Hepatic Glutathione S-transferase Activity Research Articles

Exposure to Isothiocyanates Suppresses Urinary Mutagenicity in Rats Treated With Heterocyclic Amine IQ: Lack of Association With CYP1 Activity

The principal objectives of this study were to evaluate whether exposure of rats to low doses of isothiocyanates modulates the overall metabolism of heterocyclic amine 2-amino-3-methylimidazo-[4,5-f]quinoline (IQ), as exemplified by urinary mutagenicity, a food carcinogen, and to relate any modifications in metabolism to changes in CYP1 and glutathione S-transferase activities. Animals were exposed to isothiocyanates either for 2 wk (long-term) or 1 day (short-term), and all animals were then treated with a single oral dose of IQ, and urine was collected daily for 3 days; animals continued to receive the isothiocyanates during this period. Urinary mutagenic activity was determined using the Ames mutagenicity assay in the presence of an activation system from Aroclor 1254-treated rats. At the end of the study, animals were killed and hepatic methoxy- and ethoxyresorufin dealkylations were determined as well as glutathione S-transferase activity. All isothiocyanates studied, namely sulforaphane, erucin, and phenethyl isothiocyanate, decreased urinary mutagenic activity, implying enhanced IQ metabolism, but only after long-term intake. Changes in mutagenic activity were not related to changes of any of the enzyme activities determined. It is concluded that long-term intake of isothiocyanates may stimulate the metabolism of IQ, but this effect is not linked to changes in hepatic CYP1A2 and glutathione S-transferase activities.

The protective effects of cerium oxide nanoparticles against hepatic oxidative damage induced by monocrotaline

ObjectiveThe objective of the present study was to determine the ability of cerium oxide (CeO2) nanoparticles to protect against monocrotaline (MCT)-induced hepatotoxicity in a rat model.MethodTwenty male Sprague Dawley rats were arbitrarily assigned to four groups: control (received saline), CeO2 (given 0.0001 nmol/kg intraperitoneally [IP]), MCT (given 10 mg/kg body weight IP as a single dose), and MCT + CeO2 (received CeO2 both before and after MCT). Electron microscopic imaging of the rat livers was carried out, and hepatic total glutathione (GSH), glutathione reductase (GR), glutathione peroxidase (GPX), glutathione S-transferase (GST), superoxide dismutase (SOD), and catalase (CAT) enzymatic activities were quantified.ResultsResults showed a significant MCT-induced decrease in total hepatic GSH, GPX, GR, and GST normalized to control values with concurrent CeO2 administration. In addition, MCT produced significant increases in hepatic CAT and SOD activities, which also ameliorated with CeO2.ConclusionsThese results indicate that CeO2 acts as a putative novel and effective hepatoprotective agent against MCT-induced hepatotoxicity.

