UGT1A1 dysfunction increases liver burden and aggravates hepatocyte damage caused by long-term bilirubin metabolism disorder.

UGT1A1 is the only enzyme that can metabolize bilirubin, and its encoding gene is frequently mutated. UGT1A1*6 (G71R) is a common mutant in Asia which leads to the decrease of UGT1A1 activity and abnormal bilirubin metabolism. However, it is not clear whether low UGT1A1 activity-induced bilirubin metabolism disorder increases hepatocyte fragility. ugt1a+/- mice were used to simulate the UGT1A1*6 (G71R) population. Under the same CCl4 induction condition, ugt1a+/- mice showed severer liver damage and fibrosis, indicating that ugt1a1 dysfunction increased liver burden and aggravated hepatocyte damage. In the animal experiment with a continuous intraperitoneal injection of bilirubin, the ugt1a+/- mice livers had more serious unconjugated bilirubin accumulation. The accumulated bilirubin leads to hyperphosphorylation of IκB-α, Ikk-ß, and p65 and a significant increase of inflammatory factor. The α-SMA and Collagen I proteins markedly up-regulated in the ugt1a+/- mice livers. Immunofluorescence and confocal microscopy showed that hepatic stellate cells and Kupffer cells were activated in ugt1a+/- mice. Comprehensive results show that there was a crosstalk relationship between low UGT1A1 activity-bilirubin-liver damage. Furthermore, cell experiments confirmed that unconjugated bilirubin activated the NF-κB pathway and induced DNA damage in hepatocytes, leading to the significant increase of inflammatory factors. UGT1A1 knockdown in hepatocytes aggravated the toxicity of unconjugated bilirubin. Conversely, overexpression of UGT1A1 had a protective effect on hepatocytes. Finally, Schisandrin B, an active ingredient with hepatoprotective effects, extracted from a traditional Chinese medicinal herb, which could protect the liver from bilirubin metabolism disorders caused by ugt1a1 deficiency by downregulating p65 phosphorylation, inhibiting Kupffer cells, reducing inflammation levels. Our data clarified the mechanism of liver vulnerability caused by cross-talk between low UGT1A1 activity bilirubin, and provided a reference for individualized prevention of liver fragility in Gilbert's syndrome.

A broad-spectrum substrate for the human UDP-glucuronosyltransferases and its use for investigating glucuronidation inhibitors.

Strong inhibition of the human UDP-glucuronosyltransferase enzymes (UGTs) may lead to undesirable effects, including hyperbilirubinaemia and drug/herb-drug interactions. Currently, there is no good way to examine the inhibitory effects and specificities of compounds toward all the important human UGTs, side-by-side and under identical conditions. Herein, we report a new, broad-spectrum substrate for human UGTs and its uses in screening and characterizing of UGT inhibitors. Following screening a variety of phenolic compound(s), we have found that methylophiopogonanone A (MOA) can be readily O-glucuronidated by all tested human UGTs, including the typical N-glucuronidating enzymes UGT1A4 and UGT2B10. MOA-O-glucuronidation yielded a single mono-O-glucuronide that was biosynthesized and purified for structural characterization and for constructing an LC-UV based MOA-O-glucuronidation activity assay, which was then used for investigating MOA-O-glucuronidation kinetics in recombinant human UGTs. The derived Km values were crucial for selecting the most suitable assay conditions for assessing inhibitory potentials and specificity of test compound(s). Furthermore, the inhibitory effects and specificities of four known UGT inhibitors were reinvestigated by using MOA as the substrate for all tested UGTs. Collectively, MOA is a broad-spectrum substrate for the human UGTs, which offers a new and practical tool for assessing inhibitory effects and specificities of UGT inhibitors.

Molecular Insight into Stereoselective ADME Characteristics of C20-24 Epimeric Epoxides of Protopanaxadiol by Docking Analysis.

