Buthionine sulfoximine and chemoresistance in cancer treatments: a systematic review with meta-analysis of preclinical studies

Buthionine sulfoximine (BSO) is a synthetic amino acid that blocks the biosynthesis of reduced glutathione (GSH), an endogenous antioxidant cellular component present in tumor cells. GSH levels have been associated with tumor cell resistance to chemotherapeutic drugs and platinum compounds. Consequently, by depleting GSH, BSO enhances the cytotoxicity of chemotherapeutic agents in drug-resistant tumors. Therefore, the aim of this study was to conduct a systematic review with meta-analysis of preclinical studies utilizing BSO in cancer treatments. The systematic search was carried out using the following databases: PubMed, Web of Science, Scopus, and EMBASE up until March 20, 2023, in order to collect preclinical studies that evaluated BSO, alone or in association, as a strategy for antineoplastic therapy. One hundred nine investigations were found to assess the cytotoxic potential of BSO alone or in combination with other compounds. Twenty-one of these met the criteria for performing the meta-analysis. The evidence gathered indicated that BSO alone exhibits cytotoxic activity. However, this compound is generally used in combination with other antineoplastic strategies, mainly chemotherapy ones, to improve cytotoxicity to carcinogenic cells and treatment efficacy. Finally, this review provides important considerations regarding BSO use in cancer treatment conditions, which might optimize future studies as a potential adjuvant antineoplastic therapeutic tool.

Progressive neuronal activation accompanies epileptogenesis caused by hippocampal glutamine synthetase inhibition

Loss of glutamine synthetase (GS) in hippocampal astrocytes has been implicated in the causation of human mesial temporal lobe epilepsy (MTLE). However, the mechanism by which the deficiency in GS leads to epilepsy is incompletely understood. Here we ask how hippocampal GS inhibition affects seizure phenotype and neuronal activation during epilepsy development (epileptogenesis). Epileptogenesis was induced by infusing the irreversible GS blocker methionine sulfoximine (MSO) unilaterally into the hippocampal formation of rats. We then used continuous video-intracranial electroencephalogram (EEG) monitoring and c-Fos immunohistochemistry to determine the type of seizures and spatial distribution of neuronal activation early (1-5days postinfusion) and late (16-43days postinfusion) in epileptogenesis. Early in epileptogenesis, seizures were preferentially mild (stage 1-2), activating neurons in the entorhinal-hippocampal area, the basolateral amygdala, the piriform cortex, the midline thalamus, and the anterior olfactory area. Late in epileptogenesis, the seizures were generally more severe (stages 4-5) with neuronal activation extending to the neocortex, the bed nucleus of the stria terminalis, the mediodorsal thalamu\s, and the central nucleus of the amygdala. Our findings demonstrate that inhibition of GS focally in the hippocampal formation triggers a process of epileptogenesis characterized by gradual worsening of seizure severity and involvement of progressively larger neuronal populations over a period of several weeks. Knowledge about the underlying mechanism of epileptogenesis is important because such knowledge may result in more specific and efficacious treatments of MTLE by moving away from large and poorly specific surgical resections to highly targeted surgical or pharmacological interventions of the epileptogenic process.

Effect of combined treatment of thioperamide with some antiepileptic drugs on methionine-sulfoximine induced convulsions in mice

Methionine-sulfoximine (MSO), a convulsant is known to increase the activity of histamine N-methyl transferase. The effect of a selective H3 receptor agonist R- (alpha) methylhistamine (RAMH) and antagonist (thioperamide, THP) and some antiepileptic drugs (gabapentin and sodium valproate) have been evaluated on MSO-induced convulsions in mice. The effect of THP was also evaluated in combination with these antiepileptic drugs. Sodium valproate (300 mg/kg, po) and gabapentin (400 mg/kg, po) offered protection against MSO-induced convulsions as evidenced by a significant prolongation of latency to abnormal dorsoflexion and complete protection against mortality within 6 h of administration. THP (15 mg/kg, ip) alone and in combination with sub-effective doses of gabapentin (75 mg/kg, po) and sodium valproate (75 mg/kg, po) revealed no significant differences from the control group or either drug alone. Hence, the convulsant action of MSO does not appear to be mediated via histaminergic mechanisms.

Poisoning by Cnestis ferruginea in Casamance (Senegal): An etiological approach

Since several years, in the area of Kabrousse in Casamance (Senegal), a neurotoxic syndrome has caused more than 50 human deaths. Field studies showed that epidemic could be due to consumption of leave decoction of Cnestis ferruginea, a tropical plant belonging to the Connaraceae family. An ethnobotanical study has been conducted in order to investigate the traditional uses of C. ferruginea, and describe the circumstances and the symptoms of this plant poisoning. As a first experimental approach, the leave decoction was tested for its ability to induce cytotoxic effects using the XTT method. A phytochemical approach revealed the presence of methionine sulfoximine (MSX), a neurotoxic amino acid, in the plant extract by gas chromatography-mass spectrometry (GC-MS). The description of this poisoning, the cytotoxic activity of the decoction and the occurence of MSX in leaves of C. ferruginea constituted the first etiological data on this poisoning.

An astrocyte toxin influences the pattern of breathing and the ventilatory response to hypercapnia in neonatal rats

Recent in vitro data suggest that astrocytes may modulate respiration. To examine this question in vivo, we treated 5-day-old rat pups with methionine sulfoximine (MS), a compound that alters carbohydrate and glutamate metabolism in astrocytes, but not neurons. MS-treated pups displayed a reduced breathing frequency (f) in baseline conditions relative to saline-treated pups. Hypercapnia (5% CO(2)) increased f in both groups, but f still remained significantly lower in the MS-treated group. No differences between treatment groups in the responses to hypoxia (8% O(2)) were observed. Also, MS-treated rats showed an enhanced accumulation of glycogen in neurons of the facial nucleus, the nucleus ambiguus, and the hypoglossal nucleus, structures that regulate respiratory activity and airway patency. An altered transfer of nutrient molecules from astrocytes to neurons may underlie these effects of MS, although direct effects of MS upon neurons or upon peripheral structures that regulate respiration cannot be completely ruled out as an explanation.

Chronic inhibition of glutamine synthetase is not associated with impairment of learning and memory in mice

The convulsant methionine sulfoximine (MSO) is a byproduct of the agenized flour commonly used for feeding domestic animals decades ago. MSO is a powerful glycogenic and epileptogenic agent, and it is an irreversible inhibitor of glutamine synthetase. This latter effect was hypothesized to be responsible for the increase in the incidence of some neuropathologies in humans, such as Alzheimer's disease or Parkinson's disease. In order to test this hypothesis, we chronically administered MSO to two inbred strains of mice, C57BL/6J and BALB/cJ, and analyzed possible alterations in learning and memory features of these mice. Mice were given 20 mg/kg of MSO three times a week for 10 weeks. Spatial learning capabilities assessed with a radial maze were not affected by the long-term MSO treatment, although activity was significantly decreased in BALB/cJ mice. Thus, our data suggest that long-term administration of non-convulsive and non-glycogenic doses of MSO do not alter the spatial memory of mice. Our results do not support the hypothesis that chronic treatment with MSO influences hippocampus-dependent learning abilities in mice.

