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Reaction of para-hydroxybenzoic acid esters with singlet oxygen in the presence of glutathione produces glutathione conjugates of hydroquinone, potent inducers of oxidative stress.

The determination and toxicological characterization of products of the reaction between p-hydroxybenzoic acid esters (parabens) and singlet oxygen ((1)O(2)) are very important because of the frequent use of parabens in cosmetics and possible generation of (1)O(2) in the skin. We observed (1)O(2)-dependent production of mono-, di-, and tri-substituted glutathione (GSH) conjugates of hydroquinone (HQ) during visible light-irradiation of a mixture of methyl or ethyl paraben and GSH in the presence of rose bengal (RB). 1,4-Benzoquinone (BQ) and HQ were produced during the irradiation in the absence of GSH. While a mixture of BQ and GSH produced only mono-substituted conjugate, irradiation of the mixture with RB produced mono-, di-, and tri-substituted conjugates. These observations indicate that (1)O(2) is involved both in the production of BQ and HQ from parabens and in the formation of multi-substituted GSH conjugates from mono-substituted conjugate. Tri-substituted conjugate generated larger amounts of hydrogen peroxide in an aqueous solution than mono-substituted conjugates or HQ did. Detection of semiquinone radical suggests that the autoxidation of conjugates is related to the generation of hydrogen peroxide. The results obtained in this study indicate that parabens may induce oxidative stress in the skin after conversion to GSH conjugates of HQ by reacting with (1)O(2) and GSH.

Chromatography, High Pressure Liquid↗

Hydrogen peroxide inhibits gap junctional intercellular communication in glutathione sufficient but not glutathione deficient cells.

Cell to cell communication via gap junctions is essential in the maintenance of the homeostatic balance of multicellular organisms. Aberrant intercellular gap junctional communication (GJIC) has been implicated in tumor promotion, neuropathy and teratogenesis. Oxidative stress has also been implicated in similar pathologies such as cancer. We report a potential link between oxidative stress and GJIC. Hydrogen peroxide, a known tumor promoter, inhibited GJIC in WB-F344 rat liver epithelial cells with an I50 value of 200 microM. Inhibition of GJIC by H2O2 was reversible as indicated by the complete recovery of GJIC with the removal of H2O2 via a change of fresh media. Free radical scavengers, such as t-butyl alcohol, propylgallate, and Trolox, did not prevent the inhibition of GJIC by H2O2, which indicated that the effects of H2O2 on GJIC was probably not a consequence of aqueous free radical damage. The depletion of intracellular GSH reversed the inhibitory effect of H2O2 on GJIC. The treatment of glutathione-sufficient cells with H2O2 resulted in the hyperphosphorylation of connexin43, which is the basic subunit of the hexameric gap junction protein, as determined by Western blot analysis. TPA, a well-known tumor promoter, also inhibits GJIC via hyperphosphorylation of GJIC, which is a result of protein kinase-C activation. However, H2O2 also induced hyperphosphorylation in GSH-deficient cells that had normal rates of GJIC. Therefore, the mechanism of GJIC inhibition must be different from the TPA-pathway and involves GSH.

Animals↗

Glutathione depletion suppresses conjugation of benzo[a]pyrene metabolites and (+/-)-trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene metabolites with glutathione but does not affect their binding to DNA in C3H/10T1/2 mouse fibroblasts.

