Liver UDP-glucuronosyltransferase Activity Research Articles

Effects of quercetin on protective capacity in rats fed a high-fructose diet

The purpose of the study was to determine effects of quercetin on protective capacity parameters in the experiment on rats fed a high fructose diet. Rats of the control group received a semi-synthetic (s/s) diet and water; animals from the 1st experimental group - s/s diet and 20% fructose solution instead of drinking water; rats of the 2nd experimental group- s/s diet with quercetin (0.1% indiet) and 20% fructose solution instead of drinking water for 20 weeks. Parameters of antioxidant status [total antioxidant activity (AOA), the content of malondialdehyde (MDA) and lipids hydroperoxides, the level of reduced and oxidized glutathione, activity of superoxide dismutase, catalase, glutathione peroxidase, paraoxonase-1, hemeoxygenase-1, NAD(P)H-quinone oxidoreductase], the activity of xenobiotic-metabolizing enzymes [CYP1A1, CYP1A2, CYP2B1, CYP3A, UDP-glucuronosyltransferase (UDP-GT) and glutathione transferase] were studied in plasma and liver of rats. Consumption of the high-fructose diet led to changes in some parameters: diminution of AOA in blood plasma, decrease of AOA and MDA level, unsedimentable activity of lysosomal enzymes, increase of the UDP-GT activity in liver. The inclusion of quercetin in the diet did not affect the studied parameters, except for a more pronounced decrease of the unsedimentable activity of lysosomal enzymes in rat liver. The results of the study indicated that there was no significant effect of quercetin on the protective capacity of rats at the initial stage of obesity caused by high-fructose diet.

Identification of an Unintended Consequence of Nrf2-Directed Cytoprotection against a Key Tobacco Carcinogen plus a Counteracting Chemopreventive Intervention

NF-E2-related factor 2 (Nrf2) is a major cytoprotective gene and is a key chemopreventive target against cancer and other diseases. Here we show that Nrf2 faces a dilemma in defense against 4-aminobiphenyl (ABP), a major human bladder carcinogen from tobacco smoke and other environmental sources. Although Nrf2 protected mouse liver against ABP (which is metabolically activated in liver), the bladder level of N-(deoxyguanosin-8-yl)-4-aminobiphenyl (dG-C8-ABP), the predominant ABP-DNA adduct formed in bladder cells and tissues, was markedly higher in Nrf2(+/+) mice than in Nrf2(-/-) mice after ABP exposure. Notably, Nrf2 protected bladder cells against ABP in vitro. Mechanistic investigations showed that the dichotomous effects of Nrf2 could be explained at least partly by upregulation of UDP-glucuronosyltransferase (UGT). Nrf2 promoted conjugation of ABP with glucuronic acid in the liver, increasing urinary excretion of the conjugate. Although glucuronidation of ABP and its metabolites is a detoxification process, these conjugates, which are excreted in urine, are known to be unstable in acidic urine, leading to delivery of the parent compounds to bladder. Hence, although higher liver UGT activity may protect the liver against ABP, it increases bladder exposure to ABP. These findings raise concerns of potential bladder toxicity when Nrf2-activating chemopreventive agents are used in humans exposed to ABP, especially in smokers. We further show that 5,6-dihydrocyclopenta[c][1,2]-dithiole-3(4H)-thione (CPDT) significantly inhibits dG-C8-ABP formation in bladder cells and tissues but does not seem to significantly modulate ABP-catalyzing UGT in liver. Thus, CPDT exemplifies a counteracting solution to the dilemma posed by Nrf2.

