GSH Transferase Activity Research Articles

Effects of acetyl-L-carnitine on the formation of fatty acid ethyl esters in brain and peripheral organs after short-term ethanol administration in rat.

Increasing evidence suggests that Fatty acid ethyl esters (FAEE) play a central role in ethanol induced organ damage. In the current study we measured FAEE formation in rats after short-term oral administration of ethanol, in the presence and absence of pre-treatment with acetyl-L-carnitine. Ethanol treatment caused a significant increase in the levels of FAEE, particularly in the brain and heart, but also in the kidney and liver. Increases in FAEE were associated with a significant increase in FAEE synthase activity, GSH transferase activity, and lipid hydroperoxide levels. Pretreatment with acetyl-L-carnitine resulted in a significant reduction of FAEE accumulation, decrease in FAEE synthase and GSH transferase activities, and lipid hydroperoxide levels. Administration of acetyl-L-carnitine greatly reduced the metabolic abnormalities due to non-oxidative ethanol metabolism, through an increment in lipid metabolism/turnover and by the modulation of the activities of enzymes associated with FAEE synthesis. These results suggest a potentially important pharmacological role for acetyl-L-carnitine in the prevention of alcohol-induced cellular damage.

Glutathione metabolism in cyclosporine A-treated rats: dose- and time-related changes in liver and kidney.

1. We investigated the simultaneous effects of cyclosporine A (CsA) treatment in rats on glutathione metabolism, oxidative status and their interorgan relationship in the liver and kidney. 2. Reduced and oxidized glutathione (GSH and GSSG, respectively), lipid peroxidation and the activity of several enzymes of the glutathione cycle were evaluated in adult Wistar rats treated daily (i.p.) with saline, CsA vehicle (olive oil) or CsA (10 and 20mg/kg per day) for either 1 or 4 weeks (short- and long-term treatments, respectively). 3. Cyclosporine A treatment elicited a significant depletion in liver GSH content and a decrease in the GSH/GSSG ratio that was unrelated to either the time of treatment or the dose used; these effects were already evident after 1 week of treatment. Renal GSH levels remained unaffected or increased, while those of GSSG increased markedly in all CsA-treated rats, leading to decreases in the GSH/GSSG ratio, except in rats treated in the short term with the lower dose of CsA. These changes in the GSH/GSSG ratio were time and dose dependent. Short-term CsA treatment using the higher dose and long-term treatment with both doses of CsA progressively enhanced lipid peroxidation, which was reflected by increased levels of thiobarbituric acid-reactive substances in both hepatic and renal homogenates. Hepatic gamma-glutamylcysteine synthetase activity was increased after long-term treatment with both doses of CsA, whereas the activity of GSH hepatic peroxidase and GSH transferase was not significantly modified in any of the experimental groups. In contrast, renal gamma-glutamyl transpeptidase activity decreased in a progressive fashion, with the magnitude of this decrease being dose and time dependent. The plasma levels of total glutathione increased only in rats treated in the long term, regardless of the dose of CsA used, and remained unaltered in animals treated in the short term. 4. In summary, the data collected indicate that CsA treatment alters the interorgan homeostasis of glutathione and the oxidative status of the rat liver and kidney, which is associated with increases in lipid peroxidation in both organs, and also induces modifications in the activity of some enzyme related to the glutathione cycle.

Effects of chronic administration of S-adenosyl-L-methionine on brain oxidative stress in rats.

