Oxidative damage to human red cells induced by copper and iron complexes in the presence of ascorbate

Sodium triple quantum MR signal extraction using a single-pulse sequence with single quantum time efficiency

PURPOSE

Sodium triple quantum (TQ) signal has been shown to be a valuable biomarker for cell viability. Despite its clinical potential, application of Sodium TQ signal is hindered by complex pulse sequences with long scan times. This study proposes a method to approximate the TQ signal using a single excitation pulse without phase cycling.

METHODS

The proposed method is based on a single excitation pulse and a comparison of the free induction decay (FID) with the integral of the FID combined with a shifting reconstruction window. The TQ signal is calculated from this FID only. As a proof of concept, the method was also combined with a multi-echo UTE imaging sequence on a 9.4 T preclinical MRI scanner for the possibility of fast TQ MRI.

RESULTS

The extracted Sodium TQ signals of single-pulse and spin echo FIDs were in close agreement with theory and TQ measurement by traditional three-pulse sequence (TQ time proportional phase increment [TQTPPI)]. For 2%, 4%, and 6% agar samples, the absolute deviations of the maximum TQ signals between SE and theoretical (time proportional phase increment TQTPPI) TQ signals were less than 1.2% (2.4%), and relative deviations were less than 4.6% (6.8%). The impact of multi-compartment systems and noise on the accuracy of the TQ signal was small for simulated data. The systematic error was <3.4% for a single quantum (SQ) SNR of 5 and at maximum <2.5% for a multi-compartment system. The method also showed the potential of fast in vivo SQ and TQ imaging.

CONCLUSION

Simultaneous SQ and TQ MRI using only a single-pulse sequence and SQ time efficiency has been demonstrated. This may leverage the full potential of the Sodium TQ signal in clinical applications.

Effect of Glucose on GLUT1-Dependent Intracellular Ascorbate Accumulation and Viability of Thyroid Cancer Cells

Enhanced glucose requirement of cancer cells is associated with an increased glucose transport across plasma membrane that is mediated by a family of facilitated glucose transporter proteins, named GLUTs. GLUT1 is the main transporter in thyroid cancer cells. Glucose is the principal physiological substrate of GLUT1; however, it is also capable of transporting of oxidized form of vitamin C [i.e., dehydroascorbic acid (DHAA) which inside the cells is reduced to ascorbic acid (AA)]. The objective of this study was to determine the effect of normo-, hypo-, and hyperglycemia conditions on GLUT1-dependent intracellular ascorbate accumulation and viability of thyroid cancer cells. GLUT1 seems to be the main DHAA transporter in thyroid cancer cells because its knockdown by RNAi reduced DHAA accumulation by more than 80%. The results showed that in thyroid cancer cells high glucose inhibits both transport of AA and DHAA. Inhibition of vitamin C transport by glucose had a cytotoxic effect on the cells. However, stabilization of vitamin C in one of 2 forms (i.e., AA or DHAA) abolished this effect. These results suggest that cytotoxic effect is rather associated with extracellular accumulation of vitamin C and changes of its oxidation state than with intracellular level of ascorbate.

Protein antioxidants in thalassemia

It is common knowledge that thalassemic patients are under significant oxidative stress. Chronic hemolysis, frequent blood transfusion, and increased intestinal absorption of iron are the main factors that result in iron overload with its subsequent pathophysiologic complications. Iron overload frequently associates with the generation of redox-reactive labile iron, which in turn promotes the production of other reactive oxygen species (ROS). If not neutralized, uncontrolled production of ROS often leads to damage of various intra- and extracellular components such as DNA, proteins, lipids, and small antioxidant molecules among others. A number of endogenous and exogenous defense mechanisms can neutralize and counteract the damaging effects of labile iron and the reactive substances associated with it. Endogenous antioxidant enzymes, such as superoxide dismutase, catalase, glutathione peroxidase, and ferroxidase, may directly or sequentially terminate the activities of ROS. Nonenzymatic endogenous defense mechanisms include metal binding proteins (ceruloplasmin, haptoglobin, albumin, and others) and endogenously produced free radical scavengers (glutathione (GSH), ubiquinols, and uric acid). Exogenous agents that are known to function as antioxidants (vitamins C and E, selenium, and zinc) are mostly diet-derived. In this review, we explore recent findings related to various antioxidative mechanisms operative in thalassemic patients with special emphasis on protein antioxidants.