Chirality is a common phenomenon, and it is meaningful to explore interactions between stereoselective bio-macromolecules and chiral small molecules with preclinical and clinical significance. Protopanaxadiol-type ginsenosides are main effective ingredients in ginseng and are prone to biotransformation into a pair of ocotillol C20-24 epoxide epimers, namely, (20S,24S)-epoxy-dammarane-3,12,25-triol (24S-PDQ) and (20S,24R)-epoxy dammarane-3,12,25-triol (24R-PDQ) that display stereoselective fate in vivo. However, possible molecular mechanisms involved are still unclear. The present study aimed to investigate stereoselective ADME (absorption, distribution, metabolism and excretion) characteristics of PDQ epimers based on molecular docking analysis of their interaction with some vital proteins responsible for drug disposal. Homology modeling was performed to obtain 3D-structure of the human isoenzyme UGT1A8, while calculation of docking score and binding free energy and ligand-protein interaction pattern analysis were achieved by using the Schrödinger package. Stereoselective interaction was found for both UGT1A8 and CYP3A4, demonstrating that 24S-PDQ was more susceptible to glucuronidation, whereas 24R-PDQ was more prone to oxidation catalyzed by CYP3A4. However, both epimers displayed similarly strong interaction with P-gp, a protein with energy-dependent drug-pump function, suggesting an effect of the dammarane skeleton but not C-24 stereo-configuration. These findings provide an insight into stereo-selectivity of ginsenosides, as well as a support the rational development of ginseng products.

Potential of herb-drug / herb interactions between substrates and inhibitors of UGTs derived from herbal medicines.

Herbal medicines are widely used as alternative or complementary therapies worldwide to treat and prevent chronic diseases. However, herbal medicines coadministration with therapeutic drugs may cause dramatic clinical herb-drug/herb interactions (HDIs/HHIs) that may result in low drug efficacy or serious toxic reactions. Phase II metabolism enzyme UDP-glucuronosyltransferases (UGTs) play a significant detoxification role in vivo. Most drugs and non-drug xenobiotics undergo phase II metabolic transformations to be more polar compounds that are more easily excreted. Herbal medicines are a mixed and chemically varied group that includes flavonoids, stilbenes, coumarins, quinones, and terpenes, which are potential substrates and inhibitors of UGTs. Although increasing studies about glucuronidation metabolism and the inhibition toward UGTs of many herbal medicines have been reported, it is still difficult to determine which compounds from herbal medicines are substrates or inhibitors of UGTs. This article gives an overview of UGTs studies, which mainly focuses on glucuronidation of herbal constituents as substrates catalyzed by UGTs, potential herbal inhibitors for UGTs. We summarize the negative effects of UGT1A polymorphism and single nucleotide polymorphisms (SNPs), relevant clinical situations of HDIs/HHIs induced by inhibition of UGTs, and propose establishing classification criteria for inhibitors. Finally, we also discuss future research and strategic directions to advance the understanding of the potential HDIs/HHIs and suggest some additional studies revealing more information on UGT-mediated HDIs/HHIs.

Formation of (2R)- and (2S)-8-Prenylnaringenin Glucuronides by Human UDP-Glucuronosyltransferases.

Occurring in hops (Humulus lupulus) and beer as a racemic mixture, (2R,2S)-8-prenylnaringenin (8-PN) is a potent phytoestrogen in hop dietary supplements used by women as alternatives to conventional hormone therapy. With a half-life exceeding 20 h, 8-PN is excreted primarily as 8-PN-7-O-glucuronide or 8-PN-4'-O-glucuronide. Human liver microsomes and 11 recombinant human UDP-glucuronosyltransferases (UGTs) were used to catalyze the formation of the two oxygen-linked glucuronides of purified (2R)-8-PN and (2S)-8-PN, which were subsequently identified using mass spectrometry and nuclear magnetic resonance spectroscopy. Formation of (2R)- and (2S)-8-PN-7-O-glucuronides predominated over the 8-PN-4'-O-glucuronides except for intestinal UGT1A10, which formed more (2S)-8-PN-4'-O-glucuronide. (2R)-8-PN was a better substrate for all 11 UGTs except for UGT1A1, which formed more of both (2S)-8-PN glucuronides than (2R)-8-PN glucuronides. Although several UGTs conjugated both enantiomers of 8-PN, some conjugated just one enantiomer, suggesting that human phenotypic variation might affect the routes of metabolism of this chiral estrogenic constituent of hops.

