UDP-glucuronosyltransferase Activity Research Articles

Selectivity for inhibition of nilotinib on the catalytic activity of human UDP-glucuronosyltransferases

1. Nilotinib, a tyrosine kinase inhibitor, could potently inhibit SN-38 glucuronidation mainly catalyzed by UDP-glucuronosyltransferase (UGT) 1A1. This study was designed to investigate whether nilotinib can be used as a selective inhibitor of UGT1A1 in human liver.2. Assays with recombinant UGTs indicated that nilotinib could strongly inhibit the activity of UGT1A1 and decreased the activity of extra-hepatic UGT1A7 to a much lesser extent. The inhibition on 4-methylumbelliferone (4Mu) glucuronidation by recombinant UGT1A1 obeyed competitive inhibition mechanism, with a kinetic constants (Ki) value of 0.17 μM. Assays with human liver microsomes (HLM) demonstrated that nilotinib could selectively inhibit estradiol-3-O-glucuronidation (E2-3-O-glucuronidation), a probe reaction of UGT1A1. Kinetic studies displayed that the inhibition on E2-3-O-glucuronidation followed non-competitive inhibition model, different from the inhibition on 4Mu glucuronidation. The Ki values were calculated to be 0.14 and 0.53 μM, depending on the enzyme sources of recombinant UGT1A1 or HLM, respectively.3. Given that UGT1A7 is an extra-hepatic enzyme, this study indicates that nilotinib can be used as a selective inhibitor of UGT1A1 in human liver.

Multibiomarker responses upon exposure to tetrabromobisphenol A in the freshwater fish Carassius auratus

Tetrabromobisphenol A (TBBPA) is a widely used brominated flame retardant. It has been released into aquatic environments, where it is toxic to aquatic organisms. In the present study, five enzymes, glutathione-S-transferase (GST), aspartate aminotransferase (AST), alanine aminotransferase (ALT), UDP-glucuronosyltransferase (UDPGT), and the antioxidant enzyme glutathione reductase (GR) in serum and liver of crucian carp (Carassius auratus) were selected for screening. These enzymes may be suitable for use as early warning indicators of chronic TBBPA exposure. UDPGT, AST, ALT, and GR activities in serum were found to be as more sensitive to TBBPA as those of the liver. When the concentration of TBBPA exceeded 0.50–0.71mg/L for an exposure period of 32 days, GST, AST, ALT, and UDPGT activities cannot be restored to normal levels, suggesting that fish exposed to TBBPA above this threshold may incur irreversible damage. The activities of AST, ALT, and GR increased more significantly than GST and UDPGT at the lowest concentration of 0.35mg/L. AST showed the strongest activity with respect to toxic kinetics, followed by ALT and GR. This remained true from day 4 of exposure to TBBPA to day 32. However, GR showed the clearest and most significant dose–effect relationship. This shows that each of these three enzymes can be used as a biomarker for early warning applications focusing on TBBPA pollution. AST and ALT are suitable for use in conventional monitoring of water quality in areas at risk for TBBPA pollution, and GR is more suitable for use in burst TBBPA pollution accidents where GR activity in fish would change with the TBBPA concentration of the flowing water.

Xenobiotic metabolizing enzyme activities in cells used for testing skin sensitization in vitro

For ethical and regulatory reasons, in vitro tests for scoring potential toxicities of cosmetics are essential. A test strategy for investigating potential skin sensitization using two human keratinocytic and two human dendritic cell lines has been developed (Mehling et al. Arch Toxicol 86:1273–1295, 2012). Since prohaptens may be metabolically activated in the skin, information on xenobiotic metabolizing enzyme (XME) activities in these cell lines is of high interest. In this study, XME activity assays, monitoring metabolite or cofactor, showed the following: all three passages of keratinocytic (KeratinoSens® and LuSens) and dendritic (U937 und THP-1) cells displayed N-acetyltransferase 1 (NAT1) activities (about 6–60 nmol/min/mg S9-protein for acetylation of para-aminobenzoic acid). This is relevant since reactive species of many cosmetics are metabolically controlled by cutaneous NAT1. Esterase activities of about 1–4 nmol fluorescein diacetate/min/mg S9-protein were observed in all passages of investigated keratinocytic and about 1 nmol fluorescein diacetate/min/mg S9-protein in dendritic cell lines. This is also of practical relevance since many esters and amides are detoxified and others activated by cutaneous esterases. In both keratinocytic cell lines, activities of aldehyde dehydrogenase (ALDH) were observed (5–17 nmol product/min/mg cytosolic protein). ALDH is relevant for the detoxication of reactive aldehydes. Activities of several other XME were below detection, namely the investigated cytochrome P450-dependent alkylresorufin O-dealkylases 7-ethylresorufin O-deethylase, 7-benzylresorufin O-debenzylase and 7-pentylresorufin O-depentylase (while NADPH cytochrome c reductase activities were much above the limit of quantification), the flavin-containing monooxygenase, the alcohol dehydrogenase as well as the UDP glucuronosyl transferase activities.

