Genetic defects of the UDP-glucuronosyltransferase-1 (UGT1) gene that cause familial non-haemolytic unconjugated hyperbilirubinaemias

Next-generation sequencing based newborn screening and comparative analysis with MS/MS

BACKGROUND

Newborn screening (NBS), such as tandem mass spectrometry (MS/MS), may yield false positive/negative results. Next-generation sequencing (NGS) has the potential to provide increased data output, efficiencies, and applications. This study aimed to analyze the types and distribution of pathogenic gene mutations in newborns in Huzhou, Zhejiang province, China and explore the applicability of NGS and MS/MS in NBS.

METHODS

Blood spot samples from 1263 newborns were collected. NGS was employed to screen for pathogenic variants in 542 disease-causing genes, and detected variants were validated using Sanger sequencing. Simultaneously, 26 inherited metabolic diseases (IMD) were screened using MS/MS. Positive or suspicious samples identified through MS/MS were cross-referenced with the results of NGS.

RESULTS

Among all newborns, 328 had no gene mutations detected. NGS revealed at least one gene mutation in 935 newborns, with a mutation rate of 74.0%. The top 5 genes were FLG, GJB2, UGT1A1, USH2A, and DUOX2. According to American College of Medical Genetics guidelines, gene mutations in 260 cases were classified as pathogenic or likely pathogenic mutation, with a positive rate of 20.6%. The top 5 genes were UGT1A1, FLG, GJB2, MEFV, and G6PD. MS/MS identified 18 positive or suspicious samples for IMD and 1245 negative samples. Verification of these cases by NGS results showed no pathogenic mutations, resulting in a false positive rate of 1.4% (18/1263).

CONCLUSION

NBS using NGS technology broadened the range of diseases screened, and enhanced the accuracy of diagnoses in comparison to MS/MS for screening IMD. Combining NGS and biochemical screening would improve the efficiency of current NBS.

Establishment of UGT1A1-knockout human iPS-derived hepatic organoids for UGT1A1-specific kinetics and toxicity evaluation

Uridine diphosphate glucuronosyltransferases (UGTs) are highly expressed in the liver and are involved in the metabolism of many drugs. In particular, UGT1A1 has a genetic polymorphism that causes decreased activity, leading to drug-induced hepatotoxicity. Therefore, an in vitro evaluation system that accurately predicts the kinetics of drugs involving UGT1A1 is required. However, there is no such evaluation system because of the absence of the UGT1A1-selective inhibitor. Here, using human induced pluripotent stem (iPS) cells, genome editing technology, and organoid technology, we generated UGT1A1-knockout human iPS hepatocyte-derived liver organoids (UGT1A1-KO i-HOs) as a model for UGT1A1-specific kinetics and toxicity evaluation. i-HOs showed higher gene expression of many drug-metabolizing enzymes including UGT1A1 than human iPS cell-derived hepatocyte-like cells (iPS-HLCs), suggesting that hepatic organoid technology improves liver functions. Wild-type (WT) i-HOs showed similar levels of UGT1A1 activity to primary human (cryopreserved) hepatocytes, while UGT1A1-KO i-HOs completely lost the activity. Additionally, to evaluate whether this model can be used to predict drug-induced hepatotoxicity, UGT1A1-KO i-HOs were exposed to SN-38, the active metabolite of irinotecan, an anticancer drug, and acetaminophen and confirmed that these cells could predict UGT1A1-mediated toxicity. Thus, we succeeded in generating model cells that enable evaluation of UGT1A1-specific kinetics and toxicity.

Hierarchical core-shell nanoplatforms constructed from Fe3O4@C and metal-organic frameworks with excellent bilirubin removal performance

Hemoperfusion has become the third-generation treatment strategy for patients suffering from hyperbilirubinemia, but adsorbents used for bilirubin removal mostly face intractable problems, such as unsatisfactory adsorption performance and poor hemocompatibility. Metal-organic frameworks (MOFs) are promising adsorbents for hemoperfusion due to their high specific surface areas and easily modified organic ligands. However, their microporous properties and separation have hampered their application. Here, a novel hierarchical core-shell nanoplatform (named Double-PEG) with tailored binding sites and pore sizes based on Fe3O4@C and Uio66-NH2 was constructed. Notably, Double-PEG showed excellent bilirubin uptake of up to 1738.30 mg g-1 and maintained excellent bilirubin removal efficiency in simulated biological solutions. A study on the adsorption mechanism showed that the adsorption of Double-PEG towards bilirubin tended to be chemical adsorption and in accordance with the Langmuir model. Besides, the good separability, recyclability, cytotoxicity and hemocompatibility of Double-PEG show great potential in hemoperfusion therapy. The finding of this study may provide a novel insight into the application of MOF materials in the field of hemoperfusion.

UGT1A1-related Bilirubin Encephalopathy/Kernicterus in Adults

BACKGROUND AND AIMS

Bilirubin encephalopathy/kernicterus is very rare in adults. This study is aimed to investigate the clinical manifestations and genetic features of two patients with UGT1A1-related kernicterus.

METHODS

Sanger sequencing analysis was performed to identify UGT1A1 gene mutations in the patients and their families. Bioinformatics analysis was used to predict the potential functional effects of novel missense mutations. Clinical manifestations and biochemical parameters were collected and analyzed.

RESULTS

Two patients with Crigler-Najjar syndrome type II (CNS2) developed kernicterus in adulthood. Sanger sequencing identified a compound heterozygous mutation in the UGT1A1 gene in patient 1, which was inherited from his mother (G71R) and his father (c.-3279T>G; S191F). Patient 2 carried three heterozygous mutations, namely G71R, R209W and M391K; among which, the M391K mutation has not been reported before. Multiple prediction software showed that the M391K mutation was pathogenic. Symptoms were relieved in the two patients after phenobarbital and artificial liver support treatment. Patient 1 also underwent liver transplantation.

CONCLUSIONS

Adults with CNS2 are at risk for kernicterus. Phenobarbital treatment is beneficial for maintaining bilirubin levels and preventing kernicterus.

Potential implications of DMET ontogeny on the disposition of commonly prescribed drugs in neonatal and pediatric intensive care units

Introduction: Pediatric patients, especially neonates and infants, are more susceptible to adverse drug events as compared to adults. In particular, immature small molecule drug metabolism and excretion can result in higher incidences of pediatric toxicity than adults if the pediatric dose is not adjusted.Area covered: We reviewed the top 29 small molecule drugs prescribed in neonatal and pediatric intensive care units and compiled the mechanisms of their metabolism and excretion. The ontogeny of Phase I and II drug metabolizing enzymes and transporters (DMETs), particularly relevant to these drugs, are summarized. The potential effects of DMET ontogeny on the metabolism and excretion of the top pediatric drugs were predicted. The current regulatory requirements and recommendations regarding safe and effective use of drugs in children are discussed. A few representative examples of the use of ontogeny-informed physiologically based pharmacokinetic (PBPK) models are highlighted.Expert opinion: Empirical prediction of pediatric drug dosing based on body weight or body-surface area from the adult parameters can be inaccurate because DMETs are not mature in children and the age-dependent maturation of these proteins is different. Ontogeny-informed-PBPK modeling provides a better alternative to predict the pharmacokinetics of drugs in children.

