Role of intracellular cAMP in differentiation-coupled induction of resistance against oxidative damage in Leishmania donovani

Even though the human parasite Leishmania donovani encounters tremendous oxidative burst during macrophage invasion, a set of parasites survives and proliferates intracellularly, leading to transformation from promastigote to amastigote form and disease manifestation. The striking shifts in temperature (from 22 degrees C in the insect gut to 37 degrees C in the mammalian host) and pH (7.2 in the insect gut to 5.5 in the parasitophorous vacuole of macrophages) are the key environmental triggers for differentiation as these cause an arrest in the G1 stage of the cell cycle and initiate transformation. Using an established in vitro culture and differentiation system our study demonstrates that the differentiation-triggering environment induces resistance to oxidative damage and consequently enhances infectivity. Differentiation conditions caused a three- to fourfold elevation in cAMP level as well as cAMP-dependent protein kinase activity. Similar to stress exposure, positive modulation of intracellular cAMP resulted in blockage of cell cycle progression and induction of resistance against oxidative damage. Resistance against pro-oxidants from either stress or cAMP may be associated with upregulation of the expression of three major antioxidant genes, peroxidoxin 1, trypanothione reductase, and superoxide dismutase A. Positive modulation of the intracellular cAMP response enables cells to resist the cytotoxic effects of pro-oxidants. In contrast, downregulation of intracellular cAMP by overexpression of cAMP phosphodiesterase A resulted in a decrease in resistance against oxidative damage and reduced infectivity toward activated macrophages. This study for the first time reveals the importance of cAMP response in the life cycle and infectivity of the Leishmania parasite.     

Glutathione peroxidase-1 gene knockout on body antioxidant defense in mice

To determine the in vivo role of cellular glutathione peroxidase (E.C.1.11.1.9, GPX1), we challenged the GPX1 knockout [GPX1(-/-)], the GPX1 overexpressing [GPX1(+)], and their respective wild-type (WT) mice of different Se and vitamin E status with acute oxidative stress. After these mice were injected with pro-oxidants paraquat or diquat at 12 to 125 mg/kg of body weight, their survival rate and time were a function of their GPX1 activity levels. The GPX1 protection was associated with attenuation of NADPH and NADH oxidation, protein carbonyl and F(2)-isoprostanes formation, and alanine transaminase release in various tissues, and was irreplaceable by high levels of dietary vitamin E or other selenoproteins. The GPX1 expression was also protective against moderate oxidative stress induced by low levels of paraquat or diquat, particularly in the Se-deficient mice. Alteration of GPX1 expression showed no impact on the expression of other selenoproteins and antioxidant enzymes in unstressed mice. Total Se content in liver of the Se-adequate GPX1(-/-) mice was reduced by 60% the WT controls. In conclusion, normal expression of GPX1 is essential and overexpression of GPX1 is beneficial to protect mice against acute oxidative stress.     

Induction of Haem Oxygenase as a Defence Against Oxidative Stress

Cells respond to metabolic perturbations by producing specific stress proteins. Exposure of mammalian cells to various forms of oxidative stress induces haem oxygenase, the rate-limiting enzyme in haem degradation. This response is proposed to represent an antioxidant defence operating at two different stages simultaneously. It (i) decreases the levels of the potential pro-oxidants haem and haem proteins such as cytochrome P-450 and protoporphyrinogen oxidase, and (ii) increases the tissue concentrations of antio-xidatively active bile pigments.     

Protection against oxidative stress in liver of four different vertebrates.

