The analogous mechanisms of enzymatic inactivation induced by ascorbate and superoxide in the presence of copper

Redox-active trace metal-induced release of high mobility group box 1(HMGB1) and inflammatory cytokines in fibroblast-like synovial cells is Toll-like receptor 4 (TLR4) dependent

Rheumatoid arthritis (RA) is a chronic autoimmune systemic inflammatory disease that is characterized by synovial inflammation and bone erosion. We have investigated the mechanism(s) by which essential trace metals may initiate and propagate inflammatory phenotypes in synovial fibroblasts. We used HIG-82, rabbit fibroblast-like synovial cells (FLS), as a model system for potentially initiating RA through oxidative stress. We used potassium peroxychromate (PPC, Cr⁺⁵), ferrous chloride (FeCl_2, Fe⁺²), and cuprous chloride (CuCl, Cu⁺) trace metal agents as exogenous pro-oxidants. Intracellular ROS was quantified by fluorescence microscopy and confirmed by flow cytometry (FC). Protein expression levels were measured by western blot and FC, while ELISA was used to quantify the levels of cytokines. Trace metal agents in different valence states acted as exogenous pro-oxidants that generate reactive oxygen species (ROS), which signal through TLR4 stimulation. ROS/TLR4- coupled activation resulted in the release of HMGB1, TNF-α, IL-1β, and IL-10 in conjunction with upregulation of myeloid-related protein (MRP8/14) inflammatory markers that may contribute to the RA pathophysiology. Our results indicate that oxidant-induced TLR4 activation can release HMGB1 in combination with other inflammatory cytokines to mediate pro-inflammatory actions that contribute to RA pathogenesis. The pathway by which inflammatory and tissue erosive changes may occur in this model system possibly underlies the need for functioning anti-HMGB1-releasing agents and antioxidants that possess both dual trace metal chelating and oxidant scavenging properties in a directed combinatorial therapy for RA.

Plasmalogen phospholipids protect internodal myelin from oxidative damage

Reactive oxygen species (ROS) are implicated in a range of degenerative conditions, including aging, neurodegenerative diseases, and neurological disorders. Myelin is a lipid-rich multilamellar sheath that facilitates rapid nerve conduction in vertebrates. Given the high energetic demands and low antioxidant capacity of the cells that elaborate the sheaths, myelin is considered intrinsically vulnerable to oxidative damage, raising the question whether additional mechanisms prevent structural damage. We characterized the structural and biochemical basis of ROS-mediated myelin damage in murine tissues from both central nervous system (CNS) and peripheral nervous system (PNS). To determine whether ROS can cause structural damage to the internodal myelin, whole sciatic and optic nerves were incubated ex vivo with a hydroxyl radical-generating system consisting of copper (Cu), hydrogen peroxide (HP), and ortho-phenanthroline (OP). Quantitative assessment of unfixed tissue by X-ray diffraction revealed irreversible compaction of myelin membrane stacking in both sciatic and optic nerves. Incubation in the presence of the hydroxyl radical scavenger sodium formate prevented this damage, implicating hydroxyl radical species. Myelin membranes are particularly enriched in plasmalogens, a class of ether-linked phospholipids proposed to have antioxidant properties. Myelin in sciatic nerve from plasmalogen-deficient (Pex7 knockout) mice was significantly more vulnerable to Cu/OP/HP-mediated ROS-induced compaction than myelin from WT mice. Our results directly support the role of plasmalogens as endogenous antioxidants providing a defense that protects ROS-vulnerable myelin.

Copper-dependent inhibition and oxidative inactivation with affinity cleavage of yeast glutathione reductase

Effects of copper on the activity and oxidative inactivation of yeast glutathione reductase were analyzed. Glutathione reductase from yeast was inhibited by cupric ion and more potently by cuprous ion. Copper ion inhibited the enzyme noncompetitively with respect to the substrate GSSG and NADPH. The Ki values of the enzyme for Cu(2+) and Cu(+) ion were determined to be 1 and 0.35 μM, respectively. Copper-dependent inactivation of glutathione reductase was also analyzed. Hydrogen peroxide and copper/ascorbate also caused an inactivation with the cleavage of peptide bond of the enzyme. The inactivation/fragmentation of the enzyme was prevented by addition of catalase, suggesting that hydroxyl radical produced through the cuprous ion-dependent reduction of oxygen is responsible for the inactivation/fragmentation of the enzyme. SDS-PAGE and TOF-MS analysis confirmed eight fragments, which were further determined to result from the cleavage of the Met17-Ser18, Asn20-Thr21, Glu251-Gly252, Ser420-Pro421, Pro421-Thr422 bonds of the enzyme by amino-terminal sequencing analysis. Based on the kinetic analysis and no protective effect of the substrates, GSSG and NADPH on the copper-mediated inactivation/fragmentation of the enzyme, copper binds to the sites apart from the substrate-sites, causing the peptide cleavage by hydroxyl radical. Copper-dependent oxidative inactivation/fragmentation of glutathione reductase can explain the prooxidant properties of copper under the in vivo conditions.

De novo galectin-3 expression influences the response of melanoma cells to isatin-Schiff base copper (II) complex-induced oxidative stimulus

Galectin-3, a ubiquitous member of the galectin family, has been shown to control cellular proliferation, adhesion, migration and apoptosis; thus, it has a role in tumor development and progression. Galectin-3 expression is both up- and down-regulated during melanoma progression. However, conflicting data regarding its roles in tumor biology prompted us to investigate if the presence of galectin-3 influences the response of melanoma cells to a novel metallodrug because metastatic melanoma acquires chemo resistance and is reported to be redox-sensitive. Previously, it was demonstrated that the complex [bis-(2-oxindol-3-yl-imino)-2-(2-aminoethyl) pyridine-N,N'] copper (II) perchlorate, herein referred to as [Cu(isaepy)], induces ROS formation and apoptosis in neuroblastoma cells through mitochondrial uncoupling and the activation of AMPK/p38/p53 signaling. Here, we used a model of vertical growth melanoma (TM1), in which GAL3 expression is lost during tumor progression. When de novo expressed, galectin-3 was found to be ubiquitously present in all subcellular compartments. Our results demonstrate that de novo galectin-3 expression impairs the cellular antioxidant system and renders TM1G3 cells more susceptible than GAL3-null TM1MNG3 cells to [Cu(isaepy)] treatment. This compound, in contrast with the redox inactive [dichloro (2-oxindol-3-yl-imino)-2-(2-aminoethyl) pyridine-N,N'] zinc (II), herein referred to as [Zn(isaepy)], leads to increased intracellular ROS accumulation, increased carbonyl stress, increased mitochondrial depolarization, decreased cell adhesion, increased p38 activation and apoptosis in TM1G3, compared with TM1MNG3. Cell death was shown to be dependent on a hydrogen peroxide-derived species and on the activation of p38. Because mitochondria are a target of both [Cu(isaepy)] and galectin-3, we propose that the presence of galectin-3 in this organelle favors increased ROS production, thereby inducing oxidative cellular damage and apoptotic death. Therefore, [Cu(isaepy)] may be envisaged as a possible anti-melanoma strategy, particularly for melanomas that express galectin-3.

Xanthine oxidase-induced neuronal death via the oxidation of NADH: prevention by micromolar EDTA

The oxidation of xanthine by xanthine oxidase (XO) or xanthine dehydrogenase represents an important source of reactive oxygen species (ROS), which contribute to the damaging consequences of cerebral ischemia, inflammation, and neurodegenerative disorders. However, both enzymes are also able to act on reduced nicotinamide adenine dinucleotide (NADH). The FAD binding site to which NADH binds is distinct from that of the xanthine binding site. We report that the combination of xanthine oxidase and NADH is toxic to cultures of cerebellar granule neurons. Protection by superoxide dismutase (Cu,Zn-SOD or Mn-SOD) or catalase indicates mediation of the toxicity by superoxide and hydrogen peroxide. In addition, pre-incubating XO with EDTA at concentrations as low as 2 microM, prevented the toxicity, indicating that a metal contaminating XO is involved in producing the toxic effects of XO/NADH. It is possible that such a metal might play a role in the toxicity of XO in vivo.