Effects of nutrient and hemoglobin enriched cell free perfusates upon ex vivo isolated rat heart preparation

We evaluated the effects of nutrient enriched medium and hemoglobin based oxygen carrier (HBOC) upon myocardial functional recovery after 15 minutes of warm ischemia in an isovolumic Langendorff rat heart model. Hearts (n = 8/group) were perfused at constant pressure (90 mm Hg) with Krebs-Henseleit buffer or HEPES modified cell culture medium (M199) in the absence and presence of HBOC. Hearts received 15 minutes of normothermic no flow ischemia followed by 60 minutes reperfusion. Hemodynamics, coronary flow, and tissue water content were measured, and microscopic evidence of injury including TUNEL assay was assessed. Preischemic left ventricular performance (left ventricular developed pressure and maximum rate of positive and negative change in systolic pressure) and coronary flow were similar among groups. At 60 minutes of reperfusion, M199 alone provided more stable and complete left ventricular systolic and diastolic functional recovery than any other perfusate. Coronary flow rates reflected left ventricular function observed under each perfusate condition. TUNEL assay showed arterial endothelial cell death in some hearts perfused with HBOC. Tissue water content did not reflect functional recovery. The combination of M199 and HBOC was associated with poor recovery and elevated perfusate methemoglobin. In this system, postischemic dysfunction is prevented by components in M199. Added HBOC does not improve functional recovery and negates the salutary effects of M199, possibly by augmenting methemoglobin formation.

Trace elements in human physiology and pathology: zinc and metallothioneins

Zinc is one of the most abundant nutritionally essential elements in the human body. It is found in all body tissues with 85% of the whole body zinc in muscle and bone, 11% in the skin and the liver and the remaining in all the other tissues. In multicellular organisms, virtually all zinc is intracellular, 30-40% is located in the nucleus, 50% in the cytoplasm, organelles and specialized vesicles (for digestive enzymes or hormone storage) and the remainder in the cell membrane. Zinc intake ranges from 107 to 231 micromol/d depending on the source, and human zinc requirement is estimated at 15 mg/d. Zinc has been shown to be essential to the structure and function of a large number of macromolecules and for over 300 enzymic reactions. It has both catalytic and structural roles in enzymes, while in zinc finger motifs, it provides a scaffold that organizes protein sub-domains for the interaction with either DNA or other proteins. It is critical for the function of a number of metalloproteins, inducing members of oxido-reductase, hydrolase ligase, lyase family and has co-activating functions with copper in superoxide dismutase or phospholipase C. The zinc ion (Zn(++)) does not participate in redox reactions, which makes it a stable ion in a biological medium whose potential is in constant flux. Zinc ions are hydrophilic and do not cross cell membranes by passive diffusion. In general, transport has been described as having both saturable and non-saturable components, depending on the Zn(II) concentrations involved. Zinc ions exist primarily in the form of complexes with proteins and nucleic acids and participate in all aspects of intermediary metabolism, transmission and regulation of the expression of genetic information, storage, synthesis and action of peptide hormones and structural maintenance of chromatin and biomembranes.

