Selenium redox biochemistry of zinc–sulfur coordination sites in proteins and enzymes

Selenium has been increasingly recognized as an essential element in biology and medicine. Its biochemistry resembles that of sulfur, yet differs from it by virtue of both redox potentials and stabilities of its oxidation states. Selenium can substitute for the more ubiquitous sulfur of cysteine and as such plays an important role in more than a dozen selenoproteins. We have chosen to examine zinc–sulfur centers as possible targets of selenium redox biochemistry. Selenium compounds release zinc from zinc/thiolate-coordination environments, thereby affecting the cellular thiol redox state and the distribution of zinc and likely of other metal ions. Aromatic selenium compounds are excellent spectroscopic probes of the otherwise relatively unstable functional selenium groups. Zinc-coordinated thiolates, e.g., metallothionein (MT), and uncoordinated thiolates, e.g., glutathione, react with benzeneseleninic acid (oxidation state +2), benzeneselenenyl chloride (oxidation state 0) and selenocystamine (oxidation state −1). Benzeneseleninic acid and benzeneselenenyl chloride react very rapidly with MT and titrate substoichiometrically and with a 1:1 stoichiometry, respectively. Selenium compounds also catalyze the release of zinc from MT in peroxidation and thiol/disulfide-interchange reactions. The selenoenzyme glutathione peroxidase catalytically oxidizes MT and releases zinc in the presence of t-butyl hydroperoxide, suggesting that this type of redox chemistry may be employed in biology for the control of metal metabolism. Moreover, selenium compounds are likely targets for zinc/thiolate coordination centers in vivo, because the reactions are only partially suppressed by excess glutathione. This specificity and the potential to undergo catalytic reactions at low concentrations suggests that zinc release is a significant aspect of the therapeutic antioxidant actions of selenium compounds in antiinflammatory and anticarcinogenic agents.

Antioxidative Defense System, Pigment Composition, and Photosynthetic Efficiency in Two Wheat Cultivars Subjected to Drought1

We analyzed antioxidative defenses, photosynthesis, and pigments (especially xanthophyll-cycle components) in two wheat (Triticum durum Desf.) cultivars, Adamello and Ofanto, during dehydration and rehydration to determine the difference in their sensitivities to drought and to elucidate the role of different protective mechanisms against oxidative stress. Drought caused a more pronounced inhibition in growth and photosynthetic rates in the more sensitive cv Adamello compared with the relatively tolerant cv Ofanto. During dehydration the glutathione content decreased in both wheat cultivars, but only cv Adamello showed a significant increase in glutathione reductase and hydrogen peroxide-glutathione peroxidase activities. The activation states of two sulfhydryl-containing chloroplast enzymes, NADP+-dependent glyceraldehyde-3-phosphate dehydrogenase and fructose-1,6-bisphosphatase, were maintained at control levels during dehydration and rehydration in both cultivars. This indicates that the defense systems involved are efficient in the protection of sulfhydryl groups against oxidation. Drought did not cause significant effects on lipid peroxidation. Upon dehydration, a decline in chlorophyll a, lutein, neoxanthin, and β-carotene contents, and an increase in the pool of de-epoxidized xanthophyll-cycle components (i.e. zeaxanthin and antheraxanthin), were evident only in cv Adamello. Accordingly, after exposure to drought, cv Adamello showed a larger reduction in the actual photosystem II photochemical efficiency and a higher increase in nonradiative energy dissipation than cv Ofanto. Although differences in zeaxanthin content were not sufficient to explain the difference in drought tolerance between the two cultivars, zeaxanthin formation may be relevant in avoiding irreversible damage to photosystem II in the more sensitive cultivar.

