Depletion of brain glutathione is accompanied by impaired mitochondrial function and decreased N-acetyl aspartate concentration

The effect of depletion of reduced glutathione (GSH) on brain mitochondrial function and N-acetyl aspartate concentration has been investigated. Using pre-weanling rats, GSH was depleted by L-buthionine sulfoximine administration for up to 10 days. In both whole brain homogenates and purified mitochondrial preparations complex IV (cytochrome c oxidase) activity was decreased, by up to 27%, as a result of this treatment. In addition, after 10 days of GSH depletion, citrate synthase activity was significantly reduced, by 18%, in the purified mitochondrial preparations, but not in whole brain homogenates, suggesting increased leakiness of the mitochondrial membrane. The whole brain N-acetyl aspartate concentration was also significantly depleted at this time point, by 11%. It is concluded that brain GSH is important for the maintenance of optimum mitochondrial function and that prolonged depletion leads also to loss of neuronal integrity. The relevance of these findings to Parkinson's disease and the inborn errors of glutathione metabolism are also discussed.

5-Fluorouracil cytotoxicity in human colon HT-29 cells with moderately increased or decreased cellular glutathione level

Little is known whether diet or certain components in the diet can modulate the efficacy of 5-fluorouracil (5FU) in patients with colon carcinoma. Glutathione (GSH), an important antioxidant and anticarcinogen, is present in many foods in varying amounts. This study examined whether a moderately increased or decreased cellular GSH level had any effect on the growth of human colon adenocarcinoma cells HT-29 and on the cytotoxic activity of 5FU in these cells. GSH and buthionine sulfoximine were used to enhance or reduce the GSH level respectively in these cells. A 34% increase in cellular GSH level had no effect on the growth of HT-29 cells, nor on the cytotoxic activity of 5FU as determined by the MTT colorimetric assay and cell counts. A 50% reduction in the cellular GSH level was found to enhance 5FU cytotoxicity by 20% to 31% as determined by the MTT colorimetric assay, depending on the 5FU concentration. This study shows that a moderate change in the GSH level in HT-29 cells had little or no effect on the cells' growth, but a decrease in cellular GSH level slightly enhanced the cytotoxic activity of 5FU in these cells.

Elimination of Ehrlich tumours by ATP-induced growth inhibition, glutathione depletion and X-rays

ATP-induced tumour growth inhibition is accompanied by a selective decrease in the content of the tripeptide glutathione (GSH) within the cancer cells in vivo. Depletion of cellular GSH sensitizes tumours to chemotherapy and radiation, but the usefulness of this depletion depends on whether the levels of GSH can be reduced in the tumour relative to normal tissues. We report here that administration of ATP in combination with diethylmaleate and X-rays leads to complete regression of 95% of Ehrlich ascites tumours in mice. This shows that an aggressive tumour can be eliminated by using a therapy based on modulation of GSH levels in cancer cells.

Profile of procarbazine-induced embryotoxicity in an embryo hepatocyte co-culture system and after in utero glutathione depletion

Procarbazine (PCZ) is an antineoplastic agent useful in the treatment of Hodgkin's disease, brain tumors, and chronic leukemia. PCZ is dysmorphogenic to developing embryos exposed in vivo or cultured in the serum of PCZ-treated rats. However, embryos directly cultured with PCZ (up to 400 micrograms/ml) or PCZ plus S-9 liver fractions are unaffected. Since intact liver cells provide several advantages over hepatic subcellular fractions for in vitro bioactivation, we exposed rat embryos to PCZ in an embryo/hepatocyte co-culture system. Gestation day (GD) 9.5 rat embryos exposed to 0, 200, 300, or 400 micrograms PCZ/ml in the presence of untreated or phenobarbital induced male rat hepatocytes failed to display toxicity. However, in a companion study GD 9.5 rat embryos cultured in the serum from PCZ-treated rats exhibited developmental deficiencies. Studies have shown that the formation of toxic metabolites can result from glutathione (GSH) conjugation of toxicants in the liver. Therefore, in a second set of experiments, rat embryos were cultured in serum from rats pretreated with two GSH depleters (phorone and buthionine sulfoximine) and subsequently dosed with PCZ. Effects on development were enhanced when embryos were cultured in the serum from PCZ-treated/GSH depleted rats. These data indicate that PCZ requires in vivo activation to be dysmorphogenic and further suggest that the metabolite(s) responsible for procarbazine embryo-toxicity are formed readily under conditions of low GSH levels. This argues against a glutathione conjugate as the ultimate toxicant.

Altered oxidative stress responses in nickel-resistant mammalian cells

BALB 3T3 cells exposed to NiCl2 acquired resistance to concentrations as high as 200 microM and retain resistance for many generations in the absence of nickel. This resistance was not due to alterations in uptake or to metallothionein overexpression. The nickel-resistant B200 cell line was found to also exhibit cross-resistance to hydrogen peroxide and menadione. These nickel-resistant cells had 1.8 times higher basal levels of glutathione compared to wild-type cells. Studies with the glutathione synthesis inhibitor buthionine sulfoximine showed that while glutathione turnover was more rapid in the nickel-resistant cells, its depletion following NiCl2 treatment of the parental BALB 3T3 cell line was greater than in the nickel-resistant B200 cells. The reduced level of binding of NFkB and AP-1 transcription factors to their DNA consensus sequences in B200 cells compared to wild-type cells, and their more reactive response following treatment of resistant cells with H2O2 or buthionine sulfoximine, strengthens the hypothesis that nickel resistance is closely allied to oxidative stress responses.

Glutathione stimulates A549 cell proliferation in glutamine-deficient culture: the effect of glutamate supplementation

Extracellular glutathione (GSH) is degraded by an external cell-surface enzyme, gamma-glutamyltranspeptidase (gamma-GT). The products are transported into cells to participate in important cellular processes. In the present study, we tested the hypothesis that extracellular GSH is a source of glutamic acid for cells that express gamma-GT. Under a glutamine-deficient culture condition, the extracellular GSH-supplemented glutamic acid would enhance intracellular glutamine synthesis, thereby stimulating cell proliferation. Human lung carcinoma A549 cells were cultured in glutamine-deficient Dulbecco's modified Eagle medium, and they did not proliferate unless glutamine was supplemented. Extracellular GSH, however, provoked a partial proliferation. The GSH effect correlated with a high level of gamma-GT activity and an increased intracellular level of glutamic acid. A constituent amino acid of GSH, glutamic acid but not cysteine, produced the same growth-stimulatory effect as GSH. Furthermore, neither oxothiazolidine-4-carboxylate (OTC), a cellular cysteine-delivery compound, nor cysteinylglycine, a dipeptide released from the gamma-GT reaction, stimulated cell proliferation. Moreover, buthionine sulfoximine (BSO), a selective inhibitor of gamma-glutamylcysteine synthetase, enhanced the GSH growth stimulatory effect, suggesting that increased cellular GSH synthesis does not correlate with cell growth stimulation. The results obtained demonstrated that glutamine is required for A549 cell proliferation and exogenous GSH partially substitutes for the growth stimulatory action of glutamine. It also suggests that the glutamic acid rather than the cysteine released from the GSH is responsible for the cell proliferation.

Mechanisms of endotoxin-induced haem oxygenase mRNA accumulation in mouse liver: synergism by glutathione depletion and protection by N-acetylcysteine

In in vitro systems haem oxygenase-1 (HO-1) mRNA increases after exposure to agents causing oxidative stress. We lowered cellular antioxidant defence systems in vivo by giving mice increasing doses (0.15 g/kg-1.6 g/kg) of DL-buthionine-(S,R)-sulphoximine (BSO), a specific inhibitor of glutathione synthesis. Maximum glutathione depletion (80%) coincided with maximum hepatic HO-1 mRNA accumulation (about 20 times), whereas with 50% depletion, accumulation was only doubled. It has been suggested that reactive oxygen and nitrogen intermediates are involved in hepatic toxicity of endotoxin (lipopolysaccharide, LPS); LPS even at low doses [0.1 mg/kg, intraperitoneally (i.p.)] induces HO-1 mRNA about 25-fold after 1 h. Hepatic glutathione depletion (respectively 40% and 80%) after a low (0.3 g/kg) or a high (1.6 g/kg) BSO dose, resulted in potentiation of the HO-1 mRNA accumulation induced by LPS (0.1 mg/kg, i.p.). In the absence of BSO, N-acetylcysteine (NAC) (1 g/kg orally) reduced LPS-induced HO-1 mRNA accumulation to one fourth. Under the same experimental conditions S-adenosylmethionine (SAM) was not effective. NAC also reduced HO-1 mRNA accumulation when administered to mice in which glutathione was depleted and its synthesis blocked by BSO (1.6 g/kg). Thus reactive oxygen intermediates are likely mediators of LPS-induced HO-1 mRNA accumulation, and glutathione content appears to be one of the factors regulating this accumulation in the liver. Our findings are compatible with the theory that HO-1 induction might have a protective function in vivo when defence mechanisms against oxidants are challenged.

