Regulation of the human bile acid UDP-glucuronosyltransferase 1A3 by the farnesoid X receptor and bile acids

Bile acid metabolism and signaling, the microbiota, and metabolic disease

The diversity, composition, and function of the bacterial community inhabiting the human gastrointestinal tract contributes to host health through its role in producing energy or signaling molecules that regulate metabolic and immunologic functions. Bile acids are potent metabolic and immune signaling molecules synthesized from cholesterol in the liver and then transported to the intestine where they can undergo metabolism by gut bacteria. The combination of host- and microbiota-derived enzymatic activities contribute to the composition of the bile acid pool and thus there can be great diversity in bile acid composition that depends in part on the differences in the gut bacteria species. Bile acids can profoundly impact host metabolic and immunological functions by activating different bile acid receptors to regulate signaling pathways that control a broad range of complex symbiotic metabolic networks, including glucose, lipid, steroid and xenobiotic metabolism, and modulation of energy homeostasis. Disruption of bile acid signaling due to perturbation of the gut microbiota or dysregulation of the gut microbiota-host interaction is associated with the pathogenesis and progression of metabolic disorders. The metabolic and immunological roles of bile acids in human health have led to novel therapeutic approaches to manipulate the bile acid pool size, composition, and function by targeting one or multiple components of the microbiota-bile acid-bile acid receptor axis.

UDP-glucuronosyltransferases mediate coffee-associated reduction of liver fibrosis in bile duct ligated humanized transgenic UGT1A mice

BACKGROUND

Coffee consumption has been shown to reduce the risk of liver fibrosis and is capable of inducing human UDP-glucuronosyltransferase (UGT) 1A genes. UGT1A enzymes act as indirect antioxidants catalyzing the elimination of reactive metabolites, which in turn are potent initiators of profibrotic mechanisms. The aim of this study was to analyze the role of UGT1A genes as effectors of the protective properties of coffee in bile duct ligation (BDL) induced liver fibrosis.

METHODS

Fourteen days BDL with and without coffee pre- and co-treatment was performed in htgUGT1A-WT and htgUGT1A-SNP mice. Hepatic UGT1A mRNA expression levels, serum bilirubin and aminotransferase activities were determined. Liver fibrosis was assessed by collagen deposition, computational analysis of Sirius red tissue staining and expression of profibrotic marker genes. Oxidative stress was measured by hepatic peroxidase concentrations and immunofluorescence staining.

RESULTS

UGT1A transcription was differentially activated in the livers of htgUGT1A-WT mice after BDL, in contrast to a reduced or absent induction in the presence of SNPs. Co-treated (coffee + BDL) htgUGT1A-WT-mice showed significantly increased UGT1A expression and protein levels and a considerably higher induction compared to water drinking WT mice (BDL), whereas in co-treated htgUGT1A-SNP mice absolute expression levels remained below those observed in htgUGT1A-WT mice. Collagen deposition, oxidative stress and the expression of profibrotic markers inversely correlated with UGT1A expression levels in htgUGT1A-WT and SNP mice after BDL and coffee + BDL co-treatment.

CONCLUSIONS

Coffee exerts hepatoprotective and antioxidative effects via activation of UGT1A enzymes. Attenuated hepatic fibrosis as a result of coffee-mediated UGT1A induction during cholestasis was detected, while the protective action of coffee was lower in a common low-function UGT1A SNP haplotype present in 10% of the Caucasian population. This study suggests that coffee consumption might constitute a potential strategy to support the conventional treatment of cholestasis-related liver diseases.

Tetrahydrofurofuranoid Lignans, Eudesmin, Fargesin, Epimagnolin A, Magnolin, and Yangambin Inhibit UDP-Glucuronosyltransferase 1A1 and 1A3 Activities in Human Liver Microsomes

Eudesmin, fargesin, epimagnolin A, magnolin, and yangambin are tetrahydrofurofuranoid lignans with various pharmacological activities found in Magnoliae Flos. The inhibition potencies of eudesmin, fargesin, epimagnolin A, magnolin, and yangambin on six major human uridine 5'-diphospho-glucuronosyltransferase (UGT) activities in human liver microsomes were evaluated using liquid chromatography-tandem mass spectrometry and cocktail substrates. Eudesmin, fargesin, epimagnolin A, magnolin, and yangambin inhibited UGT1A1 and UGT1A3 activities, but showed negligible inhibition of UGT1A4, UGT16, UGT1A9, and UGT2B7 activities at 200 μM in pooled human liver microsomes. Moreover, eudesmin, fargesin, epimagnolin A, magnolin, and yangambin noncompetitively inhibited UGT1A1-catalyzed SN38 glucuronidation with K_i values of 25.7, 25.3, 3.6, 26.0, and 17.1 μM, respectively, based on kinetic analysis of UGT1A1 inhibition in pooled human liver microsomes. Conversely, the aforementioned tetrahydrofurofuranoid lignans competitively inhibited UGT1A3-catalyzed chenodeoxycholic acid 24-acyl-glucuronidation with 39.8, 24.3, 15.1, 37.6, and 66.8 μM, respectively in pooled human liver microsomes. These in vitro results suggest the necessity of evaluating whether the five tetrahydrofurofuranoid lignans can cause drug-drug interactions with UGT1A1 and UGT1A3 substrates in vivo.

