Simultaneous determination of Fe(III) and Fe(II) in water solutions and tissue homogenates using desferal and 1,10-phenanthroline

Surfactant enhanced persulfate system for the synergistic oxidation and reduction of mixed chlorinated hydrocarbons

Surfactant-enhanced in-situ chemical oxidation (S-ISCO) is widely applied in soil and groundwater remediation. However, the role of surfactants in the reactive species (RSs) transformation remains inadequately explored. This work introduced nonionic surfactant Tween-80 (TW-80) into a nano zero-valent iron (nZVI) activated persulfate (PS) system. The findings indicate that PS/nZVI/TW-80 system can realize the concurrent removal of trichloroethylene (TCE), tetrachloroethene (PCE), and carbon tetrachloride (CT), whereas CT cannot be eliminated without TW-80 presence. Further analysis unveiled that hydroxyl (HO•) and sulfate radicals (SO4－•) were the primary species for TCE and PCE degradation, while CT was reductively eliminated by surfactant radicals generated from TW-80. Moreover, the surfactant radicals were found to accelerate Fe(III)/Fe(II) cycle, reduce the production of iron sludge, and increase PS decomposition. The possible degradation routes of mixed chlorinated hydrocarbons (CHCs) and the decomposition pathways of TW-80 were proposed through the density function theory (DFT) calculation and intermediates analysis. Additionally, the effects of other nonionic surfactants on the simultaneous removal of TCE, PCE, and CT, and the practical applications using the actual contaminated groundwater were also evaluated. This study provides theoretical support for the simultaneous removal of CHCs, particularly those containing perchlorinated contaminants, using the S-ISCO techniques.

A Friendly Complexing Agent for Spectrophotometric Determination of Total Iron

Iron, one of the most common metals in the environment, plays a fundamental role in many biological as well as biogeochemical processes, which determine its availability in different oxidation states. Its relevance in environmental and industrial chemistry, human physiology, and many other fields has made it necessary to develop and optimize analysis techniques for accurate determination. Spectrophotometric methods are the most frequently applied in the analytical determination of iron in real samples. Taking advantage of the fact that desferrioxamine B, a trihydroxamic acid used since the 1970s in chelation therapy for iron overload treatment, forms a single stable 1:1 complex with iron in whichever oxidation state it can be found, a smart spectrophotometric method for the analytical determination of iron concentration was developed. In particular, the full compliance with the Lambert-Beer law, the range of iron concentration, the influence of pH, and the interference of other metal ions have been taken into account. The proposed method was validated in terms of LoD, LoQ, linearity, precision, and trueness, and has been applied for total iron determination in natural water certified material and in biological reference materials such as control human urine and control serum.

Iron imaging in myocardial infarction reperfusion injury

Restoration of coronary blood flow after a heart attack can cause reperfusion injury potentially leading to impaired cardiac function, adverse tissue remodeling and heart failure. Iron is an essential biometal that may have a pathologic role in this process. There is a clinical need for a precise noninvasive method to detect iron for risk stratification of patients and therapy evaluation. Here, we report that magnetic susceptibility imaging in a large animal model shows an infarct paramagnetic shift associated with duration of coronary artery occlusion and the presence of iron. Iron validation techniques used include histology, immunohistochemistry, spectrometry and spectroscopy. Further mRNA analysis shows upregulation of ferritin and heme oxygenase. While conventional imaging corroborates the findings of iron deposition, magnetic susceptibility imaging has improved sensitivity to iron and mitigates confounding factors such as edema and fibrosis. Myocardial infarction patients receiving reperfusion therapy show magnetic susceptibility changes associated with hypokinetic myocardial wall motion and microvascular obstruction, demonstrating potential for clinical translation.

Achieving Life through Death: Redox Biology of Lipid Peroxidation in Ferroptosis

Redox balance is essential for normal brain, hence dis-coordinated oxidative reactions leading to neuronal death, including programs of regulated death, are commonly viewed as an inevitable pathogenic penalty for acute neuro-injury and neurodegenerative diseases. Ferroptosis is one of these programs triggered by dyshomeostasis of three metabolic pillars: iron, thiols, and polyunsaturated phospholipids. This review focuses on: (1) lipid peroxidation (LPO) as the major instrument of cell demise, (2) iron as its catalytic mechanism, and (3) thiols as regulators of pro-ferroptotic signals, hydroperoxy lipids. Given the central role of LPO, we discuss the engagement of selective and specific enzymatic pathways versus random free radical chemical reactions in the context of the phospholipid substrates, their biosynthesis, intracellular location, and related oxygenating machinery as participants in ferroptotic cascades. These concepts are discussed in the light of emerging neuro-therapeutic approaches controlling intracellular production of pro-ferroptotic phospholipid signals and their non-cell-autonomous spreading, leading to ferroptosis-associated necroinflammation.

Chemical, Biological and Medical Controversies Surrounding the Fenton Reaction

A critical evaluation is made of the role of the Fenton reaction (Fe2+ + H2O2 → Fe3+ + •OH + OH-) in the promotion of oxidative damage in mammalian systems. Following a brief, historical overview of the Fenton reaction, including the formulation of the Haber–Weiss cycle as a mechanism for the catalysis of hydroxyl radical production, an appraisal is made of the biological relevance of the reaction today, following recognition of the important role played by nitric oxide and its congers in the promotion of biomolecular damage. In depth coverage is then given of the evidence (largely from EPR studies) for and against the hydroxyl radical as the active oxidant produced in the Fenton reaction and the role of metal chelating agents (including those of biological importance) and ascorbic acid in the modulation of its generation. This is followed by a description of the important developments that have occurred recently in the molecular and cellular biology of iron, including evidence for the presence of ‘free’ iron that is available in vivo for the Fenton reaction. Particular attention here is given to the role of the iron-regulatory proteins in the modulation of cellular iron status and how their functioning may become dysregulated during oxidative and nitrosative stress, as well as in hereditary haemochromatosis, a common disorder of iron metabolism. Finally, an assessment is made of the biological relevance of ascorbic acid in the promotion of hydroxyl radical generation by the Fenton reaction in health and disease.

A coumarin-based fluorescent probe for monitoring labile ferrous iron in living systems

Labile Fe2+ has been considered to be a metabolically active and regulatory form of cellular iron. Monitoring the dynamic level of labile Fe2+ in biological systems is vital for evaluating the iron related biological processes and diseases as well as dissecting the exact physiological and pathophysiological functions of the labile Fe2+. Herein, we rationally constructed a coumarin-based fluorescent probe for sensing labile Fe2+ in living systems based on a novel Fe2+ meditated cyclization reaction strategy. The probe showed a highly selective and sensitive response to Fe2+, and the detection limit was determined to be 45 nM. Significantly, the probe displayed fast response to Fe2+, with the sensing reaction completed in 2 min, which is beneficial for real time sensing. The application of the probe for sensing different concentrations of labile Fe2+ in living cells has been conducted. In addition, the basal and endogenous levels of labile Fe2+ in living systems were also successfully monitored.

