Biomedical subjects

M Chevion

Publications and source records attributed to M Chevion.

At least 55 records · Page 3Linked to original sources

PubMed1992

Correlation between destruction of malarial parasites by polymorphonuclear leucocytes and oxidative stress.

The role of reactive oxygen species (ROS) generated by polymorphonuclear leucocytes (PMNs) in the host response against malaria was investigated. Non-activated human PMNs were added to cultures of P. falciparum in microtitre cells. Parasite viability was evaluated by the incorporation of radioactive hypoxanthine. Using PMN/RBC = 1/150 (starting parasitemia was 1%) the incorporation on the second day in culture was only 61% of the control cultures. An effect could be observed already after two hours of incubation (30% reduction at a 1/50 PMN/RBC ratio). A direct contact between the effector and target cells was obligatory for the expression of the damage. Parasites within G6PD-deficient erythrocytes were more sensitive to the PMNs than normal parasitized erythrocytes. This difference could be attributed to the production of reactive oxygen intermediates in the experimental system, since G6PD-deficient erythrocytes are generally more sensitive to oxidant stress. Salicylic acid was used as a scavenger and reporter molecule for hydroxyl radical fluxes. It is converted to the corresponding dihydroxybenzoic acid derivatives, which could be detected by HPLC. Uninfected NRBC or parasitized erythrocytes containing young ring forms could trigger the PMNs to produce much less ROS than the mature forms of the parasites. Other factors associated with PMNs may inactivate the parasites, such as phagocytosis, lysosomal enzymes or degradation toxic products of the PMNs. However our results indicate that increased oxidative stress induced by PMNs interfere with the growth of P. falciparum and could play a role in human evolution of abnormal erythrocytes.

Animals↗

PubMed1992

A possible role of free radicals in the transplantation of retinal pigment epithelial cells.

Oxygen-derived free radicals have been implicated in tissue injury following ischemia and reperfusion (reoxygenation). It has been hypothesized that the radicals are produced during the early reperfusion stage. Recently, submacular implantation of retinal pigment epithelium cells has been reported. It is probable that during the procedure, the transplant and the 180-degree folded outer retina underwent a period of ischemia, followed by reoxygenation. We, therefore, infer that free radicals were produced during the reoxygenation stage of the procedure, injuring both tissues. We suggest that these hypotheses be investigated with the aim of improving the surgical outcome in eyes with age-related macular degeneration.

Aging↗

PubMed1992

The effects of ascorbate-induced free radicals on Plasmodium falciparum.

Ascorbic acid has been shown to cause stage-dependent effects on the in vitro development of Plasmodium falciparum. While vitamin C marginally enhanced the development of young parasites, it proved highly destructive to the advanced forms. The present study evaluates the mechanisms by which vitamin C affects the parasite. The treatment of parasitized erythrocytes with ascorbate resulted in the conversion of added salicylate to dihydroxybenzoate products, indicating the involvement of hydroxyl radicals. There was a stage specific sensitivity, increasing conversion with progressing parasite development. This specificity could not be attributed to the altered uptake of salicylate by the parasitized erythrocyte, since salicylate uptake was similar in either parasitized or non-parasitized erythrocytes. In distinction, increased uptake of ascorbate by parasitized erythrocytes could account for an elevated oxidant stress. The treatment with ascorbate also caused the oxidation of hemoglobin to methemoglobin and the peroxidation of membrane lipids. Added catalase markedly inhibited the ascorbate-induced effects on parasite development. "Free" plasmodia were also vulnerable to treatment with ascorbate like the parasites within their host cells. These results are in accord with a free radical mechanism of damage to the infected erythrocytes. During the growth of P. falciparum the infected erythrocytes release increasing levels of iron-containing structures that are redox-active and can catalyze the formation of highly reactive oxygen derived species. The findings also indicate the multiplicity of the mode of action of ascorbate on the host-parasite system.

Animals↗

PubMed1991

The survival of Plasmodium Under oxidant stress.