Two pathways for chromium(VI)-induced DNA damage in 14 day chick embryos: Cr-DNA binding in liver and 8-oxo-2'-deoxyguanosine in red blood cells

Previous studies have shown that chromium(VI) induced cell-specific types of DNA damage, i.e. DNA cross-links in liver and DNA strand breaks in red blood cells, in 14 day chick embryos. Direct and indirect pathways for chromium(VI)-mediated DNA damage, in the form of Cr-DNA binding and 8-oxo-2'-deoxyguanosine (8-oxo-dG) respectively, were examined in liver and red blood cells of 14 day chick embryos. Levels of hepatic Cr-DNA binding increased in a Cr(VI) dose-dependent manner. Cr-DNA binding in red blood cells was 10-fold lower than in liver, although the Cr-uptake in red blood cells was only 2-fold lower than in liver. The level of 8-oxo-dG formation in red blood cells increased at all Cr(VI) doses tested but peaked at 0.10 mmol Cr(VI)/kg, whereas no increase in 8-oxo-dG levels over background levels was observed in liver of Cr(VI)-treated embryos. The possible role of glutathione in modulating Cr(VI)-induced DNA damage was examined by using L-buthionine-R,S-sulfoximine (BSO) to deplete glutathione. No changes in glutathione levels were observed in either liver or red blood cells of embryos treated with Cr(VI) in the presence or absence of BSO pretreatment. Ascorbate levels in liver and red blood cells were not affected by treatment of embryos with chromium(VI), BSO or Cr(VI) and BSO. Depletion of glutathione by BSO resulted in a small increase of chromium uptake in liver of embryos treated with 0.050 and 0.10 mmol Cr(VI)/kg, but had no effect on hepatic chromium uptake at 0.20 mmol Cr(VI)/kg. BSO had no effect on chromium uptake in red blood cells. Depletion of glutathione had no effect on hepatic or red blood cells Cr-DNA binding in embryos treated with Cr(VI). However, depletion of glutathione significantly decreased the 8-oxo-dG levels in red blood cells at all Cr(VI) doses tested. Levels of 8-oxo-dG in liver of Cr(VI)-treated embryos remained at background in the presence or absence of BSO pretreatment. These results indicate that Cr(VI)-induced DNA damage in 14 day chick embryos is through a direct interaction of chromium with DNA in liver, but is through an indirect oxidative pathway in red blood cells. It appears that glutathione plays an important role in chromium(VI)-induced formation of 8-oxo-dG in red blood cells.

Glutathione metabolism in Crohn's disease

A statistically significant decrease of glutathione (GSH) and an increase of GSH disulfide (GSSG) both in healthy and ill ileum of patients with Crohn's disease in comparison with the controls (without this pathology) is demonstrated. However, the lowering of these levels was more remarkable in ill ileum in which high levels of GSSG were detected, too. These alterations may be in part explained by the changes obtained in GSH-related enzyme levels. Finally, considering the results that others and we obtained by studies on GSH oral absorption in rat intestine, an oral therapy of GSH in Crohn's disease is suggested.

Styrene-induced hepatotoxicity in mice depleted of glutathione

In mice depleted of glutathione (GSH) by pretreatment with an inhibitor of GSH synthesis, buthionine sulfoximine (BSO; 1 hr before styrene, 2 mmol/kg or higher doses, ip), styrene (0.96-5.76 mmol/kg, po) produced hepatotoxicity characterized by an increase in serum alanine transaminase activity and cetrilobular necrosis of hepatocytes. Treatment with inhibitors of hepatic cytochrome P-450-dependent monooxygenases such as carbon disulfide, methoxsalen, piperonyl butoxide, and SKF-525A prevented or tended to reduce the hepatotoxic effect of styrene given in combination with BSO. Styrene 7,8-oxide (3.84 mmol/kg, po), a known metabolite of styrene, in combination with BSO caused an earlier and larger increase in SALT than that caused by an equimolar dose of styrene in combination with BSO. These results suggest that metabolism of styrene, possibly to styrene 7,8-oxide, is a necessary step in styrene-induced hepatotoxicity in GSH-depleted mice. Before the onset of hepatotoxicity, styrene in combination with BSO produced a larger and more prolonged depletion of hepatic GSH than that seen after the sole treatment with BSO or prolonged depletion of hepatic GSH than that seen after the sole treatment with BSO or styrene, but no depletion of hepatic protein sulfhydryls was induced by styrene in combination with BSO.

A role for the human DNA repair enzyme HAP1 in cellular protection against DNA damaging agents and hypoxic stress

The HAP1 protein (also known as APE/Ref-1) is a bifunctional human nuclear enzyme required for repair of apurinic/apyrimidinic sites in DNA and reactivation of oxidized proto-oncogene products. To gain insight into the biological roles of HAP1, the effect of expressing antisense HAP1 RNA in HeLa cells was determined. The constructs for antisense RNA expression consisted of either a full-length HAP1 cDNA or a genomic DNA fragment cloned downstream of the CMV promoter in pcDNAneo. Stable HeLa cell transfectants expressing HAP1 antisense RNA were found to express greatly reduced levels of the HAP1 protein compared to equivalent sense orientation and vector-only control transfectants. The antisense HAP1 transfectants exhibited a normal growth rate, cell morphology and plating efficiency, but were hypersensitive to killing by a wide range of DNA damaging agents, including methyl methanesulphonate, hydrogen peroxide, menadione, and paraquat. However, survival after UV irradiation was unchanged. The antisense transfectants were strikingly sensitive to changes in oxygen tension, exhibiting increased killing compared to controls following exposure to both hypoxia (1% oxygen) and hyperoxia (100% oxygen). Consistent with a requirement for HAP1 in protection against hypoxic stress, expression of the HAP1 protein was found to be induced in a time-dependent manner in human cells during growth under 1% oxygen. The possible involvement of a depletion of cellular glutathione being linked to the hypoxic stress-sensitive phenotype of the antisense HAP1 transfectants came from the finding that they also exhibited hypersensitivity to buthionine sulphoximine, an inhibitor of glutathione biosynthesis. We conclude that the HAP1 protein is a key factor in cellular protection against a wide variety of cellular stresses, including DNA damage and a change in oxygen tension.

Intracellular glutathione (GSH) levels modulate mercuric chloride (MC)- and methylmercuric chloride (MeHgCl)-induced amino acid release from neonatal rat primary astrocytes cultures

Mercuric chloride (MC) and methylmercury (MeHg) were found to increase amino acid release from astrocytes. This suggests interaction with sulfhydryl (-SH) groups which are controlled by glutathione [GSH] levels. In the present study, we evaluated the effects of alterations in intracellular glutathione concentrations [GSH]i on the outcome of MC and MeHg treatment. [GSH]i were increased in a time-dependent fashion by incubating the astrocytes with 1 mM L-2-oxothiazolidine-4-carboxylic acid (OTC), a cysteine precursor. OTC attenuated the release of [2,3-3H]D-aspartic acid from astrocytes exposed to MC- (5 microM) and MeHg-(10 microM). MeHg-induced [3H]D-taurine release was also reduced by pretreatment of astrocytes with OTC. Treatment with BSO (50 microM) decreased [GSH]i in astrocytes, and increased [2,3-3H]D-aspartate release from MC- and MeHg-treated astrocytes, and [3H]D-taurine release from MeHg-treated cells. Neither OTC nor BSO when added to cultures in the absence of MC or MeHg had an effect on amino acid release by astrocytes. The current study underscores both the sensitivity of astrocytes to mercurials in terms of amino acid release and the relationship of these effects of astrocytic [GSH]i.

