Genetic multiplicity of the human UDP-glucuronosyltransferases and regulation in the gastrointestinal tract

UGT1A4 Polymorphism is not Associated with a Clinically Relevant Change in Giredestrant Exposure

PURPOSE

Giredestrant is a potent, orally bioavailable, small-molecule selective estrogen receptor antagonist and degrader (SERD) that is being developed for the treatment of patients with estrogen receptor (ER)-positive breast cancer. In vitro, giredestrant was primarily metabolized by UGT1A4. The goal of this study was to investigate if UGT1A4 polymorphism had a clinically relevant impact on giredestrant exposure.

METHODS

Genotyping and pharmacokinetic data were obtained from 118 and 61 patients in two clinical studies, GO39932 [NCT03332797] and acelERA Breast Cancer [NCT04576455], respectively.

RESULTS

The overall allelic frequencies of UGT1A4*2 and UGT1A4*3 were 3.3% and 11%, respectively. Giredestrant exposure was consistent between patients with wild-type UGT1A4 and UGT1A4*2 and *3 polymorphisms, with no clinically relevant difference observed. In addition, haplotype analysis indicated that no other UGT1A4 variants were significantly associated with giredestrant exposure.

CONCLUSION

Therefore, this study indicates that UGT1A4 polymorphism status is unlikely a clinically relevant factor to impact giredestrant exposure and giredestrant can be administered at the same dose level regardless of patients' UGT1A4 polymorphism status.

Genetic polymorphisms in phase II metabolizing enzymes in alcoholic and idiopathic chronic pancreatitis: Indian scenario

AIM

To study polymorphisms in glutathione-S-transferases (GST-T1, GST-M1, GST-P1) and uridine-5'-diphosphate-glucuronosyl-transferases (UGT1A7) genes and the risk of developing chronic pancreatitis (CP) associated with these polymorphisms.

METHODS

This study included 49 alcoholic and 51 idiopathic chronic pancreatitis patients, 50 alcohol addicts and 50 healthy controls. Polymorphism(s) in GST-T1 and GST-M1 genes were assessed by multiplex polymerase chain reaction (PCR), while PCR-radiofrequency lesioning (RFLP) was employed to assess the same in GST-P1 and UGT1A7 genes. The differences in polymorphism frequency between groups and the risk of developing pancreatitis were assessed by the odds ratio.

RESULTS

Strong association of the null genotype of GST-T1 with CP susceptibility was observed. Alcoholics with the Val allele of GST-P1 have higher chances of having pancreatitis. Idiopathic pancreatitis patients with higher age at the onset of pain were found to have the null genotype of GST-M1.

CONCLUSION

Alcoholics with the null genotype of the GST-T1 gene and the Valine allele of the GST-P1 gene are at a higher risk of developing CP. Thus, genotyping of these genes may serve as an important screening tool for the identification of high-risk groups among alcoholics.

In vitro effects of opicapone on activity of human UDP-glucuronosyltransferases isoforms

Catechol-O-methyltransferase (COMT) inhibitors are widely used as an add-on treatment to levodopa in adults with Parkinson's disease. It has been evidenced that the second-generation COMT inhibitors entacapone and tolcapone are potent inhibitors on human UDP-glucosyltransferases (UGTs), while the effect of the third-generation COMT inhibitor opicapone on human UGTs activities is unclear. The purpose of this study is to systemically investigate the effects of opicapone on human UGTs activities, and also to assess the potential risk of drug-drug interactions (DDIs) associated with opicapone. Our results indicated that opicapone is a broad-spectrum inhibitor of UGTs. Particularly, opicapone exhibited potent inhibition against UGT1A1, 1A7, 1A8, 1A9, and 1A10, with a range of inhibition constant K_i values of 1.31-10.58 µM. Furthermore, the DDI risk was quantitatively predicted by using the in vitro-in vivo extrapolation (IVIVE). The prediction suggested that co-administration of opicapone at 25 mg/day or 50 mg/day with drugs primarily cleared by hepatic UGT1A9 or intestinal UGT1A1, 1A7, 1A8, 1A9, or 1A10 might result in potential DDI via inhibition of intestinal or hepatic UGTs.

Gene expression changes related to bone mineralization, blood pressure and lipid metabolism in mouse kidneys after space travel

Space travel burdens health by imposing considerable environmental stress associated with radioactivity and microgravity. In particular, gravity change predominantly impacts blood pressure and bone homeostasis, both of which are controlled mainly by the kidneys. Nuclear factor erythroid-2-related transcription factor 2 (Nrf2) plays essential roles in protecting the kidneys from various environmental stresses and injuries. To elucidate the effects of space travel on mammals in preparation for the upcoming space era, our study investigated the contribution of Nrf2 to kidney function in mice two days after their return from a 31-day stay in the International Space Station using Nrf2 knockout mice. Meaningfully, expression levels of genes regulating bone mineralization, blood pressure and lipid metabolism were found to be significantly altered in the kidneys after space travel in an Nrf2-independent manner. In particular, uridine diphosphate-glucuronosyltransferase 1A (Ugt1a) isoform genes were found to be expressed in an Nrf2-dependent manner and induced exclusively in the kidneys after return to Earth. Since spaceflight elevated the concentrations of fatty acids in the mouse plasma, we suggest that Ugt1a isoform expression in the kidneys was induced to promote glucuronidation of excessively accumulated lipids and excrete them into urine after the return from space. Thus, the kidneys were proven to play central roles in adaptation to gravity changes caused by going to and returning from space by controlling blood pressure and bone mineralization. Additionally, kidney Ugt1a isoform induction after space travel implies a significant role of the kidneys for space travelers in the excretion of excessive lipids.

miR-452 Reverses Abnormal Glycosylation Modification of ERα and Estrogen Resistance in TNBC (Triple-Negative Breast Cancer) Through Targeting UGT1A1

Background: The breast epithelial cells in patients with triple-negative breast cancer (TNBC) actually have specific estrogen receptor (ER) expression, and the abnormal glycosylation of UGT1A1 in TNBC cells resulted in abnormal expression and function of ERα through regulating the modification of ERα. Therefore, our study targets the role of UGT1A1 expression, then glycosylation modification of ERα (estrogen receptor α) and estrogen resistance in development of TNBC.

Methods: The differential expression of mRNA and miRNA in TNBC tissues was tested. Luciferase activity was analyzed in TNBC cells treated with miR-452. Moreover, the human mammary gland and TNBC cell lines were dealt with estrogen and miR-452 or its inhibitors, then proliferation ability was further determined. Moreover, the role of interaction between UGT1A1 and ERα in the glycosylation modification of ERα and UGT activity, and metabolism of estrogen were assessed. The effects of miR-452 on TNBC by improving abnormal glycosylation modification of ERα by targeting UGT1A1 and estrogen resistance were studied in vitro and in vivo.