Assessment of zero-valent iron-based nanotherapeutics for ferroptosis induction and resensitization strategy in cancer cells

Addressing nanomedicine resistance is critical for its ultimate clinical success; despite this, advancing the therapeutic designs for cancer therapy are rarely discussed in the literature.

Separation and Determination of Fe(III) and Fe(II) in Natural and Waste Waters Using Silica Gel Sequentially Modified with Polyhexamethylene Guanidine and Tiron

Silica gel, sequentially modified with polyhexamethylene guanidine and pyrocatechin-3,5-disulfonic acid (Tiron), was suggested for sorption separation and determination of Fe(III) and Fe(II). It was found that quantitative extraction of Fe(III) and its separation from Fe(II) were attained at pH 2.5-4.0, while quantitative extraction of Fe(II) was observed at pH 6.0-7.5. An intensive signal with g = 4.27, which is characteristic for Fe(III), appeared in EPR spectra of the sorbents after Fe(II) and Fe(III) sorption. During interaction between Fe(II) and Tiron, fixed on the sorbent surface, its oxidation up to Fe(III) occurred. Red-lilac complexes of the composition FeL₃ were formed on the sorbent surface during sorption regardless of initial oxidation level of iron. Diffuse reflectance spectrum of surface complexes exhibited wide band with slightly expressed maxima at 480 and 510 nm. Procedures for separation and photometric determination of Fe(III) and Fe(II) at the joint presence and total Fe content determination as Fe(II) in waste and natural waters was developed. The limit of detection for iron was 0.05 μg per 0.100 g of the sorbent. The calibration graph was linear up to 20.0 μg of Fe per 0.100 g of the sorbent. The RSD in the determination of more than 0.2 μg of Fe was less than 0.06.

The cytoprotective effect of nitrite is based on the formation of dinitrosyl iron complexes

Nitrite protects various organs from ischemia-reperfusion injury by ameliorating mitochondrial dysfunction. Here we provide evidence that this protection is due to the inhibition of iron-mediated oxidative reactions caused by the release of iron ions upon hypoxia. We show in a model of isolated rat liver mitochondria that upon hypoxia, mitochondria reduce nitrite to nitric oxide (NO) in amounts sufficient to inactivate redox-active iron ions by formation of inactive dinitrosyl iron complexes (DNIC). The scavenging of iron ions in turn prevents the oxidative modification of the outer mitochondrial membrane and the release of cytochrome c during reoxygenation. This action of nitrite protects mitochondrial function. The formation of DNIC with nitrite-derived NO could also be confirmed in an ischemia-reperfusion model in liver tissue. Our data suggest that the formation of DNIC is a key mechanism of nitrite-mediated cytoprotection.

Simple and Precise Quantification of Iron Catalyst Content in Carbon Nanotubes Using UV/Visible Spectroscopy

Iron catalysts have been used widely for the mass production of carbon nanotubes (CNTs) with high yield. In this study, UV/visible spectroscopy was used to determine the Fe catalyst content in CNTs using a colorimetric technique. Fe ions in solution form red-orange complexes with 1,10-phenanthroline, producing an absorption peak at λ=510 nm, the intensity of which is proportional to the solution Fe concentration. A series of standard Fe solutions were formulated to establish the relationship between optical absorbance and Fe concentration. Many Fe catalysts were microscopically observed to be encased by graphitic layers, thus preventing their extraction. Fe catalyst dissolution from CNTs was investigated with various single and mixed acids, and Fe concentration was found to be highest with CNTs being held at reflux in HClO4/HNO3 and H2SO4/HNO3 mixtures. This novel colorimetric method to measure Fe concentrations by UV/Vis spectroscopy was validated by inductively coupled plasma optical emission spectroscopy, indicating its reliability and applicability to asses Fe content in CNTs.

The low frequency modes of solvated ions and ion pairs in aqueous electrolyte solutions: iron(ii) and iron(iii) chloride

We have investigated the hydration dynamics of solvated iron(ii) and iron(iii) chloride. For this, THz/FIR absorption spectra of acidified aqueous FeCl2 and FeCl3 solutions have been measured in a frequency range of 30-350 cm(-1) (≈1-10 THz). We observe a nonlinear concentration dependence of the absorption, which is attributed to the progressive formation of chloro-complexes of Fe(ii) and Fe(iii), respectively. By principal component analysis of the concentration dependent absorption spectra, we deduced the molar extinction spectra of the solvated species Fe(2+) + 2Cl(-) and FeCl(+) + Cl(-), as well as FeCl(2+) + 2Cl(-) and FeCl2(+) + Cl(-). In addition, we obtain ion association constants log KFeCl2 = -0.88(5) and log KFeCl3 = -0.32(16) for the association of Fe(2+) and Cl(-) to FeCl(+) and the association of FeCl(2+) and Cl(-) to FeCl2(+), respectively. We performed a simultaneous fit of all the effective extinction spectra and their differences, including our previous results of solvated manganese(ii) and nickel(ii) chlorides and bromides. Thereby we were able to assign absorption peaks to vibrational modes of ion-water complexes. Furthermore, we were able to estimate a minimum number of affected water molecules, ranging from ca. 7 in the case of FeCl(+) + Cl(-) to ca. 21 in the case of FeCl(2+) + Cl(-).

Online spectrophotometric determination of Fe(II) and Fe(III) by flow injection combined with low pressure ion chromatography

A simple and new low pressure ion chromatography combined with flow injection spectrophotometric procedure for determining Fe(II) and Fe(III) was established. It is based on the selective adsorption of low pressure ion chromatography column to Fe(II) and Fe(III), the online reduction reaction of Fe(III) and the reaction of Fe(II) in sodium acetate with phenanthroline, resulting in an intense orange complex with a suitable absorption at 515nm. Various chemical (such as the concentration of colour reagent, eluant and reductive agent) and instrumental parameters (reaction coil length, reductive coil length and wavelength) were studied and were optimized. Under the optimum conditions calibration graph of Fe(II)/Fe(III) was linear in the Fe(II)/Fe(III) range of 0.040-1.0mg/L. The detection limit of Fe(III) and Fe(II) was respectively 3.09 and 1.55μg/L, the relative standard deviation (n=10) of Fe(II) and Fe(III) 1.89% and 1.90% for 0.5mg/L of Fe(II) and Fe(III) respectively. About 2.5 samples in 1h can be analyzed. The interfering effects of various chemical species were studied. The method was successfully applied in the determination of water samples.

Escherichia coli RIC is able to donate iron to iron-sulfur clusters

Escherichia coli RIC (Repair of Iron Centers) is a diiron protein previously reported to be involved in the repair of iron-sulfur proteins damaged by oxidative or nitrosative stresses, and proposed to act as an iron donor. This possible role of RIC was now examined specifically by evaluating its ability to donate iron ions to apo-iron-sulfur proteins, determining the iron binding constants and assessing the lability of its iron ions. We show, by UV-visible, EPR and resonance Raman spectroscopies that RIC may participate in the synthesis of an iron-sulfur cluster in the apo-forms of the spinach ferredoxin and IscU when in the presence of the sulfide donating system IscS and L-cysteine. Iron binding assays allowed determining the as-isolated and fully reduced RIC dissociation constants for the ferric and ferrous iron of 10-27 M and 10-13 M, respectively. Mössbauer studies revealed that the RIC iron ions are labile, namely when the center is in the mixed-valence redox form as compared with the (μ-oxo) diferric one. Altogether, these results suggest that RIC is capable of delivering iron for the formation of iron-sulfur clusters.

