Functions and transcriptional regulation of adult human hepatic UDP-glucuronosyl-transferases (UGTs): mechanisms responsible for interindividual variation of UGT levels

Pregnane X receptor as a therapeutic target for cholestatic liver injury

Cholestatic liver injury (CLI) is caused by toxic bile acids (BAs) accumulation in the liver and can lead to inflammation and liver fibrosis. The mechanisms underlying CLI development remain unclear, and this disease has no effective cure. However, regulating BA synthesis and homeostasis represents a promising therapeutic strategy for CLI treatment. Pregnane X receptor (PXR) plays an essential role in the metabolism of endobiotics and xenobiotics via the transcription of metabolic enzymes and transporters, which can ultimately modulate BA homeostasis and exert anticholestatic effects. Furthermore, recent studies have demonstrated that PXR exhibits antifibrotic and anti-inflammatory properties, providing novel insights into treating CLI. Meanwhile, several drugs have been identified as PXR agonists that improve CLI. Nevertheless, the precise role of PXR in CLI still needs to be fully understood. This review summarizes how PXR improves CLI by ameliorating cholestasis, inhibiting inflammation, and reducing fibrosis and discusses the progress of promising PXR agonists for treating CLI.

Knockdown of CYP9A9 increases the susceptibility to lufenuron, methoxyfenozide and a mixture of both in Spodoptera exigua

Lufenuron (LUF) and Methoxyfenozide (MET) as Insect Growth Regulators (IGRs) contribute to the current control of the catastrophic crop pest, Spodoptera exigua (Lepidoptera, Noctuidae). Yet S. exigua has evolved resistance to LUF and MET, which is possibly mediated by cytochrome P450 monooxygenases (P450s), particularly from the CYP3 clade family, as it plays a key role in the detoxification of insecticides. However, a mixture of LUF and MET (MML) (optimal ratio: 6:4) remains highly insecticidal. Here, we analysed the response of S. exigua to sublethal concentrations of LUF, MET, and MML via transcriptomics. Twelve differentially expressed genes (DEGs) encoding CYP3 clade members were observed in transcriptomes and CYP9A9 was significantly upregulated after treatment with LUF, MET, and MML. Further, CYP9A9 was most highly expressed in the midgut of L4 S. exigua larvae. RNAi-mediated knockdown of CYP9A9 reduced the activity of CYP450 and increased the susceptibility of S. exigua larvae to LUF, MET, and MML. Thus, CYP9A9 plays a key role in the detoxification of LUF, MET, and MML in S. exigua. These findings provide new insights into insecticidal actions of IGRs, which can be applied to the establishment of novel pest management strategies.

The Uridine diphosphate (UDP)-glycosyltransferases (UGTs) superfamily: the role in tumor cell metabolism

UDP-glycosyltransferases (UGTs), important enzymes in biotransformation, control the levels and distribution of numerous endogenous signaling molecules and the metabolism of a wide range of endogenous and exogenous chemicals. The UGT superfamily in mammals consists of the UGT1, UGT2, UGT3, and UGT8 families. UGTs are rate-limiting enzymes in the glucuronate pathway, and in tumors, they are either overexpressed or underexpressed. Alterations in their metabolism can affect gluconeogenesis and lipid metabolism pathways, leading to alterations in tumor cell metabolism, which affect cancer development and prognosis. Glucuronidation is the most common mammalian conjugation pathway. Most of its reactions are mainly catalyzed by UGT1A, UGT2A and UGT2B. The body excretes UGT-bound small lipophilic molecules through the bile, urine, or feces. UGTs conjugate a variety of tiny lipophilic molecules to sugars, such as galactose, xylose, acetylglucosamine, glucuronic acid, and glucose, thereby inactivating and making water-soluble substrates, such as carcinogens, medicines, steroids, lipids, fatty acids, and bile acids. This review summarizes the roles of members of the four UGT enzyme families in tumor function, metabolism, and multiple regulatory mechanisms, and its Inhibitors and inducers. The function of UGTs in lipid metabolism, drug metabolism, and hormone metabolism in tumor cells are among the most important topics covered.

Combination of Paclitaxel and PXR Antagonist SPA70 Reverses Paclitaxel-Resistant Non-Small Cell Lung Cancer

Paclitaxel (PTX) is one of the most efficient drugs for late-stage non-small cell lung cancer (NSCLC) patients. However, most patients gradually develop resistance to PTX with long-term treatments. The identification of new strategies to reverse PTX resistance in NSCLC is crucially important for the treatment. PTX is an agonist for the pregnane X receptor (PXR) which regulates PTX metabolism. Antagonizing PXR, therefore, may render the NSCLC more sensitive to the PTX treatment. In this study, we investigated the PXR antagonist SPA70 and its role in PTX treatment of NSCLC. In vitro, SPA70 and PTX synergistically inhibited cell growth, migration and invasion in both paclitaxel-sensitive and paclitaxel-resistant A549 and H460 lung cancer cells. Mechanistically, we found PTX and SPA70 cotreatment disassociated PXR from ABCB1 (MDR1, P-gp) promoter, thus inhibiting P-gp expression. Furthermore, the combination regimen synergistically enhanced the interaction between PXR and Tip60, which abrogated Tip60-mediated α-tubulin acetylation, leading to mitosis defect, S-phase arrest and necroptosis/apoptosis. Combination of PXT and SPA70 dramatically inhibited tumor growth in a paclitaxel-resistant A549/TR xenograft tumor model. Taken together, we showed that SPA70 reduced the paclitaxel resistance of NSCLC. The combination regimen of PTX and SPA70 could be potential novel candidates for the treatment of taxane-resistant lung cancer.

The impact of ibuprofen on valproic acid plasma concentration in pediatric patients

The combination of valproic acid (VPA) and ibuprofen is common in children with epilepsy. Three case reports investigated that ibuprofen might decrease plasma concentration of VPA, however, no cohort study was published to evaluate the interaction of ibuprofen on VPA plasma concentration in pediatric patients.Data from patients with measured VPA trough concentrations (C₀) were retrospectively collected in a Chinese teaching and tertiary Children's Hospital from January 2017 to June 2019. The samples measured within 6 weeks of the last ibuprofen administration were considered as ibuprofen combination samples. Patients with paired samples before and after ibuprofen administration were additionally analyzed. The effects of ibuprofen on the VPA trough concentration to dose (C₀/D) ratio were investigated. The proportion of samples with achieved target concentrations of VPA (50-100 mg/L) and the corresponding required dosage were compared. Moreover, subgroup analysis according to the interval between the last ibuprofen dosage and C₀ measurement was performed.A total of 616 samples from 434 patients, of whom 16 had paired samples, were included. VPA C₀/D decreased when ibuprofen was administered by 7.5% and 30.6% of the total samples and paired samples, respectively. The interaction was significant within 1 week of the last ibuprofen dose. No significant differences were observed in the proportion of target concentration achieved and VPA dose requirement when ibuprofen was combined.A moderate effect of ibuprofen on VPA C₀/D was observed within 1 week of ibuprofen administration; the target concentration and required doses of VPA were comparable.

Alternative transcript splicing regulates UDP-glucosyltransferase-catalyzed detoxification of DIMBOA in the fall armyworm (Spodoptera frugiperda)

Herbivorous insects often possess the ability to detoxify chemical defenses from their host plants. The fall armyworm (Spodoptera frugiperda), which feeds principally on maize, detoxifies the maize benzoxazinoid 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) by stereoselective re-glucosylation using a UDP-glucosyltransferase, SfUGT33F28. SfUGT33F28 activity is induced by feeding on a DIMBOA-containing diet, but how this induction is regulated is unknown. In the present work, we describe the alternative splicing of the SfUGT33F28 transcript. Variant transcripts are differentially expressed in response to DIMBOA, and this transcriptional response is mediated by an insect aryl hydrocarbon receptor. These variants have large deletions leading to the production of truncated proteins that have no intrinsic UGT activity with DIMBOA but interact with the full-length enzyme to raise or lower its activity. Therefore, the formation of SfUGT33F28 splice variants induces DIMBOA-conjugating UGT activity when DIMBOA is present in the insect diet and represses activity in the absence of this plant defense compound.