Defense Responses to Tetrapyrrole-Induced Oxidative Stress in Transgenic Plants with Reduced Uroporphyrinogen Decarboxylase or Coproporphyrinogen Oxidase Activity1

We analyzed the antioxidative defense responses of transgenic tobacco (Nicotiana tabacum) plants expressing antisense RNA for uroporphyrinogen decarboxylase or coproporphyrinogen oxidase. These plants are characterized by necrotic leaf lesions resulting from the accumulation of potentially photosensitizing tetrapyrroles. Compared with control plants, the transformants had increased levels of antioxidant mRNAs, particularly those encoding superoxide dismutase (SOD), catalase, and glutathione peroxidase. These elevated transcript levels correlated with increased activities of cytosolic Cu/Zn-SOD and mitochondrial Mn-SOD. Total catalase activity decreased in the older leaves of the transformants to levels lower than in the wild-type plants, reflecting an enhanced turnover of this photosensitive enzyme. Most of the enzymes of the Halliwell-Asada pathway displayed increased activities in transgenic plants. Despite the elevated enzyme activities, the limited capacity of the antioxidative system was apparent from decreased levels of ascorbate and glutathione, as well as from necrotic leaf lesions and growth retardation. Our data demonstrate the induction of the enzymatic detoxifying defense system in several compartments, suggesting a photosensitization of the entire cell. It is proposed that the tetrapyrroles that initially accumulate in the plastids leak out into other cellular compartments, thereby necessitating the local detoxification of reactive oxygen species.

Selenocysteine, identified as the penultimate C-terminal residue in human T-cell thioredoxin reductase, corresponds to TGA in the human placental gene.

The possible relationship of selenium to immunological function which has been suggested for decades was investigated in studies on selenium metabolism in human T cells. One of the major 75Se-labeled selenoproteins detected was purified to homogeneity and shown to be a homodimer of 55-kDa subunits. Each subunit contained about 1 FAD and at least 0.74 Se. This protein proved to be thioredoxin reductase (TR) on the basis of its catalytic activities, cross-reactivity with anti-rat liver TR antibodies, and sequence identities of several tryptic peptides with the published deduced sequence of human placental TR. Physicochemical characteristics of T-cell TR were similar to those of a selenocysteine (Secys)-containing TR recently isolated from human lung adenocarcinoma cells. The sequence of a 12-residue 75Se-labeled tryptic peptide from T-cell TR was identical with a C-terminal-deduced sequence of human placental TR except that Secys was present in the position corresponding to TGA, previously thought to be the termination codon, and this was followed by Gly-499, the actual C-terminal amino acid. The presence of the unusual conserved Cys-Secys-Gly sequence at the C terminus of TR in addition to the redox active cysteines of the Cys-Val-Asn-Val-Gly-Cys motif in the FAD-binding region may account for the peroxidase activity and the relatively low substrate specificity of mammalian TRs. The finding that T-cell TR is a selenoenzyme that contains Se in a conserved C-terminal region provides another example of the role of selenium in a major antioxidant enzyme system (i.e., thioredoxin-thioredoxin reductase), in addition to the well-known glutathione peroxidase enzyme system.

Dietary lipids and calorie restriction affect mammary tumor incidence and gene expression in mouse mammary tumor virus/v-Ha-ras transgenic mice.

We have studied the effects of food restriction (FR) and substitution of fish oil (FO; omega 3) for corn oil (CO; omega 6) on breast tumor incidence and survival in mouse mammary tumor virus/v-Ha-ras transgenic (Onco) mice. The diets were as follows: group 1, 5% (wt/wt) CO fed ad libitum (AL); group 2, 5% CO, restricted calories (40% fewer calories than AL; FR); group 3, 20% CO fed AL; and group 4, 20% FO fed AL. After 3 years, 40% of FR Onco (group 2) mice were alive, whereas there were no survivors in the other three groups. Similarly, tumor incidence was reduced to 27% (5 out of 18) in FR animals (group 2), whereas it was 83% (11 out of 13) in group 1 mice, 89% (16 out of 18) in group 3 mice, and 71% (10 out of 14) in group 4 mice. These protective effects of FR on survival and tumor incidence were paralleled by higher expression of the tumor suppressor gene p53 (wild type) and free-radical scavenging enzymes (catalase and superoxide dismutase) in breast tumors. Immunoblotting showed less ras gene product, p21, and increased p53 levels in the tumors of FR mice. In addition, FR decreased RNA levels of c-erbB-2, interleukin 6, and the transgene v-Ha-ras in tumors. In contrast, analysis of hepatic mRNA from tumor-bearing FR mice revealed higher expression of catalase, glutathione peroxidase, and superoxide dismutase. Survival and tumor incidence were not influenced significantly by dietary supplementation with FO in place of CO. Taken together, our studies suggest that moderate restriction of energy intake significantly inhibited the development of mammary tumors and altered expression of cytokines, oncogenes, and free-radical scavenging enzymes.