The xenobiotic methionine sulfoximine modulates carbohydrate anabolism and related genes expression in rodent brain

Methionine sulfoximine is a xenobiotic amino acid derived from methionine. One of its major properties is to display a glycogenic activity in the brain. After studying this property, we investigate here a possible action of this xenobiotic on the expression of genes related to carbohydrate anabolism in the brain. Glycogen was studied by the means of electron microscopy. Astrocytes were cultured and the influence of methionine sulfoximine on carbohydrate anabolism in these cells was investigated. In vivo, methionine sulfoximine induced a large increase in glycogen accumulation. It also enhanced the glycogen accumulation in cultured astrocytes principally, when the medium was enriched in glucose. The gluconeogenic enzyme fructose-1,6-bisphosphatase may account for glycogen accumulation. Plasmids were built using antisens cDNA to permanently block the expression of fructose-1,6-bisphosphatase. An eukaryotic vector was used and the expression of fructose-1,6-bisphosphatase gene was under the control of the promoter of the glial fibrillary acidic protein. In this case, the glycogen content in cultured astrocytes largely decreased. This work shows that methionine sulfoximine enhances energy carbohydrate synthesis in the brain. Since this xenobiotic also enhances the expression of some genes related to one of the key step of glucose synthesis, it is possible that genes may be one target of methionine sulfoximine. Next investigations will study the actual effect of methionine sulfoximine in the cells.

Astrocytes in methylmercury, ammonia, methionine sulfoximine and alcohol-induced neurotoxicity

Astrocytes occupy approximately 25% of the CNS volume. Their "foot" processes are closely associated with synapses, nodes of Ranvier, axonal tracts, and capillaries. Astrocytic functions include neurotrophic factor secretion, control of extracellular pH, inactivation of glutamate, as well as uptake and metabolism of neurotransmitters. Astrocyte-neuron interactions provide strategic sites for actions of numerous chemical compounds. In this manuscript, we discuss examples of toxins that directly affect astrocyte function (methylmercury, ammonia, methionine sulfoximine, and alcohol), leading to an altered homeostatic control of the extracellular milieu and neuronal dysfunction. In addition, the potential role of astrocytic proteins, the metallothioneins, in attenuating the neurotoxicity of methylmercury is discussed.

Methionine sulfoximine shows excitotoxic actions in rat cortical slices

Methionine sulfoximine (MSO) is a rare amino acid. It occurs in nature or as a by-product of some forms of food processing. A notable example of the latter was a former method for bleaching wheat flour, using nitrogen trichloride, the "agene process," in use for most of the first 50 years of this century. "Agenized" flour was found to be responsible for various neurological disorders in animals, and MSO was identified as the toxic factor. The agene process was subsequently discontinued in the United States and the United Kingdom circa 1950. MSO inhibits the synthesis of both glutathione and glutamine, and it is possible that its actions on the nervous system arise from alterations in the amount or distribution of these molecules. Structurally, MSO resembles glutamate, an observation that has also raised the possibility that it might have more direct glutamate-like actions on neurons. In the present investigation, we report excitatory and toxic actions of MSO in an in vitro preparation of adult rat cortex. Field potential recordings in this preparation show that MSO application evokes a sustained depolarization, which can be blocked by the N-methyl-D-aspartate (NMDA) antagonist L-(+)-2-amino-5-phosphonovalerate (AP5). However, competition assays using MSO on [3H]CGP-39653 (DL-(E)-2-amino-4-propyl-1-phosphono-3-pentenoate) binding in rat cortical homogenates show only 20% displacement of total binding, suggesting that MSO is acting indirectly, perhaps by releasing glutamate. To investigate this possibility, we measured glutamate release during MSO application. Time course and dose-response experiments with MSO showed significant [3H]glutamate release, which was partially attenuated by AP5. To assess cellular toxicity, we measured lactate dehydrogenase (LDH) release from cortical sections exposed to MSO. MSO treatment led to a rapid increase in LDH activity, which could be blocked by AP5. These data suggest that MSO acts by increasing glutamate release, which then activates NMDA receptors, leading to excitotoxic cell death. These data suggest the possibility that MSO in processed flour had excitotoxic actions that may have been contributing factors to some human neuronal disorders.

Effect of methionine sulfoximine on nitrogen metabolism and externally supplied ammonium assimilation in kidney bean

L-Methionine sulfoximine (MSO) at concentration 1.25 mM in vivo causes the inhibition of glutamine synthetase (GS) in both roots and leaves of young seedlings of kidney bean following the accumulation of high levels of ammonia and decrease in amounts of free amino acids that is more pronounced in leaves. The inhibition of GS by MSO in leaves in the case of externally supplied 5 mM (15NH4)2SO4 assimilation leads to ammonia accumulation and the decrease in the amounts of glutamine and glutamic acid and the intensity of the incorporation of 15N into them. In roots the inhibition of GS is not followed by the decrease of 15N content into glutamate. It is concluded that the pathway of ammonia primary assimilation in leaves is via GS and glutamate synthase (GOGAT), while in roots glutamate dehydrogenase also plays an important role in this process.

Stereospecific effects of R-lipoic acid on buthionine sulfoximine-induced cataract formation in newborn rats

This study revealed a marked stereospecificity in the prevention of buthionine sulfoximine-induced cataract, and in the protection of lens antioxidants, in newborn rats by alpha-lipoate, R- and racemic alpha-lipoate decreased cataract formation from 100% (buthionine sulfoximine only) to 55% (buthionine sulfoximine + R-alpha-lipoic acid) and 40% (buthionine sulfoximine + rac-alpha-lipoic acid) (p<0.05 compared to buthionine sulfoximine only). S-alpha-lipoic acid had no effect on cataract formation induced by buthionine sulfoximine. The lens antioxidants glutathione, ascorbate, and vitamin E were depleted to 45, 62, and 23% of control levels, respectively, by buthionine sulfoximine treatment, but were maintained at 84-97% of control levels when R-alpha-lipoic acid or rac-alpha-lipoic acid were administered with buthionine sulfoximine; S-alpha-lipoic acid administration had no protective effect on lens antioxidants. When enantiomers of alpha-lipoic acid were administered to animals, R-alpha-lipoic acid was taken up by lens and reached concentrations 2- to 7-fold greater than those of S-alpha-lipoic acid, with rac-alpha-lipoic acid reaching levels midway between the R-isomer and racemic form. Reduced lipoic acid, dihydrolipoic acid, reached the highest levels in lens of the rac-alpha-lipoic acid-treated animals and the lowest levels in S-alpha-lipoic acid-treated animals. These results indicate that the protective effects of alpha-lipoic acid against buthionine sulfoximine-induced cataract are probably due to its protective effects on lens antioxidants, and that the stereospecificity exhibited is due to selective uptake and reduction of R-alpha-lipoic acid by lens cells.

