A role of peroxides in Ca2+ ionophore-induced apoptosis in cultured rat cortical neurons

The implication of reactive oxygen species for the Ca2+ ionophore ionomycin-induced apoptosis was investigated in cultured cortical neurons from embryonic rats. Ionomycin increased the production of intracellular peroxides as measured by flow cytometric analysis with 6-carboxy-2'7'-dichorodihydrofluorescein diacetate, di(acetoxymethyl ester). Low doses of ionomycin increased the level of manganese-superoxide dismutase (Mn-SOD). In addition, N-acetyl-L-cysteine prevented apoptotic neuronal death induced by ionomycin in a dose-dependent manner. Buthionine sulfoximine suppressed the effect of N-acetyl-L-cysteine. These results suggest that peroxides and redox-regulation play an important role in the apoptosis of neurons induced by elevation of intracellular Ca2+ concentration.

Protective effects of glutathione on bromodichloromethane in vivo toxicity and in vitro macromolecular binding in Fischer 344 rats

Bromodichloromethane (BDCM), a carcinogenic water disinfection by-product, has been shown to be metabolized to intermediates that covalently bind to lipids and proteins, and this binding has been associated with trihalomethane-induced renal and hepatic toxicity. In this study, the effects of glutathione (GSH) on in vivo BDCM toxicity and in vitro BDCM macromolecular binding were evaluated. The in vivo toxicity of BDCM in animals pretreated with buthionine sulfoximine (BSO, a glutathione synthesis inhibitor) and in untreated male Fischer 344 rats was investigated. In another experiment, covalent binding to protein and lipid was quantified after [14C]BDCM was incubated with hepatic microsomal and S9 fractions and renal microsomes from F344 rats, under aerobic and anaerobic conditions, with and without added GSH. After oral dosing with BDCM, the BSO-pretreated animals had greatly increased levels of serum indicators of hepatotoxicity and serum and urinary indicators of nephrotoxicity compared to those in animals dosed solely with BDCM. Histopathological examination revealed that hepatic necrosis was more severe than renal necrosis in the BSO-treated rats. When GSH was added to an aerobic incubation, protein binding was decreased in hepatic microsomal and S9 fractions by 92 and 83%, respectively. GSH also decreased lipid binding by 55% in hepatic microsomal incubations carried out under anaerobic conditions. Addition of GSH decreased renal microsomal protein (aerobic) and lipid binding (anaerobic) by 20 and 43%, respectively. These data indicate that GSH is an important protective factor in the toxicity associated with BDCM.

Lazaroid treatment prevents death of cultured rat embryonic mesencephalic neurons following glutathione depletion

Reactive oxygen species are believed to play a crucial role in situations where dopamine neurons die, such as in Parkinson's disease or during intracerebral transplantation of embryonic mesencephalic tissue. The present study was designed to address the question whether, and to what extent, the glutathione redox system is important for the viability of rat embryonic dopamine neurons in vitro. Furthermore, we studied whether the lazaroid U-83836E, a 2-methylaminochroman that inhibits lipid peroxidation, affects the survival of cultured mesencephalic neurons subjected to experimentally induced glutathione depletion. Glutathione depletion was achieved by exposing dissociated mesencephalic cell cultures to L-buthionine sulfoximine (BSO), an inhibitor of glutathione synthesis, at four different concentrations (1, 10,100, and 1,000 microM). Dopamine neuron survival was significantly reduced by 65-94% in a concentration-dependent manner by 10-1,000 microM BSO. The neurotoxic effects of BSO were almost completely prevented by supplementing the culture medium with 0.3 microM U-83836E. As assessed by HPLC analysis, BSO treatment was associated with a marked reduction of cellular glutathione content, and this depletion was not altered by the presence of U-83836E. We conclude that in the present insult model of severe glutathione depletion, the lazaroid can afford efficient neuroprotection that does not seem to be mediated by a direct interaction with BSO or glutathione, but rather via an independent pathway.

Effect of enterotoxin on glutathione status in the intestinal mucosa

The effect of luminal exposure of enterotoxins on the intestinal mucosal glutathione (GSH) was studied in rat. Cholera toxin induced fluid secretion and decreased mucosal GSH by 35% without altering oxidized glutathione (GSSG) level. Toxin induced fluid secretion was tested after mucosal GSH depletion by compounds such as diethyl maleate (DEM) and buthionine sulfoximine (BSO) and thiol supplementation with N-Acetyl cysteine (NAC). Fluid secretion was not altered by prior thiol depletion or supplementation. Exposure of intestinal lumen to bacterial endotoxin resulted in 25% decrease in mucosal GSH with two fold increase in GSSG. Luminal exposure of Shiga toxin did not alter the mucosal thiol. The level of other low molecular weight thiols, cysteine and cystine was not altered by luminal exposure of any of these toxins. These results show that although cholera toxin decreased the mucosal GSH level, prior modulation of thiol status of the mucosa may not have any effect on toxin-induced fluid secretion.

Cysteine-dependent 5-S-cysteinyldopa formation and its regulation by glutathione in normal epidermal melanocytes

Recent evidence suggests that the melanogenesis intermediate 5-S-cysteinyldopa (5-S-CD) could display antioxidative activity. In the present study, the synthesis of 5-S-CD was examined in human epidermal melanocytes isolated from dark skin type VI (MT) and from white skin type III (GT). The MT melanocytes showed the higher melanin content and dopa oxidase activity. In addition, they produced eumelanin as shown by their ultrastructure, and the solubility and UV/visible absorption of the isolated pigment. Both MT and GT cells showed high levels of 5-S-CD (5.5-6.9 nmol/mg protein). 5-S-CD was also detected in culture supernatants from MT cells; the secretion rate was estimated to be 2.5 nmol/mg protein per 24 h. The role of cysteine and glutathione in 5-S-CD formation was investigated by exposing the melanocytes to the gamma-glutamylcysteine synthetase inhibitor L-buthionine sulfoximine (BSO). A strong reduction in glutathione levels (4-8% of the untreated controls) associated with an increase in cysteine levels (152-154%) was observed. In addition, BSO induced a moderate increase in the cellular levels of 5-S-CD (114-129%) and a decrease in dopa oxidase activity (75-83%). Our results indicate that the direct addition of cysteine to dopaquinone is the main source of 5-S-CD in human epidermal melanocytes. It is proposed that the synthesis of 5-S-CD is a mechanism regulating dopaquinone levels during pigment formation and/or a defence mechanism against oxidative stress.

