The level of 8-oxo-7,8-dihydro-2'-deoxyguanosine is positively correlated with the size of the labile iron pool in human lymphocytes

Crucial role of chelatable iron in silver nanoparticles induced DNA damage and cytotoxicity

Damage to mitochondria and subsequent ROS leakage is a commonly accepted mechanism of nanoparticle toxicity. However, malfunction of mitochondria results in generation of superoxide anion radical (O₂^•-), which due to the relatively low chemical reactivity is rather unlikely to cause harmful effects triggered by nanoparticles. We show that treatment of HepG2 cells with silver nanoparticles (AgNPs) resulted in generation of H₂O₂ instead of O₂^•-, as measured by ROS specific mitochondrial probes. Moreover, addition of a selective iron chelator diminished AgNPs toxicity. Altogether these results suggest that O₂^•- generated during NPs induced mitochondrial collapse is rapidly dismutated to H₂O₂, which in the presence of iron ions undergoes a Fenton reaction to produce an extremely reactive hydroxyl radical (^•OH). Clarification of the mechanism of NPs-dependent generation of ^•OH and demonstration of the crucial role of iron ions in NPs toxicity will facilitate our understanding of NPs toxicity and the design of safe nanomaterials.

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Superoxide radical is the main product generated by nanosilver exposed mitochondria.

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Iron chelation prevent the cell from nanosilver induced DNA damage.

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Iron chelation diminish nanosilver cytotoxicity.

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Nanosilver toxicity depends on Fenton reaction involving superoxide-derived H₂O₂.

Lipid peroxides as endogenous oxidants forming 8-oxo-guanosine and lipid-soluble antioxidants as suppressing agents

The oxidation of guanosine to 8-oxo-2'-deoxyguanosine (8-oxo-dG) in DNA is closely associated with induction of various diseases, but the endogenous oxidant species involved remains unclear. Hydrogen peroxides (H2O2) have been considered to be the oxidant, while lipid peroxides are another possible oxidant because generated easily in bio-membranes surrounding DNA. The oxidant potency was compared between lipid peroxides and H2O2. Linoleic acid hydroperoxides (LOOH) formed 8-oxo-dG at a higher level than H2O2 in guanosine or double-stranded DNA. In the presence of a physiological concentration of Fe(2+) to produce hydroxyl radicals, LOOH was also a stronger oxidant. In a lipid micelle, LOOH markedly produced 8-oxo-dG at a concentration one-tenth of that of H2O2. Upon adding to rat hepatic mitochondria, phosphatidylcholine hydroperoxides produced 8-oxo-dG abundantly. Employing HepG2 cells after pretreated with glutathione peroxidase inhibitor, LOOH formed 8-oxo-dG more abundantly than H2O2. Then, antioxidants to suppress the 8-oxo-dG formation were examined, when the nuclei of pre-incubated HepG2 with antioxidants were exposed to LOOH. Water-soluble ascorbic acid, trolox, and N-acetyl cysteine showed no or weak antioxidant potency, while lipid-soluble 2,6-dipalmitoyl ascorbic acid, α-tocopherol, and lipid-soluble phytochemicals exhibited stronger potency. The present study shows preferential formation of 8-oxo-dG upon LOOH and the inhibition by lipid-soluble antioxidants.

Anthocyans as tertiary chemopreventive agents in bladder cancer: anti-oxidant mechanisms and interaction with mitomycin C