Oxidant stress is associated with the generation of reactive oxygen-derived species, which are considered as the ultimate agents responsible for the damage of a variety of cellular components. Transition metals such as iron ions serve as catalytic centers for the repeated conversion of superoxide radicals or ascorbate to the highly reactive and deleterious hydroxyl radicals and, indeed, increasing amounts of redox-active iron become available during plasmodial development within the parasitized erythrocytes. Thus, the survival of an intracellular parasite depends on the delicate balance of oxidant stress and defense mechanisms. This balance is continuously changing and the parasite must cope with increasing oxidant stress and the decline of protective capacity.

Journal Article↗

PubMed1991

Salicylate as an in vivo free radical trap: studies on ischemic insult to the rat intestine.

Ischemia of rat intestine was induced in vivo by occlusion of the superior mesenteric artery (SMA) for 15 min. Sodium salicylate, 100 mg/kg, given IP, 30 min prior to the ischemic event served as a specific trap for hydroxyl radicals. Portions of the bowel were sequentially isolated and removed--2 min prior to ischemia, 2 min prior to declamping of the SMA, and 10 min following reperfusion. The bowel segments were homogenized in 3% TCA. The homogenate was centrifuged and filtrated through a 0.22 mu filter. The hydroxylation products of salicylate, dihydroxybenzoic acid (DHBA) derivatives, were isolated, identified, and quantified by HPLC coupled with electrochemical detection (ECD). The level of 2,5-DHBA (M +/- SE, ng/g tissue) in the preischemic bowel (N = 21) was 241.8 +/- 10.0. In the ischemic specimen the level of 2,5-DHBA increased significantly to 313.3 +/- 15.5 (p = 0.0129), and remained unchanged in the reperfusion period (322.8 +/- 15.5). The histological examination correlated well with these levels: mild villi damage in the ischemic period with no further exacerbation during the reperfusion period. This study in an in vivo animal model of intestinal ischemia-reperfusion provides direct evidence for the involvement of free radicals during the ischemic insult.

Animals↗

PubMed1991

Inverse correlation between resistance towards copper and towards the redox-cycling compound paraquat: a study in copper-tolerant hepatocytes in tissue culture.

The essential mediatory role of copper or iron in the manifestation of paraquat toxicity has been demonstrated (Kohen and Chevion (1985) Free Rad. Res. Commun. 1, 79-88; Korbashi, P. et al. (1986) J. Biol. Chem. 261, 12472-12476). Several liver cell lines, characterized by their resistance to copper, were challenged with paraquat and their cross-resistance to paraquat and copper was studied. Cell growth and survival data showed that copper-resistant cells, containing elevated copper, are more sensitive towards paraquat than wild type cells. Copper-deprived resistant cells did not have this sensitivity. Paraquat was also shown to cause a marked degradation of cellular glutathione in all cell lines. Albeit the fact that the basal glutathione levels are higher in copper-resistant than in wild type cells, there is more paraquat-induced degradation of cellular glutathione (GSH + GSSG) in resistant cells. It is suggested that in copper-resistant cells which contain elevated levels of copper, paraquat-induced cellular injury is potentiated even where glutathione levels are elevated. Additionally, in vitro experiments are presented that support the in vivo findings demonstrating a role for copper in glutathione degradation.

Animals↗

PubMed1991

Bleomycin-detectable iron in brain tissue.

The normal brain contains regions with high concentrations of iron, part of which appears to be in a low molecular mass chelatable form. Iron complexes with a molecular mass of below 10,000, were measured in ultrafiltrates of homogenized gerbil brains using the bleomycin assay, and were found to average 20.5 +/- 3.5 microM (n = 8). As expected, no bleomycin detectable iron was found in the plasma of these animals. No obvious difference in the tissue levels of bleomycin-detectable iron was recorded following ischaemia and reperfusion. This is probably due to the already abundant presence of iron in the brain and the likely release of iron from protected sites due to structural damage inherent in the preparative procedures used.

Animals↗

PubMed1991

The effect of free radicals induced by paraquat and copper on the in vitro development of Plasmodium falciparum.

The role of transition metals in paraquat toxicity was studied in cultures of Plasmodium falciparum. We showed that addition of copper led to an enhancement of the plasmodium killing, whereas addition of chelating agents, such as desferrioxamine and diethylenetriamine pentaacetic acid markedly reduced the toxic effects. Parsitized G6PD deficient erythrocytes were more sensitive than parasitized normal erythrocytes to copper and to the combination of copper and paraquat.

