Regulation of glutathione synthesis

NADPH oxidase 4 regulates homocysteine metabolism and protects against acetaminophen-induced liver damage in mice

Glutathione is the major intracellular redox buffer in the liver and is critical for hepatic detoxification of xenobiotics and other environmental toxins. Hepatic glutathione is also a major systemic store for other organs and thus impacts on pathologies such as Alzheimer's disease, Sickle Cell Anaemia and chronic diseases associated with aging. Glutathione levels are determined in part by the availability of cysteine, generated from homocysteine through the transsulfuration pathway. The partitioning of homocysteine between remethylation and transsulfuration pathways is known to be subject to redox-dependent regulation, but the underlying mechanisms are not known. An association between plasma Hcy and a single nucleotide polymorphism within the NADPH oxidase 4 locus led us to investigate the involvement of this reactive oxygen species- generating enzyme in homocysteine metabolism. Here we demonstrate that NADPH oxidase 4 ablation in mice results in increased flux of homocysteine through the betaine-dependent remethylation pathway to methionine, catalysed by betaine-homocysteine-methyltransferase within the liver. As a consequence NADPH oxidase 4-null mice display significantly lowered plasma homocysteine and the flux of homocysteine through the transsulfuration pathway is reduced, resulting in lower hepatic cysteine and glutathione levels. Mice deficient in NADPH oxidase 4 had markedly increased susceptibility to acetaminophen-induced hepatic injury which could be corrected by administration of N-acetyl cysteine. We thus conclude that under physiological conditions, NADPH oxidase 4-derived reactive oxygen species is a regulator of the partitioning of the metabolic flux of homocysteine, which impacts upon hepatic cysteine and glutathione levels and thereby upon defence against environmental toxins.

The combination of conjugated linoleic acid (CLA) and extra virgin olive oil increases mitochondrial and body metabolism and prevents CLA-associated insulin resistance and liver hypertrophy in C57Bl/6 mice

Clinical conditions associated with obesity can be improved by daily intake of conjugated linoleic acid (CLA) or extra virgin olive oil (EVOO). Here we investigated whether dietary supplementation with CLA and EVOO, either alone or in combination, changes body metabolism associated with mitochondrial energetics. Male C57Bl/6 mice were divided into one of four groups: CLA (1:1 cis-9, trans-11:trans-10, cis-12; 18:2 isomers), EVOO, CLA plus EVOO or control (linoleic acid). Each mouse received 3 g/kg body weight of the stated oil by gavage on alternating days for 60 days. Dietary supplementation with CLA, alone or in combination with EVOO: (a) reduced the white adipose tissue gain; (b) increased body VO2 consumption, VCO2 production and energy expenditure; (c) elevated uncoupling protein (UCP)-2 expression and UCP activity in isolated liver mitochondria. This organelle, when energized with NAD(+)-linked substrates, produced high amounts of H2O2 without inducing oxidative damage. Dietary supplementation with EVOO alone did not change any metabolic parameter, but supplementation with CLA itself promoted insulin resistance and elevated weight, lipid content and acetyl-CoA carboxylase-1 expression in liver. Interestingly, the in vivo antioxidant therapy with N-acetylcysteine abolished the CLA-induced rise of body metabolism and liver UCP expression and activity, while the in vitro antioxidant treatment with catalase mitigated the CLA-dependent UCP-2 expression in hepatocytes; these findings suggest the participation of an oxidative-dependent pathway. Therefore, this study clarifies the mechanisms by which CLA induces liver UCP expression and activity, and demonstrates for the first time the beneficial effects of combined CLA and EVOO supplementation.

Dietary glutamine supplementation effects on amino acid metabolism, intestinal nutrient absorption capacity and antioxidant response of gilthead sea bream (Sparus aurata) juveniles

A study was undertaken to evaluate dietary glutamine supplementation effects on gilthead sea bream performance, intestinal nutrient absorption capacity, hepatic and intestinal glutamine metabolism and oxidative status. For that purpose gilthead sea bream juveniles (mean weight 13.0g) were fed four isolipidic (18% lipid) and isonitrogenous (43% protein) diets supplemented with 0, 0.5, 1 and 2% glutamine for 6weeks. Fish performance, body composition and intestinal nutrient absorption capacity were not affected by dietary glutamine levels. Hepatic and intestinal glutaminase (GlNase), glutamine synthetase (GSase), alanine aminotransferase, aspartate aminotransferase and glutamate dehydrogenase activities were also unaffected by dietary glutamine supplementation. In the intestine GlNase activity was higher and GSase/GlNase ratio was two-fold lower than in the liver, suggesting a higher use of glutamine for energy production by the intestine than by the liver. The liver showed higher catalase and glucose-6-phosphate dehydrogenase activities, while the intestine presented higher glutathione peroxidase and glutathione reductase activities and oxidised glutathione content, which seems to reveal a higher glutathione dependency of the intestinal antioxidant response. Total and reduced glutathione contents in liver and intestine and superoxide dismutase activity in the intestine were enhanced by dietary glutamine, though lipid peroxidation values were not affected. Overall, differences between liver and intestine glutamine metabolism and antioxidant response were identified and the potential of dietary glutamine supplementation to gilthead sea bream's antioxidant response was elucidated.

Effective elimination of chronic lymphocytic leukemia cells in the stromal microenvironment by a novel drug combination strategy using redox-mediated mechanisms

Chronic lymphocytic leukemia (CLL) is the most common type of adult leukemia, and is currently incurable due to drug resistance. A previous study indicated that the redox interaction between bone marrow stromal cells and leukemia cells profoundly affected CLL cell viability and drug response. The present study aimed to further investigate the effect of the redox interaction on drug resistance of CLL cells in the bone marrow microenvironment, and to assess a novel redox-mediated strategy to eliminate stromal-protected CLL cells, and thus to achieve maximum therapeutic efficacy of antileukemic drugs. Histone deacetylase inhibitor suberoylanilide hydroxamic acid (SAHA) is a potent novel anticancer agent, however, it exerts limited activity in patients with CLL. The results of the present study demonstrated that SAHA facilitated stromal‑mediated glutathione upregulation in the CLL cells, contributing to drug resistance. The addition of β‑phenylethyl isothiocyanate (PEITC) induced severe depletion of stromal and SAHA‑upregulated glutathione, enhanced SAHA‑mediated reactive oxygen species accumulation in the CLL cells and caused oxidation of mitochondrial cardilopin, leading to substantial cell death. The results further demonstrated that stromal cells and SAHA markedly upregulated antiapoptotic protein expression levels of myeloid cell leukemia 1 (Mcl1) in CLL the cells. By inducing protein deglutathionylation and degradation, PEITC suppressed the expression of Mcl1 in co‑cultured CLL cells, and increased SAHA sensitivity. The combination of SAHA and PEITC enabled the induction of marked apoptosis of CLL cells co‑cultured with bone marrow stromal cells. The present study provided a preclinical rationale, which warrants further clinical investigation for the potential use of SAHA/PEITC as a novel combination treatment strategy for CLL.

