Iron-catalyzed Fenton Reaction Research Articles

Endogenous Iron(II) Self-Enriched Fenton Nanocatalyst via FTH1 Activity Inhibition and Iron(III) Reduction for Amplified Cancer Ferroptosis Therapy.

Due to the increased expression of iron storage proteins in cancer cells, utilizing the endogenous iron-catalyzed Fenton reaction for cancer ferroptosis therapy has recently emerged as a prominent research focus. However, endogenous iron primarily exists within ferroxidase FTH1 in the Fe (III)-bound state, hindering the effective catalysis of the Fenton reaction. Herein, an endogenous iron(II) self-enriched Fenton nanocatalyst (BAI@cLANCs) is fabricated by encapsulating the FTH1 inhibitor baicalin (BAI) in cross-linked lipoic acid nanocarriers (cLANCs) to amplify endogenous ferroptosis. Once internalized, BAI@cLANCs are disrupted by glutathione (GSH) in tumor cells to release BAI, which inhibits FTH1 activity and hinders Fe2+ oxidation. Meanwhile, cLANCs degrade into dihydrolipoic acid (DHLA), which reduces Fe3+ to Fe2+, synergically enriching endogenous Fe2+. Simultaneously, both BAI and DHLA stimulate H2O2 production and facilitate the Fenton reaction to produce abundant ·OH, thereby triggering lipid peroxidation and inducing tumor ferroptosis. Moreover, the reduction of Fe3+ to Fe2+ depletes GSH, facilitating ·OH production and inactivating glutathione peroxidase-4, ultimately amplifying tumor ferroptosis. Overall, this work highlights the potential of an endogenous iron(II) self-enriched Fenton nanocatalyst for cancer ferroptosis therapy, providing a paradigm for amplifying endogenous ferroptosis by inhibiting FTH1 activity and reducing iron(III) to enrich endogenous iron(II).

Hypoxia-responsive nanoreactors based on self-enhanced photodynamic sensitization and triggered ferroptosis for cancer synergistic therapy

BackgroundPhotodynamic therapy (PDT), a typical reactive oxygen species (ROS)-dependent treatment with high controllability, has emerged as an alternative cancer therapy modality but its therapeutic efficacy is still unsatisfactory due to the limited light penetration and constant oxygen consumption. With the development of another ROS-dependent paradigm ferroptosis, several efforts have been made to conquer the poor efficacy by combining these two approaches; however the biocompatibility, tumor-targeting capacity and clinical translation prospect of current studies still exist great concerns. Herein, a novel hypoxia-responsive nanoreactor BCFe@SRF with sorafenib (SRF) loaded inside, constructed by covalently connecting chlorin e6 conjugated bovine serum albumin (BSA-Ce6) and ferritin through azobenzene (Azo) linker, were prepared to offer unmatched opportunities for high-efficient PDT and ferroptosis synergistic therapy.ResultsThe designed BCFe@SRF exhibited appropriate size distribution, stable dispersity, excellent ROS generation property, controllable drug release capacity, tumor accumulation ability, and outstanding biocompatibility. Importantly, the BCFe@SRF could be degraded under hypoxia environment to release BSA-Ce6 for laser-triggered PDT, ferritin for iron-catalyzed Fenton reaction and SRF for tumor antioxidative defense disruption. Meanwhile, besides PDT effects, it was found that BCFe@SRF mediated treatment upon laser irradiation in hypoxic environment not only could accelerate lipid peroxidation (LPO) generation but also could deplete intracellular glutathione (GSH) and decrease glutathione peroxidase (GPX4) expression, which was believed as three symbolic events during ferroptosis. All in all, the BCFe@SRF nanoreactor, employing multiple cascaded pathways to promote intracellular ROS accumulation, presented remarkably outstanding antitumor effects both in vitro and in vivo.ConclusionBCFe@SRF could serve as a promising candidate for synergistic PDT and ferroptosis therapy, which is applicable to boost oxidative damage within tumor site and will be informative to future design of ROS-dependent therapeutic nanoplatforms.Graphic abstract

Iron-rich air pollution nanoparticles: An unrecognised environmental risk factor for myocardial mitochondrial dysfunction and cardiac oxidative stress

