Intracellular iron, but not copper, plays a critical role in hydrogen peroxide-induced DNA damage

Trace element, antioxidant activity, and lipid peroxidation levels in brain cortex of gerbils after cerebral ischemic injury

Proper trace element level and antioxidant enzyme activity are crucial for the brain in maintaining normal neurological functions. To our knowledge, alteration of lipid peroxidation status, trace element level, and antioxidant activity in the homogenates of brain cortex after cerebral ischemia in gerbil, however, has not been investigated so far. Male Mongolian gerbils were divided into control and ischemic subjects. Cerebral ischemia was induced by occlusion of the right middle cerebral artery and right common carotid artery for 1 h. Experimental results showed that a significant increase (P < 0.01) of the malondialdehyde level was found in the ischemic brain as compared with the control group. Trace element analysis indicated that a remarkable elevation (P < 0.01) of the level of iron (Fe), chromium (Cr), and a statistical decrease of selenium (Se) and zinc (Zn) (P < 0.05) concentration were observed in the ischemic brain as compared with the control subject. No significant change (P > 0.05) of the copper (Cu) level was found in both experimental groups. Additionally, antioxidant activity of superoxide dismutase (P < 0.01) and catalase (P < 0.05) was significantly decreased in the ischemic brain as compared with the control subject. Taking all results together, it is conceivable to manifest the experimental findings that cerebral ischemia not only may result in an enhanced oxidative stress but also may lead to further oxidative injury. Moreover, disturbance of trace element level combined with declined antioxidant activity seems to play a significant role in responsible for the etiology of cerebral ischemia.

Antioxidant capacity of flaxseed products: the effect of in vitro digestion

This study evaluated the effect of in vitro digestion of flaxseed products on Folin-Ciocalteu reagent reducing substances (FCRRS), its antioxidant capacity and prevention of oxidative DNA damage in human monocyte cell line U937. Flaxseed protein isolate was obtained from defatted flaxseed meal and the protein hydrolysate with high antioxidant capacity was obtained from hydrolysis of the protein isolate with Alcalase in a two factor central composite rotatable design (pH 8.5 and enzyme: substrate 1:90, w/w). The FCRRS content and antioxidant capacity measured by FRAP and ORAC in aqueous and 70 % methanol extracts were the highest in protein hydrolysate, followed by protein isolate, while the defatted meal showed the lowest values. After in vitro gastrointestinal digestion, the FCRRS content of protein isolate and hydrolysate reached similar values, however the hydrolysate had the highest antioxidant capacity, measured by FRAP while the isolate had the highest ORAC values. The defatted meal showed the lowest capacity in all assays (p < 0.05). The hydrolysate did not protect against DNA damage induced by H2O2 in U937 cells under the conditions of the present study. The results suggest that flaxseed protein isolate and hydrolysate are potential functional food ingredients with antioxidant capacity.

Signaling pathways of ESE-16, an antimitotic and anticarbonic anhydrase estradiol analog, in breast cancer cells

The aim of this study was to characterize the in vitro action of 2-ethyl-3-O-sulphamoyl-estra-1,3,5(10)16-tetraene (ESE-16) on non-tumorigenic MCF-12A, tumorigenic MCF-7 and metastatic MDA-MB-231 breast cancer cells. ESE-16 is able to inhibit the activity of a carbonic anhydrase II and a mimic of carbonic anhydrase IX in the nanomolar range. Gene and protein expression studies using various techniques including gene and antibody microarrays and various flow cytometry assays yielded valuable information about the mechanism of action of ESE-16. The JNK pathway was identified as an important pathway mediating the effects of ESE-16 while the p38 stress-induced pathway is more important in MDA-MB-231 cells exposed to ESE-16. Lysosomal rupture and iron metabolism was identified as important mediators of mitochondrial membrane depolarization. Abrogation of Bcl-2 phosphorylation status as a result of ESE-16 also plays a role in inducing mitochondrial membrane depolarization. The study provides a basis for future research projects to develop the newly synthesized compound into a clinically usable anticancer agent either alone or in combination with other agents.

Keywords: Antimitotic, anticarbonic anhydrase IX, apoptosis, autophagy, cell cycle arrest, Bcl-2, JNK, p38, mitochondrial membrane depolarization, flow cytometry, gene expression and protein microarray, anticancer.

Assessment of the ability of seaweed extracts to protect against hydrogen peroxide and tert-butyl hydroperoxide induced cellular damage in Caco-2 cells

The ability of brown seaweed extracts, Ascophyllum nodosum, Laminaria hyperborea, Pelvetia canaliculata, Fucus vesiculosus and Fucus serratus to protect against tert-butyl hydroperoxide (tert-BOOH) induced stress in Caco-2 cells was investigated. Oxidative stress was determined by measuring alteration in the enzymatic activity of catalase (CAT) and superoxide dismutases (SOD) and cellular levels of glutathione (GSH). L. hyperborea, P. canaliculata and F. serratus significantly protected against tert-BOOH induced SOD reduction but did not protect against the reduction in CAT activity or the increased cellular levels of GSH. The ability of F. serratus and F. vesiculosus to protect against H(2)O(2) and tert-BOOH induced DNA damage was also assessed. The DNA protective effects of the two seaweed extracts was compared to those of three metal chelators; deferoxamine mesylate (DFO), 1,10-phenanthroline (o-phen) and 1,2-Bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakis (BAPTA-AM). F. serratus and F. vesiculosus significantly protected (P<0.05) against H(2)O(2) (50 μM) induced DNA damage but not tert-BOOH induced damage.