Effect of quercetin, genistein and kaempferol on glutathione and glutathione-redox cycle enzymes in 3T3-L1 preadipocytes

CONTEXT AND OBJECTIVE

Many studies have shown that cellular redox potential is largely determined by glutathione (GSH), which accounts for more than 90% of cellular nonprotein thiols. The aim of this study was to delineate the effect of three flavonoids - namely, quercetin, kaempferol and genistein - and exogenous GSH on oxidative damage by the Fenton's pathway through the GSH and GSH-redox cycle enzymes in 3T3-L1 cells.

MATERIALS AND METHODS

3T3-L1 preadipocytes were exposed to each flavonoid and GSH at concentrations of 0, 5, 10, 15, 20 and 25 µM and then GSH levels and activities of glutathione peroxidase (GSH-Px), glutathione reductase (GSH-Rx) and superoxide dismutase (SOD) were measured.

RESULTS

Exogenous GSH did not have significant effect on intracellular GSH although slight decrease was observed at 15-25 µM doses. However, each of the three flavonoids sustained intracellular GSH levels in the cells as compared to the respective controls. Quercetin had the most profound effect, followed by kaempferol and genistein in that order. GSH-Px, GSH-Rx and SOD activities increased for all the doses tested compared to their respective controls. Again, quercetin had the maximum increase in enzyme activities followed by kaempferol and genistein for the enzymes tested.

DISCUSSION AND CONCLUSION

These findings suggest that the flavonoids play an important role in diminishing oxidation-induced biochemical damages. The enhancement of these enzymes may increase the resistance of the organism against oxidative damage by the Fenton's pathway.

Histopatological alterations and oxidative stress in liver and kidney of Leuciscus cephalus following exposure to heavy metals in the Tur River, North Western Romania

Pollution of the aquatic environment by heavy metals is a great concern worldwide. Freshwater fish ingests various metals through gills, skin or diet. Our aim was to investigate the oxidative stress and histopathological injuries induced by Fe, Cu, Zn, Pb, Cd in the liver and kidney of Leuciscus cephalus. Fish samples were collected from two sites in the Tur River, NW Romania, in upstream and downstream of a pollution source. Metals were differently distributed in the liver and kidney of fish. The highest concentrations of Fe, Cu and Pb were found in liver, whereas Zn and Cd concentrations were the highest in kidney in specimens collected from the downstream site. The histopathological changes were associated with metal bioaccumulation, being more severe in kidney than liver. Malondialdehyde (MDA) and advanced oxidation protein products (AOPP) increased significantly in the liver and kidney of fish from downstream site compared to upstream one, whereas reduced glutathione (GSH) decreased. The activities of superoxide dismutase (SOD), catalase (CAT) and glutathione-S-transferase (GST) increased significantly in livers, whereas SOD increased in kidney. Our study revealed that liver has a higher capacity and adaptability to counteract ROS compared to kidney. The more pronounced increase of hepatic SOD, CAT and GST activities is related milder structural changes observed in liver compared to kidney, where lesions were not reduced by antioxidant defense system.

Hepatic glutathione contributes to attenuation of thioacetamide-induced hepatic necrosis due to suppression of oxidative stress in diet-induced obese mice

We previously reported that hepatic necrosis induced by thioacetamide (TA), a hepatotoxicant, was attenuated in mice fed a high-fat diet (HFD mice) in comparison with mice fed a normal rodent diet (ND mice). In this study, we focused on investigation of the mechanism of the attenuation. Hepatic content of thiobarbituric acid reactive substances (TBARS), an oxidative stress marker, significantly increased in ND mice at 24 and 48 hr after TA administration in comparison to that in vehicle-treated ND mice. At these time points, severe hepatic necrosis was observed in ND mice. Treatment with an established antioxidant, butylated hydroxyanisole, attenuated the TA-induced hepatic necrosis in ND mice. In contrast, in HFD mice, hepatic TBARS content did not increase, and hepatic necrosis was attenuated in comparison with ND mice at 24 and 48 hr after TA dosing. Metabolomics analysis regarding hepatic glutathione, a biological antioxidant, revealed decreased glutathione and changes in the amount of glutathione metabolism-related metabolites, such as increased ophtalmate and decreased cysteine, and this indicated activation of glutathione synthesis and usage in HFD mice. Finally, after treatment with L-buthionine-S,R-sulfoxinine, an inhibitor of glutathione synthesis, TA-induced hepatic necrosis was enhanced and hepatic TBARS contents increased after TA dosing in HFD mice. These results suggested that activated synthesis and usage of hepatic GSH, which suppresses hepatic oxidative stress, is one of the factors that attenuate TA-induced hepatic necrosis in HFD mice.

Cytoprotective effects of 12-oxo phytodienoic acid, a plant-derived oxylipin jasmonate, on oxidative stress-induced toxicity in human neuroblastoma SH-SY5Y cells

BACKGROUND

Jasmonates are plant lipid-derived oxylipins that act as key signaling compounds when plants are under oxidative stress, but little is known about their functions in mammalian cells. Here we investigated whether jasmonates could protect human neuroblastoma SH-SY5Y cells against oxidative stress-induced toxicity.

METHODS

The cells were pretreated with individual jasmonates for 24h and exposed to hydrogen peroxide (H2O2) for 24h. Before the resulting cytotoxicity, intracellular reactive oxygen species (ROS) levels, and mitochondrial membrane potential were measured. We also measured intracellular glutathione (GSH) levels and investigated changes in the signaling cascade mediated by nuclear factor erythroid 2-related factor 2 (Nrf2) in cells treated with 12-oxo phytodienoic acid (OPDA).

RESULTS

Among the jasmonates, only OPDA suppressed H2O2-induced cytotoxicity. OPDA pretreatment also inhibited the H2O2-induced ROS increase and mitochondrial membrane potential decrease. In addition, OPDA induced the nuclear translocation of Nrf2 and increased intracellular GSH level and the expression of the Nrf2-regulated phase II antioxidant enzymes heme oxygenase-1, NADPH quinone oxidoreductase 1, and glutathione reductase. Finally, the cytoprotective effects of OPDA were reduced by siRNA-induced knockdown of Nrf2.

CONCLUSIONS

These results demonstrated that among jasmonates, only OPDA suppressed oxidative stress-induced death of human neuroblastoma cells, which occurred via activation of the Nrf2 pathway.

