Tissue iron overload and mechanisms of iron-catalyzed oxidative injury

Combination Antioxidant/NSAID Therapies and Oral/Topical Ocular Delivery Modes for Prevention of Oxygen-Induced Retinopathy in a Rat Model

Given the complexity of oxygen-induced retinopathy (OIR), we tested the hypothesis that combination therapies and modes of administration would synergistically optimize efficacy for prevention of OIR. Newborn rats were exposed to neonatal intermittent hypoxia (IH) from the first day of life (P0) until P14 during which they received: (1) oral glutathione nanoparticles (nGSH) with topical ocular phosphate buffered saline (PBS); (2) nGSH with topical ocular Acuvail (ACV); (3) oral coenzyme Q10 (CoQ10) + ACV; (4) oral omega 3 polyunsaturated fatty acids (n-3 PUFAs) + ACV; (5) CoQ10 + n-3 PUFAs + PBS; or (6) CoQ10 + n-3 PUFAs + ACV. Treated groups raised in room air (RA) served as controls. At P14, pups were placed in RA with no treatment until P21. Retinal vascular pathology, ocular angiogenesis biomarkers, histopathology, and morphometry were determined. All combination treatments in IH resulted in the most beneficial retinal outcomes consistent with suppression of angiogenesis growth factors during reoxygenation/reperfusion and no significant adverse effects on somatic growth. nGSH + PBS also reversed IH-induced retinopathy, but had negative effects on growth. Simultaneously targeting oxidants, inflammation, and poor growth mitigates the damaging effects of neonatal IH on the developing retina. Therapeutic synergy with combination delivery methods enhance individual attributes and simultaneously target multiple pathways involved in complex diseases such as OIR.

The Absence of Toxicity in Intraperitoneal Iron Dextran Administration: A Functional and Histological Analysis

Objective

To determine the influence of iron dextran intraperitoneal administration on the function and histology of the peritoneum in rats undergoing chronic peritoneal dialysis.

Design

Prospective, randomized experimental study.

Materials

Fifty-four Sprague-Dawley rats were divided into five groups: 3 study groups -high dose group (H), n = 12; intermediate dose (M), n = 12; and low dose group (L), n = 12 a dialysis control group (D), n = 12; and a tissue control (C), n = 7.

Interventions

The study groups were given Dianeal containing iron dextran in a concentration of 0.5,0.25, and 0.125 mg/L (groups H, M, and L respectively). Group D was given standard Dianeal. Group C was never dialyzed.

Main Outcome Measures

A 2-hour peritoneal equilibrium test (PET) was performed on the eighth day, at 3 months, and at 6 months. After the final PET, the animals were sacrificed and the peritoneal membrane was evaluated by gross inspection and light microscopy (silver, prussian blue, and trichrome staining).

Results

Peritoneal transport of small solutes followed the same pattern in all groups, increasing over time. The peritonitis index was similar in the groups. No iron deposits or morphologic differences were seen in the gross inspection of the peritoneal cavity. No peritoneal iron deposition was detected in the histological analysis with prussian blue staining. No differences were noted in the light microscopic analysis of the mesothelial cell layer (silver staining), nor did the morphometric analysis of the submesothelial space show any differences in thickness between the groups.

Conclusion

These findings suggest the absence of toxic effects of iron dextran on the peritoneal cavity of rats in the concentrat ions studied. Further studies should be performed to evaluate the effectiveness of these dosages delivered intraperitoneally to maintain iron homeostasis.

Arrhythmias and Sudden Cardiac Death in Beta-Thalassemia Major Patients: Noninvasive Diagnostic Tools and Early Markers

Beta-thalassemias are a group of inherited, autosomal recessive diseases, characterized by reduced or absent synthesis of beta-globin chains of the hemoglobin tetramer, resulting in variable phenotypes, ranging from clinically asymptomatic individuals to severe anemia. Three main forms have been described: heterozygotes, homozygotes β+, and homozygotes β°. Beta-thalassemia major (β-TM), the most serious form, is characterized by an absent synthesis of globin chains that are essential for hemoglobin formation, causing chronic hemolytic anemia. Cardiac complications represent a leading cause of mortality in β-TM patients, although an important and progressive increase of life expectancy has been demonstrated after the introduction of chelating therapies. Iron overload is the primary factor of cardiac damage resulting in thalassemic cardiomyopathy, in which diastolic dysfunction usually happens before systolic impairment and overt heart failure (HF). Although iron-induced cardiomyopathy is slowly progressive and it usually takes several decades for clinical and laboratory features of cardiac dysfunction to manifest, arrhythmias or sudden death may be present without signs of cardiac disease and only if myocardial siderosis is present. Careful analysis of electrocardiograms and other diagnostic tools may help in early identification of high-risk β-TM patients for arrhythmias and sudden cardiac death.

Electrocardiographic Presentation, Cardiac Arrhythmias, and Their Management in β-Thalassemia Major Patients

Beta-thalassemia major (β-TM) is a genetic hemoglobin disorder characterized by an absent synthesis of globin chains that are essential for hemoglobin formation, causing chronic hemolytic anemia. Clinical management of thalassemia major consists in regular long-life red blood cell transfusions and iron chelation therapy to remove iron introduced in excess with transfusions. Iron deposition in combination with inflammatory and immunogenic factors is involved in the pathophysiology of cardiac dysfunction in these patients. Heart failure and arrhythmias, caused by myocardial siderosis, are the most important life-limiting complications of iron overload in beta-thalassemia patients. Cardiac complications are responsible for 71% of global death in the beta-thalassemia major patients. The aim of this review was to describe the most frequent electrocardiographic abnormalities and arrhythmias observed in β-TM patients, analyzing their prognostic impact and current treatment strategies.

The association between serum ferritin levels and post-stroke depression

BACKGROUND

Post-stroke depression (PSD) is a common neuropsychiatric affective disorder occurring after stroke. Elevated serum ferritin levels have been reported to contribute to depression. Our aim was to determine whether there is a relationship between serum ferritin levels and PSD.

METHODS

196 ischemic stroke patients were consecutively recruited within the first 24h of stroke onset and were followed up for 2 months. Serum ferritin levels were assayed by electrochemiluminescence immunoassay at hospital admission. Clinical depression was diagnosed according to DSM-IV criteria and a HAMD -17 score of ≥ 7. Meanwhile, 100 normal control subjects were also recruited.

RESULTS

We found that 56 stroke patients (28.6%) were diagnosed with PSD at two months. There was a significant intergroup difference in serum ferritin levels within 24h after admission (F=25.044, P<0.001). Serum ferritin levels were significantly higher at admission in PSD patients than in non-PSD patients and normal controls. There was a positive correlation between serum ferritin levels and hs-CRP at admission in PSD patients (r=0.129, P=0.042). In multivariate analyses, serum levels of ferritin ≥ 130.15 µg/L were independently associated with PSD at two months [odds ratio OR=5.388, 95%CI:1.725-16.829; P=0.004] after adjusting for all possible variables.

LIMITATIONS

We excluded patients with severe aphasia and with serious conditions.In addition, the information for dietary intake was not recorded, which may influence body iron stores.

CONCLUSION

Our findings show that elevated serum ferritin levels at admission are associated with PSD and may predict its development at 2 months post-stroke.

