Showing papers on "Glutathione published in 1989"
TL;DR: Glutamate-induced cytotoxicity in N18-RE-105 cells is due to inhibition of cystine uptake, resulting in lowered glutathione levels leading to oxidative stress and cell death.
966 citations
TL;DR: An enzyme has been discovered and characterized from Silene cucubalus cell suspension cultures that catalyzes the transfer of the gamma-glutamylcysteine dipeptide moiety of glutathione to an acceptors molecule or a growing chain of [Glu(-Cys)](n)-Gly oligomers, thus synthesizing phytochelatins, the metal-binding peptides of higher plants and select fungi.
Abstract: An enzyme has been discovered and characterized from Silene cucubalus cell suspension cultures that catalyzes the transfer of the γ-glutamylcysteine dipeptide moiety of glutathione to an acceptor glutathione molecule or a growing chain of [Glu(-Cys)]n-Gly oligomers, thus synthesizing phytochelatins, the metal-binding peptides of higher plants and select fungi. The enzyme was named γ-glutamylcysteine dipeptidyl transpeptidase and given the trivial name phytochelatin synthase. The primary reaction catalyzed is [Glu(-Cys)]-Gly + [Glu(-Cys)]n-Gly → [Glu(-Cys)]n+1-Gly + Gly. The enzyme is isoelectric near pH 4.8 and has temperature and pH optima at 35°C and 7.9, respectively. Phytochelatin synthase is constitutively present in cell cultures of various plant species and its formation is not noticeably induced by heavy metal ions in the growth medium. The enzyme (Mr95,000) seems to be composed of four subunits, the dimer (Mr50,000) being also catalytically active. Cd2+ is by far the best metal activator of the enzyme followed by Ag+, Bi3+, Pb2+, Zn2+, Cu2+, Hg2+, and Au+. The Km for glutathione is 6.7 mM. The enzyme activity seems to be self-regulated in that the product of the reaction (the phytochelatins) chelates the enzyme-activating metal, thus terminating the enzyme reaction. The molar ratio of the γ-glutamylcysteine dipeptide in phytochelatin to Cd2+ in the newly formed complex was 2:1.
892 citations
TL;DR: High levels of cellular GSH levels in cultured cells in response to hyperoxia or electrophilic agents such as diethylmaleate is coupled with an increase in activity of the Xc- transport system for the amino acids cystine and glutamate.
Abstract: In addition to its participation in a variety of other biochemical reactions, glutathione (GSH) is a major antioxidant. It is regularly generated intracellularly from its oxidized form by glutathione reductase activity that is coupled with a series of interrelated reactions. Synthesis of GSH also takes place intracellularly by a two-step reaction, the first of which is catalyzed by rate-limiting gamma-glutamylcysteine synthetase activity. Intracellular substrates for GSH are provided both by direct amino acid transport and by a gamma-glutamyl transpeptidase reaction that salvages circulating GSH by coupling the gamma-glutamyl moiety to a suitable amino acid acceptor for transport into the cell. Although the liver is a net synthesizer of circulating GSH, organs such as the kidney salvage GSH through the gamma-glutamyl transpeptidase reaction. Intracellular GSH may be consumed by GSH transferase reactions that conjugate GSH with certain xenobiotics. Elevation of cellular GSH levels in cultured cells in response to hyperoxia or electrophilic agents such as diethylmaleate is coupled with an increase in activity of the Xc- transport system for the amino acids cystine and glutamate. Strategies may be developed for protection against oxidant injury by enhancement of transport systems for precursor amino acids of GSH or by providing substrate that circumvents feedback inhibition of GSH synthesis.
850 citations
TL;DR: Glutathione enhances immune function, glutathione deficiency may contribute to the progressive immune dysfunction of HIV infection, and there was no correlation between ELF and plasma concentrations of total or reduced glutATHione.
727 citations
01 Jan 1989
TL;DR: The author index refers to the Pyridine Nucleotide Derivatives Index, which describes the biochemical and physiological properties of the molecule as well as the pharmacological and nutritional aspects of Glutathione.