Glutathione plays a role in the chick intestinal calcium absorption

DL-buthionine-S,R-sulfoximine (BSO) administration to vitamin D-deficient chicks treated with cholecalciferol produces a rapid decrease in the Ca2+ transfer from lumen-to-plasma and in the intestinal glutathione content. This response was reversed by addition of glutathione monoester to the intestinal sac. Variables related to the Ca2+ homeostasis such as plasma Ca and P, and intestinal calbindin D28k were not modified by BSO given to vitamin D-deficient chicks treated with cholecalciferol. Intestinal alkaline phosphatase activity, on the contrary, was highly reduced by BSO in vitamin D-deficient chicks treated with vitamin D3. This effect showed time and dose-dependency. Although the mechanism/s of action of BSO on the intestinal Ca absorption is unknown, it is quite possible that thiol groups of protein involved in the Ca2+ transport are affected by the GSH depletion and/or by block of the antioxidant ability of vitamin D3. Thus, reactive oxygen compounds would be increased and, therefore, the Ca2+ movement from lumen to plasma decreases.

Dynamic aspects of glutathione and nitric oxide metabolism in endotoxemic rats

Glutathione is one of the most abundant thiols in mammalian tissues and plays important roles in the defense mechanism and detoxification of various metabolites, such as reactive xenobiotics and free radicals. Nitric oxide (NO) readily reacts with thiol compounds, thereby generating chemically stable S-nitrosothiols. Although endotoxin has been known to induce NO synthase in various organs, particularly liver and spleen, and enhances the production of NO, correlation between NO and glutathione metabolism in endotoxemic subjects remains to be elucidated. The present work examines the changes in NO and glutathione metabolism in endotoxemic rats. Administration of lipopolysaccharide (LPS) markedly decreased the glutathione levels in plasma and bile, whereas it decreased the hepatic level only slightly. NG-nitro-L-arginine (L-NNA), a NO synthase inhibitor, inhibited the LPS-induced decrease of glutathione in plasma and bile. Administration of LPS increased the biliary levels of gamma-glutamyl transpeptidase (gamma-GTP) without affecting its thiol levels. Acivicin, a gamma-GTP inhibitor, inhibited the LPS-induced decrease of glutathione in plasma and bile without affecting its hepatic levels. Analysis with the use of L-buthionine sulfoximine revealed that the turnover of hepatic glutathione significantly increased in LPS-treated rats by some L-NNA-inhibitable mechanism. These results suggest that endotoxin might enhance the NO production in the liver and other tissues and significantly modulate the interorgan metabolism of reduced glutathione.

Effects of buthionine sulfoximine on the outcome of the in utero administration of alcohol on fetal development

The adverse effects of the maternal consumption of alcohol on the fetus have been recognized for centuries. Fetal alcohol syndrome is characterized by pre- and postnatal growth retardation, mental retardation, behavioral deficits, and facial deformities. Despite numerous animal studies, the biochemical mechanism(s) by which alcohol produces teratogenic effects on the developing fetus are not well understood. Several studies have shown that administration of alcohol to adult rats produces a decrease in hepatic levels of glutathione (GSH). In utero administration of alcohol has also been shown to produce a decrease in GSH levels, as well as prenatal growth retardation and intrauterine death. In an effort to determine if GSH may have a vital role in protecting the fetus against the teratogenic effects of alcohol, buthionine (SR)-sulfoximine (BSO) was used to deplete GSH levels in the mother and fetus. Timed pregnant Sprague-Dawley rats were placed on a liquid BioServ diet containing either 0%, 11%, 23%, 29%, 31%, 33%, or 35% ethanol-derived calories, with or without BSO (888 mg/kg/24 hr), starting on day 1 of pregnancy. Another set of mothers were fed lab chow and water as a control group for the liquid diet. The mothers were maintained on the diet until gestation day 21 when they were anesthetized with sodium pentobarbital and the pups delivered by cesarean section. The offspring were counted, weighed, killed, and the brain and liver weighed. The effects of BSO on the alcohol dose-response curves (body weights, brain weights, and litter number) were then determined to ascertain if a depletion in GSH potentiated the effects of alcohol. In utero administration of BSO, aside from the depletion of GSH in the liver and brain in the developing fetus, produced a shift to the left in the alcohol dose-response curve.

Glutathione and trypanothione in several strains of Trypanosoma cruzi: effect of drugs

Glutathione (GSH), trypanothione (T(SH)2) and glutathionyl spermidine (GSH-SP) concentrations were determined in the Tulahuén and LQ strains and the DM 28c clone of Trypanosoma cruzi. The concentrations of GSH, T(SH)2 and GSH-SP, expressed as nmol of GSH per g of parasite fresh weight, were 60.1, 397.8 and 103.9, respectively, for the Tulahuén strain. For the DM 28c clone, the values were 113.9, 677.9 and 164.1, respectively, and for the LQ strain they were 199.1, 1100.5 and 55.3, respectively. When the parasites were treated with 10 microM nifurtimox or 50 microM benznidazole for 2 h, the concentrations of all three reduced thiols decreased strongly. The total amount of T(SH)2 decreased by more than 50%. Treatment of the parasites with 5 mM buthionine sulfoximine, an inhibitor of GSH synthesis, for 6 h diminished the concentrations of the reduced thiols by between 27% and 53% with respect to the controls. Cyclohexylamine, an inhibitor of spermidine synthesis, decreased the concentrations of T(SH)2 and GSH-SP but not that of GSH. It is possible to conclude from this study that trypanothione is the most important thiol involved in the detoxication of nifurtimox and benznidazole in T. cruzi and that electrophilic reduced metabolites of both drugs are most probably conjugated with GSH, T(SH)2 and GSH-SP, thus decreasing their concentrations. GSH biosynthesis is an important drug target.