Edaravone, a free radical scavenger, protects against retinal damage in vitro and in vivo

Edaravone (3-methyl-1-phenyl-2-pyrazolin-5-one), a free radical scavenger, is used for the treatment of acute cerebral infarction. In this study, we investigated whether edaravone is neuroprotective against retinal damage. In vitro, we used a radical-scavenging capacity assay using reactive oxygen species-sensitive probes to investigate the effects of edaravone on H(2)O(2), superoxide anion (O(2)*), and hydroxyl radical (*OH) production in a rat retinal ganglion cell line (RGC-5). The effect of edaravone on oxygen-glucose deprivation (OGD)-induced RGC-5 damage was evaluated using a 2-(2-methoxy-4-nitrophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium, monosodium salt assay of cell viability. Edaravone (3-methyl-1-phenyl-2-pyrazolin-5-one) significantly decreased radical generation and reduced the cell death induced by OGD stress. In vivo, retinal damage was induced by intravitreous injection of N-methyl-D-aspartate (NMDA; 5 nmol) and was evaluated by examining ganglion cell layer cell loss, terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) staining, and the expressions of two oxidant-stress markers [4-hydroxy-2-nonenal (4-HNE) and 8-hydroxy-2-deoxyguanosine (8-OHdG)]. In addition, activations of mitogen-activated protein kinases (MAPKs) [extracellular signal-regulated protein kinases (ERK), c-Jun NH(2)-terminal kinases (JNK), and p38 MAPK], as downstream signal pathways after NMDA receptor activation, were measured using immunoblotting and immunostaining. Edaravone at 5 and 50 nmol intravitreous injection or at 1 and 3 mg/kg i.v. significantly protected against NMDA-induced retinal cell death. At 50 nmol intravitreous injection, it 1) decreased the retinal expressions of TUNEL-positive cells, 4-HNE, and 8-OHdG and 2) reduced the retinal expressions of NMDA-induced phosphorylated JNK and phosphorylated p38 but not that of phosphorylated ERK. These findings suggest that oxidative stress plays a pivotal role in retinal damage and that edaravone may be a candidate for the effective treatment of retinal diseases.

How plants cope with foreign compounds. Translocation of xenobiotic glutathione conjugates in roots of barley (Hordeum vulgare)

BACKGROUND AND AIM

Numerous herbicides and xenobiotic organic pollutants are detoxified in plants to glutathione conjugates. Following this enzyme catalyzed reaction, xenobiotic GS-conjugates are thought to be compartmentalized in the vacuole of plant cells. In the present study, evidence is presented from experiments with roots of barley (Hordeum vulgare cv. Cherie) that part of these conjugates will undergo long range transport in plants, rather than be stored in the vacuole. To our knowledge, this is the first report about the unidirectional long-range transport of xenobiotic conjugates in plants and the exsudation of a glutathione conjugate from the root tips. This could mean that plants possess an excretion system for unwanted compounds giving them similar advantages as animals.

METHODS

Barley plants (Hordeum vulgare) were grown in Petri dishes soaked with tap water in the greenhouse. Fluorescence Microscopy. Roots of barley seedlings were cut under water, and the end at which the pesticides were applied was fixed in an aperture with a thin latex foil and transferred into a drop of water on a cover slide. The cover slide was fixed in a measuring chamber on the stage of an inverse fluorescence microscope (Zeiss Axiovert 100). Monobromo- and Monochlorobimane, two model xenobiotics that are conjugated rapidly in plant cells with glutathione, hereby forming fluorescent metabolites, were used as markers. Their transport in the root could be followed with high time resolution. Spectrometric enzyme assay. Glutathione S-transferase (GST) activity was determined in the protein extracts following established methods. Aliquots of the enzyme extract were incubated with 1-chloro-2,4-dinitrobenzene (CDNB), or monochlorobimane. Controls lacking enzyme or GSH were measured. Pitman chamber experiments. Ten days old barley plants or detached roots were inserted into special incubation chambers, either complete with tips or decapitated, as well as 10 days old barley plants without root tips. Compartment A was filled with a transport medium and GSH conjugate or L-cysteine conjugate. Compartments B and C contained sugar free media. Samples were taken from the root tip containing compartment C and the amount of conjugate transported was determined spectro-photometrically. Results. The transport in roots is unidirectional towards the root tips and leads to exsudation of the conjugates at rates between 20 and 200 nmol min(-1). The microscopic studies have been complemented by transport studies in small root chambers and spectroscopic quantification of dinitrobenzene-conjugates. The latter experiments confirm the microscopic studies. Furthermore it was shown that glutathione conjugates are transported at higher rates than cysteine conjugates, despite of their higher molecular weights. This observation points to the existence of glutathione specific carriers and a specific role of glutathione in the root.

DISCUSSION

It can be assumed that long distance transport of glutathione conjugates within the plant proceeds like GSH or amino acid transport in both, phloem and xylem. The high velocity of this translocation of the GS-X is indicative of an active transport. For free glutathione, a rapid transport-system is essential because an accumulation of GSH in the root tip inhibits further uptake of sulfur. Taking into account that all described MRP transporters and also the GSH plasmalemma ATPases have side activities for glutathione derivatives and conjugates, co-transport of these xenobiotic metabolites seems credible. On the other hand, when GS-B was applied to the root tips from the outside, no significant uptake was observed. Thus it can be concluded that only those conjugates can be transported in the xylem which are formed inside the root apex. Having left the root once, there seems to be no return into the root vessels, probably because of a lack of inward directed transporters.

CONCLUSIONS

Plants seem to possess the capability to store glutathione conjugates in the vacuole, but under certain conditions, these metabolites might also undergo long range transport, predominantly into the plant root. The transport seems dependent on specific carriers and is unidirectional, this means that xenobiotic conjugates from the rhizosphere are not taken up again. The exudation of xenobiotic metabolites offers an opportunity to avoid the accumulation of such compounds in the plant.

RECOMMENDATIONS AND PERSPECTIVES

The role of glutathione and glutathione related metabolites in the rhizosphere has not been studied in any detail, and only scattered data are available on interactions between the plant root and rhizosphere bacteria that encounter such conjugates. The final fate of these compounds in the root zone has also not been addressed so far. It will be interesting to study effects of the exsuded metabolites on the biology of rhizosphere bacteria and fungi.

Effects of combinations of ROS scavengers on oxidative DNA damage caused by visible-light-activated camphorquinone/N,N-dimethyl-p-toluidine

The objective of this investigation was to analyze whether various combinations of the ROS scavengers glutathione (GSH), N-acetyl-cysteine (NAC), and vitamins C and E decrease DNA damage due to visible-light-irradiated (VL-irradiated) camphorquinone/N,N-dimethyl-p-toluidine (CQ/DMT) compared with individual vitamin C or E. PhiX-174 RF plasmid DNA was used to determine single and double strand breaks as parameters of DNA damage. Individual ROS scavengers and combinations of the antioxidants were added to plasmid DNA treated with VL-irradiated CQ/DMT/Cu (II). After incubation, DNA was loaded into a 1% agarose gel. Following electrophoresis, gels stained with 0.5 microg/mL ethidium bromide were photographed under ultraviolet illumination and analyzed with NIH ImageJ software. Results were evaluated between groups for statistical significance using Student's paired t-test (p < 0.05). Glutathione significantly reduced oxidative DNA damage at all test concentrations when combined with vitamin C or vitamin E. The concentration of damaged DNA observed in the presence of combinations of GSH with vitamin C or vitamin E was significantly lower compared with all other combinations of antioxidants investigated in our study (p < 0.05). In contrast to GSH, NAC was not able to compensate the pro-oxidative effects of vitamin C and vitamin E. Only at a concentration of 2 mM, NAC combined with vitamin C efficiently prevented CQ/DMT/Cu (II)-associated DNA damage. Our data indicate that solely the combinations of GSH with vitamin C or vitamin E significantly reduce the severity of oxidative DNA damage caused by CQ/DMT, whereas NAC may even increase the pro-oxidant activity of vitamin C and vitamin E.