Inhibition of UGT1A1 by natural and synthetic flavonoids.

Flavonoids are widely distributed phytochemicals in vegetables, fruits and medicinal plants. Recent studies demonstrate that some natural flavonoids are potent inhibitors of the human UDP-glucuronosyltransferase 1A1 (UGT1A1), a key enzyme in detoxification of endogenous harmful compounds such as bilirubin. In this study, the inhibitory effects of 56 natural and synthetic flavonoids on UGT1A1 were assayed, while the structure-inhibition relationships of flavonoids as UGT1A1 inhibitors were investigated. The results demonstrated that the C-3 and C-7 hydroxyl groups on the flavone skeleton would enhance UGT1A1 inhibition, while flavonoid glycosides displayed weaker inhibitory effects than their corresponding aglycones. Further investigation on inhibition kinetics of two strong flavonoid-type UGT1A1 inhibitors, acacetin and kaempferol, yielded interesting results. Both flavonoids were competitive inhibitors against UGT1A1-mediated NHPN-O-glucuronidation, but were mixed and competitive inhibitors toward UGT1A1-mediated NCHN-O-glucuronidation, respectively. Furthermore, docking simulations showed that the binding areas of NHPN, kaempferol and acacetin on UGT1A1 were highly overlapping, and convergence with the binding area of bilirubin within UGT1A1. In summary, detailed structure-inhibition relationships of flavonoids as UGT1A1 inhibitors were investigated carefully and the findings shed new light on the interactions between flavonoids and UGT1A1, and will contribute considerably to the development of flavonoid-type drugs without strong UGT1A1 inhibition.

A two-phase model for the non-processive biosynthesis of homogalacturonan polysaccharides by the GAUT1:GAUT7 complex.

Homogalacturonan (HG) is a pectic glycan in the plant cell wall that contributes to plant growth and development and cell wall structure and function, and interacts with other glycans and proteoglycans in the wall. HG is synthesized by the galacturonosyltransferase (GAUT) gene family. Two members of this family, GAUT1 and GAUT7, form a heteromeric enzyme complex in Arabidopsis thaliana Here, we established a heterologous GAUT expression system in HEK293 cells and show that co-expression of recombinant GAUT1 with GAUT7 results in the production of a soluble GAUT1:GAUT7 complex that catalyzes elongation of HG products in vitro The reaction rates, progress curves, and product distributions exhibited major differences dependent upon small changes in the degree of polymerization (DP) of the oligosaccharide acceptor. GAUT1:GAUT7 displayed >45-fold increased catalytic efficiency with DP11 acceptors relative to DP7 acceptors. Although GAUT1:GAUT7 synthesized high-molecular-weight polymeric HG (>100 kDa) in a substrate concentration-dependent manner typical of distributive (nonprocessive) glycosyltransferases with DP11 acceptors, reactions primed with short-chain acceptors resulted in a bimodal product distribution of glycan products that has previously been reported as evidence for a processive model of GT elongation. As an alternative to the processive glycosyltransfer model, a two-phase distributive elongation model is proposed in which a slow phase, which includes the de novo initiation of HG and elongation of short-chain acceptors, is distinguished from a phase of rapid elongation of intermediate- and long-chain acceptors. Upon reaching a critical chain length of DP11, GAUT1:GAUT7 elongates HG to high-molecular-weight products.

Inhibition of UGT2B7 Enzyme Activity in Human and Rat Liver Microsomes by Herbal Constituents.