Oral L-2-oxo-4-thiazolidine reduces bacterial translocation after radiation in the Fischer rat

Glutathione (GSH) is important in protecting rapidly dividing intestinal cells against free radicals generated following radiation. L-2-Oxo-thiazolidine (OTZ) promotes GSH synthesis through increased cysteine delivery. We hypothesize that oral supplementation with OTZ will augment GSH levels and decrease the incidence of bacterial translocation after abdominal radiation, and these effects will be abrogated by treating with a blocker of GSH synthesis, buthionine sulfoximine (BSO). Fischer rats received by oral gavage either OTZ (OTZ/rad), OTZ plus BSO (OTZ/BSO/rad), or saline (sal/rad) 4 hr prior to and 18 hr after radiation. One group underwent saline gavage and no radiation (ctl/sal). On Day 4, animals were sacrificed and mesenteric lymph nodes (MLN) were cultured. Liver and jejunum were removed for GSH analysis by HPLC. Nonradiated, ctl/sal had higher levels of hepatic and jejunal GSH than ctl/rad (13.0 +/- 1.2 vs 9.7 +/- 1.5, 11.2 +/- 1.0 vs 7.8 +/- 2.5 micromol/g dry wt, P < 0.05). Supplementation with OTZ (OTZ/rad) increased hepatic and jejunal GSH levels but treatment with OTZ and BSO (OTZ/BSO/rad) eliminated this benefit (12.0 + 2.6 vs 9.5 + 1.7, 10.1 + 2.4 vs 5.9 + 1.3 micromol/g dry wt, P < 0.05). Ctl/rad had a high rate of positive MLN cultures (80%) compared to ctl/sal and OTZ/rad (10 and 30%, P < 0.05). Treatment with OTZ and BSO (OTZ/BSO/rad vs OTZ/rad, 70 and 30%, P < 0.05) reversed the benefit of OTZ supplementation. This study demonstrated whole abdominal radiation depleted both hepatic and jejunal levels of GSH. Uniquely, OTZ supplementation restored hepatic and jejunal levels of GSH and decreased rate of bacterial translocation.

Glutathione is involved in the granular storage of dopamine in rat PC 12 pheochromocytoma cells: implications for the pathogenesis of Parkinson's disease

Parkinson's disease (PD) is characterized by degeneration of dopamine (DA)-containing nigro-striatal neurons. Loss of the antioxidant glutathione (GSH) has been implicated in the pathogenesis of PD. Previously, we showed that the oxidant hydrogen peroxide inhibits vesicular uptake of DA in nigro-striatal neurons. Hydrogen peroxide is scavenged by GSH and, therefore, we investigated a possible link between the process of vesicular storage of DA and GSH metabolism. For this purpose, we used rat pheochromocytoma-derived PC12 cells, a model system applied extensively for studying monoamine storage mechanisms. We show that depletion of endogenous DA stores with reserpine was accompanied in PC12 cells by a long-lasting, significant increase in GSH content the extent of which appeared to be inversely related to the rate of GSH synthesis. A similar increase in GSH content was observed after depletion of DA stores with the tyrosine hydroxylase inhibitor alpha-methyl-p-tyrosine. In the presence of alpha-methyl-p-tyrosine, refilling of the DA stores by exogenous DA reduced GSH content back to control level. Lowering of PC12 GSH content, via blockade of its synthesis with buthionine sulfoximine, however, led to a significantly decreased accumulation of exogenous [3H]DA without affecting uptake of the acetylcholine precursor [14C]choline. These data suggest that GSH is involved in the granular storage of DA in PC12 cells and that, considering the molecular characteristics of the granular transport system, it is likely that GSH is used to protect susceptible parts of this system against (possibly DA-induced) oxidative damage.

Optimal NF kappa B mediated transcriptional responses in Jurkat T cells exposed to oxidative stress are dependent on intracellular glutathione and costimulatory signals

Many early response genes induced by the exposure of mammalian cells to environmental stress contain DNA sequences which bind nuclear factor (NF) kappa B. However, the effects of oxidative stress on NF kappa B activity in T cells are contradictory with evidence supporting both stimulation and suppression. The present investigation examined the effects of low levels of oxidative stress in the form of H2O2 on NF kappa B transactivation in Jurkat T cells and the regulation of NF kappa B activity by cellular glutathione (GSH) levels and costimulatory signals. Transient transfection analyses demonstrated 2-3 fold increases in transcription of an NF kappa B dependent chloramphenicol acetyl transferase (CAT) reporter after the exposure of Jurkat cells to 100-500 microM H2O2. By comparison, dual stimulation of Jurkat cells with phytohemagglutinin (PHA) plus phorbol (PMA) induced 9-10 fold increases in NF kappa B CAT activity. Although no marked changes in GSH levels were detected in cells treated with H2O2 or PHA/PMA, the depletion of GSH in cells pretreated with DL-buthionine-[S,R]-sulfoximine (BSO) substantially inhibited NF kappa B transactivation by H2O2. In addition, H2O2 was less effective than PHA/PMA in inducing NF kappa B1 (p50)/RelA (p65) complexes. However, signals induced by oxidative conditions effectively cooperated with stimulatory signals provided by PMA but not with T cell receptor/CD3 stimulation to induce significant increases in NF kappa B CAT responses. These results suggest that a functional GSH system is required for NF kappa B activation in T cells exposed to oxidative reagents and provide evidence that oxidative stress triggers signaling events capable of participating with distinct coregulatory signals to activate NF kappa B transcriptional responses.

4-Hydroxy-2-nonenal cytotoxicity in renal proximal tubular cells: protein modification and redox alteration

4-Hydroxy-2-nonenal (HNE), one of the major products of membrane lipid peroxidation, has been shown recently to be present in a form covalently attached to proteins in the renal proximal tubules of rats treated with a renal carcinogen, ferric nitrilotriacetate (Toyokuni, S., et al. (1994) Proc. Natl. Acad. Sci. USA 91, 2616-2620; Uchida, K., et al. (1995) Arch. Biochem. Biophys. 317, 405-411). In the present study, the mechanism of HNE cytotoxicity was studied using the renal tubular epithelial cells (LLC-PK1), focusing on the protein modification and alteration of cellular redox status induced by HNE. Upon treatment with HNE for 2 h, the LLC-PK1 cells were found to be resistant to the low concentration (10 microM) of HNE, while HNE at higher concentrations (> or = 50 microM) mediated cell death. The cytotoxicity of HNE appeared to be correlated with the HNE modification of cellular proteins. Among a number of proteins modified by HNE, a glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase was detected as one of the major targets of HNE in the cells. On the other hand, exposure of LLC-PK1 cells to HNE resulted in rapid reduction of cellular glutathione (GSH) levels, suggesting that HNE influenced primarily the redox status of the cells. Depletion of GSH with buthionine sulfoximine, a potent suppressor of GSH biosynthesis, before HNE treatment caused the cells to be sensitive to HNE cytotoxicity and to HNE modification of cellular proteins, whereas the increase in intracellular GSH levels by treatment with N-acetylcysteine before HNE treatment resulted in a dose-dependent inhibition of HNE-mediated protein modification. These results suggest that intracellular GSH is a determinant on cellular resistance against the HNE-mediated cytotoxicity.