The coffee ingredients caffeic acid and caffeic acid phenylethyl ester protect against irinotecan-induced leukopenia and oxidative stress response

Background and Purpose

Irinotecan, used in colorectal cancer therapy, is metabolized by glucuronidation involving different UDP‐glucuronosyltransferase (UGT)1A isoforms leading to facilitated elimination from the body. Individuals homozygous for the genetic variants UGT1A1*28 (Gilbert syndrome) and UGT1A7*3 are more susceptible to irinotecan side effects, severe diarrhoea and leukopenia. The aim of this study was to investigate the protective effects and active constituents of coffee during irinotecan therapy using humanized transgenic (htg)UGT1A‐WT and htgUGT1A‐SNP (carry UGT1A1*28 and UGT1A7*3 polymorphisms) mice.

Experimental Approach

HtgUGT1A mice were pretreated with coffee or caffeic acid (CA) + caffeic acid phenylethyl ester (CAPE) and injected with irinotecan. The effects of coffee and CA + CAPE were investigated using reporter gene assays, immunoblot, TaqMan‐PCR, siRNA analyses and blood counts.

Key Results

Only the combination of the two coffee ingredients, CA and CAPE, mediates protective effects of coffee in a model of irinotecan toxicity by activation of UGT1A genes. Coffee and CA + CAPE significantly increased UGT1A expression and activity along with SN‐38 glucuronide excretion in irinotecan‐injected htgUGT1A mice, resulting in significant improvement of leukopenia, intestinal oxidative stress and inflammation.

Conclusion and Implications

In this study, we identify the compounds responsible for mediating the previously reported coffee‐induced activation of UGT1A gene expression. CA and CAPE represent key factors for the protective properties of coffee which are capable of reducing irinotecan toxicity, exerting antioxidant and protective effects. Provided that CA + CAPE do not affect irinotecan efficacy, they might represent a novel strategy for the treatment of irinotecan toxicity.

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.

Inhibition of UDP-glucuronosyltransferases (UGTs) by bromophenols (BPs)

Bromophenols (BPs) are important organic compounds which have become dominant pollutants during these years. Our present study investigated the potential inhibition behaviour of BPs on the activity of one of the most important phase II drug-metabolizing enzymes (DMEs), UDP-glucuronosyltransferases (UGTs). Recombinant UDP-glucuronosyltransferases (UGTs)-catalyzed glucuronidation of 4-methylumbelliferone (4-MU) was utilized as the probe reaction. 100 μM of BPs was utilized as the inhibition screening concentrations, and the complete inhibition profile of UGT isoforms by BPs was obtained. UGT1A7 was the most vulnerable UGT isoform towards BPs. Some structure-activity relationship for the inhibition of UGTs by BPs was found, and this relationship can be furtherly explained by the hydrophobic contacts of BPs with the activity cavity of UGTs using in silico docking method. The inhibition kinetics determination showed that the inhibition kinetic parameter K_i value was calculated to be 2.85, 3.99 and 31.00 μM for the inhibition of UGT1A3, UGT1A7, and UGT2B7 by representative BPs, 2,4,6-TBP. Combined with in vivo exposure concentration of 2,4,6-TBP, in vitro-in vivo extrapolation (IVIVE) was employed to demonstrate the moderate possibility for the inhibition of UGT1A3 and UGT1A7 by 2,4,6-TBP. In conclusion, our study gave the full description towards the inhibition of BPs towards UGT isoforms, which will provide a new perspective for elucidating the toxicity mechanism of bromophenols (BPs).

The UDP-Glycosyltransferase (UGT) Superfamily: New Members, New Functions, and Novel Paradigms

UDP-glycosyltransferases (UGTs) catalyze the covalent addition of sugars to a broad range of lipophilic molecules. This biotransformation plays a critical role in elimination of a broad range of exogenous chemicals and by-products of endogenous metabolism, and also controls the levels and distribution of many endogenous signaling molecules. In mammals, the superfamily comprises four families: UGT1, UGT2, UGT3, and UGT8. UGT1 and UGT2 enzymes have important roles in pharmacology and toxicology including contributing to interindividual differences in drug disposition as well as to cancer risk. These UGTs are highly expressed in organs of detoxification (e.g., liver, kidney, intestine) and can be induced by pathways that sense demand for detoxification and for modulation of endobiotic signaling molecules. The functions of the UGT3 and UGT8 family enzymes have only been characterized relatively recently; these enzymes show different UDP-sugar preferences to that of UGT1 and UGT2 enzymes, and to date, their contributions to drug metabolism appear to be relatively minor. This review summarizes and provides critical analysis of the current state of research into all four families of UGT enzymes. Key areas discussed include the roles of UGTs in drug metabolism, cancer risk, and regulation of signaling, as well as the transcriptional and posttranscriptional control of UGT expression and function. The latter part of this review provides an in-depth analysis of the known and predicted functions of UGT3 and UGT8 enzymes, focused on their likely roles in modulation of levels of endogenous signaling pathways.