Supplementation with vitamin C and N-acetyl-cysteine increases oxidative stress in humans after an acute muscle injury induced by eccentric exercise

There has been no investigation to determine if the widely used over-the-counter, water-soluble antioxidants vitamin C and N-acetyl-cysteine (NAC) could act as pro-oxidants in humans during inflammatory conditions. We induced an acute-phase inflammatory response by an eccentric arm muscle injury. The inflammation was characterized by edema, swelling, pain, and increases in plasma inflammatory indicators, myeloperoxidase and interleukin-6. Immediately following the injury, subjects consumed a placebo or vitamin C (12.5 mg/kg body weight) and NAC (10 mg/kg body weight) for 7 d. The resulting muscle injury caused increased levels of serum bleomycin-detectable iron and the amount of iron was higher in the vitamin C and NAC group. The concentrations of lactate dehydrogenase (LDH), creatine kinase (CK), and myoglobin were significantly elevated 2, 3, and 4 d postinjury and returned to baseline levels by day 7. In addition, LDH and CK activities were elevated to a greater extent in the vitamin C and NAC group. Levels of markers for oxidative stress (lipid hydroperoxides and 8-iso prostaglandin F2alpha; 8-Iso-PGF2alpha) and antioxidant enzyme activities were also elevated post-injury. The subjects receiving vitamin C and NAC had higher levels of lipid hydroperoxides and 8-Iso-PGF2alpha 2 d after the exercise. This acute human inflammatory model strongly suggests that vitamin C and NAC supplementation immediately post-injury, transiently increases tissue damage and oxidative stress.

Involvement of oxidative stress in ascorbate-induced proapoptotic death of PC12 cells

Ascorbate is a reducing agent, but it is also known to oxidize cellular components under specific conditions. The mechanism of this oxidative action, however, is not well established. Ascorbate treatment increased lipid peroxide content in PC12 cells, but did not increase quantities of lipid peroxide when homogenates of PC12 cells were treated with ascorbate, suggesting that cellular integrity is required for ascorbate to generate lipid peroxidation. However, dehydroascorbate increased lipid peroxide production in both intact PC12 cells and the cell homogenates. These differential effects of ascorbate and dehydroascorbate on intact cells versus homogenates suggest that the dehydroascorbate in cytosol induces an oxidative stress. Ascorbate in culture medium is rapidly oxidized to dehydroascorbate, which is transported into cells by a glucose transporter (GLUT). The GLUT antagonists wortmannin and cytochalasin B, or a high concentration of glucose, blocked (14)C uptake (from ascorbate) in a time-dependent manner and suppressed lipid peroxide production in PC12 cells. These observations support the concept that ascorbate is oxidized to dehydroascorbate, which is transported into cells via GLUT. The dehydroascorbate induces oxidative stress. The oxidative stress triggered apoptosis according to ceramide production, caspase-3 activation, and TUNEL. We have concluded that ascorbate is taken up after oxidation to dehydroascorbate via a "dehydroascorbate transporter" (GLUT), and the dehydroascorbate generates an oxidative stress which triggers apoptosis. These studies have significant implications for conditions under which a high concentration of ascorbate in a tissue is released during a period of hypoxia (e.g., stroke) and taken up during a reperfusion period as dehydroascorbate. Inhibiting uptake of dehydroascorbate may offer novel therapeutic strategies to alleviate brain damage during a reperfusion period.

The antioxidant properties of zinc

The ability of zinc to retard oxidative processes has been recognized for many years. In general, the mechanism of antioxidation can be divided into acute and chronic effects. Chronic effects involve exposure of an organism to zinc on a long-term basis, resulting in induction of some other substance that is the ultimate antioxidant, such as the metallothioneins. Chronic zinc deprivation generally results in increased sensitivity to some oxidative stress. The acute effects involve two mechanisms: protection of protein sulfhydryls or reduction of (*)OH formation from H(2)O(2) through the antagonism of redox-active transition metals, such as iron and copper. Protection of protein sulfhydryl groups is thought to involve reduction of sulfhydryl reactivity through one of three mechanisms: (1) direct binding of zinc to the sulfhydryl, (2) steric hindrance as a result of binding to some other protein site in close proximity to the sulfhydryl group or (3) a conformational change from binding to some other site on the protein. Antagonism of redox-active, transition metal-catalyzed, site-specific reactions has led to the theory that zinc may be capable of reducing cellular injury that might have a component of site-specific oxidative damage, such as postischemic tissue damage. Zinc is capable of reducing postischemic injury to a variety of tissues and organs through a mechanism that might involve the antagonism of copper reactivity. Although the evidence for the antioxidant properties of zinc is compelling, the mechanisms are still unclear. Future research that probes these mechanisms could potentially develop new antioxidant functions and uses for zinc.

