Interaction of alpha-tocopherol with iron: antioxidant and prooxidant effects of alpha-tocopherol in the oxidation of lipids in aqueous dispersions in the presence of iron

The dual functions of alpha-tocopherol in the oxidation of lipids in aqueous dispersions in the presence of iron were studied, aiming specifically at elucidating the effect of interaction between alpha-tocopherol and iron. Ferrous ion decomposed hydroperoxide rapidly and induced the free radical chain oxidation of soybean phosphatidylcholine liposomes. alpha-Tocopherol acted primarily as a radical scavenger in the oxidation induced by ferrous ion and acted as an antioxidant. Ferric ion decomposed hydroperoxide much more slowly than ferrous ion, but it also induced the oxidation of liposomal membranes. alpha-Tocopherol incorporated into artificial liposomal membranes reduced ferric ion rapidly to give more reactive ferrous ion, and alpha-tocopherol acted either as an antioxidant or as a prooxidant depending on the experimental conditions. When alpha-tocopherol was depleted by the interaction with ferric ion, it acted solely as a prooxidant, whereas if some alpha-tocopherol remained, it acted as an antioxidant. On the other hand, alpha-tocopherol residing in the intact erythrocyte membranes did not reduce ferric ion in the aqueous region.     

Bio-oxidation of iron using Thiobacillus ferrooxidans

The effects of pH, ferrous and ferric ion concentrations on iron oxidation by Thiobacillus ferrooxidans were examined. The initial temperature and bacterial concentration were maintained at 37°C and 2±1×104cells/ml, respectively. The iron oxidation rate increased with increased initial ferrous iron concentration to 4g/l and thereafter decreased. The presence of iron(III) showed a negative effect on the bacterial iron oxidation rate. The increase of pH also showed an increase in the oxidation rate up to pH 1.75. The oxidation rate followed first order kinetics for the parameters studied. A rate equation has been developed.     

Lecithin influence on the effectiveness of the antioxidant effect of flavonoids and α-tocopherol

Influence of the widely used food additive lecithin on the effectiveness of the inhibiting effect of the natural antioxidants (quercetin, dihydroquercetin, and α-tocopherol) has been studied in dependence on the rate of free radicals generation in the model oxidation reactions. It has been found that during the initiated and autoxidation of methyl oleat, lecithin decreased the antioxidant effectiveness of flavonoids. The effect value increased with the lecithin concentration increase. Under similar conditions while oxidation inhibiting by α-tocopherol and lecithin mixtures, the latter did not influence the tocopherol antioxidant effectiveness (additivity) or led to the increase of the inhibition effectiveness (synergism).     

A Review of the Antioxidant Mechanisms of Polyphenol Compounds Related to Iron Binding

In this review, primary attention is given to the antioxidant (and prooxidant) activity of polyphenols arising from their interactions with iron both in vitro and in vivo. In addition, an overview of oxidative stress and the Fenton reaction is provided, as well as a discussion of the chemistry of iron binding by catecholate, gallate, and semiquinone ligands along with their stability constants, UV–vis spectra, stoichiometries in solution as a function of pH, rates of iron oxidation by O₂ upon polyphenol binding, and the published crystal structures for iron–polyphenol complexes. Radical scavenging mechanisms of polyphenols unrelated to iron binding, their interactions with copper, and the prooxidant activity of iron–polyphenol complexes are briefly discussed.     

Anaerobic and aerobic oxidation of ferrous iron at neutral pH by chemoheterotrophic nitrate-reducing bacteria

Nine out of ten anaerobic enrichment cultures inoculated with sediment samples from various freshwater, brackish-water, and marine sediments exhibited ferrous iron oxidation in mineral media with nitrate and an organic cosubstrate at pH 7.2 and 30° C. Anaerobic nitrate-dependent ferrous iron oxidation was a biological process. One strain isolated from brackish-water sediment (strain HidR2, a motile, nonsporeforming, gram-negative rod) was chosen for further investigation of ferrous iron oxidation in the presence of acetate as cosubstrate. Strain HidR2 oxidized between 0.7 and 4.9 mM ferrous iron aerobically and anaerobically at pH 7.2 and 30° C in the presence of small amounts of acetate (between 0.2 and 1.1 mM). The strain gained energy for growth from anaerobic ferrous iron oxidation with nitrate, and the ratio of iron oxidized to acetate provided was constant at limiting acetate supply. The ability to oxidize ferrous iron anaerobically with nitrate at approximately pH 7 appears to be a widespread capacity among mesophilic denitrifying bacteria. Since nitrate-dependent iron oxidation closes the iron cycle within the anoxic zone of sediments and aerobic iron oxidation enhances the reoxidation of ferrous to ferric iron in the oxic zone, both processes increase the importance of iron as a transient electron carrier in the turnover of organic matter in natural sediments. Received: 24 April 1997 / Accepted: 22 September 1997     

