Exploration of components and mechanisms of Polygoni Multiflori Radix-induced hepatotoxicity using siRNA -mediated CYP3A4 or UGT1A1 knockdown liver cells

ETHNOPHARMACOLOGICAL RELEVANCE

Polygoni Multiflori Radix, the dried root of Polygonum multiflorum Thunb., and its processed products have been used as restoratives for centuries in China. However, the reports of Polygoni Multiflori Radix-induced liver injury (PMR-ILI) have received wide attention in recent years, and the components and mechanism of PMR-ILI are not completely clear yet. Our previous studies found that the PMR-ILI was related to the down-regulation of some drug metabolism enzymes (DME).

AIM OF THE STUDY

To explore the effect of the inhibition of CYP3A4 or UGT1A1 on PMR-ILI, screen the relevant hepatotoxic components and unveil its mechanism.

METHODS

RT-qPCR was used to detect the effects of water extract of Polygoni Multiflori Radix (PMR) and its main components on the mRNA expression of CYP3A4 and UGT1A1 in human hepatic parenchyma cell line L02. High-performance liquid chromatography (HPLC) was employed to detect the content of major components in the PMR. And then, the stable CYP3A4 or UGT1A1 knockdown cells were generated using short hairpin RNAs (shRNA) in L02 and HepaRG cells. Hepatotoxic components were identified by cell viability assay when PMR and its four representative components, 2,3,5,4'-tetrahydroxy stilbene glycoside (TSG), emodin (EM), emodin-8-O-β-D-glucoside (EG), and gallic acid (GA), acted on CYP3A4 or UGT1A1 knockdown cell lines. The PMR-ILI mechanism of oxidative stress injury and apoptosis in L02 and HepaRG cells were detected by flow cytometry. Finally, the network toxicology prediction analysis was employed to excavate the targets of its possible toxic components and the influence on the metabolic pathway.

RESULTS

PMR and EM significantly inhibited the mRNA expression of CYP3A4 and UGT1A1 in L02 cells, while TSG and GA activated the mRNA expression of CYP3A4 and UGT1A1, and EG activated CYP3A4 expression while inhibited UGT1A1 expression. The contents of TSG, EG, EM and GA were 34.93 mg/g, 1.39 mg/g, 0.43 mg/g and 0.44 mg/g, respectively. The CYP3A4 or UGT1A1 knockdown cells were successfully constructed in both L02 and HepaRG cells. Low expression of CYP3A4 or UGT1A1 increased PMR cytotoxicity remarkably. Same as PMR, the toxicity of EM and GA increased in shCYP3A4 and shUGT1A1 cells, which suggested EM and GA may be the main components of hepatotoxicity in PMR. Besides, EM not only inhibited the expression of metabolic enzymes but also reduced the cytotoxicity threshold. EM and GA affected the level of ROS, mitochondrial membrane potential, Ca²⁺ concentration, and dose-dependent induced hepatocyte apoptosis in L02 and HepaRG cells. The network toxicology analysis showed that PMR-ILI was related to drug metabolism-cytochrome P450, glutathione metabolism, and steroid hormone biosynthesis.

CONCLUSION

The inhibition of mRNA expression of CYP3A4 or UGT1A1 enhanced hepatotoxicity of PMR. EM and GA, especially EM, may be the main hepatotoxic components in PMR. The mechanism of PMR, EM and GA induced hepatotoxicity was proved to be related to elevated levels of ROS, mitochondrial membrane potential, Ca²⁺ concentration, and induction of apoptosis in liver cells.

Metribuzin-induced non-adverse liver changes result in rodent-specific non-adverse thyroid effects via uridine 5'-diphospho-glucuronosyltransferase (UDPGT, UGT) modulation

Metribuzin is a herbicide that inhibits photosynthesis and has been used for over 40 years. Its main target organ is the liver and to some extent the kidney in rats, dogs, and rabbits. Metribuzin shows a specific thyroxine (T4) profile in rat studies with T4 increases at low doses and T4 decreases at higher doses. Only the T4 decreases occur together with histopathological changes in the thyroid and weight changes of liver and thyroid. A set of experiments was conducted to investigate metribuzin's endocrine disruptor potential according to European guidance and regulations. The results indicate that a liver enzyme modulation, i.e. of the uridine 5'-diphospho-glucuronosyltransferase (UDPGT, UGT), is most likely responsible for both increased and decreased plasma thyroxine level and for thyroid histopathological observations. Animals with high T4 levels show low UGT activity, while animals with low T4 levels show high UGT activity. A causal relationship was inferred, since other potentially human-relevant mode of action (MOA) pathways were excluded in dedicated studies, i.e. inhibition of deiodinases (DIO), inhibition of thyroid peroxidase (TPO) or of the sodium importer system (NIS). This liver metabolism-associated MOA is considered not relevant for human hazard assessment, due to species differences in thyroid homeostasis between humans and rats and, more importantly, based on experimental data showing that metribuzin affects UGT activity in rat but not in human hepatocytes. Further, we discuss whether or not increased T4 levels in the rat, in the absence of histopathological changes, should be considered as adverse and therefore used as an appropriate hazard model for humans. Based on a weight of evidence approach, metribuzin should not be classified as an endocrine disruptor with regard to the thyroid modality.

Nilotinib-induced liver injury: A case report

INTRODUCTION

Nilotinib is a selective inhibitor of the BCR-ABL tyrosine kinase receptor and is used in the management of chronic myelogenous leukemia (CML). Nilotinib therapy at high doses is associated with elevated serum bilirubin levels. If the serum bilirubin level exceeds 3 times the upper limit of normal, the recommendation is to either adjust nilotinib dosage or temporarily discontinue the treatment. However, it is unclear whether hyperbilirubinemia indicates obvious liver histology damage.

PATIENT CONCERNS

A 24-year-old man with confirmed CML was treated with nilotinib therapy and developed hyperbilirubinemia after the treatment. Although the first remission of the hyperbilirubinemia was achieved after dose adjustment, the hematological parameters deteriorated. Thus, we initiated an antineoplastic therapy (at the standard dose) until complete remission of the CML was achieved. The pathogenic mechanism of hyperbilirubinemia may be related to the inhibition of uridine diphosphate-glucuronosyltransferase (UGT1A1) activity. Liver histological analysis revealed no significant liver damage. In addition, the patient had no family history of hyperbilirubinemia and liver disease.

DIAGNOSIS

The patient was admitted to our hospital under the diagnosis of hyperbilirubinemia, and histopathology by liver biopsy showed no obvious damage. We also detected a UGT1A1 mutation [ex1 c.686C > A (p.Pro229Gln)] in the patient and his mother.

INTERVENTIONS

When the nilotinib dose was decreased to 300 mg daily, the total bilirubin (TBIL) level decreased to 30 to 50 μmol/L for 1 month. However, because the Bcr-Abl/Abl ratio did not correspond to the major molecular response (MMR; <0.1%), the nilotinib dose was readjusted to 400 mg daily. One week later, the TBIL and indirect bilirubin levels increased to 89 and 79 μmol/L, respectively. The levels of alanine transaminase and other liver functional indicators were normal.

OUTCOMES

A Naranjo Adverse Drug Reaction (ADR) Probability Scale score of 13 indicates that hyperbilirubinemia is attributed to ADR caused by nilotinib rather than by drug-induced liver injury.

CONCLUSION

Although reducing the nilotinib dose can alleviate the occurrence of hyperbilirubinemia, the effect of MMR is also reduced. Treatment of CML without dose adjustment or discontinuation of nilotinib therapy may be more advantageous.

Arsenic modifies serotonin metabolism through glucuronidation in pancreatic β-cells

In arsenic-endemic regions of the world, arsenic exposure correlates with diabetes mellitus. Multiple animal models of inorganic arsenic (iAs, as As³⁺) exposure have revealed that iAs-induced glucose intolerance manifests as a result of pancreatic β-cell dysfunction. To define the mechanisms responsible for this β-cell defect, the MIN6-K8 mouse β-cell line was exposed to environmentally relevant doses of iAs. Exposure to 0.1-1 µM iAs for 3 days significantly decreased glucose-induced insulin secretion (GIIS). Serotonin and its precursor, 5-hydroxytryptophan (5-HTP), were both decreased. Supplementation with 5-HTP, which loads the system with bioavailable 5-HTP and serotonin, rescued GIIS, suggesting that recovery of this pathway was sufficient to restore function. Exposure to iAs was accompanied by an increase in mRNA expression of UDP-glucuronosyltransferase 1 family, polypeptide a6a (Ugt1a6a), a phase-II detoxification enzyme that facilitates the disposal of cyclic amines, including serotonin, via glucuronidation. Elevated Ugt1a6a and UGT1A6 expression levels were observed in mouse and human islets, respectively, following 3 days of iAs exposure. Consistent with this finding, the enzymatic rate of serotonin glucuronidation was increased in iAs-exposed cells. Knockdown by siRNA of Ugt1a6a during iAs exposure restored GIIS in MIN6-K8 cells. This effect was prevented by blockade of serotonin biosynthesis, suggesting that the observed iAs-induced increase in Ugt1a6a affects GIIS by targeting serotonin or serotonin-related metabolites. Although it is not yet clear exactly which element(s) of the serotonin pathway is/are most responsible for iAs-induced GIIS dysfunction, this study provides evidence that UGT1A6A, acting on the serotonin pathway, regulates GIIS under both normal and pathological conditions.