Relationship of circulating total bilirubin, UDP-glucuronosyltransferases 1A1 and the development of non-alcoholic fatty liver disease: a cross-sectional study

Background

This study aimed to investigate the correlation of circulating total bilirubin (TB) and UGT1A1 with NAFLD in Chinese Han population.

Methods

172 adults were enrolled from the Qingdao Municipal Hospital from May 2019 to October 2020. All individuals were examined with MRI-PDFF and divided into no steatosis, mild steatosis, moderate steatosis, and severe steatosis groups according to the MRI-PDFF values. The biochemical indexes and UGT1A1 were measured.

Results

There was no significant difference of circulating TB and UGT1A1 levels between NAFLD group and controls. In the moderate steatosis and severe steatosis groups, the circulating TB levels were higher than that in control group (all P < 0.05). In addition, circulating TB levels were weak positively associated with liver fat fraction in NAFLD patients (ρ = 0.205, P = 0.001). There was no significant correlation between circulating UGT1A1 levels with liver fat fraction in patients with NAFLD (ρ = 0.080, P = 0.179), but positively correlation was found in patients with severe steatosis (ρ = 0.305, P = 0.026).

Conclusions

The circulating TB levels were significant high in patients with moderate and severe steatosis. Circulating TB levels were weakly associated with liver fat fraction in patients with NAFLD, and the circulating UGT1A1 levels were positively correlated with liver fat fraction in NAFLD patients with severe steatosis.

Trial registration: ChiCTR, ChiCTR1900022744. Registered 24 April 2019 – Retrospectively registered, http://www.chictr.org.cn/edit.aspx?pid=38304&htm=4.

Drug-oxidizing and conjugating non-cytochrome P450 (non-P450) enzymes in cynomolgus monkeys and common marmosets as preclinical models for humans

Many drug oxidations and conjugations are mediated by a variety of cytochromes P450 (P450) and non-P450 enzymes in humans and non-human primates. These non-P450 enzymes include aldehyde oxidases (AOX), carboxylesterases (CES), flavin-containing monooxygenases (FMO), glutathione S-transferases (GST), arylamine N-acetyltransferases (NAT),sulfotransferases (SULT), and uridine 5'-diphospho-glucuronosyltransferases (UGT) and their substrates include both endobiotics and xenobiotics. Cynomolgus macaques (Macaca fascicularis, an Old-World monkey) are widely used in preclinical studies because of their genetic and physiological similarities to humans. However, many reports have indicated the usefulness of common marmosets (Callithrix jacchus, a New World monkey) as an alternative non-human primate model. Although knowledge of the drug-metabolizing properties of non-P450 enzymes in non-human primates is relatively limited, new research has started to provide an insight into the molecular characteristics of these enzymes in cynomolgus macaques and common marmosets. This mini-review provides collective information on the isoforms of non-P450 enzymes AOX, CES, FMO, GST, NAT, SULT, and UGT and their enzymatic profiles in cynomolgus macaques and common marmosets. In general, these non-P450 cynomolgus macaque and marmoset enzymes have high sequence identities and similar substrate recognitions to their human counterparts. However, these enzymes also exhibit some limited differences in function between species, just as P450 enzymes do, possibly due to small structural differences in amino acid residues. The findings summarized here provide a foundation for understanding the molecular mechanisms of polymorphic non-P450 enzymes and should contribute to the successful application of non-human primates as model animals for humans.

Structural diversity, bioactivities, and biosynthesis of natural diterpenoid alkaloids

Covering: 2009 to 2018. Diterpenoid alkaloids, originating from the amination of natural tetracyclic diterpenes, are a diverse class of compounds having complex structural features with many stereocenters. The important pharmacological activities and structural complexity of the diterpenoid alkaloids have long interested scientists due to their medicinal uses, infamous toxicity, and unique biosynthesis. Since 2009, 373 diterpenoid alkaloids, assigned to 46 skeletons, have been isolated and identified from plants mostly in the Ranunculaceae family. The names, classes, molecular weight, molecular formula, NMR data, and plant sources of these diterpene alkaloids are collated here. This review will be a detailed update of the naturally occurring diterpene alkaloids reported from the plant kingdom from 2009-2018, providing an in-depth discussion of their diversity, biological activities, pharmacokinetics, toxicity, application, evolution, and biosynthesis.

Management of COVID-19 in patients with seizures: Mechanisms of action of potential COVID-19 drug treatments and consideration for potential drug-drug interactions with anti-seizure medications

In regard to the global pandemic of COVID-19, it seems that persons with epilepsy (PWE) are not more vulnerable to get infected by SARS-CoV-2, nor are they more susceptible to a critical course of the disease. However, management of acute seizures in patients with COVID-19 as well as management of PWE and COVID-19 needs to consider potential drug-drug interactions between antiseizure drugs and candidate drugs currently assessed as therapeutic options for COVID-19. Repurposing of several licensed and investigational drugs is discussed for therapeutic management of COVID-19. While for none of these approaches, efficacy and tolerability has been confirmed yet in sufficiently powered and controlled clinical studies, testing is ongoing with multiple clinical trials worldwide. Here, we have summarized the possible mechanisms of action of drugs currently considered as potential therapeutic options for COVID-19 management along with possible and confirmed drug-drug interactions that should be considered for a combination of antiseizure drugs and COVID-19 candidate drugs. Our review suggests that potential drug-drug interactions should be taken into account with drugs such as chloroquine/hydroxychloroquine and lopinavir/ritonavir while remdesivir and tocilizumab may be less prone to clinically relevant interactions with ASMs.

Racial Disparity in Drug Disposition in the Digestive Tract

The major determinants of drug or, al bioavailability are absorption and metabolism in the digestive tract. Genetic variations can cause significant differences in transporter and enzyme protein expression and function. The racial distribution of selected efflux transporter (i.e., Pgp, BCRP, MRP2) and metabolism enzyme (i.e., UGT1A1, UGT1A8) single nucleotide polymorphisms (SNPs) that are highly expressed in the digestive tract are reviewed in this paper with emphasis on the allele frequency and the impact on drug absorption, metabolism, and in vivo drug exposure. Additionally, preclinical and clinical models used to study the impact of transporter/enzyme SNPs on protein expression and function are also reviewed. The results showed that allele frequency of the major drug efflux transporters and the major intestinal metabolic enzymes are highly different in different races, leading to different drug disposition and exposure. The conclusion is that genetic polymorphism is frequently observed in different races and the related protein expression and drug absorption/metabolism function and drug in vivo exposure can be significantly affected, resulting in variations in drug response. Basic research on race-dependent drug absorption/metabolism is expected, and FDA regulations of drug dosing adjustment based on racial disparity are suggested.