Liver Injury Following Renal Ischemia Reperfusion in Rats

Introduction All transplanted solid organs experience some degree of ischemia-reperfusion (I-R) injury. There is some evidence that I-R injury affects remote organs. We investigated the effects of renal I-R injury on hepatic function, cytochrome P-450 enzymes, and morphology in rats. Methods A rat model of 1 hour of renal ischemia followed by 1, 4, or 8 hours of reperfusion. The assays included serum alanine aminotransferase (sALT) aspartate aminotransferase (sAST), cytochrome P-450 enzymes (CYP3A, CYP2E1), hepatic glutathione S-transferase (GST), glutathione (GSH), malondialdehyde (MDA), superoxide dysmutase (SOD), and myeloperoxidase (MPO) activities. In addition, we measured serum blood urea nitrogen (BUN) and serum creatinine (SCr), and renal MDA, glutathione peroxidase levels, and SOD activities. Morphological liver changes were observed by optical and electron microscopy. Results sALT and sAST significantly increased after 1 hour of ischemia and 4 or 8 hours of reperfusion. Hepatic CYP3A and CYP2E1 activities were significantly decreased after 1 hour of ischemia and 1 or 4 hours of reperfusion. Hepatic GST, GSH, and SOD activities decreased after renal I-R, while MDA levels and MPO increased. Serum BUN and SCr levels significantly increased after reperfusion. Changes in renal MDA, GSH-px, and SOD activities were similar to those in the liver. The only difference between them was the peak time of injury: for the kidney, 8 hours, while for the liver, some changes appeared at 4 hours. Optical microscopy showed hepatic passive venous congestion and fatty degeneration as well as local necrosis. Transmission electronic microscope showed hepatic cell membrane was damaged, which seemed to explain some data results above. For example, the release of hepatic ALT and AST increased serum ALT and AST. More importantly, the release of neutrophil chemokine induced neutrophil accumulation in the liver, which could cause further damage. Conclusion Our findings indicated that hepatic function, cytochrome P-450 enzymes and morphology were affected by renal I-R injury. These effects seemed to be mediated in part by an imbalance of oxidant and antioxidant systems and recruitment of neutrophils to the liver.

Proteomic Analysis of Propiconazole Responses in Mouse Liver‐Comparison of Genomic and Proteomic Profiles

We have performed a comprehensive profiling of changes in protein expression of soluble proteins in mouse livers treated with the liver tumorigen, propiconazole, to uncover the pathways altered by this fungicide. Using two‐dimensional gel electrophoresis (2‐DE) and mass spectrometry (MS), we identified 62 proteins altered by propiconazole treatment. These proteins were mapped using Ingenuity Pathway Analyses™ canonical pathways and Tox lists and results compared to genomics results. Seventeen pathways/lists were unique to proteomics, 21 to genomics and 27 were shared by both analyses. The protein network analysis produced interacting sub‐networks including hepatocyte nuclear factor 4α (HNF4α), MYC, and glutathione S‐transferase (GST). Five GST isoforms were identified by proteomic analysis. Hepatic GST activities were compared between mice treated with propiconazole and 2 other conazoles and higher GST activities were found in the tumorigenic conazoles. This study has shown alterations in nuclear receptor activation, metabolism of xenobiotics, biosynthesis of biochemical intermediates, and oxidative stress. It provides insights into toxic mechanisms and/or modes of action of propiconazole required for human health risk assessment. This abstract does not necessarily reflect EPA policy. Mention of trade names of commercial products does not constitute endorsement or recommendation for use.

Biochemical alterations in caged Nile tilapia Oreochromis niloticus

Joinville is an important industrial city in Santa Catarina, southern Brazil, and also a risk factor for the Babitonga drainage basin. Oxidative stress-related parameters were evaluated in caged tilapia ( Oreochromis niloticus) exposed for 7 days (sites S1 and S2) in a Babitonga drainage basin tributary river. Site S1 showed enhanced levels of hepatic CYP1A, CYP2B-like and glutathione S-transferase activity, while site S2 showed decreased levels of glutathione and increased lipoperoxidation indexes, catalase, glutathione peroxidase and glutathione reductase activity. Correlation analyses revealed that oxidative stress-related parameters behaved like a group of interrelated variables, while CYPs and glutathione S-transferase seem to be independent. New putative biomarkers were evaluated in the tilapia brain. Caspase-3 activation (both sites), decreased in p38MAPK phosphorylation (site S2) and decreased expression in HSP70 (site S1) were observed. Data indicate that employed variables, when used as a group (oxidative stress-related parameters, CYP1A/2B-like, caspase-3, HSP70 and protein kinases) can be useful as predictors of pollution.

