Chemistry of iron and copper in radical reactions

Chain Reaction of Fenton Autoxidation of Tartaric Acid: Critical Behavior at Low pH

Autoxidation of tartaric acid in air-saturated aqueous solutions in the presence of Fe(II) at low pH, 2.5, shows autocatalytic behavior with distinct initiation, propagation, and termination phases. With increasing pH, the initiation phase speeds up, while the propagation phase shortens and reduces to none. We show that the propagation phase is a chain reaction that occurs via activation of oxygen in the initiation stage with the production of hydrogen peroxide. The subsequent Fenton oxidation that regenerates hydrogen peroxide with a positive feedback is typical of a self-sustained chain reaction. The conditions for such a chain reaction are shown to be similar to those of a dynamical system with critical behavior; namely, the system becomes unstable when the kinetic matrix of pseudo-first-order reaction becomes negatively defined with a negative eigenvalue giving the rate of exponential (chain) growth of the reactive species.

Regioselective protein oxidative cleavage enabled by enzyme-like recognition of an inorganic metal oxo cluster ligand

Oxidative modifications of proteins are key to many applications in biotechnology. Metal-catalyzed oxidation reactions efficiently oxidize proteins but with low selectivity, and are highly dependent on the protein surface residues to direct the reaction. Herein, we demonstrate that discrete inorganic ligands such as polyoxometalates enable an efficient and selective protein oxidative cleavage. In the presence of ascorbate (1 mM), the Cu-substituted polyoxometalate K₈[Cu²⁺(H₂O)(α₂-P₂W₁₇O₆₁)], (Cu^IIWD, 0.05 mM) selectively cleave hen egg white lysozyme under physiological conditions (pH =7.5, 37 °C) producing only four bands in the gel electropherogram (12.7, 11, 10, and 5 kDa). Liquid chromatography/mass spectrometry analysis reveals a regioselective cleavage in the vicinity of crystallographic Cu^IIWD/lysozyme interaction sites. Mechanistically, polyoxometalate is critical to position the Cu at the protein surface and limit the generation of oxidative species to the proximity of binding sites. Ultimately, this study outlines the potential of discrete, designable metal oxo clusters as catalysts for the selective modification of proteins through radical mechanisms under non-denaturing conditions.

Iron(II) and Copper(I) Control the Total Regioselectivity in the Hydrobromination of Alkenes

A new method that allows the complete control of the regioselectivity of the hydrobromination reaction of alkenes is described. Herein, we report a radical procedure with TMSBr and oxygen as common reagents, where the formation of the anti-Markovnikov product occurs in the presence of parts per million amounts of the Cu(I) species and the formation of the Markovnikov product occurs in the presence of 30 mol % iron(II) bromide. Density functional theory calculations combined with Fukui’s radical susceptibilities support the obtained results.

Copper chloride inhibits brush border membrane enzymes, alters antioxidant and metabolic status and damages DNA in rat intestine: a dose-dependent study

Copper (Cu) is an extensively used heavy metal and an indispensible micronutrient for living beings. However, Cu is also toxic and exerts multiple adverse health effects when humans are exposed to high levels of this metal. We have examined the effect of single acute oral dose of copper chloride (CuCl₂) on parameters of oxidative stress, cellular metabolism, membrane and DNA damage in rat intestine. Adult male Wistar rats were divided into four groups and separately administered a single oral dose of 5, 15, 30 and 40 mg CuCl₂/kg body weight. Rats not administered CuCl₂ served as the control. Oral administration of CuCl₂ led to significant alterations in the activities of metabolic and membrane-bound enzymes; brush border enzymes were inhibited by 45-75% relative to the control set. Inhibition of antioxidant enzymes diminished the metal-reducing and free radical quenching ability of the cells. Oxidative damage caused cellular oxidation of thiols, proteins and lipids. Diphenylamine and comet assays showed that CuCl₂ treatment enhanced DNA damage while DNA-protein crosslinking was also increased in the intestinal cells. Examination of stained sections showed that CuCl₂ treatment led to marked histological changes in the intestine. All the changes seen were in a CuCl₂ dose-dependent manner with more prominent alterations at higher doses of CuCl₂. These results clearly show that oral administration of CuCl₂ results in oxidative damage to the intestine which can impair its digestive and absorptive functions.

