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PubMed1997

Detection of free radicals produced from the reaction of cytochrome P-450 with linoleic acid hydroperoxide.

The ESR spin-trapping technique was employed to investigate the reaction of rabbit cytochrome P-450 1A2 (P450) with linoleic acid hydroperoxide. This system was compared with chemical systems where FeSO4 or FeCl3 was used in place of P450. The spin trap 5, 5'-dimethyl-1-pyrroline N-oxide (DMPO) was employed to detect and identify radical species. The DMPO adducts of hydroxyl, O2-., peroxyl, methyl and acyl radicals were detected in the P450 system. The reaction did not require NADPH-cytochrome P-450 reductase or NADPH. The same DMPO-radical adducts were detected in the FeSO4 system. Only DMPO-.OH radical adduct and carbon-centred radical adducts were detected in the FeCl3 system. Peroxyl radical production was completely O2-dependent. We propose that polyunsaturated fatty acids are initially reduced to form alkoxyl radicals, which then undergo intramolecular rearrangement to form epoxyalkyl radicals. Each epoxyalkyl radical reacts with O2, forming a peroxyl radical. Subsequent unimolecular decomposition of this peroxyl radical eliminates O2-. radical.

Animals↗
PubMed1998

Antioxidant power of angiotensin-converting enzyme inhibitors in vitro.

AIMS: There is controversy regarding the potential antioxidant effect of captopril, therefore this study was performed to compare the in vitro antioxidant power of captopril with other angiotensin-converting enzyme (ACE) inhibitors. METHODS: Antioxidant power of captopril, enalapril, fosinopril, perindopril, quinapril and ramipril in aqueous solution was measured using the ferric reducing (antioxidant) power (FRAP) assay; captopril was also measured in ethanolic solution. RESULTS: Only captopril showed significant antioxidant power, demonstrating a stoichiometric factor of 1.0 in this assay. Concentration-related antioxidant power was seen in both aqueous and ethanolic solutions. CONCLUSIONS: Captopril shows antioxidant activity in vitro. This property could be relevant in vivo if captopril is concentrated in membranes, lipoproteins or at other important sites.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed2002

Fe(III)-mediated cellular toxicity.

Because it can undergo reversible changes in oxidation state, iron is an excellent biocatalyst but also a potentially deleterious metal. Iron-mediated toxicity has been ascribed to Fe(II), which reacts with oxygen to generate free radicals that damage macromolecules and cause cell death. However, we now report that Fe(III) exhibits microbicidal activity towards strains of Salmonella enterica, Escherichia coli and Klebsiella pneumoniae defective in the Fe(III)-responding PmrA/PmrB signal transduction system. Fe(III) bound to a pmrA Salmonella mutant more effectively than to the isogenic wild-type strain and exerted its microbicidal activity even under anaerobic conditions. Moreover, Fe(III) permeabilized the outer membrane of the pmrA mutant, rendering it susceptible to vancomycin, which is normally non-toxic to Gram-negative species. On the other hand, Fe(III) did not affect the viability of a mutant defective in Fur, the major regulator of cytosolic iron homeostasis, which is hypersensitive to Fe(II)-mediated toxicity. A functional pmrA gene was necessary for bacterial survival in soil. Our results indicate that Fe(III) exerts its microbicidal activity by a mechanism that is oxygen independent and different from that mediated by Fe(II).

Bacterial Proteins↗
PubMed2000

Resonance Raman study of multihemic c-type cytochromes from Desulfuromonas acetoxidans.

Two multihemic cytochromes c from the sulfur reducing bacteria Desulfuromonas acetoxidans have been studied by optical and resonance Raman spectroscopy: cytochrome c551.5, a trihemic cytochrome and cytochrome c Mr 50 000, a recently isolated high molecular mass cytochrome. The redox and Raman characteristics of cytochrome c551.5 are compared to those of the tetrahemic cytochromes c3 from Desulfovibrio. While the redox behavior, followed by spectroelectrochemistry, is similar to that of cytochrome c3, showing the same conformational change after reduction of the highest potential heme, the Raman data show a contribution from a His- form of the axial ligands and lead to the assignment of a band at 218 cm-1 to the Fe(III)-(His)2 stretching vibration. The Raman data on cytochrome c Mr 50 000 are in favor of an entirely low spin species with two different sets of axial ligands. A partially reduced state is easily accessible by ascorbate addition.