GENERAL SIGNIFICANCE

Plant-derived oxylipin OPDA may have the potential to provide protection against oxidative stress-related diseases.

Thiol-activated gem-dithiols: a new class of controllable hydrogen sulfide donors

A class of novel thiol-activated H2S donors has been developed on the basis of the gem-dithiol template. These donors release H2S in the presence of cysteine or GSH in aqueous solutions as well as in cellular environments.

The effect of maternal low-protein diet on the heart of adult offspring: role of mitochondria and oxidative stress

Protein restriction during perinatal and early postnatal development is associated with a greater incidence of disease in the adult, such arterial hypertension. The aim in the present study was to investigate the effect of maternal low-protein diet on mitochondrial oxidative phosphorylation capacity, mitochondrial reactive oxygen species (ROS) formation, antioxidant levels (enzymatic and nonenzymatic), and oxidative stress levels on the heart of the adult offspring. Pregnant Wistar rats received either 17% casein (normal protein, NP) or 8% casein (low protein, LP) throughout pregnancy and lactation. After weaning male progeny of these NP or LP fed rats, females were maintained on commercial chow (Labina-Purina). At 100 days post-birth, the male rats were sacrificed and heart tissue was harvested and stored at −80 °C. Our results show that restricting protein consumption in pregnant females induced decreased mitochondrial oxidative phosphorylation capacity (51% reduction in ADP-stimulated oxygen consumption and 49.5% reduction in respiratory control ratio) in their progeny when compared with NP group. In addition, maternal low-protein diet induced a significant decrease in enzymatic antioxidant capacity (37.8% decrease in superoxide dismutase activity; 42% decrease in catalase activity; 44.8% decrease in glutathione-S-transferase activity; 47.9% decrease in glutathione reductase; 25.7% decrease in glucose-6 phosphate dehydrogenase) and glutathione level (34.8% decrease) when compared with control. From these findings, we hypothesize that an increased production of ROS and decrease in antioxidant activity levels induced by protein restriction during development could potentiate the progression of metabolic and cardiac diseases in adulthood.

Health risks of space exploration: targeted and nontargeted oxidative injury by high-charge and high-energy particles

SIGNIFICANCE

During deep space travel, astronauts are often exposed to high atomic number (Z) and high-energy (E) (high charge and high energy [HZE]) particles. On interaction with cells, these particles cause severe oxidative injury and result in unique biological responses. When cell populations are exposed to low fluences of HZE particles, a significant fraction of the cells are not traversed by a primary radiation track, and yet, oxidative stress induced in the targeted cells may spread to nearby bystander cells. The long-term effects are more complex because the oxidative effects persist in progeny of the targeted and affected bystander cells, which promote genomic instability and may increase the risk of age-related cancer and degenerative diseases.

RECENT ADVANCES

Greater understanding of the spatial and temporal features of reactive oxygen species bursts along the tracks of HZE particles, and the availability of facilities that can simulate exposure to space radiations have supported the characterization of oxidative stress from targeted and nontargeted effects.

CRITICAL ISSUES

The significance of secondary radiations generated from the interaction of the primary HZE particles with biological material and the mitigating effects of antioxidants on various cellular injuries are central to understanding nontargeted effects and alleviating tissue injury.

FUTURE DIRECTIONS

Elucidation of the mechanisms underlying the cellular responses to HZE particles, particularly under reduced gravity and situations of exposure to additional radiations, such as protons, should be useful in reducing the uncertainty associated with current models for predicting long-term health risks of space radiation. These studies are also relevant to hadron therapy of cancer.

Pathophysiological processes in multiple sclerosis: focus on nuclear factor erythroid-2-related factor 2 and emerging pathways

Multiple sclerosis (MS) is a disease of the central nervous system that is characterized by the demyelination of neuronal axons. Four different patterns of demyelination have been described, showing the heterogeneity in the immunopathologic processes involved in the demyelination. This review will focus on reactive oxygen species (ROS)-related inflammation in MS. Special emphasis will be placed on the nuclear factor erythroid-2-related factor 2 (Nrf2) as it regulates the transcription of ROS-protective genes. In the cytosol, Nrf2 binds to Keap1 (Kelch-like ECH-associated protein 1), and together they are degraded by the 26S proteasome after ubiquitination. If challenged by ROS Nrf2, binding to Keap1 is abrogated, and it translocates into the nucleus. Here it binds to the antioxidant response element and to a small protein termed Maf (musculoaponeurotic fibrosarcoma oncogene homolog). This leads to an enhanced transcription of ROS protective genes and represents the physiological answer against ROS challenge. It has been shown that dimethyl fumarate (DMF) has the same effect and leads to an enhanced transcription of ROS-protective genes. This response is mediated through a reduced binding of Nrf2 to Keap1, thus resulting in a higher level of free Nrf2 in the cytosol. Consequently, more Nrf2 translocates to the nucleus, promoting transcription of its target genes. DMF has been used for the treatment of psoriasis for many years in Germany without the occurrence of major side effects. In psoriasis, DMF reduces ROS-related inflammation in skin. A DMF analog, BG-12, was recently approved for the treatment of relapsing-remitting MS by the European Union and the US Food and Drug Administration. As an oral formulation, it gives patients a convenient and effective alternative to the injectable immune modulators in the long-term treatment of MS.

Glycine restores glutathione and protects against oxidative stress in vascular tissue from sucrose-fed rats

The attenuation of oxidative stress could be an important mechanism whereby the incidence of vascular complications in the MS (metabolic syndrome) may be diminished. The present study was undertaken to investigate the mechanism by which glycine, supplemented to the diet of SF (sucrose-fed) rats, modulates glutathione biosynthesis and protects against oxidative stress and altered endothelium-dependent relaxation in isolated aorta. Glycine reduced O2•- (superoxide anion radical) release in the presence of NADPH, and decreased protein carbonyl and lipid peroxidation. This effect of glycine could be because of the increased amount of glutathione synthetase, which may be responsible for increased glutathione (GSH) content in vascular tissue from SF rats. Moreover, glycine increased the amount of Cu,Zn-SOD (copper/zinc superoxide dismutase) and eNOS (endothelial NO synthase) in aorta from SF animals. Finally, it improved the relaxation response to ACh (acetylcholine) found impaired in aortic rings from SF rats. In the presence of NAC (N-acetylcysteine), a precursor of GSH, an improved ACh-mediated aortic relaxation of aortic rings from SF rats was observed, whereas BSO (buthionine sulfoximine), an inhibitor of glutathione biosynthesis, inhibited the relaxing effect of NAC in aortas from both control and SF rats. This experiment emphasizes the role of GSH in endothelial function in SF rats. The present data suggest that glycine rectifies vascular reactivity by increasing the biosynthesis of glutathione. Glutathione protects vascular tissue against oxidative stress, and enhances the availability of NO, which exerts its relaxing effect, thus contributing to the reduction of high BP (blood pressure) in the SF rats.