Animals↗

PubMed1991

Zinc(II) protects against metal-mediated free radical induced damage: studies on single and double-strand DNA breakage.

M13 DNA was used as a source for single and double-stranded DNA. Free radical-induced damage to single and double stranded DNA was caused by ascorbate/iron and ascorbate/copper oxidative systems. The degree of breakage was estimated by running samples on an agarose gel and staining with ethidium bromide, followed by photographic analysis. DNA breakage was dependent on time and concentration of iron or copper ions. Zinc ions protected against damage caused by iron/ascorbate both to single-stranded and double-stranded DNA. In contrast, in the copper/ascorbate system zinc ions protected only against the double-stranded DNA (replicative form of M13) breakage, and not against copper-mediated single-stranded DNA breakages. It seemed to amplify the efficiency of breakage. The protection provided to the replicative form in the copper/ascorbate system is much less effective than the protection to DNA in the iron/ascorbate system. These results support the notion that redox-inactive metal ions, that compete for iron or copper binding sites, could provide protection against transition metal-mediated and free radical-induced damage.

Copper↗

PubMed1991

Induction of oxidant stress by iron available in advanced forms of Plasmodium falciparum.

Oxidative stress has been incriminated as a deleterious factor in the development of malaria parasites. Various chemical reductones which can undergo cyclic oxidation and reduction, such as ascorbate have been shown to cause oxidative stress to red blood cells. This, naturally-occurring and redox-active compound, can induce the formation of active oxygen derived species, such as superoxide radicals (.O2-), hydrogen peroxide (H2O2) and hydroxyl radical (OH.). The formation of the hydroxyl radical, the ultimate deleterious species, is mediated by the redox-active and available transition metals iron and copper in the Haber-Weiss reaction. During the development of the parasite, hemoglobin is progressively digested and a concurrent release of high levels of iron-containing breakdown products takes place within the red blood cell. Indications for the progressive increase in redox-active iron during the growth of P. falciparum have been recently found in our lab: a) adventitious ascorbate proved highly detrimental to the parasite when added to the mature forms. In contrast, if the parasitized erythrocytes were in the early phase following invasion, and only low levels of iron-containing structures had been liberated, then the observed effect was a small promotion of parasite development. b) erythrocytes containing mature parasites were more potent than erythrocytes containing ring forms as a source for redox-active iron in the ascorbate-driven metal-mediated degradation of DNA. The addition of extracts from parasitized erythrocytes and ascorbate to DNA caused a dose and time dependent DNA degradation. Non-infected erythrocytes had no effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Protection against free radical-induced and transition metal-mediated damage: the use of "pull" and "push" mechanisms.

Free radicals have been incriminated in a variety of injurious processes including the toxicity of the herbicide paraquat and the damage following ischemia and reperfusion of different organs. Based on the assumption that iron and copper could serve as mediators for the transformation of relatively low reactive species (such as superoxide radicals, hydrogen peroxide, ascorbate, and others) to the highly reactive species, in the site-specific metal-mediated mechanism, two new modes for intervention have been tried out. The first is the introduction of specific chelators that "pull" out redox-active and available metals, and by this reduce the apparent damage. Desferrioxamine was shown to protect bacterial cells and mammals against the poisonous effects of paraquat. Using the retrogradly perfused isolated rat heart, we have demonstrated that the chelator neocuproine, which effectively binds both iron and copper provides a major protection against hydrogen peroxide-induced cardiac damage and against ischemia/reperfusion-induced arrhythmias. Likewise, TPEN a heavy metal chelator, provides almost total (greater than 90%) protection against ischemia/reperfusion-induced arrhythmias. The other mode of intervention is the use of redox-inactive metal ions that could compete for the binding sites of iron and copper, and by this "push" these metal ions out, lead to their displacement, and divert the site of free radical attack. Applying Zn(II) complexes provided a marked protection against metal mediated free radical-induced damage in the copper-mediated paraquat toxicity to E. coli, and in the arrhythmias induced by ischemia and reperfusion. It is proposed that the complex zinc-desferrioxamine would be the ultimate protector being effective by both the "pull" and "push" mechanisms.