Oxygen Use in Neonatal Care: A Two-edged Sword

In the neonatal period, the clinical use of oxygen should be taken into consideration for its beneficial and toxicity effects. Oxygen toxicity is due to the development of reactive oxygen species (ROS) such as OH^• that is one of the strongest oxidants in nature. Of note, generation of ROS is a normal occurrence in human and it is involved in a myriad of physiological reactions. Anyway an imbalance between production of oxidant species and antioxidant defenses, called oxidative stress, could affect various aspect of organisms' physiology and it could determine pathological consequences to living beings. Neonatal oxidative stress is essentially due to decreased antioxidants, increased ROS, or both. Studies have demonstrated that antioxidant capacity is lower in preterm newborns than term babies. This well-known deficiency of antioxidant factors is only a piece of a cohort of factors, which can be involved in the neonatal oxidative stress and the increased production of ROS may be a main factor. Mechanisms of ROS generation are: mitochondrial respiratory chain, free iron and Fenton reaction, inflammation, hypoxia and/or ischemia, reperfusion, and hyperoxia. Oxidative stress following hyperoxia has been recognized to be responsible for lung, central nervous system, retina, red blood cell injuries, and possibly generalized tissue damage. When supplemental oxygen is needed for care, it would be prudent to avoid changes and fluctuations in SpO₂. The definition of the safest level of oxygen saturations in the neonate remains an area of active research. Currently, on the basis of the published evidences, the most suitable approach would be to set alarm limits between 90 and 95%. It should allow to avoid SpO₂ values associated with potential hypoxia and/or hyperoxia. Although the usefulness of antioxidant protection in the neonatal period is still under investigation, the risk of tissue damage due to oxidative stress in perinatal period should not be underestimated.

Insulin resistance modulates iron-related proteins in adipose tissue

OBJECTIVE Circulating markers of iron overload are associated with insulin resistance. Less is known about the impact of iron overload on adipose tissue (AT). We hypothesized that gene expression markers of iron metabolism in AT could be associated with insulin action. RESEARCH DESIGN AND METHODS The AT expression of ferroportin (SLC40A1), transferrin (TF), TF receptor (TFRC), ferritin (FT) heavy polypeptide 1 (FTH1), and FT light polypeptide (FTL) was analyzed cross-sectionally in three independent cohorts and also after weight loss-induced changes in insulin sensitivity (clamp M value) in an independent fourth cohort. RESULTS In human AT, TF mRNA and protein levels were decreased with obesity and insulin resistance in the three cohorts and were positively associated with adipogenic mRNAs and insulin action. Otherwise, FTL mRNA and protein and SLC40A1 transcripts were positively associated with BMI and negatively linked to adipogenic genes and insulin action. Bariatric surgery-induced weight loss led to increased TF and decreased TFRC, FTH1, FTL, and SLC40A1 in subcutaneous AT in parallel to improved insulin action. CONCLUSIONS These results suggest that iron overload impacts on AT in association with insulin resistance.

The relevance of iron overload and the appropriateness of iron chelation therapy for patients with myelodysplastic syndromes: a dialogue and debate

Accumulation of excessive amounts of iron in vulnerable organs and tissues, together with elevated plasma and intracellular concentrations of reactive iron molecules, are likely to be harmful to some patients with myelodysplastic syndromes (MDS) who have received numerous red blood cell transfusions. But what is the real magnitude of risks related to iron overload in MDS, and how strong is the evidence that reducing total body iron and labile plasma iron through treatment with chelating drugs is beneficial to patients? Available data can be interpreted in different ways, and as a result, these topics continue to be areas of heated debate among physicians who care for patients with MDS. Using the traditional but rarely employed format of a classical dialogue, I explore here the potential dangers of iron overload and the risks and benefits of iron chelation therapy for patients with MDS.

Antioxidant therapy and neuroprotection in the newborn

Injury to the perinatal brain is a leading cause of childhood mortality and lifelong disability. Despite recent improvements in neonatal care, no effective treatment for perinatal brain lesions is available. The newborn, especially if preterm, is highly prone to oxidative stress (OS) and to the toxic effect of free radicals (FRs). At birth, the newborn is exposed to a relatively hyperoxic environment caused by an increased oxygen bioavailability with greatly enhanced generation of FRs. Additional sources (e.g., inflammation, hypoxia, ischemia, glutamate and free iron release) occur, magnifying OS. In the preterm baby, the perinatal transition is accompanied by the immaturity of the antioxidant systems and the reduced ability to induce efficient homeostatic mechanisms designed to control overproduction of cell-damaging FRs. Improved understanding of the pathophysiological mechanism involved in perinatal brain lesions helps to identify potential targets for neuroprotective interventions, and the knowledge of these mechanisms has enabled scientists to develop new therapeutic strategies that have confirmed their neuroprotective effects in animal studies. Considering the growing role of OS in preterm newborn morbidity in respect to the higher risk of FR damage in these babies, erythropoietin, allopurinol, melatonin and hypothermia demonstrate great promise as potential neuroprotectans. This article provides an overview of the pathogenesis of FR-mediated diseases of the newborn and the antioxidant strategies now tested in order to reduce OS and its damaging effects.

Myelodysplasia paranoia: iron as the new radon

Few areas concerning the care of patients with myelodysplastic syndromes (MDS) have prompted as much disagreement among clinicians as the appropriate role of iron chelation therapy. At least eight conflicting guidelines or consensus statements on iron management in MDS have been published by medical organizations during the past 6 years. Uncertainties about the clinical importance of iron overload and the necessity for iron chelation in transfusion-requiring patients with MDS have caused confusion for patients. Here, I summarize what we have learned and what we still do not know about the diagnosis, prognosis, monitoring and treatment of iron overload in patients with MDS, including the merits and drawbacks of the oral iron chelator, deferasirox. I also draw parallels between iron and radon with respect to the possibility of biological harm, lack of definitive study results, existence of groups at special risk, and fear that the ongoing uncertainties about these elements incite in patients.

Polyol pathway mediates iron-induced oxidative injury in ischemic-reperfused rat heart

Recent studies have shown that the polyol pathway is involved in ischemia-reperfusion (I/R)-induced myocardial infarction, but the mechanism is unclear. We previously found that lack of aldose reductase (AR), the first enzyme of the polyol pathway, attenuated the increase in transferrin (Tf) level in I/R brain, suggesting that AR contributes to iron-catalyzed free radical-induced damage. We therefore investigated if this mechanism occurs in I/R hearts. We found that inhibition of AR or sorbitol dehydrogenase (SDH), the second enzyme of the polyol pathway, both attenuated the I/R-mediated increases in HIF-1alpha, Tf, TfR, and intracellular iron content and reduced the I/R-induced infarct area of the heart. Further, administration of niacin, which replenishes NAD+, the cofactor for SDH, also normalized TfR and HIF-1alpha levels in I/R hearts. These results suggest that during I/R polyol pathway activity increases the cytosolic NADH/NAD+ ratio. This activates HIF-1alpha that induces the expression of TfR, which in turn increases Tf uptake and iron accumulation and exacerbates oxidative damage that increases the lipid peroxidation. This was confirmed by the fact that administration of the iron chelator deferoxamine attenuated the I/R-induced myocardial infarction.