Kinetics of autoxidation of tartaric acid in presence of iron

The kinetics of the autoxidation reaction of tartaric acid in an air-saturated solution in the presence of Fe(II) show autocatalytic behavior with distinct initiation, propagation, and termination phases. The initiation phase, which involves activation of dissolved oxygen, decreases with increasing pH, over the test range of pH of 2.5-4.5, indicating that activation of oxygen is catalyzed by an Fe(II)-tartrate complex. The autocatalytic nature of this reaction indicates the presence of a catalytic intermediate that is produced during the initiation phase and regenerated during the propagation phase. The addition of catalase, as well as direct measurements, provided evidence of the presence and kinetic action of hydrogen peroxide as one of the intermediates. Direct addition of hydrogen peroxide resulted in shortening of the initiation stage and the propagation phase with similar rates as in the autoxidation reaction at low pH. The propagation is approximately a zero order reaction with respect to oxygen and iron. The kinetic analysis suggests that an intermediate catalytic complex(s) involving a ferryl ion (FeO²⁺) controls the rate of the propagation reaction. The Fe(III) formation shows autocatalytic behavior that mirrors the dissolved oxygen consumption patterns under all pH conditions studied. At pH values of 2.5 and 3.0, Fe(III) accumulated to a maximum, before it was partially consumed. This maximum coincided with the depletion of dissolved oxygen. The consumption of Fe(III), or the reduction of Fe(III) back to Fe(II), reflects the catalytic nature of Fe(II) and the essential role of tartaric acid in the initiation phase of Fenton's original reaction.

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.

Effect of Operating Conditions on the Chemical Phosphate Removal Using during Ferrous Iron Oxidation

In this study, the effect of operating parameters and the co-existing ions on the phosphate removal during the ferrous iron oxidation was investigated. Results showed that with the increase of DO and [Fe (II)]0, the final phosphate removal rate both increased. But with increasing of pH, the final phosphate removal rate firstly increased and then decreased when the pH was higher than 8.0. The co-existing ions affected the final removal rate significantly, and the kinetics of phosphate removal followed the pseudo-first-order kinetic model. The corresponding kobs trends for the cation followed the order of Cu2+>Mn2+>Zn2+>NH4+-N. The presence of Cu2+ promoted the phosphate removal significantly. Compared with the control, , the time required to achieve 40 % phosphate removal rate, at the condition of 0.5 mg/L Cu2+, reduced from 60 min to 10 s. However, the selective anions inhibited the phosphate removal, due to the formation of Fe-anions complexes. The effect of selective anions on the phosphate removal rate constant decreased in the order of SO42->Cl-> NO3-.

Friedreich's ataxia causes redistribution of iron, copper, and zinc in the dentate nucleus

Friedreich's ataxia (FRDA) causes selective atrophy of the large neurons of the dentate nucleus (DN). High iron (Fe) concentration and failure to clear the metal from the affected brain tissue are potential risk factors in the progression of the lesion. The DN also contains relatively high amounts of copper (Cu) and zinc (Zn), but the importance of these metals in FRDA has not been established. This report describes nondestructive quantitative X-ray fluorescence (XRF) and "mapping" of Fe, Cu, and Zn in polyethylene glycol–dimethylsulfoxide (PEG/DMSO)-embedded DN of 10 FRDA patients and 13 controls. Fe fluorescence arose predominantly from the hilar white matter, whereas Cu and Zn were present at peak levels in DN gray matter. Despite collapse of the DN in FRDA, the location of the peak Fe signal did not change. In contrast, the Cu and Zn regions broadened and overlapped extensively with the Fe-rich region. Maximal metal concentrations did not differ from normal (in micrograms per milliliter of solid PEG/DMSO as means ± S.D.): Fe normal, 364 ± 117, FRDA, 344 ± 159; Cu normal, 33 ± 13, FRDA, 33 ± 18; and Zn normal, 32 ± 16, FRDA, 33 ± 19. Tissues were recovered from PEG/DMSO and transferred into paraffin for matching with immunohistochemistry of neuron-specific enolase (NSE), glutamic acid decarboxylase (GAD), and ferritin. NSE and GAD reaction products confirmed neuronal atrophy and grumose degeneration that coincided with abnormally diffuse Cu and Zn zones. Ferritin immunohistochemistry matched Fe XRF maps, revealing the most abundant reaction product in oligodendroglia of the DN hilus. In FRDA, these cells were smaller and more numerous than normal. In the atrophic DN gray matter of FRDA, anti-ferritin labeled mostly hypertrophic microglia. Immunohistochemistry and immunofluorescence of the Cu-responsive proteins Cu,Zn-superoxide dismutase and Cu⁺⁺-transporting ATPase α-peptide did not detect specific responses to Cu redistribution in FRDA. In contrast, metallothionein (MT)-positive processes were more abundant than normal and contributed to the gliosis of the DN. The isoforms of MT, MT-1/2, and brain-specific MT-3 displayed only limited co-localization with glial fibrillary acidic protein. The results suggest that MT can provide effective protection against endogenous Cu and Zn toxicity in FRDA, similar to the neuroprotective sequestration of Fe in holoferritin.