The co-use of conventional drug and herbal medicines may lead to herb-drug interaction via modulation of drug-metabolizing enzymes (DMEs) by herbal constituents. UDP-glucuronosyltransferases (UGTs) catalyzing glucuronidation are the major metabolic enzymes of Phase II DMEs. The in vitro inhibitory effect of several herbal constituents on one of the most important UGT isoforms, UGT2B7, in human liver microsomes (HLM) and rat liver microsomes (RLM) was investigated. Zidovudine (ZDV) was used as the probe substrate to determine UGT2B7 activity. The intrinsic clearance (Vmax/Km) of ZDV in HLM is 1.65 µL/mg/min which is ten times greater than in RLM, which is 0.16 µL/mg/min. Andrographolide, kaempferol-3-rutinoside, mitragynine and zerumbone inhibited ZDV glucuronidation in HLM with IC50 values of 6.18 ± 1.27, 18.56 ± 8.62, 8.11 ± 4.48 and 4.57 ± 0.23 µM, respectively, hence, herb-drug interactions are possible if andrographolide, kaempferol-3-rutinoside, mitragynine and zerumbone are taken together with drugs that are highly metabolized by UGT2B7. Meanwhile, only mitragynine and zerumbone inhibited ZDV glucuronidation in RLM with IC50 values of 51.20 ± 5.95 µM and 8.14 ± 2.12 µM, respectively, indicating a difference between the human and rat microsomal model so caution must be exercised when extrapolating inhibitory metabolic data from rats to humans.

Sugar release and growth of biofuel crops are improved by downregulation of pectin biosynthesis.

Cell walls in crops and trees have been engineered for production of biofuels and commodity chemicals, but engineered varieties often fail multi-year field trials and are not commercialized. We engineered reduced expression of a pectin biosynthesis gene (Galacturonosyltransferase 4, GAUT4) in switchgrass and poplar, and find that this improves biomass yields and sugar release from biomass processing. Both traits were maintained in a 3-year field trial of GAUT4-knockdown switchgrass, with up to sevenfold increased saccharification and ethanol production and sixfold increased biomass yield compared with control plants. We show that GAUT4 is an α-1,4-galacturonosyltransferase that synthesizes homogalacturonan (HG). Downregulation of GAUT4 reduces HG and rhamnogalacturonan II (RGII), reduces wall calcium and boron, and increases extractability of cell wall sugars. Decreased recalcitrance in biomass processing and increased growth are likely due to reduced HG and RGII cross-linking in the cell wall.

Identification and characterization of the structure-activity relationships involved in UGT1A1 inhibition by anthraquinone and dianthrone constituents of Polygonum multiflorum.

The adverse effects of Polygonum (P.) multiflorum, including abnormal bilirubin metabolism, are a serious public health issue. As uridine diphosphate (UDP)-glucuronosyltransferase 1A1 (UGT1A1) is the only enzyme responsible for bilirubin metabolism, we investigated the inhibitory effect of a P. multiflorum extract and 10 anthraquinone and dianthrone compounds on UGT1A1 in rat liver microsomes in vitro. The P. multiflorum extract exhibited the strongest inhibitory effect on UGT1A1 activity (inhibition constant [Ki] = 0.3257 µM, 1422 µg of material/mL), followed by cis-emodin dianthrones (Ki = 0.8630 µM), trans-emodin dianthrones (Ki = 1.083 µM), emodin-8-O-glc (Ki = 3.425 µM), and polygonumnolide C2 (Ki = 4.291 µM). Analysis of the structure-activity relationships of these compounds suggested that the spatial orientation of the molecules and the presence of particular functional groups affect UGT1A1 inhibition. A mechanistic analysis showed that all the tested compounds docked into two of the nine active sites of UGT1A1 and suggested that hydrophobic interactions and hydrogen bonds are important for the affinity of the tested compounds for UGT1A1; moreover, their interaction energies were generally in agreement with the Ki values. These findings provide insight into adverse reactions to P. multiflorum and identify the pharmacophores involved in inhibition of UGT1A1.

Identification of human cytochrome P450 and UGT enzymes involved in the metabolism of ferulic acid, a major bioactive component in traditional Chinese medicines.