Effects of gamma radiation on β-lactoglobulin: Oligomerization and aggregation

The conformational changes and aggregation process of beta-lactoglobulin (beta-LG) subjected to gamma irradiation are presented. Beta-LG in solutions of different protein concentrations (3 and 10 mg/ml) and in solid state with different water activities (a(w)) (0.22; 0.53; 0.74) was irradiated using a Cobalt-60 radiation source at dose level of 1-50 kGy. Small-angle X-ray scattering (SAXS) was used to study the conformational changes of beta-LG due to the irradiation treatment. The irradiated protein was also examined by high performance size exclusion chromatography (HPSEC) and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) under nonreducing and reducing conditions and fluorescence. SAXS analysis showed that the structural conformation of irradiated beta-LG in solid state at different a(w) and dose level was essentially the same as the nonirradiated beta-LG. The scattering data also showed that the irradiation of beta-LG in solution promoted the formation of oligomers. Interestingly, from the data analysis and model building, it could be shown that the formed oligomers are linear molecules, built by linear combinations of beta-LG dimers (tetramers, hexamers, etc). The formation of oligomers was also evidenced by SDS-PAGE analysis and HPSEC chromatograms, in which products with higher molecular mass than that of the dimeric beta-LG were detected. Formation of intermolecular cross-linking between tyrosyl radicals are proposed to be at least partially responsible for this occurrence. From the results it could be shown that the samples irradiated in solution presented some conformational changes under gamma irradiation, resulting in well ordered oligomers and aggregates formed by cross-linking of beta-LG dimers subunits, while the samples irradiated in the solid state were not modified.

Hyaluronan degradation by copper(II) chloride and ascorbate: rotational viscometric, EPR spin-trapping, and MALDI–TOF mass spectrometric investigations

The degradation of high-molar-mass hyaluronan (HA) by copper(II) chloride and ascorbate was studied by means of rotational viscometry. It was found that even small amounts of CuCl(2) present in the oxidative system led to the pronounced degradation of HA, reflected in a rapid decrease of the dynamic viscosity of the biopolymer solution. Such degradation was induced by free radicals generated in elevated amounts in the presence of copper ions. Electron paramagnetic resonance investigations performed on a model oxidative system containing Cu(II) and ascorbic acid proved the formation of relatively stable ascorbate anion radicals resulting from the reaction of ascorbic acid with hydroxyl radicals. In this way, by scavenging the hydroxyl radicals, ascorbic acid protected HA from their degradative action. Matrix-assisted laser desorption ionization-time-of-flight (MALDI-TOF) mass spectrometry was applied to analyze the degraded HA. The results showed that only regular fragmentation of hyaluronan occurred using the mentioned oxidative system that led to the formation of HA oligomers with unaffected primary chemical structure.

Evaluation of IDA-PEVA hollow fiber membrane metal ion affinity chromatography for purification of a histidine-tagged human proinsulin

Inabilities to process particulate material and to allow the use of high flow rates are limitations of conventional chromatography. Membranes have been suggested as matrix for affinity separation due to advantages such as allowing high flow rates and low-pressure drops. This work evaluated the feasibility of using an iminodiacetic acid linked poly(ethylenevinyl alcohol) membrane in the immobilized metal ion affinity chromatography (IMAC) purification of a human proinsulin(His)(6) of an industrial insulin production process. The screening of metal ions showed Ni(2+) as metal with higher selectivity and capacity among the Cu(2+), Ni(2+), Zn(2+) and Co(2+). The membrane showed to be equivalent to conventional chelating beads in terms of selectivity and had a lower capacity (3.68 mg/g versus 12.26 mg/g). The dynamic adsorption capacity for human proinsulin(His)(6) was unaffected by the mode of operation (dead-end and cross-flow filtration).

Kiwifruit L-galactose dehydrogenase: molecular, biochemical and physiological aspects of the enzyme

l-Galactose dehydrogenase, an enzyme in the pathway of ascorbate biosynthesis, was purified to homogeneity from leaves of kiwifruit [Actinidia deliciosa (A.Chev.) CF Liang et AR Ferguson var. deliciosa 'Hayward']. The enzyme had a molecular mass of 34.2 kD, and behaved as a monomer during gel filtration. The K_m(galactose) and K_m(NAD) decreased as pH increased from 6.5 to 9, while the V_max increased over this range. A number of related sugars were tested as alternative substrates or inhibitors, but these were ineffective. Ascorbate caused slow inactivation of the enzyme, possibly through metal catalysed generation of oxygen radicals. Inactivation appeared to be active-site directed as it was protected by the substrate NAD, and not by NADH or l-galactose. This is not likely to be physiologically significant. Through partially sequencing the protein, the gene was identified in the HortResearch Actinidia EST database, and the translation of the full length sequence of this cDNA showed a high homology (80% identity, 90% similarity) to the translation of an Arabidopsis gene (accession CAD10386) and to translations of other genes identified in GenBank. Levels of l-GalDH activity decreased during fruit and leaf development, and levels of mRNA showed a similar reduction. Activity varied between flower parts, with ovaries and styles showing equivalent activity to young fruitlets and sink leaves. Nucleotide sequences reported are available in the Genbank database under the accession number AY176585 (kiwifruit) and AY264803 (apple).

Inactivation of Trypanosoma cruzi and Crithidia fasciculata topoisomerase I by Fenton systems

Fenton systems (H(2)O(2)/Fe(II) or H(2)O(2)/Cu(II)) inhibited Trypanosoma cruzi and Crithidia fasciculata topoisomerase I activity. About 61-71% inactivation was produced by 25 microM Fe(II) or Cu(II) with 3.0 mM H(2)O(2). Thiol compounds and free radical scavengers prevented Fenton system effects, depending on the topoisomerase assayed. With the T. cruzi enzyme, reduced glutathione (GSH), dithiothreitol (DTT), cysteine and N-acetyl-L-cysteine (NAC) entirely prevented the effect of the H(2)O(2)/Fe(II) system; mannitol protected 37%, whereas histidine and ethanol were ineffective. With C. fasciculata topoisomerase, GSH, DTT and NAC protected 100%, cysteine, histidine and mannitol protected 28%, 34% and 48%, respectively, whereas ethanol was ineffective. With the H(2)O(2)/Cu(II) system and T. cruzi topoisomerase, DTT and histidine protected 100% and 60%, respectively, but the other assayed protectors were less effective. Similar results were obtained with the C. fasciculata enzyme. Topoisomerase inactivation by the H(2)O(2)/Fe(II) or H(2)O(2)/Cu(II) systems proved to be irreversible since it was not reversed by the more effective enzyme protectors. It is suggested that topoisomerases could act either as targets of 'reactive oxygen species' (ROS) generated by Fenton systems or bind the corresponding metal ions, whose redox cycling would generate reactive oxygen species in situ.