Comparison of the inhibition potential of parthenolide and micheliolide on various UDP-glucuronosyltransferase isoforms

Parthenolide (PTL) and micheliolide (MCL) are sesquiterpene lactones with similar structures, and both of them have been reported to exhibit multiple biochemical and pharmacological activities. This study aims to investigate the inhibition of these two compounds on the activity of UDP-glucuronosyltransferases (UGTs). In vitro incubation mixture for recombinant UGTs-catalyzed glucuronidation metabolism of 4-methylumbelliferone (4-MU) was utilized to investigate the inhibition potential. Inhibition kinetics (including inhibition type and parameters) were determined, and in silico docking was employed to elucidate the inhibition difference between PTL and MCL on UGT1A1. MCL showed no inhibition toward all the UGT isoforms, and PTL showed strong inhibition toward UGT1A1. The half-maximal inhibitory concentration (IC₅₀) of PTL on the activity of UGT1A1 was determined to be 64.4 μM. Inhibition kinetics determination showed that PTL exerted noncompetitive inhibition toward UGT1A1, and the inhibition kinetic constant (K_i) was determined to be 12.1 μM. In silico docking method has been employed to show that hydrogen bonds between PTL and the activity cavity of UGT1A1 contributed to the stronger inhibition of PTL on the activity of UGT1A1 than MCL. In conclusion, PTL can more easily induce drug-drug interaction (DDI) with clinical drugs mainly undergoing UGT1A1-catalyzed glucuronidation.

Dietary effects of Sideritis scardica "mountain tea" on human in vivo activities of xenobiotic metabolizing enzymes in healthy subjects

Sideritis scardica(S. scardica) is an endemic plant of the Balkan Peninsula traditionally used as herbal tea for inflammation and gastric disorders. Aqueous herbal extracts may affect the activity of Phase I and II enzymes involved in xenobiotic metabolism. The purpose of the present study was to determine whether S. scardica decoction alters the activity of CYP1A2, CYP2A6, XO, NAT2 and UGT1A1/1A6 enzymes in humans. Fourteen healthy subjects consumed S. scardica decoction for six days. Enzyme phenotyping was assessed in saliva and urine using caffeine and paracetamol metabolite ratios as follows: CYP1A2: 17X/137X (saliva) and (AFMU+1U+1X)/17U, CYP2A6: 17U/(17U + 17X), XO: 1U/(1U+1X), NAT2: AFMU/(AFMU+1U+1X) and UGT1A1/1A6: glucuronidated/total paracetamol (urine). After S. scardica intake, CYP1A2 index was reduced by ∼16% and ∼8% in saliva (before: 0.54 ± 0.18, after: 0.46 ± 0.09; p = 0.08) and urine (before: 3.59 ± 0.52, after: 3.67 ± 0.78; p = 0.12), respectively. CYP2A6 index was significantly reduced only in males (before: 0.76 ± 0.08, after: 0.67 ± 0.07; p = 0.004), suggesting sexual dimorphism in CYP2A6 inhibition. There was no effect of Sideritis scardica treatment on XO, NAT2 or UGT1A1/1A6 indices. Usual consumption of the aerial parts of S. scardica decoction is unlikely to result in herb-drug interactions involving the enzymes studied, with the exception of potential herb-CYP2A6 substrate interaction in males.

In Vitro Inhibitory Effects of Synthetic Cannabinoid EAM-2201 on Cytochrome P450 and UDP-Glucuronosyltransferase Enzyme Activities in Human Liver Microsomes

EAM-2201, a synthetic cannabinoid, is a potent agonist of the cannabinoid receptors that is widely abused as an illicit recreational drug in combination with other drugs. To evaluate the potential of EAM-2201 as a perpetrator of drug–drug interactions, the inhibitory effects of EAM-2201 on major drug-metabolizing enzymes, cytochrome P450s (CYPs) and uridine 5′-diphospho-glucuronosyltransferases (UGTs) were evaluated in pooled human liver microsomes using liquid chromatography–tandem mass spectrometry (LC-MS/MS). EAM-2201 at doses up to 50 µM negligibly inhibited the activities of eight major human CYPs (1A2, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6 and 3A4) and five UGTs (1A1, 1A4, 1A6, 1A9 and 2B7) in human liver microsomes. EAM-2201 exhibited time-dependent inhibition of CYP2C8-catalyzed amodiaquine N-deethylation, CYP2C9-catalyzed diclofenac 4′-hydroxylation, CYP2C19-catalyzed [S]-mephenytoin 4′-hydroxylation and CYP3A4-catalyzed midazolam 1′-hydroxylation with K_i values of 0.54 µM (k_inact: 0.0633 min⁻¹), 3.0 µM (k_inact: 0.0462 min⁻¹), 3.8 µM (k_inact: 0.0264 min⁻¹) and 4.1 µM (k_inact: 0.0250 min⁻¹), respectively and competitively inhibited UGT1A3-catalyzed chenodeoxycholic acid 24-acyl-glucuronidation, with a K_i value of 2.4 µM. Based on these in vitro results, we conclude that EAM-2201 has the potential to trigger in vivo pharmacokinetic drug interactions when co-administered with substrates of CYP2C8, CYP2C9, CYP2C19, CYP3A4 and UGT1A3.

