Iron-induced Oxidative Damage Research Articles

Cellular distribution of ferritin subunits in postnatal rat brain

The normal development of the brain requires finely coordinated events, many of which require iron. Consequently, iron must be available to the brain in a timely manner and in a bioavailable form. However, the brain also requires stringent mechanisms to protect itself from iron-induced oxidative damage. The protein that is best suited to making iron available but also adequately protecting the cell is the intracellular iron storage protein ferritin. Typically, ferritin is composed of 24 subunits of H and L chains, which are functionally distinct. This study was undertaken to determine the expression of ferritin subunits during normal development of the postnatal rat brain. There is a shift in ferritin-containing cell types during development from predominantly microglia at postnatal day 5 (PND 5) to predominantly oligodendrocytes by PND 30. At PND 5, microglia are found throughout gray and white matter areas of the brain, but only amoeboid microglia in discrete foci in the subcortical white matter are ferritin positive. At PND 15, some oligodendrocytes in the subcortical white matter express ferritin, but the majority of ferritin-containing cells within white matter are still microglia. By PND 30, the predominant ferritin-containing cell type within white matter are oligodendrocytes. Generally, the cellular distribution of both ferritin subunits were identical with one major exception; H-ferritin, but not L-ferritin, was present in neuronal nuclei in the cortex. These data suggest that microglia play a role in brain iron homeostasis during normal postnatal development and may influence myelination by competing with oligodendrocytes for iron.

Iron-induced oxidative DNA damage and its repair in primary rat hepatocyte culture

Iron-overload diseases frequently develop hepatocellular carcinoma. The genotoxic mechanism whereby iron is involved in hepatocarcinogenesis might involve an oxidative process via the intermediate production of reactive oxygen species. This was presently investigated by examining kinetics of formation and repair of DNA base lesions in primary rat hepatocyte cultures supplemented with the iron chelate, ferric nitrilotriacetate Fe-NTA (10 and 100 microM). Seven DNA base oxidation products have been identified in DNA extracts by gas chromatography-mass spectrometry, which showed a predominance of oxidized-purines (8-oxo-guanine, xanthine, fapy-adenine, 2-oxo-adenine) above oxidized pyrimidines (5-OHMe-uracil, 5-OH-uracil, 5-OH-cytosine) in control cultures. All these DNA oxidation products revealed a significant dose-dependent increase at 4 to 48 h after Fe-NTA supplementation, among which fapy-adenine showed the highest increase and 5-OH-cytosine was the least prominent. Involvement of iron in this oxidative process was established by a correlation between extent in DNA oxidation and intracellular level of toxic low molecular weight iron. DNA excision-repair activity was estimated by release of DNA oxidation products in culture medium. All the seven DNA oxidation products were detected in the medium of control cultures and showed basal repair activity. This DNA repair activity was increased in a time- and dose-dependent fashion with Fe-NTA. Oxidized-pyrimidines, among which was 5-OHMe-Uracil, were preferentially repaired, which explains the low levels detected in oxidized DNA. Since oxidized bases substantially differed from one another in terms of excision rates from cellular DNA, specific excision-repair enzymes might be involved. Our findings, however, demonstrate that even though DNA repair pathways were activated in iron-loaded hepatocyte cultures, these processes were not stimulated enough to prevent an accumulation of highly mutagenic DNA oxidative products in genomic DNA. The resulting genotoxic effect of Fe-NTA might be relevant in understanding the hepatocarcinogenic evolution of iron-overload diseases.

4-Hydroxynonenal, a product of lipid peroxidation, damages cholinergic neurons and impairs visuospatial memory in rats.

The mechanisms that underlie cholinergic neuronal degeneration in Alzheimer disease (AD) are unclear, but recent data suggest that oxidative stress plays a role. We report that 4-hydroxynonenal (HNE), an aldehydic product of lipid peroxidation, damages and kills basal forebrain cholinergic neurons when administered intraparenchymally. Examination of Nissl-stained brain sections following unilateral HNE infusion revealed widespread neuronal loss in basal forebrain ipsilateral to the injection, but not on the contralateral side. Levels of choline acetyltransferase activity and immunoreactivity in the ipsilateral basal forebrain and hippocampus were significantly reduced by 60-80% seven days following HNE administration. Performance in Morris water maze tasks of visuospatial memory was severely impaired in a dose-dependent manner seven days following bilateral administration of HNE. Bilateral infusion of FeCl2 (an inducer of membrane lipid peroxidation) into the basal forebrain caused neuron loss and decreased choline acetyltransferease immunoreactivity and deficits in visuospatial memory. Additionally, FeCl2 infusion increased HNE immunoreactivity, implicating HNE in iron-induced oxidative damage. Because recent studies have demonstrated HNE adducts in degenerating neurons in AD brain, the present findings suggest a role for HNE in damage to cholinergic neurons in AD.

Melatonin inhibits iron-induced epileptic discharges in rats by suppressing peroxidation.