Adenosine deaminases acting on RNA modulate the expression of the human pregnane X receptor

The pregnane X receptor (PXR) is one of the major transcription factors that regulate the expression of different drug-metabolizing enzymes and transporters. Adenosine-to-inosine RNA editing, the most frequent nucleotide conversion on RNA, which is catalyzed by adenosine deaminase acting on RNA (ADAR) enzymes, may modulate gene expression and function. Here, we investigated the potential regulation of human PXR expression by adenosine-to-inosine RNA editing. Knockdown of ADAR1 increased PXR mRNA level, and the knockdown of ADAR1 or ADAR2 significantly increased PXR protein level in HepaRG cells. In HepG2 cells, the knockdown of ADAR1 or ADAR2 significantly increased PXR mRNA and protein levels. The increase in the PXR protein by ADAR1 knockdown resulted in increased cytochrome P450 3A4 (CYP3A4) transactivity and CYP3A4 and UDP-glucuronosyltransferase 1A1 (UGT1A1) expression. A reporter assay revealed that the 3'-untranslated region (UTR) of PXR mRNA, especially from +3371 to +3440, is responsible for the ADAR-mediated post-transcriptional control of PXR expression, despite the lack of RNA edited sites in this region. Collectively, we found that PXR is negatively regulated by ADAR1 via an indirect mechanism, which facilitates the degradation of PXR mRNA. We could demonstrate that ADAR1 can cause interindividual variability in hepatic drug metabolism potencies.

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.

Catalpol coordinately regulates phase I and II detoxification enzymes of Triptolide through CAR and NRF2 pathways to reduce Triptolide-induced hepatotoxicity

Triptolide (TP), as the main component of Tripterygium Wilfordii (TW), can induce obvious liver injury when exerting the therapeutic effect. However, in our previous study, Catalpol (CAT), the main active ingredient of Rehmannia Glutinosa (RG), was shown to increase the drug clearance rate of TP and to attenuate TP-induced hepatotoxicity. Thus the present study aims to address the roles of phase I and II metabolic enzymes and the nuclear receptors in the detoxification process of TP, to analyze the mechanism of CAT reducing hepatotoxicity. For this purpose, SD rats and human liver cell line L-02 and HepG2 cells were selected, and treated with TP or the combination of TP and CAT in our study. Then the effect of CAT on detoxification of TP was analyzed, and the roles of phase I metabolic enzymes cytochrome P450 3A2/4 (CYP3A2/4) and phase II metabolic enzyme UDP-glucuronosyltransferase 1A6 (UGT1A6) and their related nuclear receptor regulations were evaluated. It was found that TP inhibited the transcription of CYP3A2/4. And through the constitutive androstane receptor (CAR) pathway, CAT not only significantly changed this inhibition and increased the expression of CYP3A2/4 but also increased the expression of CYP2C9, both of which are phase I detoxification enzymes of TP. And with the gene-silenced experiment, it was confirmed that this regulation was CAR-dependent. We also found that CAT could continue to exert a certain protective effect after CAR was silenced, with UGT1A6, the phase II detoxification enzyme of TP, significantly induced. And this was closely related to the enhanced transcriptional regulation of the nuclear factor erythroid 2-related factor 2 (NRF2) pathway. In conclusion, our results reveal that CAT can induce TP's phase I detoxification enzymes CYP3A2/4 and CYP2C9 through the CAR pathway, and induce TP's phase II detoxification enzyme UGT1A6 via the NRF2 pathway when CAR is strongly inhibited. And this coordinate regulation of CAT may be an important source of the effect for CAT to increase TP metabolic conversion and reduce TP hepatotoxicity.

A Gilbert syndrome-associated haplotype protects against fatty liver disease in humanized transgenic mice

UDP-glucuronosyltransferases 1 A (UGT1A) enzymes are capable of detoxifying a broad range of endo- and xenobiotic compounds, which contributes to antioxidative effects, modulation of inflammation and cytoprotection. In the presence of low-function genetic UGT1A variants fibrosis development is increased in various diseases. This study aimed to examine the role of common UGT1A polymorphisms in NASH. Therefore, htgUGT1A-WT mice and htgUGT1A-SNP mice (carrying a common human haplotype present in 10% of the white population) were fed a high-fat Paigen diet for 24 weeks. Serum aminotransferase activities, hepatic triglycerides, fibrosis development and UGT1A expression were assessed. Microscopic examination revealed higher hepatic fat deposition and a significant induction of UGT1A gene expression in htgUGT1A-WT mice. In agreement with these observations, lower serum aminotransferase activities and lower expression levels of fibrosis-related genes were measured in htgUGT1A-SNP mice. This was accompanied by reduced PPARα protein levels in htgUGT1A-WT but not in SNP mice. Our data demonstrate a protective effect of a UGT1A SNP haplotype, leading to milder hepatic steatosis and NASH. Higher PPARα protein levels in animals with impaired UGT1A activity are the likely result of reduced glucuronidation of ligands involved in PPARα-mediated fatty acid oxidation and may lead to the observed protection in htgUGT1A-SNP mice.

Dysregulation of UDP-glucuronosyltransferases in CCl4 induced liver injury rats

UDP-glucuronosyltransferases (UGTs) are a family of phase II drug metabolizing enzymes that catalyze glucuronidation of numerous endogenous and exogenous substrates. Carbon tetrachloride (CCl₄) is widely used to develop liver injuries mimicking human liver diseases. However, effects of CCl₄ on the expression and activities of UGTs and the mechanism have not been fully elucidated. The present study aims to elucidate the dysregulation patterns of major UGTs induced by CCl₄. Biochemical and histopathological results showed that CCl₄ exerted hepatotoxicity in rats. The mRNA levels of UGTs were all significantly reduced in acute liver injury rats. However, mRNA levels of UGT1A1, 1A6, 2B1 and 2B2 were up-regulated while the UGT2B3, 2B6 and 2B12 levels were reduced in chronic CCl₄-induced liver fibrosis rats. The protein expression of UGT1A1, 1A6 and 2B were decreased in acute liver injury rats. UGT1A1 and 1A6 proteins were increased, whereas UGT2B protein was reduced in liver fibrosis rats. In addition, CCl₄ inhibited the enzyme activities of UGTs in rats. Moreover, the dysregulation of UGTs was accompanied by the decreased mRNA expression of Nrf2, CAR, FXR, PXR, PPAR-α and their corresponding target genes, except for Nrf2, HO-1, AhR and CYP1A1 in liver fibrosis rats. These findings suggest that dysregulation of UGTs under CCl₄ exposure is isoform-specific, which could have a complex impact on drug efficacy and endogenous metabolism. Different exposure durations of CCl₄ (single vs multiple doses) could have differential effects on rat hepatic UGTs expression.

Molecular characterization of functional UDP-glucuronosyltransferases 1A and 2B in common marmosets

UDP-glucuronosyltransferases (UGTs) are essential drug-conjugation enzymes that metabolize a variety of endobiotic and xenobiotic substrates. The molecular characteristics of UGTs have been extensively investigated in humans, but remain to be investigated in common marmosets, a nonhuman primate species widely used in drug metabolism studies. In this study, 11 UGT cDNAs (UGT1A1, 1A3, 1A4, 1A6, 1A7, and 1A9; and UGT2B49, 2B50, 2B51, 2B52, and 2B53) were isolated and characterized in marmosets. Marmoset UGT1As had high sequence identities (89-93%) with human UGT1As, but the sequence identities of marmoset UGT2Bs were lower (82-86%). Marmoset UGTs were found to be phylogenetically close to human UGTs. Just as human UGT1As do, marmoset UGT1A genes shared exons 2-5 and contained a variable exon 1 unique to each gene; in contrast, marmoset UGT2B genes contained six unique exons. Moreover, marmoset and human UGT1A and UGT2B gene clusters were located in corresponding regions in their respective genomes. Among the five tissue types tested, marmoset UGT mRNAs were most abundantly expressed in liver, jejunum, and/or kidney, i.e., in tissues important for drug metabolism, just as human UGTs are. Among the 11 marmoset UGT mRNAs investigated, marmoset UGT1A9, 1A4, and 1A6 mRNAs were the most abundantly expressed in liver, small intestine, and kidney, respectively. Marmoset liver microsomes and recombinant UGT1A proteins catalyzed the glucuronidation of the same substrates that human UGT1As catalyze, including estradiol, trifluoperazine, 4-methylumbelliferone, serotonin, 4-nitrophenol, and propofol. Trifluoperazine was glucuronidated by marmoset liver microsomes, but not by any of the UGT1A isoforms examined under the present conditions. These results collectively suggest that functional marmoset UGTs have generally similar molecular characteristics to human UGTs.