Inhibition of UDP-glucuronosyltransferases (UGTs) by phthalate monoesters

Phthalate monoesters are important metabolites of phthalate esters (PAEs) which have been extensively utilized in industry. This study aims to investigate the inhibition of phthalate monoesters on the activity of various isoforms of UDP-glucuronosyltransferases (UGTs), trying to elucidate the toxicity mechanism of environmental endocrine disruptors from the new perspectives. In vitro recombinant UGTs-catalyzed glucuronidation of 4-methylumbelliferone (4-MU) was employed to evaluate 8 kinds of phthalate monoesters on 11 sorts of main human UGT isoforms. 100 μM phthalate monoesters exhibited negligible inhibition towards the activity of UGT1A1, UGT1A3, UGT1A6, UGT1A8, UGT1A10, UGT2B4, UGT2B7, UGT2B15 and UGT2B17. The activity of UGT1A7 was strongly inhibited by monoethylhexyl phthalate (MEHP), but slightly inhibited by all the other phthalate monoesters. UGT1A9 was broadly inhibited by monobenzyl phthalate (MBZP), monocyclohexyl phthalate (MCHP), MEHP, monohexyl phthalate (MHP) and monooctyl phthalate (MOP), respectively. MEHP exhibited competitive inhibition towards UGT1A7, and MBZP, MCHP, MEHP, MHP and MOP showed competitive inhibition towards UGT1A9. The inhibition kinetic parameters (K_i) were calculated to be 11.25 μM for MEHP-UGT1A7, and 2.13, 0.09, 1.17, 7.47, 0.16 μM for MBZP-UGT1A9, MCHP-UGT1A9, MEHP-UGT1A9, MHP-UGT1A9, MOP-UGT1A9, respectively. Molecular docking indicated that both hydrogen bonds formation and hydrophobic interactions significantly contributed to the interaction between phthalate monoesters and UGT isoforms. All these information will be beneficial for understanding the adverse effects of PAEs.

Comprehensive Pharmacogenomic Study Reveals an Important Role of UGT1A3 in Montelukast Pharmacokinetics

To identify the genetic basis of interindividual variability in montelukast exposure, we determined its pharmacokinetics and sequenced 379 pharmacokinetic genes in 191 healthy volunteers. An intronic single nucleotide variation (SNV), strongly linked with UGT1A3*2, associated with reduced area under the plasma concentration–time curve (AUC_0‐∞) of montelukast (by 18% per copy of the minor allele; P = 1.83 × 10⁻¹⁰). UGT1A3*2 was associated with increased AUC_0‐∞ of montelukast acyl‐glucuronide M1 and decreased AUC_0‐∞ of hydroxymetabolites M5R, M5S, and M6 (P < 10⁻⁹). Furthermore, SNVs in SLCO1B1 and ABCC9 were associated with the AUC_0‐∞ of M1 and M5R, respectively. In addition, a candidate gene analysis suggested that CYP2C8 and ABCC9 SNVs also affect the AUC_0‐∞ of montelukast. The found UGT1A3 and ABCC9 variants associated with increased expression of the respective genes in human liver samples. Montelukast and its hydroxymetabolites were glucuronidated by UGT1A3 in vitro. These results indicate that UGT1A3 plays an important role in montelukast pharmacokinetics, especially in UGT1A3*2 carriers.

Protective effects of coffee against oxidative stress induced by the tobacco carcinogen benzo[α]pyrene

AIMS

Coffee consumption has been epidemiologically associated with a lower risk for liver cirrhosis and cancer. UDP-glucuronosyltransferases (UGT1A) catalyze the detoxification of reactive metabolites thereby acting as indirect antioxidants. Aim of the study was to examine UGT1A regulation in response to Benzo[α]pyrene (BaP) to elucidate the potentially protective effects of coffee on BaP-induced oxidative stress and toxicity.

RESULTS

In cell culture (HepG2, KYSE70 cells) and in htgUGT1A-WT mice, UGT1A transcription was activated by BaP, while it was reduced or absent htgUGT1A-SNP (containing 10 commonly occurring UGT1A-SNPs) mice. siRNA-mediated knockdown identified aryl hydrocarbon receptor (AhR) and nuclear factor erythroid2-related factor-2 (Nrf2) as mediators of BaP-induced UGT1A upregulation. Exposure to coffee led to a reduction of BaP-induced production of reactive oxygen species in vitro and in htgUGT1A-WT and -SNP mice. After UGT1A silencing by UGT1A-specific siRNA in cell culture, the coffee-mediated reduction of ROS production was significantly impaired compared to UGT1A expressing cells.

CONCLUSION

A common UGT1A haplotype, prevalent in 9% (homozygous) of the White population, significantly impairs the expression of UGT1A enzymes in response to the putative tobacco carcinogen BaP and is likely to represent a significant risk factor for reduced detoxification and increased genotoxicity. Coffee was demonstrated to inhibit BaP-induced production of oxidative stress by UGT1A activation, and is therefore an attractive candidate for chemoprotection in risk groups for HCC or other tumors.

