Iron released from an erythrocyte lysate by oxidative stress is diffusible and in redox active form

Glycated LDL generates reactive species that damage cell components, oxidize hemoglobin and alter surface morphology in human erythrocytes

Low-density lipoprotein (LDL) transports cholesterol to various tissues via the blood. Glycation of LDL occurs during hyperglycemic condition which is characterised by persistently high blood glucose level. Circulating erythrocytes can come in direct contact with glycated LDL (G-LDL). The objective of this study was to investigate the effect of G-LDL on human erythrocytes, specifically on hemoglobin, intracellular generation of reactive species and the antioxidant defence system. Isolated erythrocytes were incubated with G-LDL (3 and 6 mg/ml) and native LDL (6 mg/ml) at 37 °C for 24 h. Native LDL and G-LDL untreated erythrocytes were similarly incubated at 37 °C and served as control. G-LDL treatment increased hemolysis compared to control and native LDL-treated erythrocytes. Incubation of erythrocytes with G-LDL led to an increase in protein oxidation and lipid peroxidation while greatly decreasing the total sulfhydryl content. It also significantly enhanced hemoglobin oxidation, heme degradation, and the release of free iron moiety. Treatment with G-LDL led to an appreciable increase in the production of reactive oxygen and nitrogen species. The antioxidant power and activities of major antioxidant enzymes were drastically reduced, while critical membrane-bound enzymes were inhibited. The surface morphology of G-LDL-treated erythrocytes was altered leading to the formation of echinocytes. Importantly, treatment of erythrocytes with native LDL did not significantly affect the above-mentioned parameters and values were similar to the corresponding controls. Thus, G-LDL is cytotoxic to human erythrocytes and causes oxidative damage to cell components. This can reduce the oxygen-transporting ability of blood and also result in red cell senescence and anemia.

Ficus glumosa Del. reduces phenylhydrazine-induced hemolytic anaemia and hepatic damage in Wistar rats

OBJECTIVES

Anemia is a direct or indirect consequence of oxidative stress via free radicals on erythrocytes and subsequently on other tissues like liver. Ficus glumosa constitute a rich pharmacologically compound that can prevent or repair oxidative damage. Therefore, this study seeks to evaluate the effect of F. glumosa on phenylhydrazine-induced hemolytic anemia and hepatic damage in rats.

METHODS

Twenty-four (24) albino Wistar rats were assigned to four (4) experimental groups (n=6) as follows: Group I (non-anemic control) and Group 2 (anemic control) received normal saline, while Group III and IV (test groups) 200 and 400 mg/kg of aqueous leaf extract of F. glumosa (ALEFG), respectively. All the groups were treated orally (via a cannula) for seven consecutive days. Intraperitoneal (IP) injection of phenylhydrazine (PHZ) at 40 mg/kg for two consecutive days induced hemolytic anemia in group II to IV before treatment. Rats of all groups were anaesthetized and sacrificed 24 h after the last treatment. Blood and liver samples were collected for some hematological indices, liver function test, antioxidant parameter and histological analysis.

RESULTS

The LD₅₀ of ALEFG was assessed orally in rats and found to be above 5,000 mg/kg body weight. Significant (p<0.05) decreases in the level of red blood cell (RBC), hemoglobin (HGB) concentrations and packed cell volume (PCV) by 50% after 2 days of PHZ induction, were attenuated by more than 50% after 7 days administration of ALEFG at 200 and 400 mg/kg. The percentage change in body weight increased significantly (p<0.05) after 7 days post PHZ-induced anemia, but those that received oral administration of ALEFG (at 200 and 400 mg/kg) for 7 days increased significantly (p<0.05) by more than 2%, dose-dependently compared to anemic untreated group. Increased level of serum ALT, AST, ALP and GGT in PHZ-induced anemic animals, were significantly (p<0.05) attenuated in the groups that received oral administration of ALEFG (at 200 and 400 mg/kg) for 7 days. Decreased level of catalase (CAT) and superoxide dismutase (SOD) activities with concomitant increase in malondialdehyde (MDA) content from PHZ-induced untreated group, were significantly (p<0.05) mitigated in the rats that received oral administration of ALEFG (at 200 and 400 mg/kg) for 7 days. Histopathological analysis showed that ALEFG could remarkably though not completely mitigated PHZ-induced hepatic damage.

