Glutathione, metabolism and function via the gamma-glutamyl cycle

The impact of glycine and glutamate, as components of glutathione precursors, on the productivity, digestive performance and blood profile of weaning pigs

The impact of glycine and glutamate, as components of glutathione (GSH) precursors, was studied as a factor in determining the growth rate of weaning pigs, their digestion of nutrient supplements and their blood concentration levels. There were 180 crossbred weaning pigs with an average body weight (BW) of 7.94 ± 1.53 kg (five pigs per pen [two barrows and three gilts]; nine pens per treatment) that were randomly assigned to one of four diets. We used a basal diet as the control, TRT1 as the treatment with 0.10% precursor of GSH, TRT2 as the treatment with 0.20% precursor of GSH and TRT3 as the treatment with 0.30% precursor of GSH. The BW of weaning pigs exhibited a linear increase on days 7 (p < 0.001), 21 (p < 0.001) and 42 (p < 0.009) following the supplementation with the GSH precursor. Supplementation with GSH precursor led to a consistent and gradual increase in average daily gain (ADG) on days 8-21, 22-42 and overall, as indicated by a significant linear trend (p < 0.05). G: F was linearly increased (p < 0.05) on days 22-42 and overall with the increment in the precursor of GSH supplementation. However, GSH precursor supplementation did not have any impact on nutrient digestibility and blood profile in the treatment group. In summary, the administration of GSH precursor improved BW, ADG and G: F ratio while not affecting nutrient digestibility or blood profile.

Desipramine induces eryptosis in human erythrocytes, an effect blunted by nitric oxide donor sodium nitroprusside and N-acetyl-L-cysteine but enhanced by Calcium depletion

Background: Desipramine a representative of tricyclic antidepressants (TCAs) promotes recovery of depressed patients by inhibition of reuptake of neurotransmitters serotonin (SER) and norepinephrine (NE) in the presynaptic membrane by directly blocking their respective transporters SERT and NET.Aims: To study the effect of desipramine on programmed erythrocyte death (eryptosis) and explore the underlying mechanisms.Methods: Phosphatidylserine (PS) exposure on the cell surface as marker of cell death was estimated from annexin-V-binding, cell volume from forward scatter in flow cytometry. Hemolysis was determined photometrically, and intracellular glutathione [GSH]i from high performance liquid chromatography.Results: Desipramine dose-dependently significantly enhanced the percentage of annexin-V-binding cells and didn´t impact glutathione (GSH) synthesis. Desipramine-induced eryptosis was significantly reversed by pre-treatment of erythrocytes with either nitric oxide (NO) donor sodium nitroprusside (SNP) or N-acetyl-L-cysteine (NAC). The highest inhibitory effect was obtained by using both inhibitors together. Calcium (Ca2+) depletion aggravated desipramine-induced eryptosis. Changing the order of treatment, i.e. desipramine first followed by inhibitors, could not influence the inhibitory effect of SNP or NAC.Conclusion: Antidepressants-caused intoxication can be treated by SNP and NAC, respectively. B) Patients with chronic hypocalcemia should not be treated with tricyclic anti-depressants or their dose should be noticeably reduced.

The kinetics of glutathione in the gastrointestinal tract of weaned piglets supplemented with different doses of dietary reduced glutathione

This study aimed to investigate the kinetics of dietary GSH in the gastrointestinal tract and the effect of GSH on the intestinal redox status of weaned piglets. Forty-eight piglets with an average age of 26 days and an average body weight of 7.7 kg were used in this study. The piglets were divided into three treatment groups including the control group with a basal diet (CON) and two GSH groups with a basal diet supplemented with 0.1% GSH (LGSH) and 1.0% GSH (HGSH), respectively. The basal diet did not contain any GSH. The experiment lasted for 14 days, with eight animals sampled from each group on d5 and 14. The parts of 0-5%, 5-75%, and 75-100% of the length of the small intestine were assigned to SI1, SI2, and SI3. The results showed that GSH almost completely disappeared from the digesta at SI2. However, no difference in the GSH level in mucosa, liver, and blood erythrocytes was found. The level of cysteine (CYS) in SI1 digesta was significantly higher in HGSH than CON and LGSH on d14, and similar findings were observed for cystine (CYSS) in SI3 digesta on d5. The CYSS level in HGSH was also significantly higher than LGSH in the stomach on d14, while no CYS or CYSS was detected in the stomach for control animals, indicating the breakdown of GSH to CYS already occurred in the stomach. Irrespective of the dietary treatment, the CYS level on d14 and the CYSS level on d5 and 14 were increased when moving more distally into the gastrointestinal tract. Furthermore, the mucosal CYS level was significantly increased at SI1 in the LGSH and HGSH group compared with CON on d5. Glutathione disulfide (GSSG) was recovered in the diets and digesta from the LGSH and HGSH group, which could demonstrate the auto-oxidation of GSH. It is, therefore, concluded that GSH supplementation could not increase the small intestinal mucosal GSH level of weaned piglets, and this could potentially relate to the kinetics of GSH in the digestive tract, where GSH seemed to be prone to the breakdown to CYS and CYSS and the auto-oxidation to GSSG.

Lysophosphatidic acid modulates CD8 T cell immunosurveillance and metabolism to impair anti-tumor immunity

Lysophosphatidic acid (LPA) is a bioactive lipid which increases in concentration locally and systemically across different cancer types. Yet, the exact mechanism(s) of how LPA affects CD8 T cell immunosurveillance during tumor progression remain unknown. We show LPA receptor (LPAR) signaling by CD8 T cells promotes tolerogenic states via metabolic reprogramming and potentiating exhaustive-like differentiation to modulate anti-tumor immunity. We found LPA levels predict response to immunotherapy and Lpar5 signaling promotes cellular states associated with exhausted phenotypes on CD8 T cells. Importantly, we show that Lpar5 regulates CD8 T cell respiration, proton leak, and reactive oxygen species. Together, our findings reveal that LPA serves as a lipid-regulated immune checkpoint by modulating metabolic efficiency through LPAR5 signaling on CD8 T cells. Our study offers key insights into the mechanisms governing adaptive anti-tumor immunity and demonstrates LPA could be exploited as a T cell directed therapy to improve dysfunctional anti-tumor immunity.

Enlightening the mechanism of ferroptosis in epileptic heart

Epilepsy is a chronic neurological degenerative disease with a high incidence, affecting all age groups. Refractory Epilepsy (RE) occurs in approximately 30-40% of cases with a higher risk of sudden unexpected death in epilepsy (SUDEP). Recent studies have shown that spontaneous seizures developed in epilepsy can be related to an increase in oxidative stress and reactive oxygen derivatives (ROS) production. Increasing ROS concentration causes lipid peroxidation, protein oxidation, destruction of nuclear genetic material, enzyme inhibition, and cell death by a mechanism known as "ferroptosis" (Fts). Inactivation of glutathione peroxidase 4 (GPX4) induces Fts, while oxidative stress is linked with increased intracellular free iron (Fe+2) concentration. Fts is also a non-apoptotic programmed cell death mechanism, where a hypoxia-inducible factor 1 alpha (HIF-141) dependent hypoxic stress-like condition appears to occur with accumulation of iron and cytotoxic ROS in affected cells. Assuming convulsive crises as hypoxic stress, repetitive convulsive/hypoxic stress can be an effective inducer of the "epileptic heart" (EH), which is characterized by altered autonomic function and a high risk of malignant or fatal bradycardia. We previously reported that experimental recurrent seizures induce cardiomyocyte Fts associated with SUDEP. Furthermore, several genes related to Fts and hypoxia have recently been identified in acute myocardial infarction. An emerging theme from recent studies indicates that inhibition of GPX4 through modulating expression or activities of the xCT antiporter system (SLC7A11) governs cell sensitivity to oxidative stress from ferroptosis. Furthermore, during hypoxia, an increased expression of stress transcriptional factor ATF3 can promote Fts induced by erastin in a HIF-141-dependent manner. We propose that inhibition of Fts with ROS scavengers, iron chelators, antioxidants, and transaminase inhibitors could provide a therapeutic effect in epilepsy and improve the prognosis of SUDEP risk by protecting the heart from ferroptosis.

