Differential induction of glutathione S-transferase subunits by phenobarbital, 3-methylcholanthrene and ethoxyquin in rat liver and kidney

Effect of different river flow rates on biomarker responses in common carp (Cyprinus carpio)

The present study investigated effects of different river flow rates on basal activities of selected biomarkers and the occurrence of oxidative stress in the common carp (Cyprinus carpio). Juvenile carp were exposed to different river flow rates (5-120 cm/s) by caging for 3 weeks. After this period, one half of the fish were sacrificed and used for analysis. The other half received a single intraperitoneal injection of 3-methylcholanthrene (3-MC) and after 6 days were sacrificed and used for analysis. In order to investigate whether the physical activity of carp in the environment will influence the condition status of carp, following biomarkers were measured - activities of glutathione S-transferase (GST), catalase (CAT) and ethoxyresorufin-O-deethylase (EROD) and concentration of protein carbonyls (PC). The results showed that different flow rates significantly influenced biochemical biomarkers. The basal activity of GST did not change significantly after exposure to different river flow rates, whereas the activity of CAT increased with increasing river flow rates. The application of 3-MC caused significant increases in GST and CAT activities, but there were no difference between 3-MC control and 3-MC different flow rates. The occurrence of oxidative stress as a result of exposure to increased physical activity, i.e. increased river flow rates, was confirmed by measurement of PC levels - the level of PC increased with increasing river flow rates. Measurement of EROD basal activity showed that at lower river flow rates the EROD activity increased and at higher river flow rates decreased towards control levels demonstrating a close relationship between oxidative stress, PC levels and EROD activity. Obviously, biomarker responses in carp of different condition status can differ substantially. It can be concluded that flow rate may be an important factor in biomonitoring of rivers using biomarkers and since at different locations river water flow rate can vary significantly, the site selection is extremely important for proper design of river biomonitoring studies involving caging.

Bisphenol A induces hepatotoxicity through oxidative stress in rat model

Reactive oxygen species (ROS) are cytotoxic agents that lead to significant oxidative damage. Bisphenol A (BPA) is a contaminant with increasing exposure to it and exerts both toxic and estrogenic effects on mammalian cells. Due to limited information concerning the effect of BPA on liver, this study investigates whether BPA causes hepatotoxicity by induction of oxidative stress in liver. Rats were divided into five groups: The first four groups, BPA (0.1, 1, 10, 50 mg/kg/day) were administrated orally to rats for four weeks. The fifth group was taken water with vehicle. The final body weights in the 0.1 mg group showed a significant decrease compared to control group. Significant decreased levels of reduced glutathione, superoxide dismutase, glutathione peroxidase, glutathione-S-transferase, glutathione reductase and catalase activity were found in the 50 mg BPA group compared to control groups. High dose of BPA (50 mg/kg) significantly increased the biochemical levels of ALT, ALP and total bilirubin. BPA effect on the activity of antioxidant genes was confirmed by real time PCR in which the expression levels of these genes in liver tissue were significantly decrease compared to control. Data from this study demonstrate that BPA generate ROS and reduce the antioxidant gene expression that causes hepatotoxicity.

Honey supplementation in spontaneously hypertensive rats elicits antihypertensive effect via amelioration of renal oxidative stress

Oxidative stress is implicated in the pathogenesis and/or maintenance of elevated blood pressure in hypertension. This study investigated the effect of honey on elevated systolic blood pressure (SBP) in spontaneously hypertensive rats (SHR). It also evaluated the effect of honey on the amelioration of oxidative stress in the kidney of SHR as a possible mechanism of its antihypertensive effect. SHR and Wistar Kyoto (WKY) rats were randomly divided into 2 groups and administered distilled water or honey by oral gavage once daily for 12 weeks. The control SHR had significantly higher SBP and renal malondialdehyde (MDA) levels than did control WKY. The mRNA expression levels of nuclear factor erythroid 2-related factor 2 (Nrf2) and glutathione S-transferase (GST) were significantly downregulated while total antioxidant status (TAS) and activities of GST and catalase (CAT) were higher in the kidney of control SHR. Honey supplementation significantly reduced SBP and MDA levels in SHR. Honey significantly reduced the activities of GST and CAT while it moderately but insignificantly upregulated the Nrf2 mRNA expression level in the kidney of SHR. These results indicate that Nrf2 expression is impaired in the kidney of SHR. Honey supplementation considerably reduces elevated SBP via amelioration of oxidative stress in the kidney of SHR.