CONCLUSIONS

Our data suggests that the leaves of F. glumosa contain important antioxidant(s) that could effectively reduce hemolytic anemia and hepatic damage, especially during phenylhydrazine-induced toxicity.

Bioallethrin-induced generation of reactive species and oxidative damage in isolated human erythrocytes

Bioallethrin is an insecticide that is widely used to control mosquitoes, fleas and cockroaches. The widespread use of bioallethrin has resulted in both occupational and non-occupational human exposure. Bioallethrin enters blood, regardless of the route of exposure, where it can interact with erythrocytes. We have studied the effect of bioallethrin on isolated human erythrocytes under in vitro conditions. Erythrocytes were incubated with increasing concentrations of bioallethrin (10-200 μM) for 4 h at 37 °C. Several biochemical parameters were analyzed in bioallethrin treated and untreated (control) cells. Incubation of erythrocytes with bioallethrin increased protein oxidation, lipid peroxidation and depleted sulfhydryl group content. Membrane damage was evident from cell lysis, osmotic fragility, inhibition of bound enzymes and transmembrane electron transport system. Bioallethrin also increased hemoglobin oxidation, heme degradation and the release of free iron moiety. This will decrease the oxygen transporting ability of blood. Bioallethrin treatment altered the specific activities of antioxidant enzymes and diminished the antioxidant power of cells. Scanning electron microscopy showed that bioallethrin treatment also altered erythrocyte mophology. Almost all changes were in a bioallethrin concentration dependent manner. The cytotoxicity of bioallethrin is probably mediated by reactive oxygen and nitrogen species whose formation was significantly enhanced in treated erythrocytes. Thus bioallethrin enhances the generation of reactive species which cause oxidative damage of cell components in human erythrocytes.

Mercury chloride toxicity in human erythrocytes: enhanced generation of ROS and RNS, hemoglobin oxidation, impaired antioxidant power, and inhibition of plasma membrane redox system

Mercury is among the most toxic heavy metals and a widespread environmental pollutant. Mercury chloride (HgCl₂) is an inorganic compound of mercury which is easily absorbed in the gastrointestinal tract and then enters the blood where it can interact with erythrocytes. In this study, the effect of HgCl₂ on human erythrocytes was studied under in vitro conditions. Erythrocytes were treated with different concentrations of HgCl₂ (1-100 μM) for 1 h at 37 °C. Cell lysates were prepared and assayed for several biochemical parameters. HgCl₂ treatment resulted in oxidation of ferrous iron of hemoglobin to ferric form giving methemoglobin which is inactive as an oxygen transporter. However, the activity of methemoglobin reductase was increased. Hemoglobin oxidation was accompanied by heme degradation and the release of free iron. Protein oxidation was greatly increased with a simultaneous decrease in free amino and sulfhydryl groups and glutathione content. The antioxidant power of HgCl₂-treated erythrocytes was impaired resulting in lowered metal reducing and free radical quenching ability of these cells. This suggests that HgCl₂ induces oxidative stress in human erythrocytes. This was confirmed when superoxide anion, hydrogen peroxide, peroxynitrite, and nitric oxide generation were found to be dose-dependently increased in HgCl₂-treated erythrocytes. Glycolysis and pentose phosphate pathway, the two major pathways of glucose metabolism in erythrocytes, were also inhibited. HgCl₂ treatment also inhibited the plasma membrane redox system while the activities of AMP deaminase and glyoxalase-I were increased. These results show that HgCl₂ induces oxidative and nitrosative stress, oxidizes hemoglobin, impairs the antioxidant defense mechanism, and alters metabolic pathways in human erythrocytes.

Oxidative stress in β-thalassaemia and sickle cell disease

Sickle cell disease and β-thalassaemia are inherited haemoglobinopathies resulting in structural and quantitative changes in the β-globin chain. These changes lead to instability of the generated haemoglobin or to globin chain imbalance, which in turn impact the oxidative environment both intracellularly and extracellularly. The ensuing oxidative stress and the inability of the body to adequately overcome it are, to a large extent, responsible for the pathophysiology of these diseases. This article provides an overview of the main players and control mechanisms involved in the establishment of oxidative stress in these haemoglobinopathies.

