UDP-glucuronosyltransferase Activity Research Articles

Significance of Ethnic Factors in Immunosuppressive Therapy Management After Organ Transplantation

Clinical outcomes after organ transplantation have greatly improved in the past 2 decades with the discovery and development of immunosuppressive drugs such as calcineurin inhibitors, antiproliferative agents, and mammalian target of rapamycin inhibitors. However, individualized dosage regimens have not yet been fully established for these drugs except for therapeutic drug monitoring-based dosage modification because of extensive interindividual variations in immunosuppressive drug pharmacokinetics. The variations in immunosuppressive drug pharmacokinetics are attributed to interindividual variations in the functional activity of cytochrome P450 enzymes, UDP-glucuronosyltransferases, and ATP-binding cassette subfamily B member 1 (known as P-glycoprotein or multidrug resistance 1) in the liver and small intestine. Some genetic variations have been found to be involved to at least some degree in pharmacokinetic variations in post-transplant immunosuppressive therapy. It is well known that the frequencies and effect size of minor alleles vary greatly between different races. Thus, ethnic considerations might provide useful information for optimizing individualized immunosuppressive therapy after organ transplantation. Here, we review ethnic factors affecting the pharmacokinetics of immunosuppressive drugs requiring therapeutic drug monitoring, including tacrolimus, cyclosporine, mycophenolate mofetil, sirolimus, and everolimus.

Regional distributions of UDP-glucuronosyltransferase activities toward estradiol and serotonin in the liver and small intestine of cynomolgus macaques

The cynomolgus macaque is a nonhuman primate species that is often used in drug metabolism studies during drug development. However, the localization of UDP-glucuronosyltransferases (UGTs), essential drug-metabolizing enzymes, has not been fully investigated in the liver and small intestine of cynomolgus macaques. In this study, UGT activities were analyzed in liver (five lobes) and small intestine (the duodenum and six sections from the proximal jejunum to the distal ileum) using typical probe substrates of human UGTs: 7-hydroxycoumarin, estradiol, serotonin, propofol, and zidovudine. In liver, UGT activities with respect to all substrates were detected, and the activity levels were similar in all liver lobes of the cynomolgus macaques tested. In contrast, in the small intestine, UGT activities toward all substrates were detected, but their levels generally decreased from jejunum to ileum in cynomolgus macaques. The localization of estradiol 3-O-glucuronosyltransferases and serotonin O-glucuronosyltransferases (which are mainly UGT1A enzymes) appear to be different in liver and small intestine. These results collectively suggest that, in cynomolgus macaques, UGT1As are differentially localized in the small intestine but are relatively homogeneously distributed in the liver.

Piceatannol exhibits potential food-drug interactions through the inhibition of human UDP-glucuronosyltransferase (UGT) in Vitro

Piceatannol is a natural polyphenol compound found in passion fruit and blueberry with several biological activities. However, it is unclear whether piceatannol affects the activity of human UDP-glucuronosyltransferases (UGTs) enzymes. The present study aims to assess the potential inhibitory effect of piceatannol against UGTs enzymes, as well as to evaluate its potential food-drug interactions risk via UGTs inhibition. We systematically evaluated the inhibitory effects of piceatannol on UGTs using high-performance liquid chromatography by measuring the formation rates for 4-methylumbelliferoneglucuronide and imipramine N-glucuronide. The results indicated that piceatannol displayed broad-spectrum inhibition against human UGTs. Kinetic analysis showed that inhibition of piceatannol on UGT1A6 and UGT1A7 followed noncompetitive inhibition mechanism, while the inhibition on UGT1A8 and UGT1A9 obeyed competitive and mixed inhibition mechanism, respectively. The quantitative prediction of risks showed that the coadministration of piceatannol with drugs primarily cleared by UGT1A6, UGT1A7, UGT1A8, and UGT1A9 may result in potential food-drug interaction. In conclusion, additional caution should be taken when piceatannol and food containing piceatannol are co-administered with drugs metabolized by UGTs.

