Enhanced glutathione levels and oxidoresistance mediated by increased glucose-6-phosphate dehydrogenase expression

Effects of aging on antioxidant response and phagocytosis in senescent erythrocytes

Red blood cell (RBC) aging is a complex process affected by immunological and biochemical parameters. In this work we studied the antioxidant response in RBC of different ages. We also investigated their interaction with peripheral blood monocytes. Anticoagulated blood samples from 19 O RhD+ volunteers' donors were processed. Young (Y) RBC and Senescent (Se) RBC were obtained by self-formed gradients of Percoll. The fractionation of the erythrocytes suspensions was demonstrated by statistically significant density-related changes in hematological determinations. Activities of glucose-6-phosphate dehydrogenase (G6PD), of soluble NADH-cytochrome b5 reductase (b5Rs) and membrane-bound b5R (b5Rm) were determined spectrophotometrically. The interaction between monocytes and different RBC suspensions was evaluated by the erythrophagocytosis assay. The G6PD and b5Rm activities in SeRBC were significantly lower than that observed in YRBC. No differences were found in the b5Rs of both groups. We observed an increased rate of erythrophagocytosis the SeRBC compared to YRBC. The decline in the activities of G6PD and b5Rm would indicate a decrease in the antioxidant response associated to RBC aging. These findings would signify that the oxidative changes of membrane occurring during the life span of the RBC might be relevant in the process of removal of SeRBC from the circulation.

Antiperoxidative and anti-apoptotic effects of lycopene and ellagic acid on cyclophosphamide-induced testicular lipid peroxidation and apoptosis

The present study was conducted to investigate the possible protective effects of lycopene (LC) and ellagic acid (EA) on cyclophosphamide (CP)-induced testicular and spermatozoal toxicity associated with the oxidative stress and apoptosis in male rats. Forty-eight healthy adult male Sprague-Dawley rats were divided into six groups of eight rats each. The control group was treated with placebo; the LC, EA and CP groups were given LC (10 mg kg–1), EA (2 mg kg–1) and CP (15 mg kg–1), respectively, alone; the CP+LC group was treated with a combination of CP (15 mg kg–1) and LC (10 mg kg–1); and the CP+EA group was treated with a combination of CP (15 mg kg–1) and EA (2 mg kg–1). All treatments were maintained for 8 weeks. At the end of the treatment period, bodyweight and the weight of the reproductive organs, sperm concentration and motility, testicular tissue lipid peroxidation, anti-oxidant enzyme activity and apoptosis (i.e. Bax and Bcl-2 proteins) were determined. Administration of CP resulted in significant decreases in epididymal sperm concentration and motility and significant increases in malondialdehyde levels. Although CP significantly increased the number of Bax-positive (apoptotic) cells, it had no effect on the number of Bcl-2-positive (anti-apoptotic) cells compared with the control group. However, combined treatment of rats with LC or EA in addition to CP prevented the development of CP-induced lipid peroxidation and sperm and testicular damage. In conclusion, CP-induced lipid peroxidation leads to structural and functional damage, as well as apoptosis, in spermatogenic cells of rats. Both LC and EA protect against the development of these detrimental effects.

High glucose inhibits glucose-6-phosphate dehydrogenase, leading to increased oxidative stress and beta-cell apoptosis

Patients with type 2 diabetes lose beta cells, but the underlying mechanisms are incompletely understood. Glucose-6-phosphate dehydrogenase (G6PD) is the principal source of the major intracellular reductant, NADPH, which is required by many enzymes, including enzymes of the antioxidant pathway. Previous work from our laboratory has shown that high glucose impairs G6PD activity in endothelial and kidney cells, which leads to decreased cell survival. Pancreatic beta cells are highly sensitive to increased ROS. This study aimed to determine whether G6PD and NADPH play central roles in beta-cell survival. Human and mouse islets, MIN6 cell line, and G6PD deficient mice were studied. High glucose inhibited G6PD expression and activity. Inhibition of G6PD with siRNA led to increased ROS and apoptosis, decreased proliferation, and impaired insulin secretion. High glucose decreased insulin secretion, which was improved by overexpressing G6PD. G6PD-deficient mice had smaller islets and impaired glucose tolerance compared with control mice, which suggests that G6PD deficiency per se leads to beta-cell dysfunction and death. G6PD plays an important role in beta-cell function and survival. High-glucose-mediated decrease in G6PD activity may provide a mechanistic explanation for the gradual loss of beta cells in patients with diabetes.

Silencing of cytosolic NADP(+)-dependent isocitrate dehydrogenase by small interfering RNA enhances the sensitivity of HeLa cells toward staurosporine

Staurosporine induces the production of reactive oxygen species, which play an important causative role in apoptotic cell death. Recently, it was demonstrated that the control of cellular redox balance and the defense against oxidative damage is one of the primary functions of cytosolic NADP(+)-dependent isocitrate dehydrogenase (IDPc) by supplying NADPH for antioxidant systems. The present report shows that silencing of IDPc expression in HeLa cells greatly enhances apoptosis induced by staurosporine. Transfection of HeLa cells with an IDPc small interfering RNA (siRNA) markedly decreased activity of IDPc, enhancing the susceptibility of staurosporine-induced apoptosis reflected by DNA fragmentation, cellular redox status and the modulation of apoptotic marker proteins. These results indicate that IDPc may play an important role in regulating the apoptosis induced by staurosporine and the sensitizing effect of IDPc siRNA on the apoptotic cell death of HeLa cells offers the possibility of developing a modifier of cancer chemotherapy.

A new G6PD knockdown tumor-cell line with reduced proliferation and increased susceptibility to oxidative stress

Glucose-6-phosphate dehydrogenase (G6PD) has been implicated in the regulation of cellular antioxidative mechanisms. Tumor cells often lose the balance of oxidation and antioxidation, but the role of G6PD in such an imbalance is still largely unknown. To investigate the related function of G6PD in tumor cells, we established a stable line of A375 human melanoma cells with G6PD gene knockdown by a shRNA lentiviral cloning and expression system. The A375-G6PDDelta cells displayed the stable GFP coexpression after repeated freeze-thaw cycles and multiple passages, accompanied by an 88.83% suppression of the endogenous G6PD expression and a 78.47% decrease in G6PD activity. In comparison with the A375-WT cells, they were characterized by a reduced proliferation with the MTT proliferation assay, a 25% decrease in colony-forming efficiency, and an up to 40% increase of apoptotic rate with flow cytometry analysis. When further challenged by diamide-induced oxidative stress, these cells showed that a median lethal dose (LD(50)) of 1.2 mM decreased from that of the A375-WT cells (1.8 mM), and levels of NADPH and GSH decreased by 2.4-, 8.8-fold, respectively, with a 7.3-fold increase of H(2)O(2), as those of A375-WT cells. These results demonstrated that A375-G6PDDelta is a new, stable G6PD-deficient human tumor cell line, and that silencing G6PD expression decreased tumor-cell proliferation and enhanced apoptosis. In addition, G6PD gene knockdown rendered tumor cells more susceptible to diamide-induced oxidative stress. Together, our data support the important functions of G6PD in the regulation of cell growth and antioxidative capacity of tumor cells.