Oxidative injury in neonatal erythrocytes

Erythrocytes are continuously exposed to free radicals (FR) injury due to their high cellular oxygen concentration and heme iron. The autoxidation of oxyhaemoglobin to methaemoglobin, generating superoxide anion radical, represents the main source of FR in erythrocytes. The erythrocyte membrane is particularly sensitive to oxidative damage due to its high polyunsaturated fatty acid content, and hence, it represents an important system to evaluate the effect of oxidative stress (OS). Information on how red cells OS is triggered and mechanisms of erythrocytes oxidative pressure from plasma may provide a partial answer to questions about the causes of the anaemia of prematurity and about red cell involvement in hypoxia. The recent insights about the mechanism of oxidative injury of red cells and the evidence of relationships between erythrocyte, OS and hypoxia suggest that increased haemolysis is induced by severe hypoxia and acidosis in the perinatal period.

Free iron, total F-isoprostanes and total F-neuroprostanes in a model of neonatal hypoxic-ischemic encephalopathy: neuroprotective effect of melatonin

Oxidative stress due to free radical formation and initiation of abnormal oxidative reactions is involved in several diseases of newborns, such as hypoxic-ischemic encephalopathy. Melatonin, an endogenously produced indoleamine primarily formed in the pineal gland, is a potent free radical scavenger as well as an indirect antioxidant. The present study was conducted to evaluate the formation of oxidative damage mediators and the possible effect of melatonin treatment in a model of hypoxic-ischemic encephalopathy in 7-day-old rats. Pups were subjected to permanent ligation of the right common carotid artery and exposed for 2.5 hr to a nitrogen-oxygen mixture (92% and 8%, respectively) (hypoxia-ischemia, HI). Melatonin was injected intraperitoneally to a group of rats at the dose of 15 mg/kg 30 min before starting the ischemic procedure (HI-Melatonin). After 24 hr of treatment, in homogenized cerebral cortex, desferoxamine (DFO)-chelatable free iron, total F(2)-isoprostanes and total F(4)-neuroprostanes, originating from the free radical-catalyzed peroxidation of arachidonic and docosahexaenoic acids, respectively, were determined. HI induced a significant increase in DFO-chelatable iron, total F(2)-isoprostanes and F(4)-neuroprostanes in both right and left side of the cerebral cortex. In HI-Melatonin-treated animals the levels of free iron, F(2)-isoprostanes, and F(4)-neuroprostanes were significantly lower than that in HI rats and the values were similar to controls. These data show the important neuroprotective role of melatonin in reducing oxidative damage resulting from HI. Melatonin could represent a potential safe approach to perinatal brain damage in humans.

Redox imbalance, macrocytosis, and RBC homeostasis

The erythrocyte represents a major component of the antioxidant capacity of the blood through the enzymes contained in the cell, the glutathione system, and the low-molecular-weight antioxidants of the erythrocyte membrane. A further major red blood cell contribution is in regenerating consumed redox equivalents via the oxidative pentose phosphate pathway and glutathione reductase. Moreover, its extracellular antioxidant capacity, its mobility, and the existence of reducing equivalents far in excess of its normal requirements make erythrocytes function as an effective oxidative sink in the organism. That is why red blood cell metabolism and homeostasis strongly affect the antioxidant properties of the whole body. Conversely, the relation between macrocytosis and oxidative stress has not been fully delineated. Reviewing the mechanisms involved in red blood cell homeostasis in cases of redox imbalance is crucial in identification of factors that could potentially improve erythrocyte survival and defense against oxidant damage.

Oxidant injury in neonatal erythrocytes during the perinatal period

It has been known for many decades that oxidative stress leads to oxidation of hemoglobin and damage to the erythrocyte membrane. More recently, the factors involved in denaturating of membrane proteins and lipid peroxidation have been investigated in detail, as well as the mechanism of reactive oxygen species formation in red cells. Oxidative stress depletes adenosine triphosphate (ATP) and adenine nucleotides, whereas adenosine monophosphate (AMP) deaminase seems to depress energy metabolism by blocking the salvage pathway of purine nucleotides. Depletion of ATP and activation of AMP deaminase are related to calcium ion concentrations. Denaturating of membrane proteins generally precedes lipid peroxidation and consequent phagocytosis due to caspase activation. Extensive investigations demonstrated the key role of oxidative stress and iron release in a reactive form causing membrane protein damage via the Fenton reaction and hydroxyl radical production. In the absence of efficient protection by antioxidant factors and other molecules such as flavonoids, oxidative stress is responsible for the release of iron in reactive form, predisposing red cells to hemolysis through the formation of senescence antigen. Other well-known sources of oxidative stress in red cells are free radical production outside the red cell by activated phagocytes, endothelial metabolism, hyperoxia, ischemia-reperfusion and the arachidonic acid cascade.