Exposure to nitric oxide increases the nitrosyl-iron complexes content in sorghum embryonic axes

This work was aimed to investigate nitrosyl-Fe complexes formation by reaction of endogenous ligands and Fe, in sorghum embryonic axes exposed to NO-donors. Electron paramagnetic resonance (EPR) was employed to detect the presence of nitrosyl-Fe complexes in plant embryos, as well as changes in labile iron pool (LIP). Nitrosyl-Fe complexes formation was detected in sorghum embryonic axes homogenates incubated in vitro in the presence of 1 mM of NO donors: diethylenetriamine NONOate (DETA NONOate), S-nitrosoglutathione (GSNO) and sodium nitroprusside (SNP). In axes isolated from seeds incubated in vivo in the presence of 1 mM SNP for 24 h, the content of NO was increased by 2-fold, and the EPR spectrum from mononitrosyl-Fe complexes (MNIC) was observed with a concomitant increase in the fresh weight of sorghum axes. The simultaneous exposure to deferoxamine and the NO donor precluded the increase in fresh weight observed in the presence of excess NO. While total Fe content in the axes isolated from seeds exposed to 1mM SNP was not significantly affected as compared to control axes, the LIP was increased by over 2-fold.The data reported suggest a critical role for the generation of complexes between Fe and NO when cells faced a situation leading to a significant increase in NO content. Moreover, demonstrate the presence of MNICs as one of the important components of the LIP, which could actively participate in Fe cellular mobilization.

Flocculation of harmful algal blooms by modified attapulgite and its safety evaluation

Natural attapulgite (N-AT) and modified attapulgite (M-AT) were used in this study to evaluate their flocculation efficiencies and mechanisms in freshwater containing harmful algal blooms through conventional jar test procedure. The experimental results showed that the efficiency of flocculation can be significantly improved by M-AT under appropriate conditions. It was found that the attapulgite modified by hydrochloric acid was similar to polyaluminum ferric silicate chloride (PAFSiC). The high efficiency for M-AT to flocculate Microcystis aeruginosa in freshwater was due to the mechanism of bridging and netting effect. Caenorhabditis elegans was used to detect the toxicity of N-AT and M-AT. The results showed that there was no significant toxicity on this organism. Attapulgite is a natural material, which can be readily available, abundant, and relatively inexpensive. Using modified attapulgite to remove the harmful algal blooms could have the advantages of high effectiveness, low cost, and low impact on the environment.

Increased labile iron pool in sorghum embryonic axes after the exogenous application of nitric oxide is independent on the nature of the NO donor

The objective of this work was to explore the hypothesis that nitric oxide (NO) affects Fe bioavailability in sorghum (Sorghum bicolor (L.) Moench) embryonic axes. NO content was assessed in embryonic axes isolated from seeds control or exposed to NO-donors, employing spin trapping electron paramagnetic resonance (EPR) methodology. NO donors such as sodium nitroprusside (SNP) and diethylenetriamine NONOate (DETA NONOate), released NO that permeated inside the axes increasing NO content. Under these conditions low temperature EPR was employed to study the labile iron pool. A 2.5 fold increase was observed in NO steady state concentration after 24 h of exposure to NO donors that was correlated to a 2 fold increase in the Fe labile pool, as compared to control axes. This observation provides experimental evidence for a potential role of NO in Fe homeostasis.

Superoxide dismutase 1-mediated production of ethanol- and DNA-derived radicals in yeasts challenged with hydrogen peroxide: molecular insights into the genome instability of peroxiredoxin-null strains

Peroxiredoxins are receiving increasing attention as defenders against oxidative damage and sensors of hydrogen peroxide-mediated signaling events. In the yeast Saccharomyces cerevisiae, deletion of one or more isoforms of the peroxiredoxins is not lethal but compromises genome stability by mechanisms that remain under scrutiny. Here, we show that cytosolic peroxiredoxin-null cells (tsa1Deltatsa2Delta) are more resistant to hydrogen peroxide than wild-type (WT) cells and consume it faster under fermentative conditions. Also, tsa1Deltatsa2Delta cells produced higher yields of the 1-hydroxyethyl radical from oxidation of the glucose metabolite ethanol, as proved by spin-trapping experiments. A major role for Fenton chemistry in radical formation was excluded by comparing WT and tsa1Deltatsa2Delta cells with respect to their levels of total and chelatable metal ions and of radical produced in the presence of chelators. The main route for 1-hydroxyethyl radical formation was ascribed to the peroxidase activity of Cu,Zn-superoxide dismutase (Sod1), whose expression and activity increased approximately 5- and 2-fold, respectively, in tsa1Deltatsa2Delta compared with WT cells. Accordingly, overexpression of human Sod1 in WT yeasts led to increased 1-hydroxyethyl radical production. Relevantly, tsa1Deltatsa2Delta cells challenged with hydrogen peroxide contained higher levels of DNA-derived radicals and adducts as monitored by immuno-spin trapping and incorporation of (14)C from glucose into DNA, respectively. The results indicate that part of hydrogen peroxide consumption by tsa1Deltatsa2Delta cells is mediated by induced Sod1, which oxidizes ethanol to the 1-hydroxyethyl radical, which, in turn, leads to increased DNA damage. Overall, our studies provide a pathway to account for the hypermutability of peroxiredoxin-null strains.

Rg1 reduces nigral iron levels of MPTP-treated C57BL6 mice by regulating certain iron transport proteins

Elevated iron levels in the substantia nigra (SN) participate in neuronal death in Parkinson's disease, in which the misregulation of iron transporters such as divalent metal transporter (DMT1) and ferroportin1 (FP1) are involved. Our previous work observed that nigral iron levels were increased in MPTP-treated mice and Ginsenoside Rg1 which is one of the main components of ginseng, had neuroprotective effects against MPTP toxicity. Whether Rg1 could reduce nigral iron levels to protect the dopaminergic neurons? And whether its neuroprotective effect is achieved by regulating certain iron transporters? The present studies showed that Rg1 pre-treatment increased the dopamine and its metabolites contents in the striatum, as well as increased tyrosine hydroxylase expression in the SN. Further experiments observed that Rg1 pre-treatment substantially attenuated MPTP-elevated iron levels, decreased DMT1 expression and increased FP1 expression in the SN. These results suggest that the neuroprotective effect of Rg1 on dopaminergic neurons against MPTP is due to the ability to reduce nigral iron levels, which is achieved by regulating the expressions of DMT1 and FP1.