Ascorbic Acid↗
PubMed2002

Multiple influences of nitrate on uranium solubility during bioremediation of uranium-contaminated subsurface sediments.

Microbiological reduction of soluble U(VI) to insoluble U(IV) has been proposed as a remediation strategy for uranium-contaminated groundwater. Nitrate is a common co-contaminant with uranium. Nitrate inhibited U(VI) reduction in acetate-amended aquifer sediments collected from a uranium-contaminated site in New Mexico. Once nitrate was depleted, both U(VI) and Fe(III) were reduced concurrently. When nitrate was added to sediments in which U(VI) had been reduced, U(VI) reappeared in solution. Parallel studies with the dissimilatory Fe(III)-, U(VI)- and nitrate-reducing microorganism, Geobacter metallireducens, demonstrated that nitrate inhibited reduction of Fe(III) and U(VI) in cell suspensions of cells that had been grown with nitrate as the electron acceptor, but not in Fe(III)-grown cells. Suspensions of nitrate-grown G. metallireducens oxidized Fe(II) and U(IV) with nitrate as the electron acceptor. U(IV) oxidation was accelerated when Fe(II) was also added, presumably due to the Fe(III) being formed abiotically oxidizing U(IV). These studies demonstrate that although the presence of nitrate is not likely to be an impediment to the bioremediation of uranium contamination with microbial U(VI) reduction, it is necessary to reduce nitrate before U(VI) can be reduced. These results also suggest that anaerobic oxidation of U(IV) to U(VI) with nitrate serving as the electron acceptor may provide a novel strategy for solubilizing and extracting microbial U(IV) precipitates from the subsurface.

Ferric Compounds↗
PubMed2002

Iron (III) induces aggregation of hyperphosphorylated tau and its reduction to iron (II) reverses the aggregation: implications in the formation of neurofibrillary tangles of Alzheimer's disease.

Iron as well as aluminum is reported to accumulate in neurons with neurofibrillary tangles (NFTs) of Alzheimer's disease (AD) brain. Previously we demonstrated that aluminum (III) shows phosphate-dependent binding with hyperphosphorylated tau (PHFtau), the major constituent of NFTs, thereby inducing aggregation of PHFtau. Herein we report that iron (III) can also induce aggregation of soluble PHFtau. Importantly, for the aggregation of PHFtau to occur, iron in the oxidized state (III) is essential since iron in the reduced state (II) lacks such ability. Furthermore, iron (III)-induced aggregation is reversed by reducing iron (III) to iron (II). Thus the iron-participating aggregation is mediated not only by tau phosphorylation but also by the transition of iron between reduced (II) and oxidized (III) states. Further incubation of insoluble PHFtau aggregates isolated from AD brain with reducing agents produced liberation of solubilized PHFtau and iron (II), indicating that PHFtau in association with iron (III) constitutes the insoluble pool of PHFtau. These results indicate that iron might play a role in the aggregation of PHFtau leading to the formation of NFTs in AD brain.

Aluminum↗
PubMed1998

Differential effects of glutathione and cysteine on Fe2+, Fe3+, H2O2 and myoglobin-induced proximal tubular cell attack.