Protective effects of manganese(II) chloride on hyaluronan degradation by oxidative system ascorbate plus cupric chloride

The degradation of several high-molar-mass hyaluronan samples was investigated in the presence of ascorbic acid itself and further by an oxidative system composed of ascorbic acid plus transition metal ions, i.e. Fe(II) or Cu(II) ions. The latter oxidative system imitates conditions in a joint synovial fluid during early phase of acute joint inflammation and can be used as a model for monitoring oxidative degradation of hyaluronan under pathophysiological conditions. The system Cu(II) plus ascorbate (the Weissberger oxidative system) resulted in a more significant decrease of hyaluronan molar mass compared to the oxidative system Fe(II) plus ascorbate. Addition of manganese(II) chloride was found to decrease the rate of the oxidative damage of hyaluronan initiated by ascorbate itself and by the Weissberger system.

Catabolism of hyaluronan: involvement of transition metals

One of the very complex structures in the vertebrates is the joint. The main component of the joint is the synovial fluid with its high-molar-mass glycosaminoglycan hyaluronan, which turnover is approximately twelve hours. Since the synovial fluid does not contain any hyaluronidases, the fast hyaluronan catabolism is caused primarily by reductive-oxidative processes.Eight transition metals - V(23), Mn(25), Fe(26), Co(27), Ni(28), Cu(29), Zn(30), and Mo(42) - naturally occurring in living organism are essential for the control of various metabolic and signaling pathways. They are also the key elements in catabolism of hyaluronan in the joint.In this overview, the role of these metals in physiological and pathophysiological catabolism of hyaluronan is described. The participation of these metals in the initiation and propagation of the radical degradation hyaluronan is critically reviewed.

Reactive oxygen species in programmed death of pea guard cells

Hydrogen peroxide potentiates CN(-)-induced apoptosis of guard cells recorded as destruction of cell nuclei in the epidermis from pea leaves. A still stronger effect was exerted by the addition of H2O2 and NADH, which are the substrates of the plant cell wall peroxidase producing O2*- coupled to the oxidation of NADH. The CN(-)-or (CN(-) + H2O2)-induced destruction of guard cell nuclei was completely removed by nitroblue tetrazolium (NBT) oxidizing O2*- and preventing there-by the subsequent generation of H2O2. The reduced NBT was deposited in the cells as formazan crystals. Cyanide-induced apoptosis was diminished by mannitol and ethanol, which are OH* traps. The dyes Rose Bengal (RB) and tetramethylrhodamine ethyl ester (TMRE) photosensitizing singlet oxygen production suppressed the CN(-)-induced destruction of the cell nuclei in the light. This suppression was removed by exogenous NADH, which reacts with 1O2 yielding O2*-. Incubation of leaf slices with RB in the light lowered the photosynthetic O2 evolution rate and induced the permeability of guard cells for propidium iodide, which cannot pass across intact membranes. Inhibition of photosynthetic O2 evolution by 3-(3',4'-dichlorophenyl)-1,1-dimethylurea or bromoxynil prevented CN(-)-induced apoptosis of guard cells in the light but not in the dark. RB in combination with exogenous NADH caused H2O2 production that was sensitive to NBT and estimated from dichlorofluorescein (DCF) fluorescence. Data on NBT reduction and DCF and TMRE fluorescence obtained using a confocal microscope and data on the NADH-dependent H2O2 production are indicative of generation of reactive oxygen species in the chloroplasts, mitochondria, and nuclear region of guard cells as well as with participation of apoplastic peroxidase. Cyanide inhibited generation of reactive oxygen species in mitochondria and induced their generation in chloroplasts. The results show that H2O2, OH*, and O2*- resources utilized for H2O2 production are involved in apoptosis of guard cells. It is likely that singlet oxygen generated by RB in the light, judging from the permeability of the plasmatic membrane for propidium iodide, makes Photosystem II of chloroplasts inoperative and induces necrosis of the guard cells.