Exposure to nitric oxide protects against oxidative damage but increases the labile iron pool in sorghum embryonic axes

Sodium nitroprusside (SNP) and diethylenetriamine NONOate (DETA NONOate), were used as the source of exogenous NO to study the effect of NO upon germination of sorghum (Sorghum bicolor (L.) Moench) seeds through its possible interaction with iron. Modulation of cellular Fe status could be an important factor for the establishment of oxidative stress and the regulation of plant physiology. Fresh and dry weights of the embryonic axes were significantly increased in the presence of 0.1 mM SNP, as compared to control. Spin trapping EPR was used to assess the NO content in axes from control seeds after 24 h of imbibition (2.4+/-0.2 nmol NO g(-1) FW) and seeds exposed to 0.01, 0.1, and 1 mM SNP (3.1+/-0.3, 4.6+/-0.2, and 6.0+/-0.9 nmol NO g(-1) FW, respectively) and 1 mM DETA NONOate (6.2+/-0.6 nmol NO g(-1) FW). Incubation of seeds with 1 mM SNP protected against oxidative damage to lipids and maintained membrane integrity. The content of the deferoxamine-Fe (III) complex significantly increased in homogenates of axes excised from seeds incubated in the presence of 1 mM SNP or 1 mM DETA NONOate as compared to the control (19+/-2 nmol Fe g(-1) FW, 15.2+/-0.5 nmol Fe g(-1) FW, and 8+/-1 nmol Fe g(-1) FW, respectively), whereas total Fe content in the axes was not affected by the NO donor exposure. Data presented here provide experimental evidence to support the hypothesis that increased availability of NO drives not only protective effects to biomacromolecules, but to increasing the Fe availability for promoting cellular development as well.

Inhibition of quorum sensing-controlled virulence factor production in Pseudomonas aeruginosa by South Florida plant extracts

Quorum sensing (QS) is a key regulator of virulence and biofilm formation in Pseudomonas aeruginosa and other medically relevant bacteria. Aqueous extracts of six plants, Conocarpus erectus, Chamaesyce hypericifolia, Callistemon viminalis, Bucida buceras, Tetrazygia bicolor, and Quercus virginiana, were examined in this study for their effects on P. aeruginosa virulence factors and the QS system. C. erectus, B. buceras, and C. viminalis caused a significant inhibition of LasA protease, LasB elastase, pyoverdin production, and biofilm formation. Additionally, each plant presented a distinct effect profile on the las and rhl QS genes and their respective signaling molecules, suggesting that different mechanisms are responsible for efficacy. Extracts of all plants caused the inhibition of QS genes and QS-controlled factors, with marginal effects on bacterial growth, suggesting that the quorum-quenching mechanisms are unrelated to static or cidal effects.

Spin concentration measurements of high-spin (g' = 4.3) rhombic iron(III) ions in biological samples: theory and application

Electron paramagnetic resonance (EPR) signals at g' = 4.3 are commonly encountered in biological samples owing to mononuclear high-spin (S = 5/2) Fe3+ ions in sites of low symmetry. The present study was undertaken to develop the experimental method and a suitable g' = 4.3 intensity standard and for accurately quantifying the amount of Fe3+ responsible for such signals. By following the work of Aasa and Vänngård (J. Magn. Reson. 19:308-315, 1975), we present equations relating the EPR intensity of S = 5/2 ions to the intensities of S = 1/2 standards more commonly employed in EPR spectrometry. Of the chelates tested, Fe3+-EDTA (1:3 ratio) in 1:3 glycerol/water (v/v), pH 2, was found to be an excellent standard for frozen-solution S = 5/2 samples at 77 K. The spin concentrations of Cu2+-EDTA and aqua VO2+, both S = 1/2 ions, and of Fe3+-transferrin, an S = 5/2 ion, were measured against this standard and found to agree within 2.2% of their known metal ion concentrations. Relative standard deviations of +/-3.6, +/-5.3 and +/-2.9% in spin concentration were obtained for the three samples, respectively. The spin concentration determined for Fe3+-desferrioxamine of known Fe3+ concentration was anomalously low suggesting the presence of EPR-silent multimeric iron species in solution.

Effects of seasonal and latitudinal cold on oxidative stress parameters and activation of hypoxia inducible factor (HIF-1) in zoarcid fish

Acute, short term cooling of North Sea eelpout Zoarces viviparus is associated with a reduction of tissue redox state and activation of hypoxia inducible factor (HIF-1) in the liver. The present study explores the response of HIF-1 to seasonal cold in Zoarces viviparus, and to latitudinal cold by comparing the eurythermal North Sea fish to stenothermal Antarctic eelpout (Pachycara brachycephalum). Hypoxic signalling (HIF-1 DNA binding activity) was studied in liver of summer and winter North Sea eelpout as well as of Antarctic eelpout at habitat temperature of 0 degrees C and after long-term warming to 5 degrees C. Biochemical parameters like tissue iron content, glutathione redox ratio, and oxidative stress indicators were analyzed to see whether the cellular redox state or reactive oxygen species formation and HIF activation in the fish correlate. HIF-1 DNA binding activity was significantly higher at cold temperature, both in the interspecific comparison, polar vs. temperate species, and when comparing winter and summer North Sea eelpout. Compared at the low acclimation temperatures (0 degrees C for the polar and 6 degrees C for the temperate eelpout) the polar fish showed lower levels of lipid peroxidation although the liver microsomal fraction turned out to be more susceptible to lipid radical formation. The level of radical scavenger, glutathione, was twofold higher in polar than in North Sea eelpout and also oxidised to over 50%. Under both conditions of cold exposure, latitudinal cold in the Antarctic and seasonal cold in the North Sea eelpout, the glutathione redox ratio was more oxidised when compared to the warmer condition. However, oxidative damage parameters (protein carbonyls and thiobarbituric acid reactive substances (TBARS) were elevated only during seasonal cold exposure in Z. viviparus. Obviously, Antarctic eelpout are keeping oxidative defence mechanisms high enough to avoid accumulation of oxidative damage products at low habitat temperature. The paper discusses how HIF could be instrumental in cold adaptation in fish.

Ferrous ion-induced strand breaks in the DNA plasmid pBR322 are not mediated by hydrogen peroxide

Ferrous ion-induced generation of single and multiple strand breaks in the DNA plasmid pBR322 induces the formation of two new plasmid forms with altered electrophoretic mobility. The yield of these plasmid forms, the circular relaxed and the linear forms, depended on the applied Fe(2+) concentration. This property was independent of the presence of hydrogen peroxide in the incubation mixture indicating the lack of Fenton chemistry to explain the DNA degradation. The removal of dioxygen or the presence of superoxide dismutase diminished partially the yield of ferrous ion-induced DNA plasmid degradation, while catalase was without any effect. Autoxidation of divalent iron as followed by the formation of a coloured iron-phenanthroline complex was enhanced in a concentration-dependent manner by phosphate and bicarbonate and very efficiently using a mixture of 0.15 M NaCl, 1.2 mM phosphate, 23.8 mM bicarbonate, pH 7.4, that concentrations correspond closely to the intracellular values of buffer components. Thus, the formation of a yet unknown reactive species from Fe(2+), and dioxygen, that is complexed to buffer components especially phosphate and its contribution in DNA plasmid degradation is more likely than the often cited formation of hydroxyl radicals in result of the Fenton reaction from Fe(2+) and hydrogen peroxide.