Investigations on the metabolism and potentially adverse effects of ethoxyquin dimer, a major metabolite of the synthetic antioxidant ethoxyquin in salmon muscle

The feed additive ethoxyquin (EQ) is a commonly used synthetic antioxidant preservative in animal feeds. In farmed Atlantic salmon fillets, EQ residues are present, both as the parent compound and as EQ derivatives. One of the main EQ derivates in fish muscle is an ethoxyquin dimer (EQDM), and the potential toxicity of this metabolite is not known. The aim of this study was to evaluate the metabolism and potentially toxicological effects of EQDM. A 90-day subchronic exposure study with repeated dietary exposure to EQDM at 12.5 mg/kg of body weight per day was performed with male F344 rats. Hepatic Cyp1a1 mRNA was significantly reduced to <3% of the control in rats fed EQDM, and hepatic Cyp2b1 mRNA was increased to 192%. EQDM increased Gstpi1 mRNA expression to 144% that of the control, but the activity level of this phase II enzyme was reduced. Biomarkers of liver and kidney function did indicate adverse effects of EQDM when F344 rats were fed 12.5 mg/kg of body weight per day. The present study revealed that EQDM produces responses that are comparable to those produced by the parent compound (EQ) in terms of activating the same enzyme systems.

Effects of renal diseases on the regulation and expression of renal and hepatic drug-metabolizing enzymes: a review

1. The activity of drug-metabolizing enzymes (DMEs) in extrahepatic organs is highest in the kidneys. Generally, the kidneys contain most, if not all, of the DMEs found in the liver. Surprisingly, some of these DMEs show higher activity in the kidneys than in the liver. 2. Most of the renal DMEs are localized in the cortex of the kidneys, especially in the proximal tubules. DMEs are also found in the distal tubules and collecting ducts. 3. Renal diseases such as acute and chronic renal failure and renal cell carcinoma alter the regulation of both hepatic and extrahepatic phase I and II DMEs. Changes in the expression of these DMEs seem to be tissue and species specific. 4. Generally, there is significant down-regulation of most of the phase I and a few of phase II DMEs at the protein, mRNA and activity levels. Unfortunately, the mechanisms leading to the alteration in DMEs in renal diseases remain unclear, although many theories have been made. 5. The presence of some circulating factors such as cytokines, nitric oxide, parathyroid hormones and increased intracellular calcium play a role in the regulation of DMEs in renal diseases.

Pretreatment of rats with the inducing agents phenobarbitone and 3-methylcholanthrene ameliorates the toxicity of chromium (VI) in hepatocytes

To exert cytotoxicity chromium VI (Cr(VI)) has to be reduced inside cells. This is achieved through both enzymatic and non-enzymatic mechanisms. Enzymatic mechanisms include DT-diaphorase, cytochrome P450, and NADPH cytochrome c reductase, and non-enzymatic mechanisms involve reduced glutathione (GSH) and ascorbic acid. The extent of cytotoxicity of Cr(VI) may thus be influenced by the availability of non-enzymatic reductants, and by the activities of the reductase enzymes. In the present paper we have investigated the effect of pretreatment with the inducing agents, phenobarbitone (PB) and 3-methylcholanthrene (3-MC), on the response of rat hepatocytes to Cr(VI). Pretreatment with PB increased the activity of NADPH cytochrome c reductase, and 3-MC increased DT-diaphorase activity in hepatocytes. Both inducers increased cytochrome P450 content, while neither influenced intracellular GSH content or the activity of glutathione reductase. Pretreatment with either PB or 3-MC resulted in amelioration of Cr(VI) toxicity both in terms of hepatocyte viability, and to a greater extent, in terms of Cr(VI) induced GSH loss. We propose that the inducing agents increase the amount of enzymatic reduction of Cr(VI) relative to non-enzymatic reduction. Thus, less GSH is used in the reduction of Cr(VI), and intracellular GSH does not fall as rapidly as in cells from control animals therefore cell integrity is better maintained. Exposure to environmental inducing agents in vivo may also alter the response of human tissues to Cr(VI).