A selective and sensitive fluorescent probe for bilirubin in human serum based on europium(III) post-functionalized Zr(IV)-Based MOFs

In the present study, a kind of Eu(III) post-functionalized Zr(IV)-based metal-organic framework (UiO-66(COOH)₂, Zr-MOF: Eu³⁺) was synthesized and utilized as an independently luminescent probe for sensing bilirubin (BR) in human serum, a biomarker of jaundice hepatitis. It can be served as a turn-off fluorescent switch for BR because its red emission from Eu³⁺ can be easily quenched by BR through a fluorescent resonant energy transfer (FRET) process between BR and its ligands, and as a result, BR is recognized successfully. Particularly, Zr-MOF: Eu³⁺ has shown many appealing properties, such as high sensitivity, quick response (less than 1 min), broad response window (0-15 μM), and excellent selectivity. Most importantly, a kind of portable test paper based on Zr-MOF: Eu³⁺ probe has been developed for directly assessing the level of BR in real human serum and further diagnosing bilirubin-related diseases via visually observing the luminescent color variation.

Combined Effects of UGT1A1 and SLCO1B1 Variants on Chinese Adult Mild Unconjugated Hyperbilirubinemia

The potential for genetic variation to cause adult unconjugated hyperbilirubinemia is increasingly being recognized. However, the cumulative effects of genetic variants have not been fully illuminated. The current study aimed to investigate the effects of uridine diphospho-glucuronosyl transferase 1A1 (UGT1A1) and/or solute carrier organic anion transporter family member 1B (SLCO1B) polymorphic variants and their combined effects on mild unconjugated hyperbilirubinemia in Chinese adults. Fourteen genetic variants in the UGT1A1 or SLCO1B gene were genotyped through sequencing in 148 adults with unconjugated hyperbilirubinemia and 158 healthy controls. Variants c.-3275T > G, (TA)₆>(TA)₇, c.211G > A or c.1091C > T within the UGT1A1 gene as well as c.521T > C within the SLCO1B1 gene appear to be genetic risk factors for inherited unconjugated hyperbilirubinemia. After adjusting for covariates, the results of multivariate logistic regressions revealed that odds ratios (ORs) [(with 95% confidence interval (CI)] of these five variants were 2.35 (95% CI: 1.37–4.01, p = 0.002), 2.38 (95% CI: 1.35–4.20, p = 0.003), 2.99 (95% CI: 1.71–5.21, p < 0.001), 7.60 (95% CI: 1.99–28.96, p = 0.003), and 2.54 (95% CI: 1.27–5.11, p = 0.009), respectively. The OR for unconjugated hyperbilirubinemia is positively correlated with the cumulative number of these five variants in adults. And the greater the number of genetic variations, the higher the total bilirubin level. Adults carrying diplotype 3/4 (homozygous c.-3275T > G and heterozygous (TA)₆>(TA)₇) had higher bilirubin levels than those with diplotypes 1/3 (heterozygous c.-3275T > G and (TA)₆>(TA)₇)) or 1/4 (heterozygous c.-3275T > G) (P < 0.05). Similarly, bilirubin levels in individuals with diplotype 2/4 (heterozygous c.-3275T > G and c.211G > A) were higher than adults carrying diplotypes 1/2 (heterozygous c.211G > A) or 1/4 (P < 0.001). For subjects with heterozygous or homozygous variant c.211G> A, as the number of c.521T > C alleles variation increased, the incidence of unconjugated hyperbilirubinemia increased, but it was not statistically significant. Our results indicate that variants of UGT1A1 and/or SLCO1B1 have combined effects on Chinese adult mild unconjugated hyperbilirubinemia.

Sandwich-Cultured Hepatocytes for Mechanistic Understanding of Hepatic Disposition of Parent Drugs and Metabolites by Transporter-Enzyme Interplay

Functional interplay between transporters and drug-metabolizing enzymes is currently one of the hottest topics in the field of drug metabolism and pharmacokinetics. Uptake transporter-enzyme interplay is important to determine intrinsic hepatic clearance based on the extended clearance concept. Enzyme and efflux transporter interplay, which includes both sinusoidal (basolateral) and canalicular efflux transporters, determines the fate of metabolites formed in the liver. As sandwich-cultured hepatocytes (SCHs) maintain metabolic activities and form a canalicular network, the whole interplay between uptake and efflux transporters and drug-metabolizing enzymes can be investigated simultaneously. In this article, we review the utility and applicability of SCHs for mechanistic understanding of hepatic disposition of both parent drugs and metabolites. In addition, the utility of SCHs for mimicking species-specific disposition of parent drugs and metabolites in vivo is described. We also review application of SCHs for clinically relevant prediction of drug-drug interactions caused by drugs and metabolites. The usefulness of mathematical modeling of hepatic disposition of parent drugs and metabolites in SCHs is described to allow a quantitative understanding of an event in vitro and to develop a more advanced model to predict in vivo disposition.

North Central Cancer Treatment Group N0543 (Alliance): A phase 2 trial of pharmacogenetic-based dosing of irinotecan, oxaliplatin, and capecitabine as first-line therapy for patients with advanced small bowel adenocarcinoma

BACKGROUND

Oxaliplatin in combination with either 5-fluorouracil or capecitabine is commonly used as first-line therapy for patients with small bowel adenocarcinoma. The addition of irinotecan improves survival in other gastrointestinal tumors but at the cost of hematologic toxicity. The authors performed a phase 2 cooperative group study (North Central Cancer Treatment Group N0543, Alliance) using genotype-dosed capecitabine, irinotecan, and oxaliplatin (gCAPIRINOX), with dosing assigned based on UDP glucuronosyltransferase family 1 member A1 (UGT1A1) genotype to test: 1) whether the addition of irinotecan would improve outcomes; and 2) whether UGT1A1 genotype-based dosing could optimize tolerability.

METHODS

Previously untreated patients with advanced small bowel adenocarcinoma received irinotecan (day 1), oxaliplatin (day 1), and capecitabine (days 2-15) in a 21-day cycle and were dosed with gCAPIRINOX according to UGT1A1*28 genotypes (6/6, 6/7, and 7/7).

RESULTS

A total of 33 patients (17 with the 6/6 genotype, 10 with the 6/7 genotype, and 6 with the 7/7 genotype) were enrolled from October 2007 to November 2013; 73% were male, with a mean age of 64 years (range, 41-77 years). Location of the primary tumor included the duodenum (58%), jejunum (30%), and ileum (9%). The regimen yielded a confirmed response rate of 37.5% (95% confidence interval, 21%-56%), with a median progression-free survival of 8.9 months and a median overall survival of 13.4 months. Neither hematologic toxicity (grade ≥3 in 52.9%, 30.0%, and 33.3%, respectively, of the 6/6, 6/7, and 7/7 genotype groups) nor tumor response rate (41.2%, 33%, and 33%, respectively) were found to differ significantly by UGT1A1 genotype.