The Human UDP-Glucuronosyltransferase UGT2A1 and UGT2A2 Enzymes Are Highly Active in Bile Acid Glucuronidation

Bile acids (BA) are essential modulators of lipid, glucose, and cholesterol homeostasis, but they exert cytotoxic effects in the cholestatic liver. Glucuronidation, catalyzed by the UDP-glucuronosyltransferase (UGT) enzymes is a pharmacologically relevant BA detoxification process. The present study characterized the BA-conjugating activity of the little-studied human UGTs of subfamily 2A: UGT2A1, 2A2, and 2A3. Recombinant UGT2As, expressed in baculovirus-infected insect cells, were assayed for the glucuronidation of six major bile acids: chenodeoxycholic acid (CDCA), cholic acid (CA), lithocholic acid (LCA), deoxycholic acid (DCA), hyocholic acid (HCA) and hyodeoxycholic acid (HDCA). UGT2A3 exhibited detectable but very low activity with all the tested BA substrates. UGT2A1 was highly efficient in forming LCA-3 and LCA-24G, CDCA-24, DCA-24, HCA-24, and HDCA-24G, whereas UGT2A2 was the most active enzyme for CA-24G and CDCA-24G formation and also was able to generate HDCA-6G, HDCA-24G, LCA-24G, and HCA-24G. The Km values of UGT2A1 varied between 102.2 ± 14.3 µM and 2.4 ± 1.2 mM. With the exception of CA-24G, a low affinity substrate for UGT2A2, all the Km values for UGT2A2 were in the 100 to 400 µM range. We demonstrate the high reactivity of the human UGT2A1 and UGT2A2 for bile acid glucuronidation. The physiologic importance of these reactions to BA disposition remains, however, to be clarified in vivo.

Use of Human In Vitro Skin Models for Accurate and Ethical Risk Assessment: Metabolic Considerations

Several human skin models employing primary cells and immortalized cell lines used as monocultures or combined to produce reconstituted 3D skin constructs have been developed. Furthermore, these models have been included in European genotoxicity and sensitization/irritation assay validation projects. In order to help interpret data, Cosmetics Europe (formerly COLIPA) facilitated research projects that measured a variety of defined phase I and II enzyme activities and created a complete proteomic profile of xenobiotic metabolizing enzymes (XMEs) in native human skin and compared them with data obtained from a number of in vitro models of human skin. Here, we have summarized our findings on the current knowledge of the metabolic capacity of native human skin and in vitro models and made an overall assessment of the metabolic capacity from gene expression, proteomic expression, and substrate metabolism data. The known low expression and function of phase I enzymes in native whole skin were reflected in the in vitro models. Some XMEs in whole skin were not detected in in vitro models and vice versa, and some major hepatic XMEs such as cytochrome P450-monooxygenases were absent or measured only at very low levels in the skin. Conversely, despite varying mRNA and protein levels of phase II enzymes, functional activity of glutathione S-transferases, N-acetyltransferase 1, and UDP-glucuronosyltransferases were all readily measurable in whole skin and in vitro skin models at activity levels similar to those measured in the liver. These projects have enabled a better understanding of the contribution of XMEs to toxicity endpoints.

