Anemia is a major health condition associated with chronic kidney disease (CKD). A key underlying cause of this disorder is iron deficiency. Although intravenous iron treatment can be beneficial in correcting CKD-associated anemia, surplus iron can be detrimental and cause complications. Excessive generation of reactive oxygen species (ROS), particularly by mitochondria, leads to tissue oxidation and damage to DNA, proteins, and lipids. Oxidative stress increase in CKD has been further implicated in the pathogenesis of vascular calcification. Iron supplementation leads to the availability of excess free iron that is toxic and generates ROS that is linked, in turn, to inflammation, endothelial dysfunction, and cardiovascular disease. Histidine is indispensable to uremic patients because of the tendency toward negative plasma histidine levels. Histidine-deficient diets predispose healthy subjects to anemia and accentuate anemia in chronic uremic patients. Histidine is essential in globin synthesis and erythropoiesis and has also been implicated in the enhancement of iron absorption from human diets. Studies have found that L-histidine exhibits antioxidant capabilities, such as scavenging free radicals and chelating divalent metal ions, hence the advocacy for its use in improving oxidative stress in CKD. The current review advances and discusses evidence for iron-induced toxicity in CKD and the mechanisms by which histidine exerts cytoprotective functions.
Overproduction of reactive oxygen species (ROS) in vivo can result in damage associated with many aging-associated diseases. Defenses against ROS that have evolved include antioxidant enzymes, such as superoxide dismutases, peroxidases, and catalases, which can scavenge ROS. In addition, endogenous and dietary antioxidants play an important role in moderating damage associated with ROS. In this study, we use four common dietary antioxidants to demonstrate that, in the presence of copper (cupric sulfate and cupric gluconate) and physiologically relevant levels of hydrogen peroxide, these antioxidants can also act as pro-oxidants by producing hydroxyl radicals. Using electron spin resonance (ESR) spin trapping techniques, we demonstrate that the level of hydroxyl radical formation is a function of the pH of the medium and the relative amounts of antioxidant and copper. On the basis of the level of hydroxyl radical formation, the relative pro-oxidant potential of these antioxidants is cysteine > ascorbate > EGCG > GSH. It has been reported that copper sequestered by protein ligands, as happens in vivo, loses its redox activity (diminishing/abolishing the formation of free radicals). However, in the presence of hydrogen peroxide, cysteine and GSH efficiently react with cupric sulfate sequestered with bovine serum albumin to generate hydroxyl radicals. Overall, the results demonstrate that in the presence of copper, endogenous and dietary antioxidants can also exhibit pro-oxidative activity.
Hydroxyl radical ( OH) production in sunlit natural waters is known to be an important factor in pollutant degradation and nutrient cycling, and various probes have been developed to study this species in aquatic systems. Many of these probes have limitations in sensitivity and/or selectivity for OH, leaving room for improvement. Terephthalate (TPA) is a known probe for OH that produces a fluorescent product, hydroxyterephthalate (hTPA), upon hydroxylation, but its suitability for studying photochemical OH production has not been fully tested. To that end, the photochemical behavior of TPA and hTPA was characterized. TPA and hTPA react with OH with rate constants of (4.4 +/- 0.1) x 10(9) M(-1) s(-1) and (6.3 +/- 0.1) x 10(9) M(-1) s(-1), respectively. They were found to react with singlet oxygen ((1)O(2)) with significantly lower rate constants of <10(4) M(-1) s(-1) and (5.0 +/- 0.1) x 10(4) M(-1) s(-1), respectively, indicating that TPA is selective for OH versus(1)O(2). TPA did not undergo direct photolysis, while hTPA was shown to undergo direct photochemical degradation with a Phi(direct,365nm) of (6.3 +/- 0.1) x 10(-3). TPA was applied to monitoring photochemical OH production by nitrate, nitrite and dissolved organic matter (DOM), and OH quenching rate constants measured for DOM were similar to results from previous studies. TPA provides a stable and sensitive probe for OH under significantly shorter photo-exposure times than similarly structured probe molecules, such as benzoate. However, the photoinstability of the analyte, hTPA, makes TPA an unsuitable probe for the study of photochemical systems under ultraviolet irradiation with wavelengths shorter than 360 nm.