Ferulic acid (FA) is an active component of herbal medicines. One of the best documented activities of FA is its antioxidant property. Moreover, FA exerts antiallergic, anti-inflammatory, and hepatoprotective effects. However, the metabolic pathways of FA in humans remain unclear. To identify whether human CYP or UGT enzymes are involved in the metabolism of FA, reaction phenotyping of FA was conducted using major CYP-selective chemical inhibitors together with individual CYP and UGT Supersomes. The CYP- and/or UGT-mediated metabolism kinetics were examined simultaneously or individually. Relative activity factor and total normalized rate approaches were used to assess the relative contributions of each major human CYPs towards the FA metabolism. Incubations of FA with human liver microsomes (HLM) displayed NADPH- and UDPGA-dependent metabolism with multiple CYP and UGT isoforms involved. CYPs and UGTs contributed equally to the metabolism of FA in HLM. Although CYP1A2 and CYP3A4 appeared to be the major contributors in the CYP-mediated clearance, their contributions to the overall clearance are still minor (< 25%). As a constitute of many food and herbs, FA poses low drug-drug interaction risk when co-administrated with other herbs or conventional medicines because multiple phase I and phase II enzymes are involved in its metabolism.

Identification of human UDP-glucuronosyltransferase isoforms involved in the isofraxidin glucuronidation and assessment of the species differences of the reaction.

Isofraxidin, 7-Hydroxy-6.8-dimethoxy-2H-1-benzopyran-2-one, is a major active component of Acanthopanax senticosus, which has been used as Acanthopanax (Ciwujia) injection to treat cardiovascular and cerebrovascular diseases in China for more than thirty years. The purpose of this study was to identify the roles of human UDP-glucuronosyltransferases (UGTs) in isofraxidin glucuronidation in the liver and intestinal microsomes and to reveal the potential species differences by comparing the liver microsomal glucuronidation from different experimental animals. One metabolite was biosynthesized and characterized as isofraxidin-7-O-glucuronide by liquid chromatography tandem mass spectrometry (LC-MS/MS) and nuclear magnetic resonance (NMR). The intrinsic clearances in human liver and intestinal microsomes were 63.8 and 16.4µL/min/mg, respectively. Human liver microsomes displays higher potential for isofraxidin elimination than human intestinal microsomes. The reaction phenotyping analysis was conducted using cDNA-expressed human UGTs and chemical inhibitors. The results indicated that UGT1A1 and UGT1A9 were the main isoforms involved in the formation of isofraxidin-7-O-glucuronide. The isofraxidin glucuronidation in liver microsomes from human (HLM), rat (RLM), mouse (MLM), dog (DLM), monkey (CyLM), minipig (PLM), and guinea pig (GpLM) followed the Michealis-Menten model. The isofraxidin glucuronidation displays species differences in terms of catalytic activities. GpLM had the highest clearance with the CLint value of 152µL/min/mg. CyLM, RLM and MLM exhibit similar catalytic activities in isofraxidin glucuronidation with the intrinsic clearance values of 54.6, 58.0 and 50.2µL/min/mg, respectively, which are higher than those of PLM and DLM (23.9 and 37.7µL/min/mg, respectively). Rat exhibits the most similar intrinsic metabolic clearance (CLint) to human.

Isochlorogenic acid A affects P450 and UGT enzymes in vitro and in vivo.

Isochlorogenic acid A (ICQA), which has anti-inflammatory, hepatoprotective, and antiviral properties, is commonly presented in fruits, vegetables, coffee, plant-based food products, and herbal medicines. These herbal medicines are usually used in combination with other medicines in the clinic. However, little is known about the regulatory effects of ICQA on drug-metabolizing enzymes and the herb-drug interactions. In the present study, we evaluated the inhibitory potentials of ICQA on CYP1A2, CYP2C9, CYP2C19, CYP3A4, CYP2D6, and CYP2E1 in vitro based on a cocktail approach. The P450 and UGT activities in mice treated with ICQA for a prolonged period were also determined. Our results demonstrated that ICQA exhibited a weak inhibitory effect on CYP2C9 in human liver microsomes with IC50 being 57.25 µmol·L-1 and Ki being 26.77 µmol·L-1. In addition, ICQA inhibited UGT1A6 activity by 25%, in the mice treated with ICQA (i.p.) at 30 mg·kg-1 for 14 d, compared with the control group. Moreover, ICQA showed no mechanism-based inhibition on CYP2C9 or UGT1A6. In conclusion, our results further confirm a safe use of ICQA in clinical practice.