Effects of N-acetylcysteine and dithiothreitol on glutathione and protein thiol replenishment during acetaminophen-induced toxicity in isolated mouse hepatocytes

Isolated mouse hepatocytes were incubated with 1.0 mM acetaminophen (AA) for 1.5 h to initiate glutathione (GSH) and protein thiol (PSH) depletion and cell injury. Cells were subsequently washed to remove non-covalently bound AA and resuspended in medium containing N-acetylcysteine (NAC, 2.0 mM) or dithiothreitol (DTT, 1.5 mM). The effects of these agents on the replenishment of GSH and total PSH content were related to the development of cytotoxicity. When cells exposed to AA were resuspended in medium containing NAC or DTT, both agents replenished GSH and total PSH content to levels observed in untreated cells but only DTT was able to attenuate cytotoxicity. Addition of the GSH synthesis inhibitor, buthionine sulfoximine (BSO, 1.0 mM, 1.5 h), to cells in incubation medium containing AA, enhanced GSH and total PSH depletion and potentiated cytotoxicity. Resuspension of these cells in medium containing NAC did not alter the potentiating effects of BSO; GSH and PSH levels were not replenished and no cytoprotective effects were observed. However, when cells exposed to AA and BSO were resuspended in medium containing DTT, PSH content was replenished but GSH levels were not restored. In addition, DTT was able to delay the development of cytotoxicity. It appears that DTT, unlike NAC, has a GSH-independent mechanism of PSH replenishment. These observations suggest that while replenishment of GSH and total PSH content does not result in cytoprotection, the regeneration of critical PSH by DTT may play an important role in the maintenance of proper cell structure and/or function.

In vivo production of different chloroform metabolites: effect of phenobarbital and buthionine sulfoximine pretreatment

The regioselective attack on microsomal phospholipid (PL) polar heads (PH) and fatty acyl chains (FC) demonstrated in vitro has been exploited for the selective quantitation in vivo of the biochemical damages produced by the oxidation and reduction products of CHCl3 metabolism. Five hours after CHCl3 injection (60 mg/kg body weight, ip) to control Sprague-Dawley rats, most of the label covalently bound in the liver was associated to PH, indicating a predominant production of COCl2. The levels of radioactivity bound to both PL moieties increased proportionally when 180 mg/kg body weight 14CHCl3 was administered. Buthionine sulfoximine (BSO) pretreatment resulted in a further increase of binding either to PH or FC. The pretreatment of rats with phenobarbital (PB) reduced the PH/FC binding ratio to 3.4, still indicating the predominance of the oxidative metabolism, but giving some indication of the simultaneous presence of CHCl3 reduction. When reduced glutathione (GSH) was depleted by BSO in PB-induced animals prior to 14CHCl3 administration, only the level of radioactivity associated with oxidative intermediates was increased six times. The present results confirmed that GSH is able to exert an efficient protection mainly toward 14CHCl3 oxidation intermediates. Furthermore, they indicate that in the liver of the Sprague-Dawley rat the major pathway of CHCl3 biotransformation is its oxidation and that pretreatment of rats with a GSH-depleting agent (such as BSO) is more relevant than PB induction in enhancing the biochemical damages produced by CHCl3.

p-Dichlorobenzene-induced hepatotoxicity in mice depleted of glutathione by treatment with buthionine sulfoximine

p-Dichlorobenzene (p-DCB) is widely used as a moth repellent and a space deodorant. In mice pretreated with DL-buthionine sulfoximine (BSO; 2 mmol/kg or higher doses, i.p.), an inhibitor of glutathione (GSH) synthesis, administration of p-DCB (100-400 mg/kg, p.o.) resulted in dose-dependent hepatotoxicity as judged by increased serum alanine aminotransferase (ALT) activities and liver calcium concentrations and by histological examination of the liver, p-DCB alone (up to 1200 mg/kg) resulted in no hepatotoxicity. Administration of GSH monoethyl ester, which is known as a useful means for increasing organ GSH levels, protected against the hepatotoxicity caused by p-DCB in combination with BSO. Treatment with inhibitors of hepatic cytochrome P-450-dependent monooxygenases, carbon disulfide, metyrapone and piperonyl butoxide also prevented the hepatotoxicity. These results suggest that p-DCB is activated by a cytochrome P-450-dependent metabolic reaction and that the hepatotoxicity is caused by inadequate rates of detoxification of the resulting metabolite in mice depleted of hepatic GSH by BSO treatment. The liver injury was preceded by an extensive depletion of hepatic GSH but not accompanied by significant changes in hepatic contents of lipid peroxides and protein thiols.

Lead toxicity via arachidonate signal transduction to growth responses in the splenic macrophage

Lead chloride modulated the macrophage cell surface growth signal-transduced, lipid second messenger prostaglandin E2 (PGE2), concomitant with cell differentiation. In virgin macrophage, PGE2 was increased by lead in a dose-dependent manner, suggesting suppression of the immune function (inversely regulated by PGE2). Upon stimulation by bacterial endotoxin, lead-treated cells displayed decreased PGE2 with immune augmentation as tested by zymosan particle ingestion. These effects were simulated by a glutathione synthesis inhibitor around 10 microM lead, and by cycloheximide around 50 microM lead, suggesting a mechanism similar to viral infection.

Exercise-induced oxidative stress: glutathione supplementation and deficiency

Glutathione (GSH) plays a central role in coordinating the synergism between different lipid- and aqueous-phase antioxidants. We documented 1) how exogenous GSH and N-acetylcysteine (NAC) may affect exhaustive exercise-induced changes in tissue GSH status, lipid peroxides [thiobarbituric acid-reactive substances (TBARS)], and endurance and 2) the relative role of endogenous GSH in the circumvention of exercise-induced oxidative stress by using GSH-deficient [L-buthionine-(S,R)-sulfoximine (BSO)-treated] rats. Intraperitoneal injection of GSH remarkably increased plasma GSH; exogenous GSH per se was an ineffective delivery agent of GSH to tissues. Repeated administration of GSH (1 time/day for 3 days) increased blood and kidney total GSH [TGSH; GSH+oxidized GSH (GSSG)]. Neither GSH nor NAC influenced endurance to exhaustion. NAC decreased exercise-induced GSH oxidation in the lung and blood. BSO decreased TGSH pools in the liver, lung, blood, and plasma by approximately 50% and in skeletal muscle and heart by 80-90%. Compared with control, resting GSH-deficient rats had lower GSSG in the liver, red gastrocnemius muscle, heart, and blood; similar GSSG/TGSH ratios in the liver, heart, lung, blood, and plasma; higher GSSG/TGSH ratios in the skeletal muscle; and more TBARS in skeletal muscle, heart, and plasma. In contrast to control, exhaustive exercise of GSH-deficient rats did not decrease TGSH in the liver, muscle, or heart or increase TGSH of plasma; GSSG of muscle, blood, or plasma; or TBARS of plasma or muscle. GSH-deficient rats had approximately 50% reduced endurance, which suggests a critical role of endogenous GSH in the circumvention of exercise-induced oxidative stress and as a determinant of exercise performance.

Development of extended multidrug resistance in HL60 promyelocytic leukaemia cells

In an attempt to mimic clinical conditions for the treatment of leukaemia, the HL60 promyelocytic cell line was treated for 18 h with low, clinically relevant, levels of the anthracycline epirubicin and the Vinca alkaloid vinblastine. The resulting drug-resistant sublines not only expressed P-glycoprotein and the MDR phenotype but were also cross-resistant to chlorambucil, methotrexate and cisplatinum, and had increased resistance to radiation. Development of resistance was associated with an aberrant differentiation phenotype with decreased expression of myeloid antigens and expression of glycophorin A, an antigen normally associated with erythroid differentiation. The ability of HL60 cells to terminally differentiate in response to all-trans-retinoic acid (vitamin A acid) was lost in the sublines. These results suggest that either a single novel mechanism is responsible for multiple drug resistance or the initial response to drug treatment is the co-induction of multiple mechanisms. These cells and the method by which they were generated therefore provide a clinically relevant model for the study of the initial events in the development of not only multidrug resistance but also the extended multiple drug resistance usually encountered in the treatment of leukaemia.