S-adenosyl-L-methionine (SAM), used to treat liver diseases and as a coadjuvant in antidepressive medication, has neuroprotective effects in animal models. The aim of this study was to discover whether SAM has antioxidant effects in rat brain tissue. Ten male Wistar rats were killed by decapitation and the forebrains incubated with SAM for in vitro experiments. To study the effects of long-term administration, animals in four groups of ten rats each were given 10 mg SAM/kg per day s.c., and 40 other rats were given an equivalent volume of L-lysine (the commercial solvent for SAM). Treatment was started at the end of lactation, and animals were killed by decapitation after 15 days or 1, 6 or 22 months of treatment. The forebrain of each animal was used to test membrane lipid peroxidation by determining thiobarbituric acid-reactive substances (TBARS), glutathione level and enzyme activities related to glutathione (reduced form GSH, oxidized form GSSG) metabolism: GSH-peroxidase (GSHpx), GSSD-reductase (GSSGrd) and GSH-transferase (GSHtf). Chronic treatment with SAM decreased maximum forebrain production of TBARS by 46% compared with animals given L-lysine and increased glutathione levels by 50%, GSHpx activity by 115% and GSHtf activity by 81.4%. The results of in vitro experiments were qualitatively similar: lipid peroxidation was inhibited (13.1+/-1.3 nmol/mg protein in controls vs. 5.9+/-0.8 nmol/mg protein in samples incubated with 1000 micromol/l SAM) and glutathione levels were stimulated (0.97+/-0.06 micromol/g tissue in control samples vs. 1.55+/-0.08 micromol/g tissue in samples incubated with 1000 micromol/l SAM), as were GSHpx and GSHtf. No significant effect was seen in any of the experiments with L-lysine. We conclude that SAM has antioxidant effects in rat brain tissue both in vitro and ex vivo. The effect is seen both as inhibition of lipid peroxide production and as an enhancement of the endogenous glutathione antioxidant system.

Interaction between osmotic and oxidative stress in diabetic precataractous lens: Studies with a sorbitol dehydrogenase inhibitor

Both sorbitol accumulation-linked osmotic stress and “pseudohypoxia” [increase in NADH/NAD+, similar to that in hypoxic tissues, and attributed to increased sorbitol dehydrogenase (l-iditol:NAD+ 5-oxidoreductase; EC 1.1.1.14; SDH) activity] have been invoked among the mechanisms underlying oxidative injury in target tissues for diabetic complications. We used the specific SDH inhibitor SDI-157 [2-methyl-4(4-N,N-dimethylaminosulfonyl-1-piperazino)pyrimidine] to evaluate the role of osmotic stress versus “pseudohypoxia” in oxidative stress occurring in diabetic precataractous lens. Control and diabetic rats were treated with or without SDI-157 (100 mg/kg/day for 3 weeks). Lens malondialdehyde (MDA) plus 4-hydroxyalkenals (4-HA), MDA, GSH, and ascorbate levels, as well as the GSSG/GSH ratios, were similar in SDI-treated and untreated control rats, thus indicating that SDI-157 was not a prooxidant. Intralenticular osmotic stress, manifested by sorbitol levels, was more severe in SDI-treated diabetic rats (38.2 ± 6.8 vs 21.2 ± 3.5 μmol/g in untreated diabetic and 0.758 ± 0.222 μmol/g in control rats, P < 0.01 for both), while the decrease in the free cytosolic NAD+/NADH ratio was partially prevented (120 ± 16 vs 88 ± 11 in untreated diabetic rats and 143 ± 13 in controls, P < 0.01 for both). GSH and ascorbate levels were decreased, while MDA plus 4-HA and MDA levels were increased in diabetic rats versus controls; both antioxidant depletion and lipid aldehyde accumulation were exacerbated by SDI treatment. Superoxide dismutase (superoxide:superoxide oxidoreductase; EC 1.15.1.1), GSSG reductase (NAD[P]H:oxidized-glutathione oxidoreductase; EC 1.6.4.2), GSH transferase (glutathione S-transferase; EC 2.5.1.18), GSH peroxidase (glutathione:hydrogen-peroxide oxidoreductase; EC 1.11.1.9), and cytoplasmic NADH oxidase activities were increased in diabetic rats versus controls, and all the enzymes but GSH peroxidase were up-regulated further by SDI. In conclusion, sorbitol accumulation and osmotic stress generated oxidative stress in diabetic lens, whereas the contribution of “pseudohypoxia” was minor. SDIs provide a valuable tool for exploring mechanisms of oxidative injury in sites of diabetic complications.

Glutathione protection against hydrogen peroxide, tert-butyl hydroperoxide and diamide cytotoxicity in rat hepatoma-derived Fa32 cells.