Exposure to particulate air pollution is a major environmental risk factor for cardiovascular mortality and morbidity, on a global scale. Both acute and chronic cardiovascular impacts have so far been attributed to particulate-mediated oxidative stress in the lung and/or via ‘secondary’ pathways, including endothelial dysfunction, and inflammation. However, increasing evidence indicates the translocation of inhaled nanoparticles to major organs via the circulation. It is essential to identify the composition and intracellular targets of such particles, since these are likely to determine their toxicity and consequent health impacts. Of potential major concern is the abundant presence of iron-rich air pollution nanoparticles, emitted from a range of industry and traffic-related sources. Bioreactive iron can catalyse formation of damaging reactive oxygen species, leading to oxidative stress and cell damage or death.Here, we identify for the first time, in situ, that exogenous nanoparticles (~15–40 nm diameter) within myocardial mitochondria of young, highly-exposed subjects are dominantly iron-rich, and co-associated with other reactive metals including aluminium and titanium. These rounded, electrodense nanoparticles (up to ~ 10 x more abundant than in lower-pollution controls) are located within abnormal myocardial mitochondria (e.g. deformed cristae; ruptured membranes). Measurements of an oxidative stress marker, PrPC and an endoplasmic reticulum stress marker, GRP78, identify significant ventricular up-regulation in the highly-exposed vs lower-pollution controls. In shape/size/composition, the within-mitochondrial particles are indistinguishable from the iron-rich, combustion- and friction-derived nanoparticles prolific in roadside/urban environments, emitted from traffic/industrial sources. Incursion of myocardial mitochondria by inhaled iron-rich air pollution nanoparticles thus appears associated with mitochondrial dysfunction, and excess formation of reactive oxygen species through the iron-catalyzed Fenton reaction. Ventricular oxidative stress, as indicated by PrPC and GRP78 up-regulation, is evident even in children/young adults with minimal risk factors and no co-morbidities. These new findings indicate that myocardial iron overload resulting from inhalation of airborne, metal-rich nanoparticles is a plausible and modifiable environmental risk factor for cardiac oxidative stress and cardiovascular disease, on an international scale.

Assessment of meso scale zero valent iron catalyzed Fenton reaction in continuous-flow porous media for sustainable groundwater remediation

Removal of toxic organic compounds from the subsurface with meso zero-valent iron particles (mZVI) emplaced in porous media overcomes the concerns associated with in situ groundwater remediation technologies. The results of the continuous column experiments with mZVI is first of its kind and provide a sound basis on Fenton reaction mediated remediation of contaminated groundwater. Columns with different configurations varying in ZVI distribution and location of H2O2 were investigated for factors influencing sustainable phenol removal. The performance of columns were in the ascending order of C > A > B > D where columns A and B had full-length ZVI distribution, C and D had half-length ZVI distribution, with H2O2 injection at initial conditions in A and C and at intermittent points in B and D. Conditions maintained in column C resulted in 61–84% more interaction between Fe2+ ions and H2O2, promoted continuous corrosion, invigorated effective Fe2+-Fe3+ cycling, retained active iron surface area and circumvented precipitation and secondary sludge production. The breakthrough curves showed that mZVI particles extended the active corrosion stage by 5–8 times and resulted in 3–7 times increment in mg phenol removed/mg mZVI along with 80–99.8% utilization of mZVI. Additional sand-only columns proved that Fenton’s oxidation in in situ porous media can be improvised by 14–34% without incumbent addition of ZVI particles.

Assessment of the potential respiratory hazard of volcanic ash from future Icelandic eruptions: a study of archived basaltic to rhyolitic ash samples