Results: The expression level of UGT1A1 in TNBC tumor tissues was higher than its matched para-tumorous tissues, but the miR-452 expression was opposite. The glycosylation modification site of ERα expressed in TNBC cells was different from that of normal mammary epithelial cells. The estrogen 17β-estradiol (E2) significantly promoted mitotic entry of TNBC cells. The interaction between UGT1A1 and ERα affected the expression level of each other, as well as the UGT enzyme activity and proliferation of TNBC cells. UGT1A1 induced production of intracellular estrogens and TNBC proliferation, but it could be reversed by overexpression of ERα. Upregulation of ERα caused the downregulation of UGT1A1 and marked decrease of intracellular estrogen products, and then suppressed TNBC proliferation. Moreover, UGT1A1 was the target gene of miR-452; miR-452 antagomir restrained TNBC xenograft.

Conclusion: Our results demonstrated that estrogen was a positive factor in the proliferation of TNBC cells at onset of mitosis through accentuating the expression and enzyme activity of UGT1A1. However, miR-452 targeted to UGT1A1, then regulated glycosylation modification of ERα, estrogen metabolism, and TNBC development associated with estrogen resistance.

UDP-glucuronosyltransferase polymorphisms affect diethylnitrosamine-induced carcinogenesis in humanized transgenic mice

UDP‐glucuronosyltransferase (UGT) 1A enzymes detoxify a broad array of exogenous compounds including environmental toxins and carcinogens. Case‐control studies identified genetic variations in UGT1A genes leading to reduced glucuronidation activity, which were associated with hepatocellular carcinoma (HCC) formation and progression. The aim of the study was therefore to examine the direct effect of common UGT1A polymorphisms (SNPs) on HCC development and outcome in a diethylnitrosamine (DEN)‐induced mouse model. Therefore, a single intraperitoneal DEN injection (20 mg/kg) was administered to 15‐day‐old htgUGT1A‐WT and htgUGT1A‐SNP mice (containing a human haplotype of 10 common UGT1A SNPs) either receiving water or coffee cotreatment for the following 39 weeks. After this time, tumor incidence, size (>1 mm), histology, liver‐body ratio, serum aminotransferase activities, and UGT1A regulation and activity levels were determined. In DEN‐treated htgUGT1A‐SNP mice, a markedly higher number of tumors with a bigger cumulative diameter were detected. The relative liver weight and aminotransferase activity levels were also significantly higher in mice carrying UGT1A SNPs. After coffee + DEN cotreatment, susceptibility for tumor development and growth considerably decreased in both mouse lines, but was still higher in htgUGT1A‐SNP mice. In conclusion, our study provides experimental evidence for the protective role of UGT1A enzymes in neoplastic transformation. These data confirm case‐control studies implicating impaired UGT1A‐mediated carcinogen detoxification as a risk factor for individual cancer disposition. Coffee treatment, which is able to activate UGT1A expression and activity, reduced HCC development and provides an explanation for the protective properties of coffee on liver diseases including liver cancer.

The Segregated Intestinal Flow Model (SFM) for Drug Absorption and Drug Metabolism: Implications on Intestinal and Liver Metabolism and Drug-Drug Interactions

The properties of the segregated flow model (SFM), which considers split intestinal flow patterns perfusing an active enterocyte region that houses enzymes and transporters (<20% of the total intestinal blood flow) and an inactive serosal region (>80%), were compared to those of the traditional model (TM), wherein 100% of the flow perfuses the non-segregated intestine tissue. The appropriateness of the SFM model is important in terms of drug absorption and intestinal and liver drug metabolism. Model behaviors were examined with respect to intestinally (M1) versus hepatically (M2) formed metabolites and the availabilities in the intestine (F_I) and liver (F_H) and the route of drug administration. The %contribution of the intestine to total first-pass metabolism bears a reciprocal relation to that for the liver, since the intestine, a gateway tissue, regulates the flow of substrate to the liver. The SFM predicts the highest and lowest M1 formed with oral (po) and intravenous (iv) dosing, respectively, whereas the extent of M1 formation is similar for the drug administered po or iv according to the TM, and these values sit intermediate those of the SFM. The SFM is significant, as this drug metabolism model explains route-dependent intestinal metabolism, describing a higher extent of intestinal metabolism with po versus the much reduced or absence of intestinal metabolism with iv dosing. A similar pattern exists for drug–drug interactions (DDIs). The inhibitor or inducer exerts its greatest effect on victim drugs when both inhibitor/inducer and drug are given po. With po dosing, more drug or inhibitor/inducer is brought into the intestine for DDIs. The bypass of flow and drug to the enterocyte region of the intestine after intravenous administration adds complications to in vitro–in vivo extrapolations (IVIVE).

Higher Caloric Exposure in Critically Ill Patients Transiently Accelerates Thyroid Hormone Activation

INTRODUCTION

The inflammatory response of critical illness is accompanied by nonthyroidal illness syndrome (NTIS). Feeding has been shown to attenuate this process, but this has not been explored prospectively over time in critically ill patients.

OBJECTIVE

To explore the impact of calorie exposure on NTIS over time in critically ill patients.

METHODS

Mechanically ventilated patients with systemic inflammatory response syndrome (SIRS) were randomized to receive either 100% or 40% of their estimated caloric needs (ECN). Thyroid hormones were measured daily for 7 days or until intensive care unit discharge or death. Mixed level regression modeling was used to explore the effect of randomization group on plasma triiodothyronine (T3), reverse triiodothyronine (rT3), thyroxine (T4), and thyroid stimulating hormone (TSH), as well as the T3/rT3 ratio.

RESULTS

Thirty-five participants (n=19 in 100% ECN; n=16 in 40% ECN) were recruited. Adjusting for group differences in baseline T3/rT3 ratio, the parameters defining the fitted curves (intercept, linear effect of study day, and quadratic effect of study day) differed by randomization group (P = 0.001, P = 0.01, and P = 0.02 respectively). Plots of the fitted curves revealed that participants in the 100% ECN group had a 54% higher T3/rT3 ratio on postintervention day 1 compared with the 40% ECN group, a difference which attenuated over time. This was driven by a 23% higher plasma T3 and 10% lower plasma rT3 levels on postintervention 1.

CONCLUSIONS

Higher caloric exposure in NTIS patients transiently attenuates the drop of the plasma T3/rT3 ratio, an effect that is minimized and finally lost over the following 3 days of continued higher caloric exposure.

Humanized UGT1 Mice, Regulation of UGT1A1, and the Role of the Intestinal Tract in Neonatal Hyperbilirubinemia and Breast Milk-Induced Jaundice

Neonatal hyperbilirubinemia and the onset of bilirubin encephalopathy and kernicterus result in part from delayed expression of UDP-glucuronosyltransferase 1A1 (UGT1A1) and the ability to metabolize bilirubin. It is generally believed that acute neonatal forms of hyperbilirubinemia develop due to an inability of hepatic UGT1A1 to metabolize efficiently bilirubin for clearance through the hepatobiliary tract. Newly developed mouse models designed to study bilirubin metabolism have led to new insight into the role of the intestinal tract in controlling neonatal hyperbilirubinemia. Humanization of mice with the UGT1 locus (hUGT1 mice) and the UGT1A1 gene provide a unique tool to study the onset of hyperbilirubinemia since the human UGT1A1 gene is developmentally regulated during the neonatal period in hUGT1 mice. A new mechanism outlying developmental expression of intestinal UGT1A1 is presented and its implications in the control of neonatal hyperbilirubinemia discussed. New findings linking breast milk protection against necrotizing enterocolitis and intestinal control of UGT1A1 may help explain the contribution of breast milk toward the development of neonatal hyperbilirubinemia. Our findings outline a new model that includes an active intestinal ROS /IκB kinase/nuclear receptor corepressor 1 loop that can be applied to an understanding of breast milk-induced jaundice.