Induction of glutathione S-transferase activity and protein expression in brown bullhead (Ameiurus nebulosus) liver by ethoxyquin

The inducibility of hepatic cytosolic glutathione S-transferases (GSTs) was examined in brown bullheads, a freshwater fish that is highly susceptible to hepatic neoplasia following exposure to carcinogen-contaminated sediments. Juvenile bullheads were fed a semi-purified antioxidant-free diet supplemented with ethoxyquin (0.5% w/w dissolved in 3% corn oil), a prototypical rodent GST-inducing agent, twice daily for 14 days. Control bullheads received the antioxidant-free diet supplemented with corn oil (3% w/w). A significant increase (1.6-fold, p < or = 0.01) in hepatic cytosolic GST activity toward 1-chloro-2,4-dinitrobenzene (CDNB) was observed in the ethoxyquin-treated bullheads relative to control fish. A trend toward increased GST-NBC activity was observed in the ethoxyquin-treated fish (1.2-fold, p = 0.06), whereas no treatment-related effects were observed on GST activities toward ethacrynic acid (ECA). In contrast, GST activity toward (+/-)-anti-benzo[a]pyrene-trans-7,8-dihydrodiol-9,10-epoxide (BPDE) was repressed in affinity-purified cytosolic fractions prepared from ethoxyquin-treated bullheads relative to control bullheads. Silver staining and densitometric analysis of isoelectric-focused, affinity-purified GST proteins revealed increased expression of two basic GST-like isoforms in ethoxyquin-treated fish. In summary, exposure to ethoxyquin increases brown bullhead GST-CDNB catalytic activity and hepatic cationic GST protein expression. However, the increase in overall GST-CDNB activity by ethoxyquin is associated with repression of GST-BPDE activity, suggesting differential effects on hepatic bullhead GST isoforms by ethoxyquin. The potential repression of bullhead GST isoforms that conjugate the carcinogenic metabolites of PAH metabolism under conditions of environmental chemical exposure could be a contributing factor in the sensitivity of bullheads to pollutant-associated neoplasia.

Differential induction of glutathione S-transferase subunits by spironolactone in rat liver, jejunum and colon

The effect of spironolactone pretreatment on glutathione S-transferase activity and on the relative content of the principal subunits (Ya, Yc, Yb1, Yb2 and Yp or 1, 2, 3, 4 and 7 respectively) was studied in rat liver, jejunum and colon. Male Wistar rats were injected with spironolactone i.p. at daily doses of 50, 100 and 200 micromol/kg body wt for 3 consecutive days. Glutathione S-transferase activities were assayed using 1-chloro-2,4-dinitrobenzene as substrate. Changes in subunit composition were evaluated by Western blot analysis in rats treated with the highest dose of spironolactone. The results demonstrated a dose-dependent increase in enzyme activity in liver, while in jejunum the three tested doses exhibited the same magnitude of induction. No significant difference in glutathione S-transferase activity was observed between control and treated rats for the colon. Immunoblot analysis revealed more Ya and Yp protein in liver (140 and 118% increase respectively) and jejunum (45 and 145% increase respectively) from treated rats. While Ya and Yp relative contents were similar in jejunum, the latter subunit slightly contributed to total GST in liver, even in SL-treated animals. The inducer produced no change in subunit composition in colon. In conclusion, spironolactone was able to increase glutathione S-transferase activity mainly by induction of Ya subunit in liver and Yp subunit in jejunal mucosa, without affecting colonic enzyme.