Glutathione (GSH) is widely advocated as a cytoprotectant for preventing oxidant forms of renal damage. However, in the case of myoglobinuric tubular injury, both beneficial and adverse effects have been noted. The purpose of this study was to help elucidate this seeming paradox by assessing the impact on thiol supplementation on normal tubules and on tubules subjected to individual components of heme protein-induced oxidant attack (Fe2+, Fe3+, and H2O2). Isolated mouse proximal tubular segments (PTS) were exposed to either GSH or cysteine under normal conditions or in the presence of exogenous Fe2+, Fe3+, or H2O2. Lethal cell injury (LDH release) and lipid peroxidation (malondialdehyde) were then assessed. GSH and cysteine exerted iron dependent, H2O2 independent, pro-oxidant effects on normal PTS. Both were also pro-oxidant in the presence of an exogenous Fe3+ challenge. In contrast, each attenuated Fe2+ cytotoxicity. The importance of iron's redox status on the expression of tubular injury was further underscored by the fact that Fe3+ partially blocked Fe2+'s cytotoxic effects. GSH mitigated H2O2 toxicity (consistent with a fueling of GSH peroxidase activity). Conversely, cysteine promoted H2O2's injurious effects. To assess the impact of thiol supplementation on a fully integrated model of heme protein toxicity, proximal tubular (HK-2) cells were cultured with myoglobin x 24 hours +/- test reactants. Exogenous GSH worsened, while GSH depletion (BSO) protected, against myoglobin toxicity (indicating a predominance of GSH's pro-oxidant effects). Conversely, cysteine (but not homocysteine) decreased myoglobin toxicity. These GSH/cysteine effects were confirmed in LLC-PK1 cells subjected to iron attack. We conclude that: (1) GSH and cysteine can exert pro- and anti-oxidant effects, depending on the nature of the oxidant challenge and iron's redox status; (2) Fe3+ can function as a cytoprotectant, partially offsetting Fe2+ toxicity; and (3) cysteine, although potentially pro-oxidant, can mitigate heme protein-induced injury. Since the kidney rapidly catabolizes GSH to cysteine, the latter may be at least partially responsible for GSH's reported cytoprotective actions against myoglobinuric acute renal failure.

Animals↗
PubMed2000

Antiplatelet therapy alters iron requirements in hemodialysis patients.

Hemodialysis (HD) patients are prone to develop iron deficiency because of consumption of iron stores during erythropoietin (EPO) therapy. Data are needed to establish the factors involved in the different iron needs among these patients. Sixty-five HD patients were prospectively studied during a year. The subjects were dialyzed through polytetrafluoroethylene (PTFE) grafts (n = 23), arteriovenous native fistulae (n = 41), and a Permcath (n = 1). Twenty-four patients were administered aspirin; 23 patients, ticlopidine; 1 patient, dipyridamole; and 4 patients, anticoagulation with acenocoumarol. Iron supplementation (oral or parenteral) and laboratory parameters were recorded monthly. Significant differences in iron requirements, depending on the use of antiplatelet and/or anticoagulation agents, were found. Total parenteral iron supplements were greater in patients on antiplatelet therapy with either native or graft vascular accesses compared with the rest (2,406 +/- 1,445 versus 1,562 +/- 858 mg; P = 0.0081). Twelve of 52 patients on antiplatelet therapy required oral iron and only 1 of 13 patients not on antiplatelet therapy was administered oral iron supplements (P < 0.05). Patients on antiplatelet therapy were administered more transfusions (1.9 +/- 3.8 transfusions/y) than individuals not on antiplatelet therapy (0.15 +/- 0.3 transfusions/y; P = 0.0015). However, only patients with PTFE grafts on antiplatelet therapy had a post-HD bleeding time longer than patients not on antiplatelet therapy (9.1 +/- 3.6 versus 5.7 +/- 3.9 minutes; P < 0.0001). Multiple logistic regression analysis showed that the use of antiplatelet agents (P < 0.05) is an independent factor that increased the probability of requiring greater parenteral iron supplements (>2.5 g/y). Patients with PTFE grafts required more EPO than those with autologous fistulae (160 +/- 93 versus 100 +/- 63 U/kg/wk; P = 0.012). No differences between groups were found that could explain this finding. Antiplatelet and/or anticoagulation therapy implied the use of greater amounts of iron supplements in HD patients. Although these greater requirements of iron occurred in parallel with bleeding from the vascular access, additional data favor the existence of other factors, eg, interdialytic blood losses. The present study suggests that antiplatelet therapy may be an important factor in determining iron requirements in HD patients. Moreover, our data relate for the first time the use of prosthetic grafts with increased EPO requirements, an issue of great potential importance in the debate about vascular access policy in dialysis units.

Administration, Oral↗
PubMed2001

Inhibition of the NA(+)/H(+) exchanger reduces rat hepatic stellate cell activity and liver fibrosis: an in vitro and in vivo study.