Effect of Chitosan on Hepatic Drug-Metabolizing Enzymes and Oxidative Stress in Rats Fed Low- and High-Fat Diets

Chitosan is sold worldwide as a lipid-lowering functional food and may be taken with certain medications. To investigate the effect of chitosan on drug-metabolizing enzymes and oxidative stress in the liver, male Wistar rats were fed a low- or high-fat diet with cellulose or chitosan for 4 weeks. A significant decrease in cytochrome P450 (CYP) 3A-catalyzed testosterone 6beta-hydroxylation in liver microsomes was observed in rats fed the chitosan with low- and high-fat diets. The expression of CYP 3A1 and 3A2, however, was suppressed by chitosan in rats fed the low-fat diet only. Furthermore, rats fed the low-fat diet with chitosan had lower hepatic glutathione S-transferase (GST) activity and superoxide dismutase activity and higher total tissue and microsomal lipid hydroperoxides. Hepatic alpha-tocopherol was lower in rats fed the chitosan-containing diet. The results suggest that chitosan is likely to modulate CYP 3A activity and protein expression and GST activity partially in a dietary fat-dependent manner. This change may cause a decrease in the metabolism of drugs catalyzed by these enzymes in liver tissues. Moreover, decrease of alpha-tocopherol level and SOD activity by chitosan partly accounts for the increase of hepatic lipid peroxidation.

Assessment of biological effects of pollutants in a hyper eutrophic tropical water body, Lake Beira, Sri Lanka using multiple biomarker responses of resident fish, Nile tilapia (Oreochromis niloticus)

Biomarkers measured at the molecular and cellular level in fish have been proposed as sensitive "early warning" tools for biological effect measurements in environmental quality assessments. Lake Beira is a hypertrophic urban water body with a complex mixture of pollutants including polycyclic aromatic hydrocarbons (PAHs) and Microcystins. In this study, a suite of biomarker responses viz. biliary fluorescent aromatic compounds (FACs), hepatic ethoxyresorufin O-deethylase (EROD) and glutathione S-transferase (GST), brain and muscle cholinesterases (ChE), serum sorbitol dehydrogenase (SDH), and liver histology of Oreochromis niloticus, the dominant fish inhabiting this tropical Lake were evaluated to assess the pollution exposure and biological effects. Some fish sampled in the dry periods demonstrated prominent structural abnormalities in the liver and concomitant increase in serum SDH and reduction in hepatic GST activities in comparison to the control fish and the fish sampled in the rainy periods. The resident fish with apparently normal liver demonstrated induction of hepatic EROD and GST activities and increase in biliary FACs irrespective of the sampling period indicating bioavailability of PAHs. Muscle ChE activities of the resident fish were depressed significantly indicating exposure to anticholinesterase substances. The results revealed that fish populations residing in this Lake is under threat due to the pollution stress. Hepatic abnormalities in the fish may be mainly associated with the pollution stress due to recurrent exposure to PAHs and toxigenic Microcystis blooms in the Lake.

Modulation of ethoxyresorufin O-deethylase and glutathione S-transferase activities in Nile tilapia (Oreochromis niloticus) by polycyclic aromatic hydrocarbons containing two to four rings: implications in biomonitoring aquatic pollution

Despite ubiquity of polycyclic aromatic hydrocarbons (PAHs) in the tropical environments, little information is available concerning responses of tropical fish to PAHs and associated toxicity. In the present study, effects of five PAHs containing two to four aromatic rings on hepatic CYP1A dependent ethoxyresorufin O-deethylase (EROD), glutathione S-transferase (GST) and serum sorbitol dehydrogenase (SDH) activities in Nile tilapia, a potential fish species for biomonitoring pollution in tropical waters, were evaluated. Results showed that EROD activities were induced by the PAHs containing four aromatic rings (pyrene and chrysene) in a dose dependent manner. However PAHs with two to three aromatic rings (naphthalene, phenanthrene and fluoranthene) caused no effect or inhibition of EROD activities depending on the dose and the duration. Fluoranthene was the most potent inhibitor. SDH results demonstrated that high doses of fluoranthene induced hepatic damage. GST activity was induced by the lowest dose of phenanthrene, fluoranthene and chrysene but high doses had no effect. The results indicate that induction of EROD enzyme in Nile tilapia is a useful biomarker of exposure to PAHs such as pyrene and chrysene. However EROD inhibiting PAHs such as fluoranthene in the natural environment may modulate the EROD inducing potential of other PAHs thereby influencing PAH exposure assessments.