Oleanolic Acid and Ursolic Acid Induce UGT1A1 Expression in HepG2 Cells by Activating PXR Rather Than CAR

Background: Oleanolic acid (OA) and its isomer ursolic acid (UA) have recently emerged as research foci based on their biologic activities. We previously demonstrated that UA can inhibit the activities of UGT1A3 and UGT1A4, and OA inhibits UGT1A3 activity in liver microsomes. However, whether OA and UA affect the expression of UGT1As in HepG2 cells and the underlying regulatory mechanism remain unclear.

Purpose: The present study aimed to explore the effect of OA and UA on the expression of UGT1As in HepG2 cells and the regulatory mechanisms on UGT1A1 based on the pregnane X receptor (PXR) and constitutive androstane receptor (CAR) signaling pathways.

Methods: We analyzed the effect of OA and UA on UGT1A expression and on the PXR/CAR regulatory pathway in HepG2 cells, hPXR-silenced HepG2 cells, and hCAR-silenced HepG2 cells by Q-PCR, Western blotting, and dual-luciferase reporter gene assays.

Results: In HepG2 cells, OA and UA both significantly induced the expression of UGT1A1, UGT1A3, UGT1A4, and UGT1A9 and upregulated the expression of PXR. However, OA and UA did not affect CAR expression. A dual-luciferase reporter assay showed that OA and UA could markedly promote PXR-mediated UGT1A1 luciferase activity, whereas OA and UA did not affect CAR-mediated UGT1A1 luciferase activity. In hPXR-silenced HepG2 cells, OA and UA did not elevate UGT1A1 activity compared to the control group. However, the expression of UGT1A1 in hCAR-silenced HepG2 cells was markedly elevated compared to the control group or with non-silenced HepG2 cells treated with OA (10, 20, and 40 μM) or UA (10, 20, and 40 μM).

Conclusions: OA and UA significantly induce the expression of UGT1A1, UGT1A3, UGT1A4, and UGT1A9 in HepG2 cells, and their induction on UGT1A1 is mediated by PXR activation, not CAR.

Functional and molecular characterization of UDP-glucuronosyltransferase 2 family in cynomolgus macaques

UDP-glucuronosyltransferases (UGTs) are essential enzymes metabolizing endogenous and exogenous chemicals. However, characteristics of UGTs have not been fully investigated in molecular levels of cynomolgus macaques, one of non-human primates widely used in preclinical drug metabolism studies. In this study, three UGT2A cDNAs (UGT2A1, 2A2, and 2A3) were isolated and characterized along with seven UGT2Bs previously identified in cynomolgus macaques. Several transcript variants were found in cynomolgus UGT2A1 and UGT2A2, like human orthologs. Cynomolgus UGT2A and UGT2B amino acid sequences were highly identical (87-96%) to their human counterparts. By phylogenetic analysis, all these cynomolgus UGT2s were more closely clustered with their human homologs than with dog, rat, or mouse UGT2s. Especially, UGT2As showed orthologous relationships between humans and cynomolgus macaques. All the cynomolgus UGT2 mRNAs were expressed in livers, jejunum, and/or kidneys abundantly, except that UGT2A1 and UGT2A2 mRNAs were predominantly expressed in nasal mucosa, like human UGT2s. UGT2A and UGT2B genes together form a gene cluster in the cynomolgus and human genome. Among the seven cynomolgus UGT2Bs heterologously expressed in yeast, UGT2B9 and UGT2B30 showed activities in estradiol 17-O-glucuronidation and morphine 3-O-glucuronidation but did not show activities in estradiol 3-O-glucuronidation, similar to human UGT2Bs. In liver microsomes, cynomolgus macaques showed higher estradiol 17-O-glucuronidase and morphine 3-O-glucuronidase activities than humans, suggesting functional activities of the responsible UGT2B enzymes in cynomolgus macaques. Therefore, cynomolgus UGT2s had overall molecular similarities to human UGT2s, but also showed some differences in UGT2B enzyme properties.

The nuclear receptor Rev-erbα participates in circadian regulation of Ugt2b enzymes in mice

Circadian clock is known to modulate phase I metabolism, however whether and how the phase II enzymes UDP-glucuronosyltransferases (UGTs) are regulated by circadian clock are largely unknown. In this study, we aimed to investigate a potential role of the clock gene Rev-erbα in regulation of Ugt2b enzymes. Ugt2b mRNA and protein expression in mouse livers were determined at a 4-h interval around the clock. Ugt2b activity was probed using morphine as a specific substrate. Regulation of Ugt2b by Rev-erbα was investigated using mouse hepatoma Hepa-1c1c7 cells and Rev-erbα knock-out (Rev-erbα^-/-) mice. Luciferase reporter, mobility shift and chromatin immunoprecipitation (ChIP) assays were performed to identify the Rev-erbα binding site in Ugt2b36 promoter. Circadian variations in hepatic mRNA expression were observed for six Ugt2b genes (Ugt2b1, Ugt2b5, Ugt2b35, Ugt2b36, Ugt2b37, and Ugt2b38) in mice. Likewise, the total Ugt2b protein showed a circadian fluctuation. Glucuronidation of morphine (an Ugt2b substrate) both in vitro and in vivo was dosing-time dependent. Morphine glucuronidation was more extensive at the dosing time of ZT2 than at ZT14 consistent with the Ugt2b protein levels. Furthermore, Rev-erbα knockdown significantly increased Ugt2b mRNA and protein in Hepa-1c1c7 cells, whereas Rev-erbα overexpression or activation down-regulated Ugt2b expression. Moreover, Rev-erbα ablation in mice up-regulated the mRNA and protein expression of Ugt2b and blunted Ugt2b rhythmicity in the liver. In addition, Rev-erbα repressed the transcription of Ugt2b36 through specific binding to the -30 to -18 bp of promoter region based on a combination of luciferase reporter, mobility shift and ChIP assays. In summary, the clock gene Rev-erbα negatively regulates the expressions of Ugt2b genes, contributing to their circadian variations.

Glutathione-S-Transferases in the Olfactory Organ of the Noctuid Moth Spodoptera littoralis, Diversity and Conservation of Chemosensory Clades

Glutathione-S-transferases (GSTs) are conjugating enzymes involved in the detoxification of a wide range of xenobiotic compounds. The expression of GSTs as well as their activities have been also highlighted in the olfactory organs of several species, including insects, where they could play a role in the signal termination and in odorant clearance. Using a transcriptomic approach, we identified 33 putative GSTs expressed in the antennae of the cotton leafworm Spodoptera littoralis. We established their expression patterns and revealed four olfactory-enriched genes in adults. In order to investigate the evolution of antennal GST repertoires in moths, we re-annotated antennal transcripts corresponding to GSTs in two moth and one coleopteran species. We performed a large phylogenetic analysis that revealed an unsuspected structural—and potentially functional—diversity of GSTs within the olfactory organ of insects. This led us to identify a conserved clade containing most of the already identified antennal-specific and antennal-enriched GSTs from moths. In addition, for all the sequences from this clade, we were able to identify a signal peptide, which is an unusual structural feature for GSTs. Taken together, these data highlight the diversity and evolution of GSTs in the olfactory organ of a pest species and more generally in the olfactory system of moths, and also the conservation of putative extracellular members across multiple insect orders.