Inhibition of UDP-glucuronosyltransferases by different furoquinoline alkaloids

Herbs are often administered in combination with therapeutic drugs, raising the possibility for herb–drug interactions (HDIs). Furoquinoline alkaloids are found in Rutaceae plants, which are structurally similar and have many medicinal properties. This study aims to investigate the inhibition of four furoquinoline alkaloids on the activity of UDP-glucuronosyltransferases (UGTs).The recombinant UGTs-catalyzed glucuronidation metabolism of 4-methylumbelliferone (4-MU) was utilized to investigate the inhibition potential. Inhibition type and parameters were determined, and in silico docking was employed to elucidate the inhibition difference of furoquinoline alkaloids towards UGTs.Dictamine, haplopine, γ-fagarine and skimmianine strongly inhibited UGT1A3, UGT1A7, UGT1A9 and UGT2B4, respectively. Among them, dictamnine inhibited more than 70% of the four UGTs. Inhibition kinetics determination showed that they all exerted competitive inhibition, and the inhibition kinetic constant (Ki) was determined to be 8.3, 7.2, 3.7 and 33.9 μM, respectively. In vitro–in vivo extrapolation (IVIVE) was employed to demonstrate the inhibition possibility for four alkaloids. Skimmianine was proved to be more suitable for clinical application. In silico docking study indicated that the hydrophobic interactions played a key role in the inhibition of furoquinoline alkaloids towards three of the four UGTs. In conclusion, monitoring the interactions between furoquinoline alkaloids and drugs mainly undergoing UGTs-catalyzed metabolism is necessary.

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.

SLC35B1 significantly contributes to the uptake of UDPGA into the endoplasmic reticulum for glucuronidation catalyzed by UDP-glucuronosyltransferases

The transport of UDP-glucuronic acid (UDPGA), a co-substrate of UDP-glucuronosyltransferase (UGT), to the intraluminal side of the endoplasmic reticulum (ER) is an essential step in the glucuronidation of exogenous and endogenous compounds. According to a previous study, the expression of recombinant SLC35B1, SLC35B4, or SLC35D1, nucleotide sugar transporters, in V79 cells has the potential to transport UDPGA into the lumen of microsomes. The purpose of this study is to examine whether the transport of UDPGA by these transporters substantially affects UGT activity. Since the knockdown of UDP-glucose 6-dehydrogenase, a synthetase of UDPGA, in HEK293 cells stably expressing UGT1A1 (HEK/UGT1A1 cells) resulted in a significant decrease in 4-methylumbelliferone (4-MU) glucuronosyltransferase activity, supplementation of a sufficient amount of UDPGA is required for UGT activity. By performing qRT-PCR using cDNA samples from 21 human liver samples, we observed levels of the SLC35B1 and SLC35D1 mRNAs that were 15- and 14-fold higher, respectively, than the levels of the SLC35B4 mRNA, and SLC35B1 showed the largest (37-fold) interindividual variability. Interestingly, 4-MU glucuronosyltransferase activity was significantly decreased upon the knockdown of SLC35B1 in HEK/UGT1A1 cells, and this phenomenon was also observed in HepaRG cells. Using siRNAs targeting 23 different SLC35 subfamilies, the knockdown of SLC35B1 and SLC35E3 decreased 4-MU glucuronosyltransferase activity in HEK/UGT1A1 cells. However, the 4-MU glucuronosyltransferase activity was not altered by SLC35E3 knockdown in HepaRG cells, suggesting that SLC35B1 was the main transporter of UDPGA into the ER in the human liver. In conclusion, SLC35B1 is a key modulator of UGT activity by transporting UDPGA to the intraluminal side of the ER.

UGT1A1 genotype influences clinical outcome in patients with intermediate-risk acute myeloid leukemia treated with cytarabine-based chemotherapy.