1. Several ozonides, peroxides and aldehydes are formed during ozone therapy, recently introduced in medicine. tert-Butyl hydroperoxide (t-BHP), H2O2 and diamide were investigated as model substrate in rat hepatoma-derived Fa32 cells. 2. The cytotoxicity was measured by the neutral red uptake inhibition assay after 1 h or 24 h treatment. The relative toxicities were quantified by the determination of the NI50. This is the concentration of test compound required to induce an inhibition of 50% in neutral red uptake as compared to the control cells. All test chemicals were more toxic after 24 h than after 1 h. 3. The influence of the glutathione (GSH) alteration on the cytotoxicity was measured by treating the cells with 2-oxo-4-thiazolidine carboxylic acid (OTC) or L-buthionine sulfoximine (BSO). OTC increased the endogenous GSH content in the cells. BSO pretreatment strongly decreased the NI50 of the three chemicals. OTC pretreatment increased the NI50 of H2O2 but not of t-BHP and diamide. This can be explained by the strong GSH-depletion after 1 h by t-BHP and diamide, which contrasted with a weak GSH-depletion by H2O2 after the same time period. 4. The three test chemicals increased the endogenous GSH content after 24 h. t-BHP and H2O2, but not diamide, increased the total GSH transferase (GST) activity. Several alterations of the GST subunits were observed. Most striking was the increase of class alpha GST subunits, also for diamide. 5. Since H2O2 and t-BHP are ozone metabolites thought to be responsible for the therapeutic effects of well-dosed ozone, the results show that Fa32 cells can be used as a valuable alternative model system for studying the effects encountered in human ozone therapy.

Liver cancer is induced by a subnecrogenic dose of DENA when associated with fasting/refeeding: role of glutathione-transferase and lipid peroxidation

In previous studies, we reported that fasting/refeeding has a role in sustaining the initiation of liver cancer by a subnecrogenic (noninitiating) dose of diethylnitrosamine (DENA). This research investigated whether the metabolic alterations imposed by fasting/refeeding provide an imbalance between the generation of carcinogenic molecules and the scavenger defense mechanisms in rat liver. Metabolism of DENA, levels of reduced glutathione (GSH) and GSH transferase (GST) activity, as well as basal and stimulated malondialdehyde (MDA) production, were examined. Rats fasted for 4 days showed a decrease in the liver levels of GSH, GST activity, monounsaturated fatty acids and % of labeled nuclei. After 1 day of refeeding, at which point DENA was administered, the levels of GSH recovered, GST activity remained below control values, basal and stimulated MDA production and content of total polyunsaturated fatty acids in liver phospholipids decreased. One day after DENA treatment, MDA production further decreased, although the % of labeled nuclei increased. No significant changes in the content of arachidonic acid, the main target of peroxidation, were observed at any time. The results indicated that the induction of the hepatocellular carcinoma was associated with a depression of GST activity and lipid peroxidation when rats were given 20 mg/kg of DENA after 1 day of refeeding after 4-day fasting.

Heavy metals and glutathione metabolism in mussel tissues

Data are presented on the tissue glutathione content and on the activity of two of the main enzymes involved in GSH metabolism ( γ-glutamyl-cysteine synthetase (GCS), GSH transferase (GST)) in the gills and digestive gland of mussels ( Mytilus galloprovincialis Lam.) exposed for 1, 4 and 7 days to sublethal concentrations of copper and of mercury, both in the inorganic form of HgCl 2 and in the organic form of CH 3HgCl. The results indicate that Cu 2 + (0.6 μM) and CH 3Hg + (0.2 μM) can affect, although to a different extent, glutathione metabolism in mussel tissues; common traits were a decrease in tissue glutathione content, stimulation of GST activity and inhibition of GSH synthesis rate; on the other hand, inorganic Hg 2 + (0.2 μM) did not significantly affect glutathione content and metabolism in mussel tissues. Exposure to copper (0.6 μM) resulted in a decrease in total glutathione content in both gills and the digestive gland that was maximal after the first day, followed by a tendency to recover at longer exposure times. Such a decrease seemed to be mainly related to a stimulation of GST activity, which was transient in gills and persistent in the digestive gland. The tissue glutathione content was also decreased in mussel exposed to methylmercury (0.2 μM); however, such a decrease seemed to be mainly due to inhibition of the GSH synthesis rate and, to a lesser extent, to an increased GST activity. On the contrary, inorganic Hg 2 + (0.2 μM) did not significantly affect glutathione metabolism, although mussel exposure to the same concentration of organic and inorganic Hg 2 + resulted in similar total metal tissue load in mussel tissues. The role of glutathione as a potential defense against heavy metals is discussed in relation to different routes of metal toxicity and homeostasis in mussel tissues.