Identification of Protective Amino Acid Metabolism Events in Nursery Pigs Fed Thermally Oxidized Corn Oil

Feeding thermally oxidized lipids to pigs has been shown to compromise growth and health, reduce energy digestibility, and disrupt lipid metabolism. However, the effects of feeding oxidized lipids on amino acid metabolism in pigs have not been well defined even though amino acids are indispensable for the subsistence of energy metabolism, protein synthesis, the antioxidant system, and many other functions essential for pig growth and health. In this study, oxidized corn oil (OCO)-elicited changes in amino acid homeostasis of nursery pigs were examined by metabolomics-based biochemical analysis. The results showed that serum and hepatic free amino acids and metabolites, including tryptophan, threonine, alanine, glutamate, and glutathione, as well as associated metabolic pathways, were selectively altered by feeding OCO, and more importantly, many of these metabolic events possess protective functions. Specifically, OCO activated tryptophan-nicotinamide adenosine dinucleotide (NAD⁺) synthesis by the transcriptional upregulation of the kynurenine pathway in tryptophan catabolism and promoted adenine nucleotide biosynthesis. Feeding OCO induced oxidative stress, causing decreases in glutathione (GSH)/oxidized glutathione (GSSG) ratio, carnosine, and ascorbic acid in the liver but simultaneously promoted antioxidant responses as shown by the increases in hepatic GSH and GSSG as well as the transcriptional upregulation of GSH metabolism-related enzymes. Moreover, OCO reduced the catabolism of threonine to α-ketobutyrate in the liver by inhibiting the threonine dehydratase (TDH) route. Overall, these protective metabolic events indicate that below a certain threshold of OCO consumption, nursery pigs are capable of overcoming the oxidative stress and metabolic challenges posed by the consumption of oxidized lipids by adjusting antioxidant, nutrient, and energy metabolism, partially through the transcriptional regulation of amino acid metabolism.

Glutathione-Mediated Conjugation of Anticancer Drugs: An Overview of Reaction Mechanisms and Biological Significance for Drug Detoxification and Bioactivation

The effectiveness of many anticancer drugs depends on the creation of specific metabolites that may alter their therapeutic or toxic properties. One significant route of biotransformation is a conjugation of electrophilic compounds with reduced glutathione, which can be non-enzymatic and/or catalyzed by glutathione-dependent enzymes. Glutathione usually combines with anticancer drugs and/or their metabolites to form more polar and water-soluble glutathione S-conjugates, readily excreted outside the body. In this regard, glutathione plays a role in detoxification, decreasing the likelihood that a xenobiotic will react with cellular targets. However, some drugs once transformed into thioethers are more active or toxic than the parent compound. Thus, glutathione conjugation may also lead to pharmacological or toxicological effects through bioactivation reactions. My purpose here is to provide a broad overview of the mechanisms of glutathione-mediated conjugation of anticancer drugs. Additionally, I discuss the biological importance of glutathione conjugation to anticancer drug detoxification and bioactivation pathways. I also consider the potential role of glutathione in the metabolism of unsymmetrical bisacridines, a novel prosperous class of anticancer compounds developed in our laboratory. The knowledge on glutathione-mediated conjugation of anticancer drugs presented in this review may be noteworthy for improving cancer therapy and preventing drug resistance in cancers.

The Role of Concomitant Nrf2 Targeting and Stem Cell Therapy in Cerebrovascular Disease

Despite the reality that a death from cerebrovascular accident occurs every 3.5 min in the United States, there are few therapeutic options which are typically limited to a narrow window of opportunity in time for damage mitigation and recovery. Novel therapies have targeted pathological processes secondary to the initial insult, such as oxidative damage and peripheral inflammation. One of the greatest challenges to therapy is the frequently permanent damage within the CNS, attributed to a lack of sufficient neurogenesis. Thus, recent use of cell-based therapies for stroke have shown promising results. Unfortunately, stroke-induced inflammatory and oxidative damage limit the therapeutic potential of these stem cells. Nuclear factor erythroid 2-related factor 2 (Nrf2) has been implicated in endogenous antioxidant and anti-inflammatory activity, thus presenting an attractive target for novel therapeutics to enhance stem cell therapy and promote neurogenesis. This review assesses the current literature on the concomitant use of stem cell therapy and Nrf2 targeting via pharmaceutical and natural agents, highlighting the need to elucidate both upstream and downstream pathways in optimizing Nrf2 treatments in the setting of cerebrovascular disease.

Rat liver glutathione S-transferase-catalyzed conjugation of glutathione to the endogenous epoxides of oleic acid and cholesterol

cis-9,10-Epoxy-octadecanoic acid (oleic acid epoxide, OAE) and 5α,6α-epoxy-cholesterol (ChE) are endogenous epoxides. Unlike other epoxides, the oxirane groups of OAE and ChE are relatively stable against nucleophiles. OAE lacks toxicity and mutagenicity, while ChE is considered harmful, mutagenic and cancerogenic to animals. In humans, ChE is associated with cancer. The metabolism of OAE and ChE includes hydrolysis by cytosolic and microsomal hydrolases to their diols and glutathione (GSH) conjugation by GSH S-transferases (GST) to form the GSH conjugates (R-SG; R, residue). The GST-catalyzed GSH conjugation of OAE and ChE is poorly investigated. This article reports on the GSH conjugation of OAE, its methyl ester (OAEMe) and of ChE by rat liver homogenate GST. The GSH conjugates of OAE, OAEMe and ChE, i.e., OAE-SG, OAEMe-SG and ChE-SG, respectively, were determined by pre-column derivatization with o-phthaldialdehyde (OPA)/2-mercaptoethanol, high-performance liquid chromatography (HPLC) and fluorescence detection. Complex biphasic kinetics were observed with substrate inhibition of GST activity by OAE, OAEMe and ChE, an optimum pH of about 8.3 for OAE, and no measurable chemical GSH conjugation, underlying the importance of GST for the biotransformation of these epoxides. The results confirm the substrate concentration-dependent kinetic mechanism of GST isoforms first reported by William B. Jakoby (J. Biol. Chem. 1974) for exogenous electrophiles including the epoxide 1,2-epoxy-3-(p-nitrophenoxy)propane and the organic nitrates. This mechanism allows for maximal GST activity that can be achieved under given concentrations of GSH, epoxides and other electrophiles.

Ggct (γ-glutamyl cyclotransferase) plays an important role in erythrocyte antioxidant defense and red blood cell survival

The expression of GGCT (γ-glutamyl cyclotransferase) is upregulated in various human cancers. γ-glutamyl cyclotransferase enzyme activity was originally purified from human red blood cells (RBCs), but the physiological function of GGCT in RBCs is still not clear. Here we reported that Ggct deletion in mice leads to splenomegaly and progressive anaemia phenotypes, due to elevated oxidative damage and the shortened life span of Ggct^-/- RBCs. Ggct^-/- RBCs have increased reactive oxygen species (ROS), and are more sensitive to H₂ O₂ -induced damage compared to control RBCs. Glutathione (GSH) and GSH synthesis precursor l-cysteine are decreased in Ggct^-/- RBCs. Our study suggests a critical function of Ggct in RBC redox balance and life span maintenance through regulating GSH metabolism.

Quantitation of γ-Glutamylcysteine-Formaldehyde Conjugate in Formaldehyde- and Oxidative Stress-Exposed Cells by Liquid Chromatography-Tandem Mass Spectrometry

Humans are constantly exposed to formaldehyde (FA) of both exogenous and endogenous sources, and FA exposure is associated with the development of many human diseases, including cancers. Marker molecules that can provide information on exposure history and amounts will assist disease risk assessment and early interventions. To develop marker signatures of FA exposure, we explored in this study the conjugation reaction of FA with γ-glutamylcysteine (GGC), one of the precursors to glutathione biosynthesis, under physiologically relevant conditions. The results showed that the reaction produced a stable metabolite of FA, (S)-1-((((R)-2-amino-2-carboxyethyl)thio)methyl)-5-oxopyrrolidine-2-carboxylic acid (COCA). Using liquid chromatography-tandem mass spectrometry coupled to a stable isotope-dilution method, we then quantitated for the first time the formation of this novel metabolite in FA- and Fe²⁺-EDTA-exposed human cells. The results revealed the exposure time- and concentration-dependent formation of COCA in FA- or Fe²⁺-EDTA-exposed cells, suggesting that COCA may serve as a biomarker of FA and oxidative stress exposure. Furthermore, the study sheds light on a previously unknown protective role of GGC against FA and oxidative stress.

