Genetic polymorphism in the human UGT1A6 (planar phenol) UDP-glucuronosyltransferase: pharmacological implications

The desert woodrat (Neotoma lepida) induces a diversity of biotransformation genes in response to creosote bush resin

Liver biotransformation enzymes have long been thought to enable animals to feed on diets rich in xenobiotic compounds. However, despite decades of pharmacological research in humans and rodents, little is known about hepatic gene expression in specialized mammalian herbivores feeding on toxic diets. Leveraging a recently identified population of the desert woodrat (Neotoma lepida) found to be highly tolerant to toxic creosote bush (Larrea tridentata), we explored the expression changes of suites of biotransformation genes in response to diets enriched with varying amounts of creosote resin. Analysis of hepatic RNA-seq data indicated a dose-dependent response to these compounds, including the upregulation of several genes encoding transcription factors and numerous phase I, II, and III biotransformation families. Notably, elevated expression of five biotransformation families - carboxylesterases, cytochromes P450, aldo-keto reductases, epoxide hydrolases, and UDP-glucuronosyltransferases - corresponded to species-specific duplication events in the genome, suggesting that these genes play a prominent role in N. lepida's adaptation to creosote bush. Building on pharmaceutical studies in model rodents, we propose a hypothesis for how the differentially expressed genes are involved in the biotransformation of creosote xenobiotics. Our results provide some of the first details about how these processes likely operate in the liver of a specialized mammalian herbivore.

Mutual Modulation of the Activities of Human CYP2D6 and Four UGTs during the Metabolism of Propranolol

Cytochromes P450 (CYP) and UDP-glucuronosyltransferases (UGT) are two enzyme families that play an important role in drug metabolism, catalyzing either the functionalization or glucuronidation of xenobiotics. However, their mutual interactions are poorly understood. In this study, the functional interactions of human CYP2D6 with four human UGTs (UGT1A7, UGT1A8, UGT1A9, and UGT2A1) were investigated using our previously established co-expression model system in the fission yeast Schizosaccharomyces pombe. The substrate employed was propranolol because it is well metabolized by CYP2D6. Moreover, the CYP2D6 metabolite 4-hydroxypropranolol is a known substrate for the four UGTs included in this study. Co-expression of either UGT1A7, UGT1A8, or UGT1A9 was found to increase the activity of CYP2D6 by a factor of 3.3, 2.1 or 2.8, respectively, for the conversion of propranolol to 4-hydroxypropranolol. In contrast, UGT2A1 co-expression did not change CYP2D6 activity. On the other hand, the activities of all four UGTs were completely suppressed by co-expression of CYP2D6. This data corroborates our previous report that CYP2D6 is involved in functional CYP-UGT interactions and suggest that such interactions can contribute to both adverse drug reactions and changes in drug efficacy.

Colorectal Cancer Chemoprevention: A Dream Coming True?

Colorectal cancer (CRC) is one of the deadliest forms of cancer worldwide. CRC development occurs mainly through the adenoma-carcinoma sequence, which can last decades, giving the opportunity for primary prevention and early detection. CRC prevention involves different approaches, ranging from fecal occult blood testing and colonoscopy screening to chemoprevention. In this review, we discuss the main findings gathered in the field of CRC chemoprevention, focusing on different target populations and on various precancerous lesions that can be used as efficacy evaluation endpoints for chemoprevention. The ideal chemopreventive agent should be well tolerated and easy to administer, with low side effects. Moreover, it should be readily available at a low cost. These properties are crucial because these compounds are meant to be used for a long time in populations with different CRC risk profiles. Several agents have been investigated so far, some of which are currently used in clinical practice. However, further investigation is needed to devise a comprehensive and effective chemoprevention strategy for CRC.

Salicylic Acid and Risk of Colorectal Cancer: A Two-Sample Mendelian Randomization Study

Salicylic acid (SA) has observationally been shown to decrease colorectal cancer (CRC) risk. Aspirin (acetylsalicylic acid, that rapidly deacetylates to SA) is an effective primary and secondary chemopreventive agent. Through a Mendelian randomization (MR) approach, we aimed to address whether levels of SA affected CRC risk, stratifying by aspirin use. A two-sample MR analysis was performed using GWAS summary statistics of SA (INTERVAL and EPIC-Norfolk, N = 14,149) and CRC (CCFR, CORECT, GECCO and UK Biobank, 55,168 cases and 65,160 controls). The DACHS study (4410 cases and 3441 controls) was used for replication and stratification of aspirin-use. SNPs proxying SA were selected via three methods: (1) functional SNPs that influence the activity of aspirin-metabolising enzymes; (2) pathway SNPs present in enzymes' coding regions; and (3) genome-wide significant SNPs. We found no association between functional SNPs and SA levels. The pathway and genome-wide SNPs showed no association between SA and CRC risk (OR: 1.03, 95% CI: 0.84-1.27 and OR: 1.08, 95% CI: 0.86-1.34, respectively). Results remained unchanged upon aspirin use stratification. We found little evidence to suggest that an SD increase in genetically predicted SA protects against CRC risk in the general population and upon stratification by aspirin use.

The genome of the naturally evolved obesity-prone Ossabaw miniature pig

The feral pigs of Ossabaw Island (USA) have an outstanding propensity to obesity and develop complete metabolic syndrome (MetS) upon prolonged high energy dieting. We now report the first high quality genome of the Ossabaw pig with Contig N50 of ∼6.03 Mb, significantly higher than most other published pig genomes. Genomic comparison to Duroc reveals that variations including SNPs, INDELs and one ∼2 Mb inversion identified in Ossabaw pig may be related to its "thrifty" phenotype. Finally, an important positively selected gene (PSG) was found to be LEPR (leptin receptor) containing two positively selected sites which may lead to pseudogenization of this gene with possible significant effects on obesity and inflammation development. This work provides the first complete mapping of a genome representing a naturally 'feast and famine' evolved phenotype of MetS, serving as a blueprint to guide the search for new targets and new biomarkers for obesity comorbidities.

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.

Association of UGT1A6 gene polymorphism with clinical outcome in pediatric epileptic patients on sodium valproate monotherapy

Pediatric epilepsy comprises chronic neurological disorders characterized by recurrent seizures. Sodium valproate is one of the common antiseizure medications used for treatment. Glucuronide conjugation is the major metabolic pathway of sodium valproate, carried out by the enzyme uridine 5'-diphosphate (UDP) glucuronosyl transferase (UGT) whose gene polymorphisms may alter the clinical outcome. The objective of this study was to assess the association between UGT1A6 genetic polymorphism and clinical outcome in terms of efficacy and tolerability in pediatric epileptic patients on sodium valproate monotherapy. Pediatric epileptic patients (n=65) aged 2-18 years receiving sodium valproate monotherapy for the past one month were included. Genetic polymorphism patterns of UGT1A6 (T19G, A541G, A552C) were evaluated by PCR-RFLP. Clinical outcome was seizure control during the 6 months observation period. Tolerability was measured by estimating the hepatic, renal, and other lab parameters. Out of 65 patients, TT (40%), TG (57%), and GG (3%) patterns were observed in UGT1A6 (T19G) gene, AA (51%), AG (40%), and GG (9%) in (A541G) gene, and AA (43%), AC (43%), and CC (14%) in (A552C) gene. No statistical difference in clinical outcome was found for different UGT1A6 genetic polymorphism patterns. We concluded that different patterns of UGT1A6 genetic polymorphism were not associated with the clinical outcome of sodium valproate in terms of efficacy and tolerability. Sodium valproate was well-tolerated among pediatric patients with epilepsy and can be used as an effective antiseizure medication.