Function of the oxidative burst in hypersensitive disease resistance.

Microbial elicitors or attempted infection with an avirulent pathogen strain causes the rapid production of reactive oxygen intermediates. Recent findings indicate that H2O2 from this oxidative burst plays a central role in the orchestration of the hypersensitive response: (i) as the substrate driving the cross-linking of cell wall structural proteins to slow microbial ingress prior to the deployment of transcription-dependent defenses and to trap pathogens in cells destined to undergo hypersensitive cell death, (ii) as a local threshold trigger of this programmed death in challenged cells, and (iii) as a diffusible signal for the induction in adjacent cells of genes encoding cellular protectants such as glutathione S-transferase and glutathione peroxidase. These findings provide the basis for an integrated model for the orchestration of the localized hypersensitive resistance response to attack by an avirulent pathogen.

Biochemical mechanisms involved in pulmonary hypo-alveolarization induced by peroxides contaminating parenteral nutrition in newborn guinea pig

La dysplasie broncho-pulmonaire (DBP), caractérisée par un défaut de l’alvéolarisation, est une complication pathologique associée à un stress oxydant chez le nouveau-né prématuré. La DBP est présente chez près de 50 % des nouveau-nés de moins de 29 semaines de gestation. La nutrition parentérale (NP) que ces nouveau-nés reçoivent pour cause d’immaturité gastro-intestinale est une source importante de stress oxydant. En effet, leur NP est contaminée par des peroxydes, dont l’ascorbylperoxyde qui est une forme peroxydée du déshydroascorbate. La génération des peroxydes est catalysée par la lumière ambiante. La photoprotection de la NP, quoique difficile d’application en clinique, est associée à une diminution de l’incidence de la DBP chez les enfants prématurés. Chez l’animal nouveau-né, la photoprotection de la NP est associée à un meilleur développement alvéolaire. Ainsi, nous émettons l’hypothèse que l’ascorbylperoxide infusé avec la NP cause la perte d’alvéoles suite à une apoptose exagérée induite par l’oxydation du potentiel redox du glutathion. Cette oxydation du potentiel redox serait occasionnée par l’inhibition de la transformation hépatique de la méthionine en cystéine, menant à une diminution de la synthèse de glutathion au foie et dans les tissus tels que les poumons. La confirmation de cette hypothèse suggérera qu’un ajout de glutathion dans la NP permettra une meilleure détoxification de l’ascorbylperoxide par l’action de la glutathion peroxydase, et préviendra l’oxydation du potentiel redox et ainsi, la perte d'alvéoles par apoptose. Objectifs : Le but de mon projet de recherche est de comprendre les mécanismes biochimiques liant la NP et le développement de la DBP chez le nouveau-né prématuré et de proposer une alternative nutritionnelle prévenant le développement de cette complication fréquemment observée dans cette population. Les objectifs spécifiques sont : 1) d’évaluer l’impact, au poumon, de l’infusion de l’ascorbylperoxyde sur l’axe métabolique potentiel redox du glutathion - apoptose - le développement alvéolaire; 2) d’étudier l’impact de l’ascorbylperoxyde et du potentiel redox sur l’activité hépatique de la méthionine adénosyltransférase (MAT), première enzyme de la cascade métabolique transformant la méthionine en cystéine; et 3) de tenter de prévenir l’impact négatif de la NP ou de l’infusion d’ascorbylperoxyde sur le poumon en améliorant le statut en glutathion. Méthodes: Par un cathéter fixé dans la jugulaire, des cochons d’Inde de trois jours de vie (n = 8 par groupe) ont reçu en continu durant 4 jours une NP ou une solution de base (dextrose + NaCl) enrichie des différentes molécules à l’essai. Le premier objectif a été atteint en enrichissant la solution de base en ascorbylperoxyde à 0, 20, 60 et 180 μM. Ces solutions contenaient ou non 350 μM H2O2 pour se rapprocher des conditions cliniques. Le second objectif a été atteint en investiguant les mécanismes d’inhibition de la MAT dans des animaux infusés ou non avec des solutions contenant la solution de base, des peroxydes, du glutathion et la NP (dextrose + acides aminés + multivitamines + lipides). Le troisième objectif a été atteint en ajoutant ou non à une solution d’ascorbylperoxide ou à la NP 10 μM de glutathion (GSSG), afin d’obtenir une concentration plasmatique normale de glutathion. Après 4 jours, les poumons étaient prélevés et traités pour la détermination de GSH et GSSG par électrophorèse capillaire, le potentiel redox était calculé selon l'équation de Nernst et le niveau de caspase-3 actif (marqueur d’apoptose) par Western blot et l’index d’alvéolarisation quantifié par le nombre d’interceptes entre des structures histologiques et une droite calibrée. Les données étaient comparées par ANOVA, les effets étaient considérés comme significatifs si le p était inférieur à 0,05. Résultats: L’infusion de l’ascorbylperoxyde, indépendamment du H2O2, a induit une hypoalvéolarisation, une activation de la caspase-3 et une oxydation du potentiel redox de manière dose-dépendante. Ces effets ont été empêchés par l’ajout de GSSG à la NP ou à la solution d’ascorbylperoxyde (180 M). L’ascorbylperoxyde et le H2O2 ont inhibé l’activité de MAT tandis qu’elle était linéairement modulée par la valeur du potentiel redox hépatique. Conclusion : Nos résultats suggèrent que l’ascorbylperoxyde est l’agent actif de la NP conduisant au développement de la DBP. Ainsi la correction des bas niveaux de glutathion induits par les peroxydes de la NP favorise la détoxification des peroxydes et la correction du potentiel redox pulmonaire ; ce qui a protégé les poumons des effets délétères de la NP en outrepassant l’inhibition de la MAT hépatique. Nos résultats sont d'une grande importance car ils donnent de l'espoir pour une prévention possible de la DBP.

