Combined polymorphisms in UDP-glucuronosyltransferases 1A1 and 1A6: implications for patients with Gilbert's syndrome

Nutrition in Gilbert's Syndrome-A Systematic Review of Clinical Trials According to the PRISMA Statement

Gilbert syndrome is the most common hyperbilirubinemia, associated with a mutation in the UGT1A1 bilirubin gene, which produces an enzyme that conjugates bilirubin with glucuronic acid. Episodes of jaundice occurring in GS negatively affect patients' quality of life. This systematic review aimed to analyze clinical studies regarding nutrition in people with GS. The study followed the PRISMA guidelines and utilized the Ebsco, Embase, Cochrane, PubMed, Scopus, and Web of Science databases to search clinical trials focused on diet/nutrition in GS (1963-2023 years). The methodological quality of selected studies was assessed using the Jadad scale. As a result, 19 studies met the inclusion criteria. The research mainly focused on the impact of caloric restriction, consumption of various diet variants, and vegetables and fruits on hyperbilirubinemia and metabolic health. A nutritional intervention consisting of not applying excessive calorie restrictions and consuming fats and biologically active compounds in vegetables and fruits (Cruciferae, Apiaceous, Rutaceae) may prevent the occurrence of jaundice episodes. It is justified to conduct further research on detecting such compounds in food, which, by influencing the expression of the UGT liver enzyme gene, could contribute to regulating bilirubin concentration in the blood of people with GS.

The Mutation Hotspots at UGT1A Locus May Be Associated with Gilbert's Syndrome Affecting the Taiwanese Population

Gilbert's syndrome is mainly diagnosed through genetic analysis and is primarily detected through a mutation in the promoter region of the UGT1A1 gene. However, most of the research has been conducted on Caucasian populations. In this study, we studied the Han population in Taiwan to investigate the possibility of other mutations that could cause Gilbert's syndrome. This study comprised a test group of 45 Taiwanese individuals with Gilbert's syndrome and 180 healthy Taiwanese individuals as a control group. We extracted DNA from the blood samples and then used Axiom Genome-Wide TWB 2.0 array plates for genotyping. Out of 302,771 single nucleotide polymorphisms (SNPs) from 225 subjects, we detected 57 SNPs with the most significant shift in allele frequency; 27 SNPs among them were located in the UGT1A region. Most of the detected SNPs highly correlated with each other and are located near the first exon of UGT1A1, UGT1A3, UGT1A6, and UGT1A7. We used these SNPs as an input for the machine learning algorithms and developed prediction models. Our study reveals a good association between the 27 SNPs detected and Gilbert's syndrome. Hence, this study provides a reference for diagnosing Gilbert's syndrome in the Taiwanese population in the future.

UGT1A6 and UGT2B7 Gene Polymorphism and its Effect in Pediatric Epileptic Patients on Sodium Valproate Monotherapy

OBJECTIVES

To evaluate the pattern of UGT1A6 and UGT2B7 gene polymorphism in pediatric epileptic patients and to compare the sodium valproate concentration in different patterns of UGT gene polymorphism.

METHODS

In this cross-sectional study, 99 pediatric epileptic patients aged 2-18 y receiving Sodium valproate monotherapy for the past one month were included from JusticeK S Hegde Charitable hospital, Mangalore after obtaining informed consent. Genetic polymorphism patterns were evaluated by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Trough level serum valproate concentration was estimated by high-performance liquid chromatography (HPLC). Sodium valproate concentration in different UGT genotypes was compared by Analysis of Variance (ANOVA). P value <0.05 was considered significant.

RESULTS

In the present study population, the predominant mutant allele pattern was observed in UGT1A6 (T19G, A541G, A552C) gene. In UGT2B7 (A268G, C161T) showed predominant mutant allele pattern while (G211T) showed predominant wild type. Mean steady-state sodium valproate concentration was 105.40 ± 49.9 μg/ml and adjusted sodium valproate concentration was 5.5 ± 3.2 mg/kg/L. It was found that there was no statistical difference in sodium valproate concentration in different UGT1A6 and UGT2B7 gene polymorphism.

CONCLUSION

The present study concluded that though there was a difference in pattern of gene polymorphism with concerning UGT1A6 and UGT2B7, however, it has not contributed to variation in serum concentration of sodium valproate in the present study population.

Precipitating factors causing hyperbilirubinemia during chronic hepatitis C treatment with paritaprevir/ritonavir/ombitasvir and dasabuvir

BACKGROUND

Hepatic decompensation is a fatal on-treatment side effect during chronic hepatitis C treatment with paritaprevir/ritonavir/ombitasvir and dasabuvir (PrOD). Prompt bilirubin testing can reveal hepatic failure in susceptible patients, and clinical parameters precipitating early elevation of bilirubin can warn clinicians to avoid PrOD prescription.

METHODS

This retrospective study included 169 Hepatitis C virus (HCV)-genotype 1b patients who underwent a 12-week course of PrOD with or without ribavirin. Laboratory data underwent χ analysis with Fisher's exact test to determine the precipitating factors causing hyperbilirubinemia in patients who had received 1 week of treatment.

RESULTS

Sustained viral response was achieved in 164 patients (97.0%). Total bilirubin was ≥2 mg/dL (21.3%) in 36 patients after 1 week of treatment. Pretreatment white blood cell (WBC) <4500/µL and platelet <100,000/µL correlated with total bilirubin ≥2 mg/dL (relative risk [RR]: 21.64, 95% CI: 5.23-89.64, p < 0.001) after 1 week of treatment. Pretreatment platelet ≥100 000/µL and WBC <4500/µL correlated with direct bilirubin ≥0.45 mg/dL (RR: 6.56, 95% CI: 1.42-30.38, p = 0.016) and indirect bilirubin ≥0.6 mg/dL (RR: 4.77, 95% CI: 1.03-22.15, p = 0.046). Pretreatment platelet <100,000/µL with F3/F4 fibrosis correlated with first week total bilirubin ≥2 mg/dL (RR: 3.57, 95% CI: 1.35-9.09, p = 0.010).