Differential sensitivity of CYP1A to 3,3′,4′,4-tetrachlorobiphenyl and benzo(a)pyrene in two Lepomis species

Although Lepomis species are abundant in a wide variety of habitats throughout North America and could serve as potentially valuable biomonitoring tools, few studies have examined the induction of pollutant biomarkers in this genus. We hypothesized that the induction of cytochrome P-450 1A (CYP1A), a sensitive and widely used indicator of response to aquatic contaminants, would serve as an effective biomarker of organic pollutant exposure in Lepomis species. We examined the response of CYP1A and two of the major pollutant-responsive phase II enzymes, glutathione S-transferase (GST), and uridine diphosphate glucuronyltransferase (UDPGT), in Lepomis exposed to organic pollutants under laboratory and field conditions. Two Lepomis species (longear sunfish, Lepomis megalottis and bluegill, Lepomis macrochirus) were exposed in the laboratory via intraperitoneal injection to corn oil (vehicle), benzo(a)pyrene (BaP) (10 and 50 mg/kg), a polynuclear aromatic hydrocarbon (PAH) or 3,4,3′,4′-tetrachlorobiphenyl (PCB 77) (0.1 and 1.0 mg/kg), a dioxin-like planar halogenated aromatic hydrocarbon (HAH), and sacrificed 2 (BaP) or 7 (corn oil, PCB77) days later. Lepomis hepatic CYP1A exhibited differential sensitivity to these two classes of environmental contaminants. CYP1A activity was weakly induced in bluegill exposed to 1.0 mg/kg PCB 77 (3 fold induction over controls) but strongly induced in both bluegill and longear sunfish exposed to 50 mg/kg BaP (37 and 15 fold induction over controls, respectively). In contrast, hepatic GST activity in both species remained unchanged following the treatment with either compound and hepatic UDPGT activity, which was assessed only in BaP-treated longear sunfish, was unaffected by that chemical, indicating these phase II enzymes may not be sensitive pollutant biomarkers in this genus. Further, longear sunfish collected from a PCB contaminated site displayed relatively low levels of CYP1A activity despite PCB body burdens associated with strong induction of CYP1A activity in other fish species. The strong induction of CYP1A by BaP with much weaker CYP1A response to PCB indicates that CYP1A in Lepomis sp. could be an excellent biomarker for PAH pollution, but may not be a reliable indicator of site contamination by halogenated hydrocarbons. We conclude that Lepomis species provide a useful model for examining the regulation and potential consequences of differential pollutant sensitivity, but that CYP1A in these species should be used with caution as an indicator of halogenated contaminants.

Proteomic Analysis of Propiconazole Responses in Mouse Liver: Comparison of Genomic and Proteomic Profiles