The possible relation between respiratory capacity and antioxidant capacity and susceptibility to oxidative stress of the liver has been investigated in Rattus norvegicus, Gallus gallus domesticus, Lacerta s. sicula, and Rana esculenta. Accordingly, we measured oxygen consumption and cytochrome oxidase activity, glutathione peroxidase and glutathione reductase activity and overall antioxidant capacity, and lipid peroxidation and response to oxidative stress in vitro in liver. The order of liver oxygen consumption and cytochrome oxidase activity among the different species was rat > chick > lizard > frog. The antioxidant defenses supplied by the combined action of glutathione peroxidase and glutathione reductase were not adapted to the respiratory capacities. In particular, there was no correlation either between the activities of two enzymes or between their activities and oxygen consumption. In contrast, the overall antioxidant capacity of the liver appeared to be related to its oxidative capacity, and the malondialdehyde formation, an indirect measure of lipid peroxidation, was inversely related to antioxidant capacity. The response to oxidative stress in vitro indicated that the liver susceptibility to oxidative challenge is higher in ectothermic than in endothermic species. Such higher susceptibility appeared to depend on both lower antioxidant capacity and higher levels of free radical producing species. This finding is apparently in contrast with a higher content of cytochromes in endotherms, which are able to determine both respiratory characteristics and sensitivity to pro-oxidants. However, it could indicate the existence of species-related differences in the tissue content of either preventive antioxidants or hemoproteins able to trap the radicals produced at their active center. J. Exp. Zool. 284:610-616, 1999.     

Evolution of liver antioxidant status and iron implication during the development of deoxycorticosterone-saline hypertension in rats

Hypertension is known to be associated with an oxidative stress resulting from an imbalance of antioxidant defense mechanisms in various tissues. The purpose of this study was to investigate the relationship between the increase of arterial blood pressure, measured during the gradual development of experimental hypertension in deoxycorticosterone (DOCA)-salt-treated rats, and an early imbalance of liver antioxidant status. The levels of liver oxidant/antioxidant markers and iron were studied during the induction of hypertension in 3-, 6-, and 8-wk DOCA-salt-treated Sprague-Dawley rats. Hepatic antioxidant defenses were decreased as early as 3 wk of hypertensive treatment: the decrease of peroxidase-reductase-transferase and catalase activities was associated with a significant increase of thiobarbituric acid reactive substances (TBARS) levels. Liver oxidative stress increased until 6 wk, and remained stable at 8 wk of DOCA-salt treatment. Concurrently, liver iron levels were increased at 6 wk and returned to normal values after 8 wk of hypertensive treatment. Iron seems to be an inductor of liver oxidative stress and responsible for the persistent oxidative stress, most likely through secondary free-radical release. Thus, our data (1) confirm that hypertension in DOCA-salt-treated rats might be a free-radical-dependent disease where hepatic oxidant/antioxidant imbalance is obviously involved from the beginning of blood pressure elevation and (2) suggest that the use of suitable iron chelators might reverse liver oxidative stress associated with the increase of blood pressure.     

Effects of corticosteroids on oxidative damage and circulating carotenoids in captive adult kestrels (Falco tinnunculus)

Birds control body homeostasis through the secretion of corticosterone. This hormone is the end-product of the hypothalamic-pituitary-adrenal (HPA) axis response to stressors. High levels of corticosterone may be associated with low individual fitness and may affect balance between pro-oxidants and antioxidants. Given these points, chronic stress modulated by hormones could undermine individual fitness by increasing oxidative tissue damage. In this study, we administered corticosteroids by diet (20 mg/kg of diet) to captive adult kestrels (Falco tinnunculus) over a 14-day period to evaluate the effects of a simulated chronic stress modulated by corticosteroids. We found that dietary administration of corticosterone caused a 32% increase of reactive oxygen metabolites, but did not impair total serum antioxidant capacity, serum carotenoids or body mass. Oxidative stress had a 64% increase in treated birds compared to 30% in controls. The two groups did not differ in the total serum antioxidant capacity, which showed a significant decrease over the study period. In contrast, circulating carotenoids and body mass increased in both groups. These results suggest that stress hormones, such as corticosterone, may also act as modulators of oxidative stress in birds.     

Experimental schistosomal hepatitis: protective effect of coenzyme-Q10 against the state of oxidative stress

Schistosoma mansoni (S. mansoni) eggs trapped in the host liver elicit a chain of oxidative processes that may be, at least in part, responsible for the pathology and progression of fibrosis associated with schistosomal hepatitis. This study was designed to assess the protective effect of the antioxidant coenzyme-Q10 (Co-Q10) against experimental S. mansoni-induced oxidative stress in the liver, and its potential role as an adjuvant to praziquantel (PZQ) therapy. The oxidative stress and overall liver function were improved under Co-Q10 therapy as evidenced by significant reduction in oxidative stress markers and preservation of antioxidant factors. Liver fibrosis was also reduced with a positive impact on liver function. Moreover, addition of Co-Q10 to PZQ therapy caused: significant reduction of liver egg load, significant improvement of the redox status, and lastly decreased liver fibrosis.     