CONCLUSIONS

UGT1A1 genotype-directed dosing (gCAPIRINOX) appears to be feasible with favorable rates of hematologic toxicity compared with prior 3-drug studies in unselected patients. Larger studies would be needed to determine the regimen's comparability to oxaliplatin and capecitabine (CapeOx) alone or if response/toxicity differs among patients with different UGT1A1 genotypes. Cancer 2017;123:3494-501. © 2017 American Cancer Society.

Mice with hyperbilirubinemia due to Gilbert's syndrome polymorphism are resistant to hepatic steatosis by decreased serine 73 phosphorylation of PPARα

Gilbert's syndrome in humans is derived from a polymorphism (TA repeat) in the hepatic UGT1A1 gene that results in decreased conjugation and increased levels of unconjugated bilirubin. Recently, we have shown that bilirubin binds directly to the fat-burning nuclear peroxisome proliferator-activated receptor-α (PPARα). Additionally, we have shown that serine 73 phosphorylation [Ser(P)⁷³] of PPARα decreases activity by reducing its protein levels and transcriptional activity. The aim of this study was to determine whether humanized mice with the Gilbert's polymorphism (HuUGT*28) have increased PPARα activation and reduced hepatic fat accumulation. To determine whether humanized mice with Gilbert's mutation (HuUGT*28) have reduced hepatic lipids, we placed them and C57BL/6J control mice on a high-fat (60%) diet for 36 wk. Body weights, fat and lean mass, and fasting blood glucose and insulin levels were measured every 6 wk throughout the investigation. At the end of the study, hepatic lipid content was measured and PPARα regulated genes as well as immunostaining of Ser(P)⁷³ PPARα from liver sections. The HuUGT*28 mice had increased serum bilirubin, lean body mass, decreased fat mass, and hepatic lipid content as well as lower serum glucose and insulin levels. Also, the HuUGT*28 mice had reduced Ser(P)⁷³ PPARα immunostaining in livers and increased PPARα transcriptional activity compared with controls. A chronic but mild endogenous increase in unconjugated hyperbiliubinemia protects against hepatic steatosis through a reduction in Ser(P)⁷³ PPARα, causing an increase in PPARα transcriptional activity.

Does bilirubin prevent hepatic steatosis through activation of the PPARα nuclear receptor?

Several large population studies have demonstrated a negative correlation between serum bilirubin levels and the development of obesity, hepatic steatosis, and cardiovascular disease. Despite the strong correlative data demonstrating the protective role of bilirubin, the mechanism by which bilirubin can protect against these pathologies remains unknown. Bilirubin has long been known as a powerful antioxidant and also has anti-inflammatory actions, each of which may contribute to the protection afforded by increased levels. We have recently described a novel function of bilirubin as a ligand for the peroxisome proliferator-activated receptor-alpha (PPARα), which we show specifically binds to the nuclear receptor. Bilirubin may function as a selective PPAR modulator (SPPARM) to control lipid accumulation and blood glucose. However, it is not known to what degree bilirubin activation of PPARα is responsible for the protection afforded to reduce hepatic steatosis. We hypothesize that bilirubin, acting as a novel SPPARM, increases hepatic fatty acid metabolism through a PPARα-dependent mechanism which reduces hepatic lipid accumulation and protects against hepatic steatosis and non-alcoholic fatty liver disease (NAFLD).

Clinical Significance of UGT1A1 Genetic Analysis in Chinese Neonates with Severe Hyperbilirubinemia

BACKGROUND

Neonatal hyperbilirubinemia is common in Asia, and the importance of genetically determined conditions has been recently recognized. The aim of this study was to assess the clinical utility of genetic testing in Chinese neonates with severe hyperbilirubinemia.

METHODS

Fifty-eight term infants with bilirubin level ≥ 20 mg/dL (342 μmol/L), and 65 controls were enrolled in the study. Variation status of UGT1A1, G6PD, and thalassemia genes in our study cohort was determined by direct sequencing or genotype assays.

RESULTS

Among these case infants, seven were confirmed with G6PD deficiency, four were heterozygous for α- or β-thalassemia, and forty-four were detected with at least one heterozygous UGT1A1 functional variant, including nine homozygous for UGT1A1 variation. As well as the predominant c.211G>A (Gly71Arg) variant, three UGT1A1 coding variants [c.1091C>T (Pro364Leu), c.1352C>T (pro451leu), and c.1456C>T (Tyr486Asp)] were observed in our case neonates. The results of multivariate logistic regressions, adjusted for covariates, revealed odds ratios for neonates who carried heterozygous, homozygous variation at nucleotide 211 of UGT1A1, and G6PD deficiency of 3.47 (1.26-9.55), 12.46 (1.09-142.7) ,and 12.87 (1.32-135.87) compared with those having the wild genotype and normal G6PD activity, respectively.

CONCLUSION

Besides G6PD-deficiency screening, UGT1A1 genetic analysis, and especially the UGT1A1*6(c.211G>A, p.Arg71Gly) polymorphism detection, may be taken into consideration for early diagnosis and treatment of severe hyperbilirubinemic newborns in southern China.

Acute cholangitis in an old patient with Crigler-Najjar syndrome type II - a case report

Background

Crigler-Najjar syndrome (CN) is a very rare genetic disorder characterized by an inability to conjugate bilirubin. Contrary to CN type I, patients with CN II exhibit residual capacity to conjugate bilirubin and may present a normal life expectancy.

Case presentation

We report an unusual late diagnosis of CN type II in an 80-year-old female admitted with severe acute cholangitis. While the patient present typical clinical and radiologic signs of bile duct obstruction and cholangitis, her blood analysis showed severe unconjugated hyperbilirubinemia. Endoscopic retrograde cholangiopancreatography confirmed the diagnosis and allowed therapeutic intervention. The anatomopathologic examination of her gallbladder following cholecystectomy showed signs of chronic cholecystitis.

Conclusion

The risk of gallstone disease may be increased in patients with CN syndrome. While unusual, we alert to this curious and potential life-threatening presentation.

Inherited disorders of bilirubin clearance

Inherited disorders of hyperbilirubinemia may be caused by increased bilirubin production or decreased bilirubin clearance. Reduced hepatic bilirubin clearance can be due to defective (i) unconjugated bilirubin uptake and intrahepatic storage, (ii) conjugation of glucuronic acid to bilirubin (e.g., Gilbert syndrome, Crigler-Najjar syndrome, Lucey-Driscoll syndrome, breast milk jaundice), (iii) bilirubin excretion into bile (Dubin-Johnson syndrome), or (iv) conjugated bilirubin re-uptake (Rotor syndrome). In this review, the molecular mechanisms and clinical manifestations of these conditions are described, as well as current approaches to diagnosis and therapy.