Abstract: PART A: History of the Pyridine Nucleotides Nomenclature Evolution of Pyridine Nucleotide: Relationship Between Biosynthesis and Evolution Crystal Structure, Coenzyme Conformations, and Protein Interactions Optical Spectroscopy of Pyridine Nucleotides Excited States of Pyridine Nucleotide Coenzymes: Fluorescence and Phosphorescence Nuclear Magnetic Resonance Spectroscopy of Pyridine Nucleotides Mass Spectrometry of Pyridine Nucleotides Mechanism of Action of the Pyridine Nucleotides Chemical Stability and Reactivity of Pyridine Nucleotide Coenzymes Stereochemistry of Fatty Acid Biosynthesis and Metabolism Kinetics of Pyridine Nucleotide- Utilizing Enzymes Preparation and Properties of NAD and NADP Analog Model Studies and Biological Activity of Analogs Spin- Labeled Pyridine Nucleotide Derivatives Index. PART B: Pharmacological Aspects of Glutathione in Drug Metabolism Relationships Between Glutathione and Chemically Induced Lipid Peroxidation Hereditary Disorders Related to Glutathione Deficiency Influence of Glutathione on Membranes Metabolism of Thiosulfate and Thiosulfate Esters Glutathione in Ocular Tissues Estrogens and Glutathione Nutritional Aspects of Glutathione Metabolism and Function Author Index Subject Index.
560 citations
TL;DR: Results support a model of copper metabolism in which the metal is complexed by GSH soon after entering the cell, and suggest that resistance to metal toxicity in copper-resistant hepatoma cells is due to increases in both cellular GSH and MT.
537 citations
TL;DR: Observations of a "GSH deficiency" in IPF ELF suggest that there is a marked oxidant-antioxidant imbalance at the alveolar surface of these persons, thus increasing the susceptibility to the severe epithelial cell damage characteristic of this disease.
Abstract: Glutathione (L-gamma-glutamyl-L-cysteinyl-glycine, GSH), a sulfhydryl-containing tripeptide produced by most mammalian cells, is an efficient scavenger of toxic oxidants, including hydrogen peroxide, an oxidant that plays a major role in the oxidant burden placed on the epithelial surface of the lower respiratory tract in chronic inflammatory states. GSH is present in the epithelial lining fluid of the normal lower respiratory tract, where it is thought to play a major role in providing antioxidant protection to the epithelial cells. In this regard, we hypothesized that the lower respiratory tract of patients with IPF may be chronically depleted of this antioxidant, thus leading to an increased susceptibility of lung epithelial cells to oxidant injury. To evaluate this concept, the concentration of glutathione was determined in the epithelial lining fluid of the lower respiratory tract of 15 patients with IPF and compared to that of 19 normal subjects. Strikingly, whereas ELF glutathione concentrations were high in normal subjects (429 +/- 34 microM), a fourfold decrease was found in patients with IPF (97 +/- 18 microM, p less than 0.001). In the context of the known oxidant burden present in the lower respiratory tract of patients with IPF, these observations of a "GSH deficiency" in IPF ELF suggest that there is a marked oxidant-antioxidant imbalance at the alveolar surface of these persons, thus increasing the susceptibility to the severe epithelial cell damage characteristic of this disease.
449 citations
TL;DR: The apparent lack of defense mechanisms against oxidative stress may in part account for the 'fragility' of neurons in culture and the physiological implications of glutathione compartmentation in brain are discussed.
420 citations
TL;DR: Three models of free radical-induced cell injury are presented and, at least in the menadione-induced cytotoxicity, lipid peroxidation is not involved.
378 citations
TL;DR: A comparison of normal and acatalasemic erythrocytes in the present study indicated that catalase accounts for more than half of the destruction of H2O2 when H 2O2 is generated at a rate comparable to that which leads to hemolysis in G6PD- deficient ery Throcytes.
316 citations
Journal Article•
TL;DR: Results indicate that oxidative stress due to loss of cellular levels of GSH is one mechanism whereby Glu/quisqualate exert cytotoxicity and suggest that centrally active antioxidants may reduce neuronal damage in pathologic conditions associated with excessive Glu release.