We have performed for the first time a comprehensive profiling of changes in protein expression of soluble proteins in livers from mice treated with the mouse liver tumorigen, propiconazole, to uncover the pathways and networks altered by this fungicide. Utilizing two-dimensional gel electrophoresis (2-DE) and mass spectrometry (MS), we identified 62 proteins that were altered. Several of these protein changes detected by 2-DE/MS were verified by Western blot analyses. These differentially expressed proteins were mapped using Ingenuity Pathway Analyses (IPA) canonical pathways and IPA tox lists. Forty-four pathways/lists were identified. IPA was also used to create networks of interacting protein clusters. The protein-generated IPA canonical pathways and IPA tox lists were compared to those pathways and lists previously generated from genomic analyses from livers of mice treated with propiconazole under the same experimental conditions. There was a significant overlap in the specific pathways and lists generated from the proteomic and the genomic data with 27 pathways common to both proteomic and genomic analyses. However, there were also 17 pathways/lists identified only by proteomics analysis and 21 pathways/lists only identified by genomic analysis. The protein network analysis produced interacting subnetworks centered around hepatocyte nuclear factor 4 alpha (HNF4 alpha), MYC, proteasome subunit type 4 alpha, and glutathione S-transferase (GST). The HNF4 alpha network hub was also identified by genomic analysis. Five GST isoforms were identified by proteomic analysis and GSTs were present in 10 of the 44 protein-based pathways/lists. Hepatic GST activities were compared between mice treated with propiconazole and 2 additional conazoles and higher GST activities were found to be associated with the tumorigenic conazoles. Overall, this comparative proteomic and genomic study has revealed a series of alterations in livers induced by propiconazole: nuclear receptor activation, metabolism of xenobiotics, metabolism of biochemical intermediates, biosynthesis of biochemical intermediates, and oxidative stress in mouse liver. The present study provides novel insights into toxic mechanisms and/or modes of action of propiconazole which are required for human health risk assessment of this environmental chemical.

In vitro inhibition of camel hepatic glutathione transferases by selected organic azides

Glutathione S-transferases (GST) are a group of multifunctional enzymes, widely distributed in both animal and plant kingdom. The present study was carried out to investigate the inhibitory potential of three structurally related organic azides (n-propyl azide, n-butyl azide, and heptyl azide) on camel hepatic GST activity in vitro. The mean inhibition constants (Ki) were estimated to be 0.419 ± 0.068, 0.501 ± 0.068, and 0.563 ± 0.036 mM for n-propyl azide, n-butyl azide, and heptyl azide respectively, using Lineweaver-Burk plots. These results indicated that hepatic GST was sensitive to the organic azides used.

Nandrolone Decanoate Enhances the Activities of Cholanthrene Induced Glutathione-s-Transferase in Liver Tissue of Albino Mice

A concrete study is still fragmentary to correlate the effect of Nandrolone decanoate, a anabolic steroid, on the cholanthrene induced Glutathione-s-transferases (GST) activities in liver tissues. Administration of Nandrolone and 3-Methylcholanthrene in alone and combination is found to increase the activity of hepatic GST activity significantly (p< 0.01) suggesting Nandrolone as a potent inducer of GST activity.

Effects of Quercetin and Catechin on Hepatic Glutathione-S Transferase (GST), NAD(P)H Quinone Oxidoreductase 1 (NQO1), and Antioxidant Enzyme Activity Levels in Rats

Cell culture data indicate that quercetin and catechin may affect the activity of phase II and antioxidant enzymes. However, little is known about the impact of dietary flavonoids in vivo. Therefore, the present study aimed to investigate the in vivo effects of the flavonoids quercetin and catechin on mRNA and activity levels of phase II enzymes glutathione-S transferase (GST) and NAD(P)H quinone oxidoreductase-1 (NQO1) in rat liver. Furthermore, the activity of the hepatic antioxidant enzymes catalase (CAT), glutathione peroxidase (GPx), and superoxide dismutase (SOD) was determined. Feeding male Wistar rats (3 × 6 animals) over 3 wk with semisynthetic diets enriched with quercetin and catechin (2 g/kg diet) did not affect liver enzyme activity of CAT, GPx, and SOD as well lipid peroxidation and glutathione levels. Dietary quercetin significantly decreased activity of hepatic GST (24%), whereas dietary catechin significantly decreased NQO1 activity (26%) compared to controls. Changes in GST and NQO1 activity were partly reflected on mRNA levels. Current data indicate that dietary flavonoids have little effects on liver oxidant/antioxidant status but do significantly affect the phase II enzymes GST and NQO1 in rat liver. This in turn may affect the ability of the organism to detoxify endogenous and exogenous xenobiotics.