CONCLUSION

PrOD is an effective antiviral regimen for HCV genotype 1b patients. Total bilirubin ≥2 mg/dL after 1 week of treatment serves as an early warning of irreversible progression toward hepatic decompensation, and the current study provides a guide by which to monitor chronic hepatitis C patients undergoing PrOD treatment.

In silico and crystallographic studies identify key structural features of biliverdin IXβ reductase inhibitors having nanomolar potency

Heme cytotoxicity is minimized by a two-step catabolic reaction that generates biliverdin (BV) and bilirubin (BR) tetrapyrroles. The second step is regulated by two non-redundant biliverdin reductases (IXα (BLVRA) and IXβ (BLVRB)), which retain isomeric specificity and NAD(P)H-dependent redox coupling linked to BR's antioxidant function. Defective BLVRB enzymatic activity with antioxidant mishandling has been implicated in metabolic consequences of hematopoietic lineage fate and enhanced platelet counts in humans. We now outline an integrated platform of in silico and crystallographic studies for the identification of an initial class of compounds inhibiting BLVRB with potencies in the nanomolar range. We found that the most potent BLVRB inhibitors contain a tricyclic hydrocarbon core structure similar to the isoalloxazine ring of flavin mononucleotide and that both xanthene- and acridine-based compounds inhibit BLVRB's flavin and dichlorophenolindophenol (DCPIP) reductase functions. Crystallographic studies of ternary complexes with BLVRB-NADP⁺-xanthene-based compounds confirmed inhibitor binding adjacent to the cofactor nicotinamide and interactions with the Ser-111 side chain. This residue previously has been identified as critical for maintaining the enzymatic active site and cellular reductase functions in hematopoietic cells. Both acridine- and xanthene-based compounds caused selective and concentration-dependent loss of redox coupling in BLVRB-overexpressing promyelocytic HL-60 cells. These results provide promising chemical scaffolds for the development of enhanced BLVRB inhibitors and identify chemical probes to better dissect the role of biliverdins, alternative substrates, and BLVRB function in physiologically relevant cellular contexts.

Revisiting the Latency of Uridine Diphosphate-Glucuronosyltransferases (UGTs)-How Does the Endoplasmic Reticulum Membrane Influence Their Function?

Uridine diphosphate-glucuronosyltransferases (UGTs) are phase 2 conjugation enzymes mainly located in the endoplasmic reticulum (ER) of the liver and many other tissues, and can be recovered in artificial ER membrane preparations (microsomes). They catalyze glucuronidation reactions in various aglycone substrates, contributing significantly to the body's chemical defense mechanism. There has been controversy over the last 50 years in the UGT field with respect to the explanation for the phenomenon of latency: full UGT activity revealed by chemical or physical disruption of the microsomal membrane. Because latency can lead to inaccurate measurements of UGT activity in vitro, and subsequent underprediction of drug clearance in vivo, it is important to understand the mechanisms behind this phenomenon. Three major hypotheses have been advanced to explain UGT latency: compartmentation, conformation, and adenine nucleotide inhibition. In this review, we discuss the evidence behind each hypothesis in depth, and suggest some additional studies that may reveal more information on this intriguing phenomenon.

Prevalence of UDP-glucuronosyltransferase polymorphisms (UGT1A6∗2, 1A7∗12, 1A8∗3, 1A9∗3, 2B7∗2, and 2B15∗2) in a Saudi population

Glucuronidation is an important phase II pathway responsible for many endogenous substances and drug metabolism. The present work evaluated allele frequencies of certain UDP-glucuronosyl-transferases (UGT 1A6∗2, A7∗12, A8∗3, A9∗3, 2B7∗2, and 2B15∗2) in Saudi Arabians that could provide essential ethnic information. Blood samples from 192 healthy unrelated Saudi males of various geographic regions were collected. Genomic DNA was isolated and genotyping of various UGTs was carried out using polymerase chain reaction (PCR) followed by direct sequencing. For UGT1A6∗2 A/G genotype, the most common variant was the homozygous repeat (AA) and the most common allele was (A) with a frequency of 46.5% and 67.3%, respectively. Similarly, the most common variant for UGT1A7∗12 T/C genotype was the heterozygous repeat (TC) with a frequency of 78.7% while the mutant allele (C) was present in 60.6% of the study population. Both UGT1A8∗3 (G/A) and UGT1A9∗3 (T/C) showed only a wild homozygous pattern in all screened subjects. For UGT2B7∗2, the heterozygous repeat (TC) was found with a frequency of 57.3% and the alleles (A) showed a frequency of 50.8%. In contrast, for UGT2B15∗2 (G253T), the heterozygous repeat (TG) presented 62.3% of the subjects where the most common allele (G) was with a frequency of 66.2%. In conclusion, our data indicate that Saudis harbor some important UGT mutations known to affect enzyme activity. Additional studies are therefore, warranted to assess the clinical implications of these gene polymorphisms in this ethnic group.

UGT1A6- and UGT2B7-related valproic acid pharmacogenomics according to age groups and total drug concentration levels

AIM

The role of UGT1A6 and UGT2B7 polymorphisms and the impact of total drug plasma concentration in valproic acid (VPA) pharmacogenomics.

PATIENTS & METHODS

A total of 134 Greek patients were recruited (76 adults). Patients were genotyped for UGT1A6 19T>G, 541A>G and 552A>C and UGT2B7 802T>C polymorphisms. Patients' demographic and clinical data were registered. Natural logarithm of concentration-to-dose ratio (CDR) was also calculated as the final outcome.

RESULTS

No significant genotype-related differences in VPA metabolism were noted among various subgroups. An increased lnCDR ratio was noted in children patients compared with adults suggesting increased metabolic capability in younger ages.

CONCLUSION

UGT1A6 and UGT2B7 genotypes were not related to significant changes in VPA metabolism, even after controlling for total drug concentration levels. Younger ages were associated with increased VPA clearance rate.

Role of UGT1A1 and ADH gene polymorphisms in pegvisomant-induced liver toxicity in acromegalic patients

CONTEXT

Hepatotoxicity is one of the most serious adverse effects in acromegalic patients treated with pegvisomant (PEG-V). Recent studies have found an association between this adverse event and the UGT1A1 allele 28 polymorphism associated with Gilbert's syndrome.