Possible role of glutathione in resistance to heavy metals and hydrogen peroxide in a radioresistant Chinese hamster V79 cell strain

To understand the cellular and biochemical nature of radioresistance in the strain M5 derived from Chinese hamster V79 cells, the sensitivity of the resistant cells towards CdCl2, Zn(Ac)2, and H2O2 by the colony forming ability has been tested. D0 values for these compounds in Chinese hamster V79 cells were 5.4 microM, 27.8 microM and 4.3 micrograms/ml respectively while for M5 cells these were 8.3 microM, 142.9 microM and 11.9 micrograms/ml respectively. The resistance to heavy metals as well as the oxidative damage could be reversed by the inhibition of glutathione synthesis by the drug buthionine sulfoximine (BSO). These set of data indicate that the cellular antioxidant glutathione plays an important role in the observed oxidant-resistant phenotype as well as heavy metal resistance in M5 cells.

Inhibition of cell growth and sensitization to oxidative damage by overexpression of manganese superoxide dismutase in rat glioma cells

The effects of overexpression of human manganese superoxide dismutase (MnSOD) on cell proliferation and response to oxidative stress in rat glioma cells were studied. MnSOD-overexpressing cells had a 2- to 14-fold increase in MnSOD activity, but did not have consistent changes in the activities of CuZnSOD, catalase, or glutathione peroxidase. Cells with more than a 5-fold increase in MnSOD activity became more sensitive to radiation, 1,3-bis(2-chloroethyl)-1-nitrosourea, and buthionine sulfoximine and had a lower growth rate than parental and vector control cells. The sensitivity to 1,3-bis(2-chloroethyl)-1-nitrosourea was partially reduced by pyruvate, a H2O2 scavenger. Our results suggest that overexpression of MnSOD can cause an imbalance of antioxidant enzymes, which we hypothesize results in an elevation of intracellular H2O2. Overexpression of MnSOD can either inhibit cell proliferation or increase cell death by oxidative agents, depending on the levels of peroxide-removing enzymes.

Ca2+ mobilization during cell death induction by sodium 5, 6-benzylidene-L-ascorbate

The cytotoxic activity of sodium 5,6-benzylidene-L-ascorbate (SBA) against human KG-1-C glioma and T98G glioblastoma cell lines was augmented by pretreatment of the cells with L-buthionine-[S, R]-sulfoximine (BSO), which reduced the intracellular glutathione concentrations. SBA produced shrunken cells and large DNA fragments, without the induction of nuclear and internucleosomal DNA fragmentation. The rapid elevation of intracellular free Ca2+ concentration observed after SBA treatment was further augmented by BSO pretreatment. A confocal experiment with Fluo-3 fluorescence revealed that SBA markedly elevated the free Ca2+ concentration in the nuclear region, but did not significantly affect that in the cytoplasmic region. The present study suggests that the nuclear accumulation of Ca2+ is an important initial step for cell death induction by SBA.

Human (THP-1) macrophages oxidize LDL by a thiol-dependent mechanism

The oxidative modification of low-density lipoprotein by macrophages may be an important mechanism in the pathogenesis of atherosclerosis. The human monocytic leukaemic cell line THP-1, when stimulated with phorbol ester, shares many properties with human monocyte-derived macrophages. Oxidation of LDL by these cells was characterised by depletion of alpha-tocopherol, increases in thiobarbituric acid reactive substances and increases in electrophoretic mobility. The LDL particles were also converted to a form which increased accumulation of cholesteryl esters within macrophages. The oxidative mechanism appeared to be dependent upon the presence of thiols in the cellular medium. Oxidation of LDL by THP-1 macrophages, and production of thiols by these cells, were dependent upon the presence of L-cystine in the medium. Furthermore, cellular oxidation of LDL could be partially mimicked by the addition of cysteine to Hams F10 medium. Macrophage-independent oxidation of LDL, mediated by the addition of copper ions, was inhibited by cystine and cysteine in phosphate buffered saline, but not in Hams F10 medium. The glutathione content of THP-1 macrophages was also dependent upon the presence of cysteine or cystine in the medium, but inhibition of glutathione synthesis by buthionine sulfoximine did not prevent the production of thiols or the oxidation of LDL by THP-1 macrophages.

Comparison of drug accumulation in P-glycoprotein-expressing and MRP-expressing human leukaemia cells

P-glycoprotein- and multidrug resistance-associated protein (MRP)-mediated multidrug resistance is associated with decreased drug accumulation. The P-glycoprotein-expressing CCRF-CEM/VLB100 subline and the MRP-expressing CCRF-CEM/E1000 subline are both 50-fold resistant to daunorubicin. However, accumulation of daunorubicin and rhodamine 123 was > 85% reduced in the P-glycoprotein-expressing subline compared to 40-50% in the MRP-expressing subline. Further, the CCRF-CEM/E1000 cells were 30-fold resistant to idarubicin, without reduced accumulation. Verapamil and SDZ PSC 833 restored daunorubicin and rhodamine 123 accumulation, while buthionine sulphoximine affected only the CCRF-CEM/ E1000 subline. We conclude that the verapamil associated change in rhodamine 123 accumulation provides a sensitive functional assay for both P-glycoprotein- and MRP-mediated MDR.

Modulation of cisplatin chronotoxicity related to reduced glutathione in mice

Intracellular reduced glutathione (GSH) concentrations were measured according to the tissue sampling-time along the 24 h scale in male B6D2F1 mice. A significant circadian rhythm in GSH content was statistically validated in liver, jejunum, colon and bone-marrow (P < or = 0.02) but not in kidney. Tissue GSH concentration increased in the dark-activity span and decreased in the light-rest span of mice. The minimum and maximum of tissue GSH content corresponded respectively to the maximum and minimum of cisplatin (CDDP) toxicity. The role of GSH rhythms with regard to CDDP toxicity was investigated, using a specific inhibitor of GSH biosynthesis, buthionine sulfoximine (BSO). Its effects were assessed on both tissue GSH levels and CDDP toxicity at three circadian times. BSO resulted in a 10-fold decrease of the 24 h-mean GSH in kidney. However a moderate GSH decrease characterized liver (-23%) and jejunum (-30%). BSO pretreatment largely enhanced CDDP toxicity which varied according to a circadian rhythm. Although BSO partly and/or totally abolished the tissue GSH rhythms, it did not modify those in CDDP toxicity. We conclude that GSH have an important influence on CDDP toxicity but not in the circadian mechanism of such platinum chronotoxicity.