While it is widely believed that taurine may play an important role in protecting cells against toxic injury by functioning as an antioxidant, there is a lack of evidence to support this hypothesis. In this study, electron spin resonance (ESR) was used to investigate the reaction of taurine and hypotaurine with hydroxyl radicals (.OH). The Fenton reaction (Fe(II) + H2O2-->Fe(III) + .OH + OH-) and the Cr(V)-mediated Fenton-like reaction (Cr(V) + H2O2-->Cr(VI) + .OH + OH-) were used as sources of .OH radicals. The results show that hypotaurine but not taurine effectively scavenges .OH radicals with a reaction rate constant of k = 1.6 x 10(10) M-1s-1. That is comparable with other efficient .OH radical scavengers. The effect of taurine and hypotaurine on silica-induced lipid peroxidation was evaluated using linoleic acid as a model lipid. Hypotaurine, but not taurine, caused a significant inhibition of silica-induced lipid peroxidation. The results show that hypotaurine is an excellent antioxidant and appears to have the potential for being a therapeutic agent against silica-induced lung injury.
The antioxidant ability of thiol compounds has been the subject of much of the current research about oxidative stress. The direct scavenging of hydroxyl radicals by thiols has been suggested as their protection mechanisms. Nevertheless, the interaction of thiols with reactive radicals can generate thiyl radicals, which, in turn, may impart a pro-oxidant function. The purpose of this study has been to establish the effect of the thiol compounds N-acetyl-L-cysteine (NAC) and glutathione (GSH) against the peroxidative processes involving membrane lipids. The results obtained support the ability of NAC and GSH to suppress the 2,2'-azobis-(2-amidinopropane) dihydrochloride (AAPH)-dependent or to enhance the Fe2+/H2O2-dependent oxidative actions. The evaluation of thiobarbituric acid reactive substances (TBARS) production, the study of the influence of oxidants on membrane fluidity and the measurements of the changes in the fluorescence of bilayer probes, such as 3-(p-(6-phenyl)-1,3,5-hexatrienyl)phenylpropionic acid (DPH-PA), have shown the antioxidant and pro-oxidant effects of both NAC and GSH. Also their dependence on the nature of the radicals generated by the oxidative systems used has been shown. The use of ESR spectroscopy has allowed us to establish the ability of these compounds to scavenge the AAPH-derived radicals, to determine the formation of thiyl radicals in the iron-mediated oxidation and to evaluate the enhanced production of hydroxyl radicals by NAC and GSH.
Living beings have evolved over the past two billion years through adaptation, to an increasing atmospheric oxygen concentration, by both taking advantage of oxygen activating function and developing a complex control network. In these regards, potentially damaging species (reactive oxygen, nitrogen and chlorine species) arise as by-products of metabolism and also work as physiological mediators and signalling molecules. Oxidative stress may be an important factor in numerous pathological conditions, i.e. infection if micronutrients are deficient. Levels of these species are controlled by the antioxidant defence system, which is composed by antioxidants and pro-antioxidants. Several components of this system are micronutrients (e.g. vitamins C and E), are dependent upon dietary micronutrients (e.g. CuZn and Mn superoxide dismutase) or are produced by specific endogenous pathways. The antioxidant defences act, to control levels of these species, as a coordinated system where deficiencies in one component may affect the efficiency of the others. In this network some of the components act as direct antioxidants whereas others act indirectly (pro-antioxidants) either by modulation of direct agents or by regulation of the biosynthesis of antioxidant proteins. Thus, entities usually not considered as antioxidants, also act efficiently counteracting damaging effects of oxidative species. In this contest, the design of new molecules that take into account synergistic interactions among different antioxidants, could be useful both to address mechanistic studies and to develop possible therapeutic agents. In this review the principal categories of antioxidants and pro-antioxidants that goes from vitamins through phyto-derivatives to minerals, are critically reviewed, with particular emphasis on structure-function considerations, together with the perspective opened, in the design of possible therapeutic agents, by the antioxidants interplay.