Thiol-based mechanisms of the thioredoxin and glutaredoxin systems: implications for diseases in the cardiovascular system

Reactive oxygen species (ROS) and the cellular thiol redox state are crucial mediators of multiple cell processes like growth, differentiation, and apoptosis. Excessive ROS production or oxidative stress is associated with several diseases, including cardiovascular disorders like ischemia-reperfusion. To prevent ROS-induced disorders, the heart is equipped with effective antioxidant systems. Key players in defense against oxidative stress are members of the thioredoxin-fold family of proteins. Of these, thioredoxins and glutaredoxins maintain a reduced intracellular redox state in mammalian cells by the reduction of protein thiols. The reversible oxidation of Cys-Gly-Pro-Cys or Cys-Pro(Ser)-Tyr-Cys active site cysteine residues is used in reversible electron transport. Thioredoxins and glutaredoxins belong to corresponding systems consisting of NADPH, thioredoxin reductase, and thioredoxin or NADPH, glutathione reductase, glutathione, and glutaredoxin, respectively. Thioredoxin as well as glutaredoxin activities appear to be very important for the progression and severity of several cardiovascular disorders. These proteins function not only as antioxidants, they inhibit or activate apoptotic signaling molecules like apoptosis signal-regulating kinase 1 and Ras or transcription factors like NF-kappaB. Thioredoxin activity is regulated by the endogenous inhibitor thioredoxin-binding protein 2 (TBP-2), indicating an important role of the balance between thioredoxin and TBP-2 levels in cardiovascular diseases. In this review, we will summarize cardioprotective effects of endogenous thioredoxin and glutaredoxin systems as well as the high potential in clinical applications of exogenously applied thioredoxin or glutaredoxin or the induction of endogenous thioredoxin and glutaredoxin systems.

Enhanced NTPDase and 5'-nucleotidase activities in diabetes mellitus and iron-overload model

The activity of the enzymes NTPDase and 5'-nucleotidase was studied in both diabetes mellitus and an associated model of iron-overload. Rats were divided in five groups: citrate (CC), saline (S), diabetic (D), iron-overload (IO), and diabetic iron-overload (DIO). Diabetes was induced with alloxan (150 mg/kg), and iron-overload was induced with iron-dextran (10 intramuscular applications of +/-80 mg/kg). The enzymatic activities were evaluated in the platelets. The results demonstrated an increase in the activity of NTPDase with substrates ATP and ADP (60% and 120%, respectively; P<0.001), and 5'-nucleotidase (60%, P<0.001). This increase was more intense in the IO and DIO groups. The results obtained in vitro showed an activation in ATP, ADP, and AMP hydrolysis between 1 microM and 1,000 microM ferric nitrate concentrations, being more pronounced at 100 microM and decreasing at 1,000 microM. We concluded that diabetes mellitus in association with iron-overload increased the hydrolysis of adenine nucleotides in platelets, contributing to the abnormalities found in these pathological conditions.

Antioxidant and lysosomotropic properties of acute D-propranolol underlies its cardioprotection of postischemic hearts from moderate iron-overloaded rats

The benefits of acute D-propranolol (D-Pro, non-beta-adrenergic receptor blocker) pretreatment against enhanced ischemia/reperfusion (I/R) injury of hearts from moderate iron-overloaded rats were examined. Perfused hearts from iron-dextran-treated rats (450 mg/kg/week for 3 weeks, intraperitoneal administration) exhibited normal control function, despite iron treatment that elevated plasma iron and conjugated diene levels by 8.1-and 2.5-fold, respectively. However, these hearts were more susceptible to 25 mins of global I/R stress compared with non-loaded hearts; the coronary flow rate, aortic output, cardiac work, left ventricular systolic pressure, positive differential left ventricular pressure (dP/dt), and left ventricular developed pressure displayed 38%, 60%, 55%, 13%, 41%, and 15% lower recoveries, respectively, and a 6.5-fold increase in left ventricular end-diastolic pressure. Postischemic hearts from iron-loaded rats also exhibited 5.6-, 3.48-, 2.43-, and 3.45-fold increases in total effluent iron content, conjugated diene levels, lactate dehydrogenase (LDH) activity, and lysosomal N-acetyl-beta-glucosaminidase (NAGA) activity, respectively, compared with similarly stressed non-loaded hearts. A comparison of detection time profiles during reperfusion suggests that most of the oxidative injury (conjugated diene) in hearts from iron-loaded rats occurred at later times of reperfusion (8.5-15 mins), and this corresponded with heightened tissue iron and NAGA release. D-Pro (2 microM infused for 30 mins) pretreatment before ischemia protected all parameters compared with the untreated iron-loaded group; pressure indices improved 1.2- to 1.6-fold, flow parameters improved 1.70- to 2.96-fold, cardiac work improved 2.87-fold, and end-diastolic pressure was reduced 56%. D-Pro lowered total release of tissue iron, conjugated diene content, LDH activity, and NAGA activity 4.59-, 2.55-, 3.04-, and 4.14-fold, respectively, in the effluent of I/R hearts from the iron-loaded group. These findings suggest that the enhanced postischemic dysfunction and tissue injury of hearts from iron-loaded rats was caused by excessive iron-catalyzed free radical stress, and that the membrane antioxidant properties of D-Pro and its stabilization of sequestered lysosomal iron by D-Pro may contribute to the cardioprotective actions of D-Pro.

Ischemia-reperfusion of rat liver modulates hepcidin in vivo expression

The recently identified acute-phase response antimicrobial peptide hepcidin has been postulated to maintain iron homeostasis by modulating iron absorption at both the intestinal and macrophage levels. Hepcidin has also been reported to be responsible for anemia associated with chronic inflammatory diseases, and in anemia in patients with hepatic adenomas. Since Kupffer cells are known to be the primary contributor to early-phase ischemia-reperfusion injury in the liver and iron is known to modulate Kupffer cell production of proinflammatory cytokine and reactive oxygen species, we investigated hepcidin in vivo expression in the well-established rat partial-liver ischemia-reperfusion model. We found that both liver ischemia alone and liver ischemia-reperfusion significantly induced serum and liver hepcidin levels. Furthermore, currently proposed mediators of in vivo hepcidin expression, such as interleukin-6, signal transducers and activators of transcription-family transducers, and CCAAT/enhancing binding protein-alpha do not appear to modulate hepcidin expression in the liver ischemia-reperfusion acute inflammatory model. In this study we report the first in vivo evidence of liver ischemia and liver ischemia-reperfusion modulation of hepcidin expression. In conclusion, in the well-characterized liver ischemia-reperfusion model of acute inflammation, mechanism(s) other than interleukin-6 signal transduction via signal transducers and activators of transcription-3 may be responsible for hepcidin induction.

Liver cirrhosis as a consequence of iron overload caused by hereditary nonspherocytic hemolytic anemia

Nonspherocytic hereditary anemias are occasionally accompanied by significant iron overload but the significance for the development of chronic liver disease is not clear. We described two cases of patients with chronic liver disease and severe iron overload due to chronic hereditary hemolysis. Both patients have had signs of liver cirrhosis and severe hemolysis since childhood. A hereditary pyruvate kinase deficiency (PKD) was discovered as the underlying reason for the hemolysis. Sequencing of the pyruvate kinase gene showed a mutation within exon 11. Liver histology in both patients revealed cirrhosis and a severe iron overload but primary hemochromatosis was excluded by HFE-gene analysis. An iron reduction therapy with desferrioxamine led to significant decrease of serum ferritin and sustained clinical improvement. PKD-induced hemolysis may cause severe iron overload even in the absence of HFE-genotype abnormalities. This secondary iron overload can lead to chronic liver disease and cirrhosis. Therefore, the iron metabolism of PKD patients has to be closely monitored and iron overload should be consequently treated.