Effect of lycopene and epigallocatechin-3-gallate against 3-nitropropionic acid induced cognitive dysfunction and glutathione depletion in rat: a novel nitric oxide mechanism

Huntington's disease is a neurodegenerative disorder characterized by symptoms like chorea and dementia. There is no exact therapeutic agent available to manage and cure this disease. 3-Nitropropionic acid, a neurotoxin causes gait and memory impairment which leads to oxidative damage and upsets glutathione defense in animals. 3-NP model is a useful tool to develop suitable therapeutic agent in the treatment of Huntington's disease. Present study compares the effects of lycopene and epigallocatechin-3-gallate (EGCG) on memory impairment and disturbs glutathione system against 3-NP treatment. 3-NP treatment significantly impaired memory as assessed in Morris water maze and elevated plus maze tasks. On the 15 day, the levels of reduced glutathione, total glutathione and glutathione-S-transferase were also significantly decreased in the striatum, hippocampus and cortex areas of the brain. The treatment with lycopene (2.5, 5 and 10mg/kg) and EGCG (10, 20 and 40 mg/kg) significantly improved memory and restored glutathione system functioning. Further, L-arginine and L-NAME pretreatment with the sub effective dose of lycopene (5mg/kg) and EGCG (20mg/kg) reversed and potentiate their protective effects respectively. In conclusion, lycopene and EGCG could be used to mange 3-NP induced behavioral and biochemical alterations by involving nitric oxide pathways.

Effect of arachidonic, eicosapentaenoic and docosahexaenoic acids on the oxidative status of C6 glioma cells

n-3 polyunsaturated fatty acids (PUFAs) have been described to have beneficial effects on brain development and in the prevention and treatment of brain damage. C6 glioma cells were incubated with 100 microM of either C20:4n-6 (ARA), or C20:5n-3 (EPA), or C22:6n-3 (DHA) for different time periods to assess whether these acids altered the cellular oxidative state. The ARA and EPA were promptly metabolised to C22:4n-6 and C22:5n-3, respectively, whereas DHA treatment simply increased the amount of DHA in the cells. Cell viability was not affected by ARA, while a cytotoxic effect was observed 72 h after n-3 PUFAs supplementation. The levels of reactive oxygen species and thiobarbituric acid-reactive substances were significantly higher in DHA-treated cells than in EPA- and ARA-treated groups. This modification in the oxidative cellular status was also highlighted by a significant increase in catalase activity and a decrease in glutathione content in DHA-supplemented cells. Glucose-6-phosphate dehydrogenase activity, an enzyme involved in redox regulation, and O2*- release were significantly increased both in EPA and DHA groups. The effect of DHA was more severe than that of EPA. No significant changes were observed in the ARA group with respect to untreated cells. These data show that EPA and DHA induce alterations in the oxidative status that could affect the glial function.

IDENTIFICATION AND VALIDATION OF DIFFERENTIALLY EXPRESSED GENES IN NEURAL TUBE DEFECTS OF GOLDEN HAMSTER INDUCED BY HYPERTHERMIA USING SUPPRESSION SUBTRACTIVE HYBRIDIZATION

Hyperthermia during early pregnancy can induce neural tube defects (NTD) in embryos. In order to identify the differentially expressed genes that participate in this pathologic course, the authors performed suppression subtractive hybridization in two directions: forward and reverse. Neural tube tissues from golden hamster of normal and hyperthermia groups are used as the samples. As a result, several down-regulated genes were revealed and according to the function of their protein products they were classified into four categories: ribosomal proteins, metabolic enzymes, transcription and translation related factors, and others. On the other hand, the study found that two up-regulated gene fractions were of the same sequence and homology analysis shows that they are homologous to phosphoglycerate kinase 1 (pgk1). Of all these genes, differential expression patterns were confirmed by Northern blot analysis. The study results show that the genes identified have different expression and are stongly related to NTD induced by hyperthermia.

Changes in the glucose-6-phosphate dehydrogenase activity in granulosa cells during follicular atresia in ewes

Apoptosis of granulosa cells during follicular atresia is preceded by oxidative stress, partly due to a drop in the antioxidant glutathione (GSH). Under oxidative stress, GSH regeneration is dependent on the adequate supply of NADPH by glucose-6-phosphate dehydrogenase (G6PD). In this study, we analyzed the changes of G6PD, GSH, and oxidative stress of granulosa cells and follicular liquid and its association with apoptosis during atresia of small (4–6 mm) and large (>6 mm) sheep antral follicles. G6PD activity was found to be higher in granulosa cells of healthy small rather than large follicles, with similar GSH concentration in both cases. During atresia, increased apoptosis and protein oxidation, as well as a drop in GSH levels, were observed in follicles of both sizes. Furthermore, the activity of G6PD decreased in atretic small follicles, but not in large ones. GSH decreased and protein oxidation increased in follicular fluid. This was dependent on the degree of atresia, whereas the changes in G6PD activity were based on the type of follicle. The higher G6PD activity in the small follicles could be related to granulosa cell proliferation, follicular growth, and a lower sensitivity to oxidative stress when compared with large follicles. The results also indicate that GSH concentration in atretic follicles depends on other factors in addition to G6PD, such asde novosynthesis or activity of other NADPH-producing enzymes. Finally, lower G6PD activity in large follicles indicating a higher susceptibility to oxidative stress associated to apoptosis progression in follicle atresia.

Isoenzyme replacement of glucose-6-phosphate dehydrogenase in the cytosol improves stress tolerance in plants

In source leaves of resistant tobacco, oxidative burst and subsequent formation of hypersensitive lesions after infection with Phytophthora nicotianae was prevented by inhibition of glucose-6-phosphate dehydrogenase (G6PDH) or NADPH oxidases. This observation indicated that plant defense could benefit from improved NADPH availability due to increased G6PDH activity in the cytosol. A plastidic isoform of the G6PDH-encoding gene, G6PD, displaying high NADPH tolerance was engineered for cytosolic expression (cP2), and introduced into a susceptible cultivar. After infection, transgenic (previously susceptible) lines overexpressing cP2 showed early oxidative bursts, callose deposition, and changes in metabolic parameters. These responses resulted in timely formation of hypersensitive lesions similar to resistant plants, although their extent varied considerably between different transgenic lines. Additional RNAi suppression of endogenous cytosolic G6PD isoforms resulted in highly uniform defense responses and also enhanced drought tolerance and flowering. Cytosolic G6PDH seems to be a crucial factor for the outcome of plant defense responses; thus, representing an important target for modulation of stress resistance. Because isoenzyme replacement of G6PDH in the cytosol was beneficial under various kinds of cues, we propose this strategy as a tool to enhance stress tolerance in general.

Modulatory effects of resveratrol on attenuating the key enzymes activities of carbohydrate metabolism in streptozotocin-nicotinamide-induced diabetic rats

Resveratrol, a ubiquitous stress-induced phytoalexin, has demonstrated a wide variety of biological activities which make it a good candidate for the treatment of diabetes mellitus. The present study was aimed to evaluate its therapeutic potential by assaying the activities of key enzymes of carbohydrate metabolism in streptozotocin-nicotinamide-induced diabetic rats. The daily oral treatment of resveratrol (5 mg/kg body weight) to diabetic rats for 30 days demonstrated a significant (p<0.05) decline in blood glucose and glycosylated hemoglobin levels and a significant (p<0.05) increase in plasma insulin level. The altered activities of the key enzymes of carbohydrate metabolism such as hexokinase, pyruvate kinase, lactate dehydrogenase, glucose-6-phosphatase, fructose-1,6-bisphosphatase, glucose-6-phosphate dehydrogenase, glycogen synthase and glycogen phosphorylase in liver and kidney tissues of diabetic rats were significantly (p<0.05) reverted to near normal levels by the administration of resveratrol. Further, resveratrol administration to diabetic rats improved hepatic glycogen content suggesting the antihyperglycemic potential of resveratrol in diabetic rats. The obtained results were compared with glyclazide, a standard oral hypoglycemic drug. Thus, the modulatory effects of resveratrol on attenuating these enzymes activities afford a promise for widespread use for treatment of diabetes in the future.