Chemical Probes for Human UDP-Glucuronosyltransferases: A Comprehensive Review

UGTs play crucial roles in the metabolism and detoxification of both endogenous and xenobiotic compounds. The key roles of UGTs in human health have garnered great interest in the design and development of specific probes for human UGTs. However, in contrast to other human enzymes, the probe substrates for human UGTs are rarely reported, owing to the highly overlapping substrate specificities of UGTs and the lack of the integrated crystal structures of UGTs. Over the past decades, many efforts are made to develop specific probe substrates for UGTs and use them in both basic research and drug discovery. This review focuses on recent progress in the development of probe substrates for UGTs and their biomedical applications. A long list of chemical probes for UGTs, including non-fluorescent and fluorescent probes along with their structural information and kinetic parameters, are prepared and analyzed. Additionally, challenges and future directions in this field are highlighted in the final section. All information and knowledge presented in this review provide practical tools/methods for measuring UGT activities in complex biological samples, which will be very helpful for rapid screening and characterization of UGT modulators, and for exploring the relevance of UGT enzymes to human diseases.

New toxicogenetic insights and ranking of the selected pharmaceuticals belong to the three different classes: A toxicity estimation to confirmation approach

Tetracycline hydrochloride (TH), indomethacin (IM), and bezafibrate (BF) belong to the three different important classes of pharmaceuticals, which are well known for their toxicity and environmental concerns. However, studies are still elusive to highlight the mechanistic toxicity of these pharmaceuticals and rank them using both, the toxicity prediction and confirmation approaches. Therefore, we employed the next generation toxicity testing in 21st century (TOX21) tools and estimated the in vitro/vivo toxic endpoints of mentioned pharmaceuticals, and then confirmed them using in vitro/vivo assays. We found significant resemblance in the results obtained via both approaches, especially in terms of in vivo LC50 s and developmental toxicity that ranked IM as most toxic among the studied pharmaceuticals. However, TH appeared most toxic with the lowest estimated AC50s, the highest experimental IC50s, and DNA damages in vitro. Contrarily, IM was found as congener with priority concern to activate the Pi3k-Akt-mTOR pathway in vitro at concentrations substantially lower than that of TH and BF. Further, IM exposure at lower doses (2.79-13.97 μM) depressed the pharmaceuticals detoxification phase I (CYP450 s), phase II (UGTs, SULTs), and phase III (TPs) pathways in zebrafish, whereas, at relatively higher doses, TH (2.08-33.27 μM) and BF (55.28-884.41 μM) partially activated these pathways, which ultimately caused the developmental toxicity in the following order: IM > TH > BF. In addition, we also ranked these pharmaceuticals in terms of their particular toxicity to myogenesis, hematopoiesis, and hepatogenesis in zebrafish embryos. Our results revealed that IM significantly affected myogenesis, hematopoiesis, and hepatogenesis, while TH and BF induced prominent effects on hematopoiesis via significant downregulation of associated genetic markers, such as drl, mpx, and gata2a. Overall, our findings confirmed that IM has higher toxicity than that of TH and BF, therefore, the consumption of these pharmaceuticals should be regulated in the same manner to ensure human and environmental safety.

Population pharmacokinetics of valproic acid in epileptic children: Effects of clinical and genetic factors

Valproic acid (VPA) is a first-line anti-epileptic drug that is used in the treatment of generalized and partial seizures. Gene variants had been proved to influence the pharmacokinetics (PK) of VPA and contribute to its inter-individual variability (IIV). The aim of this study was to systematically investigate the effects of candidate gene variants (CYPs, UGTs, ABC transporters, and nuclear receptors) on VPA PK in Chinese children with epilepsy. A total of 1065 VPA serum trough concentrations at steady state were collected from 264 epileptic pediatric patients aged 3 months to 16 years. The population pharmacokinetic (PPK) model was developed using a nonlinear mixed effects modelling (NONMEM) approach. For the final PPK model, the oral clearance (CL/F) of VPA was estimated to be 0.259 L/h with IIV of 13.3%. The estimates generated by NONMEM indicated that the VPA CL/F was significantly influenced by patient body weight (increased by an exponent of 0.662), co-administration with carbamazepine (increased CL/F by 22%), and daily dose of VPA (increased by an exponent of 0.22). CL/F in patients with the LEPR rs1137101 variant (668 AG and GG genotypes) was much lower than in patients with the AA genotype (17.8% and 22.6% lower, respectively). However, none of the CYPs or UGTs gene variants was found to influence the PK of VPA in this study. Evaluation by bootstrap and normalized prediction distribution error (NPDE) showed that the final model was stable. The predictive performance was evaluated by goodness-of-fit (GOF) plots and visual predictive checks (VPC), and the results indicated satisfactory precision. Our model suggests a correlation between VPA CL/F and LEPR rs1137101 variants, which might be beneficial in the context of individual dose optimization.

Bile acid detoxifying enzymes limit susceptibility to liver fibrosis in female SHRSP5/Dmcr rats fed with a high-fat-cholesterol diet

During middle age, women are less susceptible to nonalcoholic steatohepatitis (NASH) than men. Thus, we investigated the underlying molecular mechanisms behind these sexual differences using an established rat model of NASH. Mature female and male stroke-prone spontaneously hypertensive 5/Dmcr rats were fed control or high-fat-cholesterol (HFC) diets for 2, 8, and 14 weeks. Although HFC-induced hepatic fibrosis was markedly less severe in females than in males, only minor gender differences were observed in expression levels of cytochrome P450 enzymes (CYP)7A1, CYP8B1 CYP27A1, and CYP7B1, and multidrug resistance-associated protein 3, and bile salt export pump, which are involved in fibrosis-related bile acid (BA) kinetics. However, the BA detoxification-related enzymes UDP-glucuronosyltransferase (UGT) and sulfotransferase (SULT) 2A1, and the nuclear receptors constitutive androstane receptor (CAR) and pregnane X receptor (PXR), were strongly suppressed in HFC-fed males, and were only slightly changed in HFC-diet fed females. Expression levels of the farnesoid X receptor and its small heterodimer partner were similarly regulated in a gender-dependent fashion following HFC feeding. Hence, the pronounced female resistance to HFC-induced liver damage likely reflects sustained expression of the nuclear receptors CAR and PXR and the BA detoxification enzymes UGT and SULT.

Direct comparison of UDP-glucuronosyltransferase and cytochrome P450 activities in human liver microsomes, plated and suspended primary human hepatocytes from five liver donors

UDP-glucuronosyltransferases (UGTs) and cytochrome P450s (CYPs) are the major enzymes involved in hepatic metabolism of drugs. Hepatic drug metabolism is commonly investigated using human liver microsomes (HLM) or primary human hepatocytes (PHH). We describe the development of a sensitive assay to phenotype activities of six major hepatic UGT isoforms (UGT1A1, UGT1A3, UGT1A4, UGT1A6, UGT1A9 and UGT2B7) in intact PHH by analysis of glucuronidation of selective probe substrates. The non-selective, general substrate 7-hydroxycoumarin was included for comparison. For each liver donor preparation (five donors) UGT activities in cryopreserved suspended and plated PHH were compared to HLM prepared from the same donors. Standard CYP reaction phenotyping of seven major isoforms was performed in parallel. For all donors, CYP- and UGT-isoforms activity profiles were comparable in PHH and HLM, indicating that reaction phenotyping with selective probe substrates in intact cells primarily reflects respective CYP or UGT activity. System-dependent effects on UGT and CYP isoform activity were still found. While UGT activity of UGT1A1 was equivalent in plated and suspended PHH, UGT1A3, UGT1A6 and UGT2B7 activity was higher in suspended PHH and UGT1A9 and UGT1A4 activity was higher in plated PHH. The well-known decrease in activity of most CYP isoforms in plated compared to suspended PHH was confirmed. Importantly, we found a significant loss in CYP2C19 and CYP2B6 in HLM, activity being lower than in intact cells. Taken together, these findings implicate that, dependent on the UGT or CYP isoforms involved in the metabolism of a given compound, the outcome of metabolic assays is strongly dependent on the choice of the in vitro system. The currently described UGT- and CYP- activity profiling method can be used as a standard assay in intact cells and can especially aid in reaction phenotyping of in vitro systems for which a limited number of cells are available.