Effects of L-carnitine on the formation of fatty acid ethyl esters in brain and peripheral organs after short-term ethanol administration in rat.

A study was undertaken in rats to evaluate the effects of short-term oral ethanol administration on the levels of fatty acid ethyl esters (FAEE) in brain and peripheral organs in the presence and absence of pretreatment with L-carnitine. Administration of ethanol to rats for seven days resulted in fatty acid ethyl ester formation, particularly in the heart and brain, but also in the kidney and liver. FAEE generation was associated with a significant increase of GSH transferase activity. Treatment with L-carnitine significantly reduced both FAEE and GSH transferase activity, and these effects were associated with a significant decrease in alcohol blood concentrations. The present evidence supports the hypothesis that fatty acid ethyl esters could be mediators involved in the production of alcohol-dependent syndromes. Administration of L-carnitine through an increment in lipid metabolism and turnover, and by the modulation of cellular antioxidant enzymes, greatly reduces these metabolic abnormalities supporting its potential usefulness as a pharmacological tool in alcoholism management.

Effects of S-adenosyl-L-methionine on hepatic and renal oxidative stress in an experimental model of acute biliary obstruction in rats.

We used an animal model of extrahepatic biliary obstruction of 7 days' duration to study the production of thiobarbituric acid reactive substances (TBARS), total glutathione (TG), reduced glutathione (GSH), and oxidized glutathione (GSSG), and the enzymatic activities of GSH-peroxidase, GSSG-reductase, and GSH-transferase. Four groups of six rats each were treated with saline, drug solvent, S-adenosyl-L-methionine (SAM) 5 mg/kg/d, subcutaneously, or SAM 10 mg/kg/d, subcutaneously. Extrahepatic biliary obstruction increased TBARS. SAM had the dose-dependent effects of inhibiting TBARS production and increasing TG content, mainly as a result of the increase in GSH. The activity of GSH-peroxidase and GSH-transferase was also significantly increased. In renal tissue these effects were statistically significant only in animals given the higher dose of SAM. In liver we found a reduction in biochemical values indicative of liver damage. We conclude that effect of SAM on hepatorenal function is strongly influenced by the drug's ability to reestablish equilibrium after oxidative tissue stress.

Effects of S-adenosyl-L-methionine on hepatic and renal oxidative stress in an experimental model of acute biliary obstruction in rats

We used an animal model of extrahepatic biliary obstruction of 7 days' duration to study the production of thiobarbituric acid reactive substances (TBARS), total glutathione (TG), reduced glutathione (GSH), and oxidized glutathione (GSSG), and the enzymatic activities of GSH- peroxidase, GSSG-reductase, and GSH-transferase. Four groups of six rats each were treated with saline, drug solvent, S-adenosyl-l-methionine (SAM) 5 mg/kg/d, subcutaneously, or SAM 10 mg/kg/d, subcutaneously. Extrahepatic biliary obstruction increased TBARS. SAM had the dose-dependent effects of inhibiting TBARS production and increasing TG content, mainly as a result of the increase in GSH. The activity of GSH-peroxidase and GSH-transferase was also significantly increased. In renal tissue these effects were statistically significant only in animals given the higher dose of SAM. In liver we found a reduction in biochemical values indicative of liver damage. We conclude that effect of SAM on hepatorenal function is strongly influenced by the drug's ability to reestablish equilibrium after oxidative tissue stress. (Hepatology 1997 Jul;26(1):121-7)

Effects of taurine and Guanidinoethane Sulfonate on toxicity of the pyrrolizidine alkaloid monocrotaline