Ethyl Glucuronide and Ethyl Sulphate in Urine: Caution in their use as markers of recent alcohol use

AIM

To clarify the role of the ethanol metabolites, ethyl glucuronide (EtG) and ethyl sulfate (EtS), in monitoring alcohol consumption.

METHOD

We recruited 7 female and 17 male volunteers who were instructed to consume a quantity of beer (containing 48 gm ethanol) with food in one session. We examined urinary excretion of EtG and EtS over time and looked for correlations between the concentrations of the metabolites EtG and EtS.

RESULTS

EtG concentrations in urine varied between 0.026 and 430.372 μg/ml with average values between 11.85 μg/ml (SD 19.75), 30 min after alcohol intake, and 100.39 μg/ml (SD 101.34), 4.5 h after alcohol intake. EtS urinary concentration ranged from 0.006 to 101.432 μg/ml with average values between 4.77 μg/ml (SD 5.42), 30 min after alcohol intake, and 30.14 μg/ml (SD 27.20), 4.5 h after alcohol intake. Spearman's test showed that urinary EtG and EtS correlated significantly at several time points.

CONCLUSION

The great interindividual variability in their excretion suggests caution in the use of urinary measurement of these metabolites in forensic investigations.

Evidence-based strategies for the characterisation of human drug and chemical glucuronidation in vitro and UDP-glucuronosyltransferase reaction phenotyping

Enzymes of the UDP-glucuronosyltransferase (UGT) superfamily contribute to the elimination of drugs from almost all therapeutic classes. Awareness of the importance of glucuronidation as a drug clearance mechanism along with increased knowledge of the enzymology of drug and chemical metabolism has stimulated interest in the development and application of approaches for the characterisation of human drug glucuronidation in vitro, in particular reaction phenotyping (the fractional contribution of the individual UGT enzymes responsible for the glucuronidation of a given drug), assessment of metabolic stability, and UGT enzyme inhibition by drugs and other xenobiotics. In turn, this has permitted the implementation of in vitro - in vivo extrapolation approaches for the prediction of drug metabolic clearance, intestinal availability, and drug-drug interaction liability, all of which are of considerable importance in pre-clinical drug development. Indeed, regulatory agencies (FDA and EMA) require UGT reaction phenotyping for new chemical entities if glucuronidation accounts for ≥25% of total metabolism. In vitro studies are most commonly performed with recombinant UGT enzymes and human liver microsomes (HLM) as the enzyme sources. Despite the widespread use of in vitro approaches for the characterisation of drug and chemical glucuronidation by HLM and recombinant enzymes, evidence-based guidelines relating to experimental approaches are lacking. Here we present evidence-based strategies for the characterisation of drug and chemical glucuronidation in vitro, and for UGT reaction phenotyping. We anticipate that the strategies will inform practice, encourage development of standardised experimental procedures where feasible, and guide ongoing research in the field.

Human variability in isoform-specific UDP-glucuronosyltransferases: markers of acute and chronic exposure, polymorphisms and uncertainty factors

UDP-glucuronosyltransferases (UGTs) are involved in phase II conjugation reactions of xenobiotics and differences in their isoform activities result in interindividual kinetic differences of UGT probe substrates. Here, extensive literature searches were performed to identify probe substrates (14) for various UGT isoforms (UGT1A1, UGT1A3, UGT1A4, UGT1A6, UGT1A9, UGT2B7 and UGT2B15) and frequencies of human polymorphisms. Chemical-specific pharmacokinetic data were collected in a database to quantify interindividual differences in markers of acute (Cmax) and chronic (area under the curve, clearance) exposure. Using this database, UGT-related uncertainty factors were derived and compared to the default factor (i.e. 3.16) allowing for interindividual differences in kinetics. Overall, results show that pharmacokinetic data are predominantly available for Caucasian populations and scarce for other populations of different geographical ancestry. Furthermore, the relationships between UGT polymorphisms and pharmacokinetic parameters are rarely addressed in the included studies. The data show that UGT-related uncertainty factors were mostly below the default toxicokinetic uncertainty factor of 3.16, with the exception of five probe substrates (1-OH-midazolam, ezetimibe, raltegravir, SN38 and trifluoperazine), with three of these substrates being metabolised by the polymorphic isoform 1A1. Data gaps and future work to integrate UGT-related variability distributions with in vitro data to develop quantitative in vitro-in vivo extrapolations in chemical risk assessment are discussed.

Clinical and pharmacogenetic determinants of 5-fluorouracyl/leucovorin/irinotecan toxicity: Results of the PETACC-3 trial

PURPOSE

Irinotecan (CPT-11) in combination with 5-fluorouracil (5FU) is widely used in the treatment of colorectal cancer. We assessed potential clinical variables that may predict toxicity and more specifically the role of UGT1A1 polymorphisms associated with irinotecan toxicity. We used data from the PETACC3 trial, which randomised patients in adjuvant setting to 6 months of leucovorin (LV) and 5FU (LV5/FU2) or LV5/FU2 + irinotecan.

PATIENTS AND METHODS

Clinical and toxicity data were available for 2982 patients, DNA was available for 1200 (40%) of these patients. We genotyped the polymorphisms UGT1A1*28 and UGT1A1-3156G > A. Risk factors for neutropenia and diarrhoea were assessed by univariable and multivariable analyses.

RESULTS

In univariable analysis, UGT1A*28 genotype was associated with an increased incidence of grade III-IV neutropenia (incidence: 44% versus 26%; odds ratio [OR]: 2.3; 95% confidence interval [CI]: 1.4-3.7). In multivariable analysis, the most important predictors (ordered in terms of contribution to R²) were baseline neutrophil count (OR for 1-unit (10⁹/l) decrease: 1.8, 95% CI: 1.3-1.7), female sex (OR: 1.8, 95% CI: 1.1-3.0), body surface area (OR for 0.1-unit increase: 0.8, 95% CI: 0.7-1.0), UGT1A1 (OR: 2.8, 95% CI: 1.6-5.0), age (OR per 10 years: 1.3, 95% CI: 1.1-1.6) and poor performance status (OR: 1.6, 95% CI: 1.0-2.6). The main predictors for grade IV neutropenia were sex, age, performance score and UGT1A1. The main predictors for diarrhoea were sex and age.

CONCLUSIONS

We found that a complex of risk factors is involved in the development of toxicity, including UGT1A1. Parameters that are readily available in clinical practice, notably sex, age and performance status, are stronger predictors than the UGT1A1*28 genotype. Further studies beyond the UGT1A1*28 genotype are needed to fully understand the determinants of toxicity risk, notably in females.