Abstract: The effects of reducing agents and antioxidants on L-Glutamate (Glu)-induced cytotoxicity were examined in the N18-RE-105 neuronal cell line. The cytotoxicity by Glu (1 and 10mM) was potentiated by exposure to growth medium containing a low concentration of cystine (5-100 microM), instead of the normal medium containing 200 microM cystine. In contrast, the toxicity was suppressed by increasing the cystine concentration to 500 to 1000 microM. Reducing agents, cysteine (30-1000 microM), dithiothreitol (10-250 microM) and glutathione (GSH, 10-1000 microM) also protected the cells against the cytotoxicity of 10 mM Glu in a concentration-dependent manner. The antioxidants vitamin E (10-100 microM), idebenone (0.1-3 microM) and vinpocetine (10-100 microM) also provided marked protection against the cytotoxicity of Glu (10 mM) or quisqualate (1 mM). Antioxidants also prevented the delayed cell death caused by lowering the concentration of cystine in the medium to 5 microM. Incubation of the cells with 10 mM Glu caused a marked decrease in cellular GSH levels. Although cysteine and dithiothreitol prevented the GSH reduction caused by Glu, antioxidants did not. The cellular levels of oxidants were assessed using 2,7-dichlorofluorescin, a probe that accumulates within cells and is converted to a fluorescent product by oxidation. Glu (10 mM) caused a marked increase in such fluorescence, whereas vitamin E and idebenone reduced markedly the number of fluorescent cells to control levels even added with 10 mM Glu. These results indicate that oxidative stress due to loss of cellular levels of GSH is one mechanism whereby Glu/quisqualate exert cytotoxicity and suggest that centrally active antioxidants may reduce neuronal damage in pathologic conditions associated with excessive Glu release.
TL;DR: The metabolism of glutathione and activities of its related enzymes were studied in erythrocytes from patients with non-insulin-dependent diabetes mellitus to suggest that the impairment ofglutamylcysteine synthetase weakens the defense mechanism against oxidative stress in ERY Throatcytes of diabetics.
Abstract: The metabolism of glutathione and activities of its related enzymes were studied in erythrocytes from patients with non-insulin-dependent diabetes mellitus (NIDDM). A decrease in the levels of the reduced form of glutathione and an increase in the levels of glutathione disulfide were found in erythrocytes of diabetics. To elucidate these changes in the levels of glutathione, synthetic and degradative processes were studied. The activity of gamma-glutamylcysteine synthetase was significantly lower in diabetics than in normal controls. The activity of glutathione synthetase of each group was the same. The rate of outward transport of glutathione disulfide in diabetics decreased to approximately 70% of that of normal controls. The activity of glutathione reductase decreased in diabetics. These data suggest that the decrease in the levels of reduced form of glutathione in erythrocytes of diabetics is brought about by impaired glutathione synthesis and that the increase in the levels of glutathione disulfide is brought about by the decreased transport activity of glutathione disulfide through the erythrocyte membrane together with a decrease in the activity of glutathione reductase. These data also suggest that the impairment of glutathione metabolism weakens the defense mechanism against oxidative stress in erythrocytes of diabetics.
TL;DR: Results indicate that deprenyl suppresses an oxidant stress associated with increased dopamine turnover as an index of changes in redox state in the striatum.
Abstract: Tissue glutathione disulfide (GSSG) was studied as an index of changes in redox state in the striatum When increased turnover of dopamine was provoked in mice by injection of haloperidol (1 mg/kg), the concentration of GSSG in the striatum tripled Deprenyl (25 mg/kg) suppressed the rise in GSSG by 719% These results indicate that deprenyl suppresses an oxidant stress associated with increased dopamine turnover
TL;DR: The data show that NAC leads to a marked increase in circulating Cysteine, in part by reacting with cystine and thereby forming mixed disulphides with cysteine and releasing free cysteined as shown in vitro.
Abstract: The effect of oral N-acetyl-L-cysteine (NAC) on plasma sulphhydryls has been studied in healthy volunteers. Following NAC 30 mg.kg-1, total NAC in plasma (i.e. free NAC and NAC as disulphides) reached a median peak concentration of 67 nmol.ml-1 within 45 to 60 min, and disappeared with an apparent half-life of 1.3 h. Only a fraction of total NAC (AUC 163 nmol.ml-1.h) was in the form of free NAC (AUC 12 nmol.ml-1.h, peak concentration 9 nmol.ml-1). Free cysteine was markedly increased (peak increment 49 nmol.ml-1; AUC 80 nmol.ml-1.h). Total cysteine and free and total glutathione in plasma were unchanged. Following the administration of 2 g paracetamol plasma cysteine and glutathione decreased (median decrement in AUC over 3 h was 5.1 nmol.ml-1.h and 3.8 nmol.ml-1.h, respectively). In contrast, the administration of 2 g NAC together with paracetamol resulted in an increase in the AUC of cysteine (+29.2 nmol.ml-1.h) and glutathione (+4.6 nmol.ml-1.h). The data show that NAC leads to a marked increase in circulating cysteine, in part by reacting with cystine and thereby forming mixed disulphides with cysteine and releasing free cysteine as shown in vitro. NAC had no effect on plasma glutathione in the absence of increased stress on the glutathione pools. However, NAC supports glutathione synthesis when the demand for glutathione is increased, as during the metabolism of paracetamol.