Glutathione-dependent redox status of frataxin-deficient cells in a yeast model of Friedreich's ataxia

Friedreich's ataxia is a neurodegenerative disease caused by reduced expression of the mitochondrial protein frataxin. The main phenotypic features of frataxin-deficient human and yeast cells include iron accumulation in mitochondria, iron-sulphur cluster defects and high sensitivity to oxidative stress. Glutathione is a major protective agent against oxidative damage and glutathione-related systems participate in maintaining the cellular thiol/disulfide status and the reduced environment of the cell. Here, we present the first detailed biochemical study of the glutathione-dependent redox status of wild-type and frataxin-deficient cells in a yeast model of the disease. There were five times less total glutathione (GSH+GSSG) in frataxin-deficient cells, imbalanced GSH/GSSG pools and higher glutathione peroxidase activity. The pentose phosphate pathway was stimulated in frataxin-deficient cells, glucose-6-phosphate dehydrogenase activity was three times higher than in wild-type cells and this was coupled to a defect in the NADPH/NADP(+) pool. Moreover, analysis of gene expression confirms the adaptative response of mutant cells to stress conditions and we bring evidence for a strong relation between the glutathione-dependent redox status of the cells and iron homeostasis. Dynamic studies show that intracellular glutathione levels reflect an adaptation of cells to iron stress conditions, and allow to distinguish constitutive stress observed in frataxin-deficient cells from the acute response of wild-type cells. In conclusion, our findings provide evidence for an impairment of glutathione homeostasis in a yeast model of Friedreich's ataxia and identify glutathione as a valuable indicator of the redox status of frataxin-deficient cells.

Hypochlorous acid-induced modulation of cellular redox status in HeLa cells

Myeloperoxidase catalyzes the formation of hypochlorous acid (HOCI) via reaction of H2O2 with CI(-) ions. Although HOCI plays a major role in the human immune system by killing bacteria and other invading pathogens, excessive generation of this oxidant causes damage to tissues. Exposure of HeLa cells to HOCI decreased viability, inactivated antioxidant enzymes, damaged mitochondria, and modulated cellular redox status. HOCI also induced significant increases in cellular oxidative damage reflected by lipid peroxidation, protein oxidation, and DNA damage. HOCI-mediated oxidative damage to HeLa cells may perturb the cellular antioxidant defense mechanisms and subsequently lead to a pro-oxidant state.

Interleukin-6 and leptin as markers of energy metabolic changes in advanced ovarian cancer patients

The progression of the neoplastic disease is characterized by specific alterations of energy metabolism and by symptoms like fatigue, anorexia, nausea, anaemia, immunodepression and poor performance status (PS). The main cause of these symptoms and metabolic abnormalities is the chronic action of proinflammatory cytokines released both by tumour and immune cells. The present study aimed to assess the relationship between markers of inflammation (C-Reactive Protein, Fibrinogen, proinflammatory cytokines) and energy metabolic status (BMI, leptin, oxidative stress) according to clinical parameters in 104 ovarian cancer patients at different stage and, moreover, to evaluate prospectively the changes of these parameters in accordance to tumour response in a subgroup of 70 advanced stage ovarian cancer patients. Advanced stage and poor PS were associated to high-grade inflammation and impaired energy metabolism. Among inflammatory mediators, interleukin (IL)-6 had a central role as predictive factor of leptin, reactive oxygen species and glutathione peroxidase. In turn, leptin considered the key marker of the nutritional status and energy metabolism, was independently determined from stage and IL-6, not only from BMI. Moreover, the evaluation of the changes of these parameters during the course of the neoplastic disease in the subgroup of advanced ovarian cancer patients clearly unveils the central role of IL-6 and leptin as early markers of the metabolic alterations and symptoms associated to disease progression in advanced stage ovarian cancer. Their assessment should be included in monitoring disease outcome, especially when cancer is no longer curable and quality of life becomes the primary endpoint.

Different effects of 26-week dietary intake of rapeseed oil and soybean oil on plasma lipid levels, glucose-6-phosphate dehydrogenase activity and cyclooxygenase-2 expression in spontaneously hypertensive rats

We intended to determine whether or not dietary canola oil (CO) elevates plasma lipids and oxidative stress, since both of these are, possibly, related to the CO-induced life shortening through exacerbation of hypertension-associated vascular lesions found in stroke-prone spontaneously hypertensive rats (SHRSP). Spontaneously hypertensive rats (SHR) were used in this study to avoid a potential bias in the results due to the irregular death by stroke seen in SHRSP. SHR were fed for 26 weeks on a chow containing either, 10 wt/wt% of CO or soybean oil (SO), i.e., the control. Elevated plasma lipids and glucose-6-phosphate dehydrogenase (G6PD) activation in the liver and erythrocyte were found in SHR fed CO compared to that fed SO, while anti-oxidative enzymes other than G6PD were not activated. The CO diet brought about significant vascular lesions in the kidney, in which abundant cyclooxygenase-2 (COX-2) positive foci were immunochemically located in the juxtaglomerular apparatus. These results suggest that dietary CO induces a hyperlipidemic condition, in which G6PD may serve as an NADPH provider, and aggravates genetic diseases in SHR (also, probably, in SHRSP). The increased COX-2 expression indicates a role of renin-angiotensin-aldosterone system activation in the increased vascular lesions, whereas the effects of oxidative stress remain unclear.

Ethanol induces peroxynitrite-mediated toxicity through inactivation of NADP+-dependent isocitrate dehydrogenase and superoxide dismutase

It has been reported that chronic alcohol administration increases peroxynitrite hepatotoxicity by enhancing concomitant production of nitric oxide and superoxide. Several studies have shown the importance of superoxide dismutase (SOD) in protecting cells against ethanol-induced oxidative stress. Recently, we demonstrated that the control of cytosolic and mitochondrial redox balance and the cellular defense against oxidative damage is one of the primary functions of NADP+-dependent isocitrate dehydrogenase (ICDH) through to supply NADPH for antioxidant systems. In this report, we demonstrate that ethanol induces the peroxynitrite-mediated cytotoxicity in HepG2 cells through inactivation of antioxidant enzymes such as ICDH and SOD. Upon exposure to 100mM ethanol for 3days to HepG2 cells, a significant decrease in the viability and activities of ICDH and SOD was observed. The ethanol-induced inactivation of antioxidant enzymes resulted in the cellular oxidative damage and modulation of redox status as well as mitochondrial dysfunction in HepG2 cells. The cytoxicity of ethanol and inactivation of antioxidant enzymes were effectively protected by manganeses(III) tetrakis(N-methyl-2-pyridyl) porphyrin, a manganese SOD mimetic, and N'-monomethyl-l-arginine, a nitric oxide synthase inhibitor. These results indicate that ethanol toxicity is mediated by peroxynitrite and the peroxynitrite-mediated damage to ICDH and SOD may be resulted in the perturbation of the cellular antioxidant defense systems and subsequently lead to a pro-oxidant condition.

Wound healing in plants: Cooperation of copper amine oxidase and flavin-containing polyamine oxidase

Copper amine oxidases (CuAO) and flavin-containing amine oxidases (PAO) are hydrogen peroxide (H(2)O(2))-producing enzymes responsible for the oxidative de-amination of polyamines. Currently, a key role has been ascribed to apoplastic amine oxidases in plants, i.e., to behave as H(2)O(2)-delivering systems in the cell wall during cell growth and differentiation as well as in the context of host-pathogen interactions. Indeed, H(2)O(2) is the co-substrate for the peroxidase-driven reactions during cell-wall maturation and a key signalling molecule in defence mechanisms. We recently demonstrated the involvement of an apoplastic PAO in the wound-healing process of the Zea mays mesocotyl. Experimental evidence indicated a similar role for an apoplastic PAO in Nicotiana tabacum. In this addendum we suggest that a CuAO activity is also involved in this healing event.