In Vitro Inhibition of Human UDP-Glucuronosyl-Transferase (UGT) Isoforms by Astaxanthin, ß-Cryptoxanthin, Canthaxanthin, Lutein, and Zeaxanthin: Prediction of in Vivo Dietary Supplement-Drug Interactions.

Despite the widespread use of the five major xanthophylls astaxanthin, ß-cryptoxanthin, canthaxanthin, lutein, and zeaxanthin as dietary supplements, there have been no studies regarding their inhibitory effects on hepatic UDP-glucuronosyltransferases (UGTs). Here, we evaluated the inhibitory potential of these xanthophylls on the seven major human hepatic UGTs (UGT1A1, UGT1A3, UGT1A4, UGT1A6, UGT1A9, UGT2B7 and UGT2B15) in vitro by LC-MS/MS using specific marker reactions in human liver microsomes (except UGT2B15) or recombinant supersomes (UGT2B15). We also predicted potential dietary supplement-drug interactions for ß-cryptoxanthin via UGT1A1 inhibition. We demonstrated that astaxanthin and zeaxanthin showed no apparent inhibition, while the remaining xanthophylls showed only weak inhibitory effects on the seven UGTs. ß-Cryptoxanthin mildly inhibited UGT1A1, UGT1A3, and UGT1A4, with IC50 values of 18.8 ± 2.07, 28.3 ± 4.40 and 34.9 ± 5.98 µM, respectively. Canthaxanthin weakly inhibited UGT1A1 and UGT1A3, with IC50 values of 38.5 ± 4.65 and 41.2 ± 3.14 µM, respectively; and lutein inhibited UGT1A1 and UGT1A4, with IC50 values of 45.5 ± 4.01 and 28.7 ± 3.79 µM, respectively. Among the tested xanthophyll-UGT pairs, ß-cryptoxanthin showed the strongest competitive inhibition of UGT1A1 (Ki, 12.2 ± 0.985 µM). In addition, we predicted the risk of UGT1A1 inhibition in vivo using the reported maximum plasma concentration after oral administration of ß-cryptoxanthin in humans. Our data suggests that these xanthophylls are unlikely to cause dietary supplement-drug interactions mediated by inhibition of the hepatic UGTs. These findings provide useful information for the safe clinical use of the tested xanthophylls.

Effects of diammonium glycyrrhizinate on hepatic and intestinal UDP-Glucuronosyltransferases in rats: Implication in herb-drug interactions.

Glycyrrhizin is a major bioactive component of liquorice, which exerts multiple biochemical and pharmacological activities and is frequently used in combination with other drugs in the clinic. Mycophenolate mofetil (MMF), an immunosuppressant widely used in transplant patients, is metabolized by UDP-glucuronyltransferases (UGTs). Although significant evidence supports that glycyrrhizin could interact with the cytochrome P450s (CYPs), few studies have addressed its effects on UGTs. The present study aimed at investigating the regulatory effects of diammonium glycyrrhizinate (GLN) on UGTs in vitro and in vivo. We found that long-term administration of GLN in rats induced overall metabolism of MMF, which might be due to the induction of UGT1A protein expression. Hepatic UGT1A activity and UGT1A mRNA and protein expression were significantly increased in GLN-treated rats. UGT1A expression levels were also increased in the intestine, contradicting with the observed decrease in intestinal UGT1A activities. This phenomenon may be attributed to different concentrations of glycyrrhetinic acid (GA) in liver and intestine and the inhibitory effects of GA on UGT1A activity. In conclusion, our study revealed that GLN had multiple effects on the expression and activities of UGT1A isoforms, providing a basis for a better understanding of interactions between GLN and other drugs.