Effect of acute exercise on glutathione deficient heart

The role of glutathione (GSH) in myocardial antioxidant defense was investigated in Swiss-Webster mice either performing swim exercise to exhaustion or rested in both the GSH adequate (GSH-A) and GSH deficient (GSH-D) states. GSH deficiency was accomplished by injecting mice with L-buthionine [S,R]sulfoximine (BSO; 2 nmol/kg body wt, i.p.) and providing BSO (20 mM) in drinking water for 12 days. GSH and glutathione disulfide (GSSG) contents in the GSH-D hearts were decreased to 10 and 8%, respectively, of those in the GSH-A mice. This decrease was associated with a significant decline of the total glutathione level in the liver, skeletal muscle and plasma. Myocardial GSH peroxidase and GSH sulfur-transferase activities decreased significantly following GSH deficiency, whereas superoxide dismutase activity was significantly elevated. GSH deficiency did not affect exercise endurance performance. However, exhaustive exercise decreased GSH content in the myocardium of the GSH-A and GSH-D mice by 22 and 44% (p < 0.05), respectively. The GSH:GSSG ratio was not altered significantly following exercise because of a concomitant decrease in GSSG (p < 0.05). gamma-Glutamyltranspeptidase activity was significantly increased after exercise, especially in the GSH-D hearts (72%; p < 0.05). GSH content after exercise correlated negatively with exercise time in both GSH-A and GSH-D mice (p < 0.05). These data indicate that GSH is actively used in the myocardium during prolonged exercise at moderate intensity and that GSH deficiency is tolerated by the heart, possibly compensated for by an increased GSH uptake from the plasma.

Postischemic injury in isolated rat hearts is not aggravated by prior depletion of myocardial glutathione

The aim of this study was to test the hypothesis that a decreased myocardial concentration of reduced glutathione (GSH) during ischemia renders the myocardium more susceptible to injury by reactive oxygen species generated during early reperfusion. To this end, rats were pretreated with L-buthionine-S,R-sulfoximine (2 mmol/kg), which depleted myocardial GSH by 55%. Isolated buffer-perfused hearts were subjected to 30 min of either hypothermic or normothermic no-flow ischemia followed by reperfusion. Prior depletion of myocardial GSH did not lead to oxidative stress during reperfusion, as myocardial concentration of glutathione disulfide (GSSG) was not increased after 5 and 30 min of reperfusion. In addition, prior depletion of GSH did not exacerbate myocardial enzyme release, nor did it impair the recoveries of tissue ATP, coronary flow rate and left ventricular developed pressure during reperfusion after either hypothermic or normothermic ischemia. Even administration of the prooxidant cumene hydroperoxide (20 microM) to postischemic GSH-depleted hearts during the first 10 min of reperfusion did not aggravate postischemic injury, although this prooxidant load induced oxidative stress, as indicated by an increased myocardial concentration of GSSG. These results do not support the hypothesis that a reduced myocardial concentration of GSH during ischemia increases the susceptibility to injury mediated by reactive oxygen species generated during reperfusion. Apparently, myocardial tissue possesses a large excess of GSH compared to the quantity of reactive oxygen species generated upon reperfusion.

Phase I trial of buthionine sulfoximine in combination with melphalan in patients with cancer

PURPOSE AND METHODS

Resistance to alkylating agents and platinum compounds is associated with elevated levels of glutathione (GSH). Depletion of GSH by buthionine sulfoximine (BSO) restores the sensitivity of resistant tumors to melphalan in vitro and in vivo. In a phase I trial, each patient received two cycles as follows: BSO alone intravenously (i.v.) every 12 hours for six doses, and 1 week later the same BSO as cycle one with melphalan (L-PAM) 15 mg/m2 i.v. 1 hour after the fifth dose. BSO doses were escalated from 1.5 to 17 g/m2 in 41 patients.

RESULTS

The only toxicity attributable to BSO was grade I or II nausea/vomiting in 50% of patients. Dose-related neutropenia required an L-PAM dose reduction to 10 mg/m2 at BSO 7.5 g/m2. We measured GSH in peripheral mononuclear cells (PMN), and in tumor biopsies when available, at intervals following BSO dosing. In PMNs, GSH content decreased over 36 to 72 hours to reach a nadir on day 3; at the highest dose, recovery was delayed beyond day 7. The mean PMN GSH nadirs were approximately 10% of control at BSO doses > or = 7.5 g/m2; at 13 and 17 g/m2, all but two patients had nadir values in this range. GSH was depleted in sequential tumor biopsies to a variable extent, but with a similar time course. At BSO doses > or = 13 g/m2, tumor GSH was < or = 20% of starting values on day 3 in five of seven patients; recovery had not occurred by day 5. We measured plasma concentrations of R- and S-BSO by high-performance liquid chromatography (HPLC) in 22 patients throughout the dosing period. Total-body clearance (CLt) and volume of distribution at steady-state (Vss) for both isomers were dose-independent. The CLt of S-BSO was significantly less than that of R-BSO at all doses, but no significant differences in Vss were observed between the racemates. Harmonic mean half-lives were 1.39 hours and 1.89 hours for R-BSO and S-BSO, respectively.

CONCLUSION

A biochemically appropriate dose of BSO for use on this schedule is 13 g/m2, which will be used in phase II trials to be conducted in ovarian cancer and melanoma.

BDNF or IGF-I potentiates free radical-mediated injury in cortical cell cultures

Free radical-mediated damage to cultured cortical neurons was induced by a 24 h exposure to Fe2+ (30 microM) or an inhibitor of gamma-glutamylcysteine synthetase, L-buthionine-[S,R]-sulfoximine (BSO, 1 mM). As expected, neuronal death was blocked by inclusion of the free radical scavenger trolox during the Fe2+ or BSO exposure. However, unexpectedly, pretreatment of the cultures with BDNF or IGF-I markedly potentiated neuronal death. This growth factor-potentiated death was still blocked by trolox, but was insensitive to glutamate antagonists. Concurrent addition of cycloheximide with the growth factors prevented injury potentiation. Present findings suggest that growth factors may increase free radical-induced neuronal death by mechanisms dependent upon protein synthesis.

Cytogenetic and pathogenic effects of long and short amosite asbestos

This study utilized two samples of amosite asbestos which differ in their length, but not in their diameter and which have been shown previously to have very different abilities to cause pathology in rats exposed by instillation or inhalation. The activity of these amosite samples in causing chromosomal aberrations in Chinese hamster ovary cells in culture was examined, along with the effect of the glutathione (GSH) synthesis-inhibiting agent buthionine sulphoximine. The incidence of chromosomal aberrations in cells treated with the short fibre sample was similar to control levels; the long amosite sample caused significantly more chromosomal aberrations than the short fibre sample. When cells were treated with buthionine sulphoximine to decrease the levels of intracellular glutathione, the incidence of chromosomal aberrations was increased in the control cells, but also on treatment with both short and long amosite, the long sample again being considerably more active than the short. The pathogenicity of the long amosite may result from the ability of the fibres to cause chromosome damage, while the enhancement of this damage caused by decreasing intracellular glutathione suggests that the asbestos fibres may impose an oxidant stress on the cells which contributes to these aberrations.

