scholarly journals Uric acid-iron ion complexes. A new aspect of the antioxidant functions of uric acid

1986 ◽  
Vol 235 (3) ◽  
pp. 747-754 ◽  
Author(s):  
K J A Davies ◽  
A Sevanian ◽  
S F Muakkassah-Kelly ◽  
P Hochstein
Keyword(s):  
Lipid Peroxidation ◽  
Uric Acid ◽  
Singlet Oxygen ◽  
Oxygen Radicals ◽  
Mechanistic Explanation ◽  
Antioxidant Property ◽  
Ion Concentration ◽  
Iron Ions ◽  
Iron Ion ◽  
Ascorbate Concentration

In order to survive in an oxygen environment, aerobic organisms have developed numerous mechanisms to protect against oxygen radicals and singlet oxygen. One such mechanism, which appears to have attained particular significance during primate evolution, is the direct scavenging of oxygen radicals, singlet oxygen, oxo-haem oxidants and hydroperoxyl radicals by uric acid. In the present paper we demonstrate that another important ‘antioxidant’ property of uric acid is the ability to form stable co-ordination complexes with iron ions. Formation of urate-Fe3+ complexes dramatically inhibits Fe3+-catalysed ascorbate oxidation, as well as lipid peroxidation in liposomes and rat liver microsomal fraction. In contrast with antioxidant scavenger reactions, the inhibition of ascorbate oxidation and lipid peroxidation provided by urate's ability to bind iron ions does not involve urate oxidation. Association constants (Ka) for urate-iron ion complexes were determined by fluorescence-quenching techniques. The Ka for a 1:1 urate-Fe3+ complex was found to be 2.4 × 10(5), whereas the Ka for a 1:1 urate-Fe2+ complex was determined to be 1.9 × 10(4). Our experiments also revealed that urate can form a 2:1 complex with Fe3+ with an association constant for the second urate molecule (K'a) of approx. 4.5 × 10(5). From these data we estimate an overall stability constant (Ks approximately equal to Ka × K'a) for urate-Fe3+ complexes of approx. 1.1 × 10(11). Polarographic measurements revealed that (upon binding) urate decreases the reduction potential for the Fe2+/Fe3+ half-reaction from −0.77 V to −0.67 V. Thus urate slightly diminishes the oxidizing potential of Fe3+. The present results provide a mechanistic explanation for our previous report that urate protects ascorbate from oxidation in human blood. The almost saturating concentration of urate normally found in human plasma (up to 0.6 mM) represents 5-10 times the plasma ascorbate concentration, and is orders of magnitude higher than the ‘free’ iron ion concentration. These considerations point to the physiological significance of our findings.

scholarly journals The stimulatory effects of asbestos on NADPH-dependent lipid peroxidation in rat liver microsomes

1987 ◽  
Vol 241 (2) ◽  
pp. 561-565 ◽  
Author(s):  
M Fontecave ◽  
D Mansuy ◽  
M Jaouen ◽  
H Pezerat
Keyword(s):  
Lipid Peroxidation ◽  
Rat Liver ◽  
Active Sites ◽  
Oxygen Radicals ◽  
Liver Microsomes ◽  
Rat Liver Microsomes ◽  
Iron Ions ◽  
Ferrous Ions ◽  
Solid Iron ◽  
Ferric Oxides

Lipid peroxidation in rat liver microsomes induced by asbestos fibres, crocidolite and chrysotile, is greatly increased in the presence of NADPH, leading to malondialdehyde levels comparable with those induced by CCl4, a very strong inducer of lipid peroxidation. This synergic effect only occurs during the first minutes and could be explained by an increase or a regeneration of the ferrous active sites of asbestos by NADPH, which in turn could rapidly be prevented by the adsorption of microsomal proteins on the surface of the fibres. It is not inhibited by superoxide dismutase, catalase and mannitol, indicating that oxygen radicals are not involved in the reaction. It is also not inhibited by desferrioxamine, indicating that it is not due to a release of free iron ions in solution from the fibres. Lipid peroxidation in NADPH-supplemented microsomes is also greatly increased upon addition of magnetite. This could be linked to the presence of ferrous ions in this solid iron oxide, since the ferric oxides haematite and goethite are completely inactive.

scholarly journals Механизм оптической перезарядки магнитных центров в BSO:Fe

2018 ◽  
Vol 60 (9) ◽  
pp. 1785
Author(s):  
А.В. Ильинский ◽  
В.М. Капралова ◽  
Р.А. Кастро ◽  
Л.А. Набиуллина ◽  
В.М. Стожаров ◽  
...  
Keyword(s):  
Physical Model ◽  
Transformation Process ◽  
Unit Cell ◽  
Ion Concentration ◽  
Iron Ions ◽  
Iron Ion ◽  
Paramagnetic Resonance ◽  
X Ray ◽  
Epr Signal ◽  
Optical Charge

AbstractHigh-resistance photosensitive crystals of Bi_12SiO_20 (BSO) doped with iron ions were studied. X-ray diffraction analysis reveals the compression of a unit cell in a BSO : Fe crystal with increasing impurity concentration. Electron paramagnetic resonance demonstrates a decrease in the intensity of the EPR signal when the BSO: Fe crystal is exposed to light that generates photocarriers. It is found that the characteristic time of the EPR signal decrease is close to the value of the Maxwellian relaxation time measured with the help of the longitudinal electrooptical effect. A physical model of the mechanism of optical charge exchange of magnetic iron centers is discussed, based on the statement that the nature of the crystal bonds of the iron ion with ligands without structural modification of the crystal lattice changes during the photogeneration of carriers. A physical model is proposed, according to which a trivalent Fe^3+ ion transforms into a divalent state of Fe^2+ with a change in the total spin from 5/2 to 2. The compression of the unit cell with increasing iron ion concentration in the framework of the model under discussion is due to the transformation of atomic orbitals upon replacement of silicon ions by iron ions. The transformation process affects the cells unoccupied by iron, which is proved by the absence of a bifurcation of X-ray reflections and indicates the long-range nature of the intracrystalline interactions in sillenites.