Induction of Gamma-Glutamyltransferase Activity and Consequent Pro-oxidant Reactions in Human Macrophages Exposed to Crocidolite Asbestos

Asbestos is the main causative agent of malignant pleural mesothelioma. The variety known as crocidolite (blue asbestos) owns the highest pathogenic potential, due to the dimensions of its fibers as well as to its content of iron. The latter can in fact react with macrophage-derived hydrogen peroxide in the so called Fenton reaction, giving rise to highly reactive and mutagenic hydroxyl radical. On the other hand, hydroxyl radical can as well originate after thiol-dependent reduction of iron, a process capable of starting its redox cycling. Previous studies showed that glutathione (GSH) is one such thiol, and that cellular gamma-glutamyltransferase (GGT) can efficiently potentiate GSH-dependent iron redox cycling and consequent oxidative stress. As GGT is expressed in macrophages and is released upon their activation, the present study was aimed at verifying the hypothesis that GSH/GGT-dependent redox reactions may participate in the oxidative stress following the activation of macrophages induced by crocidolite asbestos. Experiments in acellular systems confirmed that GGT-mediated metabolism of GSH can potentiate crocidolite-dependent production of superoxide anion, through the production of highly reactive dipeptide thiol cysteinyl-glycine. Cultured THP-1 macrophagic cells, as well as isolated monocytes obtained from healthy donors and differentiated to macrophages in vitro, were investigated as to their expression of GGT and the effects of exposure to crocidolite. The results show that crocidolite asbestos at subtoxic concentrations (50-250 ng/1000 cells) can upregulate GGT expression, which raises the possibility that macrophage-initiated, GSH/GGT-dependent pro-oxidant reactions may participate in the pathogenesis of tissue damage and inflammation consequent to crocidolite intoxication.

The anti-aging effect of Scutellaria baicalensis Georgi flowers extract by regulating the glutamine-glutamate metabolic pathway in d-galactose induced aging rats

Scutellaria baicalensis Georgi flowers is rich in flavonoids resources but not effectively exploited. This study aimed to investigate the anti-aging effects and potential mechanism of Scutellaria baicalensis Georgi flowers extract (SFE). The chemical components of the SFE were analyzed by UPLC-MS and the anti-aging effects of SFE were investigated in d-galactose (d-gal) induced aging rats by behavior examination and biochemical indexes, and the potential anti-aging mechanism of SFE were explored by 1H NMR-based liver metabolomics. Chemical composition research showed that 19 flavonoids were identified in SFE, and pharmacological research showed that SFE could significantly ameliorate spatial learning and memory ability. SFE could significantly regulate malondialdehyde (MDA), superoxide dismutase (SOD) and advanced glycation end products (AGEs). It also ameliorated the pathological abnormalities in liver. Additionally, anti-aging mechanism of SFE showed that total of 10 potential biomarkers were found by metabolomics techniques, which involved in 6 metabolic pathways. Among them, SFE could significantly increased the levels of d-glutamine and d-glutamate. Furthermore, the levels of glutamine and glutamate, and the levels of the key amino acids, enzymes and final product in the synthesis process of glutathione (GSH) were quantitatively determined in the liver by commercial kits and enzyme-linked immunosorbent assay. These results indicated that regulation of the glutamine-glutamate metabolic pathway is involved in the anti-aging effect of SFE in d-gal induced aging rats.

Skeletal muscle amino acid uptake is lower and alanine production is greater in late gestation intrauterine growth-restricted fetal sheep hindlimb

In a sheep model of intrauterine growth restriction (IUGR) produced from placental insufficiency, late gestation fetuses had smaller skeletal muscle mass, myofiber area, and slower muscle protein accretion rates compared with normally growing fetuses. We hypothesized that IUGR fetal muscle develops adaptations that divert amino acids (AAs) from protein accretion and activate pathways that conserve substrates for other organs. We placed hindlimb arterial and venous catheters into late gestation IUGR (n = 10) and control (CON, n = 8) fetal sheep and included an external iliac artery flow probe to measure hindlimb AA uptake rates. Arterial and venous plasma samples and biceps femoris muscle were analyzed by mass spectrometry-based metabolomics. IUGR fetuses had greater abundance of metabolites enriched within the alanine, aspartate, and glutamate metabolism pathway compared with CON. Net uptake rates of branched-chain AA (BCAA) were lower by 42%-73%, and muscle ammoniagenic AAs (alanine, glycine, and glutamine) were lower by 107%-158% in IUGR hindlimbs versus CON. AA uptake rates correlated with hindlimb weight; the smallest hindlimbs showed net release of ammoniagenic AAs. Gene expression levels indicated a decrease in BCAA catabolism in IUGR muscle. Plasma purines were lower and plasma uric acid was higher in IUGR versus CON, possibly a reflection of ATP conservation. We conclude that IUGR skeletal muscle has lower BCAA uptake and develops adaptations that divert AAs away from protein accretion into alternative pathways that sustain global energy production and nitrogen disposal in the form of ammoniagenic AAs for metabolism in other organs.

Ras Downstream Effector GGCT Alleviates Oncogenic Stress

How cells adapt to oncogenic transformation-associated cellular stress and become fully transformed is still unknown. Here we identified a novel GGCT-regulated glutathione (GSH)-reactive oxygen species (ROS) metabolic pathway in oncogenic stress alleviation. We identified GGCT as a target of oncogenic Ras and that it is required for oncogenic Ras-induced primary mouse cell proliferation and transformation and in vivo lung cancer formation in the LSL-Kras G12D mouse model. However, GGCT deficiency is compatible with normal mouse development, suggesting that GGCT can be a cancer-specific therapeutic target. Genetically amplified GGCT locus further supports the oncogenic driving function of GGCT. In summary, our study not only identifies an oncogenic function of GGCT but also identifies a novel regulator of GSH metabolism, with implications for further understanding of oncogenic stress and cancer treatment.

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GGCT is a target of Ras and is required for Ras-induced cancer formation

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GGCT deletion is compatible with normal mouse development and tissue function

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GGCT genomic locus is amplified in multiple human cancer types

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GGCT could alleviate oncogenic stress by regulating GSH-ROS metabolism

Ameliorative effect of resveratrol on testicular oxidative stress, spermatological parameters and DNA damage in glyphosate-based herbicide-exposed rats

In this study, the reproductive impacts of being exposed to glyphosate (GLF) and the protective impacts of resveratrol (RES) were assessed in 28 Wistar male rats, which were equally separated into four groups. Control group were fed normal diet without GLF or RES, group II received normal feed containing 20 mg kg-1 daily-1 RES, group III received normal feed containing 375 mg kg-1 daily-1 GLF, and group IV received normal feed containing 375 mg kg-1 daily-1 GLF+20 mg kg-1 daily-1 RES. GLF administration decreased sperm motility, sperm plasma membrane integrity, glutathione level and superoxide dismutase in the testicular tissue of rats. On the other hand, abnormal sperm rate, malondialdehyde level, and DNA damage were detected to be high in the group treated with GLF. The findings indicate that RES protects spermatological parameters and DNA damage, decreases GLF-induced lipid peroxidation, improves the antioxidant defence mechanism and regenerates tissue damage in the testis of rats.