[Hepatotoxicity of emodin based on UGT1A1 enzyme-mediated bilirubin in liver microsomes].

To study the hepatotoxicity of emodin based on bilirubin metabolism mediated by glucuronidation of UGT1A1 enzyme. In this study, three different incubation systems were established by using RLM, HLM, and rUGT1A1, with bilirubin as the substrate. Different concentrations of bilirubin and emodin were added in the incubation systems. The double reciprocal Michaelis equation was drawn based on the total amount of bilirubin glucuronidation. The apparent inhibition constant Ki was then calculated with the slope curve to predict the hepatotoxicity. The results indicated that emodin had a significant inhibition to the UGT1A1 enzyme in all of the three systems, with Ki=5.400±0.956(P<0.05) in HLM system, Ki =10.020±0.611(P<0.05) in RLM system, Ki=4.850±0.528(P<0.05) in rUGT1A1 system. Meanwhile, emodin had no significant difference between rat and human in terms of inhibition of UGT1A1 enzyme. Emodin had a potential risk of the hepatotoxicity by inhibiting the UGT1A1 enzyme activity. And the method established in this study provides a new thought and new method to evaluate hepatotoxicity and safety of traditional Chinese medicines.

[In vitro and In vivo effects of six Coptidis alkaloids on liver microsomes UGTs and UGT1A1 activities in rats and mice].

In the present study, the effects of six Coptidis alkaloids (berberine, epiberberine, coptisine, jatrorrhizine, palmatine and magnoflorine) on liver microsomes UGTs and UGT1A1 activities in rats and mice were investigated in vitro and in vivo to study the mechanism of metabolic drug-drug interactions of Coptidis Rhizoma with other drugs. In vitro rat and mice liver microsomal incubation systems combined with UDPGA were applied, as well as mice liver microsomes after administration of six Coptidis alkaloids. 4-Nitrophenol and ß-estradiol were selected as substrates to determine activities of UGTs and UGT1A1 by UV and HPLC, respectively. According to the in vitro rat study, berberine, epiberberine, coptisine and jatrorrhizine significantly inhibited rat liver microsome UGTs activity, particularly epiberberine showed the strongest inhibition. UGT1A1 activity was lowly inhibited by jatrorrhizine, with IC50 at about 227 µmol•L⁻¹, whereas coptisine and magnoflorine significantly activated UGT1A1. According to the in vitro mice study, berberine, coptisine, jatrorrhizine and palmatine significantly inhibited mice liver microsome UGTs activity, and the six alkaloids all significantly activated UGT1A1. According to the in vivo mice study, UGTs activity was significantly activated only in berberine group, while UGT1A1 activity was significantly activated only in jatrorrhizine group. In conclusion, the effects of Coptidis alkaloids on UGT activity showed significant differences in species and between in vitro and in vivo. Meanwhile, the changes in structures of Coptidis alkaloids also have a big impact on UGT activity, which may be one of the causes for the drug-drug interactions between Coptidis Rhizoma and other drugs.

Effect of an ethanol extract of Descurainia sophia seeds on Phase I and II drug metabolizing enzymes and P-glycoprotein activity in vitro.