Melatonin protects against gastric ulceration and increases the efficacy of ranitidine and omeprazole in reducing gastric damage

The antiulcer effect of melatonin on gastric lesions caused by restraint-cold stress was studied with the intent of determining the mechanism of action of this agent. Melatonin dose-dependently prevented restraint-cold stress-induced gastric damage with around 90% inhibition at a dose of 60 mg/kg BW. When compared with already marketed antiulcer drugs such as ranitidine and omeprazole, melatonin was found to be more effective than ranitidine but less effective than omeprazole in preventing stress ulcer. As stress-induced gastric lesions are mainly caused by oxidative damage because of hydroxyl radicals (*OH), the effect of melatonin in scavenging the.OH generated during stress conditions in vivo as well as in an in vitro model system were studied. The results indicate that melatonin caused an 88% reduction of endogenous *OH during stress in vivo, an observation confirmed in an established in vitro system. Furthermore, a decrease in the activity of gastric peroxidase (GPO) and an increase in the gastric mitochondrial superoxide dismutase (Mn-SOD) activity because of restraint-cold stress was attenuated by melatonin pretreatment indicating that the indole possibly exerts its gastroprotective effects through its direct as well as indirect antioxidant activities. Moreover, in separate experiments, cotreatment of rats with melatonin and ranitidine or omeprazole was found to protect against stress ulceration in doses at which either of these alone could not protect the stomach. The findings raise the possibility of melatonin being considered as an effective gastroprotective agent individually or as a cotreatment with either ranitidine and omeprazole.

Critical role of an endogenous gastric peroxidase in controlling oxidative damage in H. pylori-mediated and nonmediated gastric ulcer

The objective of the present study is to delineate the mechanism of oxidative damage in human gastric ulcerated mucosa despite the presence of some antioxidant enzymes. We report for the first time the critical role of an endogenous peroxidase, a major H(2)O(2) metabolizing enzyme, in controlling oxidative damage in gastric mucosa. Human gastric mucosa contains a highly active peroxidase in addition to the myeloperoxidase contributed by neutrophil. In both non-Helicobacter pylori (H. pylori)- and H. pylori-mediated gastric ulcer, when myeloperoxidase level increases due to neutrophil accumulation, gastric peroxidase (GPO) level decreases significantly. Moreover, gastric ulcer is associated with oxidative damage of the mucosa as evidenced by significant increase in lipid peroxidation, protein oxidation, and thiol depletion indicating accumulation of reactive oxygen metabolites (ROM). Mucosal total superoxide dismutase (Mn and Cu-Zn SOD) level also decreases significantly leading to increased accumulation of O(2)(*-). To investigate the plausible ROM-mediated inactivation of the GPO during ulceration, the enzyme was partially purified from the mucosa. When exposed to an in vitro ROM generating system, using Cu(2+), ascorbate, and H(2)O(2,) the enzyme gets inactivated, which is dependent on Cu(2+), ascorbate, or H(2)O(2). Insensitivity to SOD excludes inactivation by O(2)(*-). However, complete protection by catalase indicates that H(2)O(2) is essential for inactivation. Sensitivity to EDTA and hydroxyl radical *OH) scavengers indicates that GPO is inactivated most probably by *OH generated from H(2)O(2). We propose that GPO is inactivated in vivo by ROM generated by activated neutrophil. This leads to further accumulation of endogenous H(2)O(2) to cause more oxidative damage to aggravate the ulcer.

Specific and reversible inactivation of Phycomyces blakesleeanus isocitrate lyase by ascorbate-iron: role of two redox-active cysteines

Phycomyces blakesleeanus isocitrate lyase (EC 4.1.3.1) is in vivo reversibly inactivated by hydrogen peroxide. The purified enzyme showed reversible inactivation by an ascorbate plus Fe(2+) system under aerobic conditions. Inactivation requires hydrogen peroxide; was prevented by catalase, EDTA, Mg(2+), isocitrate, GSH, DTT, or cysteine; and was reversed by thiols. The ascorbate served as a source of hydrogen peroxide and also reduced the Fe(3+) ions produced in a "site-specific" Fenton reaction. Two redox-active cysteine residues per enzyme subunit are targets of oxidative modification; one of them is located at the catalytic site and the other at the metal regulatory site. The oxidized enzyme showed covalent and conformational changes that led to inactivation, decreased thermal stability, and also increased inactivation by trypsin. These results represent an example of redox regulation of an enzymatic activity, which may play a role as a sensor of redox cellular status.

In vivo copper-mediated free radical production: an ESR spin-trapping study

Copper has been suggested to facilitate oxidative tissue injury through a free radical-mediated pathway analogous to the Fenton reaction. By applying the electron spin resonance (ESR) spin-trapping technique, evidence for hydroxyl radical formation in vivo was obtained in rats treated simultaneously with copper and ascorbic acid or paraquat. A secondary radical spin-trapping technique was used in which the hydroxyl radical formed the methyl radical upon reaction with dimethylsulfoxide. The methyl radical was then detected by ESR spectroscopy as its adduct with the spin trap phenyl-N-t-butyl- nitrone (PBN). In contrast, lipid derived radical was detected in vivo in copper-challenged, vitamin E and selenium-deficient rats. These findings support the proposal that dietary selenium and vitamin E can protect against lipid peroxidation and copper toxicity. Since copper excreted into the bile from treated animals is expected to be maintained in the Cu(I) state (by ascorbic acid or glutathione), a chelating agent that would redox-stablilize it in the Cu(I) state was used to prevent ex vivo redox chemistry. Bile samples were collected directly into solutions of bathocuproinedisulfonic acid, a Cu(I)-stabilizing agent, and 2,2'-dipyridyl, a Fe(II)-stabilizing agent. If these precautions were not taken, radical adducts generated ex vivo could be mistaken for radical adducts produced in vivo and excreted into the bile.

Activation of ADAM 12 protease by copper

Conversion of latent proteases to the active form occurs by various mechanisms characteristic for different protease families. Here we report that the disintegrin metalloprotease ADAM 12-S is activated by Cu(II). Copper activation is distinct from the cysteine switch component of latency: elimination of the ADAM 12 cysteine switch by a point mutation in the propeptide had no effect on copper activation, whereas mutation of an unpaired cysteine residue in the catalytic domain resulted in a mutant form of ADAM 12-S that was insensitive to copper. This suggests a multi-step activation mechanism for ADAM 12 involving both furin cleavage and copper binding.

Characterization of the Streptococcus pneumoniae NADH oxidase that is required for infection

Streptococcus pneumoniae is an important human pathogen capable of causing serious infections. NADH oxidase, a factor necessary for infection, was previously identified as part of a signature-tagged mutagenesis screen of a S. pneumoniae clinical isolate, 0100993. The mutant, with a plasmid insertion disrupting the nox gene, was attenuated for virulence in a murine respiratory tract infection model. A complete refined nox deletion mutant was generated by allelic-replacement mutagenesis and found to be attenuated for virulence 10(5)-fold in the murine respiratory tract infection model and at least 10(4)-fold in a Mongolian gerbil otitis media infection model, confirming the importance of the NADH oxidase for both types of S. pneumoniae infection. NADH oxidase converts O(2) to H(2)O. If O(2) is not fully reduced, it can form superoxide anion (O2(-)) and hydrogen peroxide (H(2)O(2)), both of which can be toxic to cells. Bacterial cell extracts from the allelic-replacement mutant were found to lack NADH oxidase activity and the mutant was unable to grow exponentially under conditions of vigorous aeration. In contrast, the mutant displayed normal growth characteristics under conditions of limited aeration. The S. pneumoniae nox gene was cloned and expressed in E. coli. The purified His-tagged NADH oxidase was shown to oxidize NADH with a K:(m) of 32 microM, but was unable to oxidize NADPH. Oxidation of NADH was independent of exogenous FAD or FMN.