Different mechanisms of c-Jun NH(2)-terminal kinase-1 (JNK1) activation by ultraviolet-B radiation and by oxidative stressors.

Irradiation of mammalian cells with ultraviolet-B radiation (UV-B) triggers the activation of a group of stress-activated protein kinases known as c-Jun NH(2)-terminal kinases (JNKs). UV-B activates JNKs via UV-B-induced ribotoxic stress. Because oxidative stress also activates JNKs, we have addressed the question of whether the ribotoxic and the oxidative stress responses are mechanistically similar. The pro-oxidants sodium arsenite, cadmium chloride, and hydrogen peroxide activated JNK1 with slow kinetics, whereas UV-B potentiated the activity of JNK1 rapidly. N-acetyl cysteine (a scavenger of reactive oxygen intermediates) abolished the ability of all oxidative stressors tested to activate JNK1, but failed to affect the activation of JNK1 by UV-B or by another ribotoxic stressor, the antibiotic anisomycin. In contrast, emetine, an inhibitor of the ribotoxic stress response, was unable to inhibit the activation of JNK1 by oxidative stressors. Although UV-A and long wavelength UV-B are the spectral components of the ultraviolet solar radiation that cause significant oxidative damage to macromolecules, the use of a filter to eliminate the radiation output from wavelengths below 310 nm abolished the activation of JNK1 by UV. Our results are consistent with the notion that UV-B and oxidative stressors trigger the activation of JNK1 through different signal transduction pathways.     

Augmentation of Aluminum-Induced Oxidative Stress in Rat Cerebrum by Presence of Pro-oxidant (Graded Doses of Ethanol) Exposure

Both aluminum and ethanol are pro-oxidants and neurotoxic. Considering the possibilities of co-exposure and sharing mechanisms of producing neurotoxicity, the present study was planned to identify the level of aluminum-induced oxidative stress in altered pro-oxidant (ethanol exposure) status of cerebrum. Male rats were coexposed to aluminum and ethanol for 4 weeks. After the exposure period, cerebral levels of protein, reduced glutathione (GSH), lipid peroxidation (TBARS) were measured. Activities of catalase, superoxide dismutase (SOD), glutathione reductase (GR) and glutathione perioxidase (GPx) of cerebrum were estimated. In most of the cases significant correlations were observed between the alterations and graded ethanol doses, suggesting a dose-dependency in pushing the oxidant equilibrium toward pro-oxidants. Aluminum is found to influence significantly all the studied parameters of oxidative stress. Likewise, ethanol also influenced these parameters significantly, except GR, while the interaction between ethanol and aluminum could significantly influence only the GSH content and GR activity of cerebrum. Present study demonstrate that coexposure of aluminum with pro-oxidant might favor development of aluminum-induced oxidative stress in cerebrum. This observation might be helpful in understanding of mechanism of neurodegenerative disorders and ameliorate them.     

Comparative Study on the Inhibitory Effect of Caffeic and Chlorogenic Acids on Key Enzymes Linked to Alzheimer’s Disease and Some Pro-oxidant Induced Oxidative Stress in Rats’ Brain-In Vitro

This study sought to investigate and compare the interaction of caffeic acid and chlorogenic acid on acetylcholinesterase (AChE) and butyrylcholinesterase (BChE), and some pro-oxidants (FeSO₄, sodium nitroprusside and quinolinic acid) induced oxidative stress in rat brain in vitro. The result revealed that caffeic acid and chlorogenic acid inhibited AChE and BChE activities in dose-dependent manner; however, caffeic acid had a higher inhibitory effect on AChE and BChE activities than chlorogenic acid. Combination of the phenolic acids inhibited AChE and BChE activities antagonistically. Furthermore, pro-oxidants such as, FeSO₄, sodium nitroprusside and quinolinic acid caused increase in the malondialdehyde (MDA) contents of the brain which was significantly decreased dose-dependently by the phenolic acids. Inhibition of AChE and BChE activities slows down acetylcholine and butyrylcholine breakdown in the brain. Therefore, one possible mechanism through which the phenolic acids exert their neuroprotective properties is by inhibiting AChE and BChE activities as well as preventing oxidative stress-induced neurodegeneration. However, esterification of caffeic acid with quinic acid producing chlorogenic acid affects these neuroprotective properties.     