Bladder cancer is associated with high rates of recurrence making tertiary chemoprevention an attractive intervention strategy. Anthocyanins have been shown to possess chemopreventive properties and are detectable in urine after oral ingestion, with higher concentrations achievable via intravesical administration alongside current chemotherapeutic regimens. Yet their apparent ability to protect against certain DNA damage may in turn interfere with cancer treatments. Our aim was therefore to determine the potential of anthocyanins as chemopreventive agents in bladder cancer, their mode of action and effects, both alone and in combination with mitomycin C (MMC). In this study we showed that mirtoselect, a standardised mixture of anthocyanins, possesses significant anti-proliferative activity, causing growth inhibition and apoptosis in bladder cancer cell lines. The anti-oxidative potential of mirtoselect was examined and revealed significantly fewer H2O2-induced DNA strand breaks, as well as oxidised DNA bases in pre-treated cells. In contrast, endogenous levels of oxidised DNA bases were unaltered. Investigations into the possible protective mechanisms associated with these anti-oxidant properties revealed that mirtoselect chelates metal ions. In mirtoselect/MMC combination studies, no adverse effects on measures of DNA damage were observed compared to treatment with MMC alone and there was evidence of enhanced cell death. Consistent with this, significantly more DNA crosslinks were formed in cells treated with the combination. These results show that mirtoselect exerts effects consistent with chemopreventive properties in bladder cancer cell lines and most importantly does so without adversely affecting the effects of drugs used in current treatment regimens. We also provide evidence that mirtoselect's anti-oxidative mechanism of action is via metal ion chelation. Overall these results suggest that mirtoselect could be an effective chemopreventive agent in bladder cancer and provides the necessary pre-clinical data for future in vivo animal studies and clinical trials.

Targeting DNA damage and repair: embracing the pharmacological era for successful cancer therapy

DNA is under constant assault from genotoxic agents which creates different kinds of DNA damage. The precise replication of the genome and the continuous surveillance of its integrity are critical for survival and the avoidance of carcinogenesis. Cells have evolved an arsenal of repair pathways and cell cycle checkpoints to detect and repair DNA damage. When repair fails, typically cell cycle progression is halted and apoptosis is initiated. Here, we review the different sources and types of DNA damage including DNA replication stress and oxidative stress, the repair pathways that cells utilize to repair damaged DNA, and discuss their biological significance, especially with reference to cancer induction and cancer therapy. We also describe the main methodologies currently used for the detection of DNA damage with their strengths and limitations. We conclude with an outline as to how this information can be used to identify novel pharmacological targets for DNA repair pathways or enhancers of DNA damage to develop improved treatment strategies that will benefit cancer patients.

The role of iron redox state in the genotoxicity of ultrafine superparamagnetic iron oxide nanoparticles

Ultrafine superparamagnetic iron oxide nanoparticles (USPION) hold great potential for revolutionising biomedical applications such as MRI, localised hyperthermia, and targeted drug delivery. Though evidence is increasing regarding the influence of nanoparticle physico-chemical features on toxicity, data however, is lacking that assesses a range of such characteristics in parallel. We show that iron redox state, a subtle though important physico-chemical feature of USPION, dramatically modifies the cellular uptake of these nanoparticles and influences their induction of DNA damage. Surface chemistry was also found to have an impact and evidence to support a potential mechanism of oxidative DNA damage behind the observed responses has been demonstrated. As human exposure to ferrofluids is predicted to increase through nanomedicine based therapeutics, these findings are important in guiding the fabrication of USPION to ensure they have characteristics that support biocompatibility.

Benefits and risks of iron supplementation in anemic neonatal pigs

Iron deficiency is a common health problem. The most severe consequence of this disorder is iron deficiency anemia (IDA), which is considered the most common nutritional deficiency worldwide. Newborn piglets are an ideal model to explore the multifaceted etiology of IDA in mammals, as IDA is the most prevalent deficiency disorder throughout the early postnatal period in this species and frequently develops into a critical illness. Here, we report the very low expression of duodenal iron transporters in pigs during the first days of life. We postulate that this low expression level is why the iron demands of the piglet body are not met by iron absorption during this period. Interestingly, we found that a low level of duodenal divalent metal transporter 1 and ferroportin, two iron transporters located on the apical and basolateral membrane of duodenal absorptive enterocytes, respectively, correlates with abnormally high expression of hepcidin, despite the poor hepatic and overall iron status of these animals. Parenteral iron supplementation by a unique intramuscular administration of large amounts of iron dextran is current practice for the treatment of IDA in piglets. However, the potential toxicity of such supplemental iron implies the necessity for caution when applying this treatment. Here we demonstrate that a modified strategy for iron supplementation of newborn piglets with iron dextran improves the piglets' hematological status, attenuates the induction of hepcidin expression, and minimizes the toxicity of the administered iron.