A detailed study of Cu²⁺ ion affinities of the amino acids namely Glycine (Gly), Alanine (Ala) and Cysteine (Cys) and their Cu²⁺ complexes have been investigated using density functional theory. Interactions of a Cu²⁺ ion with oxygen, nitrogen, and sulfur (for cysteine) of the selected amino acids have been optimized. The results show that complex formation reactions are exothermic in both gas and aqueous phase and the neighboring stereochemical nature of Cu²⁺ ion is more or less same in all amino acids. The computed Cu²⁺ affinity for both O-Cu²⁺ and N-Cu²⁺ interaction in the gas phase is in this order ΔECys>ΔEAla>ΔEGly. In aqueous phase, Cu²⁺ ion affinity for O-Cu²⁺ interaction follows the same order as above, whereas in N-Cu²⁺ interaction it differs as ΔEAla≥ΔECys>ΔEGly. In NCu²⁺ interaction Zwitterterionic complexes (Cu²⁺ bind with both nitrogen and carbonyl oxygen atom) have been formed. The optimization energies are estimated to be lower relative to the other interactions and the Cu²⁺ ion affinities have been predicted more. The results have been well supported by the natural population analysis (NPA) of the atoms and hardness parameters. The charge, energetics, geometrical and electronic properties of the complexes signify that the interaction between the Cu²⁺ with the carbonyl oxygen and the amino nitrogen of free amino acids is predominantly a covalent interaction in the gas phase and which becomes more ionic in the aqueous phase.
Transition metal ions are key elements of various biological processes ranging from oxygen formation to hypoxia sensing, and therefore, their homeostasis is maintained within strict limits through tightly regulated mechanisms of uptake, storage and secretion. The breakdown of metal ion homeostasis can lead to an uncontrolled formation of reactive oxygen species, ROS (via the Fenton reaction, which produces hydroxyl radicals), and reactive nitrogen species, RNS, which may cause oxidative damage to biological macromolecules such as DNA, proteins and lipids. An imbalance between the formation of free radicals and their elimination by antioxidant defense systems is termed oxidative stress. Most vulnerable to free radical attack is the cell membrane which may undergo enhanced lipid peroxidation, finally producing mutagenic and carcinogenic malondialdehyde and 4-hydroxynonenal and other exocyclic DNA adducts. While redox-active iron (Fe) and copper (Cu) undergo redox-cycling reactions, for a second group of redox-inactive metals such as arsenic (As) and cadmium (Cd), the primary route for their toxicity is depletion of glutathione and bonding to sulfhydryl groups of proteins. While arsenic is known to bind directly to critical thiols, other mechanisms, involving formation of hydrogen peroxide under physiological conditions, have been proposed. Redox-inert zinc (Zn) is the most abundant metal in the brain and an essential component of numerous proteins involved in biological defense mechanisms against oxidative stress. The depletion of zinc may enhance DNA damage by impairing DNA repair mechanisms. Intoxication of an organism by arsenic and cadmium may lead to metabolic disturbances of redox-active copper and iron, with the occurrence of oxidative stress induced by the enhanced formation of ROS/RNS. Oxidative stress occurs when excessive formation of ROS overwhelms the antioxidant defense system, as is maintained by antioxidants such as ascorbic acid, alpha-tocopherol, glutathione (GSH), carotenoids, flavonoids and antioxidant enzymes which include SOD, catalase and glutathione peroxidase. This review summarizes current views regarding the role of redox-active/inactive metal-induced formation of ROS, and modifications to biomolecules in human disease such as cancer, cardiovascular disease, metabolic disease, Alzheimer's disease, Parkinson's disease, renal disease, blood disorders and other disease. The involvement of metals in DNA repair mechanisms, tumor suppressor functions and interference with signal transduction pathways are also discussed.
The interaction of metal cations with mono hydrated, neutral and zwitterionic histidine dimer complexes are studied using the density functional theory (DFT-B3LYP) method in both gas and liquid phase. It is found that the metal interaction with histidine is governed by two types of bonds I) N-Mn+ (Mn+= Zn2+, Cu2+, Ca2+, Mg2+ and Na+), O-Mn+ bonds and II) N H-O and N-H O hydrogen bonds. The coordination of metals with the nitrogen atom is strong in neutral systems, while the coordination with oxygen atom is strong in the zwitterions systems, for both liquid and gas phase. Among all the metal ions considered the Cu2+ ion strongly coordinates with both the neutral and the zwitterion forms of histidine dimer. AIM analysis indicates that the N-Mn+, O-Mn+ and hydrogen bonds are partially covalent and electrostatic in nature. The enthalpy of the reaction indicates that the reaction is energetically favoured and exothermic in nature. For all the metal complexes pKa values decrease with increase in hydrogen bond strength. Redox potential is high for the zwitterionic complex, due to the transfer of electrons from the carboxylic group to amine moiety in all metal complexes. From the MD calculations, we find that Mg2+ substituted complexes backbone are stabilized around 0.9 nm, while for the other metal ions it is more than 1.0 nm. Kirkwoods’s potential indicates presence of antiparallel dipole-dipole interactions.