Early loss of mitochondrial complex I and rewiring of glutathione metabolism in renal oncocytoma

Renal oncocytomas are benign kidney tumors with numerous mitochondria. Here, we analyze the mitochondrial (mtDNA) and nuclear genomes of these tumors. Our analysis finds mtDNA mutations in complex I (the first step in mitochondrial respiration) to be early genetic events that likely contribute to tumor formation. Since mtDNA mutations can lead to severe degenerative disorders, the cellular responses allowing renal oncocytoma cells to grow are important to consider. To properly understand authentic gene expression changes in tumors, we found it important to consider the gene expression pattern of the tumor’s cell of origin, the distal nephron. By doing so, we uncover alterations in glutathione synthesis and turnover that likely represent an adaptive metabolic response in renal oncocytoma.

Renal oncocytomas are benign tumors characterized by a marked accumulation of mitochondria. We report a combined exome, transcriptome, and metabolome analysis of these tumors. Joint analysis of the nuclear and mitochondrial (mtDNA) genomes reveals loss-of-function mtDNA mutations occurring at high variant allele fractions, consistent with positive selection, in genes encoding complex I as the most frequent genetic events. A subset of these tumors also exhibits chromosome 1 loss and/or cyclin D1 overexpression, suggesting they follow complex I loss. Transcriptome data revealed that many pathways previously reported to be altered in renal oncocytoma were simply differentially expressed in the tumor’s cell of origin, the distal nephron, compared with other nephron segments. Using a heuristic approach to account for cell-of-origin bias we uncovered strong expression alterations in the gamma-glutamyl cycle, including glutathione synthesis (increased GCLC) and glutathione degradation. Moreover, the most striking changes in metabolite profiling were elevations in oxidized and reduced glutathione as well as γ-glutamyl-cysteine and cysteinyl-glycine, dipeptide intermediates in glutathione biosynthesis, and recycling, respectively. Biosynthesis of glutathione appears adaptive as blockade of GCLC impairs viability in cells cultured with a complex I inhibitor. Our data suggest that loss-of-function mutations in complex I are a candidate driver event in renal oncocytoma that is followed by frequent loss of chromosome 1, cyclin D1 overexpression, and adaptive up-regulation of glutathione biosynthesis.

Sinorhizobium meliloti Glutathione Reductase Is Required for both Redox Homeostasis and Symbiosis

Glutathione (l-γ-glutamyl-l-cysteinylglycine) (GSH), one of the key antioxidants in Sinorhizobium meliloti, is required for the development of alfalfa (Medicago sativa) nitrogen-fixing nodules. Glutathione exists as either reduced glutathione (GSH) or oxidized glutathione (GSSG), and its content is regulated by two pathways in S. meliloti The first pathway is the de novo synthesis of glutathione from its constituent amino acids, namely, Glu, Cys, and Gly, catalyzed by γ-glutamylcysteine synthetase (GshA) and glutathione synthetase (GshB). The second pathway is the recycling of GSSG via glutathione reductase (GR). However, whether the S. meliloti GR functions similarly to GshA and GshB1 during symbiotic interactions with alfalfa remains unknown. In this study, a plasmid insertion mutation of the S. melilotigor gene, which encodes GR, was constructed, and the mutant exhibited delayed alfalfa nodulation, with 75% reduction in nitrogen-fixing capacity. The gor mutant demonstrated increased accumulation of GSSG and a decreased GSH/GSSG ratio in cells. The mutant also showed defective growth in rich broth and minimal broth and was more sensitive to the oxidants H₂O₂ and sodium nitroprusside. Interestingly, the expression of gshA, gshB1, katA, and katB was induced in the mutant. These findings reveal that the recycling of glutathione is important for S. meliloti to maintain redox homeostasis and to interact symbiotically with alfalfa.IMPORTANCE The antioxidant glutathione is regulated by its synthetase and reductase in cells. In the symbiotic bacterium S. meliloti, the de novo synthesis of glutathione is essential for alfalfa nodulation and nitrogen fixation. In this study, we observed that the recycling of glutathione from GSSG not only was required for redox homeostasis and oxidative stress protection in S. meliloti cells but also contributed to alfalfa nodule development and competition capacity. Our findings demonstrate that the recycling of glutathione plays a key role in nitrogen fixation symbiosis.

Sex-dependent Differences in Liver and Gut Metabolomic Profiles With Acarbose and Calorie Restriction in C57BL/6 Mice

Acarbose, an alpha-glucosidase inhibitor used in treating type 2 diabetes, impairs complex carbohydrate digestion and absorption and extends life span in mice (without a requisite reduction in food intake). To assess sex-differential effects coincident with calorie restriction versus a nonrestricted longevity enhancing intervention, we evaluated the metabolite profiles (by liquid chromatography-mass spectroscopy) from livers and cecal contents of C57BL/6J mice (n = 4/sex/group), which were maintained for 10 months under one of the three diet treatments: ad libitum control diet (CON), ad libitum control diet containing 0.1% acarbose (ACA), or 40% calorie restriction using the control diet (CR). Principal component analysis revealed sex-differential profiles with ACA in livers. Of the identified metabolites (n = 621) in liver, CR significantly altered ~44% (males:187↑/131↓, females:74↑/148↓) compared with CON, in contrast with ACA (M:165↑/61↓, F:52↑/60↓). Dissimilarity in ACA-F liver metabolites was observed for ~50% of common metabolites from ACA-M and CR-M/F. CR resulted in fewer significant cecal metabolite differences (n = 615 metabolites; M:86↑/66↓, F:51↑/48↓ vs CON), relative to ACA treatment (M:32↑/189↓, F:36↑/137↓). Metabolomic profiling identifies sex-differential and tissue-specific effects with amino acid metabolism sub-pathways including those involving tryptophan, branch-chain and sulfur amino acids, and the urea cycle, as well as bile acid, porphyrin, and cofactor metabolism pathways.

Taurine treatment prevents derangement of the hepatic γ-glutamyl cycle and methylglyoxal metabolism in a mouse model of classical homocystinuria: regulatory crosstalk between thiol and sulfinic acid metabolism

Cystathionine β-synthase-deficient homocystinuria (HCU) is a poorly understood, life-threatening inborn error of sulfur metabolism. Analysis of hepatic glutathione (GSH) metabolism in a mouse model of HCU demonstrated significant depletion of cysteine, GSH, and GSH disulfide independent of the block in trans-sulfuration compared with wild-type controls. HCU induced the expression of the catalytic and regulatory subunits of γ-glutamyl ligase, GSH synthase (GS), γ-glutamyl transpeptidase 1, 5-oxoprolinase (OPLAH), and the GSH-dependent methylglyoxal detoxification enzyme, glyoxalase-1. Multiple components of the transcription factor nuclear factor (erythroid-derived 2)-like 2 (Nrf2)-mediated antioxidant-response regulatory axis were induced without any detectable activation of Nrf2. Metabolomic analysis revealed the accumulation of multiple γ-glutamyl amino acids and that plasma ophthalmate levels could serve as a noninvasive marker for hepatic redox stress. Neither cysteine, nor betaine treatment was able to reverse the observed enzyme inductions. Taurine treatment normalized the expression levels of γ-glutamyl ligase C/M, GS, OPLAH, and glyoxalase-1, and reversed HCU-induced deficits in protein glutathionylation by acting to double GSH levels relative to controls. Collectively, our data indicate that the perturbation of the γ-glutamyl cycle could contribute to multiple sequelae in HCU and that taurine has significant therapeutic potential for both HCU and other diseases for which GSH depletion is a critical pathogenic factor.-Maclean, K. N., Jiang, H., Aivazidis, S., Kim, E., Shearn, C. T., Harris, P. S., Petersen, D. R., Allen, R. H., Stabler, S. P., Roede, J. R. Taurine treatment prevents derangement of the hepatic γ-glutamyl cycle and methylglyoxal metabolism in a mouse model of classical homocystinuria: regulatory crosstalk between thiol and sulfinic acid metabolism.