CONCLUSION

The recent insight into the mechanism of oxidative injury of red cells and evidence of relationships between erythrocyte oxidative stress and hypoxia suggest that increased hemolysis is induced by severe hypoxia and acidosis in the fetus as well as the newborn.

Iron release, oxidative stress and erythrocyte ageing

Iron, to be redox cycling active, has to be released from its macromolecular complexes (ferritin, transferrin, hemoproteins, etc.). Iron is released from hemoglobin or its derivatives in a nonprotein-bound, desferrioxamine-chelatable form (DCI) in a number of conditions in which the erythrocytes are subjected to oxidative stress. Such conditions can be related to toxicological events (haemolytic drugs) or to physiological situations (erythrocyte ageing, reproduced in a model of prolonged aerobic incubation), but can also result from more subtle circumstances in which a state of ischemia-reperfusion is imposed on erythrocytes (e.g., childbirth). The released iron could play a central role in oxidation of membrane proteins and senescent cell antigen (SCA) formation, one of the major pathways for erythrocyte removal. Iron chelators able to enter cells (such as ferrozine, quercetin, and fluor-benzoil-pyridoxal hydrazone) prevent both membrane protein oxidation and SCA formation. The increased release of iron observed in beta-thalassemia patients and newborns (particularly premature babies) suggests that fetal hemoglobin is more prone to release iron than adult hemoglobin. In newborns the release of iron in erythrocytes is correlated with plasma nonprotein-bound iron and may contribute to its appearance.

Red blood cell involvement in fetal/neonatal hypoxia

Free radical release plays an important role in the development of brain injury following hypoxic-ischemic encephalopathy. It causes endothelial cell damage and anomalies in NMDA receptors, synaptosome structure and astrocyte function. Mitochondrial dysfunctions caused by asphyxia, reperfusion after ischemia, arachidonic acid cascade, catecholamine metabolism and phagocyte activation are known sources of reactive oxygen species, particularly the superoxide anion (O2(-)). O2(-) mainly induces peroxidation by the Fenton/Haber Weiss reaction or via iron-oxygen complexes. Since both reactions require reactive heavy metals, non-protein-bound iron (NPBI) is essential for the induction of lipid peroxidation. Experimental studies have demonstrated the neurotoxicity of iron in ischemia-reperfusion. Normal axonal transport of brain iron is also reported to be disrupted in hypoxia-ischemia, leading to a buildup of iron in the white matter. The free iron content of erythrocytes (ICRBC) is considered a marker of oxidative stress. Free iron release is accompanied by the oxidation of membrane proteins and the appearance of senescent antigen, as measured by autologous IgG binding. Our preliminary results suggest a significant positive correlation between plasma free iron and the number of nucleated red cells in cord blood, currently considered a reliable index of lasting intrauterine asphyxia but also possessing a high predictive value for poor neurodevelopmental outcome. The rate of erythropoiesis and the entity of ICRBC are related to the degree of asphyxia and the probability of neurological impairment. Since even an increase in NPBI during asphyxia is related to a poor outcome, iron released by red cells could possibly also contribute to NPBI levels.

Melatonin reduces phenylhydrazine-induced oxidative damage to cellular membranes: evidence for the involvement of iron