Regioselectivity significantly impacts microsomal glucuronidation efficiency of R/S-6, 7-, and 8-hydroxywarfarin

Coumadin (R/S-warfarin) metabolism plays a critical role in patient response to anticoagulant therapy. Several cytochrome P450s oxidize warfarin into R/S-6-, 7-, 8-, 10, and 4'-hydroxywarfarin that can undergo subsequent glucuronidation by UDP-glucuronosyltransferases (UGTs); however, current studies on recombinant UGTs cannot be adequately extrapolated to microsomal glucuronidation capacities for the liver. Herein, we estimated the capacity of the average human liver to glucuronidate hydroxywarfarin and identified UGTs responsible for those metabolic reactions through inhibitor phenotyping. There was no observable activity toward R/S-warfarin, R/S-10-hydroxywarfarin or R/S-4'-hydroxywarfarin. The observed metabolic efficiencies (V_max/K_m) toward R/S-6-, 7-, and especially 8-hydroxywarfarin indicated a high glucuronidation capacity to metabolize these compounds. UGTs demonstrated strong regioselectivity toward the hydroxywarfarins. UGT1A6 and UGT1A1 played a major role in R/S-6- and 7-hydroxywarfarin glucuronidation, respectively, whereas UGT1A9 accounted for almost all of the generation of the R/S-8-hydroxywarfarin glucuronide. In summary, these studies expanded insights to glucuronidation of hydroxywarfarins by pooled human liver microsomes, novel roles for UGT1A6 and 1A9, and the overall degree of regioselectivity for the UGT reactions.

Correlations between polymorphisms in the uridine diphosphate-glucuronosyltransferase 1A and C-C motif chemokine receptor 5 genes and infection with the hepatitis B virus in three ethnic groups in China

Objective

To determine whether genetic polymorphisms in the uridine diphosphate-glucuronosyltransferase 1A (UGT1A) and the C-C motif chemokine receptor 5 (CCR5) genes are associated with hepatitis B virus (HBV) infection in Yi, Yao and Han ethnic groups in the Guizhou Province of China.

Methods

The study enrolled subjects with and without HBV infection. Whole blood was used for DNA genotyping using standard techniques. The study determined the frequencies of several polymorphic alleles (UGT1A6 [rs2070959], UGT1A1 [rs8175347], CCR5-59029 [rs1799987] and CCR5Δ32 [rs333]) and then characterized their relationship with HBV infection.

Results

A total of 404 subjects were enrolled in the study: 138 from the Yao group, 101 from the Yi group and 165 from the Han group. There was a significant difference in the frequency of UGT1A1 rs8175347 polymorphisms among the three groups. The rates of 7TA carriers of UGT1A1 rs8175347 in all three groups were significantly higher than the other genotypes. Individuals with genotype AA of UGT1A6 rs2070959 in the Yi group had a higher risk for HBV infection than in the Yao and Han groups. The frequency of genotype GG in CCR5-59029 in the Yao group was significantly higher than in the Yi group. The genotypes of CCR5Δ32 were not associated with HBV infection.

Conclusion

These findings provide genetic and epidemiological evidence for an association of UGT1A and CCR5-59029 polymorphisms with HBV infection in Chinese Yi and Yao populations.

Genetic polymorphisms and valproic acid plasma concentration in children with epilepsy on valproic acid monotherapy

PURPOSE

The aim of the study is to evaluate the association between genetic polymorphisms and valproic acid (VPA) concentration to dose ratio in children with epilepsy on VPA monotherapy.

METHODS

A total of 137 children, aged 3.5-18 years, (89 males and 48 females) with epilepsy on sustained-release VPA monotherapy were enrolled. Trough plasma concentrations of VPA at steady-state were measured using an AXSYM automatic immunity analyzer. The values were divided by body weight and total daily dose to calculate concentration to dose ratio of VPA (CDRV). Forty-eight single nucleotide polymorphisms involved in the pharmacokinetics of VPA were identified by MassARRAY system. The logarithmic transformed CDRV (lnCDRV) was normally distributed, and PLINK software was used to evaluate the association between genetic polymorphisms and lnCDRV using linear regression adjusted for gender and seizure type.

RESULTS

rs28898617 (UGT1A3/4/5/6/7/8/9/10, BETA=0.32, P=0.0089) was significantly associated with higher lnCDRV. No other associations were found.

CONCLUSIONS

In pediatric patients taking VPA monotherapy, rs28898617 was associated with a higher normalized VPA plasma concentration. Further studies are warranted to confirm the results.

Effects of UGT1A9 genetic polymorphisms on monohydroxylated derivative of oxcarbazepine concentrations and oxcarbazepine monotherapeutic efficacy in Chinese patients with epilepsy

AIM

The human UDP-glucuronosyltransferase which is genetically polymorphic catalyzes glucuronidations of various drugs. The interactions among UGT1A4, UGT1A6, UGT1A9, and UGT2B15 genetic polymorphisms, monohydroxylated derivative (MHD) of oxcarbazepine (OXC) plasma concentrations, and OXC monotherapeutic efficacy were explored in 124 Chinese patients with epilepsy receiving OXC monotherapy.

METHOD

MHD is the major active metabolite of OXC, and its plasma concentration was measured using high-performance liquid chromatography when patients reached their maintenance dose of OXC. Genomic DNA was extracted from whole blood and SNP genotyping performed using PCR followed by dideoxy chain termination sequencing. We followed the patients for at least 1 year to evaluate the OXC monotherapy efficacy. Patients were divided into two groups according to their therapeutic outcome: group 1, seizure free; group 2, not seizure free. The data were analyzed using T test, one-way analysis of variance (ANOVA), Kruskal-Wallis test, chi-square test, Fisher's exact test, correlation analysis, and multivariate regression analysis.

RESULT

T test analysis showed that MHD plasma concentrations were significantly different between the two groups (p = 0.002). One-way ANOVA followed by Bonferroni post hoc testing of four candidate SNPs revealed that carriers of the UGT1A9 variant allele I399 C > T (TT 13.28 ± 7.44 mg/L, TC 16.41 ± 6.53 mg/L) had significantly lower MHD plasma concentrations and poorer seizure control than noncarriers (CC 22.24 ± 8.49 mg/L, p < 0.05).

CONCLUSION

In our study, we have demonstrated the effects of UGT1A9 genetic polymorphisms on MHD plasma concentrations and OXC therapeutic efficacy. Through MHD monitoring, we can predict OXC therapeutic efficacy, which may be useful for the personalization of OXC therapy in epileptic patients.

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.