TL;DR: A persuasive body of evidence indicates that substantial protection against chemical carcinogenesis can be achieved by induction of enzymes concerned with the metabolism of carcinogens, and selective Phase II enzyme inducers offer intrinsically safer prospects for achieving chemoprotection.
TL;DR: The effect of metallothionein on hydroxyl-radical-induced DNA damage was investigated in an in-vitro study and the degradation of DNA was almost completely inhibited by a concentration of 13 microM MT, whereas a concentrationof glutathione was needed to achieve the same protective effect.
TL;DR: It is indicated that immediately after exposure to a large fluence of ultraviolet radiation the enzymic and nonenzymic antioxidant capacity of skin decreases significantly.
TL;DR: Low concentrations of tert-butyl hydroperoxide (less than 1.0 mM) lethally injure cultured hepatocytes by a mechanism that depends on the peroxidation of cellular lipids, and DPPD and catechol do not detoxify a radical species that kills the cells and initiates lipid per oxidation as an epiphenomenon.
TL;DR: The likelihood that sulfhydryl groups of p60v-src are involved in the inactivation of v-src tyrosine kinase activity by herbimycin A is suggested.
TL;DR: These studies show that in the absence of applied stress, very marked depletion of glutathione must occur before skeletal muscle mitochondria are affected and thus suggest that muscle has a large excess of glutATHione.
Abstract: Skeletal muscle degeneration associated with mitochondrial damage was found after marked depletion of glutathione produced by administration to mice of buthionine sulfoximine, an irreversible inhibitor of gamma-glutamylcysteine synthetase. No mitochondrial damage was found in heart. These studies show that in the absence of applied stress (such as ischemia, drug toxicity), very marked depletion (to approximately 3% of the controls) of glutathione must occur before skeletal muscle mitochondria are affected and thus suggest that muscle has a large excess of glutathione. Depletion of glutathione followed a biphasic pattern in skeletal muscle and heart, probably reflecting, in the slow phase, loss of glutathione from mitochondria. Skeletal muscle degeneration did not occur when glutathione monoisopropyl ester was given together with buthionine sulfoximine; it did occur, however, when glutathione was given together with buthionine sulfoximine. Administration of the glutathione monoester (but not of glutathione) prevented the marked decline of mitochondrial glutathione produced by buthionine sulfoximine in skeletal muscle and increased the level of glutathione in heart mitochondria to values higher than the controls. The findings suggest that glutathione monoesters may be useful agents for protection of heart and skeletal muscle against toxicity.
TL;DR: S-Adenosyl-L-methionine therapy resulted in a significant increase of hepatic glutathione levels both in patients with alcoholic and in those with non-alcoholic liver diseases as compared with placebo-treated patients, suggesting that SAMe may exert an important role in reversing liver disease.
Abstract: S-Adenosyl-l-methionine (SAMe) is a physiologic precursor of thiols and sulfurated compounds, which are known to be decreased in patients with liver disease. The effect of its administration on the hepatic glutathione content of liver patients was investigated. Four groups of subjects were selected: a) 9 patients with alcoholic liver disease treated with SAMe (1.2g/day orally for 6 months); b) 7 patients with nonalcoholic liver disease treated as above; c) 8 placebo-treated patients with alcoholic liver disease; and d) 15 normal subjects as a control group. Total and oxidized glutathione were assayed by high-performance liquid chromatography of liver biopsy specimens before and after the treatment period. In all patients pre-treatment hepatic glutathione was significantly decreased as compared with controls. SAMe therapy resulted in a significant increase of hepatic glutathione levels both in patients with alcoholic and in those with non-alcoholic liver diseases as compared with placebo-treated patients. ...
TL;DR: The chemical identity of the adduct was confirmed by mass spectrometry and the recovery of reduced and oxidized glutathione from rat liver homogenate, bile, and plasma is quantitative.