Glutathione depletion in human T lymphocytes: analysis of activation-associated gene expression and the stress response

Glutathione depletion achieved by continuous exposure of mitogen-activated human T lymphocytes to L-buthionine-(S,R)-sulfoximine, a specific inhibitor of gamma-glutamylcysteine synthetase, leads to a marked inhibition of the proliferative response. Concanavalin A-activated T cells treated with buthionine sulfoximine failed to exhibit the increase in glutathione content normally observed in activated T cells and were depleted of cellular glutathione over 4 days of culture. On Day 3 of culture, DNA synthesis was inhibited by greater than 75%. In addition, total RNA synthesis was dramatically reduced in the glutathione-depleted cells being inhibited by 26, 61, and 82% on Days 2, 3, and 4, respectively. Despite this global reduction in RNA synthesis, no specific effects on mRNA expression of a number of critical T cell genes required for activation and/or proliferation were detected. In contrast to a recent report of GSH depletion leading to down-regulation of ras mRNA expression in a number of transformed cell lines, glutathione depletion did not influence N-ras mRNA expression in T lymphocytes. No influence of glutathione depletion on the induction of histone mRNA expression was observed. However, consistent with previous studies on regulation of histone mRNA expression, histone transcript levels were reduced when DNA synthesis was markedly inhibited. A cellular stress response, characterized by an increase in mRNA levels of the two stress response genes, HSP70 and gadd 153, was evident in glutathione-depleted unstimulated cells. Additionally, in these cells at 48 hr, we observed a 3.5-fold increase in the steady-state level of mRNA encoding the catalytic subunit of gamma-glutamylcysteine synthetase, the enzyme inhibited by buthionine sulfoximine.

Effect of acute and chronic glutathione depletion on renal function in the rat

Renal function was evaluated in normal and acid-loaded rats following acute and chronic depletion of glutathione (GSH) by buthionine sulfoximine (BSO). Creatinine clearance and fractional excretion of electrolytes were normal. There was no acidification or concentration defect detected in animals with acute or chronic GSH depletion.

The antioxidant N-acetyl-cysteine protects cultured epithelial cells from menadione-induced cytopathology

The effects of the antioxidant N-acetyl-cysteine (NAC) were assessed after short term exposure of A431 epithelial cells. The drug was able to protect, at least partially, the cells from the oxidative stress induced by the quinone menadione. In particular, the oxidizing agent-induced cell rounding and detachment from the substrate were strongly impaired by pre-exposure to the compound. The mechanism of such an effect seems to be ascribable to a target effect of the drug on the adhesion properties of the cells. In fact, a modification of morphological features of NAC-exposed cells and of their ability to adhere to different coated substrates was found. These changes resulted in a significant improvement of the A431 tumor cell adhesion pattern which was associated with a noticeable rearrangement of some cytoskeletal components, mainly of the microfilament system. These data add new importance to the subcellular activity of NAC and seem to indicate that the redox status of the cells, i.e. the intracellular balance between proxidants and antioxidants, could also play a role in their adhesive properties.

Glutathione depletion potentiates 12-O-tetradecanoyl phorbol-13-acetate(TPA)-induced inhibition of gap junctional intercellular communication in WB-F344 rat liver epithelial cells: relationship to intracellular oxidative stress

Treatment of WB-F344 liver epithelial cells with buthionine sulfoximine (BSO, 100 microM) for 24 h caused a greater than 95% depletion in cellular glutathione (GSH) and potentiated the ability of 12-O-tetradecanoyl phorbol-13-acetate (TPA) to inhibit gap junctional intercellular communication (GJIC) between the cells (IC50 shifted from 5 microM to 2 microM). Similarly, acute depletion of GSH by up to 30%, either with the thiol oxidant diamide or with BSO, also potentiated the inhibitory effect of the phorbol ester on GJIC. The treatment of the control cells with TPA caused a concomitant increase in the accumulation of oxidation products of 2',7'-dichlorofluorescein (DCF), indicating elevated production of oxidants in the cells during the blockade of GJIC. The depletion of GSH over a 24 h period with BSO itself increased the flux of oxidants in the cells but did not inhibit GJIC. Treatment of these GSH-depleted cells with TPA caused an additive elevation in the accumulation of oxidised DCF metabolites. Direct application of H2O2 (25-200 microM) or benzoyl peroxide (25-150 microM) to the control cells for 60 min caused weak, dose-dependent inhibitions of gap junctional communication in these cells but these responses were accompanied by the induction of acute, sub-lethal cytotoxicity. The depletion of GSH from the cells did not potentiate these responses to the peroxides but did facilitate synergistic inhibition of gap junctional communication in response to both TPA and sub-toxic doses of either peroxide. The results of the above studies indicate that oxidants are produced in WB-F344 cells in response to TPA and that these function in a co-operative manner with other cellular responses to the phorbol ester in the inhibition of gap junctional communication. This may explain why priming the cells for the induction of oxidative stress by the depletion of GSH potentiates the inhibitory activity of TPA on gap junctional communication.

The effect of in utero administration of buthionine sulfoximine on rat development

Glutathione (GSH) is a tripeptide that is thought to be an essential cell component playing an important role as a cellular antioxidant and scavenger of free radicals. GSH depletion has been shown to render cells more sensitive to various insults. GSH has a protective effect. GSH levels can be decreased by inhibition of its synthesis with buthionine sulfoximine (BSO), which inhibits gamma-glutamylcysteine synthetase. Several studies have shown that treatment with BSO enhances the toxicity of some drugs and radiation. A previous study indicated that the effects of BSO on the developing embryo were short lived and did not persist to birth. In the above-mentioned study, mothers were treated with BSO only on days 10 and 11 of gestation. The objective of the present study was to determine the effects of BSO administration on GSH depletion throughout pregnancy on the developing rat. Timed pregnant Sprague-Dawley rats were placed on a liquid BioServ diet containing BSO starting on day 1 of pregnancy. The mothers received a daily dose of BSO ranging from 2 to 6 mmol/kg/24 h. 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. GSH levels were measured in brain and liver, and various parameters relating to development were assessed. A dose-response curve showed that a maximum depletion (86%) of GSH in the mother's liver was produced by the 6 mmol/kg dose of BSO. However, no change was seen in brain GSH levels of the mothers.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of glutathione on sister-chromatid exchanges in normal and buthionine sulfoximine-treated mice

Based on their ability to induce sister-chromatid exchanges (SCEs) it is evident that thiol-containing radioprotectors can induce DNA damage. However, there were contradictory findings when reduced glutathione (GSH) was tested using two cell lines. The present study demonstrated that GSH can induce SCEs and also delay in cell proliferation in mouse bone marrow cells in vivo. The presence of catalase significantly reduced GSH-induced SCE frequency down to catalase alone levels. An attempt was made to evaluate the effect of GSH treatment in buthionine sulfoximine (BSO)-treated mice (GSH-depleted mice) and the data indicate that induction of SCEs takes place without inducing a delay in cell proliferation or the generation of hydrogen peroxide. Probably, some unknown route is involved by which GSH-degraded product(s) induce SCEs in BSO-treated mice. Therefore, the induction of SCEs by GSH in normal mice may be largely due to hydrogen peroxide generation; however, the involvement of the binding ability of GSH to chromatin and the probable (unknown) route by which GSH-degraded product(s) may cause smaller fraction of SCEs cannot be ruled out.