[Effect of anti-helicobacter therapy on the hepatic glucuronyl transferase system of adolescents with Gilbert's syndrome]

Bilirubin biotransformation occurs with the participation of the glucuronyl transferase (GTF) system of the liver and hepatocyte membranes. Disturbances in these systems may result in a rise of blood bilirubin levels and disbalance between direct and indirect bilirubin leading to jaundice. Gilbert's syndrome (GS) is a genetic disorder associated with the enhanced level of indirect bilirubin due to GTF insufficiency.

MATERIALS AND METHODS

The study included adolescents aged 13.4 ± 0.42 yr divided into 2 groups depending on anti-Helicobacter therapy (AHBT). We measured levels of direct and indirect bilirubins, their ratio, and direct bilirubin content as percentage of total bilirubin at admission to and discharge from the hospital. The daily incremental growth of both bilirubin fractions was calculated

RESULTS

Detailed analysis revealed negative effect of AHBT on the GTF system attributable to its impaired stability in patients with abnormal genotype.

CONCLUSION

Prescription of AHBT to children with Gilbert's syndrome requires the thorough choice of medications and monitoring of their potential effect on the GFT system.

Modulatory effect of troxerutin on biotransforming enzymes and preneoplasic lesions induced by 1,2-dimethylhydrazine in rat colon carcinogenesis

Colon cancer is the third most global oncologic problem faced by medical fraternity. Troxerutin, a flavonoid present in tea, coffee, cereal grains, and a variety of fruits and vegetables, exhibits various pharmacological and biological activities. This study was carried out to investigate the effect of troxerutin on xenobiotic metabolizing enzymes, colonic bacterial enzymes and the development of aberrant crypt foci (ACF) during 1,2-dimethylhydrazine (DMH) induced experimental rat colon carcinogenesis. Male albino Wistar rats were randomly divided into six groups. Group 1 served as control. Group 2 received troxerutin (50 mg/kg b.w., p.o. every day) for 16 weeks. Groups 3-6 received subcutaneous injections of DMH (20 mg/kg b.w.) once a week, for the first four weeks. In addition, groups 4-6 received different doses of troxerutin (12.5, 25, 50 mg/kg b.w., p.o. every day respectively) along with DMH injections. Our results reveal that DMH treated rats exhibited elevated activities of phase I enzymes such as cytochrome P450, cytochrome b5, cytochrome P4502E1, NADPH-cytochrome P450 reductase and NADH-cytochrome b5 reductase and reduced activities of phase II enzymes such as glutathione-S-transferase (GST), DT-diaphorase (DTD) and uridine diphospho glucuronyl transferase (UDPGT) in the liver and colonic mucosa of control and experimental rats. Furthermore, the activities of fecal and colonic mucosal bacterial enzymes, such as β-glucronidase, β-glucosidase, β-galactosidase and mucinase were found to be significantly higher in DMH alone treated rats than those of the control rats. On supplementation with troxerutin to DMH treated rats, the alterations in the activities of the biotransforming enzymes, bacterial enzymes and the pathological changes were significantly reversed, the effect being more pronounced when troxerutin was supplemented at the dose of 25 mg/kg b.w. Thus troxerutin could be considered as a good chemopreventive agent against the formation of preneoplastic lesions in a rat model of colon carcinogenesis.

Acute exposure to offshore produced water has an effect on stress- and secondary stress responses in three-spined stickleback Gasterosteus aculeatus

Pollution is one of today's greatest problems, and the release of contaminants into the environment can cause adverse changes in vitally important biological pathways. In this study, we exposed three-spined stickleback Gasterosteus aculeatus to produced water (PW), i.e. wastewater from offshore petroleum production. PW contains substances such as alkylphenols (APs) and aromatic hydrocarbons (PAHs) known to induce toxicant stress and endocrine disruption in a variety of organisms. Following exposure to PW, a standardized confinement treatment was applied as a second stressor (PW-stress), testing how fish already under stress from the pollutant would respond to an additional stressor. The endpoint for analysis was a combination of blood levels of cortisol and glucose, in addition to transcribed levels of a set of genes related to toxicant stress, endocrine disruption and general stress. The findings of this study indicate that low doses of PW do not induce vitellogenin in immature female stickleback, but do cause an upregulation of cytochrome (CYP1A) and UDP-glucuronsyltransferase (UDP-GT), two biomarkers related to toxicant stress. However, when the second stressor was applied, both genes were downregulated, indicating that the confinement exposure had a suppressive effect on the expression of toxicant biomarkers (CYP1A and UDP-GT). Further, two of the stress related genes, heat shock protein 90 (HSP90) and stress-induced phosphoprotein (STIP), were upregulated in both PW- and PW-stress-treatment, but not in the water control confinement treatment, indicating that PW posed as a larger stress-factor than confinement for these genes. The confinement stressor caused an increased level of glucose in both control and PW-treated fish, indicating hyperglycemia, a commonly reported stress response in fish.

Effects of rifampin and mefenamic acid on the pharmacokinetics and pharmacodynamics of dapagliflozin

AIMS

Dapagliflozin is a selective sodium glucose cotransporter 2 (SGLT2) inhibitor that decreases serum glucose by reducing renal glucose reabsorption, thereby promoting urinary glucose excretion. Dapagliflozin is primarily metabolized via the uridine diphosphate-glucuronosyltransferase (UGT)1A9 pathway to its major inactive metabolite, dapagliflozin 3-O-glucuronide. The aim of this study was to evaluate the potential for drug-drug interaction between dapagliflozin and two potential UGT1A9 modulators.

METHODS

The results of two open-label, non-randomized, single-sequence studies are reported in which the effects of rifampin (a pleiotropic drug-metabolizing enzyme inducer; study 1) and mefenamic acid (a strong UGT1A9 inhibitor; study 2) were evaluated on the pharmacokinetics and pharmacodynamics (assessed by urinary glucose excretion [UGE]) of dapagliflozin in healthy subjects. In study 1, 14 subjects received single doses of dapagliflozin 10 mg alone and in the presence of rifampin 600 mg QD (6 days). In study 2, 16 subjects received single doses of dapagliflozin 10 mg alone and in the presence of mefenamic acid 250 mg q6h (5 days).

RESULTS

Rifampin reduced total exposure (area under the concentration-time curve from time 0 to infinity [AUC0-inf]) to dapagliflozin by 22% and mefenamic acid increased dapagliflozin AUC0-inf by 51%. No clinically meaningful effect of rifampin or mefenamic acid on the pharmacokinetics of dapagliflozin or on dapagliflozin-mediated urinary glucose excretion was observed.

CONCLUSION

Modest changes in dapagliflozin exposure were seen with rifampin and mefenamic acid with minor changes in UGE, none of which were considered clinically meaningful.

Drug-drug interactions of silymarin on the perspective of pharmacokinetics

Silymarin, which is extracted from the milk thistle (Silybum marianum), has been used for centuries for treating hepatic disorders and its hepatoprotective effects have been known for hundreds of years. Silymarin is a mixture of polyphenoic flavonoids, which include silibinin (silybin A and silybin B), isosilyin A and B, silychristin A and B, silydianin and other phenol compounds. The pharmacokinetics of silibinin shows fast absorption and elimination. Silymarin undergoes phase I and phase II metabolism, especially phase II conjugation reactions, it undergoes multiple conjugation reactions, and is primarily excreted into bile and urine. Silymarin has a good safety profile, but little is known regarding its potential for drug interaction. Silymarin has limited effect on the pharmacokinetics of several drugs in vivo; despite silymarin decreasing the activity of cytochrome P-450 (CYPs) enzymes, UDP-glucuronosyltransferase (UGT) enzyme, and reducing P-glycoprotein (P-gp) transport. Health-care practitioners should caution patients against co-administration of silymarin and pharmaceutical drugs.

Inhibition of human CYP3A4, UGT1A6, and P-glycoprotein with halogenated xanthene food dyes and prevention by superoxide dismutase

Synthetic food dyes are xenobiotics, and, after ingestion, portions of these dyes may be absorbed and metabolized by phase I and II drug-metabolizing enzymes, and excreted by transporters of phase III enzymes. In the previous report, it was shown that inhibition of UDP-glucuronosyltrasnferase 1A6 occurred following ingestion of phloxine, erythrosine, and rose bengal present in 12 permitted synthetic food dyes. In this report, the influence of dyes was examined on CYP3A4, a major phase I drug-metabolizing enzyme, and P-glycoprotein, a major transporter by synthetic food dyes. Human cytochrome P-450 (CYP) 3A4 and P-glycoprotein were inhibited by xanthene food dyes. The IC(50) values of these dyes to inhibit CYP3A4 and P-glycoprotein were the same as the level of inhibition of UGT1A6 produced by three haloganated xanthene food dyes in the previous report, except acid red, which inhibited only CYP3A4. Data suggest that inhibition by dyes is not enzyme specific but may be in a membrane-specific or protein-specific manner, such as conformational changes in protein. In the previous study, it was suggested that inhibition by dyes depended upon light irradiation due to generation of (1)O2 from these dyes. In this study, the influence of superoxide dismutase and catalase on inhibition by dyes was examined. Superoxide dismutase but not catalase was effective in preventing the inhibition of UGT1A6 by the dyes. Data suggest that superoxide anions, originating from dyes via light irradiation, may attack drug-metabolizing enzymes. It is possible that red cosmetics containing phloxine, erythrosine, or rose bengal react with proteins in skin and may lead to skin damage.