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.     

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.     

Bio-oxidation of iron using Thiobacillus ferrooxidans

The effects of pH, ferrous and ferric ion concentrations on iron oxidation by Thiobacillus ferrooxidans were examined. The initial temperature and bacterial concentration were maintained at 37°C and 2±1×104cells/ml, respectively. The iron oxidation rate increased with increased initial ferrous iron concentration to 4g/l and thereafter decreased. The presence of iron(III) showed a negative effect on the bacterial iron oxidation rate. The increase of pH also showed an increase in the oxidation rate up to pH 1.75. The oxidation rate followed first order kinetics for the parameters studied. A rate equation has been developed.     

Effect of lecithin on the inhibitory efficiency of α-tocopherol during methyl oleate oxidation

It has been established that the effect of lecithin on the oxidation of methyl oleate depends on the rate of the free radical initiation: lecithin does not affect the reaction rate at high rates of radical initiation (the initiated oxidation) and accelerates the oxidation at low rates (autooxidation), causing the reduction of the induction period. The inhibitory action of mixtures of lecithin and the natural antioxidant α-tocopherol depends on the concentrations of both α-tocopherol and lecithin at different rates of oxidation. The inhibitory efficiency of mixtures with low concentrations of α-tocopherol is close to additive. Increasing the initial concentration of α-tocopherol in mixtures causes a gain in the synergistic effect. The synergistic effect depends extremally on lecithin concentration at high concentrations of α-tocopherol. The mechanism of the synergistic effect for the mixtures of α-tocopherol and lecithin is discussed.     

Inhibition of Ca-induced calcium release from mitochondria by antiischemic phenol-based antioxidants

Effects of different inhibitors of lipid peroxidation (LP), such as sulphur-containing oligoquinone hypoxen, natural flavonoid dihydroquercetin (DHQ), and β-ionol, on Ca²⁺-induced calcium release from rat liver mitochondria (RLM) were investigated during oxidation of various substrates. The hypothesis about interrelation between antioxidant properties and influence of selected substances on spontaneous calcium release from mitochondria was verified. Degree of antioxidant activity of the selected substances was estimated by the inhibition of LP induced by Fe²⁺/ATP complex in phospholipid emulsion or in rat liver mitochondria (RLM). According to the inhibition efficacy the investigated substances were ordered as follows: β-ionol ≫ hypoxen > DHQ. 50% inhibition of oxygen consumption during LP of phospholipid emulsion was reached in presence of 3.2 ± 0.6 μM of β-ionol, 15.0 ± 1.1 μM of hypoxen, or 19.8 ± 1.7 μM of DHQ. Among the investigated antioxidants hypoxen only decreased spontaneous release of calcium from RLM after calcium accumulation by RLM. The impact of the antioxidants onto calcium current depended on the oxidized substrate. Hypoxen effect was most expressed during the oxidation of NAD-dependent substrate. The direct relationship between the antioxidant activity of the selected antioxidants and their influence on calcium transport in RLM was not revealed. The results indicate that the choice of antiischemic preparations should not only rely on their antioxidant activities.     