Regulation of rat olfactory glutathione S-transferase expression. Investigation of sex differences, induction, and ontogenesis

The glutathione S-transferases (GSTs) of rat olfactory epithelium have been characterised with regard to sex differences, induction, and developmental regulation, and compared to those of the liver. Olfactory cytosolic GST activity with 1-chloro-2,4-dinitrobenzene (CDNB) as substrate was similar in both male and female animals, and there were no differences in subunit profile. Administration of trans-stilbene oxide and beta-naphthoflavone had no effect on olfactory GST activity with CDNB, although phenobarbitone treatment resulted in a small, but significant, increase in activity (130% compared to controls). HPLC analysis of subunit profiles indicated that all three agents induced olfactory subunit 1b and decreased subunit 6. The effect of age (3 to 84 days) on both cytosolic and microsomal CDNB activity was examined. In the liver, cytosolic activity was low at 3 days and climbed steadily to reach maximal levels around 28 days, but microsomal activity was relatively constant at all ages. Olfactory cytosolic activity was similar at all ages; microsomal activity was low until 21 days and then increased to reach a maximum at 56 days. Changes in individual cytosolic subunits were assessed by SDS-PAGE followed by immunoblotting. The significance of these results with regard to putative physiological roles for olfactory GSTs is discussed.

Alteration of glutathione transferase subunits composition in the liver of young and aged rats submitted to hypoxic and hyperoxic conditions

In the present work, we have studied glutathione transferase (GST) activity and GST subunits distribution in the liver of young and aged rats kept under hypoxic or hyperoxic normobaric conditions as model of oxidative stress. A significant decrease of GST activity was detected in young hypoxic rat liver, whereas a significant increase occurred in aged hypoxic liver. No significant alteration of activity was obtained in both young and aged rat livers subjected to hyperoxic treatment. Substrate specificity measurements, SDS/PAGE analysis and reverse-phase HPLC, of GSH-affinity purified fractions were used to study the changes in the GST subunits pattern occurring in the liver of rat as a consequence of hypoxic and hyperoxic treatment. The results demonstrate that young and aged rat liver has a different constitutive GST subunit pattern which are markedly and differentially altered in hypoxia or hyperoxia. The hyperoxic treatment caused an increase of GST subunit 3 in aged, but not in young liver. In aged liver, both the hypoxic and hyperoxic treatment produced a decrease of GST subunit 4. After hypoxic treatment GST subunit 3 significantly increased in both young and aged liver. GST subunit 1a increased in both young and adult liver after hyperoxia. Following hypoxia a decrease of subunit 1a was seen in both young and aged liver. After hypoxic treatment, subunit 6 doubled in young, but not in aged, livers. It was concluded that the alterations in GST subunit expression occurring in the liver as a consequence of hypoxic or hyperoxic treatment respond to the necessity of a better protection of liver against the products of oxidative metabolism.

Comparative metabolism and disposition of ethoxyquin in rat and mouse. I. Disposition

1. The biological fate of the antioxidant [3-14C]ethoxyquin (EQ) was investigated in the male F344 rat and the B6C3F1 mouse following either p.o. or i.v. administration. 2. The disposition of single doses up to 25 mg/kg was similar in the rat and mouse. About 90% of a total dose was excreted in urine and faeces within 24 h post-dosing. In contrast, no more than 60% of a higher dose of 250 mg/kg was excreted within 24 h following p.o. administration. 3. Metabolism of EQ was rapid in both the rat and mouse following either p.o. or i.v. administration. Little or no parent compound was detected in cumulative 24-h excreta. 5. EQ-derived radioactivity bioaccumulated in some tissues following repeated exposure to rat of either 25 or 250 mg/kg by gavage. However, the fold-increases in concentrations of EQ-derived radioactivity in tissues following repeated administration of the higher dose were generally less than those observed following repeated administration of the lower dose. Repeated high dose administration may overcome delayed gastric emptying (observed following single dose administration of 250 mg/kg) and/or lead to auto-induction of EQ metabolism.