Mitragyna speciosa Korth leaves extracts induced the CYP450 catalyzed aminopyrine-N-demethylase (APND) and UDP-glucuronosyl transferase (UGT) activities in male Sprague-Dawley rat livers

Mitragyna speciosa leaves have been abused by drug addicts as some of the alkaloids (mainly mitragynine) from the plant possess opiate and cocaine-like effects. These bring to its prohibition in Malaysia in 2004 as consumption of M. speciosa leaves has been perceived to lead to the abuse of other drugs such as cannabis and heroin. In the current study, the in vitro and in vivo effects of M. speciosa methanolic, aqueous and total alkaloid leaves extracts on drug metabolizing enzymes, namely, cytochrome P450s (CYP450s) and UDP-glucuronosyl transferase (UGT) had been evaluated in rat liver cytosolic fraction and microsomes. Aminopyrine and p-nitrophenol (pNP) were employed as probe substrates in aminopyrine N-demethylase (APND) and UGT enzyme assays, respectively. Furthermore, mitragynine was also tested in vitro for its likelihood to inhibit APND and UGT activity. The assessment of the enzyme activity was conducted using spectrophotometric methods. In vitro, the IC50 value could only be obtained for the methanolic extract in APND study (595.30±30.78 µg/mL) and not in other studies due to the enzyme percentage inhibitions being <70%. In contrast to the in vitro study, the oral treatment of male Sprague-Dawley rats for 14 days with 50, 100 and 200 mg/kg of methanolic and aqueous extracts and with 5, 10 and 20 mg/kg of total alkaloid extract showed a profound increment on the APND and UGT activities. The current findings showed that possibilities exist for herb-drug interaction with increased clearance of drugs, which are primarily metabolized by CYP450s and UGT1A6 among M. speciosa leaves extract users.

Activity of Xenobiotic-Metabolizing Enzymes in the Liver of Rats with Multi-Vitamin Deficiency

The purpose of the study was to determine how multi-vitamin deficiency affects xenobiotic-metabolizing enzyme (XME) activities in the rat liver. Vitamin levels and XME activities were studied in the livers of male Wistar rats who were fed for 4 weeks with semi-synthetic diets containing either adequate (100 % of recommended vitamin intake) levels of vitamins (control), or decreased vitamin levels (50 % or 20 % of recommended vitamin intake). The study results have shown that moderate vitamin deficiency (50 %) leads to a decrease of vitamin A levels only, and to a slight increase, as compared with the control, in the following enzyme activities: methoxyresorufin O-dealkylase (MROD) activity of CYP1 A2 - by 34 % (p < 0.05), UDP-glucuronosyl transferase - by 26 % (p < 0.05), and quinone reductase - by 55 % (p < 0.05). Profound vitamin deficiency (20 %) led to a decrease of vitamins A, E, B1, B2, and C, and enzyme activities in the liver: MROD - to 78 % of the control level (p < 0.05), 4-nitrophenol hydroxylase - to 74 % (p < 0.05), heme oxygenase-1 - to 83 % (p < 0.05), and quinone reductase - to 60 % (p < 0.05). At the same time, the UDP-glucuronosyl transferase activity and ethoxyresorufin O-dealkylase activity of CYP1A1, pentoxyresorufin O-dealkylase activity of CYP2B1/2 and 6β-testosterone hydroxylase, as well as the total activity of glutathione transferase did not differ from the control levels. The study has demonstrated that profound multi-vitamin deficiency is associated with a decrease in the expression of CYP1A2 and CYP3A1 mRNAs to 62 % and 79 %, respectively. These data indicated that a short-term but profound multi-vitamin deficiency in rats leads to a decrease in the activities and expression of the some XME that play an important role in detoxification of xenobiotics and metabolism of drugs and antioxidant protection.