Associations between prenatal exposure to polychlorinated biphenyls and neonatal thyroid-stimulating hormone levels in a Mexican-American population, Salinas Valley, California

BACKGROUND

Studies have reported that prenatal exposure to polychlorinated biphenyls (PCBs) may alter neurodevelopment in both humans and animals. Furthermore, prenatal exposure to some PCB congeners and commercial mixtures has been shown to decrease free and total thyroxine (T(4)) blood levels in animals. Because thyroid hormones (TH) are essential for normal neurologic development, it has been suggested that the deleterious neurodevelopmental effect of PCBs may occur through TH disruption. PCBs may in turn affect TH levels by inducing the microsomal enzyme uridinediphosphate glucuronosyltransferase (UDP-GT), which is involved in TH elimination.

OBJECTIVES

Our goals were to group PCB congeners based on their potential to induce microsomal enzymes in animals, and to examine the relationship between neonatal TSH levels and prenatal exposure to PCB congeners grouped according to their structure and potential mechanisms of action.

METHODS

We measured the concentration of 34 PCB congeners in serum samples collected from 285 pregnant women and the thyroid-stimulating hormone (TSH) levels in their children's blood collected shortly after birth.

RESULTS

We found no association between the sum of PCB congeners, the toxic equivalents, or structure-based groupings (mono- or di-ortho substituted congeners), and TSH blood concentration. However, we found a positive association between the sum of congeners suspected to be UDP-GT inducers (more specifically cytochrome P450 2B inducers) in animals and neonatal TSH levels. In individual congener analyses, PCBs 99, 138, 153, 180, 183, 187, 194, and 199 were positively associated with neonatal TSH levels after adjustment for covariates. PCBs 194 and 199 remained significant after adjustment for multiple hypothesis testing.

CONCLUSIONS

Our results support grouping PCB congeners based on their potential mechanism of action of enzyme induction when investigating associations with TH. Findings also suggest that PCBs affect TH homeostasis even at the low background level of exposure found in the CHAMA-COS (Center for the Health Assessment of Mothers and Children of Salinas) population.

Increased susceptibility to hepatocarcinogenicity of Nrf2-deficient mice exposed to 2-amino-3-methylimidazo[4,5-f]quinoline

To elucidate the roles of the transcription factor NF-E2-related factor (Nrf2) in hepatocarcinogenesis induced by 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), a mutagenic and carcinogenic heterocyclic amine, Nrf2-deficient mice were treated with 300 p.p.m. IQ in their diet for 1, 4 or 52 weeks. In the long-term experiment, the multiplicity and incidence of liver tumors in male and female IQ-treated Nrf2 deficient (-/-) mice were significantly higher than those in their counterpart wild-type (+/+) mice exposed to IQ. In the short-term experiment, although IQ exposure to Nrf2(+/+) mice of both sexes did not modify UDP-glucuronosyltransferase values, glutathione S-transferase values were significantly increased due to IQ treatment, in contrast to no alteration in male and female Nrf2(-/-) mice. Levels of oxidative stress markers such as 8-hydroxydeoxyguanosine and thiobarbituric acid reactive substances in the livers of all treated mice were not changed by IQ treatment. IQ-specific DNA adduct levels were elevated only in female Nrf2(-/-) mice, although the increase was not significant. IQ treatment caused an increase in proliferating cell nuclear antigen labeling indices only in male Nrf2(-/-) mice. The present data clearly show that Nrf2(-/-) mice of both sexes are susceptible to IQ hepatocarcinogenicity, which might result from IQ accumulation due to failure of metabolizing enzyme induction. In addition, inconsistent results concerning IQ-specific adducts and proliferating cell nuclear antigen labeling indices in male and female Nrf2(-/-) mice suggest the existence of different contributions of Nrf2 to IQ hepatocarcinogenesis between mice of the two sexes.

Inhibitory potential of nonsteroidal anti-inflammatory drugs on UDP-glucuronosyltransferase 2B7 in human liver microsomes

OBJECTIVE

A number of nonsteroidal anti-inflammatory drugs (NSAIDs) are subject to glucuronidation in humans, and UDP-glucuronosyltransferase (UGT) 2B7 is involved in the glucuronidation of many NSAIDs. The objective of this study was to identify a NSAID with potent inhibitory potential against UGT2B7 using liquid chromatography with tandem mass spectrometry (LC-MS/MS).

METHODS

A rapid screening method for detecting the inhibitory potential of various drugs against UGT2B7 was established using a LC-MS/MS system. The effects of nine NSAIDs (acetaminophen, diclofenac, diflunisal, indomethacin, ketoprofen, mefenamic acid, naproxen, niflumic acid, and salicylic acid) against UGT2B7-catalyzed 3'-azido-3'-deoxythymidine glucuronidation (AZTG) were investigated in human liver microsomes (HLM) and recombinant human UGT2B7.

RESULTS

Mefenamic acid inhibited AZTG most potently, with an IC(50) value of 0.3 microM, and its inhibition type was not competitive. The IC(50) values for diclofenac, diflunisal, indomethacin, ketoprofen, naproxen, and niflumic acid against AZTG were 6.8, 178, 51, 40, 23, and 83 microM, respectively, while those for acetaminophen and salicylic acid were >100 microM. The IC(50) values for NSAIDs against AZTG in recombinant human UGT2B7 were similar to those obtained in HLM.

CONCLUSION

The method established in this study is useful for identifying drugs with inhibitory potential against human UGT2B7. Among the nine NSAIDs investigated, mefenamic acid had the strongest inhibitory effect on UGT2B7-catalyzed AZTG in HLM. Thus, caution might be exercised when mefenamic acid is coadministered with drugs possessing UGT2B7 as a main elimination pathway.

[A prevalent genetic variety of UDP-glycuronosyl transferase predicts high risk of irinotecan toxicity]

The advances in genetics and molecular biology have raised new areas in medicine, such as pharmacogenomics, which tries to predict drug responses and toxicities based on the individual genetic variability, describing the so called: pharmacogenomic syndromes. Oncology would find this development extremely useful because of the severe toxicity of chemotherapy. There are a lot of genetic loci under investigation for their potential in predicting drug toxicity, but only three of them have showed clinical usefulness up to now. In particular, quantification of the number of thymine-adenine (TA) dinucleotics in the promoter region of the UDP-glucuronosyl-transferase 1A1 enzime (TA indel) proved to be capable of predicting severe neutropenia in patients exposed to intermediate or high doses of irinotecan. Herein we report a case of a patient with small cell lung cancer who suffered severe hematological and gastrointestinal toxicity after being treated with relatively low doses (65 mg/m(2)) of irinotecan and whose leucocyte DNA analysis showed the presence of seven TA repetitions in both alleles. This case is an example of the clinical applicability and the utility of the test as a toxicity predictor. We also discuss the clinical decisions that may be taken with these patients.

Modification by curcumin of mutagenic activation of carcinogenic N-nitrosamines by extrahepatic cytochromes P-450 2B1 and 2E1 in rats

To elucidate the mechanism underlying suppression by curcumin of esophageal carcinogenesis induced by NMBA, we evaluated the CYP level and mutagenic activation of environmental carcinogens, by immunoblot analyses and Ames preincubation test, respectively, and bilirubin, 4-nitrophenol and testosterone UDPGT activities in F344 rats treated with curcumin and/or NMBA. No significant alterations in the hepatic levels of constitutive CYP proteins, mutagenic activation by liver S9 or hepatic UDPGT activities were produced by subcutaneous treatment with 0.5 mg/kg NMBA for 5 weeks and/or feeding of 0.05% and 0.2% curcumin for 6 weeks. In contrast, gavage of 0.2% curcumin decreased esophageal CYP2B1 and 2E1 by up to 60%, compared with vehicle control. Similarly, intragastric treatment with 270 mg/kg curcumin decreased esophageal and gastric CYP2B1 and CYP2E1, but not in lung, kidney or intestine. Conversely, large intestinal CYP2B1 was 2.8-fold higher in the treated rats than in control rats. Mutagenic activities of NOC, including NMBA, in the presence of esophagus and stomach S9 were markedly decreased in the treated rats, whereas those in the presence of large intestine S9 were 2.2-3.0-fold above control. These results show that modifying effects of curcumin on esophageal carcinogenesis can be attributed to a decrease in metabolic activation of NMBA by esophageal CYP2B1 during the initiation phase, without the contribution of metabolic activation and inactivation by liver. Further, the present findings suggest the potential of curcumin for modification of gastric and intestinal carcinogenesis initiated with NOC.