Alteration of gene expression profile in Niemann-Pick type C mice correlates with tissue damage and oxidative stress

Background

Niemann-Pick type C disease (NPC) is a neurovisceral lipid storage disorder mainly characterized by unesterified cholesterol accumulation in lysosomal/late endosomal compartments, although there is also an important storage for several other kind of lipids. The main tissues affected by the disease are the liver and the cerebellum. Oxidative stress has been described in various NPC cells and tissues, such as liver and cerebellum. Although considerable alterations occur in the liver, the pathological mechanisms involved in hepatocyte damage and death have not been clearly defined. Here, we assessed hepatic tissue integrity, biochemical and oxidative stress parameters of wild-type control (Npc1 ^+/+; WT) and homozygous-mutant (Npc1 ^−/−; NPC) mice. In addition, the mRNA abundance of genes encoding proteins associated with oxidative stress, copper metabolism, fibrosis, inflammation and cholesterol metabolism were analyzed in livers and cerebella of WT and NPC mice.

Methodology/Principal Findings

We analyzed various oxidative stress parameters in the liver and hepatic and cerebellum gene expression in 7-week-old NPC1-deficient mice compared with control animals. We found signs of inflammation and fibrosis in NPC livers upon histological examination. These signs were correlated with increased levels of carbonylated proteins, diminished total glutathione content and significantly increased total copper levels in liver tissue. Finally, we analyzed liver and cerebellum gene expression patterns by qPCR and microarray assays. We found a correlation between fibrotic tissue and differential expression of hepatic as well as cerebellar genes associated with oxidative stress, fibrosis and inflammation in NPC mice.

Conclusions/Significance

In NPC mice, liver disease is characterized by an increase in fibrosis and in markers associated with oxidative stress. NPC is also correlated with altered gene expression, mainly of genes involved in oxidative stress and fibrosis. These findings correlate with similar parameters in cerebellum, as has been previously reported in the NPC mice model.     

Molecular mechanisms of oxidative stress-related neonatal jaundice

Oxidative stress is a pathological condition characterized by an overload of oxidant products, named free radicals, which are not well counteracted by antioxidant systems. Free radicals induce oxidative damage to many body organs and systems. In neonatal red blood cells, free-radical mediated-oxidative stress leads to eryptosis, a suicidal death process of erythrocytes consequent to alteration of cell integrity. Neonatal red blood cells are targets and at the same time generators of free radicals through the Fenton and Haber-Weiss reactions. Enhanced eryptosis in case of oxidative stress damage may cause anemia if the increased loss of erythrocytes is not enough compensated by enhanced new erythrocytes synthesis. The oxidative disruption of the red cells may cause unconjugated idiopathic hyperbilirubinemia in neonates. High levels of bilirubin are recognized to be dangerous for the central nervous system in newborns, however, many studies have highlighted the antioxidant function of bilirubin. Recently, it has been suggested that physiologic concentration of bilirubin correlates with higher antioxidant status while high pathological bilirubin levels are associated with pro-oxidants effects. The aim of this educational review is to provide an updated understanding of the molecular mechanisms underlying erythrocyte oxidant injury and its reversal in neonatal idiopathic hyperbilirubinemia.     