Abstract 1843: An unintended consequence of Nrf2-directed cytoprotection against a major human bladder carcinogen and a counteracting solution

Abstract NF-E2 related factor 2 (Nrf2) plays a pivotal role in cytoprotection against carcinogens and oxidants. Activating Nrf2 has been widely suggested as a key chemopreventive strategy against cancer and other diseases. Here, we show that Nrf2 faces a serious dilemma in dealing with 4-aminobiphenyl (ABP), a major human bladder carcinogen from tobacco smoke and other sources. ABP is metabolized/activated primarily in the liver. While Nrf2 significantly protected mouse liver against ABP in vivo, bladder DNA damage was approximately 2.6 fold higher in Nrf2+/+ mice than in Nrf2-/- mice after ABP exposure, as measured by dG-C8-ABP, the predominant ABP-DNA adduct formed in bladder cells and tissues. Interestingly, Nrf2 significantly protected bladder cells against ABP in vitro. Subsequent experiments revealed that UDP-glucuronosyltransferase (UGT) might be the principal, if not the only mediator of the dichotomous effects of Nrf2. Nrf2 upregulated UGT, promoted glucuronide conjugation of ABP in the liver, and increased urinary excretion of the conjugate. While glucuronidation of ABP and its metabolites is generally a detoxification process, these conjugates, which are excreted in urine, are known to be unstable in acidic urine and deliver the parent compounds to bladder. Hence, higher liver UGT activity may protect liver against ABP but increases bladder exposure to ABP. We further show that 5,6-dihydrocyclopenta[c][1,2]-dithiole-3(4H)-thione (CPDT), a promising cancer chemopreventive dithiolethione, was able to significantly activate Nrf2 cytoprotective signaling and to inhibit dG-C8-ABP formation in the bladder in vivo, but did not modulate liver UGT expression. Thus, CPDT exemplifies a counteracting solution to the dilemma faced by Nrf2 with regard to ABP. In conclusion, our study shows that Nrf2 increases ABP genotoxicity in the bladder in vivo and that UGT may be the key mediator. Using CPDT, we also demonstrate how the adverse effect of Nrf2 may be mitigated. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1843. doi:10.1158/1538-7445.AM2011-1843

Gender difference in serum bisphenol A levels may be caused by liver UDP-glucuronosyltransferase activity in rats

Gender difference in human bisphenol A (BPA) concentrations was revealed by determining serum BPA. We studied the serum concentrations and the metabolism of BPA in rats by an HPLC system. Rat serum BPA concentrations were significantly higher in males (24.9 ± 7.38 ng/ml, P = 0.026, n = 10) than in females (8.27 ± 3.11 ng/ml, n = 10), as in humans. The resultant enzyme reaction products of BPA glucuronidation in the rat liver microsomes fraction were analyzed by an HPLC system. The ratio of BPA glucuronidation in the microsome reaction was significantly higher ( P = 0.015) in female than in male rats. The mRNA expression of UDP-glucuronosyltransferase 2B1 (UGT2B1), an isoform of UGT related to BPA glucuronidation, in the rat liver was analyzed by a real-time quantitative RT-PCR. The relative expression level of UGT2B1 mRNA was significantly higher ( P < 0.001) in female than in male rat livers. The gender difference in serum BPA concentrations may be explained by the difference in clearance based on the UGT activities.

Mixture effects of 2,3,7,8-tetrachlorodibenzo- p-dioxin and polychlorinated biphenyl congeners in rats

Concern of the toxic effects and bioaccumulation of 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD) and polychlorinated biphenyls in the environment continues to be a focus of research in persistent organochlorine contaminants. Groups of five adult female S.D. rats were administered by gavage 0, 2.5, 25, 250 or 1000 ng TCDD/kg body weight/day or TCDD in combination with a mixture of PCB congeners (PCBs) at 2 or 20 μg/ kg b.w./day for a period of 28 days. Growth suppression, increased absolute and relative liver weights, and decreased thymic weight were observed in either the 1000 ng TCDD group alone, or the groups receiving a mixture of 1000 ng TCDD +2 μg PCBs . The TCDD induced increases in liver and thymic weights were not altered by co-administration with PCBs, however, growth suppression appeared to be more pronounced in the group receiving 1000 ng TCDD +2 μg PCBs than with TCDD alone. Treatment with TCDD at 250 ng and 1000 ng/kg resulted in a significant increase in hepatic microsomal methoxy resorufin-O-demethylase and ethoxy resorufin-O-deethylase activities which were antagonized by co-administration with PCBs. Similarly, effects of 250 ng TCDD on serum cholesterol and liver UDP glucuronosyl transferase activity and ascorbic acid were significantly reduced by co-administration with 20 μg PCBs . Other biochemical effects elicited by treatment with 1000 ng TCDD, but not affected by co-administration with PCBs include the following: increased serum albumin, decreased liver vitamin A, and increased kidney vitamin A and liver microsomal glutathione-S-transferase activity. While decreased hemoglobin, platelet, packed cell volume and red cell indices were observed in TCDD treated rats, no interactive effects were seen. The above results indicate that the mixture effects of PCBs and TCDD may be additive or antagonistic depending on the dose level and endpoints measured. For the purpose of predicting mixture effects, knowledge of mechanisms of action and toxicokinetics is required.