Toxicity of nano-zero valent iron to freshwater and marine organisms

We tested whether three commercial forms (uncoated, organic coating, and iron oxide coating) of nano zero-valent iron (nZVI) are toxic to freshwater and marine organisms, specifically three species of marine phytoplankton, one species of freshwater phytoplankton, and a freshwater zooplankton species (Daphnia magna), because these organisms may be exposed downstream of where nZVI is applied to remediate polluted soil. The aggregation and reactivity of the three types of nZVI varied considerably, which was reflected in their toxicity. Since levels of Fe²⁺ and Fe³⁺ increase as the nZVI react, we also evaluated their toxicity independently. All four phytoplankton species displayed decreasing population growth rates, and Daphnia magna showed increasing mortality, in response to increasing levels of nZVI, and to a lesser degree with increasing Fe²⁺ and Fe³⁺. All forms of nZVI aggregated in soil and water, especially in the presence of a high concentration of calcium ions in groundwater, thus reducing their transports through the environment. However, uncoated nZVI aggregated extremely rapidly, thus vastly reducing the probability of environmental transport and potential for toxicity. This information can be used to design a risk management strategy to arrest the transport of injected nZVI beyond the intended remediation area, by injecting inert calcium salts as a barrier to transport.

Lipophilic caffeic acid derivatives protect cells against H2O2-Induced DNA damage by chelating intracellular labile iron

Naturally occurring cinnamic acid derivatives are ubiquitously distributed in the plant kingdom, and it has been proposed that their consumption contributes to the maintenance of human health. However, the molecular mechanisms underlying their health keeping effects remain unknown. In the present investigation, we evaluated the capacity of several cinnamic acid derivatives (trans-cinnamic, p-coumaric, caffeic and ferulic acids, as well as caffeic acid-methyl and -propyl esters) to protect cells from oxidative stress-induced DNA damage. It was observed that effective protection was based on the ability of each compound to (i) reach the intracellular space and (ii) chelate intracellular "labile" iron. These results support the notion that numerous lipophilic iron chelating compounds, present abundantly in plant-derived diet components, may protect cells in conditions of oxidative stress and in this way be important contributors toward maintenance of human health.

The role of iron in tumour cell proliferation

Iron has a pivotal role in homeostasis due to its participation in virtually all of the body's oxidation-reduction processes. However, iron can also be considered a double-edged weapon, as its excess may lead to an increased risk of developing cancer, presumably by the generation of reactive oxygen species, and its role as substrate to enzymes that participate in cell proliferation. Thus, iron might as well be considered a cofactor in tumour cell proliferation. In certain pathological conditions, such as haemochromatosis, hepatitis B and C virus infection, asbestosis and endometriosis, iron overload may increase the risk of cancer. By contrast, iron depletion could be considered a useful adjunct in antitumour therapy. This paper reviews the current scientific evidence behind iron's role as a protumoral agent, and the potential benefit of a state of iron depletion in patients with cancer.

Iron loading and oxidative stress in the Atm-/- mouse liver

Ataxia-Telangiectasia (A-T) is an autosomal recessive disorder resulting in a myriad of abnormalities, including progressive neurodegeneration and cancer predisposition. At the cellular level, A-T is a disease of chronic oxidative stress (OS) causing damage to proteins, lipids, and DNA. OS is contributed to by pro-oxidative transition metals such as iron that catalyze the conversion of weakly reactive oxygen species to highly reactive hydroxyl radicals. Iron-associated OS has been linked to neurodegeneration in Alzheimer's and Parkinson's diseases and development of lymphoid tumors (which afflict ∼30% of A-T patients). To investigate iron regulation in A-T, iron indexes, regulatory genes, and OS markers were studied in livers of wild-type and Ataxia telangiectasia mutated (Atm) null mice on control or high-iron diets. Atm(-/-) mice had increased serum iron, hepatic iron, and ferritin and significantly higher Hepcidin compared with wild-type mice. When challenged with the high-iron diet, Bmp6 and Hfe expression was significantly increased. Atm(-/-) mice had increased protein tyrosine nitration and significantly higher Heme Oxygenase (decycling) 1 levels that were substantially increased by a high-iron diet. Ferroportin gene expression was significantly increased; however, protein levels were unchanged. We demonstrate that Atm(-/-) mice have a propensity to accumulate iron that is associated with a significant increase in hepatic OS. The iron-induced increase in hepcidin peptide in turn suppresses ferroportin protein levels, thus nullifying the upregulation of mRNA expression in response to increased OS. Our results suggest that increased iron status may contribute to the chronic OS seen in A-T patients and development of disease pathology.

Iron and vascular calcification. Is there a link?