Oxidation of Ferrous Iron and Elemental Sulfur by Thiobacillus ferrooxidans

The oxidation of ferrous iron and elemental sulfur by Thiobacillus ferrooxidans that was absorbed and unabsorbed onto the surface of sulfur prills was studied. Unadsorbed sulfur-grown cells oxidized ferrous iron at a rate that was 3 to 7 times slower than that of ferrous iron-grown cells, but sulfur-grown cells were able to reach the oxidation rate of the ferrous iron-adapted cells after only 1.5 generations in a medium containing ferrous iron. Bacteria that were adsorbed to sulfur prills oxidized ferrous iron at a rate similar to that of unadsorbed sulfur-grown bacteria. They also showed the enhancement of ferrous iron oxidation activity in the presence of ferrous iron, even though sulfur continued to be available to the bacteria in this case. An increase in the level of rusticyanin together with the enhancement of the ferrous iron oxidation rate were observed in both sulfur-adsorbed and unadsorbed cells. On the other hand, sulfur oxidation by the adsorbed bacteria was not affected by the presence of ferrous iron in the medium. When bacteria that were adsorbed to sulfur prills were grown at a higher pH (ca. 2.5) in the presence of ferrous iron, they rapidly lost both ferrous iron and sulfur oxidation capacities and became inactive, apparently because of the deposition of a jarosite-like precipitate onto the surface to which they were attached.     

The role of ecto-5′-nucleotidase/CD73 in glioma cell line proliferation

The antioxidant activity of β-carotene and oxygenated carotenoids lutein, canthaxanthin, and astaxanthin was investigated during spontaneous and peroxyl-radical-induced cholesterol oxidation. Cholesterol oxidation, measured as generation of 7-keto-cholesterol (7-KC), was evaluated in a heterogeneous solution with cholesterol, AAPH, and carotenoids solubilized in tetrahydrofuran and in water, and in a homogeneous solution of chlorobenzene, with AIBN as a prooxidant. The formation of 7-KC was dependent on temperature and on cholesterol and prooxidant concentrations. All the carotenoids tested, exhibited significant antioxidant activity by inhibiting spontaneous, AAPH- and AIBN-induced formation of 7-KC, although the overall order of efficacy of these compounds was astaxanthin > canthaxanthin > lutein = β-carotene. The finding that carotenoids exert protective effects on spontaneous and free radical-induced cholesterol oxidation may have important beneficial effects on human health, by limiting the formation of atheroma and by inhibiting cholesterol oxidation in food processing or storage.     

Effect of ferrous iron concentration on the catalytic activity of immobilized cells of Thiobacillus ferrooxidans

 The kinetics of continuous oxidation of ferrous iron by immobilized cells of Thiobacillus ferrooxidans was studied in a packed-bed bioreactor. Polyurethane foam biomass support particles were used as carriers for cell immobilization. Effects of ferrous iron concentration and its volumetric loading on the kinetics of the reaction were investigated. Media containing different concentrations of ferrous iron in the range 5–20 kg m^-3 were tested. For each medium the kinetics of the reaction at different volumetric loadings of ferrous iron, at a constant temperature of 30^°C, were determined. With media containing 5 kg m^-3 and 10 kg m^-3 Fe²⁺, the fastest oxidation rates of 34.25 kg m^-3 h^-1 and 32 kg m^-3 h^-1 were achieved at a dilution rate of around 6 h^-1, which represents a residence time of 10 min. Employing a higher concentration of ferrous iron (20 kg m^-3) in the medium resulted in lower oxidation rates, with a maximum value of 10 kg m^-3 h^-1, indicating an inhibitory effect of ferrous iron on growth and activity of T. ferrooxidans. The reliable performance of the bioreactor during the course of the experiments confirmed the suitability of polyurethane foam biomass support particles as carriers for T. ferrooxidans immobilization. Received: 5 December 1995/Received revision: 21 April 1996/Accepted: 29 April 1996     

Antioxidant protective effect of flavonoids on linoleic acid peroxidation induced by copper(II)/ascorbic acid system