Amelioration of hepatocellular integrity and inhibition of sinusoidal oxidative stress by N-acetylcysteine pretreatment in cold ischemia-reperfusion injury of rat liver

Further improvements of donor liver preservation are still required in liver transplantation. In the present study, we investigated whether intraportal injection of N-acetylcysteine (NAC) 15 min before flush-out of UW solution (NAC pretreatment) improves liver dysfunction after cold preservation or has a protective effect on sinusoidal oxidative stress. The effect of NAC pretreatment was examined using an isolated perfused rat liver model. The NAC pretreatment significantly reduced sinusoidal oxidative stress relative to a control dextrose 5% injection. Under a glutathione-depleted condition produced by L-buthionine-[S-R]-sulfoximine, the NAC pretreatment also significantly reduced hepatocellular as well as sinusoidal oxidative stress, resulting in improvement of hepatocelllar integrity relative to a control dextrose 5% injection.

The interaction of buthionine sulphoximide (BSO) and the topoisomerase I inhibitor CPT-11

Buthionine sulphoximide (BSO)-induced depletion of glutathione (GSH) was found to be associated with an increased sensitivity to CPT-11 (topoisomerase I-reactive agent) in V79 hamster lung fibroblast cells. When V79 cells were exposed to 2.5 mM BSO for 28 h beginning 4 h prior to a 24 h coincubation with CPT-11, cytotoxicity was increased compared with CPT-11 alone. It was determined that BSO resulted in a G1 cell cycle arrest and a decrease in the percentage of cells in S-phase. Since CPT-11 is known to be S-phase-specific, this BSO-induced cell cycle redistribution did not appear to account for the chemosensitisation of CPT-11. Additionally, BSO did not alter intracellular accumulation of CPT-11, conversion of CPT-11 to its active metabolite SN-38, or efflux of either CPT-11 or SN-38 from the cell. Finally, BSO resulted in a slight reduction, rather than an increase, in the number of stabilised DNA-topoisomerase I complexes induced by CPT-11. Therefore, these results suggest that BSO-induced sensitisation of V79 cells to the cytotoxic effects of CPT-11 occurs by a mechanism independent of the stabilisation of DNA-topoisomerase I complexes.

Effect of BSO and etanidazole on neurofilament degradation in neonatal rat spinal cord cultures

Peripheral neuropathy is the major dose-limiting toxicity of the hypoxic cell sensitiser, etanidazole. Previous work from this laboratory using culture neuronal cell lines suggested that nitroimidazole-induced degradation of neurofilament proteins might be the critical biological event mediating this neurotoxicity. The purpose of the present study was to develop the neurofilament degradation assay in an organotypic spinal cord culture system with the goal of developing strategies for optimising sensitiser efficacy as well as ameliorating nitroimidazole-induced neurotoxicity. Spinal cord cultures were treated with etanidazole and neurofilament protein degradation was analysed by immunoblot analysis. Spinal cord cultures exposed to etanidazole exhibited a dose-dependent loss of parent neurofilament proteins, with concomitant appearance of low molecular weight degradation products. The potential neurotoxic effect of L, S-buthionine sulphoximine (BSO), a compound that enhances the radiosensitising effectiveness of 2-nitroimidazoles, was also screened in this assay system. BSO alone, at concentrations up to 100 microM, did not promote neurofilament degradation. BSO (20 microM) enhanced the effect of etanidazole on neurofilament degradation by a dose-modifying factor of 1.6 +/- 0.5. Since 20 microM BSO is expected to enhance etanidazole radiosensitisation of hypoxic cells by a larger factor, this suggests that a therapeutic gain could be achieved using BSO in combination with etanidazole in radiation therapy.

Intracellular glutathione level modulates the induction of apoptosis by delta 12-prostaglandin J2

We studied the effect of intracellular glutathione (GSH), which was known to conjugate readily with an alpha, beta-unsaturated carbonyl of 9-deoxy-delta 9,12-13,14-dihydroPGD2 (delta 12-PGJ2), on the cytotoxicity of delta 12-PGJ2. delta 12-PGJ2 caused DNA fragmentation in human hepatocellular carcinoma Hep 3B cells, which was blocked by cycloheximide (CHX). The delta 12-PGJ2-induced apoptosis was augmented by GSH depletion resulted from pretreatment with buthioninine sulfoximine (BSO), an inhibitor of gamma-glutamylcysteine synthetase. On the contrary, N-acetyl-cysteine (NAC), a precursor of cysteine, elevated the GSH level and protected cells from initiating apoptosis by delta 12-PGJ2. Sodium arsenite, a thiol-reactive agent, also induced apoptosis, which was potentiated or attenuated by BSO or NAC treatment respectively. These results suggest that the apoptosis-inducing activity of delta 12-PGJ2 is due to thiol-reactivity and intracellular GSH modulates the delta 12-PGJ2-induced apoptosis by regulating the accessibility of delta 12-PGJ2 to target proteins containing thiol groups.

Modulation of 5-S-cysteinyldopa formation by tyrosinase activity and intracellular thiols in human melanoma cells

The catechol 5-S-cysteinyldopa (5-S-CD) is produced in large amounts in metastatic malignant melanoma. To further understand the mechanism of formation of 5-S-CD, we investigated the effects of thiol modulating agents and melanin precursors on human melanoma cells. Under standard culture conditions (0.1 mM cystine), the cell levels of 5-S-CD were highly correlated with the degree of melanization and the dopa oxidase activity of the four cell lines investigated (Me8, JUSO, GLL19, Swift). Inhibition of glutathione (GSH) biosynthesis with buthionine sulphoximine did not affect 5-S-CD levels in the low melanotic GL 19 cells. In contrast, the highly pigmented Swift cells showed a strong increase in the cell levels of cystine (CysH) and 5-S-CD. When the cystine concentration of the growth medium was increased to 0.2 mM, a similar situation of 5-S-CD synthesis caused by an increase in intracellular CysH levels was observed in the Swift cells. The GLL19 cells showed enhanced 5-S-CD formation in the presence of 0.1 mM L-dopa. This effect was associated with a fourfold increase in dopa oxidase activity. Our data clearly indicate that 5-S-CD is formed in human melanoma cells by a tyrosinase-dependent mechanism involving the addition of CysH to dopaquinone. Based on the enhancing effect of buthionine sulphoximine on 5-S-CD formation, it is proposed that GSH is not directly implicated in 5-S-CD formation, but regulates CysH levels via the enzyme gamma-glutamylcysteine synthetase.