The liver X-receptor alpha controls hepatic expression of the human bile acid-glucuronidating UGT1A3 enzyme in human cells and transgenic mice

Glucuronidation, an important bile acid detoxification pathway, is catalyzed by enzymes belonging to the UDP-glucuronosyltransferase (UGT) family. Among UGT enzymes, UGT1A3 is considered the major human enzyme for the hepatic C24-glucuronidation of the primary chenodeoxycholic (CDCA) and secondary lithocholic (LCA) bile acids. We identify UGT1A3 as a positively regulated target gene of the oxysterol-activated nuclear receptor liver X-receptor alpha (LXRalpha). In human hepatic cells and human UGT1A transgenic mice, LXRalpha activators induce UGT1A3 mRNA levels and the formation of CDCA-24glucuronide (24G) and LCA-24G. Furthermore, a functional LXR response element (LXRE) was identified in the UGT1A3 promoter by site-directed mutagenesis, electrophoretic mobility shift assays and chromatin immunoprecipitation experiment. In addition, LXRalpha is found to interact with the SRC-1alpha and NCoR cofactors to regulate the UGT1A3 gene, but not with PGC-1beta. In conclusion, these observations establish LXRalpha as a crucial regulator of bile acid glucuronidation in humans and suggest that accumulation of oxysterols in hepatocytes during cholestasis favors bile acid detoxification as glucuronide conjugates. LXR agonists may be useful for stimulating both bile acid detoxification and cholesterol removal in cholestatic or hypercholesterolemic patients, respectively.

Endocrine alteration in juvenile cod and turbot exposed to dispersed crude oil and alkylphenols

Juvenile Atlantic cod (Gadus morhua) and turbot (Scophthalmus maximus) were exposed for 3 weeks in a continuous water flow to 0.5 ppm of dispersed North Sea crude oil, 0.5 ppm of dispersed North Sea crude oil spiked with 0.1 ppm of a mixture of alkylphenols (offshore oil production), and 30 ppb of nonylphenol (NP). As potential markers of endocrine alteration, key enzymatic activities involved in both synthesis (17beta-hydroxysteroid dehydrogenases and P450 aromatase) and metabolism (liver UDP-glucuronosyltransferases (UGT) and sulfotransferases) of steroids were assessed together with circulating levels of testosterone and estradiol in plasma. NP-exposed turbot had lower ovarian P450 aromatase, lower levels of testosterone and estradiol in plasma, and lower glucuronidation rates of sex steroids than those from the control group. In contrast, higher liver UGT-testosterone, and a trend towards higher P450 aromatase was detected in oil-exposed specimens. Those exposed to the combination oil+alkylphenols had lower levels of estradiol in plasma than controls, and no significant effects on any the enzymatic activities tested was observed. All these alterations were more evident in turbot than in cod. In fact, apart from a higher glucuronidation rate of estradiol detected in the liver of NP-exposed cod, no significant differences were observed between control and exposed cod.

Environmental and genetic factors associated with morphine response in the postoperative period

OBJECTIVE

The aim of this study was to investigate the respective influence of genetic and nongenetic factors on morphine dose requirements and adverse effects after colorectal surgery.

METHODS

Seventy-four patients who planned to undergo colorectal surgery were included in this pilot study. The cumulative 24-hour postoperative dose of morphine and postoperative nausea or vomiting requiring the antiemetic ondansetron were the 2 clinical end points. The association of patient characteristics, A118G mu-opioid receptor (OPRM1) single-nucleotide polymorphism (SNP); T802C uridine diphosphate-glucuronosyltransferase 2B7 (UGT2B7) SNP; and 2 adenosine triphosphate-binding cassette, subfamily B, member 1 (ABCB1) (multidrug resistance 1 [MDR1]) exonic SNPs (G2677T/A and C3435T) with study end points was investigated.

RESULTS

Age, creatinine clearance, and the regular use of psychotropic agents were found to be significantly associated with postoperative morphine dose requirements by univariate analysis. Multivariate analysis identified that age (P = .01) and the use of psychotropic agents before surgery (P = .03) were positively associated with a higher rate of morphine consumption. A higher weight (P = .05) and the ABCB1 homozygous GG-CC diplotype (P = .03) were significantly associated with fewer morphine side effects by univariate analysis. The homozygous ABCB1 diplotype (GG-CC) conferred an odds ratio of 0.12 (95% confidence interval, 0.01-0.98) with regard to the use of ondansetron for postoperative nausea or vomiting. Multivariate analysis identified that the ABCB1 GG-CC diplotype was the only borderline-significant (P = .07) predictive factor of morphine side effects.

CONCLUSION

Age and prior use of psychotropic agents are associated with postoperative morphine dose requirements. Whether ABCB1 polymorphisms might predict morphine side effects remains to be determined.

Suppression of 7,12-dimethylbenz[a]anthracene-induced mammary carcinogenesis by pre-initiation treatment of rats with beta-naphthoflavone coincides with decreased levels of the carcinogen-derived DNA adducts in the mammary gland

BACKGROUND

Mechanisms underlying prevention by beta-naphthoflavone (beta-NF) of mammary carcinogenesis initiated with 7,12-dimethylbenz[a]anthracene (DMBA) in the rat were elucidated.

METHODS AND RESULTS

Treatment of female Sprague-Dawley rats with beta-NF at 40 mg/kg b.wt. for 4 days by oral gavage in corn oil before a single oral dose of DMBA (112 mg/kg b.wt.) suppressed mammary gland carcinogenesis as shown by an increase in the median latent period from 10 to 24 weeks and a 60% decrease in the multiplicity of mammary adenocarcinomas. In contrast, a 20-day treatment with beta-NF starting 3 weeks after DMBA had no significant effects on mammary tumorigenesis. The activities of phase I and phase II enzymes were examined in the liver and mammary gland 24 h after treatment of rats with beta-NF, DMBA, or beta-NF followed by DMBA as in the first bioassay. Treatment with either beta-NF or DMBA increased the hepatic activities of cytochrome P450 (CYP)1A1, 1A2, and 2B1/2, and glutathione S-transferase, and the mammary activity of CYP1A1. The activity of mammary CYP2B1/2 induced by DMBA was decreased by beta-NF. In the liver, the increase of UDP-glucuronosyl transferase (GT) activity in rats treated with beta-NF and DMBA was 2.3-fold greater than in rats treated with DMBA alone. Thus, treatment with beta-NF likely increased the rate of glucuronidation of DMBA dihydrodiols leading to carcinogen detoxification. The levels of the DMBA adducts determined by 32P-postlabeling of the mammary gland DNA were decreased in the beta-NF-pretreated rats.

CONCLUSION

The beta-NF-induced increase in the hepatic UDP-GT activity and decrease in the mammary DNA-DMBA adducts occurred under the same treatment regimen that led to suppression of DMBA-induced mammary carcinogenesis.

Roles of rifampicin in drug-drug interactions: underlying molecular mechanisms involving the nuclear pregnane X receptor

Rifampicin, an important drug in the treatment of tuberculosis, is used extensively despite its broad effects on drug-drug interactions, creating serious problems. The clinical importance of such interactions includes autoinduction leading to suboptimal or failed treatment. The concomitantly administered effects of rifampicin on other drugs can result in their altered metabolism or transportation that are metabolised by cytochromes P450 or transported by p-glycoprotein in the gastrointestinal tract and liver. This review paper summarises recent findings with emphases on the molecular mechanisms used to explain these broad drug-drug interactions. In general, rifampicin can act on a pattern: rifampicin activates the nuclear pregnane X receptor that in turn affects cytochromes P450, glucuronosyltransferases and p-glycoprotein activities. This pattern of action may explain many of the rifampicin inducing drug-drug interactions. However, effects through other mechanisms have also been reported and these make any explanation of such drug-drug interactions more complex.

Glucuronidation in therapeutic drug monitoring

BACKGROUND

Glucuronidation is a major drug-metabolizing reaction in humans. A pharmacological effect of glucuronide metabolites is frequently neglected and the value of therapeutic drug monitoring has been questioned. However, this may not always be true.

METHODS

In this review the impact of glucuronidation on therapeutic drug monitoring has been evaluated on the basis of a literature search and experience from the own laboratory.

RESULTS

The potential role of monitoring glucuronide metabolite concentrations to optimize therapeutic outcome is addressed on the basis of selected examples of drugs which are metabolized to biologically active/reactive glucuronides. Furthermore indirect effects of glucuronide metabolites on parent drug pharmacokinetics are presented. In addition, factors that may modulate the disposition of these metabolites (e.g. genetic polymorphisms, disease processes, age, and drug-drug interactions) are briefly mentioned and their relevance for the clinical situation is critically discussed.

CONCLUSION

Glucuronide metabolites can have indirect as well as direct pharmacological or toxicological effects. Although convincing evidence to support the introduction of glucuronide monitoring into clinical practice is currently missing, measurement of glucuronide concentrations may be advantageous in specific situations. If the glucuronide metabolite has an indirect effect on the pharmacokinetics of the parent compound, monitoring of the parent drug may be considered. Furthermore pharmacogenetic approaches considering uridine diphosphate (UDP) glucuronosyltransferases polymorphisms may become useful in the future to optimize therapy with drugs subject to glucuronidation.