Inhibition of cytochrome P450 and uridine 5'-diphospho-glucuronosyltransferases by MAM-2201 in human liver microsomes

MAM-2201, a synthetic cannabinoid, is a potent agonist of the cannabinoid receptors and is increasingly used as an illicit recreational drug. The inhibitory effects of MAM-2201 on major drug-metabolizing enzymes such as cytochrome P450s (CYPs) and uridine 5'-diphospho-glucuronosyltransferases (UGTs) have not yet been investigated although it is widely abused, sometimes in combination with other drugs. We evaluated the inhibitory effects of MAM-2201 on eight major human CYPs (CYPs 1A2, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, and 3A4) and six UGTs (UGTs 1A1, 1A3, 1A4, 1A6, 1A9, and 2B7) of pooled human liver microsomes; we thus explored potential MAM-2201-induced drug interactions. MAM-2201 potently inhibited CYP2C9-catalyzed diclofenac 4'-hydroxylation, CYP3A4-catalyzed midazolam 1'-hydroxylation, and UGT1A3-catalyzed chenodeoxycholic acid 24-acyl-glucuronidation, with K _i values of 5.6, 5.4 and 5.0 µM, respectively. MAM-2201 exhibited mechanism-based inhibition of CYP2C8-catalyzed amodiaquine N-de-ethylation with K _i and k _inact values of 1.0 µM and 0.0738 min^-1, respectively. In human liver microsomes, MAM-2201 (50 µM) negligibly inhibited CYP1A2, CYP2A6, CYP2B6, CYP2C19, CYP2D6, UGT1A1, UGT1A4, UGT1A6, UGT1A9, and UGT2B7. Based on these in vitro results, we conclude that MAM-2201 has the potential to trigger in vivo pharmacokinetic drug interactions when co-administered with substrates of CYP2C8, CYP2C9, CYP3A4, and UGT1A3.

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.

AM-2201 Inhibits Multiple Cytochrome P450 and Uridine 5'-Diphospho-Glucuronosyltransferase Enzyme Activities in Human Liver Microsomes

AM-2201 is a synthetic cannabinoid that acts as a potent agonist at cannabinoid receptors and its abuse has increased. However, there are no reports of the inhibitory effect of AM-2201 on human cytochrome P450 (CYP) or uridine 5′-diphospho-glucuronosyltransferase (UGT) enzymes. We evaluated the inhibitory effect of AM-2201 on the activities of eight major human CYPs (1A2, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, and 3A4) and six major human UGTs (1A1, 1A3, 1A4, 1A6, 1A9, and 2B7) enzymes in pooled human liver microsomes using liquid chromatography–tandem mass spectrometry to investigate drug interaction potentials of AM-2201. AM-2201 potently inhibited CYP2C9-catalyzed diclofenac 4′-hydroxylation, CYP3A4-catalyzed midazolam 1′-hydroxylation, UGT1A3-catalyzed chenodeoxycholic acid 24-acyl-glucuronidation, and UGT2B7-catalyzed naloxone 3-glucuronidation with IC₅₀ values of 3.9, 4.0, 4.3, and 10.0 µM, respectively, and showed mechanism-based inhibition of CYP2C8-catalyzed amodiaquine N-deethylation with a K_i value of 2.1 µM. It negligibly inhibited CYP1A2, CYP2A6, CYP2B6, CYP2C19, CYP2D6, UGT1A1, UGT1A4, UGT1A6, and UGT1A9 activities at 50 μM in human liver microsomes. These in vitro results indicate that AM-2201 needs to be examined for potential pharmacokinetic drug interactions in vivo due to its potent inhibition of CYP2C8, CYP2C9, CYP3A4, UGT1A3, and UGT2B7 enzyme activities.

Role of farnesoid X receptor in cholestasis

The nuclear receptor farnesoid X receptor (FXR) plays an important role in physiological bile acid synthesis, secretion and transport. Defects of FXR regulation in these processes can cause cholestasis and subsequent pathological changes. FXR regulates the synthesis and uptake of bile acid via enzymes. It also increases bile acid solubility and elimination by promoting conjugation reactions and exports pump expression in cholestasis. The changes in bile acid transporters are involved in cholestasis, which can result from the mutations of transporter genes or acquired dysfunction of transport systems, such as inflammation-induced intrahepatic cholestasis. The modulation function of FXR in extrahepatic cholestasis is not identical to that in intrahepatic cholestasis, but the discrepancy may be reduced over time. In extrahepatic cholestasis, increasing biliary pressure can induce bile duct proliferation and bile infarcts, but the absence of FXR may ameliorate them. This review provides an update on the function of FXR in the regulation of bile acid metabolism, its role in the pathophysiological process of cholestasis and the therapeutic use of FXR agonists.