BackgroundThe eruptions of Eyjafjallajökull (2010) and Grímsvötn (2011), Iceland, triggered immediate, international consideration of the respiratory health hazard of inhaling volcanic ash, and prompted the need to estimate the potential hazard posed by future eruptions of Iceland’s volcanoes to Icelandic and Northern European populations.MethodsA physicochemical characterization and toxicological assessment was conducted on a suite of archived ash samples spanning the spectrum of past eruptions (basaltic to rhyolitic magmatic composition) of Icelandic volcanoes following a protocol specifically designed by the International Volcanic Health Hazard Network.ResultsIcelandic ash can be of a respirable size (up to 11.3 vol.% < 4 μm), but the samples did not display physicochemical characteristics of pathogenic particulate in terms of composition or morphology. Ash particles were generally angular, being composed of fragmented glass and crystals. Few fiber-like particles were observed, but those present comprised glass or sodium oxides, and are not related to pathogenic natural fibers, like asbestos or fibrous zeolites, thereby limiting concern of associated respiratory diseases. None of the samples contained cristobalite or tridymite, and only one sample contained quartz, minerals of interest due to the potential to cause silicosis. Sample surface areas are low, ranging from 0.4 to 1.6 m2 g−1, which aligns with analyses on ash from other eruptions worldwide. All samples generated a low level of hydroxyl radicals (HO•), a measure of surface reactivity, through the iron-catalyzed Fenton reaction compared to concurrently analyzed comparative samples. However, radical generation increased after ‘refreshing’ sample surfaces, indicating that newly erupted samples may display higher reactivity. A composition-dependent range of available surface iron was measured after a 7-day incubation, from 22.5 to 315.7 μmol m−2, with mafic samples releasing more iron than silicic samples. All samples were non-reactive in a test of red blood cell-membrane damage.ConclusionsThe primary particle-specific concern is the potential for future eruptions of Iceland’s volcanoes to generate fine, respirable material and, thus, to increase ambient PM concentrations. This particularly applies to highly explosive silicic eruptions, but can also hold true for explosive basaltic eruptions or discrete events associated with basaltic fissure eruptions.

Sodium ascorbate kills Candida albicans in vitro via iron-catalyzed Fenton reaction: importance of oxygenation and metabolism.

Ascorbate can inhibit growth and even decrease viability of various microbial species including Candida albicans. However the optimum conditions and the mechanism of action are unclear. Materials/methodology:Candida albicans shaken for 90 min in a buffered solution of ascorbate (90 mM) gave a 5-log reduction of cell viability, while there was no killing without shaking, in growth media with different carbon sources or at 4°C. Killing was inhibited by the iron chelator 2,2'-bipyridyl. Hydroxyphenyl fluorescein probe showed the intracellular generation of hydroxyl radicals. Ascorbate-mediated killing of C. albicans depends on oxygenation and metabolism, involves iron-catalyzed generation of hydroxyl radicals via Fenton reaction and depletion of intracellular NADH. Ascorbate could serve as a component of a topical antifungal therapy.

Dual preventive benefits of iron elimination by desferal in asbestos-induced mesothelial carcinogenesis.

Asbestos‐induced mesothelial carcinogenesis is currently a profound social issue due to its extremely long incubation period and high mortality rate. Therefore, procedures to prevent malignant mesothelioma in people already exposed to asbestos are important. In previous experiments, we established an asbestos‐induced rat peritoneal mesothelioma model, which revealed that local iron overload is a major cause of pathogenesis and that the induced genetic alterations are similar to human counterparts. Furthermore, we showed that oral administration of deferasirox modified the histology from sarcomatoid to the more favorable epithelioid subtype. Here, we used i.p. administration of desferal to evaluate its effects on asbestos‐induced peritoneal inflammation and iron deposition, as well as oxidative stress. Nitrilotriacetate was used to promote an iron‐catalyzed Fenton reaction as a positive control. Desferal significantly decreased peritoneal fibrosis, iron deposition, and nuclear 8‐hydroxy‐2′‐deoxyguanosine levels in mesothelial cells, whereas nitrilotriacetate significantly increased all of them. Desferal was more effective in rat peritoneal mesothelial cells to counteract asbestos‐induced cytotoxicity than in murine macrophages (RAW264.7). Furthermore, rat sarcomatoid mesothelioma cells were more dependent on iron for proliferation than rat peritoneal mesothelial cells. Because inflammogenicity of a fiber is proportionally associated with subsequent mesothelial carcinogenesis, iron elimination from the mesothelial environment can confer dual merits for preventing asbestos‐induced mesothelial carcinogenesis by suppressing inflammation and mesothelial proliferation simultaneously.