The role of the inhibition of glutathione-S-transferase in the protective mechanisms of ischemic postconditioning

The antioxidant glutathione-S-transferase (GST) is a crucial determinant of the development of ischaemic-reperfusion (I/R) injury, and plays a pivotal role in the regulation of the mitogen activated protein kinase (MAPK) pathways involved in stress response and apoptosis. The aim of this study was to investigate whether inhibition of GST can abolish the benefit of ischaemic postconditioning (IPoC). A neonatal rat cardiomyocyte cell culture was prepared and divided into 6 groups: (I) control group without treatment; (II) cells exposed to simulated I/R; (III) simulated I/R (sI/R) with IPoC; (IV) ethacrynic acid (EA) alone; (V) sI/R with EA; and (VI) sI/R and IPoC together with EA. Viability of the cells was measured by MTT assay, the quantity of apoptotic cells was assessed by flow cytometry following annexin V-FITC - propidium-iodide double staining. The activation of JNK, p38, ERK/p42-p44 MAPKs, and GSK-3β protein kinase was determined by flow-cytometric assay. GST inhibition markedly increased the apoptosis and decreased the cell viability despite IPoC. The protective effect of IPoC was lost in GST-inhibited groups for all MAPKs and GSK-3β. GST activity is required for the survival of cultured cardiomyocytes under stress conditions. GST inhibition was associated with differential activation of MAP and the protein kinases regulating these pathways in the process of ischaemic postconditioning.

Oxidant status and lipid composition of erythrocyte membranes in patients with type 2 diabetes, chronic liver damage, and a combination of both pathologies

There is an important set of cirrhotic and diabetic patients that present both diseases. However, information about metabolic and cellular blood markers that are altered, in conjunction or distinctively, in the 3 pathological conditions is scarce. The aim of this project was to evaluate several indicators of prooxidant reactions and the membrane composition of blood samples (serum and red blood cells (RBCs)) from patients clinically classified as diabetic (n = 60), cirrhotic (n = 70), and diabetic with liver cirrhosis (n = 25) as compared to samples from a similar population of healthy individuals (n = 60). The results showed that levels of TBARS, nitrites, cysteine, and conjugated dienes in the RBC of cirrhotic patients were significantly increased. However, the coincidence of diabetes and cirrhosis partially reduced the alterations promoted by the cirrhotic condition. The amount of total phospholipids and cholesterol was greatly enhanced in the patients with both pathologies (between 60 and 200% according to the type of phospholipid) but not in the patients with only one disease. Overall, the data indicate that the cooccurrence of diabetes and cirrhosis elicits a physiopathological equilibrium that is different from the alterations typical of each individual malady.

Beta-amyloidolysis and glutathione in Alzheimer's disease

In this review, we hypothesized the importance of the interaction between the brain glutathione (GSH) system, the proteolytic tissue plasminogen activator (t-PA)/plasminogen/ plasmin system, regulated by plasminogen activator inhibitor (PAI-1), and neuroserpin in the pathogenesis of Alzheimer’s disease. The histopathological characteristic hallmark that gives personality to the diagnosis of Alzheimer’s disease is the accumulation of neurofibroid tangles located intracellularly in the brain, such as the protein tau and extracellular senile plaques made primarily of amyloidal substance. These formations of complex etiology are intimately related to GSH, brain protective antioxidants, and the proteolytic system, in which t-PA plays a key role. There is scientific evidence that suggests a relationship between aging, a number of neurodegenerative disorders, and the excessive production of reactive oxygen species and accompanying decreased brain proteolysis. The plasminogen system in the brain is an essential proteolytic mechanism that effectively degrades amyloid peptides (“beta-amyloidolysis”) through action of the plasmin, and this physiologic process may be considered to be a means of prevention of neurodegenerative disorders. In parallel to the decrease in GSH levels seen in aging, there is also a decrease in plasmin brain activity and a progressive decrease of t-PA activity, caused by a decrease in the expression of the t-PA together with an increase of the PAI-1 levels, which rise to an increment in the production of amyloid peptides and a lesser clearance of them. Better knowledge of the GSH mechanism and cerebral proteolysis will allow us to hypothesize about therapeutic practices.

The influence of the intensity of smoking and years of work in the metallurgy on pro-oxidant/antioxidant balance in the blood of smelters

The aim of this study was to investigate the effect of cigarette smoking and occupational exposure to heavy metals on the degree of pro-oxidant/antioxidant imbalance in smelters. The investigations were performed on the blood and urine of 400 subjects: 300 male copper smelters and 100 nonexposed male subjects. Biological material was divided into three groups: nonsmokers, those who smoked less than 20 cigarettes a day and those who smoked more than 20 cigarettes a day. The results showed a significant increase in the concentration of lead, cadmium and arsenic in the blood and urine of smelters, while smoking more than 20 cigarettes a day caused a further increase in the concentration of these metals. The level of malondialdehyde was approximately twofold higher in the plasma of the smelters compared to the control group. We have observed a disturbance in the level of antioxidants in erythrocyte lysate manifested by an increase in metallothionein and glutathione concentrations as well as superoxide dismutase and glutathione peroxidase activities and the decrease in glutathione S-transferase activity. Cigarette smoking, years of work in metallurgy and age of smelters were additional factors significantly affecting the pro-oxidant/antioxidant balance.

Pioglitazone attenuates the detrimental effects of advanced glycation end-products in the pancreatic beta cell line HIT-T15

Pioglitazone is an anti-diabetic agent that preserves pancreatic beta cell mass and improves their function. Advanced Glycation End-Products (AGEs) are implicated in diabetic complications. We previously demonstrated that exposure of the pancreatic islet cell line HIT-T15 to high concentrations of AGEs significantly decreases cell proliferation and insulin secretion, and affects transcription factors regulating insulin gene transcription. The aim of this work was to investigate the effects of Pioglitazone on the function and viability of HIT-T15 cells cultured with AGEs. HIT-T15 cells were cultured for 5 days in the presence of AGEs alone, or supplemented with 1 μmol/l Pioglitazone. Cell viability, insulin secretion and insulin content, redox balance, expression of the AGE receptor (RAGE), and NF-kB activation were then determined. The results showed that Pioglitazone protected beta cells against AGEs-induced apoptosis and necrosis. Moreover, Pioglitazone restored the redox balance and improved the responsiveness to low glucose concentration. Adding Pioglitazone to the AGEs culture attenuated NF-kB phosphorylation, and prevented AGEs to down-regulate IkBα expression. These findings suggest that Pioglitazone protects beta cells from the dangerous effects of AGEs.