Antioxidants are compounds that can delay or inhibit lipid oxidation. The peroxidation of linoleic acid (LA) in the absence and presence of Cu(II) ion–ascorbate combinations was investigated in aerated and incubated emulsions at 37 °C and pH 7. LA peroxidation induced by copper(II)–ascorbic acid system followed first order kinetics with respect to hydroperoxides concentration. The extent of copper-initiated peroxide production in a LA system assayed by ferric thiocyanate method was used to determine possible antioxidant and prooxidant activities of the added flavonoids. The effects of three different flavonoids of similar structure, i.e. quercetin (QR), morin (MR) and catechin (CT), as potential antioxidant protectors were studied in the selected peroxidation system. The inhibitive order of flavonoids in the protection of LA peroxidation was: morin > catechin ≥ quercetin, i.e. agreeing with that of formal reduction potentials versus NHE at pH 7, i.e. 0.60, 0.57 and 0.33 V for MR, CT, and QR, respectively. Morin showed antioxidant effect at all concentrations whereas catechin and quercetin showed both antioxidant and prooxidant effects depending on their concentrations. The structural requirements for antioxidant activity in flavonoids interestingly coincide with those for Cu(II)-induced prooxidant activity, because as the reducing power of a flavonoid increases, Cu(II)–Cu(I) reduction is facilitated that may end up with the production of reactive species. The findings of this study were evaluated in the light of structure–activity relationships of flavonoids, and the results are believed to be useful to better understand the actual conditions where flavonoids may act as prooxidants in the preservation of heterogeneous food samples containing traces of transition metal ions.     

Oxidation of high ferrous iron concentrations by chemolithotrophic Thiobacillus ferrooxidans in packed bed bioreactors

The bacterial oxidation of high ferrous iron concentrations in batch culture has been studied in a packed bed bioreactor. It has been found that aeration rates from 0.49 to 1.2 VVM did not influence the biofilm oxidation activity during the period of biofilm formation up to 30 g l⁻¹ initial ferrous iron concentration. The contribution of swimming, attached and fixed bacteria to the Fe²⁺ oxidation process has been evaluated. Kinetics data showed that the oxidation rate depends on the aeration rate, when the initial Fe²⁺ concentration exceeded 30 g l⁻¹. The maximum overall Fe²⁺ oxidation rate was 1.8 g l⁻¹ h⁻¹, when the initial ferrous iron concentration was in the range 30 to 45 g l⁻¹.     

Effect of the combined action of flavonoids, ascorbate and alpha-tocopherol on peroxidation of phospholipid liposomes induced by Fe2+ ions

The effect of alpha-tocopherol, ascorbate, rutin and dihydroquercetin on chemiluminescence (CL) accompanying the Fe2+-induced peroxidation of unsaturated fatty acids in phospholipid liposomes has been investigated. The amplitude of CL decreased and the latent period increased in the presence of alpha-tocopherol, rutin and dihydroquercetin which is typical of peroxide radical traps. Ascorbate also reduced the CL amplitude but only at small concentrations up to about 4 microM. A further increase of ascorbate concentration had a negligible effect on the amplitude. At the same time, the latent period in CL development increased with the growth of ascorbate concentration, apparently, as a result of recycling of divalent iron oxidized in the course of lipid peroxidation. The effects of rutin and dihydroquercetin on the liposomal CL in the presence of alpha-tocopherol and ascorbate in all experiments were almost the same as when these compounds were added individually. The antioxidant effects were merely summed up without any mutual enhancement or inhibition of each other's action.     

Kinetics of ferrous iron oxidation by batch and continuous cultures of thermoacidophilic Archaea at extremely low pH of 1.1–1.3

The extreme acid conditions required for scorodite (FeAsO₄·2H₂O) biomineralization (pH below 1.3) are suboptimal for growth of most thermoacidophilic Archaea. With the objective to develop a continuous process suitable for biomineral production, this research focuses on growth kinetics of thermoacidophilic Archaea at low pH conditions. Ferrous iron oxidation rates were determined in batch-cultures at pH 1.3 and a temperature of 75°C for Acidianus sulfidivorans, Metallosphaera prunea and a mixed Sulfolobus culture. Ferrous iron and CO₂ in air were added as sole energy and carbon source. The highest growth rate (0.066 h⁻¹) was found with the mixed Sulfolobus culture. Therefore, this culture was selected for further experiments. Growth was not stimulated by increase of the CO₂ concentration or by addition of sulphur as an additional energy source. In a CSTR operated at the suboptimal pH of 1.1, the maximum specific growth rate of the mixed culture was 0.022 h⁻¹, with ferrous iron oxidation rates of 1.5 g L⁻¹ d⁻¹. Compared to pH 1.3, growth rates were strongly reduced but the ferrous iron oxidation rate remained unaffected. Influent ferrous iron concentrations above 6 g L⁻¹ caused instability of Fe²⁺ oxidation, probably due to product (Fe³⁺) inhibition. Ferric-containing, nano-sized precipitates of K-jarosite were found on the cell surface. Continuous cultivation stimulated the formation of an exopolysaccharide-like substance. This indicates that biofilm formation may provide a means of biomass retention. Our findings showed that stable continuous cultivation of a mixed iron-oxidizing culture is feasible at the extreme conditions required for continuous biomineral formation.     