Preferential Localization of Iron in The Chromatin of Fe-Enriched Cells Is Linked to DNA Cleavage Sites and Control of Carcinogenesis

DNA oxidation by oxygen-radicals generated via an iron catalyzed Fenton reaction has been extensively investigated, but little is known about iron localization in the nuclei of mammalian cells. In vitro studies showed the presence of five oxygen and one nitrogen atoms in the inner coordination sphere of the Fe(II)-DNA complex using X-ray absorption spectroscopy (XANES and EXAFS). The identification of ferritin in the nucleus of cultured cells, as well as iron-protein receptors in the nuclear membrane suggests that iron is actively transported into the nucleus. Therefore, pictures from energy-loss spectroscopic imaging (ESI) are included in this mini-review to illustrate the distribution of iron in a fibroblast cell line. These fibroblasts were iron-overloaded by being cultured in a medium containing Fe(III)-nitrilotriacetate (FeNTA). The elemental mapping of iron and phosphorus was coincident in ultrastructures and revealed a significant concentration of both in condensed chromatin; by contrast, the elemental mapping of nitrogen, used as a control, revealed a homogenous distribution across the entire cell. This observed preferential localization was surprising, considering the pro-oxidant status of iron and the importance of maintaining genome integrity. Interestingly, recent published works demonstrates that iron chelators such as genistein and daidzein, derived from soy isoflavones, can attenuate the expression of genes related to increased cancer risk and oxidative damage in the reproductive tract of female mice. In this same sense, mesenchymal stem cells also exhibit antioxidant properties by reducing superoxide, lipid peroxidation, and DNA breaks to healthful levels after transplantation into the brains of stroke prone spontaneously hypertensive rats. Therefore, we bring attention to the use of all potential antioxidants, particularly those with affinity for both iron and DNA, in therapies for several diseases.

Oxidative Stress in Plants Under Drought Conditions and the Role of Different Enzymes

The effects of drought stresses on plant metabolism are either direct or secondary. Oxidative stress is induced by a wide range of biotic and abiotic stresses including UV-light, pathogen invasion (hypersensitive reaction), herbicide action, oxygen shortage, among others. Drought and salt stresses usually lead to the production of reacting oxygen species (ROS) such as hydrogen peroxide (H2O2) and superoxide (O2 ·–), both produced in a number of cellular reactions, including the iron-catalysed Fenton reaction, and by various enzymes such as lipoxygenases, peroxidases, NADPH oxidase and xanthine oxidase. To control the level of ROS under stress conditions, plant tissues contain a series of enzyme scavengers of ROS. The main cellular components susceptible to damage by free radicals are lipids (peroxidation of unsaturated fatty acids in membranes), proteins and enzymes (denaturation), carbohydrates and nucleic acids. Plant carbon balance during a period of salt/water stress and subsequent recovery may depend as much on the speed and degree of photosynthetic recovery, as it depends on the degree and speed of photosynthesis decline during water reduction. Current knowledge about physiological limitations to photosynthetic recovery after different intensities of water and salt stress is still scarce. From the large amount of data available on transcript-profiling studies in plants subjected to drought it is becoming apparent that plants perceive and respond to these stresses by quickly altering gene expression in parallel with physiological and biochemical alterations; this occurs even under mild to moderate stress conditions. From a recent comprehensive study that compared salt and drought stress it is apparent that both stresses led to down-regulation of some photosynthetic genes, with most of the changes being small possibly reflecting the mild stress imposed. Drought and salt stresses are significant challenges for mankind. The utilization of different strategies, namely genetic and enzyme engineering, can contribute to the alleviation of the associated oxidative stresses. Regulating the expression of genes encoding for specific proteins and enzymes can result into drought and salt tolerance. Different crop genotypes, such as sugarcane, soybean, and wheat have already been engineered for drought tolerance. Wheat genotypes showed alterations in antioxidant enzymes as well as in enzymes associated with carbon metabolism. These important strategies will be a vitally important tool in the quest to alleviate the earth’s future problems concerning food, energy, and the environment. The present review focus on oxidative stresses associated with drought and salt conditions addressing the metabolomics involved in such constraints.

Dysregulated iron metabolism in patients on hemodialysis.