Kinetic data for the radicals H⋅ and ⋅OH in aqueous solution,and the corresponding radical anions, ⋅O− and eaq−, have been critically pulse radiolysis, flash photolysis and other methods. Rate constants for over 3500 reaction are tabulated, including reaction with molecules, ions and other radicals derived from inorganic and organic solutes.
The relative Cu(I) ion affinities of amino acids (A.A.) are determined in the gas phase based on the unimolecular dissociations of their Cu+-bound heterodimers, A.A.(1)-Cu+-A.A.(2) (kinetic method). For the 20 common alpha-amino acids, the Cu+ affinities increase in the order Gly < Ala < Ser < Val < Leu < Ile < Thr < Pro < Asp < Asn < Glu < Phe < Tyr < Cys < Gln < Met < Trp < His < Lys < Arg and their values fall within <20 kcal/mol. For comparison, the proton affinities of amino acids cover a range of >33 kcal/mol. Correlation of the experimentally derived Cu+ affinity order to the reported proton affinity order of amino acids points out that the Cu+-A.A. bond is longer and less covalent in nature than the H+-A.A. bond. Increasing the alkyl side chain of the amino acid, and hence inductive effects, augments the proton affinity substantially more than the Cu(I) affinity. Further, soft donor groups, such as SH of cysteine, SCH3 of methionine, or the aromatic pi-electrons of phenylalanine, stabilize Cu+-A.A. bonds more than H+-A.A. bonds.
Rotational-echo, double-resonance C-13 and N-15 NMR have been used to examine tobacco hornworm pupal exuviae labeled either with a combination of [beta-C-13]dopamine and [ring-N-15(2)]histidine or with beta-[3-C-13, N-15]alanine. The spectra are consistent with the incorporation of N-beta-alanyldopamine into insect cuticle by the formation of a variety of covalent bonds. One of these bonds links a histidyl ring nitrogen to a catechol beta-carbon. Other bonds involve the amino group of N-beta-alanyldopamine. These results are interpreted in terms of a general structure for stabilized cuticle that involves cross-linking of proteins to other proteins or chitin through catecholamines.
The organosulfur compounds allicin, methionine and methylcysteine protect against metal-mediated oxidative DNA damage, but few studies have determined the antioxidant behaviour of the oxo-sulfur derivatives of these compounds. Gel electrophoresis experiments were performed to determine the ability of MetSO, MeCysSO, MMTS, MePhSO and Me 2 SO 2 to inhibit copper-and iron-mediated DNA damage. Under these conditions, MetSO and MeCysSO significantly inhibit DNA damage, MePhSO and Me 2 SO 2 have no effect and MMTS promotes DNA damage. For iron-mediated DNA damage, significantly less antioxidant or pro-oxidant behaviour is observed for these compounds. To determine whether metal coordination is a mechanism for the antioxidant activity of these oxo-sulfur compounds, UV– vis spectroscopy and gel electrophoresis experiments using [Cu(bipy) 2 ] þ or [Fe(EDTA)] 27 as the metal source were also performed. Results of these experiments indicate that metal coordination is a significant factor for their antioxidant activity, but another mechanism also contributes to their antioxidant behaviour.