Monocrotaline (MONO), a pyrrolizidine alkaloid, causes pulmonary arterial hypertension and right ventricular hypertrophy due to hepatic metabolism to the alkylating pyrrole dehydromonocrotaline. Taurine, a sulfonic amino acid, is hepato- and cardioprotective in a variety of conditions. We have examined the effects of taurine and its amidino analog, guanidinoethane sulfonate (GES), in rats injected i.p. with MONO (65 mg/kg). Taurine and GES were given as 1% solutions in drinking water beginning 14 days before administration of MONO and continuing for 14 days thereafter, when the rats were killed. The MONO group had right ventricular hypertrophy and pulmonary hyperplasia. Compared with control, no significant changes in the right ventricle/left ventricle weight ratio, or the right ventricle/body weight ratio occurred in rats also given taurine or GES. Lung weights in these two groups were higher than in the control group, but below that of the MONO-alone group. The lethality of MONO over 14 days was decreased by taurine ( ld 50 for MONO alone 80 mg/kg; for MONO + taurine 121 mg/kg). Rats given only MONO had lower hepatic concentrations of GSH and cysteine (Cys), and higher activities of microsomal GSH transferase and γ-glutamyl transpeptidase. In rats also receiving taurine, hepatic GSH levels and GSH transferase activity were no different from control. γ-Glutamylcysteine (Glu-Cys) synthetase and γ-glutamyl transpeptidase activities were elevated. In MONO-injected rats given GES, hepatic GSH levels were higher and Cys levels were lower than in either the MONO alone or MONO + taurine groups. γ-Glu-Cys synthetase activity was depressed. Microsomal GSH transferase, GSH peroxidase and γ-glutamyl transpeptidase activities were elevated. Livers of MONO-injected animals showed higher levels of serine (reversed by both taurine and GES) and glycine (Gly; reversed by GES) and lower levels of glutamine. Compared with control rats, the following changes occurred in serum amino acids: MONO alone: increased aspartate, taurine and lysine; taurine-supplemented: increased taurine, methionine (Met) and lysine, and decreased Gly; GES-supplemented: decreased asparagine, serine, Gly, arginine, taurine, and valine. Compared with the MONO-alone group, the taurine-supplemented group had higher glutamate (Glu), Met and alanine, and the GES-supplemented group higher alanine and lower serine, Gly, arginine and valine. We conclude that taurine protects against MONO-induced lethality and right ventricular hypertrophy. GES also protects against right ventricular hypertrophy. However, these agents act by different mechanisms, taurine preventing many of the biochemical changes induced by MONO, with GES inducing additional changes.

Effects of monocrotaline, a pyrrolizidine alkaloid, on glutathione metabolism in the rat

Monocrotaline (MONO), a pyrrolizidine alkaloid, causes veno-occlusive disease of the liver, pulmonary arterial hypertension, and right ventricular hypertrophy. Toxicity is due to the hepatic formation of a pyrrolic metabolite that can be detoxified by conjugation with glutathione (GSH). We have shown that the GSH content of the liver affects the quantity of the pyrrolic metabolite that is released from the liver. We have now examined whether MONO, in turn, affects GSH metabolism. Twenty-four hours after administration of MONO to rats (65 mg/kg, i.p.), the highest concentration of bound pyrrolic metabolites was found in the liver, followed by the lung and kidney. Heart and brain contained lower concentrations of these metabolites. Significantly higher levels of GSH were found in liver and lungs of MONO-treated rats than in saline-injected control animals. In the liver, activities of the following enzymes were elevated: γ-glutamylcysteine synthetase, GSH synthetase, γ-glutamyl transpeptidase, dipeptidase, and microsomal GSH transferase. The same changes were seen in the lung. In the heart, γ-glutamyl transpeptidase activity was decreased markedly, and cytosolic GSH transferase activity was elevated. In the kidney, the activities of GSH synthetase, γ-glutamyl transpeptidase, and cytosolic GSH transferase were increased. Our results establish a mutual interaction of MONO and sulfur metabolism. It appears that an early metabolic action of MONO is to modify sulfur amino acid metabolism, diverting cysteine metabolism from oxidation to taurine towards synthesis of GSH.