Iron deficiency is frequently seen in patients with end-stage renal disease, particularly in those treated by dialysis, this is because of an impairment in gastrointestinal absorption and ongoing blood losses or alternatively, due to an impaired capacity to mobilize iron from its stores, called functional iron deficiency. Therefore, these patients may require intravenous iron to sustain adequate treatment with erythropoietin-stimulating agents. Aside from this, they are also prone to vascular calcification, which has been reported a major contributing factor in the development of cardiovascular disease and the increased mortality associated herewith. Several factors and mechanisms underlying the development of vascular calcification in chronic kidney diseased patients have been put forward during recent years. In view of the ability of iron to exert direct toxic effects and to induce oxidative stress on the one hand versus its essential role in various cellular processes on the other hand, the possible role of iron in the development of vascular calcification should be considered.

Genotoxic effects of aluminum, iron and manganese in human cells and experimental systems: A review of the literature

There is considerable evidence indicating an increase in neurodegenerative disorders in industrialized countries. The clinical symptoms and the possible mutagenic effects produced by acute poisoning and by chronic exposure to metals are of major interest. This study is a review of the data found concerning the genotoxic potential of three metals: aluminum (Al), iron (Fe) and manganese (Mn), with emphasis on their action on human cells.

Molecular cloning, characterization and mRNA expression of selenium-binding protein in abalone (Haliotis discus hannai Ino): Response to dietary selenium, iron and zinc

Selenium-binding protein (SEBP) is believed to play crucial role in controlling the oxidation/reduction in the physiological processes. In this study, the cDNA of selenium-binding protein from abalone Haliotis discus hannai Ino (HdhSEBP) was cloned by homology cloning and rapid amplification of cDNA ends (RACE) technique. The full length of HdhSEBP cDNA was 2071 bp, consisting of a 5' untranslated region (UTR) of 55 bp, a 3' UTR of 522 bp, and an open reading frame (ORF) of 1494 bp. The deduced protein has 497 amino acid residues with a calculated molecular mass of 55.6 kDa and a predicted isoelectric point of 5.47. BLAST analysis reveals that HdhSEBP shares high identities with other known SEBPs from mammal, bird, fish and mollusk, etc. The mRNA expression patterns of HdhSEBP in hepatopancreas and haemocytes were measured by real-time PCR in abalone fed with nine different diets containing graded levels of selenium (0, 1 and 50 mg kg(-1)), iron (0, 65 and 1300 mg kg(-1)) and zinc (0, 35 and 700 mg kg(-1)) for 20 weeks, respectively. The results showed that the expression of the HdhSEBP mRNA increased and reached the maximum at optimal dietary selenium (1 mg kg(-1)), iron (65 mg kg(-1)) and zinc (35 mg kg(-1)), respectively. Deficient or excessive level of dietary selenium, iron or zinc, respectively, leaded to significant depression of HdhSEBP mRNA. It is concluded that the expression levels of HdhSEBP are affected by dietary selenium, iron or zinc.

Inactivation of MS2 coliphage by Fenton's reagent

Fenton's reagent (i.e., Fe[II]/H2O2) is known to generate strong oxidants capable of oxidizing a broad spectrum of organic compounds in aqueous solution. This study demonstrates the successful inactivation of MS2 coliphage (MS2) by the oxidants produced from Fenton's reagent. The inactivation process of MS2 by Fenton's reagent was found to proceed in two distinct stages. The first stage inactivation, which took place rapidly within 1 min reaction time, was mainly achieved by the reaction of Fe(II) with H2O2 (i.e., the Fenton reaction). The second stage, which occurred by the catalytic reactions of Fe(III) with H2O2, exhibited much slower inactivation than the first stage. The rate of MS2 inactivation increased as pH decreased from 8.0 to 6.0. The addition of oxalate and humic acids significantly inhibited the MS2 inactivation, whereas 1,10-phenanthroline and bipyridine resulted in a gradual and steady inactivation of MS2. These observations on the effects of pH and iron-chelating agents indicate that oxidants formed on the surface or inside MS2 are responsible for the inactivation.

Biological actions of artemisinin: insights from medicinal chemistry studies

Artemisinins have become essential antimalarial drugs for increasingly widespread drug-resistant malaria strains. Although tremendous efforts have been devoted to decipher how this class of molecules works, their exact antimalarial mechanism is still an enigma. Several hypotheses have been proposed to explain their actions, including alkylation of heme by carbon-centered free radicals, interference with proteins such as the sarcoplasmic/endoplasmic calcium ATPase (SERCA), as well as damaging of normal mitochondrial functions. Besides artemisinins, other endoperoxides with various backbones have also been synthesized, some of which showed comparable or even higher antimalarial effects. It is noteworthy that among these artemisinin derivatives, some enantiomers displayed similar in vitro malaria killing efficacy. In this article, the proposed mechanisms of action of artemisinins are reviewed in light of medicinal chemistry findings characterized by efficacy-structure studies, with the hope of gaining more insight into how these potent drugs work.

DNA strand breakage by bivalent metal ions and ionizing radiation

PURPOSE

To investigate mechanisms of DNA breakage via the interaction of bivalent metal ion, thiol reducing agent and ionizing radiation, in *OH scavenging abilities comparable to those in cells.