Exome-Wide Association Study Identifies New Low-Frequency and Rare UGT1A1 Coding Variants and UGT1A6 Coding Variants Influencing Serum Bilirubin in Elderly Subjects: A Strobe Compliant Article

Genome-wide association studies (GWASs) have identified loci contributing to total serum bilirubin level. However, no exome-wide approaches have been performed to address this question. Using exome-wide approach, we assessed the influence of protein-coding variants on unconjugated, conjugated, and total serum bilirubin levels in a well-characterized cohort of 773 ambulatory elderly subjects from Italy. Coding variants were replicated in 227 elderly subjects from the same area. We identified 4 missense rare (minor allele frequency, MAF < 0.5%) and low-frequency (MAF, 0.5%-5%) coding variants located in the first exon of the UGT1A1 gene, which encodes for the substrate-binding domain (rs4148323 [MAF = 0.06%; p.Gly71Arg], rs144398951 [MAF = 0.06%; p.Ile215Val], rs35003977 [MAF = 0.78%; p.Val225Gly], and rs57307513 [MAF = 0.06%; p.Ser250Pro]). These variants were in strong linkage disequilibrium with 3 intronic UGT1A1 variants (rs887829, rs4148325, rs6742078), which were significantly associated with total bilirubin level (P = 2.34 × 10(-34), P = 7.02 × 10(-34), and P = 8.27 × 10(-34)), as well as unconjugated, and conjugated bilirubin levels. We also identified UGT1A6 variants in association with total (rs6759892, p.Ser7Ala, P = 1.98 × 10(-26); rs2070959, p.Thr181Ala, P = 2.87 × 10(-27); and rs1105879, p.Arg184Ser, P = 3.27 × 10(-29)), unconjugated, and conjugated bilirubin levels. All UGT1A1 intronic variants (rs887829, rs6742078, and rs4148325) and UGT1A6 coding variants (rs6759892, rs2070959, and rs1105879) were significantly associated with gallstone-related cholecystectomy risk. The UGT1A6 variant rs2070959 (p.Thr181Ala) was associated with the highest risk of gallstone-related cholecystectomy (OR, 4.58; 95% CI, 1.58-13.28; P = 3.21 × 10(-3)). Using an exome-wide approach we identified coding variants on UGT1A1 and UGT1A6 genes in association with serum bilirubin level and hyperbilirubinemia risk in elderly subjects. UGT1A1 intronic single-nucleotide polymorphisms (SNPs) (rs6742078, rs887829, rs4148324) serve as proxy markers for the low-frequency and rare UGT1A1 variants, thereby providing mechanistic explanation to the relationship between UGT1A1 intronic SNPs and the UGT1A1 enzyme activity. UGT1A1 and UGT1A6 variants might be potentially associated with gallstone-related cholecystectomy risk.

Tissue-specific patterns of gene expression in the epithelium and stroma of normal colon in healthy individuals in an aspirin intervention trial

Background

Regular aspirin use reduces colon adenoma and carcinoma incidence. UDP-glucuronosyltransferases (UGT) are involved in aspirin metabolism and clearance, and variant alleles in UGT1A6 have been shown to alter salicylic acid metabolism and risk of colon neoplasia.

Methods

In a randomized, cross-over, placebo-controlled trial of 44 healthy men and women, homozygous for UGT1A6*1 or UGT1A6*2, we explored differences between global epithelial and stromal expression, using Affymetrix U133 + 2.0 microarrays and tested effects of 60-day aspirin supplementation (325 mg/d) on epithelial and stromal gene expression and colon prostaglandin E2 (PGE2) levels.

Results

No statistically significant differences in gene expression were observed in response to aspirin or UGT1A6 genotype, but tissue PGE2 levels were lower with aspirin compared to placebo (p <0.001). Transcripts differentially expressed between epithelium and stroma (N = 4916, P <0.01, false discovery rate <0.001), included a high proportion of genes involved in cell signaling, cellular movement, and cancer. Genes preferentially expressed in epithelium were involved in drug and xenobiotic metabolism, fatty acid and lipid metabolism, apoptosis signaling, and ion transport. Genes preferentially expressed in stroma included those involved in inflammation, cellular adhesion, and extracellular matrix production. Wnt-Tcf4 pathway genes were expressed in both epithelium and stroma but differed by subcellular location.

Conclusions

These results suggest that, in healthy individuals, subtle effects of aspirin on gene expression in normal colon tissue are likely overwhelmed by inter-individual variability in microarray analyses. Differential expression of critical genes between colonic epithelium and stroma suggest that these tissue types need to be considered separately.

Electronic supplementary material

The online version of this article (doi:10.1186/s12881-015-0161-6) contains supplementary material, which is available to authorized users.

Biotransformation of xenobiotics in the human colon and rectum and its association with colorectal cancer

In humans, the liver is generally considered to be the major organ contributing to drug metabolism, but studies during the last years have suggested an important role of the extra-hepatic drug metabolism. The gastrointestinal tract (GI-tract) is the major path of entry for a wide variety of compounds including food, and orally administered drugs, but also compounds - with neither nutrient nor other functional value - such as carcinogens. These compounds are metabolized by a large number of enzymes, including the cytochrome P450 (CYP), the glutathione S-transferase (GST) family, the uridine 5'-diphospho- glucuronosyltransferase (UDP-glucuronosyltransferase - UGT) superfamily, alcohol-metabolizing enzymes, sulfotransferases, etc. These enzymes can either inactivate carcinogens or, in some cases, generate reactive species with higher reactivity compared to the original compound. Most data in this field of research originate from animal or in vitro studies, wherein human studies are limited. Here, we review the human studies, in particular the studies on the phenotypic expression of these enzymes in the colon and rectum to get an impression of the actual enzyme levels in this primary organ of exposure. The aim of this review is to give a summary of currently available data on the relation between the CYP, the GST and the UGT biotransformation system and colorectal cancer obtained from clinical and epidemiological studies in humans.

Genetic variation in UGT genes modify the associations of NSAIDs with risk of colorectal cancer: colon cancer family registry

The use of non-steroidal anti-inflammatory drugs (NSAIDs) is associated with reduced risk of colorectal neoplasia. Previous studies have reported that polymorphisms in NSAID-metabolizing enzymes central to NSAID metabolism including UDP-glucuronosyltransferases (UGT) and cytochrome P450 (CYP) 2C9 may modify this protective effect. We investigated whether 35 functionally relevant polymorphisms within CYP2C9 and UGT genes were associated with colorectal cancer risk or modified the protective effect of NSAIDs on colorectal cancer susceptibility, using 1,584 colorectal cancer cases and 2,516 unaffected sibling controls from the Colon Cancer Family Registry. A three-SNP genotype in UGT1A6 (G-A-A; Ala7-Thr181-Arg184) and the Asp85 variant in UGT2B15 increased the risk of colorectal cancer (OR 3.87; 95% CI 1.04-14.45 and OR 1.34; 95% CI 1.10-1.63, respectively). We observed interactions between UGT1A3 Thr78Thr (A>G) and NSAID use (P-interaction = 0.02), a three-SNP genotype within UGT2B4 and ibuprofen use (P-interaction = 0.0018), as well as UGT2B15 Tyr85Asp (T>G) and aspirin use (P-interaction = 0.01). The interaction with the UGT2B4 and the UGT2B15 polymorphisms were noteworthy at the 25% FDR level. This study highlights the need for further pharmacogenetic studies to identify individuals who might benefit from NSAID use as part of developing effective strategies for prevention of colorectal neoplasia. © 2014 Wiley Periodicals, Inc.