Antioxidant Properties of Bee Products of Plant- Origin Part 2. Propolis and Pollen

Over the last years, the hive products such as propolis and pollen have been highlighted due to their potential health benefits, including antioxidant abilities that have been correlated with their content in phenolic compounds. Regardless of the several factors that may affect propolis and pollen antioxidant activity, these products have been shown to possess, either through the use of in vitro or in vivo models, important features concerning the modulation of cellular oxidative stress caused by environmental factors (e.g. UV-light), metals, pesticides and other xenobiotics. This modulatory effect focus not only on the capture of radicals that these elements might eventually generate, but also by the activation of cellular antioxidant mechanisms such as enzymatic antioxidants or by modifying gene expression patterns. Although the mechanisms behind these responses are not fully known, it has been showed that caffeic acid phenethyl ester, pinocembrin and chrisin are some of the compounds responsible for some of these responses. Taking into account the gathered results, propolis and pollen can be viewed as potential agents in the re-stabilization of cellular oxidative imbalance and in the prevention of oxidative stress related diseases.

Biochemical mechanisms involved in pulmonary hypo-alveolarization induced by peroxides contaminating parenteral nutrition in newborn guinea pig

La dysplasie broncho-pulmonaire (DBP), caractérisée par un défaut de l’alvéolarisation, est une complication pathologique associée à un stress oxydant chez le nouveau-né prématuré. La DBP est présente chez près de 50 % des nouveau-nés de moins de 29 semaines de gestation. La nutrition parentérale (NP) que ces nouveau-nés reçoivent pour cause d’immaturité gastro-intestinale est une source importante de stress oxydant. En effet, leur NP est contaminée par des peroxydes, dont l’ascorbylperoxyde qui est une forme peroxydée du déshydroascorbate. La génération des peroxydes est catalysée par la lumière ambiante. La photoprotection de la NP, quoique difficile d’application en clinique, est associée à une diminution de l’incidence de la DBP chez les enfants prématurés. Chez l’animal nouveau-né, la photoprotection de la NP est associée à un meilleur développement alvéolaire. Ainsi, nous émettons l’hypothèse que l’ascorbylperoxide infusé avec la NP cause la perte d’alvéoles suite à une apoptose exagérée induite par l’oxydation du potentiel redox du glutathion. Cette oxydation du potentiel redox serait occasionnée par l’inhibition de la transformation hépatique de la méthionine en cystéine, menant à une diminution de la synthèse de glutathion au foie et dans les tissus tels que les poumons. La confirmation de cette hypothèse suggérera qu’un ajout de glutathion dans la NP permettra une meilleure détoxification de l’ascorbylperoxide par l’action de la glutathion peroxydase, et préviendra l’oxydation du potentiel redox et ainsi, la perte d'alvéoles par apoptose. Objectifs : Le but de mon projet de recherche est de comprendre les mécanismes