Chelation and determination of labile iron in primary hepatocytes by pyridinone fluorescent probes

A series of fluorescent iron chelators has been synthesized such that a fluorescent function is covalently linked to a 3-hydroxypyridin-4-one. In the present study, the fluorescent iron chelators were loaded into isolated rat hepatocytes. The intracellular fluorescence was not only quenched by an addition of a highly lipophilic 8-hydroxyquinoline-iron(III) complex but also was dequenched by the addition of an excess of the membrane-permeable iron chelator CP94 (1,2-diethyl-3-hydroxypyridin-4-one). The time course of uptake of iron and iron chelation in single, intact cells was recorded on-line by using digital fluorescence microscopy. Intracellular concentrations of various fluorescent iron chelators were determined by using a spectrofluorophotometer subsequent to lysis of probe-loaded cells and were found to depend on their partition coefficients; the more hydrophobic the compound, the higher the intracellular concentration. An ex situ calibration method was used to determine the chelatable iron pool of cultured rat hepatocytes. CP655 (7-diethylamino-N-[(5-hydroxy-6-methyl-4-oxo-1,4-dihydropyridin-3-yl)methyl]-N-methyl-2-oxo-2H-chromen-3-carboxamide), which is a moderately lipophilic fluorescent chelator, was found to be the most sensitive probe for monitoring chelatable iron, as determined by the intracellular fluorescence increase induced by the addition of CP94. The concentration of the intracellular chelatable iron pool in hepatocytes was determined by this probe to be 5.4+/-1.3 microM.

Redox cycling of iron by Abeta42

The amyloid cascade hypothesis and oxidative damage have been inextricably linked in the neurodegeneration that is characteristic of Alzheimer's disease. We have investigated this link and sought to suggest a mechanism whereby the precipitation of Abeta42 might contribute to the redox cycling of iron and hence the generation of reactive oxygen species via Fenton-like chemistry. We have shown that the critical step in the auto-oxidation of Fe(II) under the near-physiological conditions of our study involved the generation of H2O2 via O2.- and that Abeta42 influenced Fenton chemistry through aggregation state-specific binding of both Fe(II) and Fe(III). The net result of these interactions was the delayed precipitation of kinetically redox-inactive Fe(OH)3(s) such that Fe(II)/Fe(III) were cycled in redox-active forms over a substantially longer time period than if peptide had been absent from preparations. The addition of physiologically significant concentrations of either Cu(II) or Zn(II) reduced the role played by Abeta42 in the Fe(II)/Fe(III) redox cycle whereas a pathophysiologically significant concentration of Al(III) potentiated the redox cycle in favour of Fe(II) whether or not Cu(II) or Zn(II) was additionally present. The results support the notion that oxidative damage in the immediate vicinity of, for example, senile plaques, may be the result of Fenton chemistry catalysed by the codeposition of Abeta42 with metals such as Fe(II)/Fe(III) and Al(III).

Metals accelerate the formation and direct the structure of amyloid fibrils of NAC

Non-beta amyloid component of Alzheimer's disease amyloid or NAC is a highly amyloidogenic peptide consisting of 35 amino acids which was first identified associated with senile plaques in the Alzheimer's disease brain. It is a fragment of the presynaptic protein alpha-synuclein and, as such, it is implicated in the aetiologies of both Alzheimer's (AD) and Parkinson's (PD) disease. Metals are involved in the aggregation of amyloidogenic peptides such as beta amyloid (Abeta), British amyloid peptide (ABri) and alpha-synuclein though nothing is yet known about how they might influence the aggregation of NAC. We show herein that NAC will form beta-pleated conformers at a peptide concentration of only 2.0 microM and that metals, and Zn(II) and Cu(II) in particular, accelerate the formation of these fibrils. Cu(II) and Zn(II) did not influence the diameter or general structure of the fibrils which were formed though many more shorter fibrils were observed in their presence and these shorter fibrils were highly thioflavin T positive and they were efficient catalysts of the redox cycling of added Fe(II). By way of contrast, beta-pleated conformers of NAC which were formed in the presence of Al(III) showed much lower levels of thioflavin T fluorescence and were poorer catalysts of the redox cycling of added Fe(II) and these properties were commensurate with an increased abundance of a novel amyloid morphology which consisted of twisted fibrils with a periodicity of about 100 nm. These spirals of twisted fibrils were especially abundant in the presence of added Al(III) and it is speculated that NAC binding of Al(III) may be important in their formation and subsequent stability.

Novel iron-specific fluorescent probes

A series of novel iron-specific fluorescent probes is reported where the chelator function unusually forms part of the fluorescent moiety. The ability of this range of molecules to permeate human erythrocyte ghost membranes was investigated.

Ferrioxamine B Analogues: Targeting the FoxA Uptake System in the Pathogenic Yersinia enterocolitica

A series of ferrioxamine B analogues that target the bacterium Yersinia enterocolitica were prepared. These iron carriers are composed of three hydroxamate-containing monomeric units. Two identical monomers consist of N-hydroxy-3-aminopropionic acid coupled with beta-alanine, and a third unit at the amino terminal is composed of N-hydroxy-3-aminopropionic acid and one of the following amino acids: beta-alanine (1a), phenylalanine (1b), cyclohexylalanine (1c), or glycine (1d). Thermodynamic results for representatives of the analogues have shown a strong destabilization (3-4 orders of magnitude) of the ferric complexes with respect to ferrioxamine B, probably due to shorter spacers and a more strained structure around the metal center. No significant effect of the variations at the N-terminal has been observed on the stability of the ferric complexes. By contrast, using in vivo radioactive uptake experiments, we have found that these modifications have a substantial effect on the mechanism of iron(III) uptake in the pathogenic bacteria Yersinia enterocolitica. Analogues 1a and 1d were utilized by the ferrioxamine B uptake system (FoxA), while 1b and 1c either used different uptake systems or were transported to the microbial cell nonspecifically by diffusion via the cell membrane. Transport via the FoxA system was also confirmed by uptake experiments with the FoxA deficient strain of Yersinia enterocolitica. A fluorescent marker, attached to 1a in a way that did not interfere with its biological activity, provided additional means to monitor the uptake mechanism by fluorescence techniques. Of particular interest is the observation that 1a was utilized by the uptake system of ferrioxamine B in Yersinia enterocolitica (FoxA) but failed to use the ferrioxamine uptake route in Pseudomonas putida. Here, we present a case in which biomimetic siderophore analogues deliberately designed for a particular bacterium can distinguish between related uptake systems of different microorganisms.

Pro- or anti-oxidant manganese: a suggested mechanism for reconciliation

The neurodegeneration induced by manganese has been attributed to its ability to undergo redox cycling, and catalysis of reactive oxygen species (ROS) formation, as with other transition metals. However, the characterization of manganese as a pro-oxidant is confounded by increasing evidence that the metal may scavenge superoxide anions and protect cells from oxidative damage. The current study was designed to address conflicting reports pertaining to the oxidative capacity of manganese. We found that the metal has distinctive redox dynamics in which the divalent reduced form, unlike iron, possessed no intrinsic oxidative capacity. The apparent ability of Mn(2+) to promote the formation of ROS within a cortical mitochondrial-synaptosomal fraction was quenched by the depletion of contaminating nanomolar concentrations of trivalent metals. The addition of manganic ions at trace concentrations dose-dependently restored the oxidative capacity attributed to divalent manganese, whereas the presence of the ferric ion retarded the rate of ROS generation. This result was paralleled by the spectrophotometric demonstration that the kinetics of iron oxidation is accelerated by trivalent but not divalent manganese. The markedly different capacities of the lower and higher valence states of manganese to promote free-radical formation in cortical fractions and to modulate the process of iron oxidation may account for earlier contradictory reports of anti- and pro-oxidant properties of manganese.