Transition metal chelators reduce directly measured myocardial free radical production during reperfusion

Transition metals such as iron and copper are present in the myocardium and can act as catalysts for the formation of oxygen free radicals during reperfusion after myocardial ischemia. Previous studies suggested that transition metal chelators such as desferrioxamine reduce the production of such radicals and may thereby attenuate postischemic myocardial dysfunction. These studies used spin trapping agents, commonly nitrone compounds, which may themselves influence the severity of the ischemia and reperfusion events being studied. We evaluated two transition metal chelators, desferrioxamine, an iron chelator, and bathocuproine, a copper chelator, by using a new electron paramagnetic resonance technique that does not require the administration of spin traps. We measured ascorbate free radical, an index of free radical production, in the great cardiac vein effluent. Twenty-eight open-chest dogs underwent 20 min of coronary artery occlusion and 30 min of reperfusion. Ten dogs received no drug, 10 dogs received 750 mg bathocuproine, i.v., and eight dogs received 700 mg desferrioxamine, i.v. Both bathocuproine and desferrioxamine blunted the postreperfusion increase in ascorbate free radical generation: no drug, 36+/-8% increase; desferrioxamine, 13+/-5% increase; bathocuproine, 21+/-6% increase (p < 0.05 vs. baseline). Thus direct free radical measurements indicate that chelation of the transition metals iron and copper reduces free radical generation during reperfusion.

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.

Effects of acute iron overload on Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss)

Distribution of radioiron to various tissues after intraperitoneal injections was examined in Atlantic salmon and rainbow trout. Liver and spleen were found to be the major iron storage tissues. Injections of 1 or 5 mg iron as ferric ammonium citrate led to a fall in hemoglobin levels in both species after 2 d. Hemoglobin levels returned to normal levels in rainbow trout after 8 d, but Atlantic salmon had not recovered, and Hb levels fell below 3 g/100 mL. In both species, the fall in Hb was associated with a raise in iron levels in spleen and liver, suggesting damage to erythrocytes. Atlantic salmon liver ferritin showed a two- to threefold increase, while rainbow trout showed a sixfold increase, and a more rapid response. The toxic effect of iron in fish appears to be different from the effect in other vertebrates.

Ataxia with isolated vitamin E deficiency in four siblings

We describe 4 siblings of a consanguineous Bedouin family with Friedreich ataxia phenotype in whom low serum vitamin E levels without other indicators of fat malabsorption were detected. Although age of onset and some of the clinical features were alike in all 4 patients, the electrophysiological parameters were markedly abnormal in 2, but normal in the other 2. Erythrocytes revealed both membranous and intracellular evidence of oxidative damage. The mutations described in other families with ataxia with isolated vitamin E deficiency were not detectable, nor was an abnormal single-stranded conformation polymorphism pattern apparent in the three exons at the 3' region of the gene. Vitamin E administration in pharmacological doses improved the neurological condition in 2 patients and also corrected some of the patients' erythrocyte cell abnormalities. The finding of vitamin E deficiency in other cases of Friedreich ataxia phenotype may allow treatment at an early stage of the disease, when large dose Vitamin E therapy may reverse the neurological lesions.

Red blood cell permeability to thiol compounds following oxidative stress

The permeability of red blood cells (RBCs) to thiol containing compounds, reduced glutathione (GSH) and N-acetyl cysteine (NAC), has been studied in control adult and neonatal cells and after oxidative stress. NAC penetrates the cell membrane easily while GSH hardly permeates. We measured their capacity to enhance intracellular non-protein thiols (NPSH), after inducing damage to the membrane by formation of defects. Diamide, phenazine methosulfate (PMS) and t-butyl hydroperoxide (BHP) were chosen as exogenous oxidants, each inducing damage by a different mechanism. Our data indicate that although neonatal cells are more sensitive to oxidative stress, only membrane damage induced by diamide, renders adult and neonatal cells permeable to GSH. NAC treatment enhances thiol levels in cells exposed to oxidizing agents, as well as in control cells.