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.

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.

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.

Relationship between cellular glutathione level and susceptibility to LAK killing in human pharyngeal carcinoma cell line

We examined the relationship between cellular glutathione (GSH) level and susceptibility to lymphokine-activated killer (LAK) cell-mediated cytolysis in KB human pharyngeal carcinoma cells. Treatment of KB cells with D,L-buthionine-S,R-sulfoximine (BSO), a gamma-glutamyl cysteine synthetase blocker, resulted in decreased total intracellular GSH levels associated with increased susceptibility to LAK killing. In contrast, treatment with oxothiazolidine-4-carboxylate (OTZ, a precursor of cysteine), which is known to increase cellular GSH level, decreased the susceptibility of KB cells to LAK killing. Both agents had no effects on binding frequency of KB cells to LAK cells. These results suggest that intracellular GSH in tumor cells play a protective role against LAK mediated cytolysis, specially in the post-binding killing phase.

Nephrotoxicity and covalent binding of 1,1-dichloroethylene in buthionine sulphoximine-treated mice

Autoradiography of mice injected i.p. with 14C-labelled 1,1-dichloroethylene (vinylidene chloride, VDC) in C57B1/6 mice revealed a selective covalent binding of radioactivity in the proximal tubules, in the midzonal parts of the liver lobules and in the mucosa of the upper and lower respiratory tract. Since VDC is a renal carcinogen in male mice the effects of compounds modulating biotransformation and glutathione (GSH) levels on the renal covalent binding were examined following a single i.p. dose of 14C-VDC. Most pretreatments did not influence the level of binding but treatment with buthionine sulphoximine (BSO), an irreversible inhibitor of gamma-glutamylcysteine synthetase and glutathione (GSH)-depleting agent, increased the renal covalent binding of VDC three-fold. Histopathological examination of kidneys in BSO-pretreated male mice given single i.p. injections of subtoxic doses of VDC (25 and 50 mg/kg) showed necrosis in the proximal tubules (S1 and S2 segments) 24 h following administration. In mice given VDC only, no significant lesions in the kidneys were observed. The severe renal toxicity of VDC in BSO-pretreated mice is suggested to be related to metabolic activation of VDC in the proximal tubules, resulting in further GSH depletion and covalent binding.

Buthionine sulfoximine mediated enhancement of gamma-radiation induced mutation frequency in Drosophila melanogaster

Experiments were carried out to investigate whether or not depletion of the glutathione (GSH) level in Drosophila melanogaster larvae with buthionine sulfoximine (BSO) treatment can result in the modulation of the frequency of sex-linked recessive lethal (SLRL) mutations induced by gamma-radiation. Third instar larvae were fed on BSO for 24 h before exposure to 10 Gy gamma-radiation. Immediately after this the larvae were divided into two batches, which were used for determining the GSH level and the induction of SLRL mutations respectively. The results obtained suggest that the depletion of the GSH level with BSO can lead to an enhancement in the frequency of SLRL mutations (significant at the 5% level). In a subsequent experiment in which adult Drosophila melanogaster male flies were fed on BSO for 72 h before irradiation, a significant increase was observed in the incidence of SLRL mutations.

Absolute configuration of L-methionine sulfoximine as a toxic principle in Cnestis palala (Lour.) Merr

An unusual amino acid, L-methionine sulfoximine (1), has been isolated from the fresh seeds of Cnestis palala (Lour.) Merr. [Connaraceae]. The absolute configuration of the natural sulfoximine (1) was confirmed to be 2(S)-methionine S(S)-sulfoximine [(2S,SS)-2-amino-4-(S-methylsulfonimidoyl)-n-butanoic acid] by comparison of the [alpha]D value and IR spectrum with those of authentic samples obtained through the optical resolution of synthetic materials. Acute toxicity of the seeds of C. palala in a beagle dog was also studied.

Differential cytotoxicity of buthionine sulfoximine to "normal" and transformed human lung fibroblast cells

Glutathione (GSH) depletion has been studied extensively as a possible means to sensitive tumor cells to radiation treatment and chemotherapy. The present study was undertaken to compare the cytotoxicity of GSH depletion in normal and transformed cells. The results showed that specific inhibition of GSH synthesis by L-buthionine sulfoximine (BSO) caused significantly higher cytotoxicity in "normal" human-lung fibroblast cells than in their transformed counterparts. This finding suggests a possibility that depletion of GSH could be more harmful to normal cells than to transformed and/or tumor cells and that the selective cytotoxicity of BSO to normal cells could limit its potential as an effective sensitizer for cancer treatment.

Caffeic acid causes metal-dependent damage to cellular and isolated DNA through H2O2 formation

Pulsed field gel electrophoresis showed that caffeic acid induced DNA strand breaks in cultured human cells in the presence of Mn(II). With alkali treatment, DNA single-strand breaks were observed. The strand breakage was increased by the treatment of buthionine sulphoximine (a GSH synthesis inhibitor) and 3-aminotriazol (a catalase inhibitor) and decreased by catalase, indicating the involvement of H2O2. The DNA damage was decreased by o-phenanthroline, indicating the involvement of transition metal ion. Damage to isolated DNA from c-Ha-ras-1 protooncogene was investigated by a DNA sequencing technique. Caffeic acid caused DNA damage in the presence of Cu(II) but not in the presence of either Mn(II) or Fe(III). Caffeic acid plus Cu(II) induced piperidine-labile sites frequently at thymine residues, especially of the 5'-GTC-3' and 5'-CTG-3' sequences. Typical OH scavengers showed no inhibitory effects. The inhibitory effects of bathocuproine and catalase on Cu(II)-mediated DNA damage suggest that Cu(I) and H2O2 have important roles in the production of active species causing DNA damage. The Cu(II)-mediated DNA damage was enhanced by pre-incubation of caffeic acid with Mn(II). Mn(II)- or Cu(II)-catalyzed autoxidation of caffeic acid produced H2O2 with efficiency of Mn(II) greater than Cu(II). These results suggest that in the presence of Mn(II) or Cu(II), caffeic acid produces H2O2, which is activated by transition metals to cause damage to DNA in vitro and probably in cultured cells.