Phenylhydrazine and iron overload result in augmented oxidative damage and an increased likelihood of cancer. Melatonin is a well known antioxidant and free radical scavenger. The aim of this study was to determine whether melatonin would protect against phenylhydrazine-induced oxidative damage to cellular membranes and to evaluate the possible role of iron in this process. Changes in lipid peroxidation and microsomal membrane fluidity were estimated after the treatment of rats with phenylhydrazine (15 mg/kg body weight, daily, 7 days) alone and melatonin or ascorbic acid (15 mg/kg body weight, two times daily, 8 days), or their combination. Additionally, lipid peroxidation was measured in liver homogenates from untreated and melatonin or ascorbic acid-treated rats in vivo and exposed to iron in vitro. Melatonin, but not ascorbic acid, reduced phenylhydrazine-induced lipid peroxidation in vivo in spleen (3.16+/-0.06 vs. 3.83+/-0.12 nmol/mg protein, P<0.05) and plasma (7. 73+/-0.52 vs. 9.96+/-0.71 nmol/ml, P<0.05) and attenuated the decrease in hepatic microsomal membrane fluidity (1/polarization, 3. 068+/-0.007 vs. 3.027+/-0.008, P<0.05). In vitro exposure to iron significantly enhanced the lipid peroxidation in liver homogenates from untreated (3.34+/-0.75 vs. 1.25+/-0.28, P<0.05) or ascorbic acid-treated rats (2.72+/-0.39 vs. 0.88+/-0.06, P<0.05) but not from melatonin-treated rats (1.49+/-0.55 vs. 0.68+/-0.20, NS). It is concluded that free radical mechanisms are involved in the toxicity of phenylhydrazine and that the antioxidant melatonin, but not ascorbic acid, reduces the toxic affects of phenylhydrazine in vivo and of iron in vitro in cell membranes. Therefore, melatonin co-treatment in conditions of iron overload may prove beneficial.

Intraerythrocyte nonprotein-bound iron and plasma malondialdehyde in the hypoxic newborn

Intraerythrocyte nonprotein-bound iron (INPBI), malondialdehyde (MDA), and hypoxanthine plasma levels (HxPL), were determined by high-pressure liquid chromatography in 138 randomly selected newborn infants with gestational ages ranging from 23 to 42 weeks at birth and on fourth day of life. MDA plasma levels were significantly higher in cord and fourth-day blood samples of preterm babies than term infants as well as babies born by emergency Caesarean section than babies born by vaginal delivery and in intubated than in nonintubated newborns. Highly significant correlations both in cord blood and fourth-day blood samples were observed between MDA plasma levels and gestational age, birth weight, Apgar score at 1 min and 5 min, HxPL, pH, base deficit, and INPBI content. Multiple regression analysis identified HxPL as the best single predictor of MDA plasma levels in cord blood, and INPBI content in fourth-day blood as the best single predictor of MDA plasma levels in fourth-day blood. The results indicate that red cells and plasma lipoproteins are a common target of free radical-induced oxidative stress during hypoxia.

The effects of xenobiotics on erythrocytes

1. Methemoglobin formation was observed when erythrocytes were incubated with xenobiotics such as hydroxylamines or phenols, other metabolites resulting from the interaction of these compounds with erythrocytes being reactive free radicals derived from the respective xenobiotic, and a ferryl-heme oxo-complex. 2. Steady-state levels of these reaction products depended on the permeability of the erythrocyte membrane for the various methemoglobin (MetHb) generators and the presence of antioxidants that downregulate the radicals formed. 3. Electron spin resonance (ESR) spectra of xenobiotic-derived free radicals could be obtained only from the readily water soluble hydroxylamines, whereas the poorly water soluble phenolic compounds did not allow the use of concentrations required for the generation of detectable amounts of ESR-sensitive metabolites in erythrocytes. 4. Previous investigations with oxyhemoglobin solutions and with the MetHb/H2O2 model systems have shown that, apart from ESR-sensitive radical species, excited reaction intermediates such as compound 1 ferryl hemoglobin can be detected as well by using chemiluminescence measurements. 5. A strong correlation was found between the intensity of the emitted light and the MetHb formation rate, indicating that the production of compound 1 ferryl hemoglobin is closely related to the MetHb formation step. 6. The sensitivity of the photon-counting method allowed measurements of excited species in intact erythrocytes not only with the readily soluble hydroxylamines, but also with the less soluble phenolic compounds. 7. In addition, parameters indicative of xenobiotic-induced oxidative alterations were found: a significant decrease in intraerythrocytic thiol levels was a result of all compounds that initiate MetHb formation, as also described for slowly reacting xenobiotics. 8. With the most reactive compound investigated, unsubstituted hydroxylamine, a significant release of iron from the oxidatively modified hemoglobin was detected, facilitated by binding of this transition metal to hydroxylamine and its final oxidation product, nitric oxide. 9. The use of the ESR spin-labeling technique revealed membrane alterations of erythrocytes exposed to the reducing MetHb generators presented in this study. 10. A direct action of BHA and BHT on the integrity of the erythrocyte membrane was observed, leading to hemolysis independent of the formation of prooxidant species. 11. The presence of strong prooxidants (radicals) was indicated both by fluidity changes in the membrane and by an oxidative decrease in cytosolic thiol levels.