Intracortical injection of iron ion induces recurrent seizures and epileptic discharges in the electrocorticogram. This observation may be used as a model of posttraumatic epilepsy. The involvement of iron-mediated oxygen free radical species and neuronal lipid peroxidation in iron-induced seizure has been suggested. Melatonin exerts free radical scavenging properties. In this study, we examined the protective effect of melatonin against iron-induced seizures. We examined the protective effect of melatonin against in vitro iron-induced oxidative damage in homogenates from rat cerebral cortex, by measuring the concentration of thiobarbituric acid reactive substances (TBARS), as an index of oxidative damage. We also examined the effect of melatonin on the appearance of epileptic discharges in the EEG following injection of FeCl3 into the sensorimotor cortex in anesthetized rats, and by measuring the concentration of TBARS in the brain tissue. FeCl3 increased the concentration of TBARS in brain homogenates in a concentration-dependent manner, and melatonin reduced FeCl3-induced rise in TBARS in a dose-response fashion. Pretreatment with melatonin suppressed or delayed the development of FeCl3-induced epileptic discharges and decreased the concentration of TBARS in brain tissues. Our results suggest that iron ion generates oxygen free radical species that induce neuronal macromolecular peroxidation and seizure, and that melatonin inhibits iron-induced seizures by scavenging free radicals.

Comparison of oxidative damage of DNA and lipids in normal and tumor rat hepatocyte cultures treated with ferric nitrilotriacetate

Oxidative damage of DNA and lipids in normal primary rat hepatocyte cultures and in hepatoma Fao cell-line was induced by ferric nitrilotriacetate (Fe-NTA). DNA oxidation was evidenced by measuring the mutagenic oxidized nucleoside 8-hydroxy-2′-deoxyguanosine (8-oxodG). An increase in 8-oxodG production was induced by Fe-NTA in the two different cell cultures. Moreover, this increase was more important in hepatocytes than in Fao cells. In addition, the extent of lipid peroxidation was higher in normal hepatocytes than in Fao cells. These observations demonstrated a higher resistance of tumor cells than normal hepatocytes to oxidative stress. Since DNA lesions induced by oxidative stress are now recognized as being involved in the mutagenesis process and since normal hepatocytes appeared particularly sensitive to iron-induced oxidative damage, a high level of iron should be considered as a potent toxic factor involved in normal cell degeneration. This findings might partly explain the propensity of hepatic iron-overload diseases for cancerous evolution.

A Quantitative Analysis of Isoferritins in Select Regions of Aged, Parkinsonian, and Alzheimer's Diseased Brains

The brain requires a ready supply of iron for normal neurological function, but free iron is toxic. Consequently, iron bioavailability must be stringently regulated. Recent evidence has suggested that the brain iron regulatory system is dysfunctional in neurological disorders such as Alzheimer's and Parkinson's diseases (AD and PD, respectively). A key component of the iron regulatory system in the brain is ferritin. Ferritin consists of 24 subunits, which are distinguished as either a heavy-chain (H) or light-chain (L) isoform. These peptide subunits are genetically and functionally distinct. Thus, the ability to investigate separately the types of ferritin in brain should provide insight into iron management at both the cellular and the molecular level. In this study, the ratio of isoferritins was determined in select regions of adult elderly AD and PD human brains. The H-rich ferritin was more abundant in the young brain, except in the globus pallidus where the ratio of H/L ferritin was 1:1. The balance of H/L isoferritins was influenced by age, brain region, and disease state. With normal aging, both H and L ferritin increased; however, the age-associated increase in isoferritins generally failed to occur in AD and PD brain tissue. The imbalance in H/L isoferritins was disease and region specific. For example, in frontal cortex, there was a dramatic (fivefold) increase in the ratio of H/L ferritin in AD brains but not in PD brains. In PD, caudate and putamen H/L ratios were higher than in AD and the elderly control group.(ABSTRACT TRUNCATED AT 250 WORDS)

Desferrioxamine as a lipid chain-breaking antioxidant in sickle erythrocyte membranes

The mechanism of action of desferrioxamine in the inhibition of the catalysis of iron-induced oxidative damage has been ascribed to its ability to chelate available ferric ion ( K b = 10 31). However, recent work has proposed that the trihydroxamate moiety of desferrioxamine can also be involved in electron transfer reactions involving the Superoxide radical, peroxidase/hydrogen peroxide mixtures and ferryl myoglobin radicals. In this study we report evidence for the ability of desferrioxamine to inhibit peroxidative damage to pathological membranes with which non-haem iron is associated through a mechanism of action as a lipid chain breaking antioxidant, independently of its iron chelating properties.

The control of iron-induced oxidative damage in isolated rat-liver mitochondria by respiration state and ascorbate.

The reaction of iron (II) with H2O2 is believed to generate highly reactive species (e.g. .OH) capable of initiating biological damage. This study investigates the possibility that the severity of oxidative damage induced by iron in hepatic mitochondria is determined by the level of mitochondrial-H2O2 generation, which is believed to be particularly prominent in state-4 respiration. Iron-induced damage is found to be greater in state-4 than in state-3 respiration. Experiments using uncoupling agents and Ca++ to mimic state-3 conditions indicate that this effect reflects differences in the steady-state oxidation-level of the electron carriers of the respiratory chain (and hence the level of H2O2-generation), rather than changes in redox potential or transportation of the metal-ion. Evidence is also presented for a mechanism in which Fe(II) and H2O2 react inside the mitochondrial matrix. Ascorbate (vitamin C) is shown to be pro-oxidant in this system, except when present at very high concentration when it becomes antioxidant in nature.

Iron-induced oxidative damage and red cell metabolism

Iron-induced oxidative damage and red cell metabolism