Catechol-O-Methyltransferase and UDP-Glucuronosyltransferases in the Metabolism of Baicalein in Different Species

BACKGROUND

Baicalein is the major bioactive flavonoid in some herb medicines and dietary plants; however, the detailed metabolism pathway of its major metabolite oroxylin A-7-O-β-D-glucuronide in human was not clear. It was important to illustrate the major metabolic enzymes that participate in its elimination for the clinic use of baicalein.

OBJECTIVES

We first revealed a two-step metabolism profile for baicalein and illustrated the combination of catechol-O-methyltransferase (COMT) and uridine diphosphate-glucuronosyltransferases (UGTs) in drug metabolism, further evaluated its bioactivity variation during drug metabolism.

METHODS

The metabolism profiles were systematically characterized in different human biology preparations; after then, the anti-inflammatory activities of metabolites were evaluated in LPS-induced RAW264.7 cell.

RESULTS

The first-step metabolite of baicalein was isolated and identified as oroxylin A; soluble-bound COMT (S-COMT) was the major enzyme responsible for its biotransformation. Specially, position 108 mutation of S-COMT significantly decreases the elimination. Meantime, oroxylin A was rapidly metabolized by UGTs, UGT1A1, -1A3, -1A6, -1A7, -1A8, -1A9, and -1A10 which were involved in the glucuronidation. Considerable species differences were observed with 1060-fold K _m (3.05 ± 1.86-3234 ± 475 μM) and 330-fold CL_int (5.93-1973 μL/min/mg) variations for baicalein metabolism. Finally, the middle metabolite oroxylin A exhibited a potent anti-inflammatory activity with the IC₅₀ value of 28 μM.

CONCLUSION

The detailed kinetic parameters indicated that COMT provide convenience for the next glucuronidation; monkey would be a preferred animal model for the preclinical investigation of baicalein. Importantly, oroxylin A should be reconsidered in evaluating baicalein efficacy against inflammatory diseases.

Hepatic metabolism of licochalcone A, a potential chemopreventive chalcone from licorice (Glycyrrhiza inflata), determined using liquid chromatography-tandem mass spectrometry

The metabolism of the chemoprevention agent licochalcone A, which is a chemopreventive chalcone found in abundance in the licorice species Glycyrrhiza inflata, was investigated using human liver microsomes and human hepatocytes combined with analysis using high performance liquid chromatography-mass spectrometry (LC-MS). Five oxygenated phase I metabolites of licochalcone A were formed by human liver microsomes, including a catechol on the A-ring, two intramolecular cyclization products following epoxidation of the exocyclic alkene at position 5 of the B-ring, and two dioxygenated products. Nine phase II monoglucuronides of licochalcone A and its oxygenated phase I metabolites were formed during incubation with human hepatocytes. These included (E)-licochalcone A-4-glucuronide, (E)-licochalcone A-4'-glucuronide, (Z)-licochalcone A-4-glucuronide, glucuronic acid conjugates of all of the monooxygenated phase I metabolites, and glucuronides of the licochalcone catechol after methylation by catechol-O-methyl transferase. In addition, human hepatocytes formed one sulfate conjugate and one glutathione conjugate of licochalcone A. The structures of all major metabolites were determined using a combination of accurate mass measurement, LC-tandem mass spectrometry, LC-UV, nuclear magnetic resonance, and comparison with standards. The cytochrome P450 enzymes and UDP-glucuronosyltransferases responsible for the formation of the major metabolites were identified. Based on in vitro hepatic clearance calculations, licochalcone A is predicted to be metabolized primarily by phase II conjugation reactions. Graphical abstract Phase I and II metabolism of licochalcone A from the licorice species Glycyrrhiza inflata by human liver microsomes and hepatocytes determined using LC-MS/MS, LC-UV and NMR.

UDP-glucuronosyltransferases (UGTs) and their related metabolic cross-talk with internal homeostasis: A systematic review of UGT isoforms for precision medicine

UDP-glucuronosyltransferases (UGTs) are the primary phase II enzymes catalyzing the conjugation of glucuronic acid to the xenobiotics with polar groups for facilitating their clearance. The UGTs belong to a superfamily that consists of diverse isoforms possessing distinct but overlapping metabolic activity. The abnormality or deficiency of UGTs in vivo is highly associated with some diseases, efficacy and toxicity of drugs, and precisely therapeutic personality. Despite the great effects and fruitful results achieved, to date, the expression and functions of individual UGTs have not been well clarified, the inconsistency of UGTs is often observed in human and experimental animals, and the complex regulation factors affecting UGTs have not been systematically summarized. This article gives an overview of updated reports on UGTs involving the various regulatory factors in terms of the genetic, environmental, pathological, and physiological effects on the functioning of individual UGTs, in turn, the dysfunction of UGTs induced disease risk and endo- or xenobiotic metabolism-related toxicity. The complex cross-talk effect of UGTs with internal homeostasis is systematically summarized and discussed in detail, which would be of great importance for personalized precision medicine.

Characterization of genome-wide segmental duplications reveals a common genomic feature of association with immunity among domestic animals

BACKGROUND

Segmental duplications (SDs) commonly exist in plant and animal genomes, playing crucial roles in genomic rearrangement, gene innovation and the formation of copy number variants. However, they have received little attention in most livestock species.

RESULTS

Aiming at characterizing SDs across the genomes of diverse livestock species, we mapped genome-wide SDs of horse, rabbit, goat, sheep and chicken, and also enhanced the existing SD maps of cattle and pig genomes based on the most updated genome assemblies. We adopted two different detection strategies, whole genome analysis comparison and whole genome shotgun sequence detection, to pursue more convincing findings. Accordingly we identified SDs for each species with the length of from 21.7 Mb to 164.1 Mb, and 807 to 4,560 genes were harboured within the SD regions across different species. More interestingly, many of these SD-related genes were involved in the process of immunity and response to external stimuli. We also found the existence of 59 common genes within SD regions in all studied species except goat. These common genes mainly consisted of both UDP glucuronosyltransferase and Interferon alpha families, implying the connection between SDs and the evolution of these gene families.

CONCLUSIONS

Our findings provide insights into livestock genome evolution and offer rich genomic sources for livestock genomic research.