MATERIALS AND METHODS

We measured the effects of 10 min exposure to 200 microM Fe2+ vs. Fe3+ on the induction of single (SSB) and double (DSB) strand breaks in unirradiated and oxically irradiated SV40 DNA, in aqueous solution containing 75 or 750 mM glycerol and/or 5 mM glutathione (GSH).

RESULTS

Fe2+ or GSH alone produced little DNA damage. However, their combination produced a dramatic increase in the production of both SSB and DSB. Experiments with ferric ion suggest that it produces DNA damage only after partial reduction to ferrous by GSH. Induction efficiencies for SSB in the presence of Fe2+/GSH showed additivity of the effects of radiation alone with those from Fe2+/GSH. However, the corresponding induction efficiencies for DSB demonstrated a 2.5-fold enhancement.

CONCLUSIONS

Our results are consistent with a model in which reduced bivalent metal ions plus thiols, in the presence of O2, produce DSB in DNA primarily via local clusters of hydroxyl radicals arising from site specific Fenton reactions. The synergism observed between DSB production by Fe/GSH and by ionizing radiation, also believed to occur via local clusters of hydroxyl radicals, is consistent with this model. Our results suggest that both normally present intracellular iron and ionizing radiation may be important sources of oxidative stress in cells.

Ganglioside GT1b protects human spermatozoa from hydrogen peroxide-induced DNA and membrane damage

We have reported previously that various gangliosides, the sialic acid containing glycosphingolipids, provide protection against sperm injury caused by reactive oxygen species (ROS). In this study, we investigated the effect of treatment of human spermatozoa with ganglioside GT1b on hydrogen peroxide (H(2)O(2))-induced DNA fragmentation and plasma membrane damage. Single-cell gel electrophoresis (Comet assay) used in the assessment of sperm DNA integrity showed that in vitro supplemented GT1b (100 microm) significantly reduced DNA damage induced by H(2)O(2) (200 microm) (p < 0.05). Measurements of Annexin V binding in combination with the propidium iodide vital dye labelling demonstrated that the spermatozoa pre-treated with GT1b exhibited a significant increase (p < 0.05) in the percentage of live cells with intact membrane and decreased phosphatidylserine translocation after exposure to H(2)O(2). Flow cytometry using the intracellular ROS-sensitive fluorescence dichlorodihydrofluorescein diacetate dye employed to investigate the transport of the extracellularly supplied H(2)O(2) into the cell interior revealed that ganglioside GT1b completely inhibited the passage of H(2)O(2) through the sperm membrane. These results suggest that ganglioside GT1b may protect human spermatozoa from H(2)O(2)-induced damage by rendering sperm membrane more hydrophobic, thus inhibiting the diffusion of H(2)O(2) across the membrane.

Humic acid induced genotoxicity in human peripheral blood lymphocytes using comet and sister chromatid exchange assay

Humic acid (HA) in well water used by the inhabitants for drinking is one of the possible etiological factors for blackfoot disease (BFD). Moreover, within BFD endemic areas cancers occur at significantly higher rates than in areas free of BFD. In this study, the genotoxic potential of HA is assessed using human peripheral blood lymphocytes. The cells were exposed to HA (0-200 microg/mL for 2 h), and the induction of DNA primary damage in cellular DNA was evaluated by single-cell gel electrophoresis (comet assay). HA-induced DNA damage was decreased by superoxide (O(2)(-)), hydrogen peroxide (H(2)O(2)), and reactive oxygen species (ROS) scavengers (superoxide dismutase, catalase, and Trolox), and nitric oxide (NO) synthase inhibitors (N(G)-nitro-l-arginine methyl ester and N(G)-methyl-l-arginine). Moreover, formamidopyrimidine-DNA glycosylase (Fpg) and endonuclease III (Endo III), known to catalyze the excision of oxidized bases, increase the amount of DNA migration in HA-treated cells. Pretreatment of the cells with both the Ca(2+)-chelator BAPTA and EGTA completely inhibited HA-induced DNA damage, indicating that HA-induced changes in Ca(2+)-homeostasis are the predominant pathways for the HA induction of genotoxicity. Furthermore, sister chromatid exchange was found in the HA-treated lymphocytes. Our findings suggest that HA can induce oxidative DNA damage and genotoxicity in human lymphocytes.

Oxidative stress and aging: the potential role of iron

According to the free radical theory of aging proposed by Denham Harman more than 50 years ago, oxidatively modified cellular components accumulate continuously in the cells during the organism's lifespan leading to progressive decline of cellular functions. Since then, it has been shown that proteins, lipids, nucleic acids and other cell components undergo reversible and/or irreversible oxidative modifications during aging. Moreover, oxidized cell components can undergo further oxidative modifications leading to formation of products that cell degradation systems are incapable of removing. Accumulation of such non-degradable aggregates further inhibits the functionality of degradation systems, thus aggravating the effects and leading to a vicious cycle. In this presentation, we propose that the availability of intracellular iron in its redox active form (labile iron) represents the main catalyst that mediates extensive oxidative modifications of cellular components and ultimately leads to their accumulation and consequent cellular dysfunction. It is tempting to speculate that regulated restriction of labile iron may have positive effects on health in general and aging in particular.