Animals↗

PubMed1991

Direct evidence for the involvement of free radicals in ischemic insult to the intestine.

Ischemia of rat intestine was induced in vivo by occlusion of the superior mesenteric artery (SMA) for 15 min. Sodium salicylate, 100 mg/kg, given IP, 30 min prior to the ischemic event served as a specific trap for hydroxyl radicals and provided direct evidence for the involvement of free radicals during the ischemic insult. Portions of the bowel were sequentially isolated and removed. The hydroxylation products, dihydroxybenzoic acid (DHBA) derivatives were isolated, identified and quantified by HPLC coupled with electrochemical detection (ECD). The level of 2,5-DHBA (Mean +/- SE, ng/g tissue) in the preischemic bowel (N = 21) was 241.8 +/- 10.0. It rose significantly to 313.3 +/- 15.5 in the ischemic specimen (p = 0.0129) and remained unchanged in the reperfusion period (322.8 +/- 15.5). The histological examination correlated well with these levels: mild villi damage in the ischemic period with no further damage in the reperfusion period.

Animals↗

PubMed1991

The effect of chronic administration of doxorubicin on the rat cardiac and hepatic glutathione redox system.

The effect of chronic administration of doxorubicin on the rat heart and liver glutathione redox system was studied. Rats were administered doxorubicin, 1 mg/kg, ip., three times a week, on Monday, Wednesday and Friday. One week was skipped and then the cycle repeated for a total of one, four, seven or ten doses. It was determined that treatment in this manner had no effect on rat heart glutathione, glutathione peroxidase or glucose-6-phosphate dehydrogenase, at any of the time intervals tested. However, hepatic glutathione content was found to be moderately increased after the fourth dose and glucose-6-phosphate dehydrogenase activity was found to be markedly increased after the seventh and tenth doses. Hepatic glutathione peroxidase was not affected. These results suggest that the cardiac glutathione redox system does not respond to chronic administration of doxorubicin. In contrast, the hepatic systems do respond, which may explain the apparent resistance of this organ to doxorubicin toxicity.

Animals↗

PubMed1991

Free radical-induced fibrinogen coagulation: modulation of neofibe formation by concentration, pH and temperature.

The reaction of fibrinogen with Cu(II) (10-100 microM) and ascorbate (0.1-2.0 mM) leads to the formation of an insoluble clot-like material, "neofibe", which is dependent on experimental conditions. The reaction is observed with human and bovine fibrinogen, in the presence of 0.1-0.3 N NaCl, is optimal at the pH range of 7.4-7.7, and has characteristics typical of a site-specific Fenton reaction. Thus, it is inhibited by EDTA and catalase. Inhibition by mannitol is observed only at relatively high concentrations of this scavenger (greater than 100 mM). Concomitantly, the rate of oxygen utilization increases linearly with the concentration of reagents. The energy of activation of oxygen utilization by ascorbate and Cu(II) in the absence or presence of fibrinogen is Ea = 6.1 and 7.9 Kcal/mol, respectively. These values suggest that the rate-limiting step is dictated by a reaction of oxygen with "free" or protein-bound copper cations. The temperature dependency of the extent of transformation of human and bovine fibrinogen into neofibe is unusual in that it is biphasic-increasing from 5 to 25 degrees C, and decreasing thereafter, to 43 degrees C. This is not due to the temperature stability of fibrinogen. The essential requirement for copper, ascorbate and oxygen or hydrogen peroxide, as well as the low efficiency of mannitol as a scavenger, are in accord with the most likely interpretation of these data that fibrinogen undergoes a site-specific Fenton reaction. This modifies the protein and results in the formation of insoluble, polymeric, neofibe aggregates.

Animals↗

PubMed1991

Mechanistic aspects of 1-methyl-4-phenyl pyridinium iodide toxicity in Escherichia coli: the role of oxygen and hydrogen peroxide.