TL;DR: The data suggest that ethanol feeding causes a marked alteration of vitamin E metabolism in the liver and that the combination of ethanol with a low‐vitamin E intake results in a decrease of hepatic α‐tocopherol content which renders the liver more susceptible to free radical attack.
01 Jan 1989
TL;DR: The active oxygen generation in the mixture of selenite and GSH is examined by using luminol- or lucigenin-dependent chemiluminescence (CL) as an indicator to estimate the relationship between GSH and the selenites-induced lipid peroxidation.
Abstract: Increased lipid peroxidation caused by selenite treatment was observed in vivo (Dougherty and Hoekstra 1982) and in vitro (Bunyan et al. 1960; Stacey and Klaassen 1981; Seko 1986). In vitro treatment of cells with selenite resulted in the decreased content of reduced glutathione and NADPH (Tsen and Collier 1960; Anundi et al. 1984), which are important in protecting cells against oxidation. However, the decrease in GSH concentration did not always relate to cell damage (Tsen and Collier 1960; Seko 1986) or lipid peroxidation (Seko 1986) in erythrocyte suspension. On the other hand, the importance of GSH (Young et al. 1981) or reactive sulfhydryls of hemoglobin (Seko 1986) have been considered to play an important role in selenite induced in vitro hemolysis. In order to estimate the relationship between GSH and the selenite-induced lipid peroxidation, we have examined the active oxygen generation in the mixture of selenite and GSH by using luminol- or lucigenin-dependent chemiluminescence (CL) as an indicator.
TL;DR: In vivo the H2O2-scavenging system in chloroplasts is the best documented role of reduced glutathione and glutATHione reductase in plants; but the pathway, in terms of intermediates, is controversial.
Abstract: The assay and in vitro characterization of glutathione reductase (EC 1.6.4.2) is discussed. In vivo the H2O2-scavenging system in chloroplasts is the best documented role of reduced glutathione and glutathione reductase in plants. Similarly, redaction of H2O2, outside of the chloroplasts, requires glutathione and glutathione reductase; but the pathway, in terms of intermediates, is controversial. The notion that biological stress frequently causes cellular oxidation has lead to the suggestion that glutathione and glutathione reductase may play a role in stress resistance or tolerance mechanisms. The changes in glutathione reductase levels in response to low temperature, oxidative stress and drought are discussed.
Journal Article•
TL;DR: The results with Meth A suggest that the interaction of rhTNF with this cell line does not occur in the same manner as the other cell lines, perhaps due to receptor differences or to some type of "uncoupling" of the signal-response network between the TNF receptor and a putative secondary messenger(s).
Abstract: Treatment of three murine tumor cell lines, L929, P388, and Pan-02, in vitro with recombinant human tumor necrosis factor (rhTNF) produced evidence of oxidative damage as measured by (a) increases in intracellular glutathione levels, (b) the formation of intracellular oxidized glutathione and (c) the formation of thymine glycols in DNA. L929, the most sensitive of the three cell lines to the cytotoxic activity of rhTNF, had the lowest total glutathione content and was observed to have the highest levels of oxidized glutathione and thymine glycol formation. In addition, the radical buffering capacity of these cells was significantly compromised within 7 h of treatment with rhTNF. The P388 and Pan-02 cell lines, with total glutathione levels about 50-fold higher than L929, also showed evidence of oxidative attack, although to a lesser extent than L929. The radical buffering capacity of these cell lines was not altered by rhTNF treatment. A rhTNF-resistant subline of L929 (L929r), produced by successive passaging in vitro in the presence of TNF, increased its glutathione and oxidized glutathione levels in response to a subsequent rhTNF challenge. Meth A, a cell line resistant to rhTNF in vitro but not in vivo, showed no evidence of oxidative damage following rhTNF treatment, despite having a low radical scavenging capacity and a sensitivity to H2O2. The results with Meth A suggest that the interaction of rhTNF with this cell line does not occur in the same manner as the other cell lines, perhaps due to receptor differences or to some type of "uncoupling" of the signal-response network between the TNF receptor and a putative secondary messenger(s). These results are consistent with the hypothesis that: (a) the mechanism of action of rhTNF involves the production of oxidative damage, including damage to the DNA; (b) the sensitivity to rhTNF in vitro is related to the radical scavenging capacity of the cell; and (c) cells can respond to rhTNF challenge by increasing their free radical scavenging capacity.