Thiols like glutathione and cysteine form such stable complexes with copper(I) that they preclude the presence of copper(II). Conventionally seawater is titrated with copper(II) whilst monitoring the labile or reactive copper concentration by voltammetry or with other techniques, to determine the concentration of copper(II) binding complexing ligands in seawater. Titrations of seawater to which copper(I) binding ligands have been added reveal that the copper(I) binding ligands are detected when seawater is titrated with copper(II). The copper(II) in seawater is reduced to copper(I) within 2 to 40 minutes depending on the nature of the copper(I) binding ligand. The titrations of seawater with copper(II) thus give a response to the presence of copper(I) binding ligands indiscernible from that for copper(II) binding ligands. The stoichiometry of the detected apparent ligand concentrations for given concentrations of glutathione and cysteine suggest that 2 : 1 (thiol : Cu) complexes are formed. This was confirmed using voltammetry of free glutathione. Values of 21.2 and 22.2 were found for log CuL for glutathione and cysteine respectively (for the reaction of Cu + 2L CuL2). The complex stability is similar to that of natural organic species in the oceanic water column. The high stability of the copper(I) complexes was apparent from values of 32.1 and 32.6 for log Cu(I)L2 (for the reaction Cu+ + 2L CuL2) for the copper(I) complexes with glutathione and cysteine in seawater. Glutathione and other thiols are common in the marine system including the water column. It is therefore possible that at least some of the ligands detected in seawater, and previously assumed to be copper(II) binding ligands, are in fact strongly complexed as copper(I). The copper(I) oxidation state may thus be stabilised in seawater.
Amyloid-beta (Abeta), the major component of senile plaques in Alzheimer's disease, is known to complex transition metal ions mainly through histidine residues. In this study, using 1H NMR titration experiments, we show that histidine binds strongly to Zn(II), Cu(II), and Fe(III) ions at a biologically relevant pH (pH 7.4), with a stoichiometry of Zn(II): histidine binding of 1:2. The observed deshielding of the chemical shifts and relative line broadening indicate that Fenton-active Cu(II) and Fe(III) bind to histidine relatively more efficiently as compared to Zn(II). Parallel studies showed that glutamic acid and aspartic acid are relatively inefficient in metal ion binding. From these studies, we suggest that Abeta-chelated Zn(II) is readily displaced by Cu(II) and Fe(III) ions and leads to a propagation of oxidative stress.
Metals such as CuI and FeII generate hydroxyl radical (.OH) by reducing endogenous hydrogen peroxide (H2O2). Because antioxidants can ameliorate metal-mediated oxidative damage, we have quantified the ability of glutathione, a primary intracellular antioxidant, and other biological sulfur-containing compounds to inhibit metal-mediated DNA damage caused hydroxyl radical. In the CuI/H2O2 system, six sulfur compounds, including both reduced and oxidized glutathione, inhibited DNA damage with IC50 values ranging from 3.4 to 12.4 microM. Glutathione and 3-carboxypropyl disulfide also demonstrated significant antioxidant activity with FeII and H2O2. Additional gel electrophoresis and UV-vis spectroscopy studies confirm that antioxidant activity for sulfur compounds in the CuI system is attributed to metal coordination, a previously unexplored mechanism. The antioxidant mechanism for sulfur compounds in the FeII system, however, is unlike that of CuI. Our results demonstrate that glutathione and other sulfur compounds are potent antioxidants capable of preventing metal-mediated oxidative DNA damage at well below their biological concentrations. This novel metal-binding antioxidant mechanism may play a significant role in the antioxidant behavior of these sulfur compounds and help refine understanding of glutathione function in vivo.
Copper-induced oxidative damage is generally attributed to the formation of the highly reactive hydroxyl radical by a mechanism analogous to the Haber-Weiss cycle for Fe(II) and H2O2. In the present work, the reaction between the Cu(I) ion and H2O2 is studied using the EPR spin-trapping technique. The hydroxyl radical adduct was observed when Cu(I), dissolved in acetonitrile under N2, was added to pH 7.4 phosphate buffer containing 100 mM 5,5-dimethyl-1-pyrroline N-oxide (DMPO). Formation of the hydroxyl radical was dependent on the presence of O2 and subsequent formation of H2O2. The kscav/kDMPO ratios obtained were below those expected for a mechanism involving free hydroxyl radical and reflect the interference of nucleophilic addition of H2O to DMPO to form the DMPO/.OH adduct in the presence of nonchelated copper ion. Addition of ethanol or dimethyl sulfoxide to the reaction suggests that a high-valent metal intermediate, possibly Cu(III), was also formed. Spin trapping of hydroxyl radical was almost completely inhibited upon addition of Cu(I) to a solution of either nitrilotriacetate or histidine, even though the copper was fully oxidized to Cu(II) and H2O2 was formed. Bathocuproinedisulfonate, thiourea, and reduced glutathione all stabilized the Cu(I) ion toward oxidation by O2. Upon addition of H2O2, the Cu(I) in all three complexes was oxidized to varying degrees; however, only the thiourea complex was fully oxidized within 2 min of reaction and produced detectable hydroxyl radicals. No radicals were detected from the bathocuproinedisulfonate or glutathione complexes. Overall, these results suggest that the deleterious effects of copper ions in vivo are diminished by biochemical chelators, especially glutathione, which probably has a major role in moderating the toxicological effects of copper.