Hemolysis of human red blood cells induced by the combination of diethyldithiocarbamate (DDC) and divalent metals: modulation by anaerobiosis, certain antioxidants and oxidants

The objective of the present communication is to describe the role played by combinations between diethydithiocarbamate (DDC) and divalent metals in hemolysis of human RBC. RBC which had been treated with DDC (10-50 microM) were moderately hemolyzed (about 50%) upon the addition of subtoxic amounts of Cu2+ (50 microM). However, a much stronger and a faster hemolysis occurred either if mixtures of RBC-DDC were immediately treated either by Co2+ (50 microM) or by a premixture of Cu2+ and Co2+ (Cu:Co) (50 microM). While Fe2+ and Ni2+, at 50 microM, initiated 30-50% hemolysis when combined with DDC (50 microM), on a molar basis, Cd2+ was at least 50 fold more efficient than any of the other metals in the initiation of hemolysis by DDC. On the other hand, neither Mn2+ nor Zn2+, had any hemolysis-initiating effects. Co2+ was the only metal which totally blocked hemolysis if added to DDC prior to the addition of the other metals. Hemolysis by mixtures of DDC + (Cu:Co) was strongly inhibited by anaerobiosis (flushing with nitrogen gas), by the reducing agents glutathione, N-acetyl cysteine, mercaptosuccinate, ascorbate, TEMPO, and alpha-tocopherol, by the PLA2 inhibitorbromophenacylbromide (BrPACBr), by tetracycline as well as by phosphatidyl choline, cholesterol and by trypan blue. However, TEMPO, BrPACBr and PC were the only agents which inhibited hemolysis induced by DDC: Cd2+ complexes. On the other hand, none of the classical scavengers of reactive oxygen species (ROS) employed e.g dimethylthiourea, catalase, histidine, mannitol, sodium benzoate, nor the metal chelators desferal and phenanthroline, had any appreciable inhibitory effects on hemolysis induced by DDC + (Cu:Co). DDC oxidized by H2O2 lost its capacity to act in concert either with Cu2+ or with Cd2+ to hemolyze RBC. While either heating RBC to temperatures greater than 37 degrees C or exposure of the cells to glucose-oxidase-generated peroxide diminished their susceptibility to hemolysis, exposure to the peroxyl radical from AAPH, enhanced hemolysis by DDC + (Cu:Co). The cyclovoltammetry patterns of DDC were drastically changed either by Cu2+, Co2+ or by Cd2+ suggesting a strong interaction of the metals with DDC. Also, while the absorbance spectrum of DDC at 280 nm was decreased by 50% either by Co2+, Cd2+ or by H2O2, a 90% reduction in absorbance occurred if DDC + H2O2 mixtures were treated either by Cu2+ or by Co2+, but not by Cd2+. Taken together, it is suggested that DDC-metal chelates can induce hemolysis by affecting the stability and the integrity of the RBC membrane, and possibly also of the cytoskeleton and the role played by reducing agents as inhibitors might be related to their ability to deplete oxygen which is also supported by the inhibitory effects of anaeobiosis.

Oxidative inactivation of gastric peroxidase by site-specific generation of hydroxyl radical and its role in stress-induced gastric ulceration

We have shown earlier that restraint-cold stress-induced gastric ulceration in rats is caused by metal ion-dependent generation of hydroxyl radical (OH.) and oxidative inactivation of the gastric peroxidase (GPO), an important H2O2 scavenging enzyme. To study the mechanism of the oxidative damage of GPO, the purified enzyme was exposed to an OH. generating system containing Cu2+, ascorbate, and H2O2. Kinetic studies indicate that the enzyme is inactivated in a time-dependent process showing saturation with respect to Cu2+ concentration. The enzyme specifically requires Cu2+ and is not inactivated by the same concentration of Fe2+, Mn2+, or Zn2+. Sensitivity to catalase indicates the critical role of H2O2 in the inactivation. Inactivation is insensitive to superoxide dismutase, suggesting no role of superoxide. The rate of inactivation is not increased in D2O excluding the involvement of singlet oxygen in the process. However, OH. scavengers such as benzoate or mannitol cannot prevent inactivation. The results indicate a plausible generation of OH. within the enzyme molecule as the cause of inactivation. Fragmentation of peptide linkage or intramolecular crosslinking, gross change of tertiary structure, or change in intrinsic tryptophan fluorescence which occurs in "global" oxidation are not evident. Inactivation is dependent on pH and from a plot of K(obs) of inactivation against pH, the controlling role of an ionizable group of the enzyme having a pka of 7.8 could be suggested, deprotonation of which favors inactivation. Amino acid analysis shows a specific loss of two lysine residues in the inactivated enzyme. Competitive kinetic studies indicate that pyridoxal phosphate, a specific modifier of the lysine residue, prevents inactivation by competing with Cu2+ for binding at the GPO. A Cu2+ binding motif consisting at least of two lysine residues exists in GPO, which specifically binds Cu2+ and generates OH.. The radical oxidizes the lysine residues and perturbs the heme environment to cause inactivation. We suggest that oxidative damage of GPO is mediated by site-specific generation of OH. and not by the OH. generated in the bulk phase.

Does oxidative protein damage play a role in the pathogenesis of carbon tetrachloride-induced liver injury in the rat?

Free radicals have been implicated in the pathogenesis of alcohol-induced liver injury in humans and carbon tetrachloride (CCl4)-induced liver injury in rats. The most extensively studied aspect of free radical induced liver injury is lipid peroxidation. Recently it has been found that free radicals can cause oxidative damage to cellular proteins and alter cellular function. One such susceptible protein is the enzyme glutamine synthase (GS). The chemical effects of CCl4 on cell proteins and their biological consequences are not known. Hence, in our study, the effect of CCl4 on liver protein oxidation and GS activity were investigated and compared with lipid peroxidation. A significant increase in liver protein carbonyl content (2-3 fold) and a significant decrease in hepatic GS activity (44-57%) were observed. Damage to proteins was rapid in onset and increased with time. Acute exposure of rats to CCl4 resulted in an increase in hepatic protein carbonyl content and a decrease in hepatic GS within 1 h. In cirrhosis of the liver induced by CCl4, the decrease in hepatic GS activity was accompanied by a significant increase in plasma ammonia levels. We conclude that protein oxidation may play a role in the pathogenesis of CCl4 induced liver injury and that the accumulation of oxidised proteins may be an early indication of CCl4 induced liver damage.

Inactivation of yeast glutathione reductase by Fenton systems: effect of metal chelators, catecholamines and thiol compounds

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.

Both intracellular and extracellular vitamin C inhibit atherogenic modification of LDL by human vascular endothelial cells

Oxidative modification of LDL by vascular cells has been proposed as a mechanism by which LDL becomes atherogenic. Antioxidants that can prevent LDL oxidation may therefore act as antiatherogens. We used endothelial cells (ECs) from human aortas (HAECs), human saphenous veins (HSECs), and bovine aortas (BAECs) to investigate the role of intracellular and extracellular vitamin C (ascorbate) in EC-mediated LDL modification. Incubation of LDL (0.1 mg protein per milliliter) with confluent HAECs in Ham's F-10 medium led to time-dependent modification of the lipoprotein. In contrast, incubation of LDL with HAECs in medium 199, which does not contain redox-active transition metal ions, did not lead to LDL modification. Both HAEC-mediated and cell-free LDL modifications in Ham's F-10 medium were strongly inhibited in a time- and dose-dependent manner by physiological concentrations of ascorbate. Confluent HAECs cultured under conventional conditions contained very little intracellular ascorbate (< 0.5 nmol/mg protein) but could be loaded with up to 20 nmol ascorbate per milligram protein in a time- and concentration-dependent manner. Ascorbate-loaded HAECs exhibited a lower capacity to modify LDL than did non-ascorbate-loaded control cells. When LDL was incubated with HSECs instead of HAECs, similar time- and concentration-dependent inhibitory effects on LDL modification of intracellular and extracellular ascorbate were observed. In contrast to human ECs, BAECs did not take up vitamin C and therefore only coincubation but not preincubation with ascorbate inhibited BAEC-mediated LDL modification. Our data show that enrichment of human vascular ECs with vitamin C lowers their capacity to modify LDL. In addition, extracellular vitamin C strongly inhibits EC-mediated, metal ion-dependent atherogenic modification of LDL.