Investigation of ascorbate-Cu (II) induced cleavage of DNA by scanning tunneling microscopy

Scanning Tunneling Microscopy (STM) was used for the investigation of oxidative DNA damage. A PCR amplified fragment of human beta-globin gene was used as a model for time dependent cleavage reaction by ascorbate and copper. Cleavage reactions were carried out in a medium containing 0.5 microgram/20 microliters DNA, 20 nM Tris-HC1 pH, 7.8 and ascorbate-Cu (II) in the final concentrations of 1 mM and 30 microM, respectively. The mixtures were incubated at 37 degrees C for 5, 15 and 30 min. For STM studies, 3 pg/5 microliters DNA samples were deposited on the gold coated mica and dried in a water flow vacuum drier. The STM was operated in air at atmospheric pressure with a tip-to-substrate bias of 100 mV and tunneling currents of < 10 pA. Etched tips of Pt/Ir wires were used in a constant current mode. The degradated DNA structure can be distinguished from the intact DNA and the sizes of the degradation products can be identified in the STM micrographs. The size of fragments decreased from approximately 3000 A to 34 A in ascorbate-Cu (II) medium, after 30 min of incubation.

Role of antioxidants on the erythrocytes resistance to lipid peroxidation after acute iron overload in rats

Iron overload was developed in rats by ip injection of iron-dextran. Iron concentration in plasma increased 12-fold after 20 h of iron supplementation and unsaturated iron binding capacity (UIBC) drastically decreased in iron overloaded compared to control rats (69 +/- 36 and 177 +/- 19 micrograms/dl, respectively). Lipid peroxidation in plasma increased by 285% and plasma alpha-tocopherol content decreased by 40% after 20 h of iron overload. alpha-Tocopherol supplementation decreased by 30% the measured increase in TBARS content in plasma after iron injection. On the other hand, both iron and TBARS content in erythrocytes were not significantly different in control and iron loaded rats. However, red blood cells from iron treated rats exposed to pro-oxidant conditions showed a significant increase in TBARS content as compared to control erythrocytes. alpha-Tocopherol pretreatment prevented this increase. Moreover, red blood cells from iron loaded rats showed a higher content of TBARS after incubation with plasma from iron-dextran injected rats than after incubation with plasma from control animals. This measured increase was partially prevented by alpha-tocopherol supplementation. Neither the activity of antioxidant enzymes nor the content of alpha-tocopherol in red blood cells were affected by iron overload. Total thiols content was significantly lower (30%) in erythrocytes isolated from iron treated rats. The data presented here suggest that free radical generation catalyzed by metal ions may lead to consumption of thiols. The decrease in thiols content in erythrocytes could afford an appropriate degree of protection and avoid other oxidative damage to these cells.

Hydroxyl radical generation in beta-thalassemic red blood cells

To provide more experimental evidence for the proposed role of oxygen free radicals in red blood cell (RBC) damage in beta-thalassemia, hydroxyl radical generation was studied in thalassemic (Th) vs. normal (N) RBC. .OH fluxes were quantified by the conversion of salicylic acid (SA) into its hydroxylated products, 2,3- and 2,5-dihydroxybenzoic acids (DHBA) and catechol, assayed with HPLC coupled to electrochemical detection. No significant difference in spontaneous .OH generation between N-RBC and Th-RBC was found. Ascorbic acid (0.5-3.0 mM) induced many-fold increases in SA hydroxylation in a dose-dependent manner in both types of cells. In the presence of ascorbate (1.0 mM), the SA hydroxylated products were determined in Th-RBC vs. N-RBC as follows (nmol/ml): 2,5-DHBA, 1.45 +/- 0.06 vs. 1.81 +/- 0.05 (p = 0.001); 2,3-DHBA, 1.89 +/- 0.21 vs. 1.15 +/- 0.08 (p = 0.008) and catechol, 0.87 +/- 0.13 vs. 0.38 +/- 0.05 (p = 0.006). The results showed significant increase in the total SA hydroxylation in Th-RBC as compared to N-RBC with a tendency to form 2,3-DHBA and catechol at the expanse of 2,5-DHBA. The excessive .OH generation in Th-RBC is attributed to the abnormally high content of redox active iron in the cytosolic and/or membrane compartments of these cells.