Sequential Determination of Iron(II) and Iron(III) in Pharmaceutical by Flow-Injection Analysis with Spectrophotometric Detection

A flow injection procedure for the sequential spectrophotometric determination of iron(II) and iron(III) in pharmaceutical products is described. The method is based on the catalytic effect of iron(II) on the oxidation of iodide by bromate at pH = 4.0. The reaction was monitored spectrophotometrically by measuring the absorbance of produced triiodide ion at 352 nm. The activating effect for the catalysis of iron(II) was extremely exhibited in the presence of oxalate ions, while oxalate acted as a masking agent for iron(III). The iron(III) in a sample solution could be determined by passing through a Cd-Hg reductor column introduced in the FIA system to reduce iron(III) to iron(II), which allows total iron determination. Under the optimum conditions, iron(II) and iron(III) could be determined over the range of 0.05 - 5.0 and 0.10 - 5.0 microg ml(-1), respectively with a sampling rate of 17 +/- 5 h(-1). The experimental limits of detection were 0.03 and 0.04 microg ml(-1) for iron(II) and iron(III), respectively. The proposed method was successfully applied to the speciation of iron in pharmaceutical products.

Reduction of Fe(III) ions complexed to physiological ligands by lipoyl dehydrogenase and other flavoenzymes in vitro: implications for an enzymatic reduction of Fe(III) ions of the labile iron pool

Enzymatic reduction of physiological Fe(III) complexes of the "labile iron pool" has not been studied so far. By use of spectrophotometric assays based on the oxidation of NAD(P)H and formation of [Fe(II) (1,10-phenanthroline)3]2+ as well as by utilizing electron paramagnetic resonance spectrometry, it was demonstrated that the NAD(P)H-dependent flavoenzyme lipoyl dehydrogenase (diaphorase, EC 1.8.1.4) effectively catalyzes the one-electron reduction of Fe(III) complexes of citrate, ATP, and ADP at the expense of the co-enzymes NAD(P)H. Deactivated or inhibited lipoyl dehydrogenase did not reduce the Fe(III) complexes. Likewise, in the absence of NAD(P)H or in the presence of NAD(P)+, Fe(III) reduction could not be detected. The fact that reduction also occurred in the absence of molecular oxygen as well as in the presence of superoxide dismutase proved that the Fe(III) reduction was directly linked to the enzymatic activity of lipoyl dehydrogenase and not mediated by O2. Kinetic studies revealed different affinities of lipoyl dehydrogenase for the reduction of the low molecular weight Fe(III) complexes in the relative order Fe(III)-citrate > Fe(III)-ATP > Fe(III)-ADP (half-maximal velocities at 346-485 microm). These Fe(III) complexes were enzymatically reduced also by other flavoenzymes, namely glutathione reductase (EC 1.6.4.2), cytochrome c reductase (EC 1.6.99.3), and cytochrome P450 reductase (EC 1.6.2.4) with somewhat lower efficacy. The present data suggest a (patho)physiological role for lipoyl dehydrogenase and other flavoenzymes in intracellular iron metabolism.

Signaling role of intracellular iron in NF-kappaB activation

Iron chelators inhibit endotoxin-induced NF-kappaB activation in hepatic macrophages (HMs), suggesting a role for the intracellular chelatable pool of iron in NF-kappaB activation. The present study tested this hypothesis. Analysis of Fe(59)-loaded HMs stimulated with lipopolysaccharide (LPS), revealed a previously unreported, transient rise in intracellular low molecular weight (LMW).Fe(59) complex ([LMW.Fe](i)) at </=2 min returning to the basal level within 15 min. The [LMW.Fe](i) response preceded IkappaB kinase (IKK) (>/=15 min) and NF-kappaB (>/=30 min) activation. Iron chelators (1,2-dimethyl-3-hydroxypyridin-4-one and N,N'-bis-2-hydroxybenzylethylenediamine-N,N'-diacetic acid) abrogated the [LMW.Fe](i) response and IKK and NF-kappaB activation. The [LMW.Fe](i) response was also observed in tumor necrosis factor alpha (TNFalpha)-stimulated HMs and RAW264.7 cells treated with LPS and interferon-gamma but not in primary rat hepatocytes or myofibroblastic cells exposed to LPS or TNFalpha. Both [LMW.Fe](i) response and IKK activation in LPS-stimulated HMs were inhibited by diphenylene iodonium (nonspecific inhibitor for flavin-containing oxidases), l-N(6)-(1-iminoethyl)lysine (selective iNOS inhibitor), and adenoviral-mediated expression of a dominant negative mutant of Rac1 or Cu,Zn-superoxide dismutase, suggesting the role of (.)NO and O(2)() in mediating the iron signaling. In fact, this inhibition was recapitulated by a cell-permeable scavenger of ONOO(-), 5,10,15,20-tetrakis (4-sulfonatophenyl)porphyrinato iron (III) chloride. Conversely, ONOO(-) alone induced both [LMW.Fe](i) response and IKK activation. Finally, direct addition of ferrous iron to cultured HMs activated IKK and NF-kappaB. These results support a novel signaling role for [LMW.Fe](i) in IKK activation, which appears to be induced by ONOO(-) and selectively operative in macrophages.

Enhancement of iron toxicity in L929 cells by D-glucose: accelerated(re-)reduction

It has recently been shown that an increase in the cellular chelatable iron pool is sufficient to cause cell damage. To further characterize this kind of injury, we artificially enhanced the chelatable iron pool in L929 mouse fibroblasts using the highly membrane-permeable complex Fe(III)/8-hydroxyquinoline. This iron complex induced a significant oxygen-dependent loss of viability during an incubation period of 5 h. Surprisingly, the addition of L-glucose strongly enhanced this toxicity whereas no such effect was exerted by L-glucose and 2-deoxyglucose. The assumption that this increase in toxicity might be due to an enhanced availability of reducing equivalents formed during the metabolism of L-glucose was supported by NAD(P)H measurements which showed a 1.5-2-fold increase in the cellular NAD(P)H content upon addition of L-glucose. To assess the influence of this enhanced cellular reducing capacity on iron valence we established a new method to measure the reduction rate of iron based on the fluorescent iron(II) indicator PhenGreen SK. We could show that the rate of intracellular iron reduction was more than doubled in the presence of L-glucose. A similar acceleration was achieved by adding the reducing agents ascorbate and glutathione (the latter as membrane-permeable ethyl ester). Glutathione ethyl ester, as well as the thiol reagent N -acetylcysteine, also caused a toxicity increase comparable with L-glucose. These results suggest an enhancement of iron toxicity by L-glucose via an accelerated (re-)reduction of iron with NAD(P)H serving as central electron provider and ascorbate, glutathione or possibly NAD(P)H itself as final reducing agent.