The study of induced antimutagenesis of propionic acid bacteria

Using the modified Ames test it was shown that Propionibacterium shermanii (a classical propionic bacterium) excretes substances lowering 4-nitroquinoline-1-oxide (4NQO) and UV-induced mutagenesis in Salmonella typhimurium TA 100. Reconstruction experiments showed that antimutagenic properties of a cultural broth and cell dialysate are not caused by inhibition of S. typhimurium cell growth. By passing the propionic acid bacteria through a medium containing small amounts of 4NQO, induced antimutagenesis was demonstrated. Induced P. shermanii cells differ from control in having a higher level of antimutagenicity against 4NQO-induced mutagenesis, and a higher GSH transferase activity and do not differ in content of sulfhydryl compounds. Experiments with cell dialysates showed that the induction of the antimutagenesis against 4NQO is accompanied by enhancing antimutagenicity against UV-irradiation. In the model experiments it was shown that the cell dialysates, possessing GSH transferase activity, accelerate a reaction between GSH and 4NQO, but do not influence the 4NQO inactivation by some components of the cultural broth. We suggest that the mechanism of inhibition of electrophilic mutagens in the cells is connected with GSH-GSH transferase system though the inhibitory mechanism of cultural broth may be different.

Effect of liver cirrhosis and age on the glutathione concentration in the plasma, erythrocytes, and gastric mucosa of man

GSH and its related enzymes are one of the protective mechanisms vs. the oxidative damage, both in the circulation and in various tissues, including gastric mucosa. Patients with liver cirrhosis frequently suffer from a gastropathy caused by portal hypertension and they present low circulating levels of GSH. Aging processes cause an increase of gastric damage, of lipoperoxidative phenomenons, and a decrease of GSH in animals. The aim of this study was the evaluation, in humans, of the effect of both these factors, age and liver cirrhosis, on the global pool of GSH and on the antioxidant capability of the cells of gastric mucosa. Therefore, we evaluated the effect of liver cirrhosis and age on the circulating levels of GSH, both in the plasma and in the erythrocytes, and the GSH concentration and the activity of the total GSH-transferase (GSH-T) in gastric mucosa of healthy subjects and in patients affected by liver cirrhosis. Age, but not liver cirrhosis, induced a significant decrease of GSH and GSH-T activity in gastric mucosa; on the contrary, the plasma levels of GSH decreased in cirrhotics but not in elderly healthy subjects. In the erythrocytes, GSH was affected by both these factors (age and liver cirrhosis). These findings indicate that both in patients with liver disease and in elderly healthy subjects the GSH-related cellular defensive mechanisms are depressed and therefore susceptibility to oxidative damage may increase.

In vivo potentiation of 1,2-dibromoethane hepatotoxicity by ethanol through inactivation of glutathione- s-transferase

In the rat, a single ethanol (EtOH) pretreatment (2.5 g/kg b.w., per os) was able to strongly enhance the cytotoxicity of 1,2-dibromoethane (DBE) (87 mg/kg b.w., per os). The principal metabolic routes of DBE involve both oxidative and conjugative transformations. Microsomal cytochrome P 450 content and dimethyl nitrosamine demethylase activity were not changed, while a significant loss of cytosolic total GSH-transferase was observed in rats killed 6 h after EtOH pretreatment. Pretreatment with methylpyrazole, an inhibitor of alcoholdehydrogenase prevented the effects provoked by ethanol. The major EtOH metabolite, acetaldehyde, seemed thus to play a fundamental role in the mechanism responsible for the potentiation of DBE toxicity mediated by EtOH. To further support this hypothesis, disulfiram (75 mg/kg b.w.), an inhibitor of aldehyde dehydrogenase, was given i.p. to rats. When DBE was administered to disulfiram- and EtOH-pretreated rats, a marked increase of liver cytolysis was shown and cytosolic GSH-transferase activity was further inhibited if compared to that induced by EtOH treatment alone. The results are consistent with the hypothesis that EtOH given to rats increases DBE liver toxicity because its major metabolite, acetaldehyde, reduces the DBE conjugation to GSH transferase, with consequent shift of DBE metabolism to the oxidative route and accumulation of reactive oxidative intermediates no longer effectively conjugated with GSH.