The study was aimed at determining the role of glutathione (GSH) conjugation in the binding of reactive benzo[a]pyrene (BaP) species to DNA of C3H/10T1/2 cells. In order to suppress GSH conjugation cells were depleted of GSH by treatment with buthionine sulfoximine for 18 h and 1-chloro-2,4-dinitrobenzene for 1 h prior to incubation with radiolabelled substrates. Under these conditions GSH levels decreased to less than 1% of the control value. C3H/10T1/2 cells produced GSH conjugates with 7,8-dihydroxy-9,10-oxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BaPDE) comprising 6% of the total metabolites formed from BaP or (+/-)-trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene (BaP-7,8-diol). In GSH-depleted cells formation of GSH conjugates with metabolic products of BaP or BaP-7,8-diol was suppressed to 1% of total metabolites during an 8-h incubation period. Metabolic activation of BaP and BaP-7,8-diol by C3H/10T1/2 cells resulted in the formation of DNA adducts which largely consisted of BaPDE:deoxyguanosine. Depletion of GSH altered neither the degree of DNA binding nor the pattern of DNA adducts to any significant extent. When C3H/10T1/2 cells were co-incubated with microsomes from liver of 3-methylcholanthrene-treated rats for 1 h in order to activate BaP or BaP-7,8-diol extracellularly, the same pattern of GSH conjugates and DNA adducts was generated as by intracellular metabolism of the polycyclic hydrocarbons. No GSH conjugates were detected following co-incubation of microsomes with GSH-depleted C3H/10T1/2 cells. The formation of DNA adducts again remained unaffected by the suppression of conjugation. C3H/10T1/2 cells are apparently capable of conjugating BaPDE with GSH but are not capable of trapping by GSH conjugation those BaPDE moieties which bind to DNA. The results are compatible with the notion that BaPDE is partially contained in a cellular compartment--presumably the lipid environment of membranes--where it is inaccessible to GSH transferases of C3H/10T1/2 cells.

Animals↗

The selenium requirement for glutathione peroxidase mRNA level is half of the selenium requirement for glutathione peroxidase activity in female rats.

To determine critically the selenium (Se) requirement for weanling female rats, we used glutathione peroxidase (GSH: H2O2 oxidoreductase, EC 1.11.1.9) (GPX) mRNA and a number of other parameters to assess Se status. Rats were fed a basal torulayeast diet (0.007 micrograms Se/g) supplemented with Se as Na2SeO3 in graded levels from 0 to 0.3 micrograms Se/g diet for 32 d (3 rats/group). Selenium supplementation had no effect on growth, showing that the Se requirement for growth is less than 0.007 micrograms Se/g diet, whereas other parameters showed significant increases with Se supplementation. In rats fed the Se-deficient basal diet, liver Se concentration was 4 +/- 0%, plasma GPX activity was 8 +/- 1%, erythrocyte GPX activity was 40 +/- 3%, liver GPX activity was 2 +/- 1%, and liver GPX mRNA levels were 11-17% of the levels in rats fed 0.1 micrograms Se/g diet. Liver Se concentration and GPX activity in plasma, erythrocytes and liver all reached a plateau breakpoint at or near 0.1 micrograms Se/g diet, indicating that the dietary Se requirement for maximal GPX activity in growing female rats is 0.1 micrograms Se/g diet. Liver GPX mRNA levels reached the plateau breakpoint at 0.05 micrograms Se/g diet, showing that the minimum dietary Se requirement for maximal GPX mRNA levels in female rats is half of the Se requirement for maximal GPX activity. This experiment demonstrates that GPX mRNA can be used to determine the dietary Se requirement; the gap between the dietary Se necessary for maximal GPX mRNA and that for maximal GPX activity may represent an evolutionarily derived biological margin of safety.

Analysis of Variance↗

Modulation of the clastogenic activity of bleomycin by reduced-glutathione, glutathione-ester and buthionine sulphoximine.

In this study an attempt has been made to establish a relationship between bleomycin (BLM)-induced DNA damage and buthionine sulphoximine (BSO)-mediated modified endogenous glutathione (GSH) status in normal human lymphocytes. Present results demonstrate that depletion of endogenous GSH by BSO reduced the clastogenic action of BLM, whereas elevation of endogenous GSH by treating the cells with GSH and GSH-ester, potentiates the cytotoxicity of BLM. A significant reduction in the frequency of deletions and chromatid breaks was observed when BSO-treated cells were treated with BLM. Again the frequency of these two types of aberrations was increased significantly when GSH- and GSH-ester-treated cells were treated with BLM. The observed reduction in the effect of BLM in GSH-depleted cells could be explained on the basis of the failure of reactivation of the oxidized BLM by reducing agent GSH which is present endogenously. Similarly, it appears that radicals which are generated due to reduction of oxidized BLM by the increased level of cellular GSH, after treating the cells with GSH or GSH-ester, could be responsible for the increasing frequency of deletion and chromatid breaks.