Glucose-6-phosphate dehydrogenase plays a central role in modulating reduced glutathione levels in reed callus under salt stress

In the present study, we investigated the role of glucose-6-phosphate dehydrogenase (G6PDH) in regulating the levels of reduced form of glutathione (GSH) to the tolerance of calli from two reed ecotypes, Phragmites communis Trin. dune reed (DR) and swamp reed (SR), in a long-term salt stress. G6PDH activity was higher in SR callus than that of DR callus under 50-150 mM NaCl treatments. In contrast, at higher NaCl concentrations (300-600 mM), G6PDH activity was lower in SR callus. A similar profile was observed in GSH contents, glutathione reductase (GR) and glutathione peroxidase (GPX) activities in both salt-stressed calli. After G6PDH activity and expression were reduced in glycerol treatments, GSH contents and GR and GPX activity decreased strongly in both calli. Simultaneously, NaCl-induced hydrogen peroxide (H2O2) accumulation was also abolished. Exogenous application of H2O2 increased G6PDH, GR, and GPX activities and GSH contents in the control conditions and glycerol treatment. Diphenylene iodonium (DPI), a plasma membrane (PM) NADPH oxidase inhibitor, which counteracted NaCl-induced H(2)O(2) accumulation, decreased these enzymes activities and GSH contents. Furthermore, exogenous application of H2O2 abolished the N-acetyl-L: -cysteine (NAC)-induced decrease in G6PDH activity, and DPI suppressed the effect of buthionine sulfoximine (BSO) on induction of G6PDH activity. Western-blot analyses showed that G6PDH expression was stimulated by NaCl and H2O2, and blocked by DPI in DR callus. Taken together, G6PDH activity involved in GSH maintenance and H2O2 accumulation under salt stress. And H2O2 regulated G6PDH, GR, and GPX activities to maintain GSH levels. In the process, G6PDH plays a central role.

Oxidant-antioxidant imbalance in the erythrocytes of sporadic amyotrophic lateral sclerosis patients correlates with the progression of disease

Free radicals are implicated in numerous disease processes including motor neuron degeneration (MND). Antioxidant defense enzymes: superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSHPx), glutathione reductase (GR) and glucose-6-phosphate dehydrogenase (G-6-PDH) in the erythrocytes are capable of detoxifying reactive oxygen species produced endogenously or exogenously. In the present study, the extent of lipid peroxidation (LPO) and antioxidant defenses were evaluated in the erythrocytes of 20 sporadic amyotrophic lateral sclerosis (ALS) patients and 20 controls. We observed that lipid peroxidation in the erythrocytes of amyotrophic lateral sclerosis patients significantly increased with respect to controls (P<0.001). On the other hand, catalase activity was found to be significantly lower (P<0.001). The activities of glucose-6-phosphate dehydrogenase, glutathione reductase and glutathione levels were also found to be significantly reduced in ALS patients compared to healthy subjects (P<0.001, P<0.01 and P<0.01, respectively). It was further observed that lipid peroxidation started to increase and catalase, glutathione reductase, glucose-6-phosphate dehydrogenase enzyme activities and glutathione levels started to decrease as amyotrophic lateral sclerosis progressed from 6 to 24 months, suggesting a correlation between these parameters and duration of amyotrophic lateral sclerosis. This study confirms the involvement of oxidative stress during the progression of amyotrophic lateral sclerosis and the need to develop specific peripheral biomarkers.

Over expression of glutamate cysteine ligase increases cellular resistance to H2O2-induced DNA single-strand breaks

Hydrogen peroxide (H2O2) can cause single strand DNA breaks (ssDNA) in cells when the mechanisms normally in place to reduce it are overwhelmed. Such mechanisms include catalase, glutathione peroxidases (GPx), and peroxiredoxins. The relative importance of these enzymes in H2O2 reduction varies with cell and tissue type. The role of the GPx cofactor glutathione (GSH) in oxidative defense can be further understood by modulating its synthesis. The first and rate-limiting enzyme in GSH synthesis is glutamate-cysteine ligase (GCL), which has a catalytic subunit (Gclc) and a modifier subunit (Gclm). Using mouse hepatoma cells we evaluated the effects of GCL over expression on H2O2-induced changes in GSH and ssDNA break formation with the single cell gel electrophoresis assay (SCG or comet assay), and the acridine orange DNA unwinding flow cytometry assay (AO unwinding assay). Cells over expressing GCL had higher GSH content than control cells, and both SCG and AO unwinding assays revealed that cells over expressing GCL were significantly more resistant to H2O2-induced ssDNA break formation. Furthermore, using the AO unwinding assay, the prevalence of H2O2-induced breaks in different phases of the cell cycle was not different, and the degree of protection afforded by GCL over expression was also not cell cycle phase dependent. Our results support the hypothesis that GCL over expression enhanced GSH biosynthesis and protected cells from H2O2-induced DNA breaks. These results also suggest that genetic polymorphisms that affect GCL expression may be important determinants of oxidative DNA damage and cancer.

The role of corneal crystallins in the cellular defense mechanisms against oxidative stress

The refracton hypothesis describes the lens and cornea together as a functional unit that provides the proper ocular transparent and refractive properties for the basis of normal vision. Similarities between the lens and corneal crystallins also suggest that both elements of the refracton may also contribute to the antioxidant defenses of the entire eye. The cornea is the primary physical barrier against environmental assault to the eye and functions as a dominant filter of UV radiation. It is routinely exposed to reactive oxygen species (ROS)-generating UV light and molecular O(2) making it a target vulnerable to UV-induced damage. The cornea is equipped with several defensive mechanisms to counteract the deleterious effects of UV-induced oxidative damage. These comprise both non-enzymatic elements that include proteins and low molecular weight compounds (ferritin, glutathione, NAD(P)H, ascorbate and alpha-tocopherol) as well as various enzymes (catalase, glucose-6-phosphate dehydrogenase, glutathione peroxidase, glutathione reductase, and superoxide dismutase). Several proteins accumulate in the cornea at unusually high concentrations and have been classified as corneal crystallins based on the analogy of these proteins with the abundant taxon-specific lens crystallins. In addition to performing a structural role related to ocular transparency, corneal crystallins may also contribute to the corneal antioxidant systems through a variety of mechanisms including the direct scavenging of free radicals, the production of NAD(P)H, the metabolism and/or detoxification of toxic compounds (i.e. reactive aldehydes), and the direct absorption of UV radiation. In this review, we extend the discussion of the antioxidant defenses of the cornea to include these highly expressed corneal crystallins and address their specific capacities to minimize oxidative damage.

NAD kinase levels control the NADPH concentration in human cells

NAD kinases (NADKs) are vital, as they generate the cellular NADP pool. As opposed to three compartment-specific isoforms in plants and yeast, only a single NADK has been identified in mammals whose cytoplasmic localization we established by immunocytochemistry. To understand the physiological roles of the human enzyme, we generated and analyzed cell lines stably deficient in or overexpressing NADK. Short hairpin RNA-mediated down-regulation led to similar (about 70%) decrease of both NADK expression, activity, and the NADPH concentration and was accompanied by increased sensitivity toward H(2)O(2). Overexpression of NADK resulted in a 4-5-fold increase in the NADPH, but not NADP(+), concentration, although the recombinant enzyme phosphorylated preferentially NAD(+). Surprisingly, NADK overexpression and the ensuing increase of the NADPH level only moderately enhanced protection against oxidant treatment. Apparently, to maintain the NADPH level for the regeneration of oxidative defense systems human cells depend primarily on NADP-dependent dehydrogenases (which re-reduce NADP(+)), rather than on a net increase of NADP. The stable shifts of the NADPH level in the generated cell lines were also accompanied by alterations in the expression of peroxiredoxin 5 and Nrf2. Because the basal oxygen radical level in the cell lines was only slightly changed, the redox state of NADP may be a major transmitter of oxidative stress.