Are some people at increased risk of paracetamol-induced liver injury? A critical review of the literature

Purpose

Paracetamol is one of the world’s most commonly used drugs. In overdose, it is well established to be hepatotoxic. The aim of this review was to identify factors that have been, or actually are, associated with the development of liver injury after paracetamol exposure in humans.

Method

Google Scholar and PubMed were searched on various dates between December 2016 and March 2017. Papers identified had their references analysed for further studies that might be relevant.

Results

At the time of writing, there was little good quality clinical evidence—from studies of paracetamol overdose or therapeutic use—to suggest that any groups of people are relatively protected from, or are at greater risk of, liver injury. The factors that were historically used to indicate higher risk in the UK have no good quality clinical evidence to support their re-introduction into clinical practice. The safe (and still effective) oral dose of paracetamol in patients weighing less than 50 kg has not been established.

Conclusion

There is no patient group that is unequivocally at elevated risk of paracetamol-induced liver toxicity. We propose two clinical scenarios that warrant further research. Firstly, there is a need to establish whether the dose of paracetamol should be reduced in patients with low body weight. Secondly, if or when genomic information regarding individual patients becomes readily available to inform prescribing, we propose the contribution of the genome to paracetamol toxicity should be re-investigated with robustly designed studies. Such studies could enhance the safe use of one of the most frequently taken drugs.

Electronic supplementary material

The online version of this article (10.1007/s00228-017-2356-6) contains supplementary material, which is available to authorized users.

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.

Transcriptional Regulation of Human UDP-Glucuronosyltransferase 2B10 by Farnesoid X Receptor in Human Hepatoma HepG2 Cells

Little is known about transcriptional regulators of UDP-glucuronosyltransferase 2B10 (UGT2B10), an enzyme known to glucuronidate many chemicals and drugs such as nicotine and tricyclic antidepressants. Here, we uncovered that UGT2B10 was transcriptionally regulated by farnesoid X receptor (FXR), the bile acid sensing nuclear receptor. GW4064 and chenodeoxycholic acid (two specific FXR agonists) treatment of HepG2 cells led to a significant increase in the mRNA level of UGT2B10. The treated cells also showed enhanced glucuronidation activities toward amitriptyline (an UGT2B10 probe substrate). In reporter gene assays, the extent of UGT2B10 activation by the FXR agonists was positively correlated with the amount of cotransfected FXR. Consistently, knockdown of FXR by shRNA attenuated the induction effect on UGT2B10 expression. Furthermore, a combination of electrophoretic mobility shift assay and chromatin immunoprecipitation showed that the FXR receptor trans-activated UGT2B10 through its specific binding to the -209- to -197-bp region (an IR1 element) of the UGT2B10 promoter. In summary, our results for the first time established FXR as a transcriptional regulator of human UGT2B10.

Integrating Epigenomics into the Understanding of Biomedical Insight

Epigenetics is one of the most rapidly expanding fields in biomedical research, and the popularity of the high-throughput next-generation sequencing (NGS) highlights the accelerating speed of epigenomics discovery over the past decade. Epigenetics studies the heritable phenotypes resulting from chromatin changes but without alteration on DNA sequence. Epigenetic factors and their interactive network regulate almost all of the fundamental biological procedures, and incorrect epigenetic information may lead to complex diseases. A comprehensive understanding of epigenetic mechanisms, their interactions, and alterations in health and diseases genome widely has become a priority in biological research. Bioinformatics is expected to make a remarkable contribution for this purpose, especially in processing and interpreting the large-scale NGS datasets. In this review, we introduce the epigenetics pioneering achievements in health status and complex diseases; next, we give a systematic review of the epigenomics data generation, summarize public resources and integrative analysis approaches, and finally outline the challenges and future directions in computational epigenomics.

Hepatic expression of transcription factors affecting developmental regulation of UGT1A1 in the Han Chinese population

PURPOSE

Complete or partial inactivity of UGT1A1, the unique enzyme responsible for bilirubin glucuronidation, is commonly associated with hyperbilirubinemia. We investigated the dynamic expression of UGT1A1, and that of the transcription factors (TFs) involved in its developmental regulation, during human hepatic growth in Han Chinese individuals.

METHODS

Eighty-eight prenatal, pediatric, and adult liver samples were obtained from Han Chinese individuals. Quantitative real-time polymerase chain reaction was used to evaluate mRNA expression of UGT1A1 and TFs including PXR, CAR, HNF1A, HNF4A, PPARA, etc. UGT1A1 protein levels and metabolic activity were determined by western blotting and high-performance liquid chromatography. Direct sequencing was employed to genotype UGT1A1*6 (211G˃A) and UGT1A1*28 (TA6˃TA7) polymorphisms.

RESULTS

UGT1A1 expression was minimal in prenatal samples, but significantly elevated during pediatric and adult stages. mRNA and protein levels and metabolic activity were prominently increased (120-, 20-, and 10-fold, respectively) in pediatric and adult livers compared to prenatal samples. Furthermore, expression did not differ appreciably between pediatric and adult periods. Dynamic expression of TFs, including PXR, CAR, HNF1A, HNF4A, and PPARA, was consistent with UGT1A1 levels at each developmental stage. A pronounced correlation between expression of these TFs and that of UGT1A1 (P < 0.001) was observed. Moreover, UGT1A1*6 and UGT1A1*28 polymorphisms reduced levels of UGT1A1 by up to 40-60 %.

CONCLUSIONS

Hepatic expression of transcription factors is associated with developmental regulation of UGT1A1 in the Han Chinese population. Moreover, UGT1A1 polymorphisms are associated with reduced expression of UGT1A1 mRNA and protein, as well as enzyme activity.

Emerging role of NRF2 in chemoresistance by regulating drug-metabolizing enzymes and efflux transporters

Chemoresistance is a disturbing barrier in cancer therapy, which always results in limited therapeutic options and unfavorable prognosis. Nuclear factor E2-related factor 2 (NRF2) controls the expression of genes encoding cytoprotective enzymes and transporters that protect against oxidative stress and electrophilic injury to maintain intrinsic redox homeostasis. However, recent studies have demonstrated that aberrant activation of NRF2 due to genetic and/or epigenetic mutations in tumor contributes to the high expression of phase I and phase II drug-metabolizing enzymes, phase III transporters, and other cytoprotective proteins, which leads to the decreased therapeutic efficacy of anticancer drugs through biotransformation or extrusion during chemotherapy. Therefore, a better understanding of the role of NRF2 in regulation of these enzymes and transporters in tumors is necessary to find new strategies that improve chemotherapeutic efficacy. In this review, we summarized the recent findings about the chemoresistance-promoting role of NRF2, NRF2-regulated phase I and phase II drug-metabolizing enzymes, phase III drug efflux transporters, and other cytoprotective genes. Most importantly, the potential of NRF2 was proposed to counteract drug resistance in cancer treatment.

Importance of detoxifying enzymes in differentiating fibrotic development between SHRSP5/Dmcr and SHRSP rats

OBJECTIVES

High-fat and -cholesterol diet (HFC) induced fibrotic steatohepatitis in stroke-prone spontaneously hypertensive rat (SHRSP) 5/Dmcr, the fifth substrain from SHRSP, by dysregulating bile acid (BA) kinetics. This study aimed to clarify the histopathological and BA kinetic differences in HFC-induced fibrosis between SHRSP5/Dmcr and SHRSP.

METHODS

Ten-week-old male SHRSP5/Dmcr and SHRSP were randomly allocated to groups and fed with either control diet or HFC for 2 and 8 weeks. The liver histopathology, biochemical features, and molecular signaling involved in BA kinetics were measured.