biochimiques liant la NP et le développement de la DBP chez le nouveau-né prématuré et de proposer une alternative nutritionnelle prévenant le développement de cette complication fréquemment observée dans cette population. Les objectifs spécifiques sont : 1) d’évaluer l’impact, au poumon, de l’infusion de l’ascorbylperoxyde sur l’axe métabolique potentiel redox du glutathion - apoptose - le développement alvéolaire; 2) d’étudier l’impact de l’ascorbylperoxyde et du potentiel redox sur l’activité hépatique de la méthionine adénosyltransférase (MAT), première enzyme de la cascade métabolique transformant la méthionine en cystéine; et 3) de tenter de prévenir l’impact négatif de la NP ou de l’infusion d’ascorbylperoxyde sur le poumon en améliorant le statut en glutathion. Méthodes: Par un cathéter fixé dans la jugulaire, des cochons d’Inde de trois jours de vie (n = 8 par groupe) ont reçu en continu durant 4 jours une NP ou une solution de base (dextrose + NaCl) enrichie des différentes molécules à l’essai. Le premier objectif a été atteint en enrichissant la solution de base en ascorbylperoxyde à 0, 20, 60 et 180 μM. Ces solutions contenaient ou non 350 μM H2O2 pour se rapprocher des conditions cliniques. Le second objectif a été atteint en investiguant les mécanismes d’inhibition de la MAT dans des animaux infusés ou non avec des solutions contenant la solution de base, des peroxydes, du glutathion et la NP (dextrose + acides aminés + multivitamines + lipides). Le troisième objectif a été atteint en ajoutant ou non à une solution d’ascorbylperoxide ou à la NP 10 μM de glutathion (GSSG), afin d’obtenir une concentration plasmatique normale de glutathion. Après 4 jours, les poumons étaient prélevés et traités pour la détermination de GSH et GSSG par électrophorèse capillaire, le potentiel redox était calculé selon l'équation de Nernst et le niveau de caspase-3 actif (marqueur d’apoptose) par Western blot et l’index d’alvéolarisation quantifié par le nombre d’interceptes entre des structures histologiques et une droite calibrée. Les données étaient comparées par ANOVA, les effets étaient considérés comme significatifs si le p était inférieur à 0,05. Résultats: L’infusion de l’ascorbylperoxyde, indépendamment du H2O2, a induit une hypoalvéolarisation, une activation de la caspase-3 et une oxydation du potentiel redox de manière dose-dépendante. Ces effets ont été empêchés par l’ajout de GSSG à la NP ou à la solution d’ascorbylperoxyde (180 M). L’ascorbylperoxyde et le H2O2 ont inhibé l’activité de MAT tandis qu’elle était linéairement modulée par la valeur du potentiel redox hépatique. Conclusion : Nos résultats suggèrent que l’ascorbylperoxyde est l’agent actif de la NP conduisant au développement de la DBP. Ainsi la correction des bas niveaux de glutathion induits par les peroxydes de la NP favorise la détoxification des peroxydes et la correction du potentiel redox pulmonaire ; ce qui a protégé les poumons des effets délétères de la NP en outrepassant l’inhibition de la MAT hépatique. Nos résultats sont d'une grande importance car ils donnent de l'espoir pour une prévention possible de la DBP.