Antimetabolites, Antineoplastic↗

Characterization of glutathione S-transferase from dust mite, Der p 8 and its immunoglobulin E cross-reactivity with cockroach glutathione S-transferase.

BACKGROUND: Sensitization to mite and cockroach allergens is common, and diagnosis and therapy of allergy can be further complicated by the presence of allergen isoforms and panallergens. Purified recombinant and native allergens are useful for studies to resolve such problems. OBJECTIVE: To assess the allergenicity of native and recombinant mite glutathione S-transferase (GST) (Der p 8) and study the IgE cross-reactivity between Der p 8 and cockroach GST. METHODS: Der p 8 cDNA encoding a new isoform was isolated and expressed in yeast. Native Der p 8 was affinity purified from mite extract. IgE reactivity to native and recombinant Der p 8 was assessed by ELISA using sera from allergic subjects from Taiwan, Singapore and Malaysia. IgE cross-reactivity between Der p 8 and cockroach GST was examined by IgE inhibition assays. RESULTS: Our Der p 8 cDNA encoded a basic isoform (pI=8.5) containing six polymorphic residues located at positions 46, 106, 149, 160, 167 and 184. At least 8 isoforms of native Der p 8 were detected by two-dimensionalgel and immunoblot analyses. Sera from Taiwanese asthmatics showed 96% and 84% IgE reactivity to native Der p 8 and recombinant Der p 8, respectively. Native Der p 8 showed 75% and 65% IgE reactivity with sera from Malaysia and Singapore, respectively. CONCLUSIONS: A high frequency of sensitization to mite GST among allergic subjects was observed but the titres of IgE reactivity were low. The IgE cross-reactivity between mite and cockroach GST suggests that GST is a panallergen.

Adolescent↗

Modification of intracellular levels of glutathione-dependent formaldehyde dehydrogenase alters glutathione homeostasis and root development.

Glutathione (GSH)-dependent formaldehyde dehydrogenase (FALDH) is a highly conserved medium-chain dehydrogenase reductase and the main enzyme that metabolizes intracellular formaldehyde in eukaryotes. It has been recently shown that it exhibits a strong S-nitrosoglutathione (GSNO) reductase activity and could be a candidate to regulate NO-signalling functions. However, there is a lack of knowledge about the tissue distribution of this enzyme in plants. Here, we have studied the localization and developmental expression of the enzyme using immunolocalization and histochemical activity assay methods. We conclude that FALDH is differentially expressed in the organs of Arabidopsis thaliana mature plants, with higher levels in roots and leaves from the first stages of development. Spatial distribution of FALDH in these two organs includes the main cell types [epidermis (Ep) and cortex (Cx) in roots, and mesophyll in leaves] and the vascular system. Arabidopsis thaliana mutants with modified levels of FALDH (both by over- and under-expression of the FALDH-encoding gene) show a significant reduction of root length, and this phenotype correlates with an overall decrease of intracellular GSH levels and alteration of spatial distribution of GSH in the root meristem. Tansgenic roots are partially insensitive to exogenous GSH, suggesting an inability to detect reduction-oxidation (redox) changes of the GSH pool and/or maintain GSH homeostasis.

Aldehyde Oxidoreductases↗

Glutathione conjugation by isolated lung cells and the isolated, perfused lung. Effect of extracellular glutathione.

Cells isolated from rat lung by protease digestion were found to catalyze the reduced glutathione (GSH) conjugation of 1-chloro-2,4-dinitrobenzene. The rate of conjugation was stimulated severalfold in the presence of GSH, indicating uptake and utilization of extracellular GSH by the lung cells. The stimulation was dependent on the GSH concentration and not due to a spontaneous nonenzymatic reaction or to extracellular GSH-transferase activity. Conjugation of 1-chloro-2,4-dinitrobenzene was also measured using isolated perfused rat lung. The conjugation, which was linear for a longer time than with the isolated cells, was also stimulated in the presence of GSH in the perfusion medium. The results indicate the ability of rat lung to utilize extracellular GSH.

Animals↗

Cytosolic rat liver glutathione transferase 4-4. Primary structure of the protein reveals extensive differences between homologous glutathione transferases of classes alpha and mu.