Species- and gender-dependent differences in the glucuronidation of a flavonoid glucoside and its aglycone determined using expressed UGT enzymes and microsomes

Flavonoids occur naturally as glucosides and aglycones. Their common phenolic hydroxyl groups may trigger extensive UDP-glucuronosyltransferase (UGT)- catalysed metabolism. Unlike aglycones, glucosides contain glucose moieties. However, the influence of these glucose moieties on glucuronidation of glucosides and aglycones remains unclear. In this study, the flavonoid glucoside tilianin and its aglycone acacetin were used as model compounds. The glucuronidation characteristics and enzyme kinetics of tilianin and acacetin were compared using human UGT isoforms, liver microsomes and intestinal microsomes obtained from different animal species. Tilianin and acacetin were metabolized into different glucuronides, with UGT1A8 produced as the main isoform. Assessment of enzyme kinetics in UGT1A8, human liver microsomes and human intestinal microsomes revealed that compared with tilianin, acacetin displayed lower Km (0.6-, 0.7- and 0.6-fold, respectively), higher Vmax (20-, 60- and 230-fold, respectively) and higher clearance (30-, 80- and 300-fold, respectively). Furthermore, glucuronidation of acacetin and tilianin showed significant species- and gender-dependent differences. In conclusion, glucuronidation of flavonoid aglycones is faster than that of glucosides in the intestine and the liver. Understanding the metabolism and species- and gender-dependent differences between glucosides and aglycones is crucial for the development of drugs from flavonoids.

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.

Bioactivation of Heterocyclic Aromatic Amines by UDP Glucuronosyltransferases

2-Amino-9H-pyrido[2,3-b]indole (AαC) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) are carcinogenic heterocyclic aromatic amines (HAA) that arise during the burning of tobacco and cooking of meats. UDP-glucuronosyltransferases (UGT) detoxicate many procarcinogens and their metabolites. The genotoxic N-hydroxylated metabolite of AαC, 2-hydroxyamino-9H-pyrido[2,3-b]indole (HONH-AαC), undergoes glucuronidation to form the isomeric glucuronide (Gluc) conjugates N(2)-(β-d-glucosidurony1)-2-hydroxyamino-9H-pyrido[2,3-b]indole (AαC-HON(2)-Gluc) and O-(β-d-glucosidurony1)-2-hydroxyamino-9H-pyrido[2,3-b]indole (AαC-HN(2)-O-Gluc). AαC-HON(2)-Gluc is a stable metabolite but AαC-HN(2)-O-Gluc is a biologically reactive intermediate, which covalently adducts to DNA at levels that are 20-fold higher than HONH-AαC. We measured the rates of formation of AαC-HON(2)-Gluc and AαC-HN(2)-O-Gluc in human organs: highest activity occurred with liver and kidney microsomes, and lesser activity was found with colon and rectum microsomes. AαC-HN(2)-O-Gluc formation was largely diminished in liver and kidney microsomes, by niflumic acid, a selective inhibitor UGT1A9. In contrast, AαC-HON(2)-Gluc formation was less affected and other UGT contribute to N(2)-glucuronidation of HONH-AαC. UGT were reported to catalyze the formation of isomeric Gluc conjugates at the N(2) and N3 atoms of 2-hydroxyamino-1-methyl-6-phenylimidazo[4,5-b]pyridine (HONH-PhIP), the genotoxic metabolite of PhIP. However, we found that the N3-Gluc of HONH-PhIP also covalently bound to DNA at higher levels than HONH-PhIP. The product ion spectra of this Gluc conjugate acquired by ion trap mass spectrometry revealed that the Gluc moiety was linked to the oxygen atom of HONH-PhIP and not the N3 imidazole atom of the oxime tautomer of HONH-PhIP as was originally proposed. UGT1A9, an abundant UGT isoform expressed in human liver and kidney, preferentially forms the O-linked Gluc conjugates of HONH-AαC and HONH-PhIP as opposed to their detoxicated N(2)-Gluc isomers. The regioselective O-glucuronidation of HONH-AαC and HONH-PhIP, by UGT1A9, is a mechanism of bioactivation of these ubiquitous HAAs.

Association between UGT1A1 Polymorphism and Risk of Laryngeal Squamous Cell Carcinoma

Laryngeal cancer is one of the largest subgroups of head and neck cancers. In addition to smoking and alcohol consumption, genetic polymorphisms are also risk factors for the development of laryngeal cancer. However, the exact relation between genetic variants and pathogenesis of laryngeal cancer has remained elusive. The aim of this study was to examine UGT1A1*6 (rs4148323 A/G) polymorphisms in 103 patients with laryngeal cancer and 220 controls using the high resolution melting curve (HRM) technique and to explore the association between UGT1A1*6 (rs4148323 A/G) polymorphisms and laryngeal cancer. The results showed an association between the rs4148323 G allele and increased risk of laryngeal cancer. While there was no statistically significant difference between rs4148323 genotype frequencies and different histological grades or different clinical stages of laryngeal cancer, stratification analysis indicated smoking or alcohol consumption and rs4148323 G allele combined to increase the risk of laryngeal cancer. In conclusion, the rs4148323 G allele is associated with the high UGT1A1 enzyme activity, and might increase the risk of laryngeal cancer. Furthermore, smoking or alcohol consumption and the rs4148323 G allele act synergistically to increase the risk of laryngeal cancer.

Role of extrahepatic UDP-glucuronosyltransferase 1A1: Advances in understanding breast milk-induced neonatal hyperbilirubinemia

Newborns commonly develop physiological hyperbilirubinemia (also known as jaundice). With increased bilirubin levels being observed in breast-fed infants, breast-feeding has been recognized as a contributing factor for the development of neonatal hyperbilirubinemia. Bilirubin undergoes selective metabolism by UDP-glucuronosyltransferase (UGT) 1A1 and becomes a water soluble glucuronide. Although several factors such as gestational age, dehydration and weight loss, and increased enterohepatic circulation have been associated with breast milk-induced jaundice (BMJ), deficiency in UGT1A1 expression is a known cause of BMJ. It is currently believed that unconjugated bilirubin is metabolized mainly in the liver. However, recent findings support the concept that extrahepatic tissues, such as small intestine and skin, contribute to bilirubin glucuronidation during the neonatal period. We will review the recent advances made towards understanding biological and molecular events impacting BMJ, especially regarding the role of extrahepatic UGT1A1 expression.

Influence of valproic acid concentration and polymorphism of UGT1A4*3, UGT2B7 -161C > T and UGT2B7*2 on serum concentration of lamotrigine in Chinese epileptic children

PURPOSE

To investigate the impact of valproic acid (VPA) and genetic polymorphism of the major metabolizing enzyme (UGT1A4, UGT2B7) of lamotrigine (LTG) and VPA on LTG concentration in Chinese epileptic children.

METHODS

Three single nucleotide polymorphisms (UGT1A4*3, UGT2B7 -161C > T and UGT2B7*2) were analyzed by polymerase chain reaction-restriction fragment length polymorphism or direct DNA sequencing. The concentrations of LTG and VPA were measured by high-performance liquid chromatography (HPLC) and fluorescence polarization immunoassay, respectively. The adjusted concentration of LTG was defined as the concentration-to-dose-ratio (CDRLTG). Data analysis was performed using IBM SPSS Statistics 21.0.