Temporal changes in glutathione biosynthesis during the lipopolysaccharide-induced inflammatory response of THP-1 macrophages

How macrophages maintain redox homeostasis in the inflammatory process, in which a large amount of oxidants are produced, remains elusive. In this study, we investigated the temporal changes in the intracellular glutathione (GSH), the master antioxidant, and the expression of glutamate cysteine ligase (GCL), the rate-limiting enzyme for GSH biosynthesis, in the inflammatory response of human macrophages (THP1 cells) to lipopolysaccharide. Intracellular GSH concentration was decreased significantly in the early phase (~6h) of LPS exposure, and then gradually went back to the basal level in the late phase (9-24h). The expression level of the catalytic subunit of GCL (GCLC) followed a similar pattern of change as GSH: its mRNA and protein levels were reduced in the early phase and then back to basal level in the late phase. In contrast, the expression of the modifier subunit of GCL (GCLM) was significantly increased in the phase of LPS exposure. Activation Nrf2, the transcription factor involved in the induction of both GCLC and GCLM, occurred at as early as 3h after LPS exposure; whereas the activation of NF-κB occurred at as early as 30min. Inhibition of NF-κB signaling with SN50 prevented the decrease of GCLC and inhibited Nrf2 activation in response to LPS. These data demonstrate time-dependent changes in the expression of GCL and Nrf2 signaling during the inflammatory response, and that the regulation of GCLC and GCLM might be through different pathways in this process.

The Glutathione Conundrum: Stoichiometric Disconnect between Its Formation and Oxidative Stress

Glutathione (GSH) is the most abundant antioxidant and is believed to maintain redox potential in tissues, cells, and individual compartments. However, GSH concentrations in some tumor cells and tissues have been reported to be as high as 1-10 mM, a concentration that is up to 10,000-fold higher than that of reactive oxygen species. Critical quantitative evaluation of glutathione's proposed functions suggests that glutathione is an amino acid checkpoint. In this role, glutathione contributes to regulating cell proliferation and apoptosis, pending amino acid availability.

Some Biochemical and Histological Effects of 2-Chloroethanol in Rats

The effects of 2-chioroethanol (2-CE) on rat tissue following in vitro and in vivo exposure were studied. At concentrations as low as 2.5 mg/ml, protein synthesis in liver slices was inhibited; at concentrations of 25 mg/ml and above, RNA synthesis and respiration were also impaired. Single oral doses of 2-CE to young adult rats at levels of 15-40 mg/kg body weight depressed liver nonprotein sulfhydryl (GSH) concentration and liver protein but not RNA synthesis. Liver lipid was increased by 7 hr after a single oral dose of 30 mg/kg. The time courses and dose-response relationship for GSH depletion and restoration and for protein synthesis inhibition and recovery were similar. The livers of female rats were more sensitive than the livers of male rats to the effects of 2-CE. Protein synthesis was also depressed in kidneys of 2-CE-treated male rats but at higher doses than those needed for this effect to occur in livers of the same animals. Liver polysome disaggregation also occurred after oral 2-CE doses of 20 mg/kg and greater. The effects of 2-CE on ribosome profiles and protein synthesis were at least partially reversed by concurrent intraperitoneal administration of cysteine. The possible relationship of these findings to a role of GSH in protein synthesis is discussed.

Evaluating the Oxidative Stress in Renal Diseases: What Is the Role for S-Glutathionylation?

SIGNIFICANCE

Reactive oxygen species (ROS) have long been considered as toxic derivatives of aerobic metabolism displaying a harmful effect to living cells. Deregulation of redox homeostasis and production of excessive free radicals may contribute to the pathogenesis of kidney diseases. In line, oxidative stress increases in patients with renal dysfunctions due to a general increase of ROS paralleled by impaired antioxidant ability.

RECENT ADVANCES

Emerging evidence revealed that physiologically, ROS can act as signaling molecules interplaying with several transduction pathways such as proliferation, differentiation, and apoptosis. ROS can exert signaling functions by modulating, at different layers, protein oxidation since proteins have "cysteine switches" that can be reversibly reduced or oxidized, supporting the dynamic signaling regulation function. In this scenario, S-glutathionylation is a posttranslational modification involved in oxidative cellular response.

CRITICAL ISSUES

Although it is widely accepted that renal dysfunctions are often associated with altered redox signaling, the relative role of S-glutathionylation on the pathogenesis of specific renal diseases remains unclear and needs further investigations. In this review, we discuss the impact of ROS in renal health and diseases and the role of selective S-glutathionylation proteins potentially relevant to renal physiology.

FUTURE DIRECTIONS

The paucity of studies linking the reversible protein glutathionylation with specific renal disorders remains unmet. The growing number of S-glutathionylated proteins indicates that this is a fascinating area of research. In this respect, further studies on the association of reversible glutathionylation with renal diseases, characterized by oxidative stress, may be useful to develop new pharmacological molecules targeting protein S-glutathionylation. Antioxid. Redox Signal. 25, 147-164.

Aryl hydrocarbon receptor-dependent stanniocalcin 2 induction by cinnabarinic acid provides cytoprotection against endoplasmic reticulum and oxidative stress

The aryl hydrocarbon receptor (AhR) is a cytosolic ligand-activated transcription factor historically known for its role in xenobiotic metabolism. Although AhR activity has previously been shown to play a cytoprotective role against intrinsic apoptotic stimuli, the underlying mechanism by which AhR confers cytoprotection against apoptosis is largely unknown. Here, we demonstrate that activation of AhR by the tryptophan catabolite cinnabarinic acid (CA) directly upregulates expression of stanniocalcin 2 (Stc2) to elicit cytoprotection against apoptosis induced by endoplasmic reticulum stress and oxidative stress. Chromatin immunoprecipitation studies demonstrated that CA treatment induces direct AhR binding to a region of the Stc2 promoter containing multiple xenobiotic response elements. Using isolated primary hepatocytes from AhR wild-type (AhR floxed) and liver-specific AhR conditional knockout mice, we showed that pretreatment with CA conferred cytoprotection against hydrogen peroxide (H(2)O(2))-, thapsigargin-, and ethanol-induced apoptosis in an AhR-dependent manner. Furthermore, suppressing Stc2 expression using RNA interference confirmed that the cytoprotective properties of CA against H(2)O(2), thapsigargin, and ethanol injury were absolutely dependent on Stc2. Immunochemistry revealed the presence of Stc2 in the endoplasmic reticulum and on the cell surface, consistent with Stc2 secretion and autocrine and/or paracrine signaling. Finally, in vivo data using a mouse model of acute alcohol hepatotoxicity demonstrated that CA provided cytoprotection against ethanol-induced apoptosis, hepatic microvesicular steatosis, and liver injury. Collectively, our data uncovered a novel mechanism for AhR-mediated cytoprotection in the liver that is dependent on CA-induced Stc2 activity.

Cypermethrin-induced reproductive toxicity in the rat is prevented by resveratrol

AIMS

The current study was to assess the protective role of resveratrol in cypermethrin-induced reproductive toxicity in male Wistar rats.

MATERIALS AND METHODS

Rats were exposed to cypermethrin (3.83 mg/kg bw) for 14 days. Pre- and post-treatment of resveratrol (20 mg/kg bw for 14 days) was given to cypermethrin exposed rats. At the end of the experiment, rats were sacrificed, testis and epididymis were removed, sperm characteristics, sex hormones, and various biochemical parameters were studied.

RESULTS

Cypermethrin exposure resulted in a significant decrease in weight of testis and epididymis, testicular sperm head counts, sperm motility and live sperm counts and increase in sperm abnormalities. Serum testosterone (T), follicle stimulating hormone (FSH), luteinizing hormone (LH), reduced glutathione (GSH), catalase (CAT), superoxide dismutase (SOD), glutathione S-transferase (GST), glutathione reductase (GR), glutathione peroxidase (GPx) and total protein (TP) content were decreased and lipid peroxidation (LPO) level was increased on cypermethrin exposure. Pre- and post-treatment of resveratrol increased sperm head counts, sperm motility, live sperm counts, T, FSH, LH, GSH, CAT, SOD, GST, GR, GPx and TP contents and decreased LPO. Treatment with resveratrol alone has improved sperm parameters and testicular antioxidant defence system.

CONCLUSION

The study concluded that resveratrol ameliorated cypermethrin-induced testicular damage by reducing oxidative stress and by enhancing the level of sex hormones.