The Fe2+-Mediated Decomposition, PfATP6 Binding, and Antimalarial Activities of Artemisone and Other Artemisinins: The Unlikelihood of C-Centered Radicals as Bioactive Intermediates

The results of Fe(2+)-induced decomposition of the clinically used artemisinins, artemisone, other aminoartemisinins, 10-deoxoartemisinin, and the 4-fluorophenyl derivative have been compared with their antimalarial activities and their ability to inhibit the parasite SERCA PfATP6. The clinical artemisinins and artemisone decompose under aqueous conditions to give mixtures of C radical marker products, carbonyl compounds, and reduction products. The 4-fluorophenyl derivative and aminoartemisinins tend to be inert to aqueous iron(II) sulfate and anhydrous iron(II) acetate. Anhydrous iron(II) bromide enhances formation of the carbonyl compounds and provides a deoxyglycal from DHA and enamines from the aminoartemisinins. Ascorbic acid (AA) accelerates the aqueous Fe(2+)-mediated decompositions, but does not alter product distribution. 4-Oxo-TEMPO intercepts C radicals from a mixture of an antimalaria-active trioxolane, 10-deoxoartemisinin, and anhydrous iron(II) acetate to give trapped products in 73 % yield from the trioxolane, and 3 % from the artemisinin. Artemisone provides a trapped product in 10 % yield. Thus, in line with its structural rigidity, only the trioxolane provides a C radical eminently suited for intermolecular trapping. In contrast, the structural flexibility of the C radicals from the artemisinins allows facile extrusion of Fe(2+) and collapse to benign isomerization products. The propensity towards the formation of radical marker products and intermolecular radical trapping have no relationship with the in vitro antimalarial activities of the artemisinins and trioxolane. Desferrioxamine (DFO) attenuates inhibition of PfATP6 by, and antagonizes antimalarial activity of, the aqueous Fe(2+)-susceptible artemisinins, but has no overt effect on the aqueous Fe(2+)-inert artemisinins. It is concluded that the C radicals cannot be responsible for antimalarial activity and that the Fe(2+)-susceptible artemisinins may be competitively decomposed in aqueous extra- and intracellular compartments by labile Fe(2+), resulting in some attenuation of their antimalarial activities. Interpretations of the roles of DFO and AA in modulating antimalarial activities of the artemisinins, and a comparison with antimalarial properties of simple hydroperoxides and their behavior towards thapsigargin-sensitive SERCA ATPases are presented. The general basis for the exceptional antimalarial activities of artemisinins in relation to the intrinsic activity of the peroxide within the uniquely stressed environment of the malaria parasite is thereby adumbrated.

Identification of Genes Involved in the Toxic Response of Saccharomyces cerevisiae against Iron and Copper Overload by Parallel Analysis of Deletion Mutants

Iron and copper are essential nutrients for life as they are required for the function of many proteins but can be toxic if present in excess. Accumulation of these metals in the human body as a consequence of overload disorders and/or high environmental exposures has detrimental effects on health. The budding yeast Saccharomyces cerevisiae is an accepted cellular model for iron and copper metabolism in humans primarily because of the high degree of conservation between pathways and proteins involved. Here we report a systematic screen using yeast deletion mutants to identify genes involved in the toxic response to growth-inhibitory concentrations of iron and copper sulfate. We aimed to understand the cellular responses to toxic concentrations of these two metals by analyzing the different subnetworks and biological processes significantly enriched with these genes. Our results indicate the presence of two different detoxification pathways for iron and copper that converge toward the vacuole. The product of several of the identified genes in these pathways form molecular complexes that are conserved in mammals and include the retromer, endosomal sorting complex required for transport (ESCRT) and AP-3 complexes, suggesting that the mechanisms involved can be extrapolated to humans. Our data also suggest a disruption in ion homeostasis and, in particular, of iron after copper exposure. Moreover, the identification of treatment-specific genes associated with biological processes such as DNA double-strand break repair for iron and tryptophan biosynthesis for copper suggests differences in the mechanisms by which these two metals are toxic at high concentrations.

Trace element concentration in primary liver cancers--a systematic review

BACKGROUND

The incidence of primary liver cancer varies between countries. Many of the etiological factors contributing to the geographical variations in incidence are unknown. Development of hepatocellular carcinoma has been linked to levels of trace elements. This review summarizes the evidence associating HCC with trace elements.

METHODS

MEDLINE, EMBASE, and CENTRAL databases were searched. Various inclusion and exclusion criteria were applied to select the articles for inclusion. Data extraction was performed using a custom designed data extraction form.

RESULTS

A total of 12,344 references were identified. Duplicates, 1,597, were excluded. Clearly irrelevant references, 10,676, were excluded through reading titles and abstracts. Some references (59) were excluded by applying the exclusion criteria. Twelve studies including 646 patients and measuring iron content (8), copper content (11), zinc (9), and selenium (2) qualified for the review. Although a meta-analysis was not possible due to heterogeneity between the studies, a clear pattern of distribution of the trace elements was discernible.