OBJECTIVE

To determine whether UGT1A1*28 and alcohol dehydrogenase (ADH) polymorphisms influence liver toxicity during PEG-V treatment.

DESIGN AND SETTING

Multicenter observational retrospective study conducted in 13 tertiary care endocrinology units in Italy.

PATIENTS

A total of 112 patients with active disease resistant to somatostatin analogs (SSTa) and 108 controls were enrolled.

INTERVENTIONS

Clinical and biochemical data were recorded by electronic clinical reporting forms. Blood or DNA samples were sent to the coordinating center for genotyping.

RESULTS

No differences in genotypes between patients and controls were found. During PEG-V therapy liver function tests (LFT), abnormalities and overt hepatotoxicity developed in 17 and 4.5% of patients respectively. Logistic and linear regression analyses showed an association between LFT abnormalities during the follow-up visit and prior events of LFT abnormalities in medical history (odds ratio=1.25; P=0.04) and the number of concomitant medications, other than SSTa (B=3.9; P=0.03). No correlation between LFT alterations and UGT1A1 allele 28 as well as ADH1C and B polymorphisms was found.

CONCLUSIONS

UGT1A1 allele 28 and ADH1C and B polymorphisms do not predict increased risk of hepatotoxicity during PEG-V therapy. Conversely, patients with multi-therapies and with previous episodes of liver disease should be carefully managed, due to the observed association between these conditions and LFT abnormalities during PEG-V therapy.

The effects of Gilbert's syndrome on the mean platelet volume and other hematological parameters

The protective effect of increased levels of indirect bilirubin on atherosclerotic heart disease in patients of Gilbert's syndrome is well known. The aim of the study was to investigate the effects of increased levels of bilirubin on the mean platelet volume (MPV) and other hematological parameters. Thirty-two men and 36 women (a total of 68 Gilbert's syndrome patients) and a similar age group of 68 healthy individuals (32 men and 36 women) were included in the study. Hematologic tests, C-reactive protein (CRP) and biochemical values of the two groups were checked. MPV level of Gilbert's syndrome group was 7.8±1.0fl and CRP 0.2±0.27mg/dl. In the control group MPV was 8.6±1.0fl and CRP 0.3±0.38mg/dl. MPV of patients group (P<0.001) and CRP (P=0.037) were significantly lower than the control group. When dividing Gilbert's syndrome and control groups according to sex into subgroups the level of indirect bilirubin in men with Gilbert's syndrome (1.8±0.8mg/dl) was found to be higher than other groups. Healthy men had higher levels of MPV (8.8±0.9fl) whereas Gilbert's syndrome male patients had lower levels (7.7±1.1fl), (P<0.001). The elevated levels of bilirubin and decreasing levels of MPV and CRP in Gilbert's syndrome patients may have an effect on the slowing down of the atherosclerotic process.

Refining the UGT1A haplotype associated with irinotecan-induced hematological toxicity in metastatic colorectal cancer patients treated with 5-fluorouracil/irinotecan-based regimens

Despite the importance of UDP-glucuronosyltransferase (UGT) 1A1*28 in irinotecan pharmacogenetics, our capability to predict drug-induced severe toxicity remains limited. We aimed at identifying novel genetic markers that would improve prediction of irinotecan toxicity and response in advanced colorectal cancer patients treated with folic acid (leucovorin), fluorouracil (5-FU), and irinotecan (camptosar)-based regimens. The relationships between UGT1A candidate markers across the gene (n = 21) and toxicity were prospectively evaluated in 167 patients. We included variants in the 3'untranscribed region (3'UTR) of the UGT1A locus, not studied in this context yet. These genetic markers were further investigated in 250 Italian FOLFIRI-treated patients. Several functional UGT1A variants, including UGT1A1*28, significantly influenced risk of severe hematologic toxicity. As previously reported in the Italian cohort, a 5-marker risk haplotype [haplotype II (HII); UGTs 1A9/1A7/1A1] was associated with severe neutropenia in our cohort [odds ratio (OR) = 2.43; P = 0.004]. The inclusion of a 3'UTR single-nucleotide polymorphism (SNP) permitted refinement of the previously defined HI, in which HIa was associated with the absence of severe neutropenia in combined cohorts (OR = 0.55; P = 0.038). Among all tested UGT1A variations and upon multivariate analyses, no UGT1A1 SNPs remained significant, whereas three SNPs located in the central region of UGT1A were linked to neutropenia grade 3-4. Haplotype analyses of these markers with the 3'UTR SNP allowed the identification of a protective HI (OR = 0.50; P = 0.048) and two risk haplotypes, HII and HIII, characterized by 2 and 3 unfavorable alleles, respectively, revealing a dosage effect (ORs of 2.15 and 5.28; P ≤ 0.030). Our results suggest that specific SNPs in UGT1A, other than UGT1A1*28, may influence irinotecan toxicity and should be considered to refine pharmacogenetic testing.

Functional impact and prevalence of polymorphisms involved in the hepatic glucuronidation of valproic acid

Metabolism of valproic acid, a widely used drug, is only partially understood. It is mainly metabolized through glucuronidation and acts as a substrate for various UDP-glucuronosyltransferases (UGTs). UGTs metabolizing valproic acid in the liver are UGT1A3, UGT1A4, UGT1A6, UGT1A9 and UGT2B7, with UGT1A6 and UGT2B7 being the most prominent. Polymorphisms in genes expressing these enzymes may have clinical consequences, regarding dosing, blood levels of the drug and adverse reactions. Not all genes are well studied and studies, where they exist, report conflicting results. Prevalence of polymorphisms and various haplotypes is also of great importance, as it may suggest different therapeutic approaches in various populations. Presented here is a review of currently known polymorphisms, their functional impact, when known, and their prevalence in different populations, highlighting the current state of understanding and areas where there is a lack of data and suggesting new perspectives for further research.