Subchronic toxicity of PCB 105 (2,3,3',4,4'-pentachlorobiphenyl) in rats.

The toxicity of 2,3,3',4,4'-pentachlorobiphenyl (PCB 105) was investigated in Sprague-Dawley rats following dietary exposure to this substance at levels of 0, 0.05, 0.5, 5 or 50 ppm for 13 weeks. Growth rate and food consumption were not affected and no clinical signs of toxicity were observed. Increased incidences of enlarged, fatty liver and decreased thymic weight were observed in the highest-dose groups of both genders; these groups also had elevated hepatic microsomal ethoxyresorufin deethylase activity and uroporphyrin. Significant increases in serum cholesterol and hepatic pentoxyresorufin dealkylase activity were observed in the highest-dose males and two highest-dose females. By contrast, liver UDP-glucuronosyl transferase activity was elevated in the two highest-dose males and the highest-dose females. Urinary ascorbic acid excretion was increased in the highest-dose males. While the amount of vitamin A was decreased dose-dependently, starting at 0.5 ppm in the liver of both sexes and in the lung of the females, the level in the kidney of the highest-dose group was increased. Administration of PCB 105 resulted in decreased dopamine in the caudate nucleus region of the brain in males and homovanillic acid in caudate nucleus and nucleus accumbens of females. Increased 5-hydroxytryptamine and 5-hydroxyindoleacetic acid were observed in the substantia nigra region of both sexes, with most of the increases being seen in highest-dose females. Anemia, characterized by decreased hemoglobin, hematocrit and red cell indices, occurred in the highest-dose group, as did eosinophilia. Treatment with PCB 105 caused dose-dependent histopathological changes in the liver and thyroid. Thymic changes were observed in the highest-dose males and two highest-dose females. Tissue residue data showed a dose-dependent accumulation of this congener in fat, liver and spleen, kidney and brain. Based on these data the no-observable-effect level of PCB 105 was judged to be 0.05 ppm or 3.9 microg kg(-1) body wt. day(-1) in males and 4.2 microg kg(-1) body wt. day(-1) in females.

Running exercise may reduce risk for lung and liver cancer by inducing activity of antioxidant and phase II enzymes.

The effects of exercise, ethanol, and exercise plus ethanol-treatments on activity of superoxide dismutase (SOD), catalase (CAT), glutathione-S-transferase (GST) and UDP-glucuronosyl transferase (UDP-GT) in lung and liver were investigated. All treatments induced SOD and CAT activity in the lung while CAT activity was enhanced only by the combined treatments in the liver. Ethanol reduced hepatic SOD activity, while with the combined treatment SOD was normal. Exercise enhanced UDP-GT activity in liver and lung while ethanol had no effect and GST activity was induced in the liver by the combined treatment. Thus exercise may reduce risk for lung and hepatic cancer and prevent an ethanol-induced increase in risk for hepatic cancer by enhancing activity of antioxidant and phase II enzymes.