Stromal control of cystine metabolism promotes cancer cell survival in chronic lymphocytic leukaemia

Tissue stromal cells interact with leukemia cells and profoundly affect their viability and drug sensitivity. Here we show a biochemical mechanism by which bone marrow stromal cells modulate the redox status of chronic lymphocytic leukemia (CLL) cells and promote cellular survival and drug resistance. Primary CLL cells from patients exhibit limited ability to transport cystine for glutathione (GSH) synthesis due to a low expression of Xc- transporter, while bone marrow stromal cells effectively import cystine and convert it to cysteine, which is then released into the microenvironment for uptake by CLL cells to promote GSH synthesis. The elevated GSH enhances leukemia cell survival and protects them from drug-induced cytotoxicity. Furthermore, disabling this protective mechanism significantly sensitizes CLL cells to drug treatment in stromal environment. This stromal-leukemia interaction is critical for CLL cell survival and represents a key biochemical pathway for effectively targeting leukemia cells to overcome drug resistance in vivo.

Ionizing radiation-induced metabolic oxidative stress and prolonged cell injury

Cellular exposure to ionizing radiation leads to oxidizing events that alter atomic structure through direct interactions of radiation with target macromolecules or via products of water radiolysis. Further, the oxidative damage may spread from the targeted to neighboring, non-targeted bystander cells through redox-modulated intercellular communication mechanisms. To cope with the induced stress and the changes in the redox environment, organisms elicit transient responses at the molecular, cellular and tissue levels to counteract toxic effects of radiation. Metabolic pathways are induced during and shortly after the exposure. Depending on radiation dose, dose-rate and quality, these protective mechanisms may or may not be sufficient to cope with the stress. When the harmful effects exceed those of homeostatic biochemical processes, induced biological changes persist and may be propagated to progeny cells. Physiological levels of reactive oxygen and nitrogen species play critical roles in many cellular functions. In irradiated cells, levels of these reactive species may be increased due to perturbations in oxidative metabolism and chronic inflammatory responses, thereby contributing to the long-term effects of exposure to ionizing radiation on genomic stability. Here, in addition to immediate biological effects of water radiolysis on DNA damage, we also discuss the role of mitochondria in the delayed outcomes of ionization radiation. Defects in mitochondrial functions lead to accelerated aging and numerous pathological conditions. Different types of radiation vary in their linear energy transfer (LET) properties, and we discuss their effects on various aspects of mitochondrial physiology. These include short and long-term in vitro and in vivo effects on mitochondrial DNA, mitochondrial protein import and metabolic and antioxidant enzymes.

Perturbations in the antioxidant metabolism during Newcastle disease virus (NDV) infection in chicken : protective role of vitamin E

The aim of the present study was to investigate the effect of vitamin E on pro/anti-oxidant status in the liver, brain and heart of Newcastle disease virus (NDV) infected chickens. Activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR), glutathione-S-transferase (GST) and the levels of reduced glutathione and malonaldehyde were estimated in selected tissues of uninfected, NDV-infected and NDV + vit. E-treated chickens. A significant increase in MDA levels in brain and liver (p < 0.05) was observed in NDV-infected chickens when compared to controls. The activities of SOD, CAT, GPx, GR, GST and levels of GSH were significantly (p < 0.05) decreased in brain and liver of NDV-infected chickens over controls. On the other hand, a significant decreased MDA levels and enhanced antioxidant enzyme activity levels were observed in NDV + vit. E-treated animals compared to NDV-infected chickens. Histopathological studies revealed that liver of NDV infected chicken shows focal coagulation and infiltration of hepatocytes, whereas neuronal necrosis and degeneration of Purkinje cells were observed in brain and moderate infiltration of inflammatory cells was observed in heart. However such histological alterations were not observed in NDV + vit. E-treated animals. The results of the present study, thus demonstrated that antioxidant defense mechanism is impaired after the induction of NDV, suggesting its critical role in cellular injury in brain and liver. Further, the results also suggest that vitamin E treatment will ameliorate the antioxidant status in the infected animals. The findings could be beneficial to understand the role of oxidative stress in the pathogenesis of NDV and therapeutic interventions of antioxidants.

A GAG trinucleotide-repeat polymorphism in the gene for glutathione biosynthetic enzyme, GCLC, affects gene expression through translation

A guanine-adenine-guanine (GAG) repeat polymorphism with 5 different alleles (4, 7, 8, 9, and 10 repeats) in the 5' untranslated region (UTR) of GCLC has been associated with altered GCL activity and glutathione (GSH) levels. We investigated whether this polymorphism affects either transcription or translation using luciferase reporter constructs containing variant GCLC 5' UTRs. Higher luciferase activity was observed in HepG2 and human embryonic kidney 293 (HEK293) cells transfected with constructs containing either 8 or 9 repeats than in constructs containing 4, 7, or 10 repeats (P<0.05). In cell-free lysates, GAG repeat number had no effect on luciferase mRNA yield. In vitro translation of mRNAs from luciferase constructs resulted in differences similar to those found in cell cultures (P<0.05). A similar association of GAG repeat with GCLC phenotype was observed in vivo in healthy adults, as individuals with GAG-7/7 genotype had lower GCL activity and GSH levels in lymphocytes compared to those with GAG-9/9 (P<0.05). Higher GCL activity and GSH levels observed in red blood cells (RBCs) from individuals with GAG-7/7 compared to GAG-9/9 are likely due to differences in GCL regulation in RBCs. Altogether, these results suggest that GAG polymorphism affects GCLC expression via translation, and thus may be associated with altered risk for GSH-related diseases and toxicities.

Cancer-stromal interactions: role in cell survival, metabolism and drug sensitivity

It has been known for a long time that the interaction between cancer cells and tissue microenvironment plays a major role in cancer development, progression and metastasis. The biochemical aspect of cancer-stromal interactions, however, is less appreciated. This short review article first provides a brief summary of the communications between cancer cells and the tissue microenvironment by direct cell-cell interactions and by soluble factors, and then describes several biochemical pathways that are important for the interaction between stromal and cancer cells with respect to energy metabolism, redox balance, cell survival and drug resistance. The potential therapeutic implications of abolishing stromal protective mechanisms to overcome drug resistance are also discussed.