Protection against paracetamol-induced hepatic injury by prazosin pre-treatment in CD-1 mice

A synergistic depletion of glutathione has been suggested to be one critical factor in the hepatic injury in mice induced by non-toxic doses of paracetamol (APAP) when co-administered with alpha-adrenergic agonists. Prazosin (an alpha-adrenergic antagonist) could confer hepatoprotection following a toxic APAP dose (530 mg/kg) by increasing glutathione levels and enhancing bioinactivation by glucuronidation and glutathione conjugation. The effect of prazosin pre-treatment on APAP-induced gluthathione depletion and bioinactivation in vivo was assessed. Prazosin (15 mg/kg) pre-treatment provided protection against APAP-induced hepatic injury as evidenced by a significant decrease in serum transaminase (ALT) levels after 5h (p<0.05). Interestingly, prazosin pre-treatment did not prevent the dramatic depletion of glutathione by high dose APAP and it had no effect on the quantity of the glutathione conjugate formed. However, prazosin pre-treatment caused a significant increase in recovery of the administered dose (530 mg/kg) as the glucuronide metabolite (p<0.05). UDP-glucuronosyltransferase (UGT) is involved in the bioinactivation of APAP by glucuronidation and we showed that prazosin had no effect on microsomal UGT kinetics. Thus, prazosin had no effect on either APAP-mediated glutathione depletion or the extent of APAP-glutathione conjugate formation and may be affecting other mechanisms to reduce oxidative stress caused by a toxic dose of APAP.

Fibroblast Growth Factor-2 Stimulates Hyaluronan Production by Human Dental Pulp Cells

Hyaluronan (HA), is a high molecular mass extracellular matrix constituting connective tissue and plays a critical role in not only homeostasis but also inflammatory and wound-healing responses. In this study, we investigated the effect of fibroblast growth factor (FGF)-2 on the production of HA by human dental pulp cells (HDPC). An inhibition binding-protein assay showed that FGF-2 increased HA production by HDPC. In addition, expression of mRNA of hyaluronan synthase (HAS) 1 and HAS 2, both of which are related to the production of high molecular mass of HA, but not HAS 3, was enhanced in FGF-2-stimulated HDPC. These results provide new evidence for the involvement of FGF-2 in the regulation of HA production by HDPC possibly through HAS 1 and HAS 2.

In vitro inhibitory effects of non-steroidal antiinflammatory drugs on UDP-glucuronosyltransferase 1A1-catalysed estradiol 3beta-glucuronidation in human liver microsomes

The inhibitory potencies of non-steroidal antiinflammatory drugs (NSAID) on UDP-glucuronosyltransferase (UGT) 1A1-catalysed estradiol 3beta-glucuronidation (E3G) were investigated in human liver microsomes (HLM). Inhibitory effects of the following seven NSAID were investigated: acetaminophen, diclofenac, diflunisal, indomethacin, ketoprofen, naproxen and niflumic acid. Niflumic acid had the most potent inhibitory effect on E3G with an IC50 value of 22.2 microM in HLM. The IC50 values of diclofenac, diflunisal, indomethacin for E3G were 60.9, 37.8 and 51.5 microM, respectively, while acetaminophen, ketoprofen and naproxen showed less potent inhibition. Diclofenac inhibited E3G non-competitively with a Ki value of 112 microM in HLM. The IC50 value of diclofenac for 4-methylumbelliferone glucuronidation in recombinant human UGT1A1 was 57.5 microM, similar to that obtained for E3G using HLM. In conclusion, niflumic acid had the most potent inhibitory effects on UGT1A1-catalysed E3G in HLM among seven NSAID investigated.

The Role of Ah Receptor in Induction of Human UDP‐Glucuronosyltransferase 1A1

UDP-glucuronosyltransferases (UGTs) catalyze a major metabolic pathway initiating the transfer of glucuronic acid from uridine 5'-diphosphoglucuronic acid to endogenous and exogenous substances. Endogenous substances include bile acids, steroids, phenolic neurotransmitters, and bilirubin. Xenobiotic substances include dietary substances, therapeutics, and environmental compounds. The versatility in the selection of substrates for glucuronidation results from the multiplicity of the UGTs in addition to the ability of these genes to be regulated. UDP-glucuronosyltransferase 1A1 (UGT1A1), responsible for the glucuronidation of bilirubin, is controlled in a tissue-specific manner and can be regulated following environmental exposure. This chapter describes materials and methods for the examination of molecular interactions that control UGT1A1 expression and induction in response to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Using an in vitro cell culture system, we mapped a regulatory sequence that contains a xenobiotic response element core sequence in the enhancer region of the UGT1A1 gene. Similar to regulation of CYP1A1, the transcriptional activation of UGT1A1 by TCDD is mediated through the aryl hydrocarbon receptor.

Effects of?-estradiol and propofol on the 4-methylumbelliferone glucuronidation in recombinant human UGT isozymes 1A1, 1A8 and 1A9

The effects of beta-estradiol and propofol on human UGT1A1, 1A8 and 1A9 activities were investigated using 4-methylumbelliferone (4-MU) as a substrate for glucuronidation. The formation of 4-MU glucuronide (4-MUG) from 4-MU, in recombinant human UGT 1A1, 1A8 and 1A9 was determined using HPLC with fluorescence detection. The glucuronidation activity of 4-MU was the highest in UGT1A9 with an apparent K(m) value of 8.3 microM, while that in UGT1A1 and 1A8 was linear to at least 100 microM. beta-estradiol had potent inhibitory effects on UGT1A9 as well as on UGT1A1 with IC(50) values of 2.1 and 7.2 microM, respectively. Propofol inhibited UGT1A9 activity with an IC(50) of 55 microM, while the IC(50) value was much higher for UGT1A8. In contrast, beta-estradiol and propofol activated 4-MU glucuronidation in UGT1A1 and 1A8, respectively. This study therefore indicates that the use of beta-estradiol as a specific inhibitor for UGT1A1 should be used with care in the identification of UGT isozymes responsible for glucuronidation in human liver microsomes.

Effects of TGF-beta on hyaluronan anabolism in fibroblasts derived from the synovial membrane of the rabbit temporomandibular joint

Hyaluronan (HA) synthesis in the synovial membrane is affected by various chemical mediators. It is hypothesized that transforming growth factor-beta 1 (TGF-beta 1) would be a mediator to modulate HA synthesis in cultured synovial membrane fibroblasts of the temporomandibular joint (TMJ). Fibroblasts were extracted from the TMJ synovial membrane of four-week-old Japanese white rabbits. The amount of HA and expression levels of HA synthase (HAS) mRNAs induced by TGF-beta 1 treatment were analyzed by means of high-performance liquid chromatography and real-time polymerase chain-reaction, respectively. Both medium and large amounts of HA were enhanced by the stimulation of TGF-beta 1. HAS2 mRNA expression was enhanced 13-fold after six-hour stimulation with TGF-beta 1 (10 ng/mL), whereas HAS3 mRNA expression was not changed significantly. These results suggest that TGF-beta 1 enhances the expression of HAS2 mRNA in the TMJ synovial membrane fibroblasts and may contribute to the production of high-molecular-weight HA in the joint fluid.

Synergistic Effect of N-Acetylglucosamine and Retinoids on Hyaluronan Production in Human Keratinocytes

Hyaluronan (HA) is well known to reside in the extracellular matrix as a water-sorbed macromolecule. The aims of this study were twofold: to investigate the regulation of HA synthesis in keratinocytes, and to develop a method to modulate this regulatory process. We found that N-acetylglucosamine (NAG) increased the production of HA by cultured keratinocytes dose dependently, but had no effect on the production by skin fibroblasts. The effect of NAG in keratinocytes was found to be specific for HA production, as there was no change in sulfated glycosaminoglycan formation. The copresence of NAG with either of two retinoids, retinoic acid (RA) or retinol, exerted a synergistic effect on HA production. To investigate whether human HA synthase (HAS) genes were regulated by NAG or retinoids, total RNA extracted from cells treated with these agents was subjected to Northern blot analysis. We observed that RA and retinol markedly induced the expression of HA synthase-3 (HAS3) mRNA. Moreover, beta-carotene, a provitamin A, influenced HA production and HAS3 gene expression in a manner similar to the retinoids. Conversely, NAG had no effect on the expression of HAS3 transcripts. Pretreatment of cells with RA stimulated the activity of membrane-associated HAS, whereas pretreatment with NAG did not. These results suggest that HA production is regulated by at least two pathways: one involving the regulation of HAS gene expression, and the other independent of such a regulatory effect. Taken together, our findings suggest that NAG is a new modulator of HA synthesis.