Ferrous iron is transported across the peribacteroid membrane of soybean nodules

Symbiosomes and bacteroids isolated from soybean (Glycine max Merr.) nodules are able to take up ferrous iron. This uptake activity was completely abolished in the presence of ferrous-iron chelators. The kinetics of uptake were characterized by initially high rates of iron internalization, but no saturation was observed with increasing iron concentration. This process does not appear to involve the ferric reductase of the peribacteroid membrane. The transport of ferrous iron was inhibited by other transition metals, particularly copper. Ferrous iron was taken up by symbiosomes more efficiently than the ferric form. This indicates that the iron transport from the plant host cell to the microsymbiont in vivo may occur mainly as the ferrous form. Received: 11 February 1998 / Accepted: 29 May 1998     

Isolation of Fulvic Acid from Cercospora beticola

Phosphatidylethanolamine (PE) is generally more oxidizable than phosphatidylcholine (PC). To determine the difference in reactivities to oxidation between PE and PC, it is necessary for their fatty acid moieties to be uniform. Experimental results of the ferrous ion-catalyzed oxidation of dilinoleoylphosphatidylcholine, dilinoleoylphosphatidylethanolamine, and dilinoleoyldiglyceride revealed that the rate of oxidation depends on the type of base. Ferrous ion possessed a high catalytic activity in hydroperoxide formation at pH 5.8. Iron ions might initiate the oxidation of phospholipids by forming free radicals. Phosphoethanolamine was capable of trapping ferrous ion and preventing it from being autoxidized to ferric ion. Trapping of ferrous ion might be responsible for the significant oxidizability of PE at pH 5.8 ~ 7.0. In the ferrous ion-ascorbic acid (AsA) catalyzed oxidation system, PC oxidation was remarkably enhanced at pH 7.0. In this case, no reduction of ferric ion occurred, but AsA had a prooxidant effect of accelerating the formation of free radicals.     

Selective colocalization of lipid peroxidation and protein thiol loss in chemically induced hepatic preneoplastic lesions: the role of γ-glutamyltranspeptidase activity

A number of studies indicate that cell proliferation can be modulated by changes in the redox balance of (soluble and protein) cellular thiols. Free radical processes, including lipid peroxidation (LPO), can affect such a balance, and a role for LPO in multistage carcinogenesis has been envisaged. The present study was aimed to assess the relationships between the protein thiol redox status and the LPO process in chemically induced preneoplastic tissue. The Solt-Farber's initiation-promotion model of chemical carcinogenesis in the rat liver was used. In fresh cryostat sections, preneoplastic lesions were identified by the reexpression of γ-glutamyltranspeptidase (GGT) activity. In serial sections, different classes of protein thiols were stained; in additional sections, LPO was elicited by various prooxidant mixtures and determined thereafter by the hydroxynaphthoic hydrazide-Fast Blue B procedure. The incubation of sections in the presence of chelated iron plus substrates for GGT activity leads to the development of LPO in selected section areas closely corresponding to GGT-positive lesions, indicating the ability of GGT activity to initiate LPO. Protein-reactive thiols, as well as total protein sulfur, were decreased by 20–25% in cells belonging to GGT-positive preneoplastic nodules, suggesting the occurrence of oxidative conditions in vivo. The incubation of additional adjacent sections with the prooxidant mixture H₂O₂ plus iron(II), in order to induce the complete oxidation of lipid present in the section, showed a decreased basal concentration of oxidizable lipid substrate in GGT-rich areas. The decreased levels of both protein thiols and lipid-oxidizable substrate in GGT-positive nodules suggest that the observed GGT-dependent path-way of LPO initiation can be chronically operative in vivo during early stages of chemical carcinogenesis, in cells expressing GGT as part of their transformed phenotype.