BACKGROUND: Descurainia sophia seeds have a variety of pharmacological functions and been widely used in traditional folk medicine. However, their effects on human drug metabolizing enzyme (DME) activities have not been elucidated. The present study investigated the inhibitory effects of an ethanol extract of D. sophia seeds (EEDS) on human Phase I/II (DMEs) and P-glycoprotein (p-gp) in vitro. METHODS: The enzyme activities of human Phase I (cytochrome P450s, CYPs), Phase II (uridine diphosphate glucuronosyltransferases, UGTs) DMEs, and the drug transporter P-gp were determined in the presence of various concentrations of EEDS using commercially available luminogenic assay systems. The mode of enzyme inhibition and the inhibitory constant (Ki) value of EEDS were graphically determined with Lineweaver-Burk double reciprocal plots and secondary plots, respectively. RESULTS: The enzyme activity assays showed that EEDS moderately inhibited the CYP1A2, CYP2C9, and CYP2C19 isoforms with half maximal inhibitory concentrations (IC50) of 47.3, 25.8, and 38.7 µg/mL, respectively. Graphical analyses with Lineweaver-Burk double reciprocal plots and secondary plots indicated that EEDS competitively inhibited CYP2C9 with a Ki value of 19.8 µg/mL; however, it inhibited CYP2C9 and CYP2C19 in a mixed mode with Ki values of 5.2, and 11.9 µg/mL, respectively. Other Phase I (CYP2C8, CYP2D6, and CYP3A4) and Phase II (UGT1A1 and UGT2B7) enzymes as well as P-gp were weakly or negligibly affected by EEDS with concentrations up to 500 µg/mL. CONCLUSIONS: EEDS is a selective inhibitor of CYP1A2, CYP2C9, and CYP2C19 with moderate enzymatic inhibition. Clinically, full consideration should be given to a potential toxic adverse effect from a herb-drug interaction when drugs that are particularly susceptible to CYP1A2, CYP2C9, or CYP2C19-mediated metabolism are taken together with EEDS. Characterization of metabolic profiles of specific herbal drugs could help consumers and medical specialists to use them safely as a complementary and alternative medicine.

Identification of UDP-glucuronosyltransferase isoforms responsible for leonurine glucuronidation in human liver and intestinal microsomes.

Leonurine is a potent component of herbal medicine Herba leonuri. The detail information on leonurine metabolism in human has not been revealed so far. Two primary metabolites, leonurine O-glucuronide and demethylated leonurine, were observed and identified in pooled human liver microsomes (HLMs) and O-glucuronide is the predominant one. Among 12 recombinant human UDP-glucuronosyltransferases (UGTs), UGT1A1, UGT1A8, UGT1A9, and UGT1A10 showed catalyzing activity toward leonurine glucuronidation. The intrinsic clearance (CLint) of UGT1A1 was approximately 15-to 20-fold higher than that of UGT1A8, UGT1A9, and UGT1A10, respectively. Both chemical inhibition study and correlation study demonstrated that leonurine glucuronidation activities in HLMs had significant relationship with UGT1A1 activities. Leonurine glucuronide was the major metabolite in human liver microsomes. UGT1A1 was principal enzyme that responsible for leonurine glucuronidation in human liver and intestine microsomes.

[Cloning of UGT gene of Bupleurum chinense and construction of over expressing and RNAi transgenic vectors].

OBJECTIVE: To clone the full-length cDNA of a uridine diphosphate glycosyltransferase (UGT) gene which may be involved in saikosaponin biosynthesis of Bupleurum chinense, and construct the transgenic vectors for over expression and RNAi of the cloned UGT. These works will provide foundation for further its function analysis by transgene study. METHOD: RAGE and LD-PCR were used to clone the full-length cDNA of the UGT, on the basis of its partial cDNA sequence obtained from our previous 454-sequenced dataset. The ORF and partial sequences of the UGT were PCR cloned using primers with corresponding restriction enzymes cutting sites. The PCR products were digested with corresponding restriction enzymes and then were inserted into pCAMBIA-SUPER 1 300 and pHANNIBAL. The recombinant pHANNIBAL were digested with Not I and then were inserted into a binary vector, pART27. Finally, the transgenic vectors for over expression and RNAi of the cloned UGT were constructed. RESULT: The full-length cDNA of a UGT were cloned from B. chinense. The recombinant vectors for over expression and RNAi of the UGT were obtained. CONCLUSION: Our works on full-length cDNA cloning and transgenic vectors construction provide a substantial foundation for follow-up biofunction analysis of the UGT through transgenic research.