Induction of rat hepatic and intestinal UDP-glucuronosyltransferases by naturally occurring dietary anticarcinogens

Gastrointestinal tumours are among the most common malignancies in Western society, the majority of which are associated with dietary and lifestyle factors. Many dietary or lifestyle factors have been identified which may have toxic or carcinogenic properties. However, several dietary compounds also able to reduce gastrointestinal cancer rates in both humans and animals have been characterized. Though the exact mechanism leading to the anticarcinogenic action of these compounds is not fully known, it has been demonstrated that this chemopreventive capacity may be due to elevation of the glutathione S-transferase detoxification enzymes. Here we have investigated the effect of several anticarcinogens on the gastrointestinal UDP-glucuronosyltransferase (UGT) enzymes. Diets of male Wistar rats were supplemented with ellagic acid, ferulic acid, Brussels sprouts, quercetin, alpha-angelicalactone, tannic acid, coumarin, fumaric acid, curcumin and flavone, separately, and combinations of alpha-angelicalactone and flavone. Hepatic and intestinal (proximal, mid and distal small intestine and colon) UGT enzyme activities were quantified using 4-nitrophenol and 4-methylumbelliferone as substrates. All anticarcinogens tested increased UGT enzyme activity with both substrates, at one at least of the five different sites investigated. alpha-Angelicalactone, coumarin and curcumin showed enhanced UGT enzyme activities at all five sites. Both small and large intestinal UGT enzyme activities were increased by quercetin, alpha-angelicalactone, coumarin, curcumin and flavone. Except for tannic acid, all agents induced hepatic UGT enzyme activity. Furthermore, dietary administration of alpha-angelicalactone and flavone, given individually or in combination, enhanced the UGT detoxification system in the liver and, to a lesser extent, in intestine. In conclusion, induction of gastrointestinal UGT enzyme activities after consumption of dietary anticarcinogens may contribute to a better detoxification of potentially carcinogenic compounds and subsequently to the prevention of gastrointestinal cancer.

Functional characterization of human UDP-glucuronosyltransferase 1A9 variant, D256N, found in Japanese cancer patients

SN-38 (7-ethyl-10-hydroxycamptothecin), an active metabolite of the antitumor prodrug irinotecan, is conjugated and detoxified to SN-38 10-O-beta-d-glucuronide by hepatic UDP-glucuronosyltransferase (UGT) 1A1. Recent studies have revealed that other UGT1A isoforms, UGT1A7 and UGT1A9, also participate in SN-38 glucuronidation. Although several genetic polymorphisms are reported for UGT1A1 and UGT1A7 that affect the SN-38 glucuronidation activities, no such polymorphisms have been identified for UGT1A9. In the present study, UGT1A9 exon 1 and its flanking regions were sequenced from 61 Japanese cancer patients who were all treated with irinotecan. A novel nonsynonymous single nucleotide polymorphism was identified in UGT1A9 exon 1, heterozygous 766G>A resulting in the amino acid substitution of D256N. The wild-type and D256N UGT1A9s were transiently expressed at similar protein levels in COS-1 cells, and their membrane fractions were characterized in vitro for the glucuronidation activities toward SN-38. The apparent Km values were 19.3 and 44.4 microM, and the Vmax values were 2.94 and 0.24 pmol/min/mg of membrane protein for the wild-type and D256N variant, respectively. The SN-38 glucuronidation efficiency (normalized Vmax/Km) of D256N was less than 5% that of wild-type UGT1A9. These results clearly indicate that the D256N variant is essentially nonfunctional with regard to SN-38 glucuronidation. These findings highlight the importance of further studies into the potential influence of UGT1A9 D256N variant to irinotecan metabolism in vivo.

Irinotecan treatment in cancer patients with UGT1A1 polymorphisms

At the present time, pharmacogenetic investigation of irinotecan (CPT-11, Camptosar) therapy is mainly focused on the clinical relevance of genetic variation in the UDP-glucuronosyltransferase (UGT1A1) gene. The glucuronidation of the potent topoisomerase I inhibitor SN-38 is a major inactivation pathway of irinotecan metabolism. UGT1A1 genotypes associated with Gilbert's syndrome (a mild intermittent hyperbilirubinemia) are characterized by reduced glucuronidation of SN-38. Such UGT1A1 genetic variants have different distribution across individuals of different ethnicity. The (TA)n TAA polymorphism in the promoter is more frequent in Caucasians as compared to Asians, in whom missense polymorphisms in the exons are more common. Two recent pharmacogenetic trials (one performed in the United States and the other in Japan) investigated the clinical significance of UGT1A1 gene mutations for both the pharmacokinetics of irinotecan metabolites and the toxicity profile. The results of these association studies showed that preliminary genotyping of the (TA)n polymorphism might predict the occurrence of toxicity in genetically predisposed patients.

The effect of valproic acid on drug and steroid glucuronidation by expressed human UDP-glucuronosyltransferases

Valproic acid glucuronidation kinetics were carried our with three human UGT isoforms: UGT1A6, UGT1A9, and UGT2B7 as well as human liver and kidney microsomes. The glucuronidation of valproic acid was typified by high K(m) values with microsomes and expressed UGTs (2.3-5.2mM). The ability of valproic acid to interact with the glucuronidation of drugs, steroids and xenobiotics in vitro was investigated using the three UGT isoforms known to glucuronidate valproic acid. In addition to this the effect of valproic acid was investigated using two other UGT isoforms: UGT1A1 and UGT2B15 which do not glucuronidate valproic acid. Valproic acid inhibited UGT1A9 catalyzed propofol glucuronidation in an uncompetitive manner and UGT2B7 catalyzed AZT glucuronidation competitively (K(i)=1.6+/-0.06mM). Valproate significantly inhibited UGT2B15 catalyzed steroid and xenobiotic glucuronidation although valproate was not a substrate for this UGT isoform. No significant inhibition of UGT1A1 or UGT1A6 by valproic acid was observed. These data indicate that valproic acid inhibition of glucuronidation reactions is not always due to simple competitive inhibition of substrates.

Up-regulation of soyasaponin biosynthesis by methyl jasmonate in cultured cells of Glycyrrhiza glabra

Exogenously applied methyl jasmonate (MeJA) stimulated soyasaponin biosynthesis in cultured cells of Glycyrrhiza glabra (common licorice). mRNA level and enzyme activity of beta-amyrin synthase (bAS), an oxidosqualene cyclase (OSC) situated at the branching point for oleanane-type triterpene saponin biosynthesis, were up-regulated by MeJA, whereas those of cycloartenol synthase, an OSC involved in sterol biosynthesis, were relatively constant. Two mRNAs of squalene synthase (SQS), an enzyme common to both triterpene and sterol biosyntheses, were also up-regulated by MeJA. In addition, enzyme activity of UDP-glucuronic acid: soyasapogenol B glucuronosyltransferase, an enzyme situated at a later step of soyasaponin biosynthesis, was also up-regulated by MeJA. Accumulations of bAS and two SQS mRNAs were not transient but lasted for 7 d after exposure to MeJA, resulting in the high-level accumulation (more than 2% of dry weight cells) of soyasaponins in cultured licorice cells. In contrast, bAS and SQS mRNAs were coordinately down-regulated by yeast extract, and mRNA accumulation of polyketide reductase, an enzyme involved in 5-deoxyflavonoid biosynthesis in cultured licorice cells, was induced transiently by yeast extract and MeJA, respectively.

Glucuronidation of odorant molecules in the rat olfactory system: activity, expression and age-linked modifications of UDP-glucuronosyltransferase isoforms, UGT1A6 and UGT2A1, and relation to mitral cell activity

The aim of the present study was to examine the glucuronidation of a series of odorant molecules by homogenates prepared either with rat olfactory mucosa, olfactory bulb or brain. Most of the odorant molecules tested were efficiently conjugated by olfactory mucosa, whereas olfactory bulb and brain homogenates displayed lower activities and glucuronidated only a few molecules. Important age-related changes in glucuronidation efficiency were observed in olfactory mucosa and bulb. Therefore, we studied changes in expression of two UDP-glucuronosyltransferase isoforms, UGT1A6 and UGT2A1, in 1-day, 1- and 2-week-, 3-, 12- and 24-month-old rats. UGT1A6 was expressed at the same transcriptional level in the olfactory mucosa, bulb and brain, throughout the life period studied. UGT2A1 mRNA was expressed in both olfactory mucosa and olfactory bulb, in accordance with previous results [Mol. Brain Res. 90 (2001) 83], but UGT2A1 transcriptional level was 400-4000 times higher than that of UGT1A6. Moreover, age-dependent variations in UGT2A1 mRNA expression were observed. As it has been suggested that drug metabolizing enzymes could participate in olfactory function, mitral cell electrical activity was recorded during exposure to different odorant molecules in young, adult and old animals. Age-related changes in the amplitude of response after stimulation with several odorant molecules were observed, and the highest responses were obtained with molecules that were not efficiently glucuronidated by olfactory mucosa. In conclusion, the present work presents new evidence of the involvement of UGT activity in some steps of the olfactory process.

Long-term effects of a novel phosphorothionate (RPR-II) on detoxifying enzymes in brain, lung, and kidney rats

The effects of a phosphorothionate, 2-butenoic acid-3-(diethoxyphosphinothioyl) methyl ester (RPR-II), on the activities of glutathione S-transferase (GST) and UDP-glucuronyltransferase (UDPGT) and the level of glutathione (GSH) were evaluated in rats after administration of RPR-II at 0.014 (low), 0.028 (medium), and 0.042 (high) mgkg(-1)day(-1) for 90 days and also at 28 days (withdrawal) after stopping treatment. Brain GST activity and GSH level decreased significantly at the high dose on the 45th and 90th days of treatment. Dose- and time-dependent decreases in GST activity and GSH was level were observed in lung at medium and high doses and in kidneys at all three doses on both the 45th and 90th days. UDPGT activity increased significantly in kidneys at the medium and high doses at 45 and 90 days. Brain and lung did not display any significant variations in UDPGT activity when compared with the control. Interestingly, the withdrawal study revealed that the effect was reversible within 28 days of cessation of treatment, when enzyme activity reverted to levels close to those of controls. The study revealed that RPR-II affected the GSH- and GST-dependent detoxification system of the treated tissues of rat and its potential to modulate the enzymes is in the order kidneys>lung>>brain. The present subacute study suggests that RPR-II may bring about physiological upsets by altering GSH- and GST-dependent events in different tissues of exposed organisms.