New insights into the risk of phthalates: Inhibition of UDP-glucuronosyltransferases

Wide utilization of phthalates-containing products results in the significant exposure of humans to these compounds. Many adverse effects of phthalates have been documented in rodent models, but their effects in humans exposed to these chemicals remain unclear until more mechanistic studies on phthalate toxicities can be carried out. To provide new insights to predict the potential adverse effects of phthalates in humans, the recent study investigated the inhibition of representative phthalates di-n-octyl ortho-phthalate (DNOP) and diphenyl phthalate (DPhP) towards the important xenobiotic and endobiotic-metabolizing UDP-glucuronosyltransferases (UGTs). An in vitro UGTs incubation system was employed to study the inhibition of DNOP and DPhP towards UGT isoforms. DPhP and DNOP weakly inhibited the activities of UGT1A1, UGT1A7, and UGT1A8. 100 µM of DNOP inhibited the activities of UGT1A3, UGT1A9, and UGT2B7 by 41.8% (p < 0.01), 45.6% (p < 0.01), and 48.8% (p < 0.01), respectively. 100 µM of DPhP inhibited the activity of UGT1A3, UGT1A6, and UGT1A9 by 81.8 (p < 0.001), 49.1% (p < 0.05), and 76.4% (p < 0.001), respectively. In silico analysis was used to explain the stronger inhibition of DPhP than DNOP towards UGT1A3 activity. Kinetics studies were carried our to determine mechanism of inhibition of UGT1A3 by DPhP. Both Dixon and Lineweaver-Burk plots showed the competitive inhibition of DPhP towards UGT1A3. The inhibition kinetic parameter (Ki) was calculated to be 0.89 µM. Based on the [I]/Ki standard ([I]/Ki < 0.1, low possibility; 1>[I]/Ki > 0.1, medium possibility; [I]/Ki > 1, high possibility), these studies predicted in vivo drug-drug interaction might occur when the plasma concentration of DPhP was above 0.089 µM. Taken together, this study reveales the potential for adverse effects of phthalates DNOP and DPhP as a result of UGT inhibition.

Strong Specific Inhibition of UDP-glucuronosyltransferase 2B7 by Atractylenolide I and III

Drug-metabolizing enzymes inhibition-based drug-drug interaction remains to be the key limiting factor for the research and development of efficient herbal components to become clinical drugs. The present study aims to determine the inhibition of uridine 5'-diphospho-glucuronosyltransferases (UGTs) isoforms by two important efficient herbal ingredients isolated from Atractylodes macrocephala Koidz, atractylenolide I and III. In vitro recombinant UGTs-catalysed glucuronidation of 4-methylumbelliferone was used to determine the inhibition capability and kinetics of atractylenolide I and III towards UGT2B7, and in silico docking method was employed to explain the possible mechanism. Atractylenolide I and III exhibited specific inhibition towards UGT2B7, with negligible influence towards other UGT isoforms. Atractylenolide I exerted stronger inhibition potential than atractylenolide III towards UGT2B7, which is attributed to the different hydrogen bonds and hydrophobic interactions. Inhibition kinetic analysis was performed for the inhibition of atractylenolide I towards UGT2B7. Inhibition kinetic determination showed that atractylenolide I competitively inhibited UGT2B7, and inhibition kinetic parameter (Ki) was calculated to be 6.4 μM. In combination of the maximum plasma concentration of atractylenolide I after oral administration of 50 mg/kg atractylenolide I, the area under the plasma concentration-time curve ration AUCi /AUC was calculated to be 1.17, indicating the highly possible drug-drug interaction between atractylenolide I and drugs mainly undergoing UGT2B7-catalysed metabolism.

Transcriptional regulation of human UDP-glucuronosyltransferase genes

Glucuronidation is an important metabolic pathway for many small endogenous and exogenous lipophilic compounds, including bilirubin, steroid hormones, bile acids, carcinogens and therapeutic drugs. Glucuronidation is primarily catalyzed by the UDP-glucuronosyltransferase (UGT) 1A and two subfamilies, including nine functional UGT1A enzymes (1A1, 1A3-1A10) and 10 functional UGT2 enzymes (2A1, 2A2, 2A3, 2B4, 2B7, 2B10, 2B11, 2B15, 2B17 and 2B28). Most UGTs are expressed in the liver and this expression relates to the major role of hepatic glucuronidation in systemic clearance of toxic lipophilic compounds. Hepatic glucuronidation activity protects the body from chemical insults and governs the therapeutic efficacy of drugs that are inactivated by UGTs. UGT mRNAs have also been detected in over 20 extrahepatic tissues with a unique complement of UGT mRNAs seen in almost every tissue. This extrahepatic glucuronidation activity helps to maintain homeostasis and hence regulates biological activity of endogenous molecules that are primarily inactivated by UGTs. Deciphering the molecular mechanisms underlying tissue-specific UGT expression has been the subject of a large number of studies over the last two decades. These studies have shown that the constitutive and inducible expression of UGTs is primarily regulated by tissue-specific and ligand-activated transcription factors (TFs) via their binding to cis-regulatory elements (CREs) in UGT promoters and enhancers. This review first briefly summarizes published UGT gene transcriptional studies and the experimental models and tools utilized in these studies, and then describes in detail the TFs and their respective CREs that have been identified in the promoters and/or enhancers of individual UGT genes.