Enhanced elimination of oxidized guanine nucleotides inhibits oncogenic RAS-induced DNA damage and premature senescence

Approximately 20% of tumors contain activating mutations in the RAS family of oncogenes. As tumors progress to higher grades of malignancy, the expression of oncogenic RAS has been reported to increase, leading to an oncogene-induced senescence (OIS) response. Evasion of this senescence barrier is a hallmark of advanced tumors indicating that OIS serves a critical tumor-suppressive function. Induction of OIS has been attributed to either RAS-mediated production of reactive oxygen species (ROS) or to induction of a DNA damage response (DDR). However, functional links between these two processes in triggering the senescent phenotype have not been explicitly described. Our previous work has shown that, in cultured untransformed cells, preventing elimination of oxidized guanine deoxyribonucleotides, which was achieved by suppressing expression of the cellular 8-oxo-dGTPase, human MutT homolog 1 (MTH1), sufficed to induce a DDR as well as premature senescence. Here, we demonstrate that overexpression of MTH1 can prevent the oncogenic H-RAS-induced DDR and attendant premature senescence, although it does not affect the observed elevation in ROS levels produced by RAS oncoprotein expression. Conversely, we find that loss of MTH1 preferentially induces an in vitro proliferation defect in tumorigenic cells overexpressing oncogenic RAS. These results indicate that the guanine nucleotide pool is a critical target for intracellular ROS produced by oncogenic RAS and that RAS-transformed cells require robust MTH1 expression to proliferate.

Towards a unifying, systems biology understanding of large-scale cellular death and destruction caused by poorly liganded iron: Parkinson's, Huntington's, Alzheimer's, prions, bactericides, chemical toxicology and others as examples

Exposure to a variety of toxins and/or infectious agents leads to disease, degeneration and death, often characterised by circumstances in which cells or tissues do not merely die and cease to function but may be more or less entirely obliterated. It is then legitimate to ask the question as to whether, despite the many kinds of agent involved, there may be at least some unifying mechanisms of such cell death and destruction. I summarise the evidence that in a great many cases, one underlying mechanism, providing major stresses of this type, entails continuing and autocatalytic production (based on positive feedback mechanisms) of hydroxyl radicals via Fenton chemistry involving poorly liganded iron, leading to cell death via apoptosis (probably including via pathways induced by changes in the NF-κB system). While every pathway is in some sense connected to every other one, I highlight the literature evidence suggesting that the degenerative effects of many diseases and toxicological insults converge on iron dysregulation. This highlights specifically the role of iron metabolism, and the detailed speciation of iron, in chemical and other toxicology, and has significant implications for the use of iron chelating substances (probably in partnership with appropriate anti-oxidants) as nutritional or therapeutic agents in inhibiting both the progression of these mainly degenerative diseases and the sequelae of both chronic and acute toxin exposure. The complexity of biochemical networks, especially those involving autocatalytic behaviour and positive feedbacks, means that multiple interventions (e.g. of iron chelators plus antioxidants) are likely to prove most effective. A variety of systems biology approaches, that I summarise, can predict both the mechanisms involved in these cell death pathways and the optimal sites of action for nutritional or pharmacological interventions.

Does the cellular labile iron pool participate in the oxidation of 2′,7′-dichlorodihydrofluorescein?

The fluorogenic probe 2',7'-dichlorodihydrofluorescein diacetate (H(2)DCF-DA) is widely used for the estimation of oxidative stress in cells. It is known that 2',7'-dichlorodihydrofluorescein (H(2)DCF), product of intracellular hydrolysis of H(2)DCF-DA, is oxidized to the fluorescent compound, DCF, mainly by hydrogen peroxide (H(2)O(2)) in the presence of catalysts. The present study was aimed at answering the question whether the labile iron pool (LIP) may contribute to the oxidation of H(2)DCF in cellular systems. The membrane-permeable lipophilic iron chelator salicylaldehyde isonicotinoyl hydrazone (SIH) was found to inhibit oxidation of the probe by H(2)O(2) dependent on ferrous ions but not by peroxidase or superoxide dismutase in defined in vitro systems. When applied to cells, the probe inhibited considerably oxidation of H(2)DCF in V79 Chinese hamster fibroblasts and two murine lymphoma L5178Y(LY) sublines (LY-R, LY-S) differing in LIP level, the extent of inhibition being greater in the LY-R line of higher LIP level. These results demonstrate that LIP is a significant factor determining the rate of intracellular H(2)DCF oxidation.