Reduced flavins promote oxidative DNA damage in non-respiring Escherichia coli by delivering electrons to intracellular free iron

When cells are exposed to external H(2)O(2), the H(2)O(2) rapidly diffuses inside and oxidizes ferrous iron, thereby forming hydroxyl radicals that damage DNA. Thus the process of oxidative DNA damage requires only H(2)O(2), free iron, and an as-yet unidentified electron donor that reduces ferric iron to the ferrous state. Previous work showed that H(2)O(2) kills Escherichia coli especially rapidly when respiration is inhibited either by cyanide or by genetic defects in respiratory enzymes. In this study we established that these respiratory blocks accelerate the rate of DNA damage. The respiratory blocks did not substantially affect the amounts of intracellular free iron or H(2)O(2), indicating that that they accelerated damage because they increased the availability of the electron donor. The goal of this work was to identify that donor. As expected, the respiratory inhibitors caused a large increase in the amount of intracellular NADH. However, NADH itself was a poor reductant of free iron in vitro. This suggests that in non-respiring cells electrons are transferred from NADH to another carrier that directly reduces the iron. Genetic manipulations of the amounts of intracellular glutathione, NADPH, alpha-ketoacids, ferredoxin, and thioredoxin indicated that none of these was the direct electron donor. However, cells were protected from cyanide-stimulated DNA damage if they lacked flavin reductase, an enzyme that transfers electrons from NADH to free FAD. The K(m) value of this enzyme for NADH is much higher than the usual intracellular NADH concentration, which explains why its flux increased when NADH levels rose during respiratory inhibition. Flavins that were reduced by purified flavin reductase rapidly transferred electrons to free iron and drove a DNA-damaging Fenton system in vitro. Thus the rate of oxidative DNA damage can be limited by the rate at which electron donors reduce free iron, and reduced flavins become the predominant donors in E. coli when respiration is blocked. It remains unclear whether flavins or other reductants drive Fenton chemistry in respiring cells.

Role of hypolipidemic drug clofibrate in altering iron regulatory proteins IRP1 and IRP2 activities and hepatic iron metabolism in rats fed a low-iron diet

In addition to reducing the expression of transferrin and ceruloplasmin genes, hypolipidemic peroxisome proliferators may alter iron homeostasis in the liver. Therefore, this study investigates the effects of clofibrate on proteins related to liver iron metabolism in a rat model using a 2 x 2 experimental design: two dose levels of clofibrate in diet (0 and 0.5%) and two dietary iron levels (35 ppm as normal level and 15 ppm as low-iron diet). Twenty-four Wistar rats were assigned to the four diets and fed for 6 weeks. Subsequent measurements of iron parameters in the blood and the liver indicated that, in addition to mild anemia and the reduction in serum iron and total iron-binding capacity, clofibrate treatment altered IRP1 and IRP2 activities differentially and increased mitochondrial aconitase both at activity and protein levels. At both normal and low-iron intakes, clofibrate caused a 50% reduction in serum iron and TIBC with a corresponding reduction in transferrin mRNA. The RNA-binding activities of IRP1 were selectively activated by clofibrate treatment even though liver iron concentration was not depleted. The RNA-binding activity of IRP2 was selectively activated by the low iron intake and correlated with an increase of transferrin receptor mRNA, while clofibrate treatment offset the effects of the low iron intake.

The chelatable iron pool in living cells: a methodically defined quantity

A very small, predominantly cytosolic pool of iron ions plays the central role in the cellular iron metabolism. It links the cellular iron uptake with the insertion of the metal in iron storage proteins and other essential iron-containing molecules. Furthermore, this transit ('labile') pool is essentially involved in the pathogenesis of a number of diseases. Due to its high physiological and pathophysiological significance, numerous methods for its characterization have been developed during the last five decades. Most of these methods, however, influence the size and nature of the transit iron pool artificially, as they are not applicable to viable biological material. Recently, fluorescence spectroscopic methods for measurements within viable cells have become available. Although these methods avoid the artifacts of previous methods, studies using fluorescent iron indicators revealed that the 'intracellular transit iron pool', which is methodically assessed as 'chelatable iron', is substantially defined by the method and/or the iron-chelating indicator applied for its detection, since the iron ions are bound to a large number of different ligands in different metabolic compartments. A more comprehensive characterization of the nature and the role of the thus not uniform cellular transit iron pool therefore requires parallel employment of different indicator molecules, which clearly differ in their intracellular distribution and their physico-chemical characteristics.

Configuration of thiols dictates their ability to promote iron-induced reactive oxygen species generation

Iron catalyzes the production of reactive oxygen species (ROS) through the Fenton reaction. The modification of this phenomenon in the presence of various thiol compounds that are nominally reducing agents has been studied. Using the synaptosomal/mitochondrial (P2) fraction of rat cerebral cortex as a biological source of reactive oxygen species (ROS) production, we studied the influence of four compounds, glutathione (GSH), cysteine, N-acetyl-cysteine (NAC), and homocysteine on iron-induced ROS production. None of the thiol compounds alone, at the concentrations used, affected the basal rate of ROS production in the P2 fraction. GSH, homocysteine and NAC did not alter Fe-induced ROS generation, while cysteine greatly potentiated ROS formation. Measurement of the rate of ROS production in the presence of varying concentrations of cysteine together with 20 microM ferrous iron revealed a dose-response relationship. The mechanism whereby free cysteine, but not the cysteine-containing peptide GSH, homocysteine or NAC with a blocked amino group, exacerbates the pro-oxidant properties of ferrous iron probably involves formation of a complex between iron, a sulfhydryl and a free carboxyl residue located at a critical distance from the -SH group. Cysteine-iron interactions may, in part, account for the excessive toxicity of free cysteine in contrast to GSH and NAC.

The stabilization of ferrous iron by a toxic beta-amyloid fragment and by an aluminum salt

Aluminum is a recognized neurotoxin in dialysis encephalopathy and may also be implicated in the etiology of neurodegenerative disease, particularly Alzheimer's disease. Alzheimer's disease is suspected to be associated with oxidative stress, possibly due to the pro-oxidant properties of beta-amyloid present in the senile plaques. The underlying mechanism by which this occurs is not well understood although interactions between amyloid and iron have been proposed. The presence of low molecular weight iron compounds can stimulate free radical production in the brain. This study provides a possible explanation whereby both aluminum and beta-amyloid can potentiate free radical formation by stabilizing iron in its more damaging ferrous (Fe2+) form which can promote the Fenton reaction. The velocity, at which Fe2+ is spontaneously oxidized to Fe3+ at 37 degrees C in 20 mM Bis-Tris buffer at pH 5.8, was significantly slowed in the presence of aluminum salts. A parallel effect of prolongation of stability of soluble ferrous ion, was found in the presence of beta-amyloid fragment (25-35). Ascorbic acid, known to potentiate the pro-oxidant properties of iron, was also capable of markedly stabilizing ferrous ions.