Liver and intestinal propoxyphene metabolisms: An example of discreprancy in drug pre-systemic biotransformation in the rat: [formula omitted] Dept. of Gastroenterology, Experimental Surgery and Pharmacotherapy Laboratories, Catholic University of Louvain, Brussels

Previous studies have shown that several factors may influence the methylation of inorganic arsenic by rat liver in vitro (Buchet and Lauwerys, 1985). The present study attempts to assess the relevance of these observations in vivo. Like man, rat inactivates inorganic arsenic by methylation to monomethylarsoni (MMA) and dimethylarsinic (DMA) acids which are excreted in urine along with unchanged inorganic arsenic (Asi). The administration of S-adenosylmethionine alone or in association with reduced (GSH) or oxidized glutathione or acetylcysteine and the increase of hepatic GSH level by butylated hydroxytoluene pretreatment do not stimulate the urinary excretion of the methylated arsenic metabolites following a challenge dose of inorganic arsenic. Conversely a reduction of the hepatic GSH level by phorone pretreatment greatly modifies the metabolism of inorganic arsenic in vivo. A reduction exceeding 90% of the control value leads to a decreased urinary excretion of MMA and DMA and an increased urinary excretion of inorganic arsenic. This is also associated with an increased accumulation of inorganic arsenic in the liver. This suggests that a drastic reduction of GSH level in liver not only impairs the methylation of inorganic arsenic but also impairs its biliary excretion. When GSH depletion is less severe, the total amount of arsenic excreted in urine after a challenge dose of NaAsO2 is not significantly different from that found in unpretreated animals but the proportion of the three metabolic forms is different: MMA is reduced whereas Asi and DMA tend to increase. These changes resemble those found in patients with liver insufficiency (J. P. Buchet, A. Geubel, S. Pauwels, P. Mahieu, and R. Lauwerys (1984). The influence of liver disease on the methylation of arsenite in humans. Arch. Toxicol. 55, 151–154). Long-term pretreatment of rats with CCl4 slightly reduces the amount of MMA and DMA excreted in urine following a challenge dose of inorganic arsenic. This effect may result from a reduction of GSH transferase activity by CCl4. This study demonstrates the important role of liver GSH in the metabolism of inorganic arsenic in vivo

Role of beta-carotene on the changes in activity patterns and levels of biotransforming enzymes in transplantable murine lymphoma.

The differential levels of induction of hepatic microsomal cytochrome P-450 (cyt. P-450), UDP-glucuronyl transferase (UDPGT) and cytosolic glutathione-S-transferase (GST) activities were evaluated over various periods of time, following tumor transplantation in male Swiss albino mice in the presence and absence of beta-carotene supplementation in their basal diet (100 mg/kg). An increase in the total hepatic microsomal cytochrome P-450 and UDP-glucuronyl transferase and cytosolic GSH-transferase activities (1.5 to 2 fold) occurred during the later stage of tumor progression (22 +/- 2 days onwards). However, beta-carotene supplementation throughout the study increased or decreased the random activity trends of the above markers significantly (P < 0.05- < 0.01). Finally, beta-carotene supplementation could enhance the survival of the host bearing lymphoma by almost 2-fold (50-60 days) over and above the lymphoma controls (30-35 days).

Characterization of a human bladder cancer cell line selected for resistance to mitomycin C.