Membrane-associated redox cycling of copper mediates hydroperoxide toxicity in Escherichia coli

We are studying the action of tert-butylhydroperoxide (t-BOOH) on Escherichia coli as a model system for peroxide toxicity. In our previous report (De la Cruz-Rodriguez, L.C., Farías, R.N. and Massa, E.M. (1990) Biochim. Biophys. Acta 1015, 510-516), the respiratory chain was identified as a major target of t-BOOH. In the present paper, we study further the effect of t-BOOH on the NADH oxidase of the E. coli respiratory chain to clarify the mechanism of damage, especially regarding the identity and role of the metal ion involved. The results are: (a) t-BOOH toxicity is mediated by membrane-bound copper ions; (b) a small pool of the membrane-bound copper is reduced from Cu(II) to Cu(I) in the presence of NADH and other respiratory substrates (succinate, D-lactate); (c) this reduction of copper occurs at 37 degrees C but not at 0 degrees C or when the membranes are inactivated by previous heating; (d) the Cu(I) generated by reduction of Cu(II) during membrane preincubation with NADH, is oxidized by t-BOOH with simultaneous inactivation of the NADH oxidase, whereas treatment with only t-BOOH (without NADH) has no effect on the oxidase. It is concluded that the effect of t-BOOH on the respiratory chain is mediated by redox cycling of copper. It is proposed that the damage results from activation of the hydroperoxide through its interaction with Cu(I) in a site-specific Fenton-type reaction.

Dynamics of iron-ascorbate-induced lipid peroxidation in charged and uncharged phospholipid vesicles

Peroxidation of egg yolk phosphatidylcholine (egg PC) liposomes was induced by addition of ascorbic acid (AsA) and Fe(II) in the presence of a trace of autoxidized egg PC (PC-OOH), but not in the absence of PC-OOH. PC-OOH was degraded upon addition of AsA and Fe(II) but not of either one alone. The results suggest that PC-OOH is necessary to initiate lipid peroxidation by AsA/Fe(II). AsA oxidation in the bulk water phase was also associated with an increase in lipid peroxidation by AsA/Fe(II) in the presence of PC-OOH, but not in the absence of PC-OOH. Furthermore, the spin probe 12-NS [12-(N-oxyl-4,4'-dimethyloxazolidin-2-yl)stearic acid], which labels the hydrophobic region of dimyristoyl phosphatidylcholine (DMPC) liposomal membranes, was degraded upon addition of AsA and Fe(II) in the presence of PC-OOH, but not in the absence of PC-OOH. These results indicate that the "induction message" that is associated with decreases of PC-OOH and AsA in the initiation step of lipid peroxidation must be transferred from the membrane surface to the inner hydrophobic membrane region. AsA in the bulk phase was oxidized faster and more extensively upon its addition together with Fe(II) to egg PC liposomes than to DMPC liposomes, though the initial content of PC-OOH in the former was 5-10 times lower than in the latter. This suggests that, in egg PC liposomes, the OOH-groups of new PC-OOH generated in the inner membrane regions must become accessible from the surface, enabling reaction with AsA/Fe(II) which in turn would result in an extensive decrease in AsA.(ABSTRACT TRUNCATED AT 250 WORDS)

Interaction between allopurinol and copper: possible role in myocardial protection