Stereoselective pharmacokinetics of L-buthionine SR-sulfoximine in patients with cancer

Buthionine sulfoximine (BSO) is an inhibitor of glutathione synthesis that can deplete intracellular glutathione and reverse resistance to platinating and alkylating agents in vitro and in vivo. We are performing a phase I study of BSO in combination with melphalan. The BSO used in this study was provided by the National Cancer Institute and is a mixture of the R- and S-diastereomers of L-BSO. We developed a reversed-phase HPLC assay to quantitate levels of the R- and S-BSO isomers in plasma and urine. The pharmacokinetics of BSO was determined in 11 patients: 3 patients at 5 g/m2, 4 patients at 7.5 g/m2, and 4 patients at 10.5 g/m2. Plots of plasma area under the concentration-time curve vs. dose for both R-BSO (r2 = 0.798) and S-BSO (r2 = 0.752) are linear, indicating linear pharmacokinetics in this dose range. However, the individual BSO isomers exhibit stereoselective disposition and elimination. Values for steady-state volume of distribution and renal clearance were similar for both isomers, but total clearance, nonrenal clearance, and half-life were approximately 25% different, with the R-(inactive) isomer being eliminated faster (higher clearance and shorter half-life) than the S- (active) isomer. Using a paired t test, we found that the pharmacokinetic parameters, total clearance, nonrenal clearance, and half-life for R-BSO were significantly different (p < 0.05) from those for S-BSO. Renal clearance of both S- and R-isomers approximated glomerular filtration rate and accounted for 64% of S-BSO total clearance and 56% of R-BSO total clearance.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of sulfhydryl compounds and glutathione depletion on rat heart myocyte toxicity induced by 4-hydroperoxycyclophosphamide and acrolein in vitro

Neonatal rat heart myocytes were used to study the acute cardiotoxic effects of cyclophosphamide (CTX) metabolites. The myocytes were equi-sensitive to 4-hydroperoxycyclophosphamide (4HPC) and acrolein in vitro with 50% inhibitory concentrations (IC50) of 123 microM and 152 microM, respectively. The parent compound, CTX, was inactive and the myocytes were much less sensitive to the bis-chloroethylamine alkylator, mechlorethamine (IC50 = 1161 microM). Cellular glutathione (GSH) levels were initially reduced and then transiently elevated following exposure to 4HPC. With acrolein, GSH levels were reduced to unmeasurable levels at all time points. With the addition of 0.5 mM L-buthionine sulfoximine (BSO), myocyte GSH levels were reduced from control values of 120 nmol/mg protein to < 10 nmol/mg protein without causing direct cytotoxicity. However, pretreatment with BSO significantly enhanced the cardiotoxic effects of 4HPC. Finally, two exogenous sulfhydryl-containing compounds were shown to block the myotoxic effects of both 4HPC and acrolein. Mesna and N-acetylcysteine increased at concentrations of 0.01 microgram/ml and 0.1 microgram/ml roughly increased the IC50 of 4HPC by 2-3-fold. These results suggest that acrolein and 4HPC are equipotent cytotoxins and that a transient depletion in GSH accompanies this toxic effect in cardiac myocytes.

A protective effect of glutathione-dextran macromolecular conjugates on acetaminophen-induced hepatotoxicity dependent on molecular size

Glutathion (GSH) was covalently attached to dextrans with various molecular weights of 2, 5, 10, 40, and 70 kDa by the cyanogen bromide activation method. The conjugates obtained synthetically were white or pale yellowish powders containing 6-10% (w/w) of GSH. The average molecular weights of the conjugates were estimated to be larger and the molecular weight distribution was a little broader than that of each original dextran. The conjugates significantly stabilized GSH and liberated it gradually under physiological conditions (t1/2 = 0.99-1.6h). Mice depleted of GSH by treatment with buthionine sulfoximine, a potent inhibitor of gamma-glutamylcysteine synthetase, exhibited a significant increase in hepatic GSH level after intravenous injection of the conjugates. In mice given a hepatotoxic dose of acetaminophen, the survival rate increased progressively with coadministration of the conjugates, whereas a small improvement was found when free GSH was given. The conjugate of GSH attached to dextran with the molecular weight of 40 kDa exhibited the highest prophylactic effect on acetaminophen-induced hepatotoxicity in mice. The prolonged retention of the conjugates of larger molecular weight in the circulation would cause a higher hepatic accumulation. These results suggested that molecular size would be the most critical factor in the delivery of GSH, as a dextran conjugate, into the liver.

Effect of buthionine sulfoximine on the sensitivity to doxorubicin of parent and MDR tumor cell lines

We have studied the interaction of glutathione-depleting concentrations of buthionine sulfoximine (BSO) with the anti-proliferative activity of doxorubicin (DXR) in three tumor lines, the mouse B16 melanoma. Friend erythroleukemia and the human K562 leukemia, both as DXR-sensitive and-resistant (with typical multidrug resistance) variants. BSO significantly enhanced the DXR effects in the wild-type Friend and K562 leukemias, and especially in the drug-resistant subline of Friend leukemia. BSO did not modify DXR accumulation and retention in the latter clone. Moreover, neither BSO nor verapamil used alone completely reversed the resistance to DXR of this cell line; their combination was more efficient and increased its drug sensitivity to a level closer to that of the parental counterpart. These results seem to indicate that the status of glutathione and of the enzymes related to it contributes to the resistance of Friend leukemia to DXR. An interesting additional finding was that BSO significantly synergizes with the antiproliferative effects of vincristine in the drug-sensitive variants of Friend and K562 leukemias.

[Induction and prevention of kidney injury induced by GSH depletion and vitamin E deficiency in rats]

Four-week-old Wistar male rats were fed a vitamin E (VE)-deficient diet for 8 weeks, followed by intraperitoneal injection of DL-buthionine- [S, R] -sulfoximine (BSO), an inhibitor of gamma-glutamylcysteine synthetase, at the dose of 1 mmol/kg body weight. As we reported previously, GSH depletion by administration of BSO induced acute tubular necrosis in the kidney of VE-deficient rats and was accompanied by decrease of renal TBA value and marked increase of renal lipofuscin content. In this study, we examined the effect of administration of AsA or Trolox C on these kidney injuries. AsA or Trolox C treatment increased renal GSH content and inhibited the increase of renal lipofuscin production. The increase of BUN and creatinine levels and LDH activity in the sera of rats administered BSO were inhibited by AsA or Trolox C treatment. AsA treatment completely protected the necrosis of epithelia of proximal renal tubules. These results suggest that GSH has an important role in preventing lipofuscin production through the reaction of lipid peroxides with amino acids. AsA spares GSH indicating that these compounds have similar antioxidant actions and that AsA can serve as an essential antioxidant in the presence of severe GSH deficiency.

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 leukaemia 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.

Role of gamma-glutamyltranspeptidase-mediated glutathione transport on the radiosensitivity of B16 melanoma variant cell lines

PURPOSE

To elucidate the role of gamma-glutamyltranspeptidase-mediated glutathione transport on the radiosensitivity of B16 melanoma variant cell lines.

METHODS AND MATERIALS

B16 melanoma variant cell lines were examined for their levels of gamma-glutamyltranspeptidase (GGTP; E.C. 2.3.2.2), a plasma membrane-associated ectoenzyme that is involved in the transport of extracellular glutathione, by flow cytometric and biochemical analysis. B16 cell lines were examined for rates of de novo glutathione synthesis from extracellular glutathione and for their sensitivity to gamma-irradiation and glutathione synthesis inhibition. The GGTP inhibitors were examined for their effect on the radiosensitivity of B16 melanoma cells.

RESULTS

B16-F10-BL6 (BL6) melanoma cells were shown to express a 20-fold higher level of GGTP than the B16-F1 melanoma variant cells. Cultures of BL6 and B16-F1 cells depleted extracellular glutathione at rates of 2.4 and < 0.1 nmol glutathione/10(6) cells/h, respectively, and BL6 cells exported glutathione at a rate 7.2-fold higher than B16-F1 cells (710 and 98 pmol glutathione/10(6) cells/h, respectively). BL6 melanoma cells replenished exhausted intracellular glutathione levels from an extracellular glutathione source at a rate of 1.21 nmol glutathione/h (18% basal glutathione/h); however, B16-F1 cells lacked the capacity to replenish intracellular glutathione despite the presence of exogenous glutathione in the culture medium. BL6 melanoma cells were radioresistant compared to the B16-F1 cell line, exhibiting extrapolation numbers (ñ) of 14.9 and 1.0, respectively, and a lower surviving fraction to a wide range of radiation doses. The GGTP inhibitor combination of L-serine and sodium borate blocked the repletion of intracellular glutathione and in the presence or absence of buthionine sulfoximine-mediated depletion of glutathione reverses the radiation resistance in BL6 melanoma cells to near baseline levels observed with the B16-F1 parent clone. Serine-borate treatment of low-GGTP expressing B16-F1 cells had no effect on the ñ value or the surviving fraction of cells to a range of ionizing irradiation doses.