Body iron is a contributor to oxidative damage of DNA

The transition metal iron is catalytically highly active in vitro, and not surprisingly, body iron has been suggested to promote oxidative stress in vivo. In the current analysis we studied the association of serum ferritin concentration and serum soluble transferrin receptor concentration with daily urinary 8-hydroxydeoxyguanosine excretion, a marker of oxidative stress, in 48 mildly dyslipidemic men in East Finland. In multivariate linear regression analyses allowing for age, smoking, body mass index and physical exercise, serum ferritin concentration predicted the excretion rate at B = 0.17 (95% CI 0.08-0.26, P = 0.001), and serum soluble transferrin receptor to ferritin concentration ratio (TfR/ferritin) predicted the excretion rate at B = - 0.13 (95% CI - 0.21 to - 0.05, P = 0.002). Our data suggest that body iron contributes to excess oxidative stress already at non-iron overload concentrations in these subjects.

Antioxidant vitamins and cancer risk: is oxidative damage to DNA a relevant biomarker?

Oxidative damage to DNA is regarded as an important step in carcinogenesis. These lesions may arise as a consequence of exposure to xenobiotics, but are also generated as a consequence of endogenous generation of oxidizing compounds. Measurements of oxidative damage to guanines, such as 8-oxo-7, 8-dihydroguanine (8-oxodG) are increasingly being regarded as reliable biomarkers of oxidative stress and they may have a predictive value of cancer risk, although this needs to be established independently in several cohort studies. A survey of intervention studies of the ingestion of antioxidant-containing foods or tablets of antioxidants indicate that about one-third of the studies reported a protective effect in terms of lower levels of oxidative damage to DNA in white blood cells or decreased urinary excretion of 8-oxodG. Although firm conclusions cannot be reached, there appears to be links between ingestion of antioxidants, oxidative damage to DNA, and risk of cancer.

Dynamics of oxidative damage at early stages of estrogen-dependant carcinogenesis

The objective of this study was to assess the dynamics of oxidative damage to cellular macromolecules such as proteins, lipids, and DNA under conditions of oxidative stress triggering early stages of estrogen-dependent carcinogenesis. A rodent model of carcinogenesis was used. Syrian hamsters were sacrificed after 1, 3, 5 h and 1 month from the initial implantation of 17beta-estradiol (E2). Matching control groups were used. Kidneys as target organs for E2-mediated oxidative stress were excised and homogenized for biochemical assays. Subcellular fractions were isolated. Carbonyl groups (as a marker of protein oxidation) and lipid hydroxyperoxides were assessed. DNA was isolated and 8-oxodGuo was assessed. Electron paramagnetic resonance spectroscopy was used to confirm the results for lipid peroxidation. Exposition to E2 in rodent model leads to a damage of macromolecules of the cell, including proteins and DNA, but not lipids. Proteins appear to be primary target of the damage but are shortly followed by DNA. It has previously been speculated that protein peroxides can increase DNA modifications. This time sequence was observed in our study. Nevertheless, direct relation between protein and DNA damage still remains unsolved.

Blood mononucleocytes are sensitive to the DNA damaging effects of iron overload--in vitro and ex vivo results with human and rat cells

Iron exposure enhances colorectal carcinogeneis, by producing reactive oxygen species, which damage lipids, proteins and DNA. We recently demonstrated that ferric-nitrilotriacetate (Fe-NTA) damages DNA of human colon cells in different stages of malignant transformation. Opposed to this, little is known on systemic effects of iron and it is still difficult to determine the border between essential iron supplementation and iron overload in humans. The aim of this study was to determine whether Fe-NTA causes global and specific DNA damage in peripheral leucocytes. Human leucocytes were treated in vitro with Fe-NTA for 30 min at 37 degrees C. Male Sprague Dawley rats were fed (6 weeks) with an iron-overload diet (9.9 g Fe/kg DM) and whole blood was collected. DNA damage was measured in human and rat blood cells using the alkaline version of the Comet Assay with repair specific enzymes. In human cells the distribution of TP53 in the comet images was detected using fluorescence in situ hybridization (Comet FISH) to measure DNA damage in the region of the TP53 gene. Fe-NTA (10-500 microM) was clearly genotoxic in human leucocytes in vitro, and also in leucocytes of rats fed the iron overload diet. The induced damage in human leucocytes was approximately two-fold that observed previously in human colon cells. Oxidized bases were induced by iron in rat leucocytes in vivo, while they were not induced in human leucocytes in vitro. Fe-NTA enhanced the migration of TP53 signals into the comet tail of human leucocytes, indicating a high susceptibility of this tumour-relevant gene towards DNA damage induced by iron overload. In conclusion, iron markedly induced DNA damage in human and rat leucocytes, which shows that these white blood cells are sufficiently sensitive to assess exposure to iron. The measurement of DNA damage in human leucocytes could be used as a sensitive biomarker to study iron overload in vivo in humans and thus to determine whether supplementation results in genotoxic risk.