Comparative metabolism and disposition of ethoxyquin in rat and mouse. II. Metabolism

1. The major pathways of ethoxyquin (EQ) metabolism in both the rat and mouse are O-deethylation and conjugation to endogenous substrates. 2. The two major EQ-derived metabolites excreted in rat urine were in the form of sulphate conjugates, 1,2-dihydro-6-hydroxy-2,2,4-trimethylquinoline sulphate, and 1,2,3,4-tetrahydro-3,6-dihydroxy-4-methylene-2,2-dimethylquinoline sulphate. The latter apparently arises from an intramolecular rearrangement of the 3,4-epoxide of ethoxyquin. 3. Mouse urine contained one major glucuronide, 1,2-dihydro-6-hydroxy-2,2,4-trimethylquinoline glucuronide as well as one major sulphate conjugate, 1,2-dihydro-6-hydroxy-2,2,4-trimethylquinoline sulphate. 4. EQ-derived radioactivity was excreted in rat bile, mainly as GSH conjugates, with little unchanged EQ present. Two of the biliary metabolites are glutathione conjugates of ethoxyquin 3,4-epoxide; the third appears to be a conjugate of either ethoxyquin 7,8-epoxide or 2,2,4-trimethylquinol-6-one.

Rat kidney glutathione S-transferase 1 subunits have C-terminal truncations

Cytosolic glutathione S-transferases (GSTs) from rat kidneys were purified by a combination of glutathione and S-hexylglutathione affinity columns. The isolated GSTs were subjected to reverse-phase HPLC and electrospray MS analysis. The major GST isoenzymes expressed in kidney are subunits 1, 2, 7 and 8. GST 1',3 and 4 are expressed in minor amounts. GST 10 is barely detectable in the male kidney cytosol. The molecular masses of these rat kidney GST subunits were determined by MS. The values obtained for subunits 1', 2, 3, 4, 7, 8 and 10 are identical with those obtained for rat liver GSTs. Rat kidney GST 1 consists of three polypeptides, with molecular masses of 25517, 25372 and 24982 Da. Results from peptide mapping, MS and amino-acid-sequencing analyses indicate that the major components were generated by deleting the C-terminal phenylalanine (24982 Da) and the C-terminal IFKF tetrapeptide (25372 Da) from the GST 1 subunit, respectively. The 1-chloro-2,4-dinitrobenzene-conjugating and peroxidase activities of kidney GST 1 are substantially lower than for its counterpart from rat liver. In addition, rat kidney GST 1 has an arginine and a valine residue at positions 151 and 207 respectively. The results are in contradiction with the SWISS-PROT and GenBank rat liver GST 1 cDNA-sequencing data, which give a lysine and a methionine at the corresponding positions. Further analyses indicate that rat liver GST 1 also has a C-terminal phenylalanine deletion, and an arginine and a valine residue at positions 151 and 207 respectively. However, the C-terminal-tetrapeptide-deleted form was not observed for rat liver GST 1.

Time-dependent and tissue-specific variations of glutathione transferase activity during gestation in the mouse

Glutathione transferases (GSTs; EC. 2.1.5.18) activity was measured in maternal liver and conceptal tissues during gestation. In maternal liver, maximum activity was found at gestational day (GD) 9 after which it slowly decreased up to the end of gestation. The placental GSTs activity at GD18 was three times lower than that found at GD14. Conversely, fetal liver GSTs at GD14 was about 75% that at GD18. It was also observed that GSTs activity at GD9 and GD10 was higher in visceral yolk sac than in embryo proper. Substrate specificity measurements, SDS PAGE analysis and HPLC runs, carried out on GSH-affinity purified fractions, revealed that with the progress of gestation in maternal liver an increase in pi class GSTs subunit occurs, with a concomitant decrease in alpha class GSTs. With respect to the time of gestation, a significant change in alpha, mu and pi class GSTs expression also occurred in fetal liver and in chorioallantoic placenta. It was concluded that during gestation the GSTs system is subjected to a time-dependent and tissue-specific modulation which may play a protective role against developmental toxicants.