Allopurinol, a potent inhibitor of xanthine oxidase, is known to effectively protect the heart against damage in patients undergoing cardiac bypass surgery. There is still an ambiguity concerning the presence of xanthine oxidase in the human heart. Thus, the mechanism underlying the protective effect of allopurinol is unclear. Transition metal ions, such as iron and copper, can participate in single-electron reactions and mediate the formation of oxygen-derived free radicals. In this study the interaction between allopurinol and Cu(II) was investigated. Spectrophotometric investigation shows that allopurinol (0-0.8 mM) form a 1:1 complex with Cu(II) ions (0-0.8 mM) with a specific absorbance peak at 364 nm. Also, the rate constant (k) for the copper-catalyzed aerobic oxidation of ascorbate was markedly decreased in the presence of allopurinol (from 0.068 min-1 to 0.014 min-1). Allopurinol substantially reduced the copper-mediated and ascorbate-driven DNA breakage. Spectrophotometric measurements did not indicate a specific interaction between iron ions and allopurinol. It is suggested that the beneficial effects of allopurinol during reperfusion of the heart could stem from its chelation of copper, yielding a complex with low redox activity.

Mediatory role of copper in reactive oxygen intermediate-induced cardiac injury

In this report the mediatory role of copper in cardiac injury produced by reactive oxygen intermediates was examined. Isolated rat hearts were perfused with Krebs-Henseleit buffer containing 0.25 mM ascorbate plus varying concentrations of copper-bis-histidial for up to 60 min. Using salicylate as a probe, OH generation by this system was demonstrated. Copper or ascorbate alone had minimal effect on cardiac function as determined by heart rate, coronary flow, left ventricular systolic pressure development, end diastolic pressure and +/- dP/dtmax. Copper, from 0.5 microM to 20 microM, and ascorbate, 0.25 mM, resulted in concentration-dependent decreases in all of the experimental variables. Treatment with 5 or 20 microM copper resulted in complete loss of cardiac function within 40 and 30 min, respectively. By 30 min, 5 microM copper had resulted in increased end diastolic pressure to greater than 40 mmHg. By 60 min, perfusion with 1 microM copper resulted in almost 100% loss of function and end diastolic pressure greater than 25 mmHg. Copper, 0.5 microM, also decreased cardiac function, but to a lesser degree. Catalase, 100 units/ml, was effective in preventing the copper-ascorbate induced cardiac damage while superoxide dismutase, 25 units/ml, was ineffective. Observations by light and electron microscopy demonstrated patchy regions with vacuolization corresponding to swollen mitochondria. These results clearly demonstrate that copper-catalyzed redox reactions can induce cardiac injury via a mechanism which appears to be related to the production of OH.

Recent advances in the role of reactive oxygen intermediates in ischemic injury. I. Evidence demonstrating presence of reactive oxygen intermediates; II. Role of metals in site-specific formation of radicals

This article has attempted to bring the reader up to date on advances in selected facets of the area of reactive oxygen intermediate-induced ischemic injury. Specifically, we have discussed the more recent reports that provide evidence for the presence of these species in reperfused ischemic tissue. In addition, we have attempted to introduce the reader to the relatively new concept of "site-specific" formation of radicals and how the use of "push-pull" techniques, such as chelation by high-affinity chelators or displacement by non-redox-active metals such as zinc, may decrease postischemic reperfusion injury. Finally, we have identified a class of compounds that affect the oxidation state of redox-active metals, and have demonstrated how these compounds may also represent a new therapeutic modality. In conclusion, both academic and nonacademic surgeons should have profited from reading this article. For the academic surgeon, who may do research, several new cytoprotectants requiring further study in both in vitro and in vivo models have been identified. For the nonacademic surgeon in clinical practice the realization that there are several promising areas of research that may yield new therapies to mitigate postischemic reperfusion injury should have been gained.