Antihyperglycemic Effects of Fruits of Privet (Ligustrum obtusifolium) in Streptozotocin-Induced Diabetic Rats Fed a High Fat Diet

The protective effects of freeze-dried privet (Ligustrum obtusifolium) fruits (PFs) were observed in streptozotocin (STZ)-induced diabetic rats on a high fat diet by measuring levels of blood glucose, serum insulin, fructosamine, and hepatic reactive oxygen species generating and scavenging enzyme activities. A PF-supplemented diet was prepared by mixing an AIN-76 diet with powdered PF (final concentration, 1% or 2%). It was fed to STZ-induced diabetic rats on a high fat diet for 6 weeks. Diabetic animals receiving the PF-supplemented diet showed a significant increase in body weight, feed efficiency ratio, liver, kidney, and heart weight, and serum glucose, insulin, and fructosamine levels compared with high fat diet-fed diabetic animals. The treatment with PF showed improved hepatic glutathione S-transferase, superoxide dismutase, and xanthine oxidase activities as well as glutathione and lipid peroxide levels in the diabetic animals. Intracellular swelling and vacuole formation in diabetic pancreatic beta- and delta-cells were ameliorated by the PF-supplemented diet. Furthermore, necrosis of tubular epithelial cells and dilatation of luminal space in diabetic kidneys exhibited near-noninjured condition. This is the first time an antihyperglycemic effect of L. obtusifolium fruit in STZ-induced diabetic rats has been identified.

Comparison of citrus coumarins on carcinogen-detoxifying enzymes in Nrf2 knockout mice

Naturally occurring coumarins possess anti-carcinogenic activities in part by inducing carcinogen-detoxifying enzymes glutathione S-transferase (GST) and/or NAD(P)H quinone oxidoreductase (NQO1). Our goal was to determine whether citrus coumarins induce hepatic GST and/or NQO1 via activation of Nrf2 and the antioxidant response element (ARE). First, HepG2 cells stably transfected with the ARE and a green fluorescent protein (GFP) reporter were treated with increasing concentrations of coumarins and compared to positive controls. tert-Butylhydroquinone (TBHQ) and oltipraz increased GFP fluorescence, as did coumarin, limettin, auraptene, imperatorin, and 7,8-benzoflavone, suggesting that they activate the ARE, whereas isopimpinellin did not increase GFP fluorescence. Next, the effects of orally administered coumarins and oltipraz on hepatic GST and NQO1 activities were compared in Nrf2 knockout mice or Nrf2 heterozygous mice exhibiting the wild-type phenotype. Oltipraz, auraptene, imperatorin, isopimpinellin, and auraptene all significantly increased liver cytosolic GST activities in Nrf2 heterozygous mice. This effect was abrogated in Nrf2(−/−) mice dosed with oltipraz, attenuated in mice Nrf2(−/−) mice treated with auraptene and imperatorin, and still significant in Nrf2(−/−) mice treated with isopimpinellin. Of these compounds, only isopimpinellin significantly increased liver cytosolic NQO1 activities, and this effect was not attenuated in Nrf2(−/−) mice. These results strongly suggest that imperatorin and auraptene induce murine liver cytosolic GST activities via the Nrf2/ARE mechanism. Although structurally similar, isopimpinellin did not appear to activate HepG2–ARE–GFP and the Nrf2 knockout mouse study suggests that isopimpinellin may induce GST and NQO1 via additional mechanisms.