TL;DR: Results suggest that silybin dihemisuccinate, a soluble form of the flavonoid silymarin, protects rats against liver glutathione depletion and lipid peroxidation induced by acute acetaminophen intoxication.
Abstract: Acetaminophen hepatotoxicity is characterized by glutathione depletion, cellular necrosis, and, in some instances, by the induction of lipid peroxidation. Silybin dihemisuccinate, a soluble form of the flavonoid silymarin, protects rats against liver glutathione depletion and lipid peroxidation induced by acute acetaminophen intoxication. Other biochemical parameters such as serum transaminases did not show the drastic increase observed under acetaminophen intoxication when animals were treated with the flavonoid. Preliminary results suggest that silybin dihemisuccinate may be another antidote against acetaminophen hepatotoxicity.
TL;DR: It is pointed out that GSH transferase 5*-5* an enzyme extracted from the nucleus with urea which has a relatively high activity towards DNA hydroperoxide may be important participants in mechanism for the repair of free-radical damage.
Abstract: Two types of GSH peroxidase occur in the cell both of which detoxify fatty acid hydroperoxides, thymine hydroperoxide and DNA hydroperoxides. One is a Se-dependent enzyme which also detoxifies H2O2. The other contains members of the GSH transferase supergene family. These non-selenium dependent GSH peroxidases do not detoxify H2O2 and have substrate specificities varying markedly with the isoenzyme. Of particular interest is GSH transferase 5*-5* an enzyme extracted from the nucleus with urea which has a relatively high activity towards DNA hydroperoxide. The possible role of these enzymes in the detoxication of lipid and DNA hydroperoxides is discussed and it is pointed out that they may be important participants in mechanism for the repair of free-radical damage.
TL;DR: BSO treatment was found to partially inhibit DNA repair, and the addition of aphidicolin caused nearly a 100% inhibition in DNA repair activity, the significance to the chemosensitizing effects of BSO medicated glutathione reduction is discussed.
Abstract: We have studied the effect of glutathione reduction by buthionine sulfoximine (BSO), a specific inhibitor of gamma -glutamyl cysteine synthetase, on DNA repair after cisplatin damage in an ovarian cancer cell line with in vitro induced resistance to cisplatin. In addition, we have examined the effect of aphidicolin, a specific inhibitor of DNA polymerase alpha, in combination with BSO on cisplatin-associated DNA repair. BSO treatment was found to partially inhibit DNA repair, and the addition of aphidicolin caused nearly a 100% inhibition in DNA repair activity. Treatment of cells with glutathione ester after BSO resulted in complete recovery of DNA repair activity or partial recovery if aphidicolin was present. The significance of these results to the chemosensitizing effects of BSO medicated glutathione reduction is discussed.
TL;DR: The results suggest that the canalicular transport system for glutathione and glutATHione conjugates is severely impaired in TR- rats, whereas sinusoidal efflux is unaffected.
Abstract: TR- mutant rats have an autosomal recessive mutation that is expressed as a severely impaired hepatobiliary secretion of organic anions like bilirubin-(di)glucuronide and dibromosulphthalein (DBSP). In this paper, the hepatobiliary transport of glutathione and a glutathione conjugate was studied in normal Wistar rats and TR- rats. It was shown that glutathione is virtually absent from the bile of TR- rats. In the isolated, perfused liver the secretion of glutathione and the glutathione conjugate, dinitrophenyl-glutathione (GS-DNP), from hepatocyte to bile is severely impaired, whereas the sinusoidal secretion from liver to blood is not affected. The secretion of GS-DNP was also studied in isolated hepatocytes. The secretion of GS-DNP from cells isolated from TR- rat liver was significantly slower than from normal hepatocytes. Efflux of GS-DNP was a saturable process with respect to intracellular GS-DNP concentration: Vmax and Km for efflux from TR- cells was 498 nmol/min.g dry wt and 3.3 mM, respectively, as compared with 1514 nmol/min.g dry wt and 0.92 mM in normal hepatocytes. These results suggest that the canalicular transport system for glutathione and glutathione conjugates is severely impaired in TR- rats, whereas sinusoidal efflux is unaffected. Because the defect also comes to expression in isolated hepatocytes, efflux of GS-DNP from normal hepatocytes must predominantly be mediated by the canalicular transport mechanism, which is deficient in TR- rats.