Soybean greatly reduces valproic acid plasma concentrations: a food-drug interaction study

The aim of this study was to investigate the effects of soy on the pharmacokinetics and pharmacodynamics of valproic acid (VPA). In a preclinical study, rats were pretreated with two different amounts of soy extract for five days (150 mg/kg and 500 mg/kg), which resulted in decreases of 57% and 65% in the Cmax of VPA, respectively. AUC of VPA decreased to 83% and 70% in the soy pretreatment groups. Interestingly, the excretion rate of VPA glucuronide (VPAG) was higher in the soy-fed groups. Levels of UDP-glucuronosyltransferase (UGT) UGT1A3, UGT1A6, UGT2B7 and UGT2B15 were elevated in the soy-treated group, and GABA concentrations were elevated in the brain after VPA administration. However, this was less pronounced in soy extract pretreated group than for the untreated group. This is the first study to report the effects of soy pretreatment on the pharmacokinetics and pharmacodynamics of VPA in rodents.

The influence of bile acids homeostasis by cryptotanshinone-containing herbs

BACKGROUND

Herbs might affect the homeostasis of bile acids through influence of multiple metabolic pathways of bile acids.

OBJECTIVE

To investigate the inhibition of cryptotanshinone towards the glucuronidation of LCA, trying to indicate the possible influence of cryptotanshinone-containing herbs towards the homeostasis of bile acids.

METHODS

The LCA-3-glucuronidation and LCA-24-glucuronidation reaction was monitored by LC-MS.

RESULTS

Initial screening showed that 100 µM of cryptotanshinone inhibited LCA-24-glucuronidation and LCA-3-glucuronidation reaction activity by 82.6% and 79.1%, respectively. This kind of inhibition behaviour exerted cryptotanshinone concentrations-dependent and LCA concentrations-independent inhibition behaviour.

CONCLUSION

All these data indicated the possibility of cryptotanshinone's influence towards bile acids metabolism and homeostasis of bile acids.

A model of in vitro UDP-glucuronosyltransferase inhibition by bile acids predicts possible metabolic disorders

Increased levels of bile acids (BAs) due to the various hepatic diseases could interfere with the metabolism of xenobiotics, such as drugs, and endobiotics including steroid hormones. UDP-glucuronosyltransferases (UGTs) are involved in the conjugation and elimination of many xenobiotics and endogenous compounds. The present study sought to investigate the potential for inhibition of UGT enzymes by BAs. The results showed that taurolithocholic acid (TLCA) exhibited the strongest inhibition toward UGTs, followed by lithocholic acid. Structure-UGT inhibition relationships of BAs were examined and in vitro-in vivo extrapolation performed by using in vitro inhibition kinetic parameters (Ki) in combination with calculated in vivo levels of TLCA. Substitution of a hydrogen with a hydroxyl group in the R1, R3, R4, R5 sites of BAs significantly weakens their inhibition ability toward most UGTs. The in vivo inhibition by TLCA toward UGT forms was determined with following orders of potency: UGT1A4 > UGT2B7 > UGT1A3 > UGT1A1 ∼ UGT1A7 ∼ UGT1A10 ∼ UGT2B15. In conclusion, these studies suggest that disrupted homeostasis of BAs, notably taurolithocholic acid, found in various diseases such as cholestasis, could lead to altered metabolism of xenobiotics and endobiotics through inhibition of UGT enzymes.

Nuclear receptors and endobiotics glucuronidation: the good, the bad, and the UGT

The recent progresses in molecular biology and pharmacology approaches allowed the characterization of a series of nuclear receptors (NRs) as efficient regulators of uridine diphosphate glucuronosyltransferase (UGT) genes activity. These regulatory processes ensure an optimized UGT expression in response to specific endo- and/or exogenous stimuli. Many of these NRs are activated by endobiotics that also are substrates for UGTs. Thus, by activating their receptors, these endogenous substances control their own conjugation, leading to the concept that glucuronidation is an important part of feed-forward/feedback mechanisms by which bioactive molecules control their own concentrations. On the other hand, numerous studies have established the pharmacological relevance of NR-UGT regulatory pathways in the response to therapeutic ligands. The present review article aims at providing a comprehensive view of the physiological and pharmacological importance of the NR regulation of the expression and activity of endobiotics-conjugating UGT enzymes. Selected examples will illustrate how the organism profits from the feed-forward/feedback mechanisms involving NR-UGT pathways, but also how such regulatory processes are involved in the initiation and/or progression of several pathological situations. Finally, we will discuss how the present pharmacopeia involves NR-dependent regulation of endobiotics glucuronidation, and whether the unexploited NR-UGT axes could serve as pharmacological targets for novel therapeutics to restore endobiotics homeostasis.