Albumin Stimulates the Activity of the Human UDP-Glucuronosyltransferases 1A7, 1A8, 1A10, 2A1 and 2B15, but the Effects Are Enzyme and Substrate Dependent

Human UDP-glucuronosyltransferases (UGTs) are important enzymes in metabolic elimination of endo- and xenobiotics. It was recently shown that addition of fatty acid free bovine serum albumin (BSA) significantly enhances in vitro activities of UGTs, a limiting factor in in vitro–in vivo extrapolation. Nevertheless, since only few human UGT enzymes were tested for this phenomenon, we have now performed detailed enzyme kinetic analysis on the BSA effects in six previously untested UGTs, using 2–4 suitable substrates for each enzyme. We also examined some of the previously tested UGTs, but using additional substrates and a lower BSA concentration, only 0.1%. The latter concentration allows the use of important but more lipophilic substrates, such as estradiol and 17-epiestradiol. In five newly tested UGTs, 1A7, 1A8, 1A10, 2A1, and 2B15, the addition of BSA enhanced, to a different degree, the in vitro activity by either decreasing reaction’s K m, increasing its V max, or both. In contrast, the activities of UGT2B17, another previously untested enzyme, were almost unaffected. The results of the assays with the previously tested UGTs, 1A1, 1A6, 2B4, and 2B7, were similar to the published BSA only as far as the BSA effects on the reactions’ K m are concerned. In the cases of V max values, however, our results differ significantly from the previously published ones, at least with some of the substrates. Hence, the magnitude of the BSA effects appears to be substrate dependent, especially with respect to V max increases. Additionally, the BSA effects may be UGT subfamily dependent since K m decreases were observed in members of subfamilies 1A, 2A and 2B, whereas large V max increases were only found in several UGT1A members. The results shed new light on the complexity of the BSA effects on the activity and enzyme kinetics of the human UGTs.

Inhibitory effect of anthocyanidins on hepatic glutathione S-transferase, UDP-glucuronosyltransferase and carbonyl reductase activities in rat and human

1. Anthocyanins and their aglycone anthocyanidins represent the most abundant flavonoids in human diet and popular constituents of various dietary supplements. The aim of this study was to evaluate inhibitory effect of four anthocyanidins (delphinidin, cyanidin, malvidin and pelargonidin) on three families of important drug-metabolizing enzymes: carbonyl reductases (CBRs), glutathione S-transferases (GSTs) and UDP-glucuronosyltransferases (UGT).2. Human or rat hepatic subcellular fractions were incubated with or without pure anthocyanidins (100 µM) and the activities of CBR, GST and UGT were assayed using menadione, 1-chloro-2,4-dinitrobenzene and p-nitrophenol as substrates, respectively. For the most potent inhibitors, half maximal inhibitory concentrations (IC50) were determined and the inhibition kinetics study was performed.3. Anthocyanidins inhibited weakly the activity of GST and moderately the activities of CBR and UGT. Cyanidin was the most potent inhibitor of human UGT with IC50 = 69 µM (at 200 µM substrate concentration) and competitive type of action. Delphinidin acted as significant non-competitive inhibitor of human CBR with IC50 = 16 µM (at substrate concentration 500 µM). The inhibitory potency of anthocyanidins differed in rat and human samples significantly.4. Anthocyanidins are able to inhibit CBR and UGT in vitro. Possible interference of anthocyanidins (in high-dose dietary supplements) with simultaneously administered drugs, which are UGT or CBR substrates, should be checked.

Regiospecificity and Stereospecificity of Human UDP-Glucuronosyltransferases in the Glucuronidation of Estriol, 16-Epiestriol, 17-Epiestriol, and 13-Epiestradiol

The glucuronidation of estriol, 16-epiestriol, and 17-epiestriol by the human UDP-glucuronosyltransferases (UGTs) of subfamilies 1A, 2A, and 2B was examined. UGT1A10 is highly active in the conjugation of the 3-OH in all these estriols, whereas UGT2B7 is the most active UGT toward one of the ring D hydroxyls, the 16-OH in estriol and 16-epiestriol, but the 17-OH in 17-epiestriol. Kinetic analyses indicated that the 17-OH configuration plays a major role in the affinity of UGT2B7 for estrogens. The glucuronidation of the different estriols by the human liver and intestine microsomes reflects the activity of UGT1A10 and UGT2B7 in combination with the tissues' difference in UGT1A10 expression. The UGT1A10 mutant 1A10-F93G exhibited much higher V(max) values than UGT1A10 in estriol and 17-epiestriol glucuronidation, but a significantly lower value in 16-epiestriol glucuronidation. To this study on estriol glucuronidation we have added experiments with 13-epiestradiol, a synthetic estradiol in which the spatial arrangement of the methyl on C18 and the hydroxyl on C17 is significantly different than in other estrogens. In comparison with estradiol glucuronidation, the C13 configuration change decreases the turnover of UGTs that conjugate the 3-OH, but increases it in UGTs that primarily conjugate the 17-OH. Unexpectedly, UGT2B17 exhibited similar conjugation rates of both the 17-OH and 3-OH of 13-espiestradiol. The combined results reveal the strong preference of UGT1A10 for the 3-OH of physiologic estrogens and the equivalently strong preference of UGT2B7 and UGT2B17 for the hydroxyls on ring D of such steroid hormones.