The two main causes of death in patients on maintenance hemodialysis (MHD) are cardiovascular disease and infection. In the current report, we discuss the association of the iron-catalyzed Fenton reaction and iron sequestration with complications in MHD patients. In particular, we have studied the deregulation of several iron transport systems of polymorphonuclear leukocytes (PMNLs) and the effects of TNF-α on human umbilical vein endothelial cells or PMNLs obtained from MHD patients and controls, and the following results were obtained. (1) Iron was sequestered in MHD-PMNLs, in which the protein governing iron transport was dysregulated. (2) TNF-α accelerated iron accumulation and oxidative stress in human umbilical vein endothelial cells in a manner similar to that in MHD-PMNLs. (3) An endosomal iron transport protein, or natural resistance-associated macrophage protein 1, was decreased in PMNLs from MHD patients, and TNF-α caused a decline in this protein's expression in control PMNLs. (4) The mitochondrial iron chaperone protein frataxin was decreased in MHD-PMNLs, which was linked to the acceleration of oxidative stress and hypercytokinemia. (5) The index of arterial stiffness was aggravated in MHD patients and was associated with serum hepcidin and TNF-α levels, which could inhibit iron exit from cells. With regard to bacterial infections, iron availability to these intracellular pathogens is critical for their growth. In particular, iron accumulation in cells and endosomes may accelerate the spread of infection. Cardiovascular disease has been shown to be linked to oxidative stress caused by iron sequestration in vascular cells and macrophages as well as by the alteration of iron metabolism in mitochondria, and the observed increase in hepcidin and TNF-α may accelerate these crucial steps of oxidative stress in vascular disease. Thus, because surplus iron in the body may escalate the dysregulation of iron metabolism, as observed in MHD patients, iron supplementation for renal anemia treatment should be prudent.

Water-insoluble fraction of airborne particulate matter (PM10) induces oxidative stress in human lung epithelial A549 cells

Exposure to ambient airborne particulate matter (PM) with an aerodynamic diameter less than 10 μm (PM10 ) links with public health hazards and increases risk for lung cancer and other diseases. Recent studies have suggested that oxidative stress is a key mechanism underlying the toxic effects of exposure to PM10 . Several components of water-soluble fraction of PM10 (sPM10 ) have been known to be capable of inducing oxidative stress in in vitro studies. In this study, we investigated if water-insoluble fraction of PM10 (iPM10 ) could be also capable of inducing oxidative stress and oxidative damage. Human lung epithelial A549 cells were exposed to 10 μg/mL of sPM10 , iPM10 or total PM10 (tPM10 ) preparation for 24 h. Here, we observed that all three PM10 preparations reduced cell viability and induced apoptotic cell death in A549 cells. We further found that, similar to the exposure to sPM10 and tPM10 , the intracellular level of hydrogen peroxide (H2 O2 ) in the iPM10 -exposed cells was increased significantly; meanwhile the activity of catalase was decreased significantly as compared with the unexposed control cells, resulting in significant DNA damage. Our data obtained from inductively coupled plasma-mass spectrometry (ICP-MS) assays showed that iron is the most abundant metal in all three PM10 preparations. Thus, we have demonstrated that, similar to sPM10 , iPM10 is also capable of inducing oxidative stress by probably inducing generation of H2 O2 and impairing enzymatic antioxidant defense, resulting in oxidative DNA damage and even apoptotic cell death through the iron-catalyzed Fenton reaction.

Assay of the antioxidant capacity of foods using an iron(II)-catalysed lipid peroxidation model for greater nutritional relevance

The formation of free radicals by the iron-catalysed Fenton reaction is a major cause of oxidative damage in the body. Here a common assay of antioxidant capacity, inhibition of the β-carotene-linoleic acid model of lipid peroxidation, has been modified by the addition of ferrous iron (final concentration 36 μmol/l), which makes the rate of oxidation of the lipids occur 25 times faster. Such an assay can simulate the oxidative damage to membrane lipids and low density lipoproteins occurring in the body in the presence of free iron. It thus may be nutritionally more relevant than traditional chemical assays of antioxidant capacity, as it measures pre-emptive antioxidant activity, i.e. activity which prevents free radicals being formed in the first place. Pre-empting their formation is likely to be more protective than scavenging of free radicals. The relative antioxidant activity of some food products found using this new assay was very different from that found using a radical-scavenging assay. Vitamin C, at 280 mg/l, was found to be 60 times better than blackcurrant puree in scavenging free radicals, but only one eighth as good as the blackcurrant puree in preventing iron-catalysed lipid peroxidation.