Erythrocyte disorders in the perinatal period

Anemia is a commonly encountered problem in the fetal and neonatal period, and can lead to significant morbidity and mortality. Intrinsic disorders of the erythrocyte, such as the hemoglobinopathies, enzyme deficiencies, and membrane defects are common causes of neonatal anemia. Genetic diseases that lead to decreased erythrocyte production, such as Diamond-Blackfan anemia, Schwachman-Diamond syndrome, and Congential Dyserythropoietic Anemia, are rare causes of perinatal anemia, but are important to recognize as they are often associated with other congenital abnormalities and require specialized treatment. This review focuses on the perinatal presentation and management of intrinsic erythrocyte disorders, as well as on the diagnosis and management of genetic conditions leading to erythrocyte underproduction.

Phanerochaete chrysosporium soluble proteome as a prelude for the analysis of heavy metal stress response

A 2-D reference map in pI range 3-10 was constructed for the soluble protein fraction of Phanerochaete chrysosporium growing vegetatively under standard conditions. Functional annotation could be made for 517 spots out of 720 that were subjected to MALDI-TOF-MS analysis, according to the specific accession numbers from the P. chrysosporium genomic database. Further analysis of the data revealed 314 distinct ORFs, 118 of which yielded multiple spots on the master gel. Functional classification of the proteins was made according to the eukaryote orthologous groups defined in the organism's genome website. The functional class of PTMs, protein turnover and chaperones was represented with the highest number (63) of the identified ORFs. Six proteins were assigned to the hypothetical proteins and 29 were predicted to have a signal peptide sequence. Subcellular localization predictions were also made for the identified proteins. Of the protein spots detected on the master gel, 380 were found to be probably phosphorylated and 96 of these matched to the identified proteins. The reference map was efficiently used in the identification of the proteins differentially expressed under cadmium and copper stress. Three new ribosomal proteins as well as zinc-containing alcohol dehydrogenase, glucose-6-phosphate isomerase, flavonol/cinnamoyl-CoA reductase, H+-transporting two-sector ATPase, ribosomal protein S7, ribosomal protein S21e, elongation factor EF-1 alpha subunit were demonstrated as the most strongly induced.

Lycopene, a Carotenoid, Attenuates Cyclosporine-Induced Renal Dysfunction and Oxidative Stress in Rats

The aim of this study was to investigate the possible protective role of antioxidant treatment with lycopene on cyclosporine A-induced nephrotoxicity using biochemical and histopatological approaches. Adult male Sprague-Dawley rats were randomly divided into four groups. The control group received physiological saline; animals in the lycopene group received only lycopene (10 mg/kg); animals in the cyclosporine A group received only cyclosporine A (15 mg/kg) and animals in cyclosporine plus lycopene group received cyclosporine and lycopene for 21 days. The effects of lycopene on cyclosporine A-induced nephrotoxicity were evaluated by plasma creatinine, urea, sodium and calcium concentrations; kidney tissue thiobarbituric acid reactive species, reduced glutathione (GSH), glutathione peroxidase (GSH-Px) and catalase activities and histopatological examinations. Administration of cyclosporine A to rats induced a marked renal failure, characterized with a significant increase in plasma creatinine and urea concentrations. Cyclosporine A also induced oxidative stress as indicated by increased kidney tissue concentrations of thiobarbituric acid reactive species and GSH, and reduced activities of GSH-Px and catalase. Moreover, the kidneys of cyclosporine A-treated rats showed tubular necrosis, degeneration, dilatation, thickened basement membranes, luminal cast formation and inter-tubular fibrosis. Lycopene markedly reduced elevated plasma creatinine, urea levels and counteracted the deleterious effects of cyclosporine A on oxidative stress markers. In addition, lycopene ameliorated cyclosporine A-induced pathological changes including tubular necrosis, degeneration, thickened basement membranes and inter-tubular fibrosis when compared to the alone cyclosporine A group. These data indicate that the natural antioxidant lycopene might have protective effect against cyclosporine-induced nephrotoxicity and oxidative stress in rat.

The power to reduce: pyridine nucleotides--small molecules with a multitude of functions

The pyridine nucleotides NAD and NADP play vital roles in metabolic conversions as signal transducers and in cellular defence systems. Both coenzymes participate as electron carriers in energy transduction and biosynthetic processes. Their oxidized forms, NAD+ and NADP+, have been identified as important elements of regulatory pathways. In particular, NAD+ serves as a substrate for ADP-ribosylation reactions and for the Sir2 family of NAD+-dependent protein deacetylases as well as a precursor of the calcium mobilizing molecule cADPr (cyclic ADP-ribose). The conversions of NADP+ into the 2'-phosphorylated form of cADPr or to its nicotinic acid derivative, NAADP, also result in the formation of potent intracellular calcium-signalling agents. Perhaps, the most critical function of NADP is in the maintenance of a pool of reducing equivalents which is essential to counteract oxidative damage and for other detoxifying reactions. It is well known that the NADPH/NADP+ ratio is usually kept high, in favour of the reduced form. Research within the past few years has revealed important insights into how the NADPH pool is generated and maintained in different subcellular compartments. Moreover, tremendous progress in the molecular characterization of NAD kinases has established these enzymes as vital factors for cell survival. In the present review, we summarize recent advances in the understanding of the biosynthesis and signalling functions of NAD(P) and highlight the new insights into the molecular mechanisms of NADPH generation and their roles in cell physiology.

Functional characterization of the TMLH gene: promoter analysis, in situ hybridization, identification and mapping of alternative splicing variants

Carnitine is a molecule with well-documented pleiotropic functions whose biosynthesis involves four catalytic steps. Here, we report a detailed analysis of the expression and transcriptional control of TMLH gene, which codifies for the first enzyme of carnitine biosynthesis. TMLH maps at the extreme end of Xq28, a chromosomal region of high genomic instability. By 5' and 3' RACE, we identified and mapped two alternative 5' TMLH first exons and seven alternative 3'-splice variants, which are spread over a genomic region of about 250 kb. While the two alternative 5' exons have different expression profiles, all the 3' alternative forms are ubiquitously expressed. Reporter assays revealed that the 3'-UTRs of each TMLH isoform might influence its own expression at post-transcriptional level. In addition, we identified a highly conserved promoter region of TMLH. Functional analysis of this region showed the presence of a CpG island, whose methylation-status could control the level of TMLH transcription. Finally, by mRNA in situ hybridization, we found that TMLH expression is present at E12.5 dpc in the mouse liver, lung and brain, and is then maintained in the postnatal brain with a specific neuronal pattern. Collectively, our data highlight a tight transcriptional and post-transcriptional control of TMLH expression.

Fructose 1,6-Diphosphate Alleviates UV-Induced Oxidative Skin Damage in Hairless Mice

Reactive oxygen species (ROS) are involved in the deleterious effects of UV light on skin. The antioxidant defense system is considered to be crucial for protecting skin from ROS. Recently, we showed that fructose 1,6-diphosphate (FDP), a glycolytic metabolite, reduced oxidative stress in UVB-irradiated keratinocytes. This study set out to determine whether topically applied FDP could exert protective effects against UV-induced skin damage in hairless mice. An in vitro skin permeation study using Franz-type diffusion cells showed that the amount of [14C]-FDP that diffused through the skin increased in a time-dependent manner, and about 3.5% of the applied FDP penetrated the skin after 24 h. Topical application of FDP (1%) preserved the endogenous antioxidant capacity of skin such as catalase and glutathione, which were significantly reduced after UVB irradiation without FDP. FDP also reversed the loss of catalase protein and prevented the accumulation of carbonylated proteins induced by UVB irradiation. These results provide evidence that topically administered FDP could penetrate into the skin and attenuate UVB-induced oxidative skin damage in hairless mice.