Profiling serum bile acid glucuronides in humans: gender divergences, genetic determinants, and response to fenofibrate

Glucuronidation, catalyzed by UDP-glucuronosyltransferase (UGT) enzymes detoxifies cholestatic bile acids (BAs). We aimed at i) characterizing the circulating BA-glucuronide (-G) pool composition in humans, ii) evaluating how sex and UGT polymorphisms influence this composition, and iii) analyzing the effects of lipid-lowering drug fenofibrate on the circulating BA-G profile in 300 volunteers and 5 cholestatic patients. Eleven BA-Gs were determined in pre- and post-fenofibrate samples. Men exhibited higher BA-G concentrations, and various genotype/BA-G associations were discovered in relevant UGT genes. The chenodeoxycholic acid-3G concentration was associated with the UGT2B7 802C>T polymorphism. Glucuronidation assays confirmed the predominant role of UGT2B7 and UGT1A4 in CDCA-3G formation. Fenofibrate exposure increased the serum levels of 5 BA-G species, including CDCA-3G, and up-regulated expression of UGT1A4, but not UGT2B7, in hepatic cells. This study demonstrates that fenofibrate stimulates BA glucuronidation in humans, and thus reduces bile acid toxicity in the liver.

Gilbert syndrome redefined: a complex genetic haplotype influences the regulation of glucuronidation

Gilbert syndrome (GS) is characterized by intermittent unconjugated hyperbilirubinemia without structural liver damage, affecting about 10% of the white population. In GS the UGT1A1*28 variant reduces bilirubin conjugation by 70% and is associated with irinotecan and protease inhibitor side effects. The aim of this study was to characterize potential in vivo consequences of UGT1A gene variability in GS. Three hundred GS patients (UGT1A1*28 homozygous) and 249 healthy blood donors (HBD) were genotyped for UGT1A (UGT1A1*28, UGT1A3-66 T>C, UGT1A6*3a, UGT1A7*3) and transporter single nucleotide polymorphisms (SNPs) (SCLO1B1 p.V174A, SCLO1B1 p.N130D, ABCC2 p.I1324I, ABCC2-24 UTR) using TaqMan-5'-nuclease-assays. A humanized transgenic UGT1A-SNP and corresponding wildtype mouse model were established carrying the GS-associated UGT1A variant haplotype. UGT1A transcript and protein expression, and transcriptional activation were studied in vivo. Homozygous UGT1A1*28 GS individuals were simultaneously homozygous for UGT1A3-66 T>C (91%), UGT1A6*2a (77%), and UGT1A7*3 (77%). Seventy-six percent of GS and only 9% of HBD were homozygous for the variant haplotype spanning four UGT1A genes. SCLO1B1 and ABCC2 SNPs showed no differences. In transgenic humanized UGT1A SNP and wildtype mice this UGT1A haplotype led to lower UGT1A messenger RNA (mRNA) expression and UGT1A protein synthesis. UGT1A transcriptional activation by dioxin, phenobarbital, and endotoxin was significantly reduced in SNP mice.

CONCLUSION

Our data redefine the genetic basis behind GS. In vivo data studying the genotype present in 76% of GS individuals suggest that transcription and transcriptional activation of glucuronidation genes responsible for conjugation and detoxification is directly affected, leading to lower responsiveness. This study suggests that GS should be considered a potential risk factor for drug toxicity.

The impact of cholesterol and its metabolites on drug metabolism

INTRODUCTION

Global prevalence of Western-type diet has increased in the last decades resulting in occurrence of certain chronic diseases. This type of diet is also linked to high-cholesterol intake and increase in blood cholesterol. Many of the molecular mechanisms of dealing with increased levels of cholesterol and its metabolites have been elucidated in animal models and humans. It is also evident that cholesterol metabolism is closely connected to drug metabolism. Cholesterol/bile acids and drugs share many transporters, enzymes and regulatory proteins which are key points in the crosstalk.

AREAS COVERED

This review presents an overview of the effect of cholesterol and its metabolites on drug metabolism with special emphasis on species-specific differences. The article focuses on the role of nuclear receptors farnesoid X receptor, vitamin D receptor and liver X receptor in the regulation of drug metabolism genes and the role of cholesterol biosynthesis intermediates, oxysterols and bile acids in the induction of drug metabolism through pregnane X receptor.

EXPERT OPINION

Studies show that the regulation of drug metabolism by sterols is multileveled. Many species-dependent differences were observed which hinder the transfer of findings from model animals to humans. As of now, there is little evidence available for cholesterol impact on drug metabolism in vivo in humans. There is also the need to confirm the results obtained in animal models and in vitro analyses in human cells but this is very difficult given the current lack of tools.

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

Ten out of 19 UDP-glucuronosyltransferases (UGTs) are substantially expressed in adult human liver (>1% of total UGTs); 5 UGT1 isoforms (UGT1A1, 1A3, 1A4, 1A6 and 1A9) and 5 UGT2 family members (UGT2B4, 2B7, 2B10, 2B15 and 2B17) (Izukawa et al. [11]). Surprisingly, UGT2B4 and UGT2B10 mRNA were found to be abundant in human liver suggesting an underestimated role of the liver in detoxification of their major substrates, bile acids and eicosanoids. Among factors responsible for high interindividual variation of hepatic UGT levels (genetic diversity including polymorphisms and splice variants, regulation by liver-enriched transcription factors such as HNF1 and HNF4, and ligand-activated transcription factors) nuclear receptors (PXR, CAR, PPARalpha, etc.), and the Ah receptor are discussed. Unraveling the mechanisms responsible for interindividual variation of UGT expression will be beneficial for drug therapy but still remains a major challenge.