Depletion of brain glutathione results in a decrease of glutathione reductase activity; an enzyme susceptible to oxidative damage

Loss of the intracellular antioxidant glutathione (GSH) from the substantia nigra is considered to be an early event in the pathogenesis of Parkinson's disease (PD). While the cause of the loss is unclear, an imbalance in the enzymes associated with the synthesis, utilisation, degradation and translocation of GSH has been implicated. The enzyme glutathione reductase is also important in GSH homeostasis: it regenerates GSH from the oxidised from (GSSG). However, to date the activity and regulation of glutathione reductase in conditions such as PD have not been explored. In view of this we have measured the effects of GSH depletion on glutathione reductase activity of the rat brain. Other glutathione related enzymes were also measured. Using pre-weanling rats, brain GSH was depleted by up to 60% by subcutaneous administration of L-buthionine sulfoximine. The only enzyme affected by GSH depletion was glutathione reductase; its activity being reduced by approximately 40%. As GSH inactivates a number of oxidising species including peroxynitrite (ONOO-), we additionally investigated the susceptibility of glutathione reductase to ONOO- in vitro, using purified enzyme. ONOO- decreased glutathione reductase activity in a concentration dependent manner with an apparent 50% inhibition occurring at an initial concentration of 0.09 mM. These data suggest that GSH is important in the maintenance glutathione reductase activity. This may arise in part from its ability to inactivate oxidising agents such as ONOO-.

Effect of chronic glutathione deficiency on rat lung mitochondrial function

The effect of chronic glutathione deficiency on lung mitochondrial energy production using buthionine sulphoximine (BSO) as a depletor has been investigated. Prolonged depletion of mitochondrial glutathione produced an imbalance in the antioxidant defence and resulted in lipid peroxidation, which, in turn, damages the membranous structure, leading to the inactivation of inner membrane enzymes, matrix-bound enzymes and mitochondrial cytochrome content. Altered activities of energy-linked enzymes and electron transport resulted in the decreased rate of ADP-stimulated oxygen uptake, respiratory coupling ratio and ATP synthesis.

Relationship between glutathione and DL alpha-lipoic acid against cadmium-induced hepatotoxicity

Cadmium, a divalent metal toxicant, preferentially localizes in hepatocytes and causes liver injury. DL alpha-lipoic acid is a dithiol which is effective in rendering protection against cadmium-associated liver damage, by virtue of its two sulfhydryl moieties. Lipoate was administered to cadmium-exposed rats which were either prior administered with buthionine sulfoximine to deplete liver glutathione or not. During lipoate treatment, significant protection was rendered against cadmium toxicity even under glutathione-depleted experimental condition. This highlights the antioxidant property of lipoic acid and its efficacy in mitigating cadmium-associated liver assault even in the absence of glutathione synthesis.

Glutathione depletion potentiates MPTP and MPP+ toxicity in nigral dopaminergic neurones

Glutathione levels are decreased in the substantia nigra of patients with Parkinson's disease. We studied whether glutathione depletion contributes to dopaminergic cell death using a specific inhibitor of glutathione biosynthesis, L-buthionine sulfoximine (BSO). We found no significant reduction of tyrosine hydroxylase-positive cells in the substantia nigra pars compacta (SNpc) when BSO was administered systemically to preweanling mice or locally to the SNpc of adult rats. However, the combination of BSO with MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) in preweanling mice and the combination of nigral injections of BSO with intrastriatal injections of MPP+ (1-methyl-4-phenylpyridinium), the active metabolite of MPTP in adult rats, potentiated the toxic effects of MPTP and MPP+ on nigral neurones. Our data show that glutathione depletion can result in cell death if the nigrostriatal system is metabolically compromised.

Thioctic acid does not restore glutathione levels or protect against the potentiation of 6-hydroxydopamine toxicity induced by glutathione depletion in rat brain

Decreased reduced glutathione (GSH) levels are an early marker of nigral cell death in Parkinson's disease. Depletion of rat brain GSH by intracerebroventricular administration of buthionine sulphoximine (BSO) potentiates the toxicity of 6-hydroxydopamine (6-OHDA) to the nigrostriatal pathway. We have investigated whether thioctic acid can replenish brain GSH levels following BSO-induced depletion and/or prevent 6-OHDA induced toxicity. Administration of BSO (2 x 1.6 mg i.c.v.) to rats depleted striatal GSH levels by upto 75%. BSO treatment potentiated 6-OHDA (75 micrograms i.c.v.) toxicity as judged by striatal dopamine content and the number of tyrosine hydroxylase immunoreactive cells in substantia nigra. Repeated treatment with thioctic acid (50 or 100 mg/kg i.p.) over 48h had no effect on the 6-OHDA induced loss of dopamine in striatum or nigral tyrosine hydroxylase positive cells in substantia nigra. Also thioctic acid treatment did not reverse the BSO induced depletion of GSH or prevent the potentiation of 6-OHDA neurotoxicity produced by BSO. Thioctic acid (50 mg or 100 mg/kg i.p.) alone or in combination with BSO did not alter striatal dopamine levels but increased dopamine turnover. Striatal 5-HT content was not altered by thioctic acid but 5-HIAA levels were increased. Under conditions of inhibition of GSH synthesis, thioctic acid does not replenish brain GSH levels or protect against 6-OHDA toxicity. At last in this model of Parkinson's disease, thioctic acid does not appear to have a neuroprotective effect.

Inhibition of glutamine synthetase reduces ammonia-induced astrocyte swelling in rat

Astrocyte hypertrophy and swelling occur in a variety of pathophysiological conditions, including diseases associated with hyperammonemia. Ammonia is rapidly incorporated into glutamine by glutamine synthetase localized in astrocytes. We tested the hypotheses that (1) 6 h of hyperammonemia (500-600 microM) is adequate for producing astrocyte enlargement, and (2) astrocyte enlargement is attenuated by inhibition of glutamine synthetase with methionine sulfoximine. Pentobarbital-anesthetized rats received an intravenous infusion of either sodium or ammonium acetate after intraperitoneal pretreatment with vehicle, methionine sulfoximine (0.8 mmol/kg) or buthionine sulfoximine (4 mmol/kg), an analogue that does not inhibit glutamine synthetase. Hyperammonemia produced enlarged cortical astrocytes characterized by (1) decreased electron density of cytoplasmic matrix in perikaryon, processes and perivascular endfeet, (2) increased circumference of nuclear membrane, (3) increased numbers of mitochondria and rough and smooth endoplasmic reticulum in perikarya and large processes, and (4) less compact bundles of intermediate filaments. Pretreatment with methionine sulfoximine, but not buthionine sulfoximine, attenuated the decrease in cytoplasmic density and the increase in nuclear circumference; most perivascular endfeet remained as dense as occurred with sodium acetate infusion. However, increased numbers of organelles in expanded perikarya and large processes occurred after methionine sulfoximine treatment with and without ammonium acetate infusion. In separate groups of rats, hyperammonemia produced an increase in cortical tissue water content which was inhibited by methionine sulfoximine, but not buthionine sulfoximine. We conclude that clinically-relevant levels of hyperammonemia can cause astrocyte enlargement within 6 h in vivo characterized by both watery cytoplasm and increased organelles indicative of a cellular metabolic stress and altered astrocyte function. The watery cytoplasm component of astrocyte enlargement depends on glutamine synthesis rather than on ammonium ions per se, and is possibly caused by the osmotic effect accumulated glutamine.