Effects of Dietary Components on Testosterone Metabolism via UDP-Glucuronosyltransferase

The potential interference in testosterone metabolism through ingested substances has ramifications for: (i) a range of pathologies such as prostate cancer, (ii) medication contra-indications, (iii) disruption to the endocrine system, and (iv) potential confounding effects on doping tests. Conjugation of anabolic steroids during phase II metabolism, mainly driven by UDP-glucuronosyltransferase (UGT) 2B7, 2B15, and 2B17, has been shown to be impaired in vitro by a range of compounds including xenobiotics and pharmaceuticals. Following early reports on the effects of a range of xenobiotics on UGT activity in vitro, the work was extended to reveal similar effects with common non-steroidal anti-inflammatory drugs. Notably, recent studies have evidenced inhibitory effects of the common foodstuffs green tea and red wine, along with their constituent flavonoids and catechins. This review amalgamates the existing evidence for the inhibitory effects of various pharmaceutical and dietary substances on the rate of UGT glucuronidation of testosterone; and evaluates the potential consequences for health linked to steroid levels, interaction with treatment drugs metabolized by the UGT enzyme and steroid abuse in sport.

Evaluation of DA-9801, a new herbal drug for diabetic neuropathy, on metabolism-mediated interaction

DA-9801, the mixture extract of Dioscoreae rhizoma and Dioscorea nipponica Makino, is a new herbal drug currently being evaluated in a phase II clinical study for the treatment of diabetic peripheral neuropathy in Korea. The inhibitory potentials of DA-9801, D. rhizoma extract, D. nipponica Makino extract, and dioscin, an active component of DA-9801, on eight human cytochrome P450 (CYP) enzymes and four UDP-glucuronosyltransferase (UGT) enzymes were investigated in human liver microsomes using liquid chromatography-tandem mass spectrometry. DA-9801 showed slight inhibition of CYP1A2, CYP2C8, UGT1A1, and UGT1A9 enzyme activities with IC(50) values of 396.4, 449.9, 226.0, and 408.8μg/mL, respectively. D. rhizoma extract showed negligible inhibition of CYP and UGT activities, but D. nipponica extract slightly inhibited CYP1A2, CYP2C8, CYP2C9, UGT1A1, and UGT1A9 activities with IC(50) values of 264.2, 237.1, 206.8, 302.4, and 383.1μg/mL, respectively. DA-9801 showed volume per dose index values of 0.44-0.88L for a 200-mg dose, suggesting that they may not cause the inhibition of the metabolism of CYP1A2, CYP2C8, UGT1A1, and UGT1A9-catalyzed drugs in humans. These results suggest that the administration of DA-9801 in human may not cause clinically relevant inhibition of these enzymes.

Age-Related Changes in Hepatic Activity and Expression of Detoxification Enzymes in Male Rats

Process of aging is accompanied by changes in the biotransformation of xenobiotics and impairment of normal cellular functions by free radicals. Therefore, this study was designed to determine age-related differences in the activities and/or expressions of selected drug-metabolizing and antioxidant enzymes in young and old rats. Specific activities of 8 drug-metabolizing enzymes and 4 antioxidant enzymes were assessed in hepatic subcellular fractions of 6-week-old and 21-month-old male Wistar rats. Protein expressions of carbonyl reductase 1 (CBR1) and glutathione S-transferase (GST) were determined using immunoblotting. Remarkable age-related decrease in specific activities of CYP2B, CYP3A, and UDP-glucuronosyl transferase was observed, whereas no changes in activities of CYP1A2, flavine monooxygenase, aldo-keto reductase 1C, and antioxidant enzymes with advancing age were found. On the other hand, specific activity of CBR1 and GST was 2.4 folds and 5.6 folds higher in the senescent rats compared with the young ones, respectively. Interindividual variability in CBR1 activity increased significantly with rising age. We suppose that elevated activities of GST and CBR1 may protect senescent rats against xenobiotic as well as eobiotic electrophiles and reactive carbonyls, but they may alter metabolism of drugs, which are CBR1 and especially GSTs substrates.