The primary structure of the class Mu glutathione transferase 4-4 from rat liver was determined. The structural data characterize a class Mu protein within an enzyme family for which three classes have been distinguished (Alpha, Mu, Pi). The structure was determined by analysis of peptides obtained after treatment with trypsin. Glu-specific protease and CNBr. The protein is composed of two identical subunits, each with 217 amino acid residues. No evidence for microheterogeneity or for the presence of modified residues was encountered. The primary structure was found to be strictly homologous with corresponding parts in known regions of other class Mu enzymes of rat, mouse, human and bovine origin. Relationships to the cytosolic enzyme of other classes (Pi and Alpha) are considerably more distant. A comparison with the entire chain of the class Alpha subunit 1 from rat liver was carried out by three methods, alignment of amino acid sequences, correlation of hydrophilicity plots and predictions of secondary structures. All methods reveal weak similarities but also large differences. The overall positional identity is only 26%. Combined, the results establish the first complete class Mu structure, show distant inter-class relationships, and relate subunit 4 (class Mu) and subunit 1 (class Alpha) in a family of enzymes rather than in a group of isoenzymes.

Amino Acid Sequence↗

Mechanism of renal peritubular extraction of plasma glutathione. The catalytic activity of contralumenal gamma-glutamyltransferase is prerequisite to the apparent peritubular extraction of plasma glutathione.

To clarify the peritubular mechanism for renal handling of plasma glutathione (GSH), variation of GSH levels in plasma, urine, kidney and liver was examined after intravenous administration of GSH to three groups of animals; control, acivicin-treated and rats treated with buthionine sulfoximine (BSO). Treatment of animals with BSO, a potent inhibitor of de novo GSH synthesis, markedly reduced hepatorenal GSH levels. Acivicin did not affect these levels. Upon intravenous injection of GSH (0.1 mmol/kg), renal GSH levels did not appreciably change in any of three animal groups. The rate of GSH disappearance from the circulation was rapid in control and BSO-treated rats, while it was markedly retarded in animals whose renal gamma-glutamyltransferase was extensively inactivated by acivicin. At 30 min after administration a significant amount of injected GSH was localized extracellularly (urine and plasma) in acivicin-treated animals. By contrast, most of the GSH rapidly disappeared from the extracellular space in control and BSO-treated animals. Together with the immunocytochemical evidence for the peritubular gamma-glutamyltransferase [Spater, H.W., Poruchynsky, M.S., Quintana, N., Inoue, M. & Novikoff, A.B. (1982) Proc. Natl Acad. Sci. USA 79, 3547-3550] the present results are fully consistent with the contention that the catalytic function of this enzyme is principally responsible for the peritubular mechanism for the renal handling of plasma GSH.

Animals↗

Multi-institutional phase 2 study of TLK286 (TELCYTA, a glutathione S-transferase P1-1 activated glutathione analog prodrug) in patients with platinum and paclitaxel refractory or resistant ovarian cancer.

The purpose of this study was to determine the safety and efficacy of TLK286 (TELCYTA(TM)), a glutathione analog prodrug, in patients with platinum and paclitaxel refractory or resistant ovarian carcinoma. Thirty-six patients with measurable disease were enrolled. TLK286 was administered at 1000 mg/m2 intravenously every 3 weeks. The endpoints were objective response rate assessed by Response Evaluation Criteria in Solid Tumors (RECIST) and survival. Adverse events were graded using the National Cancer Institute Common Toxicity Criteria. Thirty-four platinum refractory or resistant patients (94%) were evaluable for objective tumor response. Five patients (15%) had objective tumor responses, including one durable complete response (CR) of greater than 3 years and continuing. The disease stabilization rate was 50%, including one CR (3%), four partial responses (12%), and 12 durable disease stabilizations (35%). Responses were accompanied by improvement in clinical symptoms and Eastern Cooperative Oncology Group Performance Status (ECOG PS) and decline in CA125 levels. Median survival was 423 days with survival of 60% at 1 year and 40% at 18 months. TLK286 was well tolerated in this population. TLK286 is an active agent in chemotherapy-resistant ovarian cancer. Further studies of TLK286 in platinum and paclitaxel refractory or resistant ovarian cancer are in progress.