CONCLUSION

Iron and zinc content are lower in HCC than in surrounding tissues or normal controls. Copper content is lower in HCC than in surrounding tissues and cirrhotic controls. Epidemiological and physiological reasons for the trace element alterations should be further investigated.

Quantification of oxidative single-base and intrastrand cross-link lesions in unmethylated and CpG-methylated DNA induced by Fenton-type reagents

Methylation of cytosine at CpG sites in mammalian cells plays an important role in the epigenetic regulation of gene expression. Here, we assessed the formation of single-nucleobase lesions and intrastrand cross-link lesions (i.e. G[8-5]C, C[5-8]G, mC[5m-8]G, and G[8-5m]mC, where ‘mC’ represents 5-methylcytosine) in unmethylated and the corresponding CpG-methylated synthetic double-stranded DNA upon treatment with Fenton-type reagents [i.e. H₂O₂, ascorbate together with Cu(II) or Fe(II)]. Our results showed that the yields of oxidative single-nucleobase lesions were considerably higher than those of the intrastrand cross-link lesions. Although no significant differences were found for the yields of single-base lesions induced from cytosine and mC, the G[8-5m]mC cross-link was induced ∼10 times more efficiently than the G[8-5]C cross-link. In addition, the mC[5m-8]G was induced at a level that was ∼15 times less than G[8-5m]mC, whereas the corresponding C[5-8]G intrastrand cross-link lesion was not detectable. Moreover, Cu(II) is ∼10-fold as effective as Fe(II) in inducing oxidative DNA lesions. These results suggest that oxidative intrastrand cross-link lesions formed at methylated-CpG sites may account for the previously reported mCG→TT tandem double mutations induced by Fenton-type reagents.

Involvement of heat shock protein-70 in the mechanism of hydrogen peroxide-induced DNA damage: the role of lysosomes and iron

Heat shock protein-70 (Hsp70) is the main heat-inducible member of the 70-kDa family of chaperones that assist cells in maintaining proteins functional under stressful conditions. In the present investigation, the role of Hsp70 in the molecular mechanism of hydrogen peroxide-induced DNA damage to HeLa cells in culture was examined. Stably transfected HeLa cell lines, overexpressing or lacking Hsp70, were created by utilizing constitutive expression of plasmids containing the functional hsp70 gene or hsp70-siRNA, respectively. Compared to control cells, the Hsp70-overexpressing ones were significantly resistant to hydrogen peroxide-induced DNA damage, while Hsp70-depleted cells showed an enhanced sensitivity. In addition, the "intracellular calcein-chelatable iron pool" was determined in the presence or absence of Hsp70 and found to be related to the sensitivity of nuclear DNA to H(2)O(2). It seems likely that the main action of Hsp70, at least in this system, is exerted at the lysosomal level, by protecting the membranes of these organelles against oxidative stress-induced destabilization. Apart from shedding additional light on the mechanistic details behind the action of Hsp70 during oxidative stress, our results indicate that modulation of cellular Hsp70 may represent a way to make cancer cells more sensitive to normal host defense mechanisms or chemotherapeutic drug treatment.

Prooxidant DNA breakage induced by caffeic acid in human peripheral lymphocytes: Involvement of endogenous copper and a putative mechanism for anticancer properties

Plant-derived dietary material contains several classes of polyphenols such as flavonoids, curcuminoids, stilbenes and hydroxycinnamic acids. They are recognized as naturally occurring antioxidants but also act as prooxidants catalyzing cellular DNA degradation in the presence of transition metal ions such as copper. Earlier we have shown that the stilbene resveratrol is able to mobilize endogenous copper ions leading to oxidative breakage of cellular DNA. In this paper, we show that caffeic acid (a hydroxycinnamic acid), which is a major constituent of coffee, is also capable of DNA breakage in human peripheral lymphocytes. Incubation of lymphocytes with neocuproine inhibited the DNA degradation confirming that Cu(I) is an intermediate in the DNA cleavage reaction. Further, we have also shown that caffeic acid generates oxidative stress in lymphocytes, which is inhibited by scavengers of reactive oxygen species and neocuproine. These results are in further support of our hypothesis that anticancer mechanism of plant polyphenols involves mobilization of endogenous copper, possibly chromatin bound copper, and the consequent prooxidant action.

Membrane permeability of redox active metal chelators: an important element in reducing hydroxyl radical induced NAD+ depletion in neuronal cells

There is substantial evidence implicating increased production of the hydroxyl radical and oxidative stress in the pathogenesis of neurodegenerative diseases such as Alzheimer's disease (AD). Significant amounts of hydroxyl radicals will be produced in the presence of hydrogen peroxide and redox active iron via Fenton chemistry. Increased iron levels within the cytoplasm of vulnerable neurons suggest that this may also be an important site of oxidative activity. We investigated the likelihood that intracellular, rather than extracellular chelation of ferrous or ferric iron may be more effective in reducing hydroxyl radical induced cell damage and preserving NAD(+) levels and cell viability. Using intracellular NAD(H) measurements as an indicator of cell viability we found that membrane permeable ferrous chelators were most efficient in preserving cellular NAD(+) levels. Hydrophilic, ferrous or ferric chelators and lipophilic ferric chelators were essentially ineffective in preventing cellular NAD(+) depletion when added at physiological concentrations. We propose that lipophilic ferrous chelators, due to their actions inside the cell, are effective agents for moderating neuronal damage in conditions such as AD where intracellular oxidative stress plays a significant role in disease pathology.