Association of Neonatal Hyperbilirubinemia with UGT1A1 Gene Polymorphisms: A Meta-Analysis

Background

The results of studies on association between the polymorphisms in the coding region and the promoter of uridine diphosphateglucuronosyl transferase 1A1 (UGT1A1) and neonatal hyperbilirubinemia are controversial. This study aimed to determine whether the UGT1A1 gene polymorphisms of Gly71Arg and TATA promoter were significant risk factors associated with neonatal hyperbilirubinemia.

Material/Methods

The PubMed, Cochrane Library, and Embase databases were searched for papers that describe the association between UGT1A1 polymorphisms and neonatal hyperbilirubinemia. Summary odds ratios and 95% confidence intervals (CI) were estimated based on a fixed-effects model or random-effects model, depending on the absence or presence of significant heterogeneity.

Results

A total of 32 eligible studies and 6520 participants were identified. Among them, 24 studies focused on the association of neonatal hyperbilirubinemia with UGT1A1 Gly71Arg polymorphisms, and a significant difference was found for the comparison of AA vs. AG+GG (OR=3.47, 95% CI=2.29–5.28, P<0.0001). We included 19 studies on the association of neonatal hyperbilirubinemia with UGT1A1 TATA promoter polymorphism, which also found a statistically significant difference between 7/7 and 6/7 + 6/6 (OR=2.24, 95% CI=1.29–3.92, P=0.004).

Conclusions

This meta-analysis demonstrated that UGT1A1 polymorphisms (Gly71Arg and TATA promoter) significantly increase the risk of neonatal hyperbilirubinemia.

Association between G6PD deficiency and hyperbilirubinemia in neonates: a meta-analysis

Hyperbilirubinemia is prevalent in newborns and multiple factors are responsible for the occurrence of neonatal hyperbilirubinemia. G6PD (Glucose-6-Phosphate Dehydrogenase) deficiency is recognized as one of the risk factors. However, many pediatricians did not take into account the probable effect of G6PD-deficiency when severe neonatal hyperbilirubinemia occurred. The aim of the present study was to perform a meta-analysis to investigate whether G6PD-deficiency increases the risk of hyperbilirubinemia and phototherapy in newborn. We searched PubMed and Embase databases for eligible articles according to explicit study inclusion and exclusion criteria. Risk ratios (RRs) and 95% confidence interval (CI) were selected as the evaluation indexes. Cochrane Q and I(2) test were utilized to assess the heterogeneity among studies. A total of five cohort studies were included in this meta-analysis. There were 21,585 participants enrolled in these studies including 877 newborns with hyperbilirubinemia and 261 newborns receiving phototherapy. Comparison of the incidence of hyperbilirubinemia in newborns with G6PD-deficiency to the ones with normal G6PD in each study yielded a pooled RR of 3.92 (95% CI, 2.13-7.20; P <.0001). The pooled RR of receiving phototherapy in G6PD-deficiency neonates is 3.01 (95% CI, 2.20-4.12; P <.0001) when compared to G6PD normal neonates. This study revealed a significant correlation between G6PD-deficiency and neonatal hyperbilirubinemia, as well as G6PD-deficiency and phototherapy. G6PD-deficient newborns have higher risk of hyperbilirubinemia and phototherapy than the ones with normal G6PD. Monitoring the level of G6PD in newborns is important for predicting the occurrence of hyperbilirubinemia.

Influence of UGT1A1 6, 27, and 28 polymorphisms on nilotinib-induced hyperbilirubinemia in Japanese patients with chronic myeloid leukemia

Nilotinib potently inhibits human uridine diphosphate-glucuronosyltransferase (UGT1A1) activity, causing hyperbilirubinemia. We investigated the influence of UGT1A1 polymorphisms and nilotinib plasma trough concentrations (C0) on nilotinib-induced hyperbilirubinemia in 34 Japanese patients with chronic myeloid leukemia (CML). The proportion of patients with hyperbilirubinemia was significantly higher among patients with the UGT1A1*6/*6 and *6/*28 genotypes (poor metabolizers) than among those with other genotypes (p = 0.004). The median time to elevation of bilirubin levels in UGT1A1 poor metabolizers was 2.0 weeks (hazard ratio, 6.11). The median time to reduction in nilotinib dose in UGT1A1 poor metabolizers was 4.0 weeks (hazard ratio, 7.52; p = 0.002). Consequently, in the maintenance phase 3 months following the initiation of nilotinib therapy, the median daily dose and C0 of nilotinib were 350 mg/day and 372 ng/mL, respectively, in UGT1A1 poor metabolizers, and 600 mg/day and 804 ng/mL, respectively, in the other patients. Patients at increased hyperbilirubinemia risk could be identified by prospective UGT1A1 genotyping prior to nilotinib therapy. To avoid an interruption of CML treatment due to nilotinib-induced hyperbilirubinemia, it may be beneficial to reduce the initial nilotinib dose to 300-400 mg/day for UGT1A1 poor metabolizers.

Alterations in the cell cycle in the cerebellum of hyperbilirubinemic Gunn rat: a possible link with apoptosis?

Severe hyperbilirubinemia causes neurological damage both in humans and rodents. The hyperbilirubinemic Gunn rat shows a marked cerebellar hypoplasia. More recently bilirubin ability to arrest the cell cycle progression in vascular smooth muscle, tumour cells, and, more importantly, cultured neurons has been demonstrated. However, the involvement of cell cycle perturbation in the development of cerebellar hypoplasia was never investigated before. We explored the effect of sustained spontaneous hyperbilirubinemia on cell cycle progression and apoptosis in whole cerebella dissected from 9 day old Gunn rat by Real Time PCR, Western blot and FACS analysis. The cerebellum of the hyperbilirubinemic Gunn rats exhibits an increased cell cycle arrest in the late G0/G1 phase (p < 0.001), characterized by a decrease in the protein expression of cyclin D1 (15%, p < 0.05), cyclin A/A1 (20 and 30%, p < 0.05 and 0.01, respectively) and cyclin dependent kinases2 (25%, p < 0.001). This was associated with a marked increase in the 18 kDa fragment of cyclin E (67%, p < 0.001) which amplifies the apoptotic pathway. In line with this was the increase of the cleaved form of Poly (ADP-ribose) polymerase (54%, p < 0.01) and active Caspase3 (two fold, p < 0.01). These data indicate that the characteristic cerebellar alteration in this developing brain structure of the hyperbilirubinemic Gunn rat may be partly due to cell cycle perturbation and apoptosis related to the high bilirubin concentration in cerebellar tissue mainly affecting granular cells. These two phenomena might be intimately connected.