Garlic Oil Attenuated Nitrosodiethylamine-Induced Hepatocarcinogenesis by Modulating the Metabolic Activation and Detoxification Enzymes

Nitrosodiethylamine (NDEA) is a potent carcinogen widely existing in the environment. Our previous study has demonstrated that garlic oil (GO) could prevent NDEA-induced hepatocarcinogenesis in rats, but the underlying mechanisms are not fully understood. It has been well documented that the metabolic activation may play important roles in NDEA-induced hepatocarcinogenesis. Therefore, we designed the current study to explore the potential mechanisms by investigating the changes of hepatic phase Ⅰ enzymes (including cytochrome P450 enzyme (CYP) 2E1, CYP1A2 and CYP1A1) and phase Ⅱ enzymes (including glutathione S transferases (GSTs) and UDP- Glucuronosyltransferases (UGTs)) by using enzymatic methods, real-time PCR, and western blotting analysis. We found that NDEA treatment resulted in significant decreases of the activities of CYP2E1, CYP1A2, GST alpha, GST mu, UGTs and increases of the activities of CYP1A1 and GST pi. Furthermore, the mRNA and protein levels of CYP2E1, CYP1A2, GST alpha, GST mu and UGT1A6 in the liver of NDEA-treated rats were significantly decreased compared with those of the control group rats, while the mRNA and protein levels of CYP1A1 and GST pi were dramatically increased. Interestingly, all these adverse effects induced by NDEA were simultaneously and significantly suppressed by GO co-treatment. These data suggest that the protective effects of GO against NDEA-induced hepatocarcinogenesis might be, at least partially, attributed to the modulation of phase I and phase II enzymes.

Disturbance of Hepatic and Intestinal UDP-glucuronosyltransferase in Rats with Trinitrobenzene Sulfonic Acid-induced Colitis

UDP-glucuronosyltransferase (UGT) is an important class of phase II metabolizing enzymes, playing a pivotal role in detoxifying various substances and in the pathological procedures of some diseases. The present study aims to uncover the potential dysregulation pattern of UGTs in trinitrobenzene sulfonic acid (TNBS)-induced colitis. Colitis was induced by intra-rectally administering a single dose of TNBS (100 mg/kg). The expression and enzyme activity of hepatic UGTs of colitis rats were all down-regulated significantly except UGT1A7, for which the mRNA level was up-regulated. In contrast, UGT isoforms in the small intestine were relatively unaffected. In the colon, where the inflammation occurs, the mRNA level and enzyme activity of UGT1A1 and 1A6 were down-regulated, but those of UGT1A7 and 2B1 up-regulated. The mRNA levels of various transcription factors, including AhR, CAR, PXR, PPARγ, and FXR were all decreased, except for AhR and CAR in the small intestine and colon. Our data suggests that colitis induces an isoform-dependent and tissue-specific dysregulation of UGTs and their related transcription factors.

Validated liquid chromatography–tandem mass spectrometry method for determination of totally nine probe metabolites of cytochrome P450 enzymes and UDP-glucuronosyltransferases