The glutathione S-transferase supergene family: regulation of GST and the contribution of the isoenzymes to cancer chemoprotection and drug resistance

The glutathione S-transferases (GST) represent a major group of detoxification enzymes. All eukaryotic species possess multiple cytosolic and membrane-bound GST isoenzymes, each of which displays distinct catalytic as well as noncatalytic binding properties: the cytosolic enzymes are encoded by at least five distantly related gene families (designated class alpha, mu, pi, sigma, and theta GST), whereas the membrane-bound enzymes, microsomal GST and leukotriene C4 synthetase, are encoded by single genes and both have arisen separately from the soluble GST. Evidence suggests that the level of expression of GST is a crucial factor in determining the sensitivity of cells to a broad spectrum of toxic chemicals. In this article the biochemical functions of GST are described to show how individual isoenzymes contribute to resistance to carcinogens, antitumor drugs, environmental pollutants, and products of oxidative stress. A description of the mechanisms of transcriptional and posttranscriptional regulation of GST isoenzymes is provided to allow identification of factors that may modulate resistance to specific noxious chemicals. The most abundant mammalian GST are the class alpha, mu, and pi enzymes and their regulation has been studied in detail. The biological control of these families is complex as they exhibit sex-, age-, tissue-, species-, and tumor-specific patterns of expression. In addition, GST are regulated by a structurally diverse range of xenobiotics and, to date, at least 100 chemicals have been identified that induce GST; a significant number of these chemical inducers occur naturally and, as they are found as nonnutrient components in vegetables and citrus fruits, it is apparent that humans are likely to be exposed regularly to such compounds. Many inducers, but not all, effect transcriptional activation of GST genes through either the antioxidant-responsive element (ARE), the xenobiotic-responsive element (XRE), the GST P enhancer 1(GPE), or the glucocorticoid-responsive element (GRE). Barbiturates may transcriptionally activate GST through a Barbie box element. The involvement of the Ah-receptor, Maf, Nrl, Jun, Fos, and NF-kappa B in GST induction is discussed. Many of the compounds that induce GST are themselves substrates for these enzymes, or are metabolized (by cytochrome P-450 monooxygenases) to compounds that can serve as GST substrates, suggesting that GST induction represents part of an adaptive response mechanism to chemical stress caused by electrophiles. It also appears probable that GST are regulated in vivo by reactive oxygen species (ROS), because not only are some of the most potent inducers capable of generating free radicals by redox-cycling, but H2O2 has been shown to induce GST in plant and mammalian cells: induction of GST by ROS would appear to represent an adaptive response as these enzymes detoxify some of the toxic carbonyl-, peroxide-, and epoxide-containing metabolites produced within the cell by oxidative stress. Class alpha, mu, and pi GST isoenzymes are overexpressed in rat hepatic preneoplastic nodules and the increased levels of these enzymes are believed to contribute to the multidrug-resistant phenotype observed in these lesions. The majority of human tumors and human tumor cell lines express significant amounts of class pi GST. Cell lines selected in vitro for resistance to anticancer drugs frequently overexpress class pi GST, although overexpression of class alpha and mu isoenzymes is also often observed. The mechanisms responsible for overexpression of GST include transcriptional activation, stabilization of either mRNA or protein, and gene amplification. In humans, marked interindividual differences exist in the expression of class alpha, mu, and theta GST. The molecular basis for the variation in class alpha GST is not known. (ABSTRACT TRUNCATED)