The effect of UGT1A1 promoter polymorphism in the development of hyperbilirubinemia and cholelithiasis in hemoglobinopathy patients

Present study was aimed to explore the effect of (TA)n UGT1A1 gene promoter polymorphism on bilirubin metabolism, bilirubinaemia, predisposition to cholelithiasis and subsequent cholecystectomy, in Sickle-Cell Anemia (SCA) and beta-Thalasemia major (bTH) in Kuwaiti subjects compared to other population. This polymorphism was analyzed and correlated to total bilirubin and cholelithiasis in 270 age, gender, ethnically matched subjects (92 bTH, 116 SCA and 62 Controls) using PCR, dHPLC, fragment analysis and direct sequencing. Four genotypes of UGT1A1 were detected in this study (TA6/6, TA6/7, TA6/8 and TA7/7). (TA)6/8 was found only in four individuals; hence it was not included in the analysis. There was a statistically significant association of genotypes with serum total bilirubin levels in both bTH and SCA groups (p<0.001). Subjects with (TA)7/7 had the highest total serum bilirubin level (178.7 ± 3.5 µmole/l). A significant association was observed between allele (TA)7 and cholelithiasis development (p = 0.0001). The 40%, 67.5% and 100% of SCA with (TA)6/6, (TA)6/7 and (TA)7/7 respectively developed cholelithiasis and were subsequently cholecystectomized. Our results confirm UGT1A1 (TA)7 allele as one of the factors accounting for the hyperbilirubinemia and cholelithiasis observed in SCA and bTH.

Correlation of UGT1A1 TATA-box polymorphism and jaundice in breastfed newborns-early presentation of Gilbert's syndrome

OBJECTIVE

The etiology of jaundice in otherwise healthy breastfed newborns that can present as early-onset exaggerated physiologic jaundice, or late breast milk jaundice (BMJ), is not yet entirely understood. This study tested the hypothesis that molecular marker for Gilbert's syndrome (GS), UGT1A1 TATA-box polymorphism, is associated with this disorders.

METHODS

We have investigated the UGT1A1 polymorphism frequency and its relation to severity of hyperbilirubinemia and jaundice duration among 220 exclusively breastfed term newborns; 57 of them with non-physiologic hyperbilirubinemia (NH), and 163 with BMJ, and in 187 healthy controls.

RESULTS

Significant differences in TA7/7 genotype frequency were established. The highest frequency was observed among the newborns with BMJ (42.0%), intermediate in the NH group (24.6%), while the controls had the lowest TA7/7 frequency (12.8%). Linear increase in TA7/7 frequency was observed depending on the duration of jaundice, peaking at 42.4% in newborns with the longest jaundice duration. Positive correlation between the serum bilirubin levels and the TATA-box length was established in all groups.

CONCLUSION

This study provides evidence that UGT1A1 TATA-box polymorphism is an important risk factor for developing jaundice in term breastfed newborns, presented as either early non-physiologic hyperbilirubinemia or breast milk jaundice. These results further support the original Odell's idea of neonatal jaundice as an early presentation of GS.

UGT1A1 genetic analysis as a diagnostic aid for individuals with unconjugated hyperbilirubinemia

OBJECTIVE

To assess the clinical utility of UGT1A1 genetic testing and describe the spectrum and prevalence of UGT1A1 variations identified in pediatric unconjugated hyperbilirubinemia (UCH), and to characterize specific genotype-phenotype relationships in suspected Gilbert and Crigler-Najjar syndromes.

STUDY DESIGN

A retrospective study was conducted to review clinical information and UGT1A1 genotyping data from 181 pediatric patients referred for UCH. In silico analyses were performed to aid in the assessment of novel UGT1A1 variants.

RESULTS

Overall, 146/181 pediatric patients had at least one heterozygous UGT1A1 functional variant. Identified UGT1A1 variants included 17 novel variants, 7 rare star alleles, and 1 rare variant. There were 129 individuals who possessed the TA7 (*28) promoter repeat and 15 individuals who possessed the *6 (c.211G > A) variation. Out of the 104 individuals with accompanying bilirubin levels, 41 individuals did not have identifiable UGT1A1 variants that explained their UCH, although glucose-6-phosphate dehydrogenase deficiency and other causes of UCH could not be ruled out.

CONCLUSION

Much of the observed UCH could be attributed to variation at the UGT1A1 locus, and UGT1A1 testing helped to substantiate a genetic diagnosis, thereby aiding in individual and family disease management. Although UGT1A1 variation plays a large role in UCH, genetic assessment of UGT1A1 alone may not be comprehensive. Assessment of additional genes may also be useful to evaluate genetic causes for UCH.

Metabolism and disposition of acetaminophen: recent advances in relation to hepatotoxicity and diagnosis

Acetaminophen (APAP) is one of the most widely used drugs. Though safe at therapeutic doses, overdose causes mitochondrial dysfunction and centrilobular necrosis in the liver. The first studies of APAP metabolism and activation were published more than 40 years ago. Most of the drug is eliminated by glucuronidation and sulfation. These reactions are catalyzed by UDP-glucuronosyltransferases (UGT1A1 and 1A6) and sulfotransferases (SULT1A1, 1A3/4, and 1E1), respectively. However, some is converted by CYP2E1 and other cytochrome P450 enzymes to a reactive intermediate that can bind to sulfhydryl groups. The metabolite can deplete liver glutathione (GSH) and modify cellular proteins. GSH binding occurs spontaneously, but may also involve GSH-S-transferases. Protein binding leads to oxidative stress and mitochondrial damage. The glucuronide, sulfate, and GSH conjugates are excreted by transporters in the canalicular (Mrp2 and Bcrp) and basolateral (Mrp3 and Mrp4) hepatocyte membranes. Conditions that interfere with metabolism and metabolic activation can alter the hepatotoxicity of the drug. Recent data providing novel insights into these processes, particularly in humans, are reviewed in the context of earlier work, and the effects of altered metabolism and reactive metabolite formation are discussed. Recent advances in the diagnostic use of serum adducts are covered.

Unconjugated hyperbilirubinemia is inversely associated with non-alcoholic steatohepatitis (NASH)

BACKGROUND

It has been recognised that unconjugated bilirubin contains hepatic anti-fibrogenic and anti-inflammatory properties and is a potent physiological antioxidant cytoprotectant. We believe that unconjugated hyperbilirubinemia may protect against development of non-alcoholic steatohepatitis (NASH).

AIM

This study was conducted to assess the association of serum unconjugated bilirubin levels and histological liver damage in non-alcoholic fatty liver disease (NAFLD).

METHODS

This was a retrospective analysis involving adult patients from a tertiary medical centre undergoing liver biopsy to evaluate suspected NAFLD or NASH and a control group without NAFLD based on normal liver ultrasound, labs and history. Identification of unconjugated hyperbilirubinemia was based on the presence of predominantly unconjugated bilirubin ≥1.0 mg/dL (17.1 μmol/L) while fasting, in the absence of haemolytic disease or other hepatic function alteration.