The role of oxidative stress in hemolytic anemia

The oxidative status of cells is determined by the balance between pro-oxidants and antioxidants. Pro-oxidants, referred to as reactive oxygen species (ROS), are classified into radicals and nonradicals. The radicals are highly reactive due to their tendency to accept or donate an electron and attain stability. When cells experience oxidative stress, ROS, which are generated in excess, may oxidize proteins, lipids and DNA - leading to cell death and organ damage. Oxidative stress is believed to aggravate the symptoms of many diseases, including hemolytic anemias. Oxidative stress was found in the beta-hemoglobinopathies (sickle cell anemia and thalassemia), glucose-6-phosphate dehydrogenase deficiency, hereditary spherocytosis, congenital dyserythropoietic anaemias and Paroxysmal Nocturnal Hemoglobinuria. Although oxidative stress is not the primary etiology of these diseases, oxidative damage to their erythroid cells plays a crucial role in hemolysis due to ineffective erythropoiesis in the bone marrow and short survival of red blood cells (RBC) in the circulation. Moreover, platelets and polymorphonuclear (PMN) white cells are also exposed to oxidative stress. As a result some patients develop thromboembolic phenomena and recurrent bacterial infections in addition to the chronic anemia. In this review we describe the role of oxidative stress and the potential therapeutic potential of anti-oxidants in various hemolytic anemias.     

In vivo total antioxidant capacity: comparison of different analytical methods

Several methods have been developed to measure the total antioxidant capacity of a biological sample. The use of peroxyl or hydroxyl radicals as pro-oxidants in the oxygen radical absorbance capacity (ORAC) assay makes it different and unique from the assays that involve oxidants that are not necessarily pro-oxidants. An improvement in quantitation is achieved in the ORAC assay by taking the reaction between substrate and free radicals to completion and using an area-under-curve technique for quantitation compared to the assays that measure a lag phase. The interpretation of the changes in plasma or serum antioxidant capacity becomes complicated by the different methods used in detecting these changes. The interpretation also depends upon the conditions under which the antioxidant capacity is determined because the measurement reflects outcomes in a dynamic system. An increased antioxidant capacity in plasma or serum may not necessarily be a desirable condition if it reflects a response to increased oxidative stress. Similarly, a decrease in plasma or serum antioxidant capacity may not necessarily be an undesirable condition if the measurement reflects decreased production of reactive species. Because of these complications, no single measurement of antioxidant status is going to be sufficient, but a "battery" of measurements, many of which will be described in Forum articles, will be necessary to adequately assess oxidative stress in biological systems.     

Aging alters the functional expression of enzymatic and non-enzymatic anti-oxidant defense systems in testicular rat Leydig cells

In aged rats, trophic hormone-stimulated testosterone secretion by isolated Leydig cells is greatly reduced. The current studies were initiated to establish a functional link between excess oxidative stress and the age-related decline in steroidogenesis. Highly purified Leydig cell preparations obtained from 5-month (young mature) and 24-month (old) Sprague-Dawley rats were employed to measure and compare levels of lipid peroxidation, non-enzymatic (alpha-tocopherol, ascorbic acid, and reduced/oxidized glutathione) and enzymatic (Cu, Zn-superoxide dismutase, Cu, Zn-SOD; Mn-superoxide dismutase, Mn-SOD; glutathione peroxidase-1, GPX-1, and catalase, CAT) anti-oxidants. The extent of lipid peroxidation (oxidative damage) in isolated membrane fractions was quantified by measuring the content of thiobarbituric acid-reactive substances (TBARS) under basal conditions, or in the presence of non-enzymatic or enzymatic pro-oxidants. Membrane preparations isolated from Leydig cells from old rats exhibited two- to three-fold enhancement of basal TBARS formation. However, aging had no significant effect on TBARS formation in response to either non-enzymatic or enzymatic pro-oxidants. Among the non-enzymatic anti-oxidants, the levels of reduced glutathione were drastically reduced during aging, while levels of alpha-tocopherol and ascorbic acid remained unchanged. Both steady-state mRNA levels and catalytic activities of Cu, Zn-SOD, Mn-SOD, and GPX-1 were also significantly lower in Leydig cells from 24-month-old rats as compared with 5-month-old control rats. In contrast, neither mRNA levels nor enzyme activity of catalase was sensitive to aging. From these data we conclude that aging is accompanied by reduced expression of key enzymatic and non-enzymatic anti-oxidants in Leydig cells leading to excessive oxidative stress and enhanced oxidative damage (lipid peroxidation). It is postulated that such excessive oxidative insult may contribute to the observed age-related decline in testosterone secretion by testicular Leydig cells.     