Trace element concentration in metastatic liver disease: a systematic review

BACKGROUND

There are conflicting reports about the levels of trace elements in secondary liver cancers. This review summarises the evidence associating secondary liver tumours with trace elements.

METHODS

MEDLINE, EMBASE and CENTRAL databases were searched for the period up to January 2006 using a formal search strategy. Various inclusion and exclusion criteria were applied to select the articles for inclusion. Data extraction was performed using a custom designed data extraction form.

RESULTS

A total of 6917 references were identified. About 1359 duplicates were excluded using EndNote. About 5529 clearly irrelevant references were excluded through reading titles and abstracts. Of these 24 references were excluded by applying the exclusion criteria. Five studies including 239 patients and measuring iron content (2), copper content (4) and zinc (3) qualified for the review. Both studies on iron, three studies on copper and all the studies on zinc used quantitative methods to determine mineral content. A meta-analysis was performed using the random effects model.

CONCLUSION

Copper and zinc content are lower in secondary liver cancer compared to livers from healthy patients. Iron, copper and zinc content are lower in liver secondaries compared to the normal tissues surrounding the secondaries. Reasons and implications for the trace element alterations should be further investigated.

Iron chelators reduce chromosomal breaks in ataxia-telangiectasia cells

Ataxia-telangiectasia (A-T) is characterized by ataxia, genomic instability, and increased cancer incidence. Previously, iron chelator concentrations which suppressed normal cell colony formation increased A-T cell colony formation. Similarly, iron chelators preferentially increased A-T cell colony formation following peroxide exposure compared to normal cells. Last, A-T cells exhibited increased short-term sensitivity to labile iron exposure compared to normal cells, an event corrected by recombinant ATM (rATM) expression. Since chromosomal damage is important in A-T pathology and iron chelators exert beneficial effects on A-T cells, we hypothesized that iron chelators would reduce A-T cell chromosomal breaks. We treated A-T, normal, and A-T cells expressing rATM with labile iron, iron chelators, antioxidants, and t-butyl hydroperoxide, and examined chromosomal breaks and ATM activation. Additionally, the effect of ATM-deficiency on transferrin receptor (TfR) expression and TfR activity blockage in A-T and syngeneic A-T cells expressing rATM was examined. We report that (1) iron chelators and iron-free media reduce spontaneous and t-butyl hydroperoxide-induced chromosomal breaks in A-T, but not normal, or A-T cells expressing rATM; (2) labile iron exposure induces A-T cell chromosomal breaks, an event lessened with rATM expression; (3) desferal, labile iron, and copper activate ATM; (4) A-T cell TfR expression is lowered with rATM expression and (5) blocking TfR activity with anti-TfR antibodies increases A-T cell colony formation, while lowering chromosomal breaks. ATM therefore functions in iron responses and the maintenance of genomic stability following labile iron exposure.

Iron chelators may help prevent photoaging

For years, cosmetic ingredients for anti-aging treatments have attracted consumers. Skin aging is accelerated by reactive oxygen species (ROS), generated by exposure to solar ultraviolet radiation (UVR), in a process known as photoaging. Because cutaneous iron catalyses ROS generation, it is thought to play a key role in photoaging. Iron is essential to almost all forms of life. However, excess iron is potentially toxic as its catalytic activity induces the generation of ROS. Iron-catalysed ROS generation is involved in numerous pathological conditions, including cutaneous damage. When skin is directly exposed to UVR, cutaneous intracellular catalytic iron levels increase because of the release of iron from iron-binding proteins such as ferritin. Consequently, the subsequent ROS generation may overwhelm cutaneous defense systems such as the cellular iron sequestration and ROS scavenging capacity. The harmful role of excess cutaneous iron implies that there may be a potential for topical iron chelator treatments. We now consider cutaneous photodamage skin photoaging as the result of iron-catalysed ROS generation and discuss preventative strategies based on iron chelators.

Calcium-dependent modulation of poly(ADP-ribose) polymerase-1 alters cellular metabolism and DNA repair

After genotoxic stress poly(ADP-ribose) polymerase-1 (PARP-1) can be hyperactivated, causing (ADP-ribosyl)ation of nuclear proteins (including itself), resulting in NAD(+) and ATP depletion and cell death. Mechanisms of PARP-1-mediated cell death and downstream proteolysis remain enigmatic. beta-lapachone (beta-lap) is the first chemotherapeutic agent to elicit a Ca(2+)-mediated cell death by PARP-1 hyperactivation at clinically relevant doses in cancer cells expressing elevated NAD(P)H:quinone oxidoreductase 1 (NQO1) levels. Beta-lap induces the generation of NQO1-dependent reactive oxygen species (ROS), DNA breaks, and triggers Ca(2+)-dependent gamma-H2AX formation and PARP-1 hyperactivation. Subsequent NAD(+) and ATP losses suppress DNA repair and cause cell death. Reduction of PARP-1 activity or Ca(2+) chelation protects cells. Interestingly, Ca(2+) chelation abrogates hydrogen peroxide (H(2)O(2)), but not N-Methyl-N'-nitro-N-nitrosoguanidine (MNNG)-induced PARP-1 hyperactivation and cell death. Thus, Ca(2+) appears to be an important co-factor in PARP-1 hyperactivation after ROS-induced DNA damage, which alters cellular metabolism and DNA repair.