RESULTS

A total of 56 patients treated with LTG as monotherapy and 158 patients treated with LTG plus VPA were included in this study. In the polytherapy group, LTG concentration showed a good linear relationship with gender, age, daily LTG dose, VPA concentration, and UGT1A4*3 polymorphism, but had no relationship with the polymorphism of UGT2B7 -161C > T or UGT2B7*2. Moreover, LTG concentration and CDRLTG for the UGT1A4*3 were higher compared to UGT1A4*1 (LTG: 7.24 ± 3.51 vs 5.26 ± 3.27 μg/mL, p = 0.001; CDRLTG: 2.75 ± 1.02 vs 2.14 ± 0.96 μg/mL per mg/kg, p < 0.001, respectively). In the monotherapy group, there was no statistical difference between UGT1A4*3 and UGT1A4*1 in LTG concentration or CDRLTG. The patients in the polytherapy group were divided into two subgroups according to VPA concentration (lower/higher: 10-50/50-125 μg/mL). CDRLTG values of the patients carrying the UGT1A4*3 genotype were higher compared to UGT1A4*1*1 (2.86 ± 1.03 vs 2.22 ± 0.94 μg/mL per mg/kg, p = 0.001) only when the VPA concentration was higher.

CONCLUSIONS

UGT1A4*3 polymorphism had an effect on LTG concentration only with VPA co-administration, and the effect was remarkable when VPA concentration was higher.

The molecular basis of the non-thyroidal illness syndrome

The 'sick euthyroid syndrome' or 'non-thyroidal illness syndrome' (NTIS) occurs in a large proportion of hospitalized patients and comprises a variety of alterations in the hypothalamus-pituitary-thyroid (HPT) axis that are observed during illness. One of the hallmarks of NTIS is decreased thyroid hormone (TH) serum concentrations, often viewed as an adaptive mechanism to save energy. Downregulation of hypophysiotropic TRH neurons in the paraventricular nucleus of the hypothalamus and of TSH production in the pituitary gland points to disturbed negative feedback regulation during illness. In addition to these alterations in the central component of the HPT axis, changes in TH metabolism occur in a variety of TH target tissues during NTIS, dependent on the timing, nature and severity of the illness. Cytokines, released during illness, are known to affect a variety of genes involved in TH metabolism and are therefore considered a major determinant of NTIS. The availability of in vivo and in vitro models for NTIS has elucidated part of the mechanisms involved in the sometimes paradoxical changes in the HPT axis and TH responsive tissues. However, the pathogenesis of NTIS is still incompletely understood. This review focusses on the molecular mechanisms involved in the tissue changes in TH metabolism and discusses the gaps that still require further research.

Unravelling the transcriptomic landscape of the major phase II UDP-glucuronosyltransferase drug metabolizing pathway using targeted RNA sequencing

A comprehensive view of the human UDP-glucuronosyltransferase (UGT) transcriptome is a prerequisite to the establishment of an individual's UGT metabolic glucuronidation signature. Here, we uncover the transcriptome landscape of the 10 human UGT gene loci in normal and tumoral metabolic tissues by targeted RNA next-generation sequencing. Alignment on the human hg19 reference genome identifies 234 novel exon-exon junctions. We recover all previously known UGT1 and UGT2 enzyme-coding transcripts and identify over 130 structurally and functionally diverse novel UGT variants. We further expose a revised genomic structure of UGT loci and provide a comprehensive repertoire of transcripts for each UGT gene. Data also uncover a remodelling of the UGT transcriptome occurring in a tissue- and tumor-specific manner. The complex alternative splicing program regulating UGT expression and protein functions is likely critical in determining detoxification capacity of an organ and stress-related responses, with significant impact on drug responses and diseases.

Glucuronidation of OTS167 in Humans Is Catalyzed by UDP-Glucuronosyltransferases UGT1A1, UGT1A3, UGT1A8, and UGT1A10

OTS167 is a potent maternal embryonic leucine zipper kinase inhibitor undergoing clinical testing as antineoplastic agent. We aimed to identify the UDP-glucuronosyltransferases (UGTs) involved in OTS167 metabolism, study the relationship between UGT genetic polymorphisms and hepatic OTS167 glucuronidation, and investigate the inhibitory potential of OTS167 on UGTs. Formation of a single OTS167-glucuronide (OTS167-G) was observed in pooled human liver (HLM) (Km = 3.4 ± 0.2 µM), intestinal microsomes (HIM) (Km = 1.7 ± 0.1 µM), and UGTs. UGT1A1 (64 µl/min/mg) and UGT1A8 (72 µl/min/mg) exhibited the highest intrinsic clearances (CLint) for OTS167, followed by UGT1A3 (51 µl/min/mg) and UGT1A10 (47 µl/min/mg); UGT1A9 was a minor contributor. OTS167 glucuronidation in HLM was highly correlated with thyroxine glucuronidation (r = 0.91, P < 0.0001), SN-38 glucuronidation (r = 0.79, P < 0.0001), and UGT1A1 mRNA (r = 0.72, P < 0.0001). Nilotinib (UGT1A1 inhibitor) and emodin (UGT1A8 and UGT1A10 inhibitor) exhibited the highest inhibitory effects on OTS167-G formation in HLM (68%) and HIM (47%). We hypothesize that OTS167-G is an N-glucuronide according to mass spectrometry. A significant association was found between rs6706232 and reduced OTS167-G formation (P = 0.03). No or weak UGT inhibition (range: 0-21%) was observed using clinically relevant OTS167 concentrations (0.4-2 µM). We conclude that UGT1A1 and UGT1A3 are the main UGTs responsible for hepatic formation of OTS167-G. Intestinal UGT1A1, UGT1A8, and UGT1A10 may contribute to first-pass OTS167 metabolism after oral administration.

Two unrelated patients with rare Crigler-Najjar syndrome type I: two novel mutations and a patient with loss of heterozygosity of UGT1A1 gene

Crigler-Najjar syndrome type I (CN-I) is the most severe type of hereditary unconjugated hyperbilirubinemia. It is caused by homozygous or compound heterozygous mutations of the UDP-glycuronosyltransferase gene (UGT1A1) on chromosome 2q37. Two patients clinically diagnosed with CN-I were examined in this paper. We sequenced five exons and their flanking sequences, specifically the promoter region of UGT1A1, of the two patients and their parents. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to determine the UGT1A1 gene copy number of one patient. In patient A, two mutations, c.239_245delCTGTGCC (p.Pro80HisfsX6; had not been reported previously) and c.1156G>T (p.Val386Phe), were identified. In patient B, we found that this patient had lost heterozygosity of the UGT1A1 gene by inheriting a deletion of one allele, and had a novel mutation c.1253delT (p.Met418ArgfsX5) in the other allele. In summary, we detected three UGT1A1 mutations in two CN-I patients: c.239_245delCTGTGCC (p.Pro80HisfsX6), c.1253delT (p.Met418ArgfsX5), and c.1156G>T (p.Val386Phe). The former two mutations are pathogenic; however, the pathogenic mechanism of c.1156G>T (p.Val386Phe) is unknown.