The treatment of acute myeloid leukemia (AML) is adjusted according to cytogenetic risk factors and molecular markers. Cytarabine remains the main drug to treat AML, and several studies have explored the prognostic relevance of the genotype of cytarabine metabolizing enzymes in AML. Glucuronidation has been identified to be relevant in the cytarabine clearance, but there are still few data concerning the clinical impact of genetic polymorphisms known to condition the activity of UDP-glucuronosyl transferases in AML patients. Here we report the association between the UGT1A1 rs8175347 genotype and the clinical outcome of 455 intermediate-risk cytogenetic AML patients receiving cytarabine-based chemotherapy. Patients with the UGT1A1*28 homozygous variant (associated to a lower UGT1A1 activity) had a lower overall survival (OS) (25.8% vs. 45.5%; p: 0.004). Multivariate analysis confirmed this association (p: 0.008; HR: 1.79; 95% CI: 1.16-2.76). Subgroup analysis showed the negative effect of the UGT1A1*28 homozygous genotype on OS in women (14.8% vs. 52.7%; p: 0.001) but not in men. This lower OS was associated with longer neutropenia after consolidation chemotherapy and with higher mortality without previous relapse, suggesting an association between a low glucuronidation activity and mortal toxic events.

Assessment of the inhibition risk of paris saponins, bioactive compounds from Paris polyphylla, on CYP and UGT enzymes via cocktail inhibition assays

Paris saponins, also known as polyphyllins, are natural compounds extracted from Paris polyphylla, which have many pharmacological activities, such as anti-inflammation and anti-cancer. In particular, paris saponin I, II, VII and polyphyllin VI are the components of the quality standard for Paris polyphylla. However, the inhibition risk of polyphyllins on cytochrome P450 (CYP) and UDP-glucuronosyltransferases (UGT) remains unclear. Therefore, this report investigated the potential inhibitory effects of paris saponin I, II, VII and polyphyllin VI on the activities of CYP (CYP1A2, CYP2B1, CYP2C11, CYP2D1, CYP2E1 and CYP3A2) and UGT (UGT1A1, UGT1A3, UGT1A6, PROG and AZTG) through cocktail inhibition assays in vitro. In the study of CYP, polyphyllin VI exhibited weak inhibition on CYP2D1 activity in rat liver microsomes with IC50 value at 45.2 μM, while paris saponin VII weakly inhibited CYP2C11 and CYP2E1 activities with IC50 value at 42.0 and 67.7 μM, respectively. In the study of UGT, none of the four steroidal saponins showed significant inhibition risk. In conclusion, paris saponin I, II, VII and polyphyllin VI have very low potential to cause the possible toxicity and drug interactions involving CYP and UGT enzymes, indicating that they are safe enough to take with drugs.

Hetero-oligomer formation of mouse UDP-glucuronosyltransferase (UGT) 2b1 and 1a1 results in the gain of glucuronidation activity towards morphine, an activity which is absent in homo-oligomers of either UGT

UDP-Glucuronosyltransferase (UGT, Ugt) is a major drug metabolizing enzyme family involved in the glucuronidation and subsequent elimination of drugs and small lipophilic molecules. UGT forms homo- and hetero-oligomers that enhance or suppress UGT activity. In our previous study, we characterized mouse Ugt1a1 and all the Ugt isoform belonging to the Ugt2b subfamily and revealed that mouse Ugt2b1 and Ugt1a1 cannot metabolize morphine. Mouse Ugt2b1 had been believed to function similarly to rat UGT2B1, which plays a major role in morphine glucuronidation in rat liver. Thus, in this study, we hypothesized that hetero-oligomerization with another Ugt isoform may affect Ugt2b1 catalytic ability. We co-expressed Ugt1a1 and Ugt2b1 in a baculovirus-insect cell system, and confirmed hetero-oligomer formation by co-immunoprecipitation. As reported previously, microsomes singly expressing Ugt1a1 or Ugt2b1 were inactive towards the glucuronidation of morphine. Interestingly, in contrast, morphine-3-glucuronide, a major metabolite of morphine was formed, when Ugt2b1 and Ugt1a1 were co-expressed. This effect of hetero-oligomerization of Ugt1a1 and Ugt2b1 was also observed for 17β-estradiol glucuronidation. This is the first report demonstrating that UGT acquires a novel catalytic ability by forming oligomers. Protein-protein interaction of Ugts may contribute to robust detoxification of xenobiotics by altering the substrate diversity of the enzymes.