The effects of pre-weaning undernutrition on the expression levels of free radical deactivating enzymes in the mouse brain

A mild degree of undernutrition brought about by restricting the amount of food in the diet is known to alter the life span of an animal. It has been hypothesised that this may be related to the effects of undernutrition on an animals anti-oxidant defense system. We have therefore, used real-time PCR (rt-PCR) techniques to determine the levels of mRNA expression for manganese superoxide dismutase (MnSOD), copper/zinc superoxide dismutase (Cu/ZnSOD), glutathione peroxidase 1 (GPx 1) and catalase in the brains of Quackenbush mice undernourished from conception until 21-post-natal days of age. It was found that 21- and 61-day-old undernourished mice had a deficit in the expression of Cu/ZnSOD in both the cerebellum and forebrain regions compared to age-matched controls. The expression of MnSOD was found to be greater in the cerebellum, but not the forebrain region, of 21-day-old undernourished mice. There were no significant differences in the expression of GPx 1 and catalase between control and undernourished or previously undernourished mice. Our results confirm that undernutrition during the early life of a mouse may disrupt some of the enzymes involved in the anti-oxidant defense systems.

Cyclosporine A-induced changes to erythrocyte redox balance is time course-dependent

Cyclosporine A-treated transplant recipients develop pronounced cardiovascular disease and have increased oxidative stress and altered antioxidant capacity in erythrocytes and plasma. These experiments investigated the time-course of cyclosporine A-induced changes to redox balance in plasma and erythrocytes. Rats were randomly assigned to either a control or cyclosporine A-treated group. Treatment animals received 25 mg/kg of cyclosporine A via intraperitoneal injection for either 7 days or a single dose. Control rats were injected with the same volume of the vehicle. Three hours after the final injections, plasma was analysed for total antioxidant status, a-tocopherol, malondialdehyde, and creatinine. Erythrocytes were analysed for reduced glutathione (GSH), alpha-tocopherol, methaemoglobin, malondialdehyde, and the activities of superoxide dismutase, catalase, GSH peroxidase, and glucose-6-phosphate dehydrogenase (G6PD). Cyclosporine A administration for 7 days resulted in a significant increase (P < 0.05) in plasma malondialdehyde, methaemoglobin, and superoxide dismutase and catalase activities. There was a significant decrease (P < 0.05) in erythrocyte GSH concentration and G6PD activity in cyclosporine A animals. There were no significant differences (P > 0.05) between groups following a single dose of cyclosporine A in any of the measures. In summary, cyclosporine A alters erythrocyte redox balance after 7 days administration, but not after a single dose.

Cyclosporine A induced changes to plasma and erythrocyte antioxidant defences

Organ transplant recipients develop pronounced cardiovascular disease, and decreased antioxidant capacity in plasma and erythrocytes is associated with the pathogenesis of this disease. These experiments tested the hypothesis that the immunosuppressant cyclosporine A (CsA) alters erythrocyte redox balance and reduces plasma antioxidant capacity. Female Sprague-Dawley rats were randomly assigned to a control or CsA treated group. Treatment animals received 25 mg/kg/day of CsA via intraperitoneal injection for 18 days. Control rats were injected with the same volume of the vehicle. Three hours after the final CsA injection, rats were exsanguinated and plasma analysed for total antioxidant status (TAS), alpha-tocopherol, malondialdehyde (MDA), and creatinine. Erythrocytes were analysed for superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX) and glucose-6-phosphate dehydrogenase (G6PD) activities, alpha-tocopherol, and MDA. CsA administration resulted in a significant (P < 0.05) decrease in plasma TAS and significant increases (P < 0.05) in plasma creatinine and MDA. Erythrocyte CAT was significantly (P < 0.05) increased in CsA treated rats compared to controls. There were no significant differences (P > 0.05) in erythrocyte SOD, GPX, G6PD, alpha-tocopherol or MDA between groups. In summary, CsA alters erythrocyte antioxidant defence and decreases plasma total antioxidant capacity.

alpha-tocopherol and alpha-lipoic acid enhance the erythrocyte antioxidant defence in cyclosporine A-treated rats