Effects of inactivity on human muscle glutathione synthesis by a double-tracer and single-biopsy approach

Oxidative stress is often associated to inactivity-mediated skeletal muscle atrophy. Glutathione is one of the major antioxidant systems stimulated, both at muscular and systemic level, by activation of oxidative processes. We measured changes in glutathione availability, oxidative stress induction and the extent of atrophy mediated by 35 days of experimental bed rest in vastus lateralis muscle of healthy human volunteers. To assess muscle glutathione synthesis, we applied a novel single-biopsy and double-tracer ([(2)H(2)]glycine and [(15)N]glycine) approach based on evaluation of steady-state precursor incorporation in product. The correlations between the traditional (multiple-samples, one-tracer) and new (one-sample, double-tracer infusion) methods were analysed in erythrocytes by Passing-Bablok and Altman-Bland tests. Muscle glutathione absolute synthesis rate increased following bed rest from 5.5 ± 1.1 to 11.0 ± 1.5 mmol (kg wet tissue)(-1) day(-1) (mean ± S.E.M.; n = 9; P = 0.02) while glutathione concentration failed to change significantly. Bed rest induced vastus lateralis muscle atrophy, as assessed by pennation angle changes measured by ultrasonography (from 18.6 ± 1.0 to 15.3 ± 0.9 deg; P = 0.01) and thickness changes (from 2.3 ± 0.2 to 1.9 ± 0.1 cm; P < 0.001). Moreover, bed rest increased protein oxidative stress, as measured by muscle protein carbonylation changes (from 0.6 ± 0.1 to 1.00 ± 0.1 Oxydized-to-total protein ratio; P < 0.04). In conclusion, we developed in erythrocytes a new minimally invasive method to determine peptide synthesis rate in human tissues. Application of the new method to skeletal muscle suggests that disuse atrophy is associated to oxidative stress induction as well as to compensatory activation of the glutathione system.

Determination of intracellular glutathione and cysteine using HPLC with a monolithic column after derivatization with monobromobimane

An optimized high-performance liquid chromatography (HPLC) method is used to show that, as myoblasts differentiate into multinucleated muscle fibers, there is a shift to a more oxidized cell redox state. The HPLC method incorporated derivatization with monobromobimane for the determination of the reduced (GSH) and oxidized (GSSG) forms of glutathione and the reduced (Cys) and oxidized (CysSS) forms of cysteine. The derivatization was optimized to improve the sensitivity of the approach; the limits of detection for glutathione and cysteine were 3 x 10(-8) and 5 x 10(-8) M, respectively.

Glutathione deficiency down-regulates hepatic lipogenesis in rats

BACKGROUND

Oxidative stress is supposed to increase lipid accumulation by stimulation of hepatic lipogenesis at transcriptional level. This study was performed to investigate the role of glutathione in the regulation of this process. For that purpose, male rats were treated with buthionine sulfoximine (BSO), a specific inhibitor of gamma-glutamylcysteine synthetase, for 7 days and compared with untreated control rats.

RESULTS

BSO treatment caused a significant reduction of total glutathione in liver (-70%), which was attributable to diminished levels of reduced glutathione (GSH, -71%). Glutathione-deficient rats had lower triglyceride concentrations in their livers than the control rats (-23%), whereas the circulating triglycerides and the cholesterol concentrations in plasma and liver were not different between the two groups of rats. Livers of glutathione-deficient rats had lower mRNA abundance of sterol regulatory element-binding protein (SREBP)-1c (-47%), Spot (S)14 (-29%) and diacylglycerol acyltransferase 2 (DGAT-2, -27%) and a lower enzyme activity of fatty acid synthase (FAS, -26%) than livers of the control rats. Glutathione-deficient rats had also a lower hepatic activity of the redox-sensitive protein-tyrosine phosphatase (PTP)1B, and a higher concentration of irreversible oxidized PTP1B than control rats. No differences were observed in protein expression of total PTP1B and the mature mRNA encoding active XBP1s, a key regulator of unfolded protein and ER stress response.

CONCLUSION

This study shows that glutathione deficiency lowers hepatic triglyceride concentrations via influencing lipogenesis. The reduced activity of PTP1B and the higher concentration of irreversible oxidized PTP1B could be, at least in part, responsible for this effect.

Genetic analysis of cytoprotective functions supported by graded expression of Keap1

Keap1 regulates Nrf2 activity in response to xenobiotic and oxidative stresses. Nrf2 is an essential regulator of cytoprotective genes. Keap1-null mice are lethal by weaning age due to malnutrition caused by severe hyperkeratosis of the upper digestive tract. Analysis of Keap1::Nrf2 double mutant mice revealed that currently recognizable phenotypes of Keap1-null mice are all attributable to constitutive activation of Nrf2. We previously reported that hepatocyte-specific Keap1 knockout (Keap1(flox/-)::Albumin-Cre) mice are viable and more resistant to acute toxicity of acetaminophen (APAP). In the current study, we found that the floxed Keap1 allele is hypomorphic and that Keap1 expression was decreased in all examined tissues of Keap1(flox/-) mice. Taking advantage of the hypomorphic phenotype of Keap1(flox/-) mice, we examined the effects of graded reduction of Keap1 expression in adult mice. When challenged with APAP, Keap1(flox/-) mice were more protected from mortality than wild-type and even Keap1(flox/-)::Albumin-Cre mice. In contrast, a decrease in Keap1 levels to less than 50% resulted in increased mortality in a study of 2-year-old mice. These results support our contention that the benefits of Nrf2 activation in acute toxicity are hormetic and that constitutive Nrf2 activation beyond a certain threshold is rather disadvantageous to long-term survival.

Prodrug approach for increasing cellular glutathione levels

Reduced glutathione (GSH) is the most abundant non-protein thiol in mammalian cells and the preferred substrate for several enzymes in xenobiotic metabolism and antioxidant defense. It plays an important role in many cellular processes, such as cell differentiation, proliferation and apoptosis. GSH deficiency has been observed in aging and in a wide range of pathologies, including neurodegenerative disorders and cystic fibrosis (CF), as well as in several viral infections. Use of GSH as a therapeutic agent is limited because of its unfavorable biochemical and pharmacokinetic properties. Several reports have provided evidence for the use of GSH prodrugs able to replenish intracellular GSH levels. This review discusses different strategies for increasing GSH levels by supplying reversible bioconjugates able to cross the cellular membrane more easily than GSH and to provide a source of thiols for GSH synthesis.

Analysis of endogenous glutathione-adducts and their metabolites

The ability to conduct validated analyses of glutathione (GSH)-adducts and their metabolites is critically important in order to establish whether they play a role in cellular biochemical or pathophysiological processes. The use of stable isotope dilution (SID) methodology in combination with liquid chromatography-tandem mass spectrometry (LC-MS/MS) provides the highest bioanalytical specificity possible for such analyses. Quantitative studies normally require the high sensitivity that can be obtained by the use of multiple reaction monitoring (MRM)/MS rather than the much less sensitive but more specific full scanning methodology. The method employs a parent ion corresponding to the intact molecule together with a prominent product ion that obtained by collision induced dissociation. Using SID LC-MRM/MS, analytes must have the same relative LC retention time to the heavy isotope internal standard established during the validation procedure, the correct parent ion and the correct product ion. This level of specificity cannot be attained with any other bioanalytical technique employed for biomarker analysis. This review will describe the application of SID LC-MR/MS methodology for the analysis of GSH-adducts and their metabolites. It will also discuss potential future directions for the use of this methodology for rigorous determination of their utility as disease and exposure biomarkers.