Molecular genetic mechanisms of chronic urticaria

Chronic urticaria (CU) is a common allergic skin disease that requires long-term pharmacological treatment. Some patients with severe CU suffer a poor quality of life. Although the pathogenic mechanisms of CU are not clearly understood, several groups have suggested that genetic mechanisms are involved in various CU cohorts. To further understand the molecular genetic mechanisms of CU, we summarize recent genetic data in this review. Although a few HLA alleles were suggested to be candidate markers in different ethnic groups, further replication studies that apply the recent classification are needed. Genetic polymorphisms in histamine-related genes, including FcεRI and HNMT, were suggested to be involved in mast cell activation and histamine metabolism. Several genetic polymorphisms of leukotriene-related genes, such as ALOX5, LTC4S, and the PGE2 receptor gene PTGER4, were suggested to be involved in leukotriene overproduction, a pathogenic mechanism. Further investigations using candidate gene approaches and genome-wide association studies (GWAS) will provide new insights into the molecular genetic mechanisms of CU, which will provide new marker genes for differentiation of CU phenotypes and identification of potential therapeutic targets.

The UGT1A6_19_GG genotype is a breast cancer risk factor

Validation of an association between the UGT1A6_19_T>G (rs6759892) polymorphism and overall breast cancer risk. A pilot study included two population-based case-control studies from Germany (MARIE-GENICA). An independent validation study comprised four independent breast cancer case-control studies from Finland (KBCP, OBCS), Germany (BBCC), and Sweden (SASBAC). The pooled analysis included 7418 cases and 8720 controls from all six studies. Participants were of European descent. Genotyping was done by MALDI-TOF MS and statistical analysis was performed by logistic regression adjusted for age and study. The increased overall breast cancer risk for women with the UGT1A6_19_GG genotype which was observed in the pilot study was confirmed in the set of four independent study collections (OR 1.13, 95% CI 1.05–1.22; p = 0.001). The pooled study showed a similar effect (OR 1.09, 95% CI 1.04–1.14; p = 0.001). The risk effect on the basis of allele frequencies was highly significant, the pooled analysis showed an OR of 1.11 (95% CI 1.06–1.16; p = 5.8 × 10⁻⁶). We confirmed the association of UGT1A6_19_GG with increased overall breast cancer risk and conclude that our result from a well powered multi-stage study adds a novel candidate to the panel of validated breast cancer susceptibility loci.

Effect of common single-nucleotide polymorphisms in acetylsalicylic acid metabolic pathway genes on platelet reactivity in patients with diabetes

Background

Platelet reactivity in patients on acetylsalicylic acid (ASA) therapy can be influenced by physiological or pathological conditions affecting ASA pharmacokinetics or pharmacodynamics. The mechanism of such variability in the therapeutic response to ASA, particularly in diabetic patients, is poorly understood. The rate of elimination of ASA and its metabolite, salicylic acid (SA), is likely a major factor determining drug efficacy. The objective of this study was to investigate the effect of genetic polymorphisms in the selected candidate genes within the ASA metabolic pathway on the platelet reactivity and concentration of ASA and thromboxane A₂ (TxA₂) metabolites in a population of patients with type 2 diabetes mellitus (T2DM).

Material/Methods

The study cohort consisted of 287 Caucasians with T2DM who had been taking ASA tablets at the dose of 75 mg per day for at least 3 months. Platelet reactivity analyses were performed using VerifyNow Aspirin and PFA-100 assays. The measured ASA metabolite included salicylic acid (ASA), and TxA₂ metabolites included serum TxB₂ and urinary 11-dh-TxB₂. Genotyping for the selected 18 single-nucleotide polymorphisms (SNPs) within 5 genes of the ASA metabolic pathway was performed using a Sequenom iPLEX platform.

Results

No statistically significant association was observed between the investigated SNPs genotypes, platelet reactivity, and measured metabolites in the investigated cohort of patients.

Conclusions

The results of our study failed to confirm that the selected variants in the genes within the ASA metabolic pathway might contribute to platelet reactivity in a diabetic population treated with ASA.

Substrate selectivity of human intestinal UDP-glucuronosyltransferases (UGTs): in silico and in vitro insights

The current drug development process aims to produce safe, effective drugs within a reasonable time and at a reasonable cost. Phase II metabolism (glucuronidation) can affect drug action and pharmacokinetics to a considerable extent and so its studies and prediction at initial stages of drug development are very imperative. Extensive glucuronidation is an obstacle to oral bioavailability because the first-pass glucuronidation [or premature clearance by UDP-glucuronosyltransferases (UGTs)] of orally administered agents frequently results in poor oral bioavailability and lack of efficacy. Modeling of new chemical entities/drugs for UGTs and their kinetic data can be useful in understanding the binding patterns to be used in the design of better molecules. This review concentrates on first-pass glucuronidation by intestinal UGTs, including their topology, expression profile, and pharmacogenomics. In addition, recent advances are discussed with respect to substrate selectivity at the binding pocket, structural requirements, and mechanism of enzyme actions.

Association between polymorphisms in UDP-glucuronosyltransferase 1A6 and 1A7 and colorectal cancer risk

Genetic polymorphisms of uridine diphosphate-glucuronosyltransferases 1A6 (UGT1A6) and 1A7 (UGT1A7) may lead to genetic instability and colorectal cancer carcinogenesis. Our objective was to measure the interaction between polymorphisms of these repair genes and tobacco smoking in colorectal cancer (CRC). A total of 68 individuals with CRC and 112 non-cancer controls were divided into non-smoker and smoker groups according to pack-years of smoking. Genetic polymorphisms of UGT1A6 and UGT1A7 were examined using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). We found a weak association of UGT1A6 polymorphisms with CRC risk (crude odds ratio [OR], 1.65; 95% confidence interval [95%CI], 0.9-3.1, P=0.107; adjusted OR 1.95, 95%CI 1.0-3.8, P=0.051). The ORs for the UGT1A7 polymorphisms were statistically significant (crude OR: 26.40, 95%CI: 3.5-198.4, P=0.001; adjusted OR: 21.52, 95%CI: 2.8-164.1, P=0.003). The joint effect of tobacco exposure and UGT1A6 polymorphisms was significantly associated with colorectal cancer risk in non-smokers (crude OR, 2.11; 95%CI, 0.9-5.0, P=0.092; adjusted OR 2.63, 95%CI 1.0-6.7, P=0.042). In conclusion, our findings suggest that UGT1A6 and UGT1A7 gene polymorphisms are associated with CRC risk in the Japanese population. In particular, UGT1A6 polymorphisms may strongly increase CRC risk through the formation of carcinogens not associated with smoking.