Formation of free radicals and protein mixed disulfides in rat red cells exposed to dapsone hydroxylamine

The hemolytic activity of dapsone is well known to reside in its N-hydroxylamine metabolites. Addition of dapsone hydroxylamine (DDS-NOH) to red cell suspensions causes damage such that when reintroduced into the circulation of isologous rats, the injured cells are rapidly removed by the spleen. Hemolytic activity is associated with the extensive formation of disulfide-linked hemoglobin adducts on red cell membrane skeletal proteins. To determine if free radicals could be involved in this process, rat red cells were incubated with DDS-NOH in the presence of the spin trap, 5,5'-dimethyl-1-pyrroline-N-oxide (DMPO) and subjected to EPR analysis. Addition of DDS-NOH (25-50 microM) to a red cell suspension gave rise to a four-line (1:2:2:1) EPR spectrum with coupling constants identical to those of a DMPO-hydroxyl radical adduct (DMPO-OH) standard. No other radicals were detected; however, preincubation of red cells with cysteamine caused the DDS-NOH-generated DMPO-OH signal to be replaced by a cysteamine thiyl radical adduct signal. DDS-NOH-treated red cells were also found to contain ferrylhemoglobin, indicating the presence of hydrogen peroxide. Furthermore, DDS-NOH was found to stimulate salicylate hydroxylation in red cell suspensions, confirming the presence of oxygen radicals. These data support the hypothesis that oxygen radicals are involved in the mechanism underlying dapsone-induced hemolytic anemia.

Hydroxylamine and phenol-induced formation of methemoglobin and free radical intermediates in erythrocytes

As previously shown with isolated oxyhemoglobin, methemoglobin formation can also be induced in intact erythrocytes by hydroxylamine compounds and substituted phenols such as butylated hydroxyanisole (BHA). Electron spin resonance investigations revealed that, accordingly, free radical intermediates were formed in erythrocytes from hydroxylamine, N,N-dimethylhydroxylamine, and N-hydroxyurea. Due to the low stability of the dihydronitroxyl radicals, their detection required the use of a continuous flow system and relatively high amounts of the reactants. As has already been demonstrated with the solubilized hemoglobin system, hemoglobin of intact erythrocytes also reacts with the more hydrophilic xenobiotics such as hydroxylamine. However, the reaction rate was slightly reduced, indicating the existence of an incomplete permeability barrier for these compounds. The limited solubility of phenolic compounds in the aqueous buffer of suspended erythrocytes (in combination with the strict requirement of osmolarity in order to prevent hemolysis) impeded the direct detection of the respective phenoxyl radicals previously reported in hemoglobin solutions. However, in accordance with earlier findings in homogeneous reaction systems, chemiluminescence was observed as well, indicating the existence of a further reaction intermediate, which was also obtained in pure hemoglobin solutions when mixed with the respective reactants. As has recently been demonstrated, this light emission is indicative of the existence of highly prooxidative compound I intermediates during methemoglobin formation. Prooxidant formation in erythrocytes is reflected by a significant decrease in thiol levels even with those compounds where free radical formation was not directly detectable by ESR spectroscopy. The use of the spin-labeling technique revealed membrane effects as a result of oxidative stress. Oxidative metabolism of hemoglobin with hydroxylamine caused a release of low molecular weight iron. The marked hemolysis observed in the presence of BHA results from a direct membrane effect of this compound rather than a consequence of free radical-induced oxidative stress. A correlation of the different results is discussed in terms of possible toxicological consequences.