BACKGROUND & AIMS: The Na(+)/H(+) exchanger is the main intracellular pH (pH(i)) regulator in hepatic stellate cells (HSCs) and plays a key role in regulating proliferation and gene expression. We evaluated the effect of specific inhibition of this exchanger on HSC proliferation and collagen synthesis in vivo and in vitro. METHODS: Rat HSCs were incubated in the presence of platelet-derived growth factor (PDGF), transforming growth factor (TGF)-beta1, iron ascorbate (FeAsc), and ferric nitrilotriacetate solution (FeNTA) with or without the Na(+)/H(+) exchanger inhibitor 5-N-ethyl-N-isopropyl-amiloride (EIPA). pH(i) and Na(+)/H(+) exchanger activity, cell proliferation, and type I collagen accumulation were measured by using the fluorescent dye 2',7'-bis-(carboxyethyl)-5(6)-carboxyfluorescein, by immunohistochemistry for bromodeoxyuridine, and by enzyme-linked immunosorbent assay, respectively. In vivo liver fibrosis was induced by dimethylnitrosamine administration and bile duct ligation (BDL) in rats treated or not treated with amiloride. RESULTS: PDGF, FeAsc, and FeNTA increased Na(+)/H(+) exchange activity and induced HSC proliferation. TGF-beta1 had no effect on the Na(+)/H(+) exchanger and was able, as for FeAsc and FeNTA, to induce type I collagen accumulation. EIPA inhibited all the effects determined by PDGF, FeAsc, and FeNTA and had no effect on TGF-beta1-induced collagen accumulation. In vivo, amiloride reduced HSC proliferation, activation, collagen deposition, and collagen synthesis. CONCLUSIONS: The Na(+)/H(+) exchanger can play a key role in the development of liver fibrosis and in HSC activation in vivo.

Amiloride↗
PubMed2002

[Long-term management of anemia in chronic inflammatory bowel disease].

The development of a stepwise therapy, as detailed below, can be administered to the mostly young patients with Crohn's disease and ulcerative colitis on an out-patient basis and appropriate to their needs. This is true not only for the activity of the disease, but also for extraintestinal manifestations. The numerous variations in the stepwise anti-inflammatory therapy of chronic inflammatory bowel disease, but also in the substitution therapy of deficiency states and the therapy of accompanying extraintestinal diseases provide the gastroenterologist with the possibility of a long-term treatment tailored to the needs of the individual patient.

Anemia, Iron-Deficiency↗
PubMed2004

Metals removal from aqueous solution by iron-based bonding agents.

UNLABELLED: GOAL AND SCOPE AND BACKGROUND: The application of a promising method, termed sorptive flotation, for the removal of chromium(VI) and zinc ions was the aim of the present paper. A special case of sorptive flotation is adsorbing colloid flotation. Suitable sorbent preparation techniques have been developed in the laboratory. METHODS: Sorptive flotation, consisting of the sorption and flotation processes combined in series, has proved to give fast and satisfactory treatment of the industrial streams and effluents bearing dilute aqueous solutions of zinc and chromium(VI). RESULTS AND DISCUSSION: Goethite has proved to be effective for the removal of chromium(VI) and zinc ions. Also, adsorbing colloid flotation with ferric hydroxide (as the co-precipitant) could be an alternative method to the above-mentioned separation of metal ions. In both cases, chromium(VI) (pH=4) and zinc (pH=7) removal was about 100%. CONCLUSION: The reasons for selecting the iron-based bonding materials, like goethite and/or in-situ produced ferric hydroxide, are that they are cheap, easily synthesized, suitable both for cation and anion sorption, and, furthermore, that they present low risks for adding a further pollutant to the system. Promising results were obtained. RECOMMENDATION AND OUTLOOK: The application of goethite and in-situ produced ferric hydroxide has demonstrated their effectiveness in the removal of heavy metal ions, such as chromium anions and zinc cations. A proposed continuation of current work is the utilization of similar iron oxides, for instance synthesized akaganeite. The comparison between the results reported in this paper with the results reported in the literature, also deserves attention.

Adsorption↗
PubMed1976

Observations and interpretation of x-ray absorption edges in iron compounds and proteins.