Metal-ion-directed site-specificity of hydroxyl radical detection

A wide variety of .OH detectors are in use for determination of biological .OH production. The chemical generation of .OH is site-specific with respect to the metal-binding site, and thus .OH detectors with metal-binding properties may affect the biological damage and bias .OH detection. The present study shows that both salicylate and phenylalanine, added as low molecular weight .OH indicators, decreased Cu(II) binding to erythrocyte ghosts. In a cell-free system, Cu(II) complexed to both salicylate and phenylalanine. Phenylalanine is a stronger Cu(II) chelator than salicylate, both when competing for Cu(II) bound to ghosts and when competing directly with each other. When OH radicals were generated by ascorbate and Cu(II), the amount of .OH detected as dihydroxybenzoates was proportional to the amount of .OH produced. However, when phenylalanine was added to this system, the efficiency of .OH detection by salicylate strongly decreased, concomitant with the transfer of Cu(II) binding from salicylate to the amino acid. This decrease was larger than that predicted by calculations for random competition of the two detectors for .OH. Deoxyribose and mannitol, which do not bind copper appreciably, competed poorly with salicylate for the .OH. Hydroxylation of phenylalanine, on the other hand, was only slightly affected by the presence of salicylate and unaffected by deoxyribose and mannitol. These results suggest that the detection of .OH by low molecular weight .OH indicators was related to the relative affinity of the detectors for the catalyzing metal, and thus partially site-specific. Furthermore, glutamate, which does not contain an aromatic ring but binds Cu(II) with considerable affinity, competed strongly with salicylate for the .OH, indicating that metal-binding properties rather than the presence of an aromatic ring were the cause of the deviation from random competition. The results indicate that .OH indicators with metal-binding properties affect the distribution of catalytic metal ions in a biological system, causing a shift of free radical damage and localizing a site-specific reaction of .OH on these detectors, with a resulting positive bias in the apparent .OH production.

Copper loading of hearts increases postischemic reperfusion injury

We studied the role of copper as a potential mediator of postischemic reperfusion injury in the isolated, perfused rat heart. Hearts were equilibrated with Krebs-Henseleit buffer for 10 minutes and then loaded with copper by way of perfusion with buffer containing 20 microM copper(II)-bis-histidial for 30 minutes. Control hearts were perfused with Krebs-Henseleit buffer alone during the loading period. Hearts than were washed with buffer for 10 minutes and subjected to 20 minutes of normothermic global ischemia followed by 30 minutes of reperfusion. Atomic absorption spectroscopy revealed a 67% increase in total copper content in loaded hearts by the end of the wash. By the end of the 30-minute period of reperfusion, control hearts demonstrated a 50-60% recovery of myocardial function as determined by peak systolic pressure, contractility, and heart rate. In contrast, copper-loaded hearts exhibited virtually no functional recovery within the 30-minute time period. Using salicylate as a probe, we determined that peak and duration of .OH formation appears to be increased in copper-loaded hearts during reperfusion. Furthermore, efflux of lactic dehydrogenase was significantly increased in copper-loaded hearts. Our results clearly demonstrate that increasing cardiac content of copper results in enhanced postischemic reperfusion injury associated with increased formation of .OH, thus suggesting an important catalytic role for this transition metal.

Different cellular targets for Cu- and Fe-catalyzed oxidation observed using a Cu-compatible thiobarbituric acid assay

The widely used thiobarbituric acid (TBA) assay for oxidative damage to biomolecules fails in Cu2(+)-containing solutions due to the formation of a cloudy precipitate. The chelation of Cu2+ ions with EDTA or Chelex was investigated. Both prevented precipitate formation, but only Chelex allowed proper color development in the TBA assay. The Chelex modified assay could be adapted to a variety of systems, and was applied to the detection of Cu2+/ascorbate dependent deoxyribose breakdown and oxidative damage in erythrocyte ghosts, lysates and whole cells. Using this method, it was shown that Cu2+/ascorbate caused membrane damage in ghosts but not in whole red blood cells (RBC). Fe3+/ascorbate, on the other hand, caused formation of TBA-reactive products even in whole RBC. When Cu2+ and Fe3+ were presented to isolated hemoglobin as their 1:1 nitrilotriacetate complexes, the protein bound 10-12 cupric ions per molecule, but no ferric ions. It is suggested that oxidative damage catalyzed by copper or iron ions has different cellular targets, determined by the different binding properties of the two metals to various cellular components.