Pterostilbene supplements carry the risk of drug interaction via inhibition of UDP-glucuronosyltransferases (UGT) 1A9 enzymes

Pterostilbene (PT) is a natural stilbene common in small berries and food supplements, possessing numerous pharmacological activities. However, whether PT can affect the activities of UDP-glucuronosyltransferases (UGT) enzymes remains unclear. The aim of the present study was to investigate the effect of PT on UGT activities and to quantitatively evaluate the food-drug interaction potential due to UGT inhibition. Our data indicated that PT exhibited potent inhibition against HLM, UGT1A6, UGT1A9, UGT2B7, and UGT2B15, moderate inhibition against UGT1A1, UGT1A3, UGT1A8, and UGT2B4, negligible inhibition against UGT1A4, UGT1A7, UGT1A10, and UGT2B17. Further kinetic investigation demonstrated that PT exerted potent noncompetitive inhibition 4-MU glucuronidation by UGT1A9, with IC50 and Ki values of 0.92 μM and 0.52 ± 0.04 μM, respectively. Quantitative prediction study suggested that coadministration of PT supplements at 100 mg/day or higher doses may result in at least a 50% increase in the AUC of drugs predominantly cleared by UGT1A9. Thus, the coadministration of PT supplements and drugs primarily cleared by UGT1A9 may result in potential drug interaction, and precautions should be taken when coadministration of PT supplements and drugs metabolized by UGT1A9.

Oxylipin concentrations in bovine corpora lutea during maternal recognition of pregnancy

The objective was to determine the effects of pregnancy status on oxylipin profiles and eicosanoid metabolizing enzymes and in corpora lutea (CL) or endometrial (caruncle; CAR and intercaruncle; IC) tissues. Angus crossed cattle were synchronized with the CO-Synch protocol and artificially inseminated (AI). Sixteen days after AI, cattle were euthanized, and reproductive tracts collected from 6 non-pregnant and 6 pregnant cows. Oxylipin profiles and concentrations of progesterone (P4) were obtained from CL tissues. The activity of cytochrome P450 1A (CYP1A) and UDP-glucuronosyltransferase (UGT) enzymes were determined using specific luminogenic substrates. Data were analyzed using the MIXED procedure of SAS, and the model included pregnancy status. Corpora lutea of pregnant cattle contained greater (P < 0.05) concentrations of 9,10-DiHODE, 15,16-DiHODE, and 9,10-DiHOME. These oxylipins have been observed to increase cellular proliferation and vasodilation. Activity of CYP1A in the CL and UGT in CAR and IC was not different (P > 0.05) between pregnant and non-pregnant cattle. In the CL, activity of UGT was decreased (P < 0.05) in pregnant vs. non-pregnant cattle. The decrease in CL UGT activity during pregnancy indicates alterations in local hormone metabolism, while no differences in CL weight nor amount of P4 in CL were different between pregnant and non-pregnant cattle. Moreover, the increase in specific concentrations of oxylipins in the CL may indicate a novel pathway of steroid and eicosanoid metabolism during maternal recognition of pregnancy.

In vitro and in vivo effect of Eurycoma longifolia root extract on UDP-glucuronosyltransferase activity

In vitro and in vivo effect of Eurycoma longifolia root extract on UDP-glucuronosyltransferase activity

Per- and polyfluoroalkyl substances display structure-dependent inhibition towards UDP-glucuronosyltransferases