A simplified, rapid, and selective liquid chromatography–tandem mass spectrometry method for the determination of the activities of cytochrome P450 (CYP) enzymes and UDP-glucuronosyltransferases (UGTs) in two separate settings was developed and successfully applied to 8 CYP isoenzymes and UGT2B7 enzyme activities in rat liver microsomes.The triple-quadrupole mass spectrometric detection was operated in positive mode for the probe metabolites: CYP1A2 (resorufin), CYP2B6 (hydroxybupropion), CYP2C19 (5-hydroxyomeprazole), CYP2D6 (dextrophan), CYP3A4 (6β-hydroxytestosterone), and UGT2B7 (morphine-3-glucuronide); also in negative mode for CYP2C9 (4-hydroxytolbutamide), CYP2E1 (6-hydroxychloroxazone), and CYP4A (hydroxylauric acid). The metabolic reactions were terminated with acetonitrile, containing metoprolol and acetaminophen as the internal standard for positive and negative ion electrospray ionization, respectively.The method was validated over the concentration range of 25–2500ng/mL for 5-hydroxyomeprazole, dextrophan, hydroxylauric acid, and morphine-3-glucuronide; 5–500ng/mL for resorufin; 3–300ng/mL for hydroxybupropion; 10–1000ng/mL for 4-hydroxytolbutamide; 40–4000ng/mL for 6-hydroxychloroxazone; and 63–6300ng/mL for 6β-hydroxytestosterone. All of the extraction recoveries of these analytes were greater than 85%, except for hydroxylauric acid at mid-concentration with a recovery of 83.2%±3.2%. The matrix effects were between 85.8% and 119.9%; the respective within- and between-run precisions were 0.9–12.0% and 2.0–13.9%; and the within- and between-run accuracy levels were 0.6–17.2% and 0.1–15.1%, respectively, for all these analytes. All of the analytes were stable during the assay and storage in the liver microsomes of Sprague-Dawley rats.The measurement activity of multiple enzymes was feasible using a cocktail approach. This method proved to be a robust, fast, accurate, specific and sensitive assay, and was successfully used to investigate in vivo enzyme activities of 8 major CYP isoenzymes and UGT2B7 in Sprague-Dawley rats with fatty livers. By the end of the eighth week, the CD-fed induced fatty liver rats showed a significant decrease in the activities of CYP1A2 and UGT2B7 as compared to the standard diet group.

Tissue Distribution and Relative Gene Expression of UDP-Glucuronosyltransferases (2B7, 2B15, 2B17) in the Human Fetus

UDP-glucuronosyltransferases (UGTs) catalyze phase II conjugation reactions and play an important role in the inactivation and elimination of several drugs. It is well known that the UGT activity in fetal livers is low compared with the UGT activity in adult livers. In this study the mRNA expression levels of the three human subfamilies, 2B7, 2B15, and 2B17, were determined in 20 adult and 60 fetal liver tissue specimens. The expression profile in fetal kidneys (N = 43), adrenals (N = 46), and lungs (N = 37) was also determined. All fetal and adult samples were genotyped for the UGT2B17 deletion polymorphism. Adult liver contained 13-36 times higher levels of UGT2B mRNAs as compared with fetal livers. UGT2B7 was most abundant in fetal lungs and kidneys, whereas UGT2B15 and UGT2B17 were predominant in the liver. There was a significant correlation between UGT2B7 expression levels in lungs and kidneys, whereas for the other UGT2Bs no correlation between the different tissues was observed. Fetuses expressing two UGT2B17 alleles (ins/ins) displayed significantly higher levels of UGT2B17 mRNA compared to ins/del fetuses in lungs, whereas in the other tissues no gene dose-effect was observed.

Uremic toxins inhibit renal metabolic capacity through interference with glucuronidation and mitochondrial respiration

During chronic kidney disease (CKD), drug metabolism is affected leading to changes in drug disposition. Furthermore, there is a progressive accumulation of uremic retention solutes due to impaired renal clearance. Here, we investigated whether uremic toxins can influence the metabolic functionality of human conditionally immortalized renal proximal tubule epithelial cells (ciPTEC) with the focus on UDP-glucuronosyltransferases (UGTs) and mitochondrial activity. Our results showed that ciPTEC express a wide variety of metabolic enzymes, including UGTs. These enzymes were functionally active as demonstrated by the glucuronidation of 7-hydroxycoumarin (7-OHC; Km of 12±2μM and a Vmax of 76±3pmol/min/mg) and p-cresol (Km of 33±13μM and a Vmax of 266±25pmol/min/mg). Furthermore, a wide variety of uremic toxins, including indole-3-acetic acid, indoxyl sulfate, phenylacetic acid and kynurenic acid, reduced 7-OHC glucuronidation with more than 30% as compared with controls (p<0.05), whereas UGT1A and UGT2B protein expressions remained unaltered. In addition, our results showed that several uremic toxins inhibited mitochondrial succinate dehydrogenase (i.e. complex II) activity with more than 20% as compared with controls (p<0.05). Moreover, indole-3-acetic acid decreased the reserve capacity of the electron transport system with 18% (p<0.03). In conclusion, this study shows that multiple uremic toxins inhibit UGT activity and mitochondrial activity in ciPTEC, thereby affecting the metabolic capacity of the kidney during CKD. This may have a significant impact on drug and uremic retention solute disposition in CKD patients.