RESULTS

HFC caused more severe hepatocyte ballooning, macrovesicular steatosis and fibrosis in SHRSP5/Dmcr than in SHRSP. It was noted that fibrosis was disproportionately formed in retroperitoneal side of both strains. As for BA kinetics, HFC greatly increased the level of Cyp7a1 and Cyp7b1 to the same degree in both strains at 8 weeks, while multidrug resistance-associated protein 3 was greater in SHRSP5/Dmcr than SHRSP. The diet decreased the level of bile salt export pump by the same degree in both strains, while constitutive androstane receptor, pregnane X receptor, and UDP-glucuronosyltransferase activity more prominent in SHRSP5/Dmcr than SHRSP at 8 weeks. In the fibrosis-related genes, only expression of collagen, type I, alpha 1 mRNA was greater in SHRSP5/Dmcr than SHRSP.

CONCLUSIONS

The greater progression of fibrosis in SHRSP5/Dmcr induced by HFC may be due to greater suppression of UDP-glucuronosyltransferase activity detoxifying toxicants, such as hydrophobic BAs.

4-Methylumbelliferone Diminishes Catabolically Activated Articular Chondrocytes and Cartilage Explants via a Mechanism Independent of Hyaluronan Inhibition

Depletion of the cartilage proteoglycan aggrecan is one of the earliest events that occurs in association with osteoarthritis. This loss is often accompanied by a coordinate loss in another glycosaminoglycan, hyaluronan. Chondrocytes experimentally depleted of cell-associated hyaluronan respond by switching to a pro-catabolic metabolism that includes enhanced production of endogenous inflammatory mediators and increased synthesis of matrix metalloproteinases. Hyaluronan turnover is also increased. Together, such a response provides for possible establishment of a self-perpetuating spiral of events that maintains or prolongs the pro-catabolic state. Chondrocytes or cartilage can also be activated by treatment with pro-inflammatory cytokines and mediators such as IL-1β, TNFα, LPS, fibronectin fragments, and hyaluronan oligosaccharides. To determine the mechanism of chondrocyte activation due to hyaluronan loss, a depletion method was required that did not include degrading the hyaluronan. In recent years, several laboratories have used the coumarin derivative, 4-methylumbelliferone, as a potent inhibitor of hyaluronan biosynthesis, due in part to its ability to sequester intracellular UDP-glucuronic acid and inhibition of hyaluronan synthase transcription. However, contrary to our expectation, although 4-methylumbelliferone was indeed an inhibitor of hyaluronan biosynthesis, this depletion did not give rise to an activation of chondrocytes or cartilage. Rather, 4-methylumbelliferone directly and selectively blocked gene products associated with the pro-catabolic metabolic state of chondrocytes and did so through a mechanism preceding and independent of hyaluronan inhibition. These data suggest that 4-methylumbelliferone has additional useful applications to block pro-inflammatory cell activation events but complicates how it is used for defining functions related to hyaluronan.

Paracetamol decreases steady-state exposure to lamotrigine by induction of glucuronidation in healthy subjects

AIM

Patients receiving lamotrigine therapy frequently use paracetamol concomitantly. While one study suggests a possible, clinically relevant drug-drug interaction, practical recommendations of the concomitant use are inconsistent. We performed a systematic pharmacokinetic study in healthy volunteers to quantify the effect of 4 day treatment with paracetamol on the metabolism of steady-state lamotrigine.

METHODS

Twelve healthy, male volunteers participated in an open label, sequential interaction study. Lamotrigine was titrated to steady-state (100 mg daily) over 36 days, and blood and urine sampling was performed in a non-randomized order with and without paracetamol (1 g four times daily). The primary endpoint was change in steady-state area under the plasma concentration-time curve of lamotrigine. Secondary endpoints were changes in total apparent oral clearance, renal clearance, trough concentration of lamotrigine and formation clearance of lamotrigine glucuronide conjugates.

RESULTS

Co-administration of lamotrigine and paracetamol decreased the steady-state area under the plasma concentration-time curve of lamotrigine by 20% (95% CI 10%, 25%; P < 0.001) from 166 to 127 μmol l(-1) . Concomitant administration of paracetamol increased the formation clearance of lamotrigine glucuronide conjugates by 45% (95% CI 18%, 79%, P = 0.005) from 1.7 to 2.8 l h(-1) , while the trough value of lamotrigine was reduced by 25% (95% CI 12%, 36%, P = 0.003) from 5.3 to 3.9 μmol l(-1) .

CONCLUSION

Paracetamol statistically significantly induced steady-state lamotrigine glucuronidation, resulting in a 20% decrease in total systemic exposure and a 25% decrease in trough value of lamotrigine. This interaction may be of clinical relevance in some patients.

The role of glucuronidation in drug resistance

The final therapeutic effect of a drug candidate, which is directed to a specific molecular target strongly depends on its absorption, distribution, metabolism and excretion (ADME). The disruption of at least one element of ADME may result in serious drug resistance. In this work we described the role of one element of this resistance: phase II metabolism with UDP-glucuronosyltransferases (UGTs). UGT function is the transformation of their substrates into more polar metabolites, which are better substrates for the ABC transporters, MDR1, MRP and BCRP, than the native drug. UGT-mediated drug resistance can be associated with (i) inherent overexpression of the enzyme, named intrinsic drug resistance or (ii) induced expression of the enzyme, named acquired drug resistance observed when enzyme expression is induced by the drug or other factors, as food-derived compounds. Very often this induction occurs via ligand binding receptors including AhR (aryl hydrocarbon receptor) PXR (pregnane X receptor), or other transcription factors. The effect of UGT dependent resistance is strengthened by coordinate action and also a coordinate regulation of the expression of UGTs and ABC transporters. This coupling of UGT and multidrug resistance proteins has been intensively studied, particularly in the case of antitumor treatment, when this resistance is "improved" by differences in UGT expression between tumor and healthy tissue. Multidrug resistance coordinated with glucuronidation has also been described here for drugs used in the management of epilepsy, psychiatric diseases, HIV infections, hypertension and hypercholesterolemia. Proposals to reverse UGT-mediated drug resistance should consider the endogenous functions of UGT.

The emerging role of the androgen receptor in bladder cancer

Men are three to four times more likely to get bladder cancer than women. The gender disparity characterizing bladder cancer diagnoses has been investigated. One hypothesis is that androgen receptor (AR) signaling is involved in the etiology and progression of this disease. Although bladder cancer is not typically described as an endocrine-related malignancy, it has become increasingly clear that AR signaling plays a role in bladder tumors. This review summarizes current findings regarding the role of the AR in bladder cancer. We discuss work demonstrating AR expression in bladder cancer and its role in promoting formation and progression of tumors. Additionally, we discuss the therapeutic potential of targeting the AR in this disease.

Xenobiotic Metabolism in Mice Lacking the UDP-Glucuronosyltransferase 2 Family

UDP-Glucuronosyltransferases (UGTs) conjugate a glucuronyl group from glucuronic acid to a wide range of lipophilic substrates to form a hydrophilic glucuronide conjugate. The glucuronide generally has decreased bioactivity and increased water solubility to facilitate excretion. Glucuronidation represents an important detoxification pathway for both endogenous waste products and xenobiotics, including drugs and harmful industrial chemicals. Two clinically significant families of UGT enzymes are present in mammals: UGT1s and UGT2s. Although the two families are distinct in gene structure, studies using recombinant enzymes have shown considerable overlap in their ability to glucuronidate many substrates, often obscuring the relative importance of the two families in the clearance of particular substrates in vivo. To address this limitation, we have generated a mouse line, termed ΔUgt2, in which the entire Ugt2 gene family, extending over 609 kilobase pairs, is excised. This mouse line provides a means to determine the contributions of the two UGT families in vivo. We demonstrate the utility of these animals by defining for the first time the in vivo contributions of the UGT1 and UGT2 families to glucuronidation of the environmental estrogenic agent bisphenol A (BPA). The highest activity toward this chemical is reported for human and rodent UGT2 enzymes. Surprisingly, our studies using the ΔUgt2 mice demonstrate that, while both UGT1 and UGT2 isoforms can conjugate BPA, clearance is largely dependent on UGT1s.