UGT1A6 polymorphisms modulated lung cancer risk in a Chinese population

Uridine diphosphoglucuronosyltransferases (UGTs) 1A6 is the only UGT1A isoform expressed in lung tissue. It is responsible for the detoxification of carcinogens such as benezo[a]pyrene from cigarette smoke. The purpose of this study was to evaluate the association of UGT1A6 polymorphisms and haplotypes with lung cancer risk and to evaluate the functional significance of UGT1A6 polymorphisms. Genomic DNA was isolated from leukocytes. Eight UGT1A6 polymorphisms were sequenced in a test set of 72 Chinese lung cancer patients and 62 healthy controls. Potential risk modifying alleles were validated in a separate set of 95 Chinese lung cancer patients and 100 healthy controls. UGT1A6 19T>G, 541A>G and 552A>C showed significant association with increased lung cancer risk, while UGT1A6 105C>T and IVS1+130G>T were significantly associated with reduced lung cancer risk. Multivariate logistic regression analysis demonstrated a significant association of lung cancer with UGT1A6 541A>G (OR: 3.582, 95% CI: 1.27–10.04, p = 0.015), 552A>C (OR: 5.364, 95% CI: 1.92–14.96, p = 0.001) and IVS1+130G>T (OR: 0.191, 95% CI: 0.09–0.36, p<0.001). Functional test demonstrated that UGT1A6 105C>T increased mRNA stability, providing a plausible explanation of its association with reduced lung cancer risk. Thus UGT1A6 polymorphisms may be used to identify people with increased risk of developing lung cancer.

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.

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.

The influence of UGT1A6 variants and aspirin use in a randomized trial of celecoxib for prevention of colorectal adenoma

Aspirin and celecoxib prevent colorectal adenoma recurrence. Genetic variants in the UGT1A6 enzyme are associated with delayed aspirin metabolism and greater chemopreventive efficacy. We examined the effect of combining aspirin and celecoxib in relation to UGT1A6 T181A and R184S variants among 1,647 patients in the Adenoma Prevention with Celecoxib (APC) trial who were stratified according to the use of low-dose aspirin after removal of adenomas and randomized to placebo, 200-mg twice daily, or 400-mg twice daily celecoxib for 3 years. Patients underwent follow-up colonoscopies at 1 and 3 years to assess on-treatment efficacy. At 5 years, 538 patients underwent a colonoscopy to assess risk of recurrence after treatment was discontinued for at least 1 year. During treatment, the relative risk (RR) of recurrent adenoma was 0.68 [95% confidence interval (CI), 0.59-0.79] for 200-mg twice daily celecoxib and 0.54 (95% CI, 0.46-0.64) for 400-mg twice daily celecoxib compared with placebo. Aspirin use was not independently associated with recurrent adenoma (RR, 0.98, 95% CI, 0.86-1.15). These results did not vary according to UGT1A6 genotype. However, among those with a variant UGT1A6 genotype on aspirin, the RR of adenoma was 1.60 (95% CI, 0.81-3.15) after withdrawal of 200-mg twice daily and 1.98 (95% CI, 1.06-3.70) after withdrawal of 400-mg twice daily celecoxib compared with withdrawal of placebo. In contrast, there was no increased risk associated with discontinuing celecoxib among any other groups. Concurrent use of low-dose aspirin does not influence the efficacy of celecoxib in adenoma prevention. However, discontinuing celecoxib among aspirin-using individuals who initially developed adenoma despite a UGT1A6 variant genotype resulted in rapid reemergence of disease.

Polymorphisms of Aspirin-Metabolizing Enzymes CYP2C9, NAT2 and UGT1A6 in Aspirin-Intolerant Urticaria

Acetyl salicylic acid (ASA) is metabolized by UDP-glucuronosyltransferase 1A6 (UGT1A6), cytochrome P4502C9 (CYP2C9), and N-acetyl transferase 2 (NAT2). Variations in the activities of these enzymes may modulate adverse ASA-related symptoms such as urticaria. We examined whether polymorphisms in the UGT1A6, CYP2C9, and NAT2 genes are related to ASA-intolerant urticaria (AIU). The genotypes of 148 subjects with AIU (AIU group) and 260 normal healthy control subjects (NC group) were analyzed with respect to the following single nucleotide polymorphisms: CYP2C9 -1188T>C and CYP2C9(*)3A1075C; UGT1A6 T181A A>G and UGT1A6 R184S A>C; and NAT2 9796A>T, NAT2 197G>A, NAT2 286G>A, NAT2 9601A>G, and NAT2 9306A>G. There were significant differences in the allele frequencies for the CYP2C9 polymorphisms between the two groups. The frequency of the minor allele CYP2C9 -1188T>C was significantly higher in the AIU group than in the NC group (P=0.005). The frequency of the variant genotype CC was higher in the AIU group compared with the controls in both the co-dominant (P=0.007) and recessive models (P=0.012). The frequency of haplotype 2 [CA] was also significantly higher in the AIU group in both the co-dominant (P=0.006) and dominant models (P=0.012). There was no significant difference in genotype frequencies for any of the UGT1A6 or NAT2 polymorphisms between the two groups. Clinical parameters did not differ according to genotype. These results suggest that the C allele of CYP2C9 -1188T>C may be associated with AIU.

UGT1A6 and UGT2B15 polymorphisms and acetaminophen conjugation in response to a randomized, controlled diet of select fruits and vegetables

Acetaminophen (APAP) glucuronidation is thought to occur mainly by UDP-glucuronosyltransferases (UGT) in the UGT1A family. Interindividual variation in APAP glucuronidation is attributed in part to polymorphisms in UGT1As. However, evidence suggests that UGT2B15 may also be important. We evaluated, in a controlled feeding trial, whether APAP conjugation differed by UGT1A6 and UGT2B15 genotypes and whether supplementation of known dietary inducers of UGT (crucifers, soy, and citrus) modulated APAP glucuronidation compared with a diet devoid of fruits and vegetables (F&V). Healthy adults (n = 66) received 1000 mg of APAP orally on days 7 and 14 of each 2-week feeding period and collected saliva and urine over 12 h. Urinary recovery of the percentage of the APAP dose as free APAP was higher (P = 0.02), and the percentage as APAP glucuronide (APAPG) was lower (P = 0.004) in women. The percentage of APAP was higher among UGT1A6*1/*1 genotypes, relative to *1/*2 and *2/*2 genotypes (P = 0.045). For UGT2B15, the percentage of APAPG decreased (P < 0.0001) and that of APAP sulfate increased (P = 0.002) in an allelic dose-dependent manner across genotypes from *1/*1 to *2/*2. There was a significant diet × UGT2B15 genotype interaction for the APAPG ratio (APAPG/total metabolites × 100) (P = 0.03), with *1/*1 genotypes having an approximately 2-fold higher F&V to basal diet difference in response compared with *1/*2 and *2/*2 genotypes. Salivary APAP maximum concentration (C(max)) was significantly higher in women (P = 0.0003), with F&V (P = 0.003), and among UGT1A6*2/*2 and UGT2B15*1/*2 genotypes (P = 0.02 and 0.002, respectively). APAP half-life was longer in UGT2B15*2/*2 genotypes with F&V (P = 0.009). APAP glucuronidation was significantly influenced by the UGT2B15*2 polymorphism, supporting a role in vivo for UGT2B15 in APAP glucuronidation, whereas the contribution of UGT1A6*2 was modest. Selected F&V known to affect UGT activity led to greater glucuronidation and less sulfation.

Determinants of aspirin metabolism in healthy men and women: effects of dietary inducers of UDP-glucuronosyltransferases

BACKGROUND/AIMS

Interindividual variation in aspirin (ASA) metabolism is attributed to concomitant use of drugs or alcohol, urine pH, ethnicity, sex, and genetic variants in UDP-glucuronosyltransferases (UGT). Little is known about the effects of diet.