In Vitro Antioxidant and Photo-oxidant Properties of Dipyridamole

2001 ◽  
Vol 20 (6) ◽  
pp. 363-368 ◽  
Author(s):  
Franklin Vargas ◽  
Alejandro Tse Cheng ◽  
Guillermo Velutini ◽  
Emildo Marcano ◽  
Ysbelia Sánchez ◽  
...  
Keyword(s):  
Lipid Peroxidation ◽  
Energy Transfer ◽  
Linoleic Acid ◽  
Singlet Oxygen ◽  
Antioxidant Property ◽  
Human Erythrocytes ◽  
Fluorescence Energy Transfer ◽  
Fluorescence Energy

The in vitro antioxidant and photo-oxidant activity of dipyridamole was studied by its effect on superoxide-and singlet oxygen-mediated photohemolysis and viability of neutrophils. Dipyridamole was found to be phototoxic when examined by the photohemolysis on human erythrocytes and on linoleic acid as lipid peroxidation model at concentrations above 3.0 × 10–5 M. On the contrary, when lower concentrations (1.0 × 10–5 to 1.0 × 10–6 M) were used, dipyridamole showed a protector action against singlet oxygen-mediated photohemolysis by other phototoxic compounds like triamterene. This antioxidant property is proposed to result from quenching of triamterene mediated by fluorescence energy transfer. Auto-oxidation and fluorescence-energy transfer is clearly an important mechanism for protection for this drug.

Nose-only water-pipe smoking effects on airway resistance, inflammation, and oxidative stress in mice

2013 ◽  
Vol 115 (9) ◽  
pp. 1316-1323 ◽  
Author(s):  
Abderrahim Nemmar ◽  
Haider Raza ◽  
Priya Yuvaraju ◽  
Sumaya Beegam ◽  
Annie John ◽  
...  
Keyword(s):  
Oxidative Stress ◽  
Lipid Peroxidation ◽  
Airway Resistance ◽  
Reduced Glutathione ◽  
Mechanistic Explanation ◽  
The United States ◽  
Forced Oscillation Technique ◽  
Water Pipe ◽  
Respiratory Effects ◽  
And Oxidative Stress

Water-pipe smoking (WPS) is a common practice in the Middle East and is now gaining popularity in Europe and the United States. However, there is a limited number of studies on the respiratory effects of WPS. More specifically, the underlying pulmonary pathophysiological mechanisms related to WPS exposure are not understood. Presently, we assessed the respiratory effects of nose-only exposure to mainstream WPS generated by commercially available honey flavored “moasel ” tobacco. The duration of the session was 30 min/day and 5 days/wk for 1 mo. Control mice were exposed to air only. Here, we measured in BALB/c mice the airway resistance using forced-oscillation technique. Lung inflammation was assessed histopathologically and by biochemical analysis of bronchoalveolar lavage (BAL) fluid, and oxidative stress was evaluated biochemically by measuring lipid peroxidation, reduced glutathione and several antioxidant enzymes. Pulmonary inflammation assessment showed an increase in neutrophil and lymphocyte numbers. Likewise, airway resistance was significantly increased in the WPS group compared with controls. Tumor necrosis factor α and interleukin 6 concentrations were significantly increased in BAL fluid. Lipid peroxidation in lung tissue was significantly increased whereas the level and activity of antioxidants including reduced glutathione, glutathione S transferase, and superoxide dismutase were all significantly decreased following WPS exposure, indicating the occurrence of oxidative stress. Moreover, carboxyhemoglobin levels were significantly increased in the WPS group. We conclude that 1-mo nose-only exposure to WPS significantly increased airway resistance, inflammation, and oxidative stress. Our results provide a mechanistic explanation for the limited clinical studies that reported the detrimental respiratory effects of WPS.

Study on the Antioxidation Activity of Peanut Antioxidant Peptide

2011 ◽  
Vol 140 ◽  
pp. 446-450 ◽  
Author(s):  
Li Na Yu ◽  
Qing Li Yang ◽  
Jie Sun ◽  
Jie Bi ◽  
Chu Shu Zhang ◽  
...  
Keyword(s):  
Lipid Peroxidation ◽  
Free Radical ◽  
Reducing Power ◽  
Peanut Protein ◽  
Raw Material ◽  
Iron Ion ◽  
Antioxidant Peptides ◽  
Antioxidant Peptide ◽  
Antioxidative Function

Use peanut protein powder as the raw material, the five kinds of peanut antioxidant peptides (abbreviated as AP, FP, PP1, NP and PP2, respectively) were obtained through steps of Viscozyme pretreatment and Alcalase, Flavourzyme, Protamex, Neutral protease and Papain hydrolysis, respectively. Four types of antioxidation activities evaluation methods in vitro including scavenging of DPPH free radical, reducing power, iron ion chelation and anti-lipid peroxidation were presented to evaluate the antioxidation activities of peanut antioxidant peptides. The order of antioxidation activities of five antioxidant peptides was PP2>AP>FP>PP1>NP by comprehensive analysis of the antioxidation experimental results. The results indicated that the optimum proteolytic enzyme for preparing antioxidant peptide was papain. Among the five antioxidant peptides, PP2 had the most antioxidation activities of scavenging of DPPH free radical, reducing power, anti-lipid peroxidation. Therefore, the research and development of antioxidant peptide with the antioxidative function by using papain is an effective approach to further exploit peanut protein.

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