Effects of buthionine sulfoximine treatment on cellular glutathione levels and cytotoxicities of cisplatin, carboplatin and radiation in human stomach and ovarian cancer cell lines

Chemotherapy failure remains a significant medical problem in the treatment of neoplastic disease and is thought to be due to many different factors including membrane transport, p-glycoprotein in multidrug resistance, glutathione and its related enzymes, topoisomerase II and DNA repair. Glutathione is a major constituent of non-protein thiol and participates in detoxification of chemotherapy and radiation. Thus, glutathione concentration is correlated with sensitivity to alkylating agents and radiation, and increased in resistant cell lines. Buthionine sulfoximine (BSO) is an inhibitor of glutathione biosynthesis and may increase cytotoxicities of alkylating agents, including melphalan and cisplatin, and radiation in sensitive and resistant cell lines. We studied effects on cellular glutathione levels and cytotoxicities of cisplatin, carboplatin and radiation by BSO treatment in human stomach cancer cell line (SNU-1) and ovarian cancer cell line (OVCAR-3). The results were as follow: 1) After BSO treatment of 1 mM and 2 mM for 2 days, the intracellular thiol concentration was depleted to 75.7% and 76.2% in SNU-1, and 74.1% and 63.0% in OVCAR-3, respectively. 2) The intracellular thiol concentration in SNU-1 was depleted to 33.4% after BSO 2 mM for only 2 hours incubation and 71.5% after small amount of BSO (0.02 mM) for 2 days. 3) The recovery of intracellular thiol concentration required more than 3 days after BSO removal. 4) BSO inhibited partially the growth of SNU-1 and OVCAR-3. 5) The cytotoxicities of cisplatin and carboplatin were markedly enhanced both in SNU-1 and OVCAR-3 by BSO treatment. 6) The cytotoxicities of radiation was increased in OVCAR-3 and SNU-1 by BSO treatment. Therefore, it is concluded that BSO can deplete effectively the intracellular thiol concentration and enhance the cytotoxicities of cisplatin, carboplatin and radiation.

A procedure for selecting mammalian cells with an impairment in oxidative phosphorylation

The mitochondrial encephalomyopathies in man are characterized by heterogeneous defects leading to an impairment in the pathway of aerobic energy production. As a means of investigating the molecular and genetic mechanisms underlying these disorders we have developed a procedure for selecting mammalian cell lines with features resembling the human pathological phenotypes. The principle of the selection is the use of a fluorescent amphiphilic dye, 2,4-(dimethylamino)-1-styrylmethylpyridiniumiodine, a cation showing two main features. Firstly, it is accumulated by mitochondria to an extent correlated with the magnitude of the electrochemical gradient of protons across the mitochondrial inner membrane. Secondly, upon irradiation with UV light, it gives rise to formation of free radicals, which inflict damage to the cell. Mutant cells with an impairment in oxidative phosphorylation will have more chance to survive than wild type cells. The selection procedure was applied to a stock of mutagenized Chinese hamster ovary cells. After subcloning of the cells which survived the selection procedure, twenty-six independent clones were isolated. Eighteen of the clones had a partial deficiency of cytochrome c oxidase ranging from 30 to 60% of the activity in control cells. The properties of two of the clones are described. One clone has been cultured under non-selective conditions for at least 12 months with retention of the partial deficiency of cytochrome c oxidase.

Nephrotoxicity of thiazoles structurally related to thiabendazole in mice depleted of glutathione by treatment with buthionine sulfoximine

In mice depleted of glutathione (GSH) by treatment with DL-buthionine sulfoximine (BSO), thiabendazole [2-(4'-thiazolyl)benzimidazole, TBZ] produces renal damage characterized by increases in relative kidney weight and serum urea nitrogen (SUN) concentration. Several thiazole and benzimidazole compounds related to TBZ were examined for the ability to cause nephrotoxicity in mice pretreated with BSO. 4-Methyl- and 4-phenylthiazoles were highly effective compounds. In the absence of BSO, 4-methylthiazole resulted in no nephrotoxicity; inhibitors of hepatic and renal cytochrome P-450 enzymes such as methoxsalen and piperonyl butoxide prevented the nephrotoxicity of 4-methylthiazole given in combination with BSO. In addition, there was a sex difference in the nephrotoxicity of 4-methylthiazole in combination with BSO; the nephrotoxicity was observed only in males. These features of nephrotoxicity of 4-methylthiazole are well in accord with those of TBZ previously reported. This suggests that TBZ and 4-methylthiazole share a common mechanism of nephrotoxicity.

Enhancement of melphalan-induced gastrointestinal toxicity in mice treated with regional hyperthermia and BSO-mediated glutathione depletion

Both hyperthermia and glutathione depletion have been shown to increase the antineoplastic activity of melphalan. Investigations were carried out to define the toxicity and activity of melphalan given in conjunction with local (right hind limb) hyperthermia and L-buthionine-SR-sulphoximine (BSO)-mediated glutathione depletion to athymic mice bearing the melphalan-resistant human rhabdomyosarcoma xenograft TE-671 MR. Administration of 0.5 of the 10% lethal dose of melphalan to mice treated with BSO and hyperthermia (42 degrees C for 70 min) resulted in a 53% mortality rate. The mortality rates for mice treated with melphalan alone (2.5%), hyperthermia alone (0%), melphalan plus BSO (13.5%), melphalan plus hyperthermia (12.0%) and BSO plus hyperthermia (0%) were substantially lower than triple therapy. Histological examination of kidney, liver, colon, and small intestine sections taken from non-tumour-bearing animals revealed a marked increase in damage to the small intestine (cryptal necrosis and epithelial denudement) in animals receiving triple therapy compared with animals receiving any other treatment combination. Gavage administration of sterile water (1 ml twice a day) completely prevented mortality in animals receiving triple therapy. Treatment of tumour-bearing animals with triple therapy plus gavage demonstrated a statistically significant increase in tumour growth delay compared with animals receiving any other treatment combination.

Protective roles of metallothionein and glutathione in hepatotoxicity of cadmium

The protective roles of metallothionein (MT) and glutathione (GSH) in acute hepatotoxicity of cadmium (Cd) were investigated in an in vitro system. Liver slices were incubated in a buffer containing cadmium chloride (20-50 ppm) at 37 degrees C for 3 h. Viability of the slices was monitored by measuring intra-cellular potassium (K) content and GSH concentrations. A dose-dependent decrease of intracellular K content of GSH concentrations was observed. Pre-induction of MT (100-fold increase) by injection of zinc sulphate (30 mg Zn/kg body weight) showed protection against decrease in both intracellular K and GSH concentrations in liver slices. Decrease of hepatic GSH (90%) by an injection of buthionine sulfoximine (BSO)(4 mmol/kg body weight) to the rats further enhanced the Cd toxicity in the liver slices. This enhanced toxicity resulting from BSO treatment can be totally overvome by induction of MT by Zn pre-treatment. The cellular uptake of Cd remained unaltered in all experiments. These results demonstrate that hepatic toxicity of Cd may be due to its binding to intracellular sulfhydryl groups and both intracellular GSH and MT levels may provide protection against cytotoxicity of Cd in liver. Moreover, even at low GSH levels, MT could partially protect the hepatic cells from Cd cytotoxicity.

Lack of mutagenicity of ochratoxin A and B, citrinin, patulin and cnestine in Salmonella typhimurium TA102

The Aspergillus mycotoxins ochratoxin A and B, citrinin and patulin as well as combinations of ochratoxin A and citrinin did not induce reverse mutations in Salmonella typhimurium strain TA102. Therefore there is no indication for the induction of oxidative damage or crosslinks. The same is true for cnestine, a compound extracted from the plant Cnestis glabra.