This study describes characteristics of a human bladder cancer cell line J82/MMC that is 6-fold more resistant to mitomycin C (MMC) than the parental cells. The J82/MMC subline was isolated by repeated continuous exposures of the J82/WT cells to increasing concentrations of MMC. The J82/MMC cell line showed (1) collateral sensitivity to taxol, 5-FU and topoisomerase II inhibitors; and (2) cross-resistance to cisplatin, melphalan and MMC analogues BMY 25282 and BMY 25067. Levels of two key MMC activation enzymes, NADPH cytochrome P450 reductase and DT-diaphorase, were significantly lower in J82/MMC cells compared with J82/WT, suggesting that lower sensitivity of J82/MMC cells to MMC may result from deficient drug activation. Further support is indicated by: 1) reduction in the differential in toxicity between the 2 cell lines by BMY 25282; and 2) a higher effect of DT-diaphorase inhibitor dicumarol on the wild-type cells compared with J82/MMC. Although glutathione (GSH) levels did not differ in these cells, a small but significant increase in GSH transferase (GST) activity was noticed in J82/MMC cells. GST inhibitor ethacrynic acid significantly enhanced MMC cytotoxicity in the J82/MMC cell line. A small but significant increase in the level of anti-oxidative enzyme catalase, but not GSH peroxidase, was also observed in J82/MMC cell line compared with J82/WT. Thus, the possibility that relatively lower sensitivity of J82/MMC cells to MMC may result from reduced oxygen radical generation cannot be ruled out. MMC-induced DNA interstrand cross-linking was markedly lower in the J82/MMC cell line compared with J82/WT. Our results suggest that the MMC resistance in the J82/MMC cell line may be multifactorial.

Species differences in the biotransformation of ethyl chloride. II. GSH-dependent metabolism.

Groups of male and female F-344 rats and B6C3F1 mice were exposed to 15,000 ppm ethyl chloride (monochloroethane, ECL) or to air for 5 days (6 h/day). In this report, features of GSH-dependent ECL metabolism in the animals are described. A concurrent report describes the features of the cytochrome P450-dependent oxidative ECL metabolism (Fedtke et al. 1994). ECL conjugation to GSH in hepatic cytosolic fractions was catalyzed by GSH S-transferases. The specific activities were 0.16 +/- 0.03 and 0.17 +/- 0.01 nmol ECL conjugated/(min mg protein) in air treated male and female F-344 rats, respectively. These activities were not significantly altered by the ECL treatment. Compared with rats, the GSH-transferase activities towards ECL were generally higher in male and female B6C3F1 mice (0.71 +/- 0.19 and 1.01 +/- 0.19, respectively) and were slightly decreased by ECL treatment. The ECL conjugation to GSH resulted in a marked reduction of the GSH concentration in the lung and the uterus after 5 days of exposure. In contrast, liver and kidney GSH concentrations were affected only to a minor degree. Formed S-ethyl-glutathione was converted to the mercapturic acid S-ethyl-N-acetyl-L-cysteine (SENACys), which was detected in the urine of both species. In addition, the non-acetylated intermediate S-ethyl-L-cysteine (SECys) was excreted in mouse urine but not in rat urine. The cumulative amounts of SENACys and SECys excreted after 5 days were up to fivefold higher in mice than in rats and the excretion kinetics were species specific.(ABSTRACT TRUNCATED AT 250 WORDS)

Glutathione-linked detoxification pathway in normal and malignant human bladder tissue.

This study compares the levels of glutathione (GSH) and GSH-dependent detoxification enzymes, which have been implicated in anti-cancer drug resistance, in paired normal and malignant human bladder tissues, a tumor with high incidence of inherent drug resistance. Although the mean GSH transferase (GST) activity did not differ significantly in normal and neoplastic bladder tissues, this enzyme activity was relatively higher in tumor tissues of five out of ten patients as compared with corresponding normal tissues. Similarly, the mean GSH content and GSH reductase activity did not differ significantly between normal and neoplastic bladder tissues. On the other hand, the mean GSH peroxidase activity towards cumene hydroperoxide and catalase activity in bladder tumors was higher by about 1.5 and 1.4 times, respectively (P < 0.05), compared with those of normal tissues. GST isoenzymes corresponding to the three major classes (alpha, mu and pi) were expressed in every normal bladder tissue examined in the present study. Overexpression of GST pi was observed in 60% of the bladder tumors, whereas alpha and mu type GST proteins in tumor tissues were lower at frequencies of 62.5% and 37.5%, respectively, compared with the corresponding normal tissues. These results suggest that (a) elevated levels of GSH peroxidase, catalase and GST pi in human bladder tumors may contribute, at least in part, to the intrinsic drug resistance of this neoplasm and (b) anti-oxidative enzymes GSH peroxidase and/or catalase may represent markers for this neoplasia, although a large number of tissue specimens must be analyzed to validate this hypothesis.