The role of biomarkers in the assessment of aquatic ecosystem health

Ensuring the health of aquatic ecosystems and identifying species at risk from the detrimental effects of environmental contaminants can be facilitated by integrating analytical chemical analysis with carefully selected biological endpoints measured in tissues of species of concern. These biological endpoints include molecular, biochemical, and physiological markers (i.e., biomarkers) that when integrated, can clarify issues of contaminant bioavailability, bioaccumulation, and ecological effects while enabling a better understanding of the effects of nonchemical stressors. In the case of contaminant stressors, an understanding of chemical modes of toxicity can be incorporated with diagnostic markers of aquatic animal physiology to help understand the health status of aquatic organisms in the field. Furthermore, new approaches in functional genomics and bioinformatics can help discriminate individual chemicals, or groups of chemicals among complex mixtures that may contribute to adverse biological effects. Although the use of biomarkers is not a new paradigm, such approaches have been underused in the context of ecological risk assessment and natural resource damage assessment. From a regulatory standpoint, these approaches can help better assess the complex effects from coastal development activities to assessing ecosystem integrity pre- and post development or site remediation.

The oxidative stress response of the opportunistic fungal pathogen Candida glabrata

Organisms have evolved different strategies to respond to oxidative stress generated as a by-product of aerobic respiration and thus maintain the redox homeostasis within the cell. In particular, fungal pathogens are exposed to reactive oxygen species (ROS) when they interact with the phagocytic cells of the host which are the first line of defense against fungal infections. These pathogens have co-opted the enzymatic (catalases, superoxide dismutases (SODs), and peroxidases) and non-enzymatic (glutathione) mechanisms used to maintain the redox homeostasis within the cell, to resist oxidative stress and ensure survival within the host. Several virulence factors have been related to the response to oxidative stress in pathogenic fungi. The opportunistic fungal pathogen Candida glabrata (C. glabrata) is the second most common cause of candidiasis after Candida albicans (C. albicans). C. glabrata has a well defined oxidative stress response (OSR), which include both enzymatic and non-enzymatic mechanisms. C. glabrata OSR is controlled by the well-conserved transcription factors Yap1, Skn7, Msn2 and Msn4. In this review, we describe the OSR of C. glabrata, what is known about its core elements, its regulation and how C. glabrata interacts with the host. This manuscript is part of the series of works presented at the "V International Workshop: Molecular genetic approaches to the study of human pathogenic fungi" (Oaxaca, Mexico, 2012).

Transsulfuration pathway thiols and methylated arginines: the Hunter Community Study

Background

Serum homocysteine, when studied singly, has been reported to be positively associated both with the endogenous nitric oxide synthase inhibitor asymmetric dimethylarginine [ADMA, via inhibition of dimethylarginine dimethylaminohydrolase (DDAH) activity] and with symmetric dimethylarginine (SDMA). We investigated combined associations between transsulfuration pathway thiols, including homocysteine, and serum ADMA and SDMA concentrations at population level.

Methods

Data on clinical and demographic characteristics, medication exposure, C-reactive protein, serum ADMA and SDMA (LC-MS/MS), and thiols (homocysteine, cysteine, taurine, glutamylcysteine, total glutathione, and cysteinylglycine; capillary electrophoresis) were collected from a sample of the Hunter Community Study on human ageing [n = 498, median age (IQR) = 64 (60–70) years].

Results

Regression analysis showed that: a) age (P = 0.001), gender (P = 0.03), lower estimated glomerular filtration rate (eGFR, P = 0.08), body mass index (P = 0.008), treatment with beta-blockers (P = 0.03), homocysteine (P = 0.02), and glutamylcysteine (P = 0.003) were independently associated with higher ADMA concentrations; and b) age (P = 0.001), absence of diabetes (P = 0.001), lower body mass index (P = 0.01), lower eGFR (P<0.001), cysteine (P = 0.007), and glutamylcysteine (P<0.001) were independently associated with higher SDMA concentrations. No significant associations were observed between methylated arginines and either glutathione or taurine concentrations.

Conclusions

After adjusting for clinical, demographic, biochemical, and pharmacological confounders the combined assessment of transsulfuration pathway thiols shows that glutamylcysteine has the strongest and positive independent associations with ADMA and SDMA. Whether this reflects a direct effect of glutamylcysteine on DDAH activity (for ADMA) and/or cationic amino acid transport requires further investigations.

Age-specific effects on rat lung glutathione and antioxidant enzymes after inhaling ultrafine soot

Vehicle exhaust is rich in polycyclic aromatic hydrocarbons (PAHs) and is a dominant contributor to urban particulate pollution (PM). Exposure to PM is linked to respiratory and cardiovascular morbidity and mortality in susceptible populations, such as children. PM can contribute to the development and exacerbation of asthma, and this is thought to occur because of the presence of electrophiles in PM or through electrophile generation via the metabolism of PAHs. Glutathione (GSH), an abundant intracellular antioxidant, confers cytoprotection through conjugation of electrophiles and reduction of reactive oxygen species. GSH-dependent phase II detoxifying enzymes glutathione peroxidase and glutathione S-transferase facilitate metabolism and conjugation, respectively. Ambient particulates are highly variable in composition, which complicates systematic study. In response, we have developed a replicable ultrafine premixed flame particle (PFP)-generating system for in vivo studies. To determine particle effects in the developing lung, 7-day-old neonatal and adult rats inhaled 22 μg/m(3) PFP during a single 6-hour exposure. Pulmonary GSH and related phase II detoxifying gene and protein expression were evaluated 2, 24, and 48 hours after exposure. Neonates exhibited significant depletion of GSH despite higher initial baseline levels of GSH. Furthermore, we observed attenuated induction of phase II enzymes (glutamate cysteine ligase, glutathione reductase, glutathione S-transferase, and glutathione peroxidase) in neonates compared with adult rats. We conclude that developing neonates have a limited ability to deviate from their normal developmental pattern that precludes adequate adaptation to environmental pollutants, which results in enhanced cytotoxicity from inhaled PM.

A distinct metabolic signature predicts development of fasting plasma glucose

Background

High blood glucose and diabetes are amongst the conditions causing the greatest losses in years of healthy life worldwide. Therefore, numerous studies aim to identify reliable risk markers for development of impaired glucose metabolism and type 2 diabetes. However, the molecular basis of impaired glucose metabolism is so far insufficiently understood. The development of so called 'omics' approaches in the recent years promises to identify molecular markers and to further understand the molecular basis of impaired glucose metabolism and type 2 diabetes. Although univariate statistical approaches are often applied, we demonstrate here that the application of multivariate statistical approaches is highly recommended to fully capture the complexity of data gained using high-throughput methods.

Methods

We took blood plasma samples from 172 subjects who participated in the prospective Metabolic Syndrome Berlin Potsdam follow-up study (MESY-BEPO Follow-up). We analysed these samples using Gas Chromatography coupled with Mass Spectrometry (GC-MS), and measured 286 metabolites. Furthermore, fasting glucose levels were measured using standard methods at baseline, and after an average of six years. We did correlation analysis and built linear regression models as well as Random Forest regression models to identify metabolites that predict the development of fasting glucose in our cohort.

Results

We found a metabolic pattern consisting of nine metabolites that predicted fasting glucose development with an accuracy of 0.47 in tenfold cross-validation using Random Forest regression. We also showed that adding established risk markers did not improve the model accuracy. However, external validation is eventually desirable. Although not all metabolites belonging to the final pattern are identified yet, the pattern directs attention to amino acid metabolism, energy metabolism and redox homeostasis.

Conclusions

We demonstrate that metabolites identified using a high-throughput method (GC-MS) perform well in predicting the development of fasting plasma glucose over several years. Notably, not single, but a complex pattern of metabolites propels the prediction and therefore reflects the complexity of the underlying molecular mechanisms. This result could only be captured by application of multivariate statistical approaches. Therefore, we highly recommend the usage of statistical methods that seize the complexity of the information given by high-throughput methods.