Higher leukocyte 8-oxo-7,8-dihydro-2'-deoxyguanosine and lower plasma ascorbate in aging humans?

Is oxidative damage of DNA responsible for physiological changes associated with aging? The authors note a positive correlation between the age of human subjects with the level of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) in leukocyte DNA. The levels of urinary 8-oxo-7,8-dihydroguanine and 8-oxodG followed the same pattern of correlation. Age-dependent decline in the concentration of plasma vitamin C was also evident. These interesting observations in humans point towards the need to scrutinize in detail the role of oxidative DNA damage and compromised antioxidant defense systems in age-related physiological disorders.

Interaction of Vimang (Mangifera indica L. extract) with Fe(III) improves its antioxidant and cytoprotecting activity

A standard aqueous stem bark extract from selected species of Mangifera indica L. (Anacardiaceae)--Vimang, whose major polyphenolic component is mangiferin, displays potent in vitro and in vivo antioxidant activity. The present study provides evidence that the Vimang-Fe(III) mixture is more effective at scavenging 2,2-diphenyl-1-picrylhydrazyl (DPPH) and superoxide radicals, as well as in protecting against t-butyl hydroperoxide-induced mitochondrial lipid peroxidation and hypoxia/reoxygenation-induced hepatocytes injury, compared to Vimang alone. Voltammetric assays demonstrated that Vimang, in line with the high mangiferin content of the extract, behaves electrochemically like mangiferin, as well as interacts with Fe(III) in close similarity with mangiferin's interaction with the cation. These results justify the high efficiency of Vimang as an agent protecting from iron-induced oxidative damage. We propose Vimang as a potential therapy against the deleterious action of reactive oxygen species generated during iron-overload, such as that occurring in diseases like beta-thalassemia, Friedreich's ataxia and haemochromatosis.

Evidence for attenuated cellular 8-oxo-7,8-dihydro-2'-deoxyguanosine removal in cancer patients

Measurement of the products of oxidatively damaged DNA in urine is a frequently used means by which oxidative stress may be assessed non-invasively. We believe that urinary DNA lesions, in addition to being biomarkers of oxidative stress, can potentially provide more specific information, for example, a reflection of repair activity. We used high-performance liquid chromatography prepurification, with gas chromatography-mass spectrometry (LC-GC-MS) and ELISA to the analysis of a number of oxidative [e.g., 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), 8-oxo-7,8-dihydro-guanine, 5-(hydroxymethyl)uracil], non-oxidative (cyclobutane thymine dimers) and oligomeric DNA products in urine. We analysed spot urine samples from 20 healthy subjects, and 20 age- and sex-matched cancer patients. Mononuclear cell DNA 8-oxodG levels were assessed by LC-EC. The data support our proposal that urinary DNA lesion products are predominantly derived from DNA repair. Furthermore, analysis of DNA and urinary 8-oxodG in cancer patients and controls suggested reduced repair activity towards this lesion marker in these patients.

Severe oxidatively damaged DNA after cisplatin treatment of cancer patients

There is growing evidence suggesting that cytotoxic activity of cisplatin is closely associated with increased generation of reactive oxygen species (ROS). Therefore, this study was undertaken to examine oxidative DNA damage, which arises as a result of chemotherapy with cisplatin. Using HPLC prepurification/isotope dilution GC/MS methodology, we examined the amount of 8-oxoGua and 8-oxodG excreted into urine in cancer patients (n = 66) who received chemotherapy with cisplatin. One day after the infusion of the drug, significant increase in the amount of 8-oxoGua and 8-oxodG in urine of the patients was observed, when compared to the initial value (78%, p < 0.0001 and 22%, p = 0.0051). In the "nadir days" (when the most distinct cell death based on hematological cell counts can be observed), the level of modified base and nucleoside decreased in comparison with the aforementioned time point. These results, for the first time, indicate that oxidatively damaged DNA may be, at least in part, responsible for cisplatin induced cytotoxicity. Our results also demonstrate that cell death does not contribute to urinary 8-oxoGua and 8-oxodG in humans.