METHODS

We evaluated cross-sectionally whether urinary excretion of ASA and its metabolites [salicylic acid (SA), salicyluric acid (SUA) phenolic glucuronide (SUAPG), salicylic acid acyl glucuronide (SAAG) and salicylic acid phenolic glucuronide (SAPG)] differed by UGT1A6 genotype and dietary factors shown to induce UGT. Following oral treatment with 650 mg ASA, urine was collected over 8 h in 264 men and 264 women (21-45 years old).

RESULTS

There were statistically significant differences in metabolites excreted between sexes and ethnicities. Men excreted more SUA; women more ASA (p = 0.03), SA, SAAG and SAPG (p ≤ 0.001 for all). Compared to Caucasians, Asians excreted more ASA, SA and SAAG, and less SUA and SUAPG (p ≤ 0.03 for all); African-Americans excreted more SAAG and SAPG and less SUA (p ≤ 0.04). There was no effect of UGT1A6 genotypes. Increased ASA and decreased SUAPG excretion was observed with increased servings of vegetables (p = 0.008), specifically crucifers (p = 0.05).

CONCLUSION

Diet may influence the pharmacokinetics of ASA, but effects may be through modulation of glycine conjugation rather than glucuronidation.

Genetic polymorphism in metabolism and host defense enzymes: implications for human health risk assessment

Genetic polymorphisms in xenobiotic metabolizing enzymes can have profound influence on enzyme function, with implications for chemical clearance and internal dose. The effects of polymorphisms have been evaluated for certain therapeutic drugs but there has been relatively little investigation with environmental toxicants. Polymorphisms can also affect the function of host defense mechanisms and thus modify the pharmacodynamic response. This review and analysis explores the feasibility of using polymorphism data in human health risk assessment for four enzymes, two involved in conjugation (uridine diphosphoglucuronosyltransferases [UGTs], sulfotransferases [SULTs]), and two involved in detoxification (microsomal epoxide hydrolase [EPHX1], NADPH quinone oxidoreductase I [NQO1]). This set of evaluations complements our previous analyses with oxidative and conjugating enzymes. Of the numerous UGT and SULT enzymes, the greatest likelihood for polymorphism effect on conjugation function are for SULT1A1 (*2 polymorphism), UGT1A1 (*6, *7, *28 polymorphisms), UGT1A7 (*3 polymorphism), UGT2B15 (*2 polymorphism), and UGT2B17 (null polymorphism). The null polymorphism in NQO1 has the potential to impair host defense. These highlighted polymorphisms are of sufficient frequency to be prioritized for consideration in chemical risk assessments. In contrast, SNPs in EPHX1 are not sufficiently influential or defined for inclusion in risk models. The current analysis is an important first step in bringing the highlighted polymorphisms into a physiologically based pharmacokinetic (PBPK) modeling framework.

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.

Interindividual variability in hepatic drug glucuronidation: studies into the role of age, sex, enzyme inducers, and genetic polymorphism using the human liver bank as a model system

The human liver bank has provided an invaluable model system for the study of interindividual variability in expression and activity of the major hepatic UGTs, including UGT1A1, 1A4, 1A6, 1A9, 2B7, and 2B15. Based on studies using UGT-isoform-selective probes, the rank order of activity variability is UGT 1A1>1A6>2B15>1A4 = 1A9>2B7, with coefficient of variation values ranging from 92 to 45%. Liver donor age, sex, enzyme inducers, and genetic polymorphism are factors that have been implicated as sources of this variability in UGT activity. The expression of UGTs prior to, and immediately following, birth is quite limited, explaining the susceptibility of neonates to certain drug toxicities. Old age appears to have minimal effect on UGT function. Sex differences in UGT activity are relatively small and are confined to several UGTs, including UGT2B15, which shows higher activity in males, compared with females. Enzyme inducers, including coadministered drugs, smoking, and alcohol, may increase hepatic UGT levels. Human liver bank phenotype-genotype studies, using UGT-isoform-selective probes have identified common genetic polymorphisms that are predictive of glucuronidation activity in vitro and that were subsequently verified as predictors of probe-drug clearance by glucuronidation in vivo.

UDP-glucuronosyltransferases (UGTs) in neuro-olfactory tissues: expression, regulation, and function

This work aims to review uridine diphosphate (UDP)-glucuronosyltransferase (UGT) expression and activities along different neuronal structures involved in the common physiological process of olfaction: olfactory epithelium, olfactory bulb, and olfactory cortex. For the first time, using high-throughput in situ hybridization data generated by the Allen Brain Atlas (ABA), we present quantitative analysis of spatial distribution of UGT genes in the mouse brain. The olfactory area is a central nervous system site with the highest expression of UGTs, including UGT isoforms not previously identified in the brain. Since there is evidence of the transfer of xenobiotics to the brain through the nasal pathway, circumventing the blood-brain barrier, olfactory UGTs doubtlessly share the common function of detoxification, but they are also involved in the metabolism and turnover of exogenous or endogenous compounds critical for physiological olfactory processing in these tissues. The function of olfactory UGTs will be discussed with a special focus on their participation in the perireceptor events involved in the modulation of olfactory perception.

Uridine 5'-diphospho-glucuronosyltransferase genetic polymorphisms and response to cancer chemotherapy

Pharmacogenetics aims to elucidate how genetic variation affects the efficacy and side effects of drugs, with the ultimate goal of personalizing medicine. Clinical studies of the genetic variation in the uridine 5'-diphosphoglucuronosyltransferase gene have demonstrated how reduced-function allele variants can predict the risk of severe toxicity and help identify cancer patients who could benefit from reduced-dose schedules or alternative chemotherapy. Candidate polymorphisms have also been identified in vitro, although the functional consequences of these variants still need to be tested in the clinical setting. Future approaches in uridine 5'-diphosphoglucuronosyltransferase pharmacogenetics include genetic testing prior to drug treatment, genotype-directed dose-escalation studies, study of genetic variation at the haplotype level and genome-wide studies.

UGT1A1, UGT1A6 and UGT1A7 genetic analysis: repercussion for irinotecan pharmacogenetics in the São Miguel Island Population (Azores, Portugal)

BACKGROUND

Glucuronidation reactions, catalyzed by uridine-diphosphate glucuronosyltransferase (UGT) enzymes, constitute a detoxification process that adds glucuronic acid to endogenous and exogenous compounds, aiding their excretion. UGT1A proteins have been implicated as risk factors for both the development of cancer and adverse drug effects.

METHODS

Here, we assess the genome of 469 individuals from São Miguel Island (Azores, Portugal) in order to determine the frequencies of polymorphisms and haplotypes in UGT1A1, UGT1A6, and UGT1A7, the co-occurrence of reduced enzyme activity UGT1A variants related to irinotecan toxicity, and to calculate the extent of linkage disequilibrium (LD) in the genomic region encompassing these genes.