A functional polymorphism in UGT1A1 related to hyperbilirubinemia is associated with a decreased risk for Crohn's disease

BACKGROUND

An imbalance between the production of reactive oxygen species (ROS) and their capturing by antioxidants results in oxidative stress, this may play an important role in the pathogenesis of inflammatory bowel disease (IBD). Since bilirubin is an important endogenous antioxidant, increased levels of bilirubin may protect against IBD. UDP-glucuronosyltransferase 1A1 (UGT1A1) is the only enzyme involved in the conjugation of bilirubin and the common UGT1A1*28 allele in the UGT1A1 gene, which is strongly associated with Gilbert's syndrome in Caucasians, results in elevated plasma bilirubin levels.

AIMS

To test the hypothesis that the UGT1A1*28 allele is associated with lower disease susceptibility to, and disease behavior within, IBD. In addition, a possible altered risk for developing IBD-drug related side-effects was explored.

METHODOLOGY

Genomic DNA of 751 patients with IBD (209 patients with ulcerative colitis and 542 patients with Crohn's disease) and 930 healthy controls was genotyped for the UGT1A1*28 promoter polymorphism, and genotype distribution was compared between patients and controls. Genotype phenotype interactions were also investigated.

RESULTS

Patients with Crohn's disease significantly less often bear the UGT1A1*28 homozygous genotype compared to the control group, with an odds ratio of 0.64, 95% CI: 0.42-0.98. The ulcerative colitis group showed no significant differences compared to controls.

CONCLUSION

The homozygous state of the UGT1A1*28 polymorphism, associated with higher serum bilirubin levels, may be protective for the development of Crohn's disease, suggesting that the anti-oxidant capacity of bilirubin may play a part.

Inter and intra-ethnic differences in the distribution of the molecular variants of TPMT, UGT1A1 and MDR1 genes in the South Indian population

Molecular variants of polymorphic drug metabolizing enzymes and drug transporters are attributed to differences in individual's therapeutic response and drug toxicity in different populations. We sought to determine the genotype and allele frequencies of polymorphisms for major phase II drug-metabolizing enzymes (TPMT, UGT1A1) and drug transporter (MDR1) in South Indians. Allelic variants of TPMT (*2,*3A,*3B,*3C & *8), UGT1A1 (TA)6>7 and MDR1 (2677G>T/A & 3435C>T) were evaluated in 450-608 healthy South Indian subjects. Genomic DNA was extracted by phenol-chloroform method and genotype was determined by PCR-RFLP, qRT-PCR, allele specific PCR, direct sequencing and SNaPshot techniques. The frequency distributions of TPMT, UGT1A1 and MDR1 gene polymorphisms were compared between the individual 4 South Indian populations viz., Tamilian, Kannadiga, Andhrite and Keralite. The combined frequency distribution of the South Indian populations together, was also compared with that of other major populations. The allele frequencies of TPMT*3C, UGT1A1 (TA)7, MDR1 2677T, 2677A and 3435T were 1.2, 39.8, 60.3, 3.7, and 61.6% respectively. The other variant alleles such as TPMT*2, *3A, *3B and *8 were not identified in the South Indian population. Sub-population analysis showed that the distribution of UGT1A1 (TA)6>7 and MDR1 allelic variants differed between the four ethnic groups. However, the frequencies of TPMT*3C allele were similar in the four South Indian populations. The distribution of TPMT, UGT1A1 and MDR1 gene polymorphisms of the South Indian population was significantly different from other populations.

Non tumoral hyperserotoninaemia responsive to octreotide due to dual polymorphism in UGT1A1 and UGT1A6

Gilbert's syndrome is a common inherited metabolic disorder, caused by genetic aberration in the enzyme UDP-glucuronosyl-transferase 1A1 that leads to reduced glucuronidation of bilirubin. Recent advances in molecular genetics have frequently reported the concurrence of dual genetic polymorphisms in UDP glucuronosyl-transferases 1A6 and 1A1 in patients with Gilbert's syndrome, leading to defective glucuronidation of bilirubin, as well as several other endogenous and exogenous substrates, such as serotonin. We present a case of Gilbert's syndrome with severe persistent hyperserotoninaemia, mimicking carcinoid syndrome, due to dual polymorphisms in UDP-glucuronosyl-transferases 1A1 and 1A6. The patient was treated with a long-acting somatostatin analogue (octreotide) for 8 months, resulting in a significant reduction in serum serotonin levels and immediate relief of the symptomatology, followed by a long-term remission. The frequent occurrence of hyperserotoninaemia in Gilbert's syndrome may contribute, at least partly, to the nonspecific symptomatology commonly seen in these patients and should be promptly evaluated.

Hereditary hyperbilirubinemia and its molecular diagnosis

Hereditary hyperbilirubinemia is caused by genetic defects in the enzymes that control bilirubin metabolism. It includes Gilbert syndrome (GS), Crigler-Najjar syndrome (CNS), Lucey-Driscoll syndrome (LDS), Dubin-Johnson syndrome (DJS), Rotor syndrome (RS) and progressive familial intrahepatic cholestasis (PFIC). This literature review covers the molecular basis of and laboratory detection methods for hereditary hyperbilirubinemia.

Paracetamol metabolism and related genetic differences

Paracetamol (acetaminophen) is a worldwide used analgesic and antipyretic drug. It is metabolised via several metabolic pathways, including glucuronidation, sulfation, oxidation, hydroxylation, and deacetylation: Hepatic and other organ damage may occur, especially in overdose, because of the accumulation of a toxic metabolite. Intersubject and ethnic differences have been reported in paracetamol metabolism activation, suggesting possible differences in susceptibility to toxicity and in pain alleviation, linked to different pharmacogenetic profiles. This article aims at reviewing, in the literature, the links between paracetamol metabolism and enzyme genotypes in the context of toxic side effects and efficacy of paracetamol in therapeutics.