Per- and polyfluoroalkyl substances (PFASs) are a large group of chemicals and can be detected in environmental and human samples all over the world. Toxicity of existing and emerging PFASs will be a long-term source of concern. This study aimed to investigate structure-dependent inhibitory effects of 14 PFASs towards the activity of 11 UDP-glucuronosyltransferase (UGT) isoforms. In vitro UGTs-catalyzed glucuronidation of 4-methylumbelliferone (4-MU) was employed to determine the inhibition of PFASs towards different UGT isoforms. All the PFASs showed <75% of inhibition or stimulation effects on UGT1A3, UGT1A7, UGT1A9, UGT2B4, UGT2B7 and UGT2B17. However, PFASs showed broad inhibition on the activity of UGT1A1 and UGT1A8. The activity of UGT1A1 was inhibited by 98.8%, 98%, 79.9%, 77.1%, and 76.9% at 100 μmoL/L of perfluorodecanoic acid (PFDA), perfluorooctanesulfonic acid potassium salt (PFOS), perfluorotetradecanoic acid (PFTA), perfluorooctanoic acid (PFOA) and perfluorododecanoic acid (PFDoA), respectively. UGT1A8 was inhibited by 97.6%, 94.8%, 86.3%, 83.4% and 77.1% by PFDA, PFTA, perfluorooctadecanoic acid (PFOcDA), PFDoA and PFOS, respectively. Additionally, PFDA significantly inhibited UGT1A6 and UGT1A10 by 96.8% and 91.6%, respectively. PFDoA inhibited the activity of UGT2B15 by 88.2%. PFDA and PFOS exhibited competitive inhibition towards UGT1A1, and PFDA and PFTA showed competitive inhibition towards UGT1A8. The inhibition kinetic parameter (Ki) were 3.15, 1.73, 13.15 and 20.21 μmoL/L for PFDA-1A1, PFOS-1A1, PFDA-1A8 and PFTA-1A8, respectively. The values were calculated to be 0.3 μmoL/L and 1.3 μmoL/L for the in vivo inhibition of PFDA towards UGT1A1-and UGT1A8-catalyzed metabolism of substances, and 0.2 μmoL/L and 2.0 μmoL/L for the inhibition of PFOS towards UGT1A1 and the inhibition of PFTA towards UGT1A8, respectively. Molecular docking indicated that hydrogen bonds and hydrophobic interactions contributed to the interaction between PFASs and UGT isoforms. In conclusion, exposure to PFASs might inhibit the activity of UGTs to disturb metabolism of endogenous compounds and xenobiotics. The structure-related effects of PFASs on UGTs would be very important for risk assessment of PFASs.

Evaluation of the inhibition risk of shikonin on human and rat UDP-glucuronosyltransferases (UGT) through the cocktail approach

Shikonin, a natural red colorant, is widely used for food garnishment and cosmetic ingredient in the world. Shikonin also possesses a variety of pharmacological actions, including anti-inflammation and anti-cancer activities. However, little is known about its effects on the UDP-glucuronosyltransferases (UGT) activity. Therefore, the aim of this study was to evaluate the effect of shikonin on the UGT1A1, UGT1A3, UGT1A6, UGT1A9 and UGT2B7 activities via the human and rat liver microsomal assay and cocktail approach. The results showed shikonin inhibited human and rat liver microsomal UGT activity only in a dose-dependent manner. The further enzyme kinetic studies demonstrated that shikonin was not only a competitive inhibitor of human UGT1A1, UGT1A9, and UGT2B7, but also presented competitive inhibition on rat UGT1A1 and AZTG reactions. In conclusion, shikonin as a reversible inhibitor of UGT enzyme has a high-risk potential to cause the possible toxicity, especially drug-drug or food-drug interactions.

Contributions of Hepatic and Intestinal Metabolism to the Disposition of Niclosamide, a Repurposed Drug with Poor Bioavailability.

Niclosamide, an antiparasitic, has been repositioned as a potential therapeutic drug for systemic diseases based on its antiviral, anticancer, and anti-infection properties. However, low bioavailability limits its in vivo efficacy. Our aim was to determine whether metabolic disposition by microsomal P450 enzymes in liver and intestine influences niclosamide's bioavailability in vivo, by comparing niclosamide metabolism in wild-type, liver-Cpr-null (LCN), and intestinal epithelium-Cpr-null (IECN) mice. In vitro stability of niclosamide in microsomal incubations was greater in the intestine than in liver in the presence of NADPH, but it was much greater in liver than in intestine in the presence of UDPGA. NADPH-dependent niclosamide metabolism and hydroxy-niclosamide formation were inhibited in hepatic microsomes of LCN mice, but not IECN mice, compared with wild-type mice. In intestinal microsomal reactions, hydroxy-niclosamide formation was not detected, but rates of niclosamide-glucuronide formation were ∼10-fold greater than in liver, in wild-type, LCN, and IECN mice. Apparent Km and V max values for microsomal niclosamide-glucuronide formation showed large differences between the two tissues, with the intestine having higher Km (0.47 μM) and higher V max (15.8) than the liver (0.09 μM and 0.75, respectively). In vivo studies in LCN mice confirmed the essential role of hepatic P450 in hydroxy-niclosamide formation; however, pharmacokinetic profiles of oral niclosamide were only minimally changed in LCN mice, compared with wild-type mice, and the changes seem to reflect the compensatory increase in hepatic UDP-glucuronosyltransferase activity. SIGNIFICANCE STATEMENT: These results suggest that efforts to increase the bioavailability of niclosamide by blocking its metabolism by P450 enzymes will unlikely be fruitful. In contrast, inhibition of niclosamide glucuronidation in both liver and intestine may prove effective for increasing niclosamide's bioavailability, thereby making it practical to repurpose this drug for treating systemic diseases.