Iron, oxidative stress and human health

The amount of iron within the cell is carefully regulated in order to provide an adequate level of the micronutrient while preventing its accumulation to toxic levels. Iron excess is believed to generate oxidative stress, understood as an increase in the steady state concentration of oxygen radical intermediates. The main aspects of cellular metabolism of iron, with special emphasis on the role of iron with respect to oxidative damage to lipid membranes, are briefly reviewed here. Both in vitro and in vivo models are examined. Finally, a discussion of iron overload and its impact on human health is included. Overall, further studies are required to assess more effective means to limit iron-dependent damage, by minimizing the formation and release of free radicals in tissues when the cellular iron steady state concentration is increased either as a consequence of disease or by therapeutic iron supplementation.

Helicobacter pylori infection is associated with oxidatively damaged DNA in human leukocytes and decreased level of urinary 8-oxo-7,8-dihydroguanine

Helicobacter pylori infection is responsible for inflammation, increased production of reactive oxygen species and oxidatively damaged DNA in the gastric mucosa. There is also evidence which suggests that H.pylori infection may lead to the development of several extragastroduodenal pathologies with reactive oxygen species involvement. In order to assess whether the infection may impose oxidatively damaged DNA not only in the target organ (stomach) but in other organs as well we decided, for the first time, to analyse the two kinds of oxidatively damaged DNA biomarkers: urinary excretion of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) and 8-oxo-7,8-dihydroguanine (8-oxoGua) as well as the level of oxidatively damaged DNA in leukocytes. Using high performance liquid chromatography prepurification/gas chromatography with isotope dilution mass detection methodology, we examined the amount of oxidatively damaged DNA products excreted into urine and the amount of 8-oxodG in the DNA of leukocytes' (with the the HPLC/EC technique) in three groups of children: (i) control group, (ii) H.pylori infected children and (iii) children with gastritis where H.pylori infection was excluded. The levels of 8-oxodG in DNA isolated from leukocytes of H.pylori infected patients and in the group with gastritis without H.pylori infection were significantly higher than in DNA isolated from the control group. The mean level of 8-oxoGua in urine samples of children infected with H.pylori was significantly lower than in the urine of the group with gastritis without H.pylori infection. The data suggest that inflammation itself, not just H.pylori infection, is responsible for the observed rise of 8-oxodG level in leukocytes. However, the observed decrease in the level of modified base in urine seems to be specific for H.pylori infection and possibly linked with nitric oxide mediated inhibition of a key base excision repair enzyme (human 8-oxo-7, 8-dihydroguanine glycosylase) responsible for the repair of 8-oxo-7,8-dihydroguanine.

Does measurement of oxidative damage to DNA have clinical significance?

Oxidative damage to DNA is the seemingly inevitable consequence of cellular metabolism. Furthermore, despite protective mechanisms, cellular levels of damage may increase under conditions of oxidative stress, arising from exposure to a variety of physical or chemical insults. Elevated levels of oxidatively damaged DNA have been measured in numerous diseases, and as a result, it has been hypothesised that such damage plays an integral role in the aetiology of that disease. This review examines the validity of this hypothesis, exploring the mechanisms by which oxidative DNA damage may lead to disease. We conclude that further validation of biomarkers of oxidative DNA damage, along with further elucidation of the role of damage in disease, may allow these biomarkers to become potentially useful clinical tools.