Sex-related differences in the hepatobiliary transport of phenolsulfonphthalein in the rat

Sex-related differences in the hepatobiliary transport of phenolsulfonphthalein (PSP) were investigated in male and female Wistar rats. Maximal biliary excretion of unconjugated PSP was significantly higher in females while the excretion of the conjugated dye and liver UDP-glucuronosyltransferase activity toward PSP were higher in male animals. Orchidectomy decreased enzyme activity and excretion of the conjugate, whereas ovariectomy produced the opposite effect. Both in gonadectomized males and females maximal biliary excretion of the unconjugated dye was significantly reduced. Testosterone treatment increased the excretion of both conjugated and unconjugated PSP and transferase activity in orchidectomized males. Combined treatment of gonadectomized females with estradiol plus progesterone led to excretions of both conjugated and unconjugated PSP and UDP-glucoronosyltransferase activities similar to those found in control rats. These data indicate the existence of sex-related differences in the conjugation and biliary excretion of PSP in the rat and its modulation by sex hormones.

Separation of different plaice liver UDP-glucuronosyltransferase activities according to charge heterogeneity

Separation of different plaice liver UDP-glucuronosyltransferase activities according to charge heterogeneity

DIfferential induction of human liver UDP-glucuronosyltransferase activities by phenobarbital-type inducers

(1) UDP-glucuronosyltranferase (UDP-GT) activities and their inducibility were investigated in human liver microsomes from a “liver bank”. (2) UDP-GT activities were differentially induced in liver microsomes from patients treated with the phenobarbital-type inducers phenytoin or pentobarbita, UDP-GT activity towards bilirubin was induced 3-fold. Enzyme activities towards paracetamol, benzo( a)pyrene-3, 6-quinol, 4-methylumbelliferone and 1-naphthol were moderately induced and to similar extents (2-fold). In contrast, morphine and 4-hydroxybiphenyl glucuronidation were not significantly affected. Cytochrome P-450 dependent 7-ethoxycoumarin O-deethylase was increased 5-fold. (3) A human hepatoma cell line (Hep G2) was studied to obtain information on the inducibility of human UDP-GT activities by 3-methylcholanthrene-type inducers. UDP-GT activities towards benzo( a)pyrene-3, 6-quinol and 1-naphthol were moderately but significantly induced by 3-methylcholanthrene-treatment of the cells (2-fold), whereas 7-ethoxyresorufin O-deethylase and 7-ethoxycoumarin O-deethylase were increased over 100- and 10-fold, respectively. (4) The results suggest the existence of differentially inducible UDP-GT isoenzymes in human liver. The findings may be useful as a guide to characterize human liver UDP-GT isoenzymes.

Changes of the liver UDP-glucuronosyltransferase activity in trout ( Salmo gairdneri Rich.) acutely exposed to selected aquatic toxicants

1. 1. Rainbow trout were exposed for 4 or 8 days to various types of toxicants, each applied to the test water at a high sublethal concentration. 2. 2. The activity of liver UDP-glucuronosyltransferase (UDP-GT) was assayed from the submito-chondrial fraction using p-nitrophenol as an aglycone. 3. 3. Activity of UDP-GT was inhibited by 2,4,6-trichlorophenol, pentachlorophenol and dehydroabietic acid, all toxicants regularly found in effluents of the pulp and paper industry. 4. 4. The heavy metals cadmium and zinc, the polychlorinated biphenyl, Pyralene 3010, and chloroform did not affect UDP-GT activity. 5. 5. The slimicide N-methyl-dithiocarbamate (Vapam ®) significantly increased the enzyme activity.