Iron Chelation Protects the Retinal Pigment Epithelial Cell Line ARPE-19 against Cell Death Triggered by Diverse Stimuli

Cell death can be induced by exogenous reactive oxygen species (ROS). Endogenous ROS can also play a role in cell death triggered by agents that are not themselves ROS. One of the most potent ROS-generating systems is the iron-catalyzed Fenton reaction. Herein, the authors tested whether iron plays an important role in cell death induced by diverse stimuli in retinal pigment epithelial (RPE) cells. The ability of the iron chelator salicylaldehyde isonicotinoyl hydrazone (SIH) to chelate intracellular labile iron was tested in the human cell line ARPE-19. The ability of SIH to protect against RPE cell death induced by hydrogen peroxide, staurosporine, anti-Fas, and exposure to A2E plus blue light was determined. ROS production by staurosporine was assessed in the presence and absence of SIH. The protective activity of SIH was compared with that of other iron chelators and an antioxidant. Acute exposure to SIH was nontoxic and at least partially protective against cell death induced by all tested agents. On a molar basis, SIH was more protective against hydrogen peroxide than other iron chelators and an antioxidant. SIH decreased levels of staurosporine-induced ROS. Iron chelation with SIH can decrease levels of ROS and protect RPE cells against cell death induced by diverse stimuli. These results suggest a central role for iron in cell death pathways, potentially involving the generation of oxidative stress. SIH or related iron chelators may prove useful for protection against diseases involving RPE death, such as AMD.

Hepatic Iron Overload Induces Hepatocellular Carcinoma in Transgenic Mice Expressing the Hepatitis C Virus Polyprotein

Despite the evidence of hepatic iron overload in patients with chronic hepatitis C, it remains unknown if iron overload is related to hepatocarcinogenesis in this condition. The aim of this study was to determine whether iron overload contributes to development of hepatocellular carcinoma (HCC) in transgenic mice expressing the hepatitis C virus (HCV) polyprotein. Male C57BL/6 transgenic mice expressing the HCV polyprotein and nontransgenic littermates were fed an excess-iron diet or control diet. Mice in each group were assessed for altered liver morphology and function and the development of liver tumors. Hepatic iron concentrations in mice fed the excess-iron diet were comparable to those of patients with chronic hepatitis C. There was no inflammation in transgenic and nontransgenic livers. Compared with mice in 3 other groups, transgenic mice fed the excess-iron diet showed marked hepatic steatosis including the centrilobular microvesicular type, ultrastructural alterations of the mitochondria and decreased degradation activity of fatty acid at 6 months, and greater hepatic content of lipid peroxidation products and 8-hydroxy-2'-deoxyguanosine at 12 months after initiation of feeding. The number of proliferating hepatocytes was significantly increased in mice fed the excess-iron diet but was not different between transgenic and nontransgenic mice. Hepatic tumors including HCC developed in 5 of 11 (45%) transgenic mice fed the excess-iron diet but not in mice in other groups at 12 months after initiation of feeding. Iron overload induces mitochondrial injury and increases the risk of HCC development in transgenic mice expressing the HCV polyprotein.

Antioxidants, oxidative damage and oxygen deprivation stress: a review.