Iron-induced interleukin-6 gene expression: possible mediation through the extracellular signal-regulated kinase and p38 mitogen-activated protein kinase pathways

Increased iron store in the body may increase the risk of many diseases such as cancer and inflammation. However, the precise pathogenic mechanism of iron has not yet been elucidated. In the present study, the early biological responses of cells to iron treatment were investigated in AP-1 luciferase reporter stably transfected mouse epidermal JB6 cells and primary rat hepatocytes. It was shown that water-soluble iron compounds, such as FeSO4 and Fe2(SO4)3, were more active in inducing AP-1 in JB6 cells than water-insoluble iron compounds, such as Fe2O3 and FeS. Iron stimulated mitogen-activated protein kinase (MAPK) family members of extracellular signal-regulated kinases (ERKs) and p38 MAPK but not c-jun NH2 terminal kinases (JNKs), both in JB6 cells and in primary rat hepatocytes, as determined by the phosphorylation assay. Interestingly, the increase in AP-1 luciferase activity by iron was inhibited by the pretreatment of the cells with PD98059, a specific MEK1 inhibitor, and SB202190, a p38 kinase inhibitor. Levels of interleukin-6 (IL-6), a pro-inflammatory cytokine, were increased in JB6 cells by iron in a dose-dependent manner. The increase in IL-6 and its mRNA by iron was also eliminated by the pretreatment of the cells with PD98059 and SB202190. Since the IL-6 promoter contains an AP-1 binding site, our studies indicate that the iron-induced IL-6 gene expression may be mediated through ERKs and p38 MAPK pathways, possibly one of the important mechanisms for the pathogenesis of iron overload.

Hydroxyl radical oxidation of cytochrome c by aerobic radiolysis

The reaction of radiolytically generated *OH with cytochrome c was investigated by mass spectrometry. Tryptic digestion and characterization of the oxidized peptides by MALDI-TOF and ESI tandem mass spectrometry identified eight different amino acid residues with oxidized side chains with no cleavage of the protein detected. Solvent-accessible aromatic and methionine residues are the most susceptible to oxidation by *OH. These results support the careful use of *OH in characterizing protein surfaces. Dose-response studies identified the residues most prone to oxidation to be Phe-36, Phe-46, and Met-80. Hydroxylation of Phe-36 and Phe-46 should serve as indicators of the presence of *OH in the mitochondrial intermembrane space. Using solutions containing 50 at.% (18)O, our study also provides a novel method of determining the source of oxygen during *OH-mediated oxidation of proteins and contributes to identification of the modified residue type, with Phe>Tyr>Met in (18)O incorporation. During aerobic radiolysis, UV-vis spectroscopy indicates that ferrocytochrome c reaches a steady state concomitant with reduction of the heme.

Asialoglycoprotein receptor facilitates hemolysis in patients with alcoholic liver cirrhosis

Hemolysis in patients with advanced alcoholic liver disease is a common clinical problem and indicates an unfavorable prognosis. In many cases, the etiology of the hemolysis remains unknown. We observed three patients with alcoholic liver disease, suffering from severe hemolytic anemia, requiring multiple blood transfusions. Steroid therapy was ineffective and two of the patients died. All patients had a soluble variant of the human asialoglycoprotein receptor (s-ASGP-R) in their serum, as well as high titers of autoantibodies against this receptor (anti-ASGP-R). Consecutively, examination of 60 patients with alcoholic liver disease revealed a high incidence for s-ASGP-R (36%) and anti-ASGP-R (27%) in patients with alcoholic liver cirrhosis (ALC) compared to patients with cirrhosis due to viral hepatitis. The potential etiology of hemolysis was studied in vitro on erythrocytes from patients with ALC and from healthy donors. Isolated ASGP-R but not anti-ASGP-R bound to the surface of erythrocytes preferentially of blood group A1 and caused dose-dependent agglutination and hemolysis, while this phenomenon was much lower using erythrocytes of the blood group B and almost absent with blood group O-erythrocytes. Furthermore, agglutination and hemolysis only occurred in erythrocytes from ALC-patients or after the pre-treatment of cells with neuraminidase. ASGP-R induced agglutination and hemolysis was blocked by the competitive ASGP-R inhibitor asialofetuin. In conclusion, our results indicate a new, non-immunological mechanism for hemolysis in patients with alcoholic liver disease, mediated through agglutination by a soluble variant of the human asialoglycoprotein receptor and mechanical shear stress.

Molecular changes in normal appearing white matter in multiple sclerosis are characteristic of neuroprotective mechanisms against hypoxic insult

Multiple sclerosis is a chronic inflammatory disease of the CNS leading to focal destruction of myelin, still the earliest changes that lead to lesion formation are not known. We have studied the gene-expression pattern of 12 samples of normal appearing white matter from 10 post-mortem MS brains. Microarray analysis revealed upregulation of genes involved in maintenance of cellular homeostasis, and in neural protective mechanisms known to be induced upon ischemic preconditioning. This is best illustrated by the upregulation of the transcription factors such as HIF-1alpha and associated PI3K/Akt signalling pathways, as well as the upregulation of their target genes such as VEGF receptor 1. In addition, a general neuroprotective reaction against oxidative stress is suggested. These molecular changes might reflect an adaptation of cells to the chronic progressive pathophysiology of MS. Alternatively, they might also indicate the activation of neural protective mechanisms allowing preservation of cellular and functional properties of the CNS. Our data introduce novel concepts of the molecular pathogenesis of MS with ischemic preconditioning as a major mechanism for neuroprotection. An increased understanding of the underlying mechanisms may lead to the development of new more specific treatment to protect resident cells and thus minimize progressive oligondendrocyte and axonal loss.

New biomarkers of fetal-neonatal hypoxic stress

The complex pathophysiological mechanisms underlying perinatal hypoxia make it difficult to define early markers of severe hypoxia-ischemia encephalopathy. However, as progress in the development of neuroprotective therapeutic measures continues, the early identification of neonates at risk of severe hypoxic-ischemic encephalopathy is an important goal for appropriate decision making. Although the timing of perinatal hypoxic brain damage may vary and is sometimes unknown, high levels of non-protein-bound iron and high nucleated red blood cell counts in cord blood indicate an antepartum origin of neurological impairment, because they can occur only as a consequence of a pre-existing asphyxic event.

CONCLUSION

The combined assessment of nucleated red blood cells and non-protein-bound iron at birth seems extremely useful for the early identification of newborns at high risk of brain damage. Activin A also seems to be a reliable marker of perinatal hypoxia. Prospective long-term follow-up studies are needed to verify their predictive role.

Deferoxamine promotes survival and prevents electrocardiographic abnormalities in the gerbil model of iron-overload cardiomyopathy

We investigated the time course of electrocardiographic (ECG) changes in the Mongolian gerbil model of iron overload and the effects of the iron chelator deferoxamine (DFO) on these changes. Iron overload was produced with weekly subcutaneous injections of low doses (200 mg/kg/wk) or high doses (800 mg/kg/wk) of iron-dextran. DFO was administered subcutaneously at a dose of 200 mg/kg/day to high-dose animals. Our results show that (1) survival of iron-overloaded gerbils is dose-dependent, with median survival times of 68 and 14 weeks for low- and high-dose animals, respectively; (2) both low and high doses produce prolongation of the PR interval and bradycardia in early stages and prolongation of the QT interval, premature ventricular contractions, variable degrees of atrioventricular block, changes in the ST segment, and T-wave inversion at later stages coinciding with the development of heart failure; (3) DFO prevented death during 20 weeks of high-dose iron-dextran; (4) DFO prevented ECG changes, although delayed prolongation of PR intervals and QRS complexes occurred; and (5) despite marked prolongation of survival and prevention of ECG changes, DFO had modest effects on total cardiac iron content. We speculate that DFO chelates a small iron pool located within the cytoplasm of iron-overloaded cardiomyocytes.