Changes of biological reducing activity in rat brain following closed head injury: a cyclic voltammetry study in normal and heat-acclimated rats

Reactive oxygen species (ROS) are normally generated in the brain during metabolism, and their production is enhanced by various insults. Low molecular weight antioxidants (LMWA) are one of the defense mechanisms of the living cell against ROS. The reducing capacity of brain tissue (total LMWA) was measured by cyclic voltammetry (CV), which records biological oxidation potential specific to the type of scavenger(s) present and anodic current intensity (Ia), which depends on scavenger concentration. In the present study, the reducing capacity of rat brain following closed head injury (CHI) was measured. In addition, CV of heat-acclimated traumatized rats was used to correlate endogenous cerebroprotection after CHI with LMWA activity. Sham-injured rat brains displayed two anodic potentials: at 350 +/- 50 mV (Ia = 0.75 +/- 0.06 microA/mg protein) and at 750 +/- 50 mV (Ia = 1.00 +/- 0.05 microA/mg protein). Following CHI, the anodic waves appeared at the same potentials as in the sham animals. However, within 5 min of CHI, the total reducing capacity was transiently decreased by 40% (p < 0.01). A second dip was detected at 24 h (60%, p < 0.005). By 48 h and at 7 days, the Ia levels normalized. The acclimated rats displayed anodic potentials identical to those of normothermic rats. However, the Ia of both potentials was lower (60% of control, p < 0.001). The Ia profile after CHI was the direct opposite of the normothermic Ia profile: no immediate decrease of Ia and an increase from 4 h and up to 7 days (40-50%, p < 0.001). We suggest that the lowered levels of LMWA in the post-CHI period reflect their consumption due to overproduction of free radicals. The augmented concentration of LMWA found in the brain of the heat-acclimated rats suggests that these rats are better able to cope with these harmful radicals, resulting in a more favorable outcome following CHI.

Dopamine- and L-beta-3,4-dihydroxyphenylalanine hydrochloride (L-Dopa)-induced cytotoxicity towards catecholaminergic neuroblastoma SH-SY5Y cells. Effects of oxidative stress and antioxidative factors

Enhanced oxidative stress has been suggested to be involved in the degeneration of nigrostriatal dopaminergic neurons in Parkinson's disease. The high turnover rate of dopamine and/or unsequestered dopamine may cause an increase of formation of hydrogen peroxide via either oxidative deamination of dopamine by monoamine oxidase or autoxidation. Hydrogen peroxide would be converted to more toxic hydroxyl free radicals. L-beta-3,4-Dihydroxyphenylalanine hydrochloride (L-DOPA), the most useful drug in the symptomatic treatment of Parkinson's disease, has been considered to possess deteriorating degenerative side-effects. The catecholaminergic neuroblastoma SH-SY5Y cells were chosen to investigate the cytotoxic effect of dopamine and L-DOPA. Both dopamine and L-DOPA were found to be cytotoxic towards SH-SY5Y cells. Such toxic effects were accompanied by an increase of oxidative stress in the cell cultures and could be reversed effectively by catalase and to a lesser extent by superoxide dismutase. The non-enzymatic antioxidants L-ascorbic acid, glutathione, N-acetyl-L-cysteine, but not (+)-alpha-tocopherol, also completely protected SH-SY5Y cells against the cytotoxic effects induced by dopamine and L-DOPA. Antioxidative factors, namely free radical scavengers (including N-tert-butyl-alpha-phenylnitrone, salicylic acid, and D-mannitol) and a strong iron chelator, deferoxamine, however, did not protect the SH-SY5Y cells against dopamine and L-DOPA. The generation of reactive oxygen species and the resulting enhanced oxidative stress was clearly involved in the dopamine- and L-DOPA-induced cytotoxic effects. Hydrogen peroxide played the most important role related to cytotoxicity of dopamine and L-DOPA.

Copper-specific damage in human erythrocytes exposed to oxidative stress

Ascorbate and complexes of Cu(II) and Fe(III) are capable of generating significant levels of oxygen free radicals. Exposure of erythrocytes to such oxidative stress leads to increased levels of methemoglobin and extensive changes in cell morphology. Cu(II) per mole is much more effective than Fe(III). However, isolated hemoglobin is oxidized more rapidly and completely by Fe(III)- than by Cu(II)-complexes. Both Fe(III) and Cu(II) are capable of inhibiting a number of the key enzymes of erythrocyte metabolism. The mechanism for the enhanced activity of Cu(II) has not been previously established. Using intact erythrocytes and hemolysates we demonstrate that Cu(II)-, but not Fe(III)-complexes in the presence of ascorbate block NADH-methemoglobin reductase. Complexes of Cu(II) alone are not inhibitory. The relative inability of Fe(III)-complexes and ascorbate to cause methemoglobin accumulation is not owing to Fe(III) association with the membrane, or its failure to enter the erythrocytes. The toxicity of Cu(II) and ascorbate appears to be a result of site-specific oxidative damage of erythrocyte NADH-methemoglobin reductase and the enzyme's subsequent inability to reduce the oxidized hemoglobin.

Hydroxyl radical is the major causative factor in stress-induced gastric ulceration

The role of the metal-catalyzed production of hydroxyl radicals (OH.) on gastric ulceration caused by restraint-cold stress in rat was studied. Stress causes a 50% increase in the thiobarbituric acid reactive species (TBARS) as a measure of the lipid peroxidation, nearly 70% increase in protein oxidation as measured by its carbonyl content and about 40% decrease in the glutathione content of the fundic stomach, suggesting oxidative damage by stress. Stress also causes a time-dependent increase in the mitochondrial superoxide dismutase activity and a decrease in the peroxidase activity, both of which correlate well with the increase in the severity of ulceration as measured by the ulcer index. Specific OH. scavengers such as benzoate or dimethylsulfoxide (DMSO) and the free radical trap such as alpha-phenyl N-tert-butyl nitrone (PBN) significantly inhibit gastric ulceration suggesting the role of OH. in this oxidative damage. Desferrioxamine (DFO), a nontoxic transition metal ion chelator, protects the mucosa against stress-ulceration dose dependently. Increased level of TBARS and the inactivation of gastric peroxidase are also prevented by DFO or by antioxidants such as glutathione or vitamin E, suggesting the critical role of metal ion and OH. in the oxidative damage. A metal-catalyzed OH. generating system constituted by Cu2+, H2O2 and ascorbate (reducing equivalent of O2-) causes inactivation of the purified gastric peroxidase in vitro, which can be effectively prevented by DFO. The stress-induced activation of the superoxide dismutase is completely blocked by pretreatment with alpha-amanitin indicating an increased synthesis of the enzyme by increased transcription of its m-RNA. Quantitative measurement indicates that stress causes a fivefold increase in the generation of OH., which correlates well with the increase in ulcer index with the progress of stress. The results indicate that the stress-induced gastric ulceration is a consequence of the oxidative damage of the gastric mucosa. This is caused by the OH. generated through the metal-catalyzed Haber-Weiss reaction between O2- and H2O2, the latter being formed by the stimulation of the superoxide dismutase and inactivation of the gastric peroxidase.