The aim of this study was to determine the effects of dietary antioxidant supplementation with alpha-tocopherol and alpha-lipoic acid on cyclosporine A (cyclosporine)-induced alterations to erythrocyte and plasma redox balance. Rats were randomly assigned to either control, antioxidant (alpha-tocopherol 1000 IU/kg diet and alpha-lipoic acid 1.6 g/kg diet), cyclosporine (25 mg/kg/day), or cyclosporine + antioxidant treatments. Cyclosporine was administered for 7 days after an 8 week feeding period. Plasma was analysed for alpha-tocopherol, total antioxidant capacity, malondialdehyde, and creatinine. Erythrocytes were analysed for glutathione, methaemoglobin, superoxide dismutase, catalase, glutathione peroxidase, glucose-6-phosphate dehydrogenase, alpha-tocopherol and malondialdehye. Cyclosporine administration caused a significant decrease in superoxide dismutase activity (P < 0.05 control versus cyclosporine) and this was improved by antioxidant supplementation (P < 0.05 cyclosporine versus cyclosporine + antioxidant; P < 0.05 control versus cyclosporine + antioxidant). Animals receiving cyclosporine and antioxidants showed significantly increased (P < 0.05) catalase activity compared to both groups not receiving cyclosporine. Cyclosporine administration induced significant increases in plasma malondialdehyde and creatinine concentration (P < 0.05 control versus cyclosporine). Antioxidant supplementation prevented the cyclosporine induced increase in plasma creatinine (P < 0.05 cyclosporine versus cyclosporine + antioxidant; P > 0.05 control versus cyclosporine + antioxidant), however, supplementation did not alter the cyclosporine induced increase in plasma malondialdehyde concentration (P > 0.05 cyclosporine versus cyclosporine + antioxidant). Antioxidant supplementation resulted in significant increases (P < 0.05) in plasma and erythrocyte alpha-tocopherol in both of the supplemented groups compared to non-supplemented groups. In conclusion, dietary supplementation with alpha-tocopherol and alpha-lipoic acid enhanced the erythrocyte antioxidant defence and reduced nephrotoxicity in cyclosporine treated animals.

Antioxidant supplementation enhances erythrocyte antioxidant status and attenuates cyclosporine-induced vascular dysfunction

The aim of this study was to determine the effects of dietary antioxidant supplementation with a-tocopherol and a-lipoic acid on cyclosporine-induced alterations to erythrocyte and plasma redox balance, and cyclosporine-induced endothelial and smooth muscle dysfunction. Rats were randomly assigned to either control, antioxidant, cyclosporine or cyclosporine + antioxidant treatments. Cyclosporine A was administered for 10 days after an 8-week feeding period. Plasma was analyzed for alpha-tocopherol, total antioxidant capacity, malondialdehyde and creatinine. Erythrocytes were analyzed for glutathione, methemoglobin, superoxide dismutase, catalase, glutathione peroxidase, glucose-6-phosphate dehydrogenase, alpha-tocopherol and malondialdehye. Vascular endothelial and smooth muscle function was determined in vitro. Antioxidant supplementation resulted in significant increases in erythrocyte a-tocopherol concentration and glutathione peroxidase activity in both of the antioxidant-supplemented groups. Cyclosporine administration caused significant decreases in glutathione concentration, methemoglobin concentration and superoxide dismutase activity. Antioxidant supplementation attenuated the cyclosporine-induced decrease in superoxide dismutase activity. Cyclosporine therapy impaired both endothelium-independent and -dependent relaxation of the thoracic aorta, and this was attenuated by antioxidant supplementation. In summary, dietary supplementation with alpha-tocopherol and alpha-lipoic acid attenuated the cyclosporine-induced decrease in erythrocyte superoxide dismutase activity and attenuated cyclosporine-induced vascular dysfunction.

Defenses against oxidative stress in Neisseria gonorrhoeae: A system tailored for a challenging environment

Neisseria gonorrhoeae is a host-adapted pathogen that colonizes primarily the human genitourinary tract. This bacterium encounters reactive oxygen and reactive nitrogen species as a consequence of localized inflammatory responses in the urethra of males and endocervix of females and also of the activity of commensal lactobacilli in the vaginal flora. This review describes recent advances in the understanding of defense systems against oxidative stress in N. gonorrhoeae and shows that while some of its defenses have similarities to the paradigm established with Escherichia coli, there are also some key differences. These differences include the presence of a defense system against superoxide based on manganese ions and a glutathione-dependent system for defense against nitric oxide which is under the control of a novel MerR-like transcriptional regulator. An understanding of the defenses against oxidative stress in N. gonorrhoeae and their regulation may provide new insights into the ways in which this bacterium survives challenges from polymorphonuclear leukocytes and urogenital epithelial cells.