Antioxidant function of corneal ALDH3A1 in cultured stromal fibroblasts

Aldehyde dehydrogenase 3A1 (ALDH3A1) is highly expressed in epithelial cells and stromal keratocytes of mammalian cornea and is believed to play an important role in cellular defense. To explore a potential protective role against oxidative damage, a rabbit corneal fibroblastic cell line (TRK43) was stably transfected with the human ALDH3A1 and subjected to oxidative stress induced by H(2)O(2), mitomycin C (MMC), or etoposide (VP-16). ALDH3A1-transfected cells were more resistant to H(2)O(2,) MMC, and VP-16 compared to the vector-transfected cells. All treatments induced apoptosis only in vector-transfected cells, which was associated with increased levels of 4-hydroxy-2-nonenal (4-HNE)-adducted proteins. Treatment with H(2)O(2) resulted in a rise in reduced glutathione (GSH) levels in all groups but was more pronounced in the ALDH3A1-expressing cells. Treatment with the DNA-damaging agents led to GSH depletion in control groups, although the depletion was significantly less in ALDH3A1-expressing cells. Increased carbonylation of ALDH3A1 but not significant decline in enzymatic activity was observed after all treatments. In conclusion, our results suggest that ALDH3A1 may act to protect corneal cells against cellular oxidative damage by metabolizing toxic lipid peroxidation products (e.g., 4-HNE), maintaining cellular GSH levels and redox balance, and operating as an antioxidant.

Adaptations to oxidative stress induced by vitamin E deficiency in rat liver

Vitamin E deficiency in rats led to a sequence of antioxidant defense adaptations in the liver. After three weeks, alpha-tocopherol concentration was 5% of control, but ascorbate and ubiquinol concentrations were 2- to 3-fold greater than control. During the early phase of adaptation no differences in markers of lipid peroxidation were observed, but the activities of both cytochrome b5 reductase and glucose-6-phosphate dehydrogenase were significantly greater in deficient livers. By nine weeks, accumulation of lipid peroxidation end products began to occur along with declining concentrations of ascorbate, and higher NQO1 activities. At twelve weeks, rat growth ceased, and both lipid peroxidation products and cytosolic calcium-independent phospholipase A2 reached maximum concentrations. Thus, in growing rats the changes progressed from increases in both ubiquinol and quinone reductases through accumulation of lipid peroxidation products and loss of endogenous antioxidants to finally induction of lipid metabolizing enzymes and cessation of rat growth.

Renal oxidative vulnerability due to changes in mitochondrial-glutathione and energy homeostasis in a rat model of calcium oxalate urolithiasis

Calcium oxalate monohydrate (COM) crystals are the commonest component of kidney stones. Oxalate and COM crystals in renal cells are thought to contribute to pathology via prooxidant events. Using an in vivo rat model of crystalluria induced by hyperoxaluria plus hypercalciuria [ethylene glycol (EG) plus 1,25-dihydroxycholecalciferol (DHC)], we measured glutathione and energy homeostasis of kidney mitochondria. Hyperoxaluria or hypercalciuria without crystalluria was also investigated. After 1–3 wk of treatment, kidney cryosections were analyzed by light microscopy. In kidney subcellular fractions, glutathione and antioxidant enzymes were measured. In mitochondria, oxygen consumption and superoxide formation as well as cytochrome c content were measured. EG plus DHC treatment increased formation of renal birefringent crystal. Histology revealed increased renal tubular pathology characterized by obstruction, distension, and interstitial inflammation. Crystalluria at all time points led to oxidative stress manifest as decreased cytosolic and mitochondrial glutathione and increased activity of the antioxidant enzymes glutathione reductase and -peroxidase (mitochondria) and glucose-6-phosphate dehydrogenase (cytosol). These changes were followed by a significant decrease in mitochondrial cytochrome c content at 2–3 wk, suggesting the involvement of apoptosis in the renal pathology. Mitochondrial oxygen consumption was severely impaired in the crystalluria group without increased mitochondrial superoxide formation. Some of these changes were also evident in hyperoxaluria at week 1 but were absent at later times and in all calciuric groups. Our data indicate that impaired electron flow did not cause superoxide formation; however, mitochondrial dysfunction contributes to pathological events when tubular crystal-cell interactions are uncontrolled, as in kidney stones disease.

Chlorinative stress: an under appreciated mediator of neurodegeneration?

Oxidative stress has been implicated as playing a role in neurodegenerative disorders, such as ischemic stroke, Alzheimer's, Huntington's, and Parkinson's disease. Persuasive evidences have shown that microglial-mediated oxidative stress contributes significantly to cell loss and accompanying cognitive decline characteristic of the diseases. Based on the facts that (i) levels of catalytically active myeloperoxidase are elevated in diseased brains and (ii) myeloperoxidase polymorphism is associated with the risk of developing neurodegenerative disorders, HOCl as a major oxidant produced by activated phagocytes in the presence of myeloperoxidase is therefore suggested to be involved in neurodegeneration. Its association with neurodegeneration is further showed by elevated level of 3-chlorotyrosine (bio-marker of HOCl in vivo) in affected brain regions as well as HOCl scavenging ability of neuroprotectants, desferrioxamine and uric acid. In this review, we will summary the current understanding concerning the association of HOCl and neuronal cell death where production of HOCl will lead to further formation of reactive nitrogen and oxygen species. In addition, HOCl also causes tissue destruction and cellular damage leading cell death.

Glucose 6-phosphate dehydrogenase overexpression models glucose deprivation and sensitizes lymphoma cells to apoptosis

Glucocorticoids are one component of combined treatment regimens for many types of lymphoma due to their ability to induce apoptosis in lymphoid cells. In WEHI7.2 murine thymic lymphoma cells, altering catalase and glutathione peroxidase activity by transfection or the use of chemical agents modulates the ability of glucocorticoids to induce apoptosis. This suggests that the oxidative stress response is important in determining the glucocorticoid sensitivity of the cells. For glutathione peroxidase and catalase to detoxify reactive oxygen species (ROS), reducing equivalents in the form of nicotinamide adenine dinucleotide phosphate, reduced form (NADPH) are ultimately required. The major source of NADPH in the cell is glucose 6-phosphate dehydrogenase (G6PDH). Therefore, we created G6PDH-overexpressing WEHI7.2 variants to test whether G6PDH activity is a key determinant of glucocorticoid sensitivity in WEHI7.2 cells. G6PDH-overexpressing WEHI7.2 cells were more sensitive to oxidative stress and glucocorticoids. The G6PDH-overexpressing WEHI7.2 variants appeared similar to cells undergoing glucose deprivation with decreased adenosine triphosphate (ATP) synthesis by the mitochondria and increased basal levels of ROS. Overexpression of G6PDH also sensitized the cells to other standard lymphoma chemotherapeutics including cyclophosphamide, doxorubicin, and vincristine. The decreased ATP and elevated ROS due to G6PDH overexpression may be key factors in increasing the sensitivity of the WEHI7.2 cells to lymphoma chemotherapeutics.