Acute toxicity and bioaccumulation of tributyltin in tissues of Urolophus jamaicensis (yellow stingray)

Tributyltin oxide (TBTO) is the main constituent of tin-based antifouling marine paint used on the hulls of ships to prevent the growth of fouling organisms. TBTO was shown to be hazardous to nontarget organisms. The stingray, Urolophus jamaicensis, may represent the ideal study organism for the adverse effects of TBTO to elasmobranches. This study investigated the toxicity and accumulation of tin in the gill tissue of the stingray U. jamaicensis after acute exposure to TBTO. This work demonstrates the alterations in the morphological architecture of the gill using electron and light microscopy, the induction of stress proteins, and peroxidative damage in response to tributyltin (TBT) exposure. A captured population of U. jamaicencis was housed in isolated, static tank systems. After a minimum 30-d acclimation period, the animals were exposed to one of 5 experimental doses of TBTO (4 microg/L, 2 microg/L, 1 microg/L, 0.5 microg/L, or 0.05 microg/L). A sixth group served as a control population. At 3h following treatment, animals were sacrificed and gill tissue was extracted, processed, and stored for analysis. Results indicate that U. jamaicensis is hypersensitive to TBT exposure. The elasmobranch gill showed a distorted, swollen epithelium with exfoliation following acute exposure to as little as 0.05 microg/L TBTO for 3 h. Graphite furnace atomic absorption spectroscopy (GFAAS) results indicate that tissues of treated animals contained a significantly increased tin concentration as compared to controls. Western blot analysis demonstrated the induction of the stress proteins Hsp 70 and HO1. 4-Hydroxynonenol (4HNE) adduct formation determined by Western blot analysis provides further evidence that observed membrane degradation is a result of lipid peroxidation.

H2O2 intensifies CN(-)-induced apoptosis in pea leaves

H2O2 intensifies CN(-)-induced apoptosis in stoma guard cells and to lesser degree in basic epidermal cells in peels of the lower epidermis isolated from pea leaves. The maximum effect of H2O2 on guard cells was observed at 10(-4) M. By switching on non-cyclic electron transfer in chloroplasts menadione and methyl viologen intensified H2O2 generation in the light, but prevented the CN--induced apoptosis in guard cells. The light stimulation of CN- effect on guard cell apoptosis cannot be caused by disturbance of the ribulose-1,5-bisphosphate carboxylase function and associated OH* generation in chloroplasts with participation of free transition metals in the Fenton or Haber-Weiss type reactions as well as with participation of the FeS clusters of the electron acceptor side of Photosystem I. Menadione and methyl viologen did not suppress the CN(-)-induced apoptosis in epidermal cells that, unlike guard cells, contain mitochondria only, but not chloroplasts. Quinacrine and diphenylene iodonium, inhibitors of NAD(P)H oxidase of cell plasma membrane, had no effect on the respiration and photosynthetic O2 evolution by leaf slices, but prevented the CN(-)-induced guard cell death. The data suggest that NAD(P)H oxidase of guard cell plasma membrane is a source of reactive oxygen species (ROS) needed for execution of CN(-)-induced programmed cell death. Chloroplasts and mitochondria were inefficient as ROS sources in the programmed death of guard cells. When ROS generation is insufficient, exogenous H2O2 exhibits a stimulating effect on programmed cell death. H2O2 decreased the inhibitory effects of DCMU and DNP-INT on the CN(-)-induced apoptosis of guard cells. Quinacrine, DCMU, and DNP-INT had no effect on CN(-)-induced death of epidermal cells.