CONCLUSIONS

These results suggest that GGTP plays an important role in the extracellular metabolism and transport of glutathione, which also provides radioresistance to BL6 melanoma cells in vitro.

Inhibitory effect of melatonin on cataract formation in newborn rats: evidence for an antioxidative role for melatonin

We evaluated the inhibitory effect of melatonin, a recently discovered scavenger of free radicals, on cataract formation in the newborn rat. The glutathione synthesis inhibitor, buthionine sulfoximine (BSO) (3 mmol/kg), was intraperitoneally injected into newborn rats for 3 consecutive days starting on day 2 after birth. These glutathione depleted rats develop cataracts. Melatonin (4 mg/kg) was injected intraperitoneally into half of the rats once a day beginning at day 2 after birth; the other half of the animals received solvent daily. The incidence of cataract was observed on day 16, after the eyes of the newborn animals had opened. Both reduced glutathione (GSH) and oxidized glutathione (GSSG) levels were measured. Cataracts were observed in all animals (18/18) treated with BSO plus solvent. The incidence of the cataract in the animals cotreated with melatonin was only 6.2% (1/15). Total lenticular glutathione (GSH + GSSG) levels in BSO only treated rats were reduced by 97%. The total glutathione in the lens of the BSO plus melatonin group was significantly higher (by 3%) than that of the BSO only group. The percentage of the total glutathione as GSSG for the BSO plus solvent group was higher than the control value. Cotreatment of BSO injected rats with melatonin (4 mg/kg/day) clearly reduced cataract formation proving that it is directly or indirectly protective against oxidative stress which accompanies glutathione deficiency. The inhibitory effects of melatonin on cataract formation in this study could be due to melatonin's free radical scavenging activity or due to its stimulatory effect on glutathione production.

The gold anti-rheumatic drug auranofin governs T cell activation by enhancing oxygen free radical production

Gold-containing drugs continue to be used in the treatment of rheumatoid arthritis, but their mode of action remains unknown. One model to explain gold action is that gold-containing compounds can alter free radical production in cells of the immune system, but direct evidence for this hypothesis has been lacking. In this study we show that auranofin can enhance the rapid flux of reactive oxygen species (ROS), which accompanies phytohemagglutinin activation of peripheral blood T cells. Blocking this enhancement by the addition of antioxidants can reverse the functional effects of the drug on T cell responses, which we have previously demonstrated. These results provide strong experimental support for a model in which gold anti-rheumatics act by modulating ROS production. Furthermore, our experiments suggest that auranofin may be a useful tool to investigate the postulated role of ROS in the intra cellular T cell signaling pathway.

Effect of selenium deficiency and glutathione-modulating agents on diquat toxicity and lipid peroxidation in rats

The dipyridyl herbicide diquat undergoes redox cycling in vivo resulting in superoxide generation. Diquat administration causes hepatic and renal toxicity in rodents. Selenium deficiency worsens this injury and lipid peroxidation is a prominent feature of the toxicity. However, there is limited data regarding the role of lipid peroxidation in diquat-induced toxicity in selenium-adequate animals. In addition, little is known about the effect of glutathione-modulating agents on diquat-induced toxicity and lipid peroxidation in vivo. F2-isoprostanes are novel prostanoids which, both free in plasma and esterified to phospholipids in tissues, are markers of lipid peroxidation in vivo. By using F2-isoprostane quantitation, we examined the effects of selenium deficiency and modulation of glutathione status with 1,3-bis (2-chloroethyl)-1-nitrosourea, phorone or buthionine sulfoximine on diquat-induced toxicity and lipid peroxidation. F2-isoprostanes increased 2- to 9-fold in plasma, liver, kidney and lung in selenium-adequate Fischer 344 rats with liver injury after receiving 100 mumol of diquat per kg. Selenium deficiency or modulation of glutathione status increased diquat toxicity. This was accompanied by 10- to 100-fold increases in plasma and kidney F2-isoprostane levels. Liver F2-isoprostanes were increased 2- to 5-fold. These studies suggest that glutathione, in addition to selenium, is an important defense against diquat-induced toxicity and lipid peroxidation.

Effect of doxorubicin on glutathione and glutathione-dependent enzymes in cultured rat heart cells

The effect of doxorubicin (DOX) on heart cell glutathione (GSH)-based enzyme systems was investigated in a rat heart myocyte model. Cellular levels of GSH decreased commensurate with viability following exposure to DOX or to the unrelated alkaloidal cardiotoxin emetine. GSH depletion by L-buthionine sulfoximine (L-BSO) did not alter myocyte viability nor doxorubicin (DOX) dose-response. The nitrosourea carmustine (BCNU), which impairs GSH reductase activity, also did not alter DOX cardiotoxicity. Doxorubicin significantly increased glutathione-S-transferase (GST) activity in a time-dependent fashion. In contrast, selenium-dependent glutathione peroxidase activity was reduced by 50%. These findings demonstrate that lowered GSH or GSH reductase levels do not enhance DOX cardiotoxicity in vitro and suggest that DOX may be a substrate for GST.

Methylene chloride: an inhalation study to investigate toxicity in the mouse lung using morphological, biochemical and Clara cell culture techniques

Single exposures of mice to methylene chloride (MC) cause vacuolation and necrosis of the bronchiolar Clara cells which subsequently recover normal morphology on continued exposure. Both cytochrome P-450 (CYP)- and glutathione S-transferase (GST)-dependent metabolism of MC are known to occur. The current studies have investigated the metabolism of MC in mouse lung using inhibitors of both GST and CYP-dependent routes of metabolism, the consequences of metabolic inhibition on the Clara cell vacuolation, and any changes in cell proliferation, assessed in vitro, in Clara cells cultured from exposed individuals. Vacuolated bronchiolar cells were seen in mice exposed to 2000 and 4000 ppm MC but were not seen at lower concentrations, while addition of the CYP inhibitor, piperonyl butoxide, significantly reduced the bronchiolar cell vacuolation seen following exposure to 2000 ppm MC. Treatment of mice with the glutathione depletor, buthionine sulphoximine, had no effect on the number of vacuolated bronchiolar cells following MC. Exposure of mice to 1000 ppm MC and above for 6 h caused a burst of DNA synthesis in bronchiolar Clara cells cultured in vitro from the lungs of exposed animals. The results suggest that the Clara cell vacuolation following MC exposure is mediated via CYP metabolism, that depression of the CYP metabolic pathway occurs following exposure, and that Clara cell vacuolation may have a priming role in stimulating cell proliferation in the unaffected cell population.

Sensitive enzymatic cycling assay for glutathione: measurements of glutathione content and its modulation by buthionine sulfoximine in vivo and in vitro in human colon cancer

We have measured glutathione content in small tissue samples derived from biopsies of primary and metastatic human colon tumors and from colon cancer cell lines in tissue culture and xenografts in athymic mice. Measurements were performed using an enzymatic cycling assay designed to quantitate extremely low levels of glutathione (GSH) (down to 10(-14) mol) from perchlorate extracts of tissue samples weighing less than 1 mg wet weight. Glutathione was stable in these acid extracts for at least 6 months when stored at -80 degrees C. A survey of normal tissues in mice, rats, and some human tissues showed considerable variation in GSH content of different tissues but generally similar levels were identifiable for the same tissues from different species. The highest GSH level was 56.9 nmol/mg protein in rat liver and the lowest was 1.8 nmol/mg protein in rat skeletal muscle. High GSH levels were also determined in mouse and human liver, while low GSH levels were detected in mouse muscle. Human colon cancer cell lines showed slightly higher GSH levels than did colon cancer tumor samples obtained from biopsies. These studies revealed a marked inter-individual difference in tumor GSH content, as well as a difference in GSH content between tumor deposits at different metastatic sites in the same individual. These results indicate the importance of direct tumor measurements of GSH content in clinical trials designed to modulate tumor glutathione content to try to increase sensitivity to chemotherapy or radiation therapy. Buthionine sulfoximine, an inhibitor of gamma-glutamyl cysteine synthetase, was shown to produce almost complete depletion of GSH in four different human colon cancer cell lines in 24 h. Buthionine sulfoximine was also shown to be capable of producing drastic depletion of GSH in human colon cancer grown as xenografts in athymic animals.