Associations between polymorphisms in glucuronidation and sulfation enzymes and mammographic breast density in premenopausal women in the United States

OBJECTIVE

Sex hormones are metabolized to less active compounds via (a) glucuronidation catalyzed by UDP-glucuronosyltransferases (UGT) and (b) sulfation catalyzed by sulfotransferases (SULT). Functional UGT and SULT polymorphisms can affect clearance of sex hormones, thereby influencing exposure in hormone-sensitive tissues, such as the breast. We assessed relationships between functional polymorphisms in the UGT and SULT genes and breast density in premenopausal women.

METHODS

One hundred seventy-five women ages 40 to 45 years, who had a screening mammogram taken within the previous year, provided a genomic DNA sample. Mammograms were digitized to obtain breast density measures. Using generalized linear regression, we assessed associations between percent breast density and polymorphisms in the UGT1A and UGT2B families, SULT1A1, and SULT1E1.

RESULTS

Women with the SULT1A1(H213/H213) genotype had 16% lower percent breast density compared with women with the SULT1A1(R213/R213) genotype after controlling for ethnicity (P = 0.001). Breast density was 5% lower among women carrying at least one copy of the UGT1A1(TA7)-UGT1A3(R11)-UGT1A3(A47) haplotype compared with the UGT1A1(TA6)-UGT1A3(W11R)-UGT1A3(V47A) haplotype (P = 0.07). No associations were observed between polymorphisms in the UGT2B family or SULT1E1 and breast density.

CONCLUSION

Polymorphisms in SULT1A1 and the UGT1A locus may influence percent breast density in premenopausal women.

Pegvisomant-induced liver injury is related to the UGT1A1*28 polymorphism of Gilbert's syndrome

CONTEXT

Pegvisomant (PEG) therapy has been associated with drug-induced liver dysfunction in acromegalic patients. The mechanism of its toxicity remains unknown.

OBJECTIVE

The primary objective was to determine whether or not the UGT1A1*28 polymorphism associated with Gilbert's syndrome influences the development of liver dysfunction during PEG treatment.

DESIGN AND SETTING

A cross-sectional study was conducted in four Spanish university hospitals.

PATIENTS

Thirty-six acromegalic patients with active disease, resistant to somatostatin analogs, participated.

RESULTS

The prevalence of the UGT1A1*28 homozygous and heterozygous genotypes in acromegalic patients was 14 and 44%, respectively. Ten patients (28%) developed liver function test (LFT) abnormalities. There was a tendency for more frequent liver function abnormalities in males (70% males vs. 30% females, P = 0.058). Carriers of the UGT1A1*28 polymorphism had a higher incidence of LFT abnormalities than the UGT1A1 wild type (43% carriers vs. 7% wild type, P = 0.024). This difference persisted when adjusted in an all-factors multiple regression analysis [coefficient of determination (R(2)) = 0.463; P = 0.008] for age, gender, alcohol consumption, and UGT1A1*28 polymorphism. A stepwise multivariate likelihood binary logistic regression analysis (R(2) = 0.40; P = 0.003) identified male gender (beta = 7.21; P = 0.033) and UGT1A1*28 polymorphism (beta = 14.1; P = 0.028) as the only significant predictors for the development of LFT abnormalities.

CONCLUSIONS

The UGT1A1*28 genotype and male gender predict an increased incidence of LFT abnormalities during PEG therapy in acromegaly.

UGT1A1 gene polymorphism as a potential factor inducing iron overload in the pathogenesis of type 1 hereditary hemochromatosis

Aim Hereditary hemochromatosis is a common genetic disorder characterized by iron overload and subsequent organ damage. It is caused in most cases by HFE gene mutations which penetrance can be affected by many factors. The aim of this study was to establish the role of UGT1A1 gene polymorphism and serum bilirubin concentration in the pathogenesis of hereditary hemochromatosis. Methods Biochemical, histopathological and genetic data indicating iron excess and serum total bilirubin concentration were determined in 32 patients with the type 1 hereditary hemochromatosis. Fluorescent molecular probes assays were used for genotyping of UGT1A1*28 and UGT1A1*60 mutations in these individuals. Results High incidence and a significant correlation of UGT1A1 gene mutations with increased serum bilirubin level and lower grades of liver tissue inflammatory activity were observed in study participants. UGT1A1*28 and UGT1A1*60 mutations were strongly linked together. Two of the subjects presented very rare genotypes of UGT1A1 gene: (TA)(5/7) and c.-64G>C heterozygotes. Conclusions UGT1A1 gene polymorphism and as its consequence of high serum bilirubin level may promote iron accumulation in hemochromatosis patients by reducing the activity of inflammation. We proposed a possible mechanism of this interaction.

Decreased oxidation susceptibility of plasma low density lipoproteins in patients with Gilbert's syndrome

BACKGROUND AND AIM

The association of hyperbilirubinemia in Gilbert's syndrome (GS) with a decrease in prevalence of coronary artery disease is a well-known phenomenon. In this study, the state of low-density lipoprotein (LDL) oxidation which has been postulated to be a significant determinant at the etiopathogenesis of atherosclerotic disorders was investigated among individuals with GS.

METHODS

For this purpose, serum cholesterol, LDL cholesterol, high-density lipoprotein cholesterol, triglycerides, uric acid, apolipoprotein A and B, bilirubins, thiobarbituric acid-reactive substances, and the sensitivity of LDL oxidation levels, as well as serum alanine aminotransferase, aspartate aminotranserfase, gamma glutamyl transferase, and alkaline phosphatase activities, were determined in 17 patients with Gilbert's syndrome and 15 healthy adults.

RESULTS

There was no significant difference between the groups except the indirect bilirubin parameter (P < 0.001). In comparison with the healthy individuals, LDL oxidation levels between 75 and 120 min were significantly lower (P < 0.005) along with prolonged lag-phase in GS patients, indicating a delay in oxidation susceptibility.

CONCLUSION

It is suggested that the chronic hyperbilirubinemia leading to a lag-phase prolongation in LDL oxidation and a decrease in LDL oxidation may be reason for the low percentage of coronary artery disease.

Detoxification enzyme polymorphisms are not involved in duodenal adenomatosis in familial adenomatous polyposis

Background

Patients with familial adenomatous polyposis (FAP) are at high risk of developing duodenal adenomas and carcinomas. Besides germline mutations in the adenomatous polyposis coli (APC) gene, additional factors may influence the age of onset and number of duodenal adenomas. This study compared the genotype distributions of duodenal detoxification enzyme isoforms in patients with FAP and controls.