Identification and quantification of a guanine-thymine intrastrand cross-link lesion induced by Cu(II)/H2O2/ascorbate

Reactive oxygen species (ROS) can be induced by both endogenous and exogenous processes, and they can damage biological molecules including nucleic acids. It was shown that X- or gamma-ray irradiation of aqueous solutions of DNA, during which *OH is one of the major ROS, can lead to the formation of intrastrand cross-link lesions where the neighboring nucleobases in the same DNA strand are covalently bonded. Previous 32P-postlabeling studies suggested that the intrastrand cross-link lesions may arise from Fenton reaction, which also induces the formation of *OH; the structures of the proposed intrastrand cross-link lesions, however, have not been determined. Here, we showed for the first time that the treatment of calf thymus DNA with Cu(II)/H2O2/ascorbate could lead to the formation of an intrastrand cross-link lesion, i.e., G wedge T, where the C8 of guanine is covalently bonded to the neighboring 3'-thymine through its methyl carbon. LC-MS/MS quantification results showed dose-responsive formation of G wedge T. In addition, the yield of the intrastrand cross-link was approximately 3 orders of magnitude lower than those of commonly observed single-base lesions, that is, 8-oxo-7,8-dihydro-2'-deoxyguanosine, 5-(hydroxymethyl)-2'-deoxyuridine, and 5-formyl-2'-deoxyuridine. The induction of intrastrand cross-link lesion in calf thymus DNA by Fenton reagents in vitro suggests that this type of lesion might be formed endogenously in mammalian cells.

Ascorbic acid mobilizes endogenous copper in human peripheral lymphocytes leading to oxidative DNA breakage: a putative mechanism for anticancer properties

Several decades back ascorbic acid was proposed as an effective anticancer agent. However, this idea remained controversial and the mechanism of action unclear. In this paper, we show that ascorbic acid at a concentration reported to be achievable through high doses of oral consumption is capable of cytotoxic action against normal cells. Several antioxidants of both animal as well as plant origin including ascorbic acid also possess prooxidant properties. Copper is an essential component of chromatin and can take part in redox reactions. Previously we have proposed a mechanism for the cytotoxic action of plant antioxidants against cancer cells that involves mobilization of endogenous copper ions and the consequent generation of reactive oxygen species. Using human peripheral lymphocytes and Comet assay we show here that ascorbic acid is able to cause oxidative DNA breakage in normal cells at a concentration of 100-200 microM. Neocuproine, a Cu(I) specific sequestering agent inhibited DNA breakage in a dose dependent manner indicating that Cu(I) is an intermediate in the DNA cleavage reaction. The results are in support of our above hypothesis that involves events that lead to a prooxidant action by antioxidants. The results would support the idea that even a plasma concentration of around 200 microM. would be sufficient to cause pharmacological tumor cell death particularly when copper levels are elevated. This would account for the observation of several decades back by Pauling and co-workers where oral doses of ascorbic acid in gram quantities were found to be effective in treating some cancers.

Ascorbate and H2O2 induced oxidative DNA damage in Jurkat cells

The effect of vitamin C (ascorbate) on oxidative DNA damage was examined by first incubating cells with dehydroascorbate, which boosts the intracellular concentration of ascorbate, and then exposing cells to H(2)O(2). Oxidative DNA damage was estimated by the analysis of 5-hydroxy-2'-deoxycytidine (oh(5)dCyd) and 8-oxo-7,8-dihydro-2'-deoxyguanosine (oxo(8)dGuo). The presence of a high concentration of ascorbate (30 mM), compared to the absence of ascorbate in cells, when exposed to H(2)O(2) (200 microM), resulted in a remarkable sensitization of oh(5)dCyd from 2.7 +/- 0.6 to 40.8 +/- 6.1 lesions /10(6) dCyd (15-fold). In contrast, the level of oxo(8)dGuo increased from 8.4 +/- 0.4 to 12.1 +/- 0.5 lesions/10(6) dGuo (50%). The formation of oh(5)dCyd was also observed at lower concentrations of intracellular ascorbate and exogenous H(2)O(2). Additional studies showed that replacement of H(2)O(2) with tert-butyl hydroperoxide completely abolished damage, and that preincubation with iron and desferroxamine increased and decreased this damage, respectively. The latter studies suggest that a Fenton reaction is involved in the mechanism of damage. In conclusion, we report a novel model system in which ascorbate sensitizes H(2)O(2)-induced oxidative DNA damage in cells, leading to elevated levels of oh(5)dCyd and oxo(8)dGuo, with a strong bias toward the formation of oh(5)dCyd.