The effect of in vivo glutathione depletion with buthionine sulfoximine on rat embryo development

Glutathione is an abundant endogenous nucleophile whose depletion may have adverse effects on a number of cellular processes, including protein and DNA synthesis, amino acid transport, and detoxification of reactive electrophiles. Previous studies have indicated that a certain basal level of glutathione is essential for normal development in vitro in the whole rat embryo culture system. The objective of this study was to determine the effect of glutathione depletion with buthionine sulfoximine on the development of rat embryos in vivo. Timed pregnant Sprague-Dawley rats were treated by gavage on days 10 and 11 of gestation with saline (control) or with L-buthionine-(S,R)-sulfoximine (4 or 8 mmol/kg). Pregnancy outcome was assessed on day 12 or day 20 of gestation. The glutathione content of embryos and of maternal organs was measured on day 12. Glutathione concentrations were significantly decreased in the embryos and in maternal muscle and ovary but not in maternal liver and kidney. Glutathione depletion, when assessed on day 12 of gestation, was found to result in an increase in the numbers of dead and malformed embryos. Treatment with the higher dose of buthionine sulfoximine resulted in the death of 13.2% of the total implanted embryos; of the surviving embryos, 21.7% were malformed. There was also a significant decrease on day 12 after treatment with the higher dose of buthionine sulfoximine in the embryonic total morphological score, a measure of the developmental stage of the embryos (control, 57.7 +/- 1.0; 8 mmol/kg buthionine sulfoximine, 52.8 +/- 1.8).(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative study of intracellular glutathione content in rat lymphocyte cultures treated with 2-mercaptoethanol and interleukin-2

The level of intracellular glutathione (GSH) in mitogen-stimulated mouse lymphocytes is increased in the presence of 2-mercaptoethanol (2-ME), an enhancer of lymphocyte activation and proliferation. Since proliferation of lymphocytes in response to mitogens involves direct activation by a mitogen followed by continued proliferation in response to interleukin-2 (IL-2), we have investigated the effect of 2-ME and exogenous IL-2 on the GSH content and cell proliferation of rat lymphocytes stimulated with phytohemagglutinin (PHA). PHA stimulation increased both GSH content and the magnitude of the proliferative response, as measured by thymidine incorporation into cellular DNA. However, incubation of stimulated lymphocytes with 2-ME or IL-2 for 72 hr produced a significant further elevation of GSH levels and thymidine incorporation. 2-ME also increased the GSH content in unstimulated cultures, but it had little effect on thymidine incorporation. IL-2 increased GSH content and decreased thymidine incorporation in unstimulated lymphocytes. Exposure of cells to DL-buthionine-(S,R)-sulfoximine (BSO), an inhibitor of GSH biosynthesis, significantly depleted GSH and lowered the proliferative response, suggesting a crucial role of de novo GSH synthesis for lymphocyte activation. The data suggest that both 2-ME and IL-2 promote lymphocyte proliferation, although the mechanisms by which intracellular GSH levels are increased by the agents are apparently different.

Hepatotoxicity of eugenol and related compounds in mice depleted of glutathione: structural requirements for toxic potency

Eugenol produces hepatic injury in mice depleted of glutathione (GSH) by pretreatment with buthionine sulfoximine (BSO). Several eugenol analogs were examined for their ability to cause hepatic injury after administration to mice in combination with BSO. Hepatotoxicity was assessed by measuring relative liver weight, liver blood volume, and serum GPT activity in mice. Comparison of the tested compounds showed that the structural requirements for toxic potency was a phenolic ring having an allyl substituent at the 4-position. These structural requirements can be explained by assuming that a vinylogous quinone methide formed by metabolic oxidation of eugenol plays a role in inducing hepatotoxicity in GSH-depleted mice.

Rapid deterioration of lens fibers in GSH-depleted mouse pups

Lens opacities developed within 48-72 hr in mice that received a series of eight injections of L-buthionine sulfoximine, a specific inhibitor of glutathione (GSH) biosynthesis, on postnatal days 8 and 9. Initial histopathologic features consisted of swollen fibers in the central anterior cortex and displacement of cell nuclei from the bow region to the posterior cortex. These aberrations suggest early fiber cell membrane and/or cytoskeletal dysfunction. A massive wave of fiber cell lysis then engulfed the entire lens cortex and nucleus within 24 hr and left only epithelial cells intact, suggesting a concerted mechanism of cataract generation. The acellular core of the mature cataract seen on postnatal day 16 consisted of a granular matrix in which pycnotic and fragmented cell nuclei were located near the terminus of the lens epithelium. The epithelium displayed increased mitotic activity and meridional row disorganization. During the next two weeks, rapid regeneration of lens fibers, displacement of the acellular necrotic cytoplasm to the center and rear of the lens, and vacuole formation were observed. As new fibers were differentiated, partial regeneration of the bow was seen. However, the cataract was irreversible.

Kidney injury induced by lipid peroxide produced by vitamin E deficiency and GSH depletion in rats

Four-week-old Wistar male rats were fed a vitamin E (VE)-deficient (0E) or a VE-sufficient (10E) diet for 6 weeks and then intraperitoneally treated with buthionine sulfoximine (BSO) at 1 mmol/kg body weight once a day for 3 days. Glutathione (GSH) depletion by BSO treatment caused injuries especially in the kidneys of VE-deficient rats. The kidney weight increased in the VE-deficient rats after BSO treatment (0E-BSO). It was observed that the epithelial cells of the renal tubules in this group were strongly impaired and the injuries were necrosis and desquamation. No injury was observed in the kidneys of the BSO-untreated 0E group and the 10E groups. The TBA value of the kidney of 0E-BSO group was lower than that of the BSO-untreated 0E group, but the lipofuscin content of the kidney of the 0E-BSO group was 10 times higher than that of the BSO-untreated 0E group. These results suggest that the kidney injuries in rats may be caused by lipid peroxidation induced by vitamin E deficiency and glutathione depletion.

Relationship between glutathione content and formation of organic solvent-soluble fluorescent pigments in mice treated with chloroquine

We examined the relationship between the amount of organic solvent-soluble fluorescent pigments (OFP), which are generally regarded as the products of lipid peroxidation, and the content of glutathione in chloroquine-treated mice in order to assess the toxicological significance of the formation of these fluorescent pigments. OFP extracted with chloroform/methanol (2:1, v/v) were quantified spectrophotofluorometrically (excitation, 380 nm; emission, 460 nm). The administration of chloroquine diphosphate (50 mg/kg, i.p.) greatly increased the fluorescent intensity of OFP in the kidneys, but not in the livers, whereas administration of this drug significantly decreased glutathione content in the livers. In contrast, depletion of glutathione, induced either by starvation or by pretreatment with buthionine sulfoximine, a potent inhibitor of glutathione synthesis, markedly augmented the fluorescence intensity of OFP in the livers of mice treated with chloroquine. In the serum of mice treated with chloroquine, the alteration in activity of acid phosphatase and gamma-glutamyl transpeptidase approximately paralleled changes in the formation of fluorescent pigments in the tissues. These findings suggest that glutathione is an important endogenous substance which influences the insult of chloroquine.