It has been suggested that taurine, hypotaurine and their metabolic precursors (cysteic acid, cysteamine and cysteinesulphinic acid) might act as antioxidants in vivo. The rates of their reactions with the biologically important oxidants hydroxyl radical (.OH), superoxide radical (O2.-), hydrogen peroxide (H2O2) and hypochlorous acid (HOCl) were studied. Their ability to inhibit iron-ion-dependent formation of .OH from H2O2 by chelating iron ions was also tested. Taurine does not react rapidly with O2.-, H2O2 or .OH, and the product of its reaction with HOCl is still sufficiently oxidizing to inactivate alpha 1-antiproteinase. Thus it seems unlikely that taurine functions as an antioxidant in vivo. Cysteic acid is also poorly reactive to the above oxidizing species. By contrast, hypotaurine is an excellent scavenger of .OH and HOCl and can interfere with iron-ion-dependent formation of .OH, although no reaction with O2.- or H2O2 could be detected within the limits of our assay techniques. Cysteamine is an excellent scavenger of .OH and HOCl; it also reacts with H2O2, but no reaction with O2.- could be measured within the limits of our assay techniques. It is concluded that cysteamine and hypotaurine are far more likely to act as antioxidants in vivo than is taurine, provided that they are present in sufficient concentration at sites of oxidant generation.
The application of ferrozine, a commercially available sulfonated ferroin, to the determination of submicrogram levels of iron in human serum is described. The effect of serum copper, which can be a potential source of error, is minimized by complexation with neocuproin in the reaction mixture without affecting adherence to Beer's Law. The large molar absorptivity of 28,000 for the iron-ferrozine complex makes the ligand an attractive color reagent for monitoring iron therapy in anemic patients.
DNA was incubated with glutathione (GSH) and copper and then assayed for 8-hydroxydeoxyguanosine (8-OHdG) in order to better understand the antioxidant and prooxidant characteristics of GSH in copper-dependent DNA damage. Ratios of GSH to Cu(II) less than 3 resulted in 8-OHdG production; however, higher ratios did not generate 8-OHdG. A combination of GSH and Cu(I) (10:1) was used to determine if DNA oxidation occurred upon the addition of H2O2. No increase in 8-OHdG was noted until the concentration of H2O2 was almost half that of GSH, and then a substantial increase of 8-OHdG was detected. The stoichiometry of thiol oxidation by H2O2 was 2 mol GSH oxidized per 1 mol H2O2. Oxidation of Cu(I) was not detected until most of the thiol had been oxidized. When cysteine and Cu(I) was used instead of GSH and Cu(I), there was considerable hydroxylation of deoxyguanosine. The glycyl carboxyl, the gamma-glutamate carboxyl, and the amine of GSH were altered to determine their role in the peptide's ability to inhibit Cu-dependent damage. In the presence of Cu(I), H2O2, and DNA, these GSH analogs behaved similarly to GSH. However, when S-methylglutathione was used in this system, it was very effective at promoting oxidative damage to DNA. This indicated that the thiol ligand of GSH was essential for inhibition of Cu-dependent damage, while the carboxyl groups and the amine were not essential ligands. In conclusion, GSH can catalyze the in vitro hydroxylation of deoxyguanosine when the ratio of GSH to Cu is low, however, when the ratio is high GSH is an effective antioxidant.