Changes in thyroidal function and liver UDPglucuronosyltransferase activity in rats following administration of a novel imidazole (SC-37211)

SC-37211, an imidazole with antianaerobic activity, was administered po to male rats for 2 weeks at dosages of 20, 60, and 200 mg/kg/day. Histological changes in the thyroid included irregularly shaped follicles and slightly enlarged follicular cells. Serum triiodothyronine (T 3) and/or thyroxine (T 4) were significantly decreased in treated animals at all dosages; these decreases were not observed following a 2-week recovery period. The half-life of serum [ 125I]thyroxine was also significantly decreased in rats treated with SC-37211. Morphological changes in the thyroid are likely the result of thyroidstimulating hormone (TSH) stimulation, a response to decreased serum T 3 and T 4 concentrations. The decreases in T 3 and T 4 were not due to decreases in iodide uptake or organification. There were dose-dependent increases in liver weights, liver-to-body weight ratios, and UDPglucuronosyltransferase activity toward p-nitrophenol and T 4. Therefore, the decreases in serum T 3 and T 4 were probably due to an increase in hepatic metabolism rather than to a direct effect of SC-37211 on the thyroid.

Hepatic phase I and phase II biotransformations in quail and trout: Comparison to other species commonly used in toxicity testing

The ability of quail and trout to perform a number of representative phase I and phase II biotransformations was examined. To facilitate interspecies comparisons, metabolism of the same substrates was examined simultaneously under uniform conditions for rat, mouse, rabbit, guinea pig, cat, and dog. Both nonmammalian species can metabolize four representative substrates of phase I mixed-function oxidases and one substrate of epoxide hydrolase, though activity tended to be lower than that of the mammals. Important differences in the conjugative pathways were also noted. Among these differences were the quail's relative deficiency in glutathione conjugation and the trout's low ability to conjugate sulfate compounds. Trout liver UDP-glucuronosyltransferase activity was remarkably high toward testosterone and bilirubin, while quail liver formed glucuronides of naphthol, p-nitrophenol, and digitoxigenin-monodigitoxoside. Also noteworthy was the high N-acetyltransferase activity of both quail and trout toward isoniazid, β-naphthylamine, and 2-aminofluorene. Differences in substrate specificity for a given enzymatic pathway may be an indication that multiple forms of drug metabolizing systems also occur in these nonmammalian species. Observation of several hundred- or even thousand-fold differences between species in their enzyme activities for certain substrates under uniform conditions reemphasizes the need for caution in extrapolation of xenobiotic metabolism from one species to another.

Acute toxic effects of trinitrotoluene on rat brain, liver and kidney: role of radical production

Trinitrotoluene (TNT) enhanced the formation of adrenochrome from adrenaline when added to mitochondrial and microsomal suspensions indicating increased superoxide production. The effect was observed in the presence of NADH and NADPH and was most prominent if these cofactors were combined. When injected intraperitoneally to male Wistar rats, TNT (100 mg/kg) caused damages in cerebral, hepatic and renal biomembranes and cell organelles. Morphological studies showed e.g., damaged mitochondria, dilatation of Golgi apparatus, vacuolization, swelling of cytoplasm and accumulation of lipid material. Morphological changes were more prominent in brain and kidney than in liver. TNT increased UDP-glucuronosyltransferase activity in liver and kidney. Renal epoxide hydrolase activity was also enhanced. In brain, succinate dehydrogenase activity was diminished while creatine kinase activity increased. Content of reduced glutathione increased after TNT dosage in brain, kidney and liver.

Stereochemical heterogeneity of hepatic UDP-glucuronosyltransferase activity in rat liver microsomes

Rat liver UDP glucuronosyltransferase activities may be divided into at least two groups with differential responses towards substrates. This paper deals with an attempt to describe on what chemical basis the two groups may be distinguished. We studied the glucuronidation of 24 substrates in liver-microsomes of Sprague-Dawley rats pretreated with 3-methylcholanthrene or phenobarbital. The conjugation of 11 substrates was stimulated most strongly by 3-methylcholanthrene and that of the others, by phenobarbital. The estimated thickness of the molecules in their most likely conformation was below 4 Å for molecules of the first group and more than 4 Å for the second. The thickness or the bulkiness of the molecules seems to play an important role. However, for phenol substituted in the position 2, a steric effect or intramolecular interactions may change the substrate's classification within these two groups. It was also noticed that phenobarbital stimulated more than 3-methylcholanthrene the glucuronidation of the corresponding hydroxylated metabolite.