A potential role for human UDP-glucuronosyltransferase 1A4 promoter single nucleotide polymorphisms in the pharmacogenomics of tamoxifen and its derivatives

Tamoxifen (Tam) is a selective estrogen receptor modulator used to inhibit breast tumor growth. Tam can be directly N-glucuronidated via the tertiary amine group or O-glucuronidated after cytochrome P450-mediated hydroxylation. In this study, the glucuronidation of Tam and its hydroxylated and/or chlorinated derivatives [4-hydroxytamoxifen (4OHTam), toremifene (Tor), and 4-hydroxytoremifene (4OHTor)] was examined using recombinant human UDP-glucuronosyltransferases (UGTs) from the 1A subfamily and human hepatic microsomes. Recombinant UGT1A4 catalyzed the formation of N-glucuronides of Tam and its derivatives and was the most active UGT enzyme toward these compounds. Therefore, it was hypothesized that single nucleotide polymorphisms (SNPs) in the promoter region of UGT1A4 have the ability to significantly decrease the glucuronidation rates of Tam metabolites in the human liver. In vitro activity of 64 genotyped human liver microsomes was used to determine the association between the UGT1A4 promoter and coding region SNPs and the glucuronidation rates of Tam, 4OHTam, Tor, and 4OHTor. Significant decreases in enzymatic activity were observed in microsomes for individuals heterozygous for -163G/A and -217T/G. These alterations in glucuronidation may lead to prolonged circulating half-lives and may potentially modify the effectiveness of these drugs in the treatment of breast cancer.

UGT2B gene expression analysis in multiple tobacco carcinogen-targeted tissues

The UDP-glucuronosyltransferase (UGT) 2B subfamily of enzymes plays an important role in the metabolism of numerous endogenous and exogenous compounds, including various carcinogens present in tobacco smoke. The goal of the present study was to examine the levels of expression of individual UGT2B genes in various tissues that are targets for tobacco carcinogenesis. Using MT-ATP6 as the experimentally validated housekeeping gene, the highest extrahepatic expression of UGT2B genes was observed in human tonsil, with UGT2B expression levels similar to that observed in human liver. UGT2B17 exhibited high relative expression in most tissues examined, including lung, most tissues of the aerodigestive tract, and pancreas. UGT2B7 expression was highest in pancreas but low or undetectable in most other tissues examined. UGT2B10 expression was high in both tonsil and tongue. There was wide variability between individuals in the magnitude of expression in each tissue site, and there were strong correlations between UGT2B expression levels in different individuals within many of the tissue sites, suggesting coordinated regulation of UGT2B gene expression in extrahepatic tissues. In the liver, UGTs 2B4, 2B7, 2B10, and 2B15 were significantly correlated with each other (all r(2) > 0.70, P < 0.0001). In all examined tissues of the aerodigestive tract, UGTs 2B10, 2B11, and 2B17 exhibited a strong correlation with each other (all r(2) > 0.75, P < 0.05). UGTs 2B7 and 2B10 exhibited a strong inverse correlation in the pancreas (r(2) = -0.95, P < 0.01). These data suggest that specific UGT2B enzymes important in tobacco carcinogen metabolism are expressed and coordinately regulated in various target sites for tobacco-related cancers.

Epirubicin upregulates UDP glucuronosyltransferase 2B7 expression in liver cancer cells via the p53 pathway

Anthracyclines are effective genotoxic anticancer drugs for treating human malignancies; however, their clinical use is limited by tumor resistance and severe cardiotoxicity (e.g., congestive heart failure). Epirubicin (EPI) is less cardiotoxic compared with other canonical anthracyclines (e.g., doxorubicin). This has been attributed to its unique glucuronidation detoxification pathway. EPI is primarily inactivated by UDP-glucuronosyltransferase 2B7 (UGT2B7) in the liver. Hence, the regulation of hepatic UGT2B7 expression is critical for EPI systemic clearance but remains poorly characterized. We show herein that EPI upregulates UGT2B7 expression in hepatocellular carcinoma (HCC) HepG2 and Huh7 cells. Our analyses of deleted and mutated UGT2B7 promoter constructs identified a p53 response element (p53RE) in the UGT2B7 promoter. EPI stimulated UGT2B7 promoter activity via this p53RE and enhanced in vivo p53 binding at this p53RE in HepG2 cells. Knockdown of p53 expression by small interfering RNA silencing technology significantly repressed the capacity of EPI to stimulate UGT2B7 transcription. Furthermore, the p53 activator nutlin-3α significantly enhanced UGT2B7 expression and recruited the p53 protein to the UGT2B7 p53RE in HepG2 cells. Collectively, our results demonstrated that EPI promotes its own detoxification via the p53-mediated pathway. This regulation may contribute to tumor resistance to EPI-containing HCC chemotherapy and may also provide a new explanation for the reduced cardiotoxicity of EPI compared with other anthracyclines. Our finding also suggests that upon exposure to genotoxic agents, detoxifying genes are activated by the p53-mediated pathway to clear genotoxic agents locally within the tumor site or even systemically through the liver.

Targeted quantitative proteomics for the analysis of 14 UGT1As and -2Bs in human liver using NanoUPLC-MS/MS with selected reaction monitoring

Targeted quantitative proteomics using heavy isotope dilution techniques is increasingly being utilized to quantify proteins, including UGT enzymes, in biological matrices. Here we present a multiplexed method using nanoLC-MS/MS and multiple reaction monitoring (MRM) to quantify 14 UGT1As and UGT2Bs in liver matrices. Where feasible, we employ two or more proteotypic peptides per protein, with only four proteins quantified with only one proteotypic peptide. We apply the method to analysis of a library of 60 human liver microsome (HLM) and matching S9 samples. Ten of the UGT isoforms could be detected in liver, and the expression of each was consistent with mRNA expression reported in the literature. UGT2B17 was unusual in that ∼30% of liver microsomes had no or little (<0.5 pmol/mg protein) content, consistent with a known common polymorphism. Liver S9 UGT concentrations were approximately 10-15% those of microsomes. The method was robust, precise, and reproducible and provides novel UGT expression data in human liver that will benefit rational approaches to evaluate metabolism in drug development.

PBPK models for the prediction of in vivo performance of oral dosage forms

Drug absorption from the gastrointestinal (GI) tract is a highly complex process dependent upon numerous factors including the physicochemical properties of the drug, characteristics of the formulation and interplay with the underlying physiological properties of the GI tract. The ability to accurately predict oral drug absorption during drug product development is becoming more relevant given the current challenges facing the pharmaceutical industry. Physiologically-based pharmacokinetic (PBPK) modeling provides an approach that enables the plasma concentration-time profiles to be predicted from preclinical in vitro and in vivo data and can thus provide a valuable resource to support decisions at various stages of the drug development process. Whilst there have been quite a few successes with PBPK models identifying key issues in the development of new drugs in vivo, there are still many aspects that need to be addressed in order to maximize the utility of the PBPK models to predict drug absorption, including improving our understanding of conditions in the lower small intestine and colon, taking the influence of disease on GI physiology into account and further exploring the reasons behind population variability. Importantly, there is also a need to create more appropriate in vitro models for testing dosage form performance and to streamline data input from these into the PBPK models. As part of the Oral Biopharmaceutical Tools (OrBiTo) project, this review provides a summary of the current status of PBPK models available. The current challenges in PBPK set-ups for oral drug absorption including the composition of GI luminal contents, transit and hydrodynamics, permeability and intestinal wall metabolism are discussed in detail. Further, the challenges regarding the appropriate integration of results from in vitro models, such as consideration of appropriate integration/estimation of solubility and the complexity of the in vitro release and precipitation data, are also highlighted as important steps to advancing the application of PBPK models in drug development. It is expected that the "innovative" integration of in vitro data from more appropriate in vitro models and the enhancement of the GI physiology component of PBPK models, arising from the OrBiTo project, will lead to a significant enhancement in the ability of PBPK models to successfully predict oral drug absorption and advance their role in preclinical and clinical development, as well as for regulatory applications.