Oxygen radical generating systems, namely, Cu(II)/ H2O2, Cu(II)/ascorbate, Cu(II)/NAD(P)H, Cu(II)/ H2O2/catecholamine and Cu(II)/H2O2/SH-compounds irreversibly inhibited yeast glutathione reductase (GR) but Cu(II)/H2O2 enhanced the enzyme diaphorase activity. The time course of GR inactivation by Cu(II)/H2O2 dependent on Cu(II) and H2O2 concentrations and was relatively slow, as compared with the effect of Cu(II)/ascorbate. The fluorescence of the enzyme Tyr and Trp residues was modified as a result of oxidative damage. Copper chelators, catalase, bovine serum albumin and HO. scavengers prevented GR inactivation by Cu(II)/H2O2 and related systems. Cysteine, N-acetylcysteine, N-(2-dimercaptopropionylglycine and penicillamine enhanced the effect of Cu(II)/H2O2 in a concentration- and time-dependent manner. GSH, Captopril, dihydrolipoic acid and dithiotreitol also enhanced the Cu(II)/H2O2 effect, their actions involving the simultaneous operation of pro-oxidant and antioxidant reactions. GSSG and trypanothione disulfide effectively protected GR against Cu(II)/H2O2 inactivation. Thiol compounds prevented GR inactivation by the radical cation ABTS.+. GR inactivation by the systems assayed correlated with their capability for HO. radical generation. The role of amino acid residues at GR active site as targets for oxygen radicals is discussed.
Carnosine has antioxidant properties and is efficient in the treatment of chemically-induced inflammatory lesions in animals. However, some studies question its biological significance as antioxidant and show lack of protection and even pro-oxidant effect of carnosine in systems containing nickel and iron ions. The ability of carnosine to: (1) reduce Fe(3+) into Fe(2+) ions; (2) protect deoxyribose from oxidation by Fe(2+)-, Fe(3+)-, and Cu(2+)-H(2)O(2)-EDTA systems; (3) protect DNA from damage caused by Cu(2+)-, and Fe(2+)-H(2)O(2)-ascorbate systems; (4) inhibit HClO- and H(2)O(2)-peroxidase-induced luminol dependent chemiluminescence was tested in vitro. At concentration 10 mM carnosine reduced 16.6+/-0.5 nmoles of Fe(3+) into Fe(2+) ions during 20 min. incubation and added to plasma significantly increased its ferric reducing ability. Inhibition of deoxyribose oxidation by 10 mM carnosine reached 56+/-5, 40+/-11 and 30+/-11% for systems containing Fe(2+), Fe(3+) and Cu(2+) ions, respectively. The damage to DNA was decreased by 84+/-9 and 61+/-14% when Cu(2+)-, and Fe(2+)-H(2)O(2)-ascorbate systems were applied. Combination of 10 mM histidine with alanine or histidine alone (but not alanine) enhanced 1.3 and 2.3 times (P<0.05) the DNA damage induced by Fe(2+)-H(2)O(2)-ascorbate. These amino acids added to 10 mM carnosine decreased 3.1-fold (P<0.05) its protective effect on DNA. Carnosine at 10 and 20 mM decreased by more than 90% light emission from both chemiluminescent systems. It is concluded that carnosine has significant antioxidant activity especially in the presence of transition metal ions. However, hydrolysis of carnosine with subsequent histidine release may be responsible for some pro-oxidant effects.
The complexes formed by the simplest amino acid, glycine, with different bare and hydrated metal ions (Mn(2+), Fe(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+)) were studied in the gas phase and in solvent in order to give better insight into the field of the metal ion-biological ligand interactions. The effects of the size and charge of each cation on the organization of the surrounding water molecules were analyzed. Results in the gas phase showed that the zwitterion of glycine is the form present in the most stable complexes of all ions and that it usually gives rise to an eta(2)O,O coordination type. After the addition of solvation sphere, a resulting octahedral arrangement was found around Ni(2+), Co(2+), and Fe(2+), ions in their high-spin states, whereas the bipyramidal-trigonal (Mn(2+) and Zn(2+)) or square-pyramidal (Cu(2+)) geometries were observed for the other metal species, according to glycine behaves as bi- or monodentate ligand. Despite the fact that the zwitterionic structure is in the ground conformation in solution, its complexes in water are less stable than those obtained from the canonical form. Binding energy values decrease in the order Cu(2+) > Ni(2+) > Zn(2+) approximately Co(2+) > Fe(2+) > Mn(2+) and Cu(2+) > Ni(2+) > Mn(2+) approximately Zn(2+) > Fe(2+) > Co(2+) for M(2+)-Gly and Gly-M(2+) (H(2)O)(n) complexes, respectively. The nature of the metal ion-ligand bonds was examined by using natural bond order and charge decomposition analyses.