Acute exercise stress activates Nrf2/ARE signaling and promotes antioxidant mechanisms in the myocardium

Oxidative stress has been implicated in the pathogenesis of cardiovascular diseases, including myocardial hypertrophy and infarction. Although impairment of antioxidant defense mechanisms has been thought to provoke oxidative stress-induced myocardial dysfunction, it has been difficult to clearly demonstrate. Nuclear erythroid 2 p45-related factor 2 (Nrf2) is a redox-sensitive, basic leucine zipper protein that regulates the transcription of several antioxidant genes. We previously reported that sustained activation of Nrf2 upregulates transcription of a number of endogenous antioxidants in the heart. Here, we show that acute exercise stress (AES) results in activation of Nrf2/ARE (antioxidant response element) signaling and subsequent enhancement of antioxidant defense pathways in wild-type (WT) mouse hearts, while oxidative stress, along with blunted defense mechanisms, was observed in Nrf2-/- mice. We also find that AES is associated with increased trans-activation of ARE-containing genes in exercised animals when compared to age-matched sedentary WT mice. However, enhanced oxidative stress in response to AES was observed in Nrf2-/- mice due to lower basal expression and marked attenuation of the transcriptional induction of several antioxidant genes. Thus, AES induces ROS and promotes Nrf2 function, but disruption of Nrf2 increases susceptibility of the myocardium to oxidative stress. Our findings suggest the basis for a nonpharmacological approach to activate Nrf2/ARE signaling, which might be a potential therapeutic target to protect the heart from oxidative stress-induced cardiovascular complications.

Protective effect of gallic acid against lindane induced toxicity in experimental rats

Lindane is an organochlorine pesticide that persists in the environment, bioaccumulate through food chain and has a risk of causing adverse effects to human health and the environment. It induces cell damage by producing free radicals and reactive oxygen species. The aim of the present study is to investigate the protective effect of gallic acid (a plant derived polyphenol) against lindane induced hepatic and renal toxicity in rats. Liver damage was assessed by hepatic serum marker enzymes like SGOT, SGPT and ALP and histopathological observation. Renal damage was observed by histopathological examination and serum markers like creatinine and urea. Treatment with lindane increased the levels of lipid peroxidation, serum marker enzyme activity with a concomitant decrease in GSH, CAT, SOD, GPx and GST. Histological alterations were also observed in kidney and liver tissue with lindane treatment. Co-treatment of gallic acid significantly prevented the lindane induced alterations in kidney and liver tissues with a decrease in LPO, serum marker enzyme activity and a significant increase in antioxidant levels. These results suggest that gallic acid has protective effect over lindane induced oxidative damage in rat liver and kidney.

Dose-dependent effect of oregano (Origanum vulgare L.) on lipid peroxidation and antioxidant status in 1,2-dimethylhydrazine-induced rat colon carcinogenesis

Colon cancer is a major cause of morbidity and mortality in developed and developing countries. Diet and dietary constituents play a major role in the aetiology of colon cancer. We have investigated the effect of an aqueous extract of oregano (Origanum vulgare. L.) on lipid peroxidation and anti-oxidant status in 1,2-dimethylhydrazine (DMH)-induced rat colon carcinogenesis. We aimed to identify the important antioxidants present in Indian oregano using RP-HPLC. DMH (20 mgkg−1) was administered subcutaneously once a week for the first four weeks and then discontinued. Oregano was supplemented every day orally at a dose of 20, 40 or 60 mgkg−1 to different groups of rats for 15 weeks. After this time the rats were killed and the colons were examined visually and evaluated biochemically. The levels of lipid peroxidation products, such as thiobarbituric acid reactive substances and conjugated dienes were significantly higher in the liver whereas in caecum and colon the levels were lower in DMH-treated animals as compared with control rats. The levels of the anti-oxidants superoxide dismutase, catalase, reduced glutathione, glutathione reductase, glutathione peroxidase and glutathione-S-transferase were decreased in DMH-treated rats, but were significantly reversed on oregano supplementation. Oregano supplementation (40 mgkg−1) had a modulatory role on tissue lipid peroxidation and antioxidant profile in colon cancer-bearing rats, which suggested a possible anti-cancer property of oregano.

Chemopreventive efficacy of gallic acid, an antioxidant and anticarcinogenic polyphenol, against 1,2-dimethyl hydrazine induced rat colon carcinogenesis

Colon cancer is a major cause of morbidity and mortality in developed and developing countries and its etiology is known to be a combination of hereditary, environmental, dietary factors and lack of physical activity. Chemoprevention offers a novel approach to control the incidence of colon cancer. Gallic acid (GA) is a polyphenol widely present in tea and other plants which is popularly used in the traditional medicine of China. The present study was to evaluate the efficacy of GA supplementation on tissue lipid peroxidation and antioxidant defense system in 1,2-dimethyhydrazine (DMH) induced colon carcinogenesis in male Wistar rats. The rats were assorted into six groups, viz., group1 control rats received modified pellet diet; group 2 rats received GA (50 mg/kg body weight) orally along with modified pellet diet; group 3 rats received DMH (20 mg/kg body weight) subcutaneously once a week for the first 15 weeks; groups 4, 5 and 6 rats received GA along with DMH during the initiation, post- initiation stages and the entire period of study respectively. All the rats were sacrificed at the end of 30 weeks and the tissues were evaluated biochemically. We observed decreased lipid peroxidation (LPO) products such as thiobarbituric acid reactive substances (TBARS), lipid hydroperoxides (LOOH) and conjugated dienes (CD) and diminished levels of antioxidants such as superoxide dismutase (SOD), catalase (CAT), reduced glutathione (GSH), glutathione reductase (GR) and glutathione peroxidase (GPx) in the tissues of DMH treated rats, which were elevated significantly on GA supplementation. Moreover, enhanced activity of ascorbic acid and alpha-tocopherol levels were also observed in DMH alone treated rats which were significantly reduced on GA supplementation. Our results suggest that GA could exert a significant chemopreventive effect on DMH induced colon carcinogenesis.

Glutathione: overview of its protective roles, measurement, and biosynthesis

This review is the introduction to a special issue concerning, glutathione (GSH), the most abundant low molecular weight thiol compound synthesized in cells. GSH plays critical roles in protecting cells from oxidative damage and the toxicity of xenobiotic electrophiles, and maintaining redox homeostasis. Here, the functions and GSH and the sources of oxidants and electrophiles, the elimination of oxidants by reduction and electrophiles by conjugation with GSH are briefly described. Methods of assessing GSH status in the cells are also described. GSH synthesis and its regulation are addressed along with therapeutic approaches for manipulating GSH content that have been proposed. The purpose here is to provide a brief overview of some of the important aspects of glutathione metabolism as part of this special issue that will provide a more comprehensive review of the state of knowledge regarding this essential molecule.

Can persistent organic pollutants explain the association between serum gamma-glutamyltransferase and type 2 diabetes?

The results of several epidemiological studies of serum gamma-glutamyltransferase (GGT) led us to hypothesise that associations of GGT within its normal range with type 2 diabetes may reflect detrimental effects of xenobiotics found in the environment, such as persistent organic pollutants (POPs). Epidemiological observations showed that serum GGT activity within its normal range strongly predicted future type 2 diabetes; the predictability of diabetes from obesity was low with GGT at the low end of the normal range; and GGT showed a positive association with known markers of oxidative stress or inflammation. Experimental findings on cellular GGT suggest that serum GGT levels within the normal range may reflect oxidative stress related to the re-synthesis of intracellular glutathione; however, this interpretation is not completely satisfying because, in its role of regenerating intracellular glutathione, GGT activity should be antioxidative. Alternatively, serum GGT activity may reflect amounts of glutathione conjugates formed during the metabolism of xenobiotics. Accordingly, we postulate a two-part hypothesis: that the association of serum GGT with type 2 diabetes reflects exposure to POPs, as these substances, which have a very long half-life, may influence diabetes risk by residing in adipose tissue as endocrine disruptors; and that POPs or similar substances may interact with obesity to cause type 2 diabetes. Supporting this hypothesis, cross-sectional investigation of background exposure to POPs in the National Health and Nutrition Examination Survey showed relationships similar to those observed for GGT, including a powerful association with prevalent diabetes and no association between obesity and diabetes for very low POP concentrations. Our hypothesis can be tested in both prospective studies and toxicological studies.