RESULTS

Six-hundred and forty-one patients were included. Unconjugated hyperbilirubinemia was inversely associated with NASH (OR 16.1, 95% CI 3.7-70.8 P < 0.001). Of the patients without NAFLD (133 patients), 13 (9.8%) had unconjugated hyperbilirubinemia (range 1.0-1.8, mean 1.4). Of the patients with NAFLD without NASH (285 patients), 32 (11.2%) had unconjugated hyperbilirubinemia (range 1.0-3.0, mean 1.4). Of the patients with NASH (223 patients), three (1.3%) had unconjugated hyperbilirubinemia (1.0, 1.1, 1.4).

CONCLUSIONS

Unconjugated hyperbilirubinemia is inversely associated with the histopathological severity of liver damage in non-alcoholic fatty liver disease.

Association of neonatal hyperbilirubinemia with uridine diphosphate-glucuronosyltransferase 1A1 gene polymorphisms: meta-analysis

BACKGROUND

Recent reports have suggested that genetic factors, including mutations in the coding region or promoter of uridine diphosphate-glucuronosyltransferase 1A1 (UGT1A1) may increase the risk of development of neonatal hyperbilirubinemia, but the relationship has not been evaluated on systematic review or meta-analysis.

METHODS

A meta-analysis of observational studies reporting effect estimates and 95% confidence intervals (95%CI) was conducted on the association between UGT1A1 polymorphisms and neonatal hyperbilirubinemia.

RESULTS

A total of 27 eligible studies were identified. In total, 17 studies focused on the association of neonatal hyperbilirubinemia with UGT1A1 Gly71Arg polymorphisms, which indicated that these polymorphisms were associated with an increased risk of neonatal hyperbilirubinemia (A/A+G/A vs G/G: odds ratio [OR], 2.70; P= 0.00; 95%CI: 2.22-3.29; I(2) = 0.0%; P(heterogeneity) = 0.55). Subgroup analyses by ethnicity validated this correlation in Asian, but not in Caucasian, populations (OR, 1.74; P= 0.10; 95%CI: 0.90-3.35; I(2) = 0.00%; P(heterogeneity) = 0.67). Furthermore, 18 studies focused on the association of neonatal hyperbilirubinemia with UGT1A1 TATA promoter polymorphisms. These studies concluded that TATA promoter variants were not associated with an increased risk of neonatal hyperbilirubinemia (7/7 + 6/7 vs 6/6: OR, 1.13; P= 0.23; 95%CI: 0.93-1.37; I(2) = 80.0%; P(heterogeneity) = 0.00).

CONCLUSION

UGT1A1 Gly71Arg polymorphisms are a risk factor for developing neonatal hyperbilirubinemia in Asian, but not Caucasian, subjects. UGT1A1 TATA promoter polymorphisms were not associated with an increased risk of neonatal hyperbilirubinemia in Asian subjects, but results from the Caucasian population were conflicting and require further epidemiological investigation.

Neonatal hyperbilirubinemia and Gly71Arg mutation of UGT1A1 gene: a Chinese case-control study followed by systematic review of existing evidence

AIM

To determine whether the UDP-glucuronosyltransferase 1A1 gene (UGT1A1) Gly71Arg (211G>A) mutation is associated with neonatal hyperbilirubinemia.

METHODS

The study consisted of two parts. The case-control study included 112 hyperbilirubinemic infants and 105 control subjects from the Fifth People's Hospital of Shenzhen. Polymerase chain reaction, restriction fragment length polymorphisms and agarose gel electrophoresis techniques were used to detect the UGT1A1 211G>A mutation. Meta-analyses was performed to assess the association between neonatal hyperbilirubinemia and UGT1A1 211G>A.

RESULTS

Our case-control study revealed that the likelihood of developing neonatal hyperbilirubinemia was 2.65 times higher in the infants with the A allele in the UGT1A1 211G>A than in the infants with the G allele (95% CI, 1.60-4.39). Meta-analyses (including data from our study) revealed that UGT1A1 211G>A is associated with an increased risk of neonatal hyperbilirubinemia [odds ratio (OR), 2.37; 95% CI, 2.05-2.74]. In the subgroup analyses based on ethnicity, significantly elevated risks were found in Asian populations (OR, 2.45; 95% CI, 2.10-2.84), but no significant associations were present in Caucasian populations (OR, 1.54; 95% CI, 0.87-2.75).

CONCLUSION

  The UGT1A1 211G>A mutation is associated with neonatal hyperbilirubinemia in Asians, but not in Caucasians.

Assessment of UGT polymorphisms and neonatal jaundice

Elevation of the serum bilirubin level is a common, if not universal, finding during the first week of life. This can be a transient phenomenon that resolves spontaneously or can signify a serious or even life-threatening condition. There are many causes of hyperbilirubinemia and related therapeutic and prognostic implications. The diseases in which there is a primary disorder of the metabolism of bilirubin will be reviewed regarding their clinical presentation, pathophysiology, diagnosis, and treatment. These disorders-Gilbert's syndrome and Crigler-Najjar Syndrome-both involve abnormalities in bilirubin conjugation secondary to deficiency of bilirubin uridine diphosphate glucuronosyltransferase. The purpose of this article is to review the current understanding of the genetic polymorphisms that result in these diseases and discuss recent advances in diagnosis and treatment.

Exploring the genetic architecture of neonatal hyperbilirubinemia

The potential for genetic variation to modulate neonatal hyperbilirubinemia risk is increasingly being recognized. In particular, polymorphisms across three genes involved in bilirubin production and metabolism [glucose-6-phosphate dehydrogenase (G6PD), uridine diphosphate glucuronosyl transferase 1A1 (UGT1A1), and solute carrier organic anion transporter polypeptide 1B1 (SLCO1B1)] may interact with each other and/or environmental contributors to produce significant hyperbilirubinemia. Variant gene co-expression including compound and synergistic heterozygosity enhances hyperbilirubinemia risk, contributing to the etiologic heterogeneity and complex nature of neonatal jaundice.

Complex multifactorial nature of significant hyperbilirubinemia in neonates

OBJECTIVE

To determine whether glucose-6-phosphate dehydrogenase (G6PD), uridine-diphosphoglucuronosyltransferase 1A1 (UGT1A1), and hepatic solute carrier organic anion transporter 1B1 (SLCO1B1) gene variants occur at greater frequency in neonates with significant hyperbilirubinemia.

METHODS

Infants with gestational ages of >or=37 weeks and ages of <7 days were studied. Case subjects had >or=1 bilirubin level above the 95th percentile (high-risk zone), whereas control subjects had bilirubin levels of <40th percentile (low-risk zone) at study entry.

RESULTS

A total of 153 case subjects (median bilirubin level: 15.7 mg/dL) and 299 control subjects (median bilirubin level: 4.6 mg/dL) were evaluated. There were no statistical differences in the frequencies of G6PD, UGT1A1, and SCLO1B1 gene variants between case and control subjects (G6PD: 5.2% vs 3.3%; UGT1A1: 14.4% vs 9.4%; SLCO1B1: 73.2% vs 73.6%). However, coexpression of the G6PD African A- mutation with UGT1A1 and/or SLCO1B1 variants was seen more frequently for case subjects. Case subjects more often demonstrated >or=2 factors contributing to hyperbilirubinemia, including ABO blood group heterospecificity in which the mother had blood group O (47.7% vs 11.4%), positive direct Coombs test results (33.3% vs 4%), sibling treated with phototherapy (16.3% vs 5.4%), maternal circulating blood group antibodies (10.5 vs 0.7%), maternal diabetes mellitus (13.1% vs 6.4%), and maternal East Asian ethnicity (6.5% vs 1.3%).