Histone 2A stimulates glucose-6-phosphatase activity by permeabilization of liver microsomes

Histone 2A increases glucose-6-phosphatase activity in liver microsomes. The effect has been attributed either to the conformational change of the enzyme, or to the permeabilization of microsomal membrane that allows the free access of substrate to the intraluminal glucose-6-phosphatase catalytic site. The aim of the present study was the critical reinvestigation of the mechanism of action of histone 2A. It has been found that the dose-effect curve of histone 2A is different from that of detergents and resembles that of the pore-forming alamethicin. Inhibitory effects of EGTA on glucose-6-phosphatase activity previously reported in histone 2A-treated microsomes have been also found in alamethicin-permeabilized vesicles. The effect of EGTA cannot therefore simply be an antagonization of the effect of histone 2A. Histone 2A stimulates the activity of another latent microsomal enzyme, UDP-glucuronosyltransferase, which has an intraluminal catalytic site. Finally, histone 2A renders microsomal vesicles permeable to non-permeant compounds. Taken together, the results demonstrate that histone 2A stimulates glucose-6-phosphatase activity by permeabilizing the microsomal membrane.

Inhibition of hyaluronan synthesis in Streptococcus equi FM100 by 4-methylumbelliferone

As observed previously in cultured human skin fibroblasts, a decrease of hyaluronan production was also observed in group C Streptococcus equi FM100 cells treated with 4-methylumbelliferone (MU), although there was no effect on their growth. In this study, the inhibition mechanism of hyaluronan synthesis by MU was examined using Streptococcus equi FM100, as a model. When MU was added to a reaction mixture containing the two sugar nucleotide donors and a membrane-rich fraction as an enzyme source in a cell-free hyaluronan synthesis experiment, there was no change in the production of hyaluronan. On the contrary, when MU was added to the culture medium of FM100 cells, hyaluronan production in the isolated membranes was decreased in a dose-dependent manner. However, when the effect of MU on the expression level of hyaluronan synthase was examined, MU did not decrease either the mRNA level of the has operon containing the hyaluronan synthase gene or the protein level of hyaluronan synthase. Solubilization of the enzyme from membranes of MU-treated cells and addition of the exogenous phospholipid, cardiolipin, rescued hyaluronan synthase activity. In the mass spectrometric analysis of the membrane phospholipids from FM100 cells treated with MU, changes were observed in the distribution of only cardiolipin species but not of the other major phospholipid, PtdGro. These results suggest that MU treatment may cause a decrease in hyaluronan synthase activity by altering the lipid environment of membranes, especially the distribution of different cardiolipin species, surrounding hyaluronan synthase.

Accelerated degradation of mislocalized UDP-glucuronosyltransferase family 1 (UGT1) proteins in Gunn rat hepatocytes

Gunn rat is a hyperbilirubinemic rat strain that is inherently deficient in the activity of UDP-glucuronosyltransferase form 1A1 (UGT1A1). A premature termination codon is predicted to produce truncated UGT1 proteins that lack the COOH-terminal 116 amino acids in Gunn rat. Pulse-chase experiments using primary cell cultures showed that the truncated UGT1A1 protein in Gunn rat hepatocytes was synthesized similarly to wild-type UGT1A1 protein in normal Wistar rat hepatocytes. However, the truncated UGT1A1 protein was degraded rapidly with a half-life of about 50 min, whereas the wild-type UGT1A1 protein had a much longer half-life of about 10 h. The rapid degradation of truncated UGT1A1 protein was inhibited partially but not completely by treating Gunn rat hepatocytes with proteasome inhibitors such as carbobenzoxy-Leu-Leu-leucinal and lactacystin. By contrast, neither the lysosomal cysteine protease inhibitor nor the calpain inhibitor slowed the degradation. Our findings show that the absence of UGT1 protein from Gunn rat hepatocytes is due to rapid degradation of the truncated UGT1 protein by the proteasome and elucidate the molecular basis underlying the deficiency in bilirubin glucuronidation.

UDP-glucuronic acid:soyasapogenol glucuronosyltransferase involved in saponin biosynthesis in germinating soybean seeds

We detected UDP-glucuronic acid:soyasapogenol glucuronosyltransferase (UGASGT) activity in the microsomal fraction from germinating soybean (Glycine max [L.] Merr.) seed. A microsomal fraction was isolated from germinating soybean seed and treated with various detergents to solubilize the enzyme. UGASGT activity was monitored throughout purification using UDP-[U-(14)C]glucuronic acid and soyasapogenol B as substrates. Purification of UGASGT was achieved by HiTrap Q, Superdex 200, and HiTrap Blue chromatography procedures. This resulted in >205-fold enrichment relative to the starting homogenate. UGASGT was found to require divalent cations for activity. Studies on the substrate specificity of UGASGT demonstrated that the specificity for the sugar residue transferred was very high, as activity was scarcely found when UDP-glucuronic acid was replaced by other UDP sugars: UDP-glucose and UDP-galactose. Soyasapogenols, which are the aglycons of soybean saponin, are usable acceptors, but glycyrrhetinic acid, sophoradiol, beta-amyrin, and flavonoids are not. These findings suggest that this UGASGT was a specific enzyme for UDP-glucuronic acid as a donor and soyasapogenols as acceptors, and that it was related to the biosynthesis of the sugar chain in soybean saponin. This study provides a basis for the molecular characterization of a key enzyme in saponin biosynthesis in soybean. The isolation of the gene may enable its use in the elucidation of the biosynthesis and physiological role of saponins in soybean.

Tissue-specific regulation of canine intestinal and hepatic phenol and morphine UDP-glucuronosyltransferases by beta-naphthoflavone in comparison with humans

UDP-glucuronosyltransferases (UGTs) are regulated in a species- and tissue-dependent manner by endogenous and environmental factors. The present study was undertaken to further our knowledge about regulation of UGTs in dogs, a species widely used in preclinical safety evaluation. beta-Naphthoflavone (BNF) was selected as a known aryl hydrocarbon receptor agonist and antioxidant-type inducer. The latter group of inducers is intensively investigated as dietary chemoprotectants against colon cancer. Dog UGTs were investigated in comparison with related human UGTs by examples, (i) expression of dog UGT1A6, the first sequenced dog phenol UGT, and (ii) morphine UGT activities, responsible for intestinal and hepatic first-pass metabolism of morphine. The following results were obtained: (i) dog UGT1A6 was found to be constitutively expressed in liver and marginally increased by BNF treatment. Expression was low in small intestine but ca. 6-fold higher in colon than for example in jejunum. Conjugation of 4-methylumbelliferone, one of the substrates of dog UGT1A6, was also enhanced 7-fold in colonic compared to jejunal microsomes. (ii) Compared to the corresponding human tissues, canine 3-O- and 6-O-morphine UGT activities were found to be >10-fold higher in dog liver and ca. 10-fold lower in small intestinal microsomes. Small intestinal morphine and 4-hydroxybiphenyl UGT activities appeared to be moderately (2- to 3-fold) induced by oral treatment with BNF. (iii) In contrast to dogs, morphine UGT activities were found to be similar in homogenates from human enterocytes and liver. The results suggest marked differences in tissue-specific regulation of canine vs. human hepatic and intestinal phenol or morphine UGTs.

Liver phase I and phase II enzymatic induction and genotoxic responses of beta-naphthoflavone water-exposed sea bass

Sea bass were exposed to 0 (control), 0.1, 0.3, 0.9, and 2.7 microM beta-naphthoflavone (BNF) for 0, 2, 8, and 16 h in order to assess the chronological and concentration relationships between BNF phase I and II biotransformation responses, such as liver cytochrome P450 (P450) content, ethoxyresorufin-O-deethylase (EROD), uridine diphosphate-glucuronosyl transferase (UDP-GT), and the genotoxic effects, measured either by erythrocytic micronuclei (EMN) or erythrocytic nuclear abnormalities (ENA) tests. Liver alanine aminotransferase (ALT) activity and liver somatic index (LSI) were also measured. A significant liver EROD activity was found at 8 h exposure, respectively, to 0.1, 0.3, 0.9, and 2.7 microM BNF. Maximal liver EROD activity increase was observed at 16 h exposure to 0.9 microM BNF, whereas the highest liver P450 was reached at 8 h exposure to 2.7 microM BNF. Liver UDP-GT activity was significantly increased at 2 h exposure to 0.1 and 0.3 microM BNF and at 8 h exposure to 0.1, 0.3, and 0.9 microM BNF, decreasing at 16 h, for every exposure concentration. Significant ENA increase was observed at 2h exposure, respectively, to 0.3, 0.9, and 2.7 microM BNF. Maximal ENA increase was observed at 16 h exposure to 0.9 microM BNF. The MN was significantly increased at 8 and 16 h exposure, respectively, to 2.7 and 0.9 microM BNF. Liver ALT activity significantly increases at 8 h exposure to 0.1 and 0.3 microM BNF, whereas liver somatic index was significantly increased from 2 to 16 h exposure for every BNF concentration. A slight liver EROD activity increase with a concomitant lack of liver UDP-GT activity is able to induce significant erythrocytic genotoxic effects. Liver UDP-GT high levels are important in sea bass BNF detoxification. However, high liver UDP-GT activity is not enough to prevent the BNF metabolite genotoxic effects on sea bass erythrocytes when liver EROD activity is induced at 2 and 8 h exposure to 0.3 and 0.9 microM BNF. The genotoxic effects measured as EMN and ENA suggest that the balance between the rates of liver BNF reactive and conjugated metabolites seems to be critical.