Intracellular glutathione influences collagen generation by mesangial cells

The cellular redox state is altered in a number of pathological conditions, including various forms of glomerular injury and diabetes. For example, glucose, via the pentose phosphate pathway generates NADPH, which maintains glutathione (GSH) (part of a major intracellular reducing system) in its reduced state. GSH in turn influences the activity of transcription factors on gene expression. We therefore examined whether changes in cellular GSH influence total collagen synthesis and mRNA levels for collagen I, collagen IV and TGF-beta in SV-40 transformed mouse mesangial cells (MC) maintained in either 5 or 25 mM glucose media. Total intracellular GSH was increased by N-acetylcysteine (NAC; 10 mM) or decreased with the GSH synthesis inhibitor buthionine sulfoximine (BSO; 0.2 mM) in MC. NAC increased 3H-proline incorporation into collagenase-sensitive protein while BSO decreased it under both glucose conditions. The presence of BSO did not reverse the increased collagen synthesis seen in the NAC stimulated cells. Northern blot analysis showed increased mRNA levels for collagen I, collagen IV and TGF-beta in cells grown in high glucose (25 mM). NAC increased the mRNA for all three compounds while BSO alone had no effect on these mRNA levels. However, BSO reversed the increased mRNA levels for collagen I, IV and TGF-beta seen in the presence of NAC. These findings suggest that the cellular redox state may influence gene transcription in MC, and may have implications in explaining injury-associated alterations of mesangial matrix generation.

The effect of L-buthionine-[S,R]-sulfoximine on the pancreas in mice. A model of weakening glutathione-based defense mechanisms

L-Buthionine-[S,R]-Sulfoximine (BSO) decreases glutathione levels in various organs by inhibition of gamma-glutamylcysteine synthetase. We have examined the levels of total glutathione and oxidized glutathione in the pancreas of mice, as well as serum amylase and pancreatic histology, after BSO administration in two different ways. The injection of a single dose of BSO (5 mmol/kg body wt) decreased total glutathione to 10% of the control value. A similar depletion was observed after 24 h of oral administration of a 10 mM BSO solution, without changes in the levels of oxidized glutathione. BSO-induced pancreatic glutathione depletion--even if maintained for up to 14 d--did not cause morphological alterations of the pancreas or hyperamylasemia. Thus pancreatic glutathione depletion in itself does not lead to pancreatitis, although during development of experimental acute pancreatitis, glutathione depletion has been described. BSO might be used in animal models to weaken the glutathione-based acinar defense mechanisms against oxidant stress or to alter other physiologic processes in which glutathione is involved.

Glutathione precursor and antioxidant activities of N-acetylcysteine and oxothiazolidine carboxylate compared in in vitro studies of HIV replication

N-Acetyl-L-cysteine (NAC) and L-2-oxothiazolidine 4-carboxylate (OTC) are pro-GSH drugs that been proposed for AIDS therapy. In this article we compare the antiviral activities of these compounds in various in vitro HIV infection models. Although both compounds blocked cytokine induction of HIV in acute and chronic infection models, and in HIV-LTR reporter cell systems, NAC was far more effective than OTC, even at suboptimal doses. To test whether this difference is due to GSH conversion efficacies of these compounds, we measured GSH restoration by NAC or OTC in GSH-depleted peripheral blood mononuclear cells (PBMCs), using flow cytometry. In isolated PBMCs, NAC fully replenishes depleted intracellular GSH whereas OTC only minimally replenishes GSH. This ability to replenish GSH in vitro and its ability to scavenge free radicals directly explain why NAC has more potent antiviral activities in vitro.

A model for fatal halothane hepatitis in the guinea pig

BACKGROUND

In the guinea pig, depleting hepatic glutathione before inhaling subanesthetic 0.1% halothane increases covalent binding of halothane biotransformation intermediates to hepatic protein and potentiates resultant liver injury. Because inhalation of a higher concentration of halothane is known to produce greater levels of covalent binding than with subanesthetic halothane, this study was undertaken with 0.25-1.0% halothane concentrations to further examine glutathione depletion as an etiology for halothane hepatitis.

METHODS

Male Hartley guinea pigs were injected intraperitoneally with either vehicle control solution (Veh) or 1.6 g/kg buthionine sulfoximine (BSO), to decrease hepatic glutathione by > 80%, 24 h before a 4-h exposure to 0.25%, 0.5%, or (v/v) halothane with 40% O2. Some BSO-pretreated animals also received 2.0 g/kg glutathione monoethyl ester (GEE), intraperitoneally, 2 h before inhaling halothane to replenish hepatic glutathione.

RESULTS

Glutathione-depleted animals developed significantly worse hepatic injury with each halothane concentration. One-third to one-half of BSO+halothane-treated animals developed fatal submassive to massive hepatic necrosis. Covalent binding of halothane intermediates to hepatic protein increased by 45% in BSO + 1.0% halothane-treated guinea pigs. Administration of GEE to BSO-pretreated animals before 1.0% halothane decreased binding to protein and blunted development of liver necrosis. Following Veh + 1.0% halothane, hepatic glutathione was found to be decreased by 60%.

CONCLUSIONS

Glutathione would appear to help protect hepatocytes to some degree from covalent binding by reactive halothane biotransformation intermediates. These studies present the first animal model to produce fatal halothane-induced hepatic necrosis.

Neuroprotection by glial cells through adult T cell leukemia-derived factor/human thioredoxin (ADF/TRX)

Adult T cell leukemia-derived factor (ADF) is a human homologue of thioredoxin (TRX) with many biological functions and is induced by various stimuli and stress. In the central nervous system (CNS), expression of ADF/TRX occurs in glial cells during ischemia and reperfusion. We showed that ADF/TRX was actively released from U251 astrocytoma cells upon exposure to a low concentration of H2O2. The addition of conditioned medium from H2O2-stimulated U251 cells or recombinant ADF (rADF) to the culture medium promoted the survival of neurons from embryonic mouse cortex and striatum, but the addition of mutant ADF (mADF), which has no reducing activity, did not. In addition to rADF, incubation with two other thiol compounds, 2-mercaptoethanol (2-ME) and N-acetyl-L-cysteine (NAC), also increased the neuronal cell survival rate. In contrast, L-buthionine-(S,R)-sulfoximine (BSO), which inhibited the synthesis of glutathione (GSH), decreased the neuronal cell survival rate. Intracellular GSH was increased by incubation with rADF for 24 h, as it is with 2-ME and NAC. Redox active molecules such as thiol compounds may be survival factors for central neurons in vitro, and this capacity may be supplied by endogenous molecules, such as ADF/TRX and glutathione, under certain pathologic conditions in vivo.

Radiation resistance in a melphalan-resistant subline of a rat mammary carcinoma

A subline of a rat mammary carcinoma (MATB 13762), selected for resistance to melphalan, is cross-resistant to other alkylating drugs, to unrelated drugs and to ionizing radiation. The difference in radioresponse between the sensitive wild-type cell line and the melphalan- and radiation-resistant line (MLNr) is related to the size of the alpha component in the linear-quadratic model. Reduction of dose rate does not affect the response of MLNr cells but does increase survival for wild-type cells. MLNr cells have elevated levels of reduced glutathione (GSH) and overexpress redox enzyme glutathione-S-transferase and glutathione peroxidase. Modest depletion of GSH (to 50% of control) radiosensitizes MLNr cells but not wild-type cells. On the basis of the results of an excision assay, growth delay and tumor control experiments, MATB MLNr tumors are also more radioresistant than wild-type cells when irradiated in situ. However, wild-type cells irradiated shortly after excision of the tumor are much more radioresistant than the same cells irradiated 24 h after excision or maintained in culture, and their response resembles that of MLNr cells irradiated under the same conditions. These results suggest that, in spite of some similarity between in vivo and in vitro observations, intrinsic radioresistance is not the most important factor influencing the response of MLNr cells in vivo.