Tissue-specific changes in glutathione and cysteine after buthionine sulfoximine treatment of rats and the potential for artifacts in thiol levels resulting from tissue preparation

L-Buthionine-S,R-sulfoximine (BSO), a potent inhibitor of gamma-glutamylcysteine synthetase, is commonly used as an experimental tool for the specific depletion of glutathione. Since cysteine is a key precursor for glutathione biosynthesis, we investigated the possibility that BSO might also affect the free cysteine pool in rat liver and kidney tissues in vivo. Male CD(SD)BR rats (150-200 g) were injected ip with various doses of BSO (0.25-4.0 mmol/kg), and glutathione and cysteine were measured in liver and kidney using HPLC with electrochemical detection and/or spectroscopic techniques. No hepatotoxicity or nephrotoxicity was observed at the highest BSO dose (4.0 mmol/kg) used. BSO caused the expected decreases of hepatic and renal glutathione at all doses, although glutathione depletion was more rapid, was achieved at a lower BSO dose, and was more sustained in kidney than in liver. Hepatic cysteine levels nearly doubled 20 min after BSO treatment (1.0 mmol/kg, ip), but were not significantly different from control at later time points. In contrast, renal cysteine was significantly depleted from 20 min to 25 hr postinjection with a time course closely paralleling that of renal glutathione depletion. These changes are discussed in the context of models for inter- and intraorgan transport of glutathione and cysteine. We also provide evidence that an artifact, most likely the gamma-glutamyltranspeptidase (GGT)-initiated breakdown of glutathione, leads to a rapid postmortem increase of cysteine levels in liver and particularly in kidney of rats. Simultaneous decreases in GSH levels can be demonstrated in kidney. This artifact needs to be minimized in toxicological studies of glutathione and cysteine in kidney and other GGT-rich organs, as the measured levels of these thiols may not reflect the true concentrations occurring in vivo.

Hepatotoxicity of eugenol in mice depleted of glutathione by treatment with DL-buthionine sulfoximine

Eugenol is widely used as a food flavoring agent and a dental analgesic. Mice treated with eugenol (400-600 mg/kg, po) in combination with an inhibitor of glutathione (GSH) synthesis, buthionine sulfoximine (BSO; 1 hr before eugenol, 4 mmol/kg, ip) developed hepatotoxicity characterized by increases in relative liver weight and serum GPT, hepatic congestion, and centrilobular necrosis of hepatocytes. Eugenol (up to 600 mg/kg) alone produced no hepatotoxicity. Drug metabolism inhibitors such as carbon disulfide, methoxsalen, and piperonyl butoxide prevented or significantly reduced the hepatotoxic effect of eugenol given in combination with BSO. On the other hand, pretreatment with phenobarbital (PB) increased the hepatotoxicity. These results suggest that eugenol is activated by a cytochrome-P-450-dependent metabolic reaction and that the liver injury is caused by inadequate rates of detoxification of the resulting metabolite in mice depleted of hepatic GSH by BSO treatment.

Melphalan-induced toxicity in nude mice following pretreatment with buthionine sulfoximine

Melphalan-induced toxicity in nude mice following pretreatment with a regimen of L-buthionine sulfoximine (BSO), previously shown to enhance the activity of this alkylating agent against rhabdomyosarcoma and glioma xenografts, was examined. Mice were pretreated with i.p. BSO (2.5 mmol/kg x 7 doses at 12-h intervals plus concomitant availability of a 20-mM solution in the drinking water) or vehicle prior to a single i.p. injection of melphalan (35.65 mg/m2). As compared with control animals who received no BSO pretreatment, mice pretreated with BSO lost weight prior to therapy with melphalan (6.9% weight loss vs 0.3% weight gain; P less than 0.005) and showed a greater mean nadir weight loss after melphalan (3.8% vs. 2.1%; P = 0.049). Treatment with melphalan was associated with histologic evidence of reversible gastrointestinal toxicity, reversible myelosuppression, and histologic evidence of acute renal tubular necrosis, with no differences being observed between mice that had been pretreated with BSO and those that had been pretreated with vehicle. No evidence of cardiac, hepatic, or skeletal muscle toxicity was found in melphalan-treated animals. These results suggest that treatment of nude mice with melphalan following BSO-mediated depletion of glutathione does not result in enhanced organ toxicity despite an increase in the antineoplastic activity of this alkylating agent.

Induction of rat UDP-glucuronosyltransferase and glutathione S-transferase activities by L-buthionine-S,R-sulfoximine without induction of cytochrome P-450

The effect of prolonged exposure to buthionine sulfoximine (BSO) on rat hepatic Phase I and Phase II drug-metabolizing enzymes has been examined. Exposure to 30 mM BSO in drinking water for 7 days induced hepatic microsomal UDP-glucuronosyltransferase activity (detergent-activated) toward p-nitrophenol (250%), 1-naphthol (210%), morphine (130%) and testosterone (140%), but not estrone. Glucuronosyltransferase activities were also induced after exposure for as short as 3 and as long as 13 days. When rats were returned to unsupplemented drinking water for 1 day prior to sacrifice following 6 days on 30 mM BSO, comparable induction to that seen after 7 consecutive days on the BSO solution was observed despite liver glutathione concentration having rebounded to 127% of control. Daily ingestion of BSO was similar (1 mmol/rat/day) for all periods of 30 mM BSO-drinking water exposure, with a body weight-adjusted dose range of 3.2-6.3 mmol/kg/day. An analogous inductive response caused by drinking 30 mM BSO for 3 days was elicited for p-nitrophenol and morphine glucuronidation by 6 mmol/kg doses of BSO given as single daily intraperitoneal or intragastric injections for 3 days. Intraperitoneal, intragastric and all BSO-drinking water exposures also significantly induced (130-195%) cytosolic glutathione S-transferase activity toward 1-chloro-2,4-dinitrobenzene. Significant increases in UDP-glucuronosyltransferase and glutathione S-transferase activities were also observed following 3 days of exposure to BSO in the drinking water at a concentration as low as 5 mM. Cytosolic p-nitrophenol sulfotransferase activity, with one minor exception, was not enhanced by any BSO treatment regimen. Alterations in transferase activities were not accompanied by any major changes in either overall cytochrome P-450 concentration or oxidative reactions selective for two isozymes. Thus, in addition to its well-documented glutathione-depleting property, BSO also selectively induces several Phase II drug-metabolizing enzymes, an effect to be considered in studies employing extended BSO treatment.

Role of glutathione in vanadate reduction in young and mature rats: evidence for direct participation of glutathione in vanadate inactivation

The influence of renal glutathione content, modulated by the glutathione synthesis inhibitor buthionine sulphoximine or by glutathione infusion, on the polyuric and natriuretic effects of i.v. administered vanadate was investigated in 20- and 55-day-old rats. The modulation of renal glutathione content led to significant changes in urine volume and sodium excretion, independently of age. A decrease in the renal glutathione level led to intensification and prolongation of the diuretic effects of vanadate in 55-day-old animals. Treatment with glutathione abolished and treatment with buthionine sulphoximine increased the polyuric effect of vanadate. These observations indicate a role for renal glutathione in vanadate inactivation. Age-dependent differences in the polyuric and natriuretic effectiveness of vanadate are caused by differences in renal glutathione content during maturation of the kidney.