UGT1A1, UGT1A6 and UGT1A7 genetic analysis: repercussion for irinotecan pharmacogenetics in the São Miguel Island Population (Azores, Portugal).

Glucuronidation reactions, catalyzed by uridine-diphosphate glucuronosyltransferase (UGT) enzymes, constitute a detoxification process that adds glucuronic acid to endogenous and exogenous compounds, aiding their excretion. UGT1A proteins have been implicated as risk factors for both the development of cancer and adverse drug effects. Here, we assess the genome of 469 individuals from São Miguel Island (Azores, Portugal) in order to determine the frequencies of polymorphisms and haplotypes in UGT1A1, UGT1A6, and UGT1A7, the co-occurrence of reduced enzyme activity UGT1A variants related to irinotecan toxicity, and to calculate the extent of linkage disequilibrium (LD) in the genomic region encompassing these genes. Allelic analysis disclosed the presence of rare alleles - UGT1A1*36 and UGT1A1*37--only found in individuals of African descent, and UGT1A7*4. These alleles confirm our previous results on the São Miguel Island genetic background. We identified five different genotypes in UGT1A1 and UGT1A6 and nine in UGT1A7. Haplotype analysis showed that three haplotypes constituted approximately 80% of the allelic variants. Interestingly, haplotype 3 (UGT1A1*28-UGT1A6*2-UGT1A7*3), with a frequency of 0.235, gathers the three alleles encoding the low-function UGT isoforms. Additionally, LD indicates a strong interaction between functional polymorphisms related to the alteration of the UGT enzyme activity. In summary, the results demonstrate a high variability of alleles and haplotypes, which have important roles in modifying expression and activity of UGTs. The data presented here could improve the understanding of the predisposition to cancers and susceptibility to the adverse effects of irinotecan in the São Miguel Island population.

Mangifera indica L. Extract and Mangiferin Modulate Cytochrome P450 and UDP‐Glucuronosyltransferase Enzymes in Primary Cultures of Human Hepatocytes

The aqueous stem bark extract of Mangifera indica L. (MSBE) has been reported to have antioxidant, anti-inflammatory and analgesic properties. In previous studies, we showed that MSBE and mangiferin, its main component, lower the activity of some cytochrome P-450 (P450) enzymes in rat hepatocytes and human liver microsomes. In the present study, the effects of MSBE and mangiferin on several P450 enzymes and UDP-glucuronosyltransferases (UGTs) in human-cultured hepatocytes have been examined. After hepatocytes underwent a 48-h treatment with sub-cytotoxic concentrations of the products (50-250 µg/mL), a concentration-dependent decrease of the activity of the five P450 enzymes measured (CYP1A2, 2A6, 2C9, 2D6 and 3A4) was observed. For all the activities, a reduction of at least 50% at the highest concentration (250 µg/mL) was observed. In addition, UGT activities diminished. MSBE considerably reduced UGT1A9 activity (about 60% at 250 µg/mL) and lesser effects on the other UGTs. In contrast, 250 µg/mL mangiferin had greater effects on UGT1A1 and 2B7 than on UGT1A9 (about 55% vs. 35% reduction, respectively). Quantification of specific mRNAs revealed reduced CYP3A4 and 3A5 mRNAs content, and an increase in CYP1A1, CYP1A2, UGT1A1 and UGT1A9 mRNAs. No remarkable effects on the CYP2A6, 2B6, 2C9, 2C19, 2D6 and 2E1 levels were observed. Our results suggest that the activity and/or expression of major P450 and UGT enzymes is modulated by MSBE and that potential herb-drugs interactions could arise after a combined intake of this extract with conventional medicines. Therefore, the potential safety risks of this natural product derived by altering the ADMET properties of co-administered drugs should be examined.