Mechanistic aspects of modification of radiobiological damage in barley seeds by glutathione and buthionine sulfoximine

Buthionine sulfoximine (BSO) enhances the radiosensitivity of in vitro mammalian cells, possibly by inhibiting de novo biosynthesis of glutathione (GSH); however, administration of BSO to intact animals results in no effect or possibly radioprotection. Keeping in view that BSO affords radioprotection its physico-chemical action in dry (metabolically inert) and pre-soaked (metabolizing) barley seeds has been investigated with a view that the effects of GSH and BSO on the radiation-induced O2-dependent and - independent components of damage could be unambiguously resolved. It was observed that (i) BSO does not inhibit the uptake of GSH in dry or metabolizing seeds, (ii) BSO also, like GSH, affords radioprotection against post-irradiation O2-dependent damage, and (iii) both additives enhance the O2-independent (i.e. N2- or N2O-mediated) component of damage. An equimolar mixture of these two additives also behaves as either alone on the oxic and anoxic components of radiation damage. Since GSH more efficiently reacts with electrons than it donates an H-atom to the damaged target molecules, and the glutamyl moiety is common to both GSH and BSO, physico-chemical mechanisms possibly involved in the differential modification of oxic and anoxic components are briefly discussed.

Tyrosine and phenylalanine restriction sensitizes adriamycin-resistant P388 leukemia cells to adriamycin

Cancer chemotherapy frequently fails, because tumors develop multiple drug resistance (MDR). Pharmacological efforts to reverse this MDR phenotype and sensitize resistant tumor cells have utilized verapamil (VER) to inhibit p-glycoprotein function and buthionine sulfoximine (BSO) to inhibit glutathione synthesis. Our previous results indicate that restriction of two amino acids, tyrosine (Tyr) and phenylalanine (Phe), may potentially suppress the MDR phenotype. These results show that in vivo Tyr and Phe restriction improves the therapeutic response of a metastatic variant of B16-BL6 (BL6) murine melanoma to adriamycin (ADR) and B16 melanoma to levodopa methyl ester. We examine whether in vitro limitation of Tyr and Phe suppresses ADR resistance of BL6 cells and whether Tyr-Phe modulation of the MDR phenotype is applicable to other tumor types, particularly P388 murine leukemia. Mechanisms underlying Tyr-Phe modulation of ADR resistance are examined in the presence of VER and BSO, singly and in combination. Our results indicate that in vitro Tyr and Phe restriction has no effect on BL6 resistance to ADR. However, Tyr and Phe restriction does increase the sensitivity of ADR-resistant P388 cells to ADR without affecting drug efflux, ADR uptake, or glutathione levels. In addition, this enhanced ADR sensitivity of P388 cells is even more pronounced in the presence of BSO. Suppression of ADR resistance in P388-resistant cells by Tyr and Phe restriction indicates that Tyr- and Phe-mediated modulation of the MDR phenotype is possible and that Tyr and Phe restriction may be useful as a potential adjuvant to effective cancer chemotherapy.

Effect of glutathione depletion on electrophysiological characteristics of guinea-pig ventricles

In this study the effect of acute and chronic glutathione depletion with L-buthionine-S,R-sulphoximine (BSO) on action potential characteristics of guinea-pig left ventricle papillary muscles were investigated. BSO caused significant decrease of maximum rate in rise of depolarization phase (Vmax) and duration of AP (APD) at 25%, 50%, 90% of repolarization in both cases of depletion and a slight but not significant decrease in the action potential amplitude, but did not modify the resting membrane potential. Pretreatment with bisaramil prevented the effect of BSO on APD in both cases of depletion.

NO-induced oxidative stress and glutathione metabolism in rodent and human cells

Nitric oxide (NO.), a radical species produced by many types of cells, is known to play a critical role in both regulatory processes and cell defense, yet it may also participate in collateral reactions, leading to DNA damage and cell death in both NO-generating and neighboring cells. Glutathione has been shown to protect cells from the toxic effects of free radicals and reactive oxygen species. The goal of this study was to investigate whether differences in glutathione metabolism could account for the resistance or sensitivity to cell killing by NO.. The cytotoxic effect of NO. was examined in CHO-AA8 (Chinese Hamster Ovary) cells and TK6 (human lymphoblastoid) cells pretreated with L-buthionine SR-sulfoximine (BSO), a potent inhibitor of gamma-glutamylcysteine synthetase, and with 1,3-bis-(2-chloroethyl)-1-nitrosourea (BCNU), an irreversible inhibitor of glutathione reductase. The consequences resulting from the depletion of glutathione levels and from the arrest of oxidoreduction allowed us to show the involvement of glutathione in protecting cells from NO. and to investigate the importance of changes in glutathione metabolism on NO-induced toxicity. In CHO-AA8 cells, we found that treatment with NO. resulted in the oxidation of reduced glutathione (GSH) to oxidized glutathione (GSSG) and to mixed glutathione disulfides (GSSR). The resulting depletion of GSH stimulated its de novo synthesis, enabling the cells to resist killing by NO.. A slight difference in GSH metabolism was observed in TK6 cells. NO. led to an increase in GSSG levels similar to that observed in CHO-AA8 cells, however, a decrease in GSH levels, no change in GSSR levels, and higher levels of toxicity were also found, suggesting that NO-treated TK6 cells are not as competent in GSH homeostasis as CHO cells. We conclude that GSH is involved in protecting cells from killing by NO. and that both de novo synthesis of GSH and GSSG reduction are important in maintaining an adequate level of protection for the cells.