'Free' iron, as detected by electron paramagnetic resonance spectroscopy, increases unequally in different tissues during dietary iron overload in the rat

'Free' iron concentration, as determined by electron paramagnetic resonance (EPR) spectroscopy, and lipid peroxidation (LPO), as determined by thiobarbituric acid test, were assessed in the lung, heart, liver, spleen, brain and kidney of rats subjected to experimental iron overload. Two tests, Desferal- and NO-available iron, were used to measure 'free' iron and gave comparable results. The most pronounced accumulation of 'free' iron was observed in liver, kidney and spleen. Differences between control and iron loaded animals increased during the initial 90 days of treatment. Between 90 and 180 days 'free' iron concentration reached a steady state level, or even decreased, as in the case of liver. Lipid peroxidation level, measured in the organs of both treated and matched controls, did not give any significant difference during the initial 90 days of treatment. A significant augmentation was observed in liver, kidney, spleen and heart at 180 days. The results of the present research show that, under conditions of moderate siderosis, the occurrence of LPO is partially related to the level of 'free' iron.

Protection by lazaroids of the erythrocyte (Ca2+, Mg2+)-ATPase against iron-induced inhibition

The calmodulin-stimulated (Ca2+, Mg2+)-ATPase (calmodulin-ATPase) of the erythrocyte membrane is susceptible to oxidative stress induced by heme and non-heme iron. There is a time-and concentration-dependent inhibition of the calmodulin-ATPase activity when the erythrocyte membranes are treated with either iron or hemin. In the present study, the calmodulin-ATPase has been used as a model system to evaluate the protective effects of a vitamin E analog (U83836E) and two 21-aminosteroids (U74500A and U74389G) against calmodulin-ATPase inhibition induced by iron and hemin. The drugs, lazaroids from Upjohn, can significantly protect the enzyme against iron-induced inhibition and also causes a decrease in the formation of thiobarbituric acid reactive species, with an IC50 of 0.4 microM for the drug U83836E and 4 microM for the drug U74500A. The 21-aminosteroid U74389G does not restore iron-inhibited calmodulin-ATPase activity under similar conditions. At higher concentrations (> 100 microM) all three drugs inhibit the calmodulin-ATPase activity. None of the drugs tested can restore hemin-inhibited calmodulin-ATPase activity.

Oxidation of methionyl residues in proteins: tools, targets, and reversal

Methionine (Met) is one of the most readily oxidized amino acid constituents of proteins. It is attacked by H2O2, hydroxyl radicals, hypochlorite, chloramines, and peroxynitrite, all these oxidants being produced in biological systems. The oxidation product, Met sulfoxide, can be reduced back to Met by Met sulfoxide reductase. Numerous proteins lose functional activity by Met oxidation. However, functional activation of proteins by Met oxidation has also been observed. Functional changes by Met oxidation in a given protein appear to have pathophysiological significance in some cases. Considering the reversibility of Met oxidation and the functional changes associated with the oxidation, it seems possible that Met oxidation/reduction in proteins may be one means to control homeostasis in biological systems.

Influence of the xanthine derivative denbufylline and the anti-inflammatory agent nabumetone on microsomal free radical production and lipid peroxidation in rat liver

The influence of denbufylline, nabumetone and its main metabolite BRL 10,720 on iron stimulated lipid peroxidation (LPO), cytochrome P 450 dependent H2O2 and chemiluminescence (CL) production was investigated in rat liver microsomes in vitro (10(-5)-10(-3) M) and in vivo after treatment of rats (5-300 mg/kg b.m. orally on three consecutive days). In rat liver slices the release of thiobarbituric acid reactants (TBAR) was measured after 1 hour of incubation with the drugs. Denbufylline, nabumetone and BRL 10,720 exerted a significant inhibition of iron stimulated LPO in vitro. Nabumetone showed the strongest antioxidative activity, which was also seen in liver slices. These antioxidative effects were not found after in vivo treatment of rats. Denbufylline (10(-3) M) additionally inhibited H2O2 formation and the luminol and lucigenin amplified CL in vitro. Unexpectedly, nabumetone increased H2O2 formation both in vitro and in vivo, but in vitro only lucigenin amplified CL. BRL 10,720 increased microsomal H2O2 production in vivo. Moreover, BRL 10,720 enhanced CL in vitro and in vivo significantly, which is interpreted as an increase of the production of superoxide anion radicals and other reactive oxygen species such as H2O2, but lipid peroxidation in liver microsomes was not enhanced. These results suggest that denbufylline, nabumetone and BRL 10,720 in contrast to the in vitro effects did not exert antioxidative activities after treatment of rats. On the contrary, BRL 10,720 was found to support the formation of reactive oxygen species in liver microsomes.