Comparative studies of human UDP-glucuronosyltransferase 1A8 and 1A9 proximal promoters using single base substitutions

  The nucleotide sequences of the proximal promoters of UDP-glucuronosyltransferase (UGT) 1A8 and 1A9 genes are very similar. However, UGT1A8 and 1A9 are mainly expressed in extra-hepatic and hepatic cells, respectively. Using mutants of UGT1A8 and 1A9 proximal promoters, we revealed their critical differences in terms of promoter activity and the role of the T-repeat region (T-region) conserved in both promoters. In extra-hepatic cells, Caco2, the activity of UGT1A9 proximal promoter increased to 73.4 ± 8.5% of that of the UGT1A8 proximal promoter with only 4 base changes: -160C, -152A, -62T, and -59G. The derivatives of the T-region showed that this region is not necessary for promoter activity, but the length of T repeats influences the activity somewhat. Therefore, the cause of the low activity of the UGT1A9 proximal promoter may be not only 4 base changes, but also the truncation of T repeats. From these results, the UGT1A9 proximal promoter was assumed to change into the non-active form from the original sequence, and this might be one of the reasons for the tissue-specific expression of UGT1A9.

Genistein protection against acetaminophen-induced liver injury via its potential impact on the activation of UDP-glucuronosyltransferase and antioxidant enzymes

The purpose of this study was to investigate genistein's influence on the relationship between the activation of uridine diphosphate glucuronosyltransferase (UGTs) and the protection against acetaminophen-induced liver toxicity. Animal experimental results revealed that genistein (50, 100 or 200mg/BWkg) significantly ameliorated the biomarkers alanine aminotransferase, alanine aminotransferase, lactate dehydrogenase and malondialdehyde, as indicators of acute liver damage caused by APAP (200mg/BWkg). The level of GSH declined sharply after treatment with APAP within 1h in both the liver and blood with and without genistein. However, after 16h, the levels approached or returned to the original level. Genistein may accelerate and promote APAP glucuronidation as the results showed that APAP-glucuronide increased by 18.44%, 46.79%, and 66.49% for 4h of treatment with genistein dosages of 50, 100 or 200mg/BWkg, respectively, compared with the APAP-only treatment. The activation of UGTs and glutathione peroxidase and the inhibition of CYP2E1 by genistein were observed, and UGTs mRNA expression level with genistein was measured. These findings suggest that genistein can prevent and protect against APAP-induced liver toxicity due to the inhibition of APAP biotransformation and the resistance to oxidative stress via the modulation of the activities of metabolism and the antioxidant enzyme.

Polymorphisms of Phase I and Phase II Enzymes and Breast Cancer Risk

Breast cancer is a complex disease which is provoked by a multitude of exogenous and endogenous factors including genetic variations. Recent genome-wide association studies identified a set of more than 18 novel low penetrant susceptibility loci, however, a limitation of this powerful approach is the hampered analysis of polymorphisms in DNA sequences with a high degree of similarity to other genes or pseudo genes. Since this common feature affects the majority of the highly polymorphic genes encoding phase I and II enzymes the retrieval of specific genotype data requires adapted amplification methods. With regard to breast cancer these genes are of certain interest due to their involvement in the metabolism of carcinogens like exogenous genotoxic compounds or steroid hormones. The present review summarizes the observed effects of functional genetic variants of phase I and II enzymes in well designed case control studies to shed light on their contribution to breast cancer risk.

Human UDP-glucuronosyltransferase UGT2A2: cDNA construction, expression, and functional characterization in comparison with UGT2A1 and UGT2A3

OBJECTIVES

Characterize the expression and glucuronidation activities of the human uridine 5'-diphospho (UDP)-glucuronosyltransferase (UGT) 2A2.

METHOD

UGT2A1 was cloned from nasal mucosa mRNA. Synthetic cDNA for UGT2A2 was constructed assuming exon sharing between UGT2A1 and UGT2A2 (Mackenzie et al., Pharmacogenetics and Genomics 2005, 15:677-685). Exon 1 of UGT2A2 was amplified from genomic DNA and combined with exons 2-6 of UGT2A1. UGT2A3 was cloned from liver mRNA. Quantitative reverse-transcribed-PCR (RT-PCR) was used to evaluate the expression of all the three UGTs of subfamily 2A in different tissues. Recombinant UGT2A1, UGT2A2 and UGT2A3 were expressed in baculovirus-infected insect cells and analyzed for glucuronidation activity towards different substrates.

RESULTS

DNA sequencing of RT-PCR products from human nasal mucosa mRNA, confirmed exon sharing between UGT2A1 and UGT2A2. In addition, it indicated that the N-terminal signal peptide sequence of UGT2A2 is the longest among the human UGTs. Quantitative RT-PCR revealed that both UGT2A1 and UGT2A2 are mainly expressed in the nasal mucosa, and that their expression level in fetal samples was much higher than in adults. Activity assays with recombinant UGTs 2A1-2A3 showed broad substrate selectivity for UGT2A1 and UGT2A2. Although glucuronidation rates and substrate affinities were mostly higher in UGT2A1, the Km values for UDP-glucuronic acid were similar in both UGTs. In addition, there were regioselectivity differences between the two UGTs and, with a few substrates, particularly ethinylestradiol, the activity of UGT2A2 was higher.

CONCLUSION

UGT2A2 is mainly expressed in the nasal mucosa and it has glucuronidation activity towards several different endobiotic and xenobiotic substrates.

Pharmacokinetics of the estrogen receptor subtype-selective ligands, PPT and DPN: quantification using UPLC-ES/MS/MS

Estrogen receptor (ER) subtype specific agonists, diarylpropionitrile (DPN) for ERβ and propylpyrazoletriol (PPT) for ERα, are pharmacological probes used frequently to define mechanisms for estrogen actions in vitro and in vivo. Quantitative analytical methodology was developed and validated for DPN and PPT, based on synthetic stable labeled analogs (DPN-d(4) and PPT-d(5)) using isotope dilution liquid chromatographic tandem electrospray mass spectrometric detection. The validated method produced high sensitivity, with detection limits of 0.04-0.07ng/ml serum. Serum pharmacokinetics were evaluated in Long-Evans rats following a single subcutaneous injection (2mg/kg bw) of both compounds. The role of Phase II metabolism was evaluated using β-glucuronidase and arylsulfatase hydrolysis to measure total DPN and PPT in addition to the parent compounds. The pharmacokinetic properties of DPN and PPT reported could facilitate experimental designs requiring specified levels of receptor occupancy for quantitative comparisons of ER subtype specificities for natural and synthetic estrogens in vivo.