Adult↗

Identification of a coenzyme A--glutathione disulfide (DSI), a modified coenzyme A disulfide (DSII), and a NADPH-dependent coenzyme A--glutathione disulfide reductase in E. coli.

The nucleotides DSI and DSII induced during a slowdown in growth of E. coli have been characterized using chemical and biochemical analysis and by enzymic and alkaline fragmentation. DSI consists a coenzyme A and glutathione joined by a disulfide linkage. DSI could be isolated either containing Fe(III) with an A250:260 ratio of 1.05 or not containing iron with an A250:260 of 0.87. DSII (isolated in 10% the yield of DSI) is a coenzyme A disulfide dimer that also contains two molecules of glutamic acid. DSI was a substrate for NADPH-dependent CoAS-SG reductase (EC 1.6.4.6) which was present in crude extracts of E. coli. The specific activity of CoAS-SG reductase increased during growth from early log phase into stationary phase and during a shift from aerobic to anaerobic growth.

Coenzyme A↗

Effects of chronic ethanol feeding on rat hepatocytic glutathione. Relationship of cytosolic glutathione to efflux and mitochondrial sequestration.

Chronic ethanol feeding to rats increases the sinusoidal component of hepatic glutathione (GSH) efflux, despite a lower steady-state GSH pool size. In the present studies, no increase of biliary GSH efflux in vivo was found in chronic ethanol-fed cells. Studies were performed on ethanol-fed and pair-fed cells to identify the kinetic parameters of cellular GSH concentration-dependent efflux. The relationship between cytosolic GSH and the rate of efflux was modeled by the Hill equation, revealing a similar Vmax, 0.22 +/- 0.013 vs. 0.20 +/- 0.014 nmol/min per 10(6) cells for ethanol-fed and pair-fed cells, respectively, whereas the Km was significantly decreased (25.3 +/- 2.3 vs. 33.5 +/- 1.4 nmol/10(6) cells) in ethanol-fed cells. The difference in Km was larger when the data were corrected for the increased water content in ethanol-fed cells. We found a direct correlation between mitochondria and cytosolic GSH, revealing that mitochondria from ethanol-fed cells have less GSH at all cytosolic GSH values. The rate of resynthesis in depleted ethanol-fed cells in the presence of methionine and serine was similar to control cells and gamma-glutamylcysteine synthetase remained unaffected by chronic ethanol. However, the reaccumulation of mitochondrial GSH as the cytosolic pool increased was impaired in the ethanol cells. The earliest time change in GSH regulation was a 50% decrease in the mitochondrial GSH at 2 wk.

Alcoholism↗

Inhibitory effects of S-(1,2-dicarboxyethyl)glutathione on collagen-induced platelet aggregation; enhancements of cyclic AMP level and adenylate cyclase activity in platelets by S-(1,2-dicarboxyethyl)glutathione.

S-(1,2-Dicarboxyethyl)glutathione (DCE-GS) in addition to being present in the liver, lens, and heart, also inhibited platelet aggregation. To clarify these inhibitory effects, the role of DCE-GS in the release of ATP and serotonin from platelets was studied, as was thromoboxane A2 formation, cyclic AMP level and adenylate cyclase activity in human platelets. The results are as follows: DCE-GS at a concentration of 1.3 mM inhibited ATP and serotonin release from platelets induced by collagen, by 77.4 +/- 4.3 and 78.7 +/- 6.3%, respectively. At 1.5 mM DCE-GS also inhibited the formation of thromboxane B2 by 79.6 +/- 4.1%. Incubation of human platelet rich plasma with 2 mM of DCE-GS for 10 min increased the cyclic AMP level and the activity of adenylate cyclase by 204 +/- 28 and 211 +/- 11.7%, respectively. These results suggest that the inhibitory effect of DCE-GS on the platelet aggregation induced by collagen is due to an increase in the cyclic AMP level in platelets, which in turn may be due to enhancement of the activity of adenylate cyclase.

Adenosine Triphosphate↗

Effect of glutathione on lambda deoxyribonucleic acid strand breaks in the reaction system of glutathione-alloxan in the presence of Fe(3+)-ethylenediaminetetraacetic acid.