Induction of iron regulatory protein 1 RNA-binding activity by nitric oxide is associated with a concomitant increase in the labile iron pool: implications for DNA damage

Iron regulatory protein 1 (IRP1) is a bifunctional [4Fe-4S] protein that controls iron homeostasis. Switching off its function from an aconitase to an apo-IRP1 interacting with iron-responsive element-containing mRNAs depends on the reduced availability of iron in labile iron pool (LIP). Although the modulation of IRP1 by nitric oxide has been characterized, its impact on LIP remains unknown. Here, we show that inhibition of IRP1 aconitase activity and induction of its IRE-binding activity during exposure of L5178Y mouse lymphoma cells to NO are associated with an increase in LIP levels. Removal of NO resulted in a reverse regulation of IRP1 activities accompanied by a decrease of LIP. The increased iron burden in LIP caused by NO exacerbated hydrogen peroxide-induced genotoxicity in L5178Y cells. We demonstrate that the increase in LIP levels in response to chronic but not burst exposure of L5178Y cells to NO is associated with alterations in the expression of proteins involved in iron metabolism.

Contribution of hMTH1 to the maintenance of 8-oxoguanine levels in lung DNA of non-small-cell lung cancer patients

BACKGROUND

The level of 8-oxoguanine (8-oxoG), a general marker of oxidative DNA damage, in DNA is the result of both an equilibrium between the rates of its formation and removal from DNA by DNA repair enzymes and the removal of 8-oxodGTP from the cellular nucleotide pool by hydrolysis to 8-oxodGMP, preventing its incorporation into DNA. To determine the contribution of each component to the level of 8-oxoG in DNA, we compared 8-oxoG-excising activity (encoded by hOGG1), 8-oxodGTPase activity (encoded by hMTH1), and 8-oxoG levels in DNA from tumors and surrounding normal lung tissues from non-small-cell lung cancer patients.

METHODS

We measured the level of 8-oxoG in DNA of 47 patients by high-performance liquid chromatography/electrochemical detection (HPLC/ECD), hOGG1 activity in tissue extracts of 56 patients by the nicking assay using an oligodeoxynucleotide containing a single 8-oxoG, and hMTH1 activity in tissue extracts of 33 patients by HPLC/UV detection. All statistical tests were two-sided.

RESULTS

The 8-oxoG level was lower in tumor DNA than in DNA from normal lung tissue (geometric mean: 5.81 versus 10.18 8-oxoG/10(6) G, geometric mean of difference = 1.75; P<.001). The hOGG1 activity was also lower in tumor than in normal lung tissue (geometric mean: 8.76 versus 20.91 pmol/h/mg protein, geometric mean of difference = 2.39; P<.001), whereas the hMTH1 activity was higher in tumor than in normal lung tissue (geometric mean: 28.79 versus 8.94 nmol/h/mg protein, geometric mean of difference = 0.31; P<.001). The activity of hMTH1 was three orders of magnitude higher than that of hOGG1 (nanomoles versus picomoles per hour per milligram of protein, respectively).

CONCLUSIONS

Several different components contribute to the maintenance of 8-oxoG levels in human DNA, with the greatest contributor being the removal of 8-oxodGTP from the cellular nucleotide pool by hMTH1.

Red blood cells upregulate cytoprotective proteins and the labile iron pool in dividing human T cells despite a reduction in oxidative stress

We have recently reported that red blood cells (RBC) promote T cell growth and survival by inhibiting activation-induced T cell death. In the present study, we have examined parameters of oxidative stress and intracellular iron in activated T cells and correlated these data with the expression of ferritin, heme oxygenase-1 (HO-1), and the transferrin receptor CD71. T cells growing in the presence of RBC had reduced levels of reactive oxygen species (ROS) and oxidatively modified proteins, suggesting that RBC efficiently counteracted ROS production on the activated T cells. Flow cytometry and immunodetection demonstrated that T cells dividing in the presence of RBC had increased levels of intracellular ferritin rich in L-subunits and HO-1 along with a downmodulation in CD71 expression. Finally, using the fluorescent iron indicator calcein and flow cytometry analysis, we were able to show that a relative amount of the labile iron pool (LIP) was upregulated in T cells growing in the presence of RBC. These findings are consistent with a typical response to iron overload. However, neither heme compounds nor ferric iron reproduced the levels of expansion and survival of T cells induced by intact RBC. Altogether, these data suggest that RBC inhibit apoptosis of activated T cells by a combination of ROS scavenging and upregulation of cytoprotective proteins such as ferritin and HO-1, which may counteract a possible toxic effect of the increased intracellular free iron.