Oxidative stress is induced by a wide range of environmental factors including UV stress, pathogen invasion (hypersensitive reaction), herbicide action and oxygen shortage. Oxygen deprivation stress in plant cells is distinguished by three physiologically different states: transient hypoxia, anoxia and reoxygenation. Generation of reactive oxygen species (ROS) is characteristic for hypoxia and especially for reoxygenation. Of the ROS, hydrogen peroxide (H(2)O(2)) and superoxide (O(2)(.-)) are both produced in a number of cellular reactions, including the iron-catalysed Fenton reaction, and by various enzymes such as lipoxygenases, peroxidases, NADPH oxidase and xanthine oxidase. The main cellular components susceptible to damage by free radicals are lipids (peroxidation of unsaturated fatty acids in membranes), proteins (denaturation), carbohydrates and nucleic acids. Consequences of hypoxia-induced oxidative stress depend on tissue and/or species (i.e. their tolerance to anoxia), on membrane properties, on endogenous antioxidant content and on the ability to induce the response in the antioxidant system. Effective utilization of energy resources (starch, sugars) and the switch to anaerobic metabolism and the preservation of the redox status of the cell are vital for survival. The formation of ROS is prevented by an antioxidant system: low molecular mass antioxidants (ascorbic acid, glutathione, tocopherols), enzymes regenerating the reduced forms of antioxidants, and ROS-interacting enzymes such as SOD, peroxidases and catalases. In plant tissues many phenolic compounds (in addition to tocopherols) are potential antioxidants: flavonoids, tannins and lignin precursors may work as ROS-scavenging compounds. Antioxidants act as a cooperative network, employing a series of redox reactions. Interactions between ascorbic acid and glutathione, and ascorbic acid and phenolic compounds are well known. Under oxygen deprivation stress some contradictory results on the antioxidant status have been obtained. Experiments on overexpression of antioxidant production do not always result in the enhancement of the antioxidative defence, and hence increased antioxidative capacity does not always correlate positively with the degree of protection. Here we present a consideration of factors which possibly affect the effectiveness of antioxidant protection under oxygen deprivation as well as under other environmental stresses. Such aspects as compartmentalization of ROS formation and antioxidant localization, synthesis and transport of antioxidants, the ability to induce the antioxidant defense and cooperation (and/or compensation) between different antioxidant systems are the determinants of the competence of the antioxidant system.

Ageing exacerbates the cardiotoxicity of hydrogen peroxide through the Fenton reaction in rats

Reactive oxygen species (ROS) are involved in the post-ischemic reperfusion syndrome of the myocardium. Moreover, ageing is associated with an increased cardiac sensitivity to both ischemia and reperfusion. The aim of the present study was to determine whether the lower tolerance of aged hearts to reperfusion could be due to an increased sensitivity to the ROS that are produced during the early phase of reperfusion. For this purpose isolated perfused hearts from adult (4 months) and aged (24 months) rats were perfused with a buffer containing 150 μM of hydrogen peroxide (H 2O 2) in presence or absence of deferoxamine mesylate (150 μM), an iron chelator. H 2O 2 perfusion was continued until left ventricular developed pressure had decreased up to 20% of its initial value. Ageing led to a significant reduction of the duration of the H 2O 2 perfusion required for inducing a 80% functional alteration. Although deferoxamine did not affect this parameter in adult rats, it significantly increased the duration of H 2O 2-perfusion in senescent hearts (control: 14.0±0.9 min vs. deferoxamine: 18.1±1.0, P<0.05). Similarly, ageing aggravated cardiac contracture induced by H 2O 2-perfusion. Again, deferoxamine, which had no effect on this parameter in young adult hearts, significantly reduced the contracture of senescent rat hearts. To conclude, our data clearly show that ageing is associated with an increased sensitivity of the myocardium to hydrogen peroxide, which is partly reversed by iron chelation. These results suggest that the iron-catalyzed Fenton reaction producing hydroxyl radicals might be greater in hearts from senescent rats than in hearts from young adults.

An iron-binding protein, Dpr, from Streptococcus mutans prevents iron-dependent hydroxyl radical formation in vitro.

The dpr gene is an antioxidant gene which was isolated from the Streptococcus mutans chromosome by its ability to complement an alkyl hydroperoxide reductase-deficient mutant of Escherichia coli, and it was proven to play an indispensable role in oxygen tolerance in S. mutans. Here, we purified the 20-kDa dpr gene product, Dpr, from a crude extract of S. mutans as an iron-binding protein and found that Dpr formed a spherical oligomer about 9 nm in diameter. Molecular weight determinations of Dpr in solution by analytical ultracentrifugation and light-scattering analyses gave values of 223,000 to 292,000, consistent with a subunit composition of 11.5 to 15 subunits per molecule. The purified Dpr contained iron and zinc atoms and had an ability to incorporate up to 480 iron and 11.2 zinc atoms per molecule. Unlike E. coli Dps and two other members of the Dps family, Dpr was unable to bind DNA. One hundred nanomolar Dpr prevented by more than 90% the formation of hydroxyl radical generated by 10 microM iron(II) salt in vitro. The data shown in this study indicate that Dpr may act as a ferritin-like iron-binding protein in S. mutans and may allow this catalase- and heme-peroxidase-deficient bacterium to grow under air by limiting the iron-catalyzed Fenton reaction.