Triclocarban mediates induction of xenobiotic metabolism through activation of the constitutive androstane receptor and the estrogen receptor alpha

Triclocarban (3,4,4′-trichlorocarbanilide, TCC) is used as a broad-based antimicrobial agent that is commonly added to personal hygiene products. Because of its extensive use in the health care industry and resistance to degradation in sewage treatment processes, TCC has become a significant waste product that is found in numerous environmental compartments where humans and wildlife can be exposed. While TCC has been linked to a range of health and environmental effects, few studies have been conducted linking exposure to TCC and induction of xenobiotic metabolism through regulation by environmental sensors such as the nuclear xenobiotic receptors (XenoRs). To identify the ability of TCC to activate xenobiotic sensors, we monitored XenoR activities in response to TCC treatment using luciferase-based reporter assays. Among the XenoRs in the reporter screening assay, TCC promotes both constitutive androstane receptor (CAR) and estrogen receptor alpha (ERα) activities. TCC treatment to hUGT1 mice resulted in induction of the UGT1A genes in liver. This induction was dependent upon the constitutive active/androstane receptor (CAR) because no induction occurred in hUGT1Car^−/− mice. Induction of the UGT1A genes by TCC corresponded with induction of Cyp2b10, another CAR target gene. TCC was demonstrated to be a phenobarbital-like activator of CAR in receptor-based assays. While it has been suggested that TCC be classified as an endocrine disruptor, it activates ERα leading to induction of Cyp1b1 in female ovaries as well as in promoter activity. Activation of ERα by TCC in receptor-based assays also promotes induction of human CYP2B6. These observations demonstrate that TCC activates nuclear xenobiotic receptors CAR and ERα both in vivo and in vitro and might have the potential to alter normal physiological homeostasis. Activation of these xenobiotic-sensing receptors amplifies gene expression profiles that might represent a mechanistic base for potential human health effects from exposure to TCC.

Switching to unboosted atazanavir reduces bilirubin and triglycerides without compromising treatment efficacy in UGT1A1*28 polymorphism carriers

OBJECTIVES

Hyperbilirubinaemia is a frequent complication of atazanavir-containing antiretroviral therapy and its severity is related to UDP-glucuronosyl transferase (UGT) 1A1*28 polymorphism. The aim of this study was to evaluate the safety and outcome of unboosted atazanavir-containing regimens based on the genetic constitution.

METHODS

Fifty-one HIV-1-infected patients on boosted atazanavir were prospectively enrolled in the study. Twenty-five patients with a UGT1A1*28 allele switched to 400 mg of unboosted atazanavir.

RESULTS

At baseline, UGT1A1 heterozygous and homozygous patients had significantly higher bilirubin levels than wild-type (P = 0.012 and P < 0.001, respectively). After ritonavir removal, a reduction was observed in total bilirubin (from 4.09 to 1.82 mg/dL; P < 0.001), γ-glutamyl transpeptidase (P = 0.015), triglycerides (P = 0.03) and total cholesterol (P = 0.05). No significant changes in CD4 T cell count and no increases in viral load were observed 12 months after unboosting. Plasma drug monitoring after ritonavir removal revealed the presence of therapeutic atazanavir concentrations in all patients except one with poor therapy adherence.

CONCLUSIONS

UGT1A1*28 is significantly related to hyperbilirubinaemia in HIV-1 patients receiving atazanavir. Genotyping before the initiation of antiretroviral therapy can reduce the emergence of severe hyperbilirubinaemia. Unboosted atazanavir-containing therapy is safe and efficacious in patients with an undetectable viral load with a UGT1A1*28 polymorphism, allowing the use of atazanavir in patients otherwise likely unable to receive it.

UDP-glucuronosyltransferase 1A4 (UGT1A4) polymorphisms in a Jordanian population

Glucuronidation is one of the most important phase II metabolic pathways. It is catalyzed by a family of UDP-glucuronosyltransferase enzymes (UGTs). One of the subfamilies is UGT1A. Allele frequencies in UGT1A4 differ among ethnic groups. The aim of this study was to determine the allelic frequency of two most common defective alleles: UGT1A4*2 and UGT1A4*3 in a Jordanian population. A total of 216 healthy Jordanian Volunteers (165 males and 51 females) were included in this study. Genotyping for UGT1A4*1, UGT1A4*2 and UGT1A4*3 was done using a well established polymerase chain reaction-restriction fragment length polymorphism test. Among 216 random individuals studied for UGT1A4*2 mutation there were 26 individuals who were heterozygous, giving a prevalence of 12% and an allele frequency of 6.5%. Only one individual was homozygous for UGT1A4*2. The UGT1A4*3 mutation was detected as heterozygous in 9 of 216 individuals indicating a prevalence of 4.2% and allele frequency of 3.5%. Three individuals were homozygous for the UGT1A4*3 indicating a prevalence of 1.4%. The prevalence of UGT1A4*2 is similar to the Caucasians but different from other populations whilst the UGT1A4*3 prevalence in the Jordanian population is distinct from other populations. Our results provide useful information for the Jordanian population and for future genotyping of Arab populations in general.

Quantification of human uridine-diphosphate glucuronosyl transferase 1A isoforms in liver, intestine, and kidney using nanobore liquid chromatography-tandem mass spectrometry

Uridine-disphosphate glucuronosyl transferase (UGT) enzymes catalyze the formation of glucuronide conjugates of phase II metabolism. Methods for absolute quantification of UGT1A1 and UGT1A6 were previously established utilizing stable isotope peptide internal standards with liquid chromatography-tandem mass spectrometry (LC-MS/MS). The current method expands upon this by quantifying eight UGT1A isoforms by nanobore high-performance liquid chromatography (HPLC) coupled with a linear ion trap time-of-flight mass spectrometer platform. Recombinant enzyme digests of each of the isoforms were used to determine assay linearity and detection limits. Enzyme expression level in human liver, kidney, and intestinal microsomal protein was determined by extrapolation from spiked stable isotope standards. Intraday and interday variability was <25% for each of the enzyme isoforms. Enzyme expression varied from 3 to 96 pmol/mg protein in liver and intestinal microsomal protein digests. Expression levels of UGT1A7, 1A8, and 1A10 were below detection limits (<1 pmol/mg protein) in human liver microsome (HLMs). In kidney microsomes the expression of UGT1A3 was below detection limits, but levels of UGT1A4, 1A7, 1A9, and 1A10 protein were higher relative to that of liver, suggesting that renal glucuronidation could be a significant factor in renal elimination of glucuronide conjugates. This novel method allows quantification of all nine UGT1A isoforms, many previously not amenable to measurement with traditional methods such as immunologically based assays. Quantitative measurement of proteins involved in drug disposition, such as the UGTs, significantly improves the ability to evaluate and interpret in vitro and in vivo studies in drug development.