Alkaline sucrose density gradient and agarose gel electrophoresis methods were used to observe lambda deoxyribonucleic acid (DNA) strand breaks by the reaction system of reduced glutathione (GSH) with alloxan in the presence of Fe(3+)-ethylenediaminetetraacetic acid (EDTA). When DNA was incubated in the reaction system for 10 min, DNA strand breaks were easily induced. The increasing concentrations of GSH up to 1.0 mM in the reaction system in the presence of 1.0 mM alloxan caused DNA strand breaks in a concentration-dependent fashion and GSH beyond 2.0 mM caused in the strand breaks of DNA by which the fragments with multiple ranges of molecular weight were produced. The strand breaks of DNA in the reaction system containing low concentrations of GSH were protected by catalase and hydroxyl radical (HO.) scavengers but superoxide dismutase (SOD) did not, indicating that such breaks were induced by HO.generated from the Fenton reaction. On the other hand, the strand breaks of DNA at high concentrations of GSH were protected by ethanol and desferrioxamine, but not effectively by SOD and HO.scavengers, suggesting the possible participation of some oxidizing species of iron rather than HO.. These results indicate that HO.or oxidizing species of iron generated in the GSH-alloxan system depending on the concentration of GSH attacks DNA to produce strand breaks.

Alloxan↗

Mitochondrial glutathione transferases. The alkylation of mitochondrial membrane yields a catalyst with glutathione-transferase-like properties.

The pretreatment of rat liver mitochondria with alkylating agents (N-ethylmaleimide, iodoacetamide or vinyl pyridine) increased the activity of mitochondrial glutathione transferase (GST) by 100-250%. Further experiments provided evidence that mitochondrial membranes contain an enzymatically inactive protein which can be alkylated through its sulfhydryl groups. By alkylation, this protein achieves catalytic properties similar to those of native GST.

Alkylating Agents↗

Effect of alcohol abuse and glutathione administration on the circulating levels of glutathione and on antipyrine metabolism in patients with alcoholic liver cirrhosis.

Glutathione (GSH) is a principal cellular scavenger of free radicals. Chronic alcohol abuse, as well as liver disease, induces a decrease of hepatic GSH. We evaluated the effect of GSH administration (2.4 g day-1 in saline i.v. for 15 days) on the concentration of GSH in plasma and erythrocytes and on liver function tests, including galactose and antipyrine tests. We studied 40 alcoholic cirrhotic patients: 22 treated with GSH (10 persistent alcohol abusers and 12 weaning from alcohol during the study) and 18 treated with saline only (8 persistent alcohol abusers and 10 abstainers). Treatment with GSH improved the concentration of GSH in plasma and erythrocytes only in abstainers from alcohol; it did not affect liver function tests or galactose clearance. Persistent alcohol consumption significantly prolonged antipyrine metabolism; GSH administration counteracted this effect.

Adult↗

Effect of glutathione administration on hepatic biliary and plasmatic glutathione levels in the rat.

BACKGROUND: Since the effect of exogenous glutathione (GSH) on overall hepatic GSH homeostasis is not known, the present study investigated the changes in the hepatic, biliary, and plasmatic GSH levels during GSH administration in intact rats. METHODS: An exteriorized biliary-duodenal fistula was established, and GSH (1 mmol/kg over 2 h) or saline was administered intraperitoneally to rats with or without pretreatment with 5 mmol/kg L-serine borate, an inhibitor of gamma-glutamyltransferase (GGT). RESULTS: Three hours after GSH administration, biliary GSH efflux and bile flow rose from 104.7 +/- 5.6 to 290.6 +/- 8.6 micrograms/ml bile and from 20.2 +/- 1.3 to 30.2 +/- 2.1 microliters/min, respectively; GSH-treated rats also showed increased liver (35%) and posthepatic vein plasma (68%) GSH concentrations compared with controls. By contrast, in rats pretreated with the GGT inhibitor GSH administration appeared to be devoid of any effect, except for a modest biliary GSH increase. CONCLUSIONS: This study indicates that significant changes occur in the hepatic GSH homeostasis after intraperitoneal GSH administration. The activity of hepatic GGT, most likely through degradation of circulating GSH, followed by an increase in cysteine availability, seems to account, at least partially, for the reported effects.

Animals↗