Cupric ion/ascorbate/hydrogen peroxide-induced DNA damage: DNA-bound copper ion primarily induces base modifications

The kinetics of frank DNA strand breaks and DNA base modifications produced by Cu(II)/ascorbate/H2O2 were simultaneously determined in purified human genomic DNA in vitro. Modified bases were determined by cleavage with Escherichia coli enzymes Nth protein (modified pyrimidines) and Fpg protein (modified purines). Single-stranded lesion frequency before (frank strand breaks) and after (modified bases) Nth or Fpg protein digestion was quantified by neutral glyoxal gel electrophoresis. Dialysis of EDTA-treated genomic DNA purified by standard proteinase K digestion/phenol extraction was necessary to remove low molecular weight species, probably transition metal ions and metal ion chelators, which supported frank strand breaks in the presence of ascorbate + H2O2 without supplemental copper ions. We then established a kinetic model of the DNA-damaging reactions caused by Cu(II) + ascorbate + H2O2. The principal new assumption in our model was that DNA base modifications were caused exclusively by DNA-bound Cu(I) and frank strand breaks by non-DNA-bound Cu(I). The model was simulated by computer using published rate constants. The computer simulation quantitatively predicted: (1) the rate of H2O2 degradation, which was measured using an H2O2-sensitive electrode, (2) the linearity of accumulation of DNA strand breaks and modified bases over the reaction period, (3) the rate of modified base accumulation, and (4) the dependence of modified base and frank strand production on initial Cu(II) concentration. The simulation significantly overestimated the rate of frank strand break accumulation, suggesting either that the ultimate oxidizing species that attacks the sugar-phosphate backbone is a less-reactive species than the hydroxyl radical used in the model and/or an unidentified hydroxyl radical-scavenging species was present in the reactions. Our experimental data are consistent with a model of copper ion-DNA interaction in which DNA-bound Cu(I) primarily mediates DNA base modifications and nonbound Cu(I) primarily mediates frank strand break production.

Ascorbate-induced free radical toxicity to isolated islet cells

Ascorbate is known to be cytotoxic by generating free oxygen radicals, a property shared with the diabetogenic drug alloxan. Some reports indicate that also ascorbate may be diabetogenic. In this study the cytotoxicity of ascorbate on isolated mouse islet cells has been investigated. Ascorbate (0.5-2.0 mmol/l) induced a concentration-dependent increase of trypan blue uptake by the cells, indicating an increase of membrane permeability to the dye. Trypan blue uptake induced by 2.0 mmol/l ascorbate was inhibited by concomitant incubation of the cells with 200 mg/l superoxide dismutase, 200 mg/l catalase, 3.0 mmol/l cytochrome-c or 50 mumol diethylenetriaminepentacetic acid (DTPA), but not by 50 mmol/l D-mannitol. The results indicate that ascorbate is cytotoxic to islet cells by metal-catalysed free radical generation.

Oxidative modification of fibrinogen inhibits thrombin-catalyzed clot formation

Plasma fibrinogen plays a central role in controlling hemostasis. In an earlier report, we found that fibrinogen is oxidized when whole plasma is treated with a metal-catalyzed oxidation system. These studies show that oxidative modification of purified human fibrinogen leads to an exposure-dependent loss of thrombin-induced clot formation. Inhibition of clotting occurred when either metal-catalyzed oxidation or gamma-irradiation was employed to generate oxidizing radicals. Both systems caused covalent modification of fibrinogen, assessed by measuring incorporation of protein carbonyls. Thrombin-catalyzed fibrinopeptide release was normal in irradiated fibrinogen and was only slightly diminished in protein exposed to metal-catalyzed oxidation, indicating that the inhibition of clotting activity was due to impaired fibrin monomer polymerization. Thus, oxidative modification of normal fibrinogen causes dysfibrinogenemia and constitutes a novel mechanism for inhibition of thrombosis.

Inactivation of heart dihydrolipoamide dehydrogenase by copper Fenton systems. Effect of thiol compounds and metal chelators

Copper Fenton systems (Cu(II)/H2O2 and Cu(II)/Asc) inactivated the lipoamide reductase and enhanced the diaphorase activity of pig-heart lipoamide dehydrogenase (LADH). Cupric ions alone were less effective. As a result of Cu(II)/H2O2 treatment, the number of titrated thiols in LADH decreased from 6 to 1 per subunit. NADH and ADP (not NAD+ or ATP) enhanced LADH inactivation by Cu(II). NADH also enhanced the effect of Cu(II)/H2O2. Dihydrolipoamide, dihydrolipoic acid, Captopril, acetylcysteine, EDTA, DETAPAC, histidine, bathocuproine, GSSG and trypanothione prevented LADH inactivation. 100 microM GSH, DL-dithiothreitol, N-(2-mercaptopropionylglicine) and penicillamine protected LADH against Cu(II)/Asc and Cu(II), whereas 1.0 mm GSH and DL-dithiothreitol also protected LADH against Cu(II)/H2O2. Allopurinol provided partial protection against Cu(II)/H2O2. Ethanol, mannitol, Na benzoate and superoxide dismutase failed to prevent LADH inactivation by Cu(II)/H2O2 or Cu(II). Catalase (native or denaturated) and bovine serum albumin protected LADH but that protection should be due to Cu binding. LADH inhibited deoxyribose oxidation and benzoate hydroxylation by Cu(II)/H2O2. It is concluded that site-specifically generated HO, radicals were responsible for LADH inactivation by Cu(II) Fenton systems. The latter effect is discussed in the context of ischemia-reoxygenation myocardial injury.

Differential susceptibility of plasma proteins to oxidative modification: examination by western blot immunoassay

Plasma proteins are exposed to oxidants in a variety of circumstances in vivo, such as during tissue injury and inflammation. In this report, the relative susceptibility of each of the major plasma proteins to oxidative modification was assessed by exposing whole plasma to a metal-catalyzed radical generating system and detecting oxidation (protein carbonyl groups) using a novel Western blot immunoassay. Proteins were derivitized with dinitrophenylhydrazine, separated by SDS-gel electrophoresis, and screened with antibodies against dinitrophenyl groups. As little as 1 pmol of protein-associated carbonyls could be detected (100 ng of a 50 kD protein containing 0.5 mol carbonyl/mol protein). Individual plasma proteins were identified by their comigration with standards, crossreactivity with specific antibodies, and by comparison of plasma to serum. Using this approach, we found that plasma fibrinogen was much more susceptible to oxidative modification compared to the other major plasma proteins, albumin, immunoglobulins, and transferrin. The results emphasize the utility of this method for studying oxidation of proteins in cell extracts and tissues and indicate that experiments on the effects of oxidation on fibrinogen function are merited.

Characterization of peptidylglycine alpha-amidating monooxygenase in bovine hypothalamus

In many peptide hormones and neuropeptides, the carboxyl-terminal alpha-amide structure is essential in eliciting their biological activity. In the present study, an enzymatic activity capable of converting 4-dimethylaminoazobenzene-4'-sulfonyl-Gly-L-Phe-Gly(Dabsyl-Gly-Phe -Gly) to 4-dimethylaminoazo-benzene-4'-sulfonyl-Gly-L-Phe-NH2(Dabsyl- Gly-Phe-NH2) was investigated in bovine hypothalamus. The concentrations of copper ion and ascorbic acid required for maximal enzyme activity were 16 microM and 2 mM, respectively. Amidating activity showed a pH profile with two pH optima at acidic pH (around 6.0) and neutral pH (around 7.5). Kinetic studies with the enzyme obtained from bovine hypothalamus demonstrated two distinct Km and Vmax values. The first Km and Vmax values were 142.9 microM and 22.2 pmol/microgram/h and the second Km and Vmax values were 22.7 microM and 4.44 pmol/microgram/h, respectively. Two molecular forms of amidating activity were identified by size-exclusion chromatography and the molecular weight of the two enzymes were estimated to be 49 kDa and 69 kDa.