The glucose-6-phosphate dehydrogenase from Trypanosoma cruzi: its role in the defense of the parasite against oxidative stress

The Trypanosoma cruzi glucose-6-phosphate dehydrogenase (G6PDH) is encoded by several genes located in three of the parasite chromosomes. All the sequences present two possible start codons, 111bp apart, also present in its Trypanosoma brucei counterpart. As the 37 residues comprised between the two candidate initiator methionines of T. brucei and T. cruzi G6PDHs constitute an unusual N-terminal extension only present in trypanosomatids, two forms of the T. cruzi G6PDH were expressed in Escherichia coli: a long one (Tc-G6PDH-L) translated from the first ATG codon, and a short one (Tc-G6PDH-S) translated from the second. Both were purified and their kinetic constants determined. The apparent K(m) for glucose-6-phosphate was 189.9, 98.4, and 288microM, for Tc-G6PDH-L, Tc-G6PDH-S and native Tc-G6PDH, respectively. The apparent K(m) for NADP was similar for both recombinant proteins. The Tc-G6PDH-L as well as the native enzyme, was inactivated by DTT while the Tc-G6PDH-S was unaffected by the reducing agent. This behavior could be related to the presence of two Cys groups in the N-terminal extension of the Tc-G6PDH-L similarly to the redox regulated G6PDHs from chloroplasts and cyanobacteria. This property, together with a remarkable induction (up to 46-fold) of the T. cruzi G6PDH in metacyclic trypomastigotes under oxidative stress conditions, suggests that the enzyme may play a prominent role in the defense mechanisms of the parasite against oxidative stress becoming an important target for chemotherapy. Western blots using antibodies against the N-terminal extension in Tc-G6PDH-L show that this form is expressed in the parasite.

Nitric oxide, cell bioenergetics and neurodegeneration

Following stimulation of NMDA receptors, neurons transiently synthesize nitric oxide (NO) in a calcium/calmodulin-dependent manner through the activation of neuronal NO synthase. Nitric oxide acts as a messenger, activating soluble guanylyl cyclase and participating in the transduction signalling pathways involving cyclic GMP. Nitric oxide also binds to cytochrome c oxidase, and is able to inhibit cell respiration in a process that is reversible and in competition with oxygen. This action can also lead to the release of superoxide anion from the mitochondrial respiratory chain. Here, we discuss recent evidence that this mitochondrial interaction represents a molecular switch for cell signalling pathways involved in the control of physiological functions. These include superoxide- or oxygen-dependent modulation of gene transcription, calcium-dependent cell signalling responses, changes in the mitochondrial membrane potential or AMP-activated protein kinase-dependent control of glycolysis. In pathophysiological conditions, such as brain ischaemia or neurological disorders, NO is formed excessively by NMDA receptor over-activation in neurons, or by inducible NO synthase from neighbouring glia (microglial cells and astrocytes). Elevated NO concentrations can then interact with superoxide anion, generated by the mitochondria or by other mechanisms, leading to the formation of the powerful oxidant species peroxynitrite. During pathological conditions activation of the NAD(+)-consuming enzyme poly(APD-ribose) polymerase-1 (PARP-1) is also a likely mechanism for NO-mediated energy failure and neurotoxicity. Activation of PARP-1 is, however, a repair process, which in milder forms of oxidative stress protects neurons from death. Thus, whilst NO plays a physiological role in neuronal cell signalling, its over-production may cause neuronal energy compromise leading to neurodegeneration.

Neuroprotection by transgenic expression of glucose-6-phosphate dehydrogenase in dopaminergic nigrostriatal neurons of mice

Oxidative damage to dopaminergic nigrostriatal (DNS) neurons plays a central role in the pathogenesis of Parkinson's disease (PD). Glucose-6-phosphate dehydrogenase (G6PD) is a key cytoprotective enzyme that provides NADPH, the major source of the reducing equivalents of a cell. Mutations of this enzyme are the most common enzymopathies worldwide. We have studied in vivo the role of G6PD overexpressed specifically in the DNS pathway and show that the increase of G6PD activity in the soma and axon terminals of DNS neurons, separately from other neurons or glial cells, protects them from parkinsonism. Analysis of DNS neurons by histological, neurochemical, and functional methods showed that even a moderate increase of G6PD activity rendered transgenic mice more resistant than control littermates to the toxic effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). The neuroprotective action of G6PD was also observed in aged animals despite that they had a greater susceptibility to MPTP. Therefore, overexpression of G6PD in dopaminergic neurons or pharmacological activation of the native enzyme should be considered as potential therapeutic strategies to PD.

Evidence that feedback inhibition of NAD kinase controls responses to oxidative stress

Formation of NADP+ from NAD+ is catalyzed by NAD kinase (NadK; EC 2.7.1.23). Evidence is presented that NadK is the only NAD kinase of Salmonella enterica and is essential for growth. NadK is inhibited allosterically by NADPH and NADH. Without effectors, NadK exists as an equilibrium mixture of dimers and tetramers (KD = 1.0 +/- 0.8 mM) but is converted entirely to tetramers in the presence of the inhibitor NADPH. Comparison of NadK kinetic parameters with pool sizes of NADH and NADPH suggests that NadK is substantially inhibited during normal growth and, thus, can increase its activity greatly in response to temporary drops in the pools of inhibitory NADH and NADPH. The primary inhibitor is NADPH during aerobic growth and NADH during anaerobic growth. A model is proposed in which variation of NadK activity is central to the adjustment of pyridine nucleotide pools in response to changes in aeration, oxidative stress, and UV irradiation. It is suggested that each of these environmental factors causes a decrease in the level of reduced pyridine nucleotides, activates NadK, and increases production of NADP(H) at the expense of NAD(H). Activation of NadK may constitute a defensive response that resists loss of protective NADPH.

Sugar-induced tolerance to the herbicide atrazine in Arabidopsis seedlings involves activation of oxidative and xenobiotic stress responses

Exogenous sucrose confers to Arabidopsis seedlings a very high level of tolerance to the herbicide atrazine that cannot be ascribed to photoheterotrophic growth. Important differences of atrazine tolerance between sucrose and glucose treatments showed that activation of chloroplast biogenesis per se could not account for induced tolerance. Sucrose-induced acquisition of defence mechanisms was shown by the gene expression pattern of a chloroplastic iron superoxide dismutase and by enhancement of whole-cell glucose-6-phosphate dehydrogenase activity. Activation of these defence mechanisms depended on both soluble sugar and atrazine. Moreover, acquisition of sucrose protection was shown to unmask atrazine-induced gene expression, such as that of a cytosolic glutathione-S-transferase, which remained otherwise cryptic because of the lethal effects of atrazine in the absence of soluble sugars.

Glucose-6-phosphate dehydrogenase deficiency decreases vascular superoxide and atherosclerotic lesions in apolipoprotein E(-/-) mice

OBJECTIVE

Glucose-6-phosphate dehydrogenase (G6PD) is a key enzyme in the pentose phosphate pathway that is a major source of cellular NADPH. The purpose of this study was to examine whether G6PD deficiency affects vascular oxidants and atherosclerosis in high-fat fed apolipoprotein (apo) E(-/-) mice.

METHODS AND RESULTS

G6PD-mutant mice whose G6PD activity was 20% of normal were crossbred with apoE(-/-) mice. Among male apoE(-/-) mice that were fed a western-type diet for 11 weeks, G6PD wild-type (E-WT), and G6PD hemizygous (E-Hemi) mice were compared. Basal blood pressure was significantly higher in E-Hemi. However, superoxide anion release, nitrotyrosine, vascular cell adhesion molecule (VCAM)-1, and inducible nitric oxide synthase immunohistochemical staining were less in E-Hemi compared with E-WT aorta. Serum cholesterol level was lower in E-Hemi, but aortic lesion area was decreased in E-Hemi even after adjusting for serum cholesterol.

CONCLUSIONS

Lower NADPH production in G6PD deficiency may result in lower NADPH oxidase-derived superoxide anion, and thus lower aortic lesion growth. The association of higher blood pressure with lower serum cholesterol levels in this mouse model is indicative of the complex effects that G6PD deficiency may have on vascular disease.