Low dietary copper increases fecal free radical production, fecal water alkaline phosphatase activity and cytotoxicity in healthy men

One possible dietary factor that may increase susceptibility to colon cancer is inadequate copper intake. The objective of this study was to investigate the effects of low and adequate copper intakes on copper nutriture and putative risk factors for colon cancer susceptibility in healthy men. Seventeen healthy free-living nonsmoking men aged 21-52 y completed a 13-wk controlled feeding study in a randomized crossover design. The basal diet contained 0.59 mg Cu/13.65 MJ. After a 1-wk equilibration period in which the men consumed the basal diet supplemented with 1.0 mg Cu/d, they were randomly assigned to receive either the basal diet or the basal diet supplemented with 2 mg Cu/d for 6 wk. After the first dietary period, the men immediately began to consume the other level of Cu for the last 6 wk. They collected their feces during the equilibration period and during the last 2 wk of the two dietary periods for free radical and fecal water analysis. Low dietary copper significantly (P < 0.01) increased fecal free radical production and fecal water alkaline phosphatase activity. Low dietary copper significantly (P < 0.0001) decreased fecal water copper concentrations but did not affect fecal water volume, pH, iron or zinc concentrations. In contrast to the fecal analysis, hematological indicators of copper status were not significantly affected by the dietary treatments. These results suggest that low dietary copper adversely affects fecal free radical production and fecal water alkaline phosphatase activity, which are putative risk factors for colon cancer.

Carnosol, an antioxidant in rosemary, suppresses inducible nitric oxide synthase through down-regulating nuclear factor-kappaB in mouse macrophages

Carnosol is a naturally occurring phytopolyphenol found in rosemary. Carnosol functions as antioxidant and anticarcinogen. In the present study, we compared the antioxidant activity of carnosol and other compounds extracted from rosemary. Carnosol showed potent antioxidative activity in alpha,alpha-diphenyl-beta-picrylhydrazyl (DPPH) free radicals scavenge and DNA protection from Fenton reaction. High concentrations of nitric oxide (NO) are produced by inducible NO synthase (iNOS) in inflammation and multiple stages of carcinogenesis. Treatment of mouse macrophage RAW 264.7 cell line with carnosol markly reduced lipopolysaccharide (LPS)-stimulated NO production in a concentration-related manner with an IC50 of 9.4 microM; but other tested compounds had slight effects. Western blot, reverse transcription-polymerase chain reaction, and northern blot analyses demonstrated that carnosol decreased LPS-induced iNOS mRNA and protein expression. Carnosol treatment showed reduction of nuclear factor-kappaB (NF-kappaB) subunits translocation and NF-kappaB DNA binding activity in activated macrophages. Carnosol also showed inhibition of iNOS and NF-kappaB promoter activity in transient transfection assay. These activities were referred to down-regulation of inhibitor kappaB (IkappaB) kinase (IKK) activity by carnosol (5 microM), thus inhibited LPS-induced phosphorylation as well as degradation of IkappaBalpha. Carnosol also inhibited LPS-induced p38 and p44/42 mitogen-activated protein kinase (MAPK) activation at a higher concentration (20 microM). These results suggest that carnosol suppresses the NO production and iNOS gene expression by inhibiting NF-kappaB activation, and provide possible mechanisms for its anti-inflammatory and chemopreventive action.

Aqueous infusions of Mediterranean herbs exhibit antioxidant activity towards iron promoted oxidation of phospholipids, linoleic acid, and deoxyribose

Reactive oxygen species (ROS) have been widely known to inflict biological damage upon a variety of biological sites. The ability to counteract any such activity has been the subject of this work, in an attempt to comprehend prooxidant metal ion induced oxidation and its possible physiological consequences. Five Mediterranean aqueous herb infusions have been employed in the investigation of possible pro/antioxidant activity promoted by prooxidant iron ions. In the presence of phospholipid liposomes or linoleic acid micelles or 2-deoxy-D-ribose, it was shown that all of the aqueous infusions used exhibited antioxidant activity in comparison to the iron control. The antioxidant activity, studied on 2-deoxy-D-ribose, at three concentration levels in each herb, appears to be dose dependent, albeit non-linear. The total polyphenol content of the investigated herb infusions, however, does not directly correlate with the observed antioxidant activity. The variable, yet effective, antioxidant capacity of the aqueous infusions indicates that their antioxidant components can quench ROS generating activity, brought on different substrates and likely arisen by variable mechanisms involving different ROS.