CONCLUSIONS

Clinical contributors to hyperbilirubinemia were identified more frequently for case subjects but individually G6PD, UGT1A1, and SLCO1B1 variants were not. Coexpression of the G6PD African A- mutation with UGT1A1 and SLCO1B1 variants was seen more often for case subjects.

Serum bilirubin levels, UGT1A1 polymorphisms and risk for coronary artery disease

Low levels of the antioxidative serum bilirubin are associated with vascular aging and an increased risk for coronary artery disease (CAD). UGT1A1 is the major gene influencing bilirubin concentrations. Therefore, we investigated an association of bilirubin levels and two polymorphisms in the promoter of UGT1A1 (-53(TA-repeat) polymorphism and T-3279G) in 477 patients with premature, familial CAD and 619 age- and sex-matched controls. Bilirubin concentrations were significantly lower in cases than in controls (0.62+/-0.36 vs. 0.76+/-0.41 mg/dl for men, p=1.2 x 10(-10); and 0.42+/-0.29 vs. 0.55+/-0.23 mg/dl, p=1.9 x 10(-9) for women). Both polymorphisms showed a strong association with bilirubin levels with higher levels for homozygote carriers of the minor allele. These associations were most pronounced in male controls and patients (p=5.9 x 10(-26) and p=3.4 x 10(-16), respectively, for the -53(TA-repeat) polymorphism). Logistic regression analysis revealed low bilirubin levels but not the UGT1A1 polymorphisms to be significantly associated with CAD: OR (95% CI) 0.90 (0.86-0.94), p=2.6 x 10(-6) for men and 0.77 (0.68-0.87), p=3.2 x 10(-5) for women, respectively for each 0.1mg/dl increase of bilirubin. These results indicate that it is rather decreased bilirubin levels in general than the changes in the genetic variation of this gene that increase the risk for CAD.

Gilbert syndrome

Az ismert familiáris, nem konjugált hyperbilirubinaemiák közé tartozó Gilbert-szindróma az átlagpopuláció 7–10%-át érintő benignus kórkép. Tünetei rendszerint aspecifikusak, egyedül az esetlegesen előforduló sárgaság, továbbá az enyhén emelkedett nem konjugált bilirubin szintje utal a rendellenességre. Más laborértékek és a májbiopszia általában nem mutat eltérést a normálistól. A betegség hátterében a legtöbb esetben az UDP-glükuronil-transzferáz gén részleges működészavara áll. A gén azt az enzimet kódolja, amely a bilirubin glükuronsavval való konjugációját segíti. Noha a Gilbert-szindróma diagnosztizálása korábban hagyományos laboratóriumi módszerekkel és családi anamnézis felvételével történt, napjainkban lehetőség van az UDP-glükuronil-transzferáz gén genetikai variánsainak meghatározására. A gén promoterrégiójában, homozigóta formában lévő (TA)-inszerció – (TA)7/(TA)7– a betegek 80–100%-ában jelen van, és az aktív UDP-glükuronil-transzferáz mennyiségének csökkenéséhez vezet. A kódolórégióban található missense mutációk szerepe még nem teljesen tisztázott, de a (TA)7promotervariánssal való együttes előfordulásuk magyarázatul szolgálhat az emelkedett bilirubinszintre és a sárgaságra, valamint a Gilbert-szindróma családi halmozódására.

Disruption of the ugt1 locus in mice resembles human Crigler-Najjar type I disease

The 9 UDP-glucuronosyltranferases (UGTs) encoded by the UGT1 locus in humans are key enzymes in the metabolism of most drugs as well as endogenous substances such as bile acids, fatty acids, steroids, hormones, neurotransmitters, and bilirubin. Severe unconjugated hyperbilirubinemia in humans that suffer from Crigler-Najjar type I disease results from lesions in the UGT1A1 gene and is often fatal. To examine the physiological importance of the Ugt1 locus in mice, this locus was rendered non-functional by interrupting exon 4 to create Ugt1(-/-) mice. Because UGT1A1 in humans is responsible for 100% of the conjugated bilirubin, it followed that newborn Ugt1(-/-) mice developed serum levels of unconjugated bilirubin that were 40-60 times higher than Ugt1(+/-) or wild-type mice. The result of extreme unconjugated bilirubin in Ugt1(-/-) mice, comparable to the induced levels noted in patients with Crigler-Najjar type 1 disease, is fatal in neonatal Ugt1(-/-) mice within 2 weeks following birth. The extreme jaundice is present as a phenotype in skin color after 8 h. Neonatal Ugt1(-/-) mice exhibit no detectable UGT1A-specific RNA, which corresponds to a complete absence of UGT1A proteins in liver microsomes. Conserved glucuronidation activity attributed to the Ugt1 locus can be defined in Ugt1(-/-) mice, because UGT2-dependent glucuronidation activity is unaffected. Remarkably, the loss of UGT1A functionality in liver results in significant alterations in cellular metabolism as investigated through changes in gene expression. Thus, the loss of UGT1A function in Ugt1(-/-) mice leads to a metabolic syndrome that can serve as a model to further investigate the toxicities associated with unconjugated bilirubin and the impact of this disease in humans.

Cord blood bilirubin level in relation to bilirubin UDP-glucuronosyltransferase gene missense allele in Chinese neonates

AIM

To investigate bilirubin UDP-glucuronosyltransferase (UGT1A1) gene allele in healthy Chinese neonates, their cord bilirubin level and the subsequent hyperbilirubinemia to determine relationships among them.

METHODS

Cord blood of 48 neonates was obtained to determine the exon 1 of UGT1A1 gene, total serum bilirubin, albumin, glutamic-pyruvic transaminase (GPT), glutamic-oxalacetic transaminase (GOT) and haemoglobin (Hb) concentration. Neonatal jaundice was assessed by measurement of transcutaneous bilirubin (TCB) and serum bilirubin. Neonates were divided into two groups according to mutant or normal allele to compare the variables.

RESULTS

Nineteen infants had the nucleotide 211 G-->A allele, 3 had the heterozygous variation (686C-->A, 845 A-->T, 231G-->A). In the 211 A allele group, cord bilirubin was significantly higher than in the 211 G allele group (p = 0.034), but there were no differences in albumin (p = 0.678), GPT (p = 0.460), GOT (p = 0.440) and Hb (p = 0.886). The TCB (at 48, 96 h), the frequency of the hyperbilirubinemia and prolonged jaundice were also significantly higher in the 211 A allele group.