Deoxyribose degradation catalyzed by Fe(III)-EDTA: kinetic aspects and potential usefulness for submicromolar iron measurements

Iron ions play a central role in .OH radicals formation and induction of oxidative stress in living organisms. Iron-catalyzed .OH radical formation degrades deoxyribose to thiobarbituric acid reactive substances (TBA-RS). This paper analyzes kinetic properties of the Fe(III)-EDTA-catalyzed deoxyribose degradation in the presence of ascorbate. The yield of TBA-RS formation in the presence of EDTA was 4-fold higher than in its absence, contrasting with results reported elsewhere, Cu(II)-EDTA and Fe(III)-citrate were unable to catalyze deoxyribose degradation. The dependence on deoxyribose concentration was fitted to a Lineweaver Burk-like plot and it was calculated that approximately 4.5 mM deoxyribose scavenged half of the .OH radicals formed. The data for Fe(III)-EDTA concentration dependence could also be fitted to a rectangular hyperbolic function. This function was linear up to 1 microM added FeCl3 and this property could be utilized as an assay for the estimation of submicromolar iron concentrations. Submicromolar concentrations of iron could induce measurable yields of TBA-RS. Differences of as little as 0.1 microM Fe(III)-EDTA could be reproducibly detected under optimum experimental conditions, above a consistent background absorbance that was equivalent to 0.35 +/- 0.05 microM Fe(III)-EDTA and represented contaminating iron in the reactants that could not be removed with Chelex-100. The low method determination limit makes the deoxyribose degradation reaction potentially useful as a new, highly sensitive and cost effective assay for iron quantification.

Oxidative stress: free radical production in neural degeneration

It is not yet established whether oxidative stress is a major cause of cell death or simply a consequence of an unknown pathogenetic factor. Concerning chronic diseases, as Parkinson's and Alzheimer's disease are assumed to be, it is possible that a gradual impairment of cellular defense mechanisms leads to cell damage because of toxic substances being increasingly formed during normal cellular metabolism. This point of view brings into consideration the possibility that, besides exogenous factors, the pathogenetic process of neurodegeration is triggered by endogenous mechanisms, either by an endogenous toxin or by inherited metabolic disorders, which become progressively more evident with aging. In the following review, we focus on the oxidative stress theory of neurodegeneration, on excitotoxin-induced cell damage and on impairment of mitochondrial function as three major noxae being the most likely causes of cell death either independently or in connection with each other. First, having discussed clinical, pathophysiological, pathological and biochemical features of movement and cognitive disorders, we discuss the common features of these biochemical theories of neurodegeneration separately. Second, we attempt to evaluate possible biochemical links between them and third, we discuss experimental findings that confirm or rule out the involvement of any of these theories in neurodegeneration. Finally, we report some therapeutic strategies evolved from each of these theories.

The oxidative inactivation of cytochrome P450 in monooxygenase reactions

Possible mechanisms of cytochrome P450 self-inactivation during catalytic turnover have been considered. Two ways of hemoprotein inactivation are so far known. The first, studied extensively by many authors, is the formation of active substrate intermediates, capable of modifying heme and apoenzyme. The second way, revealed quite recently and resulting from uncoupled cytochrome P450-catalyzed monooxygenase reactions, is yet to be clarified. Briefly, it involves formation of hydrogen peroxide in the hemoprotein active center, which interacts with the enzyme associated Fe2+, thereby generating hydroxyl radicals that bleach the heme and modify the apoenzyme. This mechanism operates with substrates and cytochrome P450 forms with partially coupled monooxygenase reactions, thus causing the formation of hydrogen peroxide as a byproduct.

The use of cyclic voltammetry for the evaluation of oxidative damage in biological samples

A method using cyclic voltammetry to evaluate oxidative damage in biological systems is presented. Three biological systems were tested: Escherichia coli cells, the rat jejunal mucosa, and the enzyme, lactate dehydrogenase. Exposure of E. coli cells to oxidative stress resulted in a rapid decrease in their survival and a decrease in their ability to accumulate 14C-leucine. This was accompanied by a significant increase in the oxidation potential of the cells. Similar results were obtained when the rat jejunal mucosa was exposed in a perfusion system to oxidative stress induced by the hydroxyl radical produced by either hydrogen peroxide and ferrous ions or the combination of ascorbic acid and copper ions. Loss of cellular potassium was taken as an indication of damage to the rat jejunum. Exposure of lactate dehydrogenase to oxidative stress induced by hydroxyl and peroxyl radicals also resulted in a significant loss of enzyme activity along with a pronounced change in the cyclic voltammogram of the enzyme. It was concluded that measurement of the oxidation potentials of these biological systems can give an indication of the occurrence of oxidative damage.

Mechanism of lysozyme inactivation and degradation by iron

The site-specific lysozyme damage by iron and by iron-catalysed oxygen radicals was investigated. A solution of purified lysozyme was inactivated by Fe(II) at pH 7.4 in phosphate buffer, as tested on cleavage of Micrococcus lysodeikticus cells; this inactivation was time- and iron concentration-dependent and was associated with a loss of tryptophan fluorescence. In addition, it was reversible at pH 4, as demonstrated by lysozyme reactivation and by the intensity of the 14.4-kD-band on SDS-PAGE. Desferal (1 mM) and Detapac (1 mM) added before iron, prevented lysozyme inactivation, while catalase (100 micrograms/ml), superoxide dismutase (100 micrograms/ml) and bovine serum albumin (100 micrograms/ml) gave about 30 to 40% protection by competing with lysozyme for iron binding. The denaturing effect of iron on lysozyme was studied in the presence of H2O2 (1 mM) and ascorbate (1 mM); under these conditions the enzyme underwent partly irreversible inactivation and degradation different to that produced by gamma radiolysis-generated .OH. Catalase almost fully protected lysozyme; in contrast, mannitol (10 mM), benzoate (10 mM), and formate (10 mM) provided no protection because of their inability to access the site at which damaging species are generated. In this system, radical species were formed in a site-specific manner, and they reacted essentially with lysozyme at the site of their formation, causing inactivation and degradation differently than the hydroxyl radical.

Characterization of a Xenopus laevis skin peptidylglycine alpha-hydroxylating monooxygenase expressed in insect-cell culture

The C-terminal amide structure of peptide hormones and neurotransmitters is synthesized via a two-step reaction catalyzed by peptidylglycine alpha-hydroxylating monooxygenase (PHM) and peptidylhydroxyglycine N-C lyase. A Xenopus laevis PHM expressed in insect-cell culture by the baculovirus-expression-vector system was purified to homogeneity and characterized. Using a newly established assay system for PHM, the kinetic features of this enzyme were investigated. As expected, the enzyme required copper ions, L-ascorbate and molecular oxygen for turnover. Salts like KI and KCl, and catalase stabilized the enzyme in the presence of L-ascorbate. The optimum pH value for the enzyme reaction was around six when Mes buffer was used and around seven when phosphate buffer was used under the same assay condition. Below pH 6, acetate, iodide and chloride ions activated the reaction. The kinetic analysis is consistent with a ping-pong mechanism with respect to peptide and L-ascorbate, and the peptide showed substrate inhibition. The substrate specificity of the enzyme at the penultimate position was examined by competitive assay using tripeptides with glycine at the C-termini and the inhibitory potency of these peptides in descending order was methionine > aromatic > non-polar amino acids.