X-ray absorption spectra near the Kalpha edge have been measured in various iron group compounds using the intense synchrotron radiation at the Stanford Synchrotron Research Project. In the cubic compounds KMF3 where M = Mn+2, Fe+2, Co+2, Ni+2, and Zn+2, well resolved lines were observed and assigned to the 1s leads to 3d, 1s leads to 4s, and 1s leads to 4p transitions. The observed energies agreed rather well with the spectroscopic energy levels of the Z + 1 ion and the intensities are shown to agree with those expected on the basis of one electron transitions of the form Z 1s2dn(L,S) leads to (Z + 1)1s2dnn'l'(L",S). The energies of the intense 1s leads to 4p transition increase by about 5 V going from KFeF3 to K2NaFeF6, but only by about 1 V from K4Fe(CN)6 to K3Fe(CN)6. The transitions confirm that upon oxidation of the hexacyanides the iron electronic structure barely changes. In the iron sulfur protein rubredoxin, where the iron is bound to a tetrahedron of sulfurs, the 1s leads to 3d transition was about seven times more intense than the same transition in an octahedrally coordinated compound. These intensities parallel those observed in the d-d transitions of optical spectra, because in both types of spectra the intensities depend upon 4p admixture. In the heme protein cytochrome c, upon oxidation the 1s leads to 4p transition shifts only about 1 V to higher energies similar to the iron hexacyanides. These results are discussed in terms of covalent bonding.

Cytochrome c Group↗
PubMed1980

Redox conformation changes in refined tuna cytochrome c.

Tuna ferrocytochrome c and ferricytochrome c have been refined independently at high resolution (1.5 A and 1.8 A) to crystallographic residual errors of 17.3% and 20.8%, respectively. Small but significant conformational differences are seen surrounding a buried water molecule that is hydrogen bonded to Asn-52, Tyr-67, and Thr-78. In the oxidized state, this water molecule is 1.0 A closer to the heme and the heme has moved 0.15 A out of its heme crevice; both changes lead to a more polar microenvironment for the heme. Chemical modification studies, patterns of evolutionary conservatism, structural differences in bacterial cytochromes, and x-ray studies all agree that the "active site" for cytochrome c is bounded by lysines 8, 13,27, 72, 79, 86, and 87 (thus containing the evolutionary conservative 72-87 loop) and has the buried water molecule just below its surface and the opening of the heme crevice slightly to one side.

Animals↗
PubMed1998

Central role of Ferrous/Ferric iron in the ultraviolet B irradiation-mediated signaling pathway leading to increased interstitial collagenase (matrix-degrading metalloprotease (MMP)-1) and stromelysin-1 (MMP-3) mRNA levels in cultured human dermal fibroblasts.

Reactive oxygen species (ROS) are important second messengers for the induction of several genes in a variety of physiological and pathological conditions. Ultraviolet B (UVB) irradiation has recently been shown to generate lipid peroxidation products and hydroxyl radicals (HO.) with detrimental long term effects like cancer formation and premature aging of the skin. Here, we addressed the question of whether ferric/ferrous iron via the generation of ROS may mediate the UVB response, finally leading to connective tissue degradation, a hallmark in carcinogenesis and aging. Therefore, we studied the involvement of iron and ROS in the modulation of Jun N-terminal kinase 2 (JNK2) activity, c-jun and c-fos mRNA levels, key signaling steps in the transcriptional control of matrix-degrading metalloprotease (MMP)-1/interstitial collagenase and MMP-3/stromelysin-1 after UVB irradiation of human dermal fibroblasts in vitro. The iron-driven generation of lipid peroxides and hydroxyl radicals were identified as early events in the downstream signaling pathway of the UVB response leading to a 15-fold increase in JNK2 activity, a 3.5-fold increase in c-jun, to a 6-fold increase in MMP-1, and a 3.8-fold increase in MMP-3 mRNA levels, while virtually no alteration of c-fos mRNA levels were observed. Diminished generation of reactive oxygen species resulted in a significant reduction of JNK2 activity, c-jun, MMP-1, and MMP-3 mRNA levels after UVB irradiation compared with UVB-irradiated cells. Collectively, we have identified the iron-driven Fenton reaction and lipid peroxidation as possible central mechanisms underlying signal transduction of the UVB response.