Stable-isotope dilution LC–MS for quantitative biomarker analysis

The ability to conduct validated analyses of biomarkers is critically important in order to establish the sensitivity and selectivity of the biomarker in identifying a particular disease. The use of stable-isotope dilution (SID) methodology in combination with LC–MS/MS provides the highest possible analytical specificity for quantitative determinations. This methodology is now widely used in the discovery and validation of putative exposure and disease biomarkers. This review will describe the application of SID LC–MS methodology for the analysis of small-molecule and protein biomarkers. It will also discuss potential future directions for the use of this methodology for rigorous biomarker analysis.

Silencing glycogen synthase kinase-3beta inhibits acetaminophen hepatotoxicity and attenuates JNK activation and loss of glutamate cysteine ligase and myeloid cell leukemia sequence 1

Previously we demonstrated that c-Jun N-terminal kinase (JNK) plays a central role in acetaminophen (APAP)-induced liver injury. In the current work, we examined other possible signaling pathways that may also contribute to APAP hepatotoxicity. APAP treatment to mice caused glycogen synthase kinase-3beta (GSK-3beta) activation and translocation to mitochondria during the initial phase of APAP-induced liver injury ( approximately 1 h). The silencing of GSK-3beta, but not Akt-2 (protein kinase B) or glycogen synthase kinase-3alpha (GSK-3alpha), using antisense significantly protected mice from APAP-induced liver injury. The silencing of GSK-3beta affected several key pathways important in conferring protection against APAP-induced liver injury. APAP treatment was observed to promote the loss of glutamate cysteine ligase (GCL, rate-limiting enzyme in GSH synthesis) in liver. The silencing of GSK-3beta decreased the loss of hepatic GCL, and promoted greater GSH recovery in liver following APAP treatment. Silencing JNK1 and -2 also prevented the loss of GCL. APAP treatment also resulted in GSK-3beta translocation to mitochondria and the degradation of myeloid cell leukemia sequence 1 (Mcl-1) in mitochondrial membranes in liver. The silencing of GSK-3beta reduced Mcl-1 degradation caused by APAP treatment. The silencing of GSK-3beta also resulted in an inhibition of the early phase (0-2 h), and blunted the late phase (after 4 h) of JNK activation and translocation to mitochondria in liver following APAP treatment. Taken together our results suggest that activation of GSK-3beta is a key mediator of the initial phase of APAP-induced liver injury through modulating GCL and Mcl-1 degradation, as well as JNK activation in liver.

Hydrogen sulfide increases glutathione production and suppresses oxidative stress in mitochondria

Hydrogen sulfide (H(2)S) is a synaptic modulator as well as a neuroprotectant in the brain. We recently showed that H(2)S protects neurons from oxidative stress by increasing the levels of glutathione (GSH), a major cellular antioxidant, by more than twice that of a control through enhancing the cystine transport. Here we show that H(2)S enhances the transport of cysteine to increase GSH production more than cystine transport and to redistribute the localization of GSH to mitochondria. The efficiency of GSH production enhanced by H(2)S is even greater by fourfold under oxidative stress by glutamate. H(2)S reinstated GSH levels in the fetal brain decreased by ischemia/reperfusion in utero. In addition, Neuro2a cells expressing a mitochondrial H(2)S-producing enzyme, 3-mercaptopyruvate sulfurtransferase (3MST), along with cysteine aminotransferase (CAT), showed significant resistance to oxidative stress. The present study shows that H(2)S protects cells from oxidative stress by two mechanisms. It enhances the production of GSH by enhancing cystine/cysteine transporters and redistributes GSH to mitochondria. H(2)S produced in mitochondria also may directly suppress oxidative stress. It provides a new mechanism of neuroprotection from oxidative stress by H(2)S.

S-glutathionylation of the Rpn2 regulatory subunit inhibits 26 S proteasomal function

Although increased intracellular concentrations of hydrogen peroxide (H2O2) are associated with inhibition of 26 S proteasomal activity, the mechanisms responsible for such effects have not been well delineated. In the present studies, we found that direct exposure of purified 26 S proteasomes to H2O2 had negligible effects on their activity, whereas incubation with glutathione and H2O2 produced >80% decrease in chymotrypsin-like and trypsin-like activities. Rpn1 and Rpn2, which are subunits of the 19 S regulatory particle, undergo S-glutathionylation after exposure of purified 26 S proteasomes to glutathione and H2O2, as well as in HEK 293 cells and neutrophils incubated with H2O2. Increased oxidation of Rpn1 and Rpn2 cysteine thiols was also found in lung extracts from mice in which catalase was inactivated, a condition associated with augmented intracellular concentrations of H2O2 and diminished 26 S proteasomal activity. Although unoxidized Rpn2 enhanced 20 S proteolytic function in vitro, such potentiation was not found when the 20 S core particle was incubated with oxidized Rpn2. The composition of 26 S proteasomes was not altered after exposure to glutathione and H2O2, with similar amounts of Rpn1 and Rpn2 in control or oxidized 26 S proteasomal complexes. These findings identify S-glutathionylation of Rpn2 as a contributory mechanism for H2O2-induced inhibition of 26 S proteasomal function.

Metabolic profiling of the response to an oral glucose tolerance test detects subtle metabolic changes

Background

The prevalence of overweight is increasing globally and has become a serious health problem. Low-grade chronic inflammation in overweight subjects is thought to play an important role in disease development. Novel tools to understand these processes are needed. Metabolic profiling is one such tool that can provide novel insights into the impact of treatments on metabolism.

Methodology

To study the metabolic changes induced by a mild anti-inflammatory drug intervention, plasma metabolic profiling was applied in overweight human volunteers with elevated levels of the inflammatory plasma marker C-reactive protein. Liquid and gas chromatography mass spectrometric methods were used to detect high and low abundant plasma metabolites both in fasted conditions and during an oral glucose tolerance test. This is based on the concept that the resilience of the system can be assessed after perturbing a homeostatic situation.