Oxidative stress index (OSi) as a new tool to assess redox status in dairy cattle during the transition period

Oxidative stress (OS) plays a key role in the initiation or progression of numerous diseases, and dairy cows undergo OS at the transition period. However, discrepancies between methodologies make it difficult to make comparisons between studies, and therefore research on this topic may not be implemented in farms. This study aims to test under field conditions the use of an oxidative stress index (OSi) as a combined measurement through a ratio between pro-oxidants and antioxidants throughout the transition period in dairy farms. Serum samples of high-yielding dairy cows were taken, and markers of oxidative damage and antioxidant capacity were measured in four different production stages: (i) late lactation (LL; −2 to −1 months); (ii) prepartum (PrP; −1 month until parturition); (iii) postpartum (PsP; delivery to +1 month); and (iv) peak of lactation (PkL; +1 to +2.5 months). Values were compared between production stages and against a metabolic baseline status (CTR, 4th to 5th month of gestation). To the best of our knowledge, this is the first report in the literature that discusses the values of these oxidative stress biomarkers (and the OS index) for cows with low metabolic demands, as to date most research in this area has focused on the transition period. With the joint evaluation through the OSi, differences were found that were not present with the separate evaluation of pro-oxidants or antioxidants, thus supporting our hypothesis that the OSi indicates more accurately the oxidative status of the animals. It was also confirmed that dairy cows undergo OS after parturition, and that antioxidant supplementation from 1 month before parturition until the peak of lactation may be needed to reduce the risk of OS.     

Decreased nucleotide excision repair in steatotic livers associates with myeloperoxidase-immunoreactivity

Chronic inflammation is characterized by the influx of neutrophils and is associated with an increased production of reactive oxygen species that can damage DNA. Oxidative DNA damage is generally thought to be involved in the increased risk of cancer in inflamed tissues. We previously demonstrated that activated neutrophil mediated oxidative stress results in a reduction in nucleotide excision repair (NER) capacity, which could further enhance mutagenesis. Inflammation and oxidative stress are critical factors in the progression of nonalcoholic fatty liver disease that is linked with enhanced liver cancer risk. In this report, we therefore evaluated the role of neutrophils and the associated oxidative stress in damage recognition and DNA repair in steatotic livers of 35 severely obese subjects with either nonalcoholic steatohepatitis (NASH) (n=17) or steatosis alone (n=18). The neutrophilic influx in liver was assessed by myeloperoxidase (MPO) staining and the amount of oxidative DNA damage by measuring M(1)dG adducts. No differences in M(1)dG adduct levels were observed between patients with or without NASH and also not between individuals with high or low MPO immunoreactivity. However, we found that high expression of MPO in the liver, irrespective of disease status, reduced the damage recognition capacity as determined by staining for histone 2AX phosphorylation (γH2AX). This reduction in γH2AX formation in individuals with high MPO immunoreactivity was paralleled by a significant decrease in NER capacity as assessed by a functional repair assay, and was not related to cell proliferation. Thus, the observed reduction in NER capacity upon hepatic inflammation is associated with and may be a consequence of reduced damage recognition. These findings suggest a novel mechanism of liver cancer development in patients with nonalcoholic fatty liver disease.     

Oxidative stress mediates physiological costs of begging in magpie (Pica pica) nestlings

Background

Theoretical models predict that a cost is necessary to guarantee honesty in begging displays given by offspring to solicit food from their parents. There is evidence for begging costs in the form of a reduced growth rate and immunocompetence. Moreover, begging implies vigorous physical activity and attentiveness, which should increase metabolism and thus the releasing of pro-oxidant substances. Consequently, we predict that soliciting offspring incur a cost in terms of oxidative stress, and growth rate and immune response (processes that generate pro-oxidants substances) are reduced in order to maintain oxidative balance.

Methodology/Principal Findings

We test whether magpie (Pica pica) nestlings incur a cost in terms of oxidative stress when experimentally forced to beg intensively, and whether oxidative balance is maintained by reducing growth rate and immune response. Our results show that begging provokes oxidative stress, and that nestlings begging for longer bouts reduce growth and immune response, thereby maintaining their oxidative status.

Conclusions/Significance

These findings help explaining the physiological link between begging and its associated growth and immunocompetence costs, which seems to be mediated by oxidative stress. Our study is a unique example of the complex relationships between the intensity of a communicative display (begging), oxidative stress, and life-history traits directly linked to viability.