CONCLUSIONS

The UGT1A1 gene codon G71R allele is a risk factor for neonatal hyperbilirubinemia in the Chinese population. Its effect on bilirubin metabolism may present early on, as well as late in foetal life.

(TA)n UGT 1A1 promoter polymorphism: a crucial factor in the pathophysiology of jaundice in G-6-PD deficient neonates

Increased heme catabolism has been reported in glucose-6-phosphate dehydrogenase (G-6-PD)-normal neonates who were also homozygous for (TA)7/(TA)7 (UGT1A1*28) uridine diphosphoglucuronate-glucuronosyltransferase 1A1 (UGT) promoter polymorphism (Gilbert syndrome). As G-6-PD deficiency is associated with increased hemolysis, we hypothesized that in G-6-PD-deficient neonates who also have the (TA)7/(TA)7 UGT promoter genotype, steady-state hemolysis would be even further increased. Male G-6-PD-deficient neonates were sampled for plasma total bilirubin (PTB), blood carboxyhemoglobin corrected for inhaled carbon monoxide in ambient air (COHbc) (an index of heme catabolism), and UGT (TA)n promoter genotype determination and compared with previously published G-6-PD-normal neonates. Although COHbc values were higher in the G-6-PD-deficient than in the G-6-PD-normal cohorts (0.97 +/- 0.32% of total Hb (tHb) versus 0.76 +/- 0.19% of tHb, p < 0.001), PTB values were similar (9.2 +/- 3.4 mg/dL versus 8.9 +/- 3.0 mg/dL, respectively, p = 0.3). Within the G-6-PD-deficient group, although COHbc values were alike between the three UGT promoter genotypes, PTB was higher in the (TA)7/(TA)7 homozygotes (11.1 +/- 4.0 mg/dL) compared with (TA)6/(TA)7 heterozygotes (9.1 +/- 3.2 mg/dL, p = 0.03) and wild-type (TA)6/(TA)6 homozygotes (8.8 +/- 3.4 mg/dL, p = 0.02). In the steady state, similar rates of hemolysis, but increased PTB in the G-6-PD- deficient, (TA)7/(TA)7 homozygotes, imply that (TA)7/(TA)7, homozygosity is central to increased PTB.

UGT1A1(TA)n promoter polymorphism—A new case of a (TA)8 allele in Caucasians

Gilbert's syndrome is a mild hereditary unconjugated hyperbilirubinemia caused by mutations in the bilirubin UDP-glucuronosyltransferase gene (UGT1A1). The causative mutation in Caucasians is almost exclusively a TA dinucleotide insertion in the TATA box of the UGT1A1 promoter. Affected individuals are homozygous for the variant promoter and have 7 instead of 6 TA repeats. The aim of the present study was to determine the genotypes of UGT1A1(TA)n promoter polymorphism in the healthy Slovenian population and to investigate the association of genotypes with serum bilirubin levels. 236 healthy subjects were genotyped by single-strand conformation polymorphism analysis, which was validated by sequence analysis. The frequencies of genotypes were as follows: (TA)(6/6) (38.1%), (TA)(6/7) (47.9%), (TA)(7/7) (13.6%). There was a statistically significant association of genotypes with serum bilirubin levels (p<0.001). Subjects with genotype (TA)(7/7) had the highest and subjects with genotype (TA)(6/6) the lowest total serum bilirubin levels. One individual in the group had the rare genotype (TA)(7/8) (0.4%). Analysis of his family showed the following genotypes: (TA)(6/8) in his father and sister and (TA)(7/8) in his two brothers. In conclusion, the frequency of UGT1A1(TA)n promoter polymorphism genotypes was determined for the first time in the Slovenian population and is similar to frequencies observed in other Caucasian populations. The extremely rare (TA)8 allele in Caucasians was found also in Slovenians.

In vitro studies of intestinal permeability and hepatic and intestinal metabolism of 8-prenylnaringenin, a potent phytoestrogen from hops (Humulus lupulus L.)

PURPOSE

The absorption potential and metabolism of 8-prenylnaringenin (8-PN) from hops (Humulus lupulus L.) were investigated. 8-PN is a potent estrogen with the potential to be used for the relief of menopausal symptoms in women.

METHODS

Monolayers of the human intestinal epithelial cancer cell line Caco-2 and human hepatocytes were incubated with 8-PN to model its intestinal absorption and hepatic metabolism, respectively.

RESULTS

The apparent permeability coefficients for 8-PN in the apical-to-basolateral and basolateral-to-apical directions of a Caco-2 monolayer were 5.2 +/- 0.7 x 10(-5) and 4.9 +/- 0.5 x 10(-5) cm/s, respectively, indicating good intestinal absorption via passive diffusion. Both glucuronide and sulfate conjugates of 8-PN were detected in the Caco-2 cell incubations. The 4'-O-glucuronide was the predominant Caco-2 cell metabolite, followed by 7-O-sulfate and 4'-O-sulfate. Both phase I and phase II metabolites of 8-PN were formed by human hepatocytes. The 7-O-glucuronide was the most abundant hepatocyte metabolite, and no sulfate conjugates were detected. Incubations with various cDNA-expressed UDP-glucuronosyltransferases indicated that the isozymes UGT1A1, UGT1A6, UGT1A8, and UGT1A9 were responsible for glucuronidation of 8-PN.

CONCLUSIONS

Although orally administered 8-PN should be readily absorbed from the intestine, its bioavailability should be reduced significantly by intestinal and hepatic metabolism.

Gilbert’s syndrome: High frequency of the (TA)7 TAA allele in India and its interaction with a novel CAT insertion in promoter of the gene for bilirubin UDP-glucuronosyltransferase 1 gene

AIM: To identify the variants in UDP-glucuronosyltransfe-rase 1 (UGT1A1) gene in Gilbert’s syndrome (GS) and to estimate the association between homozygosity for TA insertion and GS in India, as well as the frequency of TA insertion and its impact among normal controls in India.

METHODS: Ninety-five GS cases and 95 normal controls were selected. Liver function and other tests were done. The promoter and all 5 exons of UGT1A1 gene were resequenced. Functional assessment of a novel trinucleotide insertion was done by in silico analysis and by estimating UGT1A1 promoter activity carried out by luciferase reporter assay of appropriate constructs in Hep G2 cell line.

RESULTS: Among the GS patients, 80% were homozygous for the TA insertion, which was several-fold higher than reports from other ethnic groups. The mean UCB level was elevated among individuals with only one copy of this insertion, which was not significantly different from those with two copies. Many new DNA variants in UGT1A1 gene were discovered, including a trinucleotide (CAT) insertion in the promoter found in a subset (10%) of GS patients, but not among normal controls. In-silico analysis showed marked changes in the DNA-folding of the promoter and functional analysis showed a 20-fold reduction in transcription efficiency of UGT1A1 gene resulting from this insertion, thereby significantly elevating the UCB level.

CONCLUSION: The genetic epidemiology of GS is variable across ethnic groups and the epistatic interactions among UGT1A1 promoter variants modulate bilirubin glucuronidation.