Methods

The study included 85 patients with FAP and 218 healthy age- and sex-matched controls. Genotyping of all participants using polymerase chain reaction was performed to detect polymorphisms in isoforms of uridine 5′-diphosphate glucuronosyltransferases (UGTs) and glutathione S-transferases (GSTs): UGT1A1, UGT1A3, UGT1A4, UGT1A6, UGT1A10, UGT2B4, UGT2B7, UGT2B15, GSTA1, GSTP1, GSTM1 and GSTT1.

Results

The variant genotypes of UGT1A3 were less common in patients with FAP than in controls (odds ratio 0·39 (95 per cent confidence interval 0·22 to 0·67)). There were no associations between FAP and the other polymorphic genes. The polymorphisms investigated had no predictive value for the severity of duodenal adenomatosis in patients with FAP.

Conclusion

Although the variant genotypes of UGT1A3 were less common in patients with FAP than in those without, this did not modulate the severity of duodenal adenomatosis.

Dual polymorphisms in UDP-glucuronosyltransferases 1A1 and 1A6: a novel mechanism for hyperserotoninaemia in Gilbert's syndrome mimicking carcinoid syndrome?

Gilbert's syndrome is a common inherited disorder, in which genetic defects in uridine diphosphate-glucuronosyltransferase 1A1 lead to deficient glucuronidation of bilirubin and hence hyperbilirubinaemia. Although usually considered asymptomatic, Gilbert's syndrome can be associated with gastrointestinal and psychiatric symptoms unexplained by the metabolic defect. Genetic polymorphism of a closely related enzyme, uridine diphosphate-glucuronosyltransferase 1A6, results in altered metabolism and elimination of serotonin. On the basis of a case of hyperserotoninaemia in the absence of a detectable carcinoid tumour in a patient with Gilbert's syndrome, who presented with a history of night sweats, flushing, abdominal discomfort and intermittent diarrhoea, we propose that in a subgroup of Gilbert's syndrome patients, homozygocity for dual uridine diphosphate-glucuronosyltransferase 1A1 and uridine diphosphate-glucuronosyltransferase 1A6 polymorphisms may lead to combined hyperbilirubinaemia and hyperserotoninaemia. The latter may account for symptoms experienced by patients with Gilbert's syndrome hitherto considered unrelated to, or unexplainable by, the known defect in bilirubin metabolism.

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.

[(18)F]FDG accumulation in an experimental model of multistage progression of cholangiocarcinoma

AIM

The diagnosis of cholangiocarcinoma (CCA) is difficult, and due to the insidious course of the disease, most cases present at a relatively late stage. Positron emission tomography (PET), using [(18)F]fluoro-2-deoxyglucose ([(18)F]FDG) as a tracer is one the most powerful molecular imaging techniques available. We hypothesized that [(18)F]FDG accumulates at sites of early CCA development and that FDG-PET may be of value for the early diagnosis of CCA.

METHODS

We added 300 mg/L thioacetamide to the drinking water of rats who went on to develop CCA within 20 weeks. From eight weeks onwards, groups of three rats were injected with [(18)F]FDG, subsequently the liver was perfused, dissected and subjected to quantitative autoradiography using a phosphor imaging system. The liver sections were stained for histology, and glutathione S-transferase (GST) enzyme activity was determined. We correlated [(18)F]FDG uptake with pathological liver changes.

RESULTS

The experiments demonstrate that thioacetamide causes atypical bile ducts and invasive CCA. Rat livers harvested early after the start of administration of thioacetamide contained only cirrhosis and/or atypical bile ducts, but CCA and FDG accumulation were absent. At 20 weeks, all rats had developed CCA and all, except two animals with a very small carcinoma, had strongly elevated focal FDG uptake. Quantitative autoradiography revealed tumor-to-normal-liver ratios as high as 5:4. In all rats with a carcinoma, there was a backdrop of cirrhosis, and interestingly cirrhotic areas did not show elevated FDG accumulation.

CONCLUSION

[(18)F]FDG accumulates in CCA, is able to distinguish CCA from liver cirrhosis, but is probably unsuitable to detect very early CCA lesions.

Effects of Combined UDP-Glucuronosyltransferase (UGT) 1A1*28 and 1A6*2 on Paracetamol Pharmacokinetics in β-Thalassemia/HbE

In addition to pathophysiological changes, genetic variations can alter drug pharmacokinetics in patients with thalassemia. Numerous drugs are metabolized by UDP-glucuronosyltransferases (UGT) including paracetamol (PCM), a widely used analgesic. Co-occurrence of the UGT1A1 polymorphism (UGT1A1*28) and the UGT1A6 polymorphism (UGT1A6*2) may affect PCM glucuronidation. To elucidate the effect of these combined polymorphisms on the PCM metabolism in thalassemic patients, 15 beta-thalassemia/hemoglobin E subjects with three different UGT1A genotypes received a single oral dose of 1,000 mg PCM. Drug disposition was determined by HPLC. Patients who have UGT1A6*2 without UGT1A1*28 showed a significant, lower area under concentration-time curve (AUC(0)-->infinity) of PCM, PCM-glucuronide and PCM-sulfate than those of the patients with wild-type UGT1A1 and UGT1A6 (p < 0.05). In addition, a high elimination rate constant and clearance of PCM and its metabolites were also found in these patients (p < 0.05). Ourstudy suggests that a subtherapeutic level of PCM may occur in patients who have UGT1A6*2 without UGT1A1*28.