A role for gamma-glutamyl transpeptidase in the transport of cystine into human endothelial cells: relationship to intracellular glutathione

The mechanism of uptake of cystine into human umbilical vein endothelial (HUVE) cells was further investigated. Previous experiments have suggested that the uptake of cystine into HUVE cells is mediated by the Xc- anionic amino acid transporter. However, in our experiments, the accumulation of cystine into confluent HUVE cells was not fully inhibited by anionic amino acids, such as glutamate, aminoadipate and homocysteate. On the other hand, inhibitors of gamma-glutamyl transpeptidase (gamma-GT), such as anthglutin and AT-125, were also effective inhibitors of cystine accumulation in these human cells. Indeed, incubation of HUVE cells with anthglutin effectively depleted cellular glutathione (GSH) in association with inhibition of cystine uptake. A dose-dependent inhibitory effect of anthglutin on the initial rate of accumulation of cystine into control HUVE cells was also confirmed, which was also dependent on the carrier concentration of the disulfide. Additionally, in an effort to relate the uptake of cystine and the levels of GSH in these human cells, the incubation of HUVE cells with diethylmaleate (DEM, 25 microM) was shown to stimulate the uptake of cystine by up to 200% over the first hour of incubation, irrespective of whether DEM was coincubated or preincubated with the cells for 60 min before the addition of cystine. Under these conditions the stimulation was not associated with extensive depletion of cellular GSH. Depletion of HUVE cell GSH by an 18 h incubation in M199 medium lacking sulfur amino acids (M199-medium) also stimulated the uptake of cystine by up to 300%, which was dependent on de novo protein biosynthesis. On the other hand, the depletion of HUVE cell GSH by an 18 h preincubation with buthionine sulfoximine did not stimulate cystine uptake above controls. Again, both the anionic amino acids and the inhibitors of gamma-GT were effective in inhibiting the accumulation of cystine into M199-medium-pretreated HUVE cells, in association with impaired resynthesis of GSH. Anthglutin also dose-dependently inhibited the initial cystine uptake rate into these M199-medium-pretreated cells by a proportionally similar extent to its effects in control cells. This also indicates that gamma-GT-dependent uptake of cystine accounts for a portion of the induced uptake of this disulfide into these M199-medium-pretreated cells. These results indicate that both the Xc- carrier and gamma-GT are involved in the uptake of cystine into these human endothelial cells, illustrating another important physiological role for gamma-GT in the uptake of cystine from the circulation into the human endothelium.(ABSTRACT TRUNCATED AT 400 WORDS)

The role of glucose in cellular defences against cytotoxicity of hydrogen peroxide in Chinese hamster ovary cells

The presence of glucose in the cellular environment influences the response of cells to hydrogen peroxide. This study examines the effect of glucose on clonogenic cell survival of Chinese hamster ovary cells exposed to micromolar concentrations of exogenous hydrogen peroxide. Exposure to hydrogen peroxide (20 mumol/10(7) cells) resulted in considerable cytotoxicity that was unaffected by the presence or absence of glucose. However, glucose protected the cells from killing induced by milder exposure (1 mumol/10(7) cells) to the oxidant causing a shift in the dose-response curve. This effect was considered in terms of glucose metabolism via the pentose phosphate cycle. A low nontoxic concentration of hydrogen peroxide (0.1 mumol/10(7) cells) markedly increased pentose phosphate cycle activity in normal cells. Clonogenic survival and activity of the cycle for cells depleted of total glutathione to about 8.6% of its initial value and/or with catalase activity reduced to about 10% of control levels were also determined. Neither of these modifications alone completely abolished the protective effect of glucose. Efficacy of glucose protection against cytotoxicity of hydrogen peroxide diminished in cells depleted of glutathione, and this was not accompanied by any detectable increase in pentose phosphate cycle activity above the control level. Cells depleted of catalase alone had a profile of survival and pentose phosphate cycle activity similar to that of control cells when exposed to hydrogen peroxide. Cells depleted of both glutathione and catalase were almost as sensitive to hydrogen peroxide as the cells incubated without glucose. They also did not express any detectable increase in pentose phosphate cycle activity. Survival of those cells, when exposed to hydrogen peroxide, was almost the same regardless if glucose was present or not. These results demonstrate an important role for the glutathione redox cycle, catalase, and the pentose phosphate cycle in protection against hydrogen peroxide in Chinese hamster ovary cells. They confirm the essential role of glucose and pentose phosphate cycle activity for the detoxification of hydrogen peroxide via the glutathione redox cycle. The data suggest that the ability of catalase to metabolise peroxide may also depend on metabolism of glucose via the pentose phosphate cycle. A clear understanding of the protective mechanisms in cells against hydrogen peroxide has many applications since this common reactive oxygen species is implicated in several pathophysiologies and in the action of certain chemotherapeutic drugs.

Macromolecular synthesis inhibitors prevent oxidative stress-induced apoptosis in embryonic cortical neurons by shunting cysteine from protein synthesis to glutathione

Although macromolecular synthesis inhibitors have been demonstrated to prevent neuronal apoptosis in a number of paradigms, their mechanisms of protection remains unclear. Recently, we found that neuronal death resulting from cystine deprivation, glutathione loss, and oxidative stress is apoptotic and is prevented by inhibitors of macromolecular synthesis. We now report that protection is associated with enhanced availability of acid-soluble cyst(e)ine and restoration of cellular glutathione levels. N-acetylcysteine, an agent that delivers exogenous cysteine intracellularly and raises glutathione, is also protective, while buthionine sulfoximine, an inhibitor of glutathione synthesis, prevents protection by inhibitors of macromolecular synthesis. These results suggest that protection provided by these agents, in this paradigm, derives from shunting of the amino acid cysteine from global protein synthesis into the formation of the antioxidant glutathione.

[Potentiation of cisplatin sensitivity of cisplatin-resistant human ovarian cancer cell lines by L-buthionine-S,R-sulfoximine]

We established two human ovarian cancer cell lines (KK and MH) from the ascites of patients who did not respond to cisplatin (CDDP)-based combination chemotherapy. These cell lines showed higher resistance to CDDP in vitro than HRA cells which were established previously in our laboratory, and also have cross resistance with its analogues. The amount of intracellular glutathione (GSH) in these cells correlated with the degree of resistance to CDDP and was high, but the intracellular platinum (Pt) uptake was unchanged. Preincubation with L-buthionine-S,R-sulfoximine (BSO) reduced cellular GSH in these cells to 9-25%, while the Pt uptake remained unchanged. When the CDDP-resistant KK and MH cells were incubated in the presence of 10 microM BSO, they were sensitized to CDDP and its analogues showing a decrease to 79-38% in the IC50 values. On the basis of these results, we conclude that GSH may be involved in the mechanisms of resistance to CDDP and its analogues in the KK and MH cells.

An investigation of the role of glutathione in increased epithelial permeability induced by cigarette smoke in vivo and in vitro

Airspace epithelial permeability is known to increase in cigarette smokers. To study the role of the antioxidant reduced glutathione (GSH) in this phenomenon, we used an in vitro model of the epithelial permeability of a monolayer of human type II alveolar epithelial cells (A549 cell line). Both whole (WSC) and vapor (VSC) smoke condensates induced a recoverable, concentration-dependent increase in epithelial permeability to 125iodine-labeled bovine serum albumin (125IBSA), associated with a profound fall in intracellular GSH. Buthionine sulfoximine (BSO), a GSH synthesis inhibitor, decreased GSH levels in A549 epithelial cells, significantly increased A549 epithelial cell permeability, and enhanced both WSC and VSC-induced A549 epithelial cell permeability. Co-culturing epithelial cells and GSH (500 microM) reduced WSC-induced, but not VSC-induced A549 epithelial cell permeability. Increasing intracellular GSH also ameliorated the smoke-induced increased epithelial permeability. Concentrations of cigarette smoke condensate of < 20% increased A549 epithelial cell permeability without associated cell detachment and lysis, which was also the case with BSO-induced increased epithelial permeability. WSC and VSC, instilled intratracheally, significantly increased rat lung epithelial permeability to 125IBSA, 6 h postinstillation, associated with a significant recruitment of neutrophils into the airspaces. This was associated with a small increase in GSH in the lung tissue of VSC-treated rats. However, both WSC and VSC markedly reduced GSH in bronchoalveolar lavage (BAL) fluid. Reduction in lung GSH to 95% but not to 68% of control values by BSO increased lung epithelial permeability in vivo. However, there was no additive effect on epithelial permeability of WSC and BSO.(ABSTRACT TRUNCATED AT 250 WORDS)

Enhanced radiation-sensitivity by preincubation with nitroimidazoles: effect of glutathione depletion

PURPOSE

The mechanism of enhanced radiosensitization by nitroheterocyclics after a preincubation period under hypoxic conditions was investigated. The hypothesis that this phenomenon was caused by glutathione depletion was tested.