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 (Ki) 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.

Isolated Silymarin Flavonoids Increase Systemic and Hepatic Bilirubin Concentrations and Lower Lipoperoxidation in Mice.

Bilirubin is considered to be one of the most potent endogenous antioxidants in humans. Its serum concentrations are predominantly affected by the activity of hepatic bilirubin UDP-glucuronosyl transferase (UGT1A1). Our objective was to analyze the potential bilirubin-modulating effects of natural polyphenols from milk thistle (Silybum marianum), a hepatoprotective herb. Human hepatoblastoma HepG2 cells were exposed to major polyphenolic compounds isolated from milk thistle. Based on in vitro studies, 2,3-dehydrosilybins A and B were selected as the most efficient compounds and applied either intraperitoneally or orally for seven days to C57BL/6 mice. After, UGT1A1 mRNA expression, serum, intrahepatic bilirubin concentrations, and lipoperoxidation in the liver tissue were analyzed. All natural polyphenols used increased intracellular concentration of bilirubin in HepG2 cells to a similar extent as atazanavir, a known bilirubinemia-enhancing agent. Intraperitoneal application of 2,3-dehydrosilybins A and B (the most efficient flavonoids from in vitro studies) to mice (50 mg/kg) led to a significant downregulation of UGT1A1 mRNA expression (46 ± 3% of controls, p < 0.005) in the liver and also to a significant increase of the intracellular bilirubin concentration (0.98 ± 0.03vs.1.21 ± 0.02 nmol/mg, p < 0.05). Simultaneously, a significant decrease of lipoperoxidation (61 ± 2% of controls, p < 0.005) was detected in the liver tissue of treated animals, and similar results were also observed after oral treatment. Importantly, both application routes also led to a significant elevation of serum bilirubin concentrations (125 ± 3% and 160 ± 22% of the controls after intraperitoneal and oral administration, respectively, p < 0.005 in both cases). In conclusion, polyphenolic compounds contained in silymarin, in particular 2,3-dehydrosilybins A and B, affect hepatic and serum bilirubin concentrations, as well as lipoperoxidation in the liver. This phenomenon might contribute to the hepatoprotective effects of silymarin.

A comparative investigation of the effects of feed-borne deoxynivalenol (DON) on growth performance, nutrient utilization and metabolism of detoxification in rainbow trout (Oncorhynchus mykiss) and Nile tilapia (Oreochromis niloticus) fed diets containing different levels of digestible carbohydrates