Quantification of the impact of enzyme-inducing antiepileptic drugs on irinotecan pharmacokinetics and SN-38 exposure

The population pharmacokinetic model reported here was developed using data from 2 phase 2 trials of irinotecan for treatment of malignant glioma to quantify the impact of concomitant therapy with enzyme-inducing antiepileptic drugs (EIAEDs) on irinotecan pharmacokinetics. Patients received weekly irinotecan doses of 100 to 400 mg/m(2) , and plasma samples were collected and analyzed for irinotecan and its APC, SN-38, and SN-38G metabolites. Nonlinear mixed-effects modeling was employed for population pharmacokinetic analysis. Concomitant therapy with phenytoin, phenobarbital, or carbamazepine increased the clearances of irinotecan, SN-38, and SN-38G but not APC. SN-38 clearance was 2-fold higher with concomitant EIAED use, resulting in 40% lower SN-38 exposure. Evaluation of additional covariates revealed no clinically relevant effects of sex or concomitant corticosteroid use. The population pharmacokinetic model suggests that a 1.7-fold increase in irinotecan dose may compensate for decreases in SN-38 exposure in the presence of concomitant EIAEDs. Although slightly more conservative, this dose adjustment is consistent with those recommended based on increases in the maximally tolerated dose for malignant glioma patients receiving EIAEDs and may be an appropriate starting point for further investigation when extrapolating to other cancer types or alternative regimens.

Characterization of in vitro metabolites of cudratricusxanthone A in human liver microsomes

Cudratricusxanthone A (CTXA), isolated from the roots of Cudrania tricuspidata, exhibits several biological activities; however, metabolic biotransformation was not investigated. Therefore, metabolites of CTXA were investigated and the major metabolic enzymes engaged in human liver microsomes (HLMs) were characterized using liquid chromatography-tandem mass spectrometry (LC-MS/MS). CTXA was incubated with HLMs or human recombinant CYPs and UGTs, and analysed by an LC-MS/MS equipped electrospray ionization (ESI) to qualify and quantify its metabolites. In total, eight metabolites were identified: M1-M4 were identified as mono-hydroxylated metabolites during Phase I, and M5-M8 were identified as O-glucuronidated metabolites during Phase II in HLMs. Moreover, these metabolite structures and a metabolic pathway were identified by elucidation of MS(n) fragments and formation by human recombinant enzymes. M1 was formed by CYP2D6, and M2-M4 were generated by CYP1A2 and CYP3A4. M5-M8 were mainly formed by UGT1A1, respectively. While investigating the biotransformation of CTXA, eight metabolites of CTXA were identified by CYPs and UGTs; these data will be valuable for understanding the in vivo metabolism of CTXA.

Identifying and applying a highly selective probe to simultaneously determine the O-glucuronidation activity of human UGT1A3 and UGT1A4

Glucuronidation mediated by uridine 5′-diphospho (UDP)-glucuronosyltransferase is an important detoxification pathway. However, identifying a selective probe of UDP- glucuronosyltransferase is complicated because of the significant overlapping substrate specificity displayed by the enzyme. In this paper, desacetylcinobufagin (DACB) 3-O- and 16-O-glucuronidation were found to be isoform-specific probe reactions for UGT1A4 and UGT1A3, respectively. DACB was well characterized as a probe for simultaneously determining the catalytic activities of O-glucuronidation mediated by UGT1A3 and UGT1A4 from various enzyme sources, through a sensitive analysis method.

Posttranscriptional regulation of uridine diphosphate glucuronosyltransferases

INTRODUCTION

The uridine diphosphate (UDP)-glucuronosyltransferase (UGT) superfamily of enzymes (EC 2.4.1.17) conjugates glucuronic acid to an aglycone substrate to make them more polar and readily excreted. In general, this reaction terminates the activities of chemicals, drugs and toxins, although occasionally a more active or toxic species is produced.

AREAS COVERED

In addition to their well-known transcriptional responsiveness, UGTs are also regulated by posttranscriptional mechanisms. Here, the authors review these mechanisms, including latency, modulation of co-substrate accessibility and binding, dimerization and oligomerization, protein-protein interactions, allosteric inhibition and activation, posttranslational structural and functional modifications and developmental switching for UGTs.

EXPERT OPINION

Posttranscriptional regulation of UGTs has traditionally received less attention than nuclear regulation, in part because mechanisms involving ribosomes and endoplasmic reticula are challenging to investigate. Most promising of the posttranscriptional mechanisms reviewed are likely to be effects on co-substrate (UDP-glucuronic acid) transport and availability and structure-function changes to UGT proteins through, for example, glycosylation and phosphorylation. Although classical biochemistry continues to illuminate many aspects of UGT function, advances in proteomics and structural biology are beginning to assist in the determination of posttranscriptional regulation mechanisms for UGTs.

In vivo and in vitro metabolites from the main diester and monoester diterpenoid alkaloids in a traditional chinese herb, the aconitum species

Diester diterpenoid alkaloids (DDAs), such as aconitine (AC), mesaconitine (MA), and hypaconitine (HA), are both pharmacologically active compounds and toxic ingredients in a traditional Chinese herb, the Aconitum species. Many DDA metabolism studies have been performed to explore mechanisms for reducing toxicity in these compounds and in Aconitum species extracts for safe clinical administration. In this review, we summarize recent progress on the metabolism of toxic AC, MA, and HA and corresponding monoester diterpenoid alkaloids (MDAs) in the gastrointestinal tract and liver in different animal species and humans in vivo and/or in vitro, where these alkaloids are primarily metabolized by cytochrome P450 enzymes, carboxylesterases, and intestinal bacteria, which produces phase I metabolites, ester hydrolysed products, and lipoalkaloids. Furthermore, we classify metabolites detected in the blood and urine, where the aforementioned metabolites are absorbed and excreted. Less toxic MDAs and nontoxic alcohol amines are the primary DDA metabolites detected in the blood. Most other DDAs metabolites produced in the intestine and liver detected in the urine have not been reported in the blood. We propose an explanation for this nonconformity. Finally, taking AC, for instance, we generalize a process of toxicity reduction in the body after oral AC administration for the first time.

Placental profiling of UGT1A enzyme expression and activity and interactions with preeclampsia at term

Placental UDP-glucuronosyltransferase (UGT) enzymes have critical roles in hormone, nutrient, chemical balance and fetal exposure during pregnancy. Placental UGT1A isoforms were profiled and differences between preeclamptic (PE) and non-PE placental UGT expression determined. In third trimester villous placenta, UGT1A1, 1A4, 1A6 and 1A9 were expressed and active in all specimens (n = 10), but UGT1A3, 1A5, 1A7, 1A8 and 1A10 were absent. The UGT1A activities were comparable to human liver microsomes per milligram, but placental microsome yields were only 2 % of liver (1 mg/g of tissue vs. 45 mg/g of tissue). For successful PCR, placental collection and processing within 60 min from delivery, including DNAse and ≥300 ng of RNA in reverse transcription were essential and snap freezing in liquid nitrogen immediately was the best preservation method. Although UGT1A6 mRNA was lower in PE (P < 0.001), there were no other significant effects on UGT mRNA, protein or activities. A more comprehensive tissue sample set is required for confirmation of PE interactions with UGT. Placental UGT1A enzyme expression patterns are similar to the liver and a detoxicative role for placental UGT1A is inferred.