Functional characterization of human and cynomolgus monkey UDP-glucuronosyltransferase 1A6 enzymes

UDP-glucuronosyltransferase 1A6 (UGT1A6) is a major isoform in the human liver that glucuronidates numerous drugs, environmental chemicals and endogenous substrates. In this study, human and cynomolgus monkey UGT1A6 cDNAs (humUGT1A6 and monUGT1A6, respectively) were cloned, and the corresponding proteins were heterologously expressed in yeast cells to identify the functions of primate UGT1A6s. The enzymatic properties of UGT1A6 proteins were characterized by the kinetic analysis of serotonin (5-hydroxytryptamine, 5-HT) and 4-methylumbelliferone (4-MU) glucuronidation. humUGT1A6 and monUGT1A6 showed 96% identity in their nucleotide and amino acid sequences. Immunoblotting analysis using an antibody raised against human UGT1A6 showed that protein staining intensities were different between human and cynomolgus monkey UGT1A6 enzymes in microsomal fractions from livers and yeast cells, although both enzymes were detectable. The apparent K(m) value (15 mM) for 5-HT glucuronidation of cynomolgus monkey liver microsomes was significantly higher than that (8.6mM) of human liver microsomes, whereas V(max) values were lower in cynomolgus monkeys (2.8 nmol/min/mg protein) than in humans (8.6 nmol/min/mg protein). No significant species difference was observed in K(m) (approximately 90 microM) or V(max) (approximately 25 nmol/min/mg protein) values for liver microsomal 4-MU glucuronidation. In yeast cell microsomes, K(m) values (approximately 6mM) for 5-HT glucuronidation by recombinant UGT1A6s were similar, while a V(max) value (0.1nmol/min/mg protein) of monUGT1A6 was significantly lower than that (0.7 nmol/min/mg protein) of humUGT1A6. In 4-MU glucuronidation, both K(m) (210 microM) and V(max) (3.5 nmol/min/mg protein) values of monUGT1A6 were significantly higher than those of humUGT1A6 (K(m), 110 microM; V(max), 1.5nmol/min/mg protein). These findings suggest that the enzymatic properties of UGT1A6 were extensively different between humans and cynomolgus monkeys, although humUGT1A6 and monUGT1A6 showed high homology at the amino acid level. The information gained in this study should help with in vivo extrapolation and to assess the toxicity of xenobiotics.

Pharmacogenetics of uridine diphosphoglucuronosyltransferase (UGT) 1A family members and its role in patient response to irinotecan

Glucuronidation, catalyzed by the glucuronosyltransferase (UGT) superfamily, is a major biotransformation pathway for several drugs, including irinotecan. Irinotecan is commonly used in colorectal cancer chemotherapy. Irinotecan undergoes metabolism in humans and is converted to its active metabolite SN-38, a topoisomerase I inhibitor. SN-38 is inactivated via glucuronidation catalyzed by various hepatic and extrahepatic UGT1A isozymes. Although the role of the UGT1A1 *28 genetic variant has received much attention in altered toxicity upon irinotecan treatment, other UGT1A enzymes also play an important role. This review summarizes pharmacokinetic, toxicologic, and pharmacogenetic studies carried out to date in irinotecan and SN-38 disposition.

UGT1A polymorphisms in a Swedish cohort and a human diversity panel, and the relation to bilirubin plasma levels in males and females

OBJECTIVES

The objective of this study was to investigate the prevalence of different polymorphisms and haplotypes associated with individual variations in pharmacokinetics and drug toxicity in the uridine-diphosphate glucuronosyl transferase (UGT) 1A gene in a Swedish cohort (248 healthy volunteers) and in 14 different ethnic groups. We also estimated UGT1A genotype-dependent glucuronidation efficiency using the endogenous substrate bilirubin as an indicator.

METHODS

Pyrosequencing-based genotyping assays were used to determine the different polymorphisms and haplotypes.

RESULTS

Haplotype analysis of the UGT1A1 (*1*28), UGT1A6 (*1*2), and UGT1A7(*1*2*3*4) allelic variants showed that three major haplotypes constituted 84% of the allelic variants in the cohort. We identified 15 haplotypes altogether from all groups, including previously undescribed haplotypes. Testing for the association of genotype and total bilirubin levels (nonfasting) in plasma disclosed that homozygous carriers of the TA allele, irrespective of haplotype combinations, had increased levels of bilirubin compared with noncarriers, but a gender-associated difference was observed.

CONCLUSIONS

In a Swedish cohort, several genetic variants in the UGT1A gene are common, but prevalence in a population may differ because of ethnicity. A phenotype based on bilirubin levels has limitations in serving as an indicator of pharmacogenetic differences in glucuronidation due to the influence of gender. Because of possible substrate overlap regarding different UGT1A isoforms, determination of haplotypes of potential cis-acting polymorphisms in the UGT1A gene should be considered in pharmacogenetic association studies regarding drugs that undergo glucuronidation.

Interactions between CYP2C9 and UGT1A6 polymorphisms and nonsteroidal anti-inflammatory drugs in colorectal cancer prevention

BACKGROUND AND AIMS

Variant genotypes of uridine diphosphate glucuronsyltransferase isoenzyme 1A6 (UGT1A6) associated with decreased metabolic activity have been associated with an enhanced protective effect of aspirin on the development of colorectal adenomas. However, interactions between UGT1A6 variants or variants of another enzyme that metabolizes nonsteroidal anti-inflammatory drugs (NSAIDs), cytochrome P4502C9 (CYP2C9), and NSAIDs in the prevention of colorectal cancer have not been studied extensively.

METHODS

UGT1A6 and CYP2C9 genotypes were determined in 2295 individuals with colorectal cancer and 2903 controls. Interactions between these genotypes, aspirin or ibuprofen use, and colorectal cancer risk were determined.

RESULTS

Variant CYP2C9 genotypes enhanced the protective effect of ibuprofen on the prevention of colorectal cancer, and a dose-response relationship with respect to increasing numbers of variant alleles was seen (P interaction = .02). CYP2C9 variants were more effective in individuals with wild-type rather than variant UGT1A6 (P interaction < .007). Variant CYP2C9 genotypes showed no interaction with aspirin usage, and variant UGT1A6 genotypes showed no interaction with either NSAID with respect to colorectal cancer protection.

CONCLUSIONS

In this study, the major effect seen was an enhancement by slower-metabolizing CYP2C9 variants of the chemopreventive activity of ibuprofen against colorectal cancer.