Phytic Acid Inhibits Free Radical Formation In Vitro but Does Not Affect Liver Oxidant or Antioxidant Status in Growing Rats

The objective of this study was to determine the effects of phytic acid on free radical generation in vitro and in growing rats. Electron spin resonance spectroscopy studies using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as a spin trap indicate a complete inhibition of hydroxyl radical formation via the iron-catalyzed Fenton reaction at molar phytic acid/iron ratios >5. However, phytic acid had no scavenging effect on superoxide radicals generated in the xanthine/xanthine oxidase reaction. For the in vivo study, male growing albino rats were fed purified diets based on casein, cornstarch and vitamin E–stripped corn oil differing in the concentration of iron (30 or 300 mg/kg), phytic acid (0 or 10 g/kg) and dl-α-tocopheryl acetate (0 or 50 mg/kg). At marginal dietary iron supply, phytic acid supplementation reduced apparent Fe absorption, thereby decreasing liver Fe concentration. Dietary iron and phytate had no effect on the level of hepatic α-tocopherol, reduced glutathione, thiobarbituric acid–reactive substances and protein carbonyls. The concentration of thiobarbituric acid–reactive substances and protein carbonyls in the liver decreased as dietary vitamin E was increased from 0 to 50 mg/kg diet. The results obtained provide evidence for antioxidant properties of phytic acid under in vitro conditions. However, neither phytic acid nor iron had any significant effect on liver oxidant or antioxidant status in vivo in growing rats.

Synthesis, Properties, and Use of Copper-Chelating Amphiphilic Dithiocarbamates as Synergists of Oxidant-Generating Herbicides

The effect of herbicides that act by generating active oxygen species is often mitigated by the enzymes of the Halliwell-Asada oxygen detoxification pathway. Use of compounds interfering with this pathway synergizes herbicides, allowing the killing of weeds at lower herbicide doses. We have used different dithiocarbamate chelators (Dtcs) capable of removing copper from superoxide dismutase, the first enzyme of the pathway, suppressing its action. Dtcs with different hydrophilic-lipophilic properties (sodium salts of ethyl (2-(2-ethoxyethoxy)ethyl)-, butyl (2-(2-ethoxyethoxy)ethyl) -, hexyl (2-(2- ethoxyethoxy)ethyl)-, and dibutyldithiocarbamic acids) were synthesized so that they might penetrate plant cuticles better than sodium diethyldithiocarbamate. Octanol-water distribution ratios and the stabilities of their copper complexes were determined. All Dtcs tested had a high affinity for copper. The Dtcs did not prevent iron-catalyzed Fenton reaction leading to hydroxyl radical productionin vitro. Therefore they would not protect plants from the oxidative damage caused by herbicide, as do compounds that complex iron and thereby prevent the phytotoxic iron-catalyzed Fenton reaction. These amphiphilic compounds show some synergistic activityin vivo, with paraquat as well as lactofen, herbicides that generate active oxygen species by different mechanisms. The results demonstrate that dithiocarbamates have potential as synergists for oxidant-generating herbicides.

Enhancement of estrogen-induced renal tumorigenesis in hamsters by dietary iron

Iron participates in the generation of hydroxyl radicals by the iron-catalyzed Fenton reaction. Its role in estrogen-induced carcinogenesis has been examined in this study by investigating the effects of iron content of hamster diets on tumor induction by estradiol. The renal tumor incidence and number of tumor nodules in hamsters treated with estradiol plus a diet enriched with iron (384 p.p.m. Fe as ferric citrate) for 5 months were 2- and 4-fold higher, respectively, than those observed in animals on an iron-poor diet plus estradiol (3.9 p.p.m. Fe, as ferric citrate). Tumor incidence and number of tumor nodules in estradiol-treated hamsters on the iron-deficient diet were not different from those of animals on a normal rodent chow. No tumors were detected in hamsters treated only with the low or high iron diets. Total serum iron was significantly increased in animals treated with the high iron diet plus estradiol compared with the low iron diet plus estradiol group and the high and low iron controls. Estrogen treatment increased non-heme iron in liver of both high and low iron treatment groups and in kidney of the hamsters on the low iron diet. It is concluded that dietary iron enrichment enhances the incidence and severity of estrogen-induced tumor induction.