1-Methyl-4-phenyl pyridinium iodide (MPP+) and paraquat (PQ+2) are two structurally analogous and highly toxic pyridinium compounds. The mechanism of PQ+2 toxicity is best understood in the bacterial model system. While numerous studies in a variety of systems have indicated the causative role of free radicals and other oxygen-derived active species in PQ+2 toxicity, this question is yet unresolved in the case of MPP+. In this study we have used the Escherichia coli model and demonstrated that MPP+ is toxic to bacterial cells in dose- and time-dependent modes. Additionally, it is shown that only in the presence of molecular oxygen did bacterial inactivation occur. This requirement for oxygen can be circumvented by adventitious H2O2. The protective effects of the chemical scavenger--mannitol--and of histidine are presented. These results are in complete accord with a free radical mechanism for MPP+ toxicity.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗

PubMed1991

MPP+ toxicity in E. coli under aerobic and anaerobic conditions.

MPP+ and paraquat (PQ+2) are two structurally analogous and highly toxic pyridinium compounds. The mechanism of PQ+2 toxicity is best understood in the bacterial model system. While numerous studies, in a variety of systems, have indicated the causative role of free radicals and other oxygen-derived active species in PQ+2 toxicity, this question is yet unresolved in the case of MPP+. In this study we have used the E. coli model and have demonstrated that MPP+ is toxic to bacterial cells in a dose and time dependent modes. Additionally, it is shown that only in the presence of molecular oxygen, bacterial inactivation occurred. The protective effects of the chemical scavenger--mannitol--and of histidine are presented. These results are in complete accord with a free radical mechanism for MPP+ toxicity.

1-Methyl-4-phenylpyridinium↗

PubMed1990

Zinc--a redox-inactive metal provides a novel approach for protection against metal-mediated free radical induced injury: study of paraquat toxicity in E. coli.

The essential mediatory role of copper and iron in a variety of free radical-induced injuries, including paraquat-induced biological damage has been recently demonstrated. It was postulated that these transition metals undergo cyclic redox reactions, and serve as centers for repeated production of hydroxyl radical, which are the ultimate deleterious agents. Additionally, we had presented evidence indicating efficient protection against paraquat toxicity by agents commonly employed (chelators, chemical scavengers and protecting enzymes). In this study we have used the E. coli model in order to develop a new approach for protection against paraquat-induced metal-mediated cellular injury. It entails the administration of excess zinc (up to 50 fold over copper), which results in an inhibition of the toxic effect of paraquat. Lineweaver- Burk analysis demonstrates the competitive mode of this inhibition. The suggested mechanism involves the displacement of the redox-active copper (or iron) from its binding site and by this diverting the site of repeated production of free radicals. Thus, use of redox-inactive metals, which possess high similarity of their ligand chemistry, to that of iron and copper but are of relative low toxicity by themselves, should be considered for intervention in paraquat toxicity and in other metal-mediated free radical-induced injurious processes.

Binding Sites↗

PubMed1990

The protective role of neocuproine against cardiac damage in isolated perfused rat hearts.

The effect of neocuproine on cardiac injury was studied using retrogradely perfused isolated rat hearts in two experimental systems. In the first system, where hydrogen peroxide-induced damage was studied, neocuproine at the range of 40-175 microM provided protection at the level of 70-85%, as demonstrated by the reduced loss in the peak systolic pressure (P), in +dP/dt and in -dP/dt. In the second system, where ischemia/reperfusion-induced arrhythmias were studied, neocuproine (42 microM) provided a marked protection against cardiac injury as demonstrated by the lowering of the incidence in irreversible ventricular fibrillation, by decreasing the duration of ventricular fibrillation and by the concomitant increase of the duration of normal sinus rhythm, and by improving the post-ischemic recovery of P, +dP/dt and -dP/dt. Free radicals have already been implicated as causative agents in cardiac injury resulting from either hydrogen peroxide or ischemia followed by reperfusion. Additionally, iron and copper have already been shown to drastically exacerbate the injurious effects of free radicals. Thus, the results reported here with neocuproine, a highly effective chelator for both iron and copper, as well as with adventitious copper and with the combination of neocuproine and copper, are in accord with the mediatory role of transition metals in enhancing the deleterious effects induced by free radicals.

Animals↗