Increasing evidence suggests that variability in hepatic glucuronidation is a critical determinant of mammalian species-specific sensitivity to the Fusarium mycotoxin deoxynivalenol (DON). Concurrently, ongoing work regarding the effects of DON on fish has led to broad classifications concerning species-specific sensitivity (e.g. rainbow trout are highly sensitive to DON and channel catfish are highly tolerant to DON). This study was designed to determine if sensitivity to DON in fish is related to inherent differences in UDP-glucuronosyltransferase (UDPGT) activity and to evaluate if increased dietary digestible starch content could be an effective strategy to increase glucuronidation capacity. Rainbow trout or Nile tilapia (initial average body weight = 21.9 and 8.1 g/fish, respectively) were fed two series (12 or 24% digestible starch) of three diets containing graded levels of naturally occurring DON (0.1, 0.7 and 1.3 ppm) for 10 weeks. Significant linear decreases in weight gain, thermal-unit growth coefficient (TGC, P ≤ .05), feed efficiency (P < .001), whole body crude protein (CP) content (P < .001), retained nitrogen (RN, P ≤ .05) and nitrogen retention efficiency (NRE, P < .01) were associated with increasing levels of DON in rainbow trout regardless of the dietary digestible starch content. There were no significant effects of DON on any of these parameters in Nile tilapia (P > .05) with the exception of a quadratic increase in NRE (P < .01) in fish fed the diets containing 24% digestible starch. The effect of DON on growth performance and nutrient utilization was not altered by the digestible starch content of the diet (P > .05, DON × digestible starch). A significant quadratic decrease (P ≤ .05) in UDPGT activity was associated with increasing levels of DON in rainbow trout fed the diet containing 12% digestible starch, whereas trout and tilapia fed the diet containing 24% digestible starch experienced significant quadratic or linear increases (P ≤ .05) in UDPGT activity, respectively. However, UDPGT activity was approximately 10-fold higher in rainbow trout than in Nile tilapia. This suggests that UDPGT activity is not responsible for the observed species-specific sensitivity to DON or it is not an appropriate biomarker of DON glucuronidation. A significantly higher relative fold expression of CYP1A in tilapia compared to trout (P = .0001) may offer potential opportunity for future study. We demonstrate for the first time that Nile tilapia are unaffected by practically relevant levels of DON which are detrimental to rainbow trout. This study also extends the current knowledge of DON metabolism and represents an important contribution to the development of efficacious nutritional mycotoxin mitigation strategies.

Effect of feed restriction on hepatic estradiol metabolism and liver function in cows

In this study, the effects of restriction feeding on the liver function, hepatic uridine diphosphate glucuronosyltransferase (UGT) activity, hepatic insulin-like growth factor (IGF)-1 mRNA expression and response to high-dose estradiol-17β (E2) administration were investigated in non-lactating cows. Cows were assigned to either restricted feeding (30% of total digestible nutrient requirement) or ad libitum feeding of a dent corn-based concentrate and roughage for a 2-week feeding trial (Day 1=day of beginning the feeding trial). On day 14, a high-dose E2 administration study was carried out to examine plasma E2 levels as an indicator of hepatic E2 metabolism. Plasma E2 concentration in the restricted feeding group was consistently higher after high-dose E2 administration than in the control group. In addition, indocyanine green half-life value was prolonged by restricted feeding for 13 days, and increased liver triglyceride concentration and decreased liver UGT activity were caused by this restriction over 14 days. Restricted feeding did not affect plasma IGF-1 concentration or hepatic IGF-1 mRNA expression. These results suggest that two weeks of restriction feeding led to accumulation of triglyceride, decreased liver blood flow, and slightly impaired liver function, which in turn slowed down the hepatic metabolism of E2 without significantly impacting hepatic IGF-1 production.

In vitro UDP-Glucuronosyltransferase and Cytochrome P450 Enzymes Activities of Clinacanthus nutans Leaf Juice and Aqueous Extract

Aim: The objective of the present study was to evaluate the in vitro effect of aqueous extract of Clinacanthus nutans leaves and the juice on the activity of UDP-glucuronosyltransferase (UGT), cytochrome P (CYP) 3A4, and CYP2E1 in human liver microsomes (HLMs). Materials and Methods: The herb-drug interactions of the leaf extracts and juice were determined by a specific enzyme activity of CYP isoforms with specific probe substrate using spectrophotometry. CYP3A4 activity was measured for aminopyrine-specific metabolite (formaldehyde) at 415 nm. CYP2E1 activity was determined using p-nitrophenol-specific metabolite (p-nitrocatechol) at 535 nm. UGT activity was quantified through the consumption of p-nitrophenol by UGT at 405 nm. Results: Results obtained showed that the juice and aqueous extract of C. nutans leaves exhibited significant inhibition (P