Uridine diphosphoglucuronosyltransferase pharmacogenetics and cancer

The uridine diphosphoglucuronosyltransferases (UGTs) belong to a superfamily of enzymes that catalyse the glucuronidation of numerous endobiotics and xenobiotics. Several human hepatic and extrahepatic UGT isozymes have been characterized with respect to their substrate specificity, tissue expression and gene structure. Genetic polymorphisms have been identified for almost all the UGT family members. A wide variety of anticancer drugs, dietary chemopreventives and carcinogens are known to be conjugated by members of both UGT1A and UGT2B subfamilies. This review examines in detail each UGT isozyme known to be associated with cancer and carcinogenesis. The cancer-related substrates for several UGTs are summarized, and the functionally relevant genetic polymorphisms of UGTs are reviewed. A number of genotype-phenotype association studies have been carried out to characterize the role of UGT pharmacogenetics in several types of cancer, and these examples are discussed here. In summary, this review focuses on the role of the human UGT genetic polymorphisms in carcinogenesis, chemoprevention and cancer risk.

Cruciferae interact with the UGT1A1*28 polymorphism to determine serum bilirubin levels in humans

UDP-glucuronosyltransferase (UGT) 1A1 is a conjugating biotransformation enzyme that plays a role in maintaining levels of endogenous compounds (e.g., bilirubin) and handling exogenous compounds, including carcinogens. The UGT1A1*28 polymorphism results in decreased UGT1A1 promoter activity due to 7 thymine-adenine (TA) repeats instead of the commonly found 6 repeats. Studies indicate that foods from the botanical families Cruciferae (e.g., broccoli), Rutaceae (citrus), Liliaceae (e.g., onions), and Leguminosae (legumes) may increase UGT activity. We investigated, in an observational study, whether foods from these botanical groups were associated with increased UGT1A1 activity as indicated by serum bilirubin concentrations and whether the effect varied by UGT1A1*28 genotype, comparing those homozygous for the [TA](7)-repeat allele (7/7) to homozygous wild-types (6/6) and heterozygotes (6/7) combined. Healthy volunteers completed 3-d food records. Blood samples were drawn for genomic DNA collection and bilirubin measures. For total, direct, and indirect bilirubin measures, there was no significant association with any botanical group independently. There was a significant inverse association between all 3 bilirubin measures and interaction of UGT1A1*28 genotype with Cruciferae intake (P < 0.02 for each measure); individuals with the 7/7 genotype had reduced bilirubin concentrations with increased intake of cruciferous vegetables, whereas individuals with the 6/6 or 6/7 genotype did not. With regard to UGT1A1-conjugated carcinogens (e.g., heterocyclic amines, polycyclic aromatic hydrocarbons), individuals with decreased UGT1A1 activity due to the 7/7 genotype may be at greater risk for carcinogenesis, but our results imply that they also may have greater opportunity to decrease that risk through dietary intervention.

Functional polymorphisms of UDP-glucuronosyltransferases 1A1, 1A6 and 1A8 are not involved in chronic pancreatitis

OBJECTIVES

Chronic pancreatitis (CP) is associated with alcohol abuse, smoking and other dietary or environmental factors. UDP-glucuronosyltransferases (UGTs) are phase II detoxifying enzymes responsible for glucuronidation of various exogenous and endogenous compounds. Genetic variations, resulting in variable rates of glucuronidation, are of toxicological and physiological importance and are frequently associated with diseases. Recently, a genetic polymorphism in UGT1A7 was possibly associated with an increased risk for CP. We investigated whether polymorphisms in the genes for UGT1A1, UGT1A6 and UGT1A8 modified the risk for CP.

METHODS

DNA samples were obtained from 258 adult CP patients with alcoholic (n = 153), hereditary (n = 25) or idiopathic (n = 80) origin. DNA from 140 healthy controls was analyzed for comparison. Patients and controls were all of Caucasian origin. Genetic polymorphisms in UGTs were determined by PCR, eventually followed by restriction-fragment-length-polymorphism analyses in all subjects.

RESULTS

The distribution of the various alleles of UGT1A1, UGT1A6 and UGT1A8 did not differ between CP patients and healthy controls.

CONCLUSION

These data suggest that genetic polymorphisms in UGT1A1, UGT1A6 and in UGT1A8 do not predispose to the development of CP in Caucasians.

Variation of hepatic glucuronidation: Novel functional polymorphisms of the UDP-glucuronosyltransferase UGT1A4

UDP-glucuronosyltransferases are a family of drug metabolizing enzymes contributing to hepatic drug metabolism and protection against environmental toxins. The aim of this study was to identify polymorphisms at the human UGT1A gene locus and to characterize their function and potential association with hepatocellular carcinoma (HCC). Genomic DNA from the blood of 363 subjects (128 patients with HCC, 235 blood donors) was analyzed for polymorphisms of the UGT1A3, UGT1A4, UGT1A8, UGT1A9, UGT1A10 genes using polymerase chain reaction, sequencing analysis. Recombinant variant UGT protein was analyzed by activity assays. In the UGT1A8 gene an A173G variant and a conserved G to A exchange at position 765 were detected in 25% and 15%. UGT1A9 exhibited two variants C3Y and M33T in 1% and 3%. UGT1A10 exhibited conserved nucleotide exchanges (128 G-->A and 696 C-->T) in 2% and 13%. In the UGT1A3 gene a W11R, a V47A variant, and a conserved G to A exchange at position 81 with an incidence of 65%, 58%, and 65%, respectively, were identified. UGT1A4 exhibited a P24T and an L48V variant in 8% and 9%. UGT1A SNPs were not associated with HCC. UGT1A4 P24T and L48V exhibited reduced glucuronidation activities: beta-naphthylamine 30% and 50%, and dihydrotestosterone 50% and 0%, respectively. In conclusion, the high prevalence of SNPs throughout the human UGT1A gene locus illustrates a genetic basis of interindividual variations of hepatic metabolism. Two polymorphisms of the hepatic UGT1A4 protein show a differential metabolic activity toward mutagenic amines and endogenous steroids, altering hepatic metabolism and detoxification.