Conclusions

Metabolic changes were subtle and were only detected using metabolic profiling in combination with an oral glucose tolerance test. The repeated measurements during the oral glucose tolerance test increased statistical power, but the metabolic perturbation also revealed metabolites that respond differentially to the oral glucose tolerance test. Specifically, multiple metabolic intermediates of the glutathione synthesis pathway showed time-dependent suppression in response to the glucose challenge test. The fact that this is an insulin sensitive pathway suggests that inflammatory modulation may alter insulin signaling in overweight men.

Blood iron, glutathione, and micronutrient levels and the risk of oral cancer

The risk of oral cavity cancer was determined in relation to serological levels of iron; vitamins A, B2, C, E; zinc; thiamin; and glutathione (GSH). The study included 65 hospitalized patients with oral cancer and 85 matched controls. In comparing the highest to the lowest tertiles, the risk was odds ratio (OR) = 0.3 [95% confidence interval (CI) = 0.1-0.6] for iron; 3.2 (95% CI = 1.3-8.1) for total iron binding capacity (TIBC), which measures the concentration of the iron delivery protein transferrin; and 0.4 (95% CI = 0.2-0.9) for transferrin saturation (iron/TIBC x 100). These associations were stronger in never smokers than in ever smokers. The risk associated with the iron storage protein ferritin was significantly elevated, but this association could reflect disease-related inflammation or comorbidity. The OR for GSH was 0.4 (95% CI = 0.1-0.9), and the OR for GSH reductase activity coefficient (indicative of riboflavin deficiency) was 1.6 (95% CI = 1.3-3.7). These findings suggest that mild iron deficiency and low GSH levels, which are associated with increased oxidative stress, increase the risk of oral cavity cancer.

The thiol redox state of lymphoid organs is modified by immunization: role of different immune cell populations

Resting T lymphocytes can internalize reduced cysteine (Cys) but not cystine, the oxidized form of the amino acid that predominates extracellularly. In vitro studies have shown that DC provide Cys to T cells during antigen presentation, allowing their activation. Here, we show that increased thiol production is a hallmark of immune response in vivo. Indeed, the thiol content of LN increases dramatically after antigen injection. Non-protein thiols co-distribute with DC and are highly abundant in germinal centers. In agreement, activated but not resting B lymphocytes and macrophages release free thiols. Increased thiol release following activation requires thioredoxin and is paralleled by increased thioredoxin expression. The T zones of LN are consistently less stained, and both resting and activated T cells are unable to release thiols. Interestingly, the cystine/glutamate transporter x(c) (-) is absent in resting T lymphocytes but is rapidly induced by TCR triggering in vitro, indicating that the release of T cells from the need of exogenous Cys occurs early after activation. These results indicate that a reducing microenvironment is essential to start the immune response but dispensable for its evolution, and support the emerging concept that extracellular redox is implicated in the control of crucial cellular functions.

Decreasing peroxiredoxin II expression decreases glutathione, alters cell cycle distribution, and sensitizes glioma cells to ionizing radiation and H(2)O(2)

Glioblastomas are notorious for their resistance to ionizing radiation and chemotherapy. We hypothesize that this resistance to ionizing radiation is due, in part, to alterations in antioxidant enzymes. Here, we show that rat and human glioma cells overexpress the antioxidant enzyme peroxiredoxin II (Prx II). Glioma cells in which Prx II is decreased using shRNA exhibit increased hyperoxidation of the remaining cellular Prxs, suggesting that the redox environment is more oxidizing. Of interest, decreasing Prx II does not alter other antioxidant enzymes (i.e., catalase, GPx, Prx I, Prx III, CuZnSOD, and MnSOD). Analysis of the redox environment revealed that decreasing Prx II increased intracellular reactive oxygen species in 36B10 cells; extracellular levels of H(2)O(2) were also increased in both C6 and 36B10 cells. Treatment with H(2)O(2) led to a further elevation in intracellular reactive oxygen species in cells where Prx II was decreased. Decreasing Prx II expression in glioma cells also reduced clonogenic cell survival following exposure to ionizing radiation and H(2)O(2). Furthermore, lowering Prx II expression decreased intracellular glutathione and resulted in a significant decline in glutathione reductase activity, suggesting a possible mechanism for the observed increased sensitivity to oxidative insults. Additionally, decreasing Prx II expression increased cell cycle doubling times, with fewer cells distributed to S phase in C6 glioma cells and more cells redistributed to the most radiosensitive phase of the cell cycle, G2/M, in 36B10 glioma cells. These findings support the hypothesis that inhibiting Prx II sensitizes glioma cells to oxidative stress, presenting Prxs as potential therapeutic targets.

Glutathione level after long-term occupational elemental mercury exposure

Many in vitro and in vivo studies have elucidated the interaction of inorganic mercury (Hg) and glutathione. However, human studies are limited. In this study, we investigated the potential effects of remote long-term intermittent occupational elemental Hg vapour (Hg degrees ) exposure on erythrocyte glutathione levels and some antioxidative enzyme activities in ex-mercury miners in the period after exposure. The study included 49 ex-mercury miners divided into subgroups of 28 still active, Hg degrees -not-exposed miners and 21 elderly retired miners, and 41 controls, age-matched to the miners subgroup. The control workers were taken from "mercury-free works". Reduced glutathione (GSH) and oxidized disulphide glutathione (GSSG) concentrations in haemolysed erythrocytes were determined by capillary electrophoresis, while total glutathione (total GSH) and the GSH/GSSG ratio were calculated from the determined values. Catalase (CAT), glutathione peroxidase (GPx), and glutathione reductase (GR) activities in erythrocytes were measured using commercially available reagent kits, while urine Hg (U-Hg) concentrations were determined by cold vapour atomic absorption (CVAAS). No correlation of present U-Hg levels, GSH, GSSG, and antioxidative enzymes with remote occupational biological exposure indices were found. The mean CAT activity in miners and retired miners was significantly higher (p<0.05) than in the controls. No differences in mean GPx activity among the three groups were found, whereas the mean GR activity was significantly higher (p<0.05) in miners than in retired miners. The mean concentrations of GSH (mmol/g Hb) in miners (13.03+/-3.71) were significantly higher (p<0.05) than in the control group (11.68+/-2.66). No differences in mean total GSH, GSSG levels, and GSH/GSSG ratio between miners and controls were found. A positive correlation between GSSG and present U-Hg excretion (r=0.41, p=0.001) in the whole group of ex-mercury miners was observed. The significantly lower GSH level (p<0.05) determined in the group of retired miners (9.64+/-1.45) seems to be age-related (r= -0.39, p=0.001). Thus, the moderate but significantly increased GSH level, GR and CAT activity in erythrocytes in the subgroup of miners observed in the period after exposure to Hg degrees could be an inductive and additive response to maintain the balance between GSH and antioxidative enzymes in interaction with the Hg body burden accumulated during remote occupational exposure, which does not represent a severely increased oxidative stress.