Concentration dependence of prooxidant and antioxidant properties of catecholestrogens

Estradiol is an established antioxidant in vitro and in vivo. In contrast, prooxidant effects such as 8-hydroxylation of guanine bases of DNA have been induced by various estrogens in hamsters and by 4-hydroxyestradiol or -estrone and a microsomal activating system in vitro. As part of an examination of these conflicting reports, we studied the enhancement or inhibition of lipid peroxidation (conjugated diene formation monitored at 240 nm) by catecholestrogens in human low-density lipoprotein (LDL) incubated with cupric sulfate in phosphate buffer. Addition of 2- or 4-hydroxyestradiol, 2- or 4-methoxyestradiol, or estradiol or estriol (0.5-50 microM) increased lag times for diene formation by 30 to <300% over control values in the absence of estrogens (lag time, 1.6 h). In contrast, low concentrations (5 pM-100 nM) of catecholestrogens decreased lag times by about 40-50%, demonstrating their prooxidant activities. The prooxidant capabilities of catecholestrogens were examined by assaying the reduction by estrogens of Cu(II) to Cu(I) and of Fe(III) to Fe(II). Both 2- and 4-hydroxyestradiol and 2- and 4-methoxyestradiol reduced Cu(II) and Fe(III) ions to their lower oxidation state. In conclusion, the reduction of Cu(II) to Cu(I) by catecholestrogens is proposed to initiate lipid peroxidation and thus oxidation of LDL. In contrast, at high concentrations of catecholestrogens, the scavenging of oxygen radicals may predominate over lipid peroxidation and free radical generation by analogy to the action of similar phenolic antioxidants. With estradiol, estriol, and the methoxyestrogen metabolites, only antioxidant effects were observed.

Carvedilol inhibition of lipid peroxidation. A new antioxidative mechanism

To define the molecular mechanism(s) of carvedilol inhibition of lipid peroxidation we have utilized model systems that allow us to study the different reactions involved in this complex process. Carvedilol inhibits the peroxidation of sonicated phosphatidylcholine liposomes triggered by FeCl2 addition whereas atenolol, pindolol and labetalol are ineffective. The inhibition proved not to be ascribable (a) to an effect on Fe2+ autoxidation and thus on the generation of oxygen derived radical initiators; (b) to the scavenging of the inorganic initiators O2*- and *OH; (c) to an effect on the reductive cleavage of organic hydroperoxides by FeCl2; (d) to the scavenging of organic initiators. The observations that (a) carvedilol effectiveness is inversely proportional to the concentration of FeCl2 and lipid hydroperoxides in the assay; (b) the drug prevents the onset of lipid peroxidation stimulated by FeCl3 addition and; (c) it can form a complex with Fe3+, suggest a molecular mechanism for carvedilol action. It may inhibit lipid peroxidation by binding the Fe3+ generated during the oxidation of Fe2+ by lipid hydroperoxides in the substrate. The lag time that carvedilol introduces in the peroxidative process would correspond to the time taken for carvedilol to be titrated by Fe3+; when the drug is consumed the Fe3+ accumulates to reach the critical parameter that stimulates peroxidation. According to this molecular mechanism the antioxidant potency of carvedilol can be ascribed to its ability to bind a species, Fe3+, that is a catalyst of the process and to its lipophilic nature that concentrates it in the membranes where Fe3+ is generated by a site specific mechanism.

Iron attenuates nitric oxide level and iNOS expression in endotoxin-treated mice

The effect of exogenous Fe-citrate complex (Fe doses of 120 and 240 micromol/kg) on nitric oxide (NO) production in vivo has been studied in blood and liver tissue of endotoxin-treated mice. Fe-citrate complex was administered to mice subcutaneously at the same time with intravenous injection of Escherichia coli lipopolysaccharide (LPS). Iron-dependent decrease in NO2-/NO3- and nitrosyl hemoglobin levels in blood of animals was detected at 6 h after LPS administration, suggesting systemic attenuation of NO generation. NO production in the liver tissue of LPS-treated mice was decreased after Fe administration judging from the amount of mononitrosyl-iron complexes formed in the tissue by diethyldithiocarbamate. The iNOS protein determination in the liver tissue of LPS-treated mice demonstrated iron-dependent inhibition of iNOS expression. We have found previously that exogenous iron does not affect systemic NO level when it is given at 6 h after LPS injection, i.e. after iNOS expression. This is a first report demonstrating iron-dependent iNOS down-regulation in endotoxin-treated mice.

Generation of oxygen radicals from iron complex of orellanine, a mushroom nephrotoxin; preliminary ESR and spin-trapping studies

Orellanine, [2,2'-bipyridine]-3,3',4,4'-tetrol-1,1'-dioxide, is the toxin responsible for the lethal nephrotoxicity of some Cortinarius mushrooms. Our present ESR and spin-trapping studies of the redox properties of the system of non-illuminated orellanine, ferrous iron and dioxygen contribute to understanding the molecular mechanism of its toxicity. UV-visible spectrophotometry, cyclic voltammetry and ESR in frozen medium showed the formation of a wine-red tris complex, Fe(III)Or3. This ferric complex is easily reducible (Ep = -565 mV vs Ag/AgCl/3M KCl at pH 7), involving a one-electron reversible process. Spin-trapping using DMPO is employed to detect the generation of superoxide anion and hydroxyl radicals. The instantaneous one-electron oxidation of ferrous ions in the presence of the toxin under air is concomitant with dioxygen consumption as supported by dioxygen consumption. GSH involves the toxin and ferrous ions under air in a redox cycling process resulting in the production of glutathionyl and oxygen free radicals, observed for the first time with an iron complex of a mushroom toxin. In most cases, EDTA is not able to prevent the Fe(III)Or3 and radical formation. The ortho-dihydroxylated groups borne by the di-N-oxidized bipyridine structure and not the bipyridine structure itself, are responsible for the formation of a stable ferric complex at pH 7, as they are for the generation of an apparently stable ortho-semiquinone anion radical. These one-electron mechanisms may play a major role in some of the known toxic effects of orellanine.

Effects of additional iron-chelators on Fe(2+)-initiated lipid peroxidation: evidence to support the Fe2+ ... Fe3+ complex as the initiator

The addition of chelated Fe2+ ions in a liposomal system often results in a short lag period before peroxidation starts. The addition of a second chelator at the end of the lag period results in an inhibition of the lipid peroxidation. The degree of inhibition depends on the stability constants of the chelator in ligating Fe2+ and/or Fe3+. A more striking inhibitory effect was observed for the chelators with higher stability constant for either or both Fe(2+)- and Fe(3+)-complex, but much less inhibition was found for those with lower stability constants for both complexes. Assuming that the "initiator" for iron-dependent lipid peroxidation is formed through the redox process of iron ion and finally emerged at the end of the latent period, the inhibitory effect of the second chelator may be explained as the abstraction of either Fe2+ or Fe3+ from the initiator by an additional free chelator, which results in the decomposition of the initiator. This study supports the hypothesis that a Fe2+ ... Fe3+ complex is responsible for iron-initiated lipid peroxidation.