RESULTS

Allelic analysis disclosed the presence of rare alleles - UGT1A1*36 and UGT1A1*37--only found in individuals of African descent, and UGT1A7*4. These alleles confirm our previous results on the São Miguel Island genetic background. We identified five different genotypes in UGT1A1 and UGT1A6 and nine in UGT1A7. Haplotype analysis showed that three haplotypes constituted approximately 80% of the allelic variants. Interestingly, haplotype 3 (UGT1A1*28-UGT1A6*2-UGT1A7*3), with a frequency of 0.235, gathers the three alleles encoding the low-function UGT isoforms. Additionally, LD indicates a strong interaction between functional polymorphisms related to the alteration of the UGT enzyme activity.

CONCLUSIONS

In summary, the results demonstrate a high variability of alleles and haplotypes, which have important roles in modifying expression and activity of UGTs. The data presented here could improve the understanding of the predisposition to cancers and susceptibility to the adverse effects of irinotecan in the São Miguel Island population.

Systematic screening for polymorphisms within the UGT1A6 gene in three Chinese populations and function prediction through structural modeling

AIMS

To date, there have been relatively few studies on the UGT1A6 gene in the Chinese population. The present study was designed to determine the allele frequencies and haplotypes of this gene in the population and predict the candidate functional mutations.

MATERIALS & METHODS

We carried out the first systematic screening of polymorphisms of the gene in an SNP analysis involving 1074 Chinese subjects from three ethnic groups, namely Han, Dong and She, using direct sequencing. We identified the putative substrate binding pocket using a homology-modeled structure and produced a practical model for predicting the function of polymorphisms in UGT1A6.

RESULTS

A total of six SNPs and 10 mutations were detected including nine known and seven novel ones. The novel mutations were 73G>A (V25I), 89T>G (L30R), 222A>C, 657C>A, 773A>T (D258V), 1040A>G (N347S) and 1467C>T. In addition, we detected, for the first time in the Chinese population, SNPs 105C>T, 627G>T as well as mutations 308C>A (S103X), IVS2+15T>C and 1088C>T (P363L). Strong linkage disequilibrium was observed among 19T>G, 315A>G, 541A>G and 552A>C. There were seven haplotypes whose frequencies were more than 0.01 in one or more of the three ethnic groups. P363L in the C-terminal domain might weaken the binding of cofactor UDPGA to the domain and induce a poor metabolism genotype of UGT1A6.

CONCLUSION

Our study suggests that genetic polymorphisms in UGT1A6 may contribute to interindividual and intra-ethnic differences. The results should prove helpful in the development of pharmacogenomics in China.

No association between cyclooxygenase-2 and uridine diphosphate glucuronosyltransferase 1A6 genetic polymorphisms and colon cancer risk

AIM: To investigate the association of variations in the cyclooxygenase-2 (COX2) and uridine diphosphate glucuronosyltransferase 1A6 (UGT1A6) genes and non-steroidal anti-inflammatory drugs (NSAIDs) use with risk of colon cancer.

METHODS: NSAIDs, which are known to reduce the risk of colon cancer, act directly on COX2 and reduce its activity. Epidemiological studies have associated variations in the COX2 gene with colon cancer risk, but others were unable to replicate this finding. Similarly, enzymes in the UGT1A6 gene have been demonstrated to modify the therapeutic effect of NSAIDs on colon adenomas. Polymorphisms in the UGT1A6 gene have been statistically shown to interact with NSAID intake to influence risk of developing colon adenomas, but not colon cancer. Here we examined the association of tagging single nucleotide polymorphisms (SNPs) in the COX2 and UGT1A6 genes, and their interaction with NSAID consumption, on risk of colon cancer in a population of 422 colon cancer cases and 481 population controls.

RESULTS: No SNP in either gene was individually statistically significantly associated with colon cancer, nor did they statistically significantly change the protective effect of NSAID consumption in our sample. Like others, we were unable to replicate the association of variants in the COX2 gene with colon cancer risk (P > 0.05), and we did not observe that these variants modify the protective effect of NSAIDs (P > 0.05). We were able to confirm the lack of association of variants in UGT1A6 with colon cancer risk, although further studies will have to be conducted to confirm the association of these variants with colon adenomas.

CONCLUSION: Our study does not support a role of COX2 and UGT1A6 genetic variations in the development of colon cancer.

C-reactive protein genotypes and haplotypes, polymorphisms in NSAID-metabolizing enzymes, and risk of colorectal polyps

INTRODUCTION

C-reactive protein (CRP) is a nonspecific marker of inflammation linked to cardiovascular disease and possibly colon cancer. Polymorphisms in CRP have been associated with differential CRP concentrations among healthy adults, with some evidence for functional effects on CRP expression.

METHODS

A linkage disequilibrium-based tag single nucleotide polymorphism (SNP)-selection algorithm identified six tagSNPs for Europeans (-821A>G, -390C>T/A, 90A>T, 838G>C, 2043G>A, and 4363C>A), defining six haplotypes with more than 1% frequency. In a case-control study of adenomatous (n=491) or hyperplastic (n=184) polyps versus polyp-free controls (n=583) we investigated these SNPs in relation to colorectal polyp risk.

RESULTS

Individuals with 838 GC or CC genotypes had a modestly, although not statistically significantly, increased risk of adenomas (odds ratio: 1.4 95% confidence interval: 0.9-2.1) and a nearly 2-fold increased risk of concurrent adenomas and hyperplastic polyps (odds ratio: 2.0 95% confidence interval: 1.1-3.6). Increased risk for concurrent adenomas and hyperplastic polyps was also observed for haplotype ACACAC. No other main associations were detected. Risk of adenomas associated with 2043G>A differed with nonsteroidal anti-inflammatory drug (NSAID) use. Among NSAID nonusers, there was a suggestion that the GA or AA genotypes were associated with decreased risk of adenomas; this was not seen among NSAID users (P interaction=0.03). We also observed interactions between UGT1A1 [TA](7) promoter repeat polymorphism and CRP tagSNPs -390C>T/A and 90A>T, in which only the homozygous variant CRP genotype was associated with increased risk of adenoma among those with the UGT1A1 6rpt/6rpt genotype (P interaction=0.02 and 0.04 for -390C>T/A and 90A>T, respectively).

CONCLUSION

These results provide limited support for associations between genetic variation in CRP and colorectal polyp risk. The observed interactions should be evaluated further.

Potential role of UGT pharmacogenetics in cancer treatment and prevention: focus on tamoxifen

Tamoxifen (TAM) is a selective estrogen receptor modulator that is widely used in the prevention and treatment of estrogen receptor-positive (ER(+)) breast cancer. Its use has significantly contributed to a decline in breast cancer mortality, since breast cancer patients treated with TAM for 5 years exhibit a 30-50% reduction in both the rate of disease recurrence after 10 years of patient follow-up and occurrence of contralateral breast cancer. However, in patients treated with TAM there is substantial interindividual variability in the development of resistance to TAM therapy, and in the incidence of TAM-induced adverse events, including deep vein thrombosis, hot flashes, and the development of endometrial cancer. This article will focus on the UDP glucuronosyltransferases, a family of metabolizing enzymes that are responsible for the deactivation and clearance of TAM and TAM metabolites, and how interindividual differences in these enzymes may play a role in patient response to TAM.