UV-b-induced cataract model in brown-Norway rat eyes combined with preadministration of buthionine sulfoximine

In order to develop a more adequate ultraviolet (UV)-induced cataract model, a combination of l-buthionine sulfoximine (BSO) treatment was applied to experimental animals. A single administration of BSO 4 mmol/kg caused reduced glutathione concentration until experimental day 8. In the 0.067-J/cm2 UV-B irradiation experiment, the light-scattering intensity of the anterior lens cortex of the combination group was significantly higher than that of the other groups during the second week after irradiation commenced. After the fourth experimental week, however, there was no significant difference between the group treated by UV-B alone and the combination group. In the 0.2-J/cm2 UV-B irradiation experiment, anterior polar cataract was seen in the group receiving UV-B alone, as already reported, 6 weeks after starting UV irradiation. Meanwhile, in the combination group, shallow cortical opacity was seen at 26 weeks after the start of experiment in the deeper lenticular layer which was separated from the anterior subcapsular opacity. This anterior shallow cortical opacity seemed to move towards the nuclear region during the time course of the experiment. The results of this experiment suggested that the BSO treatment accelerated cataractogenesis through additional UV-B irradiation. Although more experiments are needed, this model is useful in investigating the connection between UV-B and other cocataractogenic factors in age-related cataract in humans.

Alterations of the glutathione redox cycle status in fumonisin B1-treated pig kidney cells

Fumonisin B1 (FB1) causes equine leukoencephalomalacia, porcine pulmonary edema, and liver tumors and chronic nephritis in rats. To investigate mechanisms by which FB1 induces toxicity, effects of FB1 on cellular glutathione (GSH) redox status and GSH depletion on FB1 toxicity in pig kidney (LLC-PK1) cells were studied. Treatment of LLC-PK1 cells with 50 microM FB1 for 24 hours significantly decreased cellular GSH contents from 56 +/- 3.2 to 42.7 +/- 4.4 nmol/mg protein (p < 0.05) and increased the activities of glutathione reductase (GR) from 25.7 +/- 2.4 to 35.7 +/- 5.0 mumol NADPH/mg protein (p < 0.05). The activities of glutathione peroxidase (GSHpx), catalase, and Cu,Zn-superoxide dismutase (SOD) were not changed by this treatment. Treatment of LLC-PK1 cells for 12 hours with 0.1 mM buthionine sulfoximine (BSO), a selective inhibitor of the enzyme gamma-glutamylcysteine synthetase that catalyzes the rate-limiting reaction in de novo GSH synthesis, decreased cellular GSH levels to about 20% of that found in the control cells. The cells pretreated with 0.1 mM BSO for 12 hours were significantly sensitized to the FB1 cytotoxicity as determined by a long-term survival assay (p < 0.05). The results demonstrate that FB1 changes GSH redox cycle status in LLC-PK1 cells, and GSH may play a role in cytoprotection against FB1 toxicity.

Glutathione depletion is accompanied by increased neuronal nitric oxide synthase activity

The effect of glutathione depletion, in vivo, on rat brain nitric oxide synthase activity has been investigated and compared to the effect observed in vitro with cultured neurones. Using L-buthionine sulfoximine rat brain glutathione was depleted by 62%. This loss of glutathione was accompanied by a significant increase in brain nitric oxide synthase activity by up to 55%. Depletion of glutathione in cultured neurones, by approximately 90%, led to a significant 67% increase in nitric oxide synthase activity, as judged by nitrite formation, and cell death. It is concluded that depletion of neuronal glutathione results in increased nitric oxide synthase activity. These findings may have implications for our understanding of the pathogenesis of neurodegenerative disorders in which loss of brain glutathione is considered to be an early event.

Enhancement of paraquat toxicity by glutathione depletion in mice in vivo and in vitro

Effect of glutathione (GSH) depletion on paraquat (PQ) toxicity in the liver and kidneys of mice was examined. Glutamic-pyruvate transaminase (GPT) and blood urea nitrogen (BUN) levels in plasma of mice were hardly changed by treatment with 150 micro mol/kg of PQ. However, significant increases in the plasma GPT and BUN levels after PQ injection were observed in mice which were pretreated with L-buthionine-SR-sulfoximine (BSO), an inhibitor of GSH synthesis, at 4 hr prior to PQ administration. This result supports the previous observation that hepatotoxicity of PQ was enhanced in diethyl maleate-pretreated mice (Cagen and Gibson, 1977). In the present study, lipid peroxidation evaluated by thiobarbituric acid-reactive substances (TBA-RS) level in the liver of mice given PQ was elevated by pretreatment with BSO. Moreover, enhancement of PQ cytotoxicity by BSO pretreatment was also observed in cultured mouse hepatoma cell line (NCTC clone 1469). Vitamin E, an antioxidant, and Desferal, an iron chelator, significantly prevented mice from the BSO-enhanced hepato- and nephrotoxicity of PQ. These findings suggest that the tissues or cells of low GSH concentration are highly vulnerable to PQ toxicity and GSH may play a major role in diminishing the toxic action of PQ exerted through oxidative stress.

Effect of glutathione depletion on metallothionein synthesis induced by paraquat in mice

The effect of Glutathione (GSH) depletion on the induction of metallothionein (MT) synthesis by paraquat (PQ) was examined in ICR mice. An increase in hepatic MT level in mice was observed after a single PQ administration. Pretreatment of mice with L-buthionine-SR-sulfoximine (BSO), an inhibitor of GSH synthesis, enhanced the induction of hepatic and renal MT synthesis by PQ depending on the decreased tissue GSH level. A similar result was obtained by pretreatment with diethylmaleate, a GSH depleting agent. The ratio of hepatic MT-I to MT-II induced by PQ was not changed by BSO pretreatment. An increase in the hepatic MT level in GSH depleted mice was observed from 3 hr to 24 hr after PQ administration. An increase in the hepatic MT-I mRNA level after treatment with PQ was observed prior to hepatic MT induction in BSO pretreated mice. Pretreatment with actinomycin D, an inhibitor of mRNA synthesis, inhibits the PQ-induced increase in hepatic MT and MT-I mRNA levels in BSO pretreated mice. Pretreatment with BSO did not affect the induction of MT synthesis by zinc, cadmium or dexamethasone. Pretreatment with dexamethasone, an anti-inflammatory agent, enhanced the hepatic MT induction by PQ treatment in GSH depleted mice, while dexamethasone reduced the MT induction by turpentine oil, which is known to induce inflammation and hepatic MT synthesis. These findings suggest that GSH depletion enhances the induction of MT synthesis by PQ because of an increase in the transcription rate, and this enhancement of MT synthesis is not due to an inflammatory response caused by PQ.