Hepatic and branchial glutathione S-transferases of two fish species: Substrate specificity and biotransformation of microcystin-LR

Liver and gills of roach ( Rutilus rutilus) and silver carp ( Hypophthalmichthys molitrix) were examined for glutathione S-transferases (GSTs) contents and their substrate specificity and capacity to biotransform microcystin-LR (MC-LR). GSTs and other glutathione (GSH) affine proteins were purified using a GSH-agarose matrix and separated by anionic chromatography (AEC). Substrate specificities were determined photometrical for 1-chloro-2,4-dinitrobenzene (CDNB), 1,2-dichloro-4-nitrobenzene (DCNB), 4-nitrobenzyl chloride (pNBC) and ethacrynic acid (ETHA). Biotransformation rate of MC-LR was determined by high performance liquid chromatography (HPLC). Roach exhibited different hepatic and branchial GST activities for used substrates (DNB, pNBC and DCNB) compared to silver carp but not for ethacrynic acid. It suggests that, both fish species have similar amount of pi and/or alpha class, which were the dominant GST classes in liver and gills. Gills of both fish species contained a higher number of GST isoenzymes, but with lower activities and ability of MC-LR biotransformation than livers. GST isoenzymes from roach had higher activity to biotransform MC-LR (conversion rate ranging up to 268 ng MC-LR min − 1 mL − 1 hepatic enzyme) than that isolated from silver carp. Without any prior contact to MC-LR or another GST inducer, roach seems to be better equipped for microcystin biotransformation than silver carp.

Protective effect of the Aralia continentalis root extract against carbon tetrachloride-induced hepatotoxicity in mice

The root of Aralia continentalis Kitagawa has been used in traditional Korean medicine to relieve pain and to treat inflammation. The purpose of this study was to investigate the protective effects of the extract of A. continentalis roots (AC) against hepatotoxicity induced by carbon tetrachloride (CCl 4) and the mechanism of its hepatoprotective effect. In mice, pretreatment with AC prior to the administration of CCl 4 significantly prevented the increased serum enzymatic activity of ALT and AST as well as the formation of hepatic malondialdehyde. Histopathological evaluation of the livers also revealed that AC reduced the incidence of liver lesions induced by CCl 4. In addition, pretreatment with AC significantly prevented both the depletion of reduced glutathione (GSH) content and the decrease in glutathione- S-transferase (GST) activity in the liver of CCl 4-intoxicated mice. Hepatic GSH levels and GST activity were increased by treatment with AC alone. Heme oxygenase-1 (HO-1) is known to be induced by oxidative stress and to confer protection against oxidative tissue injuries. Interestingly, AC markedly upregulated hepatic HO-1 expression in CCl 4-treated mice, which might provide anti-oxidative activity in the liver. These results indicate that AC plays a critical protective role in CCl 4-induced acute liver injury by promoting anti-oxidative protein expression.

Tissue differences in the modulation of rat cytochromes P450 and phase II conjugation systems by dietary doses of phenethyl isothiocyanate

Rats were fed diets supplemented with phenethyl isothiocyanate (PEITC) at 0.06 (low dose, dietary intake level), 0.6 (medium dose) and 6.0 μmole/g (high dose), and xenobiotic-metabolising enzymes were monitored in liver, lung and kidney. At the low dose, inhibition of the hepatic O-dealkylation of ethoxy- and methoxyresorufin was noted, whereas at the high dose increases in the O-depentylation of pentoxyresorufin and O-debenzylation of benzyloxyquinoline were observed, whereas p-nitrophenol hydroxylase was inhibited. Hepatic bioactivation of 2-amino-3-methylimidazo-[4,5- f]quinoline to mutagens was not influenced by the PEITC-treatment. In the lung, at the high dose, ethoxyresorufin dealkylation was elevated and that of pentoxyresorufin suppressed; no significant changes were seen in the kidney. Quinone reductase was markedly elevated at all doses in liver, but the lung enzyme was refractive whereas in the kidney a modest rise was observed at the high dose. Hepatic glutathione S-transferase activity was stimulated by PEITC-treatment, but no effect was evident in the lung or kidney. It is concluded that the effects of PEITC on xenobiotic-metabolising systems are dose- and tissue-dependent, with the liver being the most sensitive and the lung generally resistant. Increased detoxication rather than cytochrome P450 inhibition is the likely mechanism of the chemopreventive activity of PEITC.