Serum ferritin levels and early prognosis of stroke

Iron and ferritin are known to have an important role in stroke as well as in other disorders. This prospective study was designed to determine whether administering ferritin levels might help to estimate the severity and prognosis of stroke. Fifty-one patients with a diagnosis of acute stroke were included in the study within 24 h from onset of symptoms. Serum ferritin and cortisol levels were assayed at admission. Clinical status was determined by the Canadian Stroke Scale at admission and on day 21. Serum ferritin level was found to be higher in patients with large lesion size (P < 0.01), deteriorated neurologic status during clinical follow-up (P = 0.03) and deceased patients (P < 0.01). Serum ferritin level was correlated with neurologic deficit (r = 0.50, P < 0.001). No correlation was found between serum cortisol and ferritin levels (r = 0.07, P = 0.7). Serum ferritin level (P = 0.007; OR = 1.02; 95% CI, 1.01-1.03) and large size of lesion (P = 0.021, OR = 11.92; 95% CI; 1.46-197.12) were independently associated with mortality. Increased serum ferritin levels correlate to severity of stroke and the size of the lesion.

Oxidation of biological systems: oxidative stress phenomena, antioxidants, redox reactions, and methods for their quantification

Reactive oxygen species (ROS) and other radicals are involved in a variety of biological phenomena, such as mutation, carcinogenesis, degenerative and other diseases, inflammation, aging, and development. ROS are well recognized for playing a dual role as deleterious and beneficial species. The objectives of this review are to describe oxidative stress phenomena, terminology, definitions, and basic chemical characteristics of the species involved; examine the biological targets susceptible to oxidation and the defense mechanisms of the organism against these reactive metabolites; and analyze methodologies, including immunohistochemical markers, used in toxicological pathology in the visualization of oxidative stress phenomena. Direct detection of ROS and other free radicals is difficult, because these molecules are short-lived and highly reactive in a nonspecific manner. Ongoing oxidative damage is, thus, generally analyzed by measurement of secondary products including derivatives of amino acids, nuclei acids, and lipid peroxidation. Attention has been focused on electrochemical methods based on voltammetry measurements for evaluating the total reducing power of biological fluids and tissues. This approach can function as a tool to assess the antioxidant-reducing profile of a biological site and follow changes in pathological situations. This review thus includes different topics essential for understanding oxidative stress phenomena and provides tools for those intending to conduct study and research in this field.

Bimodal cardiac dysfunction in an animal model of iron overload

Iron-overload cardiomyopathy is the most common cause of death in patients with thalassemia major, yet the associated changes in cardiac function have not been quantified. We studied the effects of iron overload on cardiac function in Mongolian gerbils, a species that responds to iron overload in the same manner as human beings. We injected iron-dextran or dextran alone at low subcutaneous doses (200 mg/kg/wk) for 20 to 60 weeks and at high doses (800 mg/kg/wk) for 6 to 20 weeks. At shorter durations for either dose, the mean values of cardiac work, coronary flow, left ventricular (dP/dt)(max) and left ventricular (dP/dt)(min) in isolated perfused hearts were significantly greater than control values; at longer durations, these values were significantly less than control values. Echocardiography in intact animals showed eccentric cardiac hypertrophy, increased cardiac output, and normal exercise tolerance at shorter durations of dosage. At longer durations, concentric cardiac hypertrophy developed, and cardiac output and exercise capacity were impaired. The response to iron overload in Mongolian gerbils progresses from an initial state of high cardiac output to a subsequent state of low-output failure similar to the course of cardiomyopathy that has been inferred in patients with transfusional iron overload.

Investigations into the systemic production of aldehyde-derived peroxidation products in a murine model of acute iron poisoning: a dose response study

Acute iron poisoning remains a leading cause of morbidity and mortality in pre-school aged children in North America. Acute iron poisoning leads to organ damage, such as respiratory difficulties, cardiac arrhythmias, and possible death. The mechanism of iron toxicity is not fully understood, though it is thought that free iron is able to catalyze the production of harmful oxygen free radicals, which can damage all biochemical classes including lipid membranes, proteins, and DNA. Accordingly, we hypothesized that acute iron loading results in dose-dependent increases in oxygen free radical production, as quantified by the cytotoxic aldehydes hexanal, 4-hydroxynonenal, and malondialdehyde, in an experimental murine model. In support of our hypothesis, significant dose-dependent increases in all aldehydes investigated were reported in comparison to controls (p < 0.001). This murine model will assist in providing a better understanding of possible mechanism(s) of injury and organ dysfunction following acute iron poisoning, and for the development and evaluation of treatment regimes.

The role of Doppler left ventricular filling indexes and Doppler tissue echocardiography in the assessment of cardiac involvement in hereditary hemochromatosis

Although cardiac dysfunction in hereditary hemochromatosis (HHC) can be evaluated by conventional echocardiography, findings are often not specific. To test the hypothesis that the assessment of (1) conventional Doppler left ventricular filling indexes and (2) intrinsic elastic properties of the myocardium by Doppler tissue echocardiography can both enhance the accuracy of echocardiographic diagnosis of cardiac involvement in HHC, a group of 18 patients with HHC (mean age 50 +/- 17 years) and 22 age-matched healthy subjects were studied. The following indexes were characteristic for HHC: (1) the duration of atrial reversal measured from pulmonary venous flow (ms) was longer (118 +/- 20 vs 90 +/- 16; P <.001); (2) systolic lateral mitral, early-diastolic medial mitral, and early-diastolic lateral tricuspid annular velocities were reduced by 23%, 31%, and 13%, respectively; (3) late-diastolic mean myocardial velocity and myocardial velocity gradient (MVG) were also reduced by 22% and 34%, respectively. Late-isovolumic relaxation (late-IVR) MVG (s(-1)) was positive in HHC as opposed to negative in healthy subjects (1.72 +/- 0.85 vs -0.89 +/- 1.15; P <.001) indicating impaired early-diastolic subepicardial relaxation in HHC. The assessment of atrial reversal flow duration, the difference in duration between A-wave and atrial reversal flow, and the presence of positive late IVR-MVG findings were the most accurate variables to differentiate patients with HHC from healthy subjects (80%, 67%, 94% sensitivity and 90%, 95%, 86% specificity, respectively).

Regulation, mechanisms and proposed function of ferritin translocation to cell nuclei

Ferritin is traditionally considered a cytoplasmic iron-storage protein,but recent reports indicate that it is also found in cell nuclei. Nuclear ferritin has been proposed to be involved in both the protection of DNA and the exacerbation of iron-induced oxidative damage to DNA. We demonstrate that H-rich ferritin is present in the nucleus of human astrocytoma tumor cells. To study the mechanism and regulation of ferritin translocation to the nucleus,we developed a cell culture model using SW1088 human astrocytoma cells. Changes in cellular iron levels, cytokine treatments and hydrogen peroxide exposure affected the distribution of ferritin between the cytosol and the nucleus. Ferritin enters the nucleus via active transport through the nuclear pore and does not require NLS-bearing cytosolic factors for transport. Furthermore, H-rich ferritin is preferred over L-rich ferritin for uptake into the nucleus. Whole cell crosslinking studies revealed that ferritin is associated with DNA. Ferritin protected DNA from iron-induced oxidative damage in both in vitro and in cell culture models. These results strongly suggest a novel role for ferritin in nuclear protection. This work should lead to novel characterization of ferritin functions in the context of genomic stability and may have unparalleled biological significance in terms of the accessibility of metals to DNA. The knowledge generated as a result of these studies will also improve our understanding of iron-induced damage of nuclear constituents.