Hydroxylated polychlorinated biphenyls as inhibitors of the sulfation and glucuronidation of 3-hydroxy-benzo[a]pyrene

Polychlorinated biphenyls (PCBs) can be metabolized by cytochromes P450 to hydroxylated biotransformation products. In mammalian studies, some of the hydroxylated products have been shown to be strong inhibitors of steroid sulfotransferases. As a part of ongoing research into the bioavailability of environmental pollutants in catfish intestine, we investigated the effects of a series of hydroxylated PCBs (OH-PCBs) on two conjugating enzymes, phenol-type sulfotransferase and glucuronosyltransferase. We incubated cytosolic and microsomal samples prepared from intestinal mucosa with 3-hydroxy-benzo[a]pyrene and appropriate cosubstrates and measured the effect of OH-PCBs on the formation of BaP-3-glucuronide and BaP-3-sulfate. We used PCBs with 4, 5, and 6 chlorine substitutions and the phenolic group in the ortho, meta, and para positions. OH-PCBs with the phenolic group in the ortho position were weak inhibitors of sulfotransferase; the median inhibitory concentration (IC50) ranged from 330 to 526 microM. When the phenol group was in the meta or para position, the IC50 was much lower (17.8-44.3 microM). The OH-PCBs were more potent inhibitors of glucuronosyltransferase, with IC50s ranging from 1.2 to 36.4 microM. The position of the phenolic group was not related to the inhibitory potency: the two weakest inhibitors of sulfotransferase, with the phenolic group in the ortho position, were 100 times more potent as inhibitors of glucuronosyltransferase. Inhibition of glucuronosyltransferase by low concentrations of OH-PCBs has not been reported before and may have important consequences for the bioavailability, bioaccumulation, and toxicity of other phenolic environmental contaminants.

Induction of UDP-glucuronosyltransferase 1A8 mRNA by 3-methylcholanthene in rat hepatoma cells

UDP-glucuronosyltransferases (UGTs) catalyze the glucuronidation of a broad spectrum of endobiotic and xenobiotic compounds, which leads to the excretion of hydrophilic glucuronides via bile or urine. By a mechanism of exon sharing, isoforms of the UGT1 family are made from the complex gene locus by an alternative combination of one of the unique first exons with the other commonly used exons. This study demonstrates that the expression of the UGT1 gene UGT1A6, 1A7 and 1A8 is regulated at the transcriptional level by 3-methylcholanthene (3-MC) in rat hepatoma H-4-II-E cells. Following 3-MC treatment, there is a gradual increase in the amount of UGT1A6 and UGT1A7 mRNA to the maximum levels after 16hr of treatment. The induction effect of 3-MC led to the expression of UGT1A8 which has not been reported before. This induction is suppressed by the RNA synthesis inhibitor actinomycin D, indicating that the inducer does not act at the level of mRNA stabilization. Northern blot analysis showed a 4-fold increase in UGT1A8 transcription after treatment with 3-MC. The prolonged treatment with the protein synthesis inhibitor did not affect the induction process. The results provide experimental evidence for a transcriptional control of UGT1A8 synthesis. Transcriptional activation of the UGT1A8 by 3-MC does not appear to require de novo protein synthesis. 3-MC dependent activation is probably the result of a direct action of the compound on the aryl hydrocarbon receptor complex (AhR).

[Effect of soybean isoflavones on antioxidant status in rats fed diet with oxidized linseed oil]

The maintenance of male Wistar rats on semi-synthetic diets containing oxidized flaxseed oil for 4 weeks caused decrease in serum total antioxidant activity, significant suppression of microsomal UDP-glucuronosyl transferase activity and benzpyrene hydroxylase activity, increase in reduced glutathione level and catalase activity of liver. Supplementation of diets with 0.05% of soy isoflavones has resulted in normalization of investigated characteristics.

Alterations in hepatic detoxifying enzymes induced by new organophosphorus insecticides following subchronic exposure in rats

The present study examined the structure-toxicity relationship of two novel phosphorothionates, a methyl ester (RPR-II) and an ethyl ester (RPR-V), with regard to their interaction with certain biochemical indices in rat. Male rats were treated orally with 10% (low), 20% (medium) and 30% (high) doses of the two compounds (14, 28 and 42 microg kg(-1) day (-1) of RPR-II and 33, 66 and 99 microg kg(-1) day(-1) of RPR-V) daily for 90 days. The activity of hepatic glutathione S-transferase (GST) and UDP-glucuronyl transferase (UDPGT) and the level of glutathione (GSH) were estimated at 0, 45 and 90 days of treatment as well as 28 days after cessation of treatment. RPR-II caused statistically significant depletion of GSH after 45 and 90 days of treatment at the high dose, whereas RPR-V depleted GSH only after 90 days at the high dose. RPR-II inhibited GST after 45 and 90 days at medium and high doses, whereas RPR-V caused inhibition of GST after 45 and 90 days only at the high dose. Significantly, UDPGT activity was increased only by the high dose of RPR-II after 90 days. However, a dose and time-dependent increase in UDPGT activity was observed at all three doses of RPR-V after 45 and 90 days. There was no modulation in any of the three indices at low doses of the two organophosphorus insecticides. The withdrawal study revealed that induced changes in hepatic parameters were reversible 28 days after cessation of treatment. The results indicated that the two insecticides had different potential to modulate hepatic GST, UDPGT and GSH due to subchronic exposure and that these metabolic alterations are quite reversible after withdrawal of treatment.

Molecular basis of perinatal changes in UDP-glucuronosyltransferase activity in maternal rat liver

The molecular basis of perinatal changes occurring in major UDP-glucuronosyltransferase (UGT) family 1 isoforms and in UGT2B1, a relevant isoform belonging to family 2, was analyzed in rat liver. Nonpregnant, pregnant (19-20 days of pregnancy), and two groups of postpartum animals corresponding to early and middle stages of lactation (2-4 and 10-12 days after delivery, respectively) were studied. UGT activity determined in UDP-N-acetylglucosamine-activated microsomes revealed that bilirubin, p-nitrophenol, and ethynylestradiol (17beta-OH and 3-OH) but not androsterone and estrone glucuronidation rates, were decreased in pregnant rats. Decreased enzyme activities returned to control values after delivery. p-Nitrophenol, androsterone, and estrone conjugation rate increased in postpartum rats. Western blot analysis performed with anti-peptide-specific (anti-1A1, 1A5, 1A6, and 2B1) antibodies revealed decreased levels of all family 1 isoforms and UGT2B1 during pregnancy. In postpartum animals, protein level recovered (1A5 and 2B1) or even increased (1A1 and 1A6) with respect to control rats. Northern blot analysis suggested that expression of UGT proteins is down-regulated at a post-translational level during pregnancy and that increased levels of 1A1 and 1A6 observed in postpartum rats were associated to increased mRNA. To establish whether prolactin is involved in up-regulation of UGT1A1 and 1A6 postpartum, ovariectomized rats were treated with 300 microg of ovine prolactin per day for 7 days. The data indicated that prolactin was able to increase expression of UGT1A6 (protein and mRNA) but not 1A1. Thus, prolactin is the likely mediator of the increased expression of UGT1A6 observed in maternal liver postpartum.

The phenobarbital response enhancer module in the human bilirubin UDP-glucuronosyltransferase UGT1A1 gene and regulation by the nuclear receptor CAR

The UDP-glucuronosyltransferase, UGT1A1, is the critical enzyme responsible for detoxification of the potentially neurotoxic bilirubin by conjugating it with glucuronic acid. For decades, phenobarbital (PB) treatment for hyperbilirubinemia has been known to increase expression of the UGT1A1 gene in liver. We have now delineated the PB response activity to a 290-bp distal enhancer sequence (-3483/-3194) of the UGT1A1 gene. The enhancer contains 3 putative nuclear receptor motifs, and it was activated by the nuclear orphan receptor, human constitutive active receptor (hCAR), in cotransfected HepG2 cells. Bacterially expressed hCAR, acting as a heterodimer with in vitro-translated retinoid X receptor (RXRalpha), only bound to 1 of the 3 NR motifs, named gtNR1 in a gel-shift assay. Consistently, mutations of the gtNR1 site significantly decreased the activation by hCAR of the 290-bp DNA in transfection assays. Moreover, the 290-bp DNA was effectively activated in mouse primary hepatocytes in response to PB, offering an excellent clinical test for the examination of the responsiveness of the UGT1A1 to PB in the human population, particularly individuals with hyperbilirubinemia.