Lipid peroxidation in aging and age-dependent diseases

Aging is related with an increase in oxidation products derived from nucleic acids, sugars, sterols and lipids. Evidence will be presented that these different oxidation products are generated by processes induced by changes in the cell membrane structure (CMS), and not by superoxide, as commonly assumed. CMS activate apparently membrane bound phospholipases A2 in mammals and plants. Such changes occur by proliferation, aging and especially by wounding. After activation of phospholipases, influx of Ca2+ ions and activation of lipoxygenases (LOX) is induced. The LOX transform polyunsaturated fatty acids (PUFAs) into lipid hydroperoxides (LOOHs), which seem to be decomposed by action of enzymes to signalling compounds. Following severe cell injury, LOX commit suicide. Their suicide liberates iron ions that induce nonenzymic lipid peroxidation (LPO) processes by generation of radicals. Radicals attack all compounds with the structural element -CH=CH-CH(2)-CH=CH-. Thus, they act on all PUFAs independently either in free or conjugated form. The most abundant LPO products are derived from linoleic acid. Radicals induce generation of peroxyl radicals, which oxidise a great variety of biological compounds including proteins and nucleic acids. Nonenzymic LPO processes are induced artificially by the treatment of pure PUFAs with bivalent metal ions. The products are separable after appropriate derivatisation by gas chromatography (GC). They are identified by electron impact mass spectrometry (EI/MS). The complete spectrum of LPO products obtained by artificial LPO of linoleic acid is detectable after wounding of tissue, in aged individuals and in patients suffering from age-dependent diseases. Genesis of different LPO products derived from linoleic acid will be discussed in detail. Some of the LPO products are of high chemical reactivity and therefore escape detection in biological surrounding. For instance, epoxides and highly unsaturated aldehydic compounds that apparently induce apoptosis.

Copper and genomic stability in mammals

As the free ion and in the form of some complexes, there is no doubt that copper can promote damage to cellular molecules and structures through radical formation. At the same time, and perhaps as a consequence, mammals have evolved means of minimizing levels of free copper ions and destructive copper complexes that enter the organism and its cells. These means include tight binding of copper ions to protein carriers and transporters; direct exchange of copper between protein carriers, transporters, and cuproenzymes; and mobilization of secretory mechanisms and excretory pathways, as needed. As a consequence, normally, and except under certain genetic conditions, copper is likely to be benign to most mammals and not responsible for genomic instability, including fragmentation of and/or alterations to DNA, induction of mutations or apoptosis, or other toxic events. Indeed, cuproenzymes are important members of the antioxidant system of the organism.

Safety evaluation of ferrous bisglycinate chelate

Ferrous bisglycinate chelate (Ferrochel) is a highly stable chelate that can be added to most foods. Data from human and animal studies indicate that the ferrous iron is readily bioavailable with fewer side-effects than the more commonly used iron salts. The acute oral LD50 for male and female Sprague-Dawley (S-D) rats is 2800 mg/kg body weight (560 mg/kg body weight iron [confidence limit (CL) 399-786] as the active ingredient). Male and female CD (Sprague Dawley-derived) rats were fed ferrous bisglycinate as a dietary admixture at doses of 0, 100, 250 and 500 mg/kg body weight/day. There were no biologically or statistically significant dose-related differences between the control and treated animals with respect to body weight gain, food consumption, food efficiency, behavioural effects, clinical chemistries, haematology, absolute and relative organ weights, or gross and microscopic findings. Hepatic non-heme iron concentrations were elevated, indicating that the ferrous iron had been absorbed. The no-observed-adverse-effect level (NOAEL) was 500 mg/kg body weight/day, the highest dose tested.

Age-dependent sensitization to oxidative stress by dietary fatty acids

Experiments were designed to test the hypothesis that short-term feeding of a high polyunsaturated fatty acid (PUFA) diet would increase susceptibility to lipid peroxidation in an age-dependent manner. Young (6 month) and old (24 month) male B6C3F1 mice were fed modified AIN-76 diets containing either 5% corn oil (CO, N = 5 per age group) or 19% fish oil plus 1% corn oil (FO, N = 20 per age group) for two weeks. Five CO and five FO diet mice per age received an intraperitoneal injection of normal saline and were sacrificed one hour later; the remaining FO diet mice (N = 15 per age) were challenged with an acute systemic oxidative stress by intraperitoneal injection of 125 mg iron/kg body weight as iron dextran, and were sacrificed 1, 5, and 24 hours post-injection. Microsomal membrane fatty acid analysis revealed that increased age and a FO diet significantly increased membrane PUFA content. Serum iron levels increased significantly following iron treatment, peaking at 5 hours in both age groups. Formation of microsomal malondialdehyde (MDA), a product of lipid peroxidation, was significantly greater in the livers of the young mice. The temporal patterns of serum iron and microsomal MDA concentrations were significantly correlated in young mice, but not in old mice. Histochemical examination showed that liver iron accumulation following iron injection was similar in both age groups, but was associated with a significant temporal increase in liver apoptotic cells in young mice, but not in old mice. Thus, both age groups had similar iron exposure and iron accumulation, and the liver microsomal membranes of old mice were more unsaturated, yet there was significantly greater peroxidative damage (MDA formation) and cell death (apoptosis) in the young mouse livers. These findings suggest that the older animals have upregulated antioxidant defenses.