Amlodipine decreases iron uptake and oxygen free radical production in the heart of chronically iron overloaded mice

Hereditary hemochromatosis is a disorder of iron metabolism, which is currently the most prevalent autosomal recessive disorder in the world, with an expression of the homozygous form occurring in approximately 1 in 200 individuals of European descent. Approximately one third of patients with hemochromatosis die of iron-induced cardiac complications. Although the exact mechanism is not known, it is believed that the toxicity of excess iron in biological systems is due to its ability to catalyze the generation of harmful reactive oxygen free radical species (ROS), which can damage proteins, lipids, and DNA. There is preliminary evidence to suggest that non-transferrin-bound iron uptake in the myocardium may occur through voltage-dependent L-type calcium channels, and that calcium channel blockers (CCBs) may possess antioxidant properties. Accordingly, the authors hypothesized that the administration of amlodipine besylate would (1) decrease iron uptake in the myocardium and (2) decrease oxygen free radical production as measured by cytotoxic aldehyde-derived peroxidation products in a murine model of iron overload cardiomyopathy. The findings show that the CCB amlodipine is partially effective in limiting iron uptake in the heart and significantly inhibits the production of ROS in chronically iron-loaded mice. These are important preliminary findings because they suggest that CCBs may have significance in the clinical management of genetic disorders of iron metabolism.

Decreasing effects of iron toxicosis on selenium and glutathione peroxidase activity

Heart failure due to chronic iron overload is a leading cause of cardiovascular mortality in the second and third decades of life worldwide, but its mechanism is not known. Deficiencies of selenium have been shown to result in damage to the myocardium and to the development of various cardiomyopathies. In the current investigation, the dose-dependent effects of chronic iron toxicosis on heart tissue concentrations of selenium and the protective antioxidant enzyme glutathione peroxidase (GPx) were investigated in a murine model of iron-overload cardiomyopathy (n = 20). Significant dose-dependent decreases in heart tissue selenium concentrations (r = -0.95, p < 0.001) and selenium-dependent GPx activity (r = -0.93, p < 0.001) were observed in chronically iron-loaded mice in comparison with placebo controls. These results suggest that dietary supplementation with selenium may be beneficial in the clinical management of disorders of iron metabolism.

Ferrous ion autoxidation and its chelation in iron-loaded human liver HepG2 cells

Ferrous ion (Fe(2+)) is long thought to be the most likely active species, producing oxidants through interaction of Fe(2+) with oxygen (O(2)). Because current iron overload therapy uses only Fe(3+) chelators, such as desferrioxamine (DFO), we have tested a hypothesis that addition of a Fe(2+) chelator, 2,2'-dipyridyl (DP), may be more efficient and effective in preventing iron-induced oxidative damage in human liver HepG2 cells than DFO alone. Using ferrozine as an assay for iron measurement, levels of cellular iron in HepG2 cells treated with iron compounds correlated well with the extent of lipid peroxidation (r = 0.99 after log transformation). DP or DFO alone decreased levels of iron and lipid peroxidation in cells treated with iron. DFO + DP together had the most significant effect in preventing cells from lipid peroxidation but not as effective in decreasing overall iron levels in the cells. Using ESR spin trapping technique, we further tested factors that can affect oxidant-producing activity of Fe(2+) with dissolved O(2) in a cell-free system. Oxidant formation enhanced with increasing Fe(2+) concentrations and reached a maximum at 5 mM of Fe(2+). When the concentration of Fe(2+) was increased to 50 mM, the oxidant-producing activity of Fe(2+) sharply decreased to zero. The initial ratio of Fe(3+):Fe(2+) did not affect the oxidant producing activity of Fe(2+). However, an acidic pH (< 3.5) significantly slowed down the rate of the reaction. Our results suggest that reaction of Fe(2+) with O(2) is an important one for oxidant formation in biological system, and therefore, drugs capable of inhibiting redox activity of Fe(2+) should be considered in combination with a Fe(3+) chelator for iron overload chelation therapy.

Preliminary study on the distribution of selected elements in cancerous and non-cancerous kidney tissues

In this study special interest was given to trace elements recognized as to be carcinogenic to humans. The kidney tissue sections were analyzed in order to determine the concentrations of elements present in the sample. The Synchrotron Radiation Induced X-ray Emission (SRIXE) technique was applied using a white photon microbeam. The results from cancerous parts of the kidney tissues were compared to non-cancerous parts and to the control group. In addition the iron concentration level was determined in the serum of those patients. Two-dimensional scans are presented to illustrate the differences between perfused and not-perfused tissues. According to this study there is no significant difference in the Mn concentration between cancerous and non-cancerous parts of the kidney, but the concentrations of Cd, Cr, Ti, V, Cu, Se, and Zn are at a lower concentration level in the cancerous parts than in the non-cancerous parts. A converse observation has been made for Fe. This may be associated with different metabolism and dynamics of the cancer process and both higher vascularization and need of higher blood supply in the cancerous tissue. The two-dimensional scanning of thin kidney sections showed differences in the trace element distributions depending on the analyzed samples: perfused and non-perfused. Perfusion removed blood mostly from the peritubular capillaries while in the glomerulus some capillaries had a relatively high Fe content. A low Fe concentration was observed in nephron tubules while a converse observation has been made for Cd. This may indicate that Cd is localized in the cells but not in the blood.

Erythropoiesis: Comparison of Cytotoxic Aldehyde Generation in Beta-Thalassemia Patients Chelated with Deferoxamine or Deferiprone (L1) Versus NO Chelation

The mechanism of iron-induced organ failure in iron overload disorders is not known, but it is conjectured that excess iron-catalyzed free radical generation contributes to organ damage. We hypothesized that free radical generation, quantified by the presence of 20 separate cytotoxic aldehydes in plasma, would be significantly increased in non-chelated beta-thalassemia major patients, in comparison to those chelated with either deferiprone (L1) or deferoxamine (desferal). We also report on red cell glutathione peroxidase activity in these patient groups, an enzyme involved in averting the damaging effects of free radicals. Ten patients were chelated with nightly subcutaneous infusions of desferal and 10 received the experimental oral chelator L1. Body iron burden was assessed by serum ferritin and hepatic iron concentrations. In comparison to non-chelated controls, significant decreases of 62% and 64% in total cytotoxic aldehyde concentrations were observed in patients chelated with desferal and L1, respectively (p < 0.001). Significantly lower red cell glutathione peroxidase activity was also observed in non-chelated controls, in comparison to those chelated with either desferal or L1 (p < 0.001). This is the first report on the concentrations of cytotoxic aldehydes in non-chelated beta-thalassemia major patients, and the first to report on the effects of L1 against cytotoxic aldehyde formation in plasma of patients with iron-overload.

Selenium and glutathione peroxidase with beta-thalassemia major

BACKGROUND

Chronic iron-overload is a major cause of organ failure and mortality worldwide, but its pathogenesis remains to be elucidated.

OBJECTIVES

To examine the relationship between various measures of body iron burden, selenium concentrations and glutathione peroxidase (GPx) activity in patients with beta-thalassemia major.

METHODS

An age- and gender-matched case control study was conducted to examine the relationship between various measures of body iron burden (serum ferritin, transferrin saturation, total serum iron), plasma concentrations of selenium and glutathione peroxidase (GPx) activity in patients with homozygous beta-thalassemia major (N = 20) and healthy controls (N = 10). Ten patients received the experimental oral chelator L1 and ten received chelation therapy with subcutaneous desferal.