METHODS AND MATERIALS

The phenomenon of enhanced radiosensitization by nitroheterocyclics after a preincubation period under hypoxic conditions is potentially of importance therapeutically because essentially nonlethal preradiation exposures to the electron affinic drugs cause a much larger radiation sensitization than would otherwise be expected. We have investigated this interesting property of several 2-nitroimidazoles to determine its possible cause and to test various hypotheses about maximizing its possible therapeutic benefit. In view of many observations that thiols are depleted by incubation of cells with nitroimidazoles under hypoxic conditions, we have specifically investigated this aspect of the preincubation effect. Depletion of glutathione was either enhanced by an overnight incubation with buthionine sulfoximine or minimized by preincubation with a 2-nitroimidazole which is sterically inhibited from causing thiol depletion.

RESULTS

When conditions were chosen which minimized variations in cellular glutathione content during the preincubation period, no preincubation effect was observed. At low, therapeutically relevant radiation doses, where 2-nitroimidazoles are less efficient sensitizers, the preincubation effect may be even more important, but thiol depletion still minimizes its impact in this region of the dose-response curve.

CONCLUSION

These results suggest that the preincubation effect is caused by a "self-sensitization" involving the known enhancement of radiation sensitization by thiol depletion.

Selective in vivo accumulation of N-acetyl-4-S-cysteaminylphenol in B16F10 murine melanoma and enhancement of its in vitro and in vivo antimelanoma effect by combination of buthionine sulfoximine

In order to develop a new chemotherapeutic agent based on exploitation of the specific metabolic pathway of malignant melanoma, a phenolic thioether, N-acetyl-4-S-cysteaminylphenol (NA-CAP), the substrate of melanin-forming enzyme, tyrosinase was developed. Our previous in vivo studies have clearly shown that this compound has a significant and selective melanocytotoxicity and antimelanoma effect. This study further examined the specificity of the antimelanoma effect of NA-CAP through the study of biodistribution and accumulation of NA-CAP in B16F10 melanoma-bearing mice. We also tested the antimelanoma effect of NA-CAP by combination treatment with buthionine sulfoximine on the growth of in vitro culture cells and in vivo B16F10 melanoma lung colonies. We found a selective accumulation of 14C-labeled NA-CAP into s.c. transplants and lung colonies of melanoma grown in C57BL mice. This accumulation was mediated by selective covalent binding of NA-CAP to the melanoma tissues. The combination of NA-CAP and buthionine sulfoximine significantly increased the chemosensitivity of B16F10 melanoma cells in vitro and reduced the number of in vivo melanoma lung colonies. We conclude that NA-CAP acts as an alkylating agent to melanoma tissue and that the combination of buthionine sulfoximine enhances the therapeutic index of this potent melanoma-specific drug through the depletion of tissue glutathione.

Selective toxicity of buthionine sulfoximine (BSO) to melanoma cells in vitro and in vivo

PURPOSE

Glutathione (GSH) was found to occur in relatively high concentrations in melanoma cells. The purpose of this study was to test the possible cytotoxic effects of an artificial decrease of the elevated GSH level.

METHODS AND MATERIALS

The tests were made in vitro and in vivo. In the former case, a total of 11 rodent and human cell lines were studied of which seven were derived from melanomas. After treatment with buthionine sulfoximine (BSO), the decrease of GSH content of the cells and their clonogenic survival was determined. In the in vivo system, single cell suspensions of a subline of the B16 mouse melanoma were injected intravenously into immunocompetent and preirradiated recipients which were subsequently treated with BSO intraperitoneally. Survival time, formation of lung colonies and the weight of metastatic tumor mass in the lungs were the criteria of the BSO effect on the tumor cells.

RESULTS

The decrease of the GSH level by BSO was associated with impaired clonogenic survival of the melanoma cells in vitro. Nonmelanoma cells were less affected. BSO treatment of mice inoculated intravenously with melanoma cells resulted in prolonged survival of the animals and impaired metastatic spread of the tumor cells.

CONCLUSION

Melanoma cells are particularly sensitive to disturbance of GSH metabolism by treatment with BSO. In view of this selective cytotoxicity of BSO, treatment with this substance may afford a promising therapeutic potential for melanoma.

The toxic effects, GSH depletion and radiosensitivity by BSO on retinoblastoma

Retinoblastoma is the most common intraocular malignant tumor in children. Previous investigations have reported that buthionine sulfoximine (BSO) can deplete intracellular glutathione (GSH) by specific inhibition and increase cellular radiosensitivity. The toxic effects, GSH depletion and radiosensitivity of BSO on retinoblastoma cells are reported in this paper. GSH content of retinoblastoma cell lines Y-79, So-Rb50 and retinoblastoma xenograft is 2.7 +/- 1.3 x 1.0(-12) mmol/cell, 1.4 +/- 0.2 x 1.0(-12) mmol/cell, and 2.8 +/- 1.2 mumol/g, respectively. The ID50 of BSO on Y-79 and So-Rb50 in air for 3 h exposure is 2.5 mM and 0.2 mM, respectively. GSH depletion by 0.1 mM BSO for 24 h on Y-79 cells and 0.01 mM BSO for 24 h on So-Rb50 cells is 16.35%, and 4.7% of control. GSH depletion in tumor and other organ tissues in retinoblastoma-bearing nude mice after BSO administration is differential. GSH depletion after BSO exposure in Y-79 cells in vitro decreases the Do value of retinoblastoma cells. The SER of 0.01 mM and 0.05 mM BSO for 24 h under the hypoxic condition is 1.21 and 1.36, respectively. Based on these observations, the authors conclude that BSO toxicity on retinoblastoma cells depends on the characteristics of cell line and that BSO can increase hypoxic retinoblastoma cells' radiosensitivity in vitro. Further study of BSO radiosensitization on retinoblastoma in vivo using nude mouse xenograft is needed.

Pharmacodynamics of prolonged treatment with L,S-buthionine sulfoximine

PURPOSE

To develop dosing criteria for the use of L-buthionine-S-sulfoximine (active diastereoisomer) as a glutathione depletor in the clinic, using a pharmacodynamic and pharmacokinetic in vitro-in vivo approach.

METHODS AND MATERIALS

In vitro: L-buthionine-S-sulfoximine uptake was determined in human glioblastoma cells (T98G) and NIH-3T3 cells using 35S-labeled drug. Dose response relationships were derived for inhibition of glutathione synthesis in CHO cells, and for depletion of glutathione in exponentially growing T98G and CHO cells, as a function of extracellular L-buthionine-S-sulfoximine concentration. Steady-state glutathione levels for CHO and NIH-3T3 cells were measured using an enzymatic assay, while glutathione synthesis rates in CHO cells were determined using a flow cytometric assay. In vivo: L-buthionine-S-sulfoximine biodistribution was determined in male nude mice carrying human glioblastomas (T98G) intracranially, using 35S-labeled drug infused subcutaneously by osmotic pump. Tissue glutathione levels were measured using an enzymatic assay.

RESULTS AND CONCLUSION

The observed cellular uptake t1/2 of approximately 55 min, coupled with a previously reported, rapid in vivo clearance of buthionine sulfoximine, suggest that continuous infusion would be preferable to bolus dosing. Effective concentrations of L-buthionine-S-sulfoximine (24 h exposure), required to lower cellular glutathione content to 50% of control (EC50), were under 1 mM for both cell lines. The amount of L-buthionine-S-sulfoximine in tissues (estimated from 35S drug disposition) reached steady state within 8 h and was proportional to the rate of infusion. Brain tumors were depleted to approximately 50% of control glutathione by a infusion rate of 0.25 mumoles/h (25 g mice). At lower infusion rates an increase in glutathione content was noted in certain nude mouse tissues including brain tumor xenografts.