta bilirubin (B delta) was not detected. In the patients, the percentage of UCB was significantly higher and that of BMG was significantly lower than in the healthy subjects. The proportion of BDG tended to decrease in Gilbert's and type 2 Crigler-Najjar syndromes; the proportion of B delta tended to increase in hyperbilirubinemia, except in Gilbert's syndrome. In particular, B delta was frequently detected in serum which also contained BDG (mainly in hemolytic disorders) or which presented with high concentrations (above 100 mumol/L) of UCB (mainly in type 2 Crigler-Najjar syndrome and neonatal jaundice). Trace amounts of (Z,E)- and/or (E,Z)-UCB were detected in approximately one fourth of the serum samples analyzed.

A case of Gilbert's syndrome combined with macroamylasemia

A 30-year-old Japanese male, who had no remarkable family history, visited our hospital with a complaint of abdominal pain, and unconjugated hyperbilirubinemia and hyperamylasemia were observed. He showed negative hemolysis tests, positive nicotinic acid test, low hepatic bilirubin UDP-glucuronyltransferase activity, decreased bilirubin diglucuronide and increased bilirubin monoglucuronide in bile, and a decrease in serum bilirubin after phenobarbital administration. He also showed high serum amylase level, low urine amylase level, and low amylase-creatinine clearance ratio. Gel filtration of serum with Sephadex G-200 revealed the existence of macroamylase. Countercurrent immunoelectrophoresis proved binding of serum amylase to lambda type IgA. From these results, the case was diagnosed as Gilbert's syndrome combined with macroamylasemia.