Chelating Agents↗
PubMed2003

Role of ceruloplasmin in macrophage iron efflux during hypoxia.

The reticuloendothelial system has a central role in erythropoiesis and iron homeostasis. An important function of reticuloendothelial macrophages is phagocytosis of senescent red blood cells. The iron liberated from heme is recycled for delivery to erythrocyte precursors for a new round of hemoglobin synthesis. The molecular mechanism by which recycled iron is released from macrophages remains unresolved. We have investigated the mechanism of macrophage iron efflux, focusing on the role of ceruloplasmin (Cp), a copper protein with a potent ferroxidase activity that converts Fe2+ to Fe3+ in the presence of molecular oxygen. As shown by others, Cp markedly increased iron binding to apotransferrin at acidic pH; however, the physiological significance of this finding is uncertain because little stimulation was observed at neutral pH. Introduction of a hypoxic atmosphere resulted in marked Cp-stimulated binding of iron to apotransferrin at physiological pH. The role of Cp in cellular iron release was examined in U937 monocytic cells induced to differentiate to the macrophage lineage. Cp added at its normal plasma concentration increased the rate of 55Fe release from U937 cells by about 250%. The stimulation was absolutely dependent on the presence of apotransferrin and hypoxia. Cp-stimulated iron release was confirmed in mouse peritoneal macrophages. Stimulation of iron release required an intracellular "labile iron pool" that was rapidly depleted in the presence of Cp and apotransferrin. Ferroxidase-mediated loading of iron into apotransferrin was critical for iron release because ferroxidase-deficient Cp was inactive and because holotransferrin could not substitute for apotransferrin. The extracellular iron concentration was critical as shown by inhibition of iron release by exogenous free iron, and marked enhancement of release by an iron chelator. Together these data show that Cp stimulates iron release from macrophages under hypoxic conditions by a ferroxidase-dependent mechanism, possibly involving generation of a negative iron gradient.

Animals↗
PubMed2004

Reactivity studies of the Fe(III) and Fe(II)NO forms of human neuroglobin reveal a potential role against oxidative stress.

Neuroglobin, recently discovered in the brain and in the retina of vertebrates, belongs to the class of hexacoordinate globins, in which the distal histidine coordinates the iron center in both the Fe(II) and Fe(III) forms. As for most other hexacoordinate globins, the physiological function of neuroglobin is still unclear, but seems to be related to neuronal survival following acute hypoxia. In this study, we have addressed the question whether human neuroglobin could act as a scavenger of toxic species, such as nitrogen monoxide, peroxynitrite, and hydrogen peroxide, which are generated at high levels in the brain during hypoxia; we have also investigated the kinetics of the reactions of its Fe(III) (metNGB) and Fe(II)NO forms with several reagents. Binding of cyanide or NO* to metNGB follows bi-exponential kinetics, showing the existence of two different protein conformations. In the presence of excess NO*, metNGB is converted into NGBFe(II)NO by reductive nitrosylation, in analogy to the reactions of NO* with metmyoglobin and methemoglobin. The Fe(II)NO form of neuroglobin is oxidized to metNGB by peroxynitrite and dioxygen, two reactions that also take place in hemoglobin, albeit at lower rates. In contrast to myoglobin and hemoglobin, metNGB unexpectedly does not generate the cytotoxic ferryl form of the protein upon addition of either peroxynitrite or hydrogen peroxide. Taken together, our data indicate that human neuroglobin may be an efficient scavenger of reactive oxidizing species and thus may play a role in the cellular defense against oxidative stress.

Ferric Compounds↗
PubMed1994

Absorption of iron from ferric hydroxypyranone complexes.

The absorption of 59Fe from preparations of FeSO4 and the ferric hydroxypyranone complexes maltol and ethyl maltol was studied by whole-body counting in normal subjects and patients with Fe deficiency. Fe in the Fe3+ complexes was in general absorbed almost as well as Fe2+. It is concluded that the absorption of Fe3+ from hydroxypyranone complexes is much greater than that from simple Fe3+ salts; this may prove an efficient and less toxic form of Fe for the treatment of deficiency.

Adult↗