Linoleic acid peroxidation--the dominant lipid peroxidation process in low density lipoprotein--and its relationship to chronic diseases

Modern separation and identification methods enable detailed insight in lipid peroxidation (LPO) processes. The following deductions can be made: (1) Cell injury activates enzymes: lipoxygenases generate lipid hydroperoxides (LOOHs), proteases liberate Fe ions--these two processes are prerequisites to produce radicals. (2) Radicals attack any activated CH2-group of polyunsaturated fatty acids (PUFAs) with about a similar probability. Since linoleic acid (LA) is the most abundant PUFA in mammals, its LPO products dominate. (3) LOOHs are easily reduced in biological surroundings to corresponding hydroxy acids (LOHs). LOHs derived from LA, hydroxyoctadecadienoic acids (HODEs), surmount other markers of LPO. HODEs are of high physiological relevance. (4) In some diseases characterized by inflammation or cell injury HODEs are present in low density lipoproteins (LDL) at 10-100 higher concentration, compared to LDL from healthy individuals.

Strong dependence of the lipid peroxidation product spectrum whether Fe2+/O2 or Fe3+/O2 is used as oxidant

Catalytic amounts of Fe2+ or Fe3+ ions are widely applied to induce simulated biological lipid peroxidation reactions. Independently, whether Fe2+ or Fe3+ were used, similar products were obtained. We show in this paper that the product spectrum is indeed very different, whether one ion species, either Fe2+ or Fe3+, is present in excess; thus, decomposition of (13S,9Z,11E) 13-hydroxyperoxy-9, 11-octadecadienoic acid (13S-HPODE) generates in the presence of equimolar amounts of Fe2+ ions mainly the corresponding alcohol (13S, 9Z,11E) 13-hydroxy-9,11-octadecadienoic acid besides 12,13-epoxy-11-hydroxy-9-octadecenoic acid (12,13-epHOD) and 13-oxo-9,11-octa-decadienoic acid (13-KODE), while decomposition of 13S-HPODE with equimolar amounts of Fe3+ produces mainly 12,13-epHOD, hydrolysis products thereof and other oxidized products, e.g., hydroxyoxo acids. In addition, unusually large amounts of aldehydes are formed, e.g., the amount of 4-hydroxy-nonenal was found to exceed that obtained by Fe2+ induced air oxidation for a factor of about 100. Since these further oxidation products are suspected to cause cell damage, liberated Fe3+ ions seem to be responsible for generation of toxic products in inflammatory diseases, e.g., atherosclerosis.

A microsomal membrane component associated with iron reduction in NADPH-supported lipid peroxidation

This study was conducted to determine whether a factor responsible for reduced nicotinamide adenine dinucleotide phosphate (NADPH)-supported lipid peroxidation in rat liver microsomes is involved in iron reduction by cooperation with NADPH-cytochrome P450 reductase. Under anaerobic conditions, NADPH-dependent reduction of ferric pyrophosphate in microsomes was not dependent on cytochrome P450 levels and was not inhibited by carbon monoxide (CO). All of the iron complexes with chelators such as adenosine 5'-diphosphate, pyrophosphate, nitrilotriacetate, oxalate or citrate were reduced in microsomes, although in the reconstituted system containing purified NADPH-cytochrome P450 reductase little or no iron reduction was found. A cytochrome P450-free fraction from a cholate-solubilized preparation of microsomes after passage through a laurate sepharose column was required for reduction of iron pyrophosphate in the reconstituted system leading to lipid peroxidation. The iron reduction was not inhibited by CO and was destroyed by heat treatment or trypsin digestion of the fraction. All iron complexes were reduced in the presence of the fraction, using a reducing equivalent of NADPH via NADPH-cytochrome P450 reductase. The results indicate that a heat-labile component, which is probably a protein distinct from cytochrome P450, is associated with iron reduction responsible for lipid peroxidation in microsomes.