Analysis of time-related metabolic fluctuations induced by ethionine in the rat

The time-course of metabolic events following response to a model hepatotoxin ethionine (800 mg/kg) was investigated over a 7 day period in rats using high-resolution (1)H NMR spectroscopic analysis of urine and multivariate statistics. Complementary information was obtained by multivariate analysis of (1)H MAS NMR spectra of intact liver and by conventional histopathology and clinical chemistry of blood plasma. (1)H MAS NMR spectra of liver showed toxin-induced lipidosis 24 h postdose consistent with the steatosis observed by histopathology, while hypertaurinuria was suggestive of liver injury. Early biochemical changes in urine included elevation of guanidinoacetate, suggesting impaired methylation reactions. Urinary increases in 5-oxoproline and glycine suggested disruption of the gamma-glutamyl cycle. Signs of ATP depletion together with impairment of the energy metabolism were given from the decreased levels in tricarboxylic acid cycle intermediates, the appearance of ketone bodies in urine, the depletion of hepatic glucose and glycogen, and also hypoglycemia. The observed increase in nicotinuric acid in urine could be an indication of an increase in NAD catabolism, a possible consequence of ATP depletion. Effects on the gut microbiota were suggested by the observed urinary reductions in the microbial metabolites 3-/4-hydroxyphenyl propionic acid, dimethylamine, and tryptamine. At later stages of toxicity, there was evidence of kidney damage, as indicated by the tubular damage observed by histopathology, supported by increased urinary excretion of lactic acid, amino acids, and glucose. These studies have given new insights into mechanisms of ethionine-induced toxicity and show the value of multisystem level data integration in the understanding of experimental models of toxicity or disease.

Specific reactions of S-nitrosothiols with cysteine hydrolases: A comparative study between dimethylargininase-1 and CTP synthetase

S-Transnitrosation is an important bioregulatory process whereby NO(+) equivalents are transferred between S-nitrosothiols and Cys of target proteins. This reaction proceeds through a common intermediate R-S-N(O(-))-S-R' and it has been proposed that products different from S-nitrosothiols may be formed in protein cavities. Recently, we have reported on the formation of such a product, an N-thiosulfoximide, at the active site of the Cys hydrolase dimethylargininase-1 (DDAH-1) upon reaction with S-nitroso-l-homocysteine (HcyNO). Here we have addressed the question of whether this novel product can also be formed with the endogenously occurring S-nitrosothiols S-nitroso-l-cysteine (CysNO) and S-nitrosoglutathione (GSNO). Further, to explore the reason responsible for the unique formation of an N-thiosulfoximide in DDAH-1 we have expanded these studies to cytidine triphosphate synthetase (CTPS), which shows a similar active site architecture. ESI-MS and activity measurements showed that the bulky GSNO does not react with both enzymes. In contrast, S-nitrosylation of the active site Cys occurred in DDAH-1 with CysNO and in CTPS with CysNO and HcyNO. Although kinetic analysis indicated that these compounds act as specific irreversible inhibitors, no N-thiosulfoximide was formed. The reasons likely responsible for the absence of the N-thiosulfoximide formation are discussed using molecular models of DDAH-1 and CTPS. In tissue extracts DDAH was inhibited only by HcyNO, with an IC(50) value similar to that of the isolated protein. Biological implications of these studies for the function of both enzymes are discussed.

Dose-response efficacy of caraway (Carum carvi L.) on tissue lipid peroxidation and antioxidant profile in rat colon carcinogenesis

Colon cancer is a leading cause of cancer death and its prevention is of great interest throughout the world. This study was conducted to examine the efficacy of different doses of dietary caraway (Carum carvi L.) on tissue lipid peroxidation (LPO) and antioxidant profile in rat colon carcinogenesis. Wistar male rats were divided into 6 groups and were fed a modified pellet diet for the whole of 30 weeks. To induce colon cancer, rats were given a weekly subcutaneous injection of 1,2-dimethylhydrazine (DMH) at a dose of 20 mg kg(-1) (based on body weight) for the first 15 weeks. Caraway was supplemented every day orally at doses of 30, 60 and 90 mg kg(-1) for different groups of rats for the total period of 30 weeks. All rats were sacrificed at the end of 30 weeks, the colons were examined visually for masses and were subsequently evaluated histologically. The results showed diminished levels of intestinal, colonic and caecal LPO products, such as conjugated dienes (CD), lipid hydroperoxides (LOOH) and thiobarbituric acid reactive substances (TBARS) and also the antioxidants superoxide dismutase (SOD), catalase (CAT), reduced glutathione (GSH) and glutathione reductase (GR) in DMH treated rats, which were significantly reversed (P<0.05) on caraway supplementation. Moreover, enhanced activity of intestinal, colonic and caecal glutathione peroxidase (GPx), glutathione S-transferase (GST) and colonic ascorbic acid and alpha-tocopherol levels were observed in carcinogen-treated rats, which were significantly (P<0.05) reduced on caraway supplementation. Thus, our study showed that caraway supplementation at a dose of 60 mg kg(-1) had a modulatory role on tissue LPO, antioxidant profile and prevented DMH-induced histopathological lesions in colon cancer rats.

Oxygen-glucose deprivation decreases glutathione levels and glutamate uptake in rat hippocampal slices

Ischemia is a transitory or permanent reduction of blood flow that may provoke an excessive release of glutamate. In that condition, increased reactive oxygen species generation and/or decreased cerebral antioxidant capacity may induce cell death. Antioxidant enzymes and thiols play an important role in the cellular defenses against oxidative stress. The purpose of this study was to evaluate cell viability, glutamate uptake and antioxidant status in rat hippocampal slices exposed to oxygen-glucose deprivation (OGD), an in vitro model of ischemia. After 15 min or 1 h of OGD, hippocampal slices showed a significant reduction of cell viability. Reperfusion during 1 or 2 h did not increase cell death. In this condition, the activities of antioxidant enzymes catalase, glutathione reductase, and peroxidase did not change. However, slices exposed to 15 min OGD and reperfused for 1 or 2 h showed higher superoxide dismutase activity. A significant reduction of glutathione levels was observed after 1 or 2 h of reperfusion in slices previously exposed to 1 h of OGD, although the protein-thiol content was unchanged. Slices exposed to 1 h of OGD and reperfused for 2 h showed reduced sodium-dependent l-[(3)H]glutamate uptake. The reduction of glutamate uptake was partially reversed by dl-dithiothreitol (DTT), a thiol-reducing agent, which may reduce thiol groups in glutamate transporters. Therefore, higher glutamate levels in the synaptic cleft could promote transporter reversal and impair glutamate uptake. Increased extracellular glutamate levels associated with decreased glutathione levels might exacerbate cell damage induced by oxygen and glucose deprivation.

Kinetic characteristics of native gamma-glutamylcysteine ligase in the aging housefly, Musca domestica L

The catalytic activity of gamma-glutamylcysteine ligase (gamma-GCL; EC 6.3.2.2) was compared between relatively young (4-day-old) and old (19-day-old) houseflies (Musca domestica) in order to understand the mechanism of putative deterioration of glutathione homeostasis during the aging process. Hanes-Woolf analyses ([S]/v vs [S]) indicated that gamma-GCL had significantly higher affinities for its substrates in the young than in the old flies. The K(m) values in the young and old flies were, respectively, for glutamate 0.6 and 5.5 mM; for cysteine 0.3 and 4.6 mM; and for ATP 1.2 and 2.9 mM. Furthermore, young but not old flies exhibited substrate-dependent inhibition of gamma-GCL activity at >5 mM cysteine indicating a loss of metabolic regulation during aging. The age-associated differences in the affinity of native gamma-GCL towards its substrates suggest that de novo synthesis of glutathione would be relatively less efficient in the old houseflies.