Regulation of replicative senescence by NADP+ -dependent isocitrate dehydrogenase

The free radical hypothesis of aging postulates that senescence is due to an accumulation of cellular oxidative damage, caused largely by reactive oxygen species that are produced as by-products of normal metabolic processes. Recently, we demonstrated that the control of cytosolic and mitochondrial redox balance and the cellular defense against oxidative damage is one of the primary functions of cytosolic (IDPc) and mitochondrial NADP+ -dependent isocitrate dehydrogenase (IDPm) by supplying NADPH for antioxidant systems. In this paper, we demonstrate that modulation of IDPc or IDPm activity in IMR-90 cells regulates cellular redox status and replicative senescence. When we examined the regulatory role of IDPc and IDPm against the aging process with IMR-90 cells transfected with cDNA for IDPc or IDPm in sense and antisense orientations, a clear inverse relationship was observed between the amount of IDPc or IDPm expressed in target cells and their susceptibility to senescence, which was reflected by changes in replicative potential, cell cycle, senescence-associated beta-galactosidase activity, expression of p21 and p53, and morphology of cells. Furthermore, lipid peroxidation, oxidative DNA damage, and intracellular peroxide generation were higher and cellular redox status shifted to a prooxidant condition in the cell lines expressing the lower level of IDPc or IDPm. The results suggest that IDPc and IDPm play an important regulatory role in cellular defense against oxidative stress and in the senescence of IMR-90 cells.

Involvement of soluble sugars in reactive oxygen species balance and responses to oxidative stress in plants

Soluble sugars, especially sucrose, glucose, and fructose, play an obviously central role in plant structure and metabolism at the cellular and whole-organism levels. They are involved in the responses to a number of stresses, and they act as nutrient and metabolite signalling molecules that activate specific or hormone-crosstalk transduction pathways, thus resulting in important modifications of gene expression and proteomic patterns. Various metabolic reactions and regulations directly link soluble sugars with the production rates of reactive oxygen species, such as mitochondrial respiration or photosynthesis regulation, and, conversely, with anti-oxidative processes, such as the oxidative pentose-phosphate pathway and carotenoid biosynthesis. Moreover, stress situations where soluble sugars are involved, such as chilling, herbicide injury, or pathogen attack, are related to important changes in reactive oxygen species balance. These converging or antagonistic relationships between soluble sugars, reactive oxygen species production, and anti-oxidant processes are generally confirmed by current transcriptome analyses, and suggest that sugar signalling and sugar-modulated gene expression are related to the control of oxidative stress. All these links place soluble carbohydrates in a pivotal role in the pro-oxidant and antioxidant balance, and must have constrained the selection of adaptive mechanisms involving soluble sugars and preventing de-regulation of reactive oxygen species production. Finally, in line with the specific role of sucrose in oxygenic photosynthetic organisms, this role of soluble sugars in oxidative stress regulation seems to entail differential effects of glucose and sucrose, which emphasizes the unresolved issue of characterizing sucrose-specific signalling pathways.

Secrets of the lac operon. Glucose hysteresis as a mechanism in dietary restriction, aging and disease

Elevated blood glucose associated with diabetes produces progressive and apparently irreversible damage to many cell types. Conversely, reduction of glucose extends life span in yeast, and dietary restriction reduces blood glucose. Therefore it has been hypothesized that cumulative toxic effects of glucose drive at least some aspects of the aging process and, conversely, that protective effects of dietary restriction are mediated by a reduction in exposure to glucose. The mechanisms mediating cumulative toxic effects of glucose are suggested by two general principles of metabolic processes, illustrated by the lac operon but also observed with glucose-induced gene expression. First, metabolites induce the machinery of their own metabolism. Second, induction of gene expression by metabolites can entail a form of molecular memory called hysteresis. When applied to glucose-regulated gene expression, these two principles suggest a mechanism whereby repetitive exposure to postprandial excursions of glucose leads to an age-related increase in glycolytic capacity (and reduction in beta-oxidation of free fatty acids), which in turn leads to an increased generation of oxidative damage and a decreased capacity to respond to oxidative damage, independent of metabolic rate. According to this mechanism, dietary restriction increases life span and reduces pathology by reducing exposure to glucose and therefore delaying the development of glucose-induced glycolytic capacity.

Glucose-6-phosphate dehydrogenase activity and NADPH/NADP+ ratio in liver and pancreas are dependent on the severity of hyperglycemia in rat

Hyperglycemia is associated with metabolic disturbances affecting cell redox potential, particularly the NADPH/NADP+ ratio and reduced glutathione levels. Under oxidative stress, the NADPH supply for reduced glutathione regeneration is dependent on glucose-6-phosphate dehydrogenase. We assessed the effect of different hyperglycemic conditions on enzymatic activities involved in glutathione regeneration (glucose-6-phosphate dehydrogenase and glutathione reductase), NADP(H) and reduced glutathione concentrations in order to analyze the relative role of these enzymes in the control of glutathione restoration. Male Sprague-Dawley rats with mild, moderate and severe hyperglycemia were obtained using different regimens of streptozotocin and nicotinamide. Fifteen days after treatment, rats were killed and enzymatic activities, NADP(H) and reduced glutathione were measured in liver and pancreas. Severe hyperglycemia was associated with decreased body weight, plasma insulin, glucose-6-phosphate dehydrogenase activity, NADPH/NADP+ ratio and glutathione levels in the liver and pancreas, and enhanced NADP+ and glutathione reductase activity in the liver. Moderate hyperglycemia caused similar changes, although body weight and liver NADP+ concentration were not affected and pancreatic glutathione reductase activity decreased. Mild hyperglycemia was associated with a reduction in pancreatic glucose-6-phosphate dehydrogenase activity. Glucose-6-phosphate dehydrogenase, NADPH/NADP+ ratio and glutathione level, vary inversely in relation to blood glucose concentrations, whereas liver glutathione reductase was enhanced during severe hyperglycemia. We conclude that glucose-6-phosphate dehydrogenase and NADPH/NADP+ were highly sensitive to low levels of hyperglycemia. NADPH/NADP+ is regulated by glucose-6-phosphate dehydrogenase in the liver and pancreas, whereas levels of reduced glutathione are mainly dependent on the NADPH supply.

l-Carnitine protects mammalian cells from chromosome aberrations but not from inhibition of cell proliferation induced by hydrogen peroxide

L-carnitine is a small essential molecule indispensable in fatty acid metabolism and required in several biological pathways regulating cellular homeostasis. Despite considerable progress in understanding of L-carnitine biosynthesis and metabolism, very few data are reported concerning the protective role of L-carnitine from oxidative stress-induced DNA damage that is known to be a factor in cell transformation and tumourigenesis. In order to detect the capability of L-carnitine to protect mammalian cells from oxidative stress-induced chromosomal effects, we analysed chromosome aberrations in mitotic CHO cells, which represent an appropriate cytogenetic model to study compounds that enhance cell protection against externally induced DNA damage. We chose H2O2 as an inducer of oxidative stress. Our results demonstrate for the first time a marked and reproducible reduction of H2O2-induced chromosome damage involving an L-carnitine-mediated capacity to buffer intracellular formation of reactive oxygen species (ROS). Furthermore, by studying the mitotic index and cell cycle progression, we also demonstrated that this protective effect is highly specific, since L-carnitine itself was not able to prevent the inhibition of cell growth caused by H2O2.

Diet, metabolism and lifespan in Drosophila

Dietary restriction (DR) by dilution of the food medium can extend lifespan in Drosophila. DR results in a state that is characterized by reduced fecundity, increased starvation resistance and higher total lipid levels. In the past, each of these correlated phenotypes has been proposed to play a causal role in the lifespan-extending effects of food reduction. However, more recent data show that each phenotype can be uncoupled from the long-lived state to varying extents. In this mini-review, we summarize the principal findings of the effects of DR on Drosophila in order to address what these phenotypes can tell us about the physiological remodeling required for Drosophila to be long-lived. Current data indicate lifespan-extension by DR is likely to involve both enhancement of various defense and detoxification mechanisms and a complex range of metabolic alterations that make energy available for these processes.