RESULTS

Significantly decreased plasma concentrations of selenium (microg/L) were observed in patients chelated with L1 (1.4 +/- 0.2) or desferal (1.4 +/- 0.1), in comparison to healthy controls (1.8 +/- 0.1, p < 0.01). Significantly decreased plasma activity of GPx (microg/L) was observed in patients chelated with L1 (166 +/- 43) or desferal (178 +/- 46), in comparison to healthy controls (296 +/- 22, p < 0.001). Significantly increased concentrations of all measures of body iron burden were observed in beta-thalassemia patients, in comparison to healthy controls (p < 0.001).

CONCLUSION

Patients with beta-thalassemia major and chronic iron-overload have decreased concentrations of the essential element selenium and the protective selenium-dependent antioxidant enzyme GPx. Additional research examining the effects of dietary antioxidant supplementation with selenium on these aforementioned parameters in patients with beta-thalassemia major and iron-overload is warranted.

Sensitive method for nontransferrin-bound iron quantification by graphite furnace atomic absorption spectrometry

OBJECTIVE

To establish a sensitive method for measuring nontransferrin-bound iron (NTBI) in serum samples using graphite furnace atomic absorption spectrometry (GFAAS).

DESIGN AND METHODS

Nontransferrin-bound iron (NTBI) was chelated using nitrilotriacetic acid (NTA) and then ultrafiltered according to the method employed by Singh et al. [1]. Serum ultrafiltrates were diluted eightfold with distilled water. NTBI from the Fe-NTA complex present in the serum ultrafiltrate was measured using GFAAS.

RESULTS

Nontransferrin-bound iron (NTBI) and other parameters were measured in seven patients diagnosed with hereditary hemochromatosis by liver biopsy. Total serum iron, NTBI and transferrin saturation values (ranging from 87% to 90%) were elevated for three of the seven hemochromatosis patients tested before therapeutic phlebotomy. Six of the seven hemochromatosis patients had undergone phlebotomy and revealed normal total serum iron, NTBI and transferrin saturation values. Nine test subjects (not diagnosed with hemochromatosis) with abnormally high total serum iron and/or ferritin concentrations exhibited normal NTBI values (< or =0.14 micromol/L to 0.29 micromol/L). The detection limit was 0.1 micromol/L for a 25 microL injection volume.

CONCLUSIONS

The GFAAS method presented here provides a sensitive assay to quantitate NTBI in serum samples. The method developed is 4 to 5 times more sensitive than the only other GFAAS method [2] and more than an order of magnitude more sensitive than other colorimetric methods [1,3]. Improvement in sensitivity over the other GFAAS method [2] may be accounted for by differences in sample preparation between this method and that of Nielsen et al. [2]. Serum ultrafiltrates in this study were diluted eightfold with distilled water and mixed with a magnesium nitrate matrix modifier before GFAAS analysis. NTBI results obtained from this study indicate that the plasma iron pool in hemochromatosis patients awaiting phlebotomy increases to a level at which transferrin's ability to bind iron becomes exhausted and elevated NTBI levels appear in the serum. NTBI can mediate the production of reactive oxygen species and may cause organ damage associated with iron overload.

Systemic oxygen-free radical production in iron-loaded mice

Although iron is an essential element for normal cell metabolism, in excess quantities it is highly cytotoxic and lethal. In fact, acute iron poisoning is a leading cause of overdose mortality in young children. Hereditary hemochromatosis, a disorder of iron metabolism, is currently the most prevalent genetic disorder in the world, which results in organ failure and premature mortality. Hence, an enhanced understanding of its pathogenesis is critical for providing safe and effective nursing care to affected individuals and their families. Although the exact mechanism of iron's toxicity is not known, it was hypothesized that chronic iron loading would result in increased tissue (heart, liver, and spleen) concentrations of iron and increased free radical production in a murine model (n = 20). Our results show that chronic iron loading results in highly significant dose-dependent increases in tissue concentrations of iron and systemic free radical generation (p < 0.001).

Iron-overload cardiomyopathy: evidence for a free radical--mediated mechanism of injury and dysfunction in a murine model

Iron-overload cardiomyopathy is a restrictive cardiomyopathy that manifests itself as systolic or diastolic dysfunction secondary to increased deposition of iron in the heart and occurs with common genetic disorders such as primary hemochromatosis and beta-thalassemia major. Although the exact mechanism of iron-induced heart failure remains to be elucidated, the toxicity of iron in biological systems is believed to be attributed to its ability to catalyze the generation of oxygen-free radicals. In the current investigation, the dose-dependent effects of chronic iron-loading on heart tissue concentrations of iron, glutathione peroxidase (GPx) activity, free-radical production, and cardiac dysfunction were investigated in a murine model of iron-overload cardiomyopathy. It was shown that chronic iron-overload results in dose-dependent (a) increases in myocardial iron burden, (b) decreases in the protective antioxidant enzyme GPx activity, (c) increased free-radical production, and (d) increased mortality. These findings show that the mechanism of iron-induced heart dysfunction involves in part free radical-mediated processes.

Cytotoxic aldehyde generation in heart following acute iron-loading

Although the mechanism of myocardial failure following acute iron poisoning is not known, excess iron-catalyzed free radical generation is conjectured to play a role. The effects of time (0 to 360 minutes) on total iron concentrations, glutathione peroxidase activity, and cytotoxic aldehyde production in heart of mice (B6D2F1, n = 65) were first investigated following acute iron-loading (20 mg iron dextran i.p./mouse). In a subsequent experiment, the effects of dose (0 to 80 mg iron dextran i.p./mouse, n = 75) on the aforementioned parameters were investigated. Our results show that the concentrations of cytotoxic aldehydes: (1) significantly differ over-time, with corresponding increases in total concentrations of iron (r = 0.93, p < 0.001); and (2) increase parallel to the total dose of iron administered (r = 0.95, p < 0.001). Furthermore, dose-and time-dependent alterations to glutathione peroxidase activity are observed, which is most likely due to an acute up-regulation of the enzyme as an endogenous protective response to increased free radical activity in the heart subsequent to iron-loading. While no single mechanism is likely to account for the complex pathophysiology of acute iron-induced heart failure, our results shown that iron-loading can result in significant free radical generation, as quantified by cytotoxic aldehydes, in heart tissue of mice. This is the first report on the effects of time and dose on cytotoxic aldehyde generation and glutathione peroxidase activity in heart of mice following acute iron-loading.

A biochemical, histochemical, and electron microscopic study on the effects of iron-loading on the hearts of mice

Acute iron poisoning and chronic iron overload are well-known causes of myocardial failure. Although the exact mechanism is not known, excess iron-catalyzed free radical generation is conjectured to play a role in damaging the myocardium and altering cardiac function. We report here on the effects of acute and chronic iron-loading on the total iron concentration, glutathione peroxidase activity, and cytotoxic aldehyde production in the heart of a murine model (n = 35). Light microscopic examination for the presence of ferrous and ferric iron was undertaken following histochemical staining for these species. In addition, examination of representative samples by transmission electron microscopy was performed. Our findings show that iron-loading can result in significant increases in total iron concentrations, alterations to glutathione peroxidase activity, and increases in cytotoxic aldehyde concentrations in the hearts of mice. Furthermore, we observe that iron-loading can significantly alter and damage various cellular constituents (e.g., mitochondria, lysosomes, sarcoplasmic reticulum) and this may have bearing on the mechanism of iron-induced heart failure.