Use of biomarkers in Nile tilapia (Oreochromis niloticus) to assess the impacts of pollution in Bolgoda Lake, an urban water body in Sri Lanka

The present study reports the first analysis of water pollutants in Sri Lankan waters using a suite of biomarkers in Nile tilapia (Oreochromis niloticus) residing in Bolgoda Lake which receives urban, industrial and domestic wastes from multiple sources. The fish were collected from the lake in the dry period (April 2005) and wet periods (September 2005, October 2006) and the levels of biomarkers viz. hepatic ethoxyresorufin O-deethylase (EROD), glutathione S-transferase (GST), metallothioneins, biliary fluorescent aromatic compounds, brain and muscle cholinesterases (ChE) were compared with those of the laboratory reared control fish and the fish obtained from a less polluted water body, Bathalagoda reservoir (reference site). The results revealed that biomarker levels of the fish collected from the reference site were not significantly different from the controls. Hepatic EROD and GST activities in fish from Bolgoda Lake were induced 4.2-16.6 folds and 1.4-3.3 folds respectively compared with the control fish. Analysis of bile in the lake fish revealed recent uptake of naphthalene, pyrene and benzo(a)pyrene type polycyclic aromatic hydrocarbons (PAHs). The induction of EROD activities in feral fish reflects the exposure of fish to aryl hydrocarbon receptor agonists including PAHs present as pollutants in the Bolgoda Lake. Cholinesterase activity in the fish inhabiting one sampling site of Bolgoda Lake was lower (22-40% inhibition) than the activity measured in the control fish indicating the presence of anticholinesterase pollutants in the area. Hepatic metallothionein levels in the lake fish were higher (1.9-3.2 folds) in comparison to the controls indicating metal exposure. The results support the potential use of these biomarkers in Nile tilapia in assessing pollution in tropical water bodies.

Effects of naturally occurring coumarins on hepatic drug-metabolizing enzymes inmice

Cytochromes P450 (P450s) and glutathione S-transferases (GSTs) constitute two important enzyme families involved in carcinogen metabolism. Generally, P450s play activation or detoxifying roles while GSTs act primarily as detoxifying enzymes. We previously demonstrated that oral administration of the linear furanocoumarins, isopimpinellin and imperatorin, modulated P450 and GST activities in various tissues of mice. The purpose of the present study was to compare a broader range of naturally occurring coumarins (simple coumarins, and furanocoumarins of the linear and angular type) for their abilities to modulate hepatic drug-metabolizing enzymes when administered orally to mice. We now report that all of the different coumarins tested (coumarin, limettin, auraptene, angelicin, bergamottin, imperatorin and isopimpinellin) induced hepatic GST activities, whereas the linear furanocoumarins possessed the greatest abilities to induce hepatic P450 activities, in particular P450 2B and 3A. In both cases, this corresponded to an increase in protein expression of the enzymes. Induction of P4502B10, 3A11, and 2C9 by xenobiotics often is a result of activation of the pregnane X receptor (PXR) and/or constitutive androstane receptor (CAR). Using a pregnane X receptor reporter system, our results demonstrated that isopimpinellin activated both PXR and its human ortholog SXR by recruiting coactivator SRC-1 in transfected cells. In CAR transfection assays, isopimpinellin counteracted the inhibitory effect of androstanol on full-length mCAR, a Gal4-mCAR ligand-binding domain fusion, and restored coactivator binding. Orally administered isopimpinellin induced hepatic mRNA expression of Cyp2b10, Cyp3a11, and GSTain CAR(+/+) wild-type mice. In contrast, the induction of Cyp2b10 mRNA by isopimpinellin was attenuated in the CAR(−/−) mice, suggesting that isopimpinellin induces Cyp2b10 via the CAR receptor. Overall, the current data indicate that naturally occurring coumarins have diverse activities in terms of inducing various xenobiotic metabolizing enzymes based on their chemical structure.