Changes in iron histochemistry after hypoxic-ischemic brain injury in the neonatal rat

Iron can contribute to hypoxic-ischemic brain damage by catalyzing the formation of free radicals. The immature brain has high iron levels and limited antioxidant defenses. The objective of this study was to describe the early alterations in nonheme iron histochemistry following a hypoxic-ischemic (HI) insult to the brain of neonatal rats. We induced a HI insult to the right cerebral hemisphere in groups of 7-day-old rats. Rats were anesthetized, then their brains were perfused and fixed at 0, 1, 4, 8, 24 hr, and 1, 2, and 3 weeks of recovery. Forty-micron-thick frozen sections were stained for iron using the intensified Perls stain. Increased iron staining was first detected within the cytoplasm of cells with pyknotic nuclei at 4 hr of recovery. Staining increased rapidly over the first 24 hr in regions of ischemic injury. By 7 days recovery, reactive glia and cortical blood vessels also stained. Increased staining in gray matter persisted at 3 weeks of recovery, whereas white matter tracts had fewer iron-positive cells compared to normal. The early increase in iron staining could be caused by an accumulation of iron posthypoxicischemic injury or a change in iron from nonstainable heme iron to stainable nonheme iron. Regardless of the source, our results indicate that there is an increase in iron available to promote oxidant stress in the neonatal rat brain following hypoxia-ischemia.

Iron-mediated cardiotoxicity develops independently of extracellular hydroxyl radicals in isolated rat hearts

BACKGROUND

Myocardial iron toxicity is often attributed to free radical damage. Present studies examine the role of extracellular hydroxyl radical formation in this process.

METHODS

In vitro reactions examined the rate of hydroxyl radical formation using salicylate trapping with high-pressure liquid chromatography separation and electrochemical detection of 2,3- and 2,5- dihydroxybenzoic acid. Isolated rat hearts were perfused by the Langendorff technique under the same buffer conditions to determine changes in myocardial contractility, release of tissue lactate dehydrogenase activity, and formation of lipid peroxidation products when iron was added to the perfusate with or without the formation of extracellular radicals.

RESULTS

In vitro reactions, performed in Krebs buffer alone or with addition of iron (25 microM), produced levels of hydroxyl radicals that were nondetectable with salicylate trapping. Addition of iron/ascorbate (FeSO4 = 25 microM, ascorbate = 1 mM), or iron/ascorbate/histidine (FeSO4 = 25 microM, ascorbate = 1 mM, histidine = 15 mM) produced significant and equivalent accumulation of hydroxyl radicals. Isolated rat hearts were perfused under the same 4 conditions. Control heart contractile function was stable with little release of lactate dehydrogenase activity and low levels of thiobarbituric acid reactive substances (TBARS). There was significant and equal injury to contractile function, release of lactate dehydrogenase activity, and accumulation of TBARS in hearts in the presence (iron/ascorbate) and absence (iron alone) of extracellular hydroxyl radicals. In addition, there was significant reduction in injury with iron/ascorbate/histidine, where the formation of extracellular hydroxyl radicals was equal to those observed with iron/ascorbate alone. Additional control hearts, perfused with histidine alone, showed stable heart function.

CONCLUSIONS

These findings indicate that the extracellular formation of hydroxyl radicals is not responsible for iron-mediated cardiotoxicity.

Preclinical cardiac dysfunction in transfusion-dependent children and young adults detected with low-dose dobutamine stress echocardiography

Transfusion-dependent (TD) patients develop cardiac iron overload that will eventually lead to cardiac pump failure. Low-dose dobutamine stress echocardiography may complement resting echocardiography and identify preclinical myocardial dysfunction caused by early cardiac hemosiderosis. Twenty-six iron-overloaded TD patients had stress echocardiography with 5 microg/kg per minute of dobutamine. Indexed left ventricular (LV) mass, LV dimensions, meridional wall stress, and cardiac index were significantly increased. TD patients had similar LV shortening fraction by M-mode (40.5% +/- 5.6% vs 39.4% +/- 4.5%) but had a lower mean LV ejection fraction (53.3% +/- 3.9% vs 46.8% +/- 6.9%, P < .002) and a subnormal increase in cardiac index during dobutamine stress (35% +/- 20% vs 11% +/- 16%, P < .0001). Impairment in LV relaxation was demonstrated by a prolonged isovolumetric relaxation time (0.060 +/- 0.005 vs 0.088 +/- 0.019 seconds, P < .0001), increased peak mitral E wave, and abnormal E/A ratio. Asymptomatic TD patients demonstrate decreased systolic functional reserve and abnormal left ventricular relaxation that may be caused by cardiac hemosiderosis. Low-dose dobutamine stress echocardiography may be useful for detecting and following cardiac dysfunction in patients at risk for cardiac hemosiderosis.

Oxidative damage to sarcoplasmic reticulum Ca2+-ATPase AT submicromolar iron concentrations: evidence for metal-catalyzed oxidation

The sarcoplasmic reticulum (SR) calcium ATPase carries out active Ca2+ pumping at the expense of ATP hydrolysis. We have previously described the inhibition of SR ATPase by oxidative stress induced by the Fenton reaction (Fe2+ + H2O2 --> HO. + HO- + Fe3+). Inhibition was not related to peroxidation of the SR membrane nor to oxidation of ATPase thiols, and involved fragmentation of the ATPase polypeptide chain. The present study aims at further characterizing the mechanism of inhibition of the Ca2+-ATPase by oxygen reactive species at Fe2+ concentrations possibly found in pathological conditions of iron overload. ATP hydrolysis by SR vesicles was inhibited in a dose-dependent manner by micromolar concentrations of Fe2+, H2O2, and ascorbate. Measuring the rate constants of inactivation (k inact) at different Fe2+ concentrations in the presence of saturating concentrations of H2O2 and ascorbate (100 microM each) revealed a saturation profile with half-maximal inactivation rate at ca. 2 microM Fe2+. Inhibition was not affected by addition of 200 microM Ca2+ to the medium, indicating that it was not related to iron binding to the high affinity Ca2+ binding sites in the ATPase. Furthermore, inhibition was not prevented by the water-soluble hydroxyl radical scavengers mannitol or dimethylsulfoxide, nor by butylated hydroxytoluene (a lipid peroxidation blocker) or dithiothreitol (DTT). However, when Cu2+ was used instead of Fe2+ in the Fenton reaction, ATPase inhibition could be prevented by DTT. We propose that functional impairment of the Ca2+-pump may be related to oxidative protein fragmentation mediated by site-specific Fe2+ binding at submicromolar or low micromolar concentrations, which may occur in pathological conditions of iron overload.

Differential induction of polyamine oxidase activity in liver and heart of iron-overloaded rats

The present study was undertaken to investigate the effect of iron dextran treatment on polyamine oxidase (PAO) activity, iron accumulation, and lipid peroxidation in livers and hearts of rats. PAO catalyzes oxidative deamination of polyamines, the cellular aliphatic cations. This reaction produces highly toxic hydrogen peroxide, 3-acetamidopropanal, and precursors of higher polyamines. The rats were given iron dextran daily for 7 d. In iron-dextran-treated rats, a marked increase in the hepatic level of iron was associated with enhanced lipid peroxidation and increased PAO activity. Though iron accumulation and lipid peroxidation in the iron-treated rats increased significantly in the heart, PAO activity remained unchanged. The paraffin sections of livers stained with Perls iron stain showed the presence of iron in macrophages and hepatocytes. The sections of hearts showed iron deposits only in macrophages, while myocytes showed no iron staining. These results show that although iron dextran treatment results in accumulation of iron in both liver and heart, it induces PAO activity only in liver. The